Electrode for energy storage device

Abstract

Disclosed herein is an electrode comprising an active layer comprising a network of high aspect ratio carbon elements, the high aspect ratio carbon elements defining void spaces within the network; a plurality of electrode active material particles disposed in the void spaces within the network; and a first binder material including a water-soluble styrene-butadiene rubber. Also disclosed herein is a method of manufacturing 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.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit of U.S. Patent Application No. 63 / 403,138, filed on September 1, 2022, the entire disclosure of which is incorporated herein by reference. Background of the Invention

[0003] Storage devices such as, for example, electric double - layer capacitors and batteries are used in many products, including medical devices, electric vehicles, aircraft, and consumer products such as laptop computers, mobile phones, and cameras. Due to the high energy density, high operating voltage, and low self - discharge of lithium - ion batteries, they have replaced the secondary battery market and continue to find new uses in products and emerging industries.

[0004] Generally, a lithium - ion battery (“LIB” or “LiB”) or an electric double - layer capacitor includes an anode, a cathode, and an electrolyte material such as an organic solvent containing a lithium salt. More specifically, a paste or slurry is formed by mixing an anode active material or a cathode active material with a binder and a solvent, and then the paste or slurry is coated on a current collector such as aluminum or copper and dried to form a film on the current collector, thereby forming the anode and the cathode (collectively referred to as “electrodes”). Then the anode and the cathode are layered or wound, and then placed in a pressurized housing containing the electrolyte material, and together they form a lithium - ion battery.

[0005] In a conventional electrode, a binder having sufficient adhesiveness, cohesiveness, and chemical properties is used such that the film coated on the current collector will remain in contact with the current collector even when being manipulated for assembly into the pressurized battery housing. Since the film contains the electrode active material, if the film does not maintain sufficient contact with the current collector, there may be a significant interference with the electrochemical performance of the battery. In addition, it is important to select a binder that is mechanically compatible with the electrode active material such that it can withstand the degree of expansion and contraction of the electrode active material during charging and discharging of the battery.

[0006] Accordingly, binders such as cellulose binders or cross - linked polymer binders have been used to provide good mechanical properties. However, in a conventional electrode, the binders selected typically require environmentally unfriendly or toxic solvents for processing. Summary of the Invention

[0007] Disclosed herein is an electrode that includes an active layer that contains a network of high aspect ratio carbon elements that define void spaces within the network; a plurality of electrode active material particles disposed within the void spaces of the network; and a first binder material that includes water - soluble styrene - butadiene rubber.

[0008] The present disclosure also discloses a method of manufacturing an active layer, the method comprising mixing a water-soluble styrene-butadiene rubber, a plurality of high aspect ratio carbon elements, a plurality of electrode active material particles with a solvent to form a slurry; disposing the slurry on a surface of a metal foil; and

[0009] drying the slurry to form the active layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The following is a brief description of the drawings, where like elements are numbered alike and the drawings are presented for the purpose of illustrating the exemplary embodiments disclosed herein and not for the purpose of limiting the exemplary embodiments.

[0011] Figure 1 is a diagram of an electrode according to various embodiments;

[0012] Figure 2 is a flow chart of a method for preparing an electrode according to various embodiments;

[0013] Figure 3 is a depiction of an electrode arrangement of a pouch cell device; and

[0014] Figure 4 is a depiction of a schematic cross-sectional view showing aspects of an energy storage device (ESD). DETAILED DESCRIPTION

[0015] A more complete understanding of the components, processes, and devices disclosed herein can be obtained by reference to the drawings. These figures are merely schematic representations based on convenience and ease of demonstrating the present disclosure and are therefore not intended to indicate the relative size and dimensions of the device or its 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 specific structure of the embodiments selected for illustration in the drawings and are not intended to define or limit the scope of the present disclosure. In the drawings and the following description, it should be understood that like reference numerals represent components having the same function.

[0016] Disclosed herein is an electrolyte cell including a housing that includes electrodes (one or more anodes and one or more cathodes). The housing includes an electrolyte in contact with each of the anode and the cathode. 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 adhesion layer that contacts the electrode. The housing includes a separator material between the electrodes (anode and cathode).

[0017] Figure 1It is a diagram of an electrode (anode or cathode) according to various embodiments. In the illustrated example, electrode 100 is provided. According to various embodiments, electrode 100 includes a current collector 102 and an active layer 106. Electrode 100 may optionally include an adhesion layer 104. As an example, adhesion layer 104 includes a material that promotes adhesion between current collector 102 and active layer 106.

