Rechargeable battery using iron negative electrode and manganese oxide positive electrode

Abstract

Materials, designs, and methods of manufacture for iron-manganese oxide electrochemical cells are disclosed. In various embodiments, the negative electrode comprises a pelletized, briquetted, or compacted iron-containing component that includes metallic iron or iron-based compounds (oxides, hydroxides, sulfides, or combinations thereof), collectively referred to as "iron negative electrodes." In various embodiments, the positive electrode comprises a pelletized, briquetted, or compacted manganese-containing component that includes manganese(IV) oxide (MnO2), manganese(III) oxide (Mn2O3), manganese(III) oxyhydroxide (MnOOH), manganese(II) oxide (MnO), manganese(II) hydroxide (Mn(OH)2), or combinations thereof, collectively referred to as "manganese oxide positive electrodes." In various embodiments, the electrolyte comprises an aqueous alkali metal hydroxide that includes lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), cesium hydroxide (CsOH), or combinations thereof. In various embodiments, the battery pack assembly is assembled into a square configuration or a cylindrical configuration.

Description

[0001] Related applications This application claims priority to U.S. Provisional Patent Application No. 62 / 879,153, filed July 26, 2019, entitled “Rechargeable Battery Pack Using Iron Negative Electrode and Manganese Oxide Positive Electrode,” and U.S. Provisional Patent Application No. 63 / 021,267, filed May 7, 2020, entitled “Rechargeable Battery Pack Using Iron Negative Electrode and Manganese Oxide Positive Electrode,” the entire contents of which are incorporated herein by reference for all purposes. This application also claims priority to U.S. Provisional Patent Application No. 62 / 879,126, filed July 26, 2019, entitled “Low-Cost Metal Electrode,” and U.S. Provisional Patent Application No. 63 / 021,566, filed May 7, 2020, entitled “Low-Cost Metal Electrode,” the entire contents of which are incorporated herein by reference for all purposes. This application also claims priority to U.S. Provisional Patent Application No. 63 / 021,610, filed May 7, 2020, entitled “Iron-containing electrode for electrochemical cells,” the entire contents of which are incorporated herein by reference for all purposes. Background Technology

[0002] Energy storage technologies are playing an increasingly important role in power grids; at the most basic level, these energy storage assets provide refinement to better match grid generation and demand. The services performed by energy storage devices benefit power grids across multiple timescales, from milliseconds to years. Currently, energy storage technologies exist that can support timescales from milliseconds to hours, but long-duration and ultra-long-duration (generally >8 hours) energy storage systems are still needed. Summary of the Invention

[0003] Materials, designs, and manufacturing methods for iron-manganese oxide electrochemical batteries are disclosed. In various embodiments, the negative electrode comprises a pelletized, compacted, pressed, or sintered iron-containing component, including metallic iron or iron-based compounds (oxides, hydroxides, sulfides, or combinations thereof), collectively referred to as an "iron negative electrode." In various embodiments, the positive electrode comprises a pelletized, compacted, pressed, or sintered manganese-containing component, including manganese(IV) oxide (MnO2), manganese(III) oxide (Mn2O3), manganese(III) hydroxide (MnOOH), manganese(II) oxide (MnO), manganese(II) hydroxide (Mn(OH)2), or combinations thereof, collectively referred to as a "manganese oxide positive electrode." In various embodiments, the electrolyte comprises an aqueous alkali metal hydroxide, including lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), cesium hydroxide (CsOH), or combinations thereof. In various embodiments, the battery assembly is assembled into a prismatic or cylindrical configuration. In various embodiments, separators may be added.

[0004] Materials, design, and manufacturing methods for electrodes used in electrochemical cells are disclosed. In various embodiments, the electrode comprises iron.

[0005] Various embodiments include a battery pack comprising: a first electrode comprising manganese oxide; an electrolyte; and a second electrode comprising iron. In some embodiments, the iron comprises direct reduced iron (DRI). In some embodiments, the electrolyte is a liquid electrolyte. In some embodiments, the electrolyte comprises an alkali metal hydroxide, including lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), cesium hydroxide (CsOH), or mixtures thereof. In some embodiments, the electrolyte comprises an alkali metal sulfide or polysulfide, including lithium sulfide (Li₂S) or lithium polysulfide (Li₂S₃). x (x=2 to 6), sodium sulfide (Na2S) or sodium polysulfide (Na2S) x (x=2 to 6), potassium sulfide (K2S) or potassium polysulfide (K2S) x (x=2 to 6), cesium sulfide (Cs₂S) or cesium polysulfide (Cs₂S) xThe first electrode comprises (x=2 to 6), or mixtures thereof. In some embodiments, the second electrode is pelletized and includes a multi-peak distribution. In some embodiments, the manganese oxide comprises manganese(IV) oxide (MnO2), manganese(III) oxide (Mn2O3), manganese(III) hydroxide oxide (MnOOH), manganese(II) oxide (MnO), manganese(II) hydroxide (Mn(OH)2), or mixtures thereof. In some embodiments, the second electrode also comprises iron oxides, hydroxides, sulfides, or mixtures thereof. In some embodiments, the second electrode further comprises one or more second phases, comprising silicon dioxide (SiO2) or silicates, calcium oxide (CaO), magnesium oxide (MgO), or mixtures thereof. In some embodiments, the second electrode further comprises an inert conductive matrix comprising carbon black, activated carbon, graphite powder, carbon steel mesh, stainless steel mesh, steel wool, nickel-plated carbon steel mesh, nickel-plated stainless steel mesh, nickel-plated steel wool, or mixtures thereof. In some embodiments, the second electrode also comprises one or more hydrogen evolution reaction inhibitors. In some embodiments, the first electrode has a diameter of less than about 50 μm. 2 The specific surface area is approximately 1 m² / g. In some embodiments, the first electrode has a specific surface area of ​​less than approximately 1 m² / g. 2 The specific surface area is approximately 5 m² / g. In some embodiments, the second electrode has a specific surface area of ​​less than approximately 5 m² / g. 2 The specific surface area is approximately 1 m² / g. In some embodiments, the second electrode has a specific surface area of ​​less than approximately 1 m² / g. 2The specific surface area is / g. In some embodiments, the first electrode includes a binder comprising polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polypropylene (PP), polyethylene (PE), fluorinated ethylene propylene (FEP), polyacrylonitrile, styrene-butadiene rubber, carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (Na-CMC), polyvinyl alcohol (PVA), polypyrrole (PPy), or combinations thereof. In some embodiments, the first electrode includes an additive comprising bismuth(III) oxide (Bi₂O₃), bismuth(III) sulfide (Bi₂S₃), barium oxide (BaO), barium sulfate (BaSO₄), barium hydroxide (Ba(OH)₂), calcium oxide (CaO), calcium sulfate (CaSO₄), calcium hydroxide (Ca(OH)₂), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)₂), carbon nanotubes, carbon nanofibers, graphene, nitrogen-doped carbon nanotubes, nitrogen-doped carbon nanofibers, nitrogen-doped graphene, or combinations thereof. In some embodiments, a spacer material is used between the first electrode and the second electrode. In some embodiments, the iron comprises iron concentrate. In some embodiments, the iron comprises at least one form of iron selected from the group consisting of pellets, BF-grade pellets, DR-grade pellets, hematite, magnetite, chalcedony, pseudomorphous hematite, goethite, limonite, siderite, pyrite, ilmenite, or spinel manganese ferrite. In some embodiments, the iron comprises iron ore. In some embodiments, the iron ore contains at least 0.1% SiO2 by mass. In some embodiments, the iron ore contains at least 0.1% CaO by mass. In some embodiments, the iron comprises atomized iron powder. In some embodiments, the iron comprises iron agglomerates. In some embodiments, the average length of the iron agglomerates ranges from about 50 μm to about 50 mm. In some embodiments, the average internal porosity of the iron agglomerates ranges from about 10% to about 90% by volume. In some embodiments, the average specific surface area of ​​the iron agglomerates ranges from about 0.1 m². 2 / g to approximately 25m 2 / g. In some embodiments, the electrolyte comprises molybdate anions and divalent sulfur anions. In various embodiments, the battery pack of each embodiment may be included in a stack of one or more battery packs of a high-capacity energy storage system. In various embodiments, the high-capacity energy storage system is a long-duration energy storage (LODES) system. Various embodiments may include a method of manufacturing the battery pack, including: providing a first electrode comprising manganese oxide; providing an electrolyte; and providing a second electrode comprising iron. Attached Figure Description

[0006] Figure 1A This is a schematic diagram of an electrochemical cell with a square structure according to various embodiments of the present disclosure.

[0007] Figure 1B Based on Figure 1A A schematic diagram of the stacked structure of a publicly disclosed electrochemical cell.

[0008] Figure 1C This is a schematic diagram of a stacked structure using bipolar current collectors connected to electrochemical repeating units.

[0009] Figure 2A and 2B This is a schematic diagram of a hydrogen recombination electrode.

[0010] Figure 2C , 2D 2E and 2F are schematic diagrams of various arrangements of hydrogen recombination electrodes in the battery.

[0011] Figure 3A This is a schematic diagram of a proof-of-concept battery using approximately 1.3g of iron powder as the negative electrode and approximately 0.8g of a positive electrode containing approximately 78% by weight of MnO2.

[0012] Figure 3B Is using Figure 3A The proof-of-concept battery setup uses a graph of selected cycle data (battery voltage relative to time) and a capacity curve (battery voltage relative to capacity).

[0013] Figure 3C The discharge capacity of MnO2 on the left Y-axis in different cycles (mAh / g) MnO2 The graph shows the coulomb efficiency on the right Y-axis.

[0014] Figure 3D Is using Figure 3A The proof-of-concept battery setup uses a graph of lifetime start (BOL) polarization data (current density relative to positive electrode potential).

[0015] Figure 3E This is the second cycle charge-discharge curve (full cell voltage relative capacity) for the proof-of-concept EMD / DRI battery.

[0016] Figure 4A This is a schematic diagram of stacked square electrochemical cells, based on... Figure 1B The stacked structure uses pelletized direct reduced iron (DRI) as the negative electrode and manganese compound-based positive electrode.

[0017] Figure 4B This is a schematic diagram of an electrochemical cell with a cylindrical structure according to various embodiments of the present disclosure, which uses pelletized direct reduced iron (DRI) as the negative electrode and a manganese compound-based positive electrode.

[0018] Figure 5The negative electrode is shown according to the various implementation schemes.

[0019] Figure 6A An exemplary discharge method is shown.

[0020] Figure 6B and 6C The various aspects of the electrodes, divided into horizontal layers contained within a larger container, are shown.

[0021] Figure 6D A metal fabric with electrodes containing directly reduced iron pellets is shown.

[0022] Figure 6E and 6F Various aspects of an exemplary porous mesh container are shown.

[0023] Figure 7 An example back panel is shown.

[0024] Figure 8 The fastening guide is shown, which can also be used as a bus bar.

[0025] Figure 9 The direct reduced iron (DRI) ball bed assembly is shown.

[0026] Figure 10 The module is shown, consisting of rigid sidewalls.

[0027] Figure 11A and Figure 11B Fastening techniques according to various implementation schemes are shown.

[0028] Figure 12 The expanded material contained within the rigid iron electrode container assembly is shown.

[0029] Figure 13 Thermal bonding is shown.

[0030] Figure 14 The mechanical interactions of the pellets are shown.

[0031] Figure 15 The pellet bed is shown.

[0032] Figure 16 An exemplary current collector is shown.

[0033] Figure 17 The image shows machined pellets.

[0034] Figure 18 The distribution of discharge products is shown.

[0035] Figure 19 It's a temperature graph.

[0036] Figure 20 An exemplary method for creating a vacuum hole is shown.

[0037] Figure 21 An exemplary additive retainer construction is shown.

[0038] Figure 22 An exemplary additive incorporation process is shown.

[0039] Figure 23 The electrode formation process is shown.

[0040] Figures 24-32 Several exemplary systems are shown, wherein one or more aspects of various implementations can be used as part of a large-capacity energy storage system. Detailed Implementation

[0041] The following embodiments are provided to illustrate various embodiments of the systems and methods of the present invention. These embodiments are for illustrative purposes, may be predictive, and should not be considered limiting, nor do they otherwise limit the scope of the invention.

[0042] Various embodiments will be described in detail with reference to the accompanying drawings. Where possible, the same reference numerals are used throughout the drawings to refer to the same or similar elements. References to specific examples and embodiments are for illustrative purposes and are not intended to limit the scope of the claims. The following description of embodiments of the invention is not intended to limit the invention to these embodiments, but rather to enable those skilled in the art to make and use the invention. Unless otherwise stated, the drawings are not drawn to scale.

[0043] In this document, unless otherwise stated, the ambient temperature is 25°C. Furthermore, the standard temperature and pressure are 25°C and 1 atmosphere. Unless otherwise explicitly stated, all tests, test results, physical properties, and values ​​related to temperature, pressure, or both are provided at standard ambient temperature and pressure.

[0044] Generally, unless otherwise stated, the term “about” and the symbol “~” used herein are intended to cover a variance or range of ±10%, the experimental or instrumental error associated with the obtained labeled value, and preferably the larger of the latter.

[0045] In this document, unless otherwise stated, descriptions of numerical ranges are intended only as a convenient way to refer to each individual value falling within that range. Unless otherwise stated, each individual value within a range is incorporated into the specification as if it were cited separately herein.

[0046] In this document, unless otherwise stated, the terms %, weight %, and mass % are used interchangeably and refer to the percentage of the weight of the first component to the total weight, such as the total weight of a formulation, mixture, granules, pellets, agglomerates, material, structure, or product. In this document, unless otherwise stated, “volume %” and “%volume” and similar terms refer to the percentage of the volume of the first component to the total volume, such as the total volume of a formulation, mixture, granules, pellets, agglomerates, material, structure, or product.

[0047] The following examples are provided to illustrate various embodiments of the systems and methods of the present invention. These embodiments are for illustrative purposes, may be predictive and should not be considered limiting, and do not otherwise limit the scope of the invention.

[0048] It should be noted that it is not necessary to provide or resolve the theoretical basis for novel and inventive processes, materials, properties, or other beneficial features and characteristics that are the subject matter of or associated with embodiments of the invention. However, various theories are provided in this specification to further advance the art in this field. The theories presented in this specification, unless expressly stated otherwise, do not limit, restrict, or narrow the scope of protection provided by the claimed invention. Many of these theories are not necessary for or practiced in using the invention. It should also be understood that the invention may lead to new and previously unknown theories to explain the functional features of embodiments of the methods, articles, materials, apparatus, and systems of the invention; these subsequently developed theories should not limit the scope of protection provided by the invention.

[0049] The various embodiments of the systems, apparatus, techniques, methods, activities, and operations described in this specification can be used in a variety of other activities and in fields other than those described herein. Furthermore, for example, these embodiments can be used with other apparatus or activities that may be developed in the future; and with existing apparatus or activities that can be modified in part according to the teachings of this specification. Moreover, the various embodiments and examples described in this specification can be used in whole or in part with each other, and can be used in different and various combinations. Therefore, the configurations provided in the various embodiments of this specification can be used with each other. For example, according to the teachings of this specification, components of embodiments having A, A', and B and components of embodiments having A”, C, and D can be used with each other in various combinations, such as A, C, D and A, A”C, and D, etc. Therefore, the scope of protection provided by this invention should not be limited to the specific embodiments, configurations, or arrangements described in the embodiments of specific embodiments, examples, or specific drawings.

[0050] In this document, unless otherwise stated, the term specific gravity, also known as apparent density, should be given its broadest possible meaning and generally refers to the weight per unit up to the structural volume (e.g., the volumetric shape of a material). This property will include the internal porosity of the particles as part of their volume. It can be measured using low-viscosity fluids that wet the particle surface, as well as other techniques.

[0051] In this document, unless otherwise stated, the term actual density, also known as true density, should be given its broadest possible meaning and generally refers to the weight of a unit volume of material when there are no voids in the material. This measurement and property essentially subtracts any internal pores in the material; for example, it does not include any voids in the material.

[0052] Therefore, a batch of porous foam balls (e.g., Nerf® balls) can be used to illustrate the relationship between the three density properties. The weight of the balls filling the container will be the bulk density of the balls: The weight of a single sphere divided by its spherical volume will be its apparent density. The weight of the material that makes up the skeleton of a sphere (i.e., the sphere after removing all void volume) divided by the remaining volume of that material will be the skeleton density: In this document, unless otherwise stated, the terms agglomerate and aggregate shall be given their broadest possible meaning and generally refer to an aggregate of particles in a powder.

[0053] Electrochemical cells, such as battery packs, store electrochemical energy by using an electrochemical potential difference that creates a voltage difference between the positive and negative electrodes. This voltage difference generates a current if the electrodes are connected via conductive elements. In a battery pack, the negative and positive electrodes are connected in series via external and internal resistive elements. Typically, the external element conducts electrons, and the internal element (electrolyte) conducts ions. Because a charge imbalance cannot be maintained between the negative and positive electrodes, these two flows must provide ions and electrons at the same rate. In operation, the electron flow can be used to drive external devices. Rechargeable battery packs can be recharged by applying an opposite voltage difference, which drives the electron and ion flows in the opposite direction to the discharge flow during use.

[0054] Embodiments of the present invention include devices, systems, and methods for long-duration and ultra-long-duration, low-cost energy storage. In this document, "long-duration" and / or "ultra-long-duration" refers to an energy storage cycle of 8 hours or longer, such as an 8-hour energy storage cycle, an 8-hour to 20-hour energy storage cycle, a 20-hour energy storage cycle, a 20-hour to 24-hour energy storage cycle, a 24-hour energy storage cycle, a 24-hour to one-week energy storage cycle, a one-week to one-year energy storage cycle (e.g., days to weeks to months), etc. In other words, a "long-duration" and / or "ultra-long-duration" energy storage battery can refer to an electrochemical battery configured to store energy over time spans of days, weeks, or quarters. For example, an electrochemical battery can be configured to store energy generated by solar cells during the summer months when sunlight is abundant and solar power generation exceeds grid requirements, and release the stored energy during the winter months when sunlight may be insufficient to meet grid requirements.

[0055] Typically, in one implementation, a long-duration energy storage battery can be a long-duration electrochemical battery. Such a long-duration electrochemical battery typically stores electricity generated by a power generation system when: (i) the energy or fuel of the power generation system is available, abundant, inexpensive, and combinations thereof; (ii) the energy or electricity demand of the grid, customers, or other users is less than the amount of electricity generated by the power generation system, the price paid to provide such energy to the grid, customers, or other users is less than the economic efficiency point of generating such energy (e.g., the cost of generating electricity exceeds the market price of electricity), and combinations thereof; and (iii): combinations and variations of (i) and (ii), and other reasons. The electricity stored in the long-duration electrochemical battery can then be distributed to the grid, customers, or other users when needed for economic or other reasons. For example, the electrochemical battery can be configured to store energy generated by solar cells during the summer months when sunlight is abundant and solar power generation exceeds grid demand, and to release the stored energy during the winter months when sunlight may be insufficient to meet grid demand.

[0056] According to other embodiments, the invention includes devices, systems, and methods for storing energy for shorter durations of less than about 8 hours. For example, an electrochemical cell can be configured to store energy generated by solar cells during daytime cycles when solar power generation may exceed grid requirements at midday, and release the stored energy at night when sunlight may be insufficient to meet grid demands. As another example, the invention may include energy storage for use as a backup power source when grid power supply is insufficient, for facilities including homes, commercial buildings, factories, hospitals, or data centers, where the required discharge duration may range from minutes to days.

[0057] According to various embodiments, the electrochemical cell includes a negative electrode, a positive electrode, and an electrolyte. The negative electrode may be made of iron. The positive electrode may be made of manganese oxide. The electrolyte may be an aqueous solution. In some embodiments, the electrolyte may be an alkaline solution (pH>10). In some embodiments, the electrolyte may be a near-neutral solution (10>pH>4).

[0058] According to the various implementation schemes, the half-cell reaction that occurs at the negative electrode during discharge is: In one example, the half-cell reaction that occurs at the negative electrode during discharge is Based on the negative electrode reaction in this example, the theoretical capacity based on metallic iron is 1276 mAh / gFe. During charging, a reverse reaction occurs.

[0059] According to the various implementation schemes, the possible half-cell reactions occurring at the positive electrode during discharge are: In one example, the half-cell reaction that occurs at the positive electrode during discharge is Based on the negative electrode reaction in this example, the theoretical capacity based on MnO2 is 616 mAh / g. MnO2 During the charging process, a reverse reaction occurs.

[0060] According to the various implementation schemes, hydroxide anion (OH-) - The hydroxide ion is the working ion. In some embodiments, both the hydroxide anion and the alkali metal cation are working ions. In other words, the hydroxide anion and the alkali metal cation migrate simultaneously in opposite directions and carry ion currents.

[0061] In some implementations, if the main negative electrode reaction is in Fe 0 In some embodiments, if the main negative electrode reaction occurs between Fe(II) and Fe(III) (mechanism F1) and the main positive electrode reaction occurs between Mn(IV) and Mn(III) (mechanism M1), the nominal battery voltage is approximately 1.2V. In some embodiments, if the main negative electrode reaction occurs between Fe(II) and Fe(III) (mechanism F2) and the main positive electrode reaction occurs between Mn(IV) and Mn(III) (mechanism M1), the nominal battery voltage is approximately 1.0V. In some embodiments, if the main negative electrode reaction occurs between Fe(II) and Fe(III) (mechanism F2) and the main positive electrode reaction occurs between Mn(IV) and Mn(III) (mechanism M1), the nominal battery voltage is approximately 1.0V. 0The nominal battery voltage is approximately 0.8V if the main negative electrode reaction occurs between Fe(II) and Fe(III) (mechanism F1) and the main positive electrode reaction occurs between Mn(III) and Mn(II) (mechanism M2). In some embodiments, the nominal battery voltage is approximately 0.6V if the main negative electrode reaction occurs between Fe(II) and Fe(III) (mechanism F2) and the main positive electrode reaction occurs between Mn(III) and Mn(II) (mechanism M2). In some embodiments, the nominal battery voltage is approximately 1.0V, or other values ​​from 1.2V to 0.6V, when mechanisms F1 and F2 occur simultaneously or sequentially at the negative electrode and mechanisms M1 and M2 occur simultaneously or sequentially at the positive electrode. Residual battery resistance can further reduce the discharged battery voltage under load.

