Electrodes for energy storage devices

Abstract

Disclosed herein is an electrode comprising an active layer, the active layer comprising a network of high aspect ratio carbon elements defining voids within the network, a plurality of electrode active material particles disposed in the voids within the network, and a first binder material comprising a water-soluble styrene-butadiene rubber. Also disclosed herein is a method of making the active layer, the method comprising mixing together the water-soluble styrene-butadiene rubber, the plurality of high aspect ratio carbon elements, the plurality of electrode active material particles, and a solvent to form a slurry, disposing the slurry on a surface of a metal foil, and drying the slurry to form the active layer.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Patent Application No. 63 / 403,138, filed September 1, 2022, which is incorporated herein by reference in its entirety. [Background technology]

[0002] Storage devices, such as electric super-layer capacitors and batteries, are used in many products, including medical devices, electric vehicles, airplanes, and consumer products such as laptop computers, mobile phones, and cameras. Lithium-ion batteries have overtaken the secondary battery market due to their high energy density, high operating voltage, and low self-discharge, and continue to find new applications in products and evolving industries.

[0003] Generally, a lithium ion battery ("LIB" or "LiB") or electric double layer capacitor includes an anode, a cathode, and an electrolyte material, such as an organic solvent containing a lithium salt. More specifically, the anode and cathode (collectively "electrodes") are formed by mixing either the anode or cathode active material with a binder and a solvent to form a paste or slurry, which is then coated onto a current collector, such as aluminum or copper, and dried to form a film on the current collector. The anode and cathode are then layered or coiled before being housed within a pressurized casing containing the electrolyte material, all of which together form a lithium ion battery.

[0004] Conventional electrodes use binders with sufficient adhesive, cohesive, and chemical properties to ensure that the film coated on the current collector maintains contact with the current collector, even when manipulated to fit into a pressurized battery casing. Because the film contains the electrode active material, if the film does not maintain sufficient contact with the current collector, it is likely to significantly interfere with the electrochemical performance of the battery. Furthermore, it has been important to select a binder that is mechanically compatible with the electrode active material so that it can withstand the degree of expansion and contraction of the electrode active material during battery charging and discharging.

[0005] Therefore, binders such as cellulosic binders or cross-linked polymer binders have been used to provide good mechanical properties, however, in conventional electrodes, the binders selected generally require environmentally unfriendly or toxic solvents for processing. Summary of the Invention

[0006] Disclosed herein is an electrode comprising an active layer, the active layer including a network of high aspect ratio carbon elements defining voids within the network, a plurality of electrode active material particles disposed in the voids within the network, and a first binder material including a water-soluble styrene butadiene rubber.

[0007] Also disclosed herein is a method of making an active layer, the method comprising mixing together a water soluble styrene butadiene rubber, a plurality of high aspect ratio carbon elements, a plurality of electrode active material particles, and a solvent to form a slurry; disposing the slurry on a surface of a metal foil; and drying the slurry to form an active layer. [Brief explanation of the drawings]

[0008] The following is a brief description of the drawings, in which like elements are numbered alike and which are presented for the purpose of illustrating, but not for the purpose of limiting, exemplary embodiments disclosed herein. [Figure 1] 1A-1C are diagrams of electrodes according to various embodiments. [Figure 2] 1 is a flowchart of a method for fabricating an electrode according to various embodiments. [Figure 3] FIG. 1 is a diagram of electrode placement in a pouch cell device. [Figure 4] 1 is a schematic cross-sectional depiction showing an embodiment of an energy storage device (ESD). DETAILED DESCRIPTION OF THE INVENTION

[0009] A more complete understanding of the components, processes, and apparatus disclosed herein can be obtained by reference to the accompanying drawings. These figures are merely schematic representations based on convenience and ease of illustrating the disclosure and, as such, are not intended to indicate the relative sizes and dimensions of the devices or their components and / or to define or limit the scope of the exemplary embodiments. Although specific terms are used in the following description for clarity, these terms are intended to refer only to the particular structures of the embodiments selected for illustration in the drawings and are not intended to define or limit the scope of the disclosure. It should be understood that in the drawings and the following description, like numerical designations refer to components of similar function.

[0010] Disclosed herein is an electrolysis cell that includes a housing containing electrodes (one or more anodes and one or more cathodes). The housing contains an electrolyte in contact with each of the anodes and cathodes. Each electrode (anode and cathode) includes a current collector on which an active layer is disposed. The active layer may be disposed on an optional adhesive layer in contact with the electrode. The housing includes a separator material between the electrodes (anode and cathode).

[0011] FIG. 1 is a diagram of an electrode (anode or cathode) according to various embodiments. In the illustrated example, an electrode 100 is provided. According to various embodiments, the electrode 100 includes a current collector 102 and an active layer 106. The electrode 100 may optionally include an adhesion layer 104. By way of example, the adhesion layer 104 includes a material that promotes adhesion between the current collector 102 and the active layer 106.

[0012] In an embodiment, with reference to FIG. 1 , the electrode (anode or cathode) includes a current collector 102, which is a conductive layer. For example, the current collector 102 may be a metal, a metal alloy, or the like. As another example, the current collector 102 is a metal foil. In some embodiments, the current collector 102 is an aluminum foil or an aluminum alloy foil. In some embodiments, the current collector 102 is a copper foil or a copper alloy foil. The current collector 102 has a thickness of less than 30 μm. The current collector 102 has a thickness of less than 10 μm. The current collector 102 has a thickness of less than 8 μm. The current collector 102 has a thickness of less than 5 μm. In an embodiment, the current collector 102 has a thickness of 3 to 15 μm. In some preferred embodiments, the current collector 102 has a thickness of about 6 μm to about 8 μm. In some embodiments, the current collector 102 is an aluminum foil or an aluminum alloy foil, and the current collector 102 has a thickness of about 6 μm.

