WO2015189094A1 - Process for producing microporous polyester membranes for electronic applications - Google Patents

Process for producing microporous polyester membranes for electronic applications Download PDF

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Publication number
WO2015189094A1
WO2015189094A1 PCT/EP2015/062538 EP2015062538W WO2015189094A1 WO 2015189094 A1 WO2015189094 A1 WO 2015189094A1 EP 2015062538 W EP2015062538 W EP 2015062538W WO 2015189094 A1 WO2015189094 A1 WO 2015189094A1
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WIPO (PCT)
Prior art keywords
range
membrane
resin
polymer
μηη
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PCT/EP2015/062538
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French (fr)
Inventor
Oliver Gronwald
Martin Weber
Klaus MÜHLBACH
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Basf Se
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Publication of WO2015189094A1 publication Critical patent/WO2015189094A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
    • H01M50/406—Moulding; Embossing; Cutting
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/491—Porosity
    • 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
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/494—Tensile strength
    • 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 a process for producing a porous polyester membrane comprising at least one polyester resin (A1 ) derived from an aromatic dicarboxylic acid, to said porous polyester membrane comprising a polyester resin derived from an aromatic dicarboxylic acid obtainable or obtained by the process of the invention and to an electrochemical cell comprising said porous polyester membrane.
  • A1 polyester resin derived from an aromatic dicarboxylic acid
  • Secondary batteries, accumulators or “rechargeable batteries” are just some embodiments by which electrical energy can be stored after generation and used when required. Owing to the significantly better power density, there has in recent times been a move away from the water- based secondary batteries toward development of those batteries in which the charge transport in the electrical cell is accomplished by lithium ions. Many components are of significance, such as the electrodes and the electrolyte. However, particular attention will be paid to the separator which physically separates the anode and the cathode, thereby preventing short circuits.
  • the separator should allow lithium ions to pass.
  • a separator should have the necessary mechanical properties to effectively separate anode and cathode from each other.
  • JP2047031 A describes a method of manufacturing a microporous film made of a polyolefin.
  • JP8176330 A describes a void-containing polyester resin film such as synthetic paper, capable of evenly and efficiently forming fine voids in the whole of the film by using a crystalline polystyrene resin specified in the crystal melt peak as a void-developing agent.
  • US6287680 B describes a porous polyester film comprising a composition comprising a polyes- ter resin and a thermoplastic resin incompatible with the polyester resin, and a number of voids formed by dispersing the incompatible thermoplastic resin to provide particles in the polyester resin and stretching same, wherein the incompatible thermoplastic resin comprises a polyolefin resin.
  • US2001036545 A describes a porous polyester film containing a polyester resin as a main starting material. By optimizing the melt viscosity of a void-forming agent to be added, the ratio of the number of voids to film thickness can be set to 0.20 void/ ⁇ or above.
  • US2002160256 discloses methods of fabricating porous films and modifying said porous films, which are used in a method of fabricating electrodes of non-aqueous electrolyte secondary batteries.
  • the separators for electrochemical cells known from the literature and the processes for producing such separators still have deficiencies in view of one or more of the properties desired for such separators, for example with regard to thermal stability, mechanical stability, chemical stability, wettability with electrolyte and good ion conductivity, or desired for such production processes, in particular economic viability.
  • polyester resin (A1 ) at least one polyester resin (A1 ) derived from an aromatic dicarboxylic acid, prefera- bly a polyester resin (A1 ) selected from the group consisting of polyethylene tereph- thalate, polybutylene terephthalate and polytrimethylene terephthalate, in particular polybutylene terephthalate, and
  • (B1 ) at least one polymer resin (B1 ) incompatible with polyester resin (A1 ), preferably a polymer resin (B1 ) selected from the group consisting of polycarbonates and poly- ethers, in particular selected from the group consisting of polyethers, (b) extruding a film of the polymer blend prepared in process step (a),
  • the thickness of the porous polyester membrane which is obtainable by the inventive process, can be varied in a wide range.
  • the porous polyester membrane has a thickness in the range from 5 to 50 ⁇ , more preferably in the range from 10 to 30 ⁇ .
  • the inventive process is characterized in that the porous polyester membrane has a thickness in the range from 5 to 50 ⁇ , more preferably in the range from 10 to 30 ⁇ .
  • the porosity of the porous polyester membrane can be also varied in a wide range depending on the composition of the polymer blend prepared in process step (a).
  • the porous polyester membrane has a porosity in the range from 0.3 to 0.6.
  • the porosity is determined by the means of gravimetry after leaching out polymer resin (B1 ).
  • the inventive process is characterized in that the porous polyester membrane has a porosity in the range from 0.3 to 0.6.
  • the median pore diameter of the pores of the porous polyester membrane can also be varied in a wide range depending on the composition of the polymer blend, the conditions of the for- mation of the blend and/or the conditions of the extrusion of the film.
  • the porous polyester membrane has pores which have pore diameters in the range from 0.03 to 2 ⁇ . More preferably the porous polyester membrane has pores which have a median pore diameter in the range from 0.2 to 0.5 ⁇ . Pore diameters and the median pore diameters are determined by mercury porometry according DIN 66133 1993-06.
  • the inventive process is characterized in that the porous polyester membrane has pores which have a median pore diameter in the range from 0.2 to 0.5 ⁇ . In one embodiment of the present invention the inventive process is characterized in that the porous polyester membrane has a thickness in the range from 5 to 50 ⁇ . preferably in the range from 10 to 30 ⁇ , a porosity in the range from 0.3 to 0.6 and median pore diameter of the pores of the membrane is in the range from 0.2 to 0.5 ⁇ .
  • the porous polyester membrane might comprise besides the at least one polyester resin (A1 ) residues of the at least one polymer resin (B1 ) or portions of other chemical components, which can be extruded together with polymer blend formed in process step (a) and which are insoluble during dissolving the at least one polymer resin (B1 ) in process step (c) like inorganic materials on the nanoscale.
  • the sum of the mass fractions of all polyester resins (A1 ) in the porous polyester membrane, in particular the mass fraction of the at least one polyester resin (A1 ) in the porous polyester membrane is in the range from 0.80 to 1 , more preferably in the range from 0.95 to 1.
  • the inventive process is characterized in that the mass fraction of the at least one polyester resin (A1 ), in particular of polybutylene terephthalate, in the porous polyester membrane is in the range from 0.80 to 1 , preferably in the range from 0.95 to 1 .
  • a polymer blend which comprises as a first component (A1 ) at least one polyester resin (A1 ) derived from an aromatic dicarboxylic acid, preferably a polyester resin (A1 ) selected from the group consisting of polyethylene terephthalate, polybutylene ter- ephthalate, polytrimethylene terephthalate and mixtures thereof, more preferably polybutylene terephthalate and mixtures of polybutylene terephthalate with polyethylene terephthalate, in particular polybutylene terephthalate, and as a second component (B1 ) at least one polymer resin (B1 ) incompatible with polyester resin (A1 ), preferably a polymer resin (B1 ) selected from the group consisting of polycarbonates, polyvinylpyrrolidones, copolymers of vinylpyrrolidone with vinylacetate or vinylimidazol, and polyethers, in particular selected from the group consist- ing of polyethers.
  • incompatible means that component (B1 ) is not homogeneously miscible with component (A1 ) and vice versa.
  • the two incompatible components form two separate phases.
  • Polyester resins derived from an aromatic dicarboxylic acid are known to the person skilled in the art. Suitable polyesters are described, for example, in WO 2013/000747 on page 5, line 1 1 to page 8, line 26.
  • Preferred examples of polyester resins are polyethylene terephthalate, polybutylene terephthalate, polyethylennaphthalate, polytrimethylene terephthalate or mixtures thereof, more preferably polybutylene terephthalate and mixtures of polybutylene terephthalate with polyethylene terephthalate, in particular polybutylene terephthalate.
  • component (A1 ) consists of a single polyester resin, in particular component (A1 ) consists of polybutylene terephthalate.
  • Polymer resin (B1 ), which is incompatible with polyester resin (A1 ) can in principle be chosen from a wide range of resins, preferably from thermoplastic resins, more preferably from thermoplastic resins which are soluble in one or more solvents under such conditions wherein polyester resin (A1 ) is not soluble in these solvents.
  • Suitable examples of polymer resin (B1 ) are poly- carbonates, polyvinylpyrrolidones, copolymers of vinylpyrrolidone with vinylacetate or vinylimidazol, or polyethers.