[0062] According to various embodiments, the primary side reaction on the negative electrode during charging is the hydrogen evolution reaction (HER). According to various embodiments, the primary side reaction on the positive electrode during charging is the oxygen evolution reaction (OER) or carbon oxidation (corrosion) reaction. A key advantage of Fe-MnO2 batteries is these "self-balancing" side reactions, which can significantly mitigate thermal runaway problems if the negative electrode and / or positive electrode are damaged during charging or overcharging. In some embodiments, the positive reaction during charging is Mn(II) to Mn(III) and / or Mn(III) to Mn(IV), and the negative reaction during charging is HER if the iron-based negative electrode material cannot be charged properly. In some embodiments, the negative reaction during charging is Fe(III) to Fe(II) and / or Fe(II) to Fe 0 If the manganese-based cathode material cannot be charged normally, the positive reaction during charging is OER. In some implementations, if both the manganese-based cathode and the iron-based anode cannot be charged normally, the positive reaction during charging is OER, while the negative reaction during charging is HER.

[0063] In some implementations, the electrochemical cell includes a negative electrode, a positive electrode, an electrolyte, and a separator disposed between the positive and negative electrodes (e.g., ...). Figure 1A (As shown). Figure 1A An electrochemical cell 100 is shown, comprising a negative electrode and an electrolyte 102, which is separated from a positive electrode and an electrolyte 103 by a separator 104. The separator 104 may be supported by a polypropylene mesh 105 and a polyethylene frame 108 of the cell 100. A current collector 107 may be associated with the corresponding electrodes and electrolytes in the negative electrode and electrolyte 102 and the positive electrode and electrolyte 103 and is supported by a polyethylene backplate 106.

[0064] In some implementation schemes, Figure 1A Multiple electrochemical cells 100 can be connected in series to form a stack 120, for example Figure 1BAs shown in the diagram. For example, batteries 100 can be connected in series via metal bolts 122 passing through current collector 107 and a polyethylene backplate 106 secured by metal nuts 123, to connect one battery 100 to the next. In some other embodiments, multiple electrochemical batteries 100 can be connected in parallel. In some other embodiments, the electrochemical batteries 100 are connected in a mixed series-parallel configuration to achieve a favorable combination of delivered current and voltage.

[0065] In some embodiments, adjacent electrochemical cells 100 are physically and electrically connected using a set of metal bolts, nuts, and washers (e.g., bolts 122 and nuts 123) as described above. In some embodiments, the metal bolts, nuts, and washers are stainless steel, carbon steel, aluminum, copper, or combinations thereof. In some embodiments, adjacent electrochemical cells 100 are physically and electrically connected using metal protrusions. In some embodiments, the metal protrusions are connected by welding, brazing, or other common metal joining techniques. In some embodiments, adjacent electrochemical cells in the stack 130, such as cell 131, are electrically connected using bipolar current collectors 132, such as... Figure 1C As shown. Battery 131 can be similar to battery 100, except that current collector 132 can be a bipolar current collector and there may be no polyethylene backsheet 106 between the individual cells. In some embodiments, adjacent electrochemical cells 100 in the stack 120 are electrically connected using a unipolar current collector 107, for example as... Figure 1B As shown.

[0066] In various implementation schemes, the battery structure is square, for example, Figure 1A As shown. In some embodiments, the battery is sealed. In some embodiments, the sealed battery includes an vent for gas exchange. In a non-limiting example, the gas may be hydrogen evolved at the negative electrode at the hydrogen evolution reaction potential. In some embodiments, the battery is covered by a removable cover.

[0067] In various implementation schemes, the battery structure is cylindrical, for example, as shown below. Figure 1B As shown. In some embodiments, the battery is sealed. In some embodiments, the sealed battery includes an vent for gas exchange. In a non-limiting example, the gas may be hydrogen evolved at the negative electrode at the hydrogen evolution reaction potential. In some embodiments, the battery is covered by a removable cover.

[0068] In some implementations, the hydrogen recombination electrode is placed near the negative electrode (e.g., as shown in the image). Figures 2A-2F (as shown in the image).

[0069] According to various embodiments, the negative electrode comprises pelletized, briquetted, pressed, or sintered iron-containing compounds. Such iron-containing compounds may comprise one or more forms of iron, ranging from highly reduced (more metallized) iron to highly oxidized (more ionized) iron. In various embodiments, the pellets may comprise various iron compounds, such as iron oxides, hydroxides, sulfides, or combinations thereof. In various embodiments, the pellets may comprise one or more second phases, such as silica (SiO2) or silicates, calcium oxide (CaO), magnesium oxide (MgO), etc. In various embodiments, the negative electrode may be a sintered iron agglomerate having various shapes. In some embodiments, atomized iron powder or sponge iron powder may be used as a raw material to form the sintered iron electrode. In some embodiments, the green body may further comprise a binder, such as a polymer or an inorganic clay-like material. In various embodiments, the sintered iron agglomerate pellets may be formed in a furnace, such as a continuous feed calciner, a batch feed calciner, a shaft furnace, a rotary calciner, a rotary hearth, etc. In various embodiments, the pellets may comprise iron-containing precursors known to those skilled in the art as reduced and / or sintered direct reduced iron (DRI), and / or their byproduct materials. Various embodiments may include treating the pellets, including DRI pellets, using electrochemical, electrochemical, mechanical, chemical, and / or thermal processes prior to introducing them into an electrochemical cell.

[0070] Various embodiments of using direct reduced iron (DRI) as a material for battery packs (or cells), as a component of battery packs (or cells), and combinations and variations thereof are discussed. In various embodiments, DRI can be produced from materials obtained by reducing natural or processed iron ore, or from materials obtained by reducing natural or processed iron ore without reaching the melting temperature of iron. In various embodiments, the iron ore can be flint, magnetite, hematite, goethite, etc. In various embodiments, DRI can be in pellet form, which can be spherical or substantially spherical. In various embodiments, DRI can be porous, containing open and / or closed internal pores. In various embodiments, DRI can contain materials that have been further processed by hot or cold pressing. In various embodiments, DRI can be produced by reducing iron ore pellets to form materials with stronger metallic properties (stronger reducing power, lower oxidation level), such as iron metal (Fe). 0Iron ore (FeO) or pellets comprising iron metal and residual oxide phases. In various non-limiting embodiments, DRI can be reduced iron ore flint, direct reduced (“DR”) flint, reduced “blast furnace (BF) grade” pellets, reduced “electric arc furnace (EAF) grade” pellets, “cold direct reduced iron (CDRI)” pellets, direct reduced iron (“DRI”) pellets, hot-pressed iron (HBI) pellets, or any combination thereof. In the iron and steel industry, DRI is sometimes referred to as “sponge iron”; this usage is particularly common in India. Embodiments of iron materials, including, for example, embodiments of DRI materials, used in the various embodiments described herein, including as electrode materials, may have one, more than one, or all of the material properties described in Table 1 below. In this specification, including Table 1, unless otherwise expressly stated, the following terms have the following meanings: "Specific surface area" refers to the total surface area per unit mass of material, including the surface area of ​​pores in porous structures; "Carbon content" or "Carbon (wt%)" refers to the percentage of total carbon mass to the total mass of the DRI; "Cementite content" or "Cementite (wt%)" refers to the percentage of Fe3C mass to the total mass of the DRI; "Total Fe (wt%)" refers to the percentage of total iron mass to the total mass of the DRI; "Metallic Fe (wt%)" refers to Fe... 0 The percentage of iron in a specific state relative to the total mass of the DRI; "metallization" refers to Fe 0 The percentage of iron in a certain state relative to the total iron mass.

[0071] Table 1 The determination is preferably performed by the Brunauer-Emmett-Teller adsorption method (“BET”), more preferably by the BET method described in ISO 9277 (the entire disclosure of which is incorporated herein by reference); it is recognized that other tests (e.g., methylene blue (MB) staining, ethylene glycol monoethyl ether (EGME) adsorption, electrokinetic analysis of complex ion adsorption, and protein retention (PR) methods) can be used to provide results related to BET results.

[0072] 90% of the pore volume is in the diameter greater than d. 孔,90%体积 In the hole.

[0073] 50% of the free surface area is in areas with a diameter greater than d. 孔,50%表面积 In the hole.

[0074] Additionally, iron materials, including embodiments such as DRI materials, used in embodiments including the various embodiments described herein as electrode materials, may have one or more of the following properties, features, or characteristics as described in Table 1A (note that values ​​in a row or column may appear together with values ​​in different rows or columns).

[0075] Table 1A Preferably, it is determined by ISO 4700:20073, the entire contents of which are incorporated herein by reference.

[0076] Preferably, it is determined by ISO 4700:2007, the entire contents of which are incorporated herein by reference.

[0077] The characteristics described in Table 1 may also exist in embodiments having the characteristics in Table 1A, as a supplement to or replacement of the characteristics in Table 1A. Larger and smaller values ​​of these characteristics may also exist in various embodiments.

[0078] In the implementation plan, the specific surface area of ​​the pellets can be approximately 0.05 m². 2 / g to approximately 35 m 2 / g, approximately 0.1 m 2 / g to approximately 5m 2 / g, approximately 0.5 m 2 / g to approximately 10 m 2 / g, approximately 0.2 m 2 / g to approximately 5 m 2 / g, approximately 1 m 2 / g to approximately 5 m 2 / g, approximately 1 m 2 / g to approximately 20 m 2 / g, greater than approximately 1 m 2 / g, greater than approximately 2 m 2 / g, less than about 5 m 2 / g, less than approximately 15 m 2 / g, less than approximately 20 m 2 / g, as well as their combinations and variations, and larger and smaller values.

[0079] Typically, iron ore pellets are formed by crushing, grinding, or milling iron ore into a fine powder form, followed by concentration by removing impurity phases (so-called "gangue") released during the grinding process. Generally, the purity of the resulting iron concentrate increases as the ore is ground into finer (smaller) particle sizes. The iron concentrate is then formed into pellets using a pelletizing or granulation process (using, for example, a drum pelletizer or disc pelletizer). Generally, a larger energy input is required to produce higher purity ore pellets. Iron ore pellets are typically marketed or sold under two main categories: blast furnace (BF) grade pellets and direct reduction (DR) grade (sometimes also called electric arc furnace (EAF) grade), the main difference being that BF grade pellets have a higher SiO2 and other impurity phase content compared to DR grade pellets. Typical key specifications for DR grade pellets or feedstock are a total Fe content in the range of 63-69 wt%, e.g., 67 wt%, and an SiO2 content of less than 3 wt%, e.g., 1 wt%. Typical key specifications for BF grade pellets or raw materials are a total Fe content of 60-67% by weight, for example 63% by weight, and a SiO2 content of 2-8% by weight, for example 4% by weight.

[0080] In some implementations, DRI can be produced by reducing "blast furnace" pellets, in which case the resulting DRI can have the material properties described in Table 2 below. Since the input energy required to produce these pellets is relatively low, the cost of converting them into finished materials is also low; therefore, using reduced BF-grade DRI may be advantageous.

[0081] Table 2 The determination is preferably performed by the Brunauer-Emmett-Teller adsorption method (“BET”), more preferably by the BET method described in ISO 9277 (the entire disclosure of which is incorporated herein by reference); it is recognized that other tests (e.g., methylene blue (MB) staining, ethylene glycol monoethyl ether (EGME) adsorption, electrokinetic analysis of complex ion adsorption, and protein retention (PR) methods) can be used to provide results related to BET results.

[0082] 90% of the pore volume is in the diameter greater than d. 孔,90%体积 In the hole.

[0083] 50% of the free surface area is in areas with a diameter greater than d. 孔,50%表面积 In the hole.

[0084] The characteristics described in Table 2 may also exist in embodiments having the characteristics in Table 1 and / or Table 1A, as a supplement to or replacement of the characteristics in Table 1 and / or Table 1A. Larger and smaller values ​​for these characteristics may also exist in various embodiments.

[0085] In some implementations, DRI can be produced by reducing DR-grade pellets, in which case the resulting DRI can have the material properties described in Table 3 below. Due to the higher Fe content in the pellets, which increases the energy density of the battery pack, the use of reduced DR-grade DRI may be beneficial.

[0086] Table 3 The determination is preferably performed by the Brunauer-Emmett-Teller adsorption method (“BET”), more preferably by the BET method described in ISO 9277 (the entire disclosure of which is incorporated herein by reference); it is recognized that other tests (e.g., methylene blue (MB) staining, ethylene glycol monoethyl ether (EGME) adsorption, electrokinetic analysis of complex ion adsorption, and protein retention (PR) methods) can be used to provide results related to BET results.

[0087] 90% of the pore volume is in the diameter greater than d. 孔,90%体积 In the hole.

[0088] 50% of the free surface area is in areas with a diameter greater than d. 孔,50%表面积 In the hole.

[0089] The characteristics described in Table 3 may also be present in embodiments having the characteristics in Tables 1, 1A, and / or 2, as a supplement to or replacement of the characteristics in Tables 1, 1A, and / or 2. Larger and smaller values ​​of these characteristics may also be present in various embodiments.

[0090] In various embodiments, the bed of conductive pellets includes (e.g., for providing, being a component of, constituting, etc.) electrodes in an energy storage system. In embodiments of this electrode, the pellets comprise iron-containing materials, reduced iron materials, unoxidized iron, highly oxidized iron, iron with valence states from 0 to 3+, and combinations and variations thereof. In embodiments of this electrode, the iron contained in the pellets has one or more of the characteristics listed in Tables 1, 1A, 2, and 3. In embodiments, the pellets have porosity, such as an open-pore structure, which can have pore sizes ranging from, for example, from a few nanometers to a few micrometers. For example, embodiments may have pore sizes from about 5 nm to about 100 nm.µ m (micrometer), approximately 50 nm to approximately 10 µ m, approximately 100 nm to approximately 1 µ m, greater than 100nm, greater than 500nm, less than 1 µ m, less than 10 µ The pore sizes are m, less than 100µm, and combinations and variations of these pore sizes, as well as larger and smaller pores. In some embodiments, the pellets comprise pellets of direct reduced iron (DRI). Embodiments of these electrodes in energy storage systems, particularly embodiments of these electrodes in long-duration energy storage systems, may have one or more of these foregoing characteristics.

[0091] The filling of the pellets creates macropores, such as openings, spaces, channels, or voids, between the individual pellets. These macropores facilitate ion transport through the electrode, which in some embodiments has a minimal size compared to some other types of battery pack electrodes, yet is still very thick, measuring several centimeters. The micropores within the pellets allow the high surface area active material of the pellets to contact the electrolyte, thereby achieving high utilization of the active material. This electrode structure makes it particularly suitable for improving the rate performance of extremely thick electrodes for long-duration static energy storage, where thick electrodes may be required to achieve extremely high areal capacity.

[0092] The pellets used in these embodiments, particularly those for electrodes in long-duration energy storage systems, can be of any volumetric shape, such as spheres, disks, pucks, beads, sheets, pellets, rings, lenses, discs, panels, cones, truncated cones, square blocks, rectangular blocks, trusses, corners, channels, hollow sealed chambers, hollow spheres, blocks, sheets, membranes, granules, beams, rods, plates, columns, fibers, short fibers, tubes, cups, pipes, combinations and multiples of these, and other more complex shapes. The pellets in the electrodes can be the same shape or different shapes. The pellets in an electrode that is one of multiple electrodes in a long-duration energy storage system can be the same as or different from the pellets in other electrodes in the same energy storage system.

[0093] Unless otherwise explicitly stated, the size of the pellets refers to the maximum cross-sectional distance of the pellets, such as the diameter of a sphere. Pellet sizes can be the same or different. Understanding the shape and size of the pellets, and typically to a lesser extent, the shape and size of the container or shell holding the pellets, determines the nature and size of the macropores in the electrode. Pellet sizes can range from about 0.1 mm to about 10 cm, about 5 mm to about 100 mm, 10 mm to about 50 mm, about 20 mm, about 25 mm, about 30 mm, greater than 0.1 mm, greater than 1 mm, greater than 5 mm, greater than 10 mm, and greater than 25 mm, as well as combinations and variations thereof.

[0094] In the implementation scheme, the pellets disposed in the electrode can give the electrode a bulk density of approximately 3 g / cm³. 3 Approximately 6.5 g / cm³ 3 Approximately 0.1 g / cm³ 3 Approximately 5.5 g / cm³ 3 Approximately 2.3 g / cm³ 3 Approximately 3.5 g / cm³ 3 3.2g / cm 3 Approximately 4.9 g / cm³ 3 Greater than approximately 0.5 g / cm³ 3 Greater than approximately 1 g / cm³ 3 Greater than approximately 2g / cm 3 Greater than approximately 3g / cm 3 , as well as their combinations and variations, and larger and smaller values.

[0095] In some embodiments, a mixture of reduced DR grade and reduced BF grade pellets can be used together. In some other embodiments, reduced material (DRI) and raw ore material (DR grade or BF grade) can be used in combination.

[0096] In various embodiments, DRI can be produced using waste or byproducts of “man-made ores” such as iron oxides. As a non-limiting example, mill scale, a mixture of iron oxides formed on the surface of hot-rolled steel, is collected and ground in various embodiments to form iron oxide powder, which is then agglomerated to form pellets and subsequently reduced to form DRI. Other waste streams can be similarly used to form DRI. As another non-limiting example, pickling solution is an acidic solution that may be rich in dissolved Fe ions. In various embodiments, the iron-containing pickling solution can be neutralized with an alkali (e.g., caustic soda or sodium hydroxide) to precipitate the iron oxide powder, which is then agglomerated to form pellets and subsequently reduced to form DRI.

[0097] In various embodiments, the precursor iron oxide is first reduced and then subsequently formed into pellets or other agglomerates. In some non-limiting embodiments, iron oxide powder from natural or synthetic ores is reduced to iron metal powder by heat treatment (ranging from 700°C to 1400°C, 900°C to 1300°C, 900°C, 1000°C, and / or 1100°C) in a reducing gas environment (e.g., a linear hearth furnace with a hydrogen atmosphere ranging from 1% to 100% H2). In embodiments using hydrogen as the reducing gas, the cementite (Fe3C) content of the DRI can be as low as 0% by weight.

[0098] In various embodiments, the precursor iron oxide is reduced under conditions that promote swelling or non-densification reduction. In some non-limiting embodiments, iron oxide powder from natural or synthetic ores is reduced to iron metal powder by heat treatment (ranging from 700°C to 1400°C, from 900°C to 1300°C, 900°C, 1000°C, and / or 1100°C) in a reducing gas environment (e.g., a linear hearth furnace with a gas atmosphere such as a carbon monoxide mixture), promoting increased porosity through swelling. In some embodiments, the precursor iron oxide may be selected with preferred pelletizing chemistry that promotes swelling, or additives such as limestone may be used.

[0099] In various embodiments, DRI pellets or agglomerates are formed from iron oxide powder in a single process using a rotary kiln. The rotational motion of the kiln promotes the agglomeration of the powder into pellets or agglomerates, while the high-temperature reducing gas environment provides simultaneous reduction of the iron oxide. In various other embodiments, multi-stage rotary kilns can be used, where the agglomeration and reduction steps can be independently tuned and optimized.

[0100] In various embodiments, the DRI has a non-spherical shape. In some embodiments, the DRI may have a substantially linear or brick-like shape. In some embodiments, the DRI may have a substantially cylindrical, rod-like, or disc-like shape. In some embodiments, the DRI may have a substantially planar or sheet-like shape. In some embodiments, the iron oxide powder is dry-molded into a cylindrical shape or any other shape suitable for compression molding. In some embodiments, the iron oxide powder is dry-molded into a sheet form by roll pressing on calender rolls or a mill. In some embodiments, the iron oxide powder is mixed with a binder such as clay or a polymer and dry-processed into a rod-like shape by extrusion. In some embodiments, the iron oxide powder is mixed with a binder such as clay or a polymer and dry-processed into a sheet form by roll pressing on calender rolls. The binder may include clay such as bentonite, or polymers such as corn starch, polyacrylamide, or polyacrylates. The binder may include a combination of one or more clays and one or more polymers. In some embodiments, the iron oxide powder is dispersed in a liquid to form a slurry, which is then used for wet molding into various shapes. In some embodiments, the iron oxide slurry is poured into a mold of nearly any shape. In some embodiments, the iron oxide slurry is applied to a sheet using a doctor blade or other similar coating process.

[0101] In various embodiments, the bed of conductive microporous pellets comprises electrodes in an energy storage system. In some embodiments, the pellets comprise pellets of direct reduced iron (DRI). The filling of the pellets creates macropores between the individual pellets. These macropores facilitate ion transport through the electrodes, which in some embodiments have a minimal size compared to some other types of battery pack electrodes, yet are still very thick, measuring several centimeters. Compared to the micropores within the pellets, the macropores can create pore spaces with low curvature. The micropores within the pellets allow the high surface area active material of the pellets to contact the electrolyte, thereby achieving high utilization of the active material. This electrode structure makes it particularly suitable for improving the rate performance of extremely thick electrodes for static, long-duration energy storage, where thick electrodes may be required to achieve extremely high areal capacity.

[0102] In various embodiments, short-acting pore-forming agents are incorporated during the production of DRI to increase the porosity of the resulting DRI. In one embodiment, the porosity of the DRI pellets is altered by incorporating a sacrificial pore-forming agent, such as ice (solid H2O), during the pelletizing process, which is subsequently melted or sublimated under heat treatment. In some other embodiments, the short-acting pore-forming agent comprises naphthalene, which subsequently sublimates to leave pores. In other embodiments, the short-acting pore-forming agent comprises NH4CO3 (ammonium carbonate), and it can be introduced in solid form at different points in DRI production and will decompose upon heating and leave entirely as a gaseous or liquid substance (NH3 + CO2 + H2O). In various other embodiments, the short-acting additive can play an additional function in the battery (e.g., as an electrolyte component). In some embodiments, the short-acting additive can be an alkaline salt, such as KOH, NaOH, or LiOH. In some embodiments, the short-acting additive may be a soluble electrolyte additive that is solid under ambient dry conditions, such as lead sulfate, lead acetate, antimony sulfate, antimony acetate, sodium molybdenum oxide, potassium molybdenum oxide, thiourea, sodium stannate, or ammonium thiosulfate. In various other embodiments, the short-acting additive may be a binder for agglomerating iron ore powder to form pellets or other shapes, such as sodium alginate or carboxymethyl cellulose binder.

[0103] In some embodiments, the reducing gas used to form the DRI is hydrogen (H2). In some embodiments, hydrogen is produced by water electrolysis from renewable energy sources such as wind or solar power. In some embodiments, the electrolyzer is connected to an energy storage system. In some embodiments, the electrolyzer is a proton exchange membrane (PEM) electrolyzer. In some embodiments, the electrolyzer is an alkaline electrolyzer. In embodiments using hydrogen as the reducing gas, the cementite (Fe3C) content of the DRI can be as low as 0 by weight.

