WO2015185400A1 - Metal oxide coated cathodes comprising sulfur for electrochemical cells - Google Patents

Metal oxide coated cathodes comprising sulfur for electrochemical cells Download PDF

Info

Publication number
WO2015185400A1
WO2015185400A1 PCT/EP2015/061651 EP2015061651W WO2015185400A1 WO 2015185400 A1 WO2015185400 A1 WO 2015185400A1 EP 2015061651 W EP2015061651 W EP 2015061651W WO 2015185400 A1 WO2015185400 A1 WO 2015185400A1
Authority
WO
WIPO (PCT)
Prior art keywords
metal oxide
layer
electrode assembly
sulfur
geometric shape
Prior art date
Application number
PCT/EP2015/061651
Other languages
French (fr)
Inventor
Heino Sommer
Fernanda MARZANO
Original Assignee
Basf Se
Karlsruher Institut Für Technologie (Kit)
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Basf Se, Karlsruher Institut Für Technologie (Kit) filed Critical Basf Se
Publication of WO2015185400A1 publication Critical patent/WO2015185400A1/en

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/581—Chalcogenides or intercalation compounds thereof
    • H01M4/5815—Sulfides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/661—Metal or alloys, e.g. alloy coatings
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to an electrode assembly comprising as a first component (A) at least one three-dimensional geometric shape of an electroactive composition of at least one electroactive sulfur-containing material, which is arranged on a current collector as a second component (B), and comprising as a third component (C) a layer of at least one metal oxide, wherein the layer is deposited directly on all surfaces of the at least one three-dimensional ge- ometric shape or all parts of a surface of the at least one three-dimensional geometric shape, which are not covered with the current collector.
  • the present invention further relates to a process for preparing said electrode assembly, to an electrochemical cell comprising said electrode assembly and to a battery comprising at least one inventive electrochemical cell.
  • Secondary batteries, accumulators or rechargeable batteries are just some embodiments by which electrical energy can be stored after generation and used when required. Due to the significantly better power density, there has been a move in recent times away from the water- based secondary batteries to development of batteries in which the charge transport in the electrical cell is accomplished by lithium ions.
  • lithium-sulfur cells sulfur in the sulfur cathode is reduced via polysulfide ions to S 2_ , which is reoxidized when the cell is charged to form sulfur- sulfur bonds.
  • a problem is the solubility of the polysulfides, for example L12S4 and L12S6, which are generally soluble in the solvent and can migrate to the anode.
  • the consequences may include: loss of capacitance and deposition of electrically insulating material on the sulfur particles of the electrode.
  • the migration of the polysulfide ions from the cathode to the anode can ultimately lead to discharge of the affected cell and to cell death in the battery. This unwanted migration of polysulfide ions is also referred to as "shuttling", a term which is also used in the context of the present invention.
  • Carbon sulfur composites are important components of the cathodes of lithium sulfur cells contributing significantly to the overall performance of lithium sulfur cells in particular with respect to lowering the internal impedance by providing a conductive element.
  • the carbon framework can increase the cou- lombic efficiency, lower the degree of capacity fading, and help limit self-discharge by physically trapping polysulfide ions within the cathode, although these effects are usually limited to short- term cycling.
  • the structure and composition of the components of cathodes of lithium sulfur cells and of the cathodes themselves contribute significantly to the overall performance of lithium sulfur cells in particular with respect to coulombic efficiency, degree of capacity fading, self-discharge, durability or cycle life.
  • US 6,210,831 describes solid composite cathodes which comprise (a) sulfur-containing cathode material which, in its oxidized state, comprises a polysulfide moiety of the formula, -S m -, wherein m is an integer from 3 to 10; and (b) a non-electroactive particulate material having a strong adsorption of soluble polysulfides.
  • US 8,592,088 describes an electrode assembly comprising an porous ceramic layer comprising an inorganic oxide filler and a polymeric binder.
  • electroactive sulfur-containing electrode assemblies in particular sulfur comprising cath- odes, described in the literature still have shortcomings with regard to one or more of the properties desired for such electrodes and the electrochemical cells produced therefrom.
  • Desirable properties are, for example, high electrical conductivity of the cathode materials, maintenance of cathode capacity during lifetime, reduced self-discharge of the electrochemical cells during storage, an increase in the lifetime of the electrochemical cell, an improvement in the mechanical stability of the cathode or a reduced change in volume of the cathodes during a charge-discharge cycle.
  • the desired properties mentioned also make a crucial contribution to improving the economic viability of the electrochemical cell, which, as well as the aspect of the desired technical performance profile of an electrochemical cell, is of crucial signif- icance to the user.
  • (A3) optionally at least one binder, arranged on
  • (B) a current collector, and a layer (C) of at least one metal oxide, wherein the layer has a thickness in the range from 10 to 500 nm, preferably in the range from 15 to 50 nm, and wherein the layer is deposited directly on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three-dimensional geometric shape, which are not covered with the current collector.
  • the electrode where during discharging a net negative charge occurs is called the anode and the electrode where during discharging a net positive charge occurs is in general called cathode, and in the following description it is called the inventive electrode assembly.
  • the inventive electrode assembly comprises as a first component (A) at least one three- dimensional geometric shape of an electroactive composition, also referred to hereinafter as shape (A), which is arranged on a current collector as a second component (B) of the electrode assembly, also referred to hereinafter as collector (B), and the inventive electrode assembly comprises as a third component (C) a layer (C) of at least one metal oxide, also referred to hereinafter as layer (C).
  • the three-dimensional geometric shape of an electroactive composition which is arranged on current collector (B), can be varied in a broad range.
  • three-dimensional geometric shapes are polyhedrons, like cubes, pyramids or toroids, cylinders, ellipsoids or spheres. If several shapes (A) are arranged on collector (B), these shapes (A) can be equal or different and can be arranged in regular patterns or in irregular form. For example a regular pattern of equal cuboids or hemispheres can be arranged on collector (B), wherein the distances between adja- cent shapes are preferably less than the greatest spatial dimension of the shapes. Shape (A) is in direct contact with collector (B).
  • the direct contact can be established by at least one vertex, at least one edge or a face in each case of shape (A) with collector (B).
  • a maximum amount of electroactive composition on collector (B) preferably a single shape is chosen, which avoids free spaces present between adjacent shapes.
  • the three-dimensional geo- metric shape of an electroactive composition (A) is preferably designed as a layer, more preferably as a layer having a thickness in the range from 15 to 400 ⁇ , more preferably in the range from 25 to 200 ⁇ , in particular in the range from 30 to 100 ⁇ . While the thickness of the layer represents the smallest of its three spatial dimensions (extents), the two other dimensions of the layer are usually determined by the dimensions of the surface of the collector (B).
  • the inventive electrode assembly is characterized in that the at least one three-dimensional geometric shape of an electroactive composition (A) is designed as a layer, preferably as a layer having a thickness in the range from 15 to 400 ⁇ , more preferably in the range from 25 to 200 ⁇ , in particular in the range from 30 to 100 ⁇ .
  • the electroactive composition which is arranged in form of at least one three-dimensional geometric shape (A) on collector (B), preferably arranged in form of a layer, comprises as a first ingredient at least one electroactive sulfur-containing material, also referred to hereinafter as sulfur-containing material (A1 ) for short, as a second ingredient carbon in a polymorph comprising at least 60% sp 2 -hybridized carbon atoms, also referred to hereinafter as carbon
  • binder (A2) for short and optionally as a third ingredient at least one binder, also referred to hereinafter as binder (A3) for short.
  • Electroactive sulfur-containing materials (A1 ) are for example covalent compounds like elemental sulfur, composites produced from elemental sulfur and at least one polymer, composites produced from elemental sulfur and at least one carbon material or polymers comprising polysulfide bridges or ionic compounds like salts of sulfides or polysulfides.
  • Elemental sulfur is known as such.
  • Composites produced from elemental sulfur and at least one polymer, which find use as ingredient of electroactive compositions, are likewise known to those skilled in the art.
  • Adv. Funct. Mater. 2003, 13, 487 ff describes, for example, a reaction product of sulfur and polyacrylonitrile, which results from elimination of hydrogen from polyacrylonitrile with simultaneous formation of hydrogen sulfide.
  • Composites, produced from elemental sulfur and at least one carbon material are described for example in US 201 1/318654 or US 2012/298926.
  • Polymers comprising divalent di- or polysulfide bridges for example polyethylene tetrasulfide, are likewise known in principle to those skilled in the art. J. Electrochem. Soc, 1991 , 138, 1896 - 1901 and US 5,162,175 describe the replacement of pure sulfur with polymers comprising disulfide bridges. Polyorganodisulfides are used therein as materials for solid redox
  • Salts of sulfides or polysulfides are examples of ionic compounds comprising at least one Li-S- group like L12S, lithium polysulfides (Li2S2 to 8) or lithiated thiols (lithium thiolates).
  • a preferred electroactive sulfur-containing material (A1 ) is elemental sulfur.
  • the inventive electrode assembly is characterized in that the at least one electroactive sulfur-containing material (A1 ) is elemental sulfur.
  • Carbon (A2) which improves the electrical conductivity of the electroactive composition of the inventive electrode assembly, can be selected from graphite, carbon black, carbon nanotubes, graphene or mixtures of at least two of the aforementioned substances. Suitable carbons in a conductive polymorph are described in WO 2012/168851 page 4, line 30 to page 6, line 22.
  • the inventive electrode assembly is characterized in that carbon (A2) is selected from graphite, graphene, activated carbon and especially carbon black.
  • the inventive electrode assembly comprises at least one polymer as a binder (A3).
  • Binder (A3) can be selected from a wide range of organic polymers. Suitable binders are described in WO 2012/168851 page 6, line 40 to page 7, line 30.
  • Particularly suitable binders for the inventive electrode assembly are especially polyvinyl alcohol, poly(ethylene oxide), carboxymethyl cellulose (CMC) and halogenated (co)polymers, for example polyvinyl chloride or polyvinylidene chloride, especially fluorinated (co)polymers such as polyvinyl fluoride and especially polyvinylidene fluoride, lithiated Nafion and
  • the electroactive composition of the inventive electrode assembly comprises in the range from 10 to 80% by weight, preferably 30 to 75% by weight, of sulfur, determined by elemental analysis, based on the total weight of the
  • the electroactive composition of the inventive electrode assembly comprises in the range from 0.1 to 60% by weight of carbon (A2) in a conductive polymorph, preferably 1 to 30% by weight based on the total weight of the electroactive composition.
  • This carbon can likewise be determined by elemental analysis, for example, in which case the evaluation of the elemental analysis has to take into account the fact that carbon also arrives in organic polymers representing binders, and possibly further sources.
  • the electroactive composition of the inventive elec- trode assembly comprises in the range from 0.1 to 20% by weight of binder (A3), preferably 1 to 15% by weight and more preferably 3 to 12% by weight, based on the total weight of the electroactive composition.
  • Collector (B) as a component of the inventive electrode assembly is known by the person skilled in the art.
  • Collector (B) may be configured in the form of a metal wire, metal grid, metal mesh, expanded metal, metal sheet, metal foil or carbon paper/cloth.
  • collector (B) is configured in the form of a metal foil, more preferably in form of an aluminium foil.