  • component (B1 ) consists of a single polymer resin (B1 ) selected from the group consisting of polycarbonates, polyvinylpyrrolidones, copolymers of vinylpyrrolidone with vinylacetate or vinylimidazol, and polyethers, in particular selected from the group consisting of polyethers.
  • BPA bisphenol A
  • COC phosgene
  • Polyethers are also known to the person skilled in the art. Preferred polyethers are derived from the monomers ethylene oxide and propylene oxide, in particular from ethylene oxide. The molecular weight M w of the polyethers can be varied in a wide range.
  • polyethers with a molecular weight M w in the range from 10 000 to 10 000 000 g/mol, preferably in the range from 100 000 to 9 000 000 g/mol, in particular in the range from 300 000 to 800 000 g/mol.
  • the inventive process is characterized in that the at least one polymer resin (B1 ) is a polyether with a molecular weight M w in the range from 10 000 to 10 000 000 g/mol, preferably in the range from 100 000 to 9 000 000 g/mol, in particular in the range from 300 000 to 800 000 g/mol.
  • the inventive process is characterized in that the mass fraction of the at least one polymer resin (B1 ) related to the sum of all polymer resins (B1 ) is in the range from 0.9 to 1 , preferably in the range from 0.95 to 1.
  • the mass fraction of component (B1 ) in the polymer blend prepared in process step (a), which corresponds to the sum of the mass fractions of all polymer resins (B1 ) in the polymer blend is in the range from 0.1 to 0.8, preferably in the range from 0.3 to 0.7, in particular in the range from 0.4 to 0.6.
  • the inventive process is characterized in that the sum of the mass fractions of all polymer resins (B1 ) in the polymer blend is in the range from 0.1 to 0.8, preferably in the range from 0.3 to 0.7, in particular in the range from 0.4 to 0.6.
  • the polymer blend prepared in process step (a) might comprise besides the at least one polyester resin (A1 ) and the at least one polymer resin (B1 ) also portions of other chemical components, which can be extruded together with the polymer blend formed in process step (a) and which are insoluble during dissolving the at least one polymer resin (B1 ) in process step (c) like inorganic materials on the nanoscale.
  • the sum of the mass fraction of all polyester resins (A1 ) and of all polymer resins (B1 ) in the polymer blend prepared in process step (a) is in the range from 0.5 to 1.0, preferably in the range from 0.8 to 1 .0, in particular in the range from 0.95 to 1 .0.
  • the inventive process is characterized in that the sum of the mass fraction of all polyester resins (A1 ) and of all polymer resins (B1 ) in the polymer blend prepared in process step (a) is in the range from 0.5 to 1 .0, preferably in the range from 0.8 to 1 .0, in particular in the range from 0.95 to 1 .0.
  • an esterification inhibitor is added to the polymer resins before blending them. More preferably polymer resin (A1 ) and polymer resin (B1 ) are blended together with 0.2 to 5%, preferably 0.5 to 2%, by weight of an esterification inhibitor, in particular zinc phosphate, based on the sum of all polymer resins.
  • the inventive process is characterized in that poly- mer resin (A1 ) and polymer resin (B1 ) are blended together with 0.2 to 5%, preferably 0.5 to 2%, by weight of an esterification inhibitor, in particular zinc phosphate, based on the sum of all polymer resins.
  • the extrusion of process step (b) can be done in wide temperature range.
  • the extru- sion temperature of the polymer blend in process step (b) is in the range from 200 to 300 °C.
  • the inventive process is characterized in that the extrusion temperature of the polymer blend in process step (b) is in the range from 200 to 300 °C.
  • the inventive process is characterized in that in process step (b) the polymer blend is extruded through a flat film die.
  • the extruded film After leaving the extruder the extruded film, which is still hot, can be further treated for example to obtain a desired thickness or orientation of the final film.
  • the film extruded in process step (b) is calendered, rolled or stretched, either only in one direction or in two directions (biaxially stretched).
  • the inventive process is characterized in that the film extruded in process step (b) is calendered, rolled or stretched.
  • the morphology of the incompatible polymer phase can be varied in a wide range.
  • the processing conditions are adjusted by the person skilled in the art such that in the film of the polymer blend the at least one polyester resin (A1 ) forms a first phase and a second phase is formed by the at least one polymer resin (B1 ), wherein at least 80% by volume, preferably at least 90% by volume of the phase of polymer resin (B1 ) establishes in the phase of polyester resin (A1 ) a co-continuous phase with segments of a size in the range from 0.02 to 5 ⁇ .
  • the two incompatible polymer resins form a gy- roidal, bi-continuous phase.
  • the two incompatible polymer phases preferably form a system of co-continuous phases that allows to remove at least 75% by weight of polymer resin (B1 ), more preferably at least 85% by weight of polymer resin (B1 ), in particular at least 90% up to 100% by weight of polymer resin (B1 ).
  • the inventive process is characterized in that in the film of the polymer blend, which is prepared in process step (b), the at least one polyester resin (A1 ) forms a first phase and a second phase is formed by the at least one polymer resin (B1 ), wherein at least 80% by volume, preferably at least 90% by volume of the phase of polymer resin (B1 ) establishes in the phase of polyester resin (A1 ) a co-continuous phase with segments of a size in the range from 0.02 to 5 ⁇ .
  • a solvent or solvent mixture which does not dissolve polyester resin (A1 ).
  • Suitable solvents or solvent mixtures, appropriate temperatures for the dissolution process, necessary volumes and contact times are either known to the person skilled in the art or can easily be determined in a few solubility experiments.
  • An appropriate solvent for polycarbonates in particular the polycarbonate derived from bisphenol A and phosgene, is cyclohexanone.
  • Polyethers, in particular polyethers based on ethylene oxide, are soluble in water.
  • the porous polyester membrane which was obtained after process step (c), can be rinsed with additional suitable solvents and can be dried.
  • the porous membrane is preferably dried in order to remove any unwanted solvent.
  • the drying conditions e.g. temperature and pressure are chosen based on common knowledge considering the properties of the porous membrane and the properties of the solvents, which have to be removed.
  • the present invention further also provides a porous polyester membrane comprising a polyester resin derived from an aromatic dicarboxylic acid, preferably comprising a polyester selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate and polytri- methylene terephthalate, in particular polybutylene terephthalate, wherein the porous polyester membrane has a thickness in the range from 5 to 50 ⁇ . preferably in the range from 10 to 30 ⁇ , a porosity in the range from 0.4 to 0.6 and pores having pore diameters in the range from 0.03 to 2 ⁇ , obtainable or obtained by the process for producing a porous polyester membrane as described above.
  • This process comprises the above-described process steps (a), (b), (c) and optinally (d), especially also with regard to preferred embodiments thereof.
  • the present invention likewise also provides a porous polyester membrane comprising a polyester resin derived from an aromatic dicarboxylic acid, preferably comprising a polyester select- ed from the group consisting of polyethylene terephthalate, polybutylene terephthalate and poly- trimethylene terephthalate, in particular polybutylene terephthalate, wherein the porous polyester membrane has a thickness in the range from 5 to 50 ⁇ . preferably in the range from 10 to 30 ⁇ , a porosity in the range from 0.4 to 0.6 and pores having pore diameters in the range from 0.03 to 2 ⁇ , wherein the porous polyester membrane is prepared by a process comprising at least the process steps of
  • (a) preparation of a polymer blend comprising (A1 ) at least one polyester resin (A1 ) derived from an aromatic dicarboxylic acid, preferably a polyester resin (A1 ) selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate and polytrimethylene terephthalate, in particular polybutylene terephthalate, and
  • (B1 ) at least one polymer resin (B1 ) incompatible with polyester resin (A1 ), preferably a polymer resin (B1 ) selected from the group consisting of polycarbonates and poly- ethers, in particular selected from the group consisting of polyethers,
  • the porous polyester membrane which is obtainable or obtained by the inventive process, comprises a polyester resin derived from an aromatic dicarboxylic acid, preferably it comprises a polyester selected from the group consisting of polyethylene terephthalate, polybutylene ter- ephthalate and polytrimethylene terephthalate, in particular polybutylene terephthalate, wherein the porous polyester membrane has a thickness in the range from 5 to 50 ⁇ . preferably in the range from 10 to 30 ⁇ , a porosity in the range from 0.4 to 0.6 and pores having pore diameters in the range from 0.03 to 2 ⁇ , preferably having pores which have a median pore diameter in the range from 0.2 to 1 ⁇ .
