Synthesis of transition metal hydroxides, oxides, and their nanoparticles

Abstract

A technique for the electrochemical synthesis of rechargeable battery cathode precursor materials using porous carbon elements is disclosed. The porous carbon elements act as air cathodes for the reduction of oxygen. The reduced oxygen species can oxidize transition metal anodes, thereby promoting room-temperature redox reactions with transition metals, including those that are generally corrosion-resistant, such as nickel. The transition metal reaction product(s) can be further processed into rechargeable battery cathode materials without the synthesis of hazardous waste products.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63 / 326,353, filed April 1, 2022, entitled "Oxidation of Metals and Alloys Using a Carbon Aerogel Counter Electrode," and U.S. Provisional Patent Application No. 63 / 378,756, filed October 7, 2022, entitled "Oxidation of Metals and Alloys Using a Porous Carbon Counter Electrode," both of which are incorporated herein by reference in their entireties.

[0002] This disclosure relates to the synthesis of certain metal oxide and hydroxide nanomaterials for various applications, such as for producing rechargeable battery compositions. In particular, this disclosure relates to the synthesis of transition metal hydroxides and oxides and their nanoparticles. [Background technology]

[0003] Transition metal oxides and hydroxides have many important industrial applications, including as precursors for rechargeable battery cathode materials. However, conventional processes for synthesizing transition metal oxides and hydroxides generally generate large amounts of hazardous waste. Similarly, iron-containing microparticles and nanoparticles are used in various industrial processes. In particular, iron microparticles and nanoparticles have a high specific surface area (e.g., 0.05 m ). 2 (m 2 ) / gram (g) may be preferred in applications where this is desired.

[0004] However, conventional processes for producing nanoparticles of metals, such as iron, are generally energy intensive, time consuming, expensive, and may still not produce particles with sufficiently small or monodisperse particle sizes.

[0005] The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings. It should be noted that references to "an" or "one" embodiment or aspect in this disclosure are not necessarily to the same embodiment or aspect, but rather mean at least one. In the drawings: [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 illustrates a schematic diagram of a system for oxidizing transition metals using a porous carbon element, according to one or more embodiments of the present disclosure. [Figure 2] FIG. 2 illustrates a schematic diagram of an electrochemical cell for oxidizing transition metals using a porous carbon element, according to one or more embodiments of the present disclosure. [Figure 3] FIG. 3 is an experimentally determined graph showing the relationship between the potential applied to the system of FIG. 1 using Ni metal (Ni) as the anode and the resulting current, in accordance with one or more embodiments of the present disclosure. [Figure 4] FIG. 4 is a schematic illustration of a transition metal component having a layered oxide composition according to one or more embodiments of the present disclosure. [Figure 5A] FIG. 5A is an experimentally determined graph showing the relationship between the potential applied to a system similar to that shown schematically in FIG. 1 and the resulting current for aluminum (Al), in accordance with one or more embodiments of the present disclosure. [Figure 5B] FIG. 5B is an experimentally determined graph showing the relationship between the potential applied to a system similar to that shown schematically in FIG. 1 and the resulting current for zinc (Zn), in accordance with one or more embodiments of the present disclosure. [Figure 5C] FIG. 5C is an experimentally determined graph showing the relationship between the potential applied to a system similar to that shown schematically in FIG. 1 and the resulting current for tin (Sn), in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0007] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding. One or more aspects may be practiced without these specific details. Features described in one embodiment or aspect of the present disclosure may be combined with features described in a different embodiment. In some instances, well-known structures and devices are described with reference to block diagram form in order to avoid unnecessarily obscuring the present invention.

[0008] Before describing some example aspects of the disclosed technology, it is to be understood that the technology is not limited to the details of construction or process steps set forth in the following description. The technology is capable of other implementations and of being practiced or carried out in various ways. 1.General overview 2. Explanation of terms 3.Porous carbon component 3.1 Carbon components derived from aerogel 3.2 Other porous carbon components 4. Cathode Composition Synthesis Challenge 5. Room-Temperature Oxidation of Nickel 6. Layered transition metal electrode materials 7. Synthesis of Porous Metal Oxide Materials 8. Experimental Example 9. Preparation of magnetic iron oxide nanoparticle (IONP) precursor for LFP 10. Preparation of non-magnetic iron oxide nanoparticle (IONP) precursor for LFP

[0009] 1.General overview One or more embodiments include techniques that can oxidize transition metals at room temperature using an electrolyte and a porous carbon component. The porous carbon element can act as an "air cathode," which can reduce oxygen and thereby allow oxygen to act as a cathode in an electrochemical cell with a transition metal anode. In this manner, embodiments described herein facilitate room-temperature redox reactions with transition metals. Some embodiments described herein can oxidize corrosion-resistant transition metals, such as nickel. Embodiments of the processes described herein can react bulk transition metals (and / or their alloys) with oxygen at room temperature via a porous carbon component (or equivalently, a porous carbon element), which reduces the activation energy required for oxygen reduction. The transition metal reaction product(s) can be further processed into rechargeable battery cathode materials without the synthesis of hazardous waste products. In some examples, magnetic and / or non-magnetic nanoparticles of iron oxide are produced. In some examples, the iron oxide nanoparticles can be oxidized using a metric method. 2 (m 2 ) / gram (g), it has a high, and even unexpectedly high, specific surface area.

[0010] For ease of explanation, in embodiments relating to the active materials of a rechargeable battery, the term "cathode" refers to the active material that is oxidized during charging (e.g., Co 3+ From Co 4+ to ), which is reduced during discharge (e.g., Co 4+ From Co 3+ The term "anode" is used to refer to the battery component that is reduced during charging (e.g., C to LiC) and oxidized during discharging (e.g., LiC to C). Additionally, for brevity, the term "transitional metal" also includes alloys, intermetallic compounds, and other combinations of multiple transition metals.

[0011] One or more aspects described and / or claimed herein may not be included in this General Summary section.

[0012] 2. Explanation of terms The following definitions are provided for terms used in this disclosure: This application uses the following terms as defined below, unless the context of the sentence in which the term appears requires a different meaning.

[0013] The articles "a" and "an" are used herein to refer to one or more than one (i.e., at least one) of the grammatical object of the article. As used throughout this specification, the term "about" is used to describe and take into account small variations. For example, the term "about" can represent ±10% or less, or ±5% or less, e.g., ±2% or less, ±1% or less, ±0.5% or less, ±0.2% or less, ±0.1% or less, or ±0.05% or less. All numerical values ​​herein are modified by the term "about," whether explicitly stated or not. Values ​​modified by the word "about" naturally include the specific value. For example, "about 5.0" must include 5.0.

[0014] In the context of this disclosure, in some examples, the term "framework" or "framework structure" refers to the network of interconnected oligomeric, polymeric, or colloidal particles that form the solid structure of a gel or aerogel. The polymers or particles that make up the framework structure typically have diameters of about 100 angstroms. In the example of pyrolytic or carbonized aerogels, the term "framework" or "framework structure" refers to the interconnected network of linear fibrils that may be connected to each other at nodes to form a framework that defines pores.

[0015] As used herein, the terms "aerogel" and aerogel material refer to a solid, regardless of shape or size, comprising a framework of interconnected solid structures with a corresponding network of interconnected pores embedded within the framework, containing a gas, such as air, as a dispersed interstitial medium. Thus, an aerogel is an open, non-fluid colloidal or polymeric network that is expanded throughout its entire volume by a gas, formed by removing all swelling agents from a corresponding wet gel without substantial volume loss or network compression. Aerogels are generally characterized by the following physical and structural properties (by nitrogen porosimetry and helium pycnometry) attributed to aerogels: (a) an average pore size of about 2 nm to about 100 nm; (b) a porosity of at least 60% or greater; and (c) a porosity of about 1, about 10, or about 20 to about 100 or about 1000 m by nitrogen adsorption analysis. 2 / g specific surface area. It can be appreciated that the inclusion of additives such as reinforcing materials or electrochemically active species, e.g., silicon, can decrease the porosity and specific surface area of ​​the resulting aerogel composite. Densification can also decrease the porosity of the resulting aerogel composite. Aerogel materials (e.g., polyimide and carbon aerogels) of the present disclosure include any aerogels that meet the defining elements set forth in the previous paragraph.

[0016] Thus, the aerogel materials of the present disclosure include any aerogel or other open-cell compound that meets the defining elements set forth in the preceding paragraph, including compounds that can be otherwise categorized as xerogels, cryogels, ambigels, microporous materials (e.g., polymer foams), etc.

[0017] As used herein, the term "xerogel" refers to a gel comprising an open, non-fluid colloidal or polymeric network formed by removing all swelling agents from the corresponding gel without taking any precautions to avoid substantial volume loss or retard compaction. Xerogels generally comprise a compact structure. Xerogels undergo substantial volume loss during ambient pressure drying and generally have a porosity of about 40% or less.

