Fibrillizable polymeric binders for electrodes

Abstract

A fibrillizable binder composition is provided comprising a copolymer derived from tetrafluoroethylene (TFE) and a comonomer having at least one polar pendant group including oxygen. Also provided are binder compositions for use in making electrode films and batteries wherein the binder compositions comprise a fibrillizable tetrafluoroethylene (TFE)-based polymer or TFE-based copolymer co-coagulated with a polymer having at least one pendant polar group comprising oxygen, such as an ionomer.

Description

Attorney Docket No. FP0001-W001TITLE OF THE INVENTIONFIBRILLIZABLE POLYMERIC BINDERS FOR ELECTRODES CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority benefit of US provisional patent application no. 63 / 696,557, filed on September 19, 2024, the disclosure of which is hereby incorporated by reference in its entirety.FIELD OF THE INVENTION

[0002] This disclosure relates generally to compositions for use as binders in electrodes.BACKGROUND OF THE INVENTION

[0003] Electrodes for an electrochemical storage device typically include an active component (or active material), such as graphite, metal, or metal oxide, that undergoes an electrochemical reaction associated with energy storage; a binder, such as polyvinylidene fluoride (PVDF), that mechanically supports and binds the active component and attaches the electrode to a current collector; and optionally an electrically conductive additive (or conductive agent), such as carbon black, that increases the electrical conductivity of the electrode.

[0004] In a “dry” or “solvent-free” process, an electrode film is formed by formation of an c electrode power into a film using a calendering process, without requiring a slurry material and corresponding solvent drying process. The electrode film can then be laminated onto a current collector.SUMMARY OF THE INVENTION

[0005] In a first aspect of the present disclosure a fibrill izable binder composition is provided comprising a copolymer derived from tetrafluoroethylene (TFE) and a comonomer, and wherein the comonomer comprises at least one polar pendant group comprising oxygen.

[0006] This and other fibrillizable binder compositions according to the first aspect described herein can have one or more of at least the following embodiments.Attorney Docket No. FP0001-W001

[0007] In one embodiment, the TFE-based copolymer comprises less than 5 wt% (based on the total weight of the TFE-based copolymer) and at least 0.01 wt % of copolymerized repeat units of the comonomer; preferably wherein the copolymer comprises less than 2 wt% and at least 0.1 wt% of co-polymerized repeat units of the comonomer.

[0008] In another embodiment the polar pendant group comprises a hydroxylcontaining group, a hydroxyalkyl-containing group, a carboxyl-containing group, a phosphate-containing group, a phosphonate-containing group, a phosphinatecontaining group, a sulfonate-containing group, a hydroxyaryl-containing group, or an epoxide-containing group.

[0009] In a further embodiment the polar pendant group has a salt form, an acid form or a combination thereof; preferably wherein the polar pendant group is a lithium salt.

[0010] In another embodiment the fibrillizable binder comprises a TFE-based copolymer having co-polymerized repeat units (comonomer units) selected from the group of: a. CF2=CF(CF2)xORf-R(OH)ywith a hydroxyalkyl group, -CH2OH, or CH(OH)2 at one or more termini, where x is 0 or 1 , y is 1 , 2, or 3, Rfis a fluorinated or perfluorinated alkylene group or a fluorinated or perfluorinated alkylene oxy group, and R is a C1 to C6 hydrocarbyl, an aryl, or a fluoroaryl linking group; b. R1CR3=CR4-R'-SO2OH, R1CR3=CR4-R’-CO2OH, R1CR3=CR4-R’- PO(OH)2, R1CR3=CR4-R’-OPO(OH)2, or R1CR3=CR4-R’-OH; and c. R1CR3=CR4-R'-cyc / o-(C2R5R6R7O); wherein R1, R3, R4, R5, R6, R7are independently H, CH3, a C1 to C6 alkyl group optionally substituted with either linkages or an aryl group, and where R' is optionally present as a C1 to C12 alkylene group, arylene group, ether group, alkylene ether group, an arylene ether group or a fluorinated version of one of the foregoing groups.Atorney Docket No. FP0001-W001

[0011] In a further embodiment the TFE-based copolymer comprises copolymerized repeat units of 3-[1-[Difluoro[(1 ,2,2-trifluoroethenyl)oxy]methyl]-1 ,2,2,2- tetrafluoroethoxy]-2,2,3,3-tetrafluoro-propanol (EVE-OH), allyl glycidyl ether, 4- hydroxy butyl vinyl ether, or hydrolyzed vinyl acetate.

[0012] In another embodiment the polar pendant group is configured to interact chemically with at least one of an electrode active component, an electrode conductive additive, a current collector, or a primer layer on the current collector.

[0013] In another embodiment, the fibrillizable binder is in the form of a core-shell polymer particle having a core and one or more shell layers, wherein at least one of the shell layers is the TFE-based copolymer having a polar pendant group comprising oxygen. In a further aspect, the core of the core-shell particle comprises a fibrillizable homopolymer PTFE or a fibrillizable modified PTFE.

[0014] In another embodiment, the core forms 60 to 85 wt% of the core-shell polymer particle, and wherein the shell forms 15 to 40 wt% of the core-shell polymer particle.

[0015] In a second aspect, a binder for an electrode is provided comprising the fibrillizable binder composition of the first aspect and any related embodiments of the first aspect.

[0016] In a third aspect, an electrode film for an electrochemical device is provided, the electrode film comprising: an active component; and the binder of said second aspect and related embodiments, wherein the binder is partially or fully fibrillated, preferably wherein the electrode film has at least one of: a. a Young’s modulus of at least 0.04 MPa, over a first 1% of strain, for strain applied to a long dimension; b. a force at which the electrode film fails is in a range from 0.1 to 0.5 N / cm based on a 90° peel test conducted with a 5 lb. (-2.27 kg) load and a vertical pull rate of 2 inches (-5.08 cm) per minute conducted with the electrode film laminated to a carbon-coated copper current collector; andAttorney Docket No. FP0001-W001 c. an ultimate tensile strength (UTS) of at least 0.10 MPa; and a strain at break of at least 17%.

[0017] In another embodiment the active component comprises at least one of graphite, a metal oxide, a lithium alloy, silicon, silicon oxide, a carbon-based material, a phosphorous-based material, or a nanocomposite comprising at least one of antimony or tin.

[0018] In another embodiment the weight percentage of the binder in the electrode film is in a range from 0.2% to 10%.

[0019] In another embodiment, the electrode film according to any one of the above embodiments comprises a conductive additive.

[0020] In a fourth aspect a battery is provided, comprising: an electrolyte; a current collector; and an electrode film according to the third aspect or any embodiments thereof wherein the electrode film is in contact with the current collector and in contact with the electrolyte.

[0021] In another embodiment the current collector and the electrode film form an anode or a cathode of the battery.

[0022] In a fifth aspect, a polymer composition is provided for use as a binder in an electrochemical device comprising the f ibril lizable binder composition according to said first aspect and any embodiments thereof; co-coagulated with: a. an ionomer; b. a TFE-based polymer; or c. a combination of (a) and (b); wherein the ionomer comprises a polymer having a side chain terminating in a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, or a salt form of one of the foregoing groups.Attorney Docket No. FP0001-W001

[0023] In another embodiment the ionomer comprises a perfluoro sulfonic acid (PFSA) polymer having an equivalent weight of 700 to 1500 g / mol; preferably wherein i. the PFSA polymer has a hydrolyzed form; or ii. the PFSA polymer is terminated by an alkali metal sulfonate; or iii. the PFSA polymer is neutralized; or any combination thereof.

[0024] In a further embodiment the ionomer comprises a copolymer of ethylene and at least one of methacrylic acid or acrylic acid.

[0025] In a further embodiment the proportion of the ionomer in the co-coagulate is in a range from 0.5 wt% to 10 wt%; preferably 0.5 wt% to 5 wt% based on the total weight of the co-coagulate.

[0026] In another embodiment the polymer composition comprises an average domain size in the polymer composition is 1 pm or less.

[0027] In a sixth aspect, an electrode film for an electrochemical device is provided, the electrode film comprising: an active component; and the polymer composition of any one said fifth aspect and embodiments thereof; where the fibrillizable tetrafluoroethylene (TFE)-based polymer is partially or fully fibrillized; wherein the electrode film has at least one of: a. a Young’s modulus of the electrode film is in a range from 0.1 MPa to 2.0 MPa; b. an ultimate tensile strength of the electrode film is in a range from 0.5 MPa to 5 MPa; c. a strain at break of the electrode film is in a range from 12% to 30%; d. a strain at ultimate tensile strength of the electrode film is in a range from 6% to 25%; and e. a force at which the electrode film fails is in a range from 0.1 to 0.5 N / c as measured in a 90° peel test conducted with a 5 lb. (-2.27 kg) load and a verticalAttorney Docket No. FP0001-W001 pull rate of 2 inches (-5.08 cm) per minute conducted with the electrode film laminated to a carbon-coated copper current collector.

[0028] In a further embodiment, the electrode film has a thickness in a range from 25 pm to 300 pm.

[0029] In a further embodiment, the active component comprises at least one of graphite, a metal oxide, a lithium alloy, silicon, a carbon-based material, a phosphorous-based material, or a nanocomposite comprising at least one of antimony or tin.

[0030] In another embodiment, the electrode film further comprises a conductive additive.

[0031] In a seventh aspect, a battery is provided comprising an electrolyte; a current collector; and the electrode film of said sixth aspect and embodiments thereof wherein the electrode film is in contact (e.g., laminated to) with the current collector and in contact with the electrolyte.

[0032] In some further implementation of the above aspects and embodiments the comonomer is a first comonomer, and the TFE-based copolymer is further derived from a second comonomer different from the first comonomer.

[0033] In some implementations, the polar pendant group is configured to interact chemically with one or more polar groups, for example, surface -OH groups of an oxide or of the current collector or of carbon (carbon black or graphite).

[0034] In an eighth aspect a polymer composition is provided including: a fibrillizable tetrafluoroethylene (TFE)-based polymer (“first polymer within the cocoagulate”) co-coagulated with at least one polymer having a pendant polar group comprising oxygen (“second polymer within the co-coagulate”). As used herein, the “polymeric composition comprising the co-coagulate” may also be referred to as the “polymer agglomerate composition” or the “binder agglomerate composition.” In one embodiment, the second polymer within the co-coagulate may be the fibrillizable TFE-based copolymer having at least one polar pending group comprising oxygenAttorney Docket No. FP0001-WQ01 as described above, an ionomer or a combination thereof. In one preferred aspect, the second polymer is an ionomer.