  • the porous polyester membrane as described above is characterized in that the at least one polyester resin (A1 ) forms a first phase and the pores establish a co-continuous phase of interconnected voids in said first phase of a polyester resin (A1 ) with segments of a size in the range from 0.02 to 5 ⁇ . More preferably the polyester phase and the interconnected pores form a gyroidal, bi-continuous phase.
  • Inventive porous polyester membranes have advantageous properties. They show good wettability with electrolyte solvents and they are in particular thermally and mechanically more stable than commercially available polyolefin membranes. They also show a better limiting oxygen index compared to commercially available polyolefin membranes.
  • the inventive porous polyester membrane is particularly suitable as separator or as constituent of a separator in electrochemical cells, in particular in rechargeable electrochemical cells in order to separate anode from cathode in an electrochemical cell.
  • the porous polyester membrane can be obtained in the form of continuous belts which are processed further by the battery manufacturer, especially assembling the inventive porous polyes- ter membrane with appropriate flat cathodes and flat anodes in order to produce electrochemical cells.
  • the term electrochemical cell or battery encompasses batteries, capacitors and accumulators (secondary batteries) of any type, in particular alkali metal cells or batteries such as lithium, lithium ion and alkaline earth metal batteries and accumulators, including in the form of high-energy or high-power systems, and also electrolyte capacitors and double-layer capacitors which are known under the names Supercaps, Goldcaps, BoostCaps or Ultracaps.
  • the present invention further also provides for the use of the inventive porous polyester membrane as described above as part of an electrochemical cell, namely as separator.
  • the present invention further provides an electrochemical cell comprising at least one porous polyester membrane as described above, in particular a rechargeable electrochemical cell com- prising
  • inventive cells are preferably selected from alkali metal containing cells. More preferably, inventive cells are selected from lithium-ion containing cells. In lithium-ion containing cells, the charge transport is effected by Li + ions.
  • Anode (I) 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.
  • 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 (I) is selected from graphite anodes, lithium titanate anodes, anodes comprising In, Tl, Sb, Sn or Si, and anodes comprising metallic lithium.
  • Anode (I) 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 (I) can further comprise a binder.
  • Suitable binders can be selected from organic
  • 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, eth- ylene-acrylic acid copolymers, optional
  • 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 (I) can have a thickness in the range of from 15 to 200 ⁇ , preferably from 30 to 100 ⁇ , determined without the current collector.
  • Inventive cells further comprise a cathode (II).
  • Cathode (II) can contain solid, liquid or gaseous active materials, e. g., air (or oxygen). In a preferred embodiment, however, cathode (II) contains a solid active material.
  • Solid active materials for cathode (II) can be selected from phosphates with olivine structure such as lithium iron phosphates (LiFePC ) and lithium manganese phosphate (LiMnPC ) which can have a stoichiometric or non-stoichiometric composition and which can be doped or not doped.
  • active material for cathode (II) can be selected from lithium containing transition metal spinels and lithium transition metal oxides with a layered crystal structure.
  • cathode (II) contains at least one material selected from lithium containing transition metal spinels and lithium transition metal oxides with a layered crystal structure, respectively.
  • the electrochemical cell is characterized in that cathode (II) contains at least one material selected from lithium containing transition metal spinels and lithium transition metal oxides with a layered crystal structure.
  • cathode (II) contains at least one material selected from lithium containing transition metal spinels and lithium transition metal oxides with a layered crystal structure.
  • lithium-containing metal spinels are selected from those of the general formula (I) the variables being defined as follows:
  • M 1 is selected from one or more out of Al, Mg, Ca, Na, B, Mo, W and transition metals of the first row of the transition metals in the periodic table of the elements.
  • M 1 is selected from the group consisting of Ni, Co, Cr, Zn, and Al. Even more preferably, M 1 is defined to be Ni.
  • lithium containing metal spinels are selected from LiNio,5Mni, 5 04-d and LiM ⁇ C .
  • lithium transition metal oxides with a layered crystal structure are selected from compounds of general formula (II) the variable being defined as follows: 0 ⁇ t ⁇ 0.3 und M 2 selected from one or more elements from Al, Mg, B, Mo, W, Na, Ca and transition metals of the first row of the transition metals in the periodic table of the elements, at least one element being manganese.
  • At least 30 mole-% of M 2 are selected from man- ganese, preferably at least 35 mole-%, in each time with respect to the complete amount of M 2 .
  • M 2 is selected from combinations of Ni, Co and Mn not containing significant amounts of additional elements. In a different embodiment of the present invention M 2 is selected from combinations of Ni, Co and Mn containing significant amounts of at least one additional element, for example in the range of from 1 to 10 mole-% Al, Ca or Na.
  • lithium transition metal oxides with a lay- ered crystal structure are selected from compounds of general formula (III)
  • Li(i + x)[NieCOfMn g M 3 h](i-x)02 (HI) the variables being defined as follows: x a number in the range of from zero to 0.2, e a number in the range of from 0.2 to 0.6, f a number in the range of from 0.1 to 0.5, g a number in the range of from 0.2 to 0.6, h a number in the range of from zero to 0.1 , and: e + f + g + h 1 ,
  • M 3 selected from Al, Mg, V, Fe, Cr, Zn, Cu, Ti and Mo.
  • M 2 in formula (I I) is selected from Nio,33Coo,33Mno,33, Nio,5Coo,2Mn 0 ,3, Nio,4Coo,3Mn 0 ,4, Ni 0 ,4Coo,2Mn 0 ,4 und Ni 0 ,45Coo,ioMn 0 ,45.
  • Cathode (I I) can further comprise a current collector.
  • Suitable current collectors are, e.g., metal wires, metal grids, metal gauze and preferably metal foils such as aluminum foils.
  • Cathode (I I) can further comprise a binder.
  • Suitable binders can be selected from organic (co)polymers. Suitable organic (co)polymers may be halogenated or halogen-free. In general, the same binders used for anode (I) can also be employed for cathode (I I).
  • Preferred binders are especially polyvinyl alcohol and halogenated (co)polymers, for example polyvinyl chloride or polyvinylidene chloride, especially fluorinated (co)polymers such as polyvi- nyl fluoride and especially polyvinylidene fluoride and polytetrafluoroethylene.
  • cathode (I I) can have a thickness in the range of from 15 to 200 ⁇ , preferably from 30 to 100 ⁇ , determined without the current collector.
  • Cathode (II) can further comprise electrically conductive carbonaceous material.
  • Electrically conductive carbonaceous material can be selected, for example, from graphite, carbon black, carbon nanotubes, graphene or mixtures of at least two of the aforementioned substances. In the context of the present invention, electrically conductive, carbonaceous material can also be referred to as carbon for short.
  • electrically conductive carbonaceous material is carbon black.
  • Carbon black may, for example, be selected from lamp black, furnace black, flame black, thermal black, acetylene black and industrial black.
  • Carbon black may comprise impurities, for example hydrocarbons, especially aromatic hydrocarbons, or oxygen-containing compounds or oxygen-containing groups, for example OH groups.
  • sulfur- or iron- containing impurities are possible in carbon black.
  • electrically conductive carbonaceous material is partially oxidized carbon black.
  • the electrochemical cell is characterized in that cathode (II) contains a material based on electrically conductive carbon.
  • Inventive electrochemical cells further comprise, as well as the inventive alkali-ion conducting separator assembly, the anode (I) and the cathode (II), at least one electrolyte composition (III) comprising
  • Possible aprotic organic solvents (1111 ) may be liquid or solid at room temperature and are preferably liquid at room temperature.
  • Solvents (1111 ) are preferably selected from polymers, cyclic or noncyclic ethers, cyclic or noncyclic acetals, cyclic or noncyclic organic carbonates and ionic liquids.
  • the inventive rechargeable electrochemical cell is characterized in that the aprotic organic solvent (1111 ) 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.
  • 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.
  • suitable noncyclic organic carbonates are 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).
  • alkali metal salts (I I I2) which are used as conductive salts, have to be soluble in the aprotic organic solvent (1111 ).
  • Preferred alkali metal salts (I I I2) are lithium salts or sodium salts, in particular lithium salts.
  • the inventive rechargeable electrochemical cell is characterized in that the alkali metal salt (I I I2) 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 LiPF 6 , LiBF 4 , UCIO4, LiAsFe, UCF3SO3, LiC(C n F 2 n + iS02)3, 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:
  • m 3 when X is selected from carbon and silicon.
