Current collectors and energy storage devices

Abstract

In one aspect, a current collector comprises a polymer film, a first metallic layer bonded to the polymer film, and a second metallic layer bonded to the polymer film on a side opposite the first metallic layer. The polymer film has an electroconductive charge and a surface resistivity of 1 megaohm / square or less. The first and second metallic layers each have a thickness of 3 µm or less. The current collector exhibits a half-discharge voltage that is at least 20% lower than that of an untreated battery-grade copper foil, based on a standard lithium-ion battery half-cell test at a temperature of 25 °C and a discharge rate of 2C or higher.

Description

Title of the invention: TITLE

[0001] Current collectors and energy storage devices SCOPE OF DISCLOSURE

[0002] The field of the present invention is that of current collectors and energy storage devices. CONTEXT OF THE DISCLOSURE

[0003] Copper foils are commonly used as anodic current collectors for energy storage devices, such as lithium-ion batteries (LIBs), due to their high electrical conductivity, good chemical stability, and electrochemical stability at low potentials. A cell for a lithium-ion battery will include a positive electrode, a negative electrode, and a separator between the two electrodes. Traditional lithium-ion batteries also contain current collectors generally composed of either foils, meshes, or metallized plastics where the metal is composed of aluminum (for the cathode) and copper (for the anode). The cathodic material is coated onto a cathodic current collector (such as an aluminum foil), and the anodic material is coated onto an anodic current collector (such as a copper foil).The separator between the electrode layers is typically made of a porous plastic, and an ionically conductive organic solvent is used as the electrolyte, saturating the other components and thus providing a mechanism for ion conduction between the anode and cathode. These layers are usually wound together in a box or stacked. The ongoing drive for thinner and lighter devices presents challenges for the continued use of metal foil in these applications.

[0004] Polymer-based current collectors, such as metal-clad laminates, could be used as an alternative to metal foils. Metal-clad laminates, such as copper-clad laminates, are used in electronic devices for a variety of electronic components for flexible circuits, as well as for circuit packaging. Copper-clad laminates based on polyimide films are generally prepared either by lamination for metal thicknesses greater than 5 µm or by spraying for metal thicknesses less than 5 µm. Plating (e.g., electrochemical plating or autocatalytic plating) is an alternative process for producing laminates that has received some attention, but it is not widely used to produce laminates with less than 5 µm of copper thickness.Furthermore, it is generally accepted that the reliability of copper-clad polyimide laminates is . inferior to customer standards for electronic devices, and these laminates would therefore be poor candidates for use as current collectors.

[0005] Metal-clad laminates produced by plating have traditionally had lower thermal reliability compared to metallized platings produced by spraying or laminating copper sheets. The most reliable plated laminates have used autocatalytic nickel seed layers. Adhesion between copper-clad and polyimide films is difficult due to the presence of volatile compounds in the film, degradation of the film surface by the plating chemistry, and the use of film materials that lack functionality for strong chemical bonding to copper, among other factors. DETAILED DESCRIPTION

[0006] In a first aspect, a current collector comprises a polymer film, a first metallic layer bonded to the polymer film, and a second metallic layer bonded to the polymer film on a side opposite the first metallic layer. The polymer film has an electroconductive charge and a surface resistivity of 1 megaohm / square or less. The first and second metallic layers each have a thickness of 3 µm or less. The current collector exhibits a mid-discharge voltage that is at least 20% lower than that of an untreated battery-grade copper foil, based on a standard lithium-ion battery half-cell test at a temperature of 25 °C and a discharge rate of 2C or higher.

[0007] Polymer films bonded to metallic layers can be used to form current collectors for energy storage devices. In one embodiment, polymer compositions useful for polymer films may include polyimides (PI), poly(amide-imides) (PAI), poly(ester-imides), poly(amide-ester-imides), polycarbonates (PC), poly(ethylene naphthalates) (PEN), polystyrenes (PS), poly(methyl methacrylates) (PMMA), poly(ethylene terephthalates) (PET), poly(ethylene terephthalate) glycols (PETG), poly(cyclohexylenedimethylene terephthalate) glycols (PCTG), polyether imides (PEI), polysulfones, polyether sulfones, polyarylsulfones, a polyaryletherketone (PAEK) such as a polyether ether ketone (PEEK) and a polyetherketone ketone (PEKK), and cyclic olefin copolymers.In one embodiment, polymer compositions having an imide group are particularly useful. Polymer compositions having an imide group and containing aromatic monomers are generally very stable thermally, chemically and electrochemically at the low (anodic) and high (cathodic) potentials used in lithium-ion batteries.

[0008] Depending on the context, the term "diamine" used in this document is intended to designate: (i) the unreacted form (i.e., a diamine monomer); (ii) a partially reacted form (i.e., the part or parts of an oligomer or other polymer precursor derived from, or otherwise attributable to, the diamine monomer); or (iii) a fully reacted form (the part or parts of the polymer derived from, or attributable to, the diamine monomer). The diamine may be functionalized by one or more groups, depending on the particular embodiment chosen in implementing the present invention.

[0009] Indeed, the term "diamine" is not intended to be limiting (or interpreted literally) with respect to the number of amine groups in the diamine component. For example, (ii) and (iii) above include polymeric materials that may have two, one, or zero amine groups. Alternatively, the diamine may be functionalized by additional amine groups (in addition to the amine groups at the monomer ends that react with the dianhydride to propagate a polymer chain). Such additional amine groups may be used to crosslink the polymer or to provide other functionality to the polymer.

[0010] Similarly, the term "dianhydride," as used here, is intended to designate the component that reacts with (is complementary to) the diamine and that, in combination, is capable of reacting to form an intermediate (which can then be hardened into a polymer). Depending on the context, "anhydride," as used here, may refer not only to an anhydride group per se, but also to a precursor of an anhydride group, such as: (i) a pair of carboxylic acid groups (which can be converted to an anhydride by dehydration or a similar type of reaction); or (ii) an acid halide ester functionality (e.g., chloride) (or any other functionality already known or developed in the future that is) capable of conversion to an anhydride functionality.

[0011] Depending on the context, "dianhydride" may refer to: (i) the unreacted form (i.e., a dianhydride monomer, whether the anhydride functionality is in true anhydride form or as an anhydride precursor, as indicated in the preceding paragraph); (ii) a partially reacted form (i.e., the part or parts of an oligomer or other precursor or partially reacted polymer composition that reacted from or are attributable to the dianhydride monomer); or (iii) a fully reacted form (the part or parts of the polymer derived from or otherwise attributable to the dianhydride monomer).

[0012] The dianhydride can be functionalized by one or more groups, depending on the particular embodiment chosen in the implementation of the present invention. Indeed, the term "dianhydride" is not intended to be limiting (or interpreted literally) with regard to the number of anhydride groups in the component dianhydride. For example, (i), (ü), and (iii) (in the paragraph above) include organic substances that may have two, one, or zero anhydride groups, depending on whether the anhydride is in a precursor state or a reacted state. Alternatively, the dianhydride component may be functionalized by additional anhydride-like groups (in addition to the anhydride groups that react with the diamine to provide a polymer). These additional anhydride groups may be used to crosslink the polymer or to provide other functionality to the polymer.

[0013] Any of a number of polymer manufacturing processes can be used to prepare polymer films. It would be impossible to discuss or describe all possible manufacturing processes useful in implementing the present invention. It should be noted that the monomer systems of the present invention are capable of providing the advantageous properties described above in various manufacturing processes. The compositions of the present invention can be manufactured in the manner described herein and can be readily manufactured in any of the many (perhaps countless) ways known to those skilled in the art, using any conventional or non-conventional manufacturing technology.

[0014] Although similar or equivalent processes and materials to those described herein may be used in the implementation or testing of the present invention, suitable processes and materials are described herein.

[0015] When a quantity, concentration, or other value or parameter is given in the form of a range, preferred range, or list of preferred upper and lower values, this shall be understood as specifically disclosing all ranges formed from any pair of preferred upper or lower limits or values, regardless of whether the ranges are disclosed separately. Where a range of numerical values ​​is cited in this document, unless otherwise specified, the range is intended to include its endpoints, as well as all integers and fractions contained within the range. The scope of the invention is not intended to be limited to the specific values ​​cited when defining a range.

[0016] To describe certain polymers, it should be understood that applicants sometimes refer to polymers by the monomers used to manufacture them or the quantities of monomers used to manufacture them. Although such a description may not include the specific nomenclature used to describe the final polymer or contain the terminology produced by process, any reference to monomers and quantities should be interpreted as meaning that the polymer is manufactured from those monomers or that quantity of monomers, and the corresponding polymers and their compositions.