[0104] In some embodiments, natural gas (methane, CH4) is used as a reducing agent to produce DRI. In some embodiments, methane is steam reformed (through a reaction with water H2O), through a reaction... A mixture of carbon monoxide (CO) and hydrogen (H2) is produced. In some embodiments, the reforming reaction occurs via an auxiliary reformer, which is separate from the reactor where iron reduction occurs. In some embodiments, the reforming occurs in situ in a reduction reactor. In some embodiments, reforming occurs in both an auxiliary reformer and a reduction reactor. In some embodiments, coal is used as a reducing agent to produce DRI. In some embodiments, coke is used as a reducing agent to produce DRI. In embodiments using carbon-containing reducing gases, the cementite (Fe3C) content of the DRI can be higher, up to 80% by weight.

[0105] In some embodiments, DRI mixtures produced using various reducing gases can be used to achieve a beneficial combination of composition and properties. In one non-limiting embodiment, DRI produced by reducing BF-grade pellets in natural gas and DRI produced by reducing DR-grade pellets in hydrogen are mixed in a 50 / 50 mass ratio for use as the negative electrode of the battery. Other combinations of mass ratios, feedstock types (DR, BF, other artificial ores, etc.), and reducing media (hydrogen, natural gas, coal, etc.) can be combined in other embodiments.

[0106] In various implementations, DRI pellets may be crushed and the crushed pellets may contain a bed (with or without added powder).

[0107] In various embodiments, additives that facilitate electrochemical cycling, such as hydrogen evolution reaction (HER) inhibitors, can be added to the bed in solid form, for example, as powder or as solid pellets.

[0108] In some implementations, the metal electrode can have a low initial specific surface area (e.g., less than about 5 m²). 2 / g and preferably less than about 1 m 2 / g). This type of electrode often exhibits a low self-discharge rate in low-rate, long-duration energy storage systems. An example of a low specific surface area metal electrode is a bed of DRI pellets. In many typical modern electrochemical cells, such as lithium-ion battery packs or nickel-metal hydride battery packs, a high specific surface area is required to improve high-rate performance (i.e., high power). In long-duration systems, the requirements for rate performance are significantly reduced, so low specific surface area electrodes can meet the target rate performance requirements while minimizing the self-discharge rate.

[0109] In some implementations, the DRI pellets are treated by mechanical, chemical, electrical, electrochemical, and / or thermal methods before being used in an electrochemical cell. Such pretreatment can achieve superior chemical and physical properties and, for example, can increase the available capacity during the discharge reaction. The physical and chemical properties of purchased (sometimes referred to as “received”) DRI may not be optimal for use as the anode in an electrochemical cell. Improved chemical and physical properties may include introducing higher levels of desired impurities such as HER inhibitors, achieving lower levels of unwanted impurities (e.g., HER catalysts), achieving higher specific surface area, achieving higher total porosity, achieving a pore size distribution different from the starting DRI (e.g., a multi-peaked pore size distribution to reduce mass transfer resistance), achieving a desired pellet size distribution (e.g., a multi-peaked size distribution to allow pellets to be packed to the desired density), and altering or selecting pellets with a desired aspect ratio (to achieve the desired bed packing density). Machining may include rolling, grinding, milling, crushing, pulverizing, and powdering. Chemical treatment may include acid etching. Chemical treatment may include immersing the pellet bed in an alkaline solution to create necking between the pellets and to coarsen the micropores within the pellets. Thermal treatment may include treating the DRI at high temperatures in an inert, reducing, oxidizing, and / or carburizing atmosphere. In various embodiments, mechanical, chemical, electrochemical, and / or thermal methods for pretreating the electrode-forming materials, such as DRI pellets, may melt the electrode-forming materials into a bed, such as a bed of molten DRI pellets.

[0110] In some implementations, the negative electrode may comprise an inert conductive matrix, including carbon black, graphite powder, acetylene black, activated carbon, carbon steel mesh, stainless steel mesh, carbon steel wool, steel wool, nickel-plated carbon steel mesh, nickel-plated stainless steel mesh, nickel-plated steel wool, expanded metal carbon steel mesh, nickel-plated carbon steel mesh, stainless steel mesh, nickel-plated stainless steel mesh, or combinations thereof.

[0111] According to various embodiments, the positive electrode comprises a manganese-containing compound, including manganese(IV) oxide (MnO2), manganese(III) oxide (Mn2O3), manganese(III) hydroxide (MnOOH), manganese(II) oxide (MnO), manganese(II) hydroxide (Mn(OH)2), or combinations thereof. In some embodiments, the positive electrode may comprise one or more natural manganese oxide minerals, such as malachite, pyrolusite, malachite, hexagonal pyrolusite, manganese barium ore, orthorhombic manganese ore, hexagonal manganese ore, spinel, pyrolusite, barium magnesia ore, ferromagnesia ore, malachite, or combinations thereof. In some embodiments, the positive electrode may comprise a manganese-containing compound having a manganese oxide mineral structure, such as malachite. In some embodiments, the positive electrode may comprise electrolyzed manganese dioxide (EMD). In some embodiments, the manganese dioxide is in... α -MnO2、 β-MnO2、 γ -MnO2、 δ -MnO2、 ε -MnO2、 λ -MnO2 or combinations thereof in the phase. In some embodiments, the cathode may comprise a manganese-containing compound having a manganese oxide mineral structure, such as, but not limited to, pyrolusite, orthorhombic rhodochrosite, hexagonal rhodochrosite, barium manganese, sphaerodendronite, or hydroxymanganese. In some embodiments, the cathode may comprise manganese(II) hydroxide (Mn(OH)2). In some embodiments, the cathode may comprise a manganese hydroxide mineral, such as hydroxymanganese. In some embodiments, the cathode may comprise a manganese-containing compound having a manganese hydroxide mineral structure, such as hydroxymanganese. In some embodiments, the cathode may comprise manganese(III) hydroxide (MnOOH). In some embodiments, the cathode may comprise a manganese hydroxyoxide mineral, such as manganese bromite, hexagonal manganese bromite, orthorhombic manganese bromite, or manganese bromite. In some embodiments, the cathode may comprise a manganese-containing compound having a manganese hydroxyoxide mineral structure, such as manganese bromite. In various implementation schemes, the positive electrode comprises an inert conductive matrix, including carbon black, graphite powder, acetylene black, activated carbon, charcoal powder, coal powder, nickel-plated carbon steel mesh or expanded metal mesh, nickel-plated stainless steel mesh or expanded metal mesh, nickel-plated steel wire wool, or combinations thereof.

[0112] In the implementation scheme, the specific surface area of ​​the manganese-containing compound can be approximately 0.05 m². 2 / g to approximately 50m 2 / g, approximately 0.5m 2 / g to approximately 5m 2 / g, as well as larger and smaller values. In some embodiments, the positive electrode may contain additives to enhance its capacity and cycle life. In some embodiments, the additives in the positive electrode include oxides, sulfides, and sulfates, such as antimony(III) oxide (Sb₂O₃), barium oxide (BaO), barium sulfate (BaSO₄), barium hydroxide (Ba(OH)₂), bismuth(III) oxide (Bi₂O₃), bismuth(III) sulfide (Bi₂S₃), calcium oxide (CaO), calcium sulfate (CaSO₄), calcium hydroxide (Ca(OH)₂), cerium oxide (CeO₂), lead oxide (PbO), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)₂), strontium oxide (SrO), titanium sulfide (TiS₂), or combinations thereof. In some embodiments, the additives in the positive electrode include metals or metal cations, such as Li₂. + Na + K + Mg 2+ Ca 2+ Ba 2+ Co 2+ Cu2+ Fe 2+ Fe 3+ Bi 3+ Pb 2+ Zn 2+ Ni 2+ Or combinations thereof. In some embodiments, the additives in the cathode include carbon nanotubes, carbon nanofibers, graphene, nitrogen-doped carbon nanotubes, nitrogen-doped carbon nanofibers, nitrogen-doped graphene, or combinations thereof.

[0113] In some embodiments, the positive electrode may comprise a binder compound. In some embodiments, the binder compound includes polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polypropylene (PP), polyethylene (PE), fluorinated ethylene propylene (FEP), polyacrylonitrile, styrene-butadiene rubber, carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (Na-CMC), polyvinyl alcohol (PVA), polypyrrole (PPy), or combinations thereof.

[0114] In some embodiments, the manganese oxide-based cathode can be assembled in a “discharged” state. The “discharged” state is defined as Mn(III) (e.g., MnOOH, Mn2O3), Mn(II+III) (e.g., Mn3O4), and Mn(II) (e.g., Mn(OH)2). In some embodiments, the sources of the “discharged” manganese oxide or hydroxyl oxide species include natural ores such as rhodochrosite, orthorhombic rhodochrosite, hexagonal rhodochrosite, ferromanganese, hydroxyl manganese, rhodochrosite, malachite, hexagonal manganese, etc. In other embodiments, the sources of the “discharged” manganese oxide species can be from discarded primary alkaline battery packs (i.e., Zn / MnO2), wherein the “discharged” cathode of the primary alkaline battery pack can be reused in the assembly of a rechargeable manganese oxide-based cathode. In some embodiments, additives such as Bi2O3 or metallic bismuth can be mixed with the “discharged” manganese oxide species along with other electrode components to restore the rechargeability of these “discharged” compounds to the “charged” species (i.e., Mn(IV)) with the desired phase. In some embodiments, the "discharged" cathode and "discharged" anode are connected in a full cell configuration, and both the cathode and anode are charged in the first half of the cycle. In other embodiments, the "discharged" cathode and charged anode are connected in a full cell configuration, and the cathode is charged in the first half of the cycle, using the hydrogen evolution reaction (HER) as the counter electrode reaction.

[0115] In various embodiments, the loading of manganese-containing compounds in the positive electrode ranges from 50 to 90 wt% based on the equivalent mass of MnO2. In various embodiments, the loading of the conductive matrix in the positive electrode ranges from 5 to 40 wt%. In various embodiments, the loading of additives in the positive electrode ranges from 0 to 20 wt%. In various embodiments, the loading of binder in the positive electrode ranges from 0 to 20 wt%.

[0116] In some embodiments, the manganese-containing compound and the additive are combined through a chemical reaction or physical process, such as, but not limited to, stirring, mixing, grinding, blending, or a combination thereof. In some embodiments, the additive is incorporated into the structure of the manganese-containing compound through chemical, electrochemical, or thermal treatment.

[0117] In some embodiments, the positive electrode comprising a manganese compound, additives, a conductive matrix, and a binder is produced by a powder compaction process, such as, but not limited to, uniaxial pressing or rolling. In some embodiments, the compaction is performed dry or wet. In some embodiments, the positive electrode comprising a manganese compound, additives, a conductive matrix, and a binder is produced by an extrusion process (e.g., but not limited to a screw or piston). In some embodiments, the compaction is performed dry or wet. In some embodiments, the positive electrode comprising a manganese compound, additives, a conductive matrix, and a binder is produced by directly filling a mixed powder into the battery. In some embodiments, the mixed powder is filled in a dry state and expanded by adding electrolyte to the dry powder. In some embodiments, the mixed powder is filled in a wet state, such as a slurry or paste. In some embodiments, the mixed powder is applied to the current collector using a coating or printing process, such as, but not limited to, comma coating, screen printing, gravure coating, die coating, or comma coating.

[0118] In some embodiments, the redox medium can be used to facilitate electron transfer in the redox reaction from MnO2 to MnOOH. In some embodiments, the redox medium can be used to facilitate electron transfer in the redox reaction from MnO2 to Mn(OH)2. Requirements for the redox medium include: (1) simple, reversible redox kinetics; (2) a redox potential similar to the reaction it facilitates (i.e., MnO2 <> MnOOH or MnO2 <> Mn(OH)2); and (3) stability in the presence of an electrolyte of interest (e.g., a high concentration of alkali). In some embodiments, the redox medium is insoluble in the electrolyte. As a non-limiting example, the redox medium for a rechargeable manganese dioxide electrode is ferrocene, ferrocene derivatives, or combinations thereof. As another non-limiting example, the redox medium is 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ). As another non-limiting example, the redox medium is tetrathiofulvalene (TTF). In some embodiments, the redox medium is soluble in the electrolyte. As a non-limiting example, the redox medium for a rechargeable manganese dioxide electrode is TEMPO, TEMPO derivatives, or combinations thereof. In one embodiment, the redox medium is LiI, NaI, KI, CsI, or combinations thereof.

[0119] In various embodiments, the electrolyte comprises an aqueous alkali metal hydroxide, including lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), cesium hydroxide (CsOH), or combinations thereof. In some embodiments, the electrolyte comprises an alkali metal sulfide or polysulfide, including lithium sulfide (Li₂S) or lithium polysulfide (Li₂S₂S₃S₄ ... x (x=2 to 6), sodium sulfide (Na2S) or sodium polysulfide (Na2S) x (x=2 to 6), potassium sulfide (K2S) or potassium polysulfide (K2S) x (x=2 to 6), cesium sulfide (Cs₂S) or cesium polysulfide (Cs₂S) x(x=2 to 6). In some embodiments, the electrolyte also contains a hydrogen evolution reaction (HER) inhibitor. In some embodiments, the HER inhibitor may be selected from the non-limiting group consisting of: sodium thiosulfate, sodium thiocyanate, polyethylene glycol (PEG) 1000, trimethyl sulfoxide, zincate (by dissolving ZnO in NaOH), hexamethylenetetramine, decanethiol, sodium chloride, sodium permanganate, lead oxide (IV), lead oxide (II), magnesium oxide, sodium chlorate, sodium nitrate, sodium acetate, ferric phosphate, phosphoric acid, sodium phosphate, ammonium sulfate, ammonium thiosulfate, zinc barium white, magnesium sulfate, ferric acetylacetone (III), hydroquinone monomethyl ether, sodium metavanadate, sodium chromate, glutaric acid, dimethyl phthalate, methyl methacrylate, methylpentynol, adipic acid, allyl urea, citric acid, sulfur Malic acid, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, propylene glycol, divinylpropyltrimethoxysilane, aminopropyltrimethoxysilane, dimethyl ethynyl dicarboxylate (DMAD), 1,3-diethylthiourea, N,N'-diethylthiourea, aminomethylpropanol, methylbutynol, amino-modified organosilane, succinic acid, isopropanolamine, phenoxyethanol, dipropylene glycol, benzoic acid, N-(2-aminoethyl)-3-aminopropyl, behenamide, 2-phosphonobutane tricarboxylic acid, mipapyrate (mipa) borate), 3-methacryloyloxypropyltrimethoxysilane, 2-ethylhexanoic acid, isobutanol, tert-butylaminoethyl methacrylate, diisopropanolamine, propylene glycol n-propyl ether, sodium benzotriazole, pentasodium aminotrimethylenephosphonate, sodium cocoyl sarcosinate, dodecyl pyridine chloride, stearic acid trimethylammonium chloride, silachlorine, calcium lignite, quaternary ammonium salt-18 chloride, sodium hexametaphosphate, dicyclohexylamine nitrite, lead stearate, calcium dinonylnaphthalenesulfonate, ferrous(II) sulfide, sodium hydrosulfide, pyrite, sodium nitrite, complex alkyl phosphates (e.g., RHODAFAC® RA 600 emulsifier), 4-mercaptobenzoic acid, ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid salt (EDTA), 1,3-Propanediaminetetraacetic acid (PDTA), NTA, EDDS, DTPA and other aminopolycarboxylic acids (APC), 2-methylbenzenethiol, 1-octylthiol, bismuth sulfide, bismuth oxide, antimony(III) sulfide, antimony(III) oxide, antimony(V) oxide Bismuth selenide, antimony selenide, selenium sulfide, selenium oxide (IV), propargyl alcohol, 5-hexyn-1-ol, 1-hexyn-3-ol, N-allylthiourea, thiourea, 4-methylcatechol, trans-cinnamaldehyde, iron sulfide (III), calcium nitrate, hydroxylamine, benzotriazole, furfurylamine, quinoline, stannous chloride (II), ascorbic acid, tetraethylammonium hydroxide, calcium carbonate, magnesium carbonate, dialkyl dithiophosphate, potassium stannate, sodium stannate, tannic acid, gelatin, saponins, agar, 8-hydroxyquinoline, bismuth stannate, potassium gluconate, lithium molybdenum oxide, potassium molybdenum oxide, hydrogenated light petroleum, heavy cycloalkane petroleum (such as Ru) Stlick® 631 (for sale), antimony sulfate, antimony acetate, bismuth acetate, hydrogenated heavy naphtha (e.g., sold as WD-40®), tetramethylammonium hydroxide, sodium antimony tartrate, urea, D-glucose, C6Na2O6, potassium antimony tartrate, hydrazine sulfate, silica gel, triethylamine, potassium antimony trihydrate, sodium hydroxide, 1,3-di-o-tolyl-2-thiourea, 1,2-diethyl-2-thiourea, 1,2-diisopropyl-2-thiourea, N-phenylthiourea, N,N'-diphenylthiourea, sodium L-antimony tartrate, disodium rosinate, sodium selenide, potassium sulfide, and combinations thereof.

[0120] In various embodiments, a separator that is electron-impermeable but permeable to at least one alkali metal ion or hydroxide ion is in close contact between the negative and positive electrodes. In some embodiments, the separator is a nonwoven fiber layer, such as nylon, cellulose, etc. In some embodiments, the separator is a porous polymer layer, such as a polypropylene separator, a polyethylene separator, or a polybenzimidazole (PBI) separator. In some embodiments, the separator is a woven layer, such as a polypropylene mesh, a polyethylene mesh, a polyester mesh, or cotton yarn. In some embodiments, an anion exchange membrane that selectively conducts hydroxide ions is in close contact between the negative and positive electrodes. In various embodiments, the separator is a size exclusion separator that selectively conducts hydroxide ions and alkali metal ions while preventing divalent sulfur ions or polysulfide ions from crossing from the negative electrode side to the positive electrode side. In various embodiments, the separator is a size exclusion separator that selectively conducts hydroxide ions while preventing divalent sulfur ions or polysulfide ions from crossing from the negative electrode side to the positive electrode side. In some embodiments, the pore size of the size exclusion separator is larger than the diameter of hydroxide ions and alkali metal ions, but smaller than the diameter of divalent sulfur ions. In some embodiments, the pore size of the size exclusion separator is larger than the diameter of hydrated hydroxide ions and hydrated alkali metal ions, but smaller than the diameter of hydrated divalent sulfur ions. In some embodiments, the pore size of the size exclusion separator is larger than the diameter of hydroxide ions, but smaller than the diameter of divalent sulfur ions. In some embodiments, the pore size of the size exclusion separator is larger than the diameter of hydrated hydroxide ions, but smaller than the diameter of hydrated divalent sulfur ions.

[0121] In various embodiments, the battery pack components are assembled into a square or cylindrical configuration. In various embodiments, the current collector includes nickel, copper, aluminum, carbon steel, stainless steel, nickel-plated stainless steel, nickel-plated carbon steel, nickel-plated steel velvet, graphite, or combinations thereof. In various embodiments, the current collector is a metal plate, metal rod, metal tube, steel mesh, perforated metal, metal mesh, graphite plate, graphite rod, graphite tube, graphite foil, toner substrate, toner-based rod, toner-based tube, toner-based foil, or combinations thereof. In various embodiments, the current collector is deposited in the form of a coating or paste using techniques such as gravure coating or screen printing. In various embodiments, the battery casing material is polypropylene, high-density polyethylene, or polyvinyl chloride. In various embodiments, the electrolyte is in a static (non-circulating) mode or a flowing (circulating) mode.

[0122] In some embodiments, the current collector is a conductive and electrolyte-impermeable barrier. In some embodiments, this conductive and electrolyte-impermeable barrier comprises a carbon material and a hydrophobic binder. In some embodiments, the carbon material includes carbon black, activated carbon, graphite, or combinations thereof. In some embodiments, the hydrophobic binder includes polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polypropylene (PP), polyethylene (PE), fluorinated ethylene propylene (FEP), or combinations thereof. In prismatic batteries, this current collector is flat. In some embodiments, the flat current collector can be made by powder compaction, extrusion, coating, or printing. In some embodiments, the flat current collector and external structural components can be produced simultaneously by extrusion or co-extrusion processes. In cylindrical batteries, this current collector for the outer layer of the battery is a hollow cylinder or tubular shape. In some embodiments, the hollow cylindrical or tubular current collector can be manufactured by extrusion or co-extrusion processes or by folding or rolling sheet material. In some embodiments, the cylindrical current collector and external structural components can be produced simultaneously by paste extrusion or co-extrusion processes.

[0123] In some embodiments, a conductive and electrolyte-impermeable barrier is placed between the electrode and the current collector. In some embodiments, this conductive and electrolyte-impermeable barrier comprises a carbon material and a hydrophobic binder. In some embodiments, the carbon material includes carbon black, activated carbon, graphite, or combinations thereof. In some embodiments, the hydrophobic binder includes polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polypropylene (PP), polyethylene (PE), fluorinated ethylene propylene (FEP), or combinations thereof. In prismatic batteries, the conductive and electrolyte-impermeable barrier is flat. In some embodiments, the flat conductive and electrolyte-impermeable barrier can be manufactured by powder compaction, extrusion, coating, or printing processes. In cylindrical batteries, the conductive and electrolyte-impermeable barrier is hollow cylindrical or tubular. In some embodiments, the hollow cylindrical or tubular conductive and electrolyte-impermeable barrier can be made by extrusion or co-extrusion processes or by folding or rolling sheet material. In various implementations, the current collector that contacts the conductive and electrolyte-impermeable barrier can be alkaline-incompatible, such as copper, aluminum, or carbon steel.

[0124] In some embodiments, the proton conductor is included in the positive electrode to prevent sulfides from entering the positive electrode surface and to facilitate local proton transfer. In some embodiments, the proton conductor is liquid and coated on the positive electrode surface. In some embodiments, the liquid proton conductor is Nafion. ® Solution. In some embodiments, the proton conductor is solid and mixed with other components of the positive electrode. In some embodiments, the solid proton conductor is Nafion. ®Pearl.

[0125] In various embodiments, the battery or battery stack is charged in a current-controlled, voltage-controlled, or power-controlled mode, or a combination thereof. In various embodiments, the battery or battery stack is charged in a constant current, constant voltage, constant power mode, or a combination thereof. In various embodiments, the battery or battery stack is discharged in a constant current, constant voltage, constant power mode, or a combination thereof. In various embodiments, the battery or battery stack is discharged in a current-controlled, voltage-controlled, or power-controlled mode, or a combination thereof.

