Fluoropolymer binder coatings for use in electrochemical devices

Abstract

The present invention relates to a fluoropolymer coating composition that can be used, for example, to coat electrodes and / or separators in electrochemical devices. The fluoropolymer coating composition preferably contains multiple fluoropolymer phases. The coated electrodes and / or separators have excellent wet adhesion, excellent dry adhesion, and low leaching. Each fluoropolymer phase contains a polymer having at least 10 wt. % of a common fluoromonomer, which makes the polymer phases compatible with each other and allows the phases to be dispersed fairly uniformly at a macroscopic level throughout the composition and the dried coating formed from the composition.

Description

[Technical Field]

[0001] The present invention relates to a fluoropolymer binder composition that can be used, for example, to coat electrodes and / or separators in electrochemical devices. The fluoropolymer coating composition preferably contains multiple fluoropolymer phases. The coatings on the electrodes and / or separators have both excellent wet adhesion, excellent dry adhesion, and low leachability (low leachable content). These properties can be optimized by adjusting the polymer properties of each phase, such as crystallinity, functionality, degree of crosslinking, degree of branching, and comonomer. The phase that provides excellent wet adhesion has low swelling, such as can be achieved by a high level of crystallinity, while the phase that provides excellent dry adhesion is more flexible and more swellable in electrolyte. This flexibility and high swelling can be achieved by adding comonomer units and / or functional groups. The polymers contained in each fluoropolymer phase have at least 10% by weight of a common fluoromonomer that makes the polymer phases compatible with each other and allows the phases to be dispersed fairly uniformly at a macroscopic level throughout the composition and the dried coating formed from the composition. [Background technology]

[0002] Lithium batteries, including lithium metal batteries, lithium ion batteries, lithium polymer batteries, and lithium ion polymer batteries, are finding increasing use due to their higher voltage and energy density than conventional batteries (such as Ni-MH batteries).

[0003] Currently available lithium-ion batteries and lithium-ion polymer batteries use polyolefin-based separators to prevent short circuits between the cathode and anode. However, because the melting point of such polyolefin-based separators is 140°C or less, they may melt and shrink when the battery temperature rises due to internal and / or external factors during use, resulting in a volume change and potentially a short circuit. Furthermore, polyolefin-based separators are prone to oxidation when in contact with high-voltage active materials. Oxidation of polyolefin separators can reduce cycle life, develop pinholes, and cause short circuits. Short circuits can lead to accidents such as battery explosions and fires caused by the release of electrical energy. Therefore, it is necessary to provide a separator that does not undergo thermal shrinkage at high temperatures or oxidize at high voltages.

[0004] Fluoropolymers, especially polyvinylidene fluoride, have been found to be useful as binders or coatings for separators, cathodes, and anodes in non-aqueous electrolysis devices due to their excellent electrochemical resistance and adhesion. U.S. Patent Nos. 7,662,517, 7,704,641, U.S. Patent Application Publication No. 2010 / 00330268, U.S. Patent No. 9,548,167, and U.S. Patent Application Publication No. 2015 / 0030906 (incorporated herein by reference) describe PVDF copolymer solutions in organic solvents or aqueous dispersions used in combination with powdered metal oxide materials or nanoceramics to coat polyolefin separators used in non-aqueous-type batteries. The separator forms a barrier between the anode and cathode in the battery. Bonded inorganic particles on porous organic separators have been found to increase the volume of space available for liquid electrolyte penetration, resulting in improved ionic conductivity.

[0005] Unfortunately, the excellent properties offered by fluoropolymers can also limit the applications in which they can be used. For example, it is difficult to adhere fluoropolymers to other materials. Therefore, organic solvents and other organic additives are commonly used in coating formulations to provide good adhesion (irreversible adhesion) between the PVDF-based polymer, the porous separator or electrode, and optionally, the powder particles.

[0006] Organic solvent-based solution / slurry compositions present safety, health, and environmental hazards not present in aqueous systems. Organic solvents are generally toxic, flammable, and volatile in nature, requiring special manufacturing controls to mitigate hazards and reduce environmental contamination from organic solvents. Furthermore, the isolation of PVDF copolymers formed in aqueous media, drying the PVDF-based polymer to a powder, and then dissolving the powder in a solvent requires additional manufacturing steps, costs, time, expense, and energy. Therefore, aqueous compositions are preferred.

[0007] Organic additives such as acrylics and / or carboxylated methyl cellulose (CMC) are susceptible to electrochemical attack at high voltages, oxidizing and decomposing. The by-product of resin decomposition, i.e., water, can degrade battery performance. Furthermore, most acrylics and other additives lack sufficient solvent resistance and can dissolve in the electrolyte solvent, reducing safety factors and battery cycle life.

[0008] Functionality (functional groups) has been added to fluoropolymers to enhance adhesion to other materials, improve wettability, and provide ductility. Functionality has been added by several means, such as direct copolymerization of functional monomers into the fluoromonomer backbone, and post-polymerization grafting mechanisms, such as grafting maleic anhydride onto polyvinylidene fluoride homopolymers or copolymers, as described in U.S. Pat. No. 7,241,817 to produce KYNAR® ADX resins available from Arkema. International Publications WO 2013 / 110740 and U.S. Pat. No. 7,351,498 further describe the functionalization of fluoropolymers by monomer grafting or copolymerization. International Publication WO 16149238 and U.S. Patent Application Publication No. 2016 / 009840 further disclose the functionalization of fluoropolymers by adding small proportions of comonomers or functional chain transfer agents to the polymerization process. However, adding functional monomer units directly to a polymerizing polymer backbone, especially in a random manner, is difficult due to the aggressive nature of fluorine-containing free radicals.

[0009] Fluoropolymer-based compositions used in electrodes and / or separators of electrochemical devices should have both excellent wet adhesion and excellent dry adhesion, as well as low extractables. Good wet adhesion and mechanical strength can be obtained by using fluoropolymers with high crystallinity. Unfortunately, these highly crystalline fluoropolymers have poor dry adhesion. Functionalized polymers have good dry adhesion, but low crystallinity, which reduces the mechanical strength of the binder. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 7,662,517 [Patent Document 2] U.S. Patent No. 7,704,641 [Patent Document 3] US Patent Application Publication No. 2010 / 00330268 [Patent Document 4] U.S. Patent No. 9,548,167 [Patent Document 5] US Patent Application Publication No. 2015 / 0030906 [Patent Document 6] U.S. Patent No. 7,241,817 [Patent Document 7] International Publication No. WO2013 / 110740 [Patent Document 8] U.S. Patent No. 7,351,498 [Patent Document 9] International Publication No. WO16149238 [Patent Document 10] US Patent Application Publication No. 2016 / 009840 Summary of the Invention [Problem to be solved by the invention]

[0011] Surprisingly, it has now been found that fluoropolymer resin compositions, particularly multiphase fluoropolymer resin compositions, can provide both good wet adhesion and good dry adhesion with low leaching. The multiphase fluoropolymer composition contains at least one phase that is rigid, low swellable, and has strong mechanical properties (the rigidity of this polymer phase can result, for example, from a high level of crystallinity, crosslinking, or long-chain branching), or from containing another means of suppressing its solubility in the electrolyte (wet adhesion). The other phase is softer, more tacky, and more swellable, providing good dry adhesion and can have a functionality of 0.1 to 25 wt. %. This soft phase has high solubility and swellability in the electrolyte, while the overall binder composition as a dry coating has a leachable polymer content of less than 10%.