[0013] The active layer 106 used in the electrode includes a first conductive material, a first binder material, a second binder material (the first binder material and the second binder material are sometimes referred to as polymer binders), and a first active material. FIG. 2 shows a process 200 for preparing the electrode. The process includes mixing the first conductive material, the second binder material, the first active material, and a solvent to form a first slurry 202. The first slurry is mixed using a combination of shearing, elongation, and stretching forces to separate some or all of the carbon nanotube bundles. The first slurry can be stored in a container for as long as desired. If desired, the first slurry 202 can be mixed with a second binder to form a second slurry 204. The second slurry 204 is in a gel or paste state. The second slurry 204 can be placed on a current collector and dried to form the active layer 206. In embodiments, the slurry can be disposed on a current collector, or optionally on an adhesive layer, to form an active layer.

[0014] The first conductive material comprises one or more high aspect ratio carbon elements comprising a substantially cylindrical network of carbon atoms. The first conductive material comprises a first set of carbon nanotubes or a plurality of bundles of first carbon nanotubes. The first conductive material may be referred to herein (individually and in combination) as high aspect ratio carbon elements. In embodiments, the term "high aspect ratio carbon elements" refers to carbonaceous elements having a size in one or more dimensions ("major dimensions") that is significantly larger than the size of the element in a transverse dimension ("minor dimension").

[0015] The first conductive material forms a conductive permeating network that can transmit current between any two separated points located on the surface of the solid active layer (without solvent therein). In other words, current can be transmitted from one surface of the active layer to the opposite surface by physical contact or electron hopping between the conductive materials in the active layer. The permeating network contains voids between the high aspect ratio carbon elements that house the active material.

[0016] In some embodiments, the active layer includes (i) a network of high aspect ratio carbon elements defining voids within the network, (ii) a plurality of electrode active material particles disposed within the voids within the network, and (iii) a polymeric binder including styrene-butadiene rubber in latex form. In embodiments, the polymeric binder further includes water-soluble cellulose. The first binder material is styrene-butadiene rubber in latex form. The second binder material is cellulose.

[0017] The first conductive material includes high aspect ratio carbon elements, which can include single wall carbon nanotubes (SWCNTs), multiwall carbon nanotubes (MWNTs), or a combination thereof.

[0018] In embodiments, the first conductive material comprises single-walled carbon nanotubes. The single-walled carbon nanotubes have an outer diameter of 0.5 to 5.0 nanometers, preferably 1.0 to 3.5 nanometers. In embodiments, the single-walled carbon nanotubes have an aspect ratio (length to diameter ratio) of greater than about 2.0, preferably greater than 5.0, preferably greater than 10.0, greater than 50, and more preferably greater than 100. In exemplary embodiments, the single-walled carbon nanotubes have an average aspect ratio of 5 to 200.

[0019] In embodiments, the single-walled carbon nanotubes have a length greater than 6 nanometers, preferably greater than 10 nanometers, preferably greater than 15 nanometers, preferably greater than 30 nanometers, preferably greater than 50 nanometers, more preferably greater than 100 nanometers, preferably greater than 1 micrometer, preferably greater than 5 micrometers, preferably greater than 10 micrometers, more preferably greater than 15 micrometers, up to at least 200 micrometers. In exemplary embodiments, the single-walled carbon nanotubes have an average length of between 100 nanometers (0.1 micrometers) and 20 micrometers, preferably between 1 micrometer and 15 micrometers.

[0020] In embodiments, the first conductive material may comprise high aspect ratio carbon elements bounded by a plurality of carbon walls. In embodiments, the conductive material comprises multi-walled carbon nanotubes (MWNTs). The number of carbon layers in the multi-walled carbon nanotubes may be 2 or more, 5 or more, 10 or more, or 50 or more. According to various embodiments, the multi-walled carbon nanotubes comprise an average of 3 to 15 layers. In some embodiments, the multi-walled carbon nanotubes comprise an average of 4 to 12 layers. In some embodiments, the multi-walled carbon nanotubes comprise an average of 5 to 10 layers. In some embodiments, the multi-walled carbon nanotubes comprise an average of 6 to 7 layers. In some embodiments, the multi-walled carbon nanotubes comprise an average of at least 6 layers.

[0021] The multi-walled carbon nanotubes have an outer diameter of 2 to 50 nanometers, preferably 5 to 40 nanometers, more preferably 6 to 11 nanometers. In embodiments, the multi-walled carbon nanotubes have an aspect ratio (length to diameter ratio) greater than 5, preferably greater than 10, greater than 50, more preferably greater than 90, up to 4000.

[0022] In embodiments, the multi-walled carbon nanotubes have a length greater than 10 nanometers, preferably greater than 15 nanometers, preferably greater than 30 nanometers, preferably greater than 50 nanometers, preferably greater than 100 nanometers, preferably greater than 500 nanometers, preferably greater than 1 micrometer, preferably greater than 5 micrometers, preferably greater than 10 micrometers, more preferably greater than 15 micrometers. In exemplary embodiments, the multi-walled carbon nanotubes have an average length between 1 micrometer and 20 micrometers.

