Electrodes for energy storage devices containing binders with hydrophilic functional groups - Patent Application 20070122997

Abstract

An electrode comprising a current collector and an active layer on the current collector, the active layer comprising electrode active particles, a conductive material, and a binder, the binder comprising polymer molecules selected from the group consisting of polyacrylamide, polymethacrylic acid, and polyacrylic acid and salts thereof, can be used in an energy storage device. The electrode can be fabricated by providing a slurry comprising the conductive elements, the binder, and the electrode active material in water, alcohol, or a combination thereof, coating the slurry on a current collector, and drying to remove the solvent.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Application No. 63 / 417,127, filed October 18, 2022, the entire contents of which are incorporated herein by reference.

[0002] FIELD OF THE INVENTION The present invention relates to energy storage devices, particularly lithium ion batteries, and electrodes used in such batteries. [Background technology]

[0003] Lithium batteries are used in many products, including medical devices, electric vehicles, airplanes, and consumer products such as laptop computers, cell phones, and cameras. Due to their high energy density, high operating voltage, and low self-discharge, lithium-ion batteries have overtaken the secondary battery market and continue to find new applications in products and evolving industries.

[0004] Generally, a lithium-ion battery ("LIB" or "LiB") 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 the lithium-ion battery.

[0005] The binder functions to adhere the active material to the current collector with an appropriate coating. It is important that the binder assist in maintaining sufficient contact between the active material and the current collector. Furthermore, it was 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. The binder must also be strong enough to withstand the handling involved in fitting the electrode into the battery casing.

[0006] 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

[0007] Disclosed herein is an electrode comprising a current collector and an active layer on the current collector, the active layer comprising electrode active particles, a conductive material, and a binder, the binder comprising a polymer selected from the group consisting of polyacrylamide, polymethacrylic acid, and polyacrylic acid or a salt thereof.

[0008] Also disclosed herein are energy storage devices that include such electrodes.

[0009] Further disclosed herein is a method for making such an electrode, the method comprising providing a slurry comprising a conductive element, a binder, and an electrode active material in water, an alcohol, or a combination thereof, coating the slurry onto a current collector, and drying to remove the solvent. [Brief explanation of the drawings]

[0010] The following is a brief description of the drawings, in which like elements are numbered alike and presented for the purpose of illustrating, but not for the purpose of limiting, exemplary embodiments disclosed herein. [Figure 1] FIG. 1 is a diagram showing an example of an electrode disclosed in the present specification. [Figure 2] 1 is a flow chart illustrating an example of a method that can be used to manufacture the electrodes disclosed herein. [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

[0011] 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.

[0012] Disclosed herein is an electrolytic cell that includes a housing with electrodes (anode and cathode). The housing contains an electrolyte in contact with the anode and cathode. Both electrodes (anode and cathode) include current collectors on which an active layer is disposed. The active layer may be disposed on an optional adhesive layer in contact with the electrodes.

[0013] FIG. 1 illustrates an example of an electrode (anode or cathode) disclosed herein. In the illustrated example, electrode 100 includes a current collector 102 and an active layer 106. Electrode 100 may optionally include an adhesion layer 104. By way of example, adhesion layer 104 includes a material that promotes adhesion between current collector 102 and active layer 106. Active layer 106 includes electrode active material 110 in a binder and conductive elements 108. The conductive elements may be high aspect ratio elements.

[0014] The current collector 102 is a conductive element. The current collector can include a metal (e.g., a substantially pure metal or a metal alloy). As another example, the current collector 102 can be in the form of a metal strip or foil. For example, the current collector 102 can be an aluminum foil or strip, an aluminum alloy foil or strip, a copper foil or strip, or a copper alloy foil or strip. The current collector 102 can have a thickness of 15 μm (microns) or less, 10 μm or less, 8 μm or less, or 5 μm or less. In some embodiments, the current collector can have a thickness of at least 3 μm. For example, the current collector 102 can have a thickness of 3 to 15 μm, or 6 μm, or about 8 μm. As another example, the current collector 102 is an aluminum foil or aluminum alloy foil having a thickness of 5 to 7 μm.