[0018] 3.Porous carbon component In certain examples, the present disclosure includes forming and using nanoporous carbon-based scaffolds or structures, such as carbon aerogels, to synthesize transition metal oxides, hydroxides, and nanoparticles thereof as electrode materials in electrochemical cells. Examples of porous carbon components of the present disclosure include, but are not limited to, carbonized aerogel materials (e.g., carbonized polyimide aerogels, carbonized polyamic acid aerogels) and carbonized polymer foams (e.g., carbonized polyurethane foams). For convenience, carbonized aerogels may be equivalently referred to herein as "carbon aerogels."

[0019] It is further contemplated herein that porous carbon materials, including carbon aerogels, can be in the form of a monolithic structure. Monolithic porous carbon does not require a separate binder material. In other words, the air cathode can be binderless. As used herein, the term "monolithic" refers to a porous carbon material in which the majority (by weight) of the carbon contained in the carbon material or composition is in the form of a single, continuous, interconnected carbon structure. In the specific example of a carbonized aerogel material, this can include interconnected aerogel nanostructures. Monolithic aerogel materials include aerogel materials that are initially formed to have a single, interconnected gel or aerogel nanostructure, but may subsequently be cracked, fractured, or segmented to result in non-single aerogel nanostructures.

[0020] Monolithic porous carbon materials are distinguished from particulate porous carbon materials. The term "particulate porous carbon material" refers to a porous carbon material in which the majority (by weight) of the carbon contained in the carbon material is in the form of fine particles, particles, granules, beads, or powder. These can be combined or compressed together (i.e., via a binder, such as a polymer binder), but lack an interconnected structure between the individual particles. Collectively, materials in this form are said to have a powder or particulate morphology (as opposed to a monolithic morphology). Note that, despite the individual particles of a powder having a unitary structure, the individual particles are not considered monoliths herein.

[0021] In the context of the present disclosure, the term "binderless" or "binder-free" (or derivatives thereof) refers to a material that is substantially free of a binder or adhesive to hold a material together. For example, a monolithic nanoporous carbon material does not contain a binder because its framework is formed as a single, continuous, interconnected structure. Advantages of being binderless include avoiding any effects of a binder (e.g., on electrical conductivity and pore volume). On the other hand, aerogel particles require a binder to hold them together to form a larger, functionalized material. Such large materials are not considered monoliths herein. Additionally, the term "binder-free" does not exclude all use of binders. For example, a monolithic aerogel according to the present disclosure can be secured to another monolithic aerogel or non-aerogel material by placing a binder or adhesive on a major surface of the aerogel material. In this manner, a binder is used to create a laminate composite and provide electrical contact to a current collector, but the binder does not function to maintain the stability of the monolithic aerogel framework itself.

[0022] 3.1 Porous carbon component derived from aerogel In some examples, carbonized aerogels may be used as the porous carbon element in the systems and methods described herein. Carbonized aerogels can be formed by carbonizing some compositions of organic polymer aerogels. One example of a carbonizable organic polymer aerogel is polyimide. Other examples of porous carbon sources are provided below.

[0023] Methods for forming polyimide gels or aerogels include condensing a diamine with a tetracarboxylic dianhydride in an organic solvent solution to form a polyamic acid, and then dehydrating the polyamic acid to prepare a polyimide gel. See, for example, U.S. Patent Nos. 7,071,287 and 7,074,880 to Rhine et al. and U.S. Patent Application Publication No. 2020 / 0269207 to Zafiropoulos et al.

[0024] According to certain embodiments, producing an aerogel comprises the steps of: i) forming a solution containing gel precursors, ii) forming a gel from the solution, and iii) extracting the solvent from the gel material to obtain a dry aerogel material.

[0025] In one example, a polyimide aerogel is formed by combining at least one diamine and at least one dianhydride in a common polar aprotic solvent(s). Further details regarding the formation of polyimide gels / aerogels can be found, inter alia, in U.S. Patent Nos. 7,074,880 and 7,071,287 to Rhine et al.; U.S. Patent No. 6,399,669 to Suzuki et al.; U.S. Patent No. 9,745,198 to Leventis et al.; and Leventis et al., "Polyimide Aerogels by Ring-Opening Metathesis Polymerization (ROMP)," Chem. Mater. 2011, 23, 8, 2250-2261, each of which is incorporated herein by reference in its entirety.

[0026] Nanoporous carbons, such as carbon aerogels according to the present disclosure, can be formed from any suitable organic precursor material. Examples of such materials include, but are not limited to, RF (resorcinol-formaldehyde), PF (phenol-furfural), PI (polyimide), polyamide, polyoxyalkylene, polyurethane, polyacrylonitrile, cresol formaldehyde, polyisocyanate, polyvinyl alcohol dialdehyde, polyisocyanurate, various epoxide resins, chitosan, and combinations and derivatives thereof. In some examples, carbon aerogels are formed from pyrolyzed / carbonized polyimide-based aerogels, i.e., polymerization of polyimides. Even more specifically, polyimide-based aerogels can be produced using one or more methodologies described in U.S. Pat. Nos. 7,071,287 and 7,074,880 (Rhine et al.), for example, by imidizing poly(amide) acids and drying the resulting gel using supercritical fluids.

[0027] Carbonized aerogels of the present disclosure, such as polyimide-derived carbon aerogels, can have a residual nitrogen content of at least about 1 wt. % "heteroatoms" (i.e., non-carbon atoms) as determined by elemental analysis. For example, the carbon aerogels can have a residual nitrogen content of at least about 1 wt. % and up to about 10 wt. %. In some embodiments, the residual nitrogen content is about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, or about 10 wt. %.

[0028] In examples of the present disclosure, the dried polymer aerogel composition can be subjected to processing temperatures of 200°C or higher, 400°C or higher, 600°C or higher, 800°C or higher, 1000°C or higher, 1200°C or higher, 1400°C or higher, 1600°C or higher, 1800°C or higher, 2000°C or higher, 2200°C or higher, 2400°C or higher, 2600°C or higher, 2800°C or higher, or a range between any two of these values, for carbonization of the organic (e.g., polyimide) aerogel. In some examples, the material is carbonized in the absence of oxygen and / or in a reducing environment. Exposure to this temperature can convert the dried polymer aerogel to a carbonized aerogel. In exemplary embodiments, the dried polymer aerogel composition can be subjected to processing temperatures in the range of about 1000°C to about 1100°C, e.g., about 1050°C. Without being bound by theory, it is believed herein that the electrical conductivity of the aerogel composition increases with carbonization temperature. In some examples, some compositions or types of aerogels become electrically conductive when carbonized above a threshold carbonization temperature (e.g., above 400°C, above 500°C, above 600°C).

[0029] In some examples, carbonized aerogels, such as carbonized polyimide aerogels and carbonized poly(amic) acid aerogels, can be mechanically strong and exhibit unexpectedly high Young's moduli for carbonized materials. In certain embodiments, the carbonized aerogel materials or compositions of the present disclosure have a Young's modulus of about 0.2 GPa or greater, 0.4 GPa or greater, 0.6 GPa or greater, 1 GPa or greater, 2 GPa or greater, 4 GPa or greater, 6 GPa or greater, 8 GPa or greater, or a range between any two of these values. Young's modulus can be determined by methods known in the art, including, but not limited to, Standard Test Practice for Instrumented Indentation Testing (ASTM E2546, ASTM International, West Conshocken, PA); or Standardized Nanoindentation (ISO 14577, International Organization for Standardization, Switzerland). Within the context of the present disclosure, Young's modulus measurements are obtained in accordance with ASTM E2546 and ISO 14577 unless otherwise specified.

[0030] Within the context of the present disclosure, the term "pore size distribution" refers to the statistical distribution or relative amount of each pore size within a sample volume of a porous material. A narrower pore size distribution refers to a relatively large proportion of pores within a narrow range of pore sizes, thus increasing the amount of pores that can accommodate electrochemically active species and maximizing the use of pore volume. Conversely, a wider pore size distribution refers to a relatively small proportion of pores within a narrow range of pore sizes. Thus, pore size distribution can be measured as a function of pore volume and recorded as the unit size of the full width at half maximum of the main peak in a pore size distribution chart. The pore size distribution of a porous material can be determined by methods known in the art, including, but not limited to, surface area and porosity analyzers by nitrogen adsorption / desorption, which can calculate the pore size distribution. Within the context of the present disclosure, pore size distribution measurements are obtained according to this method unless otherwise specified. In some examples, the aerogel materials or compositions of the present disclosure have a relatively narrow pore size distribution (full width at half maximum) of about 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 5 nm or less, or a range between any two of these values.