[0017] The materials, processes and examples of the invention are given only as examples and, unless otherwise indicated, are not intended to be limiting.

[0018] In this document, the terms “includes,” “comprising,” “includes,” “containing,” “has,” “having,” or any variation thereof are intended to cover non-exclusive inclusion. For example, a method, process, article, or apparatus that includes a list of elements is not necessarily limited solely to those elements but may include other elements not expressly listed or not inherent in that method, process, article, or apparatus. Furthermore, unless expressly stated otherwise, “or” means an inclusive “or” and not an exclusive “or.” For example, a condition A or B is satisfied by any one of the following conditions: A is true (or present) and B is false (or absent), A is false (or absent) and B is true (or present), and A and B are both true (or present).

[0019] Furthermore, the use of "a" or "an" is intended to describe elements and components of the invention. This is done solely for convenience and to give a general meaning to the invention. This description should be interpreted as including one or at least one, and the singular also includes the plural, unless it is obvious that it should be otherwise.

[0020] It is understood that although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and / or sections, these elements, components, regions, layers, and / or sections shall not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, and / or section from another element, component, region, layer, and / or section. Thus, a first element, component, region, layer, and / or section could be called a second element, component, region, layer, and / or section without departing from the teachings of the present invention. Similarly, the terms "top" and "bottom" are relative only to each other. It will be understood that when an element, component, layer, or the like is inverted, what is the "bottom" before being inverted would be the "top" after being inverted, and vice versa.When an element is said to be "on" or "arranged on" another element, this refers to a positioning on or under that part of the object, but does not necessarily mean a positioning on the upper surface of that part of the object relative to a direction of gravity. It may be directly on the other element, or intermediate elements may be present between them. Conversely, when an element is said to be "directly on" or "arranged directly on" another element, there are no intermediate elements present.

[0021] Furthermore, it is also understood that when an element, component, region, layer and / or section is said to be "between" two elements, components, regions, layers and / or sections, they may be the only element, component, region, layer and / or section between the two elements, components, regions, layers and / or sections, or one or more intermediate elements, components, regions, layers and / or sections may also be present. Organic solvents

[0022] The organic solvents useful for the synthesis of polymers of the present invention are preferably capable of dissolving the polymer precursor materials. Such a solvent should also have a relatively low boiling point, for example below 225 °C, so that the polymer can be dried at moderate temperatures (i.e., more convenient and less expensive). A boiling point below 210, 205, 200, 195, 190, or 180 °C is preferred.

[0023] Useful organic solvents include: N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), methyl ethyl ketone (MEK), N,N'-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetramethylurea (TMU), glycol ethyl ether, diethylene glycol diethyl ether, 1,2-dimethoxyethane (monoglyme), diethylene glycol dimethyl ether (diglyme), 1,2-bis-(2-methoxyethoxy)ethane (triglyme), gamma-butyrolactone and bis-(2-methoxyethyl) ether, tetrahydrofuran (THF), ethyl acetate, hydroxyethyl acetate, glycol monoacetate, acetone, and corresponding mixtures. In one embodiment, preferred solvents include N-methylpyrrolidone (NMP) and dimethylacetamide (DMAc). Diamines

[0024] In one embodiment, an aromatic diamine can be used to form a polymer having an imide group. Aromatic diamines may include fluorinated aromatic diamines, such as 2,2'-bis(trifluoromethyl)benzidine (TFMB), 2,2'-bis-(4-aminophenyl)hexafluoropropane, 4,4'-diamino-2,2'-trifluoromethyldiphenyloxide, 3,3'-diamino-5,5'-trifluoromethyldiphenyloxide, 9,9'-bis(4-aminophenyl)fluorene, 4,4'-trifluoromethyl-2,2'-diaminobiphenyl, 4,4'-oxy-bis[2-trifluoromethyl)benzeneamine] (1,2,4-OBABTF), 4,4'-oxy-bis[3-trifluoromethyl)benzeneamine], 4,4'-thiobis[(2-trifluoromethyl)benzeneamine], 4,4'-thiobis[(3-trifluoromethyl)benzeneamine], 4,4'-sulfoxyl-bis[(2-trifluoromethyl)benzeneamine, 4,4'-sulfoxyl-bis[(3-trifluoromethyl)benzeneamine], 4,4'-keto-bis[(2-trifluoromethyl)benzeneamine], l,l-bis[4'-(4"-amino-2"-trifluoromethylphenoxy)phenyl]cyclopentane, l,l-bis[4'-(4"-amino-2"-trifluoromethylphenoxy)phenyl]cyclohexane, 2-trifluoromethyl-4,4'-diaminodiphenyl ether; 1,4-(2'-trifluoromethyl-4',4"-diaminodiphenoxy)benzene, 1,4-bis(4'-aminophenoxy)-2-[(3',5'-ditrifluoromethyl)phenyl]benzene (6F-amine), 1,4-bis[2'-cyano-3'("4-aminophenoxy)phenoxy]-2-[(3',5'-ditrifluoromethyl)phenyl]benzene (6FC-diamine), 3,5-, diamino-4-methyl-2',3',5',6'-tetrafluoro-4'-trifluoromethyldiphenyl oxide, 2,2-bis[4(4-aminophenoxy)phenyl]phthalein-3',5'-bis(trifluoromethyl)anilide (6FADAP) and 3,3',5,5'-tetrafluoro-4,4'-diaminodiphenylmethane (TFDAM).

[0025] Other useful diamines may include 4,4'-diaminobiphenyl, 4,4'-diaminoterphenyl, 4,4'-diaminobenzanilide (DABA), 4,4'-diaminophenylbenzoate, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenylmethane (MDA), 4,4'-diaminodiphenylsulfide, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), 4,4'-diaminodiphenyl ether (ODA), 3,4'-diaminodiphenyl ether, 4,4'-isopropylidenedianiline, 2,2'-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4-aminophenyl-3-aminobenzoate, bis(p-beta-amino-t-butylphenyl)ether, p-bis-2-(2-methyl-4-aminopentyl)benzene. In one embodiment, the diamine is a triamine, such as N,N-bis(4-aminophenyl)-n-butylamine, N,N-bis(4-aminophenyl)methylamine, or N,N-bis(4-aminophenyl)aniline.

[0026] Other useful diamines may include 1,2-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene (RODA), 1,2-bis(3-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1-(4-aminophenoxy)-3-(3-aminophenoxy)benzene, 1,4-bis-(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1-(4-aminophenoxy)-4-(3-aminophenoxy)benzene, 2,2-bis(4-[4-aminophenoxy]phenyl)propane (BAPP), 2,2'-bis(4-phenoxyaniline)isopropylidene.

[0027] Other useful diamines may include p-phenylenediamine (PPD), m-phenylenediamine (MPD), 2,5-dimethyl-l,4-diaminobenzene, 2,5-dimethyl-l,4-phenylenediamine (DPX), 1,4-naphthalenediamine, 1,5-naphthalenediamine, 1,5-diaminonaphthalene, m-xylylenediamine and p-xylylenediamine.

[0028] Other diamines useful for forming polymers having an imide group may include an aliphatic diamine, such as 1,2-diaminoethane, 1,6-diaminohexane (HMD), 1,4-diaminobutane, 1,5-diaminopentane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane (DMD), 1,11-diaminoundecane, 1,12-diaminododecane (DDD), 1,16-hexadecamethylenediamine, 1,3-bis(3-aminopropyl)-tetramethyldisiloxane, trans-1,4-diaminocyclohexane (CHDA), isophoronediamine (IPDA), bicyclo[2.2.2]octane-1,4-diamine and corresponding combinations. Other aliphatic diamines suitable for implementing the invention include those having six to twelve carbon atoms or a combination of longer- and shorter-chain diamines, provided that the polymer's development capacity and flexibility are maintained. Long-chain aliphatic diamines can increase flexibility.

[0029] Other diamines useful for forming a polymer having an imide group may include an alicyclic diamine (which may be fully or partially saturated), such as a cyclobutane diamine (e.g., cis- and tran5-l,3-diaminocyclobutane, 6-amino-3-azaspiro[3,3]heptane, and 3,6-diaminospiro[3,3]heptane), bicyclo[2,2.1]heptane-l,4-diamine, isophoronediamine, and bicyclo[2,2.2]octane-l,4-diamine. Other alicyclic diamines may be cis-1,4-cyclohexanediamine, trans-1,4-cyclohexanediamine, 1,4-bis(aminomethyl)cyclohexane, 4,4'-methylenebis(cyclohexylamine), 4,4'-methylenebis(2-methylcyclohexylamine), bis(aminomethyl)norbornane. Dianhydrides

[0030] In one embodiment, aromatic dianhydrides can be used to form a polymer having an imide group. The dianhydrides can be used in their tetraacid form (or as monoesters, diesters, triesters, or tetraesters of the tetraacid), or as their diester acid halides (chlorides). However, in some embodiments, the dianhydride form may be preferred since it is generally more reactive than the acid or ester.

