Multi-layered coating formed by different processes

A method for forming one or more layers of a lithium-ion battery includes a step of sequentially depositing a wet coating and a free-standing material layer onto a moving substrate to form a first bilayer on the substrate. The first bilayer including a wet coating-derived layer and the free-standing material layer. The first bilayer is heat roll pressed to form a second bilayer in which the wet coating-derived layer is at least partially dried and adhered to the free-standing material layer.

TECHNICAL FIELD

In at least one aspect, a method and system for continuously forming layers for a lithium-ion battery are provided.

BACKGROUND

Multi-layer coatings offer increased performance and allows active material tailoring at higher resolution. Attributes such as high energy and high power are possible with such multi-layer coating. However, the processing of multi-layered may introduce inefficiencies due to repeated, redundant processes. For example, a dual-layer coating of larger and smaller NCM cathode layers may involve running multiple coating steps that can increase process time by at least a factor of two.

Accordingly, there is a need for hybrid processes that efficiently integrate diverse layers and active materials.

SUMMARY

In at least one aspect, a method for forming one or more layers of a lithium-ion battery is provided. The method includes a step of sequentially depositing a wet coating and a free-standing material layer onto a moving substrate to form a first bilayer on the substrate. The first bilayer includes a wet coating-derived layer and the free-standing material layer. The first bilayer is heat roll pressed to form a second bilayer in which the wet coating-derived layer is at least partially dried and adhered to the free-standing material layer.

In another aspect, a multi-layer coating system for continuously forming one or more layers of a lithium-ion battery is provided. The multi-layer coating system includes a wet coating station that deposits depositing a wet coating onto a moving substrate and a free-standing material layer station that applies a free-standing material layer to the wet coating to form a first bilayer. The first bilayer includes a wet coating-derived layer and the free-standing material layer. The multi-layer coating system also includes a heat roll pressing station that heat roll presses the first bilayer to form a second bilayer in which the wet coating-derived layer is at least partially dried and adhered to the free-standing material layer.

DETAILED DESCRIPTION

Except in the examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred. Also, unless expressly stated to the contrary: when a given chemical structure includes a substituent on a chemical moiety (e.g., on an aryl, alkyl, etc.) that substituent is imputed to a more general chemical structure encompassing the given structure; percent, “parts of,” and ratio values are by weight; the term “polymer” includes “oligomer,” “copolymer,” “terpolymer,” and the like; molecular weights provided for any polymers refers to weight average molecular weight unless otherwise indicated; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among the constituents of a mixture once mixed; the first definition of an acronym or other abbreviation applies to all subsequent uses herein of the same abbreviation and applies mutatis mutandis to normal grammatical variations of the initially defined abbreviation; and, unless expressly stated to the contrary, measurement of a property is determined by the same technique as previously or later referenced for the same property.

As used herein, the term “about” means that the amount or value in question may be the specific value designated or some other value in its neighborhood. Generally, the term “about” denoting a certain value is intended to denote a range within +/−5% of the value. As one example, the phrase “about 100” denotes a range of 100+/−5, i.e. the range from 95 to 105. Generally, when the term “about” is used, it can be expected that similar results or effects according to the invention can be obtained within a range of +/−5% of the indicated value.

As used herein, the term “and/or” means that either all or only one of the elements of said group may be present. For example, “A and/or B” shall mean “only A, or only B, or both A and B”. In the case of “only A”, the term also covers the possibility that B is absent, i.e. “only A, but not B”.

The phrase “composed of” means “including” or “consisting of” Typically, this phrase is used to denote that an object is formed from a material.

The term “one or more” means “at least one” and the term “at least one” means “one or more.” The terms “one or more” and “at least one” include “plurality” and “multiple” as a subset. In a refinement, “one or more” includes “two or more.”

The term “substantially,” “generally,” or “about” may be used herein to describe disclosed or claimed embodiments. The term “substantially” may modify a value or relative characteristic disclosed or claimed in the present disclosure. In such instances, “substantially” may signify that the value or relative characteristic it modifies is within ±0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5% or 10% of the value or relative characteristic.

When referring to a numeral quantity, in a refinement, the term “less than” includes a lower non-included limit that is 5 percent of the number indicated after “less than.” For example, “less than 20” includes a lower non-included limit of 1 in a refinement. Therefore, this refinement of “less than 20” includes a range between 1 and 20. In another refinement, the term “less than” includes a lower non-included limit that is, in increasing order of preference, 20 percent, 10 percent, 5 percent, or 1 percent of the number indicated after “less than.”

The term “positive electrode” means a battery cell electrode from which current flows out when the lithium-ion battery cell or battery is discharged. Sometimes a “positive electrode” is referred to as a “cathode.”