[0126] In various embodiments, an auxiliary electrode is included in a sealed, rechargeable Fe-MnO2 battery for catalyzing the hydrogen oxidation reaction (HOR) that occurs at the negative electrode during battery charging. This auxiliary electrode is called a hydrogen recombination electrode. The consumption of hydrogen as a byproduct not only mitigates hydrogen-related safety concerns but also balances the state of charge at the positive electrode. In various embodiments, the hydrogen recombination electrode includes a catalytic core and a separator surrounding the core. The catalytic core provides reaction sites for the HOR. The separator is ion-conducting and electrically insulating. In some embodiments, the catalytic core is a solid electrode, such as... Figure 2A As shown. Figure 2A A solid electrode is shown as a hydrogen recombination electrode 200, comprising a separator 202 and a catalytic core 203. In some embodiments, the catalytic core is a porous electrode, such as... Figure 2B As shown. Figure 2B A hydrogen recombination electrode 220 is shown, which includes a separator 202 and a porous catalytic core 221. In one example, a hydrogen recombination electrode 236 is placed in a negative electrode compartment, such as a negative electrode compartment 231 comprising an anode formed by DRI, for example... Figure 2C As shown. Figure 2C A specific example electrochemical cell 230, similar to the electrochemical cell 100 described above, is shown, wherein the anode may be formed by DRI, and the cathode in the positive electrode compartment 232 may be formed by MnO2 / C. As an example, the hydrogen recombination electrode 236 may be the hydrogen recombination electrode 200 or 220 described above. Hydrogen gas generated at the anode will be consumed "in situ" by the hydrogen recombination electrode 236. The electrochemical cell 230 may include an exhaust port 235 having a threshold pressure. The threshold pressure of the exhaust port may be higher than that of an exhaust port in a battery where a hydrogen recombination electrode may not be present. In another example, a hydrogen recombination electrode 241 is placed between the anode and cathode, for example, as shown below. Figure 2DAs shown, the electrochemical cell 240 includes a hydrogen composite electrode 241 disposed between the negative electrode compartment 231 and the positive electrode compartment 232. In this configuration of the electrochemical cell 240, the hydrogen composite electrode 241 can replace the polypropylene mesh 105 and the battery separator 104; therefore, the hydrogen composite electrode 241 can have a porous catalytic core, such as the hydrogen composite electrode 220 described above. Hydrogen generated at the anode will be transferred through the pores in the anode and consumed by the hydrogen composite electrode 241. The hydrogen concentration gradient is the main driving force for hydrogen mass transfer. In another example of the electrochemical cell 250 construction, the hydrogen composite electrode 251 is placed on top of the anode at the top of the negative electrode compartment 231, for example... Figure 2E As shown. In such a configuration, the hydrogen recombination electrode 251 can be integrated with the exhaust port. In another example, the hydrogen recombination electrode is the same as the cathode 261, for example as... Figure 2F The electrochemical cell 260 is shown in the diagram. In other words, during charging, the primary electrochemical reaction at the cathode 261 is the oxidation of manganese compounds, and the "auxiliary" electrochemical reaction at the cathode 261 is HOR. The hydrogen concentration gradient is the primary driving force for the mass transfer of hydrogen from the negative electrode compartment 231 to the cathode 261 of the cell 260.

[0127] In various embodiments, an auxiliary electrode, serving as a rebalancing electrode, is placed on the positive electrode side. The primary purpose of this auxiliary electrode is to protect the positive electrode from overcharging during HER on the negative electrode side. In some embodiments, the auxiliary electrode is nickel hydroxyl oxide. In other embodiments, the auxiliary electrode is the same manganese-based positive electrode with excess capacity.

[0128] In various embodiments, the operating temperature ranges from -20°C to 60°C. In some embodiments, the preferred operating temperature range is from 20°C to 40°C.

[0129] In a non-limiting example, in a square configuration, the rechargeable Fe-MnO2 battery comprises a MnO2-based positive electrode, a sintered iron negative electrode with Bi2S3 incorporated, a polypropylene separator, and a 15 wt% KOH + 15 wt% NaOH electrolyte. In this embodiment, the positive electrode contains EMD (60-70 wt%), graphite (25-35 wt%), and PTFE (5-10 wt%), and has a nickel-plated steel wire mesh current collector. The powders of EMD, graphite, and PTFE are wet-mixed in the presence of isopropanol. The electrode is produced by calendering the mixed powder and then drying. The electrode and the nickel-plated steel wire mesh current collector are assembled using a hydraulic press. The thickness of the positive electrode is 1 to 10 mm. The thickness of the negative electrode is 1 to 10 mm. The target operating current density of the battery is 1 to 10 mA / cm². 2 .

[0130] In another non-limiting example, in a cylindrical construction, the rechargeable Fe-MnO2 battery comprises a MnO2-based positive electrode, a Bi2S3-incorporated DRI negative electrode, a polybenzimidazole (PBI) separator, and a 30 wt% KOH + 1 wt% LiOH electrolyte. In this embodiment, the positive electrode contains EMD (70-80 wt%), carbon black (15-25 wt%), and PTFE (5-10 wt%), and has a nickel-plated steel current collector. The EMD, carbon black, and PTFE powders are dry-mixed and filled into the cylindrical battery in a dry state. In some embodiments, the positive electrode “pillar” is placed at the center of the cylinder, while the negative electrode is placed around the positive electrode “center.” In some embodiments, the negative electrode “pillar” is placed at the center of the cylinder, while the positive electrode is placed around the negative electrode. A PBI separator sandwiched between two layers of polypropylene mesh is placed between the positive and negative electrodes.

[0131] In another non-limiting example, in a cylindrical configuration, the rechargeable Fe-MnO2 battery comprises a MnO2-based positive electrode, a Bi2S3-incorporated DRI negative electrode, a polybenzimidazole (PBI) separator, and a 30 wt% KOH + 1 wt% LiOH electrolyte. In this embodiment, the positive electrode contains EMD (70-80 wt%), carbon black (15-25 wt%), and PTFE (5-10 wt%). The EMD and carbon black powders are mixed by ball milling, followed by the addition of a PTFE dispersion and subsequent mixing. In some embodiments, additional processing aids are added. The mixture is then extruded through a circular die to produce a tubular structure. The tube is then cut to appropriate lengths corresponding to the electrode height, and each section is rolled by a gravure coater to deposit a patterned copper paste current collector. In some embodiments, the positive electrode “pillar” is placed at the center of the cylinder, while the negative electrode is placed around the positive electrode “center.” In some embodiments, the negative electrode “pillar” is placed at the center of the cylinder, while the positive electrode is placed around the negative electrode. The PBI separator, sandwiched between two layers of polypropylene mesh, is placed between the positive and negative electrodes.

[0132] In another non-restrictive example, according to Figure 3A A proof-of-concept battery 300 was constructed. The active area of ​​battery 300 is approximately 1.5 cm². 2The negative electrode 301 is iron powder weighing approximately 1.3 g. The positive electrode 302 is MnO2-based powder weighing approximately 0.8 g, wherein the MnO2 loading is approximately 78% by weight. The conductive matrix in this MnO2-based powder is carbon. The positive electrode 302 also includes a perforated nickel coating approximately 0.5 mm thick, which serves as a retainer for the MnO2-based powder. A polypropylene battery pack separator 303 (Celgard 3501) is used between the negative electrode 301 and the positive electrode 302. The “negative electrode / separator / positive electrode” assembly (e.g., a combination of negative electrode 301, separator 303, and positive electrode 302) is clamped between two current collectors 304, which are stainless steel plates. A spring clip 305 is used to hold the battery components together. The contact between the spring clip 305 and the current collectors 304 is insulated by a layer of ethylene propylene diene monomer (EPDM) rubber 307, such that the battery 300 is pressed against the EPDM rubber 307 by a force 306 from the clip. Figure 3A As shown on the right-hand side, the entire battery 300 (except for the end of the current collector 304) is immersed in a plastic beaker 310 containing a solution 311 of 5.5M KOH + 0.5M LiOH. A mercury / mercury oxide (MMO) reference electrode 312 is placed in the beaker 310 near the positive electrode 302 to monitor the positive half-cell potential. Assuming the positive electrode reaction is Mn(IV)⇔Mn(III), the total cell capacity is limited by the positive electrode 302 to approximately 100 mAh.

[0133] Figure 3B This demonstrates the use of a proof-of-concept battery design (i.e., such as...) Figure 3A The battery shown (300) operates at 2.7 mA / cm². 2 Under constant current (constant current) cycling, this corresponds to 6.4 mA / g MnO2 . Figure 3B There were 12 cycles, with a total duration of >400 hours. During these 12 cycles, the average charging voltage was approximately 1.35V, and the average discharging voltage was approximately 0.80V. As shown in the magnified curves (full cell voltage relative to capacity in mAh), several plateaus exist related to the charging and discharging curves, representing valence state changes in iron- and manganese-containing species. Figure 3C Summarize based on Figure 3B The graph shows the change in MnO2 capacity (left Y-axis) and coulombic efficiency (right Y-axis). The MnO2 capacity ranges from 103 mAh / g. MnO2 It becomes 62mAh / g MnO2 The average decay rate was 3.3 mAh / g / cycle. The coulombic efficiency varied from 90% to 78% from start to finish. Figure 3D This demonstrates the use of a proof-of-concept battery setup (i.e., as shown in the example). Figure 3AThe lifetime start (BOL) half-cell positive electrode polarization curve of battery 300 is shown. Mercury / mercury oxide (MMO) was used as the reference electrode. The apparent positive electrode areal resistivity (ASR) was determined to be approximately 20 Ω-cm. 2 .

[0134] In another non-limiting example, a proof-of-concept battery was constructed and tested using electrolytic manganese dioxide (EMD) as the positive electrode active material and direct reduced iron (DRI) as the negative electrode active material. The battery's active area was approximately 9 cm². 2 The area of ​​the positive electrode is determined by the negative electrode. The negative electrode consists of six DRI beads with a total mass of 13.5 grams, fixed by expanded nickel and also used as a current collector. The positive electrode has a mass of approximately 0.9 g, resulting in a MnO2 loading of 65% by weight. The conductive matrix and binder in this MnO2-based powder are graphite and PTFE powder, respectively. The positive electrode also includes a 20-mesh nickel mesh as a current collector. A PBI separator is used to wrap the positive electrode. The wrapped positive electrode is then sandwiched between two polypropylene meshes. The “negative electrode / separator / positive electrode” assembly (e.g., a combination of negative electrode, separator, polypropylene mesh, and positive electrode) is pressed between two acrylic end plates and tightened with bolts, nuts, and washers. The entire battery, except for the end with the current collector, is immersed in a plastic beaker containing a 10% by weight KOH solution. A mercury / mercury oxide (MMO) reference electrode is placed in the beaker to monitor the positive and negative half-cell potentials. Assuming the positive electrode reaction is Mn(IV)⇔Mn(III), the total battery capacity is limited by the positive electrode and is approximately 170mAh as the theoretical capacity.

[0135] Figure 3E The second cycle charge-discharge data for the proof-of-concept EMD / DRI battery, as described in the preceding paragraphs, are shown. The X-axis represents the full cell capacity in mAh, and the Y-axis represents the full cell voltage in V. Constant current constant voltage (CCCV) was used during charging. The battery was initially charged at 8.7 mA (equivalent to C / 20 based on EMD capacity) until the positive potential reached 0.5 V (vs MMO). Afterward, the battery was charged at a constant potential of 0.5 V (vs MMO) until the charging current decayed to 0.87 mA. During discharging, a constant current of 8.7 mA (i.e., constant current) was used until the positive potential dropped to -0.2 V (vs MMO). The theoretical battery capacity is approximately 170 mAh, corresponding to 300 mAh / g. EMD As shown in the figure, the discharge capacity of the EMD is 229 mAh / g. The average charging voltage is 1.22 V, and the average discharging voltage is 0.91 V. The coulombic efficiency is 93.8%. The current efficiency is 74.6%. The energy efficiency is 70.0%. Several plateaus / bumps related to the charging and discharging curves are observed, indicating valence state changes in iron- and manganese-containing species.

[0136] In another non-limiting example, pelletized direct reduced iron (DRI) is used as the negative electrode. In some embodiments, the electrochemical cell using DRI as the negative electrode and a manganese oxide-based positive electrode is a prismatic cell structure or a stacked prismatic cell structure, such as... Figure 4A As shown. For example, Figure 4A A rectangular stack 400 of six electrochemical cells 410, using pelletized DRI as the negative electrode 403 and a manganese compound-based positive electrode 407, is shown, similar to the reference above. Figure 1B The stacked structure is discussed. Each cell 410 includes a negative electrode 403 immersed in an electrolyte 401, which is separated from a positive electrode 407 by a polypropylene mesh 405 and a cell pack separator 406. A bipolar current collector 402 is disposed between each cell 410 and located on the side of the edge cells 410 in the square stack 400. A polyethylene backsheet 404 is disposed on the outside of the two end cells 410, and the bipolar current collector 402 and polyethylene frame 408 in the stack support each cell 410. In some embodiments, the electrochemical cell 450 using DRI as the negative electrode 458 and a manganese oxide-based positive electrode 460 is constructed as a cylindrical cell, such as... Figure 4B As shown. Figure 4B The left side of the figure shows a side view of battery 450, and the right side shows a top view of battery 450, with the polyethylene cap 454 removed from the view. A negative current collector 452 is located at the center of the filled DRI forming the negative electrode 458. The negative electrode 458 is supported in a polypropylene mesh 466 and immersed in electrolyte 456. A battery separator 464 separates the negative electrode 458 from the positive electrode 460 and the positive electrolyte. The positive current collector 468 surrounds the positive electrode 460. A polyethylene backsheet 462 forms the bottom of battery 450, and the polyethylene cap 454 covers the top of battery 450. As shown in the top view, the negative electrode 458 surrounds the negative current collector 452, the separator 464 surrounds the positive electrode 460, electrolyte 456, and polypropylene mesh 466, the positive electrode 460 and its electrolyte surround the separator 464, and the positive current collector 468 surrounds the positive electrode 460.

[0137] In another non-limiting example, the manganese-containing compound in the positive electrode has a layered crystal structure. δ -MnO2 (sodium manganese ore). δ The interlayer of -MnO2 may contain metal cations. The metal cation is Li. + Na + K + Mg 2+ Ca 2+ Ba 2+ Cu 2+ Fe 2+ Fe 3+ Bi 3+ Pb 2+Zn 2+ Or a combination thereof. δ -MnO2 interlayers may contain protons. δ -The MnO2 interlayer may contain water molecules. In some implementations, δ MnO2 is chemically produced prior to battery assembly from water-soluble manganese precursors such as NaMnO4, KMnO4, MnSO4, MnCl2, Mn(NO3)2, Mn(II) acetate, or combinations thereof. In some embodiments, it is produced by mixing stoichiometric amounts of aqueous solutions of NaMnO4 and MnSO4 in the presence of 1 mol / L KCl, followed by heat treatment of the mixture at 90°C for 1 hour. δ -MnO2. In some implementations, other phases of MnO2 are used, such as... α -MnO2, natural MnO2 ( β -MnO2), electrolytic manganese oxide (EMD), γ -MnO2、 ε -MnO2), or combinations thereof, to produce in-situ electrochemically during cycling after battery assembly. δ -MnO2. In some implementations, it is generated in situ during the first charge / discharge cycle. δ -MnO2. In some implementations, it is generated in situ during the first few charge / discharge cycles. δ -MnO2.

[0138] In another non-limiting example, the manganese-containing compound in the positive electrode has an open tunnel lattice structure. α -MnO2. α -MnO2 tunnels may contain metal cations such as Li + Na + K + Mg 2+ Ca 2+ Ba 2+ Cu 2+ Fe 2+ Fe 3+ Bi 3+ Pb 2+ Zn 2+ Or a combination thereof. α -MnO2 tunnels may contain protons. α -MnO2 tunnels may contain water molecules. In some implementations, αMnO2 is chemically produced prior to battery assembly from water-soluble manganese precursors such as NaMnO4, KMnO4, MnSO4, MnCl2, Mn(NO3)2, Mn(II) acetate, or combinations thereof. In some embodiments, it is produced by mixing equimolar concentrations (e.g., but not limited to 0.2 mol / L) of aqueous solutions of KMnO4 and MnCl2, followed by hydrothermal conversion at elevated temperature and pressure (e.g., 160°C in an autoclave for 6 hours). α -MnO2. In some embodiments, the temperature is in the range of 100°C to 200°C. In some embodiments, the pressure is in the range of 1 atm to 20 atm.

[0139] In another non-limiting example, a manganese-containing compound and Bi₂O₃ powder are physically mixed by ball milling in the presence of a conductive matrix. In some embodiments, the manganese-containing compound is MnO₂ powder, including but not limited to... α -MnO2, natural MnO2 ( β-MnO2), EMD, sulphurite, or combinations thereof. In some embodiments, the manganese-containing compound is a naturally occurring manganese-containing ore, including but not limited to sulphurite, pyrolusite, malachite, hexagonal pyrolusite, barium manganese ore, orthorhombic manganese ore, hexagonal manganese ore, spinel, pyrolusite, barium magnesium manganese ore, ferromanganese ore, hydroxyl manganese ore, or combinations thereof. In some embodiments, the naturally occurring manganese-containing ore is unprocessed. In some embodiments, PTFE as a binder is added to the powder mixture prior to grinding. In some embodiments, a conductive matrix such as graphite, carbon black, activated carbon, nickel powder, or combinations thereof is added to the powder mixture prior to grinding. The ground powder mixture is combined with a metal or graphite current collector and used as the positive electrode in the assembled battery. In some embodiments, the assembled battery is a full-cell construction using a DRI negative electrode. In some embodiments, the assembled battery is a full-cell construction using a sintered iron negative electrode. In some embodiments, Bi-doped MnO2 is generated by constant current cycling. In some embodiments, the cutoff potential during the reduction process is < -0.4 V relative to the mercury / mercury oxide (MMO) reference electrode. In some embodiments, the cutoff potential during the reduction process is -0.5 V to -0.7 V relative to the MMO reference electrode. In some embodiments, the cutoff potential during the oxidation process is > -0.3 V relative to the MMO reference electrode. In some embodiments, the cutoff potential during the reduction process is 0.1 V to 0.3 V relative to the MMO. In some embodiments, the charge / discharge rate is C / 24 to C / 1. In some embodiments, the charge / discharge cycle number is 1. In some embodiments, Bi-doped MnO2 is generated by constant potential cycling. In some embodiments, the reduction potential is < 0.5 V relative to the MMO reference electrode, and the oxidation potential is > 0.1 V relative to the MMO reference electrode. In some embodiments, Bi-doped MnO2 is generated by constant power cycling. In some embodiments, Bi-doped MnO2 is generated by cyclic voltammetry. In some embodiments, the upper limit potential of cyclic voltammetry relative to the MMORPG reference electrode is 0.1V to 0.3V. In some embodiments, the lower potential of cyclic voltammetry relative to the MMORPG reference electrode is -0.5V to -0.7V. In some embodiments, the scan rate is <100mV / s. In some embodiments, the scan rate is 0.1mV / s to 1.0mV / s. In some embodiments, the number of cycles is <100. In some embodiments, the number of cycles is <10.

[0140] In another non-limiting example, a nominal discharge duration of 1 hour with 15 mA / cm was constructed based on the proposed electrode reaction. 2An electrochemical cell with a rated current density and a rated battery voltage of 0.79V. MnO2 powder and Bi2O3 powder are physically mixed and ground in the presence of graphite. According to various embodiments, the MnO2 powder is... α -MnO2, natural MnO2 ( β -MnO2), EMD, naphthalene, or combinations thereof. In some embodiments, PTFE as a binder is added to the powder mixture prior to grinding. In some embodiments, 30% by weight of KOH solution is added to the powder mixture prior to grinding. In some embodiments, the MnO2 loading in the positive electrode is 65% by weight. The ground manganese-containing powder mixture is used as the positive electrode in the assembled battery. Iron-containing powder and Bi2S3 powder are physically mixed and ground in the presence of graphite. In some embodiments, the iron-containing powder is metallic iron, such as finely powdered DRI, pulverized DRI, or combinations thereof. In some embodiments, the iron-containing powder is an iron-containing compound, such as Fe(OH)2, Fe2O3, Fe3O4, or combinations thereof. In some embodiments, PTFE as a binder is added to the powder mixture prior to grinding. The ground iron-containing powder mixture is used as the negative electrode in the assembled battery. In some embodiments, the mixed positive electrode powder is coated on both sides of the current collector, with a powder thickness of 200 micrometers on each side of the current collector. In some embodiments, the mixed negative electrode powder is coated on both sides of the current collector, with a powder thickness of 200 micrometers on each side. According to various embodiments, the current collector is nickel-plated carbon steel with a nickel coating less than 10 micrometers thick. In some embodiments, the current collector is 100 micrometers thick. In some embodiments, a hydrophilic polypropylene battery separator, such as Celgard 3501, is placed between the positive and negative electrodes. In some embodiments, the electrode porosity is 20% to 30%. In some embodiments, the active area of ​​the electrode is 1000 cm². 2 In some implementations, the battery-grade energy density is higher than 50 Wh / L. In some implementations, the battery-grade energy density is 55 Wh / L. In some implementations, the battery-grade energy cost is $100 / kWh.

[0141] In one non-limiting example, the described manganese-containing positive electrode can be connected to an iron-containing negative electrode as a static electrochemical energy storage system with a target duration of 24 hours. In some embodiments, the Fe-MnO2 battery pack has a target duration of 12 to 36 hours as an energy storage system. In another non-limiting example, the described manganese-containing positive electrode can be connected to an iron-containing negative electrode as a black starter with a target duration of 30 minutes. In some embodiments, the Fe-MnO2 battery pack as a black starter has a target duration of 1 to 60 minutes. In another non-limiting example, the described manganese-containing electrode can be included as an auxiliary electrode in a large-scale, long-duration energy storage system using iron-air chemicals. In this embodiment, the manganese-containing electrode as a black starter is placed on the positive electrode side of the iron-air battery pack. In this embodiment, the manganese-containing auxiliary electrode stops discharging when the oxygen reduction reaction occurs at the main positive electrode. In this embodiment, during the regular charging process of the iron-air battery pack, the manganese-containing auxiliary electrode is charged before or simultaneously with the oxygen evolution reaction occurring at the main positive electrode.

[0142] In some embodiments, the electrolyte is a near-neutral aqueous solution with a pH of 4 to 10. In some embodiments, the electrolyte is a sulfate or chloride solution dissolved in water, such as Li₂SO₄, Na₂SO₄, K₂SO₄, CuSO₄, NaCl, LiCl, KCl, CuCl₂, or combinations thereof.