[0031] Within the context of the present disclosure, the term "pore volume" refers to the total volume of pores within a sample of porous material. Pore volume is specifically measured as the volume of voids within the porous material, which voids may be measurable and / or accessible by another material, e.g., electrochemically active species such as silicon particles. It is expressed in cubic centimeters per gram (cm 3Pore ​​volume of a porous material can be determined by methods known in the art, including, but not limited to, surface area and porosity analyzers by nitrogen adsorption / desorption, which can calculate pore volume. Within the context of the present disclosure, pore volume measurements are obtained according to this method unless otherwise specified. In certain examples, aerogel materials or compositions (including carbonized aerogels) of the present disclosure have a relatively large pore volume of about 0.5 cc / g or more, 1 cc / g or more, 1.5 cc / g or more, 2 cc / g or more, 2.5 cc / g or more, 3 cc / g or more, 3.5 cc / g or more, 4 cc / g or more, or a range between any two of these values.

[0032] In the context of the present disclosure, the term "porosity" refers to the void space within an aerogel sample as a percentage of the total (envelope) volume of the aerogel sample. Porosity can be calculated by methods known in the art, including, but not limited to, skeletal density minus bulk density divided by skeletal density. Skeletal density can be measured by helium pycnometry, among other methods. Bulk density can be determined by the ratio of the weight to the geometric volume of the aerogel sample. Within the context of the present disclosure, porosity measurements are obtained according to this method unless otherwise specified. In certain embodiments, the aerogel materials or compositions of the present disclosure have a porosity of about 99% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or a range between any two of these values.

[0033] Within the context of the present disclosure, the term "pore size at the maximum peak from the distribution" refers to the value at the peak that can be discerned on a graph illustrating the pore size distribution. The pore size at the maximum peak from the distribution is specifically measured as the pore size at which the largest percentage of pores are formed. It can be recorded as any unit length of pore size, such as μm or nm. The pore size at the maximum peak from the distribution can be determined by methods known in the art, including, but not limited to, surface area and porosity analyzers by nitrogen adsorption / desorption, which can calculate the pore size distribution and determine the pore size at the maximum peak. Within the context of the present disclosure, the measurement of the pore size at the maximum peak from the distribution is obtained according to this method, unless otherwise specified. The aerogel material or composition of the present disclosure can have a pore size at the largest peak from a distribution of about 150 nm or less, 140 nm or less, 130 nm or less, 120 nm or less, 110 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, 30 nm or less, 20 nm or less, 10 nm or less, 5 nm or less, 2 nm or less, or a range between any two of these values.

[0034] 3.2 Other porous carbon components The porous carbons of the present disclosure are not limited to carbonized aerogels. Other porous carbons that exhibit sufficient chemical activity to reduce oxygen in the systems described herein may also be used. In some examples, conventional polymer foams may be carbonized and used in any of the examples described herein. In one example, carbonized polyurethane foam was used to produce nickel hydroxide. In another example, carbonized polyurethane foam was used to synthesize iron oxide nanoparticles. It will be understood that other polymers that contribute to carbonization (e.g., those containing backbones with phenyl rings, unsaturated bonds, and other similar structures) may be foamed or synthesized to have a porous structure and then used in the systems and examples described herein. The carbonization techniques described in Section 3.1 are applicable to carbonizing non-aerogel materials, i.e., heating the polymer to carbonization temperatures in the absence of oxygen.

[0035] 4. Cathode Composition Synthesis Challenge Many common types of rechargeable batteries, such as lithium-ion batteries ("LIBs"), use transition metal oxides and / or hydroxides as precursors for the rechargeable battery cathode material. Early generations of rechargeable LIB cathode materials relied on cobalt (Co) as the primary transition metal. However, subsequent generations of rechargeable batteries have gradually reduced the amount of cobalt in the cathode material. For example, many early rechargeable battery compositions used only cobalt as the multivalent transition metal in the cathode composition (e.g., lithium cobalt oxide (LiCoO)). However, more recent compositions of cathode materials have replaced some of the cobalt with nickel and other substitutes. An example of a cathode composition containing both nickel and cobalt is LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 ("NCM 111") and LiNi 0.8 Co 0.1 Mn 0.1 O2 ("NCM 811"), but are not limited to these.

[0036] Replacing cobalt with other transition metals has many advantages. For example, cobalt is known to be environmentally toxic and to pose various threats to human health. Replacing cobalt with other materials that are less toxic and / or pose fewer health risks may reduce the environmental and health risks associated with the production, use, and disposal of rechargeable batteries. In some instances, replacing cobalt with other materials may also reduce the cost of rechargeable batteries (e.g., per unit of stored energy, per charge / discharge cycle). Furthermore, replacing cobalt with other transition metals has additional advantages. Cobalt generally has higher financial costs than other transition metals and may be mined under socially problematic conditions. Using alternatives to cobalt may address these shortcomings.

[0037] Precursor materials for nickel, cobalt, and manganese (NCM) cathode compositions are typically formed via aqueous synthesis techniques that generate large amounts of wastewater. In some examples, transition metal salts, such as sulfates, are first reacted with potassium hydroxide (KOH) to produce water-insoluble metal hydroxides. These metal hydroxides, in some examples, include Ni(OH)2, among other transition metal oxides and / or hydroxides. The metal hydroxides eventually precipitate from solution in solid form. These precipitates are washed with deionized water to remove potassium sulfate impurities and then dried. The dried precipitate is then mixed with lithium carbonate (Li2CO3) and heat-treated to produce the cathode composition (e.g., NCM 111, NCM 811). In some examples, lithium hydroxide is used in place of lithium carbonate for high Ni-content cathode materials.

[0038] The synthesis of nickel-based transition metal cathode materials has various drawbacks. For example, ammonia (NH3) is often added to aqueous solutions of transition metals such as those described above. Without wishing to be bound by theory, it is believed that ammonia forms complexes with the transition metals in aqueous solution. These complexes form hydroxy anions (e.g., OH -It is believed that the high pH stabilizes the transition metal cations in solution before controlled precipitation by HCl occurs, which may improve the compositional uniformity of the transition metal precipitate and ultimately the cathode compositions obtained therefrom.

[0039] Waste products from aqueous ammonia-containing solutions present hazards to the environment and human health. For example, these waste products can include NH3 and K2SO4. Both of these waste products require proper handling during treatment, remediation, and disposal before disposal, all of which increase battery production costs and present environmental drawbacks. Furthermore, the above-mentioned aqueous processes are voluminous. Tens or even hundreds of liters of waste can be generated for each kilogram of cathode composition. This large amount of waste is a significant drawback, especially considering the potential scale of rechargeable battery production as applied to automotive and / or grid power storage applications. Alternative synthesis techniques that produce stoichiometrically preferred cathode composition precursors without generating large amounts of hazardous waste would reduce production costs and lower environmental and human health risks.

[0040] Additionally, embodiments described herein advantageously eliminate the production of waste materials used to synthesize precursors to conventional NCM battery cathode material reactions. For example, nickel sulfate (NiSO4) used in the aqueous reaction described above can be synthesized by treating metallic nickel, or its hydroxide or carbonate, with sulfuric acid. The reaction product, NiSO4, is separated, washed, and dried, all of which require energy and produce pollutants (e.g., sulfuric acid).

[0041] 5. Room-Temperature Oxidation of Nickel Surprisingly, it has been experimentally observed that certain types of porous carbon materials (including carbon aerogels produced according to the techniques described above) can act as "air cathodes" that catalytically reduce oxygen at room temperature. When placed in an electrochemical cell with an aqueous electrolyte, oxygen can be reduced to hydroxide anions, which can oxidize a transition metal counter electrode. The techniques described herein can work effectively even with transition metals that are normally resistant to oxidation. In some examples, embodiments herein can oxidize nickel to produce nickel hydroxide. In some examples, embodiments herein can react the transition metal component to completion (i.e., completely consume the portion of the transition metal in contact with the electrolyte) at room temperature within a few hours.

[0042] The catalytic effect of carbon aerogels and other porous carbons described herein can be used to oxidize nickel in the solid state at room temperature (e.g., 5°C to 25°C). This is unexpected given the kinetic unfavorability of nickel oxide beyond the naturally occurring passivation layer and the reductive dissociation of dioxygen to hydroxide. In some examples, embodiments described herein can be used to oxidize nickel in the solid state, including NCM111, NCM811, LiNi, among others. 0.8 Co 0.15 Al 0.05 Precursor materials for use in rechargeable batteries can be synthesized, including but not limited to O2 ("NCA 85 15 5").

[0043] 1 is a schematic diagram of a system 100 used to oxidize nickel at room temperature according to one or more embodiments described herein. System 100 includes a porous carbon element 104, a separator 108, an electrolyte 112, a transition metal electrode 116, and a conductor 120. In some embodiments, electrode 116 is formed from a non-transition metal (or alloy), such as aluminum, tin, among others.

[0044] Without wishing to be bound by theory, it is believed that the porous carbon element 104, as discussed above, may reduce the activation energy for oxygen reduction, thereby allowing electrically coupled transition metals to participate in room temperature redox reactions. Also, as discussed above, room temperature oxidation of transition metals, such as those used in rechargeable battery cathode materials, is unexpected and has many advantages.

