Solid additives for iron negative electrodes

Abstract

According to one aspect, an additive for an iron negative electrode of an alkaline electrochemical cell may comprise a powder of discrete particles comprising agglomerated particles comprising at least one metal sulfide.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 398,828 filed on August 17, 2022 and U.S. Provisional Patent Application No. 63 / 378,132 filed on October 3, 2022, the entire contents of each of which are hereby incorporated by reference into this document. Background Art

[0003] Energy storage technologies play an increasingly important role in the electric grid. These energy storage assets provide smoothing to better match the generation and demand of the grid. The services performed by energy storage devices are beneficial to the grid at multiple time scales (from milliseconds to years). Today, there are energy storage technologies that can support time scales from milliseconds to hours, but long-term and ultra-long-term (in general, >8h) energy storage systems are also needed. The benefit is the potential low-cost rechargeable battery chemistry that can achieve long-term large-scale energy storage. Summary of the invention

[0004] According to one aspect, an additive for an iron negative electrode of an alkaline electrochemical cell can include a powder of discrete particles including agglomerated particles comprising at least one metal sulfide.

[0005] In some embodiments, the at least one metal sulfide of the agglomerated particles is greater than 50% by weight of the discrete particles. The at least one metal sulfide of the agglomerated particles may be greater than 80% by weight of the discrete particles.

[0006] In certain embodiments, the discrete particles may have an average particle size greater than about 30 microns and less than about 800 microns on a weight percent basis.

[0007] In some embodiments, the discrete particles of the agglomerated particles of the at least one metal sulfide have a median pore size greater than about 75 nanometers and less than about 15 microns as determined by mercury porosimetry.

[0008] In certain embodiments, the discrete particles may have a first average apparent density and the particles comprising the at least one metal sulfide may have a second average apparent density, the first average apparent density being less than the second average apparent density. The first average apparent density may be greater than 1.0 grams per cubic centimeter and less than 2.1 grams per cubic centimeter.

[0009] In some embodiments, the discrete particles may have a friability of less than about 15% weight loss according to European Pharmacopoeia 2.9.41.-2 (Method B).

[0010] In certain embodiments, solid state bonding may hold together at least some of the agglomerated particles in the discrete particles such that there is solid state bonding between the agglomerated particles.

[0011] In certain embodiments, at least some of the agglomerated particles of the discrete particles may be a metal matrix composite material bonded by infiltration.

[0012] In some embodiments, the discrete particles may include a binder by which at least some of the agglomerated particles of the discrete particles are bound. As an example, the binder may be soluble in an alkaline electrolyte and / or the binder may be reactive to form a substance that is soluble in an alkaline electrolyte.

[0013] In certain embodiments, the at least one metal sulfide may include zinc sulfide (ZnS). The powder of discrete particles may be greater than or equal to 90% by weight zinc sulfide (ZnS). As an example, greater than 60% by weight of the zinc sulfide (ZnS) may be in a sphalerite structure as determined by x-ray diffraction.

[0014] In some embodiments, the agglomerated particles of the discrete particles may have surface-connected pores. As an example, as measured by mercury intrusion porosimetry, the surface-connected pores of the agglomerated particles may be greater than or equal to 7% by volume and less than or equal to 40% by volume of the agglomerated particles.

[0015] In certain embodiments, the at least one metal sulfide may include ferrous sulfide (FeS), stannous sulfide (SnS), bismuth sulfide (Bi2S3), aluminum sulfide (Al2S3), antimony (III) sulfide (Sb2S3), antimony (V) sulfide (Sb2S5), manganese sulfide (MnS), molybdenum (IV) sulfide (MoS2), or a combination thereof.

[0016] In some embodiments, the discrete particles may further include tin oxide (SnO2), tin (Sn), bismuth (Bi), zinc selenide (ZnSe), potassium hydroxide (KOH), sodium hydroxide (NaOH), or a combination thereof.

[0017] In certain embodiments, the discrete particles may further include a conductive material. As an example, the conductive material may include tin, graphite, carbon black, or a combination thereof.

[0018] In some embodiments, the discrete particles may also include particles of at least one pore former. Based on weight percentage, the average particle size of the particles of the at least one pore former may be greater than about 5 microns and less than about 20 microns. In some cases, the particles of the at least one metal sulfide may have a first average particle size based on weight percentage, and the particles of the at least one pore former have a second average particle size based on weight percentage, and the second average particle size is greater than or equal to the first average particle size. In some cases, the at least one pore former may be soluble in an alkaline electrolyte. As an example, the at least one pore former may include potassium oxide (K2O), lithium oxide (LiO), sodium oxide (Na2O), potassium hydroxide (KOH), lithium hydroxide (LiOH), sodium hydroxide (NaOH), sodium sulfate (Na2S), potassium sulfate (K2S), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), sodium stannate (Na2[Sn(OH)6]), potassium stannate (K2[Sn(OH)6]) or a combination thereof. Additionally or alternatively, the at least one pore former can include poly(methyl methacrylate), starch, sodium chloride (NaCl), potassium chloride (KCl), ammonium bicarbonate (NH4HCO3), or combinations thereof.

[0019] According to another aspect, an iron negative electrode for an alkaline electrochemical cell may include a first powder including an iron active material and a second powder including an additive of any one or more of the above powders, wherein the first powder and the second powder form a powder blend, wherein the second powder is dispersed relative to the first powder.

[0020] In certain embodiments, the first powder may include any one or more of iron oxide, atomized iron powder, sponge iron powder or ground iron powder. As an example, the ratio of the average particle size of the discrete particles of the second powder to the average particle size of the particles of the iron active material may be 0.5 to 2.

[0021] In some embodiments, the average particle size of the discrete particles may be greater than or equal to the average pore size of the powder blend.

[0022] In certain embodiments, the apparent density of the powder blend may be less than the apparent density of the first powder alone.

[0023] In some embodiments, the iron active material may be greater than about 70% of the total weight of the first powder and the second powder.

[0024] In certain embodiments, the thickness of the active layer of the electrode may be greater than about 8 mm and less than about 50 mm.

[0025] In some embodiments, the concentration of the second powder in the powder blend may have a predetermined gradient across the thickness dimension of the active layer of the powder blend.

[0026] According to still another aspect, a method for preparing an additive for an iron negative electrode of an alkaline electrochemical cell may include: forming a raw material including a granular material having a predetermined composition, and processing the raw material including the granular material into a powder including discrete particles of agglomerated particles of the granular material, wherein the agglomerated particles include at least one metal sulfide.

[0027] In some embodiments, processing the feedstock of the granular material may include solid state bonding of the granular material. As an example, solid state bonding of the granular material may include heating the granular material to a temperature of about 500°C to about 1400°C. In addition or in contrast, solid state bonding of the granular material may include sintering the granular material into the agglomerated particles. As an example, the at least one metal sulfide includes zinc sulfide (ZnS), and the sintering is performed at a temperature greater than 900°C and less than 1300°C. In some cases, solid state bonding of the granular material may include hot pressing the granular material. As an example, the at least one metal sulfide may include zinc sulfide (ZnS), and hot pressing is performed at 900°C with a uniaxial pressure of about 410kPa for about 10 minutes.

[0028] In certain embodiments, forming the raw material may include introducing at least one polymer binder into the granular material. In some cases, processing the raw material into the discrete particles may include pyrolyzing the at least one polymer binder to form a graphitized film on the granular material. The at least one polymer binder may be pyrolyzable in an inert atmosphere, and the yield of residual solids after pyrolysis in a non-oxidizing atmosphere up to 600°C is >7% by weight. In addition or in contrast, the at least one polymer binder may include asphalt, zinc stearate, stearic acid, polyols, poly(methyl methacrylate), polyolefins, polymers with aromatic rings, poly(ethylene glycol), poly(tetrafluoroethylene), polyvinylidene fluoride, carboxymethyl cellulose, poly(acrylic acid), or copolymers of any one or more of the above. Still in addition or in contrast, the at least one polymer binder is introduced into the granular material, and the granular material can be thermomechanically bonded in a processing atmosphere including hydrogen.

[0029] In some embodiments, forming the feedstock may include introducing at least one inorganic binder into the particulate material. The at least one inorganic binder may include an oxide-based binder, a silicate-based binder, an alumina-containing binder, or a combination thereof.

[0030] In certain embodiments, processing the feedstock of granular material further comprises compacting the feedstock of granular material. As an example, compacting the feedstock of granular material comprises rolling the feedstock of granular material.

[0031] In some embodiments, the granular material may include particles of the at least one metal sulfide. The raw material forming the granular material may include mixing at least two metal sulfides in a predetermined weight ratio relative to each other. As an example, the at least two metal sulfides may include zinc sulfide (ZnS) and ferrous sulfide (FeS). In some cases, the at least two metal sulfides may include zinc sulfide (ZnS) and ferrous sulfide (FeS) in the discrete particles in the predetermined weight ratio relative to each other. In some cases, forming the raw material including the granular material may include mixing a conductive material with the at least one metal sulfide. As an example, the conductive material may include tin, graphite, carbon black or a combination thereof. In some cases, the conductive material may be solid at room temperature, and processing the raw material of the granular material includes heating the raw material of the granular material in an inert environment to melt the at least one metal sulfide and the conductive material so that the conductive material wets the at least one metal sulfide, and cooling the raw material of the granular material while the conductive material wets the at least one metal sulfide so that the at least one metal sulfide and the conductive material in the raw material of the granular material form a metal-based composite material bonded by infiltration. In some embodiments, the particles of the at least one metal sulfide may include particles of zinc sulfide (ZnS). In some cases, processing the raw material may include exposing the granular material to a chemical reduction environment including one or more reducing agents at 700° C. to 1000° C. so that zinc oxide (ZnO) in the granular material is chemically reduced to zinc sulfide (ZnS). The one or more reducing agents may include solid carbon, gaseous carbon monoxide, or gaseous hydrogen. In some cases, processing the raw material may include exposing the granular material to a sulfur-containing gas to convert zinc oxide (ZnO) into zinc sulfide (ZnS). As an example, the sulfur-containing gas may include hydrogen sulfide (H2S), carbonyl sulfide (OCS), methyl mercaptan (CH3SH), sulfur dioxide (SO2), or a combination thereof. In some cases, the feedstock for forming the granular material may include blending particles of a pore former with particles of the at least one metal sulfide, the pore former being soluble in an alkaline electrolyte. In some cases, the ratio of the average particle size of the particles of the pore former to the average particle size of the particles of the at least one metal sulfide may be greater than or equal to 1:1 and less than about 5:1.