[0035] In another embodiment, the fibrillizable TFE-based polymer is a PTFE homopolymer, a modified PTFE, the fibrillizable TFE-based copolymer having at least one polar pendant group (as described above) or any combination thereof.

[0036] In some implementations, the ionomer includes a polymer having a side chain terminating in a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, or a salt form of one of the foregoing groups. In one preferred aspect, the ionomer comprises an equivalent weight of 500 to 1500 g / mol.

[0037] In some implementations, the ionomer includes a perfluoro sulfonic acid (PFSA) polymer. In one aspect, the PFSA polymer comprises an equivalent weight of 700 to 1500 g / mol.

[0038] In some implementations, the PFSA polymer has a hydrolyzed form.

[0039] In some implementations, the PFSA polymer is terminated by an alkali metal sulfonate (e.g., lithium sulfonate).

[0040] In some implementations, the PFSA polymer is neutralized.

[0041] In some implementations, the ionomer includes a copolymer of ethylene and at least one of methacrylic acid or acrylic acid.

[0042] In some implementations, of the fibrillizable TFE-based polymer and the ionomer, a proportion of the ionomer is in a range from 0.5 wt% to 10 wt%.

[0043] In some implementations, the TFE-based polymer includes a fibrillizable copolymer derived from TFE and a comonomer. The comonomer includes a polar pendant group comprising oxygen.

[0044] In some implementations, the ionomer is a first ionomer, and the TFE- based polymer is further co-coagulated with a second ionomer different from the first ionomer.

[0045] In some implementations, the ionomer includes side chains terminated by two different groups from among a sulfonic acid group, a carboxylic acid group, aAttorney Docket No. FP0001-W001 phosphoric acid group, a phosphonic acid group, a phosphinic acid group, or a salt form of one of the foregoing groups.

[0046] Some aspects of this disclosure relate to a polymer composition including: a fibril lizable tetrafluoroethylene (TFE)-based polymer and a polymer (different from said fibril lizable TFE-based polymer) having at least one polar pendant group comprising oxygen. In one aspect, the polymer having at least one polar pendant group comprising oxygen is a TFE-based copolymer comprising a comonomer providing at least on polar pendant group comprising oxygen or an ionomer having at least one polar pendant group comprising oxygen. In another aspect, the polymer composition (co-coagulated agglomerate) comprising an average domain size in the polymer of 1 pm or less.

[0047] In some implementations, the polymer composition (co-coagulated agglomerate) comprises an average domain size is in a range from 100 nm to 300 nm.BRIEF DESCRIPTION OF THE DRAWINGS

[0048] FIG. 1 is a diagram illustrating an example of a battery.

[0049] FIGS. 2A-2B are chemical diagrams of examples of ionomers.

[0050] FIG. 3 is a diagram illustrating an example of a film manufacturing process.

[0051] FIG. 4 is a plot of strain data for electrode films.

[0052] FIG. 5 is a plot of electrochemical cycling data for a half cell.

[0053] FIG. 6 a plot of particle size data.DETAILED DESCRIPTION OF THE INVENTION

[0054] In view of the rising demand for lithium-ion batteries for consumer electronics and electric vehicles, battery manufacturers are eager to increase energy density, reduce the cost of manufacturing, and reduce their environmental footprints. Solvent-free electrode manufacturing technology has advantages over conventional wet electrode casting methods in these and other aspects.Attorney Docket No. FP0001-W001

[0055] Polytetrafluoroethylene (PTFE)-type fluoropolymer is a candidate binder material for solvent-free electrode manufacturing due to its strong fibrillation property. Fibrils derived from the fluoropolymer are generated during electrode processing when shear energy is applied, e.g., in premixing processes and / or during calendering processing. These fibrils contribute to the binding force in the electrode and can help facilitate roll-to-roll production.

[0056] However, for purposes of this disclosure, it has been observed that electrode films manufactured with unfunctionalized PTFE polymer have weak adhesion to bare current collectors (e.g., metal current collectors without an adhesive coating) or poor peel strength. Although adhesion and / or peel strength may be increased by coating the current collector with adhesive polymer and / or carbon, the use of the coating increases the overall battery cost.

[0057] For purposes of this disclosure, it has been recognized that electrode films manufactured with certain functionalized and modified polymer compositions (e.g., PTFE compositions) exhibit relatively strong mechanical properties, e.g., cohesive strength, elasticity, and / or strength. These mechanical properties can facilitate roll- to-roll manufacture of electrodes and / or provide improved long-term battery performance. Discussed herein are binders, electrodes, batteries, and corresponding manufacturing methods associated with these compositions.

[0058] In some cases, these and / or other properties are provided by a fibril lizable binder compositions comprising a copolymer derived from TFE (i.e., “TFE-based copolymer”) and at least one comonomer having a pendant group having certain characteristic(s) that result in the copolymer being advantageous for use in an electrode film. For example, the pendant group can interact with other binder and / or battery components to improve the mechanical properties of the electrode. In one embodiment, copolymerization is conducted such that the TFE-copolymer having at least one polar pendant group comprising oxygen is fibri llizable and provides additional mechanical functionality, such as improved mechanical properties between fibrils and / or active materials within the present compositions and electrode films. In one aspect, the TFE-based copolymer comprising at least on polar pendant group comprising oxygen is f ibri llizable and may be used as the fibrill izable fluoropolymer in the following co-coagulated compositions.Attorney Docket No. FP0001-W001

[0059] In another aspect, the present fi bri llizable binders and / or polymer compositions (for use as a binder) comprise at least one fibrillizable fluoropolymer (i.e., “first polymer”) co-coagulated with at least at least one polymer having at least one pendant polar end group comprising oxygen (i.e., “second polymer”). The polymer having at least one pendant polar group comprising oxygen may be one of the present TFE-based copolymers having a polar pendant group comprising oxygen, an ionomer or a combination thereof. In one aspect, the fibrillizable fluoropolymer (“first polymer”) may be a PTFE homopolymer, a modified PTFE or a fibrillizable TFE-based copolymer having at least one pendant polar group having oxygen (specifically wherein the “second polymer” is different from said “first polymer”). In one embodiment, the fibrillizable fluoropolymer (i.e., “first polymer”) and the “second polymer” can be intermixed with micron-scale or smaller domains, wherein the second polymer can interact with other binder and / or battery components to provide improved mechanical properties. In one embodiment the second polymer is at least one ionomer. In yet another embodiment, the polymer composition comprises a fibrillizable binder comprising the TFE-based polymer having at least one polar pendant group co-coagulated with at least one ionomer; preferably wherein the TFE-based polymer is fibrillizable.

[0060] Referring to FIG. 1 , an electrochemical device or energy storage device 100 such as a battery (hereinafter referred to, for purposes of illustration, as a battery 100) includes an anode current collector 102, an anode electrode 104 on the anode current collector 102 (e.g., laminated onto the anode current collector 102), a cathode current collector 106, a cathode electrode 108, and an electrolyte 110 (e.g., a lithium-based gel or solvent electrolyte) sandwiched between the electrodes 104, 108.

[0061] In more detail, as shown in the inset drawing of FIG. 1 , the anode electrode 104, includes an active component 112 (e.g., in particle form), a conductive additive 114, and a polymeric binder 116 holding together the active component 112 and the conductive additive 114, adhering the anode electrode 104 to the anode current collector 102. The cathode electrode 108 can have an analogous structure.

[0062] As shown in FIG. 1 , the fibrillizable polymer of the binder 116 can form fibrils that provide binding force in the electrodes 104, 108 and can help facilitate roll-Attorney Docket No. FP0001-W001 to-roll production. A network of the fibrils allows the electrodes 104, 108 to cohere. Accordingly, the polymer can be described as “fibrillated” in the form shown in FIG. 1 , and, generally, as “fibrillizable.” “Fibrillizable,” as used herein, mean that a polymer is capable of forming nanosized (in at least one dimension (e.g., <100 nm width) fibrils which can vary in length from submicrometer, to several microns, to tens of micrometers, in length when the polymer is subjected to shear forces, in sufficient density to form a cohered binding network.

[0063] In the anode electrode 104, the active component 112 can include, for example, graphite, graphite including silicon, graphite including SiOx; a graphite composite including SiOx; a lithium alloy (e.g., a lithium-aluminum alloy, a lithiumlead alloy, a lithium-silicon alloy, and / or a lithium-tin alloy); silicon (e.g., silicon nanoparticles); a carbon-based material such as graphite graphene, carbon nanotubes, mesocarbon microbeads (MCMB), and / or conductive carbon; a phosphorous-based material such as conductive black phosphorous; a metal oxide such as SnC>2, SnO, TiC>2, and / or an oxide of aluminum and / or molybdenum; and / or a nanocomposite including antimony and / or tin. Other suitable active components are also within the scope of this disclosure.

[0064] In the cathode electrode 108, the active component can include, for example, a metal oxide, a metal sulfide, and / or a lithium metal oxide. For example, the cathode active component can include a lithium transition metal oxide. For example, the lithium metal oxide can include lithium nickel manganese cobalt oxide (NMC), lithium manganese oxide (LMO), lithium iron phosphate (LiFePO4), lithium manganese iron phosphate, lithium cobalt oxide (LCO), and / or lithium nickel cobalt aluminum oxide (NGA). In some implementations, the cathode active component includes a layered transition metal oxide (such as LiCoC (LCO), Li(NiMnCo)O2 (NMC), LiNi0.8Co0.15AI0.05O2 (NCA)), a spinel manganese oxide (such as LiMn2O4 (LMO), LiMm 5Nio.5O4 (LMNO)) an olivine (such as LiFePO4), LiNiO2, LiNii-xCOxO2, LiNi0.85Co0.1AI0.05O2, LiNio.33Coo.33Mno.33O2, LiMn2O4, or a combination thereof.