[0023] A combination of multi-walled carbon nanotubes and single-walled carbon nanotubes can also be used in the active layer. The embodiments detailed below discuss such embodiments. According to various embodiments, the active layer 106 can include a combination of multi-walled carbon nanotubes and single-walled carbon nanotubes. The multi-walled carbon nanotubes swell more than single-walled carbon nanotubes when wetted by an electrolyte in an energy storage device in which the electrode 100 is located. In some embodiments, the multi-walled carbon nanotubes swell at least 15% more than single-walled carbon nanotubes when wetted by an electrolyte in an energy storage device in which the electrode 100 is located. For example, the length of the multi-walled carbon nanotubes expands at least 15% more than the length of the single-walled carbon nanotubes when wetted by the electrolyte. In some embodiments, the multi-walled carbon nanotubes swell at least 25% more than single-walled carbon nanotubes when wetted by an electrolyte in an energy storage device in which the electrode 100 is located. For example, the length of the multi-walled carbon nanotubes expands at least 25% more than the length of the single-walled carbon nanotubes when wetted by the electrolyte. In some embodiments, the multi-walled carbon nanotubes swell at least 50% more than single-walled carbon nanotubes when wetted by an electrolyte in an energy storage device in which electrode 100 is located. For example, the length of the multi-walled carbon nanotubes expands at least 50% more than the length of single-walled carbon nanotubes when wetted by the electrolyte. In some embodiments, the multi-walled carbon nanotubes swell up to 50% when wetted (e.g., the length of the multi-walled carbon nanotubes increases by 50% after being wetted by the electrolyte and / or the diameter of the multi-walled carbon nanotubes increases by 50% after being wetted, etc.).

[0024] According to various embodiments, the three-dimensional network of high-aspect ratio carbon elements 108 includes carbon nanotubes, where the carbon nanotubes are only multi-walled carbon nanotubes and / or carbon nanotube fragments. For example, the three-dimensional network of high-aspect ratio carbon elements 108 does not include single-walled carbon nanotubes or single-walled carbon nanotube fragments. According to various embodiments, the three-dimensional network of high-aspect ratio carbon elements 108 includes at least 99% carbon by weight. In some embodiments, the three-dimensional network of high-aspect ratio carbon elements 108 includes an electrically interconnected network of carbon elements that exhibits connectivity above a percolation threshold, where the network defines one or more highly conductive pathways having a length greater than 100 μm. The percolation threshold is the threshold at which conductive elements contact each other to provide a conductive network measured across any two points on any surface of the network.

[0025] According to various embodiments, the electrodes include multi-walled carbon nanotubes that are relatively long compared to the multi-walled carbon nanotubes included in related art electrodes. The use of relatively long multi-walled carbon nanotubes in electrodes has been found to have beneficial mechanical and / or electrical properties. For example, multi-walled carbon nanotubes provide relatively good power output at low density. As another example, shorter multi-walled carbon nanotubes generally do not swell (e.g., expand) as much as longer multi-walled carbon nanotubes. Therefore, the use of shorter multi-walled carbon nanotubes loses (or reduces) some of the beneficial properties associated with carbon nanotube swelling. As an extreme example, carbon black does not exhibit swelling because it is simply particles of carbon without entanglements such as those exhibited by sets of multi-walled carbon nanotubes.

[0026] An indication that a certain amount of multi-walled carbon nanotubes have lengths above a threshold length and therefore sufficient swelling properties is observed during the calendering process, where a relatively large amount of pressure or effort to calender the slurry in conjunction with application to the foil indicates that the collective swelling (e.g., average swelling) of the multi-walled carbon nanotubes in the active layer meets a certain performance threshold. However, multi-walled carbon nanotubes are generally difficult to process.

[0027] According to various embodiments, the length distribution of the set of multi-walled carbon nanotubes is skewed toward the nominal length of the multi-walled carbon nanotubes. For example, the multi-walled carbon nanotubes are treated and / or adapted to reduce or minimize crushing or breakage of the multi-walled carbon nanotubes. The lengths of the multi-walled carbon nanotubes in the network of high aspect ratio carbon elements are generally at the nominal length of the multi-walled carbon nanotubes, or the lengths of such multi-walled carbon nanotubes tend to be more skewed toward the nominal length.

[0028] In some embodiments, at least 75% of the multi-walled carbon nanotubes in the network of high aspect ratio carbon elements are within 10% of their nominal length (e.g., between 13.4 micrometers and about 15 micrometers). In some embodiments, at least 75% of the multi-walled carbon nanotubes in the network of high aspect ratio carbon elements have a length of at least 12 micrometers. In some embodiments, at least 75% of the multi-walled carbon nanotubes in the network of high aspect ratio carbon elements have a length of at least 13 micrometers. In some embodiments, at least 50% of the multi-walled carbon nanotubes in the network of high aspect ratio carbon elements are within 10% of their nominal length (e.g., between 13.4 micrometers and about 15 micrometers). In some embodiments, at least 50% of the multi-walled carbon nanotubes in the network of high aspect ratio carbon elements have a length of at least 12 micrometers. In some embodiments, at least 50% of the multi-walled carbon nanotubes in the network of high aspect ratio carbon elements have a length of at least 13 micrometers.

[0029] In a preferred embodiment, the first conductive material used in the active layer is multi-walled carbon nanotubes.

[0030] The high aspect ratio carbon elements (e.g., single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination thereof) are present in the first slurry (the first slurry including the first conductive material, the second binder material, the first active material, and the solvent) in an amount of 4.5 to 6 wt %, preferably 5 to 5.75 wt %, based on the total weight of the first slurry.

[0031] The high aspect ratio carbon element is present in the second slurry (the second slurry including the first conductive material, the first binder material, the second binder material, the first active material, and the solvent) in an amount of 5 to 7 wt %, preferably 5.25 to 6.25 wt %, based on the total weight of the second slurry. The high aspect ratio carbon element is present in the active layer in an amount of 8 to 12 wt %, based on the total weight of the active layer.