[0045] In various embodiments, the porous carbon element 104 can be synthesized and / or fabricated according to the techniques described above. Some embodiments of these techniques include pyrolysis of polyimide-derived carbon aerogels. In some examples, pyrolyzed polyimide-derived carbon aerogels may contain residual nitrogen or other heteroatoms (i.e., non-carbon atoms) that are not removed during aerogel synthesis or pyrolysis. By oxidizing the transition metal electrode 116 using the porous carbon element 104 as a catalyst, cathode precursor materials can be produced, including, but not limited to, nickel oxide (NiO), nickel hydroxide (Ni(OH)), NiCO (when CO is present during electrolysis), and similar compositions of cobalt, manganese, and other transition metals. The processes described herein can produce transition metal cathode precursor materials (e.g., Ni(OH)), Co(OH), Mn(OH), among others, in the solid state without producing large amounts of wastewater.

[0046] In some examples, transition metal hydroxides using some of the embodiments described herein may produce reaction products that do not require purification and / or washing of contaminants (e.g., NH3, K2SO4, NiSO4). In examples where sodium chloride is present in the electrolyte, the reaction products may include benign NaCl, which can be removed simply by washing the reaction product with water. NaCl is less polluting to the environment and poses a lower threat to human health than sulfates and ammonia produced by alternative processing techniques. In examples where the electrolyte includes ammonium chloride (NHCl), remediation is less problematic than other processes. NHCl decomposes into a gas mixture of NH3 and HCl at 338°C during calcination. The temperature of the gas mixture can be reduced below 338°C after gas evolution, allowing the NHCl to condense back into a solid form, which can be recycled. Therefore, NHCl salt impurities do not require washing and do not generate wastewater.

[0047] Without being bound by theory, in some examples, the porous carbon element 104 may reduce the activation energy to transfer electrons from a metal (e.g., the transition metal electrode 116) in electrical communication with the porous carbon to oxygen (via the conductor 120). This reduced activation energy may increase the rate at which the transition metal is oxidized when placed in electrical communication with the porous carbon. In some examples, the electrolyte (e.g., NaCl (aq) ) wets the surface of the porous carbon element 104, which may promote the generation of hydroxy anions in the porous carbon element 104. The generated hydroxy anions may then diffuse to and react with the transition metal electrode 116 to generate an oxidized form of the transition metal.

[0048] Without wishing to be bound by theory, the high specific surface area of ​​the porous carbon element 104 may contribute to the efficient catalytic reduction of oxygen and subsequent oxidation of the electrolytically coupled transition metal electrode 116. For example, a porous carbon element 104 using carbonized aerogel (an example of which is described above) can be used to measure the specific surface area of ​​100 m 2 / g~600m 2 / g of the non-pyrolytic aerogel precursor.

[0049] Without wishing to be bound by theory, some examples of porous carbon elements 104, including carbonized aerogels, may contain non-carbon "heteroatoms," some of which may increase the efficiency with which oxygen is reduced and transition metals subsequently oxidized. For example, some carbon aerogels of the present disclosure derived from the pyrolysis of polyimide aerogels may contain residual nitrogen. In some examples, the residual nitrogen content of the carbon aerogel may be at least about 4 wt%. For example, carbon aerogels according to embodiments disclosed herein may have a residual nitrogen content of at least about 0.1 wt%, at least about 0.5 wt%, at least about 1 wt%, at least about 2 wt%, at least about 3 wt%, at least about 4 wt%, at least about 5 wt%, at least about 6 wt%, at least about 7 wt%, at least about 8 wt%, at least about 9 wt%, at least about 10 wt%, or a range between any two of these values. Other heteroatoms that may participate in the reactions described herein may also include oxygen, hydrogen, and graphitic carbon in some examples.

[0050] Without wishing to be bound by theory, some examples of porous carbon elements 104, including carbonized aerogel, may have relatively high electrical conductivity compared to other forms of carbon. The high electrical conductivity of carbonized aerogel may facilitate oxygen reduction. In certain embodiments, the carbonized aerogel materials or compositions of the present disclosure have electrical conductivities of about 1 S / cm or greater, about 5 S / cm or greater, about 10 S / cm or greater, 20 S / cm or greater, 30 S / cm or greater, 40 S / cm or greater, 50 S / cm or greater, 60 S / cm or greater, 70 S / cm or greater, 80 S / cm or greater, or a range between any two of these values.

[0051] In some examples, the rate of the redox reaction (more specifically, the oxidation of the transition metal) can be selected (e.g., increased or decreased relative to a baseline reaction rate) by altering one or more conditions under which the reaction is carried out. In some examples, the reaction rate can be increased by one or more of the following: increasing the temperature at which the reaction is carried out, increasing the partial pressure of oxygen (thereby increasing the rate of hydroxy anion production), increasing the concentration of the electrolyte (e.g., from a 1 molar (M) solution to a multi-molar solution), and / or increasing the magnitude of the potential difference applied to the porous carbon / transition metal system 100. Similarly, the reaction rate can be decreased by limiting any of the aforementioned parameters. Altering the pH of the electrolyte or the composition of the electrolyte can also affect the rate of the reaction, as well as the composition and morphology of the reaction product(s).

[0052] The porous carbon element 104 can be in monolithic form, granular form, or a combination thereof.

[0053] In some instances, excluding gases other than oxygen can affect the reaction products. For example, using a gas mixture that does not contain pure oxygen or carbon dioxide can reduce the presence of carbonate species in the reaction products. This can reduce and / or eliminate the presence of undesired reaction products (e.g., carbonates) in the oxidized transition metal compound.

[0054] The separator 108 is an electrically insulating material that provides a structure through which ions can pass. This combination prevents electrical shorting of the system 100 while allowing current flow via ion migration between the porous carbon element 104 and the transition metal electrode 116. Examples of separator 108 may include cellulosic paper, fibrous polymer cloth, or felt, among others. Also, the separator may be eliminated if the electrodes are kept physically apart (e.g., a flooded cell design).

[0055] An electrolyte 112 disposed within the separator 108 facilitates ion transfer from the porous carbon element 104 to the transition metal electrode 116. Examples of electrolytes include, among others, sodium chloride (NaCl (aq) ), ammonium chloride (NH3Cl (aq) ), sodium carbonate (NaCO 3(aq) ) (e.g., distilled water, deionized water, distilled-deionized water, tap water). In some examples, the concentration of the electrolyte may be saturated with the solute. In other examples, the concentration of the electrolyte may be less than a saturated solution. In some examples, the concentration of the electrolyte may be selected according to various criteria, including, but not limited to, the desired reaction rate at the transition metal anode (higher concentrations generally accelerate the oxidation rate), the morphology and / or composition of the oxide reaction product at the transition metal anode, among others.

[0056] Without wishing to be bound by theory, it has been observed that the presence of chloride in the electrolyte promotes the separation of hydroxylated reaction products from the surface of the transition metal electrode 116. Thus, when using a chloride-containing electrolyte, as the reaction progresses, new surfaces of the transition metal electrode 116 are naturally exposed, and the process may naturally convert the entire mass of the transition metal electrode 116 into reaction products. In other examples, the composition and / or morphology of the reaction products may be altered by changing the electrolyte composition, the pH of the electrolyte, or other similar parameters. For example, the electrolyte or pH may be changed so that the reaction products remain attached to the transition metal electrode 116. The attached reaction products may be beneficial in some instances, such as processing a transition metal electrode into a rechargeable battery cathode that has a layered or graded composition and retains that composition during processing. Such examples are described in more detail below.

[0057] The transition metal electrode 116 can be a piece of transition metal in electrical and ionic communication with the porous carbon element 104, as shown in Figure 1. Examples of transition metals that can be used in the transition metal electrode 116 include transition metals used in rechargeable battery cathode materials. In some examples, these can include nickel, cobalt, manganese, aluminum, titanium, zirconium, molybdenum, tungsten, iron, zinc, copper alloys thereof, and / or intermetallic compounds thereof.

[0058] In some examples, the transition metal electrode 116 may include non-transition metal components added to improve electrical conductivity, improve oxidation kinetics, and / or improve conversion of transition metal oxide / hydroxide to the cathode composition.

[0059] In some examples, such as those described in Section 6 below and FIG. 4 , the transition metal electrode 116 can include one or more combinations of transition metals, non-transition metals, and / or other compounds. In some examples, the components of the multi-component transition metal electrode 116 can include layers of components. In one exemplary configuration, the transition metal electrode 116 can include a nickel core surrounded or otherwise encapsulated by a cobalt layer. Without wishing to be bound by theory, the cobalt layer, when converted to its hydroxylated form and then reacted with Li2CO3 to form the cathode composition, can reduce the prevalence of nickel-based side reactions at the cathode surface. These side reactions can be caused by multiple different nickel oxide and hydroxide compositions sometimes produced during the nickel oxidation reaction.