[0012] The phases of the multiphase binder composition can be a blend of two or more separate, compatible polymers, or can exist as a single multiphase particle. The highly swellable functional phase can be concentrated on the outside of the multiphase polymer particle, or the multiphase particle can be a heterogeneous, co-continuous polymer, where one phase is continuous and the other phase is discrete within the continuous phase. Separators, cathodes, and anodes coated with the multiphase polymer binder not only have good mechanical strength and good wet / dry adhesion, but also provide dimensionally stable separators or electrodes at high temperatures.

[0013] Conventional products do not possess the balance of both wet and dry adhesion and low leachability found in the fluoropolymer binder compositions of the present invention. [Means for solving the problem]

[0014] Summary of the Invention The present invention relates to a multiphase binder composition having a low swelling fluoropolymer phase and a softer, more swelling fluoropolymer phase. The present invention also relates to a multiphase binder composition having a highly crystalline phase and a phase containing a functionalized fluoropolymer.

[0015] The present invention further relates to a dry binder composition that has very good wet adhesion, very good dry adhesion and low leaching.

[0016] The present invention further relates to single multiphase fluoropolymer particles having a highly crystalline fluoropolymer core and at least one outer phase containing a functionalized fluoropolymer.

[0017] The present invention further relates to a binder composition comprising a single multiphase heterogeneous bicontinuous fluoropolymer particle having a highly crystalline phase and a phase containing a functionalized fluoropolymer.

[0018] The present invention further relates to a binder composition comprising a single multiphase heterogeneous bicontinuous fluoropolymer particle having a composition having a low swellable fluoropolymer phase and a high swellable fluoropolymer phase.

[0019] The multiphase fluoropolymer coating composition may be an aqueous or solvent dispersion or solvent solution, with or without particle loading.

[0020] Although embodiments are described herein so as to write a clear and concise specification, it is intended and understood that the embodiments can be combined or separated in various ways without departing from the invention. For example, it will be understood that all preferred features described herein are applicable to all aspects of the invention described herein. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 shows the % weight gain as a function of comonomer (HEP) content in heterogeneous and random copolymers. [Figure 2] FIG. 2 shows the % swelling ratio as a function of comonomer (HEP) content in heterogeneous and random copolymers. [Figure 3] FIG. 3 is a bar graph showing the % weight gain. [Figure 4] FIG. 4 is a bar graph showing the swelling ratio (%). [Figure 5] Figure 5 is an SEM of the bicontinuous fluoropolymer. DETAILED DESCRIPTION OF THE INVENTION

[0022] Detailed Description of the Invention All references cited herein are incorporated herein by reference. All percentages in compositions are by weight unless otherwise specified, and all molecular weights are given as weight average molecular weights measured by GPC using PMMA as the standard unless otherwise specified.

[0023] The term "polymer" is used to refer to all homopolymers, copolymers, and terpolymers (three or more types of monomer units) unless otherwise specified. "Copolymer" is used to refer to a polymer having two or more different types of monomer units. For example, as used herein, "PVDF" and "polyvinylidene fluoride" are used to include both homopolymers and copolymers unless otherwise specified.

[0024] The term "phase" is used to refer to distinct polymeric regions. Because each phase of the composition contains common monomer units, these phases coexist as fairly uniformly interdispersed polymer chains in solvent coatings, are relatively uniformly dispersed in dispersion coating blends of two or more polymer phases, and are intimately bound in coatings containing multiphase particles. Each of the various phases can be described in several ways, and are described herein, for example, as a) low-swelling phase / soft and highly swellable phase; b) highly crystalline phase / functional group-containing phase; and c) wet-adhesion-good phase / dry-adhesion-good phase.

[0025] The term "binder" is used to refer to a fluoropolymer composition that can be coated onto a substrate, optionally containing particles for improved dimensional stability, where the substrate in this invention is primarily either an anode, cathode, or separator found in an electrochemical device. The compositions described herein, particularly the multiphase fluoropolymer particles, can be used in other fluoropolymer coating and resin applications.

[0026] Dry and Wet Adhesion: To achieve dry adhesion, the fluoropolymer must be deformed sufficiently during the casting and / or pressing process to adhere to the electrodes and separator, and to any inorganic particles in the coating. Generally, the higher the adhesion, the better. Adding functionality to the polymer can enhance adhesion. Wet adhesion refers to the fluoropolymer swollen in the electrolyte. The electrolyte tends to soften the fluoropolymer in a manner similar to that caused by a plasticizer. Adding functionality to the fluoropolymer tends to soften the fluoropolymer, making it less brittle and more swellable. Thus, a very flexible binder that can produce good dry adhesion may become too flexible when swollen by the electrolyte, losing its cohesive strength and no longer producing good wet adhesion.

[0027] The present invention relates to multiphase fluoropolymer compositions having a low-swelling, highly crystalline fluoropolymer phase for good wet adhesion and mechanical properties, and a softer, more swellable, functional polymer phase for good dry adhesion. These phases can exist as separate polymer particles or chains, or they can exist in a single multiphase particle. In any multiphase composition, each phase contains fluoropolymers having at least 10 wt%, preferably at least 25 wt%, more preferably more than 50 wt%, and even more preferably at least 70 wt% of the same fluoromonomer units. In a preferred embodiment, the common fluoromonomer units in each polymer phase are vinylidene fluoride monomer units.

[0028] Fluoropolymer The fluoropolymer of the present invention is primarily composed of fluoromonomers. The term "fluoromonomer" or "fluorinated monomer" refers to a polymerizable alkene containing at least one fluorine atom, fluoroalkyl group, or fluoroalkoxy group attached to the double bond of the alkene undergoing polymerization. The term "fluoropolymer" refers to a polymer produced by polymerization of at least one fluoromonomer, including homopolymers, copolymers, terpolymers, and higher polymers of thermoplastic nature, meaning that they can be formed into useful pieces by flowing upon the application of heat, as occurs in molding and extrusion processes. The fluoropolymer preferably contains at least 50 mole % of one or more fluoromonomers.

[0029] Fluoromonomers useful in the practice of the present invention include, for example, vinylidene fluoride (VDF), tetrafluoroethylene (TFE), trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), vinyl fluoride (VF), hexafluoroisobutylene, perfluorobutylethylene (PFBE), pentafluoropropene, 2,3,3,3-tetrafluoropropene (HFO-1234yf), 2-chloro-1,1-difluoroethylene (R-1122), 3,3,3-trifluoro-1-propene, 2-fluoromethyl-3,3,3-trifluoropropene, fluorinated vinyl ethers, fluorinated allyl ethers, non-fluorinated allyl ethers, fluorinated dioxoles, and combinations thereof.

[0030] Particularly preferred polymers are homopolymers of VDF, and the copolymers produced by the method of the present invention are copolymers of VDF with HFP, TFE or CTFE, and contain about 50 to about 99% by weight, and even more preferably about 70 to about 99% by weight, of VDF.

[0031] Particularly preferred terpolymers are those of VDF, HFP and TFE, and those of VDF, trifluoroethane and TFE, with the particularly preferred terpolymers having at least 10% by weight of VDF, and the other comonomers may be present in various proportions, but together they make up to 90% by weight of the terpolymer.