[0032] In certain embodiments, processing the feedstock into the discrete particles may include introducing at least one binder into the discrete particles, the at least one binder being soluble in an alkaline electrolyte.

[0033] In some embodiments, processing the raw material into the discrete particles may include forming the granular material into one or more intermediates, and changing the size of the one or more intermediates to form the discrete particles. Forming the granular material into the one or more intermediates may include cold pressing the granular material. Cold pressing the granular material may include forming agglomerates of the granular material. In some cases, changing the size of the one or more intermediates to form the discrete particles may include sintering the one or more intermediates together to form the discrete particles. As an example, forming the granular material into the one or more intermediates may include sintering the granular material into a sintered body having at least one dimension of approximately 1 mm or greater, and changing the size of the one or more intermediates includes reducing the size of the one or more intermediates to form the discrete particles. In some cases, the one or more intermediates may include a monolith of ceramic material, at least one dimension of the monolith being approximately 1 mm or greater, and changing the size of the one or more intermediates includes reducing the size of the one or more intermediates to form the discrete particles. In some cases, changing the size of the one or more intermediates to form the discrete particles may include any one or more of the following: grinding, drum granulation, fluidized bed granulation, spray drying, high shear mixing granulation, twin screw granulation, extrusion granulation, open pan granulation / disc granulation, wet granulation or dry granulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1A is a schematic representation of an electrochemical cell.

[0035] Figure 1B is a schematic representation of a rechargeable battery pack.

[0036] Figure 2A is a schematic representation of an iron negative electrode comprising a bed of a powder blend including a first powder of an iron-containing active material and a second powder of an additive material.

[0037] Figure 2B yes Figure 2A A close-up schematic diagram of a second powder is shown, wherein the second powder includes discrete particles including agglomerated particles, the agglomerated particles including at least one metal sulfide.

[0038] Figure 2C is a diagram showing a powder of discrete particles of agglomerated particles mixed with a powder of an iron active material.

[0039] Figure 3 yes Figure 2A The measured capacity (normalized) of the iron negative electrode is Figure 2A A series of graphs showing the variation in the average particle size of discrete particles of an iron anode, the type of metal sulfide remaining constant, the different graphs corresponding to experiments performed using different electrolytes, electrolyte concentrations, amounts of discrete particles used (wt%) and cycling conditions such as temperature and C-rate.

[0040] Figure 4 is a flow chart of an exemplary method 400 of preparing an additive for an iron negative electrode of an alkaline electrochemical cell.

[0041] Figure 5A and Figure 5B It is the phase diagram of zinc sulfide (ZnS).

[0042] The same reference symbols in different drawings denote the same elements. DETAILED DESCRIPTION

[0043] The embodiments will be described in detail with reference to the accompanying drawings. Where possible, the same reference numerals will be used throughout the figures to refer to the same or similar parts. Reference to specific examples and embodiments is for illustrative purposes and is not intended to limit the scope of the claims. The following description of the embodiments of the present disclosure is not intended to limit the present disclosure to these embodiments, but is intended to enable those skilled in the art to make and use the present disclosure. Unless otherwise indicated, the drawings are not drawn to scale.

[0044] As used herein, recitation of ranges of values ​​herein is intended merely to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein. Unless otherwise indicated herein, each separate value within the range is incorporated into the specification as if it were individually recited herein.

[0045] The following examples are provided to illustrate various embodiments of the present systems and methods of the present disclosure. These examples are for illustrative purposes, may be predictive, and should not be considered limiting, and do not otherwise limit the scope of the present disclosure.

[0046] The multiple embodiments of the systems, devices, technologies, methods, activities and operations described in this specification can be used in a variety of other activities and other fields beyond those described herein. In addition, for example, these embodiments can be used together with other devices or activities that may be developed in the future; and, used together with existing devices or activities that can be modified based in part on the teachings of this specification. In addition, the multiple embodiments and examples described in this specification can be used in whole or in part with each other, and can be used with each other in different combinations and multiple combinations. Therefore, for example, the configurations provided in the multiple embodiments of this specification can be used together with each other. Therefore, the configurations provided in the multiple embodiments of this specification can be used together with each other. For example, according to the teachings of this specification, the components of the embodiments with A, A' and B and the components of the embodiments with A", C and D can be used together with each other in multiple combinations, such as A, C, D, and A, A", C and D, etc. The scope of protection provided by the present disclosure should not be limited to specific embodiments, the configurations or arrangements described in the embodiments of specific embodiments, examples, or specific figures.

[0047] As used herein, room temperature is 25° C. unless otherwise specified. Also, standard temperature and pressure are 25° C. and 1 atmosphere. Unless otherwise expressly stated, all tests, test results, physical properties, and numerical values ​​related to temperature, pressure, or both are provided at standard ambient temperature and pressure.

[0048] Unless the context indicates otherwise or clearly dictates, all references to average particle size herein should be understood to refer to average particle size on a weight percent basis. Therefore, some references to average particle size herein may occasionally omit specific reference to "weight percent basis" for the purpose of clarity and readability.

[0049] Embodiments of the present disclosure include devices, systems and methods for long-term and ultra-long-term energy storage. In this article, "long (continuous) time" and / or "ultra-long (continuous) time" may refer to an energy storage period of 8 hours or longer, such as an 8-hour energy storage period, an 8-hour to 20-hour energy storage period, a 20-hour energy storage period, a 20-hour energy storage period, a 20-hour to 24-hour energy storage period, a 24-hour energy storage period, a 24-hour to one-week energy storage period, a one-week to one-year (e.g., from several days to several weeks to several months) energy storage period, etc. In other words, "long (continuous) time" and / or "ultra-long (continuous) time" energy storage devices or systems may refer to energy storage devices or systems that can be configured to store energy over a time span of several days, weeks or seasons. For example, an energy storage device or system may be configured to store energy generated by solar cells in the summer months when there is sufficient sunlight and solar power generation exceeds grid demand, and release the stored energy in the winter months when sunlight may not be sufficient to meet grid demand.

[0050] According to other embodiments, the present invention includes devices, systems and methods for storing energy for shorter (duration) periods of less than about 8 hours. For example, the electrochemical cell can be configured to store energy generated by a solar cell during a diurnal cycle, where solar power generation during the midday period may exceed grid demand, and release the stored energy during the evening period when sunlight may not be sufficient to meet grid demand. As another example, the invention can include energy storage used as a backup power source when the grid power supply is insufficient, for facilities including homes, commercial buildings, factories, hospitals or data centers, where the required discharge duration can vary from a few minutes to several days.

[0051] Electrochemical cells such as batteries store electrochemical energy by utilizing the difference in electrochemical potential that produces a voltage difference between the positive and negative electrodes. If the electrodes are connected by a conductive element, this voltage difference produces an electric current. In a battery, the negative electrode and the positive electrode are connected in series by an internal resistance element and an external resistance element. Typically, the external element conducts electrons and the internal element (electrolyte) conducts ions. Since the charge imbalance cannot be maintained between the negative and positive electrodes, the two flows must provide ions and electrons at the same rate. In operation, the electron flow can be used to drive external devices. Rechargeable batteries can be charged by applying a reverse voltage difference, which drives the current and ion flow to flow in the opposite direction to the discharged battery in service.

[0052] Reference now Figure 1A , the electrochemical cell 100 (e.g., a battery pack) may include a negative electrode 102 separated from a positive electrode 103 by a separator 104. The separator 104 may be supported, for example, by a mesh 105 (e.g., a polypropylene mesh) and a frame 108 (e.g., polyethylene or polypropylene) of the electrochemical cell 100. The current collector 107 may be associated with the corresponding electrodes in the negative electrode 102 and the positive electrode 103 and supported by a backing plate 106 (e.g., a polyethylene backing plate or a polypropylene backing plate). In some embodiments, the temperature of the electrochemical cell 100 may be controlled, for example, by a thermal insulator around the electrochemical cell 100 and / or by a heater 150. For example, the heater 150 may increase the temperature of the electrochemical cell 100 and / or a specific composition of the battery, such as an electrolyte permeated in the negative electrode 102 and the positive electrode 103. The electrolyte may be an aqueous solution. In certain embodiments, the electrolyte may be an alkaline solution (pH>10). In certain embodiments, the electrolyte may be a near-neutral solution (10>pH>4).

[0053] Electrochemical cell 100 is merely an example of an electrochemical cell configuration according to various embodiments and is not intended to be limiting. Other configurations, such as electrochemical cells with different types of mesh and / or without mesh 105, electrochemical cells with different types of frames and / or without frames 108, electrochemical cells with different types of current collectors and / or without current collectors 107, electrochemical cells with reservoir structures, electrochemical cells with different types of backing plates and / or without backing plates 106, electrochemical cells with different types of thermal insulation and / or without thermal insulation, and / or electrochemical cells with different types of heaters and / or without heater 150, may be substituted. Figure 1A An exemplary configuration of electrochemical cell 100 is shown, and other configurations are consistent with various embodiments.

[0054] In some embodiments, multiple Figure 1A The electrochemical cells 100 in the stack can be electrically connected in series to form a stack. In certain other embodiments, multiple electrochemical cells 100 can be electrically connected in parallel. In certain other embodiments, the electrochemical cells 100 are connected in a mixed series-parallel electrical configuration to achieve a favorable combination of transmitted current and voltage.

[0055] Reference now Figure 1B , the rechargeable battery 10 may include a positive electrode 12, a negative electrode 14, and a separator 16 within a container 18, the container 18 being filled with an electrolyte 20 to a level 22, the level 22 being at least as high as the tops 32, 34 of the electrodes 12, 14, respectively. The space above the level 22 of the electrolyte 20 may be referred to as a head space 24. The positive electrode 12 may be electrically connected to a positive terminal 42 of the rechargeable battery 10, and may contain an active material that may undergo a reduction reaction during discharge and an oxidation reaction during charge. The negative electrode 14 may be electrically connected to a negative terminal 44 of the rechargeable battery 10, and may contain an active material that may undergo an oxidation reaction during discharge of the rechargeable battery 10 and may undergo a reduction reaction during charge of the rechargeable battery 10. Figure 1B The rechargeable battery pack 10 in FIG. 1 is merely an example of an electrochemical cell according to various embodiments and is not intended to be limiting.