[0060] The conductor 120 can be an electrical conductor, such as a copper wire, an aluminum wire, a gold wire, or alloys thereof, that connects the porous carbon element 104 and the transition metal electrode 116. In some examples, the conductor 120 can also be used to apply an electrical potential to the system 100 that initiates and maintains an oxidation reaction at the transition metal electrode 116.

[0061] The minimum applied potential, applied in some examples from an external source via conductor 120, varies depending on the transition metal(s) selected for transition electrode 116. The minimum applied potential required to promote an oxidation reaction at transition metal oxide 116 may be an indication of the catalytic activity of the carbon catalyst used to reduce oxygen (e.g., to produce hydroxy anions) relative to the particular transition metal used as transition metal electrode 116. The upper limit of the applied potential may be based on the electrolyte. For illustrative purposes, the potential applied to a water-based electrolyte may be selected to be lower than the voltage used for the hydrolysis of water to oxygen and hydrogen. The electrolyte may be selected to support a higher voltage.

[0062] 2 is a schematic diagram of an electrochemical cell 200 according to one embodiment of the present disclosure. Electrochemical cell 200 is an alternative representation of some embodiments of system 100. Electrochemical cell 200 includes an electrode 204, a transition metal component 208, a conductor 212, a carbon aerogel element 216, an oxidation reaction product layer 220, and an electrolyte 224.

[0063] Many of the elements shown in electrochemical cell 200 of Figure 2 are similar to those described above in connection with system 100 shown in Figure 1. Electrode 204 can be an electrical contact with which transition metal component 208 (similar to transition metal electrode 116) is in electrical communication. Conductor 212 is similar to conductor 120.

[0064] The porous carbon element 216 is similar to the porous carbon element 104. In some examples, the porous carbon element 216 is a carbon aerogel material formed by carbonizing a polyimide aerogel or a poly(amide) acid aerogel. In some examples, the porous carbon element 216 is a carbonized polyurethane foam. In some examples, the porous carbon element 216 is a combination or blend of a carbonized aerogel and a carbonized polyurethane foam.

[0065] 2, in addition to the elements already described in connection with FIG. 1, illustrates schematically the redox reactions that occur within electrochemical cell 200 upon application of an external voltage having a magnitude of 1 V. The minimum magnitude of the applied voltage required to promote the oxidation reaction (the "onset voltage") can be determined by the particular transition metal of component 208 and the catalytic efficiency of porous carbon element 216. In some instances, oxidation of the transition metal within electrochemical cell 200 may not occur for applied voltages having a magnitude less than the minimum value.

[0066] 2 schematically illustrates the exposure of a porous carbon element 216 to oxygen. In some examples, the oxygen can be a gas, such as from air or a commercially available gas mixture having a higher oxygen concentration than that found in air. The oxygen can enter a porous carbon element 216 that has been pre-wetted with electrolyte 224.

[0067] When the oxygen encounters the porous carbon element 216 that also contains and / or is coated with the electrolyte 224 , it may eventually be converted to hydroxy anions solvated by the electrolyte 224 .

[0068] The hydroxy anions may then react with the transition metal component 208 to form one or more transition metal oxides, hydroxides, and / or other reaction products 220 resulting from the reaction of the transition metal with the hydroxy anions. These reaction products are shown as shaded areas 220 in FIG. 2. While the reaction products 220 are shown in FIG. 2 as being in direct contact with the transition metal component 208, this need not be the case. As noted above, different electrolyte compositions may produce different physical configurations in the reaction products 220. For example, the presence of chloride in the electrolyte 224 may produce reaction products 220 that separate from the transition metal component 208.

[0069] In some examples, oxygen is the cathode of electrochemical cell 200. That is, the oxygen that encounters porous carbon element 216 (which functions as an "air cathode") is reduced during operation of electrochemical cell 200. -The arrow labeled "!" indicates that oxygen entering the porous carbon element 216 is an acceptor for electrons generated by operation of the electrochemical cell 200. Because the amount of oxygen can be from a non-emitting source (e.g., from the Earth's atmosphere) or from a source having a number of moles equal to or greater than the number of moles of transition metal in the electrode 208, in some instances, the transition metal electrode 208 may react to completion. In particular, the transition metal electrode 208 may react to completion when new reaction surfaces are exposed upon separation of the reaction product 220 from the transition metal component 208. In other instances, the transition metal electrode may partially or completely react when hydroxyl ions diffuse through an adhesion layer of the reaction product 220 to the unreacted portion of the transition metal electrode 208.

[0070] FIG. 3 shows cyclic voltammetry experimental data, including the current (y-axis) associated with the electrochemical cell 100 (in saturated NaCl(aq) electrolyte) at several different applied potentials (x-axis). The data in FIG. 3 was collected at room temperature (approximately 20° C. + / - 5° C.). In FIG. 3, the transition metal cathode is nickel (Ni). As shown, the magnitude of the current increases from approximately 0 to several milliamps (mA) upon application of approximately 0.2 V (i.e., between approximately 0.2 V and 0.4 V). The electrical configuration used to collect the data in FIG. 3 (and FIGS. 5A, 5B, and 5C) is that shown schematically in FIG. 2, with the negative terminal of an external potential source applied to the porous carbon element. As can be seen, a relatively low applied voltage is sufficient to convert nickel to one or more of nickel oxide, nickel hydroxide, and / or other similar reaction products at room temperature.

[0071] 6. Layered transition metal electrode materials In some embodiments, the transition metal component reacted according to one or more of the above embodiments may be a layered or graded composition. In some examples, the transition metal component may include two or more transition metals (e.g., Ni and Co; Ni, Co, and Mn). In some examples, multiple transition metals are combined into an alloy that may have a uniform composition or may include multiple phases. In other examples, multiple transition metals may include intermetallic compounds instead of, or in addition to, one or more alloys. In some examples, the composition may be graded, such that the outer surface of the transition metal component is rich in one transition metal and gradually becomes richer in another component as the distance to the center of the component decreases.

[0072] In other embodiments, such as that shown in Figure 4, the transition metal component may have an encapsulated or striated composition. As shown in Figure 4, the transition metal component 400 includes an outer layer 404 of a first composition disposed around and in contact with an inner core 408 having a second composition that is different from the first composition. The first and second compositions may be, but are not limited to, any of the compositions described above and any combination of the compositions described above.

[0073] In one embodiment, the transition metal component 400 can be treated according to the techniques described above to convert the outer layer 404 to its corresponding oxidation form (e.g., oxide, hydroxide, peroxide). Some or all of the inner core 408 can be reacted to its corresponding oxidation form. In one example of this example, the outer layer 404 can be of a first composition including cobalt, and the inner core 408 can be of a second composition including nickel. After oxidation and conversion to the cathode material during heat treatment with a lithium salt, the cobalt-rich surface layer can reduce the incidence of NiO-side reactions that degrade cathode performance in more traditionally constructed cathodes.

[0074] 7. Synthesis of Porous Metal Oxide Materials Some aspects of the present disclosure can be applied to synthesize microporous and / or nanoporous materials by selectively oxidizing one component of a multi-component and / or multi-phase system at room temperature. For illustrative purposes, a two-phase alloy of a first metal and a second metal can be formed, where the first metal oxidizes at a lower applied potential than the second metal (when placed in an electrochemical cell with a carbon aerogel air cathode). In this way, regions of the alloy rich in the first alloy can be selectively oxidized and removed from the alloy. This technique can therefore produce three-dimensional nanoporous elements that can have specific surface areas of hundreds or thousands of square meters per gram. These high-surface-area metal components can be used as catalytic substrates or themselves have high surface chemical activity. In other examples, these techniques can be used to produce lightweight metal components with mechanical properties (e.g., fracture toughness, elastic modulus, yield strength) comparable to or better than their non-nanoporous analogs.

[0075] Figures 5A, 5B, and 5C show cyclic voltammetry experimental data illustrating how embodiments herein can be used to selectively remove one phase of an alloy to produce a nanoporous metal material as described above. These figures are similar to Figure 3 (using a similar experimental setup, e.g., that shown in Figure 2), with the following exceptions: Figure 5A shows cyclic voltammetry experimental results for an aluminum (Al) / carbon aerogel (CA) system; Figure 5B shows cyclic voltammetry experimental results for a zinc (Zn) / carbon aerogel (CA) system; and Figure 5C shows cyclic voltammetry experimental results for a tin (Sn) / carbon aerogel (CA) system. All of these data were obtained using saturated NaCl. (aq) The solution was collected from an electrochemical cell. The axes in Figures 5A, 5B, and 5C are also similar to Figure 3: the x-axis represents the applied potential difference (in volts) and the y-axis represents the measured current (in milliamps (mA)).

