Low-cost metal electrodes

Abstract

To provide materials, designs and methods of fabrication for metal electrodes for electrochemical cells.SOLUTION: A battery comprises a first electrode, an electrolyte, and a second electrode, where the second electrode comprises atomized metal powder, and the electrolyte is infiltrated between the atomized metal powder particles. A method of making an electrode comprises: electrochemically producing metal powder; and forming the metal powder into an electrode.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] Related Applications This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 879,126, entitled "Low Cost Metal Electrodes," filed July 26, 2019, and U.S. Provisional Patent Application No. 63 / 021,566, entitled "Low Cost Metal Electrodes," filed May 7, 2020, the contents of both applications being incorporated herein by reference in their entirety for all purposes. [Background technology]

[0002] Energy storage technologies are playing an increasingly important role in the power grid. At the most basic level, these energy storage assets provide smoothing to better match generation and demand on the distribution grid. The services performed by energy storage devices benefit the power grid over multiple timescales, from milliseconds to years. Today, energy storage technologies exist that can support timescales from milliseconds to hours, but long-term and ultra-long-term (collectively, ≧8 hours) energy storage systems are needed.

[0003] This "Background" section is intended to introduce various aspects of the art that may be related to embodiments of the present invention. As such, the preceding discussion in this section is intended to provide a framework for better understanding the present invention, and should not be construed as admissions of prior art. Summary of the Invention

[0004] Materials, designs, and manufacturing methods for metal electrodes for electrochemical cells are disclosed. In various embodiments, the electrodes comprise iron. Various methods for achieving high surface area at low cost and simple, scalable manufacturing methods are described.

[0005] Various embodiments may include a battery including a first electrode, an electrolyte, and a second electrode, wherein at least one of the first electrode and the second electrode includes an atomized metal powder.

[0006] Various embodiments may include a battery including a first electrode, an electrolyte, and a second electrode, wherein at least one of the first electrode and the second electrode includes an iron agglomerate.

[0007] Various embodiments may include a method for fabricating an electrode that includes electrochemically producing a metal powder and forming the metal powder into an electrode.

[0008] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the claims and, together with the general description set forth above and the detailed description set forth below, serve to explain the features of the claims. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 10 is a diagram illustrating an example of a discharging method. [Figure 2] FIG. 1 shows an embodiment of horizontally layered electrodes housed in a larger container. [Figure 3] FIG. 1 shows an embodiment of horizontally layered electrodes housed in a larger container. [Figure 4] FIG. 1 shows a woven metal fabric with electrodes made of direct reduced iron pellets. [Figure 5] 1A-1C show examples of embodiments of porous mesh containers. [Figure 6] 1A-1C show examples of embodiments of porous mesh containers. [Figure 7] FIG. 10 is a diagram showing an example of a backing plate. [Figure 8] FIG. 10 shows that the tie-down rail can act as a busbar. [Figure 9] FIG. 1 shows a direct reduced iron (DRI) marble bed assembly. [Figure 10] FIG. 1 shows a module made up of rigid side walls. [Figure 11] 1A-1C illustrate fastening techniques according to various embodiments. [Figure 12] FIG. 10 illustrates an expandable material contained within a rigid iron electrode containment assembly. [Figure 13] FIG. 1 illustrates thermal coupling. [Figure 14] FIG. 1 illustrates the mechanical interaction of pellets. [Figure 15] FIG. 1 shows a pellet bed. [Figure 16] FIG. 2 is a diagram showing an example of a current collector. [Figure 17] FIG. 1 shows a mechanically processed pellet. [Figure 18] FIG. 10 is a diagram comparing the distribution of discharge products. [Figure 19] FIG. 1 shows a temperature plot. [Figure 20] FIG. 1 illustrates one exemplary method for evacuating a hole. [Figure 21] 1A and 1B illustrate examples of additive holder configurations. [Figure 22] FIG. 1 illustrates an exemplary additive incorporation process. [Figure 23] 1A to 1C are diagrams illustrating an electrode formation process. [Figure 24] 1A-1C illustrate various exemplary systems in which one or more aspects of various embodiments may be used as part of a bulk energy storage system. [Figure 25] 1A-1C illustrate various exemplary systems in which one or more aspects of various embodiments may be used as part of a bulk energy storage system. [Figure 26] 1A-1C illustrate various exemplary systems in which one or more aspects of various embodiments may be used as part of a bulk energy storage system. [Figure 27]1A-1C illustrate various exemplary systems in which one or more aspects of various embodiments may be used as part of a bulk energy storage system. [Figure 28] 1A-1C illustrate various exemplary systems in which one or more aspects of various embodiments may be used as part of a bulk energy storage system. [Figure 29] 1A-1C illustrate various exemplary systems in which one or more aspects of various embodiments may be used as part of a bulk energy storage system. [Figure 30] 1A-1C illustrate various exemplary systems in which one or more aspects of various embodiments may be used as part of a bulk energy storage system. [Figure 31] 1A-1C illustrate various exemplary systems in which one or more aspects of various embodiments may be used as part of a bulk energy storage system. [Figure 32] 1A-1C illustrate various exemplary systems in which one or more aspects of various embodiments may be used as part of a bulk energy storage system. DETAILED DESCRIPTION OF THE INVENTION

[0010] Various embodiments will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. References to specific examples and implementations are for illustrative purposes only and are not intended to limit the scope of the claims. The following description of embodiments of the invention is not intended to limit the invention to those embodiments, but rather to enable one of ordinary skill in the art to make and use the invention. Unless otherwise noted, the accompanying drawings are not drawn to scale.

[0011] As used herein, unless otherwise stated, room temperature is 25° C. and standard temperature and pressure are 25° C. and 1 atmosphere. Unless expressly stated otherwise, all tests, test results, physical properties, and values ​​that are temperature-dependent, pressure-dependent, or both, are provided at standard ambient temperature and pressure.

[0012] In general, the term "about" and the symbol "to" as used herein, unless otherwise specified, are meant to encompass a variation or range of ±10%, the experimental or instrumental error associated with obtaining the stated value, preferably whichever is greater.

[0013] As used herein, unless otherwise stated, the recitation of ranges of values ​​herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each separate value within a range is incorporated herein as if it were individually recited herein.

[0014] As used herein, unless otherwise specified, the terms "%," "wt. %," and "mass %" are used interchangeably and refer to the weight of a first component as a percentage of the weight of a total, e.g., formulation, mixture, particle, pellet, agglomerate, material, structure, or product. As used herein, unless otherwise specified, "volume %" and "% volume" and similar such terms refer to the volume of a first component as a percentage of the volume of a total, e.g., formulation, mixture, particle, pellet, agglomerate, material, structure, or product.

[0015] The following examples are provided to illustrate various embodiments of the present system and method of the present invention. These examples are illustrative and may be prophetic, and should not be considered limiting, and do not limit the scope of the invention in any way.

[0016] It should be noted that it is not necessary to provide or express the theory underlying any novel and innovative process, material, performance, or other beneficial features and characteristics that are the subject of or associated with embodiments of the present invention. Nevertheless, various theories are provided herein to further advance the art. The theories presented herein are not intended to limit, restrict, or narrow in any way the scope of protection afforded to the claimed inventions, unless expressly stated otherwise. Such theories may not be necessary to utilize the present invention or may not be put into practice. Furthermore, it is understood that the present invention may be coupled with new and previously unknown theories to explain the function-characteristics of embodiments of the methods, articles, materials, devices, and systems of the present invention. Such subsequently developed theories shall not limit the scope of protection afforded to the present invention.

[0017] The various embodiments of the systems, equipment, techniques, methods, activities, and operations described herein can be used in a variety of other activities and fields in addition to those described herein. Additionally, such embodiments can be used, for example, with other equipment or activities that may be developed in the future; and with existing equipment or activities that may be modified based on the teachings herein. Furthermore, the various embodiments and examples described herein can be used with each other, in whole or in part, and in various different combinations. Thus, the configurations provided in the various embodiments herein can be used with each other. For example, elements of an embodiment having A, A', and B and elements of an embodiment having A", C, and D can be used with each other in various combinations, e.g., A, C, D, and A, A", C, D, etc., in accordance with the teachings herein. Therefore, the scope of protection afforded the present invention should not be limited to the specific embodiments, configurations, or arrangements shown in the specific embodiments, examples, or in the specific illustrated embodiments.

[0018] As used herein, unless otherwise specified, the term "specific gravity," also called apparent density, should be given the broadest possible meaning and generally refers to the weight per unit volume of a structure, e.g., a volumetric form of a material. This property will include the internal porosity of a particle as part of its volume. It can be measured, among other techniques, with a low viscosity fluid wetting the particle surface.

[0019] As used herein, unless otherwise specified, the term "actual density," which may also be referred to as true density, should be given the broadest possible meaning and generally refers to the weight per unit volume of a material if no voids were present in that material. This measurement and property essentially excludes internal porosity from the material, e.g., does not include any voids in the material.

[0020] Therefore, a collection of porous foam balls (e.g., Nerf® balls) can be used to illustrate the relationship between the three density properties: The weight of the ball filling a container would be the bulk density of the ball.

[0021]

number

[0022] The weight of a single ball per spherical volume of the ball would be its apparent density.

[0023]

number

[0024] The weight of the material that makes up the ball's skeleton, i.e., the ball with all void volume removed, per remaining volume of that material would be the skeleton density.

[0025]

number

[0026] As used herein, unless otherwise specified, the terms agglomerate and agglomerate should be given the broadest possible meaning and generally refer to an aggregation of powder-like particles.

[0027] Embodiments of the present invention include devices, systems, and methods for long-term and ultra-long-term low-cost energy storage. As used herein, unless expressly stated otherwise, the terms "long-term" and "ultra-long-term" and similar such terms shall be given the broadest possible meaning and shall include energy storage periods of 8 hours or longer, such as an 8-hour energy storage period, an energy storage period ranging from 8 hours to 20 hours, a 20-hour energy storage period, an energy storage period ranging from 20 hours to 24 hours, a 24-hour energy storage period, an energy storage period ranging from 24 hours to 1 week, and an energy storage period ranging from 1 week to 1 year (e.g., from days to weeks, to months, etc.), and shall include LODES systems. Furthermore, the terms "long-term" and "ultra-long-term," "energy storage cell," including "electrochemical cell," and similar such terms shall be given the broadest possible interpretation and shall include electrochemical cells that may be configured to store energy for time periods of days, weeks, or seasons.

[0028] Generally, in embodiments, the long-term energy storage cell may be a long-term electrochemical cell. Generally, this long-term electrochemical cell can store electricity generated by a power generation system when: (i) the power source or fuel for that generation is available, abundant, inexpensive, and combinations and variations thereof; (ii) the power needs or demands of the power grid, customers, or other users are less than the amount of electricity generated by the power generation system, the price paid to provide such power to the power grid, customers, or other users is below the economically efficient point for generating such power (e.g., when the cost of generation exceeds the market price for electricity), and combinations and variations thereof; and (iii) combinations and variations of (i) and (ii), and other reasons. This electricity stored in the long-term electrochemical cell can then be distributed to the power grid, customers, or other users when economical or otherwise needed. For example, the electrochemical cell may be configured to store energy generated by solar cells during summer months when sunlight is abundant and solar power generation exceeds grid needs, and to discharge the stored energy during winter months when sunlight may be insufficient to meet grid needs.

[0029] Various embodiments are discussed regarding the use of direct reduced iron (DRI) as a battery (or cell) material, as a battery (or cell) component, and combinations and variations thereof. In various embodiments, DRI may be produced from or be material obtained from the reduction of natural or processed iron ore, where such reduction is carried out without reaching the melting temperature of iron. In various embodiments, the iron ore may be taconite, magnetite, hematite, goethite, or the like. In various embodiments, DRI may be in the form of pellets, which may be spherical or substantially spherical. In various embodiments, DRI may be porous and may contain open and / or closed internal porosity. In various embodiments, DRI may include material that has been further processed by hot or cold briquetting. In various embodiments, DRI is produced by reducing iron ore pellets to produce iron metal (Fe 0DRI can be produced by forming more metallic (more reduced, less oxidized) materials such as iron ore taconite, wüstite (FeO), or composite pellets containing iron metal and residual oxide phases. In various non-limiting embodiments, DRI may be reduced iron ore taconite, direct reduced (“DR”) taconite, reduced “blast furnace (BF) grade” pellets, reduced “electric arc furnace (EAF) grade” pellets, “cold direct reduced iron (CDRI)” pellets, direct reduced iron (“DRI”) pellets, hot briquetted iron (HBI), or any combination thereof. In the iron and steel industry, DRI is sometimes referred to as “sponge iron,” and its use is particularly common in India. Iron material embodiments, including exemplary embodiments of DRI materials for use in various embodiments described herein, including use as electrode materials, may have one, more than one, or all of the material properties as set forth in Table 1 below. As used herein, including in Table 1, the following terms have the following meanings unless expressly stated otherwise: "specific surface area" means the total surface area of ​​a material per unit mass, including the surface area of ​​pores in a porous structure; "carbon content" or "carbon (wt%)" means the mass of total carbon as a percentage of the total mass of the DRI; "cementite content" or "cementite (wt%)" means the mass of FeC as a percentage of the total mass of the DRI; "total Fe (wt%)" means the mass of all iron as a percentage of the total mass of the DRI; "metallic Fe (wt%)" means the mass of Fe as a percentage of the total mass of the DRI. 0 "Metallized" means the mass of iron in the Fe state as a percentage of the mass of all iron; 0 As used herein, weight and volume percentages and apparent densities are understood to exclude any electrolyte infiltrating the porosity or any transient additives within the porosity, unless otherwise stated.

[0030] [Table 1]

[0031] * The specific surface area is preferably determined by the Brunauer-Emmett-Teller adsorption method ("BET"), more preferably BET as set forth in ISO 9277, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as methylene blue (MB) staining, ethylene glycol monoethyl ether (EGME) adsorption, electrokinetic analysis of complex ion adsorption, and protein retention (PR) methods, can be used to provide results that can be correlated with BET results.

[0032] ** Actual density is preferably determined by helium (He) pycnometer method, more preferably as set forth in ISO 12154, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests can be used to provide results that can be correlated with He pycnometer results. Actual density is sometimes also referred to in the art as "true density" or "skeletal density."

[0033] *** Apparent density is preferably determined by immersion in water, more preferably as set forth in ISO 15968, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests can be used to provide results that can be correlated with He pycnometer results. Porosity can be defined as the ratio of apparent density to actual density.

[0034]

number

[0035] **** d 孔、90%容積is preferably determined by mercury (Hg) intrusion porosimetry, more preferably as set forth in ISO 15901-1, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as gas adsorption, can be used to provide results that can be correlated with Hg intrusion results. 孔、90%容積 is the pore diameter above which 90% of the total pore volume resides.

[0036] ***** d 孔、50%表面積 is preferably determined by mercury (Hg) intrusion porosimetry, more preferably as set forth in ISO 15901-1, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as gas adsorption, can be used to provide results that can be correlated with Hg intrusion results. 孔、50%表面積 is the pore diameter above which 50% of the free surface area resides.

[0037] #Total Fe (wt%) is preferably determined by dichromate titration, more preferably as set forth in ASTM E246-10, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as tin(II) chloride reduction followed by titration, titanium(III) chloride reduction followed by titration, and inductively coupled plasma (ICP) spectroscopy, can be used to provide results that can be correlated to the dichromate titration method.

[0038] ##Metallic Fe (wt%) is preferably determined by iron(III) chloride titration, more preferably as set forth in ISO 16878, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as bromine-methanol titration, can be used to provide results that can be correlated to iron(III) chloride titration.

[0039] ### Metallization (%) is preferably determined by the ratio of metallic Fe to total Fe, each preferably determined by the method described above.

[0040] #### Carbon (wt%) is preferably determined by infrared absorption after induction furnace firing, more preferably as set forth in ISO 9556, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as various combustion and inert gas fusion techniques such as those set forth in ASTM E1019-18, can be used to provide results that can be correlated to infrared absorption after induction furnace firing.

[0041] #####Fe 2+ (wt %) is preferably determined by titration, more preferably as set forth in ASTM D3872-05, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as Mössbauer spectroscopy, X-ray absorption spectroscopy, and the like, can be used to provide results that can be correlated to titration.

[0042] $Fe 3+ (wt%) is preferably total Fe (wt%), metallic Fe (wt%), Fe 2+ (wt%), and Fe 3+ It is determined by the mass balance relationship between or within the Fe (wt%). Specifically, total Fe (wt%) = metallic Fe (wt%) + Fe 2+ (Weight%)+Fe 3+ (wt%) must be true due to the law of conservation of mass, so Fe 3+ (wt%) is Fe 3+ (wt%) = total Fe (wt%) - metallic Fe (wt%) - Fe 2+ It can be calculated as a percentage by weight.

[0043] $$SiO2 (wt%) is preferably determined gravimetrically, more preferably as set forth in ISO 2598-1, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as reduced molybdosilicate spectrophotometry, X-ray diffraction (XRD), and the like, can be used to provide results that can be correlated to gravimetric methods. In certain methods, SiO2 wt% is not determined directly; rather, the Si concentration (including neutral and ionic species) is measured and SiO2 wt% is calculated assuming SiO2 stoichiometry; that is, a molar ratio of Si:O of 1:2 is assumed.

[0044] $$$Ferrite (wt%, XRD) is preferably determined by X-ray diffraction (XRD).

[0045] $$$$Wüstite (FeO, wt%, XRD) is preferably determined by X-ray diffraction (XRD).

[0046] $$$$$Goethite (FeOOH, wt%, XRD) is preferably determined by X-ray diffraction (XRD).

[0047] + Cementite (Fe3C, wt%, XRD) is preferably determined by X-ray diffraction (XRD).

[0048] Additionally, embodiments of iron materials, including, for example, embodiments of DRI materials, for use in various embodiments described herein, including for use as electrode materials, may have one or more of the following properties, characteristics, or features, as shown in Table 1A (note that values ​​in one row or one column may be present with values ​​in different rows or columns):

[0049] [Table 1A]

[0050] Total Fe (wt%) is preferably determined by dichromate titration, more preferably as set forth in ASTM E246-10, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as tin(II) chloride reduction titration, titanium(III) chloride reduction titration, and inductively coupled plasma (ICP) spectroscopy, can be used to provide results that can be correlated to the dichromate titration method.

[0051] !!SiO2 (wt%) is preferably determined gravimetrically, more preferably as set forth in ISO 2598-1, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as reduced molybdosilicate spectrophotometry, X-ray diffraction (XRD), and the like, can be used to provide results that can be correlated to gravimetric methods. In certain methods, SiO2 wt% is not determined directly; rather, the Si concentration (including neutral and ionic species) is measured and SiO2 wt% is calculated assuming SiO2 stoichiometry. That is, a molar ratio of Si:O of 1:2 is assumed.

[0052] Al2O3 (wt%) is preferably determined by flame atomic absorption spectrometry, more preferably as set forth in ISO 4688-1, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as X-ray diffraction (XRD), can be used to provide results that can be correlated to flame atomic absorption spectrometry. In certain methods, Al2O3 wt% is not determined directly; rather, the Al concentration (including neutral and ionic species) is measured and Al2O3 wt% is calculated assuming Al2O3 stoichiometry. That is, a molar ratio of Al:O of 2:3 is assumed.

[0053] !!!!MgO (wt%) is preferably determined by flame atomic absorption spectrometry, more preferably as set forth in ISO 10204, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as X-ray diffraction (XRD), can be used to provide results that can be correlated to flame atomic absorption spectrometry. In certain methods, MgO wt% is not determined directly; rather, the Mg concentration (including neutral and ionic species) is measured and the MgO wt% is calculated assuming MgO stoichiometry; that is, a 1:1 molar ratio of Mg:O is assumed.

[0054] !!!!!CaO (wt%) is preferably determined by flame atomic absorption spectrometry, more preferably as set forth in ISO 10203, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as X-ray diffraction (XRD), can be used to provide results that can be correlated to flame atomic absorption spectrometry. In certain methods, CaO wt% is not determined directly; rather, the Ca concentration (including neutral and ionic species) is measured and CaO wt% is calculated assuming CaO stoichiometry; that is, a 1:1 molar ratio of Ca:O is assumed.

[0055] & TiO2 (wt%) is preferably determined by diantipyrylmethane spectrophotometry, more preferably as set forth in ISO 4691, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as X-ray diffraction (XRD), can be used to provide results that can be correlated to diantipyrylmethane spectrophotometry. In certain methods, TiO2 wt% is not determined directly; rather, the Ti concentration (including neutral and ionic species) is measured and TiO2 wt% is calculated assuming TiO2 stoichiometry; that is, a molar ratio of Ti:O is assumed to be 1:2.

[0056] && Actual density is preferably determined by helium (He) pycnometer method, more preferably as set forth in ISO 12154, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests can be used to provide results that can be correlated with He pycnometer results. Actual density is sometimes also referred to in the art as "true density" or "skeletal density."

[0057] &&& Apparent density is preferably determined by immersion in water, more preferably as set forth in ISO 15968, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests can be used to provide results that can be correlated with He pycnometer results.

[0058] Bulk density (kg / m 3 ) is preferably determined by measuring the mass of a test portion introduced into a container of known volume until its surface is filled to the brim, more preferably as set forth in Method 2 of ISO 3852, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests can be used to provide results that can be correlated with those of gravimetric methods.

[0059] &&&&& The porosity is preferably determined by the ratio of the apparent density to the actual density.

[0060]

number

[0061] Also, the properties shown in Table 1 may be present in embodiments along with, in addition to, or instead of the properties in Table 1A. Also, greater and lesser values ​​of such properties may be present in various embodiments.