[0143] Various embodiments include a battery pack comprising: a first electrode containing manganese oxide; an electrolyte; and a second electrode containing direct reduced iron. In some embodiments, the electrolyte is a liquid electrolyte. In some embodiments, the electrolyte comprises an alkali metal hydroxide, including lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), cesium hydroxide (CsOH), or mixtures thereof. In some embodiments, the electrolyte comprises an alkali metal sulfide or polysulfide, including lithium sulfide (Li₂S) or lithium polysulfide (Li₂S₃). x (x=2 to 6), sodium sulfide (Na2S) or sodium polysulfide (Na2S) x (x=2 to 6), potassium sulfide (K2S) or potassium polysulfide (K2S) x (x=2 to 6), cesium sulfide (Cs₂S) or cesium polysulfide (Cs₂S) xThe first electrode comprises manganese oxides (x=2 to 6), or mixtures thereof. In some embodiments, the second electrode is pelletized and includes a multi-peak distribution. In some embodiments, the manganese oxide comprises manganese(IV) oxide (MnO2), manganese(III) oxide (Mn2O3), manganese(III) hydroxide oxide (MnOOH), manganese(II) oxide (MnO), manganese(II) hydroxide (Mn(OH)2), or mixtures thereof. In some embodiments, the second electrode further comprises iron oxides, hydroxides, sulfides, or mixtures thereof. In some embodiments, the second electrode further comprises one or more second phases, including silicon dioxide (SiO2) or silicates, calcium oxide (CaO), magnesium oxide (MgO), or mixtures thereof. In some embodiments, the second electrode further comprises an inert conductive matrix comprising carbon black, activated carbon, graphite powder, carbon steel mesh, stainless steel mesh, steel wool, nickel-plated carbon steel mesh, nickel-plated stainless steel mesh, nickel-plated steel wool, or mixtures thereof. In some embodiments, the second electrode further comprises one or more hydrogen evolution reaction inhibitors. In some embodiments, the first electrode has a diameter of less than about 50 μm. 2 The specific surface area is approximately 1 m² / g. In some embodiments, the first electrode has a specific surface area of ​​less than approximately 1 m² / g. 2 The specific surface area is approximately 5 m² / g. In some embodiments, the second electrode has a specific surface area of ​​less than approximately 5 m² / g. 2 The specific surface area is approximately 1 m² / g. In some embodiments, the second electrode has a specific surface area of ​​less than approximately 1 m² / g. 2The specific surface area is / g. In some embodiments, the first electrode includes a binder comprising polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polypropylene (PP), polyethylene (PE), fluorinated ethylene propylene (FEP), polyacrylonitrile, styrene-butadiene rubber, carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (Na-CMC), polyvinyl alcohol (PVA), polypyrrole (PPy), or combinations thereof. In some embodiments, the first electrode includes an additive comprising bismuth(III) oxide (Bi₂O₃), bismuth(III) sulfide (Bi₂S₃), barium oxide (BaO), barium sulfate (BaSO₄), barium hydroxide (Ba(OH)₂), calcium oxide (CaO), calcium sulfate (CaSO₄), calcium hydroxide (Ca(OH)₂), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)₂), carbon nanotubes, carbon nanofibers, graphene, nitrogen-doped carbon nanotubes, nitrogen-doped carbon nanofibers, nitrogen-doped graphene, or combinations thereof. In some embodiments, a separating material is used between the first electrode and the second electrode. In some embodiments, the battery pack stack may include multiple battery packs as described above. In some embodiments, the battery pack stack may include a current collector connecting two or more electrochemical repeating units of the same polarity. In some embodiments, the battery pack stack may include a bipolar current collector connecting two or more electrochemical repeating units of different polarities.

[0144] Various embodiments may provide a method of manufacturing a battery pack, including: providing a first electrode comprising manganese oxide; providing a second electrode comprising direct reduced iron; and providing an electrolyte located between the first and second electrodes. In some embodiments, the electrolyte comprises a liquid electrolyte.

[0145] Without being limited to any particular theory or model of the reactivity of the iron electrode, possible schemes for the oxidation of the iron electrode in an alkaline electrolyte can be carried out according to the following two reaction steps, reaction 1 and reaction 2 below. Additional or different reaction products are possible (one of which is described in reaction 3 below), but the volume change characteristic of the reaction relative to metallic iron is universal for any oxidation product. Reaction 1, reaction 2, and reaction 3 are as follows: as well as Table 4 presents some key physical properties of the selected iron-containing materials, which can be used as negative electrode active materials in alkaline iron-based electrochemical cells (including battery packs and metal-air battery packs) (e.g., in the aforementioned negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, and negative electrode 458). The Pilling-Bedworth ratio, the ratio of the volume of the basic unit of a metal oxide to the volume of the basic unit of the corresponding metal (from which the oxide is produced), is a measure of the net volume change in a one-step reaction. Table 4 shows the calculated Pilling-Bedworth ratios for the transformation from iron metal to a specific iron-containing phase. The theoretical specific capacity is calculated based on the mass of iron. Table 4 Electrochemical cells using iron-based materials as the negative electrode (e.g., cells 100, 131, 230, 240, 250, 260, 300, 410, and 450 discussed above) can be assembled in a charging state, a discharging state, or an intermediate charging state. For example, using metallic iron as the active material in the assembled cell will initiate the charging state. In contrast, starting with hematite (Fe₂O₃) in the assembled cell will initiate the discharging state. Starting with Fe(OH)₂ in the assembled cell will initiate the intermediate charging state.

[0146] This invention describes materials, systems, and methods using various iron-containing materials, starting from a discharged or partially discharged state in an alkaline electrochemical cell such as Fe-Ni, Fe-MnO2, or Fe-air battery pack. In some embodiments of the invention, the iron-containing materials include certain iron-bearing minerals, also known as iron ores. In some cases, manganese-rich ores are referred to as "manganese ore." Table 5 describes non-limiting examples of various common mineral forms of iron-containing materials according to their mineral names, common corresponding chemical formulas, and typical weight percentages of iron. Iron ores may contain one or more such iron-bearing minerals, as well as any other naturally occurring mineral forms containing iron. Table 5 Iron ore may contain iron-bearing materials, such as (but not limited to) the mineral forms described in Table 5, as well as impurity phases, such as SiO2, Al2O3, TiO2, CaO, MgO, and other impurity phases. These impurity phases are collectively referred to in the art as “gangue” phases. Iron ore is mined and, as needed, concentrated or enriched to produce a high Fe content (typically >60% Fe by weight) for subsequent processing, including but not limited to blast furnace reduction, direct reduction processes (e.g., shaft furnace reduction, rotary hearth, linear hearth, rotary kiln, or fluidized bed reduction). The main processing or classification stages prior to reduction include: (1) mining the ore. The ore is typically classified by its iron content, sometimes as low, medium, or high grade; (2) direct transport of the ore; (3) enriched ore (“iron concentrate” or “pellet feed”); and (4) pelletizing (agglomeration process). Common outputs may be referred to herein as direct reduction grade (“DR grade”) and blast furnace grade (“BR grade”). Here, the term "ore" can be used to refer to the material that has been mined. The term "iron concentrate" can be used to refer to processed ore that has had gangue phases preferentially removed to increase the weight fraction of iron. These iron concentrates are typically (but not always) in powder or slurry form. Typical compositions of various iron ores and iron concentrates are shown in Table 6. Table 6 Ore sources are sometimes named according to their composition (e.g., "hematite" or "magnetite"), and in other cases, they are named according to specific geological formations. For example, in the United States, a common source of iron ore is called "iron flint," a relatively low-grade iron ore that includes mineral forms of magnetite, hematite, flint, siderite, iron serpentine, iron talc, and black chlorite. Iron flint is typically mined with an iron content of 20-35% Fe by weight. Due to its low iron content, iron flint is often enriched (by removing gangue phases to increase the iron content). Iron flint is enriched by crushing and grinding the ore into a fine powder, which is then separated by flotation or magnetic separation to form an "iron concentrate" in which the weight percentage of iron is higher than that of the original iron flint ore. This powder is then mixed with a binder (e.g., bentonite) and agglomerated to form pellets. Depending on the residual gangue content in the pellets, they can be classified as blast furnace grade (BF grade) or direct reduction grade (DR grade). Table 7 describes the typical composition of DR-grade pellets. Table 7 Table 8 describes the typical composition of BF grade pellets. Table 8.

[0147] Higher quality iron ore may have a higher Fe content during mining and does not require enrichment. These are known as "direct transport ore".

[0148] One aspect of the present invention is the use of iron ore materials in electrochemical batteries, such as batteries 100, 131, 230, 240, 250, 260, 300, 410, and 450. Another aspect of the present invention is the use of iron concentrate as an active material in electrochemical batteries, such as batteries 100, 131, 230, 240, 250, 260, 300, 410, and 450. Another aspect of the present invention is the use of BF-grade pellets in electrochemical batteries, such as batteries 100, 131, 230, 240, 250, 260, 300, 410, and 450. Another aspect of the present invention is the use of DR-grade pellets in electrochemical batteries, such as batteries 100, 131, 230, 240, 250, 260, 300, 410, and 450. Another aspect of the invention is the use of combinations and variations of iron ore, iron concentrate, BF-grade pellets, and DR-grade pellets in electrochemical cells, such as cells 100, 131, 230, 240, 250, 260, 300, 410, 450, etc. According to this aspect of the invention, iron ore is advantageously used as a redox-active electrode in electrochemical cells comprising primary (also called "disposable") or secondary (also called "rechargeable") type rechargeable batteries.

[0149] In another aspect of the invention, iron ore materials can be processed in a manner that preferentially promotes the presence of an iron-containing phase, which optimizes performance in electrochemical devices. Performance parameters that can be improved in this way include, but are not limited to, specific capacity (measured in mAh / g), kinetic overpotential, coulombic efficiency, cycle life, and calendar life. As an example, the iron ore pellets (BF and DR grades) described above are typically processed in a manner that promotes the presence of hematite, as such pellets are primarily used in steelmaking. Iron ore materials are enriched as previously described to produce iron concentrates containing both magnetite and hematite. After being mixed with a binder and agglomerated to form pellets, these pellets undergo a heat treatment step called “hardening,” which is used to: 1) sinter the pellets to improve mechanical strength; and 2) convert magnetite to hematite. The time, temperature, and atmosphere are selected to promote this phase transformation, depending on the process optimized for the application of these pellets in steelmaking (e.g., in blast furnaces or direct reduction processes). However, hematite has a much lower electrical conductivity than magnetite, and hematite appears to be more difficult to electrochemically reduce than magnetite. In one embodiment of the invention, these heat treatment steps are omitted, thereby allowing for a larger fraction of magnetite; such unhardened pellets may be referred to in the art as “green pellets” or “green blanks.” In another embodiment, processing conditions are selected to sinter the pellets, but in a manner that maximizes the phase fraction of magnetite. In some embodiments, the hardening step involves exposure to oxygen to oxidize the magnetite to hematite. The partial pressure of the oxidation step can be controlled to remain in the magnetite field rather than entering the hematite field. In some embodiments, time and temperature are selected to promote sintering, but to minimize the coarsening of the iron ore particles, such that the primary particle size remains fine. In some embodiments, the primary particle size of the magnetite is less than 500 micrometers (micrometer = 10 μm). -6 (m), or less than 100 micrometers, or less than 50 micrometers.

[0150] In some embodiments, the iron ore is subsequently formed into electrodes via thermochemical reduction. In some embodiments, the reduction can proceed to the point of almost completely reducing the iron oxides to metallic iron. The near-complete reduction of iron oxides to metallic iron is the goal of many industrial thermochemical reduction processes for iron.

[0151] In other embodiments, iron ore is not completely reduced to metallic iron. There are several reasons why such incompletely reduced products might be particularly useful for iron-based battery packs. First, several oxide phases produced during iron reduction are semiconducting and can therefore be usefully used as electronic conductors in iron electrode materials. For example, magnetite has considerable conductivity near room temperature. While aragonite is less conductive than magnetite, it still has high conductivity relative to most oxides. In some embodiments, the semiconducting properties of aragonite and magnetite can be utilized to form battery pack electrodes, which may be complexes with metallic iron. Partially reduced products may also have higher electrochemical activity. The inventors have observed that aragonite may be more electrochemically active than metallic iron in certain situations. Because aragonite has a higher oxidation state than metallic iron, its thermochemical reduction may be less costly. Therefore, as a component of battery pack electrodes, aragonite may be cheaper and perform better than metallic iron. On the other hand, the cathode of an alkaline iron-based battery pack can be produced from hard pellets containing hematite, which is traditionally supplied for direct reduction or blast furnace processes. Pellets can be reduced in a vertical shaft furnace using a suitable mixture of hydrocarbons and other reducing gases known in the field of direct reduced iron. The reduction process can be terminated when up to 95% metallization is achieved (metallization is a term used in the field of direct reduced iron to describe the fraction of iron atoms that are entirely metallic in their oxidation state). In some cases, lower metallization may be preferred, with metallization as low as 0% yielding significant amounts of magnetite and aragonite as alternative input materials for the battery pack. The resulting partially reduced pellets, lumps, fragments, or other particles can be packed into a bed of particles for use as an iron electrode material. The electrode material can consist entirely of iron oxides and primarily comprises a mixture of magnetite and aragonite.

[0152] The iron ore materials constituting the electrodes, devices, and systems of the present invention can have a wide range of purities and may actually have relatively high impurity concentrations compared to iron-containing materials synthesized from purified iron sources. Table 9 lists several common impurities in iron ore and their typical concentration ranges (in weight percentage). In some aspects of the invention, the iron ore materials may have at least a minimum amount of such naturally occurring impurities, either alone or in combination. Table 9 The non-limiting advantages of using iron ore in such applications include the low cost and wide availability of the ore. The use of such ore does not preclude the selection of ore for specific physical and chemical properties, nor does it preclude further processing of the ore (e.g., in the cases of iron concentrate, BF-grade pellets, and DR-grade pellets).

[0153] In some implementations, the presence of certain impurity phases is preferentially increased to obtain additional performance benefits in electrochemical cells using alkaline electrolytes. For example, an alkaline electrolyte reacts with carbon dioxide (CO2) to form carbonate anions (CO3-). 2- This is a well-known degradation mechanism of such electrolytes in the art. When CaO comes into contact with water, it reacts according to the reaction CaO + H₂O -> Ca(OH)₂ to form Ca(OH)₂. It is known that Ca(OH)₂ reacts with CO₃²⁻. 2- The reaction captures carbonate ions as CaCO3 and releases hydroxide ions (OH-). - Therefore, the presence of CaO in the iron material serves as a sink for carbonate ions, which are washed away from the alkaline electrolyte. A similar reaction can be carried out using MgO and BaO. In some embodiments, the mass fraction of CaO is chosen to be as high as possible to provide maximum carbonate ion capture capacity.

[0154] In various embodiments, the electrodes and devices of the present invention may contain other materials besides iron ore. The electrodes of the present invention may comprise a composite that may include the iron ore or an ore mixed with DRI pellets and / or smaller metal particles such as fine metal powder or metal scrap. For example, as... Figure 5 As shown, the negative electrode 502 may include spherical pellets 505 containing flint and a composition of smaller metal particles 510 containing conductive material. The negative electrode 502 may be an example of the aforementioned negative electrodes (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, and negative electrode 458). Combining low-cost flint pellets, which serve as the bulk iron raw material for pellet 505, with the conductive additive 510 can reduce the cost of forming conductive electrodes during battery assembly. As another example, the composite metal electrode structure may include a mixture of iron ore particles of different sizes (e.g., larger iron ore pellets (e.g., flint, DRI, sponge iron, atomized iron, etc.) and smaller metal particle compositions, such as fine metal powders or fragments (e.g., fine powders or fragments of DRI, flint, sponge iron, atomized iron, etc.).

[0155] The iron ore used for the purposes of this article may be selected, or further processed or treated, to improve certain physical properties. These properties include, but are not limited to, improved electrical conductivity, improved surface or interfacial reaction kinetics, and regulation of volume changes caused by electrochemical conversion during cycling, characterized at least in part by the Pilling-Bedworth ratios shown in Table 4.

[0156] In some embodiments, the conductivity of the metal electrode is increased by adding conductive fibers, wires, meshes, or sheets to the pellets, thereby dispersing the conductive material between the individual pellets. In one embodiment, the conductive fibers comprise copper or iron. In another embodiment, the fibers are chopped fibers. In yet another embodiment, the fibers are iron, and their diameter is chosen to be greater than the thickness of iron that is reversibly oxidized and reduced during battery discharge and charging. Thus, the interior of the fiber retains the same metallic iron as the electrode, including the fiber's participation in the battery's electrochemical reactions, maintaining a metallic conductive path within the electrode. In another embodiment, the fibers are sintered to iron ore during electrode fabrication.

[0157] In other embodiments, a conductive additive is added to the iron-containing mineral form. Without being bound by any particular scientific explanation, the conductive additive promotes the electrochemical reactions of iron by providing an electronic conduction pathway for electrons to or from redox-active iron sites. The conductive additive can be virtually any conductive material, including but not limited to metals, metal carbides, metal nitrides, metal oxides, and allotropes of carbon, including carbon black, high-structure carbon black, graphitic carbon, carbon fibers, carbon microfibers, vapor-grown carbon fiber 65 (VGCF), fullerene carbon including "buckleballs," carbon nanotubes (CNTs), multi-walled carbon nanotubes (MWNTs), single-walled carbon nanotubes (SWNTs), graphene sheets or aggregates of graphene sheets, and materials containing fullerene fragments. Electron-conducting polymers include, but are not limited to, conductive polymers based on polyaniline or polyacetylene, or poly(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole, polythiophene, poly(p-phenylene), poly(triphenylene), polyazine, polyfluorene, polynaphthalene, polyanthracene, polyfuran, polycarbazole, tetrathiofulvalene-substituted polystyrene, ferrocene-substituted polyethylene, carbazole-substituted polyethylene, polyoxyphenazine, poly(heterophenylene), or poly(heterophenylene).

[0158] In some embodiments, the conductive additive comprises an ore or a metal salt. In some embodiments, the ore or metal salt is thermochemically or electrochemically reduced to a form with higher electronic conductivity. In some embodiments, the form with higher electronic conductivity comprises a metal salt, such as a metal oxide, or a metal. In some embodiments, the ore or metal salt that produces the conductive additive is selected to have a lower negative formation free energy (i.e., more inert) than the iron ore or mineral or salt constituting the electrode, and can be preferentially reduced than the iron ore or mineral or salt. As a non-limiting example, the metal constituting the conductive additive can be produced by thermochemically reducing a metal from its starting ore or mineral form to its metallic form. In some embodiments, the conductive additive comprises Ni, Co, Cu, Zn, Sn, brass, bronze, or Ag.

[0159] In one specific embodiment, the conductive additive comprises copper, and is prepared by reducing the copper ore to metallic copper by adding copper ore to iron ore and subsequently heating the mixture at a certain temperature in a reducing gas environment. Optionally, the reducing environment may include hydrogen. In some embodiments, copper wets the surface of the iron ore and penetrates or partially penetrates the iron ore. Optionally, the electrode may be heat-treated below the melting point of copper to allow solid copper to subsequently dewet the iron ore.

[0160] In another such embodiment, copper metal and iron ore, or copper ore and iron ore, are heat-treated and co-sintered to produce a composite electrode with high electronic conductivity provided by the metallic copper component.

[0161] In some embodiments, the conductive additive and iron ore material are arranged in physical proximity and size scale to provide improved transfer of electrons and ions to the redox-active microregions of the electrode. In some embodiments, the conductive additive can form a continuous permeation network through the electrode. In other embodiments, the iron ore is in particulate form, and the conductive additive substantially coats the surface of the particulates. In some embodiments, the conductive additive preferably constitutes less than 20% by volume of the total volume of the iron ore and the conductive additive, more preferably less than 10% by volume, and more preferably less than 5% by volume.

[0162] Even with improved conductivity through the addition of conductive additives, other factors, such as the particle size of the iron ore, can affect the rate of electrochemical reactions and, consequently, the charging and / or discharging rates and efficiency of the electrodes. While finer particles may have a higher electrochemical reaction surface area and a smaller cross-sectional size for electron or ion transport, thus increasing the rate of electrochemical reactions, they may also be more susceptible to passivation (i.e., electrical insulation) surface layers that may form during use, and may be more expensive to produce from mined materials. For the purposes of this discussion, primary particle size is considered to be the size of solid particles that generally do not have internal pores, while secondary particle size is the size of the aggregate of bound primary particles. Thus, pellets of the iron ore material mentioned above constitute secondary particles. In some embodiments, the primary or secondary iron ore particles constituting the electrodes, devices, and systems of the present invention have an average particle size corresponding to about -325 mesh (less than about 44 micrometers). In other embodiments, the iron ore particles have an average primary particle size of less than about 10 micrometers. In some embodiments, the iron ore particles have a primary particle size greater than about 10 micrometers, preferably greater than about 15 micrometers, and even more preferably greater than about 20 micrometers.

[0163] Typically, the secondary particles (including pellets of iron ore) constituting the iron ore electrode of the present invention may have significant porosity for at least two reasons. Porosity allows the electrode secondary particles or pellets to be permeated by the electrolyte of the electrochemical cell. The porosity also accommodates volume changes in the iron ore material as it cycles between a discharge (oxidation) state and a charge (reduction) state. As shown in Table 4, the Pilling-Bedworth ratio of the iron-containing mineral can be 2 to 5 times. Therefore, the porosity of the electrode comprising conductive additives and iron ore material, excluding volume changes due to subsequent electrochemical operations of the battery pack, is preferably 10% to 80% by volume, more preferably 20% to 70%, and even more preferably 30% to 50%. In some embodiments, at least 70% of the porosity is filled with a liquid electrolyte, preferably more than 80%, more preferably more than 90%.

[0164] In some embodiments, the conductive additive forms a porous structure with cavities within which iron ore particles reside, thereby allowing free volume around the iron ore particles to allow for expansion and contraction, while the iron ore particles maintain an electrical connection to the continuous structure of the conductive additive. In some such structures, the cavities in the porous conductive structure are equiaxed. In other embodiments, the cavities are non-equiaxed and may extend in one dimension in the form of tubes, or in two dimensions, to form plate-like cavities with various aspect ratios.

[0165] In some embodiments, the electrode of the present invention is a composite material comprising iron ore and an additive material that provides elastic flexibility to the electrode, thereby allowing the redox-active material to repeatedly expand and contract during discharge and charging. In some embodiments, the additive material is a polymer or polymer binder. In some cases, the conductive additive is also the flexible material. Examples of polymer binders include: sodium carboxymethyl cellulose (Na-CMC), lithium carboxymethyl cellulose (Li-CMC), potassium carboxymethyl cellulose (K-CMC), polyacrylic acid (PAA), polyacrylamide, polyether ether ketone (SPEEK), and sulfonated polyether ether ketone (SPEEK). In some embodiments, the polymer binder is also electronically conductive; examples of such polymers include trans-polyacetylene, polythiopene, polypyrrole, poly(p-phenylene), polyaniline, poly(p-phenylenevinylene), poly(3,4-ethylenedioxythiophene), and polysulfonated styrene (PEDOT:PSS).