[0076] Oxidation of the corresponding metals shown in Figures 5A, 5B, and 5C occurs at different onset potentials. In these examples, the open-circuit voltage (OCV) is the voltage at zero current. For aluminum (Figure 5A), the onset potential is approximately 0.5 V. For zinc (Figure 5B), the onset potential is approximately 0.9 V. For tin (Figure 5C), the onset potential is approximately 0.35 V. These figures are presented solely to illustrate the different onset potentials and open-circuit voltages at which oxidation begins when the corresponding metals are placed in an electrochemical cell with a carbon aerogel air cathode, as described herein. These figures also show the maximum overpotential (i.e., the difference between the OCV and the onset potential) for oxygen reduction at the carbon aerogel air cathode. For example, a system that does not form a protective passive film and exhibits a facile oxidation reaction, such as zinc metal, provides an opportunity to exclusively investigate the activation energy of the air cathode and the oxygen reduction reaction.

[0077] The difference in onset voltage can be used to selectively oxidize one metal in an alloy while leaving other metals with different onset voltages unoxidized. For example, aluminum and zinc form a solid solution of aluminum-rich (α) and zinc-rich (η) phases. In this example, aluminum may preferentially oxidize, leaving behind pores with dimensions similar to those of the α-phase regions. Annealing and composition parameters can be selected to alter the size of these α-phase regions, thereby altering the size of the pores upon pore removal. Although cyclic voltammetry data for copper is not shown, aluminum and copper are known to form solid solutions. The techniques described herein can be applied to aluminum-copper alloys, as well as many other types of alloys.

[0078] Similarly, mechanical processing can also be used to modify the inception voltage of a material. Mechanical deformation (e.g., exceeding the yield stress of a material) is known to promote oxidation at the location of the deformation. Bending, compression, cold rolling (or other types of deformation), welding, etc. can be used to promote preferential removal of material using the techniques mentioned above.

[0079] 8. Experimental Example In one example experiment, a configuration similar to that shown in Figure 1 was used. In this experiment, a block of carbon aerogel was placed in contact with an electrolyte solution. The electrolyte in this example was a saturated sodium chloride (NaCl) solution in distilled, deionized water. The pH of the electrolyte was nearly neutral (a pH of about 7). The electrolyte was contained in a submerged separator.

[0080] The nickel anode was inserted into (i.e., in direct contact with) the electrolyte solution and indirectly contacted a carbon aerogel air cathode. The nickel anode was a piece of pure nickel wire. A pure nickel current collector (same material as the pure nickel anode) was placed in contact with the nickel anode. The nickel current collector was not in contact with the electrolyte. Both the pure nickel anode and the pure nickel current collector were purchased from TEMCo®.

[0081] To complete the circuit, a first end of the stainless steel wire was placed in contact with the carbon aerogel air cathode. A second end of the stainless steel wire (opposite the first end) was placed in contact with a nickel current collector and a Ni wire anode. The current collector was electrically connected to a DC voltage source using an alligator clip.

[0082] An external power source was used to apply a potential difference to the electrochemical cell, with the carbon air cathode connected to the negative terminal of the power source. In this example, a potential difference of approximately 1 volt (V) was applied to the carbon aerogel air cathode and nickel current collector. In this experiment, the carbon aerogel air cathode was connected to the negative terminal of the power source, and the nickel anode was connected to the positive terminal of the power source. A potential difference of 1 V was chosen for convenience and to avoid parasitic water electrolysis reactions that would reduce the coulombic efficiency of the system. Water electrolysis also produces gaseous hydrogen and oxygen, which presents a further safety risk. The cyclic voltammetry data shown in Figure 3 indicate that smaller voltage magnitudes (e.g., as low as 0.2 V) are sufficient to cause oxidation of the nickel anode.

[0083] The reaction was carried out in ambient atmosphere (air) at standard temperature (about 20° C.) and pressure (1 atmosphere).

[0084] The electrochemical cell was then reacted under the conditions described above. The pure nickel anode reacted to completion in approximately 160 minutes. At this point, the portion of the nickel anode in contact with the electrolyte was consumed, thereby creating an open circuit between the electrolyte and the remaining stub of the anode that was no longer in contact with the electrolyte. The reaction product, located at the bottom of the beaker, had a green color consistent with Ni(OH)2, NiCO3, or a mixture of both.

[0085] 9. Production of magnetic IONPs (iron oxide nanoparticles) for LFP The inventors have surprisingly discovered that the disclosed method can also be used to produce both magnetic and non-magnetic iron oxide nanoparticles (IONPs) by using iron as the transition metal electrode 116 in a manner similar to that shown in Figure 1. Magnetic and non-magnetic IONPs are known to those skilled in the art as various compositions of iron (II, III) oxide. These IONPs may be particularly useful in the field of battery technology, as they may be used as a source of iron in lithium iron phosphate (LFP) batteries.

[0086] First, the disclosed method for fabricating magnetic IONPs uses iron as the transition metal anode, and as described above, a porous carbon element 104 can be used to reduce the activation energy for oxygen reduction, thereby allowing the electrically coupled iron metal to participate in room temperature redox reactions. The inventors have found that carbonized polyurethane foam can be used instead of carbon aerogel as element 104. Indeed, the inventors believe that any porous carbon material can be used.

[0087] Carbonized polyurethane foam may be advantageous in methods for producing magnetic IONPs because it may be more chemically and mechanically stable than carbon aerogel in the reactions described below. Additionally, the inventors believe that a combination of carbonized polyurethane foam and carbon aerogel may be used, for example, in which the carbon aerogel is stabilized within the pores of the carbonized polyurethane foam, where the carbonized polyurethane foam provides additional mechanical stability to the carbon aerogel material.

[0088] The fabrication of magnetic IONPs can be described with reference to FIG. 2, already described above, where reference numeral 126 denotes carbon aerogel elements and / or carbonized polyurethane foam, and reference numeral 208 denotes a transition metal component, e.g., iron foil. For the fabrication of magnetic IONPs, the inventors have discovered that sodium chloride can be used as the electrolyte 224. As an example, the concentration of the electrolyte 224 can be 1 molar (1M). However, the electrolyte is not so limited. It should be understood that the electrolyte 224 can be a solution of a salt of an alkali metal with a halogen, e.g., sodium chloride or potassium chloride, and the concentration of the electrolyte can be about 0.1M to 2.0M, 0.2M to 1.5M, 0.5M to 1M, or up to the concentration of a saturated solution of the electrolyte, e.g., up to about 6.14M (i.e., a saturated NaCl solution at room temperature). The corrosion rate of the anode metal increases monotonically with the concentration of the salt in the electrolyte. Specific examples can be 1M and 0.2M in certain embodiments.

[0089] As the electrolysis reaction proceeds, iron metal 208 oxidizes to form a "verdigris" - iron(II) hydroxide (Fe(OH)2) and / or its partially oxidized form, Fe(OH) 2-x O xis produced. In practice, this material settles and falls to the bottom of the reaction chamber, where it can be removed, for example, by gravity or by pumping to a separate chamber. In the separate chamber, the patina is left to partially oxidize under ambient conditions to form lepidocrocite (γ-FeO(OH)). This resulting (partially oxidized) iron hydroxide is further oxidized by air bubbling under basic conditions (e.g., pH > 8) to produce magnetic IONPs, and in particular, maghemite γ-Fe2O3. Air bubbling can proceed at a volume of about 1-5 L / min, e.g., about 2 L / min. The magnetic IONPs (e.g., magnetite, maghemite, and / or their solid solutions) are ferrimagnetic and can be magnetically separated from the reaction mixture (note that iron oxy / hydroxides are paramagnetic). The recovered IONPs are then washed and dried for further processing, e.g., as an iron source in LFP synthesis.

[0090] The magnetic IONPs produced in this manner were subjected to XRD analysis, which confirmed that the observed XRD pattern matched the calculated pattern for cubic spinel. The magnetic particles produced in this manner are in the form of nanoparticles, i.e., particles with sizes in the 20-100 nm region when observed using a scanning electron microscope. Surprisingly, it has been observed that the concentration of the electrolyte used in the process can affect the size of the particles produced. For example, a 1 M NaCl electrolyte has been shown to produce particles with sizes of approximately 60-70 nm (with a specific surface area of ​​22.46 m). 2 / g), 0.2 M KCl electrolyte has been shown to produce particles with sizes between 20 and 40 nm (specific surface area of ​​40.22 m 2 / g). Thus, the process can be tailored to produce particles of different sizes depending on the intended end use.

[0091] Experimental example of the production of maghemite (γ-Fe2O3) nanoparticles. The reaction was carried out in a 15 L rectangular plastic vessel filled with 10 L of 1 M NaCl solution prepared in tap water. The air cathode consisted of four rectangular blocks of carbon foam measuring 4 × 10 × 16 cm. The air cathode blocks were mechanically fixed within the reactor and electrically connected. Each carbon foam block had a central hole drilled along its length, through which air could be pumped. However, forced air diffusion is not required for the synthesis of magnetic γ-Fe2O3 (maghemite).