[0062] In an embodiment, the specific surface area of ​​the pellet is about 0.05 m 2 / g ~ approx. 35m 2 / g, approx. 0.1m 2 / g~about 5m 2 / g, approx. 0.5m 2 / g~about 10m 2 / g, approx. 0.2m 2 / g~about 5m 2 / g, approx. 1m 2 / g~about 5m 2 / g, approx. 1m 2 / g~about 20m 2 / g, and about 1m 2 / g, and is about 2m 2 / g, and is about 5m 2 / g, and may be less than about 15m 2 / g, and may be less than about 20m 2 / g, as well as combinations and variations thereof, and larger and smaller values.

[0063] Generally, iron ore pellets are produced by crushing, grinding, or milling iron ore into a fine, powder-like form, which is then concentrated by removing impurity phases (so-called "gangue") liberated by the grinding operation. Generally, grinding the ore to a finer (smaller) particle size increases the purity of the resulting concentrate. The concentrate is then formed into pellets by a pelletizing or balling process (e.g., using a drum or disc pelletizer). Producing higher purity ore pellets generally requires a greater energy input. Iron ore pellets are generally commercially or sold in two main categories: blast furnace (BF)-grade pellets and direct reduction (DR-grade) (sometimes also referred to as electric arc furnace (EAF)-grade), with the primary difference being the content of SiO2 and higher amounts of other impurity phases in BF-grade pellets compared to DR-grade pellets. Typical critical specifications for DR grade pellets or feedstock are a total Fe content by mass in the range of 63-69 wt%, such as 67 wt%, and a SiO2 content by mass of less than 3 wt%, such as 1 wt%. Typical critical specifications for BF grade pellets or feedstock are a total Fe content by mass in the range of 60-67 wt%, such as 63 wt%, and a SiO2 content by mass in the range of 2-8 wt%, such as 4 wt%.

[0064] In certain embodiments, DRI can be produced by the reduction of "blast furnace" pellets, in which case the resulting DRI may have material properties as set forth below in Table 2. The use of reduced BF grade DRI can be advantageous because less input energy is required to produce the pellets, which translates to a lower cost of the finished product.

[0065] [Table 2]

[0066] *The specific surface area is preferably determined by the Brunauer-Emmett-Teller adsorption method ("BET"), more preferably BET as set forth in ISO 9277, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as methylene blue (MB) staining, ethylene glycol monoethyl ether (EGME) adsorption, electrokinetic analysis of complex ion adsorption, and protein retention (PR) methods, can be used to provide results that can be correlated with BET results.

[0067] ** Actual density is preferably determined by helium (He) pycnometer method, more preferably as set forth in ISO 12154, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests can be used to provide results that can be correlated with He pycnometer results. Actual density is sometimes also referred to in the art as "true density" or "skeletal density."

[0068] *** Apparent density is preferably determined by immersion in water, more preferably as set forth in ISO 15968, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests can be used to provide results that can be correlated with He pycnometer results. Porosity can be defined as the ratio of apparent density to actual density.

[0069]

number

[0070] **** d 孔、90%容積is preferably determined by mercury (Hg) intrusion porosimetry, more preferably as set forth in ISO 15901-1, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as gas adsorption, can be used to provide results that can be correlated with Hg intrusion results. 孔、90%容積 is the pore diameter above which 90% of the total pore volume resides.

[0071] ***** d 孔、50%表面積 is preferably determined by mercury (Hg) intrusion porosimetry, more preferably as set forth in ISO 15901-1, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as gas adsorption, can be used to provide results that can be correlated with Hg intrusion results. 孔、50%表面積 is the pore diameter above which 50% of the free surface area resides.

[0072] #Total Fe (wt%) is preferably determined by dichromate titration, more preferably as set forth in ASTM E246-10, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as tin(II) chloride reduction followed by titration, titanium(III) chloride reduction followed by titration, and inductively coupled plasma (ICP) spectroscopy, can be used to provide results that can be correlated to the dichromate titration method.

[0073] ##Metallic Fe (wt%) is preferably determined by iron(III) chloride titration, more preferably as set forth in ISO 16878, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as bromine-methanol titration, can be used to provide results that can be correlated to iron(III) chloride titration.

[0074] ### Metallization (%) is preferably determined by the ratio of metallic Fe to total Fe, each preferably determined by the method described above.

[0075] #### Carbon (wt%) is preferably determined by infrared absorption after induction furnace firing, more preferably as set forth in ISO 9556, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as various combustion and inert gas fusion techniques such as those set forth in ASTM E1019-18, can be used to provide results that can be correlated to infrared absorption after induction furnace firing.

[0076] #####Fe 2+ (wt %) is preferably determined by titration, more preferably as set forth in ASTM D3872-05, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as Mössbauer spectroscopy, X-ray absorption spectroscopy, and the like, can be used to provide results that can be correlated to titration.

[0077] Fe 3+ (wt%) is preferably total Fe (wt%), metallic Fe (wt%), Fe 2+ (wt%), and Fe 3+ It is determined by the mass balance relationship between or within the Fe (wt%). Specifically, total Fe (wt%) = metallic Fe (wt%) + Fe 2+ (Weight%)+Fe 3+ (wt%) must be true due to the law of conservation of mass, so Fe 3+ (wt%) is Fe 3+ (wt%) = total Fe (wt%) - metallic Fe (wt%) - Fe 2+ It can be calculated as a percentage by weight.

[0078] $$SiO2 (wt%) is preferably determined gravimetrically, more preferably as set forth in ISO 2598-1, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as reduced molybdosilicate spectrophotometry, X-ray diffraction (XRD), and the like, can be used to provide results that can be correlated to gravimetric methods. In certain methods, SiO2 wt% is not determined directly; rather, the Si concentration (including neutral and ionic species) is measured and SiO2 wt% is calculated assuming SiO2 stoichiometry; that is, a molar ratio of Si:O of 1:2 is assumed.

[0079] $$$Ferrite (wt%, XRD) is preferably determined by X-ray diffraction (XRD).

[0080] $$$$Wüstite (FeO, wt%, XRD) is preferably determined by X-ray diffraction (XRD).

[0081] $$$$$Goethite (FeOOH, wt%, XRD) is preferably determined by X-ray diffraction (XRD).

[0082] + Cementite (Fe3C, wt%, XRD) is preferably determined by X-ray diffraction (XRD).

[0083] Also, the properties shown in Table 2 may be present in embodiments along with, in addition to, or instead of the properties in Table 1 and / or Table 1A, and greater and lesser values ​​of such properties may be present in various embodiments.

[0084] In certain embodiments, DRI can be produced by reduction of DR grade pellets, in which case the resulting DRI may have material properties as set forth below in Table 3. The use of reduced DR grade DRI can be advantageous due to the higher Fe content in the pellets, which increases the energy density of the battery.

[0085] [Table 3]

[0086] * The specific surface area is preferably determined by the Brunauer-Emmett-Teller adsorption method ("BET"), more preferably BET as set forth in ISO 9277, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as methylene blue (MB) staining, ethylene glycol monoethyl ether (EGME) adsorption, electrokinetic analysis of complex ion adsorption, and protein retention (PR) methods, can be used to provide results that can be correlated with BET results.

[0087] ** Actual density is preferably determined by helium (He) pycnometer method, more preferably as set forth in ISO 12154, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests can be used to provide results that can be correlated with He pycnometer results. Actual density is sometimes also referred to in the art as "true density" or "skeletal density."

[0088] *** Apparent density is preferably determined by immersion in water, more preferably as set forth in ISO 15968, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests can be used to provide results that can be correlated with He pycnometer results. Porosity can be defined as the ratio of apparent density to actual density.

[0089]

number

[0090] **** d 孔、90%容積is preferably determined by mercury (Hg) intrusion porosimetry, more preferably as set forth in ISO 15901-1, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as gas adsorption, can be used to provide results that can be correlated with Hg intrusion results. 孔、90%容積 is the pore diameter above which 90% of the total pore volume resides.

[0091] ***** d 孔、50%表面積 is preferably determined by mercury (Hg) intrusion porosimetry, more preferably as set forth in ISO 15901-1, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as gas adsorption, can be used to provide results that can be correlated with Hg intrusion results. 孔、50%表面積 is the pore diameter above which 50% of the free surface area resides.

[0092] #Total Fe (wt%) is preferably determined by dichromate titration, more preferably as set forth in ASTM E246-10, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as tin(II) chloride reduction followed by titration, titanium(III) chloride reduction followed by titration, and inductively coupled plasma (ICP) spectroscopy, can be used to provide results that can be correlated to the dichromate titration method.

[0093] ##Metallic Fe (wt%) is preferably determined by iron(III) chloride titration, more preferably as set forth in ISO 16878, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as bromine-methanol titration, can be used to provide results that can be correlated to iron(III) chloride titration.

[0094] ### Metallization (%) is preferably determined by the ratio of metallic Fe to total Fe, each preferably determined by the method described above.

[0095] #### Carbon (wt%) is preferably determined by infrared absorption after induction furnace firing, more preferably as set forth in ISO 9556, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as various combustion and inert gas fusion techniques such as those set forth in ASTM E1019-18, can be used to provide results that can be correlated to infrared absorption after induction furnace firing.

[0096] #####Fe 2+ (wt %) is preferably determined by titration, more preferably as set forth in ASTM D3872-05, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as Mössbauer spectroscopy, X-ray absorption spectroscopy, and the like, can be used to provide results that can be correlated to titration.

[0097] $Fe 3+ (wt%) is preferably total Fe (wt%), metallic Fe (wt%), Fe 2+ (wt%), and Fe 3+ It is determined by the mass balance relationship between or within the Fe (wt%). Specifically, total Fe (wt%) = metallic Fe (wt%) + Fe 2+ (Weight%)+Fe 3+ (wt%) must be true due to the law of conservation of mass, so Fe 3+ (wt%) is Fe 3+ (wt%) = total Fe (wt%) - metallic Fe (wt%) - Fe 2+ It can be calculated as a percentage by weight.

[0098] $$SiO2 (wt%) is preferably determined gravimetrically, more preferably as set forth in ISO 2598-1, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as reduced molybdosilicate spectrophotometry, X-ray diffraction (XRD), and the like, can be used to provide results that can be correlated to gravimetric methods. In certain methods, SiO2 wt% is not determined directly; rather, the Si concentration (including neutral and ionic species) is measured and SiO2 wt% is calculated assuming SiO2 stoichiometry; that is, a molar ratio of Si:O of 1:2 is assumed.

[0099] $$$Ferrite (wt%, XRD) is preferably determined by X-ray diffraction (XRD).

[0100] $$$$Wüstite (FeO, wt%, XRD) is preferably determined by X-ray diffraction (XRD).

[0101] $$$$$Goethite (FeOOH, wt%, XRD) is preferably determined by X-ray diffraction (XRD).

[0102] + Cementite (Fe3C, wt%, XRD) is preferably determined by X-ray diffraction (XRD).

[0103] Also, the properties shown in Table 3 may be present in an embodiment along with, in addition to, or instead of the properties in Table 1, Table 1A, and / or Table 2. Also, greater and lesser values ​​of such properties may be present in various embodiments.

[0104] Electrochemical cells, such as batteries, store electrochemical energy by using differences in electrochemical potential to generate a voltage difference between positive and negative electrodes. When the electrodes are connected by a conductive element, this voltage difference produces an electric current. In a battery, the negative and positive electrodes are connected in parallel by an external and internal conductive element. Generally, the external element conducts electrons, and the internal element (electrolyte) conducts ions. Because a charge imbalance cannot be maintained between the negative and positive electrodes, these two flow streams must supply ions and electrons at the same rate. During operation, the electronic current can be used to power an external device. Rechargeable batteries can be recharged by applying an opposite voltage difference, which drives the electronic and ionic currents to flow in the opposite direction from a discharging battery during use.

[0105] However, in general, electrodes and electrode materials that are low cost and easy to manufacture are desirable, especially for long-term storage applications. Production and / or manufacturing processes can be evaluated and selected based on several criteria, including capital costs, material throughput, operating costs, number of unit operations, number of material transfers, number of material handling steps, energy inputs required, amount of waste and / or by-products generated, etc.

[0106] The present invention relates to materials, electrodes, and methods for electrochemical cells, including long-term electrochemical cells for long-term energy storage response.

[0107] Various embodiments are discussed regarding the use of metal agglomerates as battery (or cell) components, battery (or cell) materials such as electrodes, and combinations and variations thereof. In various embodiments, the iron material may be iron powder, such as gas-atomized or water-atomized powder or sponge iron powder. In various embodiments, the iron agglomerates may be in the form of pellets, which may be spherical or substantially spherical. In various embodiments, the agglomerates may be porous and may contain open and / or closed internal porosity. In various embodiments, the agglomerates may include material that has been further processed by hot or cold briquetting. Embodiments of the agglomerate material for use in various embodiments described herein, including use as an electrode material, may have one, more than one, or all of the material properties as set forth in Table 4 below. As used herein, including in Table 4, the following terms have the following meanings unless expressly stated otherwise: "Specific surface area" means the total surface area of ​​a material per unit mass, including the surface area of ​​pores in a porous structure; "Total Fe (wt%)" means the mass of all iron as a percentage of the total mass of the agglomerate; "Metallic Fe (wt%)" means the mass of Fe as a percentage of the total mass of the agglomerate. 0 means the mass of iron in the state.

[0108] [Table 4]

[0109] * The specific surface area is preferably determined by the Brunauer-Emmett-Teller adsorption method ("BET"), more preferably BET as set forth in ISO 9277, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as methylene blue (MB) staining, ethylene glycol monoethyl ether (EGME) adsorption, electrokinetic analysis of complex ion adsorption, and protein retention (PR) methods, can be used to provide results that can be correlated with BET results.

[0110] ** Skeletal density is preferably determined by helium (He) pycnometer method, more preferably as set forth in ISO 12154, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests can be used to provide results that can be correlated with He pycnometer results. Skeletal density is sometimes also referred to in the art as "true density" or "actual density."

[0111] *** Apparent density is preferably determined by immersion in water, more preferably as set forth in ISO 15968, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests can be used to provide results that can be correlated with He pycnometer results. Porosity can be defined as the ratio of apparent density to actual density.

[0112]

number

[0113] #Total Fe (wt%) is preferably determined by dichromate titration, more preferably as set forth in ASTM E246-10, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as tin(II) chloride reduction followed by titration, titanium(III) chloride reduction followed by titration, and inductively coupled plasma (ICP) spectroscopy, can be used to provide results that can be correlated to the dichromate titration method.

[0114] ##Metallic Fe (wt%) is preferably determined by iron(III) chloride titration, more preferably as set forth in ISO 16878, the disclosure of which is incorporated herein by reference in its entirety. It is recognized that other tests, such as bromine-methanol titration, can be used to provide results that can be correlated to iron(III) chloride titration.

[0115] In an embodiment, the specific surface area of ​​the agglomerates is about 0.05 m 2 / g ~ approx. 35m 2 / g, approx. 0.1m 2 / g~about 5m 2 / g, approx. 0.5m 2 / g~about 10m 2 / g, approx. 0.2m 2 / g~about 5m 2 / g, approx. 1m 2 / g~about 5m 2 / g, approx. 1m 2 / g~about 20m 2 / g, and about 1m 2 / g, and is about 2m 2 / g, and is about 5m 2 / g, and may be less than about 15m 2 / g, and may be less than about 20m 2 / g, as well as combinations and variations thereof, and larger and smaller values.

[0116] The packing of the agglomerates creates macropores, e.g., openings, spaces, channels, or voids, between the individual agglomerates. The macropores facilitate ion transport across the electrode, which in some embodiments has minimum dimensions that are multiple centimeters in size, yet is very thick compared to some other types of battery electrodes. The micropores within the agglomerates allow contact between the high surface area active material of the agglomerates and the electrolyte, allowing for high availability of the active material. As such, this electrode structure is particularly useful for improving the rate capability of very thick electrodes for stationary, long-term energy storage, where thick electrodes may be necessary to achieve very high areal capacity.

[0117] In various embodiments, a bed of conductive microporous agglomerates constitutes an electrode of an energy storage system. In some embodiments, the agglomerates comprise direct reduced iron (DRI) agglomerates. Packing of the agglomerates creates macropores between the individual agglomerates. The macropores facilitate ion transport across the electrode, which in some embodiments has minimum dimensions that are multiple centimeters in size, yet is very thick compared to some other types of battery electrodes. The macropores can form a less tortuous pore space compared to the micropores within the agglomerates. The micropores within the agglomerates allow contact between the high surface area active material of the agglomerates and the electrolyte, enabling high active material availability. As such, this electrode structure is particularly useful for improving the rate capability of very thick electrodes for stationary, long-term energy storage, where thick electrodes may be necessary to achieve very high areal capacity.

[0118] The agglomerates of these embodiments, particularly those for use in electrode embodiments for long-term energy storage systems, may be any volumetric shape, such as spheres, disks, pucks, beads, tablets, pills, rings, lenses, discs, panels, cones, truncated cones, square blocks, rectangular blocks, trusses, angles, channels, hollow enclosed chambers, hollow spheres, blocks, sheets, films, particulates, beams, rods, angles, slabs, cylinders, columns, fibers, synthetic fibers, tubes, cups, pipes, and combinations and variations thereof, as well as other more complex shapes. The electrode agglomerates may be the same shape or different shapes. The agglomerates of one electrode in a long-term energy storage system may be the same or different from the agglomerates of other electrodes in the storage system.

[0119] Agglomerate size, unless expressly used otherwise, refers to the largest cross-sectional distance of the agglomerate, e.g., the diameter of a sphere. The agglomerates may be the same size or different sizes. It is recognized that both the shape and size of the agglomerate, and typically, to a lesser extent, the shape and size of the container or housing that holds the agglomerate, determine the nature and size of the electrode's macropores. Agglomerates may have sizes from about 0.1 mm to about 10 cm, from about 5 mm to about 100 mm, from 10 mm to about 50 mm, about 20 mm, about 25 mm, about 30 mm, greater than 0.1 mm, greater than 1 mm, greater than 5 mm, greater than 10 mm, and greater than 25 mm, as well as combinations and variations thereof.

[0120] In an embodiment, the agglomerates configured in the electrode have a mass of about 3 g / cm 3 ~Approx. 6.5g / cm 3 of approximately 0.1 g / cm 3 ~Approx. 5.5g / cm 3 of approximately 2.3 g / cm 3 ~Approx. 3.5g / cm 3 of 3.2g / cm 3 ~Approx. 4.9g / cm 3 of about 0.5g / cm 3 Larger than about 1 g / cm 3 Larger than about 2g / cm 3 Larger than approx. 3g / cm 3 Electrodes having bulk densities greater than or equal to 1000 .mu.m, as well as combinations and various values, as well as larger and smaller values, can be provided.

[0121] In various embodiments, additives beneficial to the electrochemical cycle, such as hydrogen evolution reaction (HER) inhibitors, may be added to the bed in solid form, for example, as a powder or as solid pellets.

[0122] In some embodiments, the metal electrode has a low initial specific surface area (e.g., about 5 m 2 / g, preferably less than about 1 m 2 / g). Such electrodes tend to exhibit low self-discharge rates in low-rate, long-term energy storage systems. One example of a low-surface-area metal electrode is a bed of agglomerates. In many typical modern electrochemical cells, such as lithium-ion or nickel-metal hydride batteries, a high specific surface area is desirable to facilitate high rate capacity (i.e., high power output). In long-term systems, the need for rate capacity is significantly reduced, so a low-surface-area electrode can meet the target rate capacity need while minimizing the self-discharge rate.

[0123] In another embodiment, desirable impurities or additives are incorporated into the agglomerates. If the impurities are solid, they can be incorporated by ball milling the powdered additives with the metal powder (e.g., using a planetary ball mill or similar device). In this case, the agglomerates themselves act as the milling media. In this way, the powdered additives are mechanically introduced into the pores or surfaces of the agglomerates. The agglomerates may also be coated with beneficial additives, for example, by rolling or immersing them in a slurry containing the additives. Such desirable impurities can include alkali sulfides. Alkali sulfide salts have been demonstrated to significantly improve active material utilization in Fe anodes. Just as soluble alkali sulfides can be added to the electrolyte, insoluble alkali sulfides can be added to the agglomerates, for example, by the methods described above.

[0124] In various embodiments, the specific surface area of ​​the agglomerates is increased by a factor of 3 or more, preferably a factor of 5 or more, as measured by techniques such as Brunauer-Emmett-Teller gas adsorption. In some embodiments, this surface area increase is achieved by using the agglomerates as electrodes in an electrochemical cell and electrochemically reducing them with an applied current.

[0125] The ratio of electrolyte to iron material, e.g., cell agglomerates, is about 0.5 mL. 電解質 :1g 鉄材料 ~about 5mL 電解質 :1g鉄材料 , approximately 0.6 mL 電解質 :1g 鉄材料 ~about 3mL 電解質 :1g 鉄材料 , approximately 0.6 mL 電解質 :1g 鉄材料 , about 0.7mL 電解質 :1g 鉄材料 , approximately 0.8 mL 電解質 :1g 鉄材料 , approximately 1 mL 電解質 :1g 鉄材料 , as well as combinations and variations thereof, and larger and smaller ratios.

[0126] A packed bed of agglomerates can be a desirable configuration for iron-based electrodes because it provides an electronically conductive percolation path through the packed bed while leaving porosity available for electrolyte occupancy to facilitate ion transport. In certain embodiments, the ratio of electrolyte volume to agglomerate mass can range from 0.5 mL / g to 20 mL / g, such as 0.5 mL / g to 5 mL / g, or 0.6 mL / g or 1.0 mL / g. Agglomerates generally contact surrounding agglomerates through a small contact area relative to the agglomerate's surface area; in some cases, the contact can be considered a "point contact." Small cross-sectional area contacts can represent constrictions for current flow, resulting in relatively low electrical conductivity throughout the agglomerate bed, which in turn can lead to high electrode overpotentials and low battery voltage efficiency.