[0065] The conductive additive in the anode electrode 104 and / or the cathode electrode 108 can include, for example, a conductive carbon agent such as carbon black, carbon nanotubes (CNT), carbon fibers, graphene, conductive graphite, and / or a combination thereof.Attorney Docket No. FP0001-W001

[0066] The current collectors 102, 106 can be metal bodies, e.g., foils / sheets. For example, the anode current collector 102 can include copper foil, and the cathode current collector can include aluminum foil.

[0067] It will be understood that FIG. 1 is diagrammatic and schematic, and that the relative scales, shapes, and forms of the various illustrated elements are not intended to accurately illustrate the microscopic morphology of a battery.Fibrillizable Binders Comprising TFE-Based Copolymers Having a Polar Pendant Group

[0068] According to some implementations of the present disclosure, an electrode binder (e.g., a binder of electrodes 104 and / or 108) includes a functionalized copolymer having a pendant group having a target characteristic. The pendant group is configured to interact with battery component(s). For example, the copolymer can be derived from TFE and at least one comonomer that has the pendant group, such that the functionalized copolymer has the pendant group.

[0069] For clarity, the following description will refer to “a” comonomer, with the understanding that in some implementations the copolymer is derived from multiple comonomers having pendant groups having the target characteristic. The copolymer can be derived from one or more comonomers, and the comonomers can have the same and / or different functional groups, all within the same copolymer. For example, the copolymer can have, or can be derived from distinct comonomers having, a phosphonate pendant group and a sulfonate pendant group. Moreover, in some implementations, one comonomer can contribute multiple pendant groups. For example, a comonomer from which a copolymer is derived can have two different pendant groups having the target characteristic. Accordingly, multiple different functional groups having the target characteristics can be on separate comonomers, and / or can be contained within one comonomer. References to “a” comonomer or “a” pendant group do not exclude the possible presence of other comonomers and / or pendant groups.

[0070] In some implementations, the pendant group includes oxygen. In some implementations, the pendant group is polar. In some implementations, the pendant group is polar and includes oxygen. In some implementations, the pendant group isAttorney Docket No. FP0001-W001 polar and has a polarity in a target range. In some implementations, the pendant group is or includes one of a certain set of chemical groups, as set forth below. As used herein, any one or more of these characteristics can be a “target characteristic” possessed by the pendant group.

[0071] In some implementations, the fibrillizable polymer can be a tetrafluoroethylene (TFE)-based polymer. The fibrillizable TFE-based polymer may be polytetrafluoroethylene (PTFE) homopolymer, modified PTFE having 1 wt% or less of modifier, fibrillizable TFE-based copolymers as described herein having at least one polar pendant group having oxygen or any combination thereof so long as the polymer is fibrillizable and can help to provide sufficient fibrillar support to make free standing electrode films. In some implementations, the fibrillizable TFE-based fluoropolymer is a modified PTFE comprising less than 1 wt% of comonomer modifiers such as perfluorobutyl ethylene (PFBE), a perfluoroalkyl vinyl ether (PAVE) such as perfluoropropyl vinyl ether (PPVE) or perfluoromethyl vinyl ether (PMVE), hexafluoropropylene, a dioxole, ethylene or combinations thereof.

[0072] Examples of the comonomer include allyl glycidyl ether, 4-hydroxy butyl vinyl ether, hydrolyzed vinyl acetate, and derivatives of EVE; such as EVE-OH and EVE-P (see, respectively, U.S. 5,093,446 to Hung and U.S. 6,177,196 to Brothers et al.). Each of these comonomers contains a polar pendant group that includes oxygen. For the purposes of this disclosure, it has been recognized that copolymers of TFE with some comonomers do not retain their high fibrillizability, such that, even if those comonomers provide a pendant group having the target characteristic, the copolymers may be less suitable for use in a binder composition. The examples of comonomers and classes of comonomers discussed herein have been found to be effective for inclusion in binder compositions.

[0073] Examples of the pendant group included in the comonomer include a hydroxyl group or a hydroxyl-containing pendant group, a hydroxyalkyl group (e.g., - CH2OH or -CH(OH)2) or a hydroxyalkyl-containing pendant group, a carboxyl group or a carboxyl-containing pendant group, a phosphate-containing group, a phosphonate group ora phosphonate-containing pendant group a phosphinate group or a phosphinate-containing group, a sulfonate group or a sulfonate-containing pendant group, an epoxide group or an epoxide-containing pendant group, anAttorney Docket No. FP0001-W001 epoxyalkyl group or an epoxyalkyl-containing pendant group, and a hydroxyaryl group or a hydroxyaryl-containing pendant group, where “containing” includes the case where the pendant group is the chemical group, e.g., a hydroxyl-containing pendant group can be a hydroxyl group. Each of the foregoing examples of pendant groups is polar and includes oxygen. For example, allyl glycidyl ether includes an epoxide pendant group and can be co-polymerized with TFE to form a fibrillizable copolymer having an epoxide pendant group. In some implementations, the pendant group (in the co-monomer and / or in the fibrillizable copolymer derived from the comonomer) is an end group. The pendant group can be part of and introduced by the co-monomer such that the copolymer has the pendant group. The foregoing groups include the acid form and all possible salts, including mono and divalent cation salts, e.g., including Li+, Na+, K+, and Mg2+. Moreover, the groups can be partially or fully neutralized without departing from the meaning of this disclosure.

[0074] As another example, either of 4-hydroxy butyl vinyl ether or hydrolyzed vinyl acetate includes a hydroxyl pendant group and can be co-polymerized with TFE to form a fibrillizable copolymer having a hydroxyl pendant group. In the case of hydrolyzed vinyl acetate, the fibrillizable copolymer can be derived from TFE and vinyl acetate, and the copolymer can be subsequently hydrolyzed to provide the hydroxyl pendant group. Derivatives of methyl (3-{1 - [difluoro(trifluoroethenyl)oxy]methyl-1 ,2,2,2-tetrafluoroethoxy}2,2,3,3-tetrafluoro- propanoate (“EVE”; CAS Number 63863-43-4; available from The Chemours Company, Wilmington, DE), discussed in further detail below, are further examples of comonomers that provide a pendant group having the target characteristic.

[0075] Examples of TFE-based copolymers derived from comonomers including an epoxide pendant-containing pendant group and a hydroxide-containing pendant group are discussed below.

[0076] “Derived from,” as used herein in reference to a first component and a second component, refers to copolymers formed by reaction(s) between the two components.

[0077] An example of a class of advantageous comonomers is the class of polymerizable fluoromonomers having the formula CF2=CF(CF2)xORf-R(OH)y, where x is 0 or 1 , y is 1 , 2, or 3, Rfis a fluorinated or perfluorinated alkylene group or aAttorney Docket No. FP0001-W001 fluorinated or perfluorinated alkylene oxy group, and R is a C1 to C6 hydrocarbyl, aryl, or fluoroaryl linking group that provides a hydroxyalkyl group as a pendant group. One such fluoromonomer is CF2=CFOCF2CF(CF3)OCF2CF2CH2OH (EVE- OH), which can be co-polymerized with TFE as, for example, (CF2CF2)z-EVE-OH wherein Z = 7 to 1000. Accordingly, the copolymer can include co-polymerized repeat units of EVE-OH.

[0078] In some implementations, the comonomer is a phosphate ester derived from a vinyl alcohol such as, for example, CF2=CFOCF2CF(CF3)OOF2CF2CH2OP(O)(OH)2 (EVE-P), which includes a phosphate pendant group and provides the phosphate pendant group to the resulting copolymer. The fibrillizable copolymer can include, for example, -(CF2CF2)z-(CF2- CF)-OCF2CF(CF3)OCF2CF2CH2OP(O)(OH)2 wherein Z= 7 to 1000.

[0079] In some implementations, a phosphinate group, in any of the polymer compositions discussed herein, can have the form RP(R’)(O)(OM) where M = H, Li, K, Mg, etc. R’ in this context can be, in some implementations, an alkylene group, an arylene group (optionally substituted with one or more ether linkages) or a fluorinated version of one of the foregoing groups.

[0080] In some implementations, the comonomer is a sulfonate salt monomer, a sulfonic acid monomer, or a sulfonic acid precursor. The comonomer can include a sulfonyl fluoride pendant group, SO2F, which may be hydrolyzed to a sulfonate salt, SO3M, where M is Li, Na, or K. The comonomer can be a sulfonic acid monomer such as CF2=CFOCF2CF(CF3)OCF2CF2SO2(OH), which includes a sulfonate pendant group and provides the sulfonate pendant group to the resulting copolymer. The fibrillizable copolymer can include, for example, -(CF2CF2)z-(CF2-CF)- OCF2CF(CF3)OCF2CF2SO2(OH) or -(CF2CF2)z-(CF2-CF)- OCF2CF(CF3)OCF2CF2SO3F wherein z = 7 to 1000.

[0081] In some implementations, the comonomer has the form R1CR3=CR4-R'- SO2OH, R1CR3=CR4-R’-COOH, R1CR3=CR4-R’-PO(OH)2, R1CR3=CR4-R’- OPO(OH)2, or R1CR3=CR4-R’-OH, where R1, R3, and R4are independently H, F, - CH3, a C1 to C6 alkyl group or an aryl group optionally substituted with one or more ether linkages or a fluorinated version of one of the foregoing groups, and where R' is optionally present as a C1 to C12 alkylene group, arylene group, alkylene etherAttorney Docket No. FP0001-W001 group, arylene ether group, or a fluorinated version of one of the foregoing groups. R1, R3, R4, and R' can be branched or unbranched. For example, R1, R3, R4, and R' can be an alkyl group which can be branched or unbranched, a fluoroalkyl group which can be branched or unbranched and where one or more or all of the hydrogens is substituted with a fluorine atom, an aryl group, a fluoroaryl group where one or more or all of the hydrogens is substituted with a fluorine atom, an ether group, a fluoroether group where one or more or all of the hydrogens is substituted with a fluorine atom, an alkyl ether group, a fluoroalkyl ether group where one or more or all of the hydrogens is substituted with a fluorine atom, an aryl ether group, or a fluoroaryl ether group where one or more or all of the hydrogens is substituted with a fluorine atom.