[0018] In one embodiment, regarding Figure 1 , the electrode (anode or cathode) includes current collector 102 as a conductive layer. For example, current collector 102 can be a metal, a metal alloy, etc. As another example, current collector 102 is a metal foil. In some embodiments, current collector 102 is an aluminum foil or an aluminum alloy foil. In some embodiments, current collector 102 is a copper foil or a copper alloy foil. Current collector 102 has a thickness less than 30 μm. Current collector 102 has a thickness less than 10 μm. Current collector 102 has a thickness less than 8 μm. Current collector 102 has a thickness less than 5 μm. In one embodiment, current collector 102 has a thickness of 3 μm to 15 μm. In some preferred embodiments, current collector 102 has a thickness between about 6 μm and about 8 μm. In some embodiments, current collector 102 is an aluminum foil or an aluminum alloy foil, and current collector 102 has a thickness of about 6 μm.

[0019] The active layer 106 used in the electrode contains 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. Figure 2 A process 200 for preparing an electrode is depicted. The method includes mixing a first conductive material, a second binder material, a first active material, and a solvent to form a first slurry 202. A combination of shear force, tensile force, and elongation force is used to mix the first slurry to separate some or all of the carbon nanotube bundles. The first slurry can be stored in a container for the required time. When needed, the first slurry 202 can be mixed with a second binder to form a second slurry 204. The second slurry 204 is in the form of a gel or a paste. The second slurry 204 can be disposed on the current collector and dried to form the active layer 206. In one embodiment, the slurry can be disposed on the current collector or optionally on an adhesion layer to form the active layer.

[0020] The first conductive material includes one or more high aspect ratio carbon elements, and the one or more high aspect ratio carbon elements include a substantially cylindrical carbon atom network. The first conductive material includes a first group of carbon nanotubes or a plurality of first carbon nanotube bundles. The first conductive material is sometimes referred to herein (individually and collectively) as high aspect ratio carbon elements. In one embodiment, the term "high aspect ratio carbon element" refers to a carbon-containing element whose dimensions in one or more dimensions ("major dimensions") are significantly greater than its dimensions in the transverse dimension ("minor dimensions").

[0021] The first conductive material forms a conductive percolation network that can conduct current between any two separated points on the surface of a solid active layer (where there is no solvent). In other words, by means of physical contact or electron hopping between the conductive materials in the active layer, current can be transmitted from one surface of the active layer to the opposite surface. The percolation network includes voids that accommodate the active material between the high aspect ratio carbon elements.

[0022] In some embodiments, the active layer comprises: (i) a network of high aspect ratio carbon elements that define void spaces within the network, (ii) a plurality of electrode active material particles disposed in the void spaces within the network, and (iii) a polymer binder that includes styrene-butadiene rubber in latex form. In one embodiment, the polymer binder further includes water-soluble cellulose. The first binder material is styrene-butadiene rubber in latex form. The second binder material is cellulose.

[0023] The first conductive material includes high aspect ratio carbon elements. The high aspect ratio carbon elements can include single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWNTs), or a combination thereof.

[0024] In one embodiment, the first conductive material includes single-walled carbon nanotubes. The outer diameter of the single-walled carbon nanotubes is from 0.5 nanometers to 5.0 nanometers, preferably from 1.0 nanometers to 3.5 nanometers. In one embodiment, the aspect ratio (length to diameter ratio) of the single-walled carbon nanotubes is 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 an exemplary embodiment, the single-walled carbon nanotubes have an average aspect ratio of 5 to 200.

[0025] In one embodiment, the length of the single-walled carbon nanotubes is 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, and more preferably greater than 15 micrometers up to at least 200 micrometers. In an exemplary embodiment, the average length of the single-walled carbon nanotubes is from 100 nanometers (0.1 micrometer) to 20 micrometers, preferably from 1 micrometer to 15 micrometers.

[0026] In one embodiment, the first conductive material may include high aspect ratio carbon elements defined by a plurality of carbon walls. In one embodiment, the conductive material comprises multi-walled carbon nanotubes (MWNT). The number of carbon walls in the multi-walled carbon nanotubes can be 2 or more, 5 or more, 10 or more, 50 or more. According to various embodiments, the multi-walled carbon nanotubes comprise an average between 3 and 15 layers. In some embodiments, the multi-walled carbon nanotubes comprise an average between 4 and 12 layers. In some embodiments, the multi-walled carbon nanotubes comprise an average between 5 and 10 layers. In some embodiments, the multi-walled carbon nanotubes comprise an average between 6 and 7 layers. In some embodiments, the multi-walled carbon nanotubes comprise an average of at least 6 layers.

[0027] The outer diameter of the multi-walled carbon nanotubes is from 2 nanometers to 50 nanometers, preferably from 5 nanometers to 40 nanometers, and more preferably from 6 nanometers to 11 nanometers. In one embodiment, the aspect ratio (length to diameter ratio) of the multi-walled carbon nanotubes is greater than 5, preferably greater than 10, greater than 50 and more preferably greater than 90 up to an aspect ratio of 4000.