[0127] In some embodiments, an additive containing molybdate ions is used in alkaline batteries containing iron anodes. Without being bound by any particular scientific interpretation, such additives can help suppress the hydrogen evolution reaction (HER) at the iron electrode and improve the cycling efficiency of the battery. The concentration of the additive is selected to suppress the HER while still allowing the desired iron charge / discharge process. As an example, molybdate ions can be added via a molybdate compound such as KMoO4. In one specific example, the electrolyte contains an additive at a concentration of 10 mM (mM is millimolar, 10 -3In another embodiment, the electrolyte contains an additive concentration of molybdate anion in the range of 1 to 100 mM.

[0128] In some embodiments, surfactants are used to control wetting and foaming during operation of metal-air batteries. During charging, at least two gas-evolving reactions can occur that lead to bubble formation. One is hydrogen evolution at the metal anode, a parasitic reaction that can contribute to poor coulombic efficiency during battery cycling. The other is the oxygen evolution reaction, which is necessary for the function of metal-air batteries. Surfactant additives can mitigate the undesirable effects associated with both reactions. In the case of HER, hydrophobic surfactant additives can suppress the hydrogen evolution reaction at the metal anode by physically blocking water (an HER reactant) from the metal anode during charging. In the case of ORR, surfactant additives can reduce the electrolyte surface tension and viscosity at the oxygen evolution electrode, allowing for the generation of smaller, more uniformly sized, and more controllable bubbles during charging. In one non-limiting example, 1-octanethiol is added to the alkaline electrolyte at a concentration of 10 mM to mitigate both of these issues.

[0129] In some embodiments, corrosion inhibitors used in the field of iron metallurgy to inhibit aqueous corrosion are used as components of batteries having iron negative electrodes to improve performance. In some embodiments, iron agglomerates are used as negative electrodes, and advantageous performance characteristics can be achieved by using one or more corrosion inhibitors in a suitable concentration range. These embodiments use principles of corrosion science to prevent undesirable side reactions (e.g., hydrogen evolution) under charging conditions, mitigate the rate of spontaneous self-discharge during electrochemical hold, and maximize the availability of iron active material during discharge. Generally, there are two types of corrosion inhibitors: interface inhibitors, which react with metal surfaces at the metal-environment interface to prevent corrosion, and environmental scavengers, which remove corrosive elements from the environment surrounding the metal surface to inhibit corrosion. Under the broad protection of corrosion inhibitors, appropriate concentrations of inhibitors can be added to electrochemical cells to achieve advantageous performance characteristics in terms of electrochemical cell efficiency and capacity. For the iron electrode of a metal-air battery, one applicable general type of inhibitor is a liquid and phase-interface inhibitor. This category encompasses three major types of interfacial inhibitors: anodic inhibitors, cathodic inhibitors, and mixed inhibitors. Anodic inhibitors create a passivating layer that inhibits the anodic metal dissolution reaction. Cathodic inhibitors can either reduce the rate of the reduction reaction (HER, in the case of iron electrodes) or precipitate at the cathodic active site to block the same reduction reaction. Mixed inhibitors can inhibit corrosion through one or both pathways and include, but are not limited to, molecules that physically or chemically adsorb to the metal surface to form a film that can block the active site for the reduction reaction. Inhibitors can be added to the base electrolyte at any concentration.

[0130] In various embodiments, an inhibitor that forms a passivating layer on the metal surface is paired with an additive that depassivates the iron surface. With the correct concentrations, an optimal balance of corrosion inhibition and active material availability can be achieved. In one specific embodiment, when direct reduced iron is used as the anode, an alkaline electrolyte composed of 5.5 M potassium hydroxide or sodium hydroxide is used with 10 mM molybdate anion as the passivating agent and 10 mM sulfide anion as the depassivating agent. Specific examples of electrolyte compositions include 5.5M KOH + 0.5M LiOH + 10mM Na2S + 10mM 1-octanethiol; 5.95M NaOH + 50mM LiOH + 50mM Na2S + 10mM 1-octanethiol; 5.95M NaOH + 50mM LiOH + 50mM Na2S + 10mM 1-octanethiol + 10mM K2MoO4; and 5.95M NaOH + 50mM LiOH + 50mM Na2S + 10mM K2MoO4. However, the present disclosure is not limited to any particular concentration of the additives in the electrolyte. For example, one or more of the additives may be included in the electrolyte at a concentration ranging from about 2mM to about 200mM, such as from about 5mM to about 50mM or from about 5mM to about 25mM.

[0131] For physically adsorbed (chemisorbed or physisorbed) inhibitors, the interaction with the metal surface is often strongly temperature dependent.

[0132] In one embodiment, an inhibitor is used where desorption of the inhibitor from the iron surface can be advantageous at temperatures lower than normal operating temperatures. During charging, the inhibitor forms a film that inhibits hydrogen evolution at the electrode. During discharge, the cell temperature can be increased or decreased to desorb the inhibitor from the metal surface, exposing the active material and allowing for improved electrode utilization. During subsequent charging, the cell temperature can be returned to normal operating temperatures to reform the film and inhibit HER. This process can be repeated to achieve high charge efficiency and high discharge utilization of the iron electrode. In one non-limiting example, octanethiol can be used as an inhibitor that can be physisorbed or chemisorbed to a metal anode (e.g., Fe, Ni). Heat treatment of the electrochemical cell to 60°C desorbs the physisorbed octanethiol, exposing more active sites that can be oxidized during discharge. Then, upon cooling, free octanethiol in the electrolyte physisorbs back to the anode. At higher temperatures (>60°C), octanethiol can chemisorb to the electrode and form a continuous, uniform film across the surface. These chemisorbed species can be desorbed more effectively at low temperatures (<100°C).

[0133] To enable performance at higher temperatures, organic film-forming inhibitors with oxygen, sulfur, silicon, or nitrogen functional groups can be used to form continuous chemisorbed films on iron particle electrodes, replicating the passivation behavior of sulfides while being resistant to decomposition or oxidation.

[0134] In one embodiment, 1-10 mM octanethiol is added to the electrolyte. During charging, the system is heated to a temperature outside of normal operating conditions (e.g., >50°C) to promote the formation of a more complete and uniform chemisorbed octanethiol film across the active sites of the iron particle electrode, preventing hydrogen evolution at the surface. During discharge, the system is cooled, causing portions of the chemisorbed film to desorb from the surface, exposing additional active sites for discharge. The remaining octanethiol acts to depassivate the electrode, promoting more complete discharge. Figure 1 illustrates an exemplary method for promoting such complete discharge. For example, Figure 1 shows an electrode 102 in a discharged state at the top of the figure. Potential hydrogen evolution reaction (HER) sites 104 were created during discharge when the octanethiol film desorbed from the surface of the electrode 102. As shown in the center of Figure 1, the next step in this method involves adding 1-10 mM octanethiol to the electrolyte 103. During charge, the system can be heated to temperatures outside normal operating conditions (e.g., >50°C) to promote the formation of a more complete and uniform chemisorbed octanethiol film across the active sites of the iron particle electrode 102, which can file onto potential HER sites 104 and prevent hydrogen evolution on the surface of the electrode 102. During discharge, the system is cooled, causing portions of the chemisorbed film to desorb from the surface, exposing additional active sites for discharge, such as HER sites 104. The remaining octanethiol acts to depassivate the electrode 102, promoting a more complete discharge.

[0135] During electrochemical rest periods, it is desirable to minimize corrosion of the metal electrode. One type of corrosive medium for iron metal electrodes in aqueous electrolytes is dissolved oxygen. During electrochemical hold, dissolved oxygen can come into contact with the iron electrode, corroding the active material and potentially discharging the iron electrode.

[0136] In one embodiment, oxygen scavengers (e.g., pyrogallol, ascorbic acid, 8-hydroxyquinoline, sodium peroxide, hydrogen peroxide) can be added to the electrolyte during electrochemical retention to reduce the concentration of dissolved oxygen in the electrolyte and prevent discharge of the iron electrode.

[0137] In one embodiment, an anodic corrosion inhibitor (e.g., K2MoO4) is added to the electrolyte at a concentration of 1-10 mM prior to electrochemical storage to create a passive film that shields the metal surface from the corrosive medium in the electrolyte and prevents self-discharge. If the electrode must be discharged after electrochemical storage, highly aggressive ions (e.g., SO4 2- , CrO4 - , NO3 - ) is added to the electrolyte to expose the active material and achieve high availability of the active material, thus reducing self-discharge.

[0138] In certain embodiments, other corrosion inhibitors are incorporated into the electrolyte as additives (i.e., as minor components). The electrolyte additives may be selected from the following non-limiting set: sodium thiosulfate, sodium thiocyanate, polyethylene glycol (PEG) 1000, trimethylsulfoxonium iodide, zincate (by dissolving ZnO in NaOH), hexanethiol, decanethiol, sodium chloride, sodium permanganate, lead (IV) oxide, lead (II) oxide, magnesium oxide, sodium chlorate, sodium nitrate, sodium acetate, iron phosphate, phosphoric acid, sodium phosphate, ammonium sulfate, ammonium thiosulfate, lithopone. , magnesium sulfate, iron(III) acetylacetonate, hydroquinone monomethyl ether, sodium metavanadate, sodium chromate, glutaric acid, dimethyl phthalate, methyl methacrylate, methylpentynol, adipic acid, allyl urea, citric acid, thiomalic acid, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, propylene glycol, trimethoxysilylpropyldiethylene, aminopropyltrimethoxysilane, dimethylacetylenedicarboxylate (DMAD), 1,3-diethylthiourea, N,N'-Diethylthiourea, aminomethylpropanol, methylbutynol, amino-modified organosilane, succinic acid, isopropanolamine, phenoxyethanol, dipropylene glycol, benzoic acid, N-(2-aminoethyl)-3-aminopropyl, behenamide, 2-phosphonobutanetricarboxylic acid, MIPA borate, 3-methacryloxypropyltrimethoxysilane, 2-ethylhexanoic acid, isobutyl alcohol, t-butylaminoethyl methacrylate, diisopropanolamine, propylene glycol n-propyl ether, sodium benzotriazole, aminotrimethylenephosphonic acid Ingredients: pentasodium cocoyl sarcosinate, sodium cocoyl sarcosinate, lauryl pyridinium chloride, steartrimonium chloride, stearalkonium chloride, calcium montanate, quaternium-18 chloride, sodium hexametaphosphate, dicyclohexylamine nitrite, lead stearate, calcium dinonylnaphthalene sulfonate, iron(II) sulfide, sodium hydrogen sulfide, iron pyrite, sodium nitrite, complex alkyl phosphate ester (e.g., RHODAfAC® RA600 emulsifier), 4-mercaptobenzoic acid, ethylenediaminetetraacetic acid, ethylenediaminetetraacetate (EDTA), 1,3-Propylenediaminetetraacetate (PDTA), nitrilotriacetate (NTA), ethylenediamine disuccinate (EDDS), diethylenetriaminepentaacetate (DTPA), and other aminopolycarboxylates (APC), diethylenetriaminepentaacetic acid, 2-methylbenzenethiol, 1-octanethiol, manganese dioxide, manganese(III) oxide, manganese(II) oxide, manganese oxyhydroxide, manganese(II) hydroxide, manganese(III) hydroxide, bismuth sulfide, bismuth oxide, antimony sulfide Iron(III), antimony(III) oxide, antimony(V) oxide, bismuth selenide, antimony selenide, selenium sulfide, selenium(IV) oxide, propargyl alcohol, 5-hexyn-1-ol, 1-hexyn-3-ol, N-allylthiourea, thiourea, 4-methylcatechol, trans-cinnamaldehyde, iron(III) sulfide, calcium nitrate, hydroxylamine, benzotriazole, furfurylamine, quinoline, tin(II) chloride, ascorbic acid, 8-hydroxyquinoline, pyrogallol, tetraethyl hydroxide ammonium, calcium carbonate, magnesium carbonate, antimony dialkyldithiophosphate, potassium stannate, sodium stannate, tannic acid, gelatin, saponin, agar, 8-hydroxyquinoline, bismuth stannate, potassium gluconate, lithium molybdenum oxide, potassium molybdenum oxide, hydrogenated light oil, heavy naphthenic petroleum fractions (e.g., sold as Rustlick® 631), antimony sulfate, antimony acetate, bismuth acetate, hydrotreated heavy naphtha (e.g., sold as WD-40®), (Illegible text - likely OCR error), tetramethylammonium hydroxide, NaSb tartrate, urea, D-glucose, C6Na2O6, potassium antimony tartrate, hydrazine sulfate, silica gel, triethylamine, potassium antimonate trihydrate, sodium hydroxide, 1,3-di-o-tolyl-2-thiourea, 1,2-diethyl-2-thiourea, 1,2-diisopropyl-2-thiourea, N-phenylthiourea, N-diphenylthiourea, sodium antimony L-tartrate, rhodizonic acid disodium salt, sodium selenide, potassium sulfide, and combinations thereof.

[0139] Additional additives include SiO2-containing minerals, which can have a beneficial effect on electrochemical performance through the uptake of carbonate from the electrolyte or electrode. Additives containing such functional groups can be usefully incorporated into iron electrode materials. While the exact SiO2-containing material to be added can be determined depending on the specific mineralogical characteristics of the ore and other factors, examples of such SiO2-containing additives include silica, cristobalite, sodium silicate, calcium silicate, magnesium silicate, and other alkali metal silicates.

[0140] In certain embodiments, electrode agglomerates are prepared by agglomerating metal powder, such as iron-containing powder, into approximately spherical agglomerates. In various embodiments, agglomeration is carried out at or near room temperature, at or near ambient outdoor temperature, or at elevated temperatures. In various embodiments, agglomeration is carried out in a rotary kiln, where the powder is simultaneously agglomerated and sintered. In certain embodiments, iron powder, such as atomized iron powder, sponge iron powder, iron filings, mill scale, carbonyl iron powder, electrolytic iron powder, and combinations or variations thereof, is used as the feedstock. In various embodiments, the heat treatment process is carried out at a temperature, such as from about 700°C to about 1200°C, such as from about 800°C to about 1000°C. In various embodiments, the gas environment is inert (including N2 or Ar) or reducing (including H2, CO2, CO, etc.), or a combination thereof. In various embodiments, the heat treatment process completely or partially sinters the powder together to create the agglomerates. In various embodiments, the agglomerates are 10 um, 100 um, or 1 mm (mm = 10 -3 m), 1um (um=10 -6 m)~1cm(cm=10 -2 The size ranges from 100 to 1200 mm.

[0141] In certain embodiments, the feedstock material is a material known in the art, such as pig iron, granular pig iron, nodular reduced iron, scrap iron, and / or scrap steel.

[0142] In various embodiments, fine iron powder, with a substantial population of powder particles less than 44 microns (often described as -325 mesh because such particles will pass through a 325 mesh sieve), may be used as part of the feedstock material or may entirely constitute the feedstock material.

[0143] In certain embodiments, the electrode is fabricated by electrochemically depositing iron from an aqueous solution. In certain embodiments, the deposition solution is acidic, having a pH less than about 4, such as about pH 3 or about pH 2. In certain embodiments, the solution is nearly neutral, having a pH between about 4 and about 10, such as about pH 5 or about pH 7 or about pH 9. In certain embodiments, the electrolyte includes a salt, such as NaCl, LiCl, or KCl. In certain embodiments, the liquid electrolyte is agitated by stirring, shaking, mixing, or turbulence to promote a non-uniform deposition rate and a porous structure. In certain embodiments, the liquid electrolyte is sparged or aspirated to introduce air bubbles into the liquid during the deposition process.

[0144] In certain embodiments, iron powder is prepared by an electrometallurgical process to fabricate porous iron. Working from the melt, iron-bearing metal is sprayed, bubbled, or cast onto a substrate or into a mold to produce low-cost, high-surface-area iron products. In certain embodiments, these powders can then be agglomerated using a rotary kiln or other method and then assembled into electrodes. In certain embodiments, the powders are assembled directly into electrodes without an intermediate agglomeration process. In certain embodiments, a mixture or combination of agglomerated and non-agglomerated powders is used in the electrode. In certain embodiments, agglomerated and / or non-agglomerated powders produced by electrometallurgical processes are combined with other metals to manufacture electrodes.

[0145] Electrochemically produced metals offer a unique opportunity for producing high surface area materials, especially when the metal is in a liquid state. In this case, the resulting liquid product can be cooled in a variety of ways to achieve desired properties. For example, iron produced by high-temperature electrometallurgy can be cooled directly in a high-surface area die, spray-deposited (atomized) into particles, or dispersed in a cooling medium.

[0146] In certain embodiments, metal electrodes are prepared directly by electrometallurgical processes such as molten oxide electrolysis. In certain embodiments, porous electrodes are fabricated by intentionally aspirating or sparging a gas into a molten oxide electrolysis cell. In certain embodiments, the gas is an inert gas such as N or Ar.

[0147] In certain embodiments, molten metal from an electrometallurgical process is sprayed, bubbled, or cast onto a substrate or into a mold to produce low-cost, high-surface-area metal electrodes. In certain embodiments, the metal is substantially iron.

[0148] In one non-limiting example, iron ore containing Fe2O3, Fe3O4, and mixtures thereof is dissolved in an electrolyte containing SiO2, Al2O3, MgO, and CaO in weight ratios of 60%, 20%, 10%, and 10%, respectively. The mixture is heated to a high temperature of approximately 1600°C. Metallic iron is electrochemically reduced from the molten oxide mixture and pooled at the cathode. The molten metal is transported by pipes and valves to a shot tower, where it is rapidly cooled in a vacuum to produce iron ore with an average diameter of 50 um (um = 10 -6 The iron powder is then passed through a rotary calciner operating at 900°C under a nitrogen (100% N2) atmosphere to form agglomerates with an average diameter of 2 mm, which are then packed together to assemble into metal electrodes.

[0149] In certain embodiments, electrodes can be fabricated by thermochemical reduction of iron oxide. In some embodiments, reduction can proceed such that the iron oxide is nearly to completely reduced to metallic iron. Nearly complete reduction of iron oxide to metallic iron is the goal of many industrial thermochemical iron reduction processes. However, there are many possible reasons why incomplete reduction of iron oxide to metallic iron would make such incompletely reduced products particularly useful for creating iron batteries. First, some of the oxide phases created during iron reduction are semiconducting and therefore can serve a useful role as electronic conductors in iron electrode materials. For example, magnetite is fairly conductive near room temperature. Wustite is less conductive than magnetite, but is still highly conductive compared to most oxides. In some embodiments, the semiconducting properties of wustite and magnetite can be exploited to form battery electrodes, which may be composites with metallic iron. Additionally, partially reduced products can be more electrochemically active. The inventors have observed that wustite can be even more electrochemically active than metallic iron in some circumstances. Because wustite has a higher oxidation state than metallic iron, thermochemical reduction can be cheaper. Therefore, wustite can be cheaper and more powerful than iron as a component of a battery electrode. In one embodiment, positive electrodes for alkaline iron batteries can be produced from hardened pellets composed of hematite, traditionally fed to a direct reduction or blast furnace process. The pellets can be reduced in a vertical shaft furnace with an appropriate mixture of hydrocarbons and other reducing gases known in the field of direct iron reduction. The reduction process may be terminated when up to 95% metallization is achieved (metallization is a term used in the field of direct iron reduction to describe the percentage of iron atoms that are fully metallic in their oxidation state). In some cases, lower metallization, as low as 0%, may be preferred, yielding large amounts of magnetite and wustite as alternative battery input materials. The resulting partially reduced pellets, chunks, shards, or other particles can be packed into a particle bed to serve as iron electrode material.The electrode material may consist entirely of iron oxide or may comprise primarily a mixture of magnetite and wustite.

[0150] Current collection, compression, and other means to enhance charge transfer

[0151] In some cases, porous iron electrode materials can suffer from high electrical resistance when assembled into a bed. Therefore, the performance of iron electrode materials in batteries can be enhanced by methods for reducing the resistance to charge transfer between and within the particulate materials and by enhanced methods for current collection from the electrode active material. This section describes methods for enhancing charge transfer from within the packed bed to the current collector.

[0152] Through experiments, the inventors have discovered that applying compressive stress to the anode bed during battery cycling can enhance the performance of porous iron electrodes. For example, applying a uniaxial compressive stress of 0.01 MPa or greater can reduce the contact resistance between porous particulate materials by more than an order of magnitude. Excessive compressive stress can lead to localized failure of the electrode material due to cracking (and thus potentially localized reductions in electrical conduction), densification due to deformation of the porous iron electrode material without cracking (which in turn can reduce the pore space available for discharge product formation or reduce mass transport through the pore space), or other mechanical failure modes. Applying compressive stresses in excess of those required to reduce contact resistance without material failure can increase the performance of the porous iron electrode material during electrochemical cycling. Within this framework, further increases in compressive stress and different configurations of compressive stress can be used to increase the conductivity of the bed, with stresses on the order of 0.1 to 10 MPa providing performance enhancements in some systems. As the applied stress (and therefore force) increases, the requirements for a mechanical enclosure capable of successfully applying such stress become more stringent, generally increasing the cost of the enclosure. Thus, in one aspect, a mechanical structure that simultaneously allows current collection and compression of the porous iron electrode material with stresses of 0.1 to 10 MPa is a particularly useful means for containing the iron electrode material within an electrochemical cell.