[0082] In some implementations, the co-monomer has the form R1CR3=CR4-R - cyc / o-(C2R5R6R7O), where R1, R3, R4, R5, R6, R7are independently H, F, -CH3, a C1 to C6 alkyl group or an aryl group, each optionally substituted with one or more ether linkages or a fluorinated version of one of the foregoing groups, and where R' is optionally present as a C1 to C12 alkylene group, arylene group, alkylene ether group, arylene ether group, or a fluorinated version of one of the foregoing groups. R1, R2, R3, R4, R5, R6, R7, and R' can be branched or unbranched. For example, one or more of these groups can be an alkyl group which can be branched or unbranched, a fluoroalkyl group which can be branched or unbranched and where one or more or all of the hydrogens is substituted with a fluorine atom, an aryl group, a fluoroaryl group where one or more or all of the hydrogens is substituted with a fluorine atom, an ether group, a fluoroether group where one or more or all of the hydrogens is substituted with a fluorine atom, an alkyl ether group, a fluoroalkyl ether group where one or more or all of the hydrogens is substituted with a fluorine atom, an aryl ether group, or a fluoroaryl ether group where one or more or all of the hydrogens is substituted with a fluorine atom. For example, the comonomer can be CH2=CHCH2OCH2-cyc / o-CHCH2O- or allyl glycidyl ether.

[0083] For example, it has been recognized that fibrillizability can depend on molecular weight, with the degree of fibrillization exhibited by a polymer increasing with increasing molecular weight. Copolymerization with the comonomers discussed herein can have the effect of reducing the molecular weight and thereby reducing the degree of fibrillization, while also providing the mechanical benefits described herein.Attorney Docket No. FP0001-W001Accordingly, the copolymers described herein can represent a balancing between fibrillizability and mechanical properties.

[0084] For purposes of this disclosure, it has been recognized that, in order for the copolymer to retain its fibrillizability, in some implementations the proportion of copolymerized repeat units of the comonomer in the copolymer can be small, e.g., 5 wt% or less, 4 wt% or less, 3 wt% or less, 2 wt% or less, 1 wt% or less, or 0.5 wt% or less. Further, the proportion of co-polymerized repeat units of the comonomer in the copolymer can be at least 0.01 wt%, at least 0.05 wt% or at least 0.1 wt% to provide mechanical benefits. These small proportions have been found to provide useful improvements in mechanical properties while still permitting the copolymer to be fibrillized. Higher wt% of the comonomer may result in the copolymer losing its fibrillizability. The wt% of the co-polymerized repeat units of the comonomer discussed herein refer specifically to a proportion of the co-polymerized repeat units of the comonomer in a portion of a copolymer derived from the comonomer. For example, in the case of the core-shell polymer particle where the core is a homopolymer, a wt% of the co-polymerized repeat units of the comonomer refers to a wt% of the co-polymerized repeat units of the comonomer in the shell. The coreshell particles described herein comprise a core with one or more outer layers surrounding the core (i.e., the shell layer(s)). In one aspect of the core-shell particle embodiment, the core is a fibri llizable PTFE homopolymer or modified PTFE while at least one shell layer is present and comprises the present TFE-based copolymers having at least one polar pendant group comprising oxygen; preferably wherein the TFE-based copolymer is also fibrillizable. Other core-shell arrangements can be envisioned such as a core comprising the present TFE-based copolymer (preferably fibrillizable) and one more shell layers comprising another polymer, such as homopolymer PTFE, modified PTFE or a TFE-based copolymer that is compositionally different from the core layer.

[0085] In some implementations, the fibrillizable TFE-based copolymer is a shell of a core-shell polymer. For example, the core of the core-shell polymer can be substantially free of polymerized repeat units of a comonomer (e.g., the core can be a homopolymer (e.g., a fibrillizable homopolymer such as PTFE), or another TFE- based polymer), and the shell of the core-shell polymer can be the copolymers discussed herein, derived from the comonomer. In some implementations, the coreAttorney Docket No. FP0001-W001 and the shell are both derived from TFE, and, in the shell, the copolymer is derived from TFE and a functional comonomer as discussed herein, while, in the core, the polymer is substantially un-copolymerized with the functional comonomer (e.g., the core is substantially free of polymerized repeat units of the comonomer).

[0086] Particles of the core-shell polymer can be composed of about 75 wt% (e.g., 60 wt% to 85 wt%) of a fibrill izable polymer (substantially free of polymerized repeat units of the comonomer), forming a core of the particle, and about 25 wt% (e.g., 15 wt% to 40 wt%) of the fibril lizable copolymer derived from TFE and the functional comonomer, forming a shell surrounding the core, wherein the wt% is relative to the total weight of the core-shell particle. The foregoing percentages can refer to the respective widths of the core and the shell, and / or to wt% of the core and the shell, respectively. For example, the core can be PTFE, and the shell can be a copolymer derived from TFE and the comonomer.

[0087] To synthesize the core-shell polymer, the core can be synthesized under conditions of a first, relatively low initiator flow. The shell can be synthesized at least partly under conditions of a second, higher initiator flow, in view of the negative effect the comonomer may have on polymerization.

[0088] It will be understood that the TFE-based copolymers discussed herein need not be included in a core-shell structure but, rather, in some implementations form a uniform copolymeric structure.

[0089] The improved mechanical characteristics provided by the TFE-based copolymer (provided in specific examples below) can derive from various chemical interactions between the pendant group having the target characteristic and components of the electrode and / or the current collector. For example, in some implementations, the ionic nature of the pendant group results in an ionic interaction (e.g., ionic bonding) between the TFE-based copolymer (e.g., the pendant group) and the active component, the conductive additive, and / or the current collector (e.g., with a metal foil or other body of the current collector). In some implementations, the pendant group interacts covalently (e.g., covalent bonding) with the active component, the conductive additive, and / or the current collector. For example, it has been observed that an epoxide pendant group can exhibit such covalent interactions.Attorney Docket No. FP0001-W001

[0090] Interactions, such as bonding, between the TFE-based copolymer and the active component and / or the conductive additive may result in improved mechanical properties of the electrode film, e.g., higher Young's modulus, ultimate tensile strength (UTS), strain at UTS, and / or strain at break. For example, the interactions can help initiate fibrillization, e.g., by aiding and / or initiating the unraveling of the polymer fibers. Accordingly, the use of the comonomer in synthesizing the fi bri llizable binder compositions comprising the TFE-based copolymer assists in the formation of an improved fibril network. Interactions between the TFE-based copolymer and the current collector may result in improved adhesion of the electrode film to the current collector, e.g., as indicated by a peel strength test.

[0091] In addition to, or instead of, interactions with components besides the binder, in some implementations the pendant group having the target characteristic can allow polymer particles to interlock more effectively with neighboring polymer particles, e.g., such that chemical interaction between particles of the TFE-based copolymer itself is enhanced. These interactions can further aid fibrillization and provide improved fibril networks that enhance electrodes’ mechanical properties.

[0092] The current collector can be primed, e.g., with carbon. The primer is an ultra-thin and protective layer for the current collector. In some implementations, without being bound to theory, the functional groups on the copolymer can interact with the surface of the primed current collector (e.g., with the primer), for example, a binding interaction that attaches the binder to the primer.Example 1 - Synthesis of TFE-based Copolymers Using Allyl Glycidyl Ether

[0093] The following is an example of the synthesis of a polymer composition having a core-shell structure with a PTFE core and a TFE-based copolymer shell having a polar pendant group comprising oxygen, the TFE-based copolymer shell derived from TFE and allyl glycidyl ether.

[0094] An initiator solution consisting of 0.3 g KMnO4 and 5.0 g of a 1.4 wt% aqueous (NH4)2HPO4 solution raised to 1000 g with deionized, deaerated water was prepared. An allyl glycidyl ether (AGE) solution containing 10 g of AGE raised to 100 mL with deionized, de-aerated was prepared. 5400 mL of deionized, de-aerated water was added to a reactor. A surfactant solution consisting of 10.0 g of GX905DAttorney Docket No. FP0001-W001 surfactant (perfluorinated ether carboxylate salt manufactured by The Chemours Company, Wilmington, DE) and 1 drop of TOMADOL® 23-1 (an ethoxylated alcohol surfactant available from Evonik Industries AG (Essen, Germany)), raised to 500 g with deionized, de-aerated water, was added to the reactor. Reactor pressure was raised to approximately 100 psig with nitrogen and then evacuated. This procedure for removing trace oxygen was repeated two more times, leaving the reactor in vacuum.

[0095] The reactor pressure was raised to approximately 30 psig with tetrafluoroethylene (TFE) and vented to atmospheric pressure three times to substantially remove nitrogen. Agitation was commenced and the reactor content was heated to 50°C. Reactor pressure was raised to 390 psig by adding TFE. Once at a pressure of 390 psig, 250 g of an acid solution containing 1 .5 g of succinic acid and 0.12 g of oxalic acid was added to the reactor. 55 mL of initiator solution was rapidly added to the reactor and then a continuous initiator feed of 0.35 mL / min was commenced. TFE was fed to the reactor at a rate sufficient to maintain reactor pressure at 400 psig. After 750 g of TFE had been fed since introduction of initiator, AGE solution was continuously added at a rate of 2 mL / min and initiator flow rate was increased to 0.75 mL / min. After a total of 50 mL of AGE solution had been fed TFE, initiator solution and AGE solution flow were stopped, agitation was ceased, and the reactor was vented to atmospheric pressure. Total TFE added to the reactor after commencement of polymerization was 1011 g and resulting polymer produced measured 1100 g. Melting point and heat of fusion on first heat as measured by DSC was 343°C and 76 J / g, respectively. On second heat, melting point and heat of fusion was 325.8°C and 35 J / g, respectively. The FTIR spectra of a cold pressed film showed clear evidence of AGE. Concentration of AGE based on the total weight of the core-shell particle was estimated to be 0.3 to 0.4 wt%, which corresponds to 1.2 wt% to 1 .3 wt% in the particle shell.Example 2A - Synthesis of TFE-based Copolymer Using Hydroxy Butyl Vinyl Ether