[0032] Preferably, PVDF for use in the binder composition has a high molecular weight. As used herein, high molecular weight refers to a PVDF that has a viscosity of 100 seconds at 450°F according to ASTM method D-3835. -1 By "PVDF" is meant a PVDF having a melt viscosity, as measured by FTIR, of greater than 1.0 kpoise, preferably greater than 5 kpoise, even more preferably greater than 10 kpoise, and even more preferably greater than 20 kpoise.

[0033] The fluoropolymers of the present invention can be produced by means well known in the art, such as emulsion polymerization, suspension polymerization, solution polymerization, or supercritical CO2 polymerization. Preferably, the fluoropolymers are produced by emulsion or suspension methods.

[0034] The fluoropolymers are polymerized using a free radical initiator. The amount of initiator required for polymerization is related to its activity and the temperature employed for polymerization. The total amount of initiator used is generally in the range of 100 to 5000 ppm by weight based on the weight of the total monomers used. Generally, sufficient initiator is added initially to start the reaction, and then additional initiator may be added optionally to maintain the polymerization at a reasonable rate.

[0035] Generally, surfactants are used to stabilize fluoropolymer emulsion particles. In a preferred embodiment, the fluoropolymer dispersion does not contain a fluorosurfactant. "Fluorosurfactant-free" means that all surfactants used in producing the aqueous fluoropolymer do not contain fluorine atoms ("non-fluorinated surfactants"). This term refers to all surfactants used in producing and processing the aqueous fluoropolymer dispersion, preferably all surfactants in the composition of the present invention, including all surfactants used in the polymerization process, including those added in advance, those continuously fed during polymerization, those partially fed in advance and then fed during polymerization, those fed after the polymerization has started and progressed for a while, and all others, and preferably also includes all surfactants added after polymerization to improve the stability of the latex. Non-fluorinated surfactants useful in PVDF polymerization can be both ionic and non-ionic and include, but are not limited to, 3-allyloxy-2-hydroxy-1-propanesulfonate, polyvinylphosphonic acid, polyacrylic acid, polyvinylsulfonic acid and their salts, polyethylene glycol and / or polypropylene glycol and their block copolymers, alkyl phosphonates, and siloxane-based surfactants.

[0036] PVDF emulsion polymerization typically results in a latex having a solids level of 10-60% by weight, preferably 10-50% by weight, and a weight average particle size of less than 1 μm, preferably less than 1000 nm, preferably less than 800 nm, and even more preferably less than 600 nm. The weight average particle size is typically at least 20 nm, preferably at least 50 nm. The weight average particle size can be 20 nm to 800 nm or 20 nm to 600 nm. The polymer particles can form agglomerates having a weight average particle size of 1-30 μm, preferably 2-10 μm or 2-8 microns. The agglomerates can break down into discrete particles (discrete particles) during formulation and application to a substrate.

[0037] Although the fluoropolymer of the present invention having good wet adhesion, good dry adhesion and low leaching can be a single polymer, in a preferred embodiment, the fluoropolymer composition of the present invention contains at least two different phases, each phase having different properties from the other phase.

[0038] low swelling phase At least one phase of the multiphase binder composition contains a fluoropolymer having low swelling properties. By "low swelling" is meant that a pure solid polymer film swells less than 100% by weight, preferably less than 50% by weight, during prolonged immersion in an electrolyte solvent under ambient conditions. See also ASTM Method 2765-16. The low swelling phase can be obtained by selectively adjusting factors such as fluoropolymer crystallinity, degree of crosslinking, comonomer, degree of branching, and other factors known in the art to reduce the swelling of fluoropolymers in electrolytes.

[0039] "Highly crystalline" means that the polymer has a crystallinity of at least 30% by weight, preferably at least 35% by weight, and more preferably at least 40% by weight, as measured using differential scanning calorimetry (DSC) analysis according to ASTM method D3418. High crystallinity helps prevent the binder from dissolving in the highly corrosive battery environment. The highly crystalline phase fluoropolymer is produced from VDF, TFE, CTFE, VF3, VF monomers and / or combinations thereof. This highly crystalline fluoropolymer can also be a copolymer with HFP, HFO-1234yf, HFO-1233zf, HFO-1225, R-1122, perfluoro(methyl vinyl) ether (PMVE), perfluoro(propyl vinyl) ether (PPVE), or other fluoromonomers, where the comonomer is a minor fraction of the polymer, generally less than 30% by weight, preferably less than 20% by weight, and more preferably less than 10% by weight. When the highly crystalline phase is a copolymer, the comonomer is preferably present in an amount greater than 0.1 wt%, or greater than 0.5 wt%, and can be present in an amount greater than 1 wt%, or greater than 2.2 wt%, or greater than 3 wt%.

[0040] The highly crystalline phase may also contain low levels of functional groups or monomer units, less than 10%, less than 5%, preferably less than 3%, and less than 1%.

[0041] The low swell fluoropolymer phase may contain crosslinks and long chain branches, which further enhance mechanical strength and wet adhesion.

[0042] The low swelling crystalline phase can be in the form of one or more separate crystalline polymers or can be part of a multiphase polymer particle.

[0043] Highly swellable and flexible polymer phase At least one phase of the multi-phase binder composition contains a more highly swellable, more flexible polymer phase. As used herein, a "highly swellable" phase means a phase that has a swellability in electrolyte that is at least 5% by weight higher, and more preferably at least 10% higher, than the less swellable phase. Thus, the more swellable phase is more flexible than the less swellable phase.

[0044] In some embodiments of the present invention, By "highly swellable" is meant that a pure solid polymer film will swell by 150% by weight or more during prolonged immersion in an electrolyte solvent under ambient conditions or deform under processing conditions to provide interparticle adhesion and interconnection and adhesion to the substrate. Fluoropolymer phases that provide good dry adhesion have high swellability and are more flexible than low-swelling phases.

[0045] In a preferred embodiment, the highly swellable phase contains 0.1 to 25 wt. %, preferably 2 to 20 wt. %, of functional groups / monomer units based on the total weight of the polymer binder. The functional groups promote adhesion of the polymer binder and, optionally, inorganic or organic particles to the separator and / or electrode (anode or cathode).

[0046] Because fluoropolymers have a higher durability in a battery environment compared to polyolefins and other thermoplastic binder polymers, the functional groups of the present invention are preferably part of a fluoropolymer, although the present invention also contemplates the use of functional polymers that are not fluoropolymers, such as functionalized acrylic polymers. One requirement of the coating of the present invention is that it has a leachability of less than 10% by weight in the electrolyte solution. One means of reducing the leachability of functional polymers can be by lightly crosslinking the polymer.

[0047] The functionalized fluoropolymers of the present invention can be prepared by copolymerization using 0.2 to 20 wt%, preferably 0.5 to 15 wt%, and even more preferably 1 to 10 wt% of at least one functional adhesion-promoting comonomer. This copolymerization can add one or more functional comonomers to the fluoropolymer backbone and can also include a grafting process. The functionalized fluoropolymers can also be polymerized using 0.1 to 25 wt%, preferably 1.0 to 15 wt%, and even more preferably 2.2 to 20 wt% of one or more low molecular weight polymeric functional chain transfer agents. By low molecular weight, it is meant that the polymer has a degree of polymerization of 1000 or less, preferably less than 800. In a preferred embodiment, the weight average molecular weight of the polymeric chain transfer agent is 20,000 g / mol or less, more preferably 15,000 g / mol or less, and even more preferably less than 10,000 g / mol, as measured by GPC. In one embodiment, the weight average molecular weight is less than 5,000 g / mol. The low molecular weight functional chain transfer agent is a polymer or oligomer having two or more monomer units, preferably three or more monomer units. The residual polymeric chain transfer agent forms a block copolymer with a low molecular weight functional block at the end. The functional fluoropolymer can have both a functional comonomer and a residual functional polymeric chain transfer agent.