  • Preferred alkali metal salts are selected from LiC(CF 3 S0 2 ) 3 , LiN(CF 3 S0 2 ) 2 , LiPF 6 , LiBF 4 , LiCI0 4 , and particular preference is given to LiPF6 and LiN(CFsS02)2.
  • the concentration of conductive salt in electrolyte is in the range of from 0.01 M to 5 M, preferably 0.5 M to 1 .5 M.
  • Inventive electrochemical cells further comprise as separator at least one inventive alkali-ion conducting separator assembly, which has been described above, wherein the separator assembly is positioned between anode (I) and cathode (II) in the electrochemical cells.
  • separator assembly is positioned between anode (I) and cathode (II) in a way that it is like a layer to either a major part of one surface of anode (I) or cathode (II).
  • separator assembly is positioned between anode
  • cathode (II) in a way that it is like a layer to both a major part of one surface of anode (I) and cathode (II).
  • separator assembly is positioned between anode (I) and cathode (II) in a way that it is like a layer to one surface of anode (I) or of cathode
  • separator assembly is positioned between anode (I) and cathode (II) in a way that it is like a layer to one surface of both anode (I) and of cathode (II).
  • Inventive alkali-ion conducting separator assemblies have overall advantageous properties.
  • 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 have overall advantageous properties. They have a long duration with very low loss of capacity, good cycling stability, and a reduced tendency towards short circuits after longer operation and/or repeated cycling.
  • a further aspect of the present invention refers to batteries, more preferably to an alkali metal ion battery, in particular to a lithium ion battery comprising at least one inventive electrochemical cell, for example two or more.
  • inventive electrochemical cells can be combined with one another in inventive alkali metal ion batteries, for example in series connection or in parallel connection. Series connection is preferred.
  • inventive batteries have advantageous properties. They have a long duration with very low loss of capacity, good cycling stability, and high temperature stability.
  • 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.
  • 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 electrochemical cell as described above.
  • mobile devices such as are 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, tele- phones or electrical power tools, for example from the construction sector, especially drills, battery-driven screwdrivers or battery-driven tackers.
  • Table 1 shows the shrinkage of inventive porous membrane M1 and the shrinkage of two conciseally available polyolefin membranes.
  • Figure 1 shows the logarithmic (log) differential intrusion volume (mL/g- y-axis) depending on the pore size diameter ( ⁇ - x-axis)
  • Figure 2 shows the cumultative intrusion volume (mL/g - y-axis) depending on the pore size diameter ( ⁇ - x-axis) IV. Production of electrochemical cells and testing thereof
  • Anode (I) graphite on copper foil as current collector with a thickness of 36 to 38 ⁇ (Fa. Gaia, Nordhausen, Germany).
  • FIG. 3 shows the schematic structure of a dismantled electrochemical cell for testing of porous membranes.
  • inventive electrochemical cell E.1 was charged with a constant current to a voltage of 4.2 V followed by a final charging with constant voltage at 4.2 V. Then, inventive electrochemical cell E.1 was discharged at constant current to a voltage of 3 V. Three such cycles with 0.1 C and, thereafter, 50 and 200 cycles with 0.5 C were determined.

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Abstract

The present invention relates to a process for producing a porous polyester membrane comprising at least one polyester resin (A1) derived from an aromatic dicarboxylic acid, to said porous polyester membrane comprising a polyester resin derived from an aromatic dicarboxylic acid obtainable or obtained by the process of the invention and to an electrochemical cell comprising said porous polyester membrane.

Description

Process for producing microporous polyester membranes for electronic applications Description The present invention relates to a process for producing a porous polyester membrane comprising at least one polyester resin (A1 ) derived from an aromatic dicarboxylic acid, to said porous polyester membrane comprising a polyester resin derived from an aromatic dicarboxylic acid obtainable or obtained by the process of the invention and to an electrochemical cell comprising said porous polyester membrane.
Secondary batteries, accumulators or "rechargeable batteries" are just some embodiments by which electrical energy can be stored after generation and used when required. Owing to the significantly better power density, there has in recent times been a move away from the water- based secondary batteries toward development of those batteries in which the charge transport in the electrical cell is accomplished by lithium ions. Many components are of significance, such as the electrodes and the electrolyte. However, particular attention will be paid to the separator which physically separates the anode and the cathode, thereby preventing short circuits.
On one hand, the separator should allow lithium ions to pass. On the other hand, a separator should have the necessary mechanical properties to effectively separate anode and cathode from each other.
JP2047031 A describes a method of manufacturing a microporous film made of a polyolefin. JP8176330 A describes a void-containing polyester resin film such as synthetic paper, capable of evenly and efficiently forming fine voids in the whole of the film by using a crystalline polystyrene resin specified in the crystal melt peak as a void-developing agent.
US6287680 B describes a porous polyester film comprising a composition comprising a polyes- ter resin and a thermoplastic resin incompatible with the polyester resin, and a number of voids formed by dispersing the incompatible thermoplastic resin to provide particles in the polyester resin and stretching same, wherein the incompatible thermoplastic resin comprises a polyolefin resin. US2001036545 A describes a porous polyester film containing a polyester resin as a main starting material. By optimizing the melt viscosity of a void-forming agent to be added, the ratio of the number of voids to film thickness can be set to 0.20 void/μΓη or above.
US2002160256 discloses methods of fabricating porous films and modifying said porous films, which are used in a method of fabricating electrodes of non-aqueous electrolyte secondary batteries.
The separators for electrochemical cells known from the literature and the processes for producing such separators still have deficiencies in view of one or more of the properties desired for such separators, for example with regard to thermal stability, mechanical stability, chemical stability, wettability with electrolyte and good ion conductivity, or desired for such production processes, in particular economic viability. It was therefore an object of the present invention to provide an efficient process for producing a membrane, which can be used as separator for a long-lived electrochemical cell, and to provide a separator, which has advantages in respect of one or more properties of a known separator, in particular a separator which displays sufficient ion conductivity, improved wettability with electrolytes, low thickness, high thermal and chemical stability and good mechanical properties, for example sufficient flexibility and sufficient stability with respect to growing metal dendrites. Furthermore, it was an objective to provide electrochemical cells comprising said membranes, wherein the electrochemical cells do not suffer from short circuits after longer operation.
This object is achieved by a process for producing a porous polyester membrane, comprising at least the process steps of
(a) preparation of a polymer blend comprising
(A1 ) at least one polyester resin (A1 ) derived from an aromatic dicarboxylic acid, prefera- bly a polyester resin (A1 ) selected from the group consisting of polyethylene tereph- thalate, polybutylene terephthalate and polytrimethylene terephthalate, in particular polybutylene terephthalate, and
(B1 ) at least one polymer resin (B1 ) incompatible with polyester resin (A1 ), preferably a polymer resin (B1 ) selected from the group consisting of polycarbonates and poly- ethers, in particular selected from the group consisting of polyethers, (b) extruding a film of the polymer blend prepared in process step (a),
(c) dissolving the polymer resin (B1 ) of the film prepared in process step (b) with a solvent, which does not dissolve polyester resin (A1 ), and (d) optionally rinsing the porous polyester membrane, which was obtained after process step (c), or drying said membrane.
The thickness of the porous polyester membrane, which is obtainable by the inventive process, can be varied in a wide range. Preferably the porous polyester membrane has a thickness in the range from 5 to 50 μηη, more preferably in the range from 10 to 30 μηη. In one embodiment of the present invention the inventive process is characterized in that the porous polyester membrane has a thickness in the range from 5 to 50 μηη, more preferably in the range from 10 to 30 μηη. The porosity of the porous polyester membrane can be also varied in a wide range depending on the composition of the polymer blend prepared in process step (a). Preferably the porous polyester membrane has a porosity in the range from 0.3 to 0.6. The porosity is determined by the means of gravimetry after leaching out polymer resin (B1 ). In one embodiment of the present invention the inventive process is characterized in that the porous polyester membrane has a porosity in the range from 0.3 to 0.6.
The median pore diameter of the pores of the porous polyester membrane can also be varied in a wide range depending on the composition of the polymer blend, the conditions of the for- mation of the blend and/or the conditions of the extrusion of the film. Preferably the porous polyester membrane has pores which have pore diameters in the range from 0.03 to 2 μηη. More preferably the porous polyester membrane has pores which have a median pore diameter in the range from 0.2 to 0.5 μηη. Pore diameters and the median pore diameters are determined by mercury porometry according DIN 66133 1993-06.