[0166] Various embodiments may include a battery pack comprising: a first electrode; an electrolyte; and a second electrode, wherein one or both of the first and second electrodes contain iron. In some embodiments, the iron is in the form of iron ore. In some embodiments, the iron is in the form of iron concentrate. In some embodiments, the iron is in the form of at least one form selected from the group consisting of: pellets, BF-grade pellets, DR-grade pellets, hematite, magnetite, chalcedony, pseudomorphous hematite, goethite, limonite, siderite, pyrite, ilmenite, or spinel manganese ferrite. In some embodiments, the iron also contains at least 0.1% SiO2 by mass. In some embodiments, the iron also contains at least 0.25% SiO2 by mass. In some embodiments, the iron also contains at least 0.5% SiO2 by mass. In some embodiments, the iron also contains at least 0.1% CaO by mass. In some embodiments, the iron also contains at least 0.25% CaO by mass. In some implementations, the iron also contains at least 0.5% CaO by mass.

[0167] Electrochemical cells, such as battery packs, store electrochemical energy by using an electrochemical potential difference that creates a voltage difference between the positive and negative electrodes. This voltage difference generates a current if the electrodes are connected via conductive elements. In a battery pack, the negative and positive electrodes are connected in parallel via external and internal resistive elements. Typically, the external element conducts electrons, and the internal element (electrolyte) conducts ions. Because a charge imbalance cannot be maintained between the negative and positive electrodes, these two flows must provide ions and electrons at the same rate. In operation, the electron flow can be used to drive external devices. Rechargeable battery packs can be recharged by applying an opposite voltage difference, which drives the electron and ion flows in the opposite direction to the discharge flow during use.

[0168] Typically, especially for long-duration storage applications, low-cost and easy-to-manufacture electrodes and electrode materials are required. Manufacturing and / or construction processes can be evaluated and selected based on a variety of criteria, including capital costs, material production volume, operating costs, number of unit operations, number of material transfers, number of material handling steps, required energy input, amount of waste and / or byproducts generated, etc.

[0169] Various embodiments of the use of metal agglomerates as materials in battery packs (or batteries) (e.g., in batteries 100, 131, 230, 240, 260, 300, 410, 450), as components of battery packs (or batteries) such as electrodes (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502), and combinations and variations thereof are discussed. In various embodiments, the iron material may be iron powder, such as gas-atomized or water-atomized powder, or sponge iron powder. In various embodiments, the iron agglomerates may be in the form of pellets, which may be spherical or substantially spherical. In various embodiments, the agglomerates may be porous, containing open and / or closed internal pores. In various embodiments, the agglomerates may contain material that has been further processed by hot or cold pressing. The various embodiments described herein, including embodiments using agglomerated materials as electrode materials, may have one, more than one, or all of the material properties described in Table 10 below. In this specification, including Table 10, unless otherwise expressly stated, the following terms have the following meanings: "specific surface area" refers to the total surface area of ​​the material per unit mass, including the surface area of ​​pores in the porous structure; "total Fe (wt%)" refers to the percentage of total iron mass to the total mass of the agglomerate; "metallic Fe (wt%)" refers to Fe... 0 The percentage of iron in its current state relative to the total mass of the aggregate. Table 10 Specific surface area is preferably determined by the Brunauer-Emmett-Teller adsorption method (“BET”), more preferably by the BET method described in ISO 9277 (the entire disclosure of which is incorporated herein by reference); it is recognized that other tests (e.g., methylene blue (MB) staining, ethylene glycol monoethyl ether (EGME) adsorption, electrokinetic analysis of complex ion adsorption, and protein retention (PR) methods) can be used to provide results related to BET results.

[0170] Skeletal density is preferably determined by a helium (He) hydrometer, more preferably as described in ISO 12154 (the entire disclosure of which is incorporated herein by reference); it is recognized that other tests may be used to provide results that can be correlated with the helium hydrometer results. Skeletal density may also be referred to in the art as “true density” or “actual density”.

[0171] Apparent density is preferably determined by immersion in water, more preferably as described in ISO 15968 (the entire disclosure of which is incorporated herein by reference); it is recognized that other tests can be used to provide results that can be correlated with the helium hydrometer results. Porosity can be defined as the ratio of apparent density to actual density: #Total Fe (wt%) is preferably determined by dichromate titration, more preferably as described in ASTM E246-10 (the entire disclosure of which is incorporated herein by reference); it is recognized that other tests (e.g., titration after reduction with tin(II) chloride, titration after reduction with titanium(III) chloride, inductively coupled plasma (ICP) spectrometry) can be used to provide results that are relevant to dichromate titration.

[0172] ##Metallic Fe (wt%) is preferably determined by ferric chloride (III) titration, more preferably as described in ISO 16878 (the entire disclosure of which is incorporated herein by reference); it is recognized that other tests (e.g., bromine-methanol titration) can be used to provide results related to ferric chloride (III) titration.

[0173] In the implementation plan, the specific surface area of ​​the aggregates can be from approximately 0.05 m². 2 / g to approximately 35m 2 / g, from approximately 0.1m 2 / g to approximately 5m 2 / g, from approximately 0.5m 2 / g to approximately 10m 2 / g, from approximately 0.2m 2 / g to approximately 5m 2 / g, from approximately 1m 2 / g to approximately 5m 2 / g, from approximately 1m 2 / g to approximately 20m 2 / g, greater than approximately 1m 2 / g, greater than approximately 2m 2 / g, less than approximately 5m 2 / g, less than approximately 15m 2 / g, less than approximately 20m 2 / g, and their combinations and variations, as well as larger and smaller values.

[0174] The filling of agglomerates creates macropores, such as openings, spaces, channels, or voids, between the individual agglomerates. These macropores facilitate ion transport through the electrode, which in some embodiments has a minimal size compared to some other types of battery pack electrodes, yet is still very thick, measuring several centimeters. The micropores within the agglomerates allow the high surface area active material of the agglomerates to contact the electrolyte, thereby achieving high utilization of the active material. This electrode structure makes it particularly suitable for improving the rate performance of extremely thick electrodes for static, long-duration energy storage, where thick electrodes may be required to achieve extremely high areal capacity.

[0175] In various embodiments, the bed of conductive microporous aggregates comprises electrodes in an energy storage system. In some embodiments, the aggregates comprise aggregates of direct reduced iron (DRI). The filling of the aggregates creates macropores between the individual aggregates. These macropores facilitate ion transport through the electrodes, which in some embodiments have a minimal size compared to some other types of battery pack electrodes, yet are still very thick, measuring several centimeters. Compared to micropores within the aggregates, macropores can form pore spaces with low curvature. The micropores within the aggregates allow the high surface area active material of the aggregates to contact the electrolyte, thereby achieving high utilization of the active material. This electrode structure makes it particularly suitable for improving the rate performance of extremely thick electrodes for static, long-duration energy storage, where thick electrodes may be required to achieve extremely high areal capacity.

[0176] Aggregates used in these embodiments, particularly those for electrodes in long-duration energy storage systems, can be of any volumetric shape, such as spheres, disks, pucks, beads, sheets, pellets, rings, lenses, discs, panels, cones, truncated cones, square blocks, rectangular blocks, trusses, corners, channels, hollow sealed chambers, hollow spheres, blocks, sheets, membranes, particles, beams, rods, corners, plates, cylinders, columns, fibers, short fibers, tubes, cups, pipes, combinations and multiples of these, and other more complex shapes. Aggregates in electrodes can be of the same shape or different shapes. Aggregates in an electrode that is one of multiple electrodes in a long-duration energy storage system can be the same as or different from those in other electrodes in the same energy storage system.

[0177] Unless otherwise explicitly stated, the size of an agglomerate refers to the maximum cross-sectional distance of the agglomerate, such as the diameter of a sphere. Agglomerates can be the same or different in size. It is understood that the shape and size of the agglomerates, and generally to a lesser extent, the shape and size of the container or shell containing the agglomerates, determine the nature and size of the macropores in the electrode. Agglomerates can have sizes ranging from about 0.1 mm to about 10 cm, about 5 mm to about 100 mm, 10 mm to about 50 mm, about 20 mm, about 25 mm, about 30 mm, greater than 0.1 mm, greater than 1 mm, greater than 5 mm, greater than 10 mm, and greater than 25 mm, as well as combinations and variations thereof.

[0178] In the implementation scheme, the aggregates configured in the electrode can give the electrode a volume density of approximately 3 g / cm³. 3 Approximately 6.5 g / cm 3 Approximately 0.1 g / cm³ 3 Approximately 5.5 g / cm 3 Approximately 2.3 g / cm³ 3 Approximately 3.5 g / cm 3 3.2g / cm 3 Approximately 4.9 g / cm³ 3 Greater than approximately 0.5 g / cm 3 Greater than approximately 1 g / cm 3 Greater than approximately 2 g / cm 3 Greater than approximately 3 g / cm 3 , as well as their combinations and variations, and larger and smaller values.

[0179] In various embodiments, additives that facilitate electrochemical cycling, such as hydrogen evolution reaction (HER) inhibitors, can be added to the bed in solid form, for example, as powder or as solid pellets.

[0180] In some implementations, the metal electrode can have a low initial specific surface area (e.g., less than about 5 m²). 2 / g and preferably less than about 1 m 2 / g). Such electrodes often exhibit low self-discharge rates in low-rate, long-duration energy storage systems. An example of a low specific surface area metal electrode is a bed of aggregates. In many typical modern electrochemical cells, such as lithium-ion or nickel-metal hydride battery packs, high specific surface areas are required to improve high-rate performance (i.e., high power). In long-duration systems, the requirements for rate performance are significantly reduced, thus low specific surface area electrodes can meet the target rate performance requirements while minimizing the self-discharge rate.

[0181] In another embodiment, desired impurities or additives are incorporated into the agglomerates. When these impurities are solids, they can be added by ball milling (e.g., using a planetary ball mill or similar equipment) with powdered additives and metal powders, the agglomerates acting as their own grinding media. In this way, the powdered additives are mechanically introduced into the pores or surfaces of the agglomerates. The agglomerates can also be coated with beneficial additives, for example, by rolling or immersion in a slurry containing the additives. These desired impurities can include alkali metal sulfides. Alkali metal sulfide salts have been shown to significantly improve the utilization of active materials in Fe anodes. Just as soluble alkali metal sulfides can be added to the electrolyte, insoluble alkali metal sulfides can also be added to the agglomerates, for example, by the methods described above.

[0182] In various embodiments, the specific surface area of ​​the aggregates is increased by 3 times or more, preferably 5 times or more, as measured by techniques such as the Brunauer-Emmett-Teller gas adsorption method. In some embodiments, this increase in surface area is achieved by using the aggregates as electrodes in an electrochemical cell and electrochemically reducing them with an applied current.

[0183] The ratio of electrolyte to iron material (e.g., agglomerates) in the battery can be from approximately 0.5 mL. 电解液 1 g 铁材料 Approximately 5 mL 电解液 1 g 铁材料 From approximately 0.6 mL 电解液 1 g 铁材料 Approximately 3 mL 电解液 1 g 铁材料 Approximately 0.6 mL 电解液 1g 铁材料 Approximately 0.7 mL 电解液 1 g 铁材料、 Approximately 0.8 mL 电解液 1 g 铁材料 Approximately 1 mL 电解液 1 g 铁材料 , as well as their combinations and variations, and larger and smaller values.

[0184] A bed of aggregates can be an ideal configuration for iron-based electrodes because it provides an electron conduction pathway through the bed while leaving pores that can be occupied by the electrolyte to facilitate ion transport. In some embodiments, the electrolyte volume to aggregate mass ratio can range from 0.5 mL / g to 20 mL / g, for example, 0.5 mL / g to 5 mL / g, or for example, 0.6 mL / g or 1.0 mL / g. The aggregates typically contact surrounding aggregates through a contact area that is relatively small compared to the surface area of ​​the aggregates; in some cases, this contact can be considered a “point contact.” Small cross-sectional area contacts can restrict current flow, which may result in relatively low conductivity of the aggregate bed as a whole, potentially leading to higher electrode overpotentials and lower battery pack voltage efficiency.

[0185] In some implementations, additives containing molybdate ions are used in alkaline battery packs that include an iron anode. Without being limited to any particular scientific explanation, such additives can help suppress the hydrogen evolution reaction (HER) at the iron electrode and improve the cycle efficiency of the battery pack. The concentration of the additive is selected to suppress HER while still achieving the desired iron charge / discharge process. For example, molybdate ions can be added using molybdate compounds such as KMoO4. In one specific example, the electrolyte contains an additive concentration of 10 mM (mM represents millimoles, 10...). -3 The electrolyte contains molybdate anions at a concentration of 1-100 mM. In other embodiments, the electrolyte contains molybdate anions at a concentration ranging from 1 to 100 mM.

[0186] In some implementations, surfactants are used to control wetting and foaming during operation of the metal-air battery pack. During charging, at least two gas release reactions that lead to bubble formation can occur. One is hydrogen evolution at the metal anode, a parasitic reaction that can result in low coulombic efficiency during battery pack cycling. The other is oxygen evolution reaction, which is essential for the metal-air battery pack to function. Surfactant additives can mitigate the adverse effects associated with both reactions. In the case of HER, hydrophobic surfactant additives can suppress the hydrogen evolution reaction at the metal anode by physically blocking the contact of water (HER reactants) with the metal anode during charging. In the case of ORR, surfactant additives can reduce the electrolyte surface tension and viscosity at the oxygen evolution electrode, thereby generating smaller, more uniform, and controllable bubbles during charging. In a non-limiting example, 1-octylthiol is added to the alkaline electrolyte at a concentration of 10 mM to mitigate these problems.

[0187] In some implementations, corrosion inhibitors used in the ferrous metallurgy field to suppress water corrosion are used as components in battery packs with iron anodes to improve performance. In some implementations, iron agglomerates are used as the anode, and favorable performance characteristics can be achieved by using one or more corrosion inhibitors within a suitable concentration range. In these implementations, principles of corrosion science are used to prevent undesirable side reactions under charging conditions (e.g., hydrogen evolution), mitigate the self-discharge rate during electrochemical hold, and maximize the utilization of iron active materials during discharge. Generally, corrosion inhibitors fall into two categories: interface inhibitors that react with the metal surface at the metal-environment interface to prevent corrosion, and environmental scavengers that remove corrosive elements from the environment surrounding the metal surface to inhibit corrosion. Within a broad range of corrosion inhibitors, appropriate concentrations of inhibitors can be added to electrochemical cells to achieve favorable performance characteristics regarding the efficiency and capacity of the electrochemical cell. For the iron electrode in metal-air battery packs, a suitable class of universal inhibitors is the interface inhibitor between the liquid and the phase. This class includes three main types of interface inhibitors: anodic inhibitors, cathodic inhibitors, and mixed inhibitors. Anodic inhibitors produce a passivation layer that inhibits the anodic metal dissolution reaction. Cathode inhibitors may reduce the rate of the reduction reaction (HER in the case of an iron electrode) or precipitate at the cathode active site to prevent the same reduction reaction. Mixed inhibitors can inhibit corrosion through one or both pathways and include, but are not limited to, molecules that are physically or chemically adsorbed onto the metal surface to form a film at the active site that blocks the reduction reaction. The inhibitors can be added to the base electrolyte at any concentration.

[0188] In various embodiments, the inhibitor that forms a passivation layer on the metal surface is paired with the additive that depassivates the iron surface. At the correct concentration, an optimal balance between corrosion inhibition and utilization of the active material can be achieved. In one specific embodiment, when using direct reduced iron as the negative electrode, 10 mM molybdate anions are used as the passivating agent in an alkaline electrolyte containing 5.5 M potassium hydroxide or sodium hydroxide, while 10 mM divalent sulfide anions are used as the depassivating agent. Specific examples of electrolyte compositions include: 5.5 M KOH + 0.5 M LiOH + 10 mM Na₂S + 10 mM 1-octylthiol; 5.95 M NaOH + 50 mM LiOH + 50 mM Na₂S + 10 mM 1-octylthiol; 5.95 M NaOH + 50 mM LiOH + 50 mM Na₂S + 10 mM 1-octylthiol + 10 mM K₂MoO₄; and 5.95 M NaOH + 50 mM LiOH + 50 mM Na₂S + 10 mM K₂MoO₄. However, the invention is not limited to any specific concentration of the above additives in the electrolyte. For example, the electrolyte may contain one or more of the above additives in a concentration range from about 2 mM to about 200 mM, for example from about 5 mM to about 50 mM or from about 5 mM to about 25 mM.

[0189] For inhibitors of physical adsorption (chemisorption or physisorption), the interaction with the metal surface is usually strongly temperature-dependent.

[0190] In one embodiment, it may be advantageous to use an inhibitor that desorbs from the iron surface at a temperature lower than the normal operating temperature. During charging, the inhibitor forms a film that suppresses hydrogen evolution at the electrode. During discharging, the battery temperature can be raised or lowered to allow the inhibitor to desorb from the metal surface and expose the active material, thereby improving electrode utilization. In subsequent charging, the battery temperature may return to the normal operating temperature to reform the film and suppress HER. This process can be repeated to achieve high charging efficiency and high discharging utilization of the iron electrode. In a non-limiting example, octahitol can be used as an inhibitor that can be physically or chemically adsorbed onto the metal anode (e.g., Fe, Ni). When the electrochemical cell is thermally treated to 60°C, the physically adsorbed octahitol is desorbed, thereby exposing more active sites that can be oxidized during discharge. Subsequently, free octahitol in the electrolyte is physically adsorbed back onto the anode during cooling. At higher temperatures (>60°C), octahitol may chemically adsorb onto the electrode, thereby forming a continuous, uniform film across the entire surface. These chemisorption types can desorb more efficiently at low temperatures (<100℃).

[0191] To enable performance at higher temperatures, organic film-forming inhibitors with oxygen, sulfur, silicon, or nitrogen functional groups can be used to form a continuous chemisorption film on iron particle electrodes to reproduce the depassivation behavior of divalent sulfur ions while resisting decomposition or oxidation.

[0192] In one embodiment, 1 to 10 mM octahitol is added to the electrolyte. During charging, the system is allowed to be heated to temperatures outside of normal operating conditions (e.g., > 50°C) to promote the formation of a more complete and uniform chemisorbed octahitol film on the active sites of the iron particle electrode and to prevent hydrogen evolution at the surface. During discharge, the system is cooled, and some portions of the chemisorbed film desorb from the surface, exposing additional active sites for discharge. The remaining octahitol acts as a depassivator for the electrode, promoting more complete discharge. Figure 6A An exemplary method for promoting such complete discharge is shown. For example, Figure 6A The top of the figure shows electrode 6102 in a discharged state (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502). During discharge, the octyl mercaptan film desorbs from the surface of electrode 6102, creating a potential hydrogen evolution reaction (HER) site 6104. Figure 6A In the next step of the method shown in the middle, 1 to 10 mM octahitol is added to the electrolyte 6103. During charging, the system is allowed to be heated to temperatures outside of normal operating conditions (e.g., >50°C), thereby promoting the formation of a more complete and uniform chemisorbed octahitol film on the active sites of the iron particle electrode 6102, and preventing hydrogen evolution on the surface of electrode 6102 when the octahitol film fills the potential HER sites 6104. During discharge, the system is cooled, and a portion of the chemisorbed film desorbs from the surface, exposing additional active sites, such as HER sites 6104, for discharge. The remaining octahitol acts as a depassivator for electrode 6102, promoting more complete discharge.

[0193] During electrochemical hold, it is desirable to minimize corrosion of the metal electrodes. One type of corrosive medium for ferrous metal electrodes in aqueous electrolytes is dissolved oxygen. During electrochemical hold, dissolved oxygen comes into contact with the ferrous electrode and corrodes the active material, thereby causing the ferrous electrode to discharge.

[0194] In one embodiment, an oxygen scavenger (e.g., pyrogallol, ascorbic acid, 8-hydroxyquinoline, sodium peroxide, hydrogen peroxide) may be added to the electrolyte during electrochemical holding to reduce the concentration of dissolved oxygen in the electrolyte and prevent iron electrode discharge.

[0195] In one embodiment, prior to electrochemical holding, an anolyte inhibitor (e.g., K₂MoO₄) at a concentration of 1 to 10 mM is added to the electrolyte to form a passivation film, preventing the metal surface from contacting the corrosive medium in the electrolyte and thus preventing self-discharge. After electrochemical holding, when the electrode must discharge, corrosive ions (e.g., SO₄²⁻) are added to the electrolyte. 2- CrO4 - NO3 - This exposes the active material, achieving high utilization of the active material and thus reducing self-discharge.