[0048] The functional copolymers contain one or more "adhesive" comonomers in low proportions of 0.1 to 20 wt. %, preferably 0.5 to 15 wt. %, and particularly preferably 1 to 10 wt. %, based on the copolymer. Lower proportions do not provide any improvement in adhesion over homopolymers. Copolymers containing higher proportions of these comonomers tend to be too soft and sticky, increasing the risk of dissolution in the battery environment.

[0049] Useful comonomers generally contain polar groups or have high surface energy. Examples of useful comonomers include, but are not limited to, vinyl acetate, 2,3,3,3-tetrafluoropropene (HFO-1234yf), 2,3,3-trifluoropropene, hexafluoropropene (HFP), and 2-chloro-1,1-difluoroethylene (R-1122). HFP provides good adhesion but may have poor solvent resistance. Phosphate, (meth)acrylate, (meth)acrylic acid, and hydroxyl-functional (meth)acrylic comonomers can also be used as comonomers. Graft copolymers are also contemplated by the present invention.

[0050] As used herein, functional polymeric chain transfer agent means that the low molecular weight polymeric chain transfer agent contains one or more different functional groups. The chain transfer agent has the formula (CH2-CH-(X)-R) y where y is an integer ranging from 2 to 1000, X is a linking group, including but not limited to a covalent bond, an ionic bond, an alkyl, an alkene, an alkyne, a substituted alkyl, a substituted alkene, an aryl, an ester, an ether, a ketone, an amine, an amide, an organosilane, and R is a functional group.

[0051] The functional group R provides functionality. This functional group R can be provided by polymerization of a functional monomer as the sole monomer or as a comonomer. Functionality can also be added by post-polymerization reactions or grafting. Useful functional groups include, but are not limited to, carboxyl, hydroxyl, siloxane, ether, ester, sulfonic acid, phosphate, phosphonic acid, sulfate, amide, and epoxy groups, or mixtures thereof.

[0052] multiphase particles In one preferred embodiment of the present invention, a low-swelling, highly crystalline phase polymer and a highly swellable, functionalized phase polymer are coexisted in a single particle. In one embodiment, multiphase particles are particularly useful in which the highly crystalline phase forms the particle core, with functional groups on the exterior of the highly crystalline core, and the use of a functionalized polymer phase for adhesion is particularly useful.

[0053] The multiphase particles can have many different morphologies, including core-shell and raspberry-type morphologies (each having a crystalline core and a functional polymer phase on the outside of the core). The multiphase polymers can also have comb or star morphologies, with a crystalline fluoropolymer backbone and functional groups pendant from the backbone.

[0054] One method for synthesizing multiphase polymer particles is by sequential polymerization to produce a core and shell structure in which the shell contains higher functionality and lower crystallinity than the core, which further promotes higher adhesion, higher malleability, and better performance, especially in aqueous formulations.

[0055] The core polymer may be present in an amount of 2 to 99% by weight of the multiphase particle, preferably 70 to 95% by weight, preferably 80 to 95% by weight, and the outer phase functional polymer may comprise 1 to 98% by weight of the multiphase particle, preferably 5 to 30% by weight, preferably 5 to 20% by weight.

[0056] In the case of sequential copolymerization, the polymer is produced by synthesizing a matrix polymer in a manner generally known to those skilled in the art for producing polyvinylidene fluoride polymers. This can be by emulsion polymerization, solution polymerization, or suspension polymerization. A functional comonomer is introduced into the reactor after at least 50%, preferably 70%, and even more preferably 90-100% of the highly crystalline phase monomer(s) have been added during polymerization. This second feed can be a single fluoromonomer, a mixture of fluoromonomers, or a functional monomer that can copolymerize with the first component monomer. The second feed can also contain a functionalized chain transfer agent. The second feed creates a functionalized polymer on the outer layer of the polymer particles, such as a shell or raspberry morphology.

[0057] As a second fluoromonomer feed, TFE, CTFE, VF3, VF, HFP, 1234yf, 1233ze, PFMV and PPME can be used in higher proportions in the shell composition than in the core composition to provide softness, flexibility and malleability.

[0058] The use of vinyl sulfonic acid, vinyl phosphoric acid, acrylic acid, methacrylic acid, and vinyl acetate as second functional non-fluoromonomer feeds in the shell can promote greater interaction with the separator surface and / or optional nanoceramic, which can result in greater adhesion of the coating to the separator, better interconnectivity within the coating, and better mechanical strength of the coating.

[0059] The second feed may also contain functional chain transfer agents such as low molecular weight polyacrylic acids, polylactic acids, polyphosphonic acids, polysulfonic acids, and polymaleic acids, which can be added in high proportions to provide the appropriate functionality to the polymer backbone during shell polymerization.

[0060] Heterogeneous, gradient / tapered multiphase particles Gradient or tapered multiphase particles can be used in the binder composition of the present invention. In the case of gradient copolymerization, polymerization is initiated by the general method known to those skilled in the art for synthesizing fluoropolymers such as polyvinylidene fluoride polymers. This can be emulsion polymerization, solution polymerization, or suspension polymerization. At a predetermined point in the polymerization of the high crystallinity phase, a functional comonomer stream is introduced into the reactor. This second feed can be a single fluoromonomer, a mixture of fluoromonomers, or a functional monomer that can copolymerize with the first component monomer. The ratio of the second monomer stream to the first monomer stream can be constant or increased as the polymerization progresses. This second stream creates a gradient of functionalized polymer from the beginning to the end of the polymer particle, with higher functionality at the end.

[0061] Heterogeneous copolymer particles useful in the present invention contain two or more co-continuous phases. These phases may be distinct from one another and can be seen in scanning electron microscope (SEM) images such as in Figure 5. These heterogeneous copolymers are described in U.S. Patent Application Publication No. 2018-0044456. U.S. Patent No. 6,187,885 also teaches multiphase copolymers.

[0062] In one embodiment of the present invention, the low swelling highly crystalline phase polymer and the high swelling functionalized phase polymer coexist in a single co-continuous particle.

[0063] The first co-continuous phase is rich in vinylidene fluoride monomer units, and contains at least 85%, at least 90%, and preferably at least 95% by weight of vinylidene fluoride monomer units. The first co-continuous phase can be a homopolymer, such as a homopolymer of polyvinylidene fluoride (PVDF), or a copolymer of polyvinylidene fluoride monomers. In the case of a copolymer, the comonomer can be one or more other fluoromonomers selected from the group consisting of tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, vinyl fluoride, pentafluoropropene, perfluoromethyl vinyl ether (PMVE), perfluoro(propyl vinyl) ether (PPVE), HFO-1234yf, HFO-1233zf, HFO-1225, R-1122, or other fluoromonomers and / or combinations thereof. When the fluorocomonomer in the first (low swelling) phase is the same as the predominant comonomer in the second (high swelling) co-continuous phase, no more than 10% of the comonomer can be present in the first co-continuous phase, because the polymers in the phases must be thermodynamically different enough to form separate phases. In one embodiment, the difference in the percentage of common comonomer between the copolymer of the first phase and the copolymer of the second phase should be at least 10% by weight.