[0028] In one embodiment, the length of the multi-walled carbon nanotubes is 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, and more preferably greater than 15 micrometers. In an exemplary embodiment, the multi-walled carbon nanotubes have an average length of from 1 micrometer to 20 micrometers.

[0029] Combinations of multi-walled carbon nanotubes and single-walled carbon nanotubes can also be used in the active layer. Embodiments discussed in detail below address such embodiments. According to various embodiments, the active layer 106 can include a combination of multi-walled carbon nanotubes and single-walled carbon nanotubes. When wetted with an electrolyte in an energy storage device having electrodes 100, the multi-walled carbon nanotubes swell more than the single-walled carbon nanotubes. In some embodiments, when wetted with an electrolyte in an energy storage device having electrodes 100, the multi-walled carbon nanotubes swell at least 15% more than the single-walled carbon nanotubes. For example, when wetted with an electrolyte, the length of the multi-walled carbon nanotubes swells at least 15% more than the length of the single-walled carbon nanotubes. In some embodiments, when wetted with an electrolyte in an energy storage device having electrodes 100, the multi-walled carbon nanotubes swell at least 25% more than the single-walled carbon nanotubes. For example, when wetted with an electrolyte, the length of the multi-walled carbon nanotubes swells at least 25% more than the length of the single-walled carbon nanotubes. In some embodiments, when wetted with an electrolyte in an energy storage device having electrodes 100, the multi-walled carbon nanotubes swell at least 50% more than the single-walled carbon nanotubes. For example, when wetted with an electrolyte, the length of the multi-walled carbon nanotubes swells at least 50% more than the length of the single-walled carbon nanotubes. In some embodiments, the multi-walled carbon nanotubes swell up to 50% when wetted (e.g., the length of the multi-walled carbon nanotubes is 50% greater after wetting with an electrolyte, and / or the diameter of the multi-walled carbon nanotubes is 50% greater after wetting, etc.).

[0030] According to various embodiments, the three-dimensional network of the high aspect ratio carbon element 108 comprises carbon nanotubes, and the carbon nanotubes are only multi-walled carbon nanotubes and / or fragments of carbon nanotubes. For example, the three-dimensional network of the high aspect ratio carbon element 108 does not comprise single-walled carbon nanotubes or fragments of single-walled carbon nanotubes. According to various embodiments, the three-dimensional network of the high aspect ratio carbon element 108 comprises at least 99 wt% carbon. In some embodiments, the three-dimensional network of the high aspect ratio carbon element 108 includes an electrical interconnect network of carbon elements presenting connectivity above the percolation threshold, and wherein 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 between any two points on any surface across the network.

[0031] According to various embodiments, the electrode includes 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 the electrode has been found to have beneficial mechanical and / or electrical properties. For example, multi-walled carbon nanotubes provide relatively good power 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. Thus, using shorter multi-walled carbon nanotubes loses (or reduces) some beneficial properties associated with carbon nanotube swelling. As an extreme example, carbon black does not exhibit swelling because carbon black is merely particles of carbon without entanglement, such as the entanglement exhibited by a group of multi-walled carbon nanotubes.

[0032] An indication that a quantity of multi-walled carbon nanotubes has a length that exceeds a threshold length and thus has sufficient swelling properties is an observation during the calendering process - calendering a relatively large amount of pressure or effort on the slurry related to the foil indicates that the total swelling (e.g., average swelling) of the multi-walled carbon nanotubes in the active layer will meet a specific performance threshold. However, multi-walled carbon nanotubes are generally difficult to process.

[0033] According to various embodiments, the length distribution of the group of multi-walled carbon nanotubes is skewed towards multi-walled carbon nanotubes of a nominal length. For example, the multi-walled carbon nanotubes are processed and / or applied in a manner that reduces or minimizes breakage or fracture of the multi-walled carbon nanotubes. The length of the multi-walled carbon nanotubes in the network of high aspect ratio carbon elements is typically the nominal length of the multi-walled carbon nanotubes, or the length of such multi-walled carbon nanotubes tends to be more severely skewed towards the nominal length.

[0034] In some embodiments, at least 75% of the multi-walled carbon nanotubes within the network of high aspect ratio carbon elements are within 10% of the nominal length (e.g., between 13.4 microns and about 15 microns). In some embodiments, at least 75% of the multi-walled carbon nanotubes within the network of high aspect ratio carbon elements have a length of at least 12 microns. In some embodiments, at least 75% of the multi-walled carbon nanotubes within the network of high aspect ratio carbon elements have a length of at least 13 microns. In some embodiments, at least 50% of the multi-walled carbon nanotubes within the network of high aspect ratio carbon elements are within 10% of the nominal length (e.g., between 13.4 microns and about 15 microns). In some embodiments, at least 50% of the multi-walled carbon nanotubes within the network of high aspect ratio carbon elements have a length of at least 12 microns. In some embodiments, at least 50% of the multi-walled carbon nanotubes within the network of high aspect ratio carbon elements have a length of at least 13 microns.