[0031] Examples of suitable aromatic dianhydrides include 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2-(3',4'-dicarboxyphenyl)-5,6-dicarboxybenzimidazole dianhydride, 2-(3',4'-dicarboxyphenyl)-5,6-dicarboxybenzoxazole dianhydride, 2-(3',4'-dicarboxyphenyl)-5,6-dicarboxybenzothiazole dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,3,3',4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 2,2',3,3'-biphenyltetracarboxylic dianhydride, dianhydride 2,3,3',4'-biphenyltetracarboxylic acid, 4,4'-thiodiphthalic anhydride, bis(3,4-dicarboxyphenyl)s ulfone dianhydride, bis(3,4-dicarboxyphenyl)sulfoxide dianhydride (DSDA), bis(3,4-dicarboxyphenyloxadiazole-1,3,4)-p-phenylene dianhydride, bis(3,4-dicarboxyphenyl)-2,5-oxadiazole-1,3,4-dianhydride, bis(3',4'-dicarboxydiphenyl ether)-2,5-oxadiazole-1,3,4-dianhydride, 4,4'-oxydiphthalic anhydride (ODPA), bis(3,4-dicarboxyphenyl)thioether dianhydride,bisphenol A dianhydride (BPADA), bisphenol S dianhydride, bis-1,3-isobenzofurandione, 1,4-bis(4,4'-oxyphthalic anhydride)benzene, bis(3,4-dicarboxyphenyl)methane dianhydride, perylene-3,4,9,10-tetracarboxylic dianhydride, 1,3-bis-(4,4'-oxydiphthalic anhydride)benzene, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 4,4'-(hexafluoroisopropylene)diphthalic anhydride (6FDA) and 9,9-bis(trifluoromethyl)-2,3,6,7-xanthenetetracarboxylic dianhydride.

[0032] Other useful dianhydrides may include 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 2,3,5,6-bicyclo- [2,2,2]-octene-(7)-2,3,5,6-tetracarboxylic acid, cyclopentadienyltetracarboxylic acid dianhydride, ethylenetetracarboxylic acid dianhydride, pyromellitic acid dianhydride (PMDA), tetrahydrofurantetracarboxylic acid dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, phenanthrene-1,8,9,10-tetracarboxylic acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic acid dianhydride, benzene-1,2,3,4-tetracarboxylic acid dianhydride and dianhydride thiophene-2,3,4,5-tetracarboxylic.

[0033] In one embodiment, the dianhydrides intended to form a polymer comprising an imide group may include alicyclic dianhydrides, such as cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclohexanetetrac carboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), hexahydro-4,8-ethano-1H,3H-benzo[1,2-c:4,5-c']difuran-1,3,5,7-tetrone (BODA), 1,4:2,3-dianhydride 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic (TCA) and meso-butane-1,2,3,4-tetracarboxylic dianhydride.

[0034] In one embodiment, in which the polymer further comprises aromatic amide components, an additional dicarbonyl chloride suitable for forming the polymer may include terephthaloyl chloride (TPCI), isophthaloyl chloride (IPCI), biphenyl dicarbonyl chloride (BPCI), naphthalene dicarbonyl chloride, terphenyl dicarbonyl chloride, 2-fluoro-terephthaloyl chloride and trimellitic anhydride.

[0035] In one embodiment, poly(amide-ester-imides) can be produced from polyols which can react with a carboxylic acid or ester acid halides to generate ester bonds.

[0036] The dihydric alcohol component can be almost any alcoholic diol containing two esterifiable hydroxyl groups. Suitable diol mixtures may also be included. Suitable diols for use in the present invention include, for example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, etc.

[0037] The polyhydric alcohol component can be almost any polyhydric alcohol containing at least three esterifiable hydroxyl groups to provide the advantages of the synthesis process of this invention described above. Mixtures of such polyhydric alcohols can be appropriately used. Suitable polyhydric polyalcohols include, for example, tris(2-hydroxyethyl)isocyanurate, glycerin, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, and mixtures thereof.

[0038] In some cases, suitable diamine and dianhydride monomers contain ester groups. Examples of such monomers include diamines, such as 4-aminophenyl-4-aminobenzoate and 4-amino-3-methylphenyl-4-aminobenzoate, and dianhydrides, such as p-phenylene bis(trimellitate) dianhydride.

[0039] In some cases, useful diamine and dianhydride monomers contain amide groups. Examples of such monomers include diamines, such as 4,4'-diaminobenzamide (DABAN) and dianhydrides, such as N,N'-(2,2'-bis(trifluoromethyl)-[l,r-biphenyl]-4,4'-diyl)bis(l,3-dioxo-l,3-dihydroisobenzofuran-5-carboxamide) and N,N'-(9H-fluoren-9-ylidenedi-4,l-phenylene)bis[l,3-dihydro-l,3-dioxo-5-isobenzofurancarboxamide].

[0040] Higher order copolymers having an imide group may comprise any of the monomers described above. Imidization catalysts

[0041] In one embodiment, an imidization catalyst (sometimes called an "imidization accelerator") can be used as a conversion chemical that can help lower the imidization temperature to form a polymer having an imide group and shorten the imidization time. The poly(amic acid) casting solutions of the present invention comprise both a poly(amic acid) solution and a certain amount of conversion chemicals. The conversion chemicals that prove useful in the present invention include, but are not limited to, (i) one or more dehydrating agents and / or cocatalysts, such as aliphatic acid anhydrides (acetic anhydride, trifluoroacetic anhydride, propionic anhydride, monochloroacetic anhydride, bromadipic anhydride, etc.).(i) and aromatic acid anhydrides; and (ii) one or more imidization catalysts, such as aliphatic tertiary amines (triethylamine, etc.), aromatic tertiary amines (dimethylaniline, N,N-dimethylbenzylamine, etc.), heterocyclic tertiary amines (pyridine, alpha, beta, gamma, picoline, 3,5-lutidine, 3,4-lutidine, isoquinoline, etc.), and guanidines (e.g., tetramethylguanidine). In one embodiment, an imidization catalyst does not include a diazole. Other useful dehydrating agents may include diacetyl oxide, butyryl oxide, benzoyl oxide, 1,3-dichlorohexyl carbodiimide, N,N-dicyclohexylcarbodiimide, benzenesulfonyl chloride, thionyl chloride, and phosphorus pentachloride. In some embodiments, the dehydrating agent may also serve as a catalyst to improve the reaction kinetics for imidization.The anhydride dehydration material is generally used in a slight molar excess of the amount of amide acid groups present in. The poly(amic acid) solution. In one embodiment, the amount of dehydrating agent used is typically about 2.0 to 4.0 moles per formula unit equivalent of poly(amic acid). Generally, a comparable amount of tertiary amine catalyst is used. The ratio of these catalysts and their concentration in the poly(amic acid) solution will influence the imidization kinetics and the film properties. Polymer films may contain imidization catalysts present within the polymer film in amounts ranging from 1 part per billion (ppb) to 1 wt%, from 10 ppb to 0.1 wt%, or from 100 ppb to 0.01 wt%. Electrically conductive charges

[0042] In one embodiment, the electroconductive charges may include metals (such as gold, silver, copper, etc.), conductive mixed metal oxides (such as cuprates, superconducting oxides, indium tin oxide, antimony tin oxide, mixed titanium / tin / zirconium oxides, etc.), organic compounds such as polyaniline, polythiophene, polypyrrole, polyphenylenevinylene, polydialkylfluorenes, carbon black, graphite, graphene, multi-walled and single-walled carbon nanotubes, and other nanotube structures, and carbon nanofibers. In one embodiment, an electroconductive charge may be an inorganic charge, an organic charge, or a mixture thereof.