[0056] In various embodiments, the electrolyte 20 may be an alkaline, neutral or acidic aqueous solution or a non-aqueous solution. For example, the electrolyte solution may include potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH) or a combination of these.

[0057] In some embodiments, the battery 10 may include a separator 16 that allows ions to be transferred between the electrodes 12, 14 through the electrolyte. In some embodiments, the separator can be selected based on the ability to allow the selective transfer of desired molecules or materials while substantially limiting or preventing the transfer of undesirable molecules or materials. For example, some separator membranes are ion-selective, allowing the transfer of negative ions (or positive ions) while substantially preventing the transfer of positive ions (or negative ions). In other examples, the separator material can be selected based on the ability to allow or prevent bubbles from crossing from one side (associated with one electrode) to the opposite side (associated with the counter electrode).

[0058] In various embodiments, the container 18 can be made of any suitable material and structure capable of containing electrolyte, electrodes, and at least a minimum amount of gas pressure. For example, the container 18 can be made of metal, plastic, composite material, or other material. In some embodiments, the battery container 18 can be sealed to prevent any gas generated during battery operation from escaping.

[0059] In some embodiments, the battery container 18 may include a pressure relief valve to allow for the release of gas when the gas pressure within the battery container 18 exceeds a predetermined threshold.

[0060] Although the electrodes 12, 14 are shown as being substantially spaced apart in the figures, in some embodiments, the electrodes may be very close to each other or even pressed against each other with the separator 16 therebetween. In addition, although the figures may show a single positive electrode 12 and a single negative electrode 14, a battery system within the scope of the present disclosure may also include two or more positive electrodes 12, and / or two or more negative electrodes 14.

[0061] Reference now Figure 1A and Figure 1B , it is generally understood that, unless otherwise specified or clearly provided by the context, the negative electrode 102 of the electrochemical cell 100 and / or the negative electrode 14 of the rechargeable battery 10 may include a metal or metal oxide, such as iron, zinc, cadmium or other metals and / or oxides or hydroxides of these or other metals. In addition, it is generally understood that, unless otherwise specified or clearly provided by the context, the negative electrode 102 of the electrochemical cell 100 and the negative electrode 14 of the rechargeable battery 10 have similar or identical features, and for the sake of efficient description, these features are not described separately for each negative electrode. Therefore, in view of the above, the embodiments in the following description are described in the context of the negative electrode 14, more specifically, in the context of the negative electrode 14 being an iron negative electrode. Therefore, the negative electrode 14 shall be referred to as "iron negative electrode 14" hereinafter, and all such references shall be understood to be intended to include references to other types of active metals described herein and other negative electrodes described herein (e.g., negative electrode 102), unless otherwise specified or clearly provided by the context.

[0062] Reference now Figure 1B , Figure 2A and Figure 2B , the iron negative electrode 14 may include a bed 201 of a powder blend 202 having pores, an electrolyte (e.g., Figure 1B The electrolyte 20 in the bed 201 of the iron negative electrode 14 can penetrate through the pores to support the flow of ions when the iron active material of the negative electrode 14 undergoes oxidation and reduction reactions during operation of the electrochemical cell (e.g., rechargeable battery 10). The powder blend 202 may include a first powder 204 and a second powder 206. As described in more detail below, the first powder 204 may include an iron active material. As also described in more detail below, the second powder 206 may include discrete particles 208, the discrete particles 208 include agglomerated particles 210, and the agglomerated particles 210 include at least one metal sulfide. As an example, the iron active material may be greater than about 70% of the total weight of the first powder 204 and the second powder 206, which may be useful for balancing competing considerations related to performance (e.g., capacity utilization of the iron active material), cost, and size of an electrochemical cell (e.g., rechargeable battery 10) including an iron negative electrode 14.

[0063] Generally, as described in the following paragraphs, the discrete particles 208 of agglomerated particles 210 overcome significant challenges of particle size matching, dry powder processing, and floating / falling off risk compared to powders of loose particles using solid additives in iron anodes.

[0064] As an example, a second powder 206 of discrete particles 208 including agglomerated particles 210 of additive material may help overcome design challenges typically associated with particle size mismatches between active materials and additive materials in an iron negative electrode. Specifically, in order to achieve large-scale economical and efficient production, many solid additive powders are formed using preparation techniques that produce small particle sizes. Although small particle sizes (e.g., <<100 microns) may be useful for achieving dissolution rates of certain types of solid additives (e.g., manganese sulfide, tin-containing additives, and zinc sulfide) in iron negative electrode electrolytes, these small particle sizes are typically incompatible with large particle sizes of iron active materials, but such large particle sizes are required to achieve the filling and flow properties required for efficient performance of the iron negative electrode. In other words, there is typically a particle size mismatch between the powder of loose particles of the additive (typically <10 microns) and the powder of the iron active material (typically 100 microns).

[0065] Due to this size contrast between the solid additive and the iron powder used, the powder mixture used in the iron negative electrode can obtain a higher packing density than expected, and only due to geometric effects, the smaller solid additive particles are filled into the interstitial space of the larger iron active material particles. In addition or on the contrary, if the particles of the solid additive are small enough relative to the larger iron active material particles, the particles of the solid additive can be used as a "flow enhancer" or "filling enhancer" by reducing inter-particle friction. Such a higher packing density may result in a low porosity of the iron negative electrode, resulting in poor performance of the resulting iron negative electrode. In this context, such poor performance may be attributed to at least one or more of rate performance, available area load, specific capacity and voltage efficiency. However, the use of agglomeration of particles to form particles 208 of the second powder 206 helps to overcome the particle size mismatch between the loose particles of the solid additive and the iron powder used in the powder mixture of the iron negative electrode. Additionally or alternatively, the use of agglomeration of particles to form discrete particles 208 of the additive renders the particle geometry of the solid additive independent of the properties of the solid additive in the iron negative electrode 14 - facilitating independent control of the specific surface area of ​​the additive material in the powder blend 202 in the bed 201, the additive chemical properties, the particle size of the additive, or any combination thereof.

[0066] As another example, the second powder 206 of discrete particles 208 including agglomerated particles 210 facilitates the use of dry powder processing to form the iron negative electrode 14. In the context of aqueous long-term energy storage, the electrode area load and thickness are much higher than in the context of other battery electrodes. In comparison, lithium-ion electrodes (typically used for shorter-term energy storage technologies) typically have an active layer (active layer strata) with a thickness of typically less than 1 mm, while the iron negative electrode 14 may have an active layer with a thickness that may be greater than about 8 mm to less than about 50 mm. As used in this context, it should be understood that the thickness of the active layer refers to the thickness of the layer of the iron negative electrode 14 comprising the first powder 204 (and therefore also the second powder 206, as part of the powder blend 202) including the iron active material. Wet methods based on slurry processing and slurry rheology are typically used in the production of lithium-ion electrodes to maintain uniform mixing of electrode active materials, additives and binders throughout the process of preparing the active layer. However, the drying time of wet processed electrodes increases superlinearly with the thickness of the active layer material, making the use of wet processing impractical when the iron anode is much thicker than the lithium-ion electrode.14 Although dry powder processing is superior to wet processing in terms of preparation time, the impact of powder rheology and the resulting segregation tendency in dry powder processing can be much more severe than in wet electrode processing.

[0067] Therefore, for the preparation of the iron negative electrode 14 using the dry powder processing powder blend 202, special close attention must be paid to the considerations around the particle size design to meet the desired powder filling (for high performance) and consistency standards, while taking into account different constraints. Therefore, while the second powder 206 of discrete particles 208 including agglomerated particles 210 may be associated with any processing route, the second powder 206 may be particularly useful in the context of dry processing the powder blend 202 to form the iron negative electrode 14. That is, dry processing the second powder 206 to form the powder blend 202 may be beneficial for simultaneously meeting the performance-based requirements of the surface area and dispersion of the additive material within the iron negative electrode 14, while also meeting the processing-based requirements of particle size matching and minimization of segregation.

[0068] As yet another example, a second powder 206 comprising discrete particles 208 of agglomerated particles 210 comprising additive material may help reduce the risk of floating / falling off of solid additives in the iron negative electrode. That is, a particular risk associated with using solid additives in the iron negative electrode is that particles of these such solid additives may attach to bubbles generated during electrochemical cycling (e.g., by hydrogen or oxygen evolution) or otherwise be bound or dragged by bubbles generated during electrochemical cycling (e.g., by hydrogen or oxygen evolution), resulting in loose particles of the solid additive being lost from the iron negative electrode. This may be particularly problematic in cases where the solid additive is intended to remain in the iron negative electrode during the life of the electrode, and any amount of solid additive lost from the iron negative electrode may result in performance degradation during the life of a given iron negative electrode and / or result in increased costs to compensate for the loss of the solid additive.

[0069] Several factors affect the floating / falling risk of solid additives. The first factor affecting the floating / falling risk is the particle size. Although it is usually the lowest cost to obtain solid additives of small size (e.g., 5 microns), the interaction of solid additives with bubbles can be severe at these length scales. In addition or on the contrary, if the particle size of the discrete particles 208 of at least one metal sulfide is approximately the same as or larger than the pore size of the iron negative electrode 14, the pores of the iron negative electrode itself can act as a "filter" for the solid additive. Although capillary interactions can be regulated by surface chemistry, viscous drag is the basis for bubbles to pass through the iron negative electrode and may cause the loss of solid additive particles, regardless of the surface chemistry of the solid additive particles. The second factor affecting the floating / falling risk is the surface chemistry. Additives with non-polar surfaces or low surface energies will tend to adsorb more strongly to the bubble surface and therefore be subject to enhanced drag by the bubbles.