[0153] In various embodiments, it may be useful for a current collector to perform multiple functions in the cell, including serving as a structural member. In one example, the current collector can extend through the center of a packed bed of particulate material to provide structural support to the electrode. In some embodiments, a packed bed can have current collectors on both sides in addition to a central current collector. In some embodiments, the current collector in the center of the packed bed may be fabricated from a sheet without perforations, while the current collectors on the outer surfaces may be perforated or otherwise contain holes to facilitate ion transport to the electrode active material. In various embodiments, the air electrode or other positive electrode material may be positioned adjacent to the iron electrode material on both sides, for example, because a plane of symmetry exists for transport, so that ions do not have to flow through the electrode material across a given depth of the electrode. In this way, the lack of perforations in the current collectors included in the center of the bed can usefully reduce the cost of the central current collecting sheet with little or no effect on transport within the system. The iron electrode material may be mounted to or compressed against a structural support and current collector combination contained in the center of the packed bed. Additional functions performed by the iron electrode current collecting components may include anode positioning / mounting, enhanced current collection, separation of adjacent cells, and voltage stacking.

[0154] The extent to which the resistivity of a porous electrode must be reduced to reach a given level of electrochemical performance is a function of the current collection method as well as the material properties. If current is collected to the current collector from more sides or over a shorter total path length, the battery may be able to operate efficiently over higher resistivity paths due to a lower final voltage drop. Thus, the compaction and current collection strategies of the porous iron electrode can be usefully co-optimized to produce a system with the lowest total cost for a given level of performance. Below are presented a set of techniques and designs for collecting current from and compacting porous electrode beds that can be used in combination or separately to produce high-performance porous battery electrodes at low cost.

[0155] The current collecting material may be any of those used in the art for collecting current in alkaline batteries at potentials to which an alkaline iron-based battery anode may be exposed. The composition of the electrolyte, the specific potentials used during battery cycling, and other process variables (e.g., temperature) will determine the degree to which various current collecting materials are stable. These materials may include nickel, nickel-plated stainless steel, copper, copper-plated stainless steel, full thickness iron, carbon fiber and other carbon-based materials, and cobalt ferrite-coated iron.

[0156] In one aspect, the reactor containing the porous iron electrode may be partitioned into horizontal layers that are contained within a larger container. Figures 2 and 3 show an exemplary aspect of such an embodiment in which a larger container 202 is partitioned into horizontal layers 203-207. With reference to Figures 2 and 3, these horizontal layers (e.g., 203-207) may be referred to as packets. Within each of these horizontal layers (e.g., 203-207), the anode, such as particulate anode material 212, may be compressed by any method applicable to compressing and storing particulate material. In doing so, current collecting dividers 210 between the packets may be inserted into the larger container 202 holding the packets (e.g., 203-207). Tabs 215 or other compliant conductive features on the dividers 210 may be used to hold the compression forcibles (e.g., dividers 210) of the packets (e.g., 203-207) in place while also serving as a means of current collection. This is illustrated in Figures 2 and 3. The divider 210 may also include an optional catch lip 216 on the side.

[0157] In one embodiment, the current collector may be a woven metallic fabric or other conductive fabric. Examples include mesh woven with nickel, copper, or graphite fibers. The current collector may surround or be laminated to the electrode material. The current collector fabric may surround a bed of direct reduced iron (DRI) pellets as the electrode, as described below. The fabric may be pinched, drawn, or otherwise in intimate mechanical contact with the electrode material to promote sufficient electrical contact. An illustrative example is shown in FIG. 4 for a woven metal fabric 402 having an electrode composed of direct reduced iron pellets 403. The woven metal fabric 402 may be a mesh or sieve that encases the DRI pellets 403 and provides a compressive force or load 404 to the DRI pellets 403, forcing them together within the mesh of the woven metal fabric 402 and establishing intimate contact between the metal fabric 402 and the DRI pellets 403. The current 405 can be collected by the metal fabric 402 .

[0158] In another embodiment, a conductive mesh pouch or bag can be used as a means for simultaneously compressing and collecting current from the electrode material. More specifically, the mesh pouch or bag can be filled with particulate iron electrode material, and the bag can be tightened or otherwise reduced in volume via a belt, string, wire, or other tightening mechanism to apply compression to the anode material. A conductive mesh tube or similar can be filled with the particulate iron electrode material, and the electrode material can be compressed by applying axial tension to the conductive mesh tube. In such cases, the mesh weave can be optimized so that the mesh tube experiences substantial compression upon application of axial tension. This can be understood similarly to a Chinese finger trap, where the diameter of the fabric tube narrows as it is stretched axially. The amount of compression applied to the particulate iron material can be adjusted by the thickness of the fabric strands, the density of the fabric strands, and the amount of axial force / tension applied to the fabric. In some cases, the porous iron electrode material can be composed of direct-reduced iron pellets. In some cases, the porous iron electrode material may be comprised of crushed direct reduced iron pellets. In some cases, a binder may be usefully included in the particulate iron material to aid in adhesion of the pellets.

[0159] In some embodiments, the porous mesh container and particulate active material may be arranged in a geometrical manner similar to a tea bag and tea leaves, as shown, for example, in Figures 5 and 6. Figure 5 shows a single-tie configuration 500 in which a porous mesh bag 501 is tied at a single tie point 503 by a current collector 502. Figure 6 shows a double-tie configuration 600 in which a porous mesh bag 501 is tied at a first tie point 503 by a current collector 502 and a second tie point 602. The tea bag container (e.g., 501) is electrically conductive and can serve as a current collector. In some embodiments, the tea bag container (e.g., 501) may have a current collector disposed inside the tea bag container envelope. The tea bag container (e.g., 501) may have knots to aid in compression, including knots that are not at the top of the tea bag container (e.g., 501), such as second tightening knot 602 or other positioned tightening knots. The tea bag container (e.g., 501) may also have knots at the top of the container to maintain actives within the container. In another aspect, the tea bag container (e.g., 501) may be non-conductive, and current collection may be accomplished only via a current collector positioned inside the envelope of the tea bag container.

[0160] In another embodiment, a loose, flexible, conductive sheet may be loosely attached at its edges to a backing plate, which may or may not be rigid, to form a pouch. The flexible sheet and a fastener, such as a wire inserted from the back, are opened to allow the pouch to be filled with pellet or powder anode material. The fastener can be pulled closed to compress the anode and used for current collection. The fastener wire may be conductive and serve as an additional current collector distributed throughout the pouch. The pouch may also be attached in a rigid manner (e.g., by welding) or by a connection that is rigid for some forms of movement and flexible for other forms of movement (e.g., a hinged connection). In some cases, current collection may occur from one side so that neither the backing plate nor the pouch collects current, but in other cases, it may be advantageous to collect current from both sides of the pouch construction. An example of such a fastener construction 700 with a backing plate 702 is shown in FIG. 7 as a non-limiting example. 7, a backing plate 702 can be used to rigidly support a pouch 705 on both sides with tightening wires 704 extending across the backing plate 702 and the pouch 705. Electrode material can be poured into the pouch 705 through an opening, which can then be tightened or welded closed to form a closure 703.

[0161] In another embodiment, the particulate electrode material can be compressed within a perforated sheet. The sheet may be conductive to serve both as a means for compressing the electrode material and as a means for collecting current from the electrode material. The perforations in the sheet can be selected to be smaller than the feature size of the particulate material, so that the particulate material cannot easily escape from the cage formed by the perforated sheet.

[0162] In various embodiments, the electrode material may be a particulate material. Because easy ion transport between the positive and negative electrodes is desired, the material surrounding the electrode material may need to be porous or otherwise perforated. In some cases, for example, because very fine perforations are difficult to fabricate, a particulate material having a particle size finer than the porosity or perforations may be desirable. When particles finer than the porosity or perforations are desired, the electrode material may be agglomerated with a binder to form secondary particles composed of numerous primary particles. Thus, the primary particle size may be finer than the perforations, but the secondary particle size may be coarser than the perforations. Such coarser particles are less likely to escape the porosity or perforations of the current collector and other compacted materials, and as a result, can be more effectively compacted. In one aspect, a polymer stable under alkaline conditions can be used to bind the agglomerates together, such as poly(ethylene) or poly(tetrafluoroethylene). In another aspect, the polymer can be introduced onto the surface of the primary particles and then pyrolyzed to form a conductive binder on the surface of the primary particles, thereby binding them together. In yet another embodiment, a polymeric binder that is only partially stable under conditions appropriate for the electrode may be introduced between the primary particles. The binder allows the electrode to be cycled, for example, through several electrochemical charge-discharge cycles, sufficiently so that bonds are electrochemically formed between the various primary particles before the polymer breaks down or degrades. In another embodiment, the porosity or perforation shape of the structure that compresses the electrode material may be designed to retain the electrode material within the structure but maximize ion transport through the perforations or porosity. As a non-limiting example, long slits may be introduced into a perforated sheet so that particles cannot exit through the slits, but the amount of open area for mass transport is increased compared to the amount that would exist if the perforations were equiaxed. In one embodiment, the particulate electrode material may be composed of direct reduced iron, and the perforated sheet may be composed of stainless steel.In another embodiment, the particulate electrode material may be comprised of direct reduced iron crushed to a particle size that is a fraction of the size of natural pellets, and the perforations in the current collector may be sized to prevent the crushed pieces from escaping the compression cage.

[0163] In one aspect, the bed of particles is vibrated, shaken, agitated, or moved so that the particles fit closer together than when initially packed. This method can also be used periodically during the life of the system to help promote new contact angles and arrangements between particles as their shape and size change. In the case of containers that provide pockets for particles, their orientation can be changed, such as rotation in the case of wheel-shaped containment.

[0164] In another embodiment, additives may be included in or added to the electrode material bed to enhance the electrode's electrical conductivity between the current collectors. The additives can be usefully concentrated at strategic points in the electrode structure. In one embodiment, the particulate anode material is attached to the current collector using a conductive adhesive. The current collector may be any shape, including rounded or hollow spheres, and may have particles on both sides. The conductive adhesive may include a binder stable in the intended environment, such as an alkaline electrolyte, and conductive particles, such as metals, including powders containing iron, filings, or steel mill dust. The binder may include, for example, poly(ethylene) or poly(tetrafluoroethylene). The conductive adhesive may further contain additives useful for battery performance, such as sulfide salt additives, or additives intended to bind carbonate ions in solution, such as calcium hydroxide. Creating a conductive bond between the electrode particulate material and the current collector can usefully enhance battery performance at little additional cost when the interfacial resistance between the particulate material and the current collector is one of the larger resistances in the electrochemical system. The composition of the conductive adhesive may be 10-80% by volume of conductive additive, with the remainder comprising the binder, any optional additives, and possible co-solvents or tackifiers.

[0165] In another embodiment, current collection can occur by creating a bond between each of the particulate materials and a conductive rod. If the particulate material is attached to the current collector by a conductive bond, compressive stress is not required. The particulate material may be attached to the rod along its length. The anode material mass may extend beyond the end of the rod. The anode mass can be attached by sintering, welding, or other metallurgical bonding techniques, by wire attachment, or by deposition onto the rod from a solution or slurry, which may occur magnetically or by solvent evaporation. The rod can be used to collect current from the anode. This rod-type anode can be snap-fitted into a flexible ring-with-a-slit-like fastening mechanism to facilitate assembly of the compound anode. This fastening rail can serve as a busbar. This is shown schematically in FIG. 8, where a rod 802 with iron particulate material 805 attached is fitted to a busbar 803. The rods 802 may have any cross section, including circular or linear, and need not be straight, but rather may be coiled or take on some other shape to enhance packing and limit the required busbar 803 volume.

[0166] In another aspect, current collection and compression can occur simultaneously through an open-top pouch, which may be made, for example, of crimped or welded sheet metal. The pouch can be filled with particulate iron electrode material and the top can be rolled down to provide compression of the particulate material. Compression can be achieved by rolling down using a horizontal rod within the roll-down section. The pouch can be made of a conductive material suitable for alkaline battery environments, specifically for iron positive electrode current collectors. Current can be collected from the end of the rod. The pouch can be porous or perforated to allow ion transport through the pouch, such as a metallic mesh made of nickel.

[0167] In another aspect, a rigid container can be formed. The rigid container may have at least one conductive wall, may be constructed of a material suitable for use in alkaline electrolytes, and may further be suitable for serving as a current collector for an iron positive electrode. The rigid container can be filled with particulate electrode material and compressed by a piston or plunger mechanism. In one exemplary embodiment, a welded can having a bottom and a wraparound exterior is filled with anode pellets (or powder) and compressed from the top using a plunger mechanism. The surface of the rigid container can be rigid but constructed of an ion-permeable material, such as perforated sheet metal or an expanding sheet. In one aspect, the expanding sheet constituted the sidewall of the rigid container. The platen or surface used by the plunger may include tabs or other compliant features that can mechanically engage with features in the sidewall of the rigid container, such that the plunger alone provides the compressive force for assembly. The mechanical engagement feature thus allows for the piston to be used for initial compression but subsequently removed. The compressive load in this and other embodiments can be applied by any of the means common in the art for applying a compressive load, including, but not limited to, bolts, hydraulic pressure, weights, threaded rods, zip ties, and rivets. Figure 9 shows an exemplary embodiment in which a perforated press 902 is used to compress iron electrode material 903 within a rigid anode container 905. In this case, the iron electrode material 903 may be direct reduced iron pellets, referred to as a DRI spheroid bed. Figure 9 shows an exploded view on the left and an assembled view on the right.

[0168] In another embodiment, the iron particulate material may be sandwiched between two sheets of conductive compliant material, such as woven metal fabric, and riveted to fasten around the edges to provide compression. In some cases, the conductive compliant material may be riveted, tightened, or otherwise reduced in volume intermittently over the area of ​​the electrode to provide more uniform compression.

[0169] In another aspect, a compliant sheet or mesh can be used in combination with rigid sidewalls to simultaneously provide compression, current collection, and containment. More specifically, in one exemplary embodiment, such as that shown in FIG. 10 , a module 1002 comprised of rigid sidewalls 1004 may be slightly overpacked with iron electrode material 1005, all enclosed by metal mesh top and bottom plates 1003 with fasteners 1006 (e.g., bolts, threaded rods, zip ties, rivets, etc.). The mesh 1003 exerts a compressive load on the iron electrode material 1005 when the fasteners 1006 are tightened, when the spheres (e.g., DRI spheres as the iron electrode material 1005) are slightly overpacked against the sidewalls 1004. The mesh 1003 can serve as a current collector. The mesh 1003 can allow for good electrolyte circulation or diffusion to the iron electrode material 1005. The fasteners 1006, in combination with other elements, can hold the iron electrode material 1005 in a contained state and apply a clamping load. In some embodiments, the fasteners 1006 can also serve as current collectors. The mesh 1003 can be a corrosion-resistant wire mesh, perforated plate, such as nickel, stainless steel, etc. The sidewalls 1004 can be any rigid material that is suitably stable in the electrochemical environment of the iron electrode 1005, such as plastic, some metals, etc. The resulting assembly of iron electrode material 1005 and current collector can be modular components or permanently connected as a whole to an electrochemical energy storage system.

[0170] In another embodiment, a compliant gasket-like material is used to contain the iron particulate electrode material on some surfaces. The compliant material allows for variable movement of the designed force-applying element depending on the local compliance and / or packing of the bed. In one example, a compliant gasket abuts a cylindrical cell, and conductive current-collecting perforated plates form the ends of the cylindrical cell. The plates are pressed together at various points around the cell circumference, for example, by bolts that penetrate the silicone gasket. The gasket may be made of a compliant, alkali-resistant material, such as ethylene propylene diene monomer (EPDM) rubber or related materials. In some cases, the gasket may need to be highly compliant, in which case a polymeric foam, such as EPDM foam, may be useful.

[0171] In another embodiment, the current collector may include divots or other positioning or contact features on its surface. Such features can serve to enhance the contact area between the current collector and the particulate iron material and / or to position the particulate material for efficient packing as a result of the templating provided by the current collector's surface. In one example, the current collector may include a series of divots sized and arranged to allow a spherical set of particles, such as those derived from a direct reduction process, to pack adjacent to the surface in a close-packed manner. Other templates, such as a body-centered cubic template, are also possible. For particulate materials with an axis of symmetry, such as rods, the templating may have an axis of symmetry such as a divot that is a cylindrical trough. The divots may be introduced by machining, sheet metal dimple formation, or other deformation processes, or may include appropriately sized perforations or through-holes in the current collector. The current collector may be shaped to optimally compress the particulate material against one another; for example, in the case of rod-shaped particulate material, the current collector may comprise a sheet rolled into a cylinder around the cylindrical agglomerates and compressed to reduce the diameter of the cylinder.

[0172] To reduce electrical resistance due to current collection, the current collector may be designed to allow current collection to occur more uniformly throughout the packed bed electrode by incorporating current collecting elements that span the entire thickness of the electrode or penetrate the thickness of the electrode in a reasonable manner.

[0173] In certain embodiments, the current collector may comprise spikes, bars, tabs, or other high aspect ratio features that can protrude into the electrode bed from the current collecting sheet or other boundary of the packed-bed electrode. These high aspect ratio features may be sized and shaped to contact many electrode material particles in the bed that a simple, flat sheet current collector would not. In certain embodiments, a sheet metal current collector with tabs that protrude into the space filled with particulate material is used as the current collector. In another aspect, an expanded sheet metal sheet is used as the current collector, with some posts in the sheet cut and bent inward to serve as tabs that protrude into the space filled with active material.

[0174] In one particular embodiment, a conductive brush or series of wires is attached to the current collector. The wires flexibly project into the space filled with the iron electrode material. The wires contact the material according to a spring constant, and compressive pressure can be used to improve contact.

[0175] In many embodiments, fasteners or other compression-providing elements are desirable to hold the current collectors in a compressed position relative to each other. Hereinafter, the term fastener shall be understood to mean any element of a mechanical assembly that provides a fastening or compression function by using an additional part that mechanically engages with other parts of the assembly. Applying a sustained compressive load before operating the cell increases the performance of iron positive electrodes composed of individual pellets. However, using metallic fasteners, such as stainless steel bolts, to maintain the load is disadvantageous because it adds both part count and assembly time, and may require electrically insulating the bolts from the current collectors to mitigate the hydrogen evolution reaction (an undesirable parasitic side reaction that reduces coulombic efficiency) that occurs on the bolts, which likely adds greater complexity and part count to the design. Thus, while fasteners are desirable from a mechanical standpoint, metallic fasteners are disadvantageous. Some methods for replacing metallic fasteners with alternatives are discussed below.

[0176] In some embodiments, non-metallic fasteners can be used instead of metallic fasteners. In one exemplary embodiment, two sandwich current collector plates can surround the iron electrode bed. The current collector plates can be fabricated to apply a compressive force to the anode bed through fasteners fabricated from an electrically insulating, non-metallic material that is resistant to degradation in the alkaline environment of the electrolyte. The electrically insulating, non-metallic nature of the fasteners results in a lack of electron transport to the electrolyte-exposed surface of the fastener, preventing the undesired hydrogen evolution reaction from occurring at the exposed surface of the fastener. A reduced HER rate means more electrons participate in the desired anode reduction reaction, resulting in a higher Coulombic efficiency. In certain embodiments, the fasteners are bolts and nuts. In certain embodiments, the fasteners are fabricated from one or more of acrylic, polytetrafluoroethylene, polyethylene, low-density polyethylene, high-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, or polyetheretherketone. In another exemplary embodiment, two sandwiched current collector plates surrounding the anode bed can be fabricated to apply a compressive force to the anode bed via fasteners, which saves assembly time by using a "snap-in" mechanism rather than a screw mechanism that requires the fasteners to be turned. In one particular embodiment, the fasteners are double-locking snap-in supports of appropriate length. Any combination of the above fastening techniques can be used to provide compression while avoiding the use of metallic fasteners. Some fastening techniques are illustrated in FIGS. 11A and 11B. The illustration in FIG. 11A shows an electrically insulating nut 1103 sandwiching two current collector sheets 1105 against iron electrode material 1100, labeled "anode active material" in FIG. 11A. The nut 1103 tightens on a bolt 1102 to draw the sheets 1105 together, thereby compressing the anode active material 1100. FIG. 11B shows a second example of a snap-in compression feature, such as a snap-in support 1110, which is used in place of the bolt 1102 and nut 1103 of FIG. 11A and acts in a similar manner.

[0177] In some embodiments, it may be useful to use a compliant mechanism capable of applying a large, distributed load to the current collector or compression platen. In one example, the final face dimension of a rectangular prism box for storing the anode is a leaf spring mechanism that rebounds after anode loading to compress and store the pellet anode. The current collector itself may be a compliant mechanism such that applying the load to a relatively few points (as occurs with leaf springs) can result in the distribution of the load across the system.

[0178] The application of compressive stress can be applied by means other than compression applied by mechanical fastening of the structure. In certain cases, the iron electrode material may be contained in a rigid body (e.g., a prismatic cell with current collectors or other mechanical support on all sides), but the need for applying a compressive load during assembly can be eliminated by using an expandable material lining one side of the anode containment body. The expandable material can be expanded after assembly of the cell, thus providing a compressive load on the anode bed after the cell is filled with electrolyte. In certain embodiments, the expandable material can be disposed between the iron electrode material and one of the minor faces of the iron electrode material containment body. In certain embodiments, the expandable material is an expandable hydrogel that swells upon contact with aqueous electrolyte, thus providing a compressive load on the anode active material when filled with electrolyte. In certain embodiments, the expandable material is an expandable plastic balloon with a port for pumping air, thus providing a compressive load on the anode active material when air is pumped through it. The plastic balloon may be composed of poly(ethylene), poly(propylene), or similar polymers that are flexible and resistant to degradation in alkaline solutions. Figure 12 shows an example embodiment of an expandable material contained within a rigid iron electrode containment assembly 1202. The left side of Figure 12 illustrates an uninflated state, while the right side of Figure 12 illustrates an inflated state of the expandable material 1200 compressing the anode active material 1205 within the anode containment assembly 1202.