  • the thickness of a foil can be varied in a wide range.
  • the thickness of a suitable aluminium foil is preferably in the range from 5 to 100 ⁇ , in particular in the range from 10 to 20 ⁇ .
  • the inventive electrode assembly is characterized in that the current collector (B) is an aluminium foil, preferably having a thickness in the range from 5 to 100 ⁇ , in particular having a thickness in the range from 10 to 20 ⁇ .
  • the inventive electrode assembly comprises as a third component (C) a layer (C) of at least one metal oxide, wherein layer (C) has a thickness in the range from 10 to 500 nm, preferably in the range from 15 to 50 nm, and wherein layer (C) is deposited directly on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three- dimensional geometric shape, which are not covered with the current collector.
  • Metal oxides can be produced in crystalline form or in amorphous form, depending on the applied reaction conditions, used starting materials and intended chemical composition of the metal oxide.
  • the metal oxide of layer (C) is preferably deposited in amorphous form on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three-dimensional geometric shape, which are not covered with the current collector.
  • the inventive electrode assembly is characterized in that the metal oxide of layer (C) is deposited in amorphous form.
  • the metal oxide of layer (C) can be chosen from a wide variety of metal oxide, main group metal oxides as well as transition metal oxides or lanthanide oxides.
  • the metal oxide of layer (C) is selected from the group consisting of ⁇ 2, S1O2, B2O3, AI2O3, V2O5, V02 and Zr02, in particular selected from the group consisting of amorphous Ti02 and amorphous S1O2.
  • the inventive electrode assembly is characterized in that the metal oxide of layer (C) is selected from the group consisting of ⁇ 2, S1O2, B2O3, AI2O3, V2O5, VO2 and Zr02, in particular selected from the group consisting of amorphous ⁇ 2 and amorphous S1O2.
  • Layer (C) comprises at least one metal oxide, e.g. layer (C) comprises one metal oxide or a mixture of two or more metal oxides.
  • layer (C) comprises one metal oxide wherein traces of other metal oxides in amounts of less than 1 % by weight based on the total weight of all metal oxides are not considered as additional metal oxides.
  • layer (C) might comprise additional compounds, e.g. organic polymers, tenside molecules, nano-scaled carbons like fullerenes or carbon nanotubes or solvents like water or alco- hols.
  • the sum of the mass fractions of all metal oxides based on layer (C) can be varied in a wide range depending on the amount of components in addition to the metal oxides.
  • the mass fraction of the major metal oxide based the total weight of layer (C) is in the range from 0.5 to 1 , more preferably in the range from 0.8 to 1 , in particular in the range from 0.9 to 1 .
  • the metal oxide of layer (C) is preferably produced by a sol-gel process, which is also known to the person skilled in the art, and then deposited as a layer on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three- dimensional geometric shape, which are not covered with the current collector. More preferably the metal oxide forming layer (C) is produced by a sol-gel process comprising the hydrolysis of a corresponding metal alkoxide followed by condensation.
  • Alternatively layer (C) comprises at least one metal oxide can be produced by depositing a layer of an metal oxide precursor, preferably a metal alkoxide, directly on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three- dimensional geometric shape, which are not covered with the current collector, followed by converting said metal oxide precursor to the corresponding metal oxide, e.g. hydrolyzing a metal alkoxide to the corresponding metal hydroxide followed by condensation to the corresponding metal oxide.
  • an metal oxide precursor preferably a metal alkoxide
  • the inventive electrode assembly is characterized in that the metal oxide of layer (C) was produced by a sol-gel process, preferably by hydrolysis of a corresponding metal alkoxide followed by condensation.
  • Metal alkoxides are generally known to the person skilled in the art.
  • suitable metal alkoxides are titanium tetraethoxide, titanium tetraisopropoxide, titanium tetrabutoxide, tetra- ethoxysilane, tetramethoxysilane, trimethyl borate, aluminium triisopropoxide, titanium tetraethoxide, triisopropoxyvanadium(V) oxide, vanadium(V) oxytriethoxide, zirconium tetra- isopropoxide or zirconium tetrabutoxide.
  • a sol of the selected metal oxide is formed and this sol is then deposited on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three-dimensional geometric shape, which are not covered with the current collector by methods known to the person skilled in the art, like spray coating, brushing, screen printing, tape casting, dip coating or spin coating an appropriate sole, preferably dip coating or spin coating, in particular spin coating.
  • the deposited sol of a metal oxide which is a suspension of na- noparticles of said metal oxide, forms then a layer of a gel, also called xerogel film, which can be converted to a dense film by further heating.
  • the concentration of nanoparticles of said metal oxide in the suspension is in the range of from 0.01 to 50 wt%, preferably 0.1 to 5 wt%.
  • the inventive electrode assembly is characterized in that the layer of the at least one metal oxide was deposited by means of dip coating or spin coating of a sol of said metal oxide.
  • the inventive electrode assembly is characterized in that the metal oxide of layer (C) is selected from the group consisting of amorphous Ti02 and amorphous S1O2, and in that the layer of the at least one metal oxide was deposited by means of dip coating or spin coating of a sol of said metal oxide.
  • the deposited layer (C) of at least one metal oxide is usually not impervious to solvents, in particular aprotic, dipolar solvents, which are usually used as component of an electrolyte for elec- trochemical cells.
  • the deposited layer (C) of at least one metal oxide is pervious to electrolytes, which are used in non-aqueous electrochemical cells.
  • the present invention further provides a process for producing an electrode assembly as described above, comprising the process steps of
  • (A3) optionally at least one binder, on a current collector (B), and
  • Methods of arranging the at least one three-dimensional geometric shape of an electroactive composition on current collector (B) are known to the person skilled in the art. It is possible to place solid three-dimensional geometric shapes of the electroactive composition in the desired pattern on current collector (B) or to deposit a slurry of the electroactive composition in the desired form and pattern on current collector (B), for example using stencils, molding tools, ink jet printing or doctor blade techniques, and afterward remove the liquid medium of the deposited slurry.
  • layer (C) is formed by sol-gel methods as described above, more preferably by sol-gel methods in combination with dip coating, spin coating, screen printing or tape casting.
  • the inventive process is characterized in that in process step ( ⁇ ) the metal oxide of layer (C) is produced by a sol-gel process, preferably by hydrolysis of a corresponding metal alkoxide followed by condensation.
  • the inventive process is characterized in that in process step ( ⁇ ) the layer of the at least one metal oxide is deposited by means of screen printing, tape casting, dip coating or spin coating, preferably dip coating or spin coating, in particular spin coating, of a sol or paste of said metal oxide, preferably wherein a sol, that is a dispersion of nanoparticles of said metal oxide, is obtained by the first step of the known sol-gel method optionally followed by further dilution of the initially obtained sol, in particular by hydrolysis of a corresponding metal alkoxide followed by condensation.
  • the nanoparticles of said metal oxide of the sole comprise reactive functional groups on their surfaces, in particular hydroxide groups.
  • hydroxyl groups of different nanoparticles of said metal oxide react with each other under elimination of water and formation of a gel of interconnected nanoparticles of said metal oxide.
  • layer (C) comprises at least one metal oxide by depositing a layer of a metal oxide precursor, preferably a metal alkoxide, by means of screen printing, tape casting, dip coating or spin coating directly on all surfaces of the at least one three- dimensional geometric shape or all parts of a surface of the at least one three-dimensional geometric shape, which are not covered with the current collector, followed by converting said metal oxide precursor to the corresponding metal oxide, e.g. hydrolyzing a metal alkoxide to the corresponding metal hydroxide followed by condensation to the corresponding metal oxide.
  • a metal oxide precursor preferably a metal alkoxide
  • inventive electrode assemblies are particularly suitable as a component of electrochemical cells, in particular rechargeable lithium-sulfur cells.
  • the present invention further provides an electrochemical cell comprising
  • the inventive electrochemical cell comprises in addition to the inventive electrode assembly, which has been described above and which is also referred to hereinafter as electrode (a) or cathode (a) for short, as a second component (b) at least one anode (b), as a third component
  • inventive cathode (a) comprises usually a mixture of different electroactive sulfur-containing materials, since more and more S-S-bonds are formed.
  • inventive electrochemical cells comprise, as well as inventive electrode assembly, at least one anode (b) comprising at least one metal, preferably magnesium, aluminium, zinc or an alkali metal like lithium, sodium or potassium.
  • anode (b) of the inventive electrochemical cell comprises an alkali metal, in particular lithium.
  • the metal of anode (b) of the inventive electrochemical cell can be present in the form of a pure metal phase, preferably a pure alkali metal phase, in form of an alloy together with other metals or metalloids, in form of an intercalation compound or in form of an ionic compound comprising at least one metal, preferably an alkali metal and at least one transition metal.
  • Anode (b) of the inventive electrochemical cell, in particular of the inventive lithium-sulfur cell can be selected from anodes being based on various active materials.
  • Suitable active materials are metallic lithium, carbon-containing materials such as graphite, graphene, charcoal, expanded graphite, in particular graphite, furthermore lithium titanate (Li4Ti 5 0i2), anodes comprising In, Tl, Sb, Sn or Si, in particular Sn or Si, for example tin oxide (Sn02) or nanocrystalline silicon, and anodes comprising metallic lithium.
  • anode (b) of the inventive electrochemical cell is selected from graphite anodes, lithium titanate anodes, anodes comprising In, Tl, Sb, Sn or Si, and anodes comprising metallic lithium.
  • the inventive electrochemical cell is characterized in that the metal of anode (b) is lithium.
  • Anode (b) of the inventive electrochemical cell can further comprise a current collector.
  • Suitable current collectors are, e.g., metal wires, metal grids, metal gauze and preferably metal foils such as copper foils.
  • Anode (b) of the inventive electrochemical cell can further comprise a binder.
  • Suitable binders can be selected from organic (co)polymers. Suitable organic (co)polymers may be halogenated or halogen-free. Examples are polyethylene oxide (PEO), cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyethylene, polypropylene, polytetrafluoroethylene, polyacrylonitrile-methyl methacrylate, styrene-butadiene copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, vinylidene fluoride-hexafluoropropylene copolymers (PVdF-HFP), vinylidene fluoride- tetrafluoroethylene copolymers, perfluoroalkyl vinyl ether copolymers, ethylene- tetrafluoroethylene copolymers, vinylidene fluoride-chlorotrifluoroethylene copoly
  • Suitable binders are especially polyvinyl alcohol and halogenated (co)polymers, for example polyvinyl chloride or polyvinylidene chloride, especially fluorinated (co)polymers such as polyvinyl fluoride and especially polyvinylidene fluoride and polytetrafluoroethylene.
  • the average molecular weight M w of binder may be selected within wide limits, suitable examples being 20,000 g/mol to 1 ,000,000 g/mol.
  • anode (b) of the inventive electrochemical cell can have a thickness in the range of from 15 to 200 ⁇ , preferably from 30 to 100 ⁇ , determined without the current collector.
  • inventive electrochemical cells comprise one or more separators (c) by which the electrodes are mechanically separated from one another.
  • Suitable separators (c) are polymer films, especially porous polymer films, which are unreactive toward elemental metals, in particular metallic lithium and toward lithium sulfides and lithium polysulfides.
  • Particularly suitable materials for separators (c) are polyolefins, especially porous polyethylene films and porous polypropylene films.
  • Polyolefin separators especially of polyethylene or polypropylene, may have a porosity in the range from 35 to 45%. Suitable pore diameters are, for example, in the range from 30 to 500 nm.