[0070] Therefore, compared with the powder of loose particles of solid additive, the second powder 206 including discrete particles 208 of agglomerated particles 210 of solid additive can reduce the risk of solid additive material particle loss. That is, the discrete particles 208 of agglomerated particles 210 are significantly larger than each individual particle, and therefore, can be more resistant to the drag force of bubbles or other forces used to remove solid additives from the iron negative electrode 14. In addition or on the contrary, since the size of the discrete particles 208 of agglomerated particles 210 is independent of the size of individual particles, the size of the discrete particles 208 can be selected so that the discrete particles 208 do not "fit" through the pores of the iron negative electrode 14. As an example, the iron negative electrode 12 can be molded into a packed bed filter, and hydrogen bubbles and electrolytes move / flow through the packed bed filter, exerting accompanying viscous drag and capillary drag. Discrete particles 208 with a size roughly the same as the pore size of the iron negative electrode 14 can be geometrically prevented from migrating out of the iron negative electrode, thus keeping the solid additive in the desired position in the iron negative electrode 14. Therefore, in some embodiments, the average particle size of the discrete particles 208 is greater than or equal to the average pore size of the powder blend 202, which may help reduce the risk of solid additives floating / falling off from the iron negative electrode 14. In addition or on the contrary, in a packed bed filter, good filtration usually occurs if the filter pore size is within 4 times the particle size to be filtered. Therefore, in some cases, the average particle size of the discrete particles 208 can be smaller than the average pore size of the powder blend 202 of the iron negative electrode, in which case the discrete particles 208 can be fully retained in the iron negative electrode 14.

[0071] Reference now Figure 1B , Figure 2A , Figure 2B and Figure 3 Although a larger average size of the discrete particles 208 is generally useful for addressing the risk of floating / falling off, it has been experimentally determined that the average size of the discrete particles 208 may affect the capacity of the iron negative electrode 14. Specifically, as Figure 3 As shown in the experimental results, the capacity performance of the iron negative electrode 14 increases with the increase of the average particle size of the discrete particles 208 up to a certain optimal capacity, and then decreases with the further increase of the average particle size of the discrete particles 208. In other words, the range of reduced floating / falling-off risk based on the size of the discrete particles 208 may be limited by the effect of the size of the discrete particles 208 on the capacity of the iron negative electrode 14. Specifically, based on these experimental results, on a weight percentage basis, as determined by laser diffraction particle size analysis, the average particle size of the discrete particles 208 is greater than about 30 microns and less than about 800 microns. This range may be useful for balancing the competing size considerations of reducing the risk of floating / falling-off relative to achieving the peak capacity of the iron negative electrode 14.

[0072] In some embodiments, the risk of floating / falling off can be additionally or alternatively reduced by generating bubbles in the iron negative electrode 14 of the second powder 206 away from the discrete particles 208 including the agglomerated particles 210. For example, the concentration of the second powder 206 in the powder blend 202 can be within the thickness dimension of the active layer of the iron negative electrode 14 (corresponding to Figure 2A Thus, with such a gradient in the active layer of the iron negative electrode, hydrogen evolution in the iron negative electrode 14 can occur at a position away from the second powder 206, minimizing its floating / falling risk.

[0073] Typically, the first powder 204 of the powder blend 202 in the iron negative electrode 14 may include any one or more types of iron active materials suitable for use in any one or more of the various different electrochemical cells described herein. For example, the iron active material of the first powder 204 may include one or more iron-containing compounds, which may be any one or more of a variety of different shapes (e.g., spherical, agglomerated, flattened, or sintered) in the first powder 204. The one or more iron-containing compounds may range from highly reduced forms of iron (more metallic) to highly oxidized forms of iron (more ionic). Thus, for example, the one or more iron-containing compounds may include iron-containing alloys or iron-containing compounds, such as iron oxides, mixed iron oxides, iron hydroxides, iron sulfates, iron carbonates, iron sulfides, or any combination of these. Additionally or alternatively, the one or more iron-containing compounds may include purified or refined iron materials, such as carbonyl iron or electrolytic iron, or iron ores such as magnetite, hematite, siderite, hematite, goethite, limonite, or other iron materials. In certain embodiments, the iron active material of the first powder 204 may include one or more of iron oxides, atomized iron powder, sponge iron powder, ground iron powder, other additives including conductive carbon additives, or any combination of these.

[0074] Typically, in a powder blend 202 with a first powder 204, a second powder 206 may be helpful in forming an iron negative electrode 14 by dry material filling. As an example, the powder blend 202 may be added to a mold, and the powder blend 202 may be pressed to form an iron negative electrode 14. According to this technology and other preparation techniques, the apparent density of the powder blend 202 may be less than the apparent density of the first powder blend 202 alone under other similar compression. That is, compared to an iron negative electrode formed without the second powder 206, the powder blend 202 may be advantageous in forming an iron negative electrode 14 as a low density / high porosity electrode. For example, such low density / high porosity may be advantageous in exposing more of the iron active material of the first powder 204 to the electrolyte, thereby improving the performance of the iron negative electrode 14.

[0075] The size of the iron active material of the first powder 204 may be adjusted relative to the size of the discrete particles 208 to facilitate dry powder processing to form the iron active electrode 14 and / or to achieve a target porosity of the iron active electrode 14. To reduce the likelihood of accidental separation of the second powder 206 from the first powder 204 in the powder blend 202, the discrete particles 208 of the second powder 206 and the iron active material of the second powder may have similar particle sizes so that the first powder 204 and the second powder 206 have similar flow characteristics. The average particle size of the discrete particles 208 that minimizes separation from the first powder 204 may be close to, but not necessarily equal to, the average particle size of the first powder 204. Matching or nearly matching the average particle size of the discrete particles 208 with the average particle size of the first powder 204 may remove solid particles of at least one metal sulfide from the interstitial spaces between the particles of the iron active material of the first powder 204. As an example, the ratio of the average particle size of the discrete particles 208 of the second powder 206 to the average particle size of the particles of the iron active material of the first powder 204 may be 0.5 to 2. At this relative size, the first powder 204 and the second powder 206 can generally flow together during the dry material filling process, while also increasing the porosity of the iron negative electrode to facilitate better ion transport / rate performance of the iron negative electrode 14 .

[0076] In certain embodiments, the at least one metal sulfide of the agglomerated particles 210 may be greater than 50% by weight (e.g., greater than 80% by weight) of the discrete particles 208. That is, the agglomerated particles 210 may be primarily formed of the at least one metal sulfide such that the volume occupied by the agglomerated particles 210 is not significantly greater than the volume when useful as an additive in the iron negative electrode 14. As described in more detail below, the technique for agglomerating particles of the at least one metal sulfide to form the agglomerated particles 210 may be performed without the use of a binder or by the efficient use of a binder.

[0077] Although the powder blend 202 in the iron negative electrode 14 has a porosity defined by the first powder 204 and the second powder 206, it should be understood that the discrete particles 208 can contribute to the overall porosity of the powder blend 202 through the porosity of the discrete particles 208 themselves. For example, as determined by mercury intrusion, the median pore size of the discrete particles 208 of the agglomerated particles 210 of at least one metal sulfide can be greater than about 75 nanometers and less than about 15 microns. Therefore, more generally, the discrete particles 208 can have a first average apparent density, the particles forming the agglomerated particles 210 include a second average apparent density, and the first average apparent density is less than the second average apparent density. As an example, the first average apparent density can be greater than 1.0 grams per cubic centimeter and less than 2.1 grams per cubic centimeter. Relative to the apparent density of the particles forming the agglomerated particles 210, the lower apparent density of the discrete particles 208 can be beneficial for exposing a large amount of surface area of ​​at least one metal sulfide to the electrolyte in the electrochemical cell. In some cases, the agglomerated particles 210 of the discrete particles 208 may have surface-connected pores to facilitate economical and efficient preparation of the discrete particles 208 while also facilitating exposure of a large surface area of ​​the at least one metal sulfide to the electrolyte in the electrochemical cell. As an example, the surface-connected pores of the discrete particles 208 may be greater than or equal to 7% by volume and less than or equal to 40% by volume of the agglomerated particles 210 as measured by mercury porosimetry.

[0078] In certain embodiments, at least one metal sulfide of the agglomerated particles 210 may include zinc sulfide (ZnS), which may be useful for improving the capacity of the iron negative electrode 14 relative to a similar electrode without zinc sulfide. In order to achieve such improvements in the performance of the iron negative electrode 14 using the volumetric efficiency of the size of the discrete particles 208, the second powder 206 of the discrete particles 208 may be greater than or equal to 90% by weight of zinc sulfide. In some embodiments, the zinc sulfide may be a low-temperature sphalerite structure (e.g., greater than 60% by weight of the zinc sulfide may be a low-temperature sphalerite structure) as determined by x-ray diffraction. As described in more detail below, in the case where at least one metal sulfide includes zinc sulfide, the low-temperature sphalerite structure of the zinc sulfide may be useful for certain types of agglomeration (e.g., sintering) that can be used to form the agglomerated particles 210.

[0079] Although the at least one metal sulfide of the agglomerated particles 210 has been described as including zinc sulfide, it should be understood that any one or more other types of metal sulfides may additionally or alternatively be included in the agglomerated particles 210. For example, the one or more metal sulfides of the discrete particles 208 may additionally or alternatively include iron sulfide (e.g., FeS, Fe3S4, Fe2S3, and / or other forms), stannous sulfide (SnS), bismuth sulfide (Bi2S3), aluminum sulfide (Al2S3), antimony (III) sulfide (Sb2S3), antimony (V) sulfide (Sb2S5), manganese sulfide (MnS), molybdenum (IV) sulfide (MoS2), iron disulfide, iron copper sulfide, tin sulfide, copper sulfide, cadmium sulfide, silver sulfide, titanium disulfide, lead sulfide, nickel sulfide, antimony sulfide, including any one or more of polymorphs thereof. In some cases, discrete particles 208 may also include suboxides of metal sulfides, or solid solutions of metal sulfides with oxides or hydroxides. In some cases, discrete particles 208 may also include minerals such as sulfonate minerals, which are salts of metals (e.g., Cu, Pb, Ag, Fe, Hg, Zn, V), semimetals (e.g., As, Sb, Bi, Ge), and sulfur. Exemplary sulfonates include pyroxenite Ag3SbS3 and tetrahedrite Cu 12 A4S 13 In some cases (e.g., depending on electrolyte composition or other factors), discrete particles 208 may additionally include a non-metal sulfide compound. In addition or instead, discrete particles 208 may also include tin oxide (SnO2), tin (Sn), bismuth (Bi), ferrous selenide (FeSe), stannous selenide (SnSe), zinc selenide (ZnSe), potassium hydroxide (KOH), sodium hydroxide (NaOH), or a combination thereof.