[0015] The active layer 106 includes a conductive material, a binder material, and an electrode active material. The active layer can be made by mixing the conductive material, binder material, and electrode active material with a solvent to form a mixture. This mixture can be applied directly to a current collector or to an adhesive layer that allows it to adhere to the current collector. If an adhesive layer is used, it can be conductive. The mixture can be dried to remove the solvent, leaving a solid active layer.

[0016] Conductive element The conductive elements (also referred to as conductive materials) can include carbon. For example, the conductive elements can be high aspect ratio carbon elements. The term "high aspect ratio carbon elements" refers to carbonaceous elements in which the size of one or more dimensions ("major dimensions") is significantly greater than the size of the element in its transverse dimension ("minor dimension"). The high aspect ratio carbon elements can include a substantially cylindrical network of carbon atoms. The conductive material can include carbon nanotubes or bundles of carbon nanotubes.

[0017] The conductive material can form a conductive permeating network that allows current to be transmitted between any two distant points located on the surface of the solid active layer (without solvent). In other words, current can be transmitted from one surface or end of the active layer to the opposite surface or end by physical contact or electron hopping between the conductive elements of the electrode active layer. This permeating network can include voids between the high aspect ratio carbon elements that contain or can accommodate the electrode active material. The high aspect ratio conductive material can be substantially oriented in the electrode active layer 106 in a direction substantially parallel to the current collector to support current conduction from one end of the electrode to the other, while still maintaining some degree of less orientation throughout the thickness of the active layer.

[0018] The conductive material can be present in the mixture in an amount of 0.1 to 1.3, or 0.15 to 1.2, or 0.3 to 1 weight percent, based on the total weight of the mixture (the mixture including the conductive material, electrode active material, binder material, and solvent). The conductive material can be present in the active layer in an amount of 0.2 to 3.5, or 0.3 to 3, or 0.5 to 2 weight percent, based on the total weight of solids in the active layer (the total weight solids includes the conductive material, binder material, and electrode active material excluding solvent).

[0019] The high aspect ratio carbon elements can be single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWNTs), or a mixture of both.

[0020] The single-walled carbon nanotubes can have an outer diameter of 0.5 to 5.0 nanometers, preferably 1.0 to 3.5 nanometers. The single-walled carbon nanotubes can have an aspect ratio (ratio of length to diameter) of greater than about 2.0, preferably greater than 5.0, more preferably greater than 10.0, greater than 50, and even more preferably greater than 100. In exemplary embodiments, the single-walled carbon nanotubes can have an average aspect ratio of 5 to 200.

[0021] The single-walled carbon nanotubes can have a length of 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, even more preferably greater than 15 micrometers up to at least 200 micrometers. In exemplary embodiments, the single-walled carbon nanotubes can have an average length of 10 nanometers to 20 micrometers, preferably 20 nanometers to 15 micrometers.

[0022] The single-walled carbon nanotubes can be present in the mixture of the conductive material, binder material, electrode active material, and solvent in an amount of 0.1 to 2 weight percent, based on the total weight of the mixture. For example, the amount of single-walled nanotubes in the mixture can be 0.1 to 0.3, or 0.15 to 9.25 weight percent. As another example, the amount of single-walled nanotubes in the mixture can be 0.4 to 2 weight percent.

[0023] The single-walled carbon nanotubes can be present in the electrode active layer (electrode active material excluding conductive material, binder material, and solvent) in an amount of 0.2 to 4 weight percent, based on the total weight of the electrode active layer. For example, the amount of single-walled nanotubes in the electrode active layer can be 0.2 to 0.6, or 0.3 to 0.5 weight percent. As another example, the amount of single-walled nanotubes in the electrode active layer can be 0.5 to 4 weight percent.

[0024] The number of carbon layers in the multi-walled carbon nanotubes can be 2 or more, 5 or more, 10 or more, or 50 or more. The multi-walled carbon nanotubes can include an average of 3 to 15 layers, 4 to 12 layers, 5 to 10 layers, or 6 to 8 layers.

