Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/52—Separators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G9/00—Electrolytic capacitors, rectifiers, detectors, switching devices, light-sensitive or temperature-sensitive devices; Processes of their manufacture
  • H01G9/004—Details
  • H01G9/02—Diaphragms; Separators
• • 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
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
  • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
• • 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
• • 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
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/431—Inorganic material
• • 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
  • H01M50/44—Fibrous material
• • 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
  • H01M50/446—Composite material consisting of a mixture of organic and inorganic materials
• • 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
  • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
• • 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
• • 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
• • 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
  • Y02E60/13—Energy storage using capacitors

Definitions

• the invention relates to a separator for non-aqueous-type electrochemical device that has been coated with an aqueous fluoropolymer coating.
• fluoropolymer is preferably polyvinylidene fluoride (PVDF), and more preferably a copolymer of polyvinylidene fluoride.
• PVDF polyvinylidene fluoride
• the fluoropolymer coating provides a porous coating on porous substrate used in non-aqueous-type electrochemical devices, such as batteries and electric double layer capacitors.
• the fluoropolymer coating improves the thermal resistance and mechanical integrity, and lowers the interfacial electrical impedance of the porous separator.
• porous separator is coated with an aqueous fluoropolymer-based composition.
• the starting fluoropolymer dispersion is free of fluorinated surfactant.
• Lithium batteries including lithium metal batteries, lithium ion batteries, lithium polymer batteries, and lithium ion polymer batteries are finding increased usage due to drive voltages and higher energy densities than those of conventional batteries using aqueous electrolytes (such as Ni-MH batteries).
• aqueous electrolytes such as Ni-MH batteries.
• lithium secondary batteries have different safety characteristics depending on several factors. The safety of these batteries is strictly restricted in terms of ignition and combustion.
• Currently available lithium ion batteries and lithium ion polymer batteries use polyolefin-based separators in order to prevent a short circuit between a cathode and an anode.
• polyolefin-based separators have a melting point of 140 °C or less, they can be shrink melted to cause a change in volume when the temperature of a battery is increased by internal and/or external factors, and that may cause a short-circuit.
• the short circuit can result in accidents such as explosion or fire in a battery caused by emission of electric energy.
• the role of the organic solvent is generally to dissolve PVDF copolymer in order to provide good adhesion (non-reversible adhesion) between PVDF copolymer and porous separator and also optionally added the powdery particles and porous separator which upon evaporation of the organic solvent is leaving behind a porous coating on the polyolefin separator.
• organic- solvent-based solution / slurry presents safety, health and environmental dangers that are not present in an aqueous system.
• Organic solvents are generally toxic and flammable, volatile in nature, and involve special
• Some common criteria include: a) stability of the waterborne fluoropolymer dispersion, having sufficient shelf-life, b) stability of the slurry after formulation and admixing optionally the powdery material, c) appropriate viscosity of the slurry to facilitate good aqueous casting, and d) sufficient adhesion to the separator which is nonreversible after drying, e) and foaming porous coating on polyolefin separator upon drying. Additionally, from a regulatory view, fluoropolymers made without fluoro surfactants are preferred.
• the coating composition contains fluoropolymer and optionally inorganic particles or organic fibers.
• the separator coated with the aqueous composition of the invention provides many performance, manufacturing and environmental advantages over solvent-based PVDF compositions and solvent: a) Aqueous PVDF-based compositions are safer to use and process, less hazardous to health, and more environmentally friendly than solvent-based PVDF compositions. b) Aqueous PVDF dispersions were advantageously synthesized using non- fluorinated surfactant. c) Aqueous PVDF dispersions can be used as synthesized, without the need for isolating and drying to a powder, or concentration of the latex - saving time and energy.
• Aqueous PVDF dispersions contain PVDF copolymer particles that can be softened to adhere to metal oxide particles and a polyolefin separator by using fugitive adhesion promoters - resulting in a porous coating on a separator upon drying.
• the PVDF-based copolymers have advantageously low melting temperature or low to zero crystalline content so that can have lower film forming temperature and/or require less fugitive solvents.
• the invention relates to a porous separator having directly coated thereon a composition comprising:
• c) optionally from 0 to 10 parts of one or more thickeners; optionally, one or more pH adjusting agents;
• g optionally from 0 to 150 parts of one or more fugitive adhesion promoters
• composition contains no fluorosurfactant.
• the fluoropolymer is a polyvinylidene fluoride-based polymer.
• the invention further relates to a method for coating the separator.