In one embodiment of the present invention the inventive process is characterized in that the porous polyester membrane has pores which have a median pore diameter in the range from 0.2 to 0.5 μπι. In one embodiment of the present invention the inventive process is characterized in that the porous polyester membrane has a thickness in the range from 5 to 50 μηη. preferably in the range from 10 to 30 μηη, a porosity in the range from 0.3 to 0.6 and median pore diameter of the pores of the membrane is in the range from 0.2 to 0.5 μηη. The porous polyester membrane might comprise besides the at least one polyester resin (A1 ) residues of the at least one polymer resin (B1 ) or portions of other chemical components, which can be extruded together with polymer blend formed in process step (a) and which are insoluble during dissolving the at least one polymer resin (B1 ) in process step (c) like inorganic materials on the nanoscale. Preferably the sum of the mass fractions of all polyester resins (A1 ) in the porous polyester membrane, in particular the mass fraction of the at least one polyester resin (A1 ) in the porous polyester membrane, is in the range from 0.80 to 1 , more preferably in the range from 0.95 to 1.
In one embodiment of the present invention the inventive process is characterized in that the mass fraction of the at least one polyester resin (A1 ), in particular of polybutylene terephthalate, in the porous polyester membrane is in the range from 0.80 to 1 , preferably in the range from 0.95 to 1 . In process step (a) a polymer blend is prepared which comprises as a first component (A1 ) at least one polyester resin (A1 ) derived from an aromatic dicarboxylic acid, preferably a polyester resin (A1 ) selected from the group consisting of polyethylene terephthalate, polybutylene ter- ephthalate, polytrimethylene terephthalate and mixtures thereof, more preferably polybutylene terephthalate and mixtures of polybutylene terephthalate with polyethylene terephthalate, in particular polybutylene terephthalate, and as a second component (B1 ) at least one polymer resin (B1 ) incompatible with polyester resin (A1 ), preferably a polymer resin (B1 ) selected from the group consisting of polycarbonates, polyvinylpyrrolidones, copolymers of vinylpyrrolidone with vinylacetate or vinylimidazol, and polyethers, in particular selected from the group consist- ing of polyethers.
In the present invention the term "incompatible" means that component (B1 ) is not homogeneously miscible with component (A1 ) and vice versa. The two incompatible components form two separate phases.
Polyester resins derived from an aromatic dicarboxylic acid are known to the person skilled in the art. Suitable polyesters are described, for example, in WO 2013/000747 on page 5, line 1 1 to page 8, line 26. Preferred examples of polyester resins are polyethylene terephthalate, polybutylene terephthalate, polyethylennaphthalate, polytrimethylene terephthalate or mixtures thereof, more preferably polybutylene terephthalate and mixtures of polybutylene terephthalate with polyethylene terephthalate, in particular polybutylene terephthalate.
Preferably component (A1 ) consists of a single polyester resin, in particular component (A1 ) consists of polybutylene terephthalate.
Polymer resin (B1 ), which is incompatible with polyester resin (A1 ) can in principle be chosen from a wide range of resins, preferably from thermoplastic resins, more preferably from thermoplastic resins which are soluble in one or more solvents under such conditions wherein polyester resin (A1 ) is not soluble in these solvents. Suitable examples of polymer resin (B1 ) are poly- carbonates, polyvinylpyrrolidones, copolymers of vinylpyrrolidone with vinylacetate or vinylimidazol, or polyethers.
Preferably component (B1 ) consists of a single polymer resin (B1 ) selected from the group consisting of polycarbonates, polyvinylpyrrolidones, copolymers of vinylpyrrolidone with vinylacetate or vinylimidazol, and polyethers, in particular selected from the group consisting of polyethers.
Polycarbonates are known to the person skilled in the art. They represent a class of polymers containing carbonate groups (-0-(C=0)-0-) in the main chain. Most polycarbonates of commercial interest are derived from rigid monomers. Preferred is a polycarbonate, which is pro- duced by the reaction of bisphenol A (BPA) and phosgene (COC ). Suitable polycarbonates are described, for example, in WO 01/02488 on page 6, line 42 to page 8, line 34. Polyethers are also known to the person skilled in the art. Preferred polyethers are derived from the monomers ethylene oxide and propylene oxide, in particular from ethylene oxide. The molecular weight Mw of the polyethers can be varied in a wide range. Preferred are polyethers with a molecular weight Mw in the range from 10 000 to 10 000 000 g/mol, preferably in the range from 100 000 to 9 000 000 g/mol, in particular in the range from 300 000 to 800 000 g/mol.
In one embodiment of the present invention the inventive process is characterized in that the at least one polymer resin (B1 ) is a polyether with a molecular weight Mw in the range from 10 000 to 10 000 000 g/mol, preferably in the range from 100 000 to 9 000 000 g/mol, in particular in the range from 300 000 to 800 000 g/mol.
In one embodiment of the present invention the inventive process is characterized in that the mass fraction of the at least one polymer resin (B1 ) related to the sum of all polymer resins (B1 ) is in the range from 0.9 to 1 , preferably in the range from 0.95 to 1.
The mass fraction of component (B1 ) in the polymer blend prepared in process step (a), which corresponds to the sum of the mass fractions of all polymer resins (B1 ) in the polymer blend is in the range from 0.1 to 0.8, preferably in the range from 0.3 to 0.7, in particular in the range from 0.4 to 0.6.
In one embodiment of the present invention the inventive process is characterized in that the sum of the mass fractions of all polymer resins (B1 ) in the polymer blend is in the range from 0.1 to 0.8, preferably in the range from 0.3 to 0.7, in particular in the range from 0.4 to 0.6. The polymer blend prepared in process step (a) might comprise besides the at least one polyester resin (A1 ) and the at least one polymer resin (B1 ) also portions of other chemical components, which can be extruded together with the polymer blend formed in process step (a) and which are insoluble during dissolving the at least one polymer resin (B1 ) in process step (c) like inorganic materials on the nanoscale. Preferably the sum of the mass fraction of all polyester resins (A1 ) and of all polymer resins (B1 ) in the polymer blend prepared in process step (a) is in the range from 0.5 to 1.0, preferably in the range from 0.8 to 1 .0, in particular in the range from 0.95 to 1 .0.
In one embodiment of the present invention the inventive process is characterized in that the sum of the mass fraction of all polyester resins (A1 ) and of all polymer resins (B1 ) in the polymer blend prepared in process step (a) is in the range from 0.5 to 1 .0, preferably in the range from 0.8 to 1 .0, in particular in the range from 0.95 to 1 .0.
In order to avoid transesterification reactions between polyester resin (A1 ) and polymer resin (B1 ) during the formation of the polymer blend and during the extrusion of said polymer blend during process step b) preferably an esterification inhibitor is added to the polymer resins before blending them. More preferably polymer resin (A1 ) and polymer resin (B1 ) are blended together with 0.2 to 5%, preferably 0.5 to 2%, by weight of an esterification inhibitor, in particular zinc phosphate, based on the sum of all polymer resins.
In one embodiment of the present invention the inventive process is characterized in that poly- mer resin (A1 ) and polymer resin (B1 ) are blended together with 0.2 to 5%, preferably 0.5 to 2%, by weight of an esterification inhibitor, in particular zinc phosphate, based on the sum of all polymer resins.
Processes to form a blend of two different, incompatible i.e. immiscible, thermoplastic polymer resins are known to the person skilled in the art. Suitable processes are described, for example, in WO 2013/000747 on page 24, lines 23 to 35. In particular the blend formation can be done in the extruder which is used to extrude the film of the polymer resin.
The extrusion of process step (b) can be done in wide temperature range. Preferably the extru- sion temperature of the polymer blend in process step (b) is in the range from 200 to 300 °C.
In one embodiment of the present invention the inventive process is characterized in that the extrusion temperature of the polymer blend in process step (b) is in the range from 200 to 300 °C.
In another embodiment of the present invention the inventive process is characterized in that in process step (b) the polymer blend is extruded through a flat film die.
After leaving the extruder the extruded film, which is still hot, can be further treated for example to obtain a desired thickness or orientation of the final film. Preferably the film extruded in process step (b) is calendered, rolled or stretched, either only in one direction or in two directions (biaxially stretched).
In one embodiment of the present invention the inventive process is characterized in that the film extruded in process step (b) is calendered, rolled or stretched.