The term “negative electrode” means a battery cell electrode to which current flows in when the lithium-ion battery cell is discharged. Sometimes a “negative electrode” is referred to as an “anode.”

The term “cell” or “battery cell” means an electrochemical cell made of at least one positive electrode, at least one negative electrode, an electrolyte, and a separator membrane.

The term “battery” or “battery pack” means an electric storage device made of at least one battery cell. In a refinement, “battery” or “battery pack” is an electric storage device made of a plurality of battery cells.

Abbreviations

“LCO” means lithium cobalt oxide.“NCM” means lithium nickel cobalt manganese oxide.“NCMA” means lithium nickel cobalt manganese aluminum oxide.“NCA” means lithium nickel cobalt aluminum oxide.“LFP” means lithium iron phosphate.“LMP” means lithium manganese phosphate.“LVP” means lithium vanadium phosphate.“LMO” means lithium manganate.

Referring toFIGS.1A and1B, methods for continuously forming one or more layers of a lithium-ion battery with a multi-layer coating system are schematically illustrated. Multilayer coating systems10and10′ include a wet coating station12, a free-standing material layer station14, and a heat roll pressing station16. The method includes a step of sequentially depositing a wet coating20from the wet coating station12and a free-standing material layer22from free-standing material layer station14onto a moving substrate24to form a first bilayer26on the substrate. Examples of wet coating stations include slot-die systems, gravure systems, reverse comma systems, and the like. The wet coating system12can directly apply to active material slurry onto the moving substrate.

Still referring toFIGS.1A and1B, first bilayer26includes a wet coating-derived layer and the free-standing material layer. The first bilayer is heat roll pressed by heat roll pressing station16to form a second bilayer28in which the wet coating-derived layer is at least partially dried. Moreover, the pressing can at least partially adhere the wet coating layer to the free-standing material layer. In a refinement, the first bilayer is (mildly) pressed under heat (e.g., from about 70 to 100° C.) to form the second bilayer. The second bilayer28can then be further dried, for example by drier32. In the variation depicted inFIG.1A, the wet coating is applied before the free-standing material layer is applied. In another variation as depicted inFIG.1B, the wet coating is applied after the free-standing material layer is applied. In this variation, surface priming for effective adhesion of the free-standing material layer to the substrate can be implemented.

In a variation, substrate24is a current collector. Therefore, substrate24can be composed of a metal. Examples of suitable metals include but are not limited to aluminum, copper, platinum, zinc, titanium, and the like. In the case when bilayer28includes a positive electrode active material, the current collector is typically composed of aluminum.

In one variation, the wet coating-derived layer includes a first positive electrode active material and the free-standing material layer each includes a second positive electrode active material such that the second bilayer is a positive electrode. In a variation, the primary positive electrode material includes nickel in an amount from about 35 weight percent to about 75 weight percent of the total weight of the primary positive electrode material. In some refinements, the primary positive electrode material includes nickel in an amount of at least 30 weight percent, 35 weight percent, 40 weight percent, 45 weight percent, 50 weight percent, or 55 weight percent of the total weight of the primary positive electrode material and at most in increasing order of preference 99 weight percent, 95 weight percent, 90 weight percent, 85 weight percent, 80 weight percent, or 70 weight percent of the total weight of the primary positive electrode material. In a refinement, the first positive electrode active material can include a component selected from the group consisting of lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCM, lithium nickel cobalt manganese aluminum oxide (NCMA), and combinations thereof. In a refinement, the first positive electrode active material is different than the second positive electrode active material. In another refinement, the first positive electrode active material is the same as the second positive electrode active material. In another refinement, the first positive electrode active material has a different average particle size and particle size distribution than the second positive electrode active material. This latter refinement is particularly applicable when the first positive electrode active material is the same as the second positive electrode active material. In a further refinement, the first positive electrode active material has a larger average particle size than the second positive electrode active material.

In another variation, the free-standing material layer includes a dry coating binder. The dry coating binder can include a component selected from the group consisting of polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, and combinations thereof. In a refinement, the dry coating binder has pores of sufficient size to pass lithium ions. The pores can have an average size greater than 50 Å. In a refinement, the pores have an average size greater than 100 Å. In a variation, the wet coating-derived layer includes a positive electrode active material. In a refinement, the second bilayer includes a positive electrode attached to a separator.