  • the separators (c) selected may be separators composed of PET nonwovens filled with inorganic particles.
  • Such separators may have a porosity in the range from 40 to 55%. Suitable pore diameters are, for example, in the range from 80 to 750 nm.
  • the inventive electrochemical cell further comprises, as well as the inventive cathode (a), an anode (b) and a separator (c), at least one electrolyte composition (d) comprising at least one solvent (d1 ) and at least one metal salt (d2), preferably at least one alkali metal salt (d2).
  • a inventive cathode
  • b an anode
  • a separator c
  • at least one electrolyte composition comprising at least one solvent (d1 ) and at least one metal salt (d2), preferably at least one alkali metal salt (d2).
  • suitable solvents and further additives for non-aqueous liquid electrolytes for lithium- based rechargeable batteries reference is made to the relevant prior art, e.g. Chem. Rev. 2004, 104, 4303-4417, in particular table 1 on page 4307, table 2 on page 4308 and table 12 on page 4379.
  • the inventive electrochemical cell further comprises, as well as the inventive cathode (a), an anode (b) and an separator (c), at least one electrolyte composition (d) comprising at least one solvent (d1 ) aprotic organic and at least one metal salt (d2) alkali.
  • the solvents (d1 ) of the electrolyte composition (d) can be chosen from a wide range of solvents, in particular from solvents which dissolve metal salts, in particular alkali metal salts easily.
  • Solvents or solvent systems which dissolve metal salts, in particular alkali metal salts are for example ionic liquids, polar solvents or combinations of apolar solvents combined with polar additives like crown ethers, like 18-crown-6, or cryptands.
  • polar solvents are polar protic solvents or dipolar aprotic solvents.
  • polar protic solvents are water, alcohols like methanol, ethanol or iso-propanol, carbonic acids like acetic acid, ammonia, primary amines or secondary amines.
  • Polar protic solvents can only be used in an electrochemical cell comprising an anode, which comprises an alkali metal, if any contact between that anode and the polar protic solvent is strictly precluded by an appropriate separator.
  • dipolar aprotic solvents examples include organic carbonates, esters, ethers, sulfones like DMSO, sulfamides, amides like DMF or DMAc, nitriles like acetonitrile, lactams like NMP, lactones, linear or cyclic peralkylated urea derivatives like TMU or DMPU, fluorinated ether, fluori- nated carbamates, fluorinated carbonated or fluorinated esters.
  • Suitable solvents of the electrolyte composition (d) may be liquid or solid at room temperature and are preferably liquid at room temperature.
  • the inventive electrochemical cell is characterized in that the solvent (d1 ) is a dipolar aprotic solvent.
  • a suitable solvent (d1 ) is preferably selected from polymers, cyclic or noncyclic ethers, cyclic or noncyclic acetals, cyclic or noncyclic organic carbonates and ionic liquids.
  • the inventive electrochemical cell is characterized in that the solvent (d1 ) is selected from polymers, cyclic or noncyclic ethers, noncyclic or cyclic acetals and cyclic or noncyclic organic carbonates.
  • suitable polymers are especially polyalkylene glycols, preferably poly-Ci-C4- alkylene glycols and especially polyethylene glycols.
  • Polyethylene glycols may comprise up to 20 mol% of one or more Ci-C4-alkylene glycols in copolymerized form.
  • Polyalkylene glycols are preferably doubly methyl- or ethyl-capped polyalkylene glycols.
  • the molecular weight M w of suitable polyalkylene glycols and especially of suitable polyethylene glycols may be at least 400 g/mol.
  • the molecular weight M w of suitable polyalkylene glycols and especially of suitable polyethylene glycols may be up to 5 000 000 g/mol, preferably up to 2 000 000 g/mol.
  • suitable noncyclic ethers are, for example, diisopropyl ether, di-n-butyl ether, 1 ,2- dimethoxyethane, 1 ,2-diethoxyethane, preference being given to 1 ,2-dimethoxyethane.
  • Suitable cyclic ethers are tetrahydrofuran and 1 ,4-dioxane.
  • noncyclic acetals are, for example, dimethoxymethane, diethoxymethane, 1 ,1 -dimethoxyethane and 1 ,1 -diethoxyethane.
  • Suitable cyclic acetals are 1 ,3-dioxane and especially 1 ,3-dioxolane.
  • noncyclic organic carbonates examples include dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.
  • Suitable cyclic organic carbonates are compounds of the general formulae (X) and (XI)
  • R 1 , R 2 and R 3 may be the same or different and are each selected from hydrogen and Ci-C4-alkyl, for example methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert- butyl, where R 2 and R 3 are preferably not both tert-butyl.
  • R 1 is methyl and R 2 and R 3 are each hydrogen, or R 1 , R 2 and R 3 are each hydrogen.
  • Another preferred cyclic organic carbonate is vinylene carbonate, formula (XII).
  • the solvent(s) in what is called the anhydrous state, i.e. with a water content in the range from 1 ppm to 0.1 % by weight, determinable, for example, by Karl Fischer titration.
  • Possible alkali metal salts, which are used as conductive salts, have to be soluble in the solvent (d1 ).
  • Preferred metal salts (d2) are alkali metal salts, more preferably lithium salts or sodium salts, in particular lithium salts.
  • the inventive electrochemical cell is characterized in that the metal salt (d) is a lithium salt or sodium salt, preferably a lithium salt.
  • Suitable alkali metal salts are especially lithium salts.
  • suitable lithium salts are LiPF 6 , LiBF 4 , UCIO4, LiAsFe, UCF3SO3, LiC(CnF 2n+ iS02)3, LiNOs, lithium imides such as LiN(C n F2n+iS02)2, where n is an integer in the range from 1 to 20, LiN(S02F)2, Li2SiF6, LiSbF6, LiAICU, and salts of the general formula (C n F2n+iS02)mXLi, where m is defined as follows:
  • alkali metal salts are selected from LiC(CF 3 S0 2 ) 3 , LiN(CF 3 S0 2 ) 2 , LiPF 6 , LiBF 4 , LiCI0 4 , L1NO3 and particular preference is given to LiPF6 and LiN(CF3S02)2.
  • the concentration of conductive salt in electrolyte is in the range of from 0.01 M to 5 M, preferably 0.1 M to 1 .5 M.
  • inventive electrochemical cells can contain additives such as wetting agents, corrosion inhibitors, or protective agents such as agents to protect any of the electrodes or agents to protect the salt(s).
  • inventive electrochemical cells can have a disc-like shape. In another embodiment, inventive electrochemical cells can have a prismatic shape.
  • inventive electrochemical cells can include a housing that can be from steel or aluminium.
  • inventive electrochemical cells are combined to stacks including electrodes that are laminated.
  • inventive electrochemical cells are selected from pouch cells.
  • inventive electrochemical cells in particular rechargeable lithium sulfur cells, comprising the inventive electrode assembly (a) have overall advantageous properties. They exhibit good capacity, a low capacity fade rate per cycle, and good cycling stability on extended cycling.
  • a further aspect of the present invention refers to batteries, more preferably alkali metal-sulfur batteries, in particular to rechargeable lithium sulfur batteries, comprising at least one inventive electrochemical cell, for example two or more.
  • inventive electrochemical cells can be combined with one another in inventive batteries, for example in series connection or in parallel connection. Series connection is preferred.
  • inventive batteries in particular rechargeable lithium sulfur batteries, have advantageous properties. They exhibit good capacity, a low capacity fade rate per cycle, and good cycling stability on extended cycling.
  • inventive electrochemical cells or inventive batteries can be used for making or operating cars, computers, personal digital assistants, mobile telephones, watches, camcorders, digital cameras, thermometers, calculators, laptop BIOS, communication equipment or remote car locks, and stationary applications such as energy storage devices for power plants.
  • a further aspect of the present invention is a method of making or operating cars, computers, personal digital assistants, mobile telephones, watches, camcorders, digital cameras, thermometers, calculators, laptop BIOS, communication equipment, remote car locks, and stationary applications such as energy storage devices for power plants by employing at least one inventive battery or at least one inventive electrochemical cell.
  • a further aspect of the present invention is the use of the electrochemical cell as described above in motor vehicles, bicycles operated by electric motor, aircraft, ships or stationary energy stores.
  • inventive electrochemical cells in devices gives the advantage of prolonged run time before recharging and a smaller loss of capacity in the course of prolonged run time. If the intention were to achieve an equal run time with electrochemical cells with lower energy density, a higher weight for electrochemical cells would have to be accepted.
  • the present invention further provides a device comprising at least one inventive electrochemi- cal cell as described above.
  • mobile devices such as vehicles, for example automobiles, bicycles, aircraft, or water vehicles such as boats or ships.
  • Other examples of mobile devices are those which are portable, for example computers, especially laptops, telephones or electrical power tools, for example from the construction sector, especially drills, battery-driven screwdrivers or battery-driven tackers.
  • a 23 wt% colloidal suspension of 5 nm anatase ⁇ 2 crystallites in aqueous solution was synthesized based on the hydrolysis of titanium isopropoxide. Titanium isopropoxide was added to water and stirred for 1 h. The precipitate was filtered, washed, peptized in a Teflon reactor at 120 °C for 3 h with tetramethylammonium hydroxide, followed by centrifugation to eliminate the large aggregates from the suspension.
  • T1O2 precursor solution was prepared by diluting the above colloidal suspension (23 wt%) to a 5 wt% concentration using a mixture of methanol : water (79 : 21 by volume). To ensure minimal aggregation of the T1O2 colloids, the diluted suspensions were placed in ultrasonic bath for 15 min and filtered using 0.2 ⁇ cellulose acetate filters.
  • S1O2 precursor solutions for thin film deposition were prepared by diluting LUDOX ® TM 40, a 40 wt% suspension of amorphous S1O2 colloid in water, to a 5 wt% concentration using the same solvent as in 1.1 . To ensure minimal aggregation of the S1O2 colloids, the diluted suspensions were placed in ultrasonic bath for 15 min and filtered using 0.45 ⁇ cellulose acetate filters.
  • T1O2 precursor solution was prepared by diluting the 23 wt% colloidal suspension described on
  • the 40 wt% suspension of amorphous S1O2 colloid in water was diluted to a 10 wt% concentration using a mixture of methanol : water (79 : 21 by volume), with aid of a ultrasonic bath for 15 min, followed by filtration with 0.45 ⁇ cellulose acetate filters.
  • T1O2 soles (S1 and S3) prepared in example 1.1 was spin coated at 8000 rpm during 40 s on an uncoated sulfur cathode (C-E1 ) prepared in example 11.1 , covering it with an amorphous T1O2 layer. This step was repeated 5 times, until the desired weight percentage of T1O2 (20 wt%) was obtained. After coating, the best coated electrodes were selected (E2, the ones obtained with S1 ) and dried at 40°C under vacuum during 16 h.
  • Si02 Sole (S2 and S4) prepared in example 1.2 was spin coated at 8000 rpm during 40 s on an uncoated sulfur cathode (C-E1 ) prepared in example 11.1 , covering it with an amorphous S1O2 layer. This step was repeated 2 times until the desired weight percentage of S1O2 (20 wt%) was obtained. After coating, the best coated electrodes were selected (E3, obtained with S2) and dried at 40°C under vacuum during 16 h.
  • comparative electrode (C-E4) comprising S1O2 particles in same wt% as inventive electrode (E3)
  • Electrodes with same amount of metal oxide as the inventive electrode (E3) were prepared by mixing carbon blacks (Super C65 and Printex ® XE2), S1O2 powder, sulfur and polyvinyl alcohol (28 : 20 : 48 : 4 by weight) in a mixture of water, 2-propanol and 1 -methoxy-2-propanol (liquid mixture-1 , 65 : 30 : 5 by weight). This slurry was coated in a carbon coated aluminium foil by doctor blade and dried at 40 °C under vacuum.
  • the electrochemical tests were done using coin-type cells.
  • the cells were assembled in an argon-filled glove box using lithium foil as the counter electrode and a porous monolayer polyeth- ylene membrane (thickness: 20 ⁇ ; porosity: 45%) as separator.
  • the electrolyte used was a solution of lithium bis(tri-fluoromethanesulfonyl)imide, L1NO3 in 1 ,2-dimethoxyethane and 1 ,3- dioxolane (8 : 4 : 44 : 44 by weight).
  • Galvanostatic charge-discharge cycling were carried out using a Maccor battery tester in the potential range of 1.7-2.5 V (vs LiVLi) at a current density of 0.02 C rate for the first cycle and 0.2 C discharge rate and 0.125 C charge rate for the subse- quent cycles at controlled 25 °C. 111.1 .
  • Inventive electrodes comprising sulfur/ carbon electrode coated with metal oxide layer