[0064] In one embodiment, the final copolymer composition contains 40-99 wt.%, preferably 50-97 wt.%, even more preferably 60-95 wt.% of the first co-continuous phase, and correspondingly 1-60 wt.%, preferably 3-50 wt.%, even more preferably 5-40 wt.% of the second co-continuous phase. Preferably, the total comonomer in the multiphase particles is greater than 10%, preferably at least 11%, preferably at least 12%.

[0065] The second co-continuous phase contains a thermodynamically different copolymer from the first co-continuous phase in the solid-state formulation. The copolymer contains an effective amount of a co-monomer selected from hexafluoropropylene (HFP) and perfluoroalkyl ether (PAVE), chlorotrifluoroethylene (CTFE), and trifluoroethylene, with a majority (greater than 50 wt%) of vinylidene fluoride monomer units. Preferably, the second co-continuous phase contains at least 1 wt% HFP or PSVE. The copolymer may also contain other co-monomers copolymerizable with VDF.

[0066] An effective amount of comonomer is the proportion of comonomer that allows the copolymer to form a separate and independent phase from the first phase polymer. For HFP, an effective amount of HFP monomer in the second phase is 5 to 40 wt%, preferably 10 to 40 wt%, and even more preferably 11 to 35 wt%, 12 to 35 wt%, or 13 to 35 wt%.

[0067] Perfluoroalkyl ethers useful in the present invention include CF2=CF-OR f where R f is one or more perfluoroalkyl groups selected from -CF3, -CF2-CF3 and -CF2CF2CF3. A preferred perfluoroalkyl vinyl ether is perfluoromethyl vinyl ether.

[0068] The second co-continuous phase may contain 5 to 40 wt. %, more preferably greater than 10 to 40 wt. %, and even more preferably 11 to 35 wt. %, 12 to 35 wt. %, 13 to 35 wt. %, or 15 to 25 wt. % HFP and / or PAVE, based on the combined amount of all monomers fed to the reactor.

[0069] It is understood that TFE, CTFE, VF3, VF monomers and / or combinations thereof can be used in conjunction with or in place of VDF in the co-continuous polymer.

[0070] Copolymer compositions containing both the first and second co-continuous phases together are generally polymerizable at 450°F for 100 seconds according to ASTM method D-3835. -1 The gradient fluoropolymer preferably has a melting point greater than 155°C, preferably greater than 160°C, preferably 165°C or higher.

[0071] Multiphase Binder Composition The multiphase binder composition of the present invention can be an aqueous or solvent dispersion or slurry containing at least one low-swelling polymer phase and at least one high-swelling polymer phase. The polymer particles should be discrete and as small as possible to ensure good dispersion and reduce the gap between the separator and the electrode. The polymer particles of the multiphase fluoropolymer preferably have a weight-average particle size of less than 1 μm, preferably less than 800 nm, even more preferably less than 600 nm, and even more preferably less than 500 nm. The average particle size is at least 10 nm, preferably greater than 50 nm.

[0072] The multiphase binder composition can be a blend of at least one low-swelling polymer dispersion and at least one high-swelling polymer dispersion. The blend can be a solvent-borne or aqueous dispersion. In one embodiment, at least two latexes (at least one low-swelling polymer and at least one high-swelling polymer) are blended to form the binder composition. In the blend, the low-swelling polymer comprises 2 to 99 wt%, 70 to 99 wt%, preferably 70 to 95 wt%, or 80 to 95 wt%, of the blend composition, and the high-swelling polymer comprises 1 to 98 wt%, preferably 30 to 1 wt%, preferably 5 to 30 wt%, or 20 to 5 wt%.

[0073] In the preferred case of multiphase particle dispersion, this dispersion can be used as synthesized or can be blended with other functional or non-functional fluoropolymer dispersions.When multiphase particles have a functional phase on the outside, they maximize the use of functional polymers without sacrificing the mechanical strength provided by high crystalline polymers.Multiphase bicontinuous particles provide low swelling of particles, while incorporating large functionality, for example, more than 10% by weight of the total comonomers in PVDF copolymers or more than 11% or 15% of the total comonomers in multiphase particles, and still maintain an acceptable level of swelling of less than 100%, preferably less than 90%.

[0074] inorganic particles The binder composition may optionally contain, and preferably does contain, inorganic particles, which serve to form micropores and maintain the physical shape of spacers in the separator coating, and to serve as active components (e.g., powdered electrode material) in the anode and cathode. The inorganic particles also aid in the heat resistance of the battery components. The nature of the powdered electrode-forming material depends on whether the composition is being used to form a positive electrode or a negative electrode.

[0075] In the separator coating, the inorganic particles are powdered granular materials that must be electrochemically stable (not undergo oxidation / reduction within the range of operating voltages). Furthermore, the powdered inorganic material preferably has high ionic conductivity. Low density materials are preferred over high density materials because they reduce the weight of the manufactured battery. A dielectric constant of 5 or greater is preferred. Inorganic powder materials useful in the present invention include, but are not limited to, BaTiO3, Pb(Zr,Ti)O3, Pb 1-x La x Zr y O3(0 <x<1、0<y<1)、PBMg3Nb 2 / 3)3, PbTiO3, hafnia (HfO(HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, YO3, boehmite (y-AlO(OH)), Al2O3, TiO2, SiC, ZrO2, borosilicate, BaSO4, nanoclay, ceramic or mixtures thereof. Useful inorganic fibers include, but are not limited to, aramid fillers and fibers, polyetheretherketone and polyetherketoneketone fibers, PTFE fibers and nanofibers.

[0076] In the cathode, the active inorganic electrode material can be an oxide, sulfide, or hydroxide of lithium and / or a transition metal (including but not limited to cobalt, manganese, aluminum, titanium, or nickel), as well as iron phosphate, manganese phosphate. Double or triple salts of lithium are also contemplated. Preferred positive electrode materials include, but are not limited to, LiCoO, LiNi x Co 1-x O2, LiMn2O2, LiNiO2, LiFePO4, LiNi x Co y Mn z O m , LiNi x Mn y Al z O m (where x+y+z is 1 and m represents the number of oxygen atoms in the oxide to result in an electron-balanced molecule); as well as lithium-metal oxides such as lithium cobalt oxide, lithium iron phosphate, lithium manganese phosphate, lithium nickel oxide, and lithium manganese oxide.

[0077] For the negative electrode, the active inorganic material is typically a carbonaceous material, nanotitanate, silicon, or other matrix that can be doped with lithium ions. Useful carbonaceous materials include, but are not limited to, graphite, artificial graphite, carbon, carbon black, carbon nanotubes, acetylene black, phenolic resin, pitch, tar, etc., as well as combinations thereof, including combinations with silicon or silicon oxide. Carbon fibers can also be used in the present invention.

[0078] The ratio of polymer solids to inorganic material is 75 to 99.5 parts by weight of inorganic powder material to 0.5 to 25 parts by weight of polymer binder solids, preferably 85 to 99.5 parts by weight of powdered inorganic material to 0.5 to 15 parts by weight of polymer binder solids, and even more preferably 90 to 99 parts by weight of powdered electrode material to 1 to 10 parts by weight of polymer binder solids. In one embodiment, it is 92 to 99.5 parts by weight of powdered inorganic material to 0.5 to 8 parts by weight of polymer binder solids. In one embodiment, a preferred binder comprises PVDF polymer. Using less polymer may result in incomplete interconnection, while using more polymer may result in reduced conductivity and increased volume and weight of the composition. One use of the composition is for very small, lightweight batteries.