[0032] As mentioned above, the high aspect ratio carbon elements are preferably multi-walled carbon nanotubes.

[0033] In an embodiment, the first and second slurries can include a second conductive material. The second conductive material differs in structure or composition from the first conductive material. The second conductive material is preferably carbonaceous and includes at least one of carbon black, graphite flakes, single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination thereof. For example, if the first conductive material includes carbon nanotubes (e.g., single-walled and / or multi-walled carbon nanotubes), the second conductive material can include carbon black, graphite flakes, or a combination thereof. In another example, if the first conductive material includes single-walled carbon nanotubes, the second conductive material can include one of multi-walled carbon nanotubes, carbon black, graphite flakes, or a combination thereof. The second conductive material can be present in the active layer (after removal of the solvent) in an amount of 0.5 to 10 wt %, preferably 1 to 5 wt %, based on the total weight of the active layer.

[0034] The first binder material comprises a first polymer that is at least water-soluble. In embodiments, the first binder material comprises a random or block copolymer of an alkenyl aromatic compound and a conjugated diene. For brevity, this component will be referred to as a "copolymer." The copolymer generally comprises a poly(alkenyl aromatic) content of 10 to 55 weight percent, based on the weight of the copolymer. Within this range, the poly(alkenyl aromatic) content can be 20 to 50 weight percent, specifically 25 to 45 weight percent.

[0035] In some embodiments, the copolymer has a weight average molecular weight of at least 100,000 atomic mass units. In some embodiments, the copolymer comprises a polystyrene-poly(butadiene)-polystyrene diblock or triblock copolymer having a weight average molecular weight of 20,000 to 1,000,000 grams / mole, specifically 50,000 to 400,000 grams / mole. In some embodiments, the copolymer comprises a styrene-butadiene random copolymer having a weight average molecular weight of 20,000 to 1,000,000 grams / mole, specifically 50,000 to 400,000 grams / mole.

[0036] The alkenyl aromatic monomers used to prepare the copolymers can have the following structures:

[0037] [ka] In the formula, R 7 and R 8 each independently represents a hydrogen atom, a C1-C8 alkyl group, or a C2-C8 alkenyl group; R 9 and R 13 are each independently a hydrogen atom, C1 to C8R are an alkyl group, a chlorine atom or a bromine atom, and R 10 , R 11 and R 12 each independently represents a hydrogen atom, a C1 to C8 alkyl group, or a C2 to C8 alkenyl group, or R 10 and R 11 together with the central aromatic ring to form a naphthyl group, or R 11 and R 12 together with the central aromatic ring form a naphthyl group. Specific alkenyl aromatic monomers include, for example, styrene, chlorostyrenes such as p-chlorostyrene, methylstyrenes such as α-methylstyrene and p-methylstyrene, and t-butylstyrenes such as 3-t-butylstyrene and 4-t-butylstyrene. In some embodiments, the alkenyl aromatic monomer is styrene.

[0038] The conjugated dienes used to prepare the copolymers are C4-C 20 The conjugated diene may be a conjugated diene. Suitable conjugated dienes include, for example, 1,3-butadiene, 2-methyl-1,3-butadiene, 2-chloro-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, and the like, and combinations thereof. In some embodiments, the conjugated diene is 1,3-butadiene, 2-methyl-1,3-butadiene, or a combination thereof. In some embodiments, the conjugated diene comprises 1,3-butadiene.

[0039] The copolymer comprises (A) at least one block derived from an alkenyl aromatic compound and (B) at least one block derived from a conjugated diene, wherein the aliphatic unsaturation content in block (B) is at least partially reduced by hydrogenation. In some embodiments, the aliphatic unsaturation in block (B) is reduced by at least 50 percent, specifically at least 70 percent. The arrangement of blocks (A) and (B) includes linear structures, graft structures, and radial teleblock structures with or without branching. Linear block copolymers include tapered linear structures and non-tapered linear structures. In some embodiments, the block copolymer is a diblock copolymer, a triblock copolymer, or a combination thereof. In some embodiments, the copolymer is a random copolymer.

[0040] In some embodiments, the block copolymer does not contain residues of monomers other than the alkenyl aromatic compound and the conjugated diene. In some embodiments, the block copolymer is composed of blocks derived from the alkenyl aromatic compound and the conjugated diene, and at least one of the blocks is carboxylated (i.e., grafted with a carboxylic acid or a carboxylic acid derivative). Examples of unsaturated carboxylic acids include maleic acid, fumaric acid, itaconic acid, methacrylic acid, crotonic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, citraconic acid, etc., or combinations thereof. Examples of derivatives of unsaturated carboxylic acids are maleic anhydride, citraconic anhydride, itaconic anhydride, malonic anhydride, succinic anhydride, glutaric anhydride, adipic anhydride, pimelic anhydride, suberic anhydride, azelaic anhydride, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, glycidyl acrylate, glycidyl methacrylate, etc., or combinations thereof. Maleic anhydride is the preferred grafting compound.

[0041] Carboxylation of the block copolymer allows styrene-butadiene copolymers to be used in latex form, where they exist as small particles dispersed in water. A latex is a dispersion of polymer particles or droplets in a liquid. The particles do not settle or float in an aqueous emulsion, nor do they aggregate due to ionic or steric instability. Ionic stability is the result of ionic charges on the particles, creating repulsive forces that prevent aggregation. Steric stabilization occurs when the surfaces of the polymer particles extend into the solution, physically keeping the particles apart. Additives can be incorporated into the latex to ensure its steric stability and enhance its resistance to aggregation.