[0092] A pure iron (approximately 15 x 2 x 0.04 cm) anode foil was introduced between the carbon air cathodes and electrically connected. An overhead mixer with a mixing speed of approximately 250 rpm was introduced into the reactor to homogenize the concentration of hydroxide reagent produced by the reduction of atmospheric oxygen. Initially, a voltage of 1 V was applied to the electrodes. Immediately, a current of approximately 2 A began to flow due to the following reaction: Cathode: 1 / 2O2+H2O+2e→2OH - Anode: Fe→Fe 2+ +2e

[0093] As corrosion increases the surface roughness of the Fe anode, the magnitude of the current increases with time to approximately 4 amperes (A). 2+ and OH - The release of ions leads to the formation of nanoparticulate Fe(OH)2, a patina. Partial oxidation of the patina by contact with atmospheric oxygen results in FeO, which adopts a cubic crystal structure similar to maghemite. 1-x (OH) 2-x This causes oxidation of some to intermediate oxidation states such as lepidocrocite. After about 24 hours of reaction, the Fe anode corrodes.

[0094] In the second step, the lepidocrocite fine sludge is extracted, the pH of the solution is raised to 9 by adding an appropriate amount of Na2CO3, and air is bubbled through the solution for oxidative dihydroxylation to maghemite γ-Fe2O3 (1 L / min, 3 h). A magnetic test is used to determine the complete conversion of lepidocrocite to maghemite. The nanoparticulate maghemite is then easily separated from the sodium chloride / carbonate electrolyte by magnetic separation and subsequent washing until chloride ions are free (2-3 washes with 1 L of water each time).

[0095] 10. Generation of Non-magnetic IONPs for LFP The production of non-magnetic IONPs can proceed in a manner similar to that of the magnetic IONPs described above with reference to FIG. 2, where reference numeral 126 indicates that carbon aerogel elements and / or carbonized polyurethane foam with air are pumped through the central hole at a rate of 2 L / min, and reference numeral 208 indicates a transition metal component, such as iron foil. For the production of non-magnetic IONPs, the inventors have discovered that sodium chloride can be used as the electrolyte 224. As an example, the concentration of the electrolyte 224 can be 1 molar (1M). However, the electrolyte is not so limited. It should be understood that the electrolyte 224 can be a solution of a salt of an alkali metal with a halogen, such as sodium chloride or potassium chloride, and the concentration of the electrolyte can be about 0.1M to 2.0M, 0.2M to 1.5M, 0.5M to 1M, or up to the concentration of a saturated solution of the electrolyte, for example, up to about 6.14M (i.e., a saturated NaCl solution at room temperature). Specific examples can be 1M and 0.2M in certain embodiments.

[0096] As the electrolysis reaction proceeds, iron metal 208 oxidizes to form a "verdigris" - iron (II) hydroxide, Fe(OH)2, and / or its partially oxidized form, Fe(OH). 2-x O xIt is generated. In the first alternative method of the present disclosure, this material precipitates and falls to the bottom of the reaction chamber and can be removed, for example, by gravity or by pumping to a separate chamber. In another chamber, the green rust can be further oxidized by bubbling air to obtain non-magnetic IONPs and especially goethite (FeOOH). The air bubbling can proceed at a rate of about 1 to 5 L / min, for example about 2 L / min. The nanoparticle goethite is separated from the solution by at least one, preferably multiple cycles of washing and decantation, or filtration, or centrifugation. The recovered IONPs are then dried for subsequent processing, for example, as an iron source in LFP synthesis.

[0097] In another method of the present disclosure, Fe(OH)2 formed by an electrolytic reaction can be directly oxidized in situ to form goethite nanoparticles, for example, by bubbling air, optionally and conveniently through a porous carbon anode during electrolysis, or by introducing oxygen into the electrochemical cell. The air bubbling can proceed at a rate of about 1 to 5 L / min, for example about 2 L / min. Such an alternative method can be carried out under neutral to slightly acidic pH conditions (e.g., 5 < pH < 7, for example a pH of about 6). The nanoparticle goethite is separated from the sodium chloride electrolyte by similar cycles of washing and decantation, or filtration, or centrifugation. The recovered IONPs are then dried for subsequent processing, for example, as an iron source in LFP synthesis.

[0098] Experimental example of preparing goethite (α-FeOOH) nanoparticles The reaction was carried out in a 15-L rectangular plastic vessel filled with 10 L of 1 M NaCl solution prepared in tap water. The air cathode consisted of four rectangular blocks of carbon foam measuring 4 × 10 × 16 cm. The air cathode blocks were mechanically fixed within the reactor and electrically connected. Each carbon foam block had a central hole drilled along its length, through which air could be pumped as needed. A foil of pure iron (approximately 15 × 2 × 0.04 cm) anode was introduced between the carbon air cathodes and electrically connected. An overhead mixer with a mixing speed of approximately 250 rpm was introduced into the reactor to homogenize the hydroxide reagent concentration. Initially, a voltage of 1 V was applied to the electrodes while air was pumped through the carbon cathodes at a rate of 2 L / min. Immediately, a current of approximately 4 A began to flow due to the following reaction: Cathode: 1 / 2O2+H2O+2e→2OH - Anode: Fe→Fe 2+ +2e

[0099] Due to the high concentration of dissolved O2 in the electrolyte, the formed Fe(OH)2 nanoparticles are directly oxidized to become goethite nanoparticles. Under the above conditions, complete etching of the Fe anode occurs within 7–10 h.

[0100] The nanoparticulate goethite is then separated from the sodium chloride electrolyte by successive cycles of washing and decanting, or filtering, or centrifugation.

[0101] Without wishing to be bound by theory, the inventors believe that for all metals (M) capable of forming stable divalent cations (e.g., Fe, Mn, Ni, Co, Cu, Zn, Sn, etc.), the immediate reaction product formed at the surface of the M anode is a metal double hydroxide salt, M(OH). Furthermore, for metals for which +2 is the highest possible oxidation state (e.g., Zn) or for which oxidation states higher than +2 are energetically unfavorable in air at low temperatures (e.g., Ni, Co, Cu), M(OH) is likely to be the final reaction product. In the specific case of Fe (and Mn), since the +3 oxidation state is readily obtainable in air at low temperatures, M(OH) is likely to be an intermediate, leading to higher oxidation states depending on the potential, pH, and oxidation conditions.

[0102] Specific examples of Fe include Fe(OH)2 and / or its partially oxidized forms, FeO x (OH) 2-x , or patina, is believed to be the first intermediate formed during electrolysis. Without further specific treatment at neutral pH, the patina gradually oxidizes to goethite, FeO(OH). On the other hand, in the method described in this invention, increasing the pH above 8 and controlling oxidation with air leads to the formation of maghemite, FeO (or FeO in the spinel representation of magnetite). 8 / 3 V 1 / 3 O4, where V = vacancy). A similar transformation is expected due to the availability of the +3 oxidation state for manganese.

[0103] The inventors have found that by controlling the reaction conditions, and in particular the amount of oxygen from the air available for oxidation, magnetic or non-magnetic IONPs can be produced by the disclosed method. In the above example, both were performed at the same scale (15 L electrolysis reactor, 10 L electrolyte), and the limited oxygen in the reactor without air being bubbled through the carbon anode oxidized the patina to lepidocrocite FeO(OH), which subsequently underwent forced oxidation by air bubbling under alkaline conditions to magnetic maghemite FeO. Alternatively, air bubbling during electrolysis under basic conditions immediately oxidized the patina directly to non-magnetic goethite FeO(OH). Thus, air, and therefore oxygen, was introduced into the electrolyte, which promoted in situ oxidation to the alpha form of iron(III) oxide-hydroxide, i.e., goethite, rather than the gamma form of lepidocrocite. However, we have also observed that when these reactions are carried out on a smaller scale (e.g., 1.5 L of electrolyte), even with air bubbling through a carbon cathode, the reaction proceeds to lepidocrocite and then later to maghemite. Without wishing to be bound by theory, it is believed that at smaller scales, there is insufficient oxygen in the electrolyte to directly oxidize the patina to goethite.

[0104] Although magnetic IONPs produced by the methods of the present disclosure have been described as useful for synthesizing LFPs, magnetic IONPs have many industrial applications, for example, in catalysis, in the defense industry, e.g., as microwave and radar absorbing materials (RAMs), as magnetic fluids, for recording tape, in pollution remediation, and in medical applications.

[0105] The method for producing magnetic IONPs as described above is semi-continuous in that the electrochemical reaction can proceed in a first vessel and the reaction products can be transferred to a second vessel using a pump as described above, while the electrochemical reaction continues and does not need to be stopped. The electrolyte can be reused, thereby avoiding waste.

[0106] Table 1 shows particle size and specific surface area data for various experimental conditions. Note that some embodiments include ball milling to access an unexpectedly 10 times larger specific surface area than commercially available materials. [Table 1]

[0107] As used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. These terms are not to be interpreted as excluding the presence of other features, steps or components.