[0043] In one embodiment, an electrically conductive filler is carbon black. In one embodiment, the electrically conductive filler is selected from the group consisting of acetylene blacks, superabrasive furnace blacks, conductive furnace blacks, conductive channel-type blacks, carbon nanotubes, carbon fibers, fine thermal blacks, and mixtures thereof. For carbon black, oxygen complexes on the surface of the carbon particles act as an electrically insulating layer. Thus, a low volatility content is generally desired for high conductivity. However, the difficulty of dispersing carbon black must also be considered. Surface oxidation improves the deagglomeration and dispersion of carbon black.In some embodiments, when the electroconductive charge is carbon black, the carbon black has a volatile matter content of less than or equal to 1%. Other charges

[0044] In one embodiment, other fillers for a polymer film may include other inorganic and organic fillers not described above for electrically conductive fillers. The inorganic fillers may include thermally conductive fillers, such as metal oxides, inorganic nitrides and metal carbides. In one embodiment, inorganic fillers may include diamond, clay, talc, sepiolite, mica, dicalcium phosphate, metal oxides, including magnetic metal oxides, transparent conductive oxides and smoky metal oxides. In one embodiment, the inorganic fillers may include inorganic oxides, such as silicon, aluminum, zinc and titanium oxides, hollow (porous) silicon oxide, antimony oxide, zirconium oxide, indium tin oxide, antimony tin oxide, mixed titanium / tin / zirconium oxides and binary, ternary, quaternary and higher-order oxides of one or more cations selected from silicon, titanium, aluminum, antimony, zirconium, indium, tin, zinc, niobium and tantalum.In one embodiment, particle composites (e.g., simple or multiple core / shell structures) may be used, in which one oxide encapsulates another oxide within a particle.

[0045] In one embodiment, inorganic fillers may include other ceramic compounds, such as boron nitride, aluminum nitride, ternary or higher-order compounds containing boron, aluminum and nitrogen, gallium nitride, silicon nitride, aluminum nitride, zinc selenide, zinc sulfide, zinc telluride, silicon carbide and their combinations, or higher-order compounds containing several cations and several anions and which may include oxycarbides and oxynitrides.

[0046] In one embodiment, the fillers for a polymer film may have a median particle size, d50, ranging from 0.1 to 10 pm, 0.1 to 5 pm, 0.2 to 5 pm, or 0.2 to 3 pm. The filler size can be determined using a laser particle size analyzer, with the filler dispersed in an organic solvent (optionally with the aid of a dispersant, an adhesion promoter, and / or a coupling agent). The median particle size, d50, is the equivalent spherical diameter based on a median volumetric particle distribution. If the median particle size is less than 0.1 pm, the filler particles may tend to agglomerate or become unstable in the organic solvents used in polymer manufacturing.If the median particle size of the agglomerated particles exceeds 10 pm, the dispersion of the filler component in the polymer film may be too inhomogeneous (or of an inappropriate size for the film thickness). A relatively inhomogeneous dispersion of the filler component in the film can lead to poor mechanical elongation of the film, poor flexural life of the film, and / or low dielectric strength. In one embodiment, the fillers may require extensive grinding and filtration to break up the unwanted particle agglomeration, as is usually the case when attempting to [[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]) ... Dispersing certain fillers within a polymer matrix. This grinding and filtration process can be costly and may not eliminate all undesirable agglomerates. In one embodiment, the average aspect ratio of the filler may be equal to or greater than 1. In some embodiments, the filler is selected from the group consisting of needle-type (acicular) fillers, fibrous fillers, platelet fillers, polymer fibers, and mixtures thereof. In one embodiment, the fillers may have an aspect ratio of at least 1, 2, 4, 6, 8, 10, 12, 15, 25, 50, 100, 200, or 300 to 1.

[0047] In one embodiment, the charge comprises a mixture, or assembly, of charges having any number of particle types, particle sizes and particle shapes, a mixture, or assembly, which may be of the same type of charge or of a different type of charge.

[0048] In one embodiment, the fillers may be coated with a coupling agent. For example, a filler particle may be coated with an aminosilane, a phenylsilane, or acrylic or methacrylic coupling agents derived from the corresponding alkoxysilanes. Trimethylsilyl surface-coating agents may be introduced onto the surface of the particles by reacting the fillers with hexamethyldisilazane. In one embodiment, the fillers may be coated with a dispersant. In another embodiment, the fillers may be coated with a combination of a coupling agent and a dispersant. Alternatively, the coupling agent, the dispersant, or a combination thereof may be incorporated directly into the polymer film and need not be coated onto the fillers. Polymer films

[0049] In one embodiment, a polymer film that is a polyimide film can be produced by combining a diamine and a dianhydride (monomer or other precursor form of polyimide) with a solvent to form a solution of poly(amic acid) (also called polyamide acid). The dianhydride and diamine can be combined in a molar ratio of approximately 0.90 to 1.10. The molecular weight of the poly(amic acid) formed from these can be adjusted by adjusting the molar ratio of the dianhydride and the diamine.

[0050] In one embodiment, a poly(amic acid) molding solution is derived from the poly(amic acid) solution. The poly(amic acid) molding solution and / or the poly(amic acid) solution are combined with conversion chemicals such as: (i) one or more dehydrating agents, such as aliphatic acid anhydrides (acetic anhydride, etc.) and / or aromatic acid anhydrides; and (ii) one or more catalysts, such as tertiary amines. Aliphatic tertiary amines (triethylamine, etc.), aromatic tertiary amines (dimethylaniline, etc.), and heterocyclic tertiary amines (pyridine, picoline, isoquinoline, etc.) are used. The anhydride dehydration material is often used in molar excess relative to the amount of acidic amide groups in the poly(amic acid). The amount of acetic anhydride used is typically on the order of 2.0 to 4.0 moles per equivalent (repeating pattern) of poly(amic acid). Generally, a comparable amount of tertiary amine catalysts is used. Dispersed or solvent-suspended fillers, as described above, are then added to the poly(amic acid) solution.

[0051] In one embodiment, the poly(amic acid) solution is dissolved in an organic solvent at a concentration of approximately 5.0 or 10 percent at 15, 20, 25, 30, 35, or 40 percent by weight. In another embodiment, a suspension comprising an electrically conductive filler is prepared, the suspension having an electrically conductive filler content ranging from 0.1 to 70, from 0.5 to 60, from 1 to 55, from 2 to 50, or from 5 to 45 percent by weight. The suspensions may or may not be ground using a ball mill to achieve the desired particle size. The suspensions may or may not be filtered to remove any large residual particles. A poly(amic acid) solution can be prepared by methods well known in the art. The poly(amic acid) solution may or may not be filtered. In some embodiments, the solution is mixed in a high-shear mixer with the charge suspension.When a poly(amic acid) solution is prepared with a slight excess of diamine, an additional dianhydride solution may or may not be added to increase the viscosity of the mixture to the desired level for film casting. The amount of poly(amic acid) solution and the amount of filler suspension can be adjusted to obtain the desired filler levels in the cured film. In some embodiments, the mixture is cooled to a temperature below 10 °C and mixed with conversion chemicals before casting.

[0052] The solvated mixture (the poly(amic acid) casting solution) can then be poured or applied onto a support, such as an endless belt or a rotating drum, to give a partially imidized gel film. Alternatively, it can be poured onto a polymeric support such as PET, other forms of Kapton® polyimide film (e.g., Kapton® HN or Kapton® E films), or other polymeric supports. The gel film can be removed from the drum or belt, placed on a ramming frame, and cured in an oven, using convective and radiant heat to remove solvent and complete imidization to a solids level above 98%. The film can then be separated from the support, oriented as such by ramming, with continuous heating (drying and curing) to provide a polyimide film.

[0053] Useful processes for producing polyimide films can be found in U.S. patents Nos. 5,166,308 and 5,298,331, which are incorporated by reference in this specification for all the teachings contained therein. Numerous variations are also possible, such as,

[0054] (a) a process in which the diamine and dianhydride components are pre- mixed together, then the mixture is added in portions to a solvent while stirring.

[0055] (b) a process in which a solvent is added to a stirred mixture of components diamine and dianhydride. (unlike (a) above)

[0056] (c) a process in which diamines are exclusively dissolved in a solvent, then dianhydrides are added in a ratio that allows the reaction rate to be regulated.

[0057] (d) a process in which the dianhydride components are exclusively dissolved in a solvent, then amine components are added in a ratio that allows the reaction rate to be regulated.

[0058] (e) a process in which the diamine and dianhydride components are dissolved separately in solvents, then these solutions are mixed in a reactor.

[0059] (f) a process in which the poly(amic acid) with an excess of amine component and another poly(amic acid) with an excess of dianhydride component are formed beforehand and then reacted with each other in a reactor, specifically in such a way as to create a non-statistical or block copolymer.

[0060] (g) a process in which a specific portion of the amine components and dianhydride are first put to react, then the residual diamine components are put to react, or vice versa.

[0061] (h) a process in which the conversion chemicals (catalysts) are mixed with poly(amic acid) to form a poly(amic acid) casting solution, then poured to form a gel film.

[0062] (i) a process in which the components are added in part or in whole into any order to a part or all of the solvent, also in which a part or all of a component may be added as a solution to a part or all of the solvent.

[0063] (j) a process where, first, one of the dianhydride components is reacted with a Diamine components are used to give a first poly(amic acid). Then, another dianhydride component is reacted with another amine component to give a second poly(amic acid). Finally, the amic acids are combined in any number of ways before the film forms.