[0035] In a preferred embodiment, the first conductive material for the active layer is multi-walled carbon nanotubes.

[0036] Based on the total weight of the first slurry, 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 comprising a first conductive material, a second binder material, a first active material, and a solvent) in an amount of 4.5 wt% to 6 wt%, and preferably 5 wt% to 5.75 wt%.

[0037] Based on the total weight of the second slurry, high aspect ratio carbon elements are present in the second slurry (the second slurry comprising a first conductive material, a first binder material, a second binder material, a first active material, and a solvent) in an amount of 5 wt% to 7 wt%, preferably 5.25 wt% to 6.25 wt%. Based on the total weight of the active layer, high aspect ratio carbon elements are present in the active layer in an amount of 8 wt% to 12 wt%.

[0038] As described above, the high aspect ratio carbon elements are preferably multi-walled carbon nanotubes.

[0039] In one embodiment, the first and second slurries may comprise a second conductive material. The second conductive material is different from the first conductive material in structure or composition. The second conductive material is preferably carbon-containing and comprises 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 comprises carbon nanotubes (e.g., single-walled carbon nanotubes and / or multi-walled carbon nanotubes), the second conductive material may comprise carbon black, graphite flakes, or a combination thereof. In another example, if the first conductive material comprises single-walled carbon nanotubes, the second conductive material may comprise one of multi-walled carbon nanotubes, carbon black, graphite flakes, or a combination thereof. Based on the total weight of the active layer, the second conductive material may be present in the active layer (after removal of the solvent) in an amount of 0.5 wt% to 10 wt%, preferably 1 wt% to 5 wt%.

[0040] The first binder material comprises at least a first polymer soluble in water. In one embodiment, the first binder material comprises a random or block copolymer of a vinyl aromatic compound and a conjugated diene. For simplicity, this component is referred to as a "copolymer". Based on the weight of the copolymer, the copolymer typically comprises a poly(vinyl aromatic compound) content of 10 wt% to 55 wt%. Within this range, the poly(vinyl aromatic compound) content may be 20 wt% to 50 wt%, particularly 25 wt% to 45 wt%.

[0041] 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 from 20,000 g / mol to 1,000,000 g / mol, particularly from 50,000 g / mol to 400,000 g / mol. In some embodiments, the copolymer comprises a styrene-butadiene random copolymer having a weight-average molecular weight of from 20,000 g / mol to 1,000,000 g / mol, particularly from 50,000 g / mol to 400,000 g / mol.

[0042] The vinyl aromatic monomer used to prepare the copolymer may have the following structure,

[0043]

[0044] wherein R 7 and R 8 each independently represents a hydrogen atom, a C 1 -C 8 alkyl group or a C 2 -C 8 alkenyl group; R 9 and R 13 each independently represents a hydrogen atom, a C 1 -C 8 alkyl group, a chlorine atom or a bromine atom; and R 10 , R 11 and R 12 each independently represents a hydrogen atom, a C 1 -C 8 alkyl group, or a C 2 -C 8 alkenyl group, or R 10 and R 11 together with the central aromatic ring form a naphthyl group, or R 11 and R 12 together with the central aromatic ring form a naphthyl group. Specific vinyl aromatic monomers include, for example, styrene, chlorostyrenes such as p-chlorostyrene, methylstyrenes such as α-methylstyrene and p-methylstyrene, and tert-butylstyrenes such as 3-tert-butylstyrene and 4-tert-butylstyrene. In some embodiments, the vinyl aromatic monomer is styrene.

[0045] The conjugated diene used to prepare the copolymer may be a C 4 -C 20Conjugated 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, etc. 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 consists of 1,3-butadiene.

[0046] The copolymer is a copolymer comprising (A) at least one block derived from an alkenyl aromatic compound and (B) at least one block derived from a conjugated diene, wherein the content of aliphatic unsaturated groups 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%, specifically at least 70%. The arrangement of blocks (A) and (B) includes linear structures, graft structures, and star teleblock structures with or without branches. Linear block copolymers include gradient linear structures and non-gradient 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.

[0047] In some embodiments, the block copolymer does not contain residues of monomers other than alkenyl aromatic compounds and conjugated dienes. In some embodiments, the block copolymer consists of blocks derived from alkenyl aromatic compounds and conjugated dienes, wherein at least one block is carboxylated (i.e., grafted with a carboxylic acid or a carboxylic acid derivative). Examples of unsaturated carboxylic acids are 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.