[0025] The active layer 106 can include 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. For example, the multi-walled carbon nanotubes can swell at least 15%, or at least 25%, or at least 50% 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 can expand at least 15%, or at least 25%, or at least 50% more than the length of single-walled carbon nanotubes when wetted by the electrolyte. As another example, 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 wetted with the electrolyte and / or the diameter of the multi-walled carbon nanotubes increases by 50% after wetted, etc.).

[0026] The multi-walled carbon nanotubes can have an outer diameter of 2.0 to 50 nanometers, 5.0 to 40 nanometers, or 6 to 10 nanometers. The multi-walled carbon nanotubes can have a length of greater than 10 nanometers, greater than 15 nanometers, greater than 30 nanometers, greater than 50 nanometers, greater than 100 nanometers, greater than 500 nanometers, greater than 1 micrometer, greater than 5 micrometers, greater than 10 micrometers, or greater than 15 micrometers. At the same time, the multi-walled carbon nanotubes can have an average length of up to 25 micrometers, or up to 20 micrometers. In exemplary embodiments, the multi-walled carbon nanotubes have an average length of 10 nanometers to 20 micrometers, or 20 nanometers to 15 micrometers. The multi-walled carbon nanotubes can have an aspect ratio (ratio of length to diameter) of greater than 5.0, greater than 10.0, greater than 50, greater than 100, or greater than 500.

[0027] The electrode may include multi-walled carbon nanotubes that are relatively long compared to those 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 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 merely a particle of carbon without entanglements such as those exhibited by a set of multi-walled carbon nanotubes. An indication that a certain amount of multi-walled carbon nanotubes has a length exceeding a threshold length and therefore has sufficient swelling properties is observed during the calendering process, where a relatively large amount of pressure or effort to calender the slurry in connection 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.

[0028] Processing of multi-walled carbon nanotubes in connection with the preparation / formation of the active layer and / or electrode is gentler than processing of related art electrodes. Accordingly, processes according to various embodiments preserve longer multi-walled carbon nanotubes (e.g., fewer multi-walled carbon nanotubes are crushed, fragmented, broken, etc.). In some embodiments, the active layer of the electrode includes a set of multi-walled carbon nanotubes having an average length longer than the average length of the multi-walled carbon nanotubes in the related art electrodes. 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. In one example, the nominal length of the multi-walled carbon nanotubes is about 16 microns. For example, the multi-walled carbon nanotubes are processed and / or adapted to reduce or minimize crushing or breaking of the multi-walled carbon nanotubes. The length of the multi-walled carbon nanotubes in the network of high aspect ratio carbon elements is generally the nominal length of the multi-walled carbon nanotubes, or the lengths of such multi-walled carbon nanotubes tend to be more skewed relative to the nominal length. 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 microns and about 15 microns). 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 microns. 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 microns. 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 microns and about 15 microns). 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 microns. 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 8 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.

[0029] 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.

[0030] 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.

[0031] The multi-walled carbon nanotubes can be present in the mixture (the mixture including the conductive material, the electrode active material, the binder material, and the solvent) in an amount of 0.3 to 1.0 weight percent, preferably 0.4 to 0.9 weight percent, based on the total weight of the mixture. The multi-walled carbon nanotubes can be present in the solid anode active layer (the solid active layer including the conductive material, the binder material, and the electrode active material without the solvent) in an amount of 0.8 to 2.6 weight percent, preferably 1.0 to 1.8 weight percent, based on the total weight of the solid anode active layer.

[0032] In embodiments in which both multi-walled and single-walled carbon nanotubes are used, the ratio of the weight of multi-walled carbon nanotubes to the weight of single-walled carbon nanotubes in the mixture or solid active material layer can be at least 2:1.

[0033] In one example, the three-dimensional network of high aspect ratio carbon elements 108 includes carbon nanotubes, which may be multi-walled carbon nanotubes and / or fragments of such carbon nanotubes only.

[0034] In another example, the multi-walled carbon nanotubes are present in the mixture or in the solid anode active material layer in an amount at least twice as large as the single-walled carbon nanotubes, based on the weight of the conductive material.

[0035] The network of the three-dimensional network of high aspect ratio carbon elements 108 can comprise at least 99% carbon by weight.