[0064] In one embodiment, the solvated mixture (the poly(amic acid) casting solution) can be mixed with a crosslinking precursor and then cast to form a polymer film. In one embodiment, a polymer film contains a polymer crosslinked in a range of 80 to 99% by weight. In some embodiments, the polymer film contains any two of the following, inclusive: 80, 85, 90, 95, and 99% by weight of crosslinked polymer. In yet another embodiment, the polymer film contains 91 to 98% by weight of crosslinked polymer.

[0065] In one embodiment, a crosslinking reaction includes chemical compounds, such as reactive amines, which can participate in a chemical reaction that crosslinks the polymer chains in the film. In one embodiment, heat can be used to crosslink the polymer. In one embodiment, irradiation with a light source can be used to crosslink the polymer by a photo-initiated process. In one embodiment, an additional reactive chemical species can be used to crosslink the polymer. In one embodiment, any combination of these processes can be used to crosslink the polymer.

[0066] The crosslinking of the polymer can be determined by a variety of methods. In one embodiment, the gel fraction of the polymer can be determined using an equilibrium swelling method, by comparing the weight of a dried film before and after crosslinking. In one embodiment, a crosslinked polymer may exhibit a gel fraction in the range of 20 to 100%, 40 to 100%, 50 to 100%, 70 to 100%, or 85 to 100%. In one embodiment, the crosslinked network can be identified using rheological methods. An oscillatory time-scan measurement at a specific stress, frequency, and temperature can be used to confirm the formation of a crosslinked network. Initially, the value of the loss modulus (G") is greater than the value of the storage modulus (G'), indicating that the polymer solution behaves like a viscous liquid.Over time, the formation of a cross-linked polymer network is evidenced by the intersection of the G' and G" curves. The intersection, called the "gel point", represents the moment when the elastic component takes over from the viscous component.

[0067] In one embodiment, an electrically conductive filler is first dispersed in a solvent to form a suspension. The suspension is then dispersed in the poly(amic acid) solution. In one embodiment, the concentration of electrically conductive filler relative to the polyimide (in the final film) is in the range of 5 to 65 wt%, 5 to 50 wt%, 10 to 40 wt%, or 15 to 35 wt% based on the total weight of the polymer film. In one embodiment, the concentration of electrically conductive filler relative to the polyimide (in the final film) is at least 5, 10, 15, 20, or 25 wt% relative to the total weight of the polymer film. The composition of the cured film can be calculated from the composition components in the mixtures, excluding the DMAc solvent (which is removed during curing) and taking into account the removal of water during the conversion of poly(amic acid) to polyimide. When using electrically conductive fillers, the conductivity of the polyimide film also increases as the filler concentration increases. In one embodiment, an electrically conductive polymer film may exhibit a surface resistivity of 1 megaohm / square or less, 0.5 megaohm / square or less, 0.1 megaohm / square or less, or 50,000 ohm / square or less. Those skilled in the art will understand that, in addition to the filler content, the characteristics of the electrically conductive filler, such as particle size, morphology, aspect ratio, surface oxidation, etc., will affect the surface resistivity of the polymer film containing it.

[0068] In one embodiment, the mixing of the filler suspension with a poly(amic acid) solution to form the filled poly(amic acid) casting solution is carried out by high-shear mixing. In this embodiment, if the filler is present in more than 65 percent by weight in the final film, the film may be too brittle and not sufficiently flexible to form a mechanically strong, self-supporting flexible sheet. Furthermore, if the filler is present at a rate of less than 5 percent by weight, the films formed from it may not be sufficiently conductive.

[0069] In one embodiment, the casting solution may further comprise any of a number of additives, such as processing aids (e.g. oligomers), antioxidants, photostabilizers, flame retardant additives, antistatic agents, thermal stabilizers, ultraviolet absorbing agents or various strengthening agents.

[0070] In one embodiment, a coextrusion process can be used to form a multilayer polymer film having two or more layers, for example, a three-layer polymer film having an inner core layer sandwiched between two outer layers. In this process, for a three-layer polyimide film, a finished poly(amic acid) solution is filtered and pumped to a slotted die, where the flow is split to form the first and second outer layers of a three-layer coextruded film. In some embodiments, a second polymer flow is filtered and then pumped to a casting die to form the intermediate polymer core layer of a three-layer coextruded film. The flow rates of the solutions can be adjusted to obtain the desired layer thickness.In one embodiment, the polymer composition and filler content of the first and second outer layers are identical, while in another embodiment, the polymer composition and / or filler content of the first and second outer layers are different. In some embodiments, the polymer composition and filler content of the central layer may be identical or different from those of one or both of the outer layers.

[0071] In one embodiment, the multilayer film is prepared by simultaneous extrusion of the first outer layer, the middle layer, and the second outer layer. In some embodiments, the layers are extruded through a single-cavity or multi-cavity extrusion die. In another embodiment, the multilayer film is produced using a single-cavity die. If a single-cavity die is used, the laminar flow of the streams must have a sufficiently high viscosity to prevent mixing of the streams and provide uniform layering. In some embodiments, the multilayer film is prepared by casting from the slotted die onto a moving stainless steel belt.In one embodiment, for a polymer having an imide group, the belt is then passed through a convection oven to evaporate solvent and partially imidize the polymer, producing a "green" film. The green film can be removed from the casting belt and wound up. The green film can then be passed through a ramming oven to produce a fully cured polymer film. In some embodiments, during ramming, shrinkage can be minimized by constraining the film along the edges (i.e., using clamps or pins).

[0072] In one embodiment, the outer layers of the present invention can also be applied to the central layer during an intermediate stage of polymer film manufacturing such as a gel film or a green film.

[0073] In the formation of an imide-containing polymer, the term "gel film" refers to a sheet of poly(amic acid) that is loaded with volatile compounds, primarily solvent, to such an extent that the poly(amic acid) is in a swollen, gel-like, or rubbery state and can be formed in a chemical conversion process. The volatile compound content is generally in the range of 70 to 90% by weight, and the polymer content is generally in the range of 10 to 30% by weight of the gel film. The final film becomes "self-supporting" in the gel film stage. It can be removed from the support onto which it was poured and heated to a final curing temperature. The gel film typically has an amic acid / imide ratio of between 10:90 and 50:50, most often 30:70.

[0074] The gel film structure can be prepared by the process described in U.S. Patent No. 3,410,826. This patent discloses the mixing of a chemical converting agent and a catalyst, such as a lower fatty acid anhydride and a tertiary amine, in a poly(amic acid) solution at a low temperature. The poly(amic acid) solution is then poured as a film onto a casting drum. The film is slightly heated after casting, for example to a temperature of 100 °C, to activate the conversion agent and catalyst in order to transform the cast film into a poly(amic acid) / polyimide gel film.

[0075] Another type of polymer film is a "green film," which, for a polyimide film, is partly poly(amic acid) and partly polyimide, and can be formed by a thermal conversion process. The green film typically contains about 50 to 75% by weight of polymer and 25 to 50% by weight of solvent. In general, it should be strong enough to be substantially self-supporting. The green film can be prepared by pouring the poly(amic acid) solution as a film onto a suitable support such as a casting drum or belt and removing the solvent by gently heating it to a temperature of 150 °C. A small proportion of the amic acid units in the polymer, for example up to 25%, can be converted into imide units.

[0076] The application of the polymer films of the present invention can be carried out in several ways. Such methods include the use of a slotted die, dip coating, or transfer roller coating of a film, followed by application with a doctor knife, doctor rollers, compression rollers, or an air knife. The coating can also be applied by brushing or spraying. Using such techniques, it is possible to prepare both single-sided and double-sided coated laminates. When preparing double-sided coated structures, the coatings can be applied to both sides of a polymer either simultaneously or consecutively before proceeding to the polymer curing and drying stage.

[0077] The thickness of the polymer film can be adjusted, depending on the intended use of the film or the specifications of the final application. In one embodiment, the polymer film has a total thickness in a range from 1 to 300 µm, from 2 to 200 µm, from 5 to 150 µm, from 10 to 100 µm or from 20 to 80 µm.