[0096] To synthesize a polymer composition having a core-shell structure with a PTFE core and a f ibri llizable copolymer shell, the fibrillizable copolymer shell derived from TFE and hydroxy butyl vinyl ether, the procedure of Example 1 was essentiallyAttorney Docket No. FP0001-W001 followed but the AGE solution was replaced with a solution of 20 g of KOH stabilized hydroxy butyl vinyl ether (HBVE) (CAS: 17832-28-9) raised to 100 mL with Vertrel™ XF (1 ,1 ,1 ,2,2,3,4,5,5,5-decafluoropentane; CAS 138495-42-8). HBVE is also known as tetramethylene glycol monovinyl ether. The HBVE solution was fed at 1 .0 mL / min until a total of 25 mL had been fed. Total TFE added to the reactor after commencement of polymerization was 1088 g and resulting polymer produced measured 1181 g. Melting point and heat of fusion on first heat as measured by DSC was 342°C and 75.5 J / g, respectively. On second heat, melting point and heat of fusion was 326.2°C and 36.7 J / g, respectively. The FTIR spectra of a cold pressed film showed clear evidence of HBVE. Concentration and distribution of HBVE was estimated to be similar to AGE concentrations in Example 1.Example 2B - Synthesis of TFE-based Copolymer - TFE / EVE-OH

[0097] Briefly, an initiator solution consisting of 5.0 g of 70 wt% active disuccinic acid peroxide, 0.25 g of ammonium persulfate and 2.0 g of succinic acid raised to 400 g with deionized, deaerated water was prepared. An 11 ,7-liter horizontal reactor was purged with nitrogen and then evacuated. 5300 mL of deionized, deaerated water was charged to the reactor. A surfactant solution consisting of 10.0 g of GX905D surfactant (perfluorinated ether carboxylate salt manufactured by The Chemours Company) raised to 500 g with deionized, deaerated water was added to the reactor. Reactor pressure was raised to approximately 30 psig (-207 kPa) with nitrogen and then evacuated. This procedure for further removing trace oxygen was repeated two more times, leaving the reactor in vacuum. The reactor pressure was raised to approximately 30 psig (-207 kPa) with tetrafluoroethylene (TFE) and vented to atmospheric pressure 3 times to substantially remove nitrogen. Agitation was commenced at 70 rpm and the reactor content was heated to 70°C. TFE flow was set to 1500 g / hr and reactor pressure was raised to 390 psig (-2.67 MPa) by adding 693 g of TFE. Once at a pressure of 390 psig, 100 mL of initiator solution was rapidly added to the reactor and then 10 g of EVE-OH monomer (e.g., Example 2 of U.S. Patent 5,093,446 to Hung) was charged to the reactor by pumping from a burette into a water filled feed line of approximately 70 mL volume and then flushing the EVE-OH to the reactor by pumping an additional 100 mL of water from the burette. TFE monomer was fed to the reactor at a rate sufficient to maintain reactor pressure at 400 psig (-2.76 MPa). After 1000 g of TFE has been fed sinceAttorney Docket No. FP0001-W001 introduction of initiator, TFE flow was stopped, agitation was ceased, and reactor was vented to atmospheric pressure. The resulting reactor contents consisted of60.5 g of undispersed polymer and 7145.6 g of fluoropolymer dispersion containing 13.98 wt% polymer with a raw dispersion particle size, Dso as measured by laser light scattering using a Malvern Zetasizer, of 178 nm. Total polymer produced was1059.5 g. Analysis by Differential Scanning Calorimeter (DSC) showed a melting peak on first heat of 344.1 °C with a heat of fusion of 74.9 J / g. Melting point on second heat was 325.1 °C with a heat of fusion of 33 J / g. Fourier Transform Infrared Spectroscopy (FTIR) analysis showed the unmistakable presence of EVE-OH. Analysis by F19NMR measured EVE-OH content in the polymer particle was 0.64 wt% based on the total weight of the core-shell particle.Comparative Example 1 - Synthesis of Homopolymer PTFE

[0098] As a control, homopolymer PTFE (Comparative Example 1) was also synthesized. The procedure of Example 1 was followed except no comonomer was added to the reactor. Total TFE added to the reactor after commencement of polymerization was 1000 g. The resulting polymer weighed 1108 g. Melting point and heat of fusion on first heat, as measured by DSC, was 342.5°C and 76.4 J / g, respectively. On second heat, melting point and heat ef fusion was 326.3°C and 36.7 J / g, respectively.Preparation of Anode Electrodes (Examples 3 and 4; Comparative Example 2)

[0099] Anode electrodes were prepared using each of the three polymers. To manufacture the electrodes, graphite and SUPER P® carbon black (Imerys S.A., Paris, France) were combined in a mortar and pestle and mixed. The resulting mixture was combined with each polymer and rolled for 30 minutes to obtain a powder having a composition of 97 wt% graphite, 2 wt% SUPER P® carbon black, and 1 wt% of the polymer.

[0100] A free-standing film was created by manually grinding 3-5 g of the powder until the powder formed solid flakes. The flakes were placed onto a hot plate and heated to 100°C. The flakes were rolled at 100°C until a uniform film was formed. A calendering machine was pre-heated to 90°C and set with an initial calendering gap matching the initial film thickness. The film was repeatedly rolled through the rolls and the calendering gap was repeatedly reduced (e.g., in 50 pm increments) until aAttorney Docket No. FP0001-W001 final film thickness of 100-110 m was reached. “Film,” as used herein, refers both to a free-standing electrode film and to an electrode film after lamination onto a current collector. The rolling processes act to fibrillate the polymer of the binder to hold the electrode together. In some implementations, the electrode films described herein have a weight percentage of the binder in a range from 0.2% to 10%.

[0101] For strain-related measurements, the free-standing films were cut into 15 x 6 mm sections, and the sections were analyzed in tension (in a pure tensile mode) using an MTEST® quattro (Admet, Inc., Norwood, MA) electromechanical testing machine. In the measurements, strain was applied to the films’ long dimension at a rate of 10% per minute until break. Young’s modulus was measured using the first 1 % of strain. Measurements were repeated five times using different sections to obtain mean values and standard deviations, as shown in Tablel . In Table 1 , “Example 3” refers to the electrode formed using Example 1 (TFE and allyl glycidyl ether), “Example 4” refers to the electrode formed using Example 2 (TFE and hydroxy butyl vinyl ether), and “Comparative Example 2” refers to the electrode formed using Comparative Example 1 (homopolymer PTFE).Table 1

[0102] Peel strength tests were performed using an MTEST® quattro (Admet, Inc., Norwood, MA) electromechanical testing machine. Strips of the free-standing films were prepared and laminated to a carbon-coated copper current collector (copper foil) under a vertically translating mechanical clamp. Duct tape (0.5"x2") (-1.27 cm x -5.08 cm) was pressed onto the upper surface of the films (opposite the side laminated to the copper foil) using a 5 lb. (-2.27 kg) roller 3 times. A portion of the duct tape was detached to be clamped onto the clamp, which was vertically hangingAttorney Docket No. FP0001-W001 from a 5 lb. (-2.27 kg) load cell. The clamped tape was then subjected to a vertical pull at a rate of 2 inches (-5.08 cm) per minute, so as to be slowly peeled away from the copper foil. The peel strength value was computed by dividing the average load by the width of the sample. The samples were pulled for at least 2.25 inches (-5.72 cm) (in a process sometimes referred to as a “90° peel test”), and the measurements for the first 0.25 inches (-0.64 cm) of pulling were discarded. Measurements were repeated three times using different sections to obtain mean values and measurement standard deviations, as shown in Table 2.

[0103] Cohesive failure (failure inside the electrode film) was eventually observed for each sample, rather than de-bonding between the electrode film and the current collector. This demonstrates an improvement in cohesive strength provided by the use of the co-monomer.Table 2

[0104] As illustrated by the examples of Tables 1-2, in some implementations, electrode films including binders having the fibril lizable copolymers discussed herein can have a Young’s modulus of at least 0.04 MPa. In some implementations, the electrode films can have a Young’s modulus of at least 0.08 MPa, at least 0.1 MPa, at least 0.15 MPa, at least 0.2 MPa, at least 0.3 MPa, at least 0.5 MPa, or at least 1.0 MPa. In some implementations, the Young’s modulus is 2.0 MPa or less. In some implementations, the electrode films can have a Young’s modulus at least double a Young’s modulus of a similar electrode film manufactured using the corresponding homopolymer instead of the copolymer. In some implementations, the electrode films can have a UTS of at least 0.10 MPa or at least 0.14 MPa. In some implementations, the UTS can be at least 0.5 MPa, at least 0.7 MPa, at least 0.9 MPa, at least 1 .0 MPa, at least 1 .25 MPa, at least 1 .5 MPa, or at least 2.0 MPa. In some implementations, the UTS is 5 MPa or less. In some implementations, theAttorney Docket No. FP0001-W001 electrode films can have a strain at break of at least 17%, at least 20%, at least 25%, or at least 28%. In some implementations, the strain at break is at least 30%, at least 35%, or at least 40%. In some implementations, the strain at break is 50% or less. In some implementations, the electrode films can have a peel force, measured as described above, of at least 0.30 N / cm, e.g., in a range from 0.1 or 0.3 to 0.4 N / cm or in a range from 0.1 or 0.3 to 0.5 N / cm. In some implementations, the electrode films have a thickness in a range from 25 pm to 300 pm.

[0105] The foregoing and / or other mechanical values can provide advantages for both processing / manufacturing and device operation. For example, these values can reduce occurrence of faults during manufacturing (e.g., electrode cohesive failure and / or electrode detachment). These values can also allow for a broader space of device designs, e.g., permitting the manufacture of devices in which current collectors lack an adhesive coating. As noted above, the adhesive coating may increase costs and / or manufacturing complexity / time compared to the use of uncoated current collectors. Moreover, in some implementations, the foregoing values can provide a long-term electrochemical cycling stability advantage due to improved mechanical durability.Preparation of Co-coagulated Polymers as Binders

[0106] According to some implementations of the present disclosure, an electrode binder (e.g., a binder of electrodes 104 and / or 108 in FIG. 1) includes a fibrillizable fluoropolymer co-coagulated with at least one polymer having at least one polar pendant group comprising oxygen. In one embodiment, the polymer having at least one polar pendant group comprising oxygen is a fibrillizable TFE-based copolymer comprising said polar pendant group comprising oxygen as described above under “Fibrillizable Binders Comprising TFE-Based Copolymers Having a Polar Pendant Group”, an ionomer or a combination thereof. In one embodiment, the polymer having at least one polar pendant group comprising oxygen is an ionomer. The polymer having at least one polar pendant group comprising oxygen can interact with other elements of the electrode, the current collector on which the electrode is disposed, and / or with itself within the binder, to improve mechanical properties such as strength, cohesion, peel strength, and / or elasticity.Atorney Docket No. FP0001-W001

[0107] The co-coagulated polymers described here can be provided in binders with or without the fibril lizable copolymers discussed above. For example, in some implementations, a fibrillizable copolymer as discussed above (derived from a comonomer with a pendant group having the target characteristic, such as derived from TFE and a comonomer with a pendant group having the target characteristic) is itself the polymer that, as discussed in this section, is co-coagulated with an ionomer. As another example, a binder can include (i) a first polymer component that is a fibrillizable copolymer as discussed above and, separately, (ii) a second polymer component that includes a polymer which is not derived from a comonomer having a pendant group having the target characteristic, where the second polymer component is co-coagulated with an ionomer. And, in some implementations, the binder includes a fibrillizable polymer co-coagulated with an ionomer, without the binder including a copolymer derived from a comonomer having a pendant group having the target characteristic.