Abstract

The present invention relates to an electrode assembly comprising as a first component (A) at least one three-dimensional geometric shape of an electroactive composition of at least one electroactive sulfur-containing material, which is arranged on a current collector as a second component (B), and comprising as a third component (C) a layer of at least one metal oxide, wherein the layer is deposited directly on all surfaces of the at least one three-dimensional ge- ometric shape or all parts of a surface of the at least one three-dimensional geometric shape, which are not covered with the current collector. The present invention further relates to a process for preparing said electrode assembly, to an electrochemical cell comprising said electrode assembly and to a battery comprising at least one inventive electrochemical cell.

Description

Metal oxide coated cathodes comprising sulfur for electrochemical cells Description The present invention relates to an electrode assembly comprising as a first component (A) at least one three-dimensional geometric shape of an electroactive composition of at least one electroactive sulfur-containing material, which is arranged on a current collector as a second component (B), and comprising as a third component (C) a layer of at least one metal oxide, wherein the layer is deposited directly on all surfaces of the at least one three-dimensional ge- ometric shape or all parts of a surface of the at least one three-dimensional geometric shape, which are not covered with the current collector.
The present invention further relates to a process for preparing said electrode assembly, to an electrochemical cell comprising said electrode assembly and to a battery comprising at least one inventive electrochemical cell.
Secondary batteries, accumulators or rechargeable batteries are just some embodiments by which electrical energy can be stored after generation and used when required. Due to the significantly better power density, there has been a move in recent times away from the water- based secondary batteries to development of batteries in which the charge transport in the electrical cell is accomplished by lithium ions.
However, the energy density of conventional lithium ion batteries which have a carbon anode and a cathode based on metal oxides is limited. New horizons with regard to energy density have been opened up by lithium-sulfur cells. In lithium-sulfur cells, sulfur in the sulfur cathode is reduced via polysulfide ions to S2_, which is reoxidized when the cell is charged to form sulfur- sulfur bonds.
A problem, however, is the solubility of the polysulfides, for example L12S4 and L12S6, which are generally soluble in the solvent and can migrate to the anode. The consequences may include: loss of capacitance and deposition of electrically insulating material on the sulfur particles of the electrode. The migration of the polysulfide ions from the cathode to the anode can ultimately lead to discharge of the affected cell and to cell death in the battery. This unwanted migration of polysulfide ions is also referred to as "shuttling", a term which is also used in the context of the present invention.
Carbon sulfur composites are important components of the cathodes of lithium sulfur cells contributing significantly to the overall performance of lithium sulfur cells in particular with respect to lowering the internal impedance by providing a conductive element. Depending on the porous carbon architecture and its surface modification, the carbon framework can increase the cou- lombic efficiency, lower the degree of capacity fading, and help limit self-discharge by physically trapping polysulfide ions within the cathode, although these effects are usually limited to short- term cycling. The structure and composition of the components of cathodes of lithium sulfur cells and of the cathodes themselves contribute significantly to the overall performance of lithium sulfur cells in particular with respect to coulombic efficiency, degree of capacity fading, self-discharge, durability or cycle life.
US 6,210,831 describes solid composite cathodes which comprise (a) sulfur-containing cathode material which, in its oxidized state, comprises a polysulfide moiety of the formula, -Sm-, wherein m is an integer from 3 to 10; and (b) a non-electroactive particulate material having a strong adsorption of soluble polysulfides.
US 7,175,937 describes a separator having an inorganic protective film and a lithium battery using the separator.
US 8,592,088 describes an electrode assembly comprising an porous ceramic layer comprising an inorganic oxide filler and a polymeric binder.
S. Evers et al, J. Phys. Chem. C 2012, 1 16, 19653-19658, describes the absorption/adsorption in nanoporous polysulfide sorbents for the Li-S battery. US 2013/0065127 describes sulfur cathodes for use in an electric current producing cells or rechargeable batteries. The sulfur cathode comprises an electroactive sulfur containing material, an electrically conductive filler and a non-electroactive component.
The electroactive sulfur-containing electrode assemblies, in particular sulfur comprising cath- odes, described in the literature still have shortcomings with regard to one or more of the properties desired for such electrodes and the electrochemical cells produced therefrom.
Desirable properties are, for example, high electrical conductivity of the cathode materials, maintenance of cathode capacity during lifetime, reduced self-discharge of the electrochemical cells during storage, an increase in the lifetime of the electrochemical cell, an improvement in the mechanical stability of the cathode or a reduced change in volume of the cathodes during a charge-discharge cycle. In general, the desired properties mentioned also make a crucial contribution to improving the economic viability of the electrochemical cell, which, as well as the aspect of the desired technical performance profile of an electrochemical cell, is of crucial signif- icance to the user.
It was thus an object of the present invention to provide beneficial sulfur-containing electrode assemblies for lithium-sulfur cells and the corresponding electrochemical cells, which have advantages over one or more properties of a known electrode assembly and the corresponding electrochemical cell respectively, in particular with respect to an increase of cycle life and of coulombic efficiency reflected by improved cycling stability and reduction of capacity fading. It was also an object of the present invention to find a simple, flexible and economic process for producing said improved electrode assemblies. In general, the desired properties mentioned also make a crucial contribution to improving the economic viability of the lithium-sulfur battery, which, as well as the aspect of the desired technical performance profile of the lithium-sulfur battery, is of crucial significance to the user.
This object is achieved by an electrode assembly comprising
(A) at least one three-dimensional geometric shape of an electroactive composition
comprising
(A1 ) at least one electroactive sulfur-containing material,
(A2) carbon in a polymorph comprising at least 60% sp2-hybridized carbon atoms, and
(A3) optionally at least one binder, arranged on
(B) a current collector, and a layer (C) of at least one metal oxide, wherein the layer has a thickness in the range from 10 to 500 nm, preferably in the range from 15 to 50 nm, and wherein the layer is deposited directly on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three-dimensional geometric shape, which are not covered with the current collector.
In the context with the present invention, the electrode where during discharging a net negative charge occurs is called the anode and the electrode where during discharging a net positive charge occurs is in general called cathode, and in the following description it is called the inventive electrode assembly.
The inventive electrode assembly comprises as a first component (A) at least one three- dimensional geometric shape of an electroactive composition, also referred to hereinafter as shape (A), which is arranged on a current collector as a second component (B) of the electrode assembly, also referred to hereinafter as collector (B), and the inventive electrode assembly comprises as a third component (C) a layer (C) of at least one metal oxide, also referred to hereinafter as layer (C).
The three-dimensional geometric shape of an electroactive composition, which is arranged on current collector (B), can be varied in a broad range. Examples of three-dimensional geometric shapes are polyhedrons, like cubes, pyramids or toroids, cylinders, ellipsoids or spheres. If several shapes (A) are arranged on collector (B), these shapes (A) can be equal or different and can be arranged in regular patterns or in irregular form. For example a regular pattern of equal cuboids or hemispheres can be arranged on collector (B), wherein the distances between adja- cent shapes are preferably less than the greatest spatial dimension of the shapes. Shape (A) is in direct contact with collector (B). The direct contact can be established by at least one vertex, at least one edge or a face in each case of shape (A) with collector (B). In order to arrange a maximum amount of electroactive composition on collector (B) preferably a single shape is chosen, which avoids free spaces present between adjacent shapes. The three-dimensional geo- metric shape of an electroactive composition (A) is preferably designed as a layer, more preferably as a layer having a thickness in the range from 15 to 400 μηη, more preferably in the range from 25 to 200 μηη, in particular in the range from 30 to 100 μηη. While the thickness of the layer represents the smallest of its three spatial dimensions (extents), the two other dimensions of the layer are usually determined by the dimensions of the surface of the collector (B).
In one embodiment of the present invention, the inventive electrode assembly is characterized in that the at least one three-dimensional geometric shape of an electroactive composition (A) is designed as a layer, preferably as a layer having a thickness in the range from 15 to 400 μηη, more preferably in the range from 25 to 200 μηη, in particular in the range from 30 to 100 μηη.
The electroactive composition, which is arranged in form of at least one three-dimensional geometric shape (A) on collector (B), preferably arranged in form of a layer, comprises as a first ingredient at least one electroactive sulfur-containing material, also referred to hereinafter as sulfur-containing material (A1 ) for short, as a second ingredient carbon in a polymorph comprising at least 60% sp2-hybridized carbon atoms, also referred to hereinafter as carbon
(A2) for short, and optionally as a third ingredient at least one binder, also referred to hereinafter as binder (A3) for short.
Electroactive sulfur-containing materials (A1 ) are for example covalent compounds like elemental sulfur, composites produced from elemental sulfur and at least one polymer, composites produced from elemental sulfur and at least one carbon material or polymers comprising polysulfide bridges or ionic compounds like salts of sulfides or polysulfides.
Elemental sulfur is known as such.
Composites produced from elemental sulfur and at least one polymer, which find use as ingredient of electroactive compositions, are likewise known to those skilled in the art. Adv. Funct. Mater. 2003, 13, 487 ff describes, for example, a reaction product of sulfur and polyacrylonitrile, which results from elimination of hydrogen from polyacrylonitrile with simultaneous formation of hydrogen sulfide. Composites, produced from elemental sulfur and at least one carbon material, are described for example in US 201 1/318654 or US 2012/298926.