[0179] In another embodiment, the container for the iron electrode material is not rigid, but its volume is still conserved or, as in the case of some woven metal fabrics, has a maximum volume within a reasonable approximation over a stress range of less than about 10 MPa. This may be referred to as a flexible cage. In such cases, an expandable material may be placed within the flexible cage, and compression is provided by expansion of the expandable material within the flexible cage. Similarly, the expandable materials described above may also be used. The flexible cage may be electrically conductive and may serve as both a current collector and a means for providing compression to the iron electrode material that fills it.

[0180] In another embodiment, the iron electrode material can exhibit a substantial magnetic moment in the presence of a magnetic field. The iron electrode material can be ferromagnetic, as is the case with iron. Thus, a magnetic field established by one or more permanent magnets or electromagnets can be used to induce a magnetic force that urges the iron electrode material toward a rigid wall, thereby providing a compressive load on the anode active material.

[0181] In another embodiment, a pump present in the system, such as a pump intended to move the electrolyte, is used to provide suction to the particle bed. The suction provided by the pump draws the particle bed together, causing the particles to contact one another. Particles are prevented from being drawn into the pump by a sieve or mesh with openings smaller than the smallest expected particle.

[0182] In another aspect, phosphates (including iron phosphate), phosphoric acid, or similar phosphorus-containing additives can be usefully incorporated into particulate iron electrode materials to promote mechanical contact and bonding between the particulate materials. Phosphate groups can form phosphate bridges between metal oxide groups, thereby anchoring the particulate materials of the electrode bed together and forming a better mechanically and electrically connected electrode. Iron oxides can serve as useful conductors because some of them (particularly magnetite and wüstite) are semiconductive. When bonded oxides are electrochemically reduced to metallic species, such metallic species may be electrochemically sintered or otherwise bonded. Thus, such oxide bonding, even if temporary, can lead to enhanced electrochemical performance over multiple cycles. The electrode material can be pretreated with a phosphorus-containing solution before placement in the electrolyte, or a phosphorus-containing compound can be introduced into the electrolyte for the purpose of forming such phosphate bonds. Phosphate bonding can occur in a variety of metal oxide systems, including cadmium, magnesium, aluminum, and zinc. Phosphate additives can be particularly beneficial with iron electrodes because they can reduce the tendency for hydrogen to evolve at the iron surface during charging.

[0183] In some embodiments, it may be desirable to create a conductive pathway between particles of iron electrode material by metallurgically bonding the particles prior to insertion into the electrolyte. Such metallurgical bonding may lead to sufficient conductivity across the iron electrode material that does not require compression to achieve satisfactory electrochemical performance. Below are described various methods for eliminating the need for compression of the iron electrode material.

[0184] In one embodiment, iron electrode materials are thermally assembled by a high-temperature process, including sintering or brazing. The thermal step for bonding iron electrode materials to current collectors can reduce contact resistance between particulate materials by fusing like metals together for a more robust electrical connection. While sintering has been considered for the production of iron electrode materials, sintering some particulate iron materials has not previously been considered due to their unique grain structure. In one example, direct reduced iron is an attractive feedstock for iron electrode materials, but its coarse grain size makes it not an obvious candidate for thermal bonding via a sintering process. In the sintering process, the direct reduced iron may be used directly or in combination with another bonding material to form a suitable metallurgical bond at the surface of the direct reduced iron. The bonding material may be painted, sprayed, or otherwise introduced onto the direct reduced iron or other particulate iron material to enable bonding with other direct reduced iron particles during the heat treatment process. The bonding material may be usefully concentrated at the contact points between the direct reduced iron or other particulate materials as a means of achieving maximum electrical contact at minimal added cost. An example of a bonding material is a material with a low sintering temperature that can cause a metallurgical bond during the sintering process, such as a carbonyl iron suspension that is applied or sprayed onto direct reduced iron or other particulate material. In a second example, the bonding material can melt or cause a fusion weld or braze when exposed to heat. In a second example, a nickel brazing compound can be coated onto the iron electrode material, and the material can then be heated to an appropriate temperature to form a metallurgical bond. A thermal bonding method is illustrated in FIG. 13. FIG. 13 shows that multiple metal pellets 1300 are provided on an anode current collector 1302. Heat is applied to the pellets 1300 and the anode current collector 1302, resulting in the fusion of the pellets 1300 with the current collector, as shown in FIG. 13.

[0185] A possible manufacturing technique for a thermally bonded particle bed system may feature a rolled steel sheet that can serve as a furnace belt. The belt would be unwound from a coil and straightened into a horizontally translating surface within a continuous hydrogen furnace. At the furnace entrance, iron electrode material (such as direct reduced iron) would be loaded onto the belt from a hopper. The iron electrode material and belt sheet would travel through a furnace where it would be heated to a maximum temperature that would bond the iron electrode material and belt. The iron electrode material and current collector sheet would then be cut into small pieces that could be used as the reactor anodes.

[0186] In various embodiments, the particulate material for the iron electrode achieves excellent contact with one another because stress concentrations at the contact points create "flats." In some cases, it may not be necessary to hold the electrode material with high force over its lifetime; rather, the particulate material may be pressed together during manufacture to create flat spots and then held with less force over its lifetime. To accomplish this, the electrode cage can be supported during application of high load stress to create flats in the particulate material and reduce inter-particle contact resistance. The force can then be partially released, the cage removed from the support structure, and the electrode cage can then be placed into the reactor under this lower compressive force, but with the contact resistance reduced by the application of a higher compressive force. At any point during its lifetime, if the cage becomes disintegrated or the cell resistance becomes too great, the cage can be removed and placed back into the support structure and recompressed, the force can be released again, and the cage can be placed back into the cell.

[0187] In various embodiments, the dissolution of iron intermediates in alkaline media can be exploited to form necks between particles of iron electrode material that make up the packed bed. The iron electrode can be maintained at an appropriate pH, temperature, and optionally voltage range, and a sufficiently high concentration of HFeO2 can be added to the packed bed to develop interparticle bonds through solution precipitation reactions mediated by soluble species, as shown in the diagram below, where the particles are referred to as spheroids. -Soluble intermediates can form. Interparticle bonds are sometimes called necks. Such neck formation can be a pre-processing step or can occur in situ in an electrochemical cell for energy storage. Coarsening can form necks between pellets to enhance inter-pellet conductivity and reduce overpotential at the anode. In one aspect of neck formation, the process involves immersing the pellet bed in an alkaline solution for >3 days, such that soluble species coarsen the bed to the micron- to millimeter-scale and enhance inter-pellet contact. In another embodiment, electrochemical cycling is used to enhance the deposition of soluble intermediate species. In a third embodiment, the pellets are coated with iron powder, such as atomized iron powder or sponge iron powder, to promote "neck" formation and reduce contact resistance between DRI pellets. With continued cycling, the powder particles can "sinter" to the host DRI pellet. Mechanistically, this involves the formation of soluble intermediate Fe species (HFeO2), which promotes the deposition of discharge products at the interfaces between small and large particles, as shown, for example, in Figure 14. - ) can result from mass transport. Specifically, FIG. 14 shows that a bed 1400 of individual DRI pieces 1402 (e.g., DRI spheres) can be provided. Electrochemical and / or chemical reactions can result in the bed 1400 forming into a necked-up bed 1405 of DRI pieces 1402 (e.g., spheres) joined together by necks 1406 therebetween. In this manner, the bed 1405 can be a solid mass of joined DRI pieces, as opposed to the original starting bed 1400 of separate pieces.

[0188] In various embodiments, the particulate material may be bonded by techniques commonly used for welding metallic materials. In one aspect, the particulate material may be resistance welded by passing a large electrical current through a packed bed. The electrical current may be applied by a densification roller assembly to bring the particles into contact before or simultaneously with the resistance welding process. In various embodiments, the particles may be mechanically deformed at high temperatures to form metallurgical bonds at the contact points between the particles. In one example, a hot briquetting or hot briquetting machine for direct reduced iron may be operated at a low densification pressure so that the particulate material deforms at the contact points to form metallurgical bonds. For particulate materials with internal porosity (such as direct reduced iron), densification can take advantage of stress concentrations at the contact points between the particles to form metallurgical bonds between the particles, while leaving most of the internal porosity of the particulate material away from the contact points unchanged. In various embodiments, creating the metallurgical bond may occur in an inert atmosphere to prevent oxidation of the iron electrode material. In various embodiments, the bed of particulate material may be ultrasonically compacted or compacted by other vibrational means. Ultrasonic or vibrational compaction may involve axial pressure. In various embodiments, the particulate material may be fusion welded together by any of the fusion welding techniques common in the art, including, but not limited to, tungsten inert gas welding, metal inert gas welding, and gas metal arc welding. In another aspect, the material may be explosively welded.

[0189] In various embodiments, a conductive metallic solder may be placed at the contact points between the particulate materials such that a metallic bond can be formed between the materials. In one example, tin may be dip-coated onto a bed of particulate material. In another example, copper may be dip-coated onto the particulate material. In additional embodiments, a conductive liquid is coated onto the particles by passing both through a tube or nozzle and depositing the coated particles. Precise control of the nozzle allows for precise placement of individual particles, which can help achieve optimized electrode shapes. Particles deposited in this manner can be stacked to produce three-dimensional structures.

[0190] In various embodiments, the particulate material may be etched with any one of a variety of acids and then mechanically deformed before insertion into the electrochemical cell. The etching action can remove any surface oxides that interfere with bonding and allow electrical contact between the anode materials. Acids such as hydrochloric acid, nitric acid, or any other aid used to strip iron oxide from metallic iron surfaces may be used. In some cases, compression may be performed while the particulate material is in the acid.

[0191] In various embodiments, the particulate material for the iron electrode may include a direct reduced iron material. The direct reduced iron material can be produced without the cement coating used to reduce sticking during the reduction process. Such cement can inhibit charge transfer across the interface between pellets. In this manner, the direct reduced iron material can exhibit enhanced charge transfer characteristics for electrochemical cycling. In one example, a fluidized bed reduction process is used to enable the use of a direct reduced iron material that does not require a cement coating.

[0192] In various embodiments, particulate material including iron electrode material can be compressed with a current collector mesh. The current collector mesh can then be heated (e.g., by electrical resistance) to weld the wire mesh to the particulate material surrounding it. The pellets can then be interconnected by the mesh and welded together. The mesh can be relatively thick and open, like wire fence material.

[0193] Pellet size and shape modification prior to battery assembly

[0194] During operation of a battery with a pellet-bed electrode, the size of the pellets can make mass and electron transport within the pellets difficult, resulting in polarization. Polarization can reduce the energy efficiency of the battery through (1) a voltage drop during charge and discharge, resulting in reduced voltage efficiency, and (2) coulombic inefficiency due to insufficient competition with the hydrogen evolution reaction during charging. Insufficient charging also reduces the specific capacity of the resulting iron electrode. For example, in certain cases, polarization is dominated by mass transport of hydroxide ions through the pellet pores from the exterior of the pellet to the iron reaction site at the center of the pellet. In other cases, polarization is dominated by electron transport through the intrapellet network of iron material from electrical contact points at the exterior of the pellet to the center of the pellet. Either of these polarization factors can result in a local electrochemical potential within the pellet that favors the hydrogen evolution reaction during charging over the desired reduction reaction of iron oxide species, thereby reducing coulombic efficiency.

[0195] In one embodiment, the particle size can be selected to promote better packing. In one non-limiting example, a bed may be composed of 50% particles greater than 5 mm in diameter, 25% particles between 5 mm and 1 mm in diameter, and 25% particles less than 1 mm in diameter, with the smaller particles filling the spaces between the larger particles. Particles smaller than the native DRI size can be fabricated from DRI by methods detailed below. These particles may be added to their storage location in a specific order to ensure optimal packing. In one non-limiting example, a layer of larger particles is added first, followed by smaller particles to fill the spaces, followed by another layer of larger particles and another smaller particle.

[0196] As a method for addressing one or more of the energy efficiency loss and specific capacity loss due to pellet size, reducing the size of the iron pellets prior to battery assembly has been disclosed. Reducing the pellet size reduces the characteristic length of mass transport and electrical transport within the pellet, thereby reducing polarization and enhancing one or more of the energy efficiency and specific capacity.

[0197] Reducing the size of pellets by a comminution process, such as a jaw crusher ("crushing"), before assembly into a pellet bed has been shown to result in higher voltage efficiencies. However, crushing pellets should result in less interparticle contact on a per-particle basis (irregular particles achieve less contact than spherical particles) and higher interfacial resistance per particle in a given bed thickness. Furthermore, "rattlers," particles that are not in electrical contact with their neighbors due to the geometric packing of the bed, are more likely to be polydisperse and irregularly shaped than relatively monodisperse spheres. Consequently, the gain in voltage efficiency due to enhanced mass and electrical transport within the pellets is presumed to partially mask the increased voltage drop due to electronic resistance and the lack of electrically available material (and therefore reduced capacity) due to increased rattler fraction.

[0198] In certain embodiments, the size of the pellets is reduced to half or less of their original size by crushing, resulting in a reduction in the overpotential of the iron electrode of more than 10 mV (mV = millivolt = 10-3 V).

[0199] It is believed that crushing pellets can result in substantial performance gains if a secondary conductive additive is added to the pellet bed to enhance one or more of the inter-pellet or pellet-to-current collector electrical conductivity. The additive would increase conductivity by increasing the conductive surface area in contact with the pellets, mitigating additional interfacial resistance in the pellet bed of crushed pellets. An additive that does not inhibit mass transport and results in substantially higher bed electrical conductivity is desirable. The optimal additive would leach at a low volume fraction and be highly conductive.

[0200] In certain embodiments, the additive is one or more of carbon black or graphite added to the crushed pellet bed at a volume fraction greater than 1% so that the carbon black or graphite bridges the crushed pellets together. In certain other embodiments, activated carbon, or biochar, or low to medium conductivity, is used as a low-cost alternative to graphite.

[0201] In one particular embodiment, the additive is small pieces of conductive mesh, such as stainless steel wire mesh.

[0202] In one particular embodiment, the additive is a conductive rod, such as a stainless steel rod, of a diameter smaller than the average pellet size.

[0203] Prior to nominal battery operation, additives that enhance iron electrode performance may be chemically incorporated into the iron electrode via various processes that rely on intra-pellet mass transport of chemical species in the electrolyte to active iron sites within the pellet's porous structure. Homogeneous infiltration of the additive into the pellet is often necessary to achieve the maximum desired performance-enhancing effect of the additive. However, it is often difficult to homogeneously infiltrate certain liquid-soluble, solid-state additives into the pellets typically output from the direct reduction process, particularly for additives with low solubility that react with direct reduced iron.

[0204] Reducing the size of the iron pellets prior to battery assembly has been disclosed as a way to achieve more uniform penetration of liquid-soluble and solid-state additives into the pellets during the additive incorporation process. Reducing the pellet size reduces the characteristic length of intrapellet mass transport, thereby reducing additive concentration gradients, allowing for more uniform penetration and incorporation of the additive into the electrode.

[0205] In certain embodiments, the additive incorporation process is one or more of electrolyte immersion, electrochemical plating, and electrochemical cycling.

[0206] In certain embodiments, the additive is an initially liquid soluble hydrogen evolution inhibitor that is incorporated into the solid-state electrode by electrochemical or spontaneous chemical reaction.

[0207] In certain embodiments, the additive is a hydrogen evolution inhibitor that is initially in a solid state that is further incorporated into the solid-state electrode by an electrochemical or chemical dissolution-reprecipitation reaction.

[0208] In certain embodiments, the additives include one or more of the following: sodium thiosulfate, sodium thiocyanate, polyethylene glycol (PEG) 1000, trimethylsulfoxonium iodide, zincate (by dissolving ZnO in NaOH), hexanethiol, decanethiol, sodium chloride, sodium permanganate, lead (IV) oxide, lead (II) oxide, magnesium oxide, sodium chlorate, sodium nitrate, sodium acetate, iron phosphate, phosphoric acid, sodium phosphate, ammonium sulfate, ammonium thiosulfate, Lithopone, magnesium sulfate, iron(III) acetylacetonate, hydroquinone monomethyl ether, sodium metavanadate, sodium chromate, glutaric acid, dimethyl phthalate, methyl methacrylate, methylpentynol, adipic acid, allyl urea, citric acid, thiomalic acid, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, propylene glycol, trimethoxysilylpropyldiethylene, aminopropyltrimethoxysilane, dimethyl acetylenedicarboxylate (DMAD), 1,3-diethylthiourea, N,N'-Diethylthiourea, aminomethylpropanol, methylbutynol, amino-modified organosilane, succinic acid, isopropanolamine, phenoxyethanol, dipropylene glycol, benzoic acid, N-(2-aminoethyl)-3-aminopropyl, behenamide, 2-phosphonobutanetricarboxylic acid, MIPA borate, 3-methacryloxypropyltrimethoxysilane, 2-ethylhexanoic acid, isobutyl alcohol, t-butylaminoethyl methacrylate, diisopropanolamine, propylene glycol n-propyl ether, sodium benzotriazole, aminotrimethylenephosphonic acid Ingredients: pentasodium cocoyl sarcosinate, sodium cocoyl sarcosinate, lauryl pyridinium chloride, steartrimonium chloride, stearalkonium chloride, calcium montanate, quaternium-18 chloride, sodium hexametaphosphate, dicyclohexylamine nitrite, lead stearate, calcium dinonylnaphthalene sulfonate, iron(II) sulfide, sodium hydrogen sulfide, iron pyrite, sodium nitrite, complex alkyl phosphate ester (e.g., RHODAFAC® RA600 emulsifier), 4-mercaptobenzoic acid, ethylenediaminetetraacetic acid, ethylenediaminetetraacetate (EDTA), 1,3-Propylenediaminetetraacetate (PDTA), nitrilotriacetate (NTA), ethylenediamine disuccinate (EDDS), diethylenetriaminepentaacetate (DTPA), and other aminopolycarboxylates (APC), diethylenetriaminepentaacetic acid, 2-methylbenzenethiol, 1-octanethiol, bismuth sulfide, bismuth oxide, antimony(III) sulfide, antimony(III) oxide, antimony(V) oxide, bismuth selenide, and antimony selenide. Thione, selenium sulfide, selenium(IV) oxide, propargyl alcohol, 5-hexyn-1-ol, 1-hexyn-3-ol, N-allylthiourea, thiourea, 4-methylcatechol, trans-cinnamaldehyde, iron(III) sulfide, calcium nitrate, hydroxylamine, benzotriazole, furfurylamine, quinoline, tin(II) chloride, ascorbic acid, tetraethylammonium hydroxide, calcium carbonate, magnesium carbonate, antimony dialkylphosphorodithioate, Potassium stannate, sodium stannate, tannic acid, gelatin, saponin, agar, 8-hydroxyquinoline, bismuth stannate, potassium gluconate, lithium molybdenum oxide, potassium molybdenum oxide, hydrogenated light oil, heavy naphthenic petroleum fractions (e.g., sold as Rustlick® 631), antimony sulfate, antimony acetate, bismuth acetate, hydrotreated heavy naphtha (e.g., sold as WD-40®), tetramethylammonium hydroxide, Na Sb tartrate, urea, D-glucose, C6Na2O6, potassium antimony tartrate, hydrazine sulfate, silica gel, triethylamine, potassium antimonate trihydrate, sodium hydroxide, 1,3-di-o-tolyl-2-thiourea, 1,2-diethyl-2-thiourea, 1,2-diisopropyl-2-thiourea, N-phenylthiourea, N-diphenylthiourea, sodium antimony L-tartrate, rhodizonic acid disodium salt, sodium selenide, potassium sulfide, and combinations thereof.

[0209] FIG. 15 shows exemplary pellet beds 1501 and 1502 according to various embodiments. During operation of a battery with pellet bed electrodes, the overall thickness of the pellet bed can make mass and electron transport through the pellet bed difficult, resulting in polarization. Polarization can reduce the energy efficiency of the battery through (1) a voltage drop during charge and discharge, resulting in reduced voltage efficiency, and (2) coulombic inefficiency due to insufficient competition with the hydrogen evolution reaction during charge. Insufficient charge also reduces the specific capacity of the resulting iron electrode. For example, in certain cases, polarization is dominated by mass transport of hydroxide ions from the exterior of the pellet bed to the center of the pellet bed. In other cases, polarization is due, in part, to electron transport through the iron pellet network. Either of these polarization factors can result in a local electrochemical potential within the pellet that favors the hydrogen evolution reaction during charge over the desired reduction reaction of iron oxide species, thereby reducing coulombic efficiency.

[0210] Increasing the volumetric packing density of the pellets is one way to address one or more of the energy efficiency loss and specific capacity loss due to the total thickness of the pellet bed. Increasing the volumetric packing density reduces the pellet bed thickness for a given electrode capacity, thereby reducing polarization of the bed and enhancing one or more of the energy efficiency or specific capacity. For example, FIG. 15 shows a pellet bed 1501 having porous pellets 1503 formed as spheres or spherical bodies, and a pellet bed 1502 having porous pellet pieces 1505 that can be formed by crushing spheres, spheres, or other shapes into small pieces. The intra-pellet transport length t1 of the pellet bed 1501 may be longer than the intra-pellet piece length t2 of the pellet bed 1502.

[0211] Processing the pellets with a jaw crusher ("crushing") before assembling them into a pellet bed is disclosed as a method for increasing volumetric packing density and reducing polarization. Crushing can thus result in pellet bed 1502 rather than pellet bed 1501. The pellets before crushing may be approximately spherical and have a narrow size range. The crushing operation can break the pellets into multiple pieces with non-spherical shapes and a wider size distribution, resulting in a higher volumetric packing density. The resulting higher volumetric packing density reduces the thickness of the pellet bed for a given projected area and mass of electrode material, thus reducing bed polarization and enhancing one or more of energy efficiency or specific capacity (e.g., when pellet bed 1502 may have the same material composition for porous pellets 1503 and porous pellet pieces 1505, comparing pellet bed 1502 to pellet bed 1501, pellet bed 1502 reduces bed polarization and enhances one or more of energy efficiency or specific capacity compared to pellet bed 1502). 16 shows pellet beds 1501 and 1502 with attached current collector 1601. Even though the same amount of pellet material may be present in pellet beds 1501 and 1502, the height h1 of uncrushed pellet bed 1501 may be greater than the height h2 of crushed pellet bed 1502. Thus, crushing can reduce the size of the electrode.