[0042] In a preferred embodiment, the first polymer is a styrene-butadiene random copolymer. In an embodiment, the styrene-butadiene block copolymer is added to the slurry in latex form.

[0043] The first binder material is present only in the second slurry. As described above, the second slurry includes a first conductive material, a first binder material, a second binder material, a first active material, and a solvent. The first slurry becomes a second slurry upon addition of the first binder material. The first binder material is present in the second slurry in an amount of 4.5 to 6.5 wt %, preferably 5 to 6 wt %, based on the total weight of the second slurry. The first binder is present in the active layer in an amount of 7 to 13 wt %, preferably 8 to 12 wt %, based on the weight of the active layer.

[0044] The second binder material present in the active layer is also a water-soluble polymer. The second binder material is chemically different from the first binder material. In embodiments, the second binder material is a water-soluble, naturally occurring polymer. Examples of naturally occurring polymers for use as the second binder material include cellulose and cellulose derivatives (e.g., hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose (CMC), sodium carboxymethylcellulose, cellulose acetate, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose acetate butyrate, and cellulose ethers such as ethylcellulose, or combinations thereof), sugars (glucose, sucrose, lactose, galactose, fructose, mannitol, sorbitol, or combinations thereof), ionic complexes of cellulose, gums (e.g., acacia, alginates, carrageenan, guar, karaya, pectin, tragacanth, xanthan, or combinations thereof).

[0045] In a preferred embodiment, the second binder is carboxymethylcellulose (CMC).

[0046] The second binder is present in an amount of 2 to 4 wt%, preferably 2.25 to 3.75 wt%, based on the total weight of the first slurry. The second binder is present in an amount of 2.25 to 5 wt%, preferably 2.35 to 4.6 wt%, based on the total weight of the second slurry. The second binder is present in the active layer in an amount of 3 to 7 wt%, based on the weight of the active layer.

[0047] The active material for use in the active layer 106 (see FIG. 1 ) is located within the voids surrounded by the conductive network formed by the high-aspect ratio carbon elements. The active layer may also include other activated carbonaceous materials, including, for example, activated carbon granules, activated carbon fibers, activated carbon nanotubes, carbon aerogels, or combinations thereof. Other active materials that can be used in the active layer include lithium cobalt oxide (LCO), lithium nickel manganese cobalt (LiNiMnCo), lithium manganese oxide (LMO), lithium titanate oxide (LTO), lithium iron phosphate (LFP), lithium nickel cobalt aluminum oxide (LiNiCoALO), as well as other similar materials.

[0048] Activated carbon is generally a form of carbon that has been physically or chemically treated to increase its porosity and surface area available for adsorption and chemical reaction. Powdered activated carbon (PAC) and granular activated carbon (GAC) are common forms. In embodiments, the active material is activated powdered carbon. Activated carbon can have a surface area of ​​500 to 3000 square meters per gram.

[0049] In embodiments, the active materials used in both electrodes (anode and / or cathode) can be lithium cobalt oxide (LCO, sometimes called "lithium cobaltate" or "lithium cobaltite." One variation of the possible LCO formulation is LiCoO), lithium nickel manganese cobalt oxide (NMC, having a formula variant of LiNiMnCo), lithium manganese oxide (LMO, having a formula variant of LiMnO, LiMnO, etc., or combinations thereof), lithium titanate oxide (LTO, one variation is LiTiO), or lithium tantalum oxide (LTO). 12 The active material may include lithium iron phosphate oxide (LFP, one variant is LiFePO4), lithium nickel cobalt aluminum oxide (and its variants as NCA), and other similar materials. Other variants of the foregoing may be included. In some embodiments where NMC is used as the active material, nickel-rich NMC may be used. In some embodiments where NMC is used as the active material, nickel-rich NMC may be used.

[0050] For example, in some embodiments, the NMC variant is LiNi x Mn y Co (1-x-y) where x is about 0.7, 0.75, 0.80, 0.85, or greater. In embodiments, y may be 0.1, 0.15, 0.2, or 0.25, or greater. In some embodiments, NMC811 can be used, where x is about 0.8 and y is about 0.1.

[0051] In some embodiments, the active material is other forms of lithium nickel manganese cobalt oxide (LiNi x Mn y Co z O2). Variations of this formula that may be used in the active material layer include NMC111 (discussed in more detail below), NMC532 (LiNi 0.5 Mn 0.3 Co 0.2 O2), NMC622(LiNi 0.6 Mn0.2 Co 0.2 O2), or a combination thereof.

[0052] In embodiments, the active material used in both electrodes (anode and / or cathode) can also include a nickel-rich combination of nickel, manganese, and cobalt. Lithium-nickel-manganese-cobalt-oxide (LiNiMnCoO), abbreviated as NMC, offers high overall performance, excellent specific energy, and the lowest self-heating rate of all mainstream cathode powders. NMC powder may contain 20-40 wt% nickel, 20-40 wt% manganese, and 20-40 wt% cobalt, based on the total weight of the NMC blend. While the term "NMC powder" can refer to various blends, it is desirable to use a blend containing 33 wt% nickel, 33 wt% manganese, and 33 wt% cobalt. This blend, sometimes referred to as 1-1-1 (NMC111), is useful for frequently cycling applications (automotive, energy storage) due to the reduced material cost resulting from the lower cobalt content.

[0053] The active material is contained in the active layer in an amount of 67 to 85% by weight, preferably 70 to 80% by weight, based on the total weight of the active layer.