Depending on the exact processing conditions during the blend formation and the film formation during process steps (a) and (b) the morphology of the incompatible polymer phase can be varied in a wide range. Preferably the processing conditions are adjusted by the person skilled in the art such that in the film of the polymer blend the at least one polyester resin (A1 ) forms a first phase and a second phase is formed by the at least one polymer resin (B1 ), wherein at least 80% by volume, preferably at least 90% by volume of the phase of polymer resin (B1 ) establishes in the phase of polyester resin (A1 ) a co-continuous phase with segments of a size in the range from 0.02 to 5 μηη. More preferably the two incompatible polymer resins form a gy- roidal, bi-continuous phase. The two incompatible polymer phases preferably form a system of co-continuous phases that allows to remove at least 75% by weight of polymer resin (B1 ), more preferably at least 85% by weight of polymer resin (B1 ), in particular at least 90% up to 100% by weight of polymer resin (B1 ).
In one embodiment of the present invention the inventive process is characterized in that in the film of the polymer blend, which is prepared in process step (b), the at least one polyester resin (A1 ) forms a first phase and a second phase is formed by the at least one polymer resin (B1 ), wherein at least 80% by volume, preferably at least 90% by volume of the phase of polymer resin (B1 ) establishes in the phase of polyester resin (A1 ) a co-continuous phase with segments of a size in the range from 0.02 to 5 μηη.
In process step (c) polymer resin (B1 ), which is present in the film prepared in process step (b), is extracted with a solvent or solvent mixture, which does not dissolve polyester resin (A1 ). Suitable solvents or solvent mixtures, appropriate temperatures for the dissolution process, necessary volumes and contact times are either known to the person skilled in the art or can easily be determined in a few solubility experiments. An appropriate solvent for polycarbonates, in particular the polycarbonate derived from bisphenol A and phosgene, is cyclohexanone. Polyethers, in particular polyethers based on ethylene oxide, are soluble in water. It is also possible to add at least one oxidizer, like a salt of hypochlorite, to the solvent or solvent mixture, in order to accelerate the dissolution of polymer resin (B1 ) by oxidative degradation of its polymer chains. J. Appl. Poly. Sci., 33, 49 - 54 (1995) describes for example the reaction between polyvinyl pyrrolidone) and hypochlorite.
In the optional process step (d) the porous polyester membrane, which was obtained after process step (c), can be rinsed with additional suitable solvents and can be dried. In case that a solvent was used in process step (c) or the optional rinsing step, wherein said solvent has to be avoided in the intended use of the produced membrane, the porous membrane is preferably dried in order to remove any unwanted solvent. The drying conditions e.g. temperature and pressure are chosen based on common knowledge considering the properties of the porous membrane and the properties of the solvents, which have to be removed.
The present invention further also provides a porous polyester membrane comprising a polyester resin derived from an aromatic dicarboxylic acid, preferably comprising a polyester selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate and polytri- methylene terephthalate, in particular polybutylene terephthalate, wherein the porous polyester membrane has a thickness in the range from 5 to 50 μηη. preferably in the range from 10 to 30 μηη, a porosity in the range from 0.4 to 0.6 and pores having pore diameters in the range from 0.03 to 2 μηη, obtainable or obtained by the process for producing a porous polyester membrane as described above. This process comprises the above-described process steps (a), (b), (c) and optinally (d), especially also with regard to preferred embodiments thereof.
The present invention likewise also provides a porous polyester membrane comprising a polyester resin derived from an aromatic dicarboxylic acid, preferably comprising a polyester select- ed from the group consisting of polyethylene terephthalate, polybutylene terephthalate and poly- trimethylene terephthalate, in particular polybutylene terephthalate, wherein the porous polyester membrane has a thickness in the range from 5 to 50 μηη. preferably in the range from 10 to 30 μηη, a porosity in the range from 0.4 to 0.6 and pores having pore diameters in the range from 0.03 to 2 μηη, wherein the porous polyester membrane is prepared by a process comprising at least the process steps of
(a) preparation of a polymer blend comprising (A1 ) at least one polyester resin (A1 ) derived from an aromatic dicarboxylic acid, preferably a polyester resin (A1 ) selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate and polytrimethylene terephthalate, in particular polybutylene terephthalate, and
(B1 ) at least one polymer resin (B1 ) incompatible with polyester resin (A1 ), preferably a polymer resin (B1 ) selected from the group consisting of polycarbonates and poly- ethers, in particular selected from the group consisting of polyethers,
(b) extruding a film of the polymer blend prepared in process step (a),
(c) dissolving the polymer resin (B1 ) of the film prepared in process step (b) with a solvent, which does not dissolve polyester resin (A1 ), and
(d) optionally rinsing the porous polyester membrane, which was obtained after process step (c), or drying said membrane.
The process steps a), b), c) and d) have been described above. In particular, preferred embod- iments of the process steps have been described above.
The porous polyester membrane, which is obtainable or obtained by the inventive process, comprises a polyester resin derived from an aromatic dicarboxylic acid, preferably it comprises a polyester selected from the group consisting of polyethylene terephthalate, polybutylene ter- ephthalate and polytrimethylene terephthalate, in particular polybutylene terephthalate, wherein the porous polyester membrane has a thickness in the range from 5 to 50 μηη. preferably in the range from 10 to 30 μηη, a porosity in the range from 0.4 to 0.6 and pores having pore diameters in the range from 0.03 to 2 μηη, preferably having pores which have a median pore diameter in the range from 0.2 to 1 μηη.
Preferably the porous polyester membrane as described above is characterized in that the at least one polyester resin (A1 ) forms a first phase and the pores establish a co-continuous phase of interconnected voids in said first phase of a polyester resin (A1 ) with segments of a size in the range from 0.02 to 5 μηη. More preferably the polyester phase and the interconnected pores form a gyroidal, bi-continuous phase. Inventive porous polyester membranes have advantageous properties. They show good wettability with electrolyte solvents and they are in particular thermally and mechanically more stable than commercially available polyolefin membranes. They also show a better limiting oxygen index compared to commercially available polyolefin membranes. The inventive porous polyester membrane is particularly suitable as separator or as constituent of a separator in electrochemical cells, in particular in rechargeable electrochemical cells in order to separate anode from cathode in an electrochemical cell. By the above-described process the porous polyester membrane can be obtained in the form of continuous belts which are processed further by the battery manufacturer, especially assembling the inventive porous polyes- ter membrane with appropriate flat cathodes and flat anodes in order to produce electrochemical cells.
For the purposes of the present invention, the term electrochemical cell or battery encompasses batteries, capacitors and accumulators (secondary batteries) of any type, in particular alkali metal cells or batteries such as lithium, lithium ion and alkaline earth metal batteries and accumulators, including in the form of high-energy or high-power systems, and also electrolyte capacitors and double-layer capacitors which are known under the names Supercaps, Goldcaps, BoostCaps or Ultracaps. The present invention further also provides for the use of the inventive porous polyester membrane as described above as part of an electrochemical cell, namely as separator.
The present invention further provides an electrochemical cell comprising at least one porous polyester membrane as described above, in particular a rechargeable electrochemical cell com- prising
(I) at least one anode (I),
(II) at least one cathode (II),
(III) at least one electrolyte composition (III) comprising
(1111 ) at least one aprotic organic solvent (1111 ), and
(III2) at least one alkali metal salt (III2), and
(IV) at least one porous polyester membrane as described above. As regards suitable cathode materials, suitable anode materials, suitable electrolytes and possible arrangements, reference is made to the relevant prior art, e.g. appropriate monographs and reference works: e.g. Wakihara et al. (editor): Lithium ion Batteries, 1 st edition, Wiley VCH, Weinheim, 1998; David Linden: Handbook of Batteries (McGraw-Hill Handbooks), 3rd edition, Mcgraw-Hill Professional, New York 2008; J. O. Besenhard: Handbook of Battery Materials. Wiley-VCH, 1998.
Inventive cells are preferably selected from alkali metal containing cells. More preferably, inventive cells are selected from lithium-ion containing cells. In lithium-ion containing cells, the charge transport is effected by Li+ ions.
In the context with the present invention, the electrode where during discharging a net negative charge occurs is called the anode. Anode (I) 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 (I) is selected from graphite anodes, lithium titanate anodes, anodes comprising In, Tl, Sb, Sn or Si, and anodes comprising metallic lithium. Anode (I) 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 (I) 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, eth- ylene-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 (I) can have a thickness in the range of from 15 to 200 μηη, preferably from 30 to 100 μηη, determined without the current collector.