• the invention further relates to a non-aqueous electrochemical device having the separator of the invention as a barrier between the anode and the cathode.
• Figures 1 and 2 are FTIR spectra of coated and non-coated separators, showing the durability of the separator coatings of the invention.
• the invention relates to a porous separator coated with an aqueous
• fluoropolymer-based composition and optionally containing particles, and in particular to a polyvinylidene fluoride-based composition.
• fluorosurfactant free is meant that all surfactants used in making the aqueous fluoropolymer dispersion do not contain a fluorine atom (i.e. they are “non- fluorinated surfactants”).
• the term refers to all surfactants used in making and processing the aqueous fluoropolymer dispersion, and preferably to all the surfactants in the composition of the invention, including: all surfactants used during the polymerization process - whether added up-front, fed continuously during the polymerization, fed partly before and then during polymerization, or fed after the polymerization has started and progressed for a time; and preferably all surfactants added post-polymerization to improve latex stability.
• irreversible as used herein in relation to a separator coated by the polymer of the aqueous composition, is meant that following the drying of the aqueous composition in which the polymer adheres to the porous substrate, the polymer coating is not soluble or redispersible in electrolyte solutions, such as carbonates.
• electrolyte solutions such as carbonates.
• the irreversibility is due to the fact that the polymer particles flow and adhere to each other, and adhere to the separator and act as a binder for optional powdery inorganic materials, and organic fibers , providing interconnect! vity and adhesion.
• PVDF polyvinylidene fluoride polymer
• Such copolymers include those containing at least 50 mole percent, preferably at least 75 mole , more preferably at least 80 mole , and even more preferably at least 85 mole % of vinylidene fluoride copolymerized with at least one comonomer selected from the group consisting of tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, vinyl fluoride, pentafluoropropene, tetrafluoropropene, perfluoromethyl vinyl ether, perfluoropropyl vinyl ether and any other monomer that would readily copolymerize with vinylidene fluoride.
• comonomer selected from the group consisting of tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, vinyl fluoride, pentafluoropropene, tetrafluoropropene, perfluor
• copolymers composed of from at least about 70 and up to 90 mole percent vinylidene fluoride, and correspondingly from 10 to 30 mole percent hexafluoropropene.
• Terpolymers of vinylidene fluoride, hexafluoropropene and tetrafluoroethylene are also representatives of the class of vinylidene fluoride copolymers, embodied herein.
• HFP hexafluoropropene
• VDF hexafluoropropene
• the copolymer of PVDF for use in the separator coating composition preferably has a high molecular weight.
• high molecular weight as used herein, is meant PVDF having a melt viscosity of greater than 1.0 kilopoise according to ASTM method D-3835 measured at 450 °F and 100 sec "1 .
• the copolymer of PVDF used in the invention is preferably prepared by aqueous free-radical emulsion polymerization - although suspension, solution and supercritical C0 2 polymerization processes may also be used.
• a reactor is charged with deionized water, water-soluble surfactant capable of emulsifying the reactant mass during polymerization and optional paraffin wax antifoulant. The mixture is stirred and deoxygenated.
• a predetermined amount of chain transfer agent (CTA) is then introduced into the reactor, the reactor temperature raised to the desired level and vinylidene fluoride and one or more comonomers is fed into the reactor.
• CTA chain transfer agent
• an initiator emulsion or solution is introduced to start the polymerization reaction.
• the temperature of the reaction can vary depending on the characteristics of the initiator used and one of skill in the art will know how to do so. Typically the temperature will be from about 30° to 150°C, preferably from about 60° to 110°C.
• the surfactant used in the polymerization can be any surfactant known in the art to be useful in PVDF emulsion polymerization, including perfluorinated, partially fluorinated, and non-fluorinated surfactants.
• the PVDF emulsion of the invention is made without fluorinated surfactants.
• Non- fluorinated surfactants useful in the PVDF polymerization could be both ionic and non-ionic in nature including, but are not limited to, 3-allyloxy-2-hydroxy-l -propane sulfonic acid salts, polyvinylphosphonic acid, polyacrylic acids, polyvinyl sulfonic acid, and salts thereof, polyethylene glycol and/or polypropylene glycol and the block copolymers thereof, alkyl phosphonates and siloxane -based surfactants.
• the PVDF polymerization results in a latex generally having a solids level of 10 to 60 percent by weight, preferably 10 to 50 percent, and having a weight average particle size of less than 500 nm, preferably less than 400 nm, and more preferably less than 300 nm.