[0036] The three-dimensional network of high aspect ratio carbon elements 108 can include 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 lengths 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.

[0037] electrode active material Typically, the active materials are different for the anode and cathode.

[0038] For example, the anode active material can include silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), cadmium (Cd), alloys of two or more of these or alloys of these with other elements, oxides, carbides, nitrides, sulfides, phosphides, selenides, and tellurides of these metals, and mixtures or lithium-containing complexes thereof; salts and hydroxides of Sn; lithium titanate; lithium manganate; lithium aluminate; lithium-containing titanium oxide; lithium transition metal oxide; prelithiated versions thereof; particles of Li having at least 60% lithium by weight; Li alloys; or surface-stabilized Li; or combinations thereof. Alternatively or additionally, the active material can include graphite. For example, the anode active material can include silicon oxide and / or silicon carbide. Such anode active materials comprising silicon oxide or silicon carbide can further comprise graphite.

[0039] For example, the cathode active material can include lithium cobalt oxide (LCO, sometimes referred to as "lithium cobaltate" or "lithium cobaltite"). Example LCO formulations include LiCoO, lithium nickel manganese cobalt oxide (NMC, having a variant formula of LiNiMnCo), lithium manganese oxide (LMO, having a variant formula of LiMnO, LiMnO, etc., or combinations thereof), lithium titanate oxide (LTO, having one variant formula of LiTiO), lithium iron phosphate oxide (LFP, having one variant formula of LiFePO), lithium nickel cobalt aluminum oxide (and variants such as NCA), and other similar materials. Other variants of the foregoing may also be included.

[0040] When NMC is used as the active material, nickel-rich NMC can be used. For example, a variant of NMC can be LiNixMnyCo(1-xy), where x is about 0.7, 0.75, 0.80, 0.85 or more, y is 0.1, 0.15, 0.2, or 0.25 or more, and x + y is less than 1. For example, NMC811 can be used when x is about 0.8 and y is about 0.1. Alternatively, the active material can include an oxide of lithium nickel manganese cobalt (LiNixMnyCozO2). Variations of this formula that can be used in the active material layer include NMC111 (discussed in more detail below), NMC532 (LiNiO.5MnO.3CoO.2O2), NMC622 (LiNiO.6MnO.2CoO.2O2), or combinations thereof.

[0041] 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 powders 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 in applications involving frequent cycling (automotive, energy storage) due to the reduced material cost resulting from the lower cobalt content of this nickel-rich combination of nickel, manganese, and cobalt (NMC). The 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, is useful in applications involving frequent cycling (automotive, energy storage) due to the reduced material cost resulting from the lower cobalt content. Lithium-nickel-manganese-cobalt-oxide (LiNiMnCoO2) offers high overall performance, excellent specific energy, and the lowest self-heating rate of all mainstream cathode powders.

[0042] As described above, the active material can be contained or housed in a network of high aspect ratio active material present in the electrode active layer. The active material can be present in the mixture used to form the electrode in an amount of 40 to 75 wt %, preferably 50 to 70 wt %, based on the total weight of the electrode mixture (the mixture used to prepare the electrode active layer, including the electrode polymer binder material, the electrode active material, the conductive material, and the solvent). The electrode active material can be present in the electrode active material layer (excluding the solvent) in an amount of 95 to 98.5 wt %, based on the total weight of the cathode active layer.

[0043] Binder The binders described herein can provide the ability to fabricate electrodes using water and / or alcohol as a solvent. Such binders can also provide good adhesive bonding strength, good dispersion of slurry components (i.e., electrode active material, binder, and conductive material), and / or good stability during battery charging and discharging. The binders are polymeric and characterized by the presence of hydrophilic pendant groups, which aid in at least processing in water and / or alcohol and good dispersion of slurry components while reducing the solubility of the binder in carbonate-based electrolytes. The binders are characterized by their ability to provide good mechanical properties and / or electrochemical and chemical stability when used in energy storage devices (e.g., batteries, particularly lithium-ion batteries). The binders described herein are selected from the group consisting of polyacrylamide, polymethacrylic acid or its salts, and polyacrylic acid or its salts. These polymers may be homopolymers.