[0108] The fibrillizable polymer can be any of the fibrillizable polymers discussed in the foregoing section, for example, can be a TFE-based polymer, such as homopolymer PTFE or a modified PTFE as describe above.

[0109] In some implementations, the ionomer is a polymer with one or more side chains terminating in (as an end group), or having as a pendant group, a sulfonate group (e.g., sulfonic acid / a sulfonic acid group), a carboxyl group (e.g., carboxylic acid / a carboxylic acid group), a phosphate or phosphonate group (e.g., phosphoric acid / a phosphoric acid group, or phosphonic acid / a phosphonic acid group), a phosphinate group (e.g., phosphinic acid, a phosphinic acid group), or an end group or pendant group containing any of the foregoing groups. As used herein, a reference to a group includes the acidic form of the group except where noted otherwise, e.g., “sulfonate group” includes the case of a sulfonic acid group terminating in H. The foregoing groups include the acid form and all possible salts, including mono and divalent cation salts, e.g., including Li+, Na+, K+, and Mg2+. Moreover, the groups can be partially or fully neutralized without departing from the meaning of this disclosure. The side chains can be linear or branched.

[0110] For example, in some implementations, the ionomer is a perfluoro sulfonic acid ionomer (PFSA) such as NAFION™. The PFSAs can include a PTFE backboneAttorney Docket No. FP0001-W001 and perfluorinated vinyl ether sidechains terminated with sulfonate groups (SO3-) and a counterion, such as a proton (H+), to form a terminating sulfonic acid group (SO3H). It has been observed that, in some cases, the improvement in mechanical properties provided by the inclusion of the co-coagulated ionomers is larger when the ionomer (e.g., the PFSA) is in a hydrolyzed form, e.g., either in the acidic form or with a counter cation such as lithium. FIG. 2A illustrates an example of NAFION™, where R is H in the acidic form (to provide a sulfonic acid group), or R can be a counter cation such as Li, Na, or K (to provide a sulfonate group). In one aspect of FIG. 2A, n=1 to 10 and m=1 to 10; preferably where n=7 and m=1 . In one embodiment, the PFSA has an equivalent weight ranging from 700 g / mol to 1500 g / mol.

[0111] As another example, in some implementations, the ionomer is a copolymer of ethylene and at least one of methacrylic acid or acrylic acid. For example, one such suitable copolymer / ionomer is SLIRLYN™ (an ethylene-methacrylic acid copolymer), shown in FIG. 2B below. R is H in the acidic form (to provide a carboxylic acid group), or R can be a neutralizing counter cation such as Li, Na, Zn, or K (to provide a carboxylate group). In one embodiment of FIG. 2B, n=1 to 10 and m= 1 to 10.

[0112] It will be understood that, in some implementations, the ionomer is a TFE- based copolymer, e.g., when the ionomer is a PFSA polymer. In some implementations, the ionomer can be a TFE-based copolymer as discussed above in the “Fibri llizable Binders Comprising TFE-Based Copolymers Having a Polar Pendant Group” section, e.g., derived from TFE and a comonomer having a target characteristic as discussed above.

[0113] As described for the copolymers above, it will be understood that in some implementations multiple ionomers are present in the co-coagulate. The multiple ionomers can have the same or different end groups / pendant groups, e.g., the groups discussed above. In addition, or instead, a single ionomer can have two or more such end groups / pendant groups. Any combination of the groups disclosed herein can be contributed to the co-coagulate by any number of the ionomers disclosed herein. References to “an” ionomer, “a” side chain, or “an” end / pendantAttorney Docket No. FP0001-W001 group do not exclude the possible presence of other ionomers, side chains, and / or end / pendant groups.

[0114] The fibrillizable polymer and the ionomer are co-coagulated with one another. In a co-coagulation process, dispersions of the polymer and the ionomer are formed. The dispersions are combined into a solution, and the solution is stirred. Coagulation of aqueous dispersions of TFE polymer primary particles to form agglomerates can be performed, for example, as described in U.S. Patent No. 7,947,775, the entirety of which is incorporated herein by reference. To form the cocoagulated compositions discussed herein, these methods can be utilized to coagulate an aqueous dispersion of a fibrillizable first polymer in the presence of a second polymer comprising said pendant polar group comprising oxygen..

[0115] For example, in some implementations, the second polymer is in the form of an aqueous dispersion capable of being coagulated, and the aqueous dispersions of the first and second polymers are combined and mixed. Instead of or in addition to aqueous dispersion forms, any other suitable suspended fine particulate form can be used. The resulting mixture of the first and second polymer aqueous dispersions is then co-coagulated. The co-coagulation can be conducted by known processes, such as by vigorously agitating and / or stirring the mixture, optionally supplemented by addition of electrolyte or surfactant and / or water-immiscible solvent having low surface tension, and / or by freeze-thaw procedures. In some implementations, the co- coagulation includes diluting the mixture of the aqueous dispersions to a polymer concentration of about 10 to about 20 weight percent and optionally adjusting the pH to neutral or basic. In some implementations, a coagulating agent such as a water- soluble organic compound, an inorganic salt, or acid is included in the mixture. Coagulation can be helped by adding a water-soluble organic compound (e.g., methanol or acetone), an inorganic salt (e.g., potassium nitrate or ammonium carbonate), and / or an inorganic acid (e.g., hydrochloric acid, sulfuric acid, or nitric acid) as a coagulating agent.

[0116] The vigorous agitation and / or stirring causes co-coagulation of the polymer and the ionomer, which “crash out” in the form of a powder including the polymer and the ionomer co-coagulated with one another. Crashing out can be spontaneous or aided, e.g., by freezing to initiate precipitation. The powder, which includes coAttorney Docket No. FP0001-W001 coagulated agglomerates, can be separated from the aqueous phase by conventional techniques, such as skimming and / or filtration. Drying of the agglomerates can be conducted by vacuum, high frequency, and / or heated air, such that the wet powder is not excessively fluidized. Excessive friction or contact between the particles, especially at a high temperature, may adversely affect the agglomerates due to fibrillation and resulting loss of particulate structure leading to potentially poorer properties of electrode compositions and films made from the agglomerates. In some implementations, the powder is dried at drying temperature(s) in a range from 100°C to 180°C.

[0117] The resulting structure has the fibrillizable TFE-containing polymer and at least one polymer containing at least one polar pendant group comprising oxygen physically intermixed with one another on the micron or submicron scale with respect to at least one of the polymer components. As used herein, the “average domain size” of a polymer, that is the TFE containing polymer or the polymer containing a polar pendant group comprising oxygen, as used herein is defined as the average agglomerate diameter of contiguous polymer particles of the same composition. The average domain size can be measured by scanning electron microscopy (SEM) and can also include elemental areal mapping of the powder by techniques, for instance, such as EDX (Energy-Dispersive X-ray analysis). In this analysis, typically at least three scanning electron micrograph images are examined by visual inspection.

[0118] The average domain size / diameter of at least one of the polymer components is 10 pm or less, 1 pm or less, 500 nm or less, or 100 nm or less. The average domain size / diameter can be at least 1 nm or at least 10 nm. This cocoagulated structure and its properties differ from a simple mechanically blended mixture of the fibrillizable tetrafluoroethylene (TFE)-based polymer (the first polymer) and the at least one polymer containing at least one polar pendant group comprising oxygen (the second polymer). In one embodiment the polymer containing at least one polar pendant group comprising oxygen is a fibrillizable TFE-based copolymer as described herein, an ionomer (e.g. NAFION™) or a combination thereof, e.g., an agglomerate comprising a mixture of the first and second polymers.. In the latter case, the mixture includes large domains of the first or second polymer, large particle sizes, agglomerations of the first polymer or second polymer, etc. This microstructure has not been observed to provide the mechanical improvementsAttorney Docket No. FP0001-W001 discussed herein. By contrast, the co-coagulated structure is a homogenous or substantially homogenous mixture with the micron or submicron domain sizes of at least one polymer composition as noted above.

[0119] The foregoing small domain sizes, and the extremely close physical intermixing associated therewith, permit chemical interactions between the first polymer (e.g. the f ibril lizable TFE-based polymer) and the second polymer (e.g. the ionomer and / or the fibrillizable TFE-based copolymer comprising said polar pendant group comprising oxygen) and other components (e.g., the active component, conductive additive, and / or current collector) to translate into effectively improved binding between the fibrillized binder and the other components, providing improvements in modulus, tensile strength, peel strength, etc.

[0120] For example, in some implementations, the end group of the ionomer (e.g., a sulfonate group, carboxyl group, phosphonate group, phosphinate group, or other group disclosed herein) interacts chemically (e.g., ionically or covalently) with an oxide of the current collector (e.g., copper oxide in the case of a Cu current collector in the anode, or aluminum oxide in the case of an Al current collector in the cathode), improving adhesion between the electrode film and the current collector. The same end group-current collector interaction can occur in the case of the fibrillizable copolymers discussed earlier in this disclosure. The oxide can be a native oxide or an oxide arising from a treatment, e.g., a chemical treatment of the metal of the current collector.

[0121] The current collector can be primed, e.g., with carbon. The primer is a thin layer on the current collector. In some implementations, without being bound to theory, the functional groups on the ionomers can interact with the surface of the primed current collector (e.g., with the primer), for example, a binding interaction that attaches the binder to the primer.