[0054] The mixture for producing the active layer further includes a solvent, preferably one used to disperse the first binder, the second binder, the first conductive material, and the second conductive material to form the mixture, which is then disposed on a current collector to form the active layer.

[0055] Suitable solvents are water, alcohol, or a combination thereof. Examples of alcohols include ethanol, methanol, propanol, butyl alcohol, ethylene glycol, propylene glycol, or a combination thereof. In addition to water and alcohol, other solvents may be added to facilitate solubilization and / or dispersion of the polymer. Examples of other solvents include polar solvents, nonpolar solvents, etc. The addition of other solvents should preferably not change the solubility of the polymer in water or alcohol. Liquid aprotic polar solvents, such as propylene carbonate, ethylene carbonate, butyrolactone, acetonitrile, benzonitrile, nitromethane, nitrobenzene, sulfolane, dimethylformamide, N-methylpyrrolidone, etc., or combinations thereof, can be added to water or alcohol to dissolve the polymer. Polar protic solvents, such as acetonitrile, nitromethane, acetone, dimethyl sulfoxide, dimethylformamide, etc., or combinations thereof, can also be used. Other nonpolar solvents, such as benzene, toluene, methylene chloride, carbon tetrachloride, hexane, diethyl ether, tetrahydrofuran, etc., or combinations thereof, can also be used. Co-solvents, including at least one aprotic polar solvent and at least one non-polar solvent, can also be utilized to modify the solubilizing power of the solvent.

[0056] In a preferred embodiment, the solvent is water. In another preferred embodiment, the solvent is alcohol. When water and alcohol are used as solvents for the active layer, the ratio of water to alcohol is 80:20 to 95:5, preferably 88:12 to 92:8. In an exemplary embodiment, the ratio of water to alcohol is 90:10.

[0057] The solvent is present in an amount of 45 to 60 wt %, preferably 48 to 55 wt %, based on the total weight of the first slurry. The solvent is preferably removed from the active layer after it is disposed on the current collector. The solid active layer is preferably free of solvents (water and alcohol).

[0058] The active layer 106 has an average thickness between 20 microns and 200 microns. In some embodiments, the active layer 106 has an average thickness between 20 microns and 30 microns. In some embodiments, the active layer 106 has an average thickness of about 100 microns.

[0059] According to various embodiments, the active layer 106 expands (e.g., swells) by less than 10% when wetted by the electrolyte. For example, the thickness of the active layer 106 (after being wetted by the electrolyte) is less than 110% of the thickness of the active layer 106 in the absence of the electrolyte.

[0060] In an embodiment, the cathode polymer binders (first and second cathode polymer binders), the cathode active material, the cathode conductive material, and the solvent are blended together to form a cathode mixture in the form of a slurry. The blending process promotes dispersion of the cathode conductive material and the cathode active material to form a permeable network throughout the volume of the cathode active layer when the solvent is removed. In an embodiment, the cathode mixture (in slurry form) is placed on a current collector after mixing is complete. The current collector with the cathode mixture placed thereon is sheared and compressed in a roll mill. The use of the roll mill facilitates bonding between the cathode active layer and the current collector.

[0061] Figure 2 is a flowchart of a method of making an electrode according to various embodiments. A description of process 200 is provided with respect to electrode 100 of Figure 1. Referring to Figure 2, in some embodiments, active layer 106 of electrode 100 can be formed using process 200. At 202, high aspect ratio carbon elements (e.g., MWNTs), a second binder (e.g., CMC), and an active material (e.g., activated carbon) and optional surface treatment materials (e.g., surfactants) are combined with a solvent (of the type described herein) to form an initial slurry (also referred to as a first slurry).

[0062] At 202, the first slurry is treated to ensure good dispersion of the solid material in the slurry. In some embodiments, this treatment involves introducing mechanical energy into the mixture of solvent and solid material (e.g., using an ultrasonicator, sometimes called a "sonifier") or other suitable mixing device (e.g., a high-shear mixer). In some embodiments, the mechanical energy introduced into the mixture is at least 0.4 kilowatt-hours per kilogram (kWh / kg), 0.5 kWh / kg, 0.6 kWh / kg, 0.7 kWh / kg, 0.8 kWh / kg, 0.9 kWh / kg, 1.0 kWh / kg, or more. For example, the mechanical energy introduced into the mixture per kilogram of mixture can be in the range of 0.4 kWh / kg to 1.0 kWh / kg, or any subrange thereof, such as 0.4 kWh / kg to 0.6 kWh / kg.

[0063] In some embodiments, an ultrasonic bath mixer may be used. In other embodiments, a probe sonicator may be used. Probe sonication can be significantly more powerful and effective when compared to an ultrasonic bath for nanoparticle applications. The high shear forces generated by ultrasonic cavitation have the ability to break down particle agglomerates, resulting in smaller, more uniform particle sizes. Among other things, sonication can result in a stable and homogeneous suspension of solids in a slurry. Generally, this results in dispersion and deagglomeration and other breakdown of solids. An example of a probe sonication device is the Q Series Probe Sonicator available from QSonica LLC (Newtown, Connecticut). Another example is the Branson Digital SFX-450 sonicator available from Thomas Scientific (Swedesboro, New Jersey).

[0064] However, in some embodiments, the localized nature of each probe within a probe assembly can result in non-uniform mixing and suspension. This can be the case, for example, with large samples. This can be addressed by using a setup with a continuous flow cell and appropriate mixing. For example, in such a setup, mixing of a slurry achieves a reasonably uniform dispersion.

[0065] In some embodiments, the first slurry, once processed, has a viscosity in the range of 2,000 cps to 25,000 cps, or any subrange thereof, for example, 6,000 cps to 19,000 cps.