[0048] The carboxylation of the block copolymer allows the styrene-butadiene copolymer to be used in the form of a latex, in which it exists as small particles dispersed in water. A latex is a dispersion of polymer particles or droplets in a liquid. The particles do not sink or float in the aqueous emulsion and do not coagulate due to ionic or steric instability. Ionic stability is the result of the ionic charge on the particles, creating a repulsive force that prevents agglomeration. Steric stability occurs when the surface of the polymer particles extends into the solution, thus keeping the particles physically separated. Additives can be placed in the latex to ensure its steric stability and support its anti-coagulation properties.

[0049] In a preferred embodiment, the first polymer is a styrene-butadiene random copolymer. In one embodiment, the styrene-butadiene block copolymer is added to the slurry in the form of a latex.

[0050] The first binder material is present only in the second slurry. As described above, the second slurry comprises a first conductive material, a first binder material, a second binder material, a first active material, and a solvent. When the first binder material is added, the first slurry becomes the second slurry. Based on the total weight of the second slurry, the first binder material is present in the second slurry in an amount of 4.5 wt% to 6.5 wt%, preferably 5 wt% to 6 wt%. Based on the weight of the active layer, the first binder is present in the active layer in an amount of 7 wt% to 13 wt%, preferably 8 wt% to 12 wt%.

[0051] 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 one embodiment, the second binder material is a water-soluble and naturally occurring polymer. Examples of naturally occurring polymers used as the second binder material include cellulose and cellulose derivatives (e.g., hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose, cellulose acetate, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose acetate butyrate, and cellulose ethers such as ethyl cellulose, etc. or combinations thereof), sugars (glucose, sucrose, lactose, galactose, fructose, mannitol, sorbitol, or combinations thereof), ionic complexes of cellulose (gums (e.g., gum arabic, alginate, carrageenan, guar gum, karaya gum, pectin, tragacanth gum, xanthan gum, etc. or combinations thereof).

[0052] In a preferred embodiment, the second binder is carboxymethyl cellulose (CMC).

[0053] Based on the total weight of the first slurry, the second binder is present in an amount of 2 wt% to 4 wt%, preferably 2.25 wt% to 3.75 wt%. Based on the total weight of the second slurry, the second binder is present in an amount of 2.25 wt% to 5 wt%, preferably 2.35 wt% to 4.6 wt%. Based on the weight of the active layer, the second binder is present in the active layer in an amount of 3 wt% to 7 wt%.

[0054] For the active layer 106 (see Figure 1) The active material is located in voids surrounded by a conductive network formed by carbon elements with a high aspect ratio. The active layer may include other activated carbon materials, including, for example, activated carbon particles, 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 oxide (LiNiMnCO), lithium manganese oxide (LMO), lithium titanate oxide (LTO), lithium iron phosphate oxide (LFP), lithium nickel cobalt aluminum oxide (LiNiCoAlO), and other similar materials.

[0055] 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 reactions. Powdered activated carbon (PAC) and granular activated carbon (GAC) are common forms. In one embodiment, the active material is powdered activated carbon. Activated carbon can have a surface area of from 500 square meters per gram to 3,000 square meters per gram.

[0056] In one embodiment, the active materials used in the two electrodes (anode and / or cathode) can include lithium cobalt oxide (LCO, sometimes referred to as "lithium cobaltate" or "lithium cobaltite". One variant of a possible LCO formulation is LiCoO 2 ); lithium nickel manganese cobalt oxide (NMC, having the variant formula LiNiMnCO); lithium manganese oxide (having LiMn 2 O 4 、Li 2 MnO 3 etc. or variants of LMO in combination thereof); lithium titanate oxide (LTO, one variant of which is Li 4 Ti 5 O 12 ); lithium iron phosphate oxide (LFP, one variant of which is LiFePO 4 ), lithium nickel cobalt aluminum oxide (and its variant as NCA), and other similar other materials. Other variants of the foregoing may be included. In some embodiments where NMC is used as the active material, nickel-rich NMC can be used. In some embodiments, when NMC is used as the active material, nickel-rich NMC can be used.

[0057] For example, in some embodiments, a variant of NMC can be LiNi x Mn y Co (1-x-y) , where x is equal to or greater than about 0.7, 0.75, 0.80, 0.85 or greater. In one embodiment, y can be equal to or greater than 0.1, 0.15, 0.2 or 0.25. In some embodiments, NMC811 can be used, where x is about 0.8 and y is about 0.1.

[0058] In some embodiments, the active material includes other forms of lithium nickel manganese cobalt oxide (LiNi x Mn y Co z O 2 ). Variants of this formula that can be used in the active material layer include NMC 111 (described in detail below), NMC532 (LiNi 0.5 Mn 0.3 Co 0.2 O 2 ), NMC622 (LiNi 0.6 Mn 0.2 Co 0.2 O 2 ), or combinations thereof.