[0080] In some embodiments, the discrete particles 208 may also include particles of a pore former 212 to impart strength to the discrete particles 208, even if the discrete particles 208 are porous. The average particle size of the pore former 212 may be selected based on geometric considerations related to the initial size of the particles of the at least one metal sulfide that form the agglomerated particles 210 and geometric considerations related to the final desired size of the discrete particles 208 after the particles of the at least one metal sulfide form the agglomerated particles 210. Generally, effective pores may be formed when the average particle size of the pore former 212 may be significantly smaller than the average particle size of the discrete particles 208 and equal to or larger than the average particle size of the particles of the at least one metal sulfide that form the agglomerated particles 210. For example, where the average particle size of the particles agglomerated to form the agglomerated particles 210 is ˜5 microns and the average particle size of the discrete particles 208 is 100 microns, the average particle size of the pore former 212 may be greater than about 5 microns and less than about 20 microns on a weight percent basis. In addition or in contrast, the particles forming the agglomerated particles 210 of at least one metal sulfide may have a first average particle size based on weight percentage, the particles of the pore former 212 may have a second average particle size based on weight percentage, and the second average particle size may be greater than or equal to the first average particle size. That is, the size of the pore former 212 may be designed to give the discrete particles 208 of the second powder 206 a greater porosity than can be achieved using only the particles forming the agglomerated particles 210. In addition or in contrast, the particles of the pore former 212 may be soluble in an alkaline electrolyte, such that the particles of the pore former 212 dissolve (e.g., quickly or over time) and leave pores in the powder blend 202 of the iron negative electrode 14.

[0081] The particles of the pore former 212 may include any one or more different types of materials that function as low-cost and easily removable spaceholders. As an example, the particles of the pore former 212 may include potassium oxide (KO), lithium oxide (LiO), sodium oxide (NaO), potassium hydroxide (KOH), lithium hydroxide (LiOH), sodium hydroxide (NaOH), sodium sulfate (NaS), potassium sulfate (KS), sodium carbonate (NaCO), potassium carbonate (KCO), sodium stannate (Na[Sn(OH)6]), potassium stannate (K[Sn(OH)6]), or a combination thereof. A subset of these materials including KOH, NaOH, NaCO, KCO can be effectively thermally dissociated into constituent salts and gaseous byproducts (e.g., 2KOH+heat→KO+HO or KCO+heat→KO+CO). Producing gaseous byproducts is useful because the spaceholder is bulky but low cost. Additionally or alternatively, the particles of the pore former 212 may include poly(methyl methacrylate), starch, sodium chloride (NaCl), potassium chloride (KCl), ammonium bicarbonate (NH4HCO3), or combinations thereof.

[0082] Reference now FIG. 2A to FIG. 2C In general, the second powder 206 of discrete particles 208 should generally be capable of being blended and processed with the first powder 204 without disintegrating or otherwise losing its intended size. Disintegration or partial disintegration can be defined as a significant reduction in size of the solid additive secondary particles after blending and processing. A significant reduction in size can be defined as a measurable shift in the particle size distribution toward smaller particle sizes, including the formation of a measurable "second mode" of the particle size distribution (due to the formation of smaller particles by disintegration), which is approximately the original particle size.

[0083] Disintegration can also be identified using a microscope. For example, the other powders in the blend can be imaged before and after blending, and the surface of the other powders can be examined to understand whether portions of the solid additive material are deposited on the surface. Additionally or alternatively, by monitoring the particle shape of the secondary particles throughout the blending process, the solid additive can be shown to be non-disintegrated during blending. If the particles appear to become rounded or otherwise change shape throughout the blending, the particles are at least partially disintegrated during the blending process.

[0084] Disintegration resistance can be quantified as the friability of the second powder 206 of discrete particles 208 according to European Pharmacopoeia 2.9.41.-2 (Method B), the entire contents of which are hereby incorporated by reference. The test procedure can be adjusted for different materials to distinguish between particles that are not suitable for use as a battery additive and particles that are suitable for use as a battery additive. In one embodiment, the friability is defined based on ZnS particles. Shaking at a frequency of 400 vibrations per minute for 240 seconds in a friability tester with 10±1 grams of material in the tester bottle, it has been demonstrated that high friability materials produce a large amount of fine powder, which amount is considered unusable for the second powder 206. Specifically, according to the steps outlined below, a friability of 20% was observed. Friability less than about 15% (e.g., less than 10%, less than 5%) can be used for the second powder 206, and the test tolerance allows for small variations. The starting material is a powder with a particle size of 150 to 500 microns. Since the starting material particle size was fine, a dry particle size analyzer (Camsizer X2, dispersion pressure of 30 kPa) was used to obtain the particle size distribution of the material and to quantify the difference in particle size distribution before and after shaking the material in the friability tester. After shaking in the friability tester, a second mode was found in the particle size distribution at a finer particle size; this was interpreted as originating from particle breakage.

[0085] The amount of material attributed to this mode is quantified by:

[0086] 1) Plot q3 (derivative of cumulative particle size distribution) versus particle size before and after shaking the powder in the friability tester.

[0087] 2) If the friability of the material is low enough, the particle size distribution before and after shaking in the friability tester should have a substantially similar particle size distribution, with the mode in the particle size distribution being approximately the same as the particle size before shaking, and possibly adding a new mode at finer particle sizes - the new mode at finer particle sizes is called the fine powder mode. In the case where no mode appears in the particle size distribution at approximately the same particle size before and after shaking in the friability tester, the material is too friable because it has disintegrated in the tester. These materials are defined as having a higher friability than the expected level, even if an exact value cannot be calculated.

[0088] 3) By comparing the particle size distribution before and after shaking in a friability tester, a particle size can be selected that separates the fine powder mode from the original mode in the particle size distribution. This is usually chosen as the local minimum in the variation of q3 with particle size. This particle size is called the cut-off size.

[0089] As a quantitative measure, a friability of less than about 10% weight loss of the original sample as fine powder according to European Pharmacopoeia 2.9.41.-2 (Method B) can indicate suitable resistance to disintegration, which is useful for reliable processing using the second powder 206 to form the iron negative electrode 14 and use in the iron negative electrode 14.

[0090] Figure 2C is a powder showing discrete particles (e.g. Figure 2A and Figure 2B The second powder 206 of discrete particles 208 in the powder 206) and the powder of the iron active material (e.g., Figure 2A and Figure 2B Figure 204 of a first powder (204) mixed with Fe electrode powder. In the figure, the powder of discrete particles is light-colored and the powder of iron active material is dark. In this example, a solid additive (ZnS) is granulated with poly (vinyl alcohol) and carboxymethyl cellulose. Both binders can produce agglomerates. In some cases, the particle size produced by this process is similar to that of the iron active material. These materials were incorporated into the Fe electrode powder mixture, successfully reducing the apparent density of the powder mixture, proving that the electrode pores can be retained. The concept of sintering ZnS was verified, and materials with suitable strength and performance were also generated. These additives were incorporated into electrochemical tests, showing performance enhancement.

[0091] Figure 4 4 is a flow chart of an exemplary method 400 for preparing an additive for an iron negative electrode of an alkaline electrochemical cell. Unless otherwise indicated or clearly required by the context, any one or more aspects of the exemplary method 400 may be used to prepare an additive for a rechargeable battery pack 10 ( Figure 1B ) of the iron negative electrode 14 ( Figure 1B and Figure 2A ) of the second powder 206 ( Figure 2Aand Figure 2B ).

[0092] As shown in step 410, the exemplary method 400 may include forming a feedstock including a granular material having a predetermined composition. The granular material is understood to refer to agglomerated together to form any one or more agglomerated particles 210 ( Figure 2B ). Thus, the granular material may include particles of at least one metal sulfide prior to agglomeration into agglomerated particles. By way of example and not limitation, the particles of at least one metal sulfide may include particles of zinc sulfide (ZnS).

[0093] In some embodiments, the granular material of the raw material may include a combination of various types of solid additive particles with different chemical properties and / or particle sizes. As an example, in order to facilitate achieving optimal performance in an electrochemical cell, it may be useful to substantially uniformly mix various types of particles with the iron active particles of any one or more powder blends described herein. Before processing, the various types of solid additive particles in the raw material are mixed with a predetermined weight ratio relative to each other, which can be conducive to achieving such approximately uniformity in the powder blend, which will then be formed by processing with the iron active particles. That is, for any two additives A and B, only A and only B granular materials will inevitably produce A-rich pockets and B-rich pockets, and the granular material of a suitable A+B mixture will generally result in better distribution uniformity of both additives A and B. As an example, the raw material of the granular material may include mixing at least two metal sulfides (e.g., zinc sulfide and iron sulfide). In some embodiments, the granular material of at least two sulfides can be mixed with a predetermined weight ratio relative to each other. This weight ratio may advantageously be maintained by processing the feedstock to form discrete particles such that the discrete particles may have a predetermined weight ratio of at least two metal sulfides.

[0094] In some embodiments, forming a feedstock comprising a granular material having a predetermined composition may include blending particles of a pore former (e.g., any one or more of a plurality of different pore formers described herein) with particles of at least one metal sulfide. In some cases, the pore former may be soluble in an alkaline electrolyte. The ratio of the average particle size of the particles of the pore former to the average particle size of the particles of the at least one metal sulfide in the feedstock may be greater than or equal to 1:1 and less than about 5:1.

[0095] In some embodiments, forming the feedstock may include mixing a conductive material with at least one metal sulfide. The conductive material may include tin, graphite, carbon black, or a combination thereof. Where the feedstock includes a conductive material, it is understood that the discrete particles produced by any one or more of the processing techniques described below may include the conductive material.