[0066] The first slurry is then mixed with a first binder material (eg, SBR latex) to form a final slurry.

[0067] At 204, the final slurry is processed to ensure good dispersion of the solid materials in the final slurry. In various embodiments, any suitable mixing process known in the art may be used. In some embodiments, this processing may use the techniques described above with reference to 202. In some embodiments, a planetary mixer, such as a multi-shaft (e.g., three or more) planetary mixer, may be used. In some such embodiments, the planetary mixer may feature multiple blades, for example, two or more mixing blades and one or more (e.g., two, three, or more) dispersion blades, such as a disk dispersion blade.

[0068] In some embodiments, the matrix surrounding the active material may fully or partially self-assemble during 204. In some embodiments, an interaction between the surface treatment and the active material facilitates the self-assembly process.

[0069] In some embodiments, the final slurry, once processed, has a viscosity in the range of 1,000 cps to 10,000 cps, or any subrange thereof, for example, 2,500 cps to 6000 cps.

[0070] At 206, the active layer 106 is formed from the final slurry. In some embodiments, the final slurry may be wet cast directly onto the current collector conductive layer 102 (or optional adhesive layer 104) and dried. As an example, casting may form the active layer 106 by applying at least one of heat and vacuum until substantially all of the solvent and any other liquids are removed. In some such embodiments, it may be desirable to protect various portions of the underlying layers. For example, protecting the underside of the conductive layer 102 may be desirable if the electrode 100 is intended for double-sided operation. Protection may include, for example, protecting from the solvent by masking certain areas or providing a drain for removing the solvent.

[0071] In other embodiments, the final slurry can be at least partially dried elsewhere using any suitable technique (e.g., roll-to-roll layer application) and then transferred onto adhesive layer 104 or conductive layer 102 to form active layer 106. In some embodiments, the wet final slurry can be placed onto an intermediate material having a suitable surface and dried to form a layer (e.g., active layer 106). While any material having a suitable surface can be used as the intermediate material, an exemplary intermediate material includes PTFE because its properties facilitate its subsequent removal from the surface. In some embodiments, the specified layer is formed in a press to provide a layer exhibiting a desired thickness, area, and density.

[0072] In some embodiments, the final slurry may be formed into a sheet and coated onto the adhesive layer 104 or the conductive layer 102, as appropriate. For example, in some embodiments, the final slurry may be applied through a slot die to control the thickness of the applied layer. In other embodiments, the slurry may be applied and then leveled to the desired thickness using, for example, a doctor blade. Various other techniques can be used to apply the slurry. For example, coating techniques may include, but are not limited to, comma coating, comma reverse coating, doctor blade coating, slot die coating, direct gravure coating, air doctor coating (air knife), chamber doctor coating, offset gravure coating, one-roll kiss coating, reverse kiss coating with a small diameter gravure roll, bar coating, three reverse roll coating (top feed), three reverse roll coating (fountain die), reverse roll coating, etc.

[0073] The viscosity of the final slurry can vary depending on the application technique. For example, for comma coating, the viscosity can range from about 1,000 cps to about 200,000 cps. Lip die coating provides a coating with a slurry exhibiting a viscosity of about 500 cps to about 300,000 cps. Reverse kiss coating provides a coating with a slurry exhibiting a viscosity of about 5 cps to 1,000 cps. In some applications, each layer can be formed in multiple passes.

[0074] In some embodiments, the active layer 106 formed from the final slurry may be compressed (e.g., using a calendering device) before or after being applied to the electrode 100. In some embodiments, the slurry may be partially or completely dried (e.g., by applying heat, vacuum, or a combination thereof) before or during the compression process. For example, in some embodiments, the active layer may be compressed to a final thickness (e.g., in a direction perpendicular to the current collector layer 102) that is less than 90%, 80%, 70%, 50%, 40%, 30%, 20%, or 10% or less of its pre-compression thickness.

[0075] In various embodiments, if a partially dried layer is formed during the coating or pressing process, the layer may then be completely dried (e.g., by applying heat, vacuum, or a combination thereof). In some embodiments, substantially all of the solvent is removed from the active layer 106.

[0076] In some embodiments, the solvent used to form the slurry is recovered and recycled into the slurry making process.

[0077] In some embodiments, the active layer 106 may be compressed, for example, to break down some of the constituent high aspect ratio carbon elements or other carbonaceous materials and increase the surface area of ​​each layer. In some embodiments, this compression process may increase one or more of adhesion between the layers, ion transport rates within the layers, and surface area of ​​the layers. In various embodiments, compression may be applied before or after each layer is applied or formed into the electrode 100.

[0078] In some embodiments where calendering is used to compress the active layer 106, the calendering apparatus may be set with a gap spacing equal to 90%, 80%, 70%, 50%, 40%, 30%, less than 20%, or 10% or less of the pre-compression thickness of the layer (e.g., set at about 33% of the pre-compression thickness of the layer). The calender rolls can be configured to provide a suitable pressure, for example, greater than 1 ton per cm of roll length, greater than 1.5 ton per cm of roll length, greater than 2.0 ton per cm of roll length, greater than 2.5 ton per cm of roll length, or more. In some embodiments, the compressed active layer has a density in the range of 0.1 g / cc to 10 g / cc, or any subrange thereof, such as 2.5 g / cc to 4.0 g / cc.

[0079] In some embodiments, the calendering process can be carried out at a temperature ranging from 20° C. to 140° C., or any subrange thereof. In some embodiments, the active layer 106 can be preheated prior to calendering, for example, to a temperature ranging from 20° C. to 100° C., or any subrange thereof.