[0044] For example, the binder polymer can have the formula: formula: [ka] wherein R, in each occurrence, is independently H, but one of R can be an alkyl group having 1 to 3 carbon atoms, and P is -COOR 1 where R 1 H, Na + , K.+ , or Li + or a hydrocarbon group having 1 to 3 carbon atoms, preferably R 1 is H or a monovalent metal ion. Alternatively, P can be —C(O)N(R 2 )2, where R 2 is independently in each occurrence H or an alkyl group having 1 to 3 carbon atoms, preferably 1 carbon atom.

[0045] Polyacrylamide, polymethacrylic acid, polyacrylic acid can be prepared by known polymerization techniques involving ethylenically unsaturated monomers, such as addition polymerization, which can be, for example, solution polymerization or emulsion polymerization.

[0046] The weight average molecular weight of the polymer, as determined by gel permeation chromatography, can be from 5,000 to 2,000,000 grams per mole, alternatively from 10,000 to 1,000,000 grams per mole.

[0047] If desired, the polymer can contain cross-linking functional groups, or a cross-linking agent can be added to enable cross-linking of the binder polymer before fabrication of the electrode active layer is complete.

[0048] The above polymers can be used as the only polymer in the binder. Alternatively, the above polymers can be used as a blend with a second, different polymer as described above. As yet another alternative, the above polymers can be blended with one or more other known polymer binders. However, to fully utilize the value of the above polymers, the additional polymers are also preferably soluble or dispersible in water, alcohol, or a combination thereof. When used in a blend, the above polymers preferably comprise at least 10, at least 20, at least 30, at least 40, at least 50, at least 60, at least 70, at least 80, at least 90, at least 95, or at least 99 weight percent of the blend, based on the total weight of the polymers in the blend.

[0049] Electrode formation Electrodes can be manufactured by first preparing a mixture (also called a slurry) of conductive elements, active materials, and binder in a solvent. An advantage of the binders described herein is that a useful slurry can be formed using water, alcohol, or a combination thereof as the solvent. The slurry can then be coated directly onto a current collector or applied to the current collector using an intermediate adhesive layer.

[0050] The slurry can be prepared in a single step. Alternatively, the slurry can be prepared according to a multiple step process, as shown in the flowchart of Figure 2, which illustrates an example process 600 provided for the electrode 100 of Figure 1. At 610, a conductive material, e.g., high aspect ratio carbon elements, and a surface treatment material (e.g., a surfactant, a binder material described herein, or both) are combined with a solvent (e.g., water, alcohol, or a combination thereof) to form an initial slurry.

[0051] At 620, the initial slurry is treated to ensure good dispersion of the solid materials within the slurry. This treatment can include introducing mechanical energy into the mixture of solvent and solid materials (e.g., using a sonicator, sometimes also referred to as a "sonifier") or other suitable mixing device (e.g., a high shear mixer). For example, the mechanical energy introduced into the mixture can be 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.

[0052] As an example, an ultrasonic bath mixer can be used. As another example, a probe sonicator can be used. Probe sonication can be significantly more powerful and effective when compared to ultrasonic baths 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 the 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).

[0053] The local nature of each probe within the probe assembly can sometimes 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 slurries achieves reasonably uniform dispersion.

[0054] The initial slurry, once processed, can have a viscosity in the range of 5,000 cps to 25,000 cps, or any subrange thereof, such as, for example, in the range of 6,000 cps to 19,000 cps.

[0055] In optional step 630, a binder (e.g., used if no binder was added in step 610) or additional binder can be applied as a surface treatment, which can be fully or partially formed on the conductive material (e.g., high aspect ratio carbon elements) in the initial slurry. In some embodiments, the surface treatment can be self-assembled at this stage.

[0056] The resulting surface treatment can include functional groups or other features that can promote adhesion between the high aspect ratio carbon elements and the active material particles, as described in further steps below. For example, functional groups on a binder can provide the described surface treatment.

[0057] At 640, the active material particles may be combined with the initial slurry to form a final slurry containing the active material particles along with the high aspect ratio carbon elements having the surface treatment formed thereon.

