DRY ELECTRODES FOR LITHIUM-ION BATTERIES

Abstract

An electrode assembly for a lithium-ion battery is provided. The electrode assembly can comprise a metal foil with a conductive coating containing a polymeric binder, and a self-supporting electrode foil made of active material and fibrillated composite binder, laminated to the metal foil such that the conductive coating is located between the metal foil and the self-supporting electrode foil. The fibrillated composite binder can contain carbon particles and a similar polymeric binder.

Description

FIELD OF TECHNOLOGYThe present disclosure relates to dry electrodes for lithium ion batteries and methods of making the same.GENERAL STATE OF THE ARTA lithium ion battery is a rechargeable battery in which lithium ions move in the opposite direction during discharge from a negative electrode to a positive electrode and during charging. Batteries generally include a separator between the electrodes to physically separate the electrodes.Electrodes are typically constructed by applying an active material to a current collector in the presence of a binder that promotes adhesion between the active materials and adhesion to the current collector. The typical manufacturing process involves a wet coating or slurry casting process in which a solvent or aqueous solution is used to dissolve binder and mixed with the active materials to form a slurry. The slurry is then coated onto a current collector. The current collector is then dried together with the coating layer to remove the solvent from the electrode. An electrode formed without the use of solvents can allow easier mass production, but may interfere with the dispersion of conductive agents.SUMMARYAccording to one embodiment, there is provided an electrode assembly comprising: a metal foil having a conductive coating comprising a polymeric binder; and a self-supporting electrode active material foil and fibrillated composite binder laminated to the metal foil such that the conductive coating is between the metal foil and the self-supporting electrode foil. The fibrillated composite binder includes carbon particles and a same polymeric binder.In an alternative embodiment, a battery is provided that includes a separator and a pair of electrodes enclosing the separator therebetween. At least one of the electrodes includes laminated layers of metal foil having thereon a conductive coating comprising a polymeric binder and a self-supporting electrode active material foil and fibrillated composite binder comprising carbon particles and a same polymeric binder.In yet another embodiment, a method of dry-fabricating a battery electrode is provided, comprising hot pressing a dry electrode mixture of active material and fibrillated composite binder having carbon particles and polymeric binder to form a self-supporting electrode foil, and coating a current collector with a conductive coating including carbon particles and a same polymeric binder to form a coated current collector. The self-supporting electrode sheet is then laminated on the coated current collector to form the battery electrode.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a cross-sectional view of a dry electrode according to an embodiment. FIG. 2 is a cross-sectional view of a battery device including an example dry electrode. FIG. 3 is a schematic illustration of a method for dry-fabricating an electrode according to an embodiment.DETAILED DESCRIPTIONEmbodiments are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments may take various and alternative forms. The figures are not necessarily to scale. Some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art.Various features illustrated and described with respect to any of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not expressly illustrated or described. The illustrated combinations of features provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desirable for specific applications or implementations.One of the steps in battery manufacture generally involves coating a metal foil with active material to produce an electrode. Electrode active materials facilitate the movement of ions during charging and discharging of a battery. Positive electrode or cathode active materials are typically metal oxides including lithium cobalt oxide (LiCoO 2), lithium manganese oxide (LiMn 2 O 4), lithium iron phosphate (LiFePO 4) and lithium nickel manganese cobalt oxide (LiNiMnCoO 2). Negative electrode or anode active materials are usually graphite, but also include materials such as silicon and lithium titanate (Li 4 Ti 5 O 12). The metal foil is typically referred to as a current collector and is typically aluminum foil in a positive electrode or copper foil in a negative electrode.Electrode fabrication generally involves combining binder materials with active electrode materials and other additives and is processed in a manner by which an electrode foil is formed before the electrode foil is coated onto metal foil. Electrodes may be fabricated using wet or dry processes. Wet processes involve the use of solvents to form a slurry comprising binders, electrode active material and other additives. The slurry may then be applied to a current collector and calendered to form an electrode, after which the electrode must dry. Dry electrode processes reduce the time and energy required for fabrication because they do not require a drying step.However, dry, solvent-free electrode fabrication processes can affect the dispersion of conductive agents over the active electrode material in the electrode foil. Fine conductive particles can agglomerate without a solvent or other dispersant. Thus, electrochemical performance of a battery cell including the electrode may be impaired.According to an embodiment, an effect on dispersion of conductive agents over active electrode material in a dry manufacturing process may be alleviated by using a composite binder filled with conductive agents. The composite binder may include a polymeric binder and one or more conductive agents. The polymeric binder may include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene (PE), polyethylene oxide (PEO), elastomer, or a combination thereof. The conductive agent may include carbon black, a multi-wall carbon nanotube, a single-wall carbon nanotube, carbon nanostructures, graphene, or a combination thereof. The composite binder may be dry blended with active electrode material and then dry fibrillated. Dry fibrillation can provide well dispersed, less agglomerated conductive