[0078] In one embodiment, for a two-layer or three-layer polymer film, the middle layer has a thickness in the range of 0.75 to 225 µm, 1.5 to 150 µm, 3.75 to 112.5 µm, or 7.5 to 75 µm, and the outer layer(s) each have a thickness in the range of 0.25 to 75 µm, 0.5 to 50 µm, 1.25 to 37.5 µm, or 2.5 to 25 µm. In one embodiment, for a three-layer film, the thicknesses of the outer layers may be identical or different. Current collectors

[0079] In one embodiment, a current collector for an energy storage device may comprise a polymer film and a metallic layer bonded to the polymer film. Current collectors provide a pathway for supplying an electrical charge (electricity) to an external circuit. However, in a LIB, the collectors of Current collectors are passive elements, meaning they do not participate in the intercalation reactions of Li+ ions. Therefore, thin and lightweight materials are preferred for current collectors to allow the gravimetric and volumetric energy density of a battery to remain high. The materials should be ionically insulating and electronically conductive, and maintain good chemical and electrochemical stability in the electrolyte during battery operation. Other requirements include providing a mechanically robust framework for the battery construction that adheres well to the electrode suspensions. In one embodiment, a current collector may comprise a polymer film having metallic layers bonded to both sides of the polymer film.

[0080] Current collectors can be formed as double-sided metal-clad polymer films by any number of well-known processes. In one embodiment, a metal plating process can be used to form a metallic coating with a polymer film, such as a polyimide film. In one embodiment, a polyimide film includes a thermoplastic polyimide layer. A metallic layer can be formed on the thermoplastic polyimide layer of the polymer film by plating a thin metallic layer. In one embodiment, a thin metallic layer can be 10 µm or less, 5 µm or less, 3 µm or less, or 1 µm or less. By using a plating process to form metallic layers on polymer films, smoother interfaces between the current collectors and the electrodes can be formed.Conventional lamination of metal foils onto polymer films relies on the surface roughness of the foils to provide good adhesion to the polymer film, but may also require roughnesses that are greater than the thickness of a thin metal layer.

[0081] In one embodiment, a polymer film can be bonded to first and second metallic layers in a plating process to form a double-sided metal-clad polymer film. A plating process can include autocatalytic plating followed by electrolytic plating. The autocatalytic plating process is used to form an initial metallic layer, typically less than 250 nm thick, or sufficient to provide uniform conductivity over the entire surface. The electrolytic plating process is then used to build up the metallic layers to the desired thickness, providing the preferred Cu grain structure for good conductivity. In one embodiment, the surface of the polymer film to be plated can be plasma-treated before the formation of the metallic layers. Thus, a formed metal-clad polymer film comprises the polymer film and two thin conductive layers.In one embodiment, for a multilayer polymer film, the use of a thermoplastic polymer layer. as an outer layer to bond to the metallic layers makes possible a strong adhesion between the polymer film and the metallic layers despite the smoothness of the interface between the layers, and without the use of additional primer or adhesive layers between the layers.

[0082] In other embodiments, other metal plating processes can be used to form a seed layer prior to electrolytic plating. In one embodiment, atomic layer deposition (ALD) can be used to form a conductive seed layer of a metal, such as Pd or Ag, prior to electrolytic plating. In another embodiment, a polymer film can be bonded to a metal layer by means of a physical vapor deposition or sputtering process. Physical vapor deposition occurs when the seed layer is deposited onto the polymer film from a solid by vaporizing a solid source material under vacuum conditions. In another embodiment, a polymer film can be bonded to a metal layer by chemical vapor deposition. In this process, the deposition species are introduced into a deposition chamber in the gas phase.

[0083] In one embodiment, a polymer film can be bonded to a first metallic layer by direct electrochemical deposition of a metallic layer onto a polymer film (direct metallization). The terms "direct electrochemical deposition of a metallic layer" or "direct plating" onto a polymer film mean that an electrolytic deposition process is used to form and build a metallic layer on a polymer film without initially using an autocatalytic plating, physical vapor deposition, or chemical vapor deposition process to form an initial metallic layer on the polymer film. Eliminating this seed layer from the process makes direct metallization faster and less expensive than using traditional copper sheathing fabrication processes. Energy storage devices

[0084] In one embodiment, current collectors having a polymer film and first and second metallic layers bonded to the polymer film can be used in energy storage devices, such as lithium-ion batteries, capacitors, supercapacitors, fuel cells, and redox flow batteries. Any energy storage device in which the conductivity of a current collector can be useful for completing a circuit and supplying energy to an external device could benefit from the use of current collectors having a polymer film and metallic layers bonded to the polymer film. For example, a lithium-ion battery includes a positive electrode (cathode), an electrode negative (anode) and a separator, at least one of them, preferably all of them, being in ionically conductive contact with an electrolyte solvent.

[0085] In one embodiment, the electrolyte solvent can be combined with one or more electrolytes that will supply ions to the electrolyte, thereby making it ionically conductive. Suitable electrolytes include low molecular weight lithium salts and ionic polymers, known as ionomers. Suitable low molecular weight lithium salts include both organic and inorganic salts such as LiPF6, LiBF4, LiC104, LiAsF6, LiN(SO2CF3)2, LiN(SO2CF2CF3)2, LiC(SO2CF3)3, among others. The molar concentration of lithium ions in the electrolyte solution can be from 0.1 to 4.0 M, with a preferred range of 0.5 to 2.0 M. When the ionic species is an ionomer, it may still be desirable to add to the electrolyte solvent an amount of low molecular weight lithium salt in concentrations in the range of 0.01 to 1.0 M.

[0086] In one embodiment, the electrolyte solvent may comprise acyclic and cyclic organic carbonates, primarily dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), ethylene carbonate (EC) and fluorinated ethylene carbonate (FEC), phosphorus-containing compounds such as trimethyl phosphate (TMP), tris(2,2,2-trifluoroethyl) phosphate (TFP), tris(2,2,2-trifluoroethyl) phosphite (TTFPi), bis(2,2,2-trifluoroethyl) methylphosphonate (TFMP), (ethoxy)pentafluorocyclotriphosphazene (PFPN) and (phenoxy)pentafluorocyclotriphosphazene (FPPN), and monoesters such as methyl acetate (MA), ethyl acetate (EA), methyl formate (MF), methyl propionate (MP), ethyl propionate (EP) and gamma-butyrolactone (GBL).Most often, these electrolyte solvents are used in combinations comprising a cyclic organic carbonate, usually EC or PC, and an acyclic carbonate, usually DMC, DEC, or EMC. These combinations have proven effective in practice for achieving an excellent combination of desirable properties such as high ionic conductivity over a wide temperature range and relatively low volatility, while also achieving excellent lifespan and performance in lithium-ion batteries.

[0087] In one embodiment, the cathode comprises a cathode active material, such as a lithium-containing transition metal oxide or phosphate, capable of absorbing and releasing lithium ions up to a capacity greater than 100 mAh / g, such as LiCoO2, LiNiO2, Li(Ni,Co)O2, Li(Ni,Co,Mn)O2, LiMn2O4, LiV3O8, Li(Ni,Mn)O4, LiFePO4, LiMnPO4, LiCoPO4, and LiVPO4F. In another embodiment, the cathode active material may be a material exhibiting a Capacity greater than 30 mAh / g in the potential range above 4.6 V relative to a Li / Li+ reference electrode. In other embodiments, the electrochemical cell is charged to a potential greater than or equal to 4.00 V, 4.10 V, 4.20 V, 4.30 V, 4.35 V, 4.40 V, 4.45 V, 4.5 V, 4.55 V, or more than 4.6 V relative to a Li / Li+ reference electrode. An example of such a cathode active material is a stabilized manganese cathode comprising a lithium-containing manganese composite oxide having a spinel structure as the cathode active material. Publication of U.S. Patent Application No. 2016 / 0087307 A1 discloses a wide range of cathode active materials and is incorporated herein by reference.

[0088] The active cathode material can be prepared by processes such as, for example, the hydroxide precursor process described by Liu et al. (J. Phys. Chem. C 13:15073-15079, 2009). In this process, hydroxide precursors are precipitated from a solution containing the required amounts of manganese, nickel, and other desired metal acetates by adding KOH. The resulting precipitate is oven-dried and then reacted with the required amount of LiOH*H2O at a temperature of approximately 800 to approximately 950 °C in oxygen for 3 to 24 hours. Alternatively, the active cathode material can be prepared using a solid-phase reaction process or a sol-gel process as described in U.S. Patent No. 5,738,957.The cathode, which contains the cathode active material, can be prepared by processes such as mixing an effective amount of the cathode active material (e.g., about 70 wt% to about 97 wt%), a polymer binder, such as poly(vinylidene difluoride), and conductive carbon in a suitable solvent, such as N-methylpyrrolidone, to produce a paste, which is then coated onto a current collector and dried to form the cathode.