[0058] The active material can be added directly to the initial slurry. Alternatively, the active material can be first dispersed in a solvent (e.g., water, alcohol, or a combination thereof, using the techniques described above for the initial solvent) to form an active material slurry. This active material slurry can then be combined with the initial slurry to form the final slurry.

[0059] At 650, the final slurry is processed to ensure good dispersion of the solid materials in the final slurry. Any suitable mixing process known in the art may be used. For example, this processing may use the techniques described above with reference to 620. Alternatively, a planetary mixer, such as a multi-shaft (e.g., three or more) planetary mixer, may be used. The planetary mixer may include multiple blades, e.g., two or more mixing blades and one or more (e.g., two, three or more) dispersion blades, such as a disk dispersion blade.

[0060] During 650, the matrix enveloping the active materials may fully or partially self-assemble as interactions between the surface treatment (eg, binder) and the active materials facilitate the self-assembly process.

[0061] 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.

[0062] Viscosity should be measured between 0.1 and 100 seconds at 25°C using a suitable commercial rheometer, such as the TA Instruments Model HR10. -1 It can be measured at a shear rate of .

[0063] At 660, 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. It may be desirable to protect various portions of the base layer. For example, protecting the underside of the conductive layer 102 may be desirable if the electrode 100 is intended for single-sided operation. Protection may include, for example, protecting certain areas from the solvent by masking them or providing a drain for removing the solvent.

[0064] In another example, the final slurry can be at least partially dried elsewhere before being transferred onto the adhesive layer 104 or the conductive layer 102 using a suitable technique (e.g., roll-to-roll layer coating) to form the active layer 106. As another example, the wet mixed slurry can be placed onto 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, an exemplary intermediate material includes PTFE because its properties facilitate its subsequent removal from the surface. The layer can be formed in a press to provide a layer exhibiting a desired thickness, area, and density.

[0065] As yet another example, the final slurry can be formed into a sheet and coated onto the adhesive layer 104 or the conductive layer 102, as appropriate. For example, the final slurry can be applied through a slot die to control the thickness of the applied layer. As another example, the slurry can 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 can 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.

[0066] 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.

[0067] If desired, 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. 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., 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.

[0068] If a partially dried layer is formed during the coating or pressing process, the layer can 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.

[0069] The solvent used to form the slurry can be recovered and recycled into the slurry making process.

[0070] The active layer 106 can 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. This compression process can 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 can be applied before or after each layer is applied or formed into the electrode 100.

[0071] If calendering is used to compress the active layer 106, the calendering apparatus can be set with a gap spacing equal to less than 90%, 80%, 70%, 50%, 40%, 30%, 20%, or 10% of the layer's pre-compression thickness (e.g., set at about 33% of the layer's pre-compression thickness). 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 even greater. The compressed active layer can have a density in the range of 1 g / cc to 10 g / cc, or any subrange thereof, such as 2.5 g / cc to 4.0 g / cc. The calendering process can be performed at a temperature in the range of 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 in the range of 20°C to 100°C, or any subrange thereof.

[0072] The process 600 may include any of the following features (individually or in any suitable combination): The initial slurry has a solids content in the range of 0.1% to 20.0% by weight (or any subrange thereof), and / or the final slurry has a solids content in the range of 10.0% to 80% by weight (or any subrange thereof).

[0073] As previously mentioned, a scaffold or matrix of conductive agent and binder can hold the active material particles together to form a cohesive layer that is also strongly attached to a metal current collector. Such active material structures can be 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.

[0074] The matrix can be formed during slurry preparation using the techniques described herein. Specifically, high-aspect ratio carbon materials are appropriately dispersed and, if desired, chemically functionalized, e.g., as described above with reference to process 600 in FIG. 2. The chemical functionalization is designed to form an organized self-assembled structure with the surface of active material particles, e.g., NMC particles for use in a cathode, or silicon particles ("Si") or silicon oxide ("SiOx") particles in the case of an anode. The slurry thus formed can be based on water and / or alcohol solvents for the cathode and water for the anode, as such solvents are highly volatile and easy to handle during the manufacturing process. Electrostatic interactions promote the self-assembled structure in the slurry, and after the drying process, bonding between the carbon matrix with the thus-formed active material particles and the surface of the current collector is promoted by the surface treatment (e.g., functional groups on the matrix) and the strong entanglement of the active material in the carbon matrix.