agents relative to active electrode materials due to the physical orientation of the fibrillated composite binder.A self-supporting electrode sheet may then be formed by hot pressing the dry electrode mixture of active electrode material and fibrillated composite binder. In one embodiment, the self-supporting electrode sheet may comprise about 1 to 30 weight percent fibrillated composite binder and about 70 to 99 weight percent electrode active material. The self-supporting electrode sheet may then be laminated to a current collector to form an electrode.According to another embodiment, the lamination and adhesion of the self-supporting electrode foil to the current collector may be improved by using a thin conductive coating applied to the current collector prior to lamination. The conductive coating can provide greater surface area and increased compatibility with the fibrillated composite binder. The conductive coating may include binder and conductive particles. The binder may have a surface energy similar to the fibrillated composite binder of the electrode sheet, and may include PTFE, PVDF, PE, PEO, elastomer, or a combination thereof. The similar surface energy can improve the lamination and adhesion strength of the electrode foil to the current collector. The conductive particles may be carbon particles including carbon black, carbon nanostructures, or combinations thereof having an average particle size of less than 2 μm. In one embodiment, the conductive coating may comprise about 50 to 99 weight percent conductive particles and about 1 to 50 weight percent binder. The conductive coating may have a thickness of less than 10 μm.After the conductive coating is applied to the current collector, the self-supporting electrode foil and the coated current collector may be laminated to form a dry electrode with improved adhesion.FIG. 1 is a cross-sectional view of a dry electrode 10 according to an embodiment. The dry electrode 10 comprises a metal foil 12 having a conductive coating 14 thereon and a self-supporting electrode foil 16 laminated to the metal foil 12, the conductive coating 14 being located between the metal foil 12 and the self-supporting electrode foil 16. The metal foil 12 may be aluminum or copper foil and may be referred to as a current collector.The self-supporting electrode sheet 16 includes an electrode active material and a fibrillated composite binder. The self-supporting electrode sheet 16 can mesh from about 1 to 30 weight percent of the fibrillated composite binder and from about 70 to 99 weight percent of the active material. The fibrillated composite binder includes carbon particles and polymeric binder. The polymeric binder may include PTFE, PVDF, PE, PEO, elastomer, or a combination thereof, and the carbon particles may include carbon black, multi-wall carbon nanotubes, single-wall carbon nanotubes, carbon nanostructures, graphene, or a combination thereof.The conductive coating 14 includes a polymeric binder that may include PTFE, PVDF, PE, PEO, elastomer, or a combination thereof. The polymeric binder may be the same polymeric binder as the fibrillated composite binder of the self-supporting electrode sheet 16. The conductive coating 14 may further include carbon particles, including carbon black, carbon nanostructures, or combinations thereof. The conductive coating 14 may constitute about 50 to 99 weight percent of the carbon particles and about 1 to 50 weight percent of the polymeric binder. The conductive coating 14 may have a thickness of 10 μm or less.FIG. 2 is a cross-sectional view of a battery device 200 including an example dry electrode according to an embodiment. The battery device 200 includes a separator 202 between an electrode 204 and an electrode 206. In one variation, electrode 204 may be a positive electrode and electrode 206 may be a negative electrode. In another variation, electrode 204 may be a negative electrode and electrode 206 may be a positive electrode. As shown, the electrode 204 includes a metal foil 208 having a conductive coating 210 thereon and a self-supporting electrode foil 212 laminated to the metal foil 208, wherein the conductive coating 210 is located between the metal foil 208 and the self-supporting electrode foil 212. The metal foil 208 may be aluminum or copper foil.The self-supporting electrode sheet 212 includes an electrode active material and a fibrillated composite binder. The self-supporting electrode sheet 212 may constitute about 1 to 30 weight percent of the fibrillated composite binder and about 70 to 99 weight percent of the active material. The fibrillated composite binder includes carbon particles and polymeric binder. The polymeric binder may include PTFE, PVDF, PE, PEO, elastomer, or a combination thereof, and the carbon particles may include carbon black, multi-wall carbon nanotubes, single-wall carbon nanotubes, carbon nanostructures, graphene, or a combination thereof.The conductive coating 210 includes a polymeric binder that may include PTFE, PVDF, PE, PEO, elastomer, or a combination thereof. The polymeric binder may be the same polymeric binder as the fibrillated composite binder of the self-supporting electrode sheet 212. The conductive coating 210 may further include carbon particles including carbon black, carbon nanostructures, or combinations thereof. The conductive coating 210 may constitute about 50 to 99 weight percent of the carbon particles and about 1 to 50 weight percent of the polymeric binder. The conductive coating 210 may have a thickness of 10 μm or less.The electrode 206 includes a metal foil 214 and a self-supporting electrode foil 216. The self-supporting electrode sheet 216 may include an electrode active material and a fibrillated composite binder. The self-supporting electrode sheet 216 may constitute about 1 to 30 weight percent of the fibrillated composite binder and about 70 to 99 weight percent of the active material. The fibrillated composite binder includes carbon particles and polymeric binder. The polymeric binder may include PTFE, PVDF, PE, PEO, elastomer, or a combination thereof, and the carbon particles may include carbon black, multi-wall carbon nanotubes, single-wall carbon nanotubes, carbon nanostructures, graphene, or a combination thereof. In an embodiment, the electrode 206 may further include a conductive coating between the metal foil 214 and the self-supporting electrode foil 216.FIG. 3 is a schematic diagram showing a method for dry-manufacturing an electrode 38. First, a dry electrode mixture of active electrode