[0122] In addition, or alternatively, as discussed with respect to fibrillizable binder compositions comprising the fibrillizable copolymers, in some implementations, the end group of the ionomer interacts ionically (e.g., in an ionic or covalent bond bond) with the active component of the electrode and / or the conductive additive of the electrode, improving the Young’s modulus and / or tensile strength of the electrode film. For example, the ionomer can interact with a transition metal oxide that is theAttorney Docket No. FP0001-W001 active component of the electrode and / or with a conductive carbon additive of the electrode.Examples 5-7 and Comparative Examples 3-5: Co-coagulated Binders for Anodes

[0123] Binders were synthesized by co-coagulating a fibrillizable polymer (a TFE- based polymer or TFE-based copolymer having at least one polar pendant group comprising oxygen) co-coagulated with NAFION™. As shown in Table 3 below, for two samples, the fibrillizable polymer was PTFE. For one sample, the fibrillizable polymer was a fibrillizable copolymer of TFE and EVE-OH, of the kind discussed above. In addition, as a control sample, a PTFE-only binder was synthesized.

[0124] Herein, “PTFE1” refers to modified tetrafluoroethylene polymer, containing 0.128 wt% of copolymerized PPVE (perfluoro(propyl vinyl ether)) as modifier, having a melt creep viscosity of 1 .47 x 1010poise (1 .47 x 109Pa S), manufactured by The Chemours Company FC, LLC, Wilmington, DE (Teflon™ PTFE 62 X) “PTFE2” refers to tetrafluoroethylene homopolymer having a melt creep viscosity of 4.0 x 1011poise (4.0 x 101° Pa S) manufactured by The Chemours Company FC, LLC, Wilmington, DE (Teflon™ PTFE 601 X).

[0125] Co-coagulation was performed according to the process 300 shown in FIG.3. In the process 300, a dispersion of the fibrillizable polymer and the ionomer was prepared (302). Relative proportions of the fibrillizable polymer and ionomer are shown in Table 3. Water was added to the dispersion to achieve 14% of solids in a solution. In some implementations, the dispersion includes between 10% and 20% of solids of the polymer and the ionomer.

[0126] The solution was mixed (304), to co-coagulate the fibrillizable polymer and the ionomer. In the case of the examples of Table 6, the solution was stirred at 500 rpm, to generate a powder composed of the co-coagulated fibrillizable polymer and ionomer. The solution was stirred for an additional four minutes after generation of the powder. The powder was filtered and rinsed three times in deionized water. The powder, which had a composition as shown in Table 3, was dried at 85 - 95°C under vacuum. Bulk composition of the resulting polymer is measured by solid state19FAttorney Docket No. FP0001-W001MAS NMR. These powder compositions are also applicable to relative proportions of the polymer and the ionomer in electrode films using the powder as a binder.Table 3

[0127] The binder powder was mixed with the electrode active component and, optionally, a conductive additive (FIG. 3, 306). In the case of the samples of Table 3, the mixed composition was 90 wt% graphite, 5 wt% SUPER P® carbon black, and 5 wt% of the binder. In some implementations, the electrode films described herein have a weight percentage of the binder in a range from 0.2% to 10%. The mixed composition was rolled using cylindrical pellets for about 30 minutes, and the resulting powder was then separated from its milling media.

[0128] The mixture was formed into a film (FIG. 3, 308). In the case of the samples of Table 3, a free-standing film was created by grinding 3 g of the powder until the powder formed solid flakes. The flakes were placed onto a hot plate, heated to 100°C, and rolled at 100°C until a uniform film was formed.

[0129] The film was calendered (FIG. 3, 310), thinning the film and fibrillating the fibrillizable polymer in the binder to bind the film together. In the case of the samples of Table 3, the rolls of a calendering machine were pre-heated to 50°C, and theAttorney Docket No. FP0001-W001 calendering gap was set to 50-100 pm below the initial thickness of the film. The film was repeatedly rolled through the rolls and the calendering gap was repeatedly reduced (e.g., in 50 pm increments) until a final film thickness of 70-80 pm was achieved for the free-standing film (an electrode film).

[0130] To prepare an electrode / current collector structure, the electrode film can be laminated onto a current collector (FIG. 3, 312), e.g., a copper foil or aluminum foil.

[0131] In addition to the co-coagulated samples and the control sample, Comparative Examples 4 and 5 were fabricated using a physical blend of PTFE and NAFION™, to illustrate the difference in products produced by co-coagulation compared to physical blending. For Comparative Examples 4 and 5, separate PTFE powder and NAFION™ powder were mixed with the graphite and carbon black, rather than using a single powder obtained by co-coagulation. The process was otherwise identical to that described with respect to FIG. 3.

[0132] For strain-related measurements, the free-standing films were cut into 15x6 mm sections, and the sections were analyzed in tension (in a pure tensile mode) using a mechanical analyzer. In the measurements, strain was applied to the films’ long dimension at a rate of 10% per minute until break. Young’s modulus was measured using the first 1% of strain. Results are shown in Table 4.Table 4Atorney Docket No. FP0001-W001

[0133] As shown in Table 4 and FIG. 4, Examples 5-7, which include a binder having co-coagulated PTFE and NAFION™, have significantly higher ultimate tensile strength (UTS) than do Comparative Examples 4-5, in which PTFE and NAFION™ are combined as a physical blend rather than being co-coagulated. The improvement represents at least a 50% increase in UTS. Examples 6-7 achieve a significantly higher strain at break than the control films (an improvement of about 50% to about 100%), and each of Examples 5-7 has a higher strain at UTS than the control films.

[0134] In addition, Example 7, in which a copolymer derived from a co-monomer having a pendant group (see Example 2B) having the target characteristic is cocoagulated with NAFION™, exhibits a very high UTS in excess of 0.9 MPa, representing at least a 150% increase compared to Comparative Examples 4-5. Example 7also exhibits a significantly higher Young’s modulus than the control samples, representing about a 100% increase.

[0135] In some implementations, based at least on the foregoing results, an electrode film (e.g., in which a fibrillizable polymer is co-coagulated with an ionomer) has a Young’s modulus of at least 0.2 MPa, at least 0.3 MPa, at least 0.4 MPa, or at least 0.5 MPa. The Young’s modulus can be 2.0 MPa or less.

[0136] In some implementations, based at least on the foregoing results, an electrode film (e.g., in which a fibrillizable polymer is co-coagulated with an ionomer) has a UTS of at least 0.5 MPa, at least 0.7 MPa, at least 0.9 MPa, at least 1 .0 MPa, at least 1 .25 MPa, at least 1.5 MPa, or at least 2.0 MPa. The UTS can be 5 MPa or less.

[0137] In some implementations, based at least on the foregoing results, an electrode film (e.g., in which a fibrillizable polymer is co-coagulated with an ionomer) has a strain at break of at least 12%, at least 15%, at least 18%, at least 20%, or at least 25%. The strain at break can be 30% or less or 50% or less.

[0138] In some implementations, based at least on the foregoing results, an electrode film (e.g., in which a fibrillizable polymer is co-coagulated with an ionomer) has a strain at UTS of at least 6%, at least 7%, at least 8%, at least 10%, at least 12%, or at least 14%. The strain at UTS can be 25% or less.Attorney Docket No. FP0001-W001

[0139] In some implementations, the electrode films have a thickness in a range from 25 pm to 300 pm.

[0140] Peel properties of the electrode films were also investigated. Measurements were performed as discussed above in reference to Table 2, using a 90° peel test. Cohesive failure (failure inside the electrode film) was eventually observed for each sample at the indicated forces, rather than de-bonding between the electrode film and the current collector. Measurement results are shown below in Table 5.Table 5

[0141] In some implementations, an electrode film including a co-coagulated polymer composition with an ionomer, as described herein, has a peel force of at least 0.3 N / cm, at least 0.4 N / cm. For example, the peel force can be in a range from 0.1 or 0.3 N / cm to 0.5 N / cm or in a range from 0.4 N / cm to 0.5 N / cm. The relatively high peel force can, for example, result from beneficial interaction (s) between the ionomer and other component(s).

[0142] Electrochemical performance was also measured. The electrode films, laminated onto carbon-coated copper current collectors, were integrated into a halfcell structure in EC / DEC (3 / 7) + 5% FEC 1.2 M LiPFe electrolyte. As shown in FIG. 5, Example 5 has improved cycling performance compared to Comparative Example 3, for example, exhibiting reduced falloff in specific capacity for cycle numbers above 30.Atorney Docket No. FP0001-W001Examples 11-12: Cocoaqulation with SURLYN™ as Binder Ionomer and Preparation of Electrode Film

[0143] Further samples were manufactured using SURLYN™ as the binder ionomer, as shown below in Table 6.Table 6

[0144] Co-coagulation was performed according to the process 300 shown in FIG.3. In the process 300, a dispersion of the PTFE1 polymer and the SURLYN™ (ADCOTE™ 37-220, Dow Chemical Company) was mixed (302) by 98 / 2 solid weight. Water was added to the dispersion to achieve 14% of solids in a solution and coagulant of (NH4)2COs was added. The solution was stirred at 500 rpm to generate a powder composed of the co-coagulated polymer and ionomer. The solution was stirred for an additional four minutes after generation of the powder. The powder was filtered and rinsed three times in deionized water. The powder, which had a composition as shown in Table 6, was dried at 120°C. Bulk composition of the resulting polymer is measured by solid state19F MAS NMR.

[0145] In some implementations, of the TFE-based polymer and the ionomer in the dispersion, a proportion of the ionomer is in a range from 0.2 wt% to 10 wt% or from 0.1 wt% to 10 wt%, proportions that can result in efficient co-coagulation and target mechanical effects from inclusion of the ionomer.

[0146] The binder powder was mixed with an electrode active component and a conductive additive (506). In the case of the examples of Table 6, the mixed composition was 97.5 wt% graphite, 1 wt% SUPER P® carbon black, and 1.5 wt% of the binder.

[0147] The mixture was formed into a film (508). In the case of the examples of Table 6, the electrode mixture was first prepared by blending 50g of powder in a highAttorney Docket No. FP0001-W001 speed blender at 28000 rpm for 3 minutes. A free-standing film was created by adding 5 grams of electrode powder into a calender machine with 50% slip at 100°C, an 80pm gap, and a 3 m / min rolling speed.