[0080] Once the electrode 100 is assembled, it can be used to assemble an energy storage device. Assembly of the energy storage device may follow conventional steps used to assemble an electrode with a separator and place it into a housing, such as a canister or pouch, and may further include additional steps to add electrolyte and seal the housing.

[0081] In various embodiments, the process 200 may include any of the following features (individually or in any suitable combination):

[0082] In some embodiments, the initial slurry has a solids content in the range of 0.1% to 20.0% by weight (or any subrange thereof), hi some embodiments, the final slurry has a solids content in the range of 10.0% to 80% by weight (or any subrange thereof).

[0083] A 3D carbon scaffold or matrix holds the active material particles together, forming a cohesive layer that is also strongly attached to the metal current collector. Such an active material structure is created during slurry preparation, followed by a roll-to-roll ("R2R") coating and drying process. One of the main advantages of this technology is its scalability and "drop-in" nature, as various embodiments are compatible with conventional electrode manufacturing processes.

[0084] The teachings herein provide a 3D matrix that dramatically increases electrode conductivity by 10 to 100 times compared to electrodes using conventional binders such as PVDF, enabling rapid charging at the battery level. This technology enables thick electrode coatings at the cathode, up to 150 μm thick per side (or more) of the current collector. The solvent used in the slurry, combined with the strong 3D carbon matrix, is designed to achieve a thick wet coating without cracking during the drying process. The thick cathode with a high-capacity anode enables a substantial jump in energy density, reaching 400 Wh / kg or more.

[0085] A schematic diagram of the electrode arrangement of a pouch cell device is shown in Figure 3. As shown, a double-sided cathode 700, using cathode layers 760 (e.g., active layers according to various embodiments disclosed herein) on either side of an aluminum foil current collector 710, is disposed between two single-sided anodes 720 and 730, each having anode layers 740 and 750 (e.g., active layers comprising a network of carbon elements as disclosed herein) disposed on a copper foil current collector. The electrodes are separated by a permeable separator material 780 wetted by the electrolyte (not shown). This arrangement can be housed within a pouch cell of a type well known in the art.

[0086] 4 shows a cross section of an energy storage device (ESD) 810. The energy storage device (ESD) 810 includes a housing 811. The housing 811 has two terminals 800 disposed on its exterior. The terminals 800 provide an internal electrical connection to a storage cell 812 contained within the housing 811 and an external electrical connection to an external device, such as a load or charging device (not shown). The energy storage devices disclosed herein can be batteries, capacitors, ultracapacitors, etc.

[0087] The materials and structures disclosed herein are illustrated by the following non-limiting examples.

[0088] While the present invention has been described with reference to several embodiments, those skilled in the art will recognize that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is not intended that the invention be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but rather that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. An electrode comprising an active layer, The active layer is said network of high aspect ratio carbon elements defining void spaces within the network; a plurality of electrode active material particles disposed in the voids within the network; a first binder material comprising a water soluble styrene butadiene rubber.

2. The electrode of claim 1 , wherein the network of high aspect ratio carbon elements comprises multi-walled carbon nanotubes.

3. 3. The electrode of claim 2, wherein the multi-walled carbon nanotubes have an average diameter of 6 to 12 nanometers and an average length of 1 to 20 micrometers.

4. 4. The electrode of claim 3, wherein the multi-walled carbon nanotubes are present in the active layer in an amount of 8 to 12 wt %, based on the total weight of the active layer.

5. The electrode of claim 1 , wherein the electrode active material particles comprise activated carbon.

6. 6. The electrode of claim 5, wherein the activated carbon is selected from the group consisting of activated carbon granules, activated carbon powder, activated carbon fibers, activated carbon nanotubes, or combinations thereof.

7. 7. The electrode of claim 6, wherein the activated carbon is present in the active layer in an amount of 67 to 85 wt %, based on the total weight of the active layer.

8. 8. The electrode of claim 7, wherein the activated carbon is present in the active layer in an amount of 70 to 80 wt %, based on the total weight of the active layer.

9. The electrode of claim 1 , wherein the active layer comprises a second binder material that contains cellulose.

10. 10. The electrode of claim 9, wherein the cellulose is carboxymethyl cellulose.

11. 10. The electrode of claim 9, wherein the second binder is present in the active layer in an amount of 3 to 7 wt %, based on the weight of the active layer.

12. 10. The electrode of claim 1, wherein the styrene butadiene rubber is present in the active layer in an amount of 7 to 13 weight percent based on the weight of the active layer.

13. 10. The electrode of claim 1, wherein the styrene butadiene rubber is present in the active layer in an amount of 8 to 12 weight percent based on the weight of the active layer.

14. 10. The electrode of claim 1, wherein the styrene butadiene rubber is in the form of a latex.

15. 1. An energy storage device comprising: Electrolytes, 10. An energy storage device comprising: the electrode of claim 1; and the multi-walled nanotubes forming a percolation network through the active layer.

16. 1. A method for manufacturing an active layer, comprising: mixing together a water soluble styrene butadiene rubber, a plurality of high aspect ratio carbon elements, a plurality of electrode active material particles, and a solvent to form a slurry; disposing the slurry on a surface of a metal foil; and drying the slurry to form an active layer.

17. 17. The method of claim 16, further comprising mixing cellulose with the slurry.

18. 18. The method of claim 17, wherein the solvent is water.

19. 17. The method of claim 16, wherein the high aspect ratio carbon elements define a network having voids within the network, and the plurality of electrode active material particles are contained within the voids.

20. 17. The method of claim 16, wherein the styrene butadiene rubber is in the form of a latex.

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