[0096] In the specific case of incorporating solid additives into the iron negative electrode, the particle size of the iron active material can be about 50 microns to about 900 microns, and the size of the particulate material of at least one metal sulfide can generally be about 10 microns or less. There are several reasons for this: 1) many solid additives are produced by chemical synthesis and related technologies for battery applications, which are generally the highest yield and lowest cost when producing particles with a size of ~500nm to 10μm; 2) the effect of the additive may rely on uniform and fine dispersion throughout the iron negative electrode to enhance electrode performance; or 3) the additive may require a high surface area to enhance electrode performance. The size of the particulate material of one or more additives may be affected by one or more of these reasons. Some examples of additives that are most effective in using particulate materials with a particle size finer than the iron particle size in the iron negative electrode include MnS, Al2S3, Sb2S3, Sb2S5, FeS, Bi2S3, MoS2, conductive additives such as graphite or carbon black, tin-containing solid compounds, and ZnS.

[0097] In some embodiments, forming the feedstock may include introducing at least one polymer binder to the granular material. As described in more detail below, the at least one polymer binder may be used as part of a sintering process to solid-state bond together agglomerated particles formed from the granular material of the feedstock.

[0098] As shown in step 420, the exemplary method 400 may include processing a feedstock including a granular material into a powder of discrete particles including agglomerated particles of the granular material, the agglomerated particles including at least one metal sulfide. As described in more detail below, processing the feedstock including the granular material into a powder of discrete particles may include any one or more of a variety of different granulation techniques that may be economically and effectively implemented to produce a powder of discrete particles having a target friability to achieve a performance target for an iron negative electrode formed using the powder of discrete particles.

[0099] In some embodiments, the granular material of the raw material can be combined together in the solid state to form discrete particles of agglomerated particles. For example, such solid-state bonding can include bonding materials in the solid state using bonds of the same material. Solid-state bonding can be performed according to any one or more of a variety of different techniques. However, the solid-state bonding formed according to such techniques can be defined by the presence of a neck or solid-state contact between agglomerated particles (for example, it can be observed by microscopic examination of the surface and / or cross-section of the agglomerated particles), including the case where the neck or bond size is >5% of the particle diameter. In addition or on the contrary, the solid-state bonding is characterized in that the strength of the material subjected to the process is significantly increased by processing the material by any one or more processes, provided that the increase in strength is attributed to solid-state bonding. Examples of processes that can be used to form solid-state bonds include sintering (including sintering at a temperature exceeding half of the melting temperature of the material), hot pressing (including hot pressing at a temperature of 30% of the melting temperature of the material or at a temperature exceeding 30% of the melting temperature of the material), cold sintering, infiltration and reaction bonding. The equipment for performing solid-state bonding can include a calcining furnace, a continuous linear furnace (for example, a belt furnace, a pusher furnace and a walking beam furnace) and / or an intermittent furnace.

[0100] As an example, the granular material of the raw material can be solid-state combined at about 500 degrees Celsius to about 1400 degrees Celsius. This solid-state combination can occur in a non-oxidizing atmosphere such as a reducing atmosphere or an inert atmosphere. In the case where at least one metal sulfide includes zinc sulfide, an oxidizing atmosphere may be less desirable due to the possible formation of harmful sulfur dioxide and sulfur oxide gases and the reduction of ZnS content by forming ZnO from ZnS. An inert atmosphere may include nitrogen or argon. A reducing atmosphere may include hydrogen or carbon monoxide. A mixture of these atmospheres (e.g., a combination of nitrogen and hydrogen) can be used. For fine ZnS granular material, satisfactory sintering can be observed experimentally at a temperature above 900 degrees Celsius and below 1300 degrees Celsius (e.g., ~1100°C), and for fine ZnS powder, hot pressing is shown to be satisfactory at 900°C, a uniaxial pressure of about 60psi (about 410kPa), and a time of about 10 minutes. Sintering and / or hot pressing temperatures, pressures and other processing conditions will vary depending on the materials used and the density desired.

[0101] In certain embodiments, processing the feedstock into discrete particles may include introducing at least one binder into the discrete particles of the agglomerated particles. Continuing with this example, the at least one binder introduced into the discrete particles may be soluble and / or reactive to form a soluble material in an alkaline electrolyte, such that the binder may bind the granular material into the discrete particles of the agglomerated particles to facilitate processing of the powder of the discrete particles to form an iron negative electrode, and the binder may dissolve in the iron negative electrode when the rechargeable battery is cycled.

[0102] Returning to the example where forming the feedstock includes introducing at least one polymer binder into the granular material, processing the feedstock into discrete particles may include pyrolyzing at least one polymer binder to form a graphitized film on the granular material. The type of binder used may vary depending on how the material being bonded and the electrode are processed. In the case of ZnS agglomeration, at least one binder may include CMC, poly(vinyl alcohol) and poly(ethylene glycol). At least one binder and subsequent processing may be selected so that the binder keeps the solid additive in the powder bed during the electrochemical cycle, and in particular so that small particles are bound in place during the electrochemical cycle. Binders that have a large amount of char due to pyrolysis during high temperature processing (e.g., sintering, hot pressing) can produce discrete particles of agglomerated particles that keep the particles in discrete particles / reduce the risk of particle floating. A high char binder may be defined as a binder that is pyrolyzed in an inert atmosphere and has a residual solid yield of >7% by weight after pyrolysis in a non-oxidizing atmosphere up to 600°C. Carboxymethyl cellulose (CMC) or poly(acrylic acid) may be used as a high char binder. Polyacrylonitrile (PAN) or other polymers with aromatic rings can be used as high coke binder systems. In such cases, pyrolysis behavior can be used to graphitize coke at the same time, thereby producing a strong and coherent graphitized film on the solid additives that retain the additives. Pitch can be used as an adhesive or adhesion promoter. In many cases, a mixture of adhesives can be used for granulation processes. These adhesives can be used for different purposes. For example, poly (vinyl alcohol) can be used in combination with CMC and / or PAN to customize the rheology, particle strength and coke level of particles. In some embodiments, the adhesive can be maintained in discrete particles during the entire life of the electrochemical cell. In such cases, the adhesive can be compatible with alkaline electrolytes, and therefore can include poly (tetrafluoroethylene), carboxymethyl cellulose, poly (ethylene), poly (propylene) and polyvinylidene fluoride. In some cases, adhesive pyrolysis and residual coke may be harmful to solid additives, and low coke adhesives may be needed. In such cases, poly (ethylene), poly (propylene), poly (vinyl alcohol) or other adhesives that produce low residual carbon can be usefully used to form discrete particles of agglomerated particles. In some embodiments, an inorganic binder may be used, such as a clay or silicate-based binder, an alumina-containing binder, or any other oxide-based binder commonly used in the art to bind powdered materials together.

[0103] In certain embodiments, the technique for processing the raw material to form discrete particles of agglomerated particles may include a granulation process that does not involve a binder. Such a process may include compacting (e.g., rolling) or sintering a powdered body and reducing the sintered body to a suitable size by, for example, pulverizing.

[0104] Processing the raw materials to form discrete particles may additionally or alternatively include any of the following or any other suitable granulation techniques useful for bonding smaller powder particles together into coarse powder particles: fluidized bed granulation, spray drying, high shear mixing granulation, twin screw granulation, roller compaction, intensive mixing, wet granulation and extrusion granulation, and open pan granulation / disc granulation.

[0105] In some cases, a combination of any one or more of the granulation techniques described herein may be used. For example, sometimes the strength required may be greater than what can reasonably be achieved by granulation using a binder, but a compact particle size and high sphericity may also be required. In such cases, spray drying techniques may be used to agglomerate the granulated material, and the resulting material may then be sintered in a process known as an agglomeration and sintering process.

[0106] In some cases, the inter-particle attraction may be sufficient and no binder is required to form discrete particles of agglomerated particles. For example, nano-sized powders can be agglomerated without the need for a binder.

[0107] In some embodiments, processing the feedstock to form discrete particles of agglomerated particles may include binder-based granulation, including drum granulation, spray drying, wet granulation, or dry granulation.

[0108] In some cases, the additive can act as a binder for other additives. For example, the first additive can be heated in the presence of a second low melting point additive that solidifies when cooled to room temperature. For example, the first additive can be FeS or ZnS, and the second additive can be Sn. The heating can be performed in an inert atmosphere to prevent oxidation of the molten phase. The crystallographic properties and chemical properties of both the first additive and the second additive can be adjusted to ensure that the first additive is wetted by the second additive, and thus ensure uniform bonding and high strength after cooling. The resulting material can be considered to be a metal-based composite material bonded by infiltration. The incorporation of a combined / infiltrated second additive in powder form during the infiltration process makes the uniformity of the material properties of the resulting discrete particles higher, and more pores can be created in the discrete particles, thereby usefully increasing the rate performance of the resulting iron negative electrode formed using a powder of discrete particles and / or reducing its impedance.

[0109] In some embodiments, the granular material of the raw material can be solid-state combined with a form factor close to the desired size and shape. For example, the agglomerated powder can be solid-state combined by many techniques known in the art for powder agglomeration and / or sintering. As a specific example, the ZnS powder can be briquette, and in some cases, it can be ground into a desired size distribution, and then the resulting agglomerate can be sintered (for example in a continuous sintering furnace). In some cases, the ZnS powder can be spray-dried to form agglomerates of a suitable size range, and then the resulting agglomerates can be sintered. The resulting sintered material can be lightly ground in a rod mill or similar equipment to destroy any slight bonding between the secondary particles that occurs during the sintering step without further destroying the discrete particles of the agglomerated particles.

[0110] In certain embodiments, the raw materials may be cold pressed together to form discrete particles that may remain sufficiently cohesive for handling, such as in the case of cold pressing of tin powders or various briquetting techniques for ceramic powders.

[0111] Using any one or more of the various techniques described herein, the bonding / granulation process can result in a bonded material particle that is larger than the desired average particle size of the powder of discrete particles (e.g., at least one dimension is approximately 1 mm or larger). In such cases, the resulting bonded / sintered block can be an intermediate that can be mechanically processed (e.g., by suitable crushing, grinding, milling, and grading / screening techniques) to achieve the target average particle size of the powder of discrete particles. Such processing usefully separates the bonding process from the grading process, thus facilitating a wider process window and material combinations.

[0112] In some embodiments, the feedstock may be processed into a monolithic mass of larger ceramic material (e.g., by pressing and sintering a geometry having at least one dimension of approximately 1 mm or greater). The resulting larger-scale solid bonded material may then be crushed, ground, or otherwise reduced in size to produce discrete particles of a desired size.