Inventive cells further comprise a cathode (II). Cathode (II) can contain solid, liquid or gaseous active materials, e. g., air (or oxygen). In a preferred embodiment, however, cathode (II) contains a solid active material. Solid active materials for cathode (II) can be selected from phosphates with olivine structure such as lithium iron phosphates (LiFePC ) and lithium manganese phosphate (LiMnPC ) which can have a stoichiometric or non-stoichiometric composition and which can be doped or not doped. In one embodiment of the present invention, active material for cathode (II) can be selected from lithium containing transition metal spinels and lithium transition metal oxides with a layered crystal structure. In such cases, cathode (II) contains at least one material selected from lithium containing transition metal spinels and lithium transition metal oxides with a layered crystal structure, respectively.
In one embodiment of the present invention the electrochemical cell is characterized in that cathode (II) contains at least one material selected from lithium containing transition metal spinels and lithium transition metal oxides with a layered crystal structure. In one embodiment of the present invention, lithium-containing metal spinels are selected from those of the general formula (I)
Figure imgf000012_0001
the variables being defined as follows:
0.9 < a < 1 .3, preferably 0.95 < a < 1 .15,
0 < b < 0.6, for example 0.0 or 0.5, wherein, if M1 = Ni, 0.4 < b < 0.55, -0.1 < d < 0.4, preferably 0 < d < 0.1 ,
M1 is selected from one or more out of Al, Mg, Ca, Na, B, Mo, W and transition metals of the first row of the transition metals in the periodic table of the elements. In a preferred embodi- ment, M1 is selected from the group consisting of Ni, Co, Cr, Zn, and Al. Even more preferably, M1 is defined to be Ni.
In one embodiment of the present invention, lithium containing metal spinels are selected from LiNio,5Mni,504-d and LiM^C .
In one embodiment of the present invention, lithium transition metal oxides with a layered crystal structure are selected from compounds of general formula (II)
Figure imgf000013_0001
the variable being defined as follows: 0 < t < 0.3 und M2 selected from one or more elements from Al, Mg, B, Mo, W, Na, Ca and transition metals of the first row of the transition metals in the periodic table of the elements, at least one element being manganese.
In one embodiment of the present invention, at least 30 mole-% of M2 are selected from man- ganese, preferably at least 35 mole-%, in each time with respect to the complete amount of M2.
In one embodiment of the present invention M2 is selected from combinations of Ni, Co and Mn not containing significant amounts of additional elements. In a different embodiment of the present invention M2 is selected from combinations of Ni, Co and Mn containing significant amounts of at least one additional element, for example in the range of from 1 to 10 mole-% Al, Ca or Na.
In a particular embodiment of the present invention, lithium transition metal oxides with a lay- ered crystal structure are selected from compounds of general formula (III)
Li(i+x)[NieCOfMngM3h](i-x)02 (HI) the variables being defined as follows: x a number in the range of from zero to 0.2, e a number in the range of from 0.2 to 0.6, f a number in the range of from 0.1 to 0.5, g a number in the range of from 0.2 to 0.6, h a number in the range of from zero to 0.1 , and: e + f + g + h = 1 ,
M3 selected from Al, Mg, V, Fe, Cr, Zn, Cu, Ti and Mo.
In one embodiment of the present invention, M2 in formula (I I) is selected from Nio,33Coo,33Mno,33, Nio,5Coo,2Mn0,3, Nio,4Coo,3Mn0,4, Ni0,4Coo,2Mn0,4 und Ni0,45Coo,ioMn0,45.
Cathode (I I) can further comprise a current collector. Suitable current collectors are, e.g., metal wires, metal grids, metal gauze and preferably metal foils such as aluminum foils.
Cathode (I I) can further comprise a binder. Suitable binders can be selected from organic (co)polymers. Suitable organic (co)polymers may be halogenated or halogen-free. In general, the same binders used for anode (I) can also be employed for cathode (I I).
Preferred binders are especially polyvinyl alcohol and halogenated (co)polymers, for example polyvinyl chloride or polyvinylidene chloride, especially fluorinated (co)polymers such as polyvi- nyl fluoride and especially polyvinylidene fluoride and polytetrafluoroethylene.
In one embodiment of the present invention, cathode (I I) can have a thickness in the range of from 15 to 200 μηη, preferably from 30 to 100 μηη, determined without the current collector.
Cathode (II) can further comprise electrically conductive carbonaceous material.
Electrically conductive carbonaceous material can be selected, for example, from graphite, carbon black, carbon nanotubes, graphene or mixtures of at least two of the aforementioned substances. In the context of the present invention, electrically conductive, carbonaceous material can also be referred to as carbon for short.
In one embodiment of the present invention, electrically conductive carbonaceous material is carbon black. Carbon black may, for example, be selected from lamp black, furnace black, flame black, thermal black, acetylene black and industrial black. Carbon black may comprise impurities, for example hydrocarbons, especially aromatic hydrocarbons, or oxygen-containing compounds or oxygen-containing groups, for example OH groups. In addition, sulfur- or iron- containing impurities are possible in carbon black. In one variant, electrically conductive carbonaceous material is partially oxidized carbon black.
In one embodiment of the present invention the electrochemical cell is characterized in that cathode (II) contains a material based on electrically conductive carbon.
Inventive electrochemical cells further comprise, as well as the inventive alkali-ion conducting separator assembly, the anode (I) and the cathode (II), at least one electrolyte composition (III) comprising
(1111 ) at least one aprotic organic solvent (1111 ), and
(III2) at least one alkali metal salt (III2).
Possible aprotic organic solvents (1111 ) may be liquid or solid at room temperature and are preferably liquid at room temperature. Solvents (1111 ) are 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 rechargeable electrochemical cell is characterized in that the aprotic organic solvent (1111 ) 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 imgf000016_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
X
0 ° (XII)
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 (I I I2), which are used as conductive salts, have to be soluble in the aprotic organic solvent (1111 ). Preferred alkali metal salts (I I I2) are lithium salts or sodium salts, in particular lithium salts.
In one embodiment of the present invention the inventive rechargeable electrochemical cell is characterized in that the alkali metal salt (I I I2) 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, 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, and particular preference is given to LiPF6 and LiN(CFsS02)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 0.5 M to 1 .5 M. Inventive electrochemical cells further comprise as separator at least one inventive alkali-ion conducting separator assembly, which has been described above, wherein the separator assembly is positioned between anode (I) and cathode (II) in the electrochemical cells.
In one embodiment of the present invention, separator assembly is positioned between anode (I) and cathode (II) in a way that it is like a layer to either a major part of one surface of anode (I) or cathode (II).
In one embodiment of the present invention, separator assembly is positioned between anode
(I) and cathode (II) in a way that it is like a layer to both a major part of one surface of anode (I) and cathode (II).
In a preferred embodiment of the present invention, separator assembly is positioned between anode (I) and cathode (II) in a way that it is like a layer to one surface of anode (I) or of cathode
(II) .
In another preferred embodiment of the present invention, separator assembly is positioned between anode (I) and cathode (II) in a way that it is like a layer to one surface of both anode (I) and of cathode (II). Inventive alkali-ion conducting separator assemblies have overall advantageous properties.
They help to secure a long duration of electrochemical cells with very low loss of capacity, good cycling stability, and a reduced tendency towards short circuits after longer operation and/or repeated cycling. They can help batteries to have a long duration with very low loss of capacity, good cycling stability, and high temperature stability. 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 have overall advantageous properties. They have a long duration with very low loss of capacity, good cycling stability, and a reduced tendency towards short circuits after longer operation and/or repeated cycling.
A further aspect of the present invention refers to batteries, more preferably to an alkali metal ion battery, in particular to a lithium ion battery comprising at least one inventive electrochemical cell, for example two or more. Inventive electrochemical cells can be combined with one another in inventive alkali metal ion batteries, for example in series connection or in parallel connection. Series connection is preferred.
Inventive batteries have advantageous properties. They have a long duration with very low loss of capacity, good cycling stability, and high temperature stability. 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 electrochemical cell as described above. Preferred are mobile devices such as are 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, tele- phones 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 do not restrict the invention. Figures in percent are each based on % by weight, unless explicitly stated otherwise. I. Film preparation
I. a Preparation of a PBT/POE film
Polybutylene terephthalate (Viscosity number: 21 cm3/10min (solution 0,005 g/ml Phenole/1 ,2 Dichlorbenzol 1 :1 ); Ultradur® B4500 from BASF) was compounded with polyethylene glycol (Mw = 300000 g/mol; POLYOX™ WSR-N 750 ( from Dow Chemical) in 50 / 50 wt/wt ratio at 245 °C (torque 4200 N) and extruded through a 100 μηη x 3 cm slot die (650 m/h) to a film by the means of a DSM micro extruder. An opaque, transparent film (F1 ) with 67 μηη thickness was obtained.