[0212] In certain embodiments, the pellets after the crushing operation have jagged edges and are broken into pieces with a polydisperse size distribution such that the smaller pieces fit within the interstices between the larger pellets, thus increasing the packing density.

[0213] Method for restoring performance after performance decay

[0214] Certain performance attributes of pellet bed electrodes can deteriorate due to time-dependent or charge throughput-dependent mechanisms during battery operation. Deteriorating performance attributes include, but are not limited to, specific capacity (mAh / g), electrode overpotential (mV), self-discharge rate (mAh / mo.), and coulombic efficiency (%). Several methods are disclosed herein for restoring iron electrode performance by treating batteries after use.

[0215] In certain cases, the specific capacity of an electrode may decrease with battery cycling because cycle-dependent changes in the electrode microstructure impede mass or electron transport, thereby reducing the available capacity at a given polarization. More specifically, pores within the pellets may gradually narrow with cycling as they fill with residual electrochemical discharge products, which have a larger molar volume (per mole of iron) than metallic iron. The gradual filling of the pores may impede mass transport to the iron within these pores, making the iron within the pores increasingly unavailable for electrochemical reaction, thereby reducing the specific capacity. In other cases, electrical resistance to certain iron sites may increase due to narrowing of the conductive pathways provided by the metallic network within the pellet. In other cases, there may be cores of unreacted metallic iron within each pellet that are completely covered by a passivation layer.

[0216] Loss of usable capacity due to battery use can be regained through ex-situ treatment of the pellets after the electrode capacity has decayed to a minimum threshold. Various embodiments include treating used pellets with mechanical, chemical, electrochemical, and / or thermal processes before reintroducing the pellets into an electrochemical cell (i.e., treating the pellets ex-situ) to restore the electrode to a state with better chemical and / or physical properties. Better chemical and physical properties can include a higher content of desirable impurities (e.g., hydrogen evolution reaction (HER) inhibitors), a lower content of undesirable impurities (e.g., HER catalysts), a higher specific surface area, a higher total porosity, a different pore size distribution (e.g., multimodal to reduce mass transport resistance), a different pellet size distribution (e.g., multimodal to enhance bed packing), a different aspect ratio (e.g., to enhance bed packing), and the like. Mechanical processes that can be applied ex-situ to the pellets can include crushing, pulverization, and / or powdering, including, but not limited to, size reduction. Mechanical size reduction re-exposes the passivated metallic iron in the pellet core, providing access to previously inaccessible iron and thus increasing capacity. Note that mechanical processes that expose the initially passivated iron in the pellet core may not be desirable prior to battery use, since more exposed metallic iron provides more sites for hydrogen evolution reactions, either through Faradaic parasitic reactions during charging or through spontaneous self-discharge reactions. However, ex-situ mechanical processes may be desirable once the battery is in use, as a way to restore and / or improve capacity electrical resistance, which is diminished due to the passivated and inaccessible bulk of the iron, as shown, for example, in FIG. 17 . Specifically, FIG. 17 shows a post-battery use pellet 1702 that has been treated ex-situ by crushing, pulverization, etc. to expose the iron core 1703 of the pellet 1702.FIG. 17 shows a passivation layer 1705 that may prevent access to the core 1703 until after processing.

[0217] Thermal processes that can be applied to pellets ex-situ include treating the pellets at high temperatures in a reducing (e.g., hydrogen), oxidizing, and / or carburizing (e.g., carbon monoxide and / or carbon dioxide) atmosphere. In one particular embodiment, the reducing conditions are a gas mixture of 10% nitrogen, 30% carbon monoxide, 15% carbon dioxide, and 45% hydrogen at 800°C for 90 minutes. Electrochemical processes that can be applied to pellets ex-situ include reverse electroplating, electrochemical dissolution, and the like. Chemical processes that can be applied to pellets ex-situ include acid etching, and the like. In various embodiments, to increase the available capacity of the pellets during the discharge reaction, the pellets can be pretreated by immersion in an acid bath (e.g., concentrated HCl), which etches the iron and enlarges the pores of the pellets, increasing the overall porosity of the pellets compared to used pellets. In various embodiments, to increase the available capacity of the pellets during the discharge reaction, the pellets can be pretreated by immersion in a neutral or weakly basic bath, which removes excess discharge products from the electrodes. For example, iron(II) hydroxide, one of the expected discharge products, is typically unstable at pH < 8. By immersing in a bath with a pH < 8, iron(II) hydroxide is preferentially removed, while metallic iron is preserved in the electrode. For pH ranges > 7 and < 8, the bath can be a diluted form of the electrolyte used during electrochemical operation of the battery. After pretreatment, the etched, now more porous pellet can be reassembled into the negative electrode. The chemical process time can be optimized to increase the usable capacity of the pellet without excessive loss of active material to the acid etching solution. Any of the above processes can be optimized to preferentially enlarge the small pores in the pellet. In certain embodiments, the electrochemical process uses one or more high-current pulses that result in a non-uniform current distribution within the pellet, focusing the current at sharp, small physical features within the pellet, thereby preferentially driving electrochemical dissolution at the small physical features and thus enlarging the initially small pores.Additionally, any of the above processes may be performed prior to battery operation to improve the chemical and physical properties of the pellets compared to their unmodified, virgin state.

[0218] Electrolyte additives for controlling the morphological characteristics of discharge products

[0219] The shape and size of the discharge products within the pores of the iron pellet can affect performance in various ways. For example, a thin, uniform layer of discharge products can avoid pore clogging, thereby improving capacity retention. On the other hand, a thin, uniform layer of non-porous discharge products can passivate the underlying metallic iron, hindering mass transport of hydroxide ions through the discharge product layer during discharge and thus reducing the available capacity of the electrode. In another example, a non-uniform, high-surface-area porous discharge product can facilitate mass transport through the discharge layer while increasing the active surface area for the next discharge, both of which can increase the total available capacity. Figure 18 compares discharge product distributions. The left side of Figure 18 shows discharge products 1803, which are non-uniformly distributed on the surface of anode 1802. The right side of Figure 18 shows discharge products 1804, which form a uniform layer on the surface of anode 1802. Discharge product formation can be mediated by electrolyte additives, anode additives, and / or surface coatings on anode 1802. Various methods have been disclosed to control the morphological characteristics of discharge products at iron electrodes.

[0220] Additives and counterions in the electrolyte and / or electrodes can be used to control the morphological characteristics of the discharge products. Additives and counterions can alter the porosity and accessibility of electrochemically active sites in the discharge layer through the following mechanisms: Fe forms a two-layer discharge product with a relatively static inner layer of Fe3O4 and a highly porous outer layer, which is strongly influenced by the electrolyte composition. Divalent cations tend to inhibit uniform discharge and favor the production of a more porous outer layer. Monovalent cations inhibit uniform discharge and produce a more porous outer layer if they are not sufficiently size-matched to the Fe cations in the discharge product outer layer. For example, lithium and cesium cations tend to produce a more porous outer layer than sodium and potassium cations because their size is poorly matched to that of iron cations. Additives and counterions for controlling the morphological characteristics of the discharge products include, but are not limited to, sulfide (S2-), hydrosulfide (HS-), lithium cation (Li+), sodium cation (Na+), calcium cation (Ca2+), selenide (Se2-), cesium cation (C+), and barium cation (Ba2+). In certain embodiments, sodium sulfide, lithium hydroxide, sodium hydroxide, calcium hydroxide, sodium selenide, and / or barium hydroxide are added to the electrolyte at various concentrations to provide soluble additives and counterions that act to control the morphological characteristics of the discharge products.

[0221] In certain embodiments, an additive for controlling the morphological characteristics of the discharge products is initially contained within the solid-state electrode. The solid-state additive may be in the form of a solid-state metal oxide and / or metal sulfide that is introduced as a solid to the iron electrode. Metal sulfides and metal oxides of interest include, among others, FeS, FeS2, MnS, Bi2S3, Bi2O3, Sb2S3, FeAsS, PbS, SnS, HgS, AsS, Pb4FeSb6S 14 , Pb3Sn4FeSb2S 14 , SeS2.

[0222] In certain embodiments, additives for controlling the morphological characteristics of the discharge products include one or more of the following: sodium thiosulfate, sodium thiocyanate, polyethylene glycol (PEG) 1000, trimethylsulfoxonium iodide, zincate (by dissolving ZnO in NaOH), hexanethiol, decanethiol, sodium chloride, sodium permanganate, lead (IV) oxide, lead (II) oxide, magnesium oxide, sodium chlorate, sodium nitrate, sodium acetate, iron phosphate, phosphoric acid, sodium phosphate, ammonium sulfate, thio Ammonium sulfate, lithopone, magnesium sulfate, iron(III) acetylacetonate, hydroquinone monomethyl ether, sodium metavanadate, sodium chromate, glutaric acid, dimethyl phthalate, methyl methacrylate, methylpentynol, adipic acid, allyl urea, citric acid, thiomalic acid, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, propylene glycol, trimethoxysilylpropyldiethylene, aminopropyltrimethoxysilane, dimethylacetylenedicarboxylate (DMAD), 1,3-diethylthiourea, N,N'-Diethylthiourea, aminomethylpropanol, methylbutynol, amino-modified organosilane, succinic acid, isopropanolamine, phenoxyethanol, dipropylene glycol, benzoic acid, N-(2-aminoethyl)-3-aminopropyl, behenamide, 2-phosphonobutanetricarboxylic acid, MIPA borate, 3-methacryloxypropyltrimethoxysilane, 2-ethylhexanoic acid, isobutyl alcohol, t-butylaminoethyl methacrylate, diisopropanolamine, propylene glycol n-propyl ether, sodium benzotriazole, aminotrimethylenephosphonic acid Ingredients: pentasodium cocoyl sarcosinate, sodium cocoyl sarcosinate, lauryl pyridinium chloride, steartrimonium chloride, stearalkonium chloride, calcium montanate, quaternium-18 chloride, sodium hexametaphosphate, dicyclohexylamine nitrite, lead stearate, calcium dinonylnaphthalene sulfonate, iron(II) sulfide, sodium hydrogen sulfide, iron pyrite, sodium nitrite, complex alkyl phosphate ester (e.g., RHODAFAC® RA600 emulsifier), 4-mercaptobenzoic acid, ethylenediaminetetraacetic acid, ethylenediaminetetraacetate (EDTA), 1,3-Propylenediaminetetraacetate (PDTA), nitrilotriacetate (NTA), ethylenediamine disuccinate (EDDS), diethylenetriaminepentaacetate (DTPA), and other aminopolycarboxylates (APC), diethylenetriaminepentaacetic acid, 2-methylbenzenethiol, 1-octanethiol, bismuth sulfide, bismuth oxide, antimony(III) sulfide, antimony(III) oxide, antimony(V) oxide, bismuth selenide, and antimony selenide. Thione, selenium sulfide, selenium(IV) oxide, propargyl alcohol, 5-hexyn-1-ol, 1-hexyn-3-ol, N-allylthiourea, thiourea, 4-methylcatechol, trans-cinnamaldehyde, iron(III) sulfide, calcium nitrate, hydroxylamine, benzotriazole, furfurylamine, quinoline, tin(II) chloride, ascorbic acid, tetraethylammonium hydroxide, calcium carbonate, magnesium carbonate, antimony dialkylphosphorodithioate, Potassium stannate, sodium stannate, tannic acid, gelatin, saponin, agar, 8-hydroxyquinoline, bismuth stannate, potassium gluconate, lithium molybdenum oxide, potassium molybdenum oxide, hydrogenated light oil, heavy naphthenic petroleum fractions (e.g., sold as Rustlick® 631), antimony sulfate, antimony acetate, bismuth acetate, hydrotreated heavy naphtha (e.g., sold as WD-40®), tetramethylammonium hydroxide, Na Sb tartrate, urea, D-glucose, C6Na2O6, potassium antimony tartrate, hydrazine sulfate, silica gel, triethylamine, potassium antimonate trihydrate, sodium hydroxide, 1,3-di-o-tolyl-2-thiourea, 1,2-diethyl-2-thiourea, 1,2-diisopropyl-2-thiourea, N-phenylthiourea, N-diphenylthiourea, sodium antimony L-tartrate, rhodizonic acid disodium salt, sodium selenide, potassium sulfide, and combinations thereof.

[0223] Pretreatment involving electrochemical cycling can also play a role in controlling the morphological characteristics of the discharge products of the iron electrode. For example, the inventors have observed that the density of the discharge products varies with temperature and current density. Pretreatment involving electrochemical cycling at temperatures and current densities that are not necessarily the nominal operating conditions of the battery can be used to create morphological characteristics of the discharge products that are conductive to high available capacity and persist when operating conditions are set to nominal values ​​after pretreatment. In various embodiments, the pretreatment consists of 100 deep electrochemical charge-discharge cycles at a gravimetric current density of 25 mA / gFe at 10°C.

[0224] Using temperature as a means to improve performance

[0225] The inventors have found that lowering the operating temperature of iron electrodes below 30°C improves various performance attributes, including specific capacity, retention of specific capacity over multiple electrochemical cycles, and electrode coulombic efficiency. Various mechanisms may operate simultaneously to produce these effects. For example, lower temperatures can improve specific capacity by increasing the electrical conductivity of electrode materials, including, but not limited to, iron and iron oxide discharge products. Increased electrical conductivity of the electrode material enhances electrical transport to electrochemical reaction sites, leading to increased specific capacity at a given polarization limit of the electrode. In another example, lowering the temperature can slow the kinetics of undesirable electrolyte degradation or poisoning reactions that occur during the life of a battery, such as carbonate formation from atmospheric carbon dioxide. For example, carbonate formation consumes OH ions and reduces the conductivity of the electrolyte, lowering the solution pH and leading to a decrease in specific capacity. Lowering the temperature slows these undesirable reactions, resulting in better specific capacity retention in the iron electrode over the life of the battery. In another example, lowering the temperature can make the kinetics of the undesired hydrogen evolution reaction much slower than the desired iron reduction reaction during charging of the battery, thus resulting in higher coulombic efficiency during charging. In various embodiments, the iron electrode is maintained at 20°C ± 5°C to improve electrode performance. In other embodiments, the iron electrode is maintained at 10°C ± 5°C to improve electrode performance. Figure 19 is a plot of specific capacity and coulombic efficiency versus temperature for cycle number.

[0226] Redox mediators for improved performance

[0227] Better electrochemical kinetics of the charge (reduction) and discharge (oxidation) reactions at iron-based electrodes will improve both the voltage and coulombic efficiency of the cell. Redox mediators can be used to improve the electrochemical kinetics of iron-based electrodes. Redox mediators are chemical compounds that act as electron "shuttles" to mediate reduction or oxidation reactions. Also, typically used in biocatalysis, redox mediators can be used to promote desired oxidation and reduction reactions at iron-based electrodes. Requirements for a redox mediator include: (1) rapid and reversible redox kinetics; (2) a redox potential similar to that of the reaction it promotes (including, but not limited to, Fe⇔Fe(OH)2 and / or Fe(OH)2⇔Fe3O4); and (3) stability in the presence of the desired electrolyte. Redox mediators can be either soluble or insoluble in the desired electrolyte. In some embodiments, the redox mediator contains one or more unsaturated basic groups, saturated basic groups, or a combination thereof. In some embodiments, the basic groups contain electron-withdrawing functional groups, electron-donating functional groups, or a combination thereof. In certain embodiments, the unsaturated basic groups include, but are not limited to, cyclopenta-1,3-diene, benzene, 1H-pyrrole, pyridine, pyrazine, furan, 4H-pyran, 1,4-dioxin, thiophene, 4H-thiopyran, 1,4-dithiin, 1-methyl-1H-pyrrole, or a combination thereof. In certain embodiments, the saturated basic groups include, but are not limited to, cyclopentane, cyclohexane, 1,4-dioxane, tetrahydrofuran, tetrahydro-2H-pyran, 1,4-dithiane, tetrahydrothiophene, tetrahydro-2H-thiopyran, 1,4-dimethylpiperazine, 1,3,5-toluoxane, 1,3,5-trithiane, or a combination thereof. In certain embodiments, electron-withdrawing functional groups include, but are not limited to, nitro, trichloro, cyano, carboxyl, fluoro, hydroxyl, or combinations thereof.In certain embodiments, the electron-donating functional group includes, but is not limited to, a primary amine, a secondary amine, a tertiary amine, an amide, a methoxy, a methyl, an alkyl, an alkenyl, an alkynyl, a phenyl, or a combination thereof. In one embodiment, the redox mediator of the iron-based anode is a viologen-based compound. In certain embodiments, the viologen-based compound includes, but is not limited to, methyl viologen, propyl viologen, hexyl viologen, octyl viologen, or a combination thereof.

[0228] Electrolyte-mediated sulfide uptake into iron electrodes.

[0229] In electrochemical cells with iron electrodes, adding sulfur to the cell unlocks the utilization of the iron electrode. However, because sulfur is a known catalyst poison, electrochemical cell embodiments with catalytic cathodes may be optimal with a high sulfur concentration near the iron electrode and a low sulfur concentration at the catalytic electrode.

[0230] In one embodiment, sulfur can be concentrated at the iron electrode by immersing the iron electrode in a highly concentrated sulfur solution before placing it in an electrochemical cell. Furthermore, when the iron electrode is subjected to a single formation cycle of charge and then discharge, sulfur will be electrochemically added to the structure of the iron electrode. When then added to the desired electrochemical cell, sulfur will remain concentrated near the anode.

[0231] In certain embodiments, the iron electrode is immersed in a high sulfide (i.e., >50 mM) electrolyte before cycling in a low sulfide (i.e., 50 mM) electrolyte.

[0232] In one particular embodiment, a porous iron electrode is immersed in an electrolyte bath along with any alkali or transition metal sulfide (NaS, KS, BiS, SbS, etc.) to increase the presence of sulfide.

[0233] In certain embodiments, sulfide is incorporated by immersion in a high sulfide concentration electrolyte prior to cycling, after which the positive electrode is inserted into the complete cell, and the initial sulfide concentration may range from 10 to 250 mM (1.4 to 33.8 mg S / g Fe) or even higher.

[0234] In one non-limiting example, the porous iron electrode described above comprises a bed of DRI pellets.

[0235] It is difficult to incorporate sulfide or other beneficial additives uniformly or in a controlled manner into porous iron electrodes. One method for uniformly incorporating additives into porous materials is vacuum infiltration. In this method, the substrate is exposed to a vacuum (<1 atm) to evacuate the pores, and then exposed to a liquid or molten additive to fill any voids in the material.

[0236] In various embodiments, the substrate is subjected to a vacuum sufficient to evacuate the pores. One exemplary method for evacuating the pores is shown in Figure 20. In a first step, the substrate 2000 is subjected to a high vacuum to evacuate the pores 2001.

[0237] In one embodiment, in a second step, the evacuated substrate is then exposed to an aqueous electrolyte formulation containing additives as previously specified at a temperature of 0-250° C., resulting in pores that are completely or partially filled with additive 2002. After a specified time, such as less than 48 hours, in a third step, the substrate 2000 can be rinsed or centrifuged to remove excess electrolyte.

[0238] In one embodiment, the evacuated substrate is then exposed to an additive in liquid or molten form at a temperature of 25-250°C or 250-2000°C, where the additive is one previously specified in Section ## (e.g., octanethiol, FeS) that one skilled in the art can identify as compatible with the melting process. After the specified time of less than 48 hours, the substrate can be rinsed or centrifuged to remove excess liquid or molten material.

[0239] In one embodiment, the evacuated substrate is then exposed to a gaseous additive (e.g., H2S, H2Se, CS2, PH3 above 50° C.) After a specified time, such as less than 48 hours, the substrate can be purged with an inert gas or under vacuum to remove excess gaseous additive.

[0240] In a non-limiting example, a solution containing sodium sulfide is vacuum infiltrated into the pores of the porous iron electrode 2000 prior to cycling to improve permeation. Better permeation of sulfide into the anode can improve overall performance capabilities.

[0241] In a non-limiting example, sodium thiosulfate is heated until molten (>45° C.) and vacuum infiltrated into the pores of a porous iron electrode prior to cycling.

[0242] An additional method for localizing sulfide to an iron particulate electrode involves encapsulating the sulfide additive in a variable permeability holder within or adjacent to the electrode. In this way, controlled amounts of sulfide can be added to the iron particulate electrode by passive or active electrochemical or chemical dissolution.

[0243] In one embodiment, the additive may be contained in a fully permeable or semi-permeable holder, the holder being made of a plastic (e.g., polypropylene, polyethylene) that is stable in alkaline solutions.

[0244] In one embodiment, the additive may be stored in a holder behind an ion-selective membrane, allowing the electrolyte to flow into the holder and the additive to slowly diffuse into solution.

[0245] In one embodiment, the additive may be housed in an electrically conductive material (eg, a conductive polymer mesh, a metallic wire mesh).

[0246] In one embodiment, the holder may be made from a layer of porous oxide (eg, silica).

[0247] In one embodiment, the additive holder may be in physical, electrical, or physical and electrical contact with the iron particulate material electrode.

[0248] In one embodiment, the additive holder may be in contact with the electrolyte or may only be in contact with the iron particulate material electrode via ion transport in the electrolyte.

[0249] In one embodiment, the additive holder may be immersed in a separate container of electrolyte to provide a constant sulfide source, and the electrolyte in contact with the iron particulate material electrode is then replaced with the electrolyte in contact with the additive holder.