• the weight average particle size is generally at least 20 nm and preferably at least 50 nm.
• the composition of the invention contains 2 to 150 parts by weight of PVDF copolymer binder particles per 100 parts of water, preferably 1 to 25 parts by weight. Additional adhesion promoters may also be added to improve the binding characteristics and provide connectivity and adhesion that is non-reversible. A minor amount of one or more other water- miscible solvents, such as ethylene glycol, may be mixed into the PVDF latex to improve freeze-thaw stability.
• PVDF based-polymer binder is generally used in the coating composition, however a blend of several different polymer binders, preferably all fluoropolymer binders, and most preferably all PVDF binders may also be used. In one embodiment, only thermoplastic fluoropolymers that can be softened by fugitive adhesion promoters are used as the polymeric coating / binder.
• the powdery particular materials, or powdery particle in the coating composition permit an interstitial volume to be formed among them, thereby serving to form micropores and to maintain the physical shape as spacer. Additionally, because the powdery particles are characterized in that their physical properties are not changed even at a high temperature of 200 ° C. or higher, the coated separator using the inorganic particles can have excellent heat resistance.
• the powdery particles may be inorganic, organic, and may be in the form of particles or fibers. Mixtures of these are also anticipated.
• the powdery particular materials must be electrochemically stable (not subjected to oxidation and/or reduction at the range of drive voltages). Moreover, the powdery materials preferably have a high ion conductivity. Materials of low density are preferred over higher density materials, as the weight of the battery produced can be reduced. The dielectric constant is preferably 5 or greater.
• Useful inorganic powdery materials in the invention include, but are not limited to BaTi0 3 ,
• Pb(Zr,Ti)0 3 Pb 1-x La x Zr y 0 3 (0 ⁇ x ⁇ l, 0 ⁇ y ⁇ l), PBMg 3 Nb 2/3 ) 3 ,PbTi0 3 , hafnia (HfO (Hf0 2 ), SrTiO 3 , Sn0 2 , Ce0 2 , MgO, NiO, CaO, ZnO, Y 2 0 3 , A1 2 0 3 , Ti0 2 , SiC, Zr0 2 , boron silicate, BaS0 4 , nano-clays, ceramics, or mixtures thereof.
• Useful organic fibers include, but are not limited to aramid fillers and fibers, polyetherether ketone and polyetherketone ketone fibers, PTFE fibers, and nanofibers.
• the particles or fibers may be surface treated, chemically
• the separator of the invention can form pores having a size from several nanometers up to several micrometers by controlling the size of the powdery materials, content of inorganic materials and the mixing ratio of inorganic materials and binder polymer. It is also possible to control the pore size and porosity.
• the powdery materials preferably have an average diameter of 0.001-10 microns.
• fibers Preferably fibers have diameters below 1 micron, and fiber overlap does not amount to more than about 4-5 microns in thickness.
• the size is less than 0.001 micron the particles have poor dispersibility.
• the size is greater than 10 micron the coating has an increased thickness under the same solid content, resulting in degradation in mechanical properties. Furthermore, such excessively large pores may increase a possibility of internal short circuit being generated during repeated charge/discharge cycles.
• the powdery materials are present in coating composition at 50 to 99 weight percent, preferably 60 - 95 weight percent, based on the total of polymer solids and powdery material.
• the content of the inorganic materials is less than 50 weight percent, the PVDF binder polymer is present in such a large amount as to decrease the interstitial volume formed among the powdery particles and thus to decrease the pore size and porosity, resulting in degradation in the quality of a battery.
• the total solid content of aqueous dispersion can be adjusted to a lower level.
• the content of the powdery materials is greater than 99 weight percent, the polymer content is too low to provide sufficient adhesion among the particles, resulting in degradation in mechanical properties of a finally formed coated separator.
• the coating composition of the invention contains 0 to 10 parts, preferably from 0.1 to 10 parts, and more preferably 0.5 to 5 parts of one or more anti-settling agents and/or surfactants per 100 parts of water.
• the level of anti- settling agent or surfactant is from 2.7 to 10 parts per 100 parts of water.
• These anti- settling agents or surfactants are added to the PVDF dispersion post-polymerization, generally to improve the shelf stability, and provide additional stabilization during slurry preparation.
• the surfactant/anti- settling agent used in this invention could be added all upfront prior to polymerization, fed continuously during the polymerization, fed partly before and then during polymerization, or fed after polymerization started and progressed for a while.