Polymers comprising divalent di- or polysulfide bridges, for example polyethylene tetrasulfide, are likewise known in principle to those skilled in the art. J. Electrochem. Soc, 1991 , 138, 1896 - 1901 and US 5,162,175 describe the replacement of pure sulfur with polymers comprising disulfide bridges. Polyorganodisulfides are used therein as materials for solid redox
polymerization electrodes in rechargeable cells, together with polymeric electrolytes. Salts of sulfides or polysulfides are examples of ionic compounds comprising at least one Li-S- group like L12S, lithium polysulfides (Li2S2 to 8) or lithiated thiols (lithium thiolates).
A preferred electroactive sulfur-containing material (A1 ) is elemental sulfur. In one embodiment of the present invention, the inventive electrode assembly is characterized in that the at least one electroactive sulfur-containing material (A1 ) is elemental sulfur.
Carbon (A2), which improves the electrical conductivity of the electroactive composition of the inventive electrode assembly, can be selected from graphite, carbon black, carbon nanotubes, graphene or mixtures of at least two of the aforementioned substances. Suitable carbons in a conductive polymorph are described in WO 2012/168851 page 4, line 30 to page 6, line 22.
In one embodiment of the present invention, the inventive electrode assembly is characterized in that carbon (A2) is selected from graphite, graphene, activated carbon and especially carbon black.
In one embodiment of the present invention, the inventive electrode assembly comprises at least one polymer as a binder (A3). Binder (A3) can be selected from a wide range of organic polymers. Suitable binders are described in WO 2012/168851 page 6, line 40 to page 7, line 30.
Particularly suitable binders for the inventive electrode assembly are especially polyvinyl alcohol, poly(ethylene oxide), carboxymethyl cellulose (CMC) and halogenated (co)polymers, for example polyvinyl chloride or polyvinylidene chloride, especially fluorinated (co)polymers such as polyvinyl fluoride and especially polyvinylidene fluoride, lithiated Nafion and
polytetrafluoroethylene.
In one embodiment of the present invention, the electroactive composition of the inventive electrode assembly comprises in the range from 10 to 80% by weight, preferably 30 to 75% by weight, of sulfur, determined by elemental analysis, based on the total weight of the
electroactive composition of the inventive electrode assembly. In one embodiment of the present invention, the electroactive composition of the inventive electrode assembly comprises in the range from 0.1 to 60% by weight of carbon (A2) in a conductive polymorph, preferably 1 to 30% by weight based on the total weight of the electroactive composition. This carbon can likewise be determined by elemental analysis, for example, in which case the evaluation of the elemental analysis has to take into account the fact that carbon also arrives in organic polymers representing binders, and possibly further sources.
In one embodiment of the present invention, the electroactive composition of the inventive elec- trode assembly comprises in the range from 0.1 to 20% by weight of binder (A3), preferably 1 to 15% by weight and more preferably 3 to 12% by weight, based on the total weight of the electroactive composition.
Collector (B) as a component of the inventive electrode assembly is known by the person skilled in the art. Collector (B) may be configured in the form of a metal wire, metal grid, metal mesh, expanded metal, metal sheet, metal foil or carbon paper/cloth. Preferably collector (B) is configured in the form of a metal foil, more preferably in form of an aluminium foil. The thickness of a foil can be varied in a wide range. The thickness of a suitable aluminium foil is preferably in the range from 5 to 100 μηη, in particular in the range from 10 to 20 μηη.
In one embodiment of the present invention, the inventive electrode assembly is characterized in that the current collector (B) is an aluminium foil, preferably having a thickness in the range from 5 to 100 μηη, in particular having a thickness in the range from 10 to 20 μηη. The inventive electrode assembly comprises as a third component (C) a layer (C) of at least one metal oxide, wherein layer (C) has a thickness in the range from 10 to 500 nm, preferably in the range from 15 to 50 nm, and wherein layer (C) is deposited directly on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three- dimensional geometric shape, which are not covered with the current collector.
Metal oxides can be produced in crystalline form or in amorphous form, depending on the applied reaction conditions, used starting materials and intended chemical composition of the metal oxide. The metal oxide of layer (C) is preferably deposited in amorphous form on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three-dimensional geometric shape, which are not covered with the current collector.
In one embodiment of the present invention, the inventive electrode assembly is characterized in that the metal oxide of layer (C) is deposited in amorphous form. The metal oxide of layer (C) can be chosen from a wide variety of metal oxide, main group metal oxides as well as transition metal oxides or lanthanide oxides. Preferably the metal oxide of layer (C) is selected from the group consisting of ΤΊΟ2, S1O2, B2O3, AI2O3, V2O5, V02 and Zr02, in particular selected from the group consisting of amorphous Ti02 and amorphous S1O2.
In one embodiment of the present invention, the inventive electrode assembly is characterized in that the metal oxide of layer (C) is selected from the group consisting of ΤΊΟ2, S1O2, B2O3, AI2O3, V2O5, VO2 and Zr02, in particular selected from the group consisting of amorphous ΤΊΟ2 and amorphous S1O2.
Layer (C) comprises at least one metal oxide, e.g. layer (C) comprises one metal oxide or a mixture of two or more metal oxides. Preferably layer (C) comprises one metal oxide wherein traces of other metal oxides in amounts of less than 1 % by weight based on the total weight of all metal oxides are not considered as additional metal oxides. Beside the at least one metal oxide, layer (C) might comprise additional compounds, e.g. organic polymers, tenside molecules, nano-scaled carbons like fullerenes or carbon nanotubes or solvents like water or alco- hols. The sum of the mass fractions of all metal oxides based on layer (C) can be varied in a wide range depending on the amount of components in addition to the metal oxides. Preferably the mass fraction of the major metal oxide based the total weight of layer (C) is in the range from 0.5 to 1 , more preferably in the range from 0.8 to 1 , in particular in the range from 0.9 to 1 .
Different processes for the preparation of metal oxides and the deposition of a layer of said metal oxides on a substrate are known to the person skilled in the art. Applicable methods ; chemical vapor deposition, reactive sputtering, pulsed layer deposition or applying sol-gel methods. The metal oxide of layer (C) is preferably produced by a sol-gel process, which is also known to the person skilled in the art, and then deposited as a layer on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three- dimensional geometric shape, which are not covered with the current collector. More preferably the metal oxide forming layer (C) is produced by a sol-gel process comprising the hydrolysis of a corresponding metal alkoxide followed by condensation.
Alternatively layer (C) comprises at least one metal oxide can be produced by depositing a layer of an metal oxide precursor, preferably a metal alkoxide, directly on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three- dimensional geometric shape, which are not covered with the current collector, followed by converting said metal oxide precursor to the corresponding metal oxide, e.g. hydrolyzing a metal alkoxide to the corresponding metal hydroxide followed by condensation to the corresponding metal oxide.
In one embodiment of the present invention, the inventive electrode assembly is characterized in that the metal oxide of layer (C) was produced by a sol-gel process, preferably by hydrolysis of a corresponding metal alkoxide followed by condensation. Metal alkoxides are generally known to the person skilled in the art. Examples of suitable metal alkoxides are titanium tetraethoxide, titanium tetraisopropoxide, titanium tetrabutoxide, tetra- ethoxysilane, tetramethoxysilane, trimethyl borate, aluminium triisopropoxide, titanium tetraethoxide, triisopropoxyvanadium(V) oxide, vanadium(V) oxytriethoxide, zirconium tetra- isopropoxide or zirconium tetrabutoxide.
Preferably first a sol of the selected metal oxide is formed and this sol is then deposited on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three-dimensional geometric shape, which are not covered with the current collector by methods known to the person skilled in the art, like spray coating, brushing, screen printing, tape casting, dip coating or spin coating an appropriate sole, preferably dip coating or spin coating, in particular spin coating. The deposited sol of a metal oxide, which is a suspension of na- noparticles of said metal oxide, forms then a layer of a gel, also called xerogel film, which can be converted to a dense film by further heating.
In one embodiment of the present invention, the concentration of nanoparticles of said metal oxide in the suspension is in the range of from 0.01 to 50 wt%, preferably 0.1 to 5 wt%.
In one embodiment of the present invention, the inventive electrode assembly is characterized in that the layer of the at least one metal oxide was deposited by means of dip coating or spin coating of a sol of said metal oxide.
In one embodiment of the present invention, the inventive electrode assembly is characterized in that the metal oxide of layer (C) is selected from the group consisting of amorphous Ti02 and amorphous S1O2, and in that the layer of the at least one metal oxide was deposited by means of dip coating or spin coating of a sol of said metal oxide.
The deposited layer (C) of at least one metal oxide is usually not impervious to solvents, in particular aprotic, dipolar solvents, which are usually used as component of an electrolyte for elec- trochemical cells. Preferably the deposited layer (C) of at least one metal oxide is pervious to electrolytes, which are used in non-aqueous electrochemical cells.
The present invention further provides a process for producing an electrode assembly as described above, comprising the process steps of
(a) arranging at least one three-dimensional geometric shape of an electroactive composition comprising
(A1 ) at least one electroactive sulfur-containing material,
(A2) carbon in a polymorph comprising at least 60% sp2-hybridized carbon atoms, and
(A3) optionally at least one binder, on a current collector (B), and
(β) depositing a layer (C) of at least one metal oxide directly on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three- dimensional geometric shape, which are not covered with the current collector (B).
The description and preferred embodiments of the three-dimensional geometric shape, of the electroactive composition and its components, in particular the description of the electroactive sulfur-containing material (A1 ), of the current collector, and of layer (C) and its components, in particular the description of the metal oxide of said layer (C), in the inventive process corre- spond to the above description for these components for the electrode assembly of the present invention.
Methods of arranging the at least one three-dimensional geometric shape of an electroactive composition on current collector (B) are known to the person skilled in the art. It is possible to place solid three-dimensional geometric shapes of the electroactive composition in the desired pattern on current collector (B) or to deposit a slurry of the electroactive composition in the desired form and pattern on current collector (B), for example using stencils, molding tools, ink jet printing or doctor blade techniques, and afterward remove the liquid medium of the deposited slurry.