[0075] The mechanical properties of the electrodes can be modified depending on the application and mass loading requirements by tuning the surface functionalization versus the entanglement effect.

[0076] After coating and drying, the electrode can undergo a calendaring process to control the density and porosity of the active material. Densities of 3.5 g / cc or greater and porosities of 20% or greater can be achieved for NMC cathode electrodes. Porosity can be optimized depending on the mass loading and requirements of the lithium-ion battery cell. For silicon oxide or silicon-based anodes, porosity can be specifically controlled to accommodate the expansion of the active material during the lithiation process.

[0077] The teachings herein can provide a $ / kWh reduction of up to about 20%. By using water, alcohol, or a mixture of water and alcohol as the solvent, these solvents evaporate easily, allowing for increased throughput in electrode production, and more importantly, significantly reducing the energy consumption associated with lengthy drying times. Traditional recovery systems, required when using NMP or similar compounds as the solvent, are also significantly simplified when using water, alcohol, or a combination thereof.

[0078] The teachings herein provide an active layer with a 3D matrix that can dramatically increase the electrode's conductivity by 10 to 100 times compared to electrodes using conventional binders such as PVDF, thereby enabling rapid charging at the battery level. This technology enables thick electrode coatings in the cathode, up to 150 μm (or more) per side 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. A thick cathode with a high-capacity anode enables a substantial jump in energy density, reaching 400 Wh / kg or more.

[0079] Energy Storage Devices 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.

[0080] One exemplary embodiment includes a pouch cell format Li-ion battery energy storage device that combines a Ni-rich NMC active material in the cathode and a SiOx and graphite blend active material in the anode, where both the anode and cathode are fabricated using the 3D carbon matrix process as described herein.

[0081] A schematic diagram of the electrode arrangement of an example pouch cell device is shown in Figure 3. As shown, cathode active layers 760 (e.g., active layers according to various embodiments disclosed herein) on opposite sides of a current collector 710 (e.g., an aluminum foil current collector) constitute a double-sided cathode disposed between two single-sided anodes. Each single-sided anode has an anode layer 740 or 750 (e.g., an active layer comprising a network of carbon elements, such as those disclosed herein) disposed on a current collector 720 or 730 (e.g., a copper 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 known in the art.

[0082] 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. [Example]

[0083] The sodium salt of polymethacrylic acid is dissolved in water to form a clear solution at a concentration of 10% (by weight). The solubility of this polymer in water is greater than 30% by weight. An initial slurry of conductive material in water and / or alcohol solvent is mixed with the polymer solution, active material, and water / alcohol solvent. The amount of polymer in the total solids content (including the carbon conductive agent, active material, and binder, but excluding the solvent) is approximately 1% by weight. This mixture is subjected to the blending process described above to obtain the final slurry. This slurry is coated onto a metal foil and dried to form an electrode.

[0084] The present disclosure further encompasses the following aspects.

[0085] Aspect 1. An electrode comprising: a current collector; and an active layer on the current collector, the active layer comprising electrode active particles, a conductive material, and a binder, the binder comprising polymer molecules selected from the group consisting of polyacrylamide, polymethacrylic acid, and polyacrylic acid and salts thereof.

[0086] Embodiment 2. The electrode of embodiment 1, wherein the conductive elements form a network.

[0087] Aspect 3. The electrode of any one of Aspects 1-2, wherein the conductive elements are high aspect ratio carbon elements.

[0088] Embodiment 4. The electrode of embodiment 3, wherein the high aspect ratio carbon elements comprise carbon nanotubes.

[0089] Embodiment 5. The polymer comprises a repeating unit of the following formula: [ka] wherein R, in each occurrence, is independently H; or one of R can be an alkyl group having 1 to 3 carbon atoms; and P is -COOR 1 where R 1 is H, a monovalent metal ion, or P is -C(O)N(R 2 )2, where R 2

[0023] Aspect 5. The electrode of any one of aspects 1-4, wherein, in each occurrence, is independently H or an alkyl group having 1 to 3 carbon atoms.