[0079] Other additives The binder compositions of the present invention may optionally contain 0 to 15 wt. %, preferably 0.1 to 10 wt. %, based on the polymer, of additives, including but not limited to thickeners, pH adjusters, anti-settling agents, surfactants, wetting agents, fillers, defoamers, and temporary adhesion promoters.

[0080] The multiphase polymer binder of the present invention has excellent dry adhesion, which can be measured by casting a solution of the multiphase polymer on aluminum foil, forming a solid, unfilled polymer film 3 microns thick after drying, and measuring the peel strength. The peel strength should be at least 10 N / m, preferably at least 15 N / m, as measured by the 180° peel test common in the battery industry at a peel rate of 55 mm / min.

[0081] Wet adhesion can be measured by immersing a 3 micron solid film on aluminum foil in an electrolyte solution at 60°C for 72 hours and examining for defects and delamination. Leachability can be tested by forming a 10 micron film and placing it in the electrolyte at room temperature for 72 hours. There should be less than 10% leachability.

[0082] Formation of Coated Anode, Cathode and Separator For use as an electrode coating: The binder composition is applied to at least one surface, preferably both surfaces, of an electrically conductive substrate by means well known in the art, such as by brush, roller, inkjet, squeegee, foam applicator, curtain coating, vacuum coating, or spray. The electrically conductive substrate is generally thin and usually consists of a foil, mesh, or net of a metal such as aluminum, copper, lithium, iron, stainless steel, nickel, titanium, or silver. The coated electrically conductive substrate is then dried to form a coherent composite electrode layer, which is then calendered to provide an interconnected composite electrode usable in non-aqueous-type batteries. The aqueous electrode composition can optionally be baked at high temperatures to achieve high adhesion strength. The dried electrode can optionally be subjected to calendering at high pressure and temperature to further improve electrode adhesion.

[0083] For use as a separator coating: at least one surface of a porous separator is coated with the coating composition. There are no particular restrictions on the selection of a separator substrate to be coated with the aqueous coating composition of the present invention, as long as it is a porous substrate having pores. Preferably, the substrate is a heat-resistant porous substrate with a melting point of more than 140°C. Such a heat-resistant porous substrate can improve the thermal stability of the coated separator under external and / or internal thermal shock.

[0084] The porous substrate may be in the form of a membrane or in the form of a fibrous web. If the porous substrate is fibrous, it may be a nonwoven fabric forming a porous web, such as a spunbonded web or a meltblown web.

[0085] Examples of porous substrates useful as separators in the present invention include, but are not limited to, polyolefins, polyethylene terephthalate, polybutylene terephthalate, polyesters, polyacetals, polyamides, polycarbonates, polyimides, polyether ether ketones, polyether sulfones, polyphenylene oxides, polyphenylene sulfides, polyethylene naphthalenes, or mixtures thereof. Other heat-resistant engineering plastics can also be used without particular limitation. Nonwoven materials made from natural and synthetic materials can also be used as separator substrates.

[0086] The porous substrate generally has a thickness of 1 micron to 50 microns and is generally a cast membrane of nonwoven fabric. The porous substrate preferably has a porosity of 5% to 95%. The pore size (diameter) is preferably in the range of 0.001 to 50 microns, more preferably in the range of 0.01 to 10 microns. If the pore size and porosity are less than 0.01 micron and less than 5%, respectively, the porous substrate may act as a resistance layer. If the pore size and porosity are greater than 50 microns and greater than 95%, respectively, it is difficult to maintain mechanical properties.

[0087] Conventional lithium-ion and lithium-ion polymer batteries typically use polyolefin-based separators (either alone or coated with aluminum oxide or ceramic particles). The porous substrate preferably has a porosity in the range of 15% to 85%. The pore size (diameter) is preferably in the range of 0.001 to 0.20 microns, and even more preferably in the range of 0.002 to 0.10 microns.

[0088] The binder coating composition can be a solution, solvent dispersion, or aqueous dispersion and is applied to at least one surface of the porous substrate by means well known in the art, such as by brush, roller, inkjet, dipping, knife, gravure, wire rod, squeegee, foam applicator, curtain coating, vacuum coating, or spraying. The coating is then dried on a separator at room temperature or at an elevated temperature. The final dried coating thickness is 0.5 to 15 microns, preferably 1 to 8 microns, and even more preferably 1 to 5 microns thick.

[0089] The coated separators, anodes, and cathodes of the present invention can be used to form electrochemical devices such as batteries, capacitors, electric double layer capacitors, membrane electrode assemblies (MEAs) for fuel cells, etc. Non-aqueous type batteries can be formed by placing a negative electrode and a positive electrode on either side of the coated separator. [Example]

[0090] Example

[0091] The core-shell polymer is produced by an emulsion process: a reactor is charged with deionized water, a water-soluble surfactant capable of keeping the mixture of reactants emulsified during polymerization, and optionally, paraffin wax for antifouling, and the mixture is stirred to remove oxygen.

[0092] A predetermined amount of chain transfer agent (functional and / or non-functional) is then introduced into the reactor, the reactor temperature is raised to the desired level, and vinylidene fluoride (VDF) or a combination of VDF and other fluoromonomers is fed into the reactor. After the initial charge of monomer(s) is introduced and the pressure in the reactor reaches the desired level, an initiator solution is introduced to start the polymerization reaction. The reaction temperature can vary depending on the characteristics of the initiator used, and those skilled in the art will know how to do so. Generally, this temperature will be about 30-130°C, preferably about 50-110°C.

[0093] Similarly, polymerization pressure can vary but will typically be in the range of 40-50 atmospheres. After initiation of the reaction, the monomer(s) are continuously fed along with additional initiator to maintain the desired pressure. Once the desired amount of major component monomers (greater than 50% of the high-crystalline phase monomer(s) fed) is reached in the reactor, a second stream is added to the reactor feed to form the shell component (forming the functional phase). This second stream is typically charged continuously with the monomers, but can also be added as a slug during the shell formation stage. Once the major phase monomer feed is complete, the initiator feed is continued for a period of time to promote polymerization of all of these monomers. All feeds are then stopped. Residual gas (containing unreacted monomers) is vented, and the latex is recovered from the reactor. The polymer can then be isolated from the latex by standard methods such as acid coagulation, freeze-thaw, or high shear.

[0094] In one preferred embodiment, polyvinylidene fluoride homopolymer is formed as the major phase, after which at least 50% of the total monomers are charged to make the shell by introducing a second stream of a monomer mixture of vinylidene fluoride and a functional fluoromonomer and / or a functional chain transfer agent, the proportion of the second stream to make the shell being up to 30% by weight of the major monomer feed, preferably up to 20% by weight, and even more preferably up to 10% by weight.

[0095] Furthermore, polyvinylidene fluoride homopolymer synthesis can be initiated in a typical manner. After 25% by weight of VDF monomer has been charged, a functional comonomer stream is introduced into the reactor. The ratio of the second stream to the VDF monomer stream can be constant or can be increased as the polymerization progresses. The proportion of the second stream to create a gradient structure is up to 30% by weight, preferably up to 20% by weight, and even more preferably up to 10% by weight of the main monomer feed.