Methods of depositing a layer (C) of at least one metal oxide directly on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three- dimensional geometric shape, which are not covered with the current collector, are known to the person skilled in the art and they have been described above. Preferably layer (C) is formed by sol-gel methods as described above, more preferably by sol-gel methods in combination with dip coating, spin coating, screen printing or tape casting.
In one embodiment of the present invention, the inventive process is characterized in that in process step (β) the metal oxide of layer (C) is produced by a sol-gel process, preferably by hydrolysis of a corresponding metal alkoxide followed by condensation.
In another embodiment of the present invention, the inventive process is characterized in that in process step (β) the layer of the at least one metal oxide is deposited by means of screen printing, tape casting, dip coating or spin coating, preferably dip coating or spin coating, in particular spin coating, of a sol or paste of said metal oxide, preferably wherein a sol, that is a dispersion of nanoparticles of said metal oxide, is obtained by the first step of the known sol-gel method optionally followed by further dilution of the initially obtained sol, in particular by hydrolysis of a corresponding metal alkoxide followed by condensation. The nanoparticles of said metal oxide of the sole comprise reactive functional groups on their surfaces, in particular hydroxide groups. By increasing the concentration of the nanoparticles of said metal oxide during removing the dispersion medium, usually water, hydroxyl groups of different nanoparticles of said metal oxide react with each other under elimination of water and formation of a gel of interconnected nanoparticles of said metal oxide.
Alternatively it is possible to produce layer (C) comprises at least one metal oxide by depositing a layer of a metal oxide precursor, preferably a metal alkoxide, by means of screen printing, tape casting, dip coating or spin coating directly on all surfaces of the at least one three- dimensional geometric shape or all parts of a surface of the at least one three-dimensional geometric shape, which are not covered with the current collector, followed by converting said metal oxide precursor to the corresponding metal oxide, e.g. hydrolyzing a metal alkoxide to the corresponding metal hydroxide followed by condensation to the corresponding metal oxide.
The inventive electrode assemblies are particularly suitable as a component of electrochemical cells, in particular rechargeable lithium-sulfur cells.
The present invention further provides an electrochemical cell comprising
(a) at least one electrode assembly as described above,
(b) at least one anode (b), (c) at least one separator (c), and
(d) at least one electrolyte composition (d) comprising (d1 ) at least one aprotic organic solvent (d1 ), and
(d2) at least one alkali metal salt (d2).
The inventive electrochemical cell comprises in addition to the inventive electrode assembly, which has been described above and which is also referred to hereinafter as electrode (a) or cathode (a) for short, as a second component (b) at least one anode (b), as a third component
(c) at least one separator (c), and as a fourth component (d) at least one electrolyte composition
(d) .
The description and preferred embodiments of the inventive electrode assembly and its components correspond to the above description. During the charging process of an inventive electrochemical cell, inventive cathode (a) comprises usually a mixture of different electroactive sulfur-containing materials, since more and more S-S-bonds are formed. In one embodiment of the present invention, inventive electrochemical cells comprise, as well as inventive electrode assembly, at least one anode (b) comprising at least one metal, preferably magnesium, aluminium, zinc or an alkali metal like lithium, sodium or potassium. Preferably anode (b) of the inventive electrochemical cell comprises an alkali metal, in particular lithium. The metal of anode (b) of the inventive electrochemical cell can be present in the form of a pure metal phase, preferably a pure alkali metal phase, in form of an alloy together with other metals or metalloids, in form of an intercalation compound or in form of an ionic compound comprising at least one metal, preferably an alkali metal and at least one transition metal. Anode (b) of the inventive electrochemical cell, in particular of the inventive lithium-sulfur cell, can be selected from anodes being based on various active materials. Suitable active materials are metallic lithium, carbon-containing materials such as graphite, graphene, charcoal, expanded graphite, in particular graphite, furthermore lithium titanate (Li4Ti50i2), anodes comprising In, Tl, Sb, Sn or Si, in particular Sn or Si, for example tin oxide (Sn02) or nanocrystalline silicon, and anodes comprising metallic lithium.
In one embodiment of the present invention the electrochemical cell is characterized in that anode (b) of the inventive electrochemical cell is selected from graphite anodes, lithium titanate anodes, anodes comprising In, Tl, Sb, Sn or Si, and anodes comprising metallic lithium.
In one embodiment of the present invention, the inventive electrochemical cell is characterized in that the metal of anode (b) is lithium.
Anode (b) of the inventive electrochemical cell can further comprise a current collector. Suitable current collectors are, e.g., metal wires, metal grids, metal gauze and preferably metal foils such as copper foils.
Anode (b) of the inventive electrochemical cell can further comprise a binder. Suitable binders can be selected from organic (co)polymers. Suitable organic (co)polymers may be halogenated or halogen-free. Examples are polyethylene oxide (PEO), cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyethylene, polypropylene, polytetrafluoroethylene, polyacrylonitrile-methyl methacrylate, styrene-butadiene copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, vinylidene fluoride-hexafluoropropylene copolymers (PVdF-HFP), vinylidene fluoride- tetrafluoroethylene copolymers, perfluoroalkyl vinyl ether copolymers, ethylene- tetrafluoroethylene copolymers, vinylidene fluoride-chlorotrifluoroethylene copolymers, ethylene- chlorofluoroethylene copolymers, ethylene-acrylic acid copolymers, optionally at least partially neutralized with alkali metal salt or ammonia, ethylene-methacrylic acid copolymers, optionally at least partially neutralized with alkali metal salt or ammonia, ethylene-(meth)acrylic ester copolymers, polysulfones, polyimides and polyisobutene.
Suitable binders are especially polyvinyl alcohol and halogenated (co)polymers, for example polyvinyl chloride or polyvinylidene chloride, especially fluorinated (co)polymers such as polyvinyl fluoride and especially polyvinylidene fluoride and polytetrafluoroethylene.
The average molecular weight Mw of binder may be selected within wide limits, suitable examples being 20,000 g/mol to 1 ,000,000 g/mol.
In one embodiment of the present invention, anode (b) of the inventive electrochemical cell can have a thickness in the range of from 15 to 200 μηη, preferably from 30 to 100 μηη, determined without the current collector. In one embodiment of the present invention, inventive electrochemical cells comprise one or more separators (c) by which the electrodes are mechanically separated from one another. Suitable separators (c) are polymer films, especially porous polymer films, which are unreactive toward elemental metals, in particular metallic lithium and toward lithium sulfides and lithium polysulfides. Particularly suitable materials for separators (c) are polyolefins, especially porous polyethylene films and porous polypropylene films.
Polyolefin separators, especially of polyethylene or polypropylene, may have a porosity in the range from 35 to 45%. Suitable pore diameters are, for example, in the range from 30 to 500 nm.
In another embodiment of the present invention, the separators (c) selected may be separators composed of PET nonwovens filled with inorganic particles. Such separators may have a porosity in the range from 40 to 55%. Suitable pore diameters are, for example, in the range from 80 to 750 nm.
The inventive electrochemical cell further comprises, as well as the inventive cathode (a), an anode (b) and a separator (c), at least one electrolyte composition (d) comprising at least one solvent (d1 ) and at least one metal salt (d2), preferably at least one alkali metal salt (d2). As regards suitable solvents and further additives for non-aqueous liquid electrolytes for lithium- based rechargeable batteries reference is made to the relevant prior art, e.g. Chem. Rev. 2004, 104, 4303-4417, in particular table 1 on page 4307, table 2 on page 4308 and table 12 on page 4379. The inventive electrochemical cell further comprises, as well as the inventive cathode (a), an anode (b) and an separator (c), at least one electrolyte composition (d) comprising at least one solvent (d1 ) aprotic organic and at least one metal salt (d2) alkali. The solvents (d1 ) of the electrolyte composition (d) can be chosen from a wide range of solvents, in particular from solvents which dissolve metal salts, in particular alkali metal salts easily. Solvents or solvent systems, which dissolve metal salts, in particular alkali metal salts are for example ionic liquids, polar solvents or combinations of apolar solvents combined with polar additives like crown ethers, like 18-crown-6, or cryptands. Examples of polar solvents are polar protic solvents or dipolar aprotic solvents.
Examples of polar protic solvents are water, alcohols like methanol, ethanol or iso-propanol, carbonic acids like acetic acid, ammonia, primary amines or secondary amines. Polar protic solvents can only be used in an electrochemical cell comprising an anode, which comprises an alkali metal, if any contact between that anode and the polar protic solvent is strictly precluded by an appropriate separator.
Examples of dipolar aprotic solvents are organic carbonates, esters, ethers, sulfones like DMSO, sulfamides, amides like DMF or DMAc, nitriles like acetonitrile, lactams like NMP, lactones, linear or cyclic peralkylated urea derivatives like TMU or DMPU, fluorinated ether, fluori- nated carbamates, fluorinated carbonated or fluorinated esters.
Suitable solvents of the electrolyte composition (d) may be liquid or solid at room temperature and are preferably liquid at room temperature.
In one embodiment of the present invention the inventive electrochemical cell is characterized in that the solvent (d1 ) is a dipolar aprotic solvent. A suitable solvent (d1 ) is preferably selected from polymers, cyclic or noncyclic ethers, cyclic or noncyclic acetals, cyclic or noncyclic organic carbonates and ionic liquids.
In one embodiment of the present invention the inventive electrochemical cell is characterized in that the solvent (d1 ) is selected from polymers, cyclic or noncyclic ethers, noncyclic or cyclic acetals and cyclic or noncyclic organic carbonates.
Examples of suitable polymers are especially polyalkylene glycols, preferably poly-Ci-C4- alkylene glycols and especially polyethylene glycols. Polyethylene glycols may comprise up to 20 mol% of one or more Ci-C4-alkylene glycols in copolymerized form. Polyalkylene glycols are preferably doubly methyl- or ethyl-capped polyalkylene glycols.