With reference toFIG.2A, a schematic of a rechargeable lithium-ion battery cell that can be constructed from second bilayer28ofFIG.1is provided. Battery cell40includes positive electrode42. Positive electrode42includes second bilayer28disposed over substrate24fabricated in accordance with the method ofFIG.1A. In this variation, second bilayer28is the positive electrode active layer and substrate24is the positive electrode current collector. Typically, positive electrode current collector is a metal plate or metal foil composed of a metal such as aluminum, copper, platinum, zinc, titanium, and the like. Currently, aluminum is most commonly used for the negative electrode current collector. Battery cell40also includes negative electrode46and separator48interposed between the positive electrode and the negative electrode. Similarly, negative electrode46includes a negative electrode current collector50and a negative active material layer52disposed over and typically contacting the negative electrode current collector. Typically, negative electrode current collector50is a metal plate or metal foil composed of a metal such as aluminum, copper, platinum, zinc, titanium, and the like. Currently, copper is most commonly used for the negative electrode current collector. The battery cell is immersed in electrolyte54which is enclosed by battery cell case56. Electrolyte50imbibes into separator36. In other words, the separator48includes the electrolyte thereby allowing lithium ions to move between the negative and positive electrodes. The electrolyte includes a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent serves as a medium for transmitting ions taking part in the electrochemical reaction of a battery.

With reference toFIG.2B, a schematic of a rechargeable lithium-ion battery cell that can be constructed from second bilayer28ofFIG.1is provided. Battery cell40′ includes positive electrode42. Positive electrode42includes second bilayer28disposed over substrate24fabricated in accordance with the method ofFIG.1A. In this variation, substrate24is the positive electrode current collector as described above. Second bilayer28includes positive electrode active layer58and separator48. Battery cell40′ also includes negative electrode46and separator48interposed between the positive electrode and the negative electrode. Similarly, negative electrode46includes a negative electrode current collector50and a negative active material layer52disposed over and typically contacting the negative electrode current collector as set forth above. The battery cell is immersed in electrolyte54which is enclosed by battery cell case56. Electrolyte50imbibes into separator36. In other words, the separator48includes the electrolyte thereby allowing lithium ions to move between the negative and positive electrodes. As set forth above, the electrolyte includes a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent serves as a medium for transmitting ions taking part in the electrochemical reaction of a battery.

With reference toFIG.3, a schematic of a rechargeable lithium-ion battery incorporating the battery cells ofFIGS.2A-Bis provided. Rechargeable lithium-ion battery60includes at least one battery cell of the design inFIG.2. Typically, rechargeable lithium-ion battery60includes a plurality of battery cells62iof the design ofFIG.2A or2Bwhere i is an integer label for each battery cell. The label i runs from 1 to nmax, where nmax is the total number of battery cells in rechargeable lithium-ion battery60.

Referring toFIGS.2A-Band3, separator48physically separates the negative electrode46from the positive electrode32thereby preventing shorting while allowing the transport of lithium ions for charging and discharging. Therefore, separator48can be composed of any material suitable for this purpose. Examples of suitable materials from which separator48can be composed include but are not limited to, polytetrafluoroethylene (e.g., TEFLON®), glass fiber, polyester, polyethylene, polypropylene, and combinations thereof. Separator48can be in the form of either a woven or non-woven fabric. Separator36can be in the form of a non-woven fabric or a woven fabric. For example, a polyolefin-based polymer separator such as polyethylene and/or polypropylene is typically used for a lithium-ion battery. In order to ensure heat resistance or mechanical strength, a coated separator includes a coating of ceramic or a polymer material may be used.

Referring toFIGS.2and3, electrolyte54includes a lithium salt dissolved in the non-aqueous organic solvent. Therefore, electrolyte54includes lithium ions that can intercalate into the positive electrode active material during charging and into the anode active material during discharging. Examples of lithium salts include but are not limited to LiPF6, LiBF4, LiSbF6, LiAsF6, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiCl, LiI, LiB(C2O4)2, and combinations thereof. In a refinement, the electrolyte includes the lithium salt in an amount from about 0.1 M to about 2.0 M.

Still referring toFIGS.2and3, the electrolyte includes a non-aqueous organic solvent and a lithium salt. Advantageously, the non-aqueous organic solvent serves as a medium for transmitting ions, and in particular, lithium ions participate in the electrochemical reaction of a battery. Suitable non-aqueous organic solvents include carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, aprotic solvents, and combinations thereof. Examples of carbonate-based solvents include but are not limited to dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, and combinations thereof. Examples of ester-based solvents include but are not limited to methyl acetate, ethyl acetate, n-propyl acetate, methylpropionate, ethylpropionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, and combinations thereof. Examples of ether-based solvents include but are not limited to dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and the like, and the ketone-based solvent may include cyclohexanone, and the like. Examples of alcohol-based solvent include but are not limited to methanol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, and the like. Examples of the aprotic solvent include but are not limited to nitriles such as R—CN (where R is a C2-20linear, branched, or cyclic hydrocarbon that may include a double bond, an aromatic ring, or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like. Advantageously, the non-aqueous organic solvent can be used singularly. In other variations, mixtures of the non-aqueous organic solvent can be used. Such mixtures are typically formulated to optimize battery performance. In a refinement, a carbonate-based solvent is prepared by mixing a cyclic carbonate and a linear carbonate. In a variation, electrolyte54can further include vinylene carbonate or an ethylene carbonate-based compound to increase battery cycle life.