[0250] In one embodiment, the additive holder may be in electrical contact with a potentiostat or system that maintains the holder at a potential that prevents dissolution of the additive within the holder. Example additive holder configurations are shown in Figure 21. In the configuration shown in the top of Figure 21, an additive-storing bag 2104 may be in contact with iron particulate material 2103 disposed between current collectors 2102 in electrolyte 2100 along with iron particulate material 2103. In the configuration shown in the bottom of Figure 21, the additive-storing bag 2104 may be suspended in electrolyte 2100, separate from iron particulate material 2103 and current collectors 2102, such as by optional electrical connection 2110.

[0251] Solid sulfur-containing additives

[0252] Sulfide ions in electrolyte solutions have been shown to increase the available capacity and cycling performance of iron electrodes in alkaline secondary batteries. However, as sulfide ions decrease in concentration in the electrolyte with cycle count and aging over time, it has been shown that the positive impact of dissolved sulfide on anode performance may be reduced. One way to enable performance improvements over lifetime is to incorporate sulfur-containing species directly into the iron electrode material.

[0253] In one embodiment, elemental sulfur is introduced directly into the porous iron anode by melt diffusing the sulfur into the porous metal. The sulfur is then introduced to the anode as a solid, coming into intimate contact with the active metal anode material and promoting positive interactions that improve available capacity and cycle life.

[0254] In another embodiment, the metal sulfide is introduced to the iron anode as a solid. Metal sulfides of interest include, among others, FeS, FeS2, MnS, Bi2S3, Sb2S3, FeAsS, PbS, SnS, HgS, AsS, Pb4FeSb6S 14 , Pb3Sn4FeSb2S 14 , SeS2. Cations in metal sulfides can contribute to the battery capacity (i.e., Fe), be inert to the charge / discharge reactions (i.e., Mn), or retard the hydrogen evolution reaction (i.e., Pb, Sb, Hg, As, Bi).

[0255] In one non-limiting example, metal sulfides are incorporated into a bed of direct reduced iron (DRI) pellets.

[0256] Methods for incorporating sulfur-containing species into iron electrodes include, but are not limited to, the following: (1) incorporating bulk solid particles, powder, or agglomerates into the voids between materials in the electrode bed; (2) incorporating metal sulfides (i.e., BiS) with melting points lower than that of iron metal into the electrode pores by melt diffusion; (3) incorporating metal sulfide powder by mixing into oxide ore pellets (i.e., taconite pellets) during the pelletizing process (in such embodiments, the metal sulfide remains in the pellets after the reduction process, producing pellets having metallic iron, metal sulfide, and impurities); (4) incorporating metal sulfide into pellets containing only metal sulfide and binder; in one non-binding example, such pellets can be directly incorporated into a pellet bed of a DRI in a specific ratio with the DRI pellets; and (5) incorporating metal sulfide powder using mixing, milling, or rolling equipment, such as a ball mill.

[0257] In another embodiment, the above-referenced incorporation methods are used with sulfur-containing additives, including but not limited to metal sulfides.

[0258] In another embodiment, sulfur-containing additives, including but not limited to metal sulfides, are incorporated into the iron anode material by a trommel sieving step of DRI production, such as that shown in FIG. 22, where DRI pellets 2200 in a mesh cylinder are injected with the sulfur additive during production, resulting in DRI 2202 with sulfur additive pellets.

[0259] Incorporation of sulfide and other anionic species into Fe anodes.

[0260] Uniform or controlled incorporation of additives into preformed metal electrodes is difficult, limiting the effectiveness of the additives.

[0261] Various embodiments include selective precipitation with reactive counterions. In various embodiments, metals are incorporated into particulate iron material electrodes in a neutral or oxidized state and then reacted with selected counterions. The concentration of the metal additive is determined by the solubility of the source compound or the final desired concentration of the reactive counterion in the electrode. In certain embodiments, the electrode forms compounds (e.g., CdS, BiS, BiSe) in situ upon exposure to an electrolyte containing a source of reactive counterions (e.g., NaS, KS, NaSe, NaTe), with localization and concentration determined by the presence, concentration, and solubility of the additive metal, reactive counterion, or resulting compound. In certain embodiments, the availability of such additives can be further tuned by using fugitive pore-forming agents. In certain embodiments, to control the incorporation of reactive counterions, the electrode is electrochemically cycled before or after exposure to an electrolyte containing a specified concentration of reactive counterions.

[0262] In a non-binding example, 0.5-10 wt% Bi2O3 is incorporated into an electrode and then electrochemically cycled to a potential where it is sufficiently reduced to form Bi(s). Exposure to an electrolyte containing 250 mM Na2S can form Bi2S3, which is distributed throughout the electrode, via the reaction shown below:

[0263] [ka]

[0264] [ka]

[0265] In various embodiments, the additive of interest, which is a source of sulfur, selenium, tellurium, nitrogen, or phosphorus (e.g., NaS, NaSe, NaPO), is incorporated into the electrode at a concentration determined by the solubility of the source compound or the final desired concentration of the final compound in the electrode.

[0266] In certain embodiments, the electrode is exposed to an electrolyte containing a reactive metal (e.g., Fe, Bi, Hg, As, Cd, Cu, Ni, In, Tl, Zn, Mn, Ag) or metal-containing ion (e.g., Bi(NO3)3, NaAsO4, Cd(NO3)2, CuSO4·xH2O (where x = 0-12)) to form a compound (e.g., CdS, Bi2S3, Bi2Se3) in situ, with localization and concentration determined by the presence, concentration, and solubility of the additive metal, reactive counterion, or resulting compound. The solubility of non-metallic additives can create local concentration gradients in the electrolyte, resulting in regions where precipitation is more favored. In certain embodiments, the availability of such additives can be further tuned by using fugitive pore-forming agents. In certain embodiments, to control the uptake of the metal or metal-containing ion, the electrode is electrochemically cycled before or after exposure to an electrolyte containing a specified concentration of the metal or metal-containing ion.

[0267] In a non-binding example, Na2S may be incorporated into a metal electrode by exposure to an electrolyte containing Bi(NO3)3 to form Bi2S3, which is distributed throughout the electrode, via the reaction shown below:

[0268] [ka]

[0269] In various embodiments, a target additive (e.g., S or Se metal), which is a source of sulfur, selenium, tellurium, nitrogen, or phosphorus, but which may not itself be ionic, is incorporated into the electrode at a concentration determined by the solubility of the source compound or the final desired concentration of the final compound in the electrode.

[0270] In various embodiments, this electrode containing a non-reactive additive, in one embodiment NaOH or KOH, in one embodiment, when electrochemically cycled, generates anionic species (e.g., S2) at the anode or in the electrolyte. - , S2 2- The anode may be exposed to an electrolyte that generates counterions (BiS, polysulfides). As shown in Figure 23, these species may react to form BiS on the surface or may be encapsulated in the anode. Exposing the anode to this electrolyte allows the counterions to react and increase overall porosity, which may be beneficial to overall available capacity.

[0271] Improved lifespan of sulfides in electrolyte

[0272] Additives that are water and air sensitive can decompose rapidly in aqueous alkaline electrolytes. For example, sulfides (S), such as NaS or NaSH, 2- ) and disulfide (HS - )-containing compounds decompose when exposed to oxygen by forming sulfates or other sulfur-containing compounds (e.g., sulfites, thiosulfates, sulfur, polysulfides).

[0273] [ka]

[0274] [ka]

[0275] [ka]

[0276] [ka]

[0277] Because it is difficult to reduce sulfates or other oxidized sulfur-containing compounds to sulfide, disulfide, or hydrogen sulfide, it is advantageous to maintain the sulfur species in the electrode or electrolyte as sulfide or disulfide.

[0278] In one embodiment, oxidized sulfur-containing species (e.g., Na2SO4, Na2S2O3, Na2SO3, S metal) are added to the electrolyte in an amount sufficient to reduce or completely suppress the formation of oxidized sulfur species by shifting the equilibrium in favor of reduced sulfur species according to Le Chatelier's principle.

[0279] In one embodiment, sulfur-containing oxide species (e.g., Na2SO4, Na2S2O3, Na2SO3, S metal) are added to the electrode. Upon exposure to the electrolyte, these soluble additives dissolve in the electrolyte, increasing the porosity of the electrode and reducing or inhibiting the formation of sulfur-containing oxide species in solution.

[0280] In one embodiment, oxidized sulfur-containing species (e.g., FeSO4, FeS2O3, FeSO3) that further contain metallic cations are added to inhibit oxidation of reduced sulfur species as well as dissolution of metallic species from the iron electrode.

[0281] High sulfide compatibility of DRI-based iron-air batteries

[0282] The DRI-based iron anode exhibits compatibility over a wide range of initial sulfide concentrations in the electrolyte. Additionally, it has been shown that the driving factor is the initial sulfide concentration in gS / gFe, not the sulfide concentration in the electrolyte.

[0283] In one particular embodiment, an initial sulfide concentration of 1 mM Na2S (0.1 mgS / gFe) is sufficient for stable capacity performance.

[0284] In one particular embodiment, an initial sulfide concentration of 10 mM Na2S (1.4 mgS / gFe) is sufficient for stable capacity performance.

[0285] In one particular embodiment, an initial sulfide concentration of 50 mM Na2S (6.8 mgS / gFe) is sufficient for stable capacity performance.

[0286] In one particular embodiment, an initial sulfide concentration of 175 mM Na2S (23.6 gS / gFe) is sufficient for stable capacity performance.

[0287] In certain embodiments, an initial sulfide concentration of >=250 mM Na2S (33.8 gS / gFe) is sufficient for stable capacity performance.

[0288] Furthermore, the method for incorporating sulfide into the iron anode can be accomplished by a variety of techniques.

[0289] In one particular embodiment, sulfide is incorporated via a high sulfide concentration electrolyte in a complete cell.

[0290] In certain embodiments, sulfide is incorporated by immersion in a high sulfide concentration electrolyte before cycling, which can be completed in a non-sulfide containing electrolyte (which can be beneficial to the positive electrode).

[0291] In certain embodiments, sulfide is incorporated by immersion in a high sulfide concentration electrolyte prior to cycling, after which the positive electrode is inserted into the complete cell, and the sulfide concentration may range from 10 to 250 mM (1.4 to 33.8 mg S / g Fe).

[0292] Optimal sulfide incorporation can also be achieved through maintenance methods, including, but not limited to: 1) periodic addition of high sulfide concentration in solution or solid form; and 2) continuous addition of sulfide in solid or solution form, in which case the sulfide concentration may range from 10 to 250 mM (1.4 to 33.8 mg S / g Fe) or higher.

[0293] In an embodiment, -325 mesh iron sponge powder, with open porosity to the interior of the particles, is thermally bonded by sintering to form the substrate of the iron electrode material. Bismuth oxide and iron sulfide are incorporated throughout the sintered electrode material, and the material is thermally bonded to a current-collecting perforated sheet. The sintered connection to the current collector and between the powder particles eliminates the need for compression to achieve electrical conductivity. The alkaline electrolyte is composed of a mixture of 80% potassium hydroxide, 15% sodium hydroxide, and 5% lithium hydroxide on a molar basis, with a total hydroxide concentration in the aqueous solution of 6 molar (mol / L).

[0294] In one embodiment, the iron electrode material may include direct-reduced iron pellets, and the electrolyte may include 6 molar potassium hydroxide, 0.1 molar lithium hydroxide, and 0.05 molar sodium sulfide. The iron electrode may further include 1 wt. % bismuth sulfide finely distributed among the direct-reduced iron pellets. The electrode material may be compressed within a rigid cage containing nickel-plated current-collecting stainless steel plates that apply uniaxial pressure to compress the pellets within a rigid wall structure composed of poly(methyl methacrylate), with the current-collecting plates held in place by stainless steel bolts that are electrically insulated from the current collector. The bed thickness of such an embodiment may range from 1 to 10 centimeters thick.

[0295] In one embodiment, the iron electrode material may include carbonyl iron powder, lead oxide, and iron sulfide. 0.1 wt. % lead oxide is added, and 1.5 wt. % iron sulfide is included, both based on the total weight of the solids in the electrode. The solids are lightly sintered to bond and agglomerate them, then pressed into a woven nickel mesh cloth, which is compressed by expanding a polyethylene balloon. The electrolyte is 5 molar sodium hydroxide with additives of 0.005 molar sodium sulfide and 0.01 molar octanethiol.

[0296] In another embodiment, direct reduced iron pellets are crushed to form particle sizes ranging from 1 to 6 mm. The particles are mixed with 1% by weight of the solid mixture of natural flake graphite having a particle size of 200 microns and 0.05% by weight of iron sulfide having a particle size of 100 microns. The electrolyte is aqueous and has 6.5 molar potassium hydroxide, 0.5 molar lithium hydroxide, 0.25 molar sodium sulfide, and 0.001 molar octanethiol. The solid mixture is loaded into a nickel mesh bag with a mesh size of approximately 0.5 mm, and the bag is compressed with a clamping mechanism to lightly compress the solid material.

[0297] Various embodiments may provide devices and / or methods for use in bulk energy storage systems, such as long-term energy storage (LODES) systems and short-term energy storage (SDES) systems. As an example, various embodiments may provide batteries for bulk energy storage systems, such as batteries for LODES systems. Renewable energy sources are becoming increasingly prevalent and cost-effective. However, many renewable energy sources face intermittency issues that hinder their adoption. The impact of renewable energy sources' tendency toward intermittency can be mitigated by pairing them with bulk energy storage systems, such as LODES systems and SDES systems. To support the adoption of combined generation, transmission, and storage systems (e.g., renewable generation sources paired with bulk energy storage systems, and power plants with transmission facilities at either the power plant and / or bulk energy storage system), devices and methods are needed to support the design and operation of such combined generation, transmission, and storage systems, such as the various embodiment devices and methods described herein.

[0298] An integrated generation, transmission, and storage system may be a power plant that includes one or more power generation sources (e.g., one or more renewable power generation sources, one or more non-renewable power generation sources, a combination of renewable and non-renewable power generation sources, etc.), one or more transmission facilities, and one or more bulk energy storage systems. The transmission facilities in either the power plant and / or the bulk energy storage systems may be co-optimized with the power generation and storage systems or may impose constraints on the design and operation of the power generation and storage systems. Integrated generation, transmission, and storage systems can be configured to meet various output targets under various design and operational constraints.

[0299] 24-32 illustrate various exemplary systems in which one or more aspects of various embodiments can be used as part of a bulk energy storage system, such as a LODES system, an SDES system, etc. For example, various embodiments described herein with reference to FIGS. 1-32 can be used as batteries for a bulk energy storage system, such as a LODES system, an SDES system, etc., and / or various electrodes as described herein can be used as components of a bulk energy storage system. As used herein, the term "LODES system" refers to a bulk energy storage system configured to have a rated duration (energy / power ratio) of 24 hours (h) or longer, such as a 24-hour duration, a duration between 24 hours and 50 hours, a duration greater than 50 hours, a duration between 24 hours and 150 hours, a duration greater than 150 hours, a duration between 24 hours and 200 hours, a duration greater than 200 hours, a duration between 24 hours and 500 hours, or a duration greater than 500 hours.

[0300] 24 illustrates an exemplary system in which one or more aspects of various embodiments can be used as part of a bulk energy storage system. As a specific example, a bulk energy storage system incorporating one or more aspects of various embodiments may be a LODES system 2404. By way of example, the LODES system 2404 may include various embodiment batteries described herein, various electrodes described herein, etc. The LODES system 2404 may be electrically connected to a wind farm 2402 and one or more transmission facilities 2406. The wind farm 2402 may be electrically connected to the transmission facility 2406. The transmission facility 2406 may be electrically connected to an electrical grid 2408. The wind farm 2402 may generate electrical power, and the wind farm 2402 may output the generated electrical power to the LODES system 2404 and / or the transmission facility 2406. The LODES system 2404 may store electrical power received from the wind farm 2402 and / or the transmission facility 2406. LODES system 2404 can output the stored power to transmission facility 2406. Transmission facility 2406 can output power received from one or both of wind farm 2402 and LODES system 2404 to the grid 2408 and / or can receive power from the grid 2408 and output the power to LODES system 2404. Wind farm 2402, LODES system 2404, and transmission facility 2406 can together comprise power plant 2400, which may be an integrated power, transmission, and storage system. Power generated by wind farm 2402 may be fed directly to the grid 2408 via transmission facility 2406 or may first be stored in LODES system 2404. In certain cases, the power supplied to the power grid 2408 may be entirely from the wind farm 2402, entirely from the LODES system 2404, or from a combination of the wind farm 2402 and the LODES system 2404.The distribution of power from the combined wind farm 2402 and LODES system 2404 power plant 2400 may be controlled according to a predetermined long-term (multi-day or even multi-year) schedule, or may be controlled according to a day-ahead (24-hour advance notice) market, or may be controlled according to an hour-ahead market, or may be controlled in response to real-time pricing signals.

[0301] In one example of the operation of the power plant 2400, the LODES system 2404 can be used to reshape and "stabilize" the power produced by the wind farm 2402. In one such example, the wind farm 2402 may have a peak power output (capacity) of 260 megawatts (MW) and a capacity factor (CF) of 41%. The LODES system 2404 may have a power rating (capacity) of 106 MW, a rated duration (energy / power ratio) of 150 hours (h), and a rated energy of 15,900 megawatt-hours (MWh). In another such example, the wind farm 2402 may have a peak power output (capacity) of 300 MW and a capacity factor (CF) of 41%. The LODES system 2404 may have a power rating (capacity) of 106 MW, a rated duration (energy / power ratio) of 200 hours, and a rated energy of 21,200 MWh. In another such example, the wind farm 2402 may have a peak power output (capacity) of 176 MW and a capacity factor (CF) of 53%. The LODES system 2404 may have a power rating (capacity) of 88 MW, a rated duration (energy / power ratio) of 150 hours, and a rated energy of 13,200 MWh. In another such example, the wind farm 2402 may have a peak power output (capacity) of 277 MW and a capacity factor (CF) of 41%. The LODES system 2404 may have a power rating (capacity) of 97 MW, a rated duration (energy / power ratio) of 50 hours, and a rated energy of 4,850 MWh. In another such example, the wind farm 2402 may have a peak power output (capacity) of 315 MW and a capacity factor (CF) of 41%. The LODES system 2404 may have a power rating (capacity) of 110 MW, a rated duration (energy / power ratio) of 25 hours, and a rated energy of 2,750 MWh.

[0302] FIG. 25 illustrates an exemplary system in which one or more aspects of various embodiments can be used as part of a bulk energy storage system. As a specific example, a bulk energy storage system incorporating one or more aspects of various embodiments may be a LODES system 2404. By way of example, the LODES system 2404 may include various embodiment batteries described herein, various electrodes described herein, etc. The system of FIG. 25 may be similar to the system of FIG. 24, except that a photovoltaic (PV) station 2502 may be used instead of the wind power station 2402. The LODES system 2404 may be electrically connected to the PV station 2502 and one or more transmission facilities 2406. The PV station 2502 may be electrically connected to the transmission facility 2406. The transmission facility 2406 may be electrically connected to the power grid 2408. The PV station 2502 may generate power, and the PV station 2502 may output the generated power to the LODES system 2404 and / or the transmission facility 2406. The LODES system 2404 can store power received from the PV station 2502 and / or the transmission facility 2406. The LODES system 2404 can output the stored power to the transmission facility 2406. The transmission facility 2406 can output power received from one or both of the PV station 2502 and the LODES system 2404 to the grid 2408 and / or can receive power from the grid 2408 and output the power to the LODES system 2404. The PV station 2502, the LODES system 2404, and the transmission facility 2406 can together comprise a power plant 2500, which may be an integrated power, transmission, and storage system. Power generated by the PV station 2502 may be fed directly to the grid 2408 via the transmission facility 2406 or may first be stored in the LODES system 2404. In certain cases, the power supplied to the power grid 2408 may be entirely from the PV station 2502, entirely from the LODES system 2404, or from a combination of the PV station 2502 and the LODES system 2404.The distribution of power from the combined PV base 2502 and LODES system 2404 power plant 2500 may be controlled according to a predetermined long-term (multi-day or even multi-year) schedule, or may be controlled according to a day-ahead (24-hour advance notice) market, or may be controlled according to an hour-ahead market, or may be controlled in response to real-time pricing signals.

[0303] As one example of the operation of the power plant 2500, the LODES system 2404 may be used to reshape and "balance" the power produced by the PV station 2502. In one such example, the PV station 2502 may have a peak power output (capacity) of 490 MW and a capacity factor (CF) of 24%. The LODES system 2404 may have a power rating (capacity) of 340 MW, a rated duration (energy / power ratio) of 150 hours, and a rated energy of 51,000 MWh. In another such example, the PV station 2502 may have a peak power output (capacity) of 680 MW and a capacity factor (CF) of 24%. The LODES system 2404 may have a power rating (capacity) of 410 MW, a rated duration (energy / power ratio) of 200 hours, and a rated energy of 82,000 MWh. In another such example, the PV station 2502 may have a peak power output (capacity) of 330 MW and a capacity factor (CF) of 31%. The LODES system 2404 may have a power rating (capacity) of 215 MW, a rated duration (energy / power ratio) of 150 hours, and a rated energy of 32,250 MWh. In another such example, the PV station 2502 may have a peak power output (capacity) of 510 MW and a capacity factor (CF) of 24%. The LODES system 2404 may have a power rating (capacity) of 380 MW, a rated duration (energy / power ratio) of 50 hours, and a rated energy of 19,000 MWh. In another such example, the PV station 2502 may have a peak power output (capacity) of 630 MW and a capacity factor (CF) of 24%. The LODES system 2404 may have a power rating (capacity) of 380 MW, a rated duration (energy / power ratio) of 25 hours, and a rated energy of 9,500 MWh.