[0113] In some embodiments, alloying elements may be included that extend the stability of the ZnS cubic phase to higher temperatures, thereby maintaining the cubic phase or facilitating the transformation of the hexagonal phase to the cubic phase during hot working operations.

[0114] Reference now Figure 4 , Figure 5A and Figure 5B, which is a ZnS phase diagram showing phase behavior as a function of temperature and composition. The phase diagram shows the solubility of FeS in ZnS and doping FeS can be useful to control the phase transition temperature. It can be noted that the dissolution of Fe in ZnS is up to ~40mol%. In some embodiments, it may be useful to have ZnS in a low-temperature sphalerite structure. Iron reduces the phase transition temperature from sphalerite to wurtzite, making it easier for ZnS to be transformed into a wurtzite crystal structure. Relatedly, iron contamination inhibits the transformation of the wurtzite structure into a sphalerite structure. This transformation may be slow relative to the time scale (10 minutes to several hours) associated with industrial processing. After the introduction of Fe alloying elements, the reduction of the phase transition temperature, the generation of chemical partitioning and drag effects and the slow diffusion kinetics accompanying at lower temperatures combine to make the phase transition slow.

[0115] In the case where at least one metal sulfide includes ZnS, the cubic ZnS phase can be retained during the hot working process. For example, in such cases, the raw material can be sintered at a temperature exceeding the sphalerite ZnS / wurtzite ZnS phase transition temperature (1020°C for pure ZnS) and annealed at a temperature below the sphalerite ZnS / wurtzite ZnS phase transition temperature during cooling to promote the transformation back to sphalerite ZnS. Annealing to transform to sphalerite ZnS may require careful balancing of the kinetics and driving force of the transformation so that the transformation occurs on a useful time scale (10 minutes to several hours). Generally, at temperatures below the phase transition temperature, as supercooling increases, the driving force for the transformation to the cubic phase increases, but the kinetics of the transformation are somewhat slow. The annealing conditions for achieving the transformation of the wurtzite structure to the sphalerite structure can be about 700°C to about 1000°C (e.g., about 800°C to about 950°C), with a time scale of about 15 minutes to about 4 hours. In some cases, the thermal exposure can include isothermal maintenance in the listed temperature range. The material can be intentionally cooled slowly enough in the temperature range listed for the crystal structure transition. In some embodiments, a combination of slow cooling and isothermal holding can be used to achieve the transition of the crystal structure. In some cases, the material can be reheated to achieve the transition to the cubic phase of the ZnS material (compared to solid state bonding and crystal structure transition in one step).

[0116] Continuing with this example, sintering can usefully be carried out at a temperature below the sphalerite ZnS / wurtzite ZnS phase transition temperature to produce sintered particles having a sphalerite ZnS crystal structure without the need for further processing to transform the ZnS to the sphalerite structure, thus saving expensive processing time and energy.

[0117] In some embodiments, processing the feedstock to form discrete particles may include managing C and O impurities.

[0118] As an example, ZnO and C-based impurities may be undesirable in a ZnS additive. ZnO, if left in discrete particles, may be reduced in subsequent thermal processing, or dissolve to form zincate ions when discrete particles of agglomerated particles enter the electrolyte. Reduction may result in evaporation of metallic Zn and subsequent deposition in thermal processing equipment. Alternatively, if ZnO enters an electrochemical cell, it may dissolve in the alkaline electrolyte of the electrochemical cell, potentially affecting electrochemical performance. Therefore, both reduction and dissolution may be undesirable.

[0119] Thus, continuing with this example, ZnO can be removed in a controlled manner using a reducing and / or decarburizing atmosphere. ZnO reduction typically occurs at 700°C to 1000°C, producing gaseous Zn metal and redox species. In various embodiments, the reduction can be performed with a reducing agent such as solid carbon, gaseous carbon monoxide, or gaseous hydrogen.

[0120] In some embodiments, a S-containing gas can be used to reduce the possibility of ZnO evaporation. ZnS typically contains trace amounts of ZnO, and in the processing atmosphere, ZnS can react with O to produce ZnO. ZnO can be reduced to form Zn-based vapor, especially during high-temperature anode processing. Zn evaporation may be harmful to thermal processing equipment, so it is necessary to avoid or at least reduce the possibility of this possibility. Therefore, in some embodiments, a sulfur-containing gas can be added to increase the sulfur potential in the processing atmosphere. ZnO can be converted into ZnS to prevent evaporation of Zn. The gas can be selected as a reducing gas. As an example, the sulfur-containing gas can be any one or combination of the following: 1) hydrogen sulfide, H2S; 2) carbonyl sulfide, OCS; 3) methyl mercaptan, CH3SH; and / or 4) sulfur dioxide, SO2.

[0121] In some embodiments, the effect of the formation of gaseous zinc on electrode formation and / or furnace operation can be reduced. In the presence of a carbon source, an oxide (e.g., ZnO) present in the zinc sulfide source or zinc oxide formed by oxidation on other oxide-free surfaces may result in ZnO being carbon-thermally reduced to Zn(g) when heated to a temperature exceeding 800°C. The formation of this gaseous zinc can be controlled to prevent or at least reduce the possibility of interfering with furnace operation or electrode preparation. Carbon thermal reduction may include each of the following: 1) both carbon and zinc oxide are present in the heated electrode; and 2) sufficiently high temperature. Therefore, preventing or controlling the formation of gaseous zinc from a zinc source containing any amount of zinc oxide may require removing one of the above factors. In one embodiment, the granular material may include zinc sulfide, an iron source, and some carbon source, which may be compacted at a temperature of about 750°C, about 750°C to 800°C, about 800°C, about 800°C to 850°C, or about 850°C to reduce the possibility of excess zinc oxide being reduced.

[0122] As an additional or alternative example, C-based contamination in ZnS may be undesirable. It has been found that when ZnS is processed with Fe at high temperatures, C contamination can increase undesirable side reactions. In multiple embodiments, carbon management can be carried out through three routes: 1) minimize or eliminate the use of binders or other carbon-containing materials during processing; 2) when used, use low coke binders; 3) use a suitable atmosphere for heating and sintering of ZnS. In some embodiments, ZnS can be pressed and sintered in the absence of a polymer binder, thereby eliminating the risk of C contamination. In some embodiments, C-containing polymers can be added as a pressure aid, binder or other functional agent. Polymers with acceptable coke levels can include any low coke binder for low residual C pyrolysis in an inert or reducing atmosphere, such as: zinc stearate, stearic acid, polymeric alcohols such as poly (vinyl alcohol), poly (methyl methacrylate), polyolefins (e.g., poly (propylene), poly (ethylene), low molecular weight analogs such as paraffin wax and microcrystalline wax) and copolymers of these materials. Additionally or alternatively, an inorganic binder may be used, such as a soluble silicate, a soluble phosphate, or a soluble aluminate. Silicates can reduce the battery performance of iron anodes, so the use of aluminates as inorganic binders may be useful. Additionally or alternatively, gaseous hydrogen may be included in the processing atmosphere to react Cs+2H 2,g →CH 4,g (or other related reactions) to promote the removal of residual C in ZnS.

[0123] The above method description is provided only as an illustrative example and is not intended to require or imply that the steps of the multiple embodiments must be performed in the order presented. As will be appreciated by those skilled in the art, the order of steps in the above embodiments can be performed in any order. For example, words such as "thereafter", "then", "next", etc. are not necessarily intended to limit the order of the steps; these words can be used to guide the reader to understand the description of the method. In addition, any reference to a claim element in the singular form, such as the use of the article "a / an" or "the", should not be interpreted as limiting the element to the singular.

[0124] The foregoing description of the disclosed embodiments is provided to enable any person skilled in the art to prepare or use the embodiments. In addition, any step of any embodiment described herein can be used for any other embodiment. Multiple modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments without departing from the scope of the present disclosure. Therefore, the present disclosure is not intended to be limited to the embodiments shown herein, but to conform to the broadest scope consistent with the following claims and the principles and novel features disclosed herein.

Claims

1. An additive for an iron negative electrode of an alkaline electrochemical cell, the additive comprising: A powder comprising discrete particles of agglomerated particles comprising at least one metal sulfide.

2. The additive of claim 1, wherein the at least one metal sulfide of the agglomerated particles is greater than 50% by weight of the discrete particles.

3. The additive of claim 2, wherein the at least one metal sulfide of the agglomerated particles is greater than 80% by weight of the discrete particles.

4. The additive according to claim 1, wherein On a weight percent basis, the discrete particles have an average particle size greater than about 30 microns and less than about 800 microns.

5. The additive according to claim 1, wherein The discrete particles of the agglomerated particles of the at least one metal sulfide have a median pore size greater than about 75 nanometers and less than about 15 microns as determined by mercury porosimetry.

6. The additive of claim 1, wherein the discrete particles have a first average apparent density and the particles comprising the at least one metal sulfide have a second average apparent density, the first average apparent density being less than the second average apparent density.

7. The additive of claim 6, wherein the first average apparent density is greater than 1.0 grams per cubic centimeter and less than 2.1 grams per cubic centimeter.

8. The additive according to claim 1, wherein The discrete particles have a friability of less than about 15% weight loss according to European Pharmacopoeia 2.9.41.-2 (Method B).

9. The additive according to claim 1, wherein The solid state bonding holds at least some of the agglomerated particles in the discrete particles together so that there is solid state bonding between the agglomerated particles.

10. The additive of claim 1 wherein at least some of said agglomerated particles of said discrete particles are metal matrix composites bonded by infiltration.

11. The additive of claim 1, wherein the discrete particles include a binder, at least some of the agglomerated particles of the discrete particles being bound by the binder.

12. The additive of claim 11, wherein the binder is soluble in an alkaline electrolyte and / or the binder is reactive to form a substance that is soluble in an alkaline electrolyte.

13. The additive of claim 1, wherein the at least one metal sulfide comprises zinc sulfide (ZnS).

14. The additive of claim 13, wherein the powder of discrete particles is greater than or equal to 90 weight percent zinc sulfide (ZnS).

15. The additive according to claim 13, wherein Greater than 60 weight percent of the zinc sulfide (ZnS) is in the sphalerite structure as determined by x-ray diffraction.