[0196] In some embodiments, other electrolyte additives are incorporated into the electrolyte. Electrolyte additives may be selected from the non-limiting group consisting of: sodium thiosulfate, sodium thiocyanate, polyethylene glycol (PEG) 1000, trimethyl sulfoxide, zincate (by dissolving ZnO in NaOH), hexamethylenetetramine, decanethiol, sodium chloride, sodium permanganate, lead oxide (IV), lead oxide (II), magnesium oxide, sodium chlorate, sodium nitrate, sodium acetate, ferric phosphate, phosphoric acid, sodium phosphate, ammonium sulfate, ammonium thiosulfate, zinc barium white, magnesium sulfate, ferric acetylacetone (III), hydroquinone monomethyl ether, sodium metavanadate, sodium chromate, glutaric acid, dimethyl phthalate, methyl methacrylate, methylpentynol, adipic acid, allyl urea, citric acid, sulfur Malic acid, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, propylene glycol, divinylpropyltrimethoxysilane, aminopropyltrimethoxysilane, dimethyl ethynyl dicarboxylate (DMAD), 1,3-diethylthiourea, N,N'-diethylthiourea, aminomethylpropanol, methylbutynol, amino-modified organosilane, succinic acid, isopropanolamine, phenoxyethanol, dipropylene glycol, benzoic acid, N-(2-aminoethyl)-3-aminopropyl, behenamide, 2-phosphonobutane tricarboxylic acid, mipapyrate (mipa) borate), 3-methacryloyloxypropyltrimethoxysilane, 2-ethylhexanoic acid, isobutanol, tert-butylaminoethyl methacrylate, diisopropanolamine, propylene glycol n-propyl ether, sodium benzotriazole, pentasodium aminotrimethylenephosphonate, sodium cocoyl sarcosinate, dodecyl pyridine chloride, stearic acid trimethylammonium chloride, silachlor, calcium lignite, quaternium-18 chloride, sodium hexametaphosphate, dicyclohexylamine nitrite, lead stearate, calcium dinonylnaphthalenesulfonate, ferrous(II) sulfide, sodium hydrosulfide, pyrite, sodium nitrite, complex alkyl phosphates (e.g., RHODAFAC® RA 600 emulsifier), 4-mercaptobenzoic acid, ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid (EDTA), 1,3-Propanediaminetetraacetic acid (PDTA), NTA, EDDS, DTPA and other aminopolycarboxylic acids (APC), 2-methylbenzenethiophenol, 1-octylthiol, manganese dioxide, manganese oxide (III), manganese oxide (II), manganese hydroxide, manganese hydroxide (II), bismuth sulfide, bismuth oxide, antimony sulfide (III), antimony oxide (III), antimony oxide (V) Bismuth selenide, antimony selenide, selenium sulfide, selenium oxide (IV), propargyl alcohol, 5-hexyn-1-ol, 1-hexyn-3-ol, N-allylthiourea, thiourea, 4-methylcatechol, trans-cinnamaldehyde, iron sulfide (III), calcium nitrate, hydroxylamine, benzotriazole, furfurylamine, quinoline, stannous chloride (II), ascorbic acid, 8-hydroxyquinoline, pyrogallol, tetraethylammonium hydroxide, calcium carbonate, magnesium carbonate, antimony dialkyl dithiophosphate, potassium stannate, sodium stannate, tannic acid, gelatin, saponins, agar, 8-hydroxyquinoline, bismuth stannate, potassium gluconate, lithium molybdenum oxide, potassium molybdenum oxide, hydrogenated light petroleum, heavy rings Alkane petroleum (such as sold as Rustlick® 631), antimony sulfate, antimony acetate, bismuth acetate, hydrogenated heavy naphtha (such as sold as WD-40®), tetramethylammonium hydroxide, sodium antimony tartrate, urea, D-glucose, C6Na2O6, potassium antimony tartrate, hydrazine sulfate, silica gel, triethylamine, potassium antimony trihydrate, sodium hydroxide, 1,3-di-o-tolyl-2-thiourea, 1,2-diethyl-2-thiourea, 1,2-diisopropyl-2-thiourea, N-phenylthiourea, N,N'-diphenylthiourea, sodium L-antimony tartrate, disodium rosinate, sodium selenide, potassium sulfide, and combinations thereof.

[0197] Additional additives include SiO2-containing minerals, which can have a beneficial effect on electrochemical performance due to their absorption of carbonates from the electrolyte or electrode. Additives containing such functional groups can be usefully incorporated into iron electrode materials. While the specific mineralogical characteristics and other factors of the ore can determine the specific SiO2-containing material to be added, examples of such SiO2-containing additives are silica, cristobalite, sodium silicate, calcium silicate, magnesium silicate, and other alkali metal silicates.

[0198] In some embodiments, electrode agglomerates are prepared by agglomerating metal powder, such as iron-containing powder, into approximately spherical agglomerates. In various embodiments, the agglomeration is carried out at room temperature or approximately room temperature, or at ambient temperature or approximately ambient temperature, or at elevated temperatures. In various embodiments, the agglomeration is carried out in a rotary kiln, wherein the powder is simultaneously agglomerated and sintered. In some embodiments, iron powder, such as atomized iron powder, sponge iron powder, iron scrap, mill scale, carbonyl iron powder, electrolytic iron powder, and combinations or variations thereof, is used as a raw material. In various embodiments, the heat treatment process is carried out at temperatures such as about 700°C to about 1200°C, or such as about 800°C to about 1000°C. In various embodiments, the gaseous environment is inert (containing N2 or Ar) or reducing (containing H2, CO2, CO, etc.), or combinations thereof. In various embodiments, the heat treatment process completely or partially sintersulates the powder together to produce agglomerates. In various embodiments, the size of the agglomerates ranges from 1 μm (μm = 10⁻⁶). -6 m) to 1 cm (cm = 10) -2 (m), for example, 10 μm, 100 μm or 1 mm (mm = 10 μm). -3 m).

[0199] In some embodiments, the raw materials are materials known in the art, such as pig iron, granular pig iron, ductile iron, scrap iron and / or scrap steel.

[0200] In various implementations, a large amount of fine iron powder with particles smaller than 44 micrometers (usually written as -325 mesh, because such particles can pass through a 325-mesh sieve) can be used as part of the raw material or constitute the entire raw material.

[0201] In some embodiments, the electrode is fabricated by electrochemical deposition of iron from an aqueous solution. In some embodiments, the deposition solution is acidic, with a pH less than about 4, for example, a pH of about 3, or a pH of about 2. In some embodiments, the solution is near neutral, with a pH of about 4 to about 10, for example, a pH of about 5, a pH of about 7, or a pH of about 9. In some embodiments, the electrolyte contains a salt, such as NaCl, LiCl, or KCl. In some embodiments, the liquid electrolyte is agitated by stirring, shaking, mixing, or turbulence to promote a non-uniform deposition rate and a porous structure. In some embodiments, the liquid electrolyte is sprayed or aspirated to introduce air bubbles into the liquid during the deposition process.

[0202] In some embodiments, iron powder is prepared using electrometallurgical processes for manufacturing porous iron. Starting with molten material, the ferrous metal is sprayed, bubbled, or molded onto a substrate or in a mold to produce a low-cost, high-surface-area iron product. In some embodiments, these powders are subsequently agglomerated using a rotary kiln or other methods and can then be assembled into electrodes. In some embodiments, the powder is directly assembled into electrodes without an intermediate agglomeration process. In some embodiments, a mixture or combination of agglomerated and unagglomerated powders is used in the electrodes. In some embodiments, agglomerated and / or unagglomerated powders produced by electrometallurgical methods are combined with other metals to manufacture electrodes.

[0203] Electrochemically produced metals offer unique opportunities for the production of high surface area materials, especially if the metal is in a liquid state, in which case the resulting liquid product can be cooled by various methods to achieve the desired properties. For example, iron produced by high-temperature electrometallurgy is directly cooled in a high surface area mold, spray-deposited (atomized) into particles, or dispersed in a cooling medium.

[0204] In some embodiments, the metal electrode is prepared directly by an electrometallurgical process, such as the electrolysis of molten oxides. In some embodiments, the porous electrode is manufactured by intentionally drawing or injecting a gas into a molten oxide electrolytic cell. In some embodiments, the gas is an inert gas, such as N2 or Ar.

[0205] In some embodiments, molten metal from an electrometallurgical process is sprayed, bubbled through, or molded onto a substrate or into a mold to produce a low-cost, high-surface-area metal electrode. In some embodiments, the metal is essentially iron.

[0206] In a non-limiting example, iron ore comprising Fe₂O₃, Fe₃O₄, and mixtures thereof is dissolved in an electrolyte containing SiO₂, Al₂O₃, MgO, and CaO in weight percentages of 60 wt%, 20 wt%, 10 wt%, and 10 wt%, respectively. The mixture is heated to a high temperature of approximately 1600°C. Metallic iron is electrochemically reduced from the molten oxide mixture and collected at the cathode. The molten metal is conveyed through pipes and valves to a shot tower, where it is rapidly cooled in a vacuum, producing an average diameter of 50 μm (μm = 10⁻⁶). -6 Fine iron powder (m) was then fed into a rotary calcining furnace operating at 900°C in a nitrogen (N2, 100%) atmosphere to form aggregates with an average diameter of 2 mm, which were then assembled by filling them into metal electrodes.

[0207] In some embodiments, the electrode can be made by the thermochemical reduction of iron oxides. In some embodiments, the reduction can proceed to almost completely reduce the iron oxides to metallic iron. Almost completely reducing iron oxides to metallic iron is the goal of many industrial thermochemical reduction processes for iron. However, the incomplete reduction of many iron oxides to metallic iron makes the products of such incomplete reduction particularly suitable for manufacturing iron battery packs for many potential reasons. First, several oxide phases produced during the reduction of iron are semiconducting and can therefore be effectively used as electronic conductors in iron electrode materials. For example, magnetite has considerable conductivity near room temperature. While wüstite is less conductive than magnetite, it still has high conductivity relative to most oxides. In some embodiments, the semiconducting properties of wüstite and magnetite can be utilized to form battery pack electrodes that may be compositions with metallic iron. Partially reduced products can also have higher electrochemical activity. The inventors have observed that wüstite may be more electrochemically active than metallic iron in certain situations. Due to its higher oxidation state than metallic iron, thermochemically reduced aragonite may be cheaper, thus making it a potentially cheaper and higher-performing component of battery electrode materials. On one hand, the positive electrode of an alkaline iron battery can be produced from hard pellets containing carbon hematite, traditionally supplied for direct reduction or blast furnace processes. These pellets can be reduced in a vertical combustion furnace using a suitable mixture of hydrocarbons and other reducing gases known in the field of direct reduced iron. The reduction process can be terminated when up to 95% metallization is achieved (metallization is a term used in the field of direct reduced iron to describe the fraction of iron atoms that are entirely metallic in their oxidation state). In some cases, lower metallization may be preferred, with metallization as low as 0% yielding significant amounts of magnetite and aragonite as alternative input materials for the battery. The resulting partially reduced pellets, blocks, fragments, or other particles can be packed into a particle bed for use as an iron electrode material. The electrode material can consist entirely of iron oxides and primarily comprises a mixture of magnetite and aragonite.

[0208] In some cases, porous iron electrode materials may experience high resistance when assembled into a bed. Therefore, the performance of iron electrode materials within a battery pack can be improved by reducing the charge transfer resistance between particulate materials and by enhancing current collection from the electrode active materials. This section describes methods for enhancing charge transfer to current collectors within a packed bed.

[0209] The inventors discovered through experiments that the performance of porous iron electrodes can be improved by applying compressive stress to the anode bed during battery cycling. For example, the contact resistance between porous particulate materials can be reduced by more than an order of magnitude by applying a uniaxial compressive stress of 0.01 MPa or greater. Excessive compressive stress can cause localized failure of the electrode material due to material cracking (and thus a potential local reduction in current conduction), densification due to deformation of the porous iron electrode material without cracking (which in turn may lead to a reduction in the pore space available for the formation of discharge products or a reduction in mass transfer through the pore space), or other mechanical failure modes. Applying compressive stress that does not cause material failure but is higher than the stress required to reduce contact resistance can lead to improved performance of the porous iron electrode material during electrochemical cycling. In this case, further increases in compressive stress and different configurations of compressive stress can be used to increase the conductivity of the bed; in some systems, stresses of about 0.1–10 MPa produce enhanced performance. As the applied stress (and therefore the force) increases, the requirements for the mechanical housing capable of successfully applying such stress become more stringent, and the cost of the housing typically increases. Therefore, in one respect, the mechanical structure that allows for the simultaneous collection of current and the compression of porous iron electrode materials with stresses of 0.1 to 10 MPa is a particularly useful means of incorporating iron electrode materials in electrochemical cells.

[0210] In various embodiments, it may be useful for current collectors to provide multiple functions in the battery, including serving as structural members. In one example, a current collector can provide structural support for the electrode by passing through the middle of a bed of particulate material. In some embodiments, the bed may have current collectors on both sides in addition to a central current collector. In some embodiments, the current collector located in the middle of the bed may be made of a non-perforated sheet, while the current collector on the outer surface may be perforated or otherwise contain pores to facilitate ion transport to the electrode active material. In various embodiments, air electrodes or other positive electrode materials may be placed adjacent to each other on both sides of the ferroelectrode material, such that ions do not need to cross a given depth in the electrode to flow through the electrode material, which may be due to, for example, symmetry for transport. Therefore, the absence of perforations in the current collector included in the middle of the bed can effectively reduce the cost of the central current collection sheet while having little or no impact on transport within the system. The ferroelectrode material may be mounted to or pressed against the combined structural support and current collector included in the middle of the bed. Additional functions performed by the current collection components in the ferroelectrode may include: anode positioning / mounting, enhanced current collection, adjacent cell separation, and voltage stacking.

[0211] The resistivity of porous electrodes must be reduced to achieve a given level of electrochemical performance, which varies depending on the current harvesting method and material properties. If current is harvested from more sides, or the total path length to the current collector is shorter, the battery pack may be able to operate efficiently with a higher resistivity path, resulting in a lower final voltage drop. Thus, compression strategies for porous iron electrodes and current harvesting strategies can be effectively optimized together to produce a system with the lowest total cost for a given performance level. Below, a set of techniques and designs for harvesting current from porous electrode beds and compressing porous electrode beds can be used in combination or individually to produce cost-effective, high-performance porous battery pack electrodes.

[0212] The current harvesting material can be any material used in the art to harvest current from an alkaline battery pack at a potential where the anode in the alkaline iron-based battery pack is exposed. The composition of the electrolyte, the specific potential used during battery pack cycling, and other process variables (such as temperature) will determine the stability of various current harvesting materials. These materials can include nickel, nickel-plated stainless steel, copper, copper-plated stainless steel, iron of sufficient thickness, carbon fibers and other carbon-based materials, as well as iron coated with cobalt ferrite.

[0213] In one aspect, a reactor containing porous iron electrodes (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102) can be divided into horizontal layers contained in a larger container. Figure 6B and Figure 6C An exemplary aspect of this embodiment is shown, wherein a larger container 6202 is divided into horizontal layers 6203-6207. The larger container 6202 itself can operate as a negative electrode (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102). Refer to Figure 6B and... Figure 6C These horizontal layers (e.g., 6203-6207) can be referred to as packets. In each of these horizontal layers (e.g., 6203-6207), the anode, such as particulate anode material 6212, can be compressed by any method suitable for compressing and containing the particulate material. In doing so, a current-collecting separator 6210 between the packets can be inserted into a larger container 6202 that contains the packets (e.g., 6203-6207). A protrusion 66215 or other flexible conductive mechanism on the separator 6210 can be used to hold the compression force applicator (e.g., separator 6210) of the packets (e.g., 6203-6207) in place while also functioning as a current-collecting device. This in Figure 6B and Figure 6C As shown in the diagram. The separator 6210 may also include an optional catch lip 6216 on the side.

[0214] In one aspect, the current collector can be a metal or other conductive fabric. Examples include a mesh woven from nickel, copper, or graphite fibers. The current collector can surround or be laminated within the electrode material. The current-collecting fabric can surround a bed of direct reduced iron (DRI) pellets, which serves as the electrode, as shown below. The fabric can be stretched, tightened, or otherwise brought into close mechanical contact with the electrode material to facilitate adequate electrical contact with the electrode material. Figure 6D The illustrative example shown is for a case with a metal fabric 6402 containing electrodes (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102, or larger container 6202) comprising direct reduced iron pellets 6403. The metal fabric 6402 can be a mesh or sieve that wraps around the DRI pellets 6403 and provides a compressive force or load 6404 on the DRI pellets 6403 to compress the DRI pellets 6403 together within the mesh of the metal fabric 6402 and to establish a tight contact between the metal fabric 6402 and the DRI pellets 6403. Current 6405 can be collected by the metal fabric 6402.

[0215] On the other hand, conductive mesh bags or pouches can be used as devices for simultaneously compressing electrode material and collecting current from the electrode material. More specifically, the mesh bags or pouches can be filled with particulate iron electrode material, and the pouches can be tightened or otherwise reduced in volume by means of straps, ropes, threads, or other tightening mechanisms to compress the anode material. Conductive mesh tubes or the like can be filled with particulate iron electrode material, and the electrode material can be compressed by applying an axial tensile force to the conductive mesh tube. In this case, the weaving of the mesh can be optimized so that the mesh tube undergoes considerable compression when an axial tensile force is applied. This can be understood as similar to a Chinese finger trap, where the axial extension of the braided tube results in a narrowing of the tube's diameter. The amount of compression applied to the particulate iron material can be adjusted by the thickness of the strands in the braid, the density of the strands in the braid, and the amount of axial force / extension applied to the braid. In some cases, porous iron electrode materials can contain directly reduced iron pellets. In some cases, porous iron electrode materials can contain crushed directly reduced iron pellets. In some cases, adhesives can be usefully included in granular iron materials to help the pellets adhere.

[0216] In some respects, porous mesh containers and particulate active materials can be arranged in a geometry similar to that of tea bags and tea leaves, for example... Figure 6E and Figure 6F As shown. Figure 6EAn electrode 6500 with a single-strand construction is shown, wherein a porous mesh bag 6501 is secured at a single tightening point 6503 by a current collector 6502. Electrode 6500 can be a negative electrode (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102). Figure 6 shows an electrode 6600 with a double-strand construction, wherein a porous mesh bag 6501 is secured at a first tightening point 6503 and a second tightening point 6602 by a current collector 6502. Electrode 6600 with a double-strand construction can be a negative electrode (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102). The tea bag container (e.g., 6501) can be conductive and serve as a current collector. In some aspects, the tea bag container (e.g., 6501) may have a current collector placed within the sash of the tea bag container. The tea bag container (e.g., 6501) may have straps that facilitate compression, including straps not located at the top of the tea bag container (e.g., 6501), such as a second tightening strap 6602 or tightening straps at other locations. The tea bag container (e.g., 6501) may also have a strap located at the top of the container to retain the active material within the container. In another aspect, the tea bag container (e.g., 6501) may be non-conductive, and current collection may be performed solely by the current collector placed within the sash of the tea bag container.

[0217] On the other hand, a loose, flexible conductive sheet can be loosely attached to a backing plate at its edges to form a bag; the backing plate may or may not be rigid. Straps, such as wires, inserted through the flexible sheet and backing plate are opened to allow the bag to be filled with pellet or powdered anode material. The straps are tightened to compress the anode and can be used for current collection. The tightening wires can be conductive and serve as additional current collectors distributed throughout the bag. The bag can also be attached rigidly (e.g., by welding) or via a connection that is rigid for some forms of movement and flexible for others (e.g., a hinged connection). In some cases, current collection can be performed from one side, such that the backing plate or bag does not collect current, while in other cases, collecting current from both sides of the bag structure may be advantageous. An example of such an electrode 700 with a tightening structure and a backing plate 702 is shown in... Figure 7 The diagram is shown by way of non-limiting example, illustrating a construction for a negative electrode (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102). In some embodiments, a backplate 702 may be used to rigidly support the bag 705 on both sides, as... Figure 7As shown, the tensioning wire 704 passes through the back plate 702 and the bag 705. Electrode material can be poured into the bag 705 through the opening, which can then be tightened or welded closed to form a closure 703.

[0218] In another embodiment, the particulate electrode material can be compressed within a perforated sheet. The sheet can be conductive, such that it serves both as a device for compressing the electrode material and as a device for collecting current from the electrode material. The perforations in the sheet can be selected such that they are smaller than the characteristic dimensions of the particulate material, and therefore the particulate material will not easily escape from the cage formed by the perforated sheet.

[0219] In various embodiments, the electrode material can be particulate. For easy ion transport between the positive and negative electrodes, the material surrounding the electrode material may need to be porous or otherwise perforated. In some cases, particulate materials with particle sizes finer than pores or perforations may be required due to the difficulty, for example, in fabricating very fine perforations. Where finer particles than pores or perforations are required, the electrode material can be agglomerated using an adhesive to form secondary particles comprising a number of primary particles. The primary particle size can therefore be finer than the perforations, but the secondary particle size can be coarser. These coarser particles will be less likely to escape through the pores or perforations of the current collector and other compressible materials, and thus can be compressed more effectively. In one aspect, polymers stable under alkaline conditions, such as poly(ethylene) or poly(tetrafluoroethylene), can be used to bind the aggregates together. In another aspect, a polymer adhesive, only partially stable under conditions suitable for the electrode, can be introduced between the primary particles. The binder allows the electrode to be cycled a sufficient number of times, for example, several electrochemical charge and discharge cycles, thereby electrochemically forming bonds between the primary particles before the polymer decomposes or degrades. On the other hand, the shape of the pores or perforations in the structure of the compressed electrode material can be designed to retain the electrode material within the structure but maximize ion transport through the perforations or pores. By way of a non-limiting example, long slits can be introduced into the perforated sheet so that particles cannot escape through the slit, but the number of areas open for mass transfer increases relative to the amount present if the perforations were equiaxed. On one hand, the particulate electrode material can comprise direct reduced iron, while the perforated sheet can comprise stainless steel. On the other hand, the particulate electrode material can comprise crushed direct reduced iron with particle sizes several times smaller than natural pellet sizes, and the size of the perforations in the current collector can be adjusted such that crushed fragments do not escape from the compression cage.

[0220] On one hand, the bed of particles is vibrated, shaken, agitated, or moved, causing the particles to settle closer together than when initially filled. This method can also be used periodically throughout the system's lifespan to help promote new contact angles or arrangements between the particles as they change shape or size. In the case of a container providing bags for the particles, its orientation can be changed, for example, by rotating it in the case of a wheel-shaped container.

[0221] On the other hand, additives can be included in or added to the bed of electrode material to enhance conduction between the electrodes via the current collector. Additives can be usefully concentrated at critical points in the electrode structure. In one aspect, a conductive adhesive is used to adhere particulate anode material to the current collector, which can take any shape, including spherical or hollow spheres, and may have particles on both sides. The conductive adhesive may contain a binder stable in the intended environment (e.g., alkaline electrolyte) and conductive particles such as metals (e.g., iron), debris, or powder including steel mill dust. The binder may, for example, include poly(ethylene) or poly(tetrafluoroethylene). The conductive adhesive may also additionally contain additives useful for battery pack performance, such as sulfide salt additives, or additives designed to bind with carbonate ions in solution, such as calcium hydroxide. When the interfacial resistance between the particulate material and the current collector is one of the larger resistances in the electrochemical system, creating a conductive bond between the electrode particulate material and the current collector can effectively improve battery pack performance at a low additional cost. The composition of the conductive adhesive may be 10-80% by volume of conductive additives, with the remainder including binders, any additives, and possibly co-solvents or thickeners.

[0222] On the other hand, current collection can occur by creating a bond between each particulate material and the conductive rod. If the particulate material is attached to the current collector via a conductive bond, compressive stress is not required. The particulate material can be attached to the rod along its length. The bulk of anode material can extend beyond the end of the rod. The anode bulk can be attached by sintering, welding, or other metal bonding techniques, by wire attachment, or by deposition from a solution or slurry onto the rod, which can be done by magnetic attraction or solvent evaporation. The rod can be used to collect current from the anode. This rod-shaped anode can snap-fit ​​into a flexible slit-ring fastening mechanism for easy assembly of the composite anode. This fastening guide can also serve as a busbar. This is in Figure 8The diagram schematically illustrates a rod 802 with attached iron granular material 805 being mounted to a busbar 803. The rod 802 can have any cross-section, including circular or linear, and does not have to be straight; it can be coiled or some other shape to improve packing and limit the required volume of the busbar 803. The rod 802, or multiple rods 802 together, can be a negative electrode (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102).