[0089] In one embodiment, the anode comprises an anode active material capable of storing and releasing lithium ions. Examples of suitable anode active materials include silicon, lithium metal, lithium alloys such as lithium-aluminum alloy, lithium-lead alloy, lithium-silicon alloy, lithium-tin alloy and the like; carbon materials such as graphite and mesocarbon microbeads (MCMB); phosphorus-containing materials such as black phosphorus, MnP4 and COP3, metal oxides such as SnO2, SnO and TiO2, nanocomposites containing antimony or tin, for example nanocomposites containing antimony, aluminum, titanium or molybdenum oxides, carbon and lithium titanates. In one embodiment, the active anode material is lithium titanate, graphite, lithium alloys, silicon and combinations thereof.In another embodiment, the anode is made of graphite. In one embodiment, the active materials are graphite-based. These include MCMB (available from Osaka Gas Chemical Co., Ltd., Japan) or carbon fibers (Melblon ground carbon fiber available from Petoca Materials, Ltd., Japan), both of which are capable of achieving a reversible capacity greater than 280 mAh / g for lithium insertion. Other suitable carbon-based active materials for anodes include graphite flakes, polycrystalline graphite (PCG), petroleum coke, hard carbon, and natural graphite.

[0090] An anode, containing an anode active material, can be prepared by a process similar to that described above for a cathode, in which, for example, a binder such as a vinylidene fluoride copolymer or a styrene-butadiene rubber is dissolved or dispersed in an organic solvent or water, which is then mixed with the conductive active material to obtain a paste. The paste is then coated onto the current collector. The paste is dried, preferably by heating, so that the active mass is bonded to the current collector. Suitable anode active materials and anodes are commercially available from companies such as Hitachi NEI Inc. (Somerset, NJ) and Farasis Energy Inc. (Hayward, CA).

[0091] In one embodiment, a lithium-ion battery also includes a porous separator between the anode and the cathode. The porous separator prevents short circuits between the anode and the cathode. The porous separator is generally made of a single-layer or multi-layer sheet of a microporous polymer such as polyethylene, polypropylene, polyamide, or polyimide, or a combination thereof. The pore size of the porous separator is large enough to allow ion transport to provide ionically conductive contact between the anode and the cathode, but small enough to prevent contact between the anode and the cathode either directly or through the penetration of particles or dendritic formations. Examples of porous separators suitable for use in the present invention are described in U.S. Patent No. 8,518,525, which is incorporated into the present invention by reference.

[0092] The casing of a lithium-ion battery can be any suitable container for housing the lithium-ion battery components described above. Such a container can be made in the form of a button cell, a small or large cylinder, a prismatic case, or a pouch.

[0093] In one embodiment, energy storage devices, such as lithium-ion batteries, can be used for grid storage or as a power source in various electronic devices such as a computer, camera, radio, or power tool, various telecommunications devices, or various transportation devices (including a motor vehicle, automobile, truck, bus, or aircraft). Various cell configurations can be used for different battery applications, including pocket batteries, prismatic cells, button batteries, cylindrical batteries, wound prismatic batteries, wound pocket batteries, and others.

[0094] The advantageous properties of the present invention can be observed by referring to the following examples, which illustrate, but do not limit, the invention. All parts and percentages are expressed by weight unless otherwise indicated. Examples Test methods Particle size

[0095] The particle size of the filler particles in the suspensions was measured by laser diffraction using a particle size analyzer (Mastersizer 3000, Malvem Instruments, Inc., Westborough, MA). DMAc was used as the carrier fluid. Surface resistivity

[0096] In accordance with ASTM D257, to measure surface resistivity, a Loresta AX MCP-T370 equipped with a 4-point PSP linear probe (Mitsubishi Chemical Analytech Co., LTD, Kanagawa, Japan) was used to measure the surface resistivity at 15 locations evenly distributed on a piece of polymer film approximately 12" x 2". An average of the 15 measurements was calculated to determine the surface resistivity of the film. The surface resistivity can be measured on both sides of the polymer film. Battery evaluation

[0097] A battery test system (CT3002A, Landt Instruments, Vestal, NY) was used to evaluate battery performance in a half-cell configuration. All measurements were performed at 25 °C. Charging and discharging were performed between 2 V and 0.002 V vs. Li+ / Li°. The cells were activated for one cycle at 0.05 C before being cycled under constant current conditions. In all cases, the charge rate was 0.1 C for the cell evaluations. The discharge rate increased from 0.1 C to 5 C in each subsequent cycle. The C rates were based on the capacitance of the graphitic electrode in the cell. During a charge / discharge cycle, the half-discharge voltage is the cell voltage, at a given current or C rate, where half of the electrode's charge capacity is depleted. Carbon black suspension

[0098] In some embodiments, a carbon black suspension was prepared to provide an electroconductive filler, consisting of 9.5% by weight of carbon black powder (Conductex® 7055U, Aditya Birla Group, Marietta, GA), 17.25% by weight of poly(amic acid) (13.06% by weight of PMDA / ODA and 4.19% by weight of PMDA / BPDA / ODA / PPD), and 73.25% by weight of DMAc. High-shear grinding and mixing were used for complete uniform dispersion. particles of the suspension. The average particle size, d50 (equivalent spherical diameter based on a median volume distribution of particles), of the charged particles was less than 1 pm. Multilayer polymer film

[0099] Poly(amic acid) solutions for the production of the core and outer layers were prepared separately by a chemical reaction between the appropriate molar equivalents of the monomers in the dimethylacetamide (DMAc) solvent. Typically, the diamine dissolved in DMAc was stirred under nitrogen, and the dianhydride was added in solid form over a period of a few minutes. Stirring was continued to obtain the maximum viscosity of the poly(amic acid). In some embodiments, a 15–60 wt% carbon black suspension was added to the poly(amic acid) solutions and mixed using a high-shear mixer. The composition of the cured film was calculated from the composition of the components in the mixtures, excluding the DMAc solvent (which is removed during curing) and taking into account the removal of water during the conversion of the poly(amic acid) to the polyimide.The viscosity was adjusted by regulating the amount of dianhydride in the poly(amic acid) composition.

[0100] Multilayer films were cast by coextrusion. Three separate polyamic polymer streams were extruded simultaneously through a multi-cavity extrusion die on a heated moving belt to form a co-extruded three-layer polyimide film. The thicknesses of the central polyimide layer and the upper and lower outer thermoplastic polyimide layers were adjusted by varying the amounts of poly(amic acids) fed into the extruder.

[0101] The extruded multilayer film was dried at an oven temperature in the range of approximately 95 to approximately 150 °C. The self-supporting film was peeled from the belt and heated with radiant heating elements in a ram oven at a temperature ranging from approximately 110 to approximately 805 °C (surface temperature of the radiant heating element) to dry completely and imidize the polymers. Examples 1 and 3

[0102] For Examples 1 and 3 (E1 and E3), the polymer composition of the core layer contained a polyimide derived from a dianhydride-to-diamine molar ratio of approximately 1:1, the dianhydride being PMDA and the diamine being ODA. The outer thermoplastic layers also contained a polyimide derived from a dianhydride-to-diamine molar ratio of approximately 1:1. The dianhydride composition contained the PMDA and ODPA monomers in a molar ratio of 20:80, and the diamine composition contained 100 mole percent of the RODA monomer. The flow rates Poly(amic acid) solutions were adjusted to produce a three-layer film in which the outer thermoplastic layers each had a thickness of about 6 pm and the middle layer had a thickness of about 38 pm. Example 2

[0103] For Example 2 (E2), the polymer composition of the core layer contained a polyimide derived from a dianhydride-to-diamine molar ratio of approximately 1:1. The dianhydride composition contained the BPDA / PMDA monomers in a molar ratio of 88:12, and the diamine composition contained the PPD / ODA monomers in a molar ratio of 95:5. The thermoplastic outer layers also contained a polyimide derived from a dianhydride-to-diamine molar ratio of approximately 1:1. The dianhydride composition contained the PMDA and ODPA monomers in a molar ratio of 20:80, and the diamine composition contained 100 mole percent of the RODA monomer. The flow rates of the poly(amic acid) solutions were adjusted to produce a three-layer film in which the outer thermoplastic layers each had a thickness of approximately 6 pm and the middle layer had a thickness of approximately 38 pm. Comparative example 1

[0104] For comparative example 1 (E1), the polymer composition of the core layer contained a polyimide derived from a dianhydride-to-diamine molar ratio of approximately 1:1. The dianhydride composition contained the BPDA / PMDA monomers in a molar ratio of 88:12, and the diamine composition contained the PPD / ODA monomers in a molar ratio of 95:5. The thermoplastic outer layers also contained a polyimide derived from a dianhydride-to-diamine molar ratio of approximately 1:1. The dianhydride composition contained the PMDA and ODPA monomers in a molar ratio of 20:80, and the diamine composition contained 100 mole percent of the RODA monomer. The flow rates of the poly(amic acid) solutions were adjusted to produce a three-layer film in which the outer thermoplastic layers each had a thickness of approximately 6 pm and the middle layer had a thickness of approximately 38 pm.