[0090] Aspect 6. The electrode of any one of Aspects 1 to 5, wherein the polymer is a homopolymer.

[0091] Aspect 7. An energy storage device comprising an electrode according to any one of claims 1 to 6.

[0092] Embodiment 8. The energy storage device of embodiment 7, wherein the energy storage device is a pouch cell device.

[0093] Embodiment 9. The energy storage device of embodiment 7 or 8, comprising a double-sided cathode disposed between two single-sided anodes, at least one of the cathodes or anodes being an electrode according to any one of claims 1 to 6.

[0094] Embodiment 10. The energy storage device of any one of embodiments 7-9, comprising an electrolyte between two electrodes, e.g., a cathode and an anode.

[0095] Embodiment 11. The energy storage device of any one of embodiments 7-10, further comprising a permeable separator material between the electrodes, e.g., the cathode and anode(s).

[0096] Embodiment 12. The energy storage device of any one of embodiments 7-11, comprising a housing.

[0097] Embodiment 13. The energy storage device of embodiment 12, further comprising one, preferably two, terminals on the exterior of the housing for providing electrical connection to the electrodes.

[0098] Embodiment 14. A method of making the electrode of any one of embodiments 1-6, comprising providing a slurry comprising the conductive element, the binder, and the electrode active material in water, an alcohol, or a combination thereof; coating the slurry onto a current collector, and drying to remove solvent.

[0099] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., the range "up to 25% by weight, and more specifically, 5% to 20% by weight" includes its endpoints and all intermediate values ​​in the range "5% to 25% by weight," etc.). Additionally, stated upper and lower limits can be combined to form ranges (e.g., "at least 1 or at least 2% by weight" and "up to 10 or 5% by weight" can be combined to form the ranges "1 to 10% by weight," or "1 to 5% by weight," or "2 to 10% by weight," or "2 to 5% by weight").

[0100] The present disclosure may alternatively comprise, consist of, or consist essentially of any suitable components disclosed herein. The present disclosure may additionally or alternatively be formulated to be free or substantially free of any component, material, ingredient, adjuvant, or species used in prior art compositions or that are not otherwise necessary to achieve the function and / or purpose of the present disclosure.

[0101] All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in this application contradicts or conflicts with a term in an incorporated reference, the term from this application takes precedence over the conflicting term from the incorporated reference.

[0102] Unless otherwise specified herein, all test standards are the latest standards in effect as of the filing date of this application or, if priority is claimed, the filing date of the earliest priority application in which the test standard appears.

Claims

1. An electrode, A current collector; an active layer on the current collector, the active layer comprising electrode active particles, a conductive material, and a binder, the binder comprising polymer molecules selected from the group consisting of polyacrylamide, polymethacrylic acid, and polyacrylic acid and salts thereof.

2. The electrode of claim 1 , wherein the conductive elements form a network.

3. 3. The electrode of claim 1, wherein the conductive elements are high aspect ratio carbon elements.

4. The electrode of claim 3 , wherein the high aspect ratio carbon elements comprise carbon nanotubes.

5. The polymer comprises repeat units of the formula: 【Chemical 1】 wherein R in each occurrence is independently H, or one of R can be an alkyl group of 1 to 3 carbon atoms; P is -COOR １ where R １ is H, a monovalent metal ion, or P is —C(O)N(R ２ ) ２ where R ２ The electrode of any one of claims 1 to 4, wherein, in each occurrence, is independently H or an alkyl group having 1 to 3 carbon atoms.

6. The electrode according to any one of claims 1 to 5, wherein the polymer is a homopolymer.

7. An energy storage device comprising an electrode according to any one of claims 1 to 6.

8. The method for manufacturing the electrode according to any one of claims 1 to 6, providing a slurry comprising the conductive element, the binder, and the electrode active material in water, alcohol, or a combination thereof; coating the slurry onto a current collector and drying to remove the solvent.

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