• Useful anti-settling agents include, but are not limited to, ionic substances, such as salts of alkyl sulfates, sulfonates, phosphates, phophonates (such as sodium lauryl sulfate and ammonium lauryl sulfate) and salts of partially fluorinated alkyl sulfates, carboxylates, phosphates, phosphonates (such as those sold under the
• non-ionic surfactants such as the TRITON X series (from Dow) and PLURONIC series (from BASF). In one embodiment, only anionic surfactants are used. It is preferred that no fluorinated surfactants are present in the composition, either residual surfactant from the polymerization process, or added post-polymerization in forming or concentrating an aqueous dispersion.
• the coating composition of the invention optionally contains 0 to 5 parts, preferably from 0 to 3 parts of one or more wetting agents per 100 parts of water.
• Surfactants can serve as wetting agents, but wetting agents may also include non- surfactants.
• the wetting agent can be an organic solvent. The presence of optional wetting agents permits uniform dispersion of powdery
• Useful wetting agents include, but are not limited to, ionic and non-ionic surfactants such as the TRITON series (from Dow) and the PLURONIC series (from BASF), BYK-346 (from BYK Additives)and organic liquids that are compatible with the aqueous dispersion, including but not limited to NMP, DMSO, and acetone.
• Thickener/rheologv modifier such as the TRITON series (from Dow) and the PLURONIC series (from BASF), BYK-346 (from BYK Additives)and organic liquids that are compatible with the aqueous dispersion, including but not limited to NMP, DMSO, and acetone.
• the coating composition of the invention may contain 0 to 10 parts, preferably from 0 to 5 parts of one or more thickeners or rheology modifiers per 100 parts of water. Addition of water-soluble thickener or rheology modifier to the above dispersion prevents or slows down the settling of powdery materials while providing appropriate slurry viscosity for a casting process.
• Useful thickeners include, but are not limited to the ACRYSOL series (from Dow Chemical); partially neutralized poly (acrylic acid) or poly (methacrylic acid) such as CARBOPOL from Lubrizol; and carboxylated alkyl cellulose, such as carboxylated methyl cellulose (CMC).
• Adjustment of the formulation pH can improve the effectiveness of some of the thickeners.
• inorganic rheology modifiers can also be used alone or in combination.
• Useful inorganic rheology modifiers include, but are not limited to, inorganic rheology modifiers including but not limited to natural clays such as montmorillonite and bentonite, manmade clays such as laponite, and others such as silica, and talc.
• the thickeners are used in the aqueous composition containing the PVDF and powdery material, and are not used in pure form as a second coating composition as has been described in the JP 2000357505 reference.
• a fugitive adhesion promoter is preferably present to produce the adhesion needed in coatings formed from the composition of the invention.
• fugitive adhesion promoter is meant an agent that increases the adhesion of the composition after coating on the porous substrate. The fugitive adhesion promoter is then capable of being removed from the formed substrate generally by evaporation (for a chemical) or by dissipation (for added energy).
• the fugitive adhesion promoter can be a chemical material, an energy source combined with pressure, or a combination, used at an effective amount to cause interconnectivity of the components of the aqueous composition during coating formation.
• the composition contains 0 to 150 parts, preferably 1 to 100 parts, and more preferably from 2 to 30 parts, of one or more fugitive adhesion promoters per 100 parts of water.
• this is an organic liquid, that is soluble or miscible in water. This organic liquid acts as a plasticizer for PVDF particles, making them tacky and capable of acting as discrete adhesion points during the drying step.
• the PVDF polymer particles are able to soften, flow and adhere to separator and optionally the powdery materials during manufacture, resulting in separator coatings with high adhesion and connectivity that are nonreversible.
• the organic liquid is a latent solvent, which is a solvent that does not dissolve or substantially swell PVDF resin at room temperature, but will solvate the PVDF resin at elevated temperatures.
• a useful organic solvent is N-methyl-2-pyrrolidone.
• fugitive adhesion promoter agents include, but are not limited to, dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide (DMSO), hexamethylphosphamide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, trimethyl phosphate, dimethyl succinate, diethyl succinate and tetraethyl urea.
• useful energy sources include, but are not limited to, heat, IR radiation, and radio frequency (RF).
• RF radio frequency
• the coating composition of the invention may further contain effective amounts of other additives, including but not limited to fillers, leveling agents, anti- foaming agents, pH buffers, and other adjutants typically used in waterborne formulation while meeting desired electrode requirements.