[0096] In addition to being formed by sequential copolymerization, the multiphase compositions of the present invention can also be formed by blending a polyvinylidene fluoride-based polymer with another fluoropolymer, which can be a homopolymer, copolymer, or terpolymer. The blending of the two polymers can be in the form of melt blending, solution blending, or latex or aqueous dispersion blending of the corresponding two polymers. Melt blending can be done with powders or pellets, which must be dissolved in a solvent to form a homogeneous blend.

[0097] Without being bound to any particular theory, it is believed that the core matrix is ​​more crystalline than the shell, and the shell phase is much less crystalline, providing softness, flexibility, greater adhesion and malleability.

[0098] Comparative Example 1: Copolymer The following comparative example is based on the teachings of U.S. Pat. No. 8,765,890. An 80-gallon stainless steel reactor was charged with 345 pounds of deionized water, 250 g of PLURONIC 31R1 (a non-fluorinated nonionic surfactant from BASF), and 0.35 pounds of ethyl acetate. After venting, stirring was started at 23 rpm, and the reactor was heated. After the reactor temperature reached the desired set point of 100°C, VDF and HFP monomers were introduced into the reactor at a HFP ratio of 13.2 wt.% of total monomers. The reactor pressure was then increased to 650 psi by charging approximately 35 pounds of total monomers to the reactor. After the reactor pressure stabilized, 3.5 pounds of an initiator solution consisting of 1.0 wt.% potassium persulfate and 1.0 wt.% sodium acetate were added to the reactor to initiate polymerization. At initiation, the HFP to VDF ratio was adjusted to reach 4.4% HFP relative to the total monomers in the feed. The rate of further addition of the initiator solution was also adjusted to maintain a final VDF and HFP total polymerization rate of approximately 90 pounds per hour. The VDF and HFP copolymerization continued until approximately 160 pounds of monomers had been introduced into the reaction mixture. The HFP feed was stopped, but the VDF feed was continued until approximately 180 pounds of total monomer had been fed to the reactor. The VDF feed was stopped, and the batch was allowed to react out at reaction temperature to consume residual monomer at decreasing pressure. After 40 minutes, the initiator feed and agitation were stopped, the reactor was cooled and vented, and the latex was recovered. The solids content in the recovered latex was approximately 32% by weight, as determined by gravimetric techniques, and the melt viscosity was 100 s at 450°F according to ASTM Method D-3835. -1 The viscosity was about 38 kP as measured by FTIR. The melting temperature of the resin was about 152° C. as measured according to ASTM method D-3418. The weight average particle size was about 160 nm as measured by a NICOMP laser light scattering instrument.

[0099] Comparative Example 2: Homopolymer An 80-gallon stainless steel reactor was charged with 345 pounds of deionized water, 250 g of PLURONIC 31R1 (a non-fluorinated nonionic surfactant from BASF), and 0.3 pounds of propane. After venting, stirring was started at 23 rpm, and the reactor was heated. After the reactor temperature reached the desired set point of 100°C, vinylidene fluoride (VDF) charging was initiated. The reactor pressure was then increased to 650 psi by charging approximately 35 pounds of VDF into the reactor. After the reactor pressure stabilized, 4.5 pounds of an initiator solution consisting of 1.0 wt. % potassium persulfate and 1.0 wt. % sodium acetate was added to the reactor to initiate polymerization. The rate of further addition of the initiator solution was adjusted to achieve and maintain a final VDF polymerization rate of approximately 70 pounds per hour. VDF homopolymerization continued until approximately 150 pounds of VDF had been introduced into the reaction mixture. The VDF feed was stopped and the batch was allowed to react out at reaction temperature to consume residual monomer at decreasing pressure. After 25 minutes, the agitation was stopped, the reactor was cooled, vented, and the latex was recovered. The solids content in the recovered latex was about 27% by weight as determined by gravimetric techniques, and the melt viscosity was 100 s at 450°F according to ASTM method D-3835. -1 The viscosity was about 27 kP as measured by FTIR. The melting temperature of the resin was about 162° C. as measured according to ASTM method D-3418. The weight average particle size was about 150 nm as measured by a NICOMP laser light scattering instrument.

[0100] Comparative Example 3: Sensory An 80-gallon stainless steel reactor was charged with 345 pounds of deionized water and 270 g of PLURONIC 31R1 (a non-fluorinated nonionic surfactant from BASF). After venting, agitation was started at 23 rpm, and the reactor was heated. After the reactor temperature reached the desired set point of 100°C, VDF and HFP monomers were introduced into the reactor at a HFP ratio of 22.3 wt% of total monomers. The reactor pressure was then increased to 650 psi by charging approximately 35 pounds of total monomers to the reactor. After the reactor pressure stabilized, 3.5 pounds of an initiator solution consisting of 1.0 wt% potassium persulfate and 6.0 wt% functional chain transfer agent (low molecular weight PAA with a molecular weight of approximately 3000 daltons) was added to the reactor to initiate polymerization and induce functionality. During initiation, the HFP to VDF ratio was adjusted to reach 8% HFP relative to the total monomers in the feed. The rate of further addition of the initiator solution was also adjusted to maintain a final VDF and HFP total polymerization rate of approximately 60 pounds per hour. The VDF and HFP copolymerization continued until approximately 160 pounds of monomers had been introduced into the reaction mixture. The HFP feed was stopped, but the VDF feed was continued until approximately 180 pounds of total VDF monomer had been fed to the reactor. The VDF feed was stopped, and the batch was allowed to react out at reaction temperature to consume residual monomer at decreasing pressure. After 20 minutes, the initiator feed and agitation were stopped, the reactor was cooled and vented, and the latex was recovered. The solids content in the recovered latex was approximately 32% by weight, as determined by gravimetric techniques, and the melt viscosity was 100 s at 450°F according to ASTM Method D-3835. -1 The viscosity was about 68 kP as measured by FTIR. The melt temperature of the resin was about 138° C. as measured according to ASTM method D-3418. The weight average particle size was about 160 nm as measured by a NICOMP laser light scattering instrument.

[0101] Characterization: After drying, an 8 wt. % solution of each of the above resins in NMP was prepared. The solution was cast onto 15 micron aluminum foil (6 x 15 inches) at room temperature using a doctor blade or drawdown bar and then placed in a 120°C oven for 0.5 hours to form a solid film of approximately 3 microns. The adhesion of the multiphase polymer onto the aluminum foil was measured using an Instron in an 80° peel test configuration at a peel rate of 55 mm / min.

[0102] Wet adhesion was measured by placing the coated Al foil in a common electrolyte solvent, i.e., EC / DEC / DMC, for 72 hours at 60° C. Visual inspection was used to measure the number and size of blisters on the coated Al foil.

[0103] Swellability: 10 micron thick dry films were cast onto glass substrates from 8 wt% NMP solutions and placed in an oven at 120°C to dry. The films were lifted off and then placed in a common electrolyte solvent, i.e., EC / DEC / DMC, at 60°C for 72 hours. Swellability was measured by measuring the weight change of the swollen film relative to the dry film for each phase. % Swelling = [m (swelling) / m (initial)] x 100 %Leakability=[{m(initial)-m(dry)} / m(initial)]×100

[0104] where m(initial) is the weight of the initial dry polymer, m(swollen) is the weight of the swollen polymer, and m(dry) is the weight of the polymer dried after solvent exposure.