[0304] Figure 26 illustrates an exemplary system in which one or more aspects of various embodiments can be used as part of a bulk energy storage system. As a specific example, the bulk energy storage system incorporating one or more aspects of various embodiments may be a LODES system 2404. By way of example, the LODES system 2404 may include various embodiment batteries described herein, various electrodes described herein, etc. The system of Figure 26 may be similar to the systems of Figures 24 and 25, except that a wind farm 2402 and a photovoltaic (PV) farm 2502 may both be power generating devices operating together in a power generation plant 2600. The PV farm 2502, wind farm 2402, LODES system 2404, and transmission facility 2406 may together comprise a power generation plant 2600, which may be a combined power generation, transmission, and storage system. Electricity generated by the PV sites 2502 and / or wind farms 2402 may be fed directly into the grid 2408 via transmission equipment 2406, or may first be stored in the LODES system 2404. In certain cases, the electricity supplied to the grid 2408 may come entirely from the PV sites 2502, entirely from the wind farms 2402, entirely from the LODES system 2404, or from a combination of the PV sites 2502, wind farms 2402, and LODES system 2404. The distribution of electricity from the combined wind farm 2402, PV sites 2502, and LODES system 2404 power plant 2600 may be controlled according to a predetermined long-term (multi-day or even multi-year) schedule, or according to a day-ahead (24-hour advance notice) market, or according to an hour-ahead market, or in response to real-time pricing signals.

[0305] In one example of the operation of the power plant 2600, the LODES system 2404 may be used to reshape and "stabilize" the power produced by the wind farm 2402 and the PV farm 2502. In one such example, the wind farm 2402 may have a peak power output (capacity) of 126 MW and a capacity factor (CF) of 41%, and the PV farm 2502 may have a peak power output (capacity) of 126 MW and a capacity factor (CF) of 24%. The LODES system 2404 may have a power rating (capacity) of 63 MW, a rated duration (energy / power ratio) of 150 hours, and a rated energy of 9,450 MWh. In another such example, the wind farm 2402 may have a peak power output (capacity) of 170 MW and a capacity factor (CF) of 41%, and the PV farm 2502 may have a peak power output (capacity) of 110 MW and a capacity factor (CF) of 24%. The LODES system 2404 may have a power rating (capacity) of 57 MW, a rated duration (energy / power ratio) of 200 hours, and a rated energy of 11,400 MWh. In another such example, the wind farm 2402 may have a peak power output (capacity) of 105 MW and a capacity factor (CF) of 51%, and the PV farm 2502 may have a peak power output (capacity) of 70 MW and a capacity factor (CF) of 31%. The LODES system 2404 may have a power rating (capacity) of 61 MW, a rated duration (energy / power ratio) of 150 hours, and a rated energy of 9,150 MWh. In another such example, wind farm 2402 may have a peak power output (capacity) of 135 MW and a capacity factor (CF) of 41%, and PV farm 2502 may have a peak power output (capacity) of 90 MW and a capacity factor (CF) of 24%. LODES system 2404 may have a power rating (capacity) of 68 MW, a rated duration (energy / power ratio) of 50 hours, and a rated energy of 3,400 MWh. In another such example, wind farm 2402 may have a peak power output (capacity) of 144 MW and a capacity factor (CF) of 41%, and PV farm 2502 may have a peak power output (capacity) of 96 MW and a capacity factor (CF) of 24%.The LODES system 2404 may have a power rating (capacity) of 72 MW, a rated duration (energy / power ratio) of 25 hours, and a rated energy of 1,800 MWh.

[0306] FIG. 27 illustrates an exemplary system in which one or more aspects of various embodiments can be used as part of a bulk energy storage system. As a specific example, a bulk energy storage system incorporating one or more aspects of various embodiments may be a LODES system 2404. By way of example, the LODES system 2404 may include various embodiment batteries described herein, various electrodes described herein, etc. The LODES system 2404 may be electrically connected to one or more transmission facilities 2406. In this manner, the LODES system 2404 may operate in a "standalone" manner to arbitrate energy near market prices and / or avoid transmission constraints. The LODES system 2404 may be electrically connected to one or more transmission facilities 2406. The transmission facilities 2406 may be electrically connected to a distribution grid 2408. The LODES system 2404 may store power received from the transmission facilities 2406. The LODES system 2404 may output the stored power to the transmission facilities 2406. The power transmission facility 2406 may output power received from the LODES system 2404 to the power grid 2408 and / or may receive power from the power grid 2408 and output the power to the LODES system 2404.

[0307] The LODES system 2404 and the transmission facility 2406 together may comprise a power generation plant 900. As an example, the power generation plant 900 may be located downstream of a transmission constraint, close to the power consumption. In such an exemplary downstream power generation plant 2700, the LODES system 2404 may have a duration of 24 to 500 hours and may fully discharge once or multiple times per year to support peak power consumption when transmission capacity is insufficient to serve customers. Additionally, in such an exemplary downstream power generation plant 2700, the LODES system 2404 may shallowly discharge several times (daily or more frequently) to arbitrage the difference between nighttime and daytime electricity prices and reduce the overall cost of electricity service to customers. As a further example, the power generation plant 2700 may be located upstream of a transmission constraint, close to the generation. In such an exemplary upstream power generation plant 2700, the LODES system 2404 may have a duration of 24 hours to 500 hours and may undergo one or more full charges per year to absorb excess generation at times when transmission capacity is insufficient to distribute electricity to customers. Additionally, in such an exemplary upstream power generation plant 2700, the LODES system 2404 may undergo several shallow charge / discharge cycles (daily or more frequently) to arbitrage the difference between nighttime and daytime electricity prices and maximize the value of the power generation facility's output.

[0308] FIG. 28 illustrates an exemplary system in which one or more aspects of various embodiments may be used as part of a bulk energy storage system. As a specific example, a bulk energy storage system incorporating one or more aspects of various embodiments may be a LODES system 2404. By way of example, the LODES system 2404 may include various embodiment batteries described herein, various electrodes described herein, etc. The LODES system 2404 may be electrically connected to commercial and industrial (C&I) customers 2802, such as data centers, factories, etc. The LODES system 2404 may be electrically connected to one or more transmission facilities 2406. The transmission facilities 2406 may be electrically connected to a distribution grid 2408. The transmission facilities 2406 may receive power from the distribution grid 2408 and output the power to the LODES system 2404. The LODES system 2404 may store the power received from the transmission facilities 2406. The LODES system 2404 may output the stored power to the C&I customers 2802. In this manner, the LODES system 2404 can operate to reshape the power purchased from the grid 2408 to match the consumption patterns of the C&I customers 2802 .

[0309] The LODES system 2404 and the transmission facility 2406 together can comprise a power generation plant 2800. As an example, the power generation plant 2800 may be located near the electricity consumption, i.e., near the C&I customers 2802, such as between the power distribution grid 2408 and the C&I customers 2802. In such an example, the LODES system 2404 may have a duration of 24 hours to 500 hours and may purchase electricity from the market at a time when electricity is cheaper, thereby charging the LODES system 2404. The LODES system 2404 may then discharge and provide electricity to the C&I customers 2802 at a time when market prices are higher, thus offsetting the C&I customers' 2802 market purchases. In an alternative configuration, the power generation plant 2800 may be located not between the power distribution grid 2408 and the C&I customers 2802, but between a renewable resource, such as a PV farm, a wind farm, or the like, and the transmission facility 2406, which may be connected to the renewable resource. In such an alternative example, the LODES system 2404 may have a duration of 24 hours to 500 hours, and the LODES system 2404 may be charged at times when renewable output may be available. The LODES system 2404 may then discharge to cover a portion or all of the C&I customer 2802 power needs and provide the C&I customer 2802 with renewable generated electricity.

[0310] 29 illustrates an exemplary system in which one or more aspects of various embodiments may be used as part of a bulk energy storage system. As a specific example, a bulk energy storage system incorporating one or more aspects of various embodiments may be a LODES system 2404. By way of example, the LODES system 2404 may include various embodiment batteries described herein, various electrodes described herein, etc. The LODES system 2404 may be electrically connected to a wind farm 2402 and one or more transmission facilities 2406. The wind farm 2402 may be electrically connected to the transmission facility 2406. The transmission facility 2406 may be electrically connected to C&I customers 2802. The wind farm 2402 may generate power, and the wind farm 2402 may output the generated power to the LODES system 2404 and / or the transmission facility 2406. The LODES system 2404 may store the power received from the wind farm 2402.

[0311] LODES system 2404 can output the stored power to transmission facility 2406. Transmission facility 2406 can output the power received from one or both of wind farm 2402 and LODES system 2404 to C&I customers 2802. Wind farm 2402, LODES system 2404, and transmission facility 2406 can together comprise power plant 2900, which may be an integrated power, transmission, and storage system. Power generated by wind farm 2402 can be delivered directly to C&I customers 2802 via transmission facility 2406 or can first be stored in LODES system 2404. In certain cases, the power supplied to C&I customers 2802 can be delivered entirely from wind farm 2402, entirely from LODES system 2404, or from a combination of wind farm 2402 and LODES system 2404. The LODES system 2404 may be used to reshape the electricity generated by the wind farm 2402 to match the consumption patterns of the C&I customers 2802. In one such example, the LODES system 2404 may have a duration of 24 hours to 500 hours and may charge when the renewable generation by the wind farm 2402 exceeds the C&I customers 2802 load. The LODES system 2404 may then discharge when the renewable generation by the wind farm 2402 falls below the C&I customers 2802 load to provide the C&I customers 2802 with a stable renewable profile that offsets some or all of the C&I customers 2802 electricity consumption.

[0312] FIG. 30 illustrates an exemplary system in which one or more aspects of various embodiments can be used as part of a bulk energy storage system. As a specific example, the bulk energy storage system incorporating one or more aspects of various embodiments may be a LODES system 2404. By way of example, the LODES system 2404 may include various embodiment batteries described herein, various electrodes described herein, etc. The LODES system 2404 may integrate a large amount of renewable power generation into a microgrid, for example, by integrating renewable power output from a PV site 2402 and a wind power site 2402 with existing thermal power generation from a thermal power plant 3002 (e.g., a gas plant, a coal plant, a diesel generator set, etc., or a combination of thermal generation methods), and may be part of a power plant 3000 in which the renewable and thermal power supply C&I customer 2802 loads when availability is high. A microgrid, such as the microgrid comprised of the power plant 3000 and the thermal power plant 3002, may provide an availability factor of 90% or higher. The power generated by the PV farm 2502 and / or wind farm 2402 may be delivered directly to the C&I customers 2802 or may first be stored in the LODES system 2404 .

[0313] In one particular case, the power supplied to C&I customers 2802 may be entirely from PV sites 2502, entirely from wind farms 2402, entirely from LODES systems 2404, entirely from thermal power plants 3002, or from any combination of PV sites 2502, wind farms 2402, LODES systems 2404, and / or thermal power plants 3002. As an example, the LODES systems 2402 of power plants 3000 may have a duration of 24 to 500 hours. As a specific example, the C&I customers 2802 load may be 100 MW peak, the LODES systems 2404 may have a power rating of 14 MW and a duration of 150 hours, the cost of natural gas may be $6 / million British thermal units (MMBTU), and the renewable occupancy may be 58%. As another specific example, the C&I customer 2802 load may be 100 MW peak, the LODES system 2404 may have a power rating of 25 MW and a duration of 150 hours, the cost of natural gas may be $8 / million British thermal units (MMBTU), and the renewable occupancy may be 65%.

[0314] 31 illustrates an exemplary system in which one or more aspects of various embodiments can be used as part of a bulk energy storage system. As a specific example, the bulk energy storage system incorporating one or more aspects of various embodiments may be a LODES system 2404. By way of example, the LODES system 2404 may include various embodiment batteries described herein, various electrodes described herein, etc. The LODES system 2404 can be used to enhance a nuclear power plant 3102 (or other inflexible power generation facilities, such as thermal, biomass, and / or any other type of power plant with a ramp rate of less than 50% of rated power per hour and a capacity factor of 80% or higher) to add flexibility to the combined output of the power plant 3100 comprised of the integrated LODES system 2404 and the nuclear power plant 3102. The nuclear power plant 3102 can operate at a high capacity factor and at its highest efficiency point, and the LODES system 2404 can charge and discharge to effectively reshape the output of the nuclear power plant 3102 to match customer electricity consumption and / or the market price of electricity. As an example, the LODES system 2404 of the power plant 3100 may have a duration of 24 hours to 500 hours. In one specific example, the nuclear power plant 3102 may have a rated output of 1,000 MW, and the nuclear power plant 3102 may be forced to operate at minimum stable power generation or even shut down for an extended period of time due to a drop in the market price of electricity. The LODES system 2404 can avoid shutting down the facility during the market price drop and charge, and then the LODES system 2404 can discharge during a market price rise and restore full power generation.

[0315] 32 illustrates an exemplary system in which one or more aspects of various embodiments may be used as part of a bulk energy storage system. As a specific example, the bulk energy storage system incorporating one or more aspects of various embodiments may be a LODES system 2404. By way of example, the LODES system 2404 may include various embodiment batteries described herein, various electrodes described herein, etc. The LODES system 2404 may operate in conjunction with an SDES system 3202. The LODES system 2404 and the SDES system 3202 may together comprise a power plant 3200. By way of example, the LODES system 2404 and the SDES system 3202 may be co-optimized, thereby enabling the LODES system 2404 to provide various services, including long-term backup and / or bridging, across multi-day variations (e.g., multi-day variations in market prices, renewable generation, electricity consumption, etc.). The SDES system 3202 can provide various services, including rapid support services (e.g., voltage control, frequency regulation, etc.) and / or bridging across diurnal variations (e.g., diurnal variations in market prices, renewable generation, electricity consumption, etc.). The SDES system 3202 may have a duration of less than 10 hours and a round-trip efficiency of greater than 80%. The LODES system 2404 may have a duration of 24 to 500 hours and a round-trip efficiency of greater than 40%. In one such example, the LODES system 2404 may have a duration of 150 hours and can support customer electricity consumption for up to a week of renewable generation shortages. The LODES system 2404 can also support customer electricity consumption during daytime generation shortage events, enhancing the capacity of the SDES system 3202. Additionally, the SDES system 3202 can supply customers during daytime generation shortage events and provide quality services such as power conditioning and voltage control and frequency regulation.

[0316] Various embodiments may include a battery including a first electrode, an electrolyte, and a second electrode, wherein at least one of the first electrode and the second electrode comprises an iron agglomerate. In some embodiments, the electrolyte comprises a soluble sulfide. In some embodiments, at least one of the first electrode and the second electrode further comprises a solid sulfide. In some embodiments, at least one of the first electrode or the second electrode is subjected to a compressive load. In some embodiments, the compressive load is applied to one side of at least one of the first electrode or the second electrode by a current collecting member. In some embodiments, the iron agglomerate comprises at least one of magnetite, hematite, or wustite. In some embodiments, the electrolyte comprises a corrosion inhibitor. In some embodiments, the iron agglomerate has an average length ranging from about 50 μm to about 50 mm. In some embodiments, the iron agglomerate has an average internal porosity ranging from about 10% to about 90% by volume. In some embodiments, the iron agglomerate has a thickness of about 0.1 m. 2 / g ~ approx. 25m 2 / g。 In some embodiments, the electrolyte is infiltrated between the iron agglomerates. In some embodiments, the electrolyte includes 1-octanethiol. In some embodiments, the electrolyte includes molybdate anions and sulfide anions. In some embodiments, the iron agglomerates are supported within a woven metal mesh that provides compressive force and current collection for the iron agglomerates. In some embodiments, the iron agglomerates are bonded to each other and to a current collector.

[0317] Various embodiments may include a battery including a first electrode, an electrolyte, and a second electrode, wherein at least one of the first electrode and the second electrode comprises an atomized metal powder. In some embodiments, the electrolyte comprises a soluble sulfide. In some embodiments, at least one of the first electrode and the second electrode further comprises a solid sulfide. In some embodiments, at least one of the first electrode or the second electrode is subjected to a compressive load. In some embodiments, the compressive load is applied to one side of at least one of the first electrode or the second electrode by a current collecting member. In some embodiments, the atomized metal powder comprises at least one of magnetite, hematite, or wustite. In some embodiments, the electrolyte comprises a corrosion inhibitor. In some embodiments, the electrolyte is infiltrated between the atomized metal powder. In some embodiments, the electrolyte comprises 1-octanethiol. In some embodiments, the electrolyte comprises molybdate anions and sulfide anions. In some embodiments, the atomized metal powder is supported within a woven metal mesh that provides a compressive force and current collection for the atomized metal powder, hi some embodiments, the atomized metal powder is bound together and bonded to a current collector.

[0318] Various embodiments may be methods for fabricating an electrode that include electrochemically producing a metal powder and forming the metal powder into an electrode. In some embodiments, the electrochemical production of the metal powder includes electrochemically producing the metal powder at least in part using molten salt electrochemistry. In some embodiments, the electrochemical production of the metal powder includes electrochemically producing the metal powder at least in part using gas atomization. In some embodiments, the electrochemical production of the metal powder includes electrochemically producing the metal powder at least in part using water atomization.

[0319] Various embodiments may include a bulk energy storage system including one or more batteries, at least one of which includes a first electrode, an electrolyte, and a second electrode, wherein at least one of the first electrode and the second electrode includes an iron agglomerate. In some embodiments, the bulk energy storage system is a long-term energy storage (LODES) system. In some embodiments, the electrolyte includes a soluble sulfide. In some embodiments, at least one of the first electrode and the second electrode further includes a solid sulfide. In some embodiments, at least one of the first electrode or the second electrode is subjected to a compressive load. In some embodiments, the compressive load is applied to one side of at least one of the first electrode or the second electrode by a current collecting member. In some embodiments, the iron agglomerate includes at least one of magnetite, hematite, or wustite. In some embodiments, the electrolyte includes a corrosion inhibitor. In some embodiments, the iron agglomerate has an average length ranging from about 50 μm to about 50 mm. In some embodiments, the iron agglomerates have an average internal porosity ranging from about 10% to about 90% by volume. 2 / g ~ approx. 25m 2 / g。 In some embodiments, the electrolyte is infiltrated between the iron agglomerates. In some embodiments, the electrolyte includes 1-octanethiol. In some embodiments, the electrolyte includes molybdate anions and sulfide anions. In some embodiments, the iron agglomerates are supported within a woven metal mesh that provides compressive force and current collection for the iron agglomerates. In some embodiments, the iron agglomerates are bonded to each other and to a current collector.

[0320] Various embodiments may include a bulk energy storage system including one or more batteries, at least one of which includes a first electrode, an electrolyte, and a second electrode, wherein at least one of the first electrode and the second electrode includes an atomized metal powder. In some embodiments, the bulk energy storage system is a long-term energy storage (LODES) system. In some embodiments, the electrolyte includes a soluble sulfide. In some embodiments, at least one of the first electrode and the second electrode further includes a solid sulfide. In some embodiments, at least one of the first electrode or the second electrode is subjected to a compressive load. In some embodiments, the compressive load is applied to one side of at least one of the first electrode or the second electrode by a current collecting member. In some embodiments, the atomized metal powder includes at least one of magnetite, hematite, or wustite. In some embodiments, the electrolyte includes a corrosion inhibitor. In some embodiments, the electrolyte is infiltrated between the atomized metal powder. In some embodiments, the electrolyte includes 1-octanethiol. In some embodiments, the electrolyte includes molybdate anions and sulfide anions. In some embodiments, the atomized metal powder is supported within a woven metal mesh that provides a compressive force and current collection for the atomized metal powder. In some embodiments, the atomized metal powder is bound together and attached to a current collector.

[0321] The above method descriptions are provided merely as illustrative examples and are not intended to require or imply that the steps of the various embodiments must be performed in the order presented. As one skilled in the art will understand, the order of steps in the above embodiments can be performed in any order. Words such as "then," "then," and "next" are not necessarily intended to limit the order of steps; such words may be used to guide the reader through the method description. Furthermore, any reference to a claim element in the singular, for example, using the article "a," "an," or "the," should not be construed as limiting the element to the singular. Furthermore, any step of any embodiment described herein can be used in any other embodiment.

[0322] The foregoing description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the basic principles defined herein may be applied to other embodiments without departing from the scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. a first electrode; electrolytes, and A battery including a second electrode, the second electrode comprises atomized metal powder; The battery, wherein the electrolyte is wetted between the atomized metal powder.

2. 10. The battery of claim 1, wherein the atomized metal powder comprises atomized iron powder.

3. 10. The battery of claim 1, wherein the electrolyte comprises a sulfide.

4. 10. The battery of claim 1, wherein the electrolyte comprises molybdate anions and sulfide anions.

5. 10. The battery of claim 1, wherein the atomized metal powder comprises at least one of magnetite, hematite, or wustite.

6. the second electrode further comprises a woven metal mesh; the atomized metal powder is supported within the woven metal mesh; 10. The battery of claim 1, wherein the woven metal mesh compresses the atomized metal powder.

7. the second electrode further includes a current collector; 10. The battery of claim 1, wherein the atomized metal powder is bonded together and to the current collector.

8. A method for fabricating an electrode, comprising electrochemically producing a metal powder and forming the metal powder into an electrode.

9. The method of claim 8 , wherein the electrochemical production of the metal powder comprises electrochemically producing the metal powder at least in part using molten salt electrochemistry.

10. 10. The method of claim 8, wherein the electrochemical production of the metal powder comprises electrochemically producing the metal powder at least in part using a gas atomization process.

11. 10. The method of claim 8, wherein the electrochemical production of the metal powder comprises electrochemically producing the metal powder at least in part using a water atomization process.

12. 10. The method of claim 8, wherein forming the metal powder into an electrode comprises bonding the metal powder together and to a current collector.

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