[0105] [Tables 1] Example Central layer polyimide Composition Thermoplastic polyimide Composition Surface resistivity (Q / square) PMDA / / ODA PMDA / ODPA / / RODA 97 E2 PMDA / BPDA / / PPD / OD A PMDA / ODPA / / RODA 983 E3 PMDA / / 0DA PMDA / ODPA / / RODA 97 CEI PMDA / BPDA / / PPD / OD A PMDA / ODPA / / RODA -

[0106] The E1-E3 films comprised the carbon black suspension (at the appropriate charge to produce the desired surface resistivity). The IEC film had no electrically conductive charge in any of the layers.

[0107] The E1-E3 and CEI films were metallized with copper to form a metallic layer on a polymer film and tested as current collectors in a half-cell battery configuration. Before metallization, film samples were cut to a size of approximately 5 x 7 inches and clipped into a stainless steel frame. The film surface was cleaned using a two-stage plasma process. Cleaning was performed at 300 mTorr of plasma exposure with an N2 / CF4 / O2 mixture for 5 minutes, followed by 30 seconds of O2 plasma exposure. After plasma treatment, the film was immersed in an aqueous IM NaOH solution at 45 °C for 90 seconds with gentle stirring, then rinsed with running tap water for 2 minutes and directly immersed in the electrodeposition bath as described below.

[0108] IEC was first prepared by exposure to the plasma step above and to a 1 M NaOH bath. Then, the sample was plated using a CIRCUPOSIT™ 6500 autocatalytic copper deposition process without the need for an impurity removal step and processed as follows:

[0109] 1. The films were immersed in CIRCUPOSIT™ 6520A Pre-Dip (DuPont de Nemours, Inc., Wilmington, DE) at pH 2 at room temperature for 30 seconds under gentle stirring.

[0110] 2. The films were then immersed in the CIRCUPOSIT™ 6530 catalyst (DuPont) prepared at a Pd2+ ion concentration of 200 ppm at a temperature of 50 °C for 60 seconds under gentle stirring.

[0111] 3. The films were then rinsed under running tap water for 60 seconds.

[0112] 4. The films were then immersed in the CIRCUPOSIT™ reduction solution 6540 (DuPont) at a temperature of 32 °C for 60 seconds under gentle agitation.

[0113] 5. The films were then rinsed under running tap water for 60 seconds.

[0114] 6. The films were then immersed in an autocatalytic plating bath of copper CIRCUPOSIT™ 6550 (DuPont) at a temperature of approximately 34 °C for 2.5 minutes.

[0115] 7. The films were then rinsed under running tap water for 60 seconds.

[0116] After autocatalytic plating, the film was dried and stored in a desiccator before being used for electrodeposition.

[0117] The autocatalytic plating process forms a copper layer of approximately 80-120 nm on the polyimide film. The autocatalytic plating process is then followed by an electrolytic plating process. For IEC, the autocatalytically plated sample was pre-cleaned before the electrolytic bath as follows:

[0118] 1. The films were pre-treated with RONACLEAN™ LP-200 cleaner (DuPont) for 120 seconds at a temperature of 40 °C.

[0119] 2. The films were then rinsed in deionized water (DI) for 120 seconds.

[0120] 3. The films were then treated in sulfuric acid at 40 g / l for 30 seconds before being transferred to the electrolytic plating bath.

[0121] All examples were electrolytically plated sequentially using a MICROFILL™ EVF-II process.

[0122] Copper electrodeposition baths were prepared by combining 200 g / L of copper as copper sulfate pentahydrate, 100 g / L of sulfuric acid, 60 ppm of chloride ions, 1.25 mL / L of MICROFILL™ EVF-II XB, 33 mL / L of MICROFILL™ EVF-II XL, and 10 mL / L of MICROFILL™ EVF-II XC (all DuPont). The films were electrolytically plated in a 5.5 L plating stack with air agitation set at 2 LPM and the temperature regulated to 75 °F (24 °C) via a heated water bath. The films were removed from the desiccator, mounted between two 5" x 7" stainless steel frames with 4.5" x 5.5" windows, and processed as follows:

[0123] 1. The films were plated at a current density of 5 ASF in a copper bath bright acid up to a target thickness of 1 pm.

[0124] 2. After electrolytic copper plating, the films were rinsed with deionized water for 120 seconds, removed from frame, immersed in ANTITARNISH™ 7130 (DuPont) for 15 seconds, rinsed with deionized water for 30 seconds and air dried.

[0125] To prepare a half-cell battery, a graphitic electrode was prepared by coating the current collector in contact with the film layer with a graphitic suspension using a squeegee. The graphitic suspension was prepared from battery-grade graphitic powder, Super P carbon black (Imerys SA, France), and styrene-butadiene rubber (SBR) binder in a weight ratio of 95.7:1.5:2.8 (graphite:Super P carbon:SBR binder) to create a 46% by weight solids suspension in water, mixed with a magnetic stirrer for approximately 24 hours. After coating the current collector, the assembly was dried in a convection oven at a temperature of 70 °C for at least 24 hours before use. The charge of the active component of graphite on the electrode was 5 mg (total solids) / cm2, i.e. 5 * 0.957 = 4.785 g of graphite / cm2.3 / 8" circles were drilled from the electrode for battery evaluations. A 0.25 mm (10 mil) thick lithium metal foil (Aldrich, Milwaukee, WI) was used as a counter electrode in the half-cell measurements. As with the graphitic electrode, 3 / 8" circles were used.

[0126] The half-cell battery was prepared in the form of a button cell and assembled using a Celgard® 2325 separator (Celgard, LLC, Charlotte, NC), a lithium foil counter electrode (0.25 mm thick), a graphitic electrode, and a few drops of the non-aqueous electrolyte composition (LiPF6 EC / EMC / DMC 1 M, 1:1:1 by volume) obtained from Aldrich. The lithium foil counter electrode, the graphitic electrode, the separator, and the anode were stacked and sandwiched in 2032 stainless steel button cell boxes (MTI, CA) to form the half-cells in a dry box filled with argon. For testing purposes, all C rates were calculated based on an assumed charge capacity of 300 mAh / g. Therefore, each button cell battery had an estimated capacity of 1.44 mAh. All measurements were taken at a temperature of 25 °C.The battery was cycled at 0.1 C for the charge rate and the discharge rate was increased from 0.1 C to 0.2 C, 1 C, 2 C and 5 C in subsequent cycles.

[0127] For each discharge cycle, the mid-discharge voltage (the voltage at which half the battery's charge capacity is reached during discharge) was determined from the discharge curve. This was used to characterize the battery's bias, which is related to the battery's internal resistance. Two to three button cells were prepared from each current collector. The average mid-discharge voltages of the 2C and 5C current collectors are shown in Table 1. For CE2, a 9 µm battery-grade copper foil (having a purity greater than 99.95%, a resistivity of 0.168 ohm-g / m², a surface roughness of less than 0.4 µm, and a tensile strength of 41 kg / m²) was used as the current collector in the same half-cell configuration as in the other examples.

[0128] [Tables] Example 2C 5C El 0.271 0.473 E2 0.349 0.636 E3 0.285 0.486 CEI 0.463 0.657 CE2 0.543 0.863

Claims

Claims

1. A current collector comprising a polymer film, a first metal layer bonded to the polymer film, and a second metal layer bonded to the polymer film on a side opposite the first metal layer, wherein: the polymer film comprises an electroconductive filler and has a surface resistivity of 1 megaohm / square or less; the first and second metal layers each have a thickness of 3 μm or less; and the current collector has a mid-discharge voltage that is at least 20% lower than an untreated battery-grade copper foil, based on a standard lithium-ion battery half-cell test at a temperature of 25°C and a discharge rate of 2C or more.

2. The current collector of claim 1, wherein the polymer film comprises a polymer comprising an imide group.

3. The current collector of claim 1, wherein the polymer film comprises a multilayer film comprising: a first outer layer comprising a first polymer; a second outer layer comprising a second polymer; and a core layer comprising a third polymer, the core layer being located between the first and second outer layers and the electrically conductive filler being present in one or more of the layers.

4. The current collector of claim 3, wherein one or more of the first, second, and third polymers comprises a polymer comprising an imide group.

5. The current collector of claim 1, wherein the electrically conductive filler is present in the polymer film at a concentration in a range of 5 to 65 weight percent based on the total weight of the polymer film.

6. An energy storage device comprising the current collector of claim 1.

7. The energy storage device of claim 6, wherein the energy storage device is selected from the group consisting of lithium-ion batteries, capacitors, supercapacitors, fuel cells and redox flow batteries.