material and fibrillated composite binder is hot pressed to form a self-supporting electrode sheet 30. The fibrillated composite binder includes carbon particles and polymeric binder. The polymeric binder may include PTFE, PVDF, PE, PEO, elastomer, or a combination thereof, and the carbon particles may include carbon black, multi-wall carbon nanotubes, single-wall carbon nanotubes, carbon nanostructures, graphene, or a combination thereof. The self-supporting electrode sheet 30 may constitute about 1 to 30 weight percent of the fibrillated composite binder and about 70 to 99 weight percent of the active material.Next, the metal foil 32 is coated with the conductive coating 34 to form a coated current collector 36. The metal foil 32 may be aluminum or copper foil. The conductive coating 34 includes a polymeric binder that may include PTFE, PVDF, PE, PEO, elastomer, or a combination thereof. The polymeric binder may be the same polymeric binder as the fibrillated composite binder of the self-supporting electrode sheet 30. The conductive coating 34 may further include carbon particles including carbon black, carbon nanostructures, or combinations thereof. The conductive coating 34 may constitute about 50 to 99 weight percent of the carbon particles and about 1 to 50 weight percent of the polymeric binder. The conductive coating 34 may have a thickness of 10 μm or less.Finally, the self-supporting electrode sheet 30 is laminated to the coated current collector 36 to form the electrode 38. It should be noted that the dry manufacturing process does not involve the use of solvents.The algorithms, methods, or processes disclosed herein may be executable or implemented by a computer, controller, or processing device, which may include any dedicated electronic control unit or programmable electronic control unit. Additionally, the algorithms, methods, or processes may be stored in many forms as computer or controller executable data and instructions including, without limitation, information permanently stored on non-writable storage media such as read-only memory devices and information alterably stored on writeable storage media such as compact discs, random access memory devices, or other magnetic and optical media. The algorithms, methods, or processes may also be implemented in software executable objects. Alternatively, the algorithms, methods, or processes may be implemented in whole or in part using suitable hardware components, such as application specific integrated circuits, field programmable gate arrays, state machines, or other hardware components or devices, or a combination of firmware, hardware, and software components.While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The terms used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure.As previously described, the features of various embodiments may be combined to form further embodiments of the invention that may not be expressly described or illustrated. While various embodiments could have been described as providing or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art will understand that one / more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes may include, but are not limited to, strength, durability, marketability, appearance, packaging, size, serviceability, weight, mikroability, ease of assembly, etc. Thus, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.According to the present invention, there is provided an electrode assembly comprising: a metal foil having a conductive coating thereon comprising a polymeric binder; and a self-supporting electrode active material foil and fibrillated composite binder comprising carbon particles and a same polymeric binder laminated to the metal foil such that the conductive coating is between the metal foil and the self-supporting electrode foil.According to one embodiment, the carbon particles include carbon soot and nanostructures.According to one embodiment, the nanostructures are multi-walled, single-walled, graphene, or combinations thereof.In one embodiment, the self-supporting electrode sheet comprises 1 to 30 weight percent of the fibrillated composite binder.According to one embodiment, the self-supporting electrode foil comprises 70 to 99 weight percent of the active material.According to an embodiment, the conductive coating further includes carbon particles.According to an embodiment, the carbon particles of the conductive coating include carbon black, nanostructures, or combinations thereof.According to one embodiment, the conductive coating comprises 50 to 99 weight percent of the carbon particles of the conductive coating.In one embodiment, the conductive coating comprises from 1 to 50 weight percent of the polymeric binder.According to an embodiment, a thickness of the conductive coating is 10 μm or less.According to the present invention, there is provided a battery comprising: a separator; and a pair of electrodes enclosing the separator therebetween, wherein at least one of the electrodes comprises laminated layers of (i) metal foil having thereon a conductive coating comprising a polymeric binder, and (ii) a self-supporting electrode active material foil and fibrillated composite binder comprising carbon particles and a same polymeric binder.According to one embodiment, the carbon particles include carbon soot and nanostructures.According to one embodiment, the nanostructures are multi-walled, single-walled, graphene, or combinations thereof.In one embodiment, the self-supporting electrode sheet comprises 1 to 30 weight percent of the fibrillated composite binder.In one embodiment, the conductive coating comprises from 1 to 50 weight percent of the polymeric binder.According to an embodiment, the conductive coating further includes carbon particles.According to an embodiment, the carbon particles of the conductive coating include carbon black, nanostructures, or combinations thereof.According to an embodiment, a thickness of the conductive coating is 10 μm or less.According to the present invention, there is provided a method of dry-manufacturing a battery electrode, comprising: hot pressing a dry electrode mixture of active material and fibrillated composite binder comprising carbon particles and polymeric binder to form a self-supporting electrode sheet; coating a current collector with a conductive coating comprising carbon particles and a same polymeric binder to form a coated current collector; and laminating the self-supporting electrode sheet on the coated current collector to form the battery electrode.