16. The additive of claim 1, wherein the agglomerated particles of the discrete particles have surface-connected pores.

17. The additive according to claim 16, wherein As measured by mercury porosimetry, the surface-connected pores of the agglomerated particles are greater than or equal to 7 volume % and less than or equal to 40 volume % of the agglomerated particles.

18. The additive of claim 1, wherein the at least one metal sulfide comprises ferrous sulfide (FeS), stannous sulfide (SnS), bismuth sulfide (Bi2S3), aluminum sulfide (Al2S3), antimony (III) sulfide (Sb2S3), antimony (V) sulfide (Sb2S5), manganese sulfide (MnS), molybdenum (IV) sulfide (MoS2), or a combination thereof.

19. The additive of claim 1, wherein the discrete particles further comprise tin oxide (SnO2), tin (Sn), bismuth (Bi), zinc selenide (ZnSe), potassium hydroxide (KOH), sodium hydroxide (NaOH), or a combination thereof.

20. The additive of claim 1, wherein the discrete particles further comprise a conductive material.

21. The additive of claim 20, wherein the conductive material comprises tin, graphite, carbon black, or a combination thereof.

22. The additive of claim 1, wherein the discrete particles further comprise particles of at least one pore former.

23. The additive according to claim 22, wherein On a weight percent basis, the particles of the at least one pore former have an average particle size greater than about 5 microns and less than about 20 microns.

24. The additive of claim 22, wherein the particles of the at least one metal sulfide have a first average particle size on a weight percent basis, and the particles of the at least one pore former have a second average particle size on a weight percent basis, the second average particle size being greater than or equal to the first average particle size.

25. The additive of claim 22, wherein the at least one pore former is soluble in an alkaline electrolyte.

26. The additive of claim 25, wherein the at least one pore former comprises potassium oxide (KO), lithium oxide (LiO), sodium oxide (NaO), potassium hydroxide (KOH), lithium hydroxide (LiOH), sodium hydroxide (NaOH), sodium sulfate (NaS), potassium sulfate (KS), sodium carbonate (NaCO), potassium carbonate (KCO), sodium stannate (Na[Sn(OH)6]), potassium stannate (K[Sn(OH)6]), or a combination thereof.

27. The additive of claim 22, wherein the at least one pore former comprises poly(methyl methacrylate), starch, sodium chloride (NaCl), potassium chloride (KCl), ammonium bicarbonate (NH4HCO3), or a combination thereof.

28. An iron negative electrode for an alkaline electrochemical cell, the iron negative electrode comprising: a first powder comprising an iron active material; and A second powder comprising the additive of any one or more of claims 1 to 34, the first powder and the second powder forming a powder blend, wherein the second powder is dispersed relative to the first powder.

29. The iron negative electrode of claim 28, wherein the first powder comprises any one or more of iron oxide, atomized iron powder, sponge iron powder or ground iron powder. 30 . The iron negative electrode of claim 29 , wherein a ratio of an average particle size of discrete particles of the second powder to an average particle size of particles of the iron active material is 0.5 to 2.

31. The iron negative electrode of claim 28, wherein the average particle size of the discrete particles is greater than or equal to the average pore size of the powder blend.

32. The iron negative electrode of claim 28, wherein the apparent density of the powder blend is less than the apparent density of the first powder alone.

33. The iron negative electrode of claim 28, wherein the iron active material is greater than about 70% of the total weight of the first powder and the second powder.

34. The iron negative electrode of claim 28, wherein the thickness of the active layer of the electrode is greater than about 8 mm and less than about 50 mm.

35. The iron negative electrode of claim 28, wherein the concentration of the second powder in the powder blend has a predetermined gradient across the thickness dimension of the active layer of the powder blend.

36. A method for preparing an additive for an iron negative electrode of an alkaline electrochemical cell, the method comprising: forming a feedstock comprising a particulate material having a predetermined composition; and The feedstock including the granular material is processed into a powder including discrete particles of agglomerated particles of the granular material, the agglomerated particles including at least one metal sulfide.

37. The method of claim 36, wherein processing the feedstock of the granular material comprises solid state bonding the granular material.

38. The method of claim 37, wherein solid state bonding the particulate material comprises heating the particulate material to a temperature of about 500°C to about 1400°C.

39. The method of claim 37, wherein solid state combining the granular material comprises sintering the granular material into the agglomerated particles.

40. The method of claim 39, wherein the at least one metal sulfide comprises zinc sulfide (ZnS) and the sintering is performed at a temperature greater than 900°C and less than 1300°C.

41. The method of claim 37, wherein solid state bonding the granular material comprises hot pressing the granular material.

42. The method of claim 41, wherein the at least one metal sulfide comprises zinc sulfide (ZnS) and the hot pressing is performed at 900°C at a uniaxial pressure of about 410 kPa for about 10 minutes.

43. The method of claim 36, wherein forming the feedstock comprises introducing at least one polymer binder into the particulate material.

44. The method of claim 43, wherein processing the feedstock into the discrete particles comprises pyrolyzing the at least one polymer binder to form a graphitized film on the particulate material.

45. The method of claim 43, wherein the at least one polymer binder is pyrolyzable in an inert atmosphere and provides a yield of >7 wt% residual solids after pyrolysis in a non-oxidizing atmosphere up to 600°C.

46. ​​The method of claim 43, wherein the at least one polymer binder comprises asphalt, zinc stearate, stearic acid, a polymer alcohol, poly(methyl methacrylate), a polyolefin, a polymer having an aromatic ring, poly(ethylene glycol), poly(tetrafluoroethylene), polyvinylidene fluoride, carboxymethyl cellulose, poly(acrylic acid), or a copolymer of any one or more of the foregoing.

47. The method of claim 43, wherein: The at least one polymer binder is introduced into the particulate material and the particulate material is thermomechanically bonded in a processing atmosphere comprising hydrogen.

48. The method of claim 37, wherein forming the feedstock comprises introducing at least one inorganic binder into the particulate material.

49. The method of claim 48, wherein the at least one inorganic binder comprises an oxide-based binder, a silicate-based binder, an alumina-containing binder, or a combination thereof.

50. The method of claim 36, wherein processing the feedstock of granular material further comprises compacting the feedstock of granular material.

51. The method of claim 50, wherein compacting the feedstock of granular material comprises rolling the feedstock of granular material.

52. The method of claim 36, wherein the particulate material comprises particles of the at least one metal sulfide.

53. The method of claim 52, wherein the feedstock to form the particulate material comprises mixing at least two metal sulfides in a predetermined weight ratio relative to each other.

54. The method of claim 53, wherein the at least two metal sulfides comprise zinc sulfide (ZnS) and ferrous sulfide (FeS).

55. The method of claim 54, wherein the at least two metal sulfides include zinc sulfide (ZnS) and ferrous sulfide (FeS) in the predetermined weight ratio relative to each other in the discrete particles.

56. The method of claim 52, wherein forming the feedstock comprising the particulate material comprises mixing a conductive material with the at least one metal sulfide.

57. The method of claim 56, wherein the conductive material comprises tin, graphite, carbon black, or a combination thereof.

58. The method of claim 56, wherein the conductive material is solid at room temperature, processing the feedstock of the granular material comprises heating the feedstock of the granular material in an inert environment to melt the at least one metal sulfide and the conductive material so that the conductive material wets the at least one metal sulfide, and cooling the feedstock of the granular material while the conductive material wets the at least one metal sulfide so that the at least one metal sulfide and the conductive material in the feedstock of the granular material form a metal-based composite material bonded by infiltration.

59. The method of claim 52, wherein the particles of the at least one metal sulfide comprise particles of zinc sulfide (ZnS).

60. The method of claim 59, wherein processing the feedstock comprises exposing the granular material to a chemical reducing environment comprising one or more reducing agents at 700°C to 1000°C such that zinc oxide (ZnO) in the granular material is chemically reduced to zinc sulfide (ZnS).

61. The method of claim 60, wherein the one or more reducing agents comprise solid carbon, gaseous carbon monoxide, or gaseous hydrogen.

62. The method of claim 59, wherein processing the feedstock comprises exposing the particulate material to a sulfur-containing gas to convert zinc oxide (ZnO) to zinc sulfide (ZnS).

63. The method of claim 62, wherein the sulfur-containing gas comprises hydrogen sulfide (H2S), carbonyl sulfide (OCS), methyl mercaptan (CH3SH), sulfur dioxide (SO2), or a combination thereof.

64. The method of claim 52, wherein forming the feedstock of the particulate material comprises blending particles of a pore former with particles of the at least one metal sulfide, the pore former being soluble in an alkaline electrolyte.

65. The method of claim 64, wherein the ratio of the average particle size of the particles of the pore former to the average particle size of the particles of the at least one metal sulfide is greater than or equal to 1:1 and less than about 5:

1.

66. The method of claim 36, wherein processing the feedstock into the discrete particles comprises introducing at least one binder into the discrete particles, the at least one binder being soluble in an alkaline electrolyte.

67. The method of claim 36, wherein processing the feedstock into the discrete particles comprises forming the granular material into one or more intermediates, and changing the size of the one or more intermediates to form the discrete particles.

68. The method of claim 67, wherein forming the granular material into the one or more intermediate bodies comprises cold pressing the granular material.

69. The method of claim 68, wherein cold pressing the granular material comprises forming agglomerates of the granular material.

70. The method of claim 67, wherein changing the size of the one or more intermediate bodies to form the discrete particles comprises sintering the one or more intermediate bodies together to form the discrete particles.

71. The method of claim 67, wherein forming the granular material into the one or more intermediates comprises sintering the granular material into a sintered body having at least one dimension approximately 1 mm or greater, and changing the size of the one or more intermediates comprises reducing the size of the one or more intermediates to form the discrete particles.

72. The method of claim 67, wherein the one or more intermediates comprise a monolithic body of ceramic material, at least one dimension of the monolithic body being approximately 1 mm or greater, and altering the size of the one or more intermediates comprises reducing the size of the one or more intermediates to form the discrete particles.

73. The method of claim 67, wherein changing the size of the one or more intermediates to form the discrete particles comprises any one or more of: grinding, drum granulation, fluidized bed granulation, spray drying, high shear mixing granulation, twin screw granulation, extrusion granulation, open pan granulation / disc granulation, wet granulation, or dry granulation.

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