[0059] In one embodiment, the active material used in both electrodes (anode and / or cathode) may also include a nickel-rich combination of nickel, manganese, and cobalt. Lithium-nickel-manganese-cobalt-oxide (LiNiMnCoO 2 ), abbreviated as NMC, provides strong overall performance, excellent specific energy, and the lowest self-heating rate among all mainstream cathode powders. Based on the total weight of the NMC blend, the NMC powder may include nickel in an amount of 20 wt% to 40 wt%, manganese in an amount of 20 wt% to 40 wt%, and cobalt in an amount of 20 wt% to 40 wt%. Although the term "NMC powder" may refer to a variety of blends, it is desirable to use a blend including 33 wt% nickel, 33 wt% manganese, and 33 wt% cobalt. Such a blend (sometimes referred to as 1-1-1 (NMC 111)) is useful for applications that use frequent cycling (automotive, energy storage) because of the reduced material cost achieved by the lower cobalt content.

[0060] Based on the total weight of the active layer, the content of the active material in the active layer is 67 wt% to 85 wt%, preferably 70 wt% to 80 wt%.

[0061] The mixture used to fabricate the active layer further includes a solvent. The solvent is preferably a solvent for dispersing the first binder, the second binder, the first conductive material, and the second conductive material to form the mixture. The mixture is then disposed on the current collector to form the active layer.

[0062] Suitable solvents are water, alcohols, or combinations thereof. Examples of alcohols are ethanol, methanol, propanol, butanol, ethylene glycol, propylene glycol, or combinations thereof. In addition to water and alcohols, other solvents can be added to facilitate the dissolution and / or dispersion of the polymer. Other solvents include polar solvents, non-polar 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 be used. Other non-polar solvents such as benzene, toluene, dichloromethane, carbon tetrachloride, hexane, diethyl ether, tetrahydrofuran, etc., or combinations thereof can also be used. Cosolvents including at least one aprotic polar solvent and at least one non-polar solvent can also be used to change the dissolution ability of the solvent.

[0063] In a preferred embodiment, the solvent is water. In another preferred embodiment, the solvent is alcohol. When water and alcohol are used as the solvent for the active layer, the ratio of water to alcohol is from 80:20 to 95:5, preferably from 88:12 to 92:8. In an exemplary embodiment, the ratio of water to alcohol is 90:10.

[0064] Based on the total weight of the first slurry, the solvent is present in an amount of 45 wt% to 60 wt%, preferably 48 wt% to 55 wt%. Preferably, the solvent is removed from the active layer after the active layer is disposed on the current collector. The solid active layer is preferably free of solvents (water and alcohol).

[0065] 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 of 20 microns to 30 microns. In some embodiments, the active layer 106 has an average thickness of about 100 microns.

[0066] According to various embodiments, when wetted with an electrolyte, the active layer 106 swells (e.g., expands) less than 10%. For example, the thickness of the active layer 106 (after wetting with the electrolyte) is less than 110% of the thickness of the active layer 106 in the absence of the electrolyte.

[0067] In one embodiment, a cathode polymer binder (a first cathode polymer binder and a second cathode polymer binder), a cathode active material, a cathode conductive material, and a solvent are blended together to form a cathode mixture in the form of a slurry. The blending process facilitates the dispersion of the cathode conductive material and the cathode active material to form a percolation network through the volume of the cathode active layer upon removal of the solvent. In one embodiment, after mixing is complete, the cathode mixture (in slurry form) is disposed on a current collector. The current collector having the cathode mixture disposed thereon is sheared and compressed in a roll mill. The use of the roll mill facilitates the bonding of the cathode active layer to the current collector.

[0068] Figure 2 is a flow chart of a method of fabricating an electrode according to various embodiments. With respect to Figure 1 electrode 100 provides a description of process 200. Referring to Figure 2 , in some embodiments, the active layer 106 of electrode 100 can be formed using process 200. At 202, a high aspect ratio carbon element (e.g., MWNT), a second binder (e.g., CMC), and an active material (e.g., activated carbon) and any optional surface treatment material (e.g., surfactant) are combined with a solvent (a solvent of the type described herein) to form an initial slurry (also referred to as a first slurry).

[0069] At 202, the first slurry is processed to ensure good dispersion of the solid materials in the slurry. In some embodiments, the processing includes introducing mechanical energy into the mixture of the solvent and the solid materials (e.g., using an ultrasonic device, which may sometimes also be referred to as an “ultrasonic”) 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 greater. For example, the mechanical energy introduced into the mixture per kilogram of the mixture can be in the range of 0.4 kWh / kg to 1.0 kWh / kg or any sub-range thereof, such as 0.4 kWh / kg to 0.6 kWh / kg.

[0070] In some embodiments, an ultrasonic bath mixer can be used. In other embodiments, a probe sonicator can 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 up particle aggregates and produce smaller and more uniform particle sizes. In addition, sonication can achieve a stable and uniform suspension of solids in a slurry. Typically, this results in the dispersion and depolymerization of the solids and other breakdown. Examples of probe sonication devices include Q-series probe sonicators that can be commercially obtained from QSonica LLC of Newtown, Connecticut. Another example includes the Branson Digital SFX-450 sonicator that can be commercially obtained from Thomas Scientific of Swedesboro, New Jersey.