[0108] The present invention may also be broadly configured in any and all combinations of two or more of the parts, elements, steps, examples, and / or features referred to or shown herein, individually or collectively. In particular, one or more features in any of the embodiments described herein may be combined with one or more features from any other embodiment(s) described herein.

[0109] Protection may be sought for any feature disclosed in any one or more of the published documents referenced herein in connection with this disclosure.

[0110] Although specific exemplary embodiments of the present invention have been described, the appended claims are not intended to be limited to only these embodiments. The claims should be interpreted literally, objectively, and / or to encompass equivalents. Some of the embodiments of the invention related to the present invention are shown below. [Embodiment 1] 1. A method comprising: 1. Constructing an electrochemical cell, the electrochemical cell comprising: a transition metal anode; A catalyst; an oxygen source, the oxygen functioning as a cathode in the electrochemical cell; an electrolyte in contact with the transition metal anode and the catalyst; reducing the oxygen with the catalyst, the reduction of the oxygen producing hydroxy anions in the electrolyte; reacting the hydroxy anion with the transition metal anode, the reaction oxidizing the transition metal of the transition metal anode. [Embodiment 2] 10. The method of claim 1, further comprising applying an electrical potential to the electrochemical cell. [Embodiment 3] 3. The method of claim 1 or 2, wherein the reduction of oxygen and the oxidation of the transition metal oxide are carried out at one or more temperatures between 15°C and 35°C. [Embodiment 4] 4. The method of any one of embodiments 1 to 3, wherein the transition metal anode comprises nickel. [Embodiment 5] 5. The method of embodiment 4, wherein the reaction of the hydroxy anion with the nickel-containing transition metal anode produces at least nickel hydroxide. [Embodiment 6] 6. The method of any one of embodiments 1-5, further comprising reacting the transition metal oxide with a lithium salt to produce a rechargeable lithium-ion battery cathode material. [Embodiment 7] 4. The method of any one of embodiments 1 to 3, wherein the transition metal anode comprises iron. [Embodiment 8] 8. The method of embodiment 7, wherein the electrolyte is a solution of an alkali metal halide, such as sodium chloride. [Embodiment 9] Iron(II) hydroxide Fe(OH) 2 , and / or its partially oxidized form Fe(OH) 2-x O x from said electrochemical cell; said iron (II) hydroxide Fe(OH) 2 and / or its partially oxidized form Fe(OH) 2-x O x and oxidizing under basic conditions, for example, a pH greater than 7, 8, 9, or 10, preferably greater than 8. [Embodiment 10] 10. The method of embodiment 9, further comprising magnetically separating the magnetic IONPs from the reaction vessel. [Embodiment 11] 11. The method of any of embodiments 7 to 10, further comprising introducing oxygen into the electrochemical cell, preferably by air bubbling. [Embodiment 12] 12. The method of any of embodiments 7-11, further comprising separating non-magnetic IONPs from said electrochemical cell using physical separation optionally selected from the list comprising filtration, centrifugation, decantation, and mixtures thereof. [Embodiment 13] 13. The method of any one of claims 1-12, wherein the catalyst comprises a porous carbon material such as carbonized polyurethane foam, and optionally, oxygen is introduced into the electrochemical cell by bubbling air through the catalyst. [Embodiment 14] 14. The method of any one of the preceding embodiments, wherein the catalyst comprises a carbon aerogel catalyst. [Embodiment 15] 15. The method of embodiment 14, wherein the carbon aerogel catalyst comprises one or both of monolithic carbon aerogel elements or granular carbon aerogel elements. [Embodiment 16] A rechargeable battery cathode material having a non-spherical shape and a fill factor greater than 40%. [Embodiment 17] 17. A rechargeable battery cathode material as described in embodiment 16, wherein the non-spherical shape is one or more of a wire having a circular cross section or a rectangular cross section. [Embodiment 18] 18. A rechargeable battery cathode material as described in embodiment 16 or 17, wherein the non-spherical shapes comprise elongated structures in one of a spiral configuration, a parallel array configuration, a zigzag configuration, a bull's eye configuration, or a grid configuration. [Embodiment 19] 19. The rechargeable battery cathode material of any of embodiments 16-18, further comprising one or more of NCM 111 or NCM 811. [Embodiment 20] A composition comprising nickel hydroxide and sodium. [Embodiment 21] iron-containing nanoparticles having a characteristic dimension between 20 nm and 1000 nm; and 10 meters 2 (m 2 ) / gram (g) ~ 65m 2 / g specific surface area. [Embodiment 22] The characteristic dimension is 30 nm to 70 nm, and the specific surface area is 20 m 2 / g~40m 2 / g. [Embodiment 23] The characteristic dimension is 30 nm to 60 nm, and the specific surface area is 22 m 2 / g~40m 2 / g. [Embodiment 24] The characteristic dimension is 20 nm to 40 nm, and the specific surface area is 60 m 2 / g~80m 2 / g. [Embodiment 25] 22. The composition of embodiment 21, wherein the iron-containing nanoparticles are magnetite. [Embodiment 26] 22. The composition of embodiment 21, further comprising a surface comprising potassium, sodium, or both. [Embodiment 27] 22. The composition of embodiment 21, wherein the nanoparticles further comprise manganese. [Embodiment 28] 28. An energy storage system comprising the composition of embodiment 27. [Embodiment 29] 22. An energy storage system comprising the composition of embodiment 21. [Embodiment 30] LiFePO with characteristic dimensions from 20nm to 1000nm 4 (LFP) nanoparticles, and 10 meters 2 (m 2 ) / gram (g) ~ 65m 2 / g specific surface area. [Embodiment 31] The characteristic dimension is 30 nm to 70 nm, and the specific surface area is 20 m 2 / g~65m 2 / g. [Embodiment 32] The characteristic dimension is 30 nm to 60 nm, and the specific surface area is 22 m 2 / g~40m 2 / g. [Embodiment 33] The characteristic dimension is 20 nm to 40 nm, and the specific surface area is 60 m 2 / g~80m 2 / g. [Embodiment 34] 31. The composition of embodiment 30, wherein the LFP nanoparticles further comprise magnetite. [Embodiment 35] 31. The composition of embodiment 30, wherein the nanoparticles further comprise manganese. [Embodiment 36] 36. An energy storage system comprising the composition of embodiment 35. [Embodiment 37] 31. An energy storage system comprising the composition of embodiment 30.

Claims

1. 1. A method comprising:

1. Constructing an electrochemical cell, the electrochemical cell comprising: a transition metal anode; a catalyst comprising a porous carbon material; an oxygen source, the oxygen functioning as a cathode in the electrochemical cell; configuring the electrochemical cell to include an electrolyte in contact with the transition metal anode and the catalyst; applying a potential of at least 0.2 volts (V) to the electrochemical cell; exposing the electrochemical cell to oxygen, whereby the oxygen is reduced by the catalyst, and whereby the reduction of the oxygen produces hydroxy anions in the electrolyte; Including, The method, wherein the hydroxy anion reacts with the transition metal anode to oxidize the transition metal of the transition metal anode and form a transition metal oxide.

2. The method described in claim 1, wherein the potential is 0.2V to 1V.

3. 10. The method of claim 1, wherein the reduction of oxygen and the oxidation of the transition metal anode are carried out at one or more temperatures between 15°C and 35°C.

4. The method of claim 1 , wherein the transition metal anode comprises nickel.

5. 5. The method of claim 4, wherein the reaction of the hydroxy anion with the nickel-containing transition metal anode produces at least nickel hydroxide.

6. 10. The method of claim 1, further comprising reacting the transition metal oxide with a lithium salt to produce a rechargeable lithium-ion battery cathode material.

7. The method of claim 1 , wherein the transition metal anode comprises iron.

8. The method of claim 7 wherein the electrolyte is a solution of an alkali metal halide.

9. Iron(II) hydroxide Fe(OH) ２ , and / or its partially oxidized form Fe(OH) ２－ｘ O ｘ from said electrochemical cell; said iron (II) hydroxide Fe(OH) ２ and / or its partially oxidized form Fe(OH) ２－ｘ O ｘ and oxidizing under basic conditions having a pH greater than 7.

10. 10. The method of claim 9, further comprising magnetically separating the magnetic iron oxide nanoparticles (IONPs) from the reaction vessel.

11. The method of claim 7 , wherein exposing the electrochemical cell to oxygen comprises bubbling air through the electrochemical cell.

12. 8. The method of claim 7, further comprising separating non-magnetic IONPs from the electrochemical cell using a physical separation selected from filtration, centrifugation, decantation, and mixtures thereof.

13. The method of claim 1 , wherein the porous carbon material is a carbonized polyurethane foam.

14. The method of claim 1 , wherein the catalyst comprises a carbon aerogel.

15. 15. The method of claim 14, wherein the carbon aerogel comprises monolithic carbon aerogel elements, granular carbon aerogel elements, or a combination thereof.

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