Referring toFIGS.2B and3, the negative electrode46can be fabricated by methods known to those skilled in the art of lithium-ion batteries. The positive electrode is fabricated as shown above. Typically, an active material (e.g., the negative active material) is mixed with a conductive material, and a binder in a solvent (e.g., N-methylpyrrolidone) into an active material composition and coating the composition on a current collector. In the case of the positive electrode, the active material composition is coated using the coating systems described above.

Referring toFIGS.2A-Band3, the positive electrode active material layer includes positive electrode active material, a binder, and a conductive material. The positive electrode active materials used herein can be those positive electrode materials known to one skilled in the art of lithium-ion batteries. In particular, the positive electrode may be formed from a lithium-based active material that can sufficiently undergo lithium intercalation and deintercalation. The positive electrode32active materials may include one or more transition metals, such as manganese (Mn), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), vanadium (V), and combinations thereof. Common classes of positive electrode active materials include lithium transition metal oxides with layered structure and lithium transition metal oxides with spinel phase. Examples of lithium transition metal oxides with layered structure include, but are not limited to lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), a lithium nickel manganese cobalt oxide (e.g., Li(NixMnyCoz)O2), where 0≤x≤1, 0≤y≤1, 0≤z≤1, and x+y+z=1), a lithium nickel cobalt metal oxide (e.g., LiNi(1-x-y)CoxMyO2), where 0<x<1, 0<y<1 and M is Al, Mn). Other known lithium-transition metal compounds such as lithium iron phosphate (LiFePO4) or lithium iron fluorophosphate (Li2FePO4F) can also be used. In certain aspects, the positive electrode32may include an electroactive material that includes manganese, such lithium manganese oxide (Li(1+x)Mn(2-x)O4), a mixed lithium manganese nickel oxide (LiMn(2-x)NixO4), where 0≤x≤1, and/or a lithium manganese nickel cobalt oxide.

The binder for the positive electrode active material can increase the binding properties of positive electrode active material particles with one another and with the positive electrode current collector42. Examples of suitable binders include but are not limited to polyvinyl alcohol, carboxylmethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinylchloride, carboxylated polyvinylchloride, polyvinylfluoride, an ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, a styrene-butadiene rubber, an acrylate styrene-butadiene rubber, an epoxy resin, nylon, and the like, and combinations thereof. The conductive material provides positive electrode10with electrical conductivity. Examples of suitable electrically conductive materials include but are not limited to natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, copper, metal powders, metal fibers, and combinations thereof. Examples of metal powders and metal fibers are composed of including nickel, aluminum, silver, and the like.

Referring toFIGS.2A-Band3, the negative active material layer52includes a negative active material, includes a binder, and optionally a conductive material. The negative active materials used herein can be those negative materials known to one skilled in the art of lithium-ion batteries. Negative active materials include but are not limited to, carbon-based negative active materials, silicon-based negative active materials, and combinations thereof. A suitable carbon-based negative active material may include graphite and graphene. A suitable silicon-based negative active material may include at least one selected from silicon, silicon oxide, silicon oxide coated with conductive carbon on the surface, and silicon (Si) coated with conductive carbon on the surface. For example, silicon oxide can be described by the formula SiOzwhere z is from 0.09 to 1.1. Mixtures of carbon-based negative active materials, silicon-based negative active materials can also be used for the negative active material.

The negative electrode binder increases the binding properties of negative active material particles with one another and with a current collector. The binder can be a non-aqueous binder, an aqueous binder, or a combination thereof. Examples of non-aqueous binder may be polyvinylchloride, carboxylated polyvinylchloride, polyvinylfluoride, an ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof. Aqueous binders can be rubber-based binders or polymer resin binders. Examples of rubber-based binders include but are not limited to styrene-butadiene rubbers, acrylated styrene-butadiene rubbers, acrylonitrile-butadiene rubbers, acrylic rubbers, butyl rubbers, fluorine rubbers, and combinations thereof. Examples of polymer resin binders include but are not limited to polyethylene, polypropylene, ethylenepropylene copolymer, polyethyleneoxide, polyvinylpyrrolidone, epichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, a polyester resin, an acrylic resin, a phenolic resin, an epoxy resin, polyvinyl alcohol and combinations thereof.