The molecular weight Mw of suitable polyalkylene glycols and especially of suitable polyethylene glycols may be at least 400 g/mol. The molecular weight Mw of suitable polyalkylene glycols and especially of suitable polyethylene glycols may be up to 5 000 000 g/mol, preferably up to 2 000 000 g/mol. Examples of suitable noncyclic ethers are, for example, diisopropyl ether, di-n-butyl ether, 1 ,2- dimethoxyethane, 1 ,2-diethoxyethane, preference being given to 1 ,2-dimethoxyethane.
Examples of suitable cyclic ethers are tetrahydrofuran and 1 ,4-dioxane.
Examples of suitable noncyclic acetals are, for example, dimethoxymethane, diethoxymethane, 1 ,1 -dimethoxyethane and 1 ,1 -diethoxyethane.
Examples of suitable cyclic acetals are 1 ,3-dioxane and especially 1 ,3-dioxolane.
Examples of suitable noncyclic organic carbonates are dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.
Examples of suitable cyclic organic carbonates are compounds of the general formulae (X) and (XI)
Figure imgf000015_0001
in which R1, R2 and R3 may be the same or different and are each selected from hydrogen and Ci-C4-alkyl, for example methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert- butyl, where R2 and R3 are preferably not both tert-butyl.
In particularly preferred embodiments, R1 is methyl and R2 and R3 are each hydrogen, or R1, R2 and R3 are each hydrogen. Another preferred cyclic organic carbonate is vinylene carbonate, formula (XII).
O Preference is given to using the solvent(s) in what is called the anhydrous state, i.e. with a water content in the range from 1 ppm to 0.1 % by weight, determinable, for example, by Karl Fischer titration. Possible alkali metal salts, which are used as conductive salts, have to be soluble in the solvent (d1 ). Preferred metal salts (d2) are alkali metal salts, more preferably lithium salts or sodium salts, in particular lithium salts.
In one embodiment of the present invention the inventive electrochemical cell is characterized in that the metal salt (d) is a lithium salt or sodium salt, preferably a lithium salt.
Suitable alkali metal salts are especially lithium salts. Examples of suitable lithium salts are LiPF6, LiBF4, UCIO4, LiAsFe, UCF3SO3, LiC(CnF2n+iS02)3, LiNOs, lithium imides such as LiN(CnF2n+iS02)2, where n is an integer in the range from 1 to 20, LiN(S02F)2, Li2SiF6, LiSbF6, LiAICU, and salts of the general formula (CnF2n+iS02)mXLi, where m is defined as follows:
m = 1 when X is selected from oxygen and sulfur,
m = 2 when X is selected from nitrogen and phosphorus, and
m = 3 when X is selected from carbon and silicon. Preferred alkali metal salts are selected from LiC(CF3S02)3, LiN(CF3S02)2, LiPF6, LiBF4, LiCI04, L1NO3 and particular preference is given to LiPF6 and LiN(CF3S02)2.
In one embodiment of the present invention, the concentration of conductive salt in electrolyte is in the range of from 0.01 M to 5 M, preferably 0.1 M to 1 .5 M.
In one embodiment of the present invention, inventive electrochemical cells can contain additives such as wetting agents, corrosion inhibitors, or protective agents such as agents to protect any of the electrodes or agents to protect the salt(s). In one embodiment of the present invention, inventive electrochemical cells can have a disc-like shape. In another embodiment, inventive electrochemical cells can have a prismatic shape.
In one embodiment of the present invention, inventive electrochemical cells can include a housing that can be from steel or aluminium.
In one embodiment of the present invention, inventive electrochemical cells are combined to stacks including electrodes that are laminated.
In one embodiment of the present invention, inventive electrochemical cells are selected from pouch cells. Inventive electrochemical cells, in particular rechargeable lithium sulfur cells, comprising the inventive electrode assembly (a) have overall advantageous properties. They exhibit good capacity, a low capacity fade rate per cycle, and good cycling stability on extended cycling. A further aspect of the present invention refers to batteries, more preferably alkali metal-sulfur batteries, in particular to rechargeable lithium sulfur batteries, comprising at least one inventive electrochemical cell, for example two or more. Inventive electrochemical cells can be combined with one another in inventive batteries, for example in series connection or in parallel connection. Series connection is preferred.
Inventive batteries, in particular rechargeable lithium sulfur batteries, have advantageous properties. They exhibit good capacity, a low capacity fade rate per cycle, and good cycling stability on extended cycling. The inventive electrochemical cells or inventive batteries can be used for making or operating cars, computers, personal digital assistants, mobile telephones, watches, camcorders, digital cameras, thermometers, calculators, laptop BIOS, communication equipment or remote car locks, and stationary applications such as energy storage devices for power plants. A further aspect of the present invention is a method of making or operating cars, computers, personal digital assistants, mobile telephones, watches, camcorders, digital cameras, thermometers, calculators, laptop BIOS, communication equipment, remote car locks, and stationary applications such as energy storage devices for power plants by employing at least one inventive battery or at least one inventive electrochemical cell. A further aspect of the present invention is the use of the electrochemical cell as described above in motor vehicles, bicycles operated by electric motor, aircraft, ships or stationary energy stores.
The use of inventive electrochemical cells in devices gives the advantage of prolonged run time before recharging and a smaller loss of capacity in the course of prolonged run time. If the intention were to achieve an equal run time with electrochemical cells with lower energy density, a higher weight for electrochemical cells would have to be accepted.
The present invention further provides a device comprising at least one inventive electrochemi- cal cell as described above. Preferred are mobile devices such as vehicles, for example automobiles, bicycles, aircraft, or water vehicles such as boats or ships. Other examples of mobile devices are those which are portable, for example computers, especially laptops, telephones or electrical power tools, for example from the construction sector, especially drills, battery-driven screwdrivers or battery-driven tackers.
The invention is illustrated by the examples which follow, but these do not restrict the invention. Figures in percent are each based on % by weight, unless explicitly stated otherwise.
I. Sole preparation 1.1 Preparation of a T1O2 sole (S1 )
A 23 wt% colloidal suspension of 5 nm anatase ΤΊΟ2 crystallites in aqueous solution was synthesized based on the hydrolysis of titanium isopropoxide. Titanium isopropoxide was added to water and stirred for 1 h. The precipitate was filtered, washed, peptized in a Teflon reactor at 120 °C for 3 h with tetramethylammonium hydroxide, followed by centrifugation to eliminate the large aggregates from the suspension.
T1O2 precursor solution was prepared by diluting the above colloidal suspension (23 wt%) to a 5 wt% concentration using a mixture of methanol : water (79 : 21 by volume). To ensure minimal aggregation of the T1O2 colloids, the diluted suspensions were placed in ultrasonic bath for 15 min and filtered using 0.2 μηη cellulose acetate filters.
1.2 Preparation of a Si02 sole (S2)
S1O2 precursor solutions for thin film deposition were prepared by diluting LUDOX® TM 40, a 40 wt% suspension of amorphous S1O2 colloid in water, to a 5 wt% concentration using the same solvent as in 1.1 . To ensure minimal aggregation of the S1O2 colloids, the diluted suspensions were placed in ultrasonic bath for 15 min and filtered using 0.45 μηη cellulose acetate filters.
1.3 Preparation of a T1O2 sole (S3)
T1O2 precursor solution was prepared by diluting the 23 wt% colloidal suspension described on
I.1 to a 10 wt% concentration using a mixture of methanol : water (79 : 21 by volume), with aid of the ultrasonic bath for 15 min, followed by filtration with 0.2 μηη cellulose acetate filters. 1.4 Preparation of a S1O2 sole (S4)
The 40 wt% suspension of amorphous S1O2 colloid in water was diluted to a 10 wt% concentration using a mixture of methanol : water (79 : 21 by volume), with aid of a ultrasonic bath for 15 min, followed by filtration with 0.45 μηη cellulose acetate filters.
II. Preparation of cathodes comprising a metal oxide layer
11.1 Preparation of uncoated sulfur cathodes (C-E1 ) The working electrodes were prepared by a mixture of carbon blacks (Super C65 and Printex XE2), sulfur and polyvinyl alcohol in a ratio 35 : 60 : 5 by weight in a mixture of water, 2- propanol and 1 -methoxy-2-propanol (liquid mixture-LM, 65 : 30 : 5 by weight). The resulting mix- ture was ball milled during 20 h to form a homogeneous slurry, which was coated by doctor blade in a carbon coated aluminium foil and dried at 40 °C under vacuum for 16h. To study the effect of metal oxide layers coating the whole working electrode, these cathodes were then coated with metal oxide layers, as described below.
11.2 Preparation of electrodes coated with T1O2 layer (E2)
The T1O2 soles (S1 and S3) prepared in example 1.1 was spin coated at 8000 rpm during 40 s on an uncoated sulfur cathode (C-E1 ) prepared in example 11.1 , covering it with an amorphous T1O2 layer. This step was repeated 5 times, until the desired weight percentage of T1O2 (20 wt%) was obtained. After coating, the best coated electrodes were selected (E2, the ones obtained with S1 ) and dried at 40°C under vacuum during 16 h.
11.3 Preparation of electrode coated with S1O2 layer (E3)
The Si02 Sole (S2 and S4) prepared in example 1.2 was spin coated at 8000 rpm during 40 s on an uncoated sulfur cathode (C-E1 ) prepared in example 11.1 , covering it with an amorphous S1O2 layer. This step was repeated 2 times until the desired weight percentage of S1O2 (20 wt%) was obtained. After coating, the best coated electrodes were selected (E3, obtained with S2) and dried at 40°C under vacuum during 16 h.
11.4 Preparation of comparative electrode (C-E4) comprising S1O2 particles in same wt% as inventive electrode (E3) Electrodes with same amount of metal oxide as the inventive electrode (E3) were prepared by mixing carbon blacks (Super C65 and Printex® XE2), S1O2 powder, sulfur and polyvinyl alcohol (28 : 20 : 48 : 4 by weight) in a mixture of water, 2-propanol and 1 -methoxy-2-propanol (liquid mixture-1 , 65 : 30 : 5 by weight). This slurry was coated in a carbon coated aluminium foil by doctor blade and dried at 40 °C under vacuum.
III. Electrochemical Testing
The electrochemical tests were done using coin-type cells. The cells were assembled in an argon-filled glove box using lithium foil as the counter electrode and a porous monolayer polyeth- ylene membrane (thickness: 20 μηη; porosity: 45%) as separator. The electrolyte used was a solution of lithium bis(tri-fluoromethanesulfonyl)imide, L1NO3 in 1 ,2-dimethoxyethane and 1 ,3- dioxolane (8 : 4 : 44 : 44 by weight). Galvanostatic charge-discharge cycling were carried out using a Maccor battery tester in the potential range of 1.7-2.5 V (vs LiVLi) at a current density of 0.02 C rate for the first cycle and 0.2 C discharge rate and 0.125 C charge rate for the subse- quent cycles at controlled 25 °C. 111.1 . Inventive electrodes comprising sulfur/ carbon electrode coated with metal oxide layer
Figure imgf000020_0001
III.2 Comparison of discharge capacity between inventive electrode and electrode containing same wt% of metal oxide as inventive electrode
Figure imgf000020_0002
III.3 Comparison of discharge capacity between inventive electrode (E3) and a comparative electrode without metal oxide (C-E1 ), at C/10 rate
Discharge capacity [mAh/gs]
Cycle no.
C-E1 E3
1 1438 1339
5 725 868
50 662 790
100 596 815
200 393 790
250 299 770