[0148] To prepare an electrode / current collector structure, the electrode film was laminated onto a carbon coated copper foil.

[0149] Peeling strength of the electrode films were investigated. Measurements were performed as discussed above in reference to Table 2. Cohesive failure (failure inside the electrode film) was eventually observed for each sample at the indicated forces, rather than de-bonding between the electrode film and the current collector. Measurement results are shown below in Table 7. As shown in Table 7, the electrode film fabricated using SURLYN™ (Example 12, using the Example 11 binder) shows much higher peel force than the electrode film (Comparative Example 6) fabricated with the Comparative Example 3 binder.Table 7Examples 8-10 and Comparative Example 7: Co-coagulated Binders for Cathodes

[0150] Electrode films for use as cathode electrodes, such as the cathode electrode 108 of FIG. 1 , were also fabricated. The electrode composition was LiNio.6Mno2Coo.2O2 (NMC622) / SUPER P® / binder (95 / 3 / 2 wt%), where NMC622 is the active component and SUPER P® is the conductive additive.

[0151] It was observed that an NMC cathode film made with the Example 5 binder more easily formed a film compared to a cathode film made with the Comparative Example 3, which was more brittle, needed more folding to form an initial film, and tended to split during calendering.Atorney Docket No. FP0001-W001

[0152] Further, PTFE2 was co-coagulated with NAFION™ 920EW, in one example with an LiOH co-coagulant. The presence of LiOH in the mixture that is cocoagulated (i) can help the NAFION™ agglomerations to crash out and (ii) converts SO3H in the NAFION™ to SO3LL, which can promote the ionic conductivity of the electrode film. Co-coagulation was performed as described with respect to Examples 5-7.

[0153] For Example 10, the NAFION™ dispersion was treated with KOH to convert SO3H to SOsK -. This treatment can improve co-coagulation efficiency and / or promote the ionic conductivity of the electrode film.

[0154] Binder composition is shown in Table 8.Table 8

[0155] As shown Table 8, co-coagulation is more efficient using an LiOH additive or neutralized NAFION™, compared to using NAFION™ in its acidic form, as indicated by the higher ionomer composition in the co-coagulated powder. For example, in some implementations, efficient co-coagulation can be achieved when a wt% of the ionomer in the co-coagulated powder (which is a binder composition) is at least half or at least two-thirds a wt% of the ionomer in the joint dispersion.

[0156] Particle size of the binder powder under pressure was also analyzed. As shown in FIG. 6, Example 8 exhibited smaller average particle size at 60 psi (-414 kPa) pressure than did Examples 9-10 and Comparative Example 7, corresponding to improved friability. Improved friability is associated with better incorporation of binders into electrode films, for example, to improve the uniformity of mixing with lithium iron phosphate (LFP) as a cathode active component.Atorney Docket No. FP0001-W001

[0157] Particular examples have been described. Other examples are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results in some cases. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results, in some cases. In certain implementations, multitasking and parallel processing may be advantageous.

Claims

Atorney Docket No. FP0001-W001CLAIMSWhat is claimed is:

1. A fibril lizable binder composition comprising a TFE-based copolymer derived from tetrafluoroethylene (TFE) and a comonomer, and wherein the comonomer comprises at least one polar pendant group comprising oxygen.

2. The fibrillizable binder composition of claim 1 , wherein the TFE-based copolymer comprises less than 5 wt% and at least 0.01 wt% of copolymerized repeat units of the comonomer; preferably wherein the copolymer comprises less than 2 wt% and at least 0.1 wt% of co-polymerized repeat units of the comonomer.

3. The fibrillizable binder composition of any one of the preceding claims wherein the polar pendant group comprises at least one of a hydroxyl-containing group, a hydroxyalkyl-containing group, a carboxyl-containing group, a phosphate- containing group, a phosphonate-containing group, a phosphinate-containing group, a sulfonate-containing group, a hydroxyaryl-containing group, or an epoxide-containing group.

4. The fibrillizable binder composition of claim 3 wherein the polar pendant group has a salt form, an acid form or a combination thereof; preferably wherein the salt form of the polar pendant group is a lithium salt.

5. The fibrillizable binder composition of any one of the preceding claims, wherein the TFE-based copolymer comprises co-polymerized repeat units selected from the group of: a. CF2=CF(CF2)xORf-R(OH)ywith a hydroxyalkyl group, -CH2OH, or CH(OH)2 at one or more termini, where x is 0 or 1 , y is 1 , 2, or 3, Rfis a fluorinated or perfluorinated alkylene group or a fluorinated or perfluorinatedAtorney Docket No. FP0001-W001 alkylene oxy group, and R is a C1 to 06 hydrocarbyl, an aryl, or a fluoroaryl group;c. R1CR3=CR4-R ~ cycle (C2R5R6R7O); and d. any combination of (a), (b) and (c); wherein R1, R3, R4, R5, R6, R7are independently H, CH3, a C1 to 06 alkyl group optionally substituted with ether linkages or an aryl group, and where R' is optionally present as a 01 to 012 alkylene group, arylene group, an alkylene ether group, an arylene ether group, or a fluorinated version of one of the foregoing groups.

6. The fibrillizable binder composition of claim 5, wherein the TFE-based copolymer comprises co-polymerized repeat units of 3-[1 -[Difluoro[(1 ,2,2- trifluoroethenyl)oxy]methyl]-1 ,2,2,2-tetrafluoroethoxy]-2,2,3,3-tetrafluoro- propanol (EVE-OH), allyl glycidyl ether, 4-hydroxy butyl vinyl ether, or hydrolyzed vinyl acetate.

7. The fibrillizable binder composition of any one of the preceding claims wherein the polar pendant group is configured to interact chemically with at least one of an electrode active component, an electrode conductive additive, a current collector, or a primer layer on the current collector.

8. The fibrillizable binder composition of any one of the preceding claims wherein the TFE-based copolymer comprising a polar pendant group comprising oxygen is at least one layer a core-shell polymer particle.Attorney Docket No. FP0001-W0019. The fibrillizable binder composition of claim 8, wherein the core forms 60 to 85 wt% of the core-shell polymer particle, and wherein the shell forms 15 to 40 wt% of the core-shell polymer particle.

10. A binder for an electrode film comprising the fibrillizable binder composition of any one of the preceding claims.

11. An electrode film for an electrochemical device, the electrode film comprising: an active component; and the binder of claim 10 wherein the binder is partially or fully fibrillated, wherein the electrode film has at least one of: a. a Young’s modulus of at least 0.04 MPa, over a first 1 % of strain, for strain applied to a long dimension; b. a force at which the electrode film fails in a range from 0.1 to 0.5 N / c min when measured in a 90° peel test conducted with a 5 lb. (-2.27 kg) load and a vertical pull rate of 2 inches (-5.08 cm) per minute conducted with the electrode film laminated to a carbon-coated copper current collector; and c. an ultimate tensile strength (UTS) of at least 0.10 MPa; and a strain at break of at least 17%.

12. The electrode film of claim 11 , wherein the active component comprises at least one of graphite, a metal oxide, a lithium alloy, silicon, silicon oxide, a carbonbased material, a phosphorous-based material, or a nanocomposite comprising at least one of antimony or tin.

13. The electrode film of claim 11 or 12, wherein a weight percentage of the binder in the electrode film is in a range from 0.2 wt% to 10 wt%.Attorney Docket No. FP0001-W00114. The electrode film of any one of the preceding claims further comprising a conductive additive.

15. A battery, comprising: an electrolyte; a current collector; and the electrode film of any one of the preceding claims on the current collector and in contact with the electrolyte.

16. The battery of claim 15, wherein the current collector and the electrode film form an anode or a cathode of the battery.

17. A polymer composition for use as a binder in an electrochemical device comprising a co-coagulate of fibrillizable fluoropolymer particles and particles of: a. an ionomer; b. the TFE-based copolymer having at least one polar pendant group having oxygen of any one of claims 1 to 9; c. or a combination of (a) and (b); wherein the ionomer comprises a polymer having a side chain terminating in a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, or a salt form of one of the foregoing groups.

18. The polymer composition of claim 17 wherein the ionomer comprises a perfluoro sulfonic acid (PFSA) polymer having an equivalent weight of 700 to 1500 g / mol; preferably wherein i. the PFSA polymer in a hydrolyzed form; or ii. the PFSA polymer is terminated by an alkali metal sulfonate; or iii. the PFSA polymer is neutralized; orAttorney Docket No. FP0001-W001 iv. any combination thereof.

19. The polymer composition of claim 17, wherein the ionomer comprises a copolymer of ethylene and at least one of methacrylic acid or acrylic acid.

20. The polymer composition of any one of claims 17-20, wherein the ionomer is in a range from 0.5 wt% to 10 wt% of the polymer composition.21 . The polymer composition of any one of the claims 17-20 wherein an average domain size of at least one polymer in the polymer composition is 1 pm or less.

22. An electrode film for an electrochemical device, the electrode film comprising: an active component; and the polymer composition of any one of claims 17 to 21 ; where the fibril lizable binder is partially or fully fi bril lized ; wherein the electrode film has at least one of: a. a Young’s modulus of the electrode film is in a range from 0.1 MPa to 2.0 MPa; b. an ultimate tensile strength of the electrode film is in a range from 0.5 MPa to 5 MPa; c. a strain at break of the electrode film is in a range from 12% to 30%; d. a strain at ultimate tensile strength of the electrode film is in a range from 6% to 25%; and e. a force at which the electrode film fails is in a range from 0.1 to 0.5 N / cm when measured in a 90° peel test conducted with a 5 lb. (-2.27 kg) load and a vertical pull rate of 2 inches (-5.08 cm) per minute conducted with the electrode film laminated to a carbon-coated copper current collector.

23. The electrode film of claim 22, wherein the electrode film has a thickness in a range from 25 pm to 300 pm.Attorney Docket No. FP0001-W00124. The electrode film of claim 22 or 23, wherein the active component comprises at least one of graphite, a metal oxide, a lithium alloy, silicon, a carbon-based material, a phosphorous-based material, or a nanocomposite comprising at least one of antimony or tin.

25. The electrode film of any one of claims 22 to 24 further comprising a conductive additive.

26. A battery comprising an electrolyte; a current collector; and the electrode film of any one of claims 22 to 25 laminated on the current collector and in contact with the electrolyte.

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