[0071] However, in some embodiments, the local properties of each probe within the probe assembly can lead to non-uniform mixing and suspension. This may be the case for, for example, large sample situations. This can be addressed by using a setup with a continuous flow cell and proper mixing. For example, with such a setup, mixing of the slurry will achieve a reasonably uniform dispersion.

[0072] In some embodiments, once processed, the first slurry will have a viscosity of 2,000 cps to 25,000 cps or any sub-range thereof (e.g., 6,000 cps to 19,000 cps).

[0073] The first slurry is then mixed with a first binder material (e.g., SBR latex) to form a final slurry.

[0074] 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 can be used. In some embodiments, this processing can use the techniques described above with reference to 202. In some embodiments, a planetary mixer such as a multi-axis (e.g., three-axis or more) planetary mixer can be used. In some such embodiments, the planetary mixer can be characterized by multiple blades, such as two or more mixing blades and one or more (e.g., two, three, or more) dispersion blades such as disk dispersion blades.

[0075] In some embodiments, during 204, the matrix encapsulating the active material can self-assemble completely or partially. In some embodiments, the interaction between the surface treatment and the active material promotes the self-assembly process.

[0076] In some embodiments, once processed, the final slurry will have a viscosity of 1,000 cps to 10,000 cps or any sub-range thereof (e.g., 2,500 cps to 6,000 cps).

[0077] At 206, the active layer 106 is formed from the final slurry. In some embodiments, the final slurry can be directly wet cast onto the current collector conductive layer 102 (or optional adhesion layer 104) and dried. As an example, casting can be performed by applying at least one of heat and vacuum until substantially all of the solvent and any other liquid have been removed, thereby forming the active layer 106. In some such embodiments, it may be desirable to protect various portions of the underlying layer. For example, in the case where the electrode 100 is intended for dual-sided operation, it may be desirable to protect the underside of the conductive layer 102. Protection can include, for example, protecting from the solvent by masking certain areas or providing a drainage device to direct the solvent away.

[0078] In other embodiments, the final slurry can be at least partially dried elsewhere and then transferred to the adhesion layer 104 or the conductive layer 102 using any suitable technique (e.g., roll-to-roll layer application) to form the active layer 106. In some embodiments, the wet final slurry can be placed on an intermediate material having a suitable surface and dried to form a layer (e.g., the active layer 106). While any material having a suitable surface can be used as the intermediate material, exemplary intermediate materials include PTFE because its properties facilitate subsequent removal from the surface. In some embodiments, the specified layer is formed in a press to provide a layer exhibiting the desired thickness, area, and density.

[0079] In some embodiments, the final slurry can be formed into a sheet and appropriately coated onto the adhesion layer 104 or the conductive layer 102. For example, in some embodiments, the final slurry can be applied by a slot die to control the thickness of the applied layer. In other embodiments, the slurry can be applied and then, for example, leveled to the desired thickness using a doctor blade. A variety of other techniques can be used to apply the slurry. For example, coating techniques can include, but are not limited to: comma coating; reverse comma coating; doctor blade coating; slot die coating; direct gravure coating; air knife coating; chamber doctor blade coating; displacement gravure coating; single pass roll kiss coating; reverse kiss coating with a small diameter gravure roll; rod coating; triple reverse roll coating (top feed); triple reverse roll coating (feed die); reverse roll coating, etc.

[0080] The viscosity of the final slurry can vary depending on the application technique. For example, for comma coating, the viscosity can be in the range of about 1,000 cps to about 200,000 cps. Lip die coating provides coating of slurries having a viscosity of about 500 cps to about 300,000 cps. Reverse kiss coating provides coating of slurries having a viscosity between about 5 cps and 1,000 cps. In some applications, the corresponding layer can be formed by multiple passes.

[0081] In some embodiments, the active layer 106 formed from the final slurry can be compressed (e.g., using calendering equipment) before or after being applied to the electrode 100. In some embodiments, the slurry is partially or fully 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 can be compressed to a final thickness less than 90%, 80%, 70%, 50%, 40%, 30%, 20%, 10%, or less of its pre-compression thickness (e.g., in a direction perpendicular to the current collector layer 102).

[0082] In various embodiments, when a partially dried layer is formed during the coating or compression process, the layer can subsequently be fully 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.

[0083] In some embodiments, the solvent used to form the slurry is recovered and recycled into the slurry preparation process.