Claims

Claims
An electrode assembly comprising
(A) at least one three-dimensional geometric shape of an electroactive composition comprising
(A1 ) at least one electroactive sulfur-containing material,
(A2) carbon in a polymorph comprising at least 60% sp2-hybridized carbon atoms, and
(A3) optionally at least one binder, arranged on
(B) a current collector, and
(C) a layer (C) of at least one metal oxide, wherein the layer has a thickness in the
range from 10 to 500 nm, and wherein the layer is deposited directly on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three-dimensional geometric shape, which are not covered with the current collector.
The electrode assembly according to claim 1 , wherein the at least one three-dimensional geometric shape of an electroactive composition (A) is designed as a layer.
The electrode assembly according to claim 1 or 2, wherein the at least one electroactive sulfur-containing material (A1 ) is elemental sulfur.
The electrode assembly according to any of claims 1 to 3, wherein the current collector
(B) is an aluminium foil.
The electrode assembly according to any of claims 1 to 4, wherein the metal oxide of layer
(C) is deposited in amorphous form.
The electrode assembly according to any of claims 1 to 5, wherein the metal oxide of layer (C) is selected from the group consisting of T1O2, S1O2, B2O3, AI2O3, V2O5, VO2 and Zr02.
The electrode assembly according to any of claims 1 to 6, wherein the metal oxide of layer (C) was produced by a sol-gel process.
8. The electrode assembly according to any of claims 1 to 7, wherein the layer of the at least one metal oxide was deposited by means of dip coating or spin coating of a sol of said metal oxide. 9. A process for producing an electrode assembly according to any of claims 1 to 8, comprising the process steps of
(a) arranging at least one three-dimensional geometric shape of an electroactive
composition comprising
(A1 ) at least one electroactive sulfur-containing material,
(A2) carbon in a polymorph comprising at least 60% sp2-hybridized carbon atoms, and
(A3) optionally at least one binder, on a current collector (B), and
(β) depositing a layer (C) of at least one metal oxide directly on all surfaces of the at least one three-dimensional geometric shape or all parts of a surface of the at least one three-dimensional geometric shape, which are not covered with the current collector (B).
10. The process according to claim 9, wherein in process step (β) the metal oxide of layer (C) is produced by a sol-gel process.
1 1 . The process according to claim 9 or 10, wherein in process step (β) the layer of the at least one metal oxide is deposited by means of dip coating or spin coating of a sol of said metal oxide.
12. An electrochemical cell comprising (a) at least one electrode assembly according to any of claims 1 to 8 or produced according to any of claims 9 to 1 1 ,
(b) at least one anode (b),
(c) at least one separator (c), and
(d) at least one electrolyte composition (d) comprising (d1 ) at least one solvent (d1 ), and
(d2) at least one metal salt (d2).
3. Battery comprising at least one electrochemical cell according to claim 12.
4. A device comprising at least one electrochemical cell according to claim 12.
PCT/EP2015/061651 2014-06-06 2015-05-27 Metal oxide coated cathodes comprising sulfur for electrochemical cells WO2015185400A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP14171587 2014-06-06
EP14171587.0 2014-06-06

Publications (1)

Publication Number Publication Date
WO2015185400A1 true WO2015185400A1 (en) 2015-12-10

Family

ID=50942073

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/EP2015/061651 WO2015185400A1 (en) 2014-06-06 2015-05-27 Metal oxide coated cathodes comprising sulfur for electrochemical cells

Country Status (1)

Country Link
WO (1) WO2015185400A1 (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106981637A (en) * 2017-04-26 2017-07-25 清华大学 SiO2/TiO2/ C/S lithium sulfur battery anode materials and preparation method thereof
CN107017385A (en) * 2016-01-28 2017-08-04 株式会社Lg化学 Anode active material, its manufacture method and lithium secondary battery
RU2670597C1 (en) * 2016-09-12 2018-10-24 Джонсон Энд Джонсон Вижн Кэа, Инк. Bivalve batteries for biomedical device
US10734668B2 (en) 2016-09-12 2020-08-04 Johnson & Johnson Vision Care, Inc. Tubular form biomedical device batteries

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20040101753A1 (en) * 2002-11-26 2004-05-27 Hwang Duck-Chul Positive electrode for lithium-sulfur battery and lithium-sulfur battery comprising same
US20090226809A1 (en) * 2008-03-05 2009-09-10 Eaglepicher Technologies, Llc Lithium-sulfur battery and cathode therefore
JP2011198550A (en) * 2010-03-18 2011-10-06 Daihatsu Motor Co Ltd Electrode for secondary battery and secondary battery
CN102280614A (en) * 2011-07-07 2011-12-14 天津大学 Preparation method of sulfur positive electrode of lithium sulfur battery
CN102820454A (en) * 2011-06-11 2012-12-12 苏州宝时得电动工具有限公司 Electrode composite material, its preparation method, its anode, and battery possessing anode
US20130224594A1 (en) * 2012-02-28 2013-08-29 Sila Nanotechnologies Inc. Core-Shell Composites for Sulfur-Based Cathodes in Metal-Ion Batteries

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20040101753A1 (en) * 2002-11-26 2004-05-27 Hwang Duck-Chul Positive electrode for lithium-sulfur battery and lithium-sulfur battery comprising same
US20090226809A1 (en) * 2008-03-05 2009-09-10 Eaglepicher Technologies, Llc Lithium-sulfur battery and cathode therefore
JP2011198550A (en) * 2010-03-18 2011-10-06 Daihatsu Motor Co Ltd Electrode for secondary battery and secondary battery
CN102820454A (en) * 2011-06-11 2012-12-12 苏州宝时得电动工具有限公司 Electrode composite material, its preparation method, its anode, and battery possessing anode
CN102280614A (en) * 2011-07-07 2011-12-14 天津大学 Preparation method of sulfur positive electrode of lithium sulfur battery
US20130224594A1 (en) * 2012-02-28 2013-08-29 Sila Nanotechnologies Inc. Core-Shell Composites for Sulfur-Based Cathodes in Metal-Ion Batteries

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107017385A (en) * 2016-01-28 2017-08-04 株式会社Lg化学 Anode active material, its manufacture method and lithium secondary battery
CN107017385B (en) * 2016-01-28 2020-05-22 株式会社Lg化学 Positive electrode active material, method for producing same, and lithium secondary battery
RU2670597C1 (en) * 2016-09-12 2018-10-24 Джонсон Энд Джонсон Вижн Кэа, Инк. Bivalve batteries for biomedical device
RU2670597C9 (en) * 2016-09-12 2018-11-21 Джонсон Энд Джонсон Вижн Кэа, Инк. Bivalve batteries for biomedical device
US10734668B2 (en) 2016-09-12 2020-08-04 Johnson & Johnson Vision Care, Inc. Tubular form biomedical device batteries
CN106981637A (en) * 2017-04-26 2017-07-25 清华大学 SiO2/TiO2/ C/S lithium sulfur battery anode materials and preparation method thereof
CN106981637B (en) * 2017-04-26 2019-07-26 清华大学 SiO2/TiO2/ C/S lithium sulfur battery anode material and preparation method thereof

Similar Documents

Publication Publication Date Title
WO2016012275A1 (en) Composites comprising mxenes for cathodes of lithium sulfur cells
CN103443991B (en) Secondary cell and electrolyte
JP6848435B2 (en) Lithium ion secondary battery
KR20140013729A (en) Electrode active material for secondary battery
US20090191458A1 (en) Porous network negative electrodes for non-aqueous electrolyte secondary battery
JP2010062113A (en) Lithium ion secondary battery
KR102292727B1 (en) Lithium metal secondary battery with improved safety and including the same
KR20140048153A (en) Lithium/sulphur accumulator
WO2013122868A1 (en) Mesoporous metal oxide microsphere electrode compositions and their methods of making
JP2014017199A (en) Electrode for lithium secondary battery and method for manufacturing the same, and lithium secondary battery and method for manufacturing the same
JP5403711B2 (en) Method for producing lithium ion secondary battery
KR20150083381A (en) Rechargeable lithium battery
JP2023510989A (en) Electrolytes, electrochemical devices and electronic devices
WO2015185400A1 (en) Metal oxide coated cathodes comprising sulfur for electrochemical cells
JP6384596B2 (en) Anode materials for lithium-ion batteries
TWI623132B (en) Negative electrode material for lithium ion secondary battery and method of manufacturing the same, negative electrode material for lithium ion secondary battery and lithium ion secondary battery
KR20160038294A (en) Cathode Active Material for Lithium Secondary Battery Which Ionized Metal Is Coated on Surface Thereof and Method for Preparation of the Same
WO2015165762A1 (en) Process for producing a monolithic body of a porous carbon material, monolithic bodies of special porous carbon materials and their use
CN116190633B (en) Layered oxide positive electrode material, preparation method thereof, positive electrode composition, sodium ion secondary battery and application
EP3244472A1 (en) Composites comprising hollow microspheres of a vanadium oxide for lithium sulfur cells
JP2022530294A (en) Electrolyte and electrochemical equipment
KR20130140395A (en) Anode for lithium secondary battery, method for preparing the same, and lithium secondary battery using the same
KR101611198B1 (en) Cathode Active Material for Lithium Secondary Battery Having Novel Fine Crystal Structure
JP2002175836A (en) Nonaqueous electrolyte battery
CN115207284A (en) Preparation method of composite negative electrode material, negative plate and battery

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 15724679

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 15724679

Country of ref document: EP

Kind code of ref document: A1