• other additives including but not limited to fillers, leveling agents, anti- foaming agents, pH buffers, and other adjutants typically used in waterborne formulation while meeting desired electrode requirements.
• the aqueous coating composition of the invention can be obtained in many different ways.
• a PVDF formulation is formed (preferably without any fluorosurfactant) and a predetermined amount of any anti-settling agent(s) or surfactant(s), is diluted in water and post-added to the PVDF dispersion latex with stirring, in order to provide adequate storage stability for the latex.
• a PVDF dispersion/anti- settling mixture is added, with stirring, optional wetting agent(s), followed by adding any thickener(s), fugitive adhesion promoter(s), and then bringing the pH up to the appropriate range for the thickener to be effective, if necessary.
• Some thickeners such as CMC are effective in a wide range of pH, i.e. from 3 to 9 pH for CMC.
• the powdery material(s) and other ingredients are then added to the mixture. It may be advantageous to disperse the powdery material(s) in the fugitive adhesion promoter, the latent solvent or wetting agent to provide wetting of the materials prior to admixing with the aqueous PVDF binder formulation.
• the substrate that is coated with the aqueous coating composition of the invention is a porous substrate having pores.
• the substrate is a heat resistant porous substrate having a melting point of greater than 200°C. Such heat resistant porous substrates can improve the thermal safety of the coated separator under external and/or internal thermal impacts.
• porous substrates useful in the invention as the separator include, but are not limited to: polyolefins, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetherether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfidro, polyethylene naphthalene or mixtures thereof.
• polyolefins polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetherether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfidro, polyethylene naphthalene or mixtures thereof.
• other heat resistant engineering plastics may be used with no particular limitation.
• Non-woven materials of natural and synthetic materials may also be used as the substrate of the separator.
• the porous substrate generally has a thickness of from 1 micron to 50 microns, and are typically cast membranes of non-wovens.
• the porous substrate preferably has a porosity of between 5% and 95%.
• the pore size (diameter) preferably ranges from 0.001 micron to 50 micron, more preferably from 0.01 micron to 10 micron. When the pore size and porosity are less than 0.01 micron and 5%, respectively, the porous substrate may function as resistance layer. When the pore size and porosity are greater than 50 micron and 95%, respectively, it is difficult to maintain mechanical properties.
• the porous substrate may take the form of a membrane, or fibrous web.
• the porous substrate may be a nonwoven web forming a porous web, such as a spunbond or melt blown web.
• An alternative method is to use a fluoropolymer powder, that is redispersed in water for form a fluoropolymer dispersion. In this case the particles will have been agglomerated, and the agglomerated particle size will be greater than 500 nm.
• the aqueous coating composition is applied onto at least one surface, and preferably both face surfaces, of an porous substrate by means known in the art, such as by brush, roller, ink jet, squeegee, foam applicator, curtain coating, vacuum coating, or spraying.
• the coating is then dried onto the separator.
• the final dry coating thickness is from 0.5 to 15 microns, preferably from 1 to 8 microns, and more preferably from 2 to 4 microns in thickness.
• the fhioropolymer coating may further be cross-linked to control swelling and dissolution.
• Useful crosslinking mechanisms include chemical crosslinking, and crosslinking by irradiation, and in particular by e-beam, UV radiation, LED radiation, and gamma irradiation.
• the separators of the invention can be used to form an electrochemical device, such as a battery, capacitor, electric double layer capacitor, membrane electrode assembly (MEA) or fuel cell, by means known in the art.
• a non-aqueous-type battery can be formed by placing a negative electrode and positive electrode on either side of the coated separator.
• the latexes of the invention are prepared by a typical process for making fluoropolymers using emulsifiers.
• the emulsifiers may be ionic or non-ionic, such as those containing blocks of polyethylene glycol, polypropylene glycol and/or polytetramethylene glycol.
• the process and fhioropolymer produced contain no fluorinated or partially fluorinated surfactant.
• the fhioropolymer dispersions produced have good latex stability and shelf-life, and are coagulum-free. These preferred dispersions are absolutely free of fluorinated or partially fluorinated surfactant- with no fluorinated surfactant being used in either the synthesis or in a post-addition.
• the emulsifier may be added all upfront prior to polymerization, fed continuously during the polymerization, fed partly before and then during polymerization, or fed after polymerization started and progressed for a while.