II. Preparation of porous membranes
I I. a Preparation of porous membrane M1 from film F1
Film F1 obtained in example I. a was washed three times with water and dried under vacuum until the weight was constant and the inventive porous membrane M1 was obtained. Gravimetric analysis indicated weight loss of 46.1 % which is equivalent to 46.1 % film porosity. The extraction rate of polyethylene glycol POLYOX™ WSR-N 750 was calculated to 92.2 %. III. Characterization of porous membranes
I I I. a Thermal stability
For evaluation of thermal stability circular samples of 2.0 cm diameter were punched out (do) and subjected to temperature treatment of 170 °C for 5 hours. Then the diameter (dwc) is evaluated again and the shrinkage calculated based on the formula (1 ). The inventive porous membrane M1 obtained in example II. a showed shrinkage of less than 1 % shrinkage [%] = ( 1 - j >: 1UU (1)
Table 1 shows the shrinkage of inventive porous membrane M1 and the shrinkage of two mercially available polyolefin membranes.
Table 1
Figure imgf000020_0001
lll.b Mechanical stability
Tensile testing was carried out according ISO 527-2 and DIN 53504 S3A in order to assess the mechanical stability of inventive porous membrane M1 (Zwick & Roell, force sensor: 50 N, speed: 100 mm/min, 30 mm test specimen). Table 2 summarizes the result obtained compared to a polyethyleneterephthalate non-woven ("PES20" nonwoven from APODIS Filtertechnik OHG).
Table 2
Figure imgf000020_0002
lll.c Pore size distribution
Mercury porometry was conducted according DIN 66133 1993-06 in order to obtain insight view on the pore size distributions. For the inventive porous membrane M1 a median pore diameter of 0.4248 μηη was evaluated.
Figure 1 shows the logarithmic (log) differential intrusion volume (mL/g- y-axis) depending on the pore size diameter (μηη - x-axis)
Figure 2 shows the cumultative intrusion volume (mL/g - y-axis) depending on the pore size diameter (μηη - x-axis) IV. Production of electrochemical cells and testing thereof
The following electrodes and electrolyte were always used: Anode (I): graphite on copper foil as current collector with a thickness of 36 to 38 μηη (Fa. Gaia, Nordhausen, Germany).
Cathode (II): LiNio.8Coo.15Alo.05O2, on aluminium foil as current collector (Fa. Gaia, Nordhausen, Germany).
As cathode (II), a nickel manganese spinel electrode was used which had been manufactured as follows:
85% LiNio.8Coo.15Alo.05O2
6% PVdF, commercially available as Kynar Flex® 2801 of Arkema Group,
6% carbon black, BET surface 62 m2/g, commercially available as„Super P Li" by Timcal, 3% graphite, commercially available as KS6 by Timcal,
were mixed in a container with a lid. Under stirring, an amount of NMP was added until a viscous lump-free paste was obtained. Stirring was performed over a time of 16 hours. The paste so obtained was applied to an aluminium foil (thickness of the aluminium foil: 20 μηη) with a knife blade. Then, the aluminium foil so coated was dried in a drying cabinet at 120 °C under vacuum. The thickness of the dried coating was 30 μηη. Then round segments were punched out, diameter: 12 mm. The following electrolyte (III) was used:
1 M solution of LiPFe in a 1 :1 (by weight) mixture of ethylene carbonate / ethyl methyl carbonate (commercially available as LP 50 SelectiLyte™).
IV.1 Production of inventive electrochemical cell E.1 comprising inventive porous membrane M1
An inventive electrochemical cell (E.1 ) according to figure 3 was assembled. Figure 3 shows the schematic structure of a dismantled electrochemical cell for testing of porous membranes.
The annotations in Figure 3 mean:
1 , 1 ' die
2, 2' nut
3, 3' sealing ring - two in each case; the second, somewhat smaller sealing ring in each case is not shown here 4 spiral spring
5 nickel output conductor
6 housing In an argon-filled glovebox, electrolyte (III) was dripped onto the inventive porous membrane M1 produced according to II. a and it was positioned between a cathode (II) and an anode (I) such that both the anode and the cathode had direct contact with the separator. This gave inventive electrochemical cell E.1. Inventive electrochemical cell E.1 was charged with a constant current to a voltage of 4.2 V followed by a final charging with constant voltage at 4.2 V. Then, inventive electrochemical cell E.1 was discharged at constant current to a voltage of 3 V. Three such cycles with 0.1 C and, thereafter, 50 and 200 cycles with 0.5 C were determined.
Table 3: Discharge capacities of electrochemical cells with inventive porous membrane M.1
Membrane ElectroSpecific capacity Specific capacity
chemical [mA/g] [mA/g]
cell 50th 200th
M.1 E.1 90 100

Claims

Claims
1 . A process for producing a porous polyester membrane, comprising at least the process steps of
(a) preparation of a polymer blend comprising
(A1 ) at least one polyester resin (A1 ) derived from an aromatic dicarboxylic acid, and
(B1 ) at least one polymer resin (B1 ) incompatible with polyester resin (A1 ),
(b) extruding a film of the polymer blend prepared in process step (a),
(c) dissolving the polymer resin (B1 ) of the film prepared in process step (b) with a solvent, which does not dissolve polyester resin (A1 ), and
(d) optionally rinsing the porous polyester membrane, which was obtained after process step (c), or drying said membrane.
2. The process according to claim 1 , wherein the porous polyester membrane has a thickness in the range from 5 to 50 μηη.
3. The process according to claim 1 or 2, wherein the porous polyester membrane has a porosity in the range from 0.3 to 0.6.
4. The process according to any of claims 1 to 3, wherein the porous polyester membrane has pores which have a median pore diameter in the range from 0.2 to 1 μηη.
5. The process according to any of claims 1 to 4, wherein the sum of the mass fractions of all polymer resins (B1 ) in the polymer blend prepared in process step (a) is in the range from 0.1 to 0.8.
6. The process according to any of claims 1 to 5, wherein the at least one polymer resin (B1 ) is a polyether with a molecular weight Mw in the range from 10 000 to 10 000 000 g/mol.
7. The process according to any of claims 1 to 6, wherein the extrusion temperature of the polymer blend in process step (b) is in the range from 200 to 300 °C.
The process according to any of claims 1 to 7, wherein in the film of the polymer blend, which is prepared in process step (b), the at least one polyester resin (A1 ) forms a first phase and a second phase is formed by the at least one polymer resin (B1 ), wherein at least 80% by volume of the phase of polymer resin (B1 ) establishes in the phase of polyester resin (A1 ) a co-continuous phase with segments of a size in the range from 0.02 to 5 μηη.
A porous polyester membrane comprising a polyester resin derived from an aromatic di- carboxylic acid, wherein the porous polyester membrane has a thickness in the range from 5 to 50 μηη, a porosity in the range from 0.4 to 0.6 and pores having pore diameters in the range from 0.03 to 2 μηη, obtainable or obtained by a process according to any of claims 1 to 8.
0. A porous polyester membrane comprising a polyester resin derived from an aromatic di- carboxylic acid, wherein the porous polyester membrane has a thickness in the range from 5 to 50 μηη, a porosity in the range from 0.4 to 0.6 and pores having pore diameters in the range from 0.03 to 2 μηη, wherein the porous polyester membrane is prepared by a process comprising at least the process steps of
(a) preparation of a polymer blend comprising
(A1 ) at least one polyester resin (A1 ) derived from an aromatic dicarboxylic acid, and
(B1 ) at least one polymer resin (B1 ) incompatible with polyester resin (A1 ),
(b) extruding a film of the polymer blend prepared in process step (a),
(c) dissolving the polymer resin (B1 ) of the film prepared in process step (b) with a solvent, which does not dissolve polyester resin (A1 ), and
(d) optionally rinsing the porous polyester membrane, which was obtained after process step (c), or drying said membrane.
13. A lithium ion battery comprising at least one electrochemical cell according to claim 12.
14. The use of an electrochemical cell according to claim 12 in motor vehicles, bicycles oper- ated by electric motor, aircraft, ships or stationary energy stores.
15. A device comprising at least one electrochemical cell according to claim 12.
PCT/EP2015/062538 2014-06-12 2015-06-05 Process for producing microporous polyester membranes for electronic applications WO2015189094A1 (en)

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