[0105] Application examples: The PVDF-based latex is then formulated with or without inorganic particles into an aqueous coating composition, applied to a polyolefin separator, and dried at elevated temperatures but below 90°C, or a temporary adhesion promoter is used to improve interconnectivity and adhesion. The temporary adhesion promoter is a chemical, an energy source combined with pressure, or a combination, used in an amount effective to cause the components of the aqueous composition to bond together in forming the electrode. Useful organic solvents are N-methyl-2-pyrrolidone, dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide (DMSO), hexamethylphosphamide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, trimethyl phosphate, dimethyl succinate, diethyl succinate, and tetraethyl urea.

[0106] In the case of energy as a temporary adhesion promoter, useful energy sources are heat, infrared and radio frequency (RF).

[0107] Additionally, a portion of the above latex was spray dried to a fine powder with an average particle size of 1 to 30 microns, then redispersed and formulated in an aqueous medium with or without inorganic particles, applied to a polyolefin separator, and dried at a high temperature but below 90°C.

[0108] Additionally, portions of the spray-dried powdered resins described above were formulated into non-aqueous coating compositions with or without inorganic particles, applied to polyolefin separators, and dried at elevated temperatures but below 90°C.

[0109] Random and co-continuous copolymers of VDF and HFP with various weight percent HFP as shown in the table were tested for weight gain, swelling, and leaching. The results are shown in Table 1.

[0110] [Table 1]

[0111] The electrolyte mixture was EC (ethylene carbonate), DMC (dimethyl carbonate) and EMC (ethylene methyl carbonate) in a ratio of about 1:1:1.

[0112] The polymer in Table 1 is a PVDF / HFP copolymer.

[0113] The data in Table 1 are plotted in Figures 1-4. These data show that the rate of increase as a function of HFP content for the heterogeneous copolymers is relatively slow or linear compared to the random copolymers. From Polymer A to Polymer X, the slope is unexpectedly large, and since Polymer X is completely soluble in the electrolyte, its weight gain and swelling ratio cannot be calculated. In contrast, from Polymer C to Polymer B, the slope appears to be slower compared to the random copolymers.

[0114] Among the heterogeneous grades, the trend of increasing electrolyte uptake / swelling with increasing HFP content remains the same, but is still measurably less than random copolymers of similar HFP content (especially above 10 wt. % HFP in the total copolymer). Heterogeneous grades can be used to balance adhesion and swelling.

Claims

1. A binder composition for a separator coating comprising two or more distinct phases, the phases being: a) a low swelling fluoropolymer phase that expands less than 50% by weight in the electrolyte solvent; b) a highly swellable fluoropolymer phase having a swelling property in an electrolyte that is at least 10% greater than the swelling property of said low-swellable fluoropolymer phase; Including, The binder composition, wherein the low swelling fluoropolymer phase and the high swelling fluoropolymer phase have at least 10 wt% of fluoromonomer units in common, and the binder composition comprises discrete polymer particles having an average particle size of less than 1 μm.

2. 2. The binder composition of claim 1, wherein the common fluoromonomer unit between the fluoropolymer of the low swelling fluoropolymer phase and the fluoropolymer of the high swelling fluoropolymer phase is vinylidene fluoride.

3. 10. The binder composition of claim 1, wherein the binder composition is either a blend of one or more low swelling fluoropolymers and one or more high swelling fluoropolymers, or a single multiphase particle having a core of low swelling fluoropolymer and a high swelling fluoropolymer outside the core.

4. 10. The binder composition of claim 1, wherein the low swelling fluoropolymer phase and the high swelling fluoropolymer phase are heterogeneous and / or co-continuous.

5. 4. The binder composition of claim 3, wherein the single multiphase particle has a core-shell or raspberry morphology or a gradient composition.

6. The binder composition further comprises 75 to 99.5 parts by weight of inorganic particles relative to 0.5 to 25 parts by weight of the polymer binder solid content, and the inorganic particles are electrochemically stable and include BaTiO 3 , Pb(Zr,Ti)O 3 , Pb 1-x La x Zr y O 3 (0<x<1, 0<y<1), PbMg 3 Nb 2 / 3 O 3 , PbTiO 3 , hafnia (HfO 2 ), SrTiO 3 , SnO 2 , CeO 2 , MgO, NiO, CaO, ZnO, Y 2 O 3 , boehmite (y-AlO(OH)), Al 2 O 3 , TiO 2 , SiC, ZrO 2 , boron silicate, BaSO 4 the inorganic particles selected from the group consisting of: nanoclay, ceramic or a mixture thereof; The binder composition of claim 1 comprising:

7. 10. The binder composition of claim 1 for use in a separator coating, comprising: a) the low swelling fluoropolymer phase comprises at least one fluoropolymer having a crystallinity of 35 wt% or higher; b) the highly swellable fluoropolymer phase comprises 0.1 to 25 wt. % of a fluoropolymer phase containing functional groups, based on the total polymer binder; Binder composition.

8. 8. The binder composition of claim 7, wherein the common fluoromonomer unit between the phases is vinylidene fluoride.

9. The binder composition further comprises 75 to 99.5 parts by weight of inorganic particles relative to 0.5 to 25 parts by weight of the polymer binder solid content, and the inorganic particles are electrochemically stable and include BaTiO 3 , Pb(Zr,Ti)O 3 , Pb 1-x La x Zr y O 3 (0<x<1, 0<y<1), PbMg 3 Nb 2 / 3 O 3 , PbTiO 3 , hafnia (HfO 2 ), SrTiO 3 , SnO 2 , CeO 2 , MgO, NiO, CaO, ZnO, Y 2 O 3 , boehmite (y-AlO(OH)), Al 2 O 3 , TiO 2 , SiC, ZrO 2 , boron silicate, BaSO 4 the inorganic particles selected from the group consisting of: nanoclay, ceramic or a mixture thereof; The binder composition of claim 7 comprising:

10. A separator for an electrochemical device, comprising: the separator having a coating on at least one surface thereof comprising the dried binder composition of claim 1; The dried binder composition has the following properties: a) a dry adhesive strength of greater than 10 N / m as measured by 180° peel strength measurement; and b) Less than 10% by weight leachables measured on a 10 micron dry film: The separator of the electrochemical device,

11. 11. The separator of claim 10, wherein the binder composition comprises a blend of one or more low swelling fluoropolymers and one or more high swelling fluoropolymers, or is a single multiphase particle having a core of low swelling fluoropolymer and a high swelling fluoropolymer outside the core, or is a single multiphase particle, the phases being heterogeneous and / or co-continuous.

12. The binder composition further comprises 75 to 99.5 parts by weight of inorganic particles relative to 0.5 to 25 parts by weight of the polymer binder solid content, and the inorganic particles are electrochemically stable and include BaTiO 3 , Pb(Zr,Ti)O 3 , Pb 1-x La x Zr y O 3 (0<x<1, 0<y<1), PbMg 3 Nb 2 / 3 O 3 , PbTiO 3 , hafnia (HfO 2 ), SrTiO 3 , SnO 2 , CeO 2 , MgO, NiO, CaO, ZnO, Y 2 O 3 , boehmite (y-AlO(OH)), Al 2 O 3 , TiO 2 , SiC, ZrO 2 , boron silicate, BaSO 4 the inorganic particles selected from the group consisting of: nanoclay, ceramic or a mixture thereof; The separator of claim 10 comprising:

13. 10. A method of forming a coated separator, comprising dip coating, spray coating, or microgravure coating at least one surface of a separator with the coating composition of claim 1, and then drying the coated separator to form a dried coated separator.

14. The method of claim 13, wherein the coating on the dried coated separator has a thickness of 0.5 to 15 μm.

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