• Example 1 Into an 80-gallon stainless steel reactor was charged, 345 lbs of deionized water, 250 grams of PLURONIC 31R1 (non- fluorinated non-ionic surfactant from BASF), and 0.3 lbs of propane. Following evacuation, agitation was begun at 23 rpm and the reactor was heated. After reactor temperature reached the desired set point of 100 °C, the VDF charge was started. Reactor pressure was then raised to 650 psi by charging approximately 35 lbs VDF into the reactor. After reactor pressure was stabilized, 4.5 lbs of initiator solution made of 1.0 wt potassium persulfate and 1.0 wt % sodium acetate was added to the reactor to initiate polymerization.
• PLURONIC 31R1 non- fluorinated non-ionic surfactant from BASF
• the rate of further addition of the initiator solution was adjusted to obtain and maintain a final VDF polymerization rate of roughly 70 pounds per hour.
• the VDF homopolymerization was continued until approximately 150 pounds VDF was introduced in the reaction mass.
• the VDF feed was stopped and the batch was allowed to react-out at the reaction temperature to consume residual monomer at decreasing pressure.
• the agitation was stopped and the reactor was cooled, vented and the latex recovered.
• Solids in the recovered latex were determined by gravimetric technique and were about 27 weight and melt viscosity of about 27 kp according to ASTM method D-3835 measured at 450 °F and 100 sec "1 .
• the melting temperature of resin was measured in accordance with ASTM method D- 3418 and was found to be about 162 °C.
• the weight average particle size was measured by NICOMP laser light scattering instrument and was found to be about 150 nm.
• Examples 2 Into an 80-gallon stainless steel reactor was charged, 345 lbs of deionized water, 250 grams of PLURONIC 31R1 (non- fluorinated non-ionic surfactant from BASF), and 0.6 lbs of ethyl acetate. Following evacuation, agitation was begun at 23 rpm and the reactor was heated. After reactor temperature reached the desired set point of 100 °C, the VDF and HFP monomer were introduced to reactor with HFP ratio of 40 wt of total monomers. Reactor pressure was then raised to 650 psi by charging approximately 35 lbs total monomers into the reactor.
• PLURONIC 31R1 non- fluorinated non-ionic surfactant from BASF
• the VDF feed was stopped and the batch was allowed to react-out at the reaction temperature to consume residual monomer at decreasing pressure. After 40 minutes, the initiator feed and agitation were stopped and the reactor was cooled, vented and the latex recovered. Solids in the recovered latex were determined by gravimetric technique and were about 32 weight and melt viscosity of about 28 kp according to ASTM method D-3835 measured at 450 °F and 100 sec "1 . The melting temperature of resin was measured in accordance with ASTMD3418 and was found to be about 120 °C. The weight average particle size was measured by NICOMP laser light scattering instrument and was found to be about 160 nm.
• the VDF feed was stopped and the batch was allowed to react-out at the reaction temperature to consume residual monomer at decreasing pressure. After 40 minutes, the initiator feed and agitation were stopped and the reactor was cooled, vented and the latex recovered. Solids in the recovered latex were determined by gravimetric technique and were about 32 weight% and melt viscosity of about 38 kp according to ASTM method D-3835 measured at 450 °F and 100 sec "1 . The melting temperature of resin was measured in accordance with ASTM method D-3418 and was found to be about 152 °C. The weight average particle size was measured by NICOMP laser light scattering instrument and was found to be about 160 nm.
• PVDF based latexes of example 1-3 were then formulated into an aqueous separator coating composition and applied to a separator and dried.
• Aqueous separator coating compositions were prepared by making first, stock solution of A comprised 1.5% BYK-346 (from BYK-Chemie) in DI water; second stock solution B comprised of 50-50 mixture of tri-ethyl-phosphate (TEP) and stock solution A. Then stock solutions A and B were added to 50 g plus 0.5 g BYK-346 latex of Example-3 as tabulated in Table- 1.
• Aqueous separator coating compositions were prepared by using stock solutions and BYK-346 provided above and adding them to 50 g latex of Example-2 as shown in Table-2.
• Aqueous separator coating compositions were prepared by using stock solutions provided above and adding them to 50 g latex of Example- 1 according to Table-3.
• the quality of film formation was evaluated by placing 10 g of each of aqueous separator coating compositions and comparative examples in a convection oven for 4 hrs at 80 °C.
• the dried resins from examples 4 to 11 were well fused and made nice continuous film without any cracks.
• samples of polyolefin separator, M 2400 by CELGARD 25 micrometer thick polypropylene film with 43nm average pore diameter
• CELGARD 25 micrometer thick polypropylene film with 43nm average pore diameter

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