Claims

An electrode assembly comprising: a metal foil having a conductive coating thereon that includes a polymeric binder; and a self-supporting electrode active material foil and fibrillated composite binder that includes carbon particles and a same polymeric binder laminated to the metal foil such that the conductive coating is between the metal foil and the self-supporting electrode foil.The electrode assembly of claim 1, wherein the carbon particles include carbon soot and nanostructures.The electrode assembly of claim 2, wherein the nanostructures are multi-walled, single-walled, graphene, or combinations thereof.The electrode assembly of claim 1, wherein the self-supporting electrode sheet comprises 1 to 30 weight percent of the fibrillated composite binder.The electrode assembly of claim 1, wherein the self-supporting electrode foil comprises 70 to 99 weight percent of the active material.The electrode assembly of claim 1, wherein the conductive coating further includes carbon particles.The electrode assembly of claim 6, wherein the carbon particles of the conductive coating include carbon black, nanostructures, or combinations thereof.The electrode assembly of claim 6, wherein the conductive coating constitutes 50 to 99 weight percent of the carbon particles of the conductive coating.The electrode assembly of claim 1, wherein the conductive coating comprises 1 to 50 weight percent of the polymeric binder.The electrode assembly of claim 1, wherein a thickness of the conductive coating is 10 μm or less.A battery comprising: a separator; and a pair of electrodes enclosing the separator therebetween, wherein at least one of the electrodes comprises laminated layers of (i) metal foil having thereon a conductive coating comprising a polymeric binder, and (ii) a self-supporting electrode active material foil and fibrillated composite binder comprising carbon particles and a same polymeric binder.The battery of claim 11, wherein the carbon particles include carbon soot and nanostructures.The battery of claim 12, wherein the nanostructures are multi-walled, single-walled, graphene, or combinations thereof.The battery of claim 11, wherein the self-supporting electrode sheet comprises 1 to 30 weight percent of the fibrillated composite binder.A method of dry-fabricating a battery electrode, comprising: hot pressing a dry electrode mixture of active material and fibrillated composite binder having carbon particles and polymeric binder to form a self-supporting electrode foil; coating a current collector with a conductive coating including carbon particles and a same polymeric binder to form a coated current collector; and laminating the self-supporting electrode foil to the coated current collector to form the battery electrode.

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