[0084] In some embodiments, the active layer 106 can be compressed, for example, to break some of the high aspect ratio carbon elements or other carbon-containing materials of the composition to increase the surface area of the corresponding layer. In some embodiments, such a compression treatment can increase one or more of the adhesion between layers, the ion transport rate within the layer, and the surface area of the layer. In various embodiments, the compression can be applied before or after applying the corresponding layer to the electrode 100 or forming it on the electrode 100.

[0085] In some embodiments where calendering is used to compress the active layer 106, the calendering equipment can be set to a nip spacing equal to less than 90%, 80%, 70%, 50%, 40%, 30%, 20%, 10%, or less of the pre-compression thickness of the layer (e.g., set to about 33% of the pre-compression thickness of the layer). The calendering rolls can be configured to provide a suitable pressure, such as greater than 1 ton / cm of roll length, greater than 1.5 ton / cm of roll length, greater than 2.0 ton / cm of roll length, greater than 2.5 ton / cm of roll length, or greater. In some embodiments, the compressed active layer will have a density in the range of 0.1 g / cc to 10 g / cc or any sub-range thereof (such as 2.5 g / cc to 4.0 g / cc).

[0086] In some embodiments, the calendering process can be carried out at a temperature in the range of 20 °C to 140 °C or any sub-range thereof. In some embodiments, the active layer 106 can be preheated before calendering (e.g., at a temperature in the range of 20 °C to 100 °C or any sub-range thereof).

[0087] Once the electrode 100 has been assembled, the electrode 100 can be used to assemble an energy storage device. The assembly of the energy storage device can follow the conventional steps for assembling the electrode with a separator and placing it inside a housing (e.g., a can or a pouch), and can also include additional steps for adding an electrolyte and sealing the housing.

[0088] In various embodiments, the process 200 can include any one of the following features (individually or in any suitable combination).

[0089] In some embodiments, the initial slurry has a solids content in the range of 0.1% to 20.0% (by weight) (or any sub-range thereof). In some embodiments, the final slurry has a solids content in the range of 10.0% to 80% (by weight) (or any sub-range thereof).

[0090] The 3D carbon scaffold or matrix holds the active material particles together to form a cohesive layer that is also firmly attached to the metal current collector. This active material structure is generated during the slurry preparation process and subsequently during the roll-to-roll ("R2R") coating and drying processes. One of the main advantages of this technique is its scalability and "drop-in" nature, as various embodiments are compatible with conventional electrode manufacturing processes.

[0091] The teachings herein provide a 3D matrix that significantly increases the electrode conductivity by 10 to 100 times compared to electrodes using conventional binders such as PVDF, which enables fast charging at the battery level. With this technique, thick electrode coatings in the cathode can reach 150 μm (or more) on each side of the current collector. The solvent used in the slurry in combination with the strong 3D carbon matrix is designed to enable a thick wet coating without cracking during the drying step. A thick cathode with a high-capacity anode can achieve a significant jump in energy density up to 400 Wh / kg or higher.

[0092] Figure 3A schematic diagram of the electrode arrangement of a pouch cell device is shown. As shown, a double-sided cathode 700 using a cathode layer 760 (e.g., an active layer according to various embodiments disclosed herein) on the opposite side of an aluminum foil current collector 710 is disposed between two single-sided anodes 720 and 730, each single-sided anode having an anode layer 740 and 750 (e.g., including an active layer such as a carbon element network disclosed herein) disposed on a copper foil current collector. The electrodes are separated by a permeable separator material 780 wetted with an electrolyte (not shown). This arrangement can be accommodated in a pouch cell of a type known in the art.

[0093] In Figure 4 a cross-section of an energy storage device (ESD) 810 is shown. 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 element 812 housed within the housing 811 and an external electrical connection to an external device such as a load or a charging device (not shown). The energy storage devices disclosed herein can be batteries, capacitors, supercapacitors, etc.

[0094] The materials and structures disclosed herein are illustrated by the following non-limiting examples.

[0095] Although the invention has been described with reference to some embodiments, those skilled in the art will understand that various changes can be made and elements thereof can be replaced with equivalents without departing from the scope of the invention. Additionally, 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. Accordingly, the invention is not limited to the specific embodiments disclosed as the best mode contemplated for carrying out the invention, but 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 comprising: a network of high aspect ratio carbon elements that define interstitial spaces within the network; a plurality of electrode active material particles disposed within the interstitial spaces of the network; and a first binder material comprising water-soluble styrene-butadiene rubber.

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

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

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

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

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

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

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

9. The electrode according to claim 1, wherein the active layer comprises a second binder material containing cellulose.

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

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

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

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

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

15. An energy storage device, comprising: an electrolyte; and the electrode according to claim 1, wherein the multi-walled nanotubes form a percolation network through the active layer.

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

17. The method according to claim 16, further comprising mixing cellulose into the slurry.

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

19. The method according to claim 16, wherein the high aspect ratio carbon element defines a network having void spaces therein; and wherein the plurality of electroactive material particles are contained within the void spaces.

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

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