[0223] On the other hand, current collection and compression can be performed simultaneously through a bag with an open top, which can be made, for example, from a corrugated or welded metal sheet. The bag can be filled with particulate iron electrode material, and the top can be rolled to provide compression of the particulate material. This compression can be performed using a horizontal bar within a rolling section. The bag can be made of a conductive material suitable for use as a current collector in alkaline battery pack environments, particularly at the iron positive electrode. Current can be collected from the end of the bar. The bag can be porous or perforated to allow ion transport through the bag, such as in a metal mesh made of nickel.

[0224] On the other hand, a rigid container can be formed. The rigid container may have at least one conductive wall and may be constructed of a material suitable for use in alkaline electrolytes and also suitable for use as a current collector in an iron cathode. The rigid container may be filled with particulate electrode material and compressed by a piston or plunger mechanism. In one exemplary embodiment, a welded can with a bottom and a wraparound exterior is filled with anode pellets (or powder) and compressed from the top using a plunger mechanism. The surface of the rigid container may be constructed of a rigid but ion-permeable material (e.g., perforated metal sheet or expanded sheet). In one aspect, the expanded sheet forms the sidewall of the rigid container. The pressure plate or face used by the plunger may include protrusions or other flexible mechanisms that can mechanically engage with features in the sidewall of the rigid container, making it possible that only a piston is needed to provide the compressive force for assembly. Thus, the mechanical engagement feature allows the piston to be used for initial compression but subsequently removed. The compressive load in this and other embodiments can be applied by any common means in the art for applying compressive loads, including but not limited to bolts, hydraulic devices, counterweights, threaded rods, zipper straps, and rivets. Figure 9 An exemplary embodiment is shown in which a perforating press 902 is used to compress ferroe electrode material 903 within a rigid anode container 905. In this case, the ferroe electrode material 903 may be direct reduced iron pellets, referred to as a DRI marble bed. Figure 9The left side is an exploded view, and the right side is an assembly view. The anode container 905, which has an assembly of iron electrode material 903 compressed therein, can be a negative electrode (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102).

[0225] On the other hand, iron particles can be sandwiched between two pieces of conductive flexible material (such as metal fabric) and riveted together to secure them around the edges to provide compression. In some cases, the conductive flexible material can be intermittently riveted, tightened, or otherwise reduced in volume throughout the electrode area to provide more uniform compression.

[0226] On the other hand, flexible sheets or meshes can be used in conjunction with rigid sidewalls to simultaneously provide compression, current harvesting, and containment. More specifically, in one exemplary embodiment, for example... Figure 10 As shown, module 1002, consisting of rigid sidewalls 1004, can be slightly overfilled with ferroe electrode material 1005 using a metal mesh 1003 and completely enclosed with fasteners 1006 (e.g., bolts, threaded rods, zipper straps, rivets, etc.). Module 1002 can be a negative electrode (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102). When the fasteners 1006 are tightened, the mesh 1003 applies a compressive load to the ferroe electrode material 1005 because the sidewalls 1004 may be slightly overfilled with beads (e.g., DRI beads serving as ferroe electrode material 1005). The mesh 1003 can serve as a current collector. The mesh 1003 allows for good electrolyte circulation or diffusion to the ferroe electrode material 1005. Fastener 1006, in combination with other components, can hold the ferroelectrode material 1005 in place and allow for the application of clamping loads. In some embodiments, fastener 1006 can also function as a current collector. The mesh 1003 can be a metal wire mesh, a perforated plate, or something corrosion-resistant, such as nickel or stainless steel. The sidewall 1004 can be any rigid material that is appropriately stable in the electrochemical environment of the ferroelectrode 1005, such as plastics or some metals. The resulting assembly of the ferroelectrode material 1005 and the current harvesting device can be a modular component or can be permanently attached to an electrochemical energy storage system.

[0227] On the other hand, flexible, gasket-like materials are used to contain iron particle electrode material on several surfaces. Flexible materials allow for variable displacement of the designed force-applying element based on local flexibility and / or bed filling. In one example, a flexible gasket abuts a cylindrical battery, and a conductive, current-collecting perforated plate forms the end of the cylindrical battery. The plates are pressed together at various points along the battery periphery by, for example, bolts through the silicon gasket. The gasket can be made of a flexible, alkali-resistant material (e.g., ethylene propylene diene monomer (EPDM) rubber or related materials). In some cases, the gasket may require high flexibility, in which case a foam of polymeric material (e.g., EPDM foam) may be useful.

[0228] On the other hand, the current collector may include divots or other positioning or contact features on its surface. These features can be used to increase the contact area between the current collector and the particulate iron material and / or to position the particulate material so that it is effectively filled due to the template provided by the current collector surface. In one example, the current collector may include a series of divots of such size and location that spherical sets of particles, such as those from a direct reduction process, can be filled adjacent to the surface in a close-fill manner. Other templates, such as body-centered cubic templates, are possible. For particulate materials with an axis of symmetry, such as rods, the template may have an axis of symmetry, like the divots of cylindrical grooves. Dips may be introduced by machining, sheet metal recesses, or other deformation processes, or the current collector may include perforations or through-holes of appropriate size. The current collector may be shaped to optimally compress the particulate materials against each other; for example, in the case of rod-shaped particulate materials, the current collector may comprise a sheet rolled into a cylinder around a cylindrical aggregate and compressed to limit the diameter of the cylinder.

[0229] To reduce the resistance caused by current collection, the current collector can be designed to allow current collection to occur more uniformly throughout the packed bed electrode. This can be achieved by introducing current collection components across the entire thickness of the electrode or by having the current collection components pass through the thickness of the electrode in a reasonable manner.

[0230] In some embodiments, the current collector may have spikes, rods, protrusions, or other high aspect ratio features that can protrude from the current collecting sheet or other boundaries of the filled bed electrode into the electrode bed. These high aspect ratio features can be configured in size and shape such that they contact numerous electrode material particles in the bed that would not be contacted by a simple flat sheet current collector. In some embodiments, a metal sheet current collector with protrusions into the space filled with particulate material is used as the current collector. On the other hand, a mesh metal sheet is used as the current collector, and some of the struts within the sheet are cut and bent inward to serve as protrusions into the space filled with active material.

[0231] In some implementations, a conductive brush or a series of wires is attached to the current collector. The wires protrude flexibly into the space filled with ferroelectric electrode material. The wires contact the material due to their spring constant, and this contact can be improved by using compressive pressure.

[0232] In many implementations, fasteners or other elements providing compression are required to hold the current collectors in a compressed position relative to each other. Hereinafter, the term "fastener" should be understood to refer to any element of a mechanical assembly that provides a fastening or compression function through the use of an additional component that mechanically engages with other parts of the assembly. The performance of the iron cathode, including the individual pellets, is improved when a sustained compressive load is applied to it prior to operation of the battery. However, using metal fasteners (e.g., stainless steel bolts) to bear the load is disadvantageous because it increases the number of parts and assembly time, and because the bolts may need to be electrically isolated from the current collector to mitigate the hydrogen evolution reaction (an undesirable parasitic side reaction that reduces coulombic efficiency) occurring on the bolts, this increases design complexity and potentially the number of parts. Therefore, while fasteners are mechanically desirable, metal fasteners are disadvantageous. Several alternative methods to replace metal fasteners are considered below.

[0233] In some embodiments, non-metallic fasteners can be used instead of metallic fasteners. In one exemplary embodiment, two sandwich current collectors can surround the ferroe electrode bed. The current collectors can apply compressive force to the anode bed via fasteners made of an electrically insulating non-metallic material that is resistant to degradation in the alkaline environment of the electrolyte. The electrically insulating and non-metallic properties of the fasteners will result in a lack of electron transfer on the surface of the fasteners exposed to the electrolyte, which will prevent undesirable hydrogen evolution reactions from occurring on the exposed surfaces of the fasteners. A lower HER rate means more electrons participating in the desired anodic reduction reaction, i.e., a higher coulombic efficiency. In some embodiments, the fasteners are bolts and nuts. In some embodiments, the fasteners are made of one or more of acrylic acid, polytetrafluoroethylene, polyethylene, low-density polyethylene, high-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, or polyetheretherketone. In another exemplary embodiment, the two sandwich current collectors surrounding the anode bed can apply compressive force to the anode bed via fasteners, which saves assembly time by using a "clamp-in" mechanism instead of a bolt mechanism that requires rotating the fasteners. In some embodiments, the fasteners are appropriately long, double-locking clamp-in supports. Any combination of the above-described fastening techniques can be used to provide compression while avoiding the use of metal fasteners. Some fastening techniques are shown in Figures 11A and 11B. Figure 11A and 11BVarious aspects that can be used to secure the negative electrode (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102) in various embodiments are shown. Figure 11A The illustration shows two current-collecting sheets 1105 clamped to an electrically insulating nut 1103 on an iron electrode material 1100, and the iron electrode material 1100 is in Figure 11A The label is "Anodic Active Material". Nut 1103 is tightened on bolt 1102 to pull sheet 1105 together, thereby compressing ferroelectrode material 1100. A second example of a snap-fit ​​compression feature is, for example, a snap-fit ​​support 1110 in... Figure 11B As shown in the image, it replaced Figure 11A Bolts 1102 and nuts 1103, and operated in a similar manner.

[0234] In some implementations, it may be useful to use a compliant mechanism capable of applying large distributed loads to the current collector or pressure plate. In one example, the last face dimension of the rectangular prism box used to house the anode is a leaf spring mechanism that springs back after the anode is loaded to compress and accommodate the pellet anode. The current collector itself can be a compliant mechanism, such that applying loads at relatively few points (like a leaf spring) can result in distributed loading throughout the system.

[0235] Compressive stress can be applied not only through mechanical fastening of the structure but also through alternative methods. In some cases, the ferroe electrode material may be housed in a rigid body (e.g., a square battery with current collectors or other mechanical supports on all sides), but the need to apply compressive loads during assembly can be eliminated by using an expandable material lining one side of the anode container body. This expandable material expands after the battery pack is assembled, thereby providing a compressive load on the anode bed after the battery is filled with electrolyte. In some embodiments, the expandable material may be placed between the ferroe electrode material and a small facet of the ferroe electrode material container body. In some embodiments, the expandable material is an expandable hydrogel that expands upon contact with an aqueous electrolyte, thereby providing a compressive load on the anode active material during electrolyte filling. In some embodiments, the expandable material is an inflatable plastic balloon with a port for pumping in air, thus providing a compressive load on the anode active material once air is pumped in. The plastic balloon may be made of poly(ethylene), poly(propylene), or similar polymers that are flexible in alkaline solutions and resistant to degradation. Figure 12 An example embodiment of an expansion material 1200 contained within a rigid iron electrode container assembly 1202 is shown. The unexpanded state is... Figure 12 The left side is shown. Figure 12The right side shows the expansion state of the expanding material 1200 when the anode active material 1205 is compressed within the rigid iron electrode container assembly 1202. The rigid iron electrode container assembly 1202 can be a negative electrode (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102).

[0236] In another embodiment, the container for the ferroe electrode material is not rigid, but still maintains its volume, or has a maximum volume within a reasonably approximate range of stress less than ~10 MPa, similar to some metal fabrics—this can be referred to as a flexible cage. In this case, an expandable material can be placed inside the flexible cage, and compression is provided by the expansion of the expandable material within the flexible cage. The expandable material described above can also be used. The flexible cage can be conductive and can serve both as a current collector and as a means of providing compression to the ferroe electrode material filling it.

[0237] In another embodiment, the ferroelectrode material can exhibit a significant magnetic moment in the presence of a magnetic field. The ferroelectrode material can be ferromagnetic, as in the case of iron. Therefore, a magnetic field established by one or more permanent magnets or electromagnets can be used to induce magnetic forces on the rigid wall of the ferroelectrode material, thereby providing a compressive load to the anode active material.

[0238] In another embodiment, a pump present within the system, such as those designed to move the electrolyte, provides suction over the particle bed. The suction provided by the pump pulls the particle bed together and brings the particles into contact with each other. Particles are prevented from being drawn into the pump by a sieve or mesh with an opening smaller than the expected minimum particle size.

[0239] On the other hand, phosphates (including iron phosphate), phosphoric acid, or similar phosphorus-containing additives can be usefully incorporated into particulate iron electrode materials to promote mechanical contact and bonding between the particulate materials. Phosphate groups can form phosphate bridges between metal oxide groups, thereby binding the particulate materials of the electrode bed together to form an electrode with better mechanical and electrical connections. Iron oxides can serve as useful conductors, as several of them (especially magnetite and aragonite) are semiconductors. In cases where the bonded oxides are electrochemically reduced to a metal species, this metal species can be electrochemically sintered or otherwise bonded. Therefore, such bonding of oxides, even transiently, can improve electrochemical performance over many cycles. The electrode material can be pretreated with a phosphorus-containing solution before entering the electrolyte, or a phosphorus-containing compound can be introduced into the electrolyte to facilitate the formation of such phosphate bonds. These phosphate bonds can occur in various metal oxide systems, including cadmium, magnesium, aluminum, and zinc. Phosphate additives can be particularly beneficial in iron electrodes because they can also reduce the tendency for hydrogen evolution at the iron surface during charging.

[0240] In some implementations, it may be desirable to create conductive paths between the particles of the iron electrode material by metallurgically bonding the particles before insertion into the electrolyte. This metallurgical bonding can lead to sufficient conduction through the iron electrode material, achieving satisfactory electrochemical performance without the need for compression. Several methods for eliminating the need for compression of the iron electrode material are described below.

[0241] In one embodiment, the ferroe electrode material is thermally assembled via a high-temperature process including sintering or brazing. The thermal steps used to bond the ferroe electrode material to the current collector can reduce the contact resistance between the particulate materials by melting similar metals together, thus achieving a more robust electrical connection. While sintering has been considered for the manufacture of ferroe electrode materials, the sintering of some particulate iron materials has not yet been considered due to their unique particle structure. In one example, direct reduced iron (DRI) is an attractive raw material for ferroe electrode materials, but due to its coarse particle size, it is not a recognized candidate for thermal bonding via sintering. DRI can be used directly in the sintering process, or it can be combined with another bonding material on its surface to form a suitable metallurgical bond. The bonding material can be brushed, sprayed, or otherwise introduced onto DRI or other particulate iron materials to bond them with other DRI particles during heat treatment. The bonding material can be usefully concentrated at the contact points between DRI or other particulate materials as a means of obtaining the most electrical contact with minimal additional cost. An example of a bonding material is a material with a low sintering temperature that can induce metallurgical bonding during sintering, such as a suspension of carbonyl iron brushed or sprayed onto direct reduced iron or other particulate materials. In a second example, the bonding material may melt or result in fusion welding or brazing upon exposure to heat. In a second example, a nickel brazing compound can be coated onto an iron electrode material, which can then be heated to a suitable temperature to form a metallurgical bond. Thermal bonding methods are used in... Figure 13 As shown in the image. Figure 13 The illustration shows a plurality of metal pellets 1300 provided on an anode current collector 1302. Heat is applied to the plurality of metal pellets 1300 and the anode current collector 1302, causing the plurality of metal pellets 1300 to melt into the current collector, as shown. Figure 13 As shown. In this way, the plurality of metal pellets 1300 can form a negative electrode (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102).

[0242] One possible manufacturing technique for a thermally bonded granular bed system is characterized by rolled steel sheets that can be used as furnace belts. The furnace belt is unwound from a coil and straightened to become a horizontal transport surface within a continuous hydrogen furnace. At the furnace inlet, ferroe electrode material (such as direct reduced iron) is deposited onto the furnace belt via a hopper. This ferroe electrode material and the furnace belt sheet are passed through the furnace, which is heated to a maximum temperature that bonds the ferroe electrode material and the furnace belt. This ferroe electrode material and the current collector sheet can then be cut into segments for use as anodes in the reactor.

[0243] In various implementations, the particulate materials used for the iron electrode achieve good contact with each other by creating a “planar” surface due to stress concentration at the contact points. In some cases, the electrode material may not need to be held under high forces throughout its lifespan; instead, the particulate materials can be compressed together during manufacturing to form flat points, and then held under lower forces throughout the lifespan. To achieve this, the electrode cage can be supported during periods of high load stress to create a planar surface on the particulate material and reduce interparticle contact resistance. The force can then be partially released, the cage can be removed from the support structure, and the electrode cage can be placed into the reactor under this lower compressive force, but with reduced contact resistance due to the applied higher compressive force. If at any point in the lifespan the cage becomes disordered or the cell resistance becomes too high, the cage can be removed, placed back into the support structure, recompressed, and the force can be released again, allowing the cage to be returned to the cell.

[0244] In various embodiments, the solubility of the iron intermediate in an alkaline medium can be used to form necks between the particulate materials in the iron electrode material constituting the packed bed. The iron electrode can be maintained within a suitable pH, temperature, and optionally voltage range, allowing HFeO2 to... - Soluble intermediates can form at sufficiently high concentrations, increasing the interparticle bonding within the packed bed due to solution precipitation reactions mediated by the soluble species, as shown in the figure below, where the particles are referred to as beads. This interparticle bonding can be termed a neck. This neck formation can be a pretreatment step or can occur in situ in an electrochemical cell used for energy storage. Coarsening may form necks between pellets to enhance inter-particle conductivity and reduce overpotential at the anode. In one aspect of neck formation, the process involves soaking the pellet bed in an alkaline solution for >3 days, thereby coarsening the bed at the micrometer to millimeter level and enhancing inter-particle contact with the soluble species. In another embodiment, electrochemical cycling is employed to enhance the deposition of soluble intermediates. In a third embodiment, the pellets are coated with iron powder, such as atomized iron powder or sponge iron powder, to promote neck formation and reduce the contact resistance between DRI pellets. As cycling continues, the powder particles can be “sintered” into the bulk DRI pellets. Mechanistically, this may be due to the soluble intermediate Fe species (HFeO2).- Mass transfer facilitates the deposition of discharge products at the interface between small and large particles, for example, Figure 14 As shown. Specifically, Figure 14 A bed 1400 of individual DRI blocks 1402 (e.g., DRI beads) is shown as being available. Electrochemical and / or chemical reactions may cause the bed 1400 to form a bed 1405 consisting of necked-together DRI blocks 1402 (e.g., DRI beads) connected together by a neck 1406 between them. In this way, the necked-together bed 1405 may be a solid block of connected DRI blocks, rather than the original starting bed 1400 of individual blocks. In various embodiments, the necked-together bed 1405 may be used at a negative electrode (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102).

[0245] In various embodiments, the particulate materials can be bonded using techniques commonly used in metal welding. On one hand, the particulate materials can be resistively welded by passing a high current through a packed bed. The current can be applied via a compaction roller assembly, causing the particles to come into contact before or simultaneously with the resistance welding process. In various embodiments, the particles can be mechanically deformed at high temperatures, thereby forming a metallurgical bond at the contact points between the particles. In one example, a hot briquetting machine for hot briquettes or direct reduced iron can operate at low compaction pressures, causing the particulate material to deform at the contact points to form a metallurgical bond. For particulate materials with internal porosity (e.g., direct reduced iron), compaction can utilize stress concentration at the contact points between particles to form a metallurgical bond, but the internal porosity of the particulate material may remain substantially unchanged due to its distance from the contact points. In various embodiments, metallurgical bonding can be performed in an inert atmosphere to prevent oxidation of the ferroe electrode material. In various embodiments, the bed of particulate material can be ultrasonically consolidated or consolidated by other vibrational methods. Ultrasonic or vibratory compaction can be accompanied by axial pressure. In various embodiments, the particulate materials can be welded together using any fusion welding technique common in the art, including but not limited to tungsten inert gas welding, gas metal arc welding, and gas metal arc welding. Alternatively, the material can be explosively welded.

[0246] In various embodiments, conductive metal solder can be placed at the contact points between the particulate materials, thereby forming a metallic bond between the materials. In one example, tin or copper can be dip-coated onto a bed of particulate materials. In another example, copper can be dip-coated onto the particulate materials. In yet another embodiment, a conductive liquid is coated onto the particles by passing it through a tube or nozzle and depositing it onto the coated particles. Precise control of the nozzle allows for precise placement of individual particles, which can potentially help achieve optimized electrode geometries. Particles deposited in this manner can be stacked to create three-dimensional structures.

[0247] In various embodiments, the particulate material can be etched using any of a variety of acids and subsequently mechanically deformed before insertion into the electrochemical cell. The etching process removes any surface oxides that hinder bonding and allows for electrical contact between the anodic materials. Acids such as hydrochloric acid, nitric acid, or any other acid used to strip iron oxides from the surface of metallic iron can be used. In some cases, the particulate material can be compressed while in acid.

[0248] In various embodiments, the particulate material used for the iron electrode may include a direct reduced iron (DRI) material. DRI materials can be manufactured without a cement coating to reduce adhesion during the reduction process. These cements can inhibit charge transfer across the interface between pellets. In this way, DRI materials can exhibit enhanced charge transfer properties for electrochemical cycling. In one example, a fluidized bed reduction process is used to enable the use of DRI materials, which do not require a cement coating.

[0249] In various embodiments, particulate material containing iron electrode material can be compressed around a current collecting mesh. The current collecting mesh can then be heated (e.g., by resistance), causing the wire mesh to weld to the surrounding particulate material. The pellets are then interconnected through the mesh and can be welded together. The mesh may be relatively thick and open, like a wire mesh fence material.

[0250] During operation of a battery pack with a pellet bed electrode, mass and electron transport within the pellets can be difficult due to their size, leading to polarization. This can reduce the energy efficiency of the battery pack by: (1) voltage drops during charging and discharging resulting in lower voltage efficiency; and (2) low coulombic efficiency due to insufficient competition with the hydrogen evolution reaction during charging. The specific capacity of the resulting iron electrode is also reduced due to insufficient charging. For example, in some cases, polarization is primarily controlled by mass transport of hydroxide ions through the pellet pores from the outside of the pellet to the iron reaction sites at the center of the pellet. In other cases, polarization is controlled by electron transport through the intra-pellet network of iron material from the electrical contact points at the outside of the pellet to the center of the pellet. Any of these polarization sources can generate localized electrochemical potentials within the pellet that favor the hydrogen evolution reaction during charging rather than the reduction reaction of the desired iron oxide species, which reduces coulombic efficiency.

[0251] On one hand, the particle size can be selected to facilitate better filling. For a non-limiting example, the bed may comprise 50% particles with a diameter greater than 5 mm, 25% particles with a diameter between 5 mm and 1 mm, and 25% particles with a diameter less than 1 mm, so that the smaller particles fill the spaces between the larger particles. Particles smaller than the natural DRI size can be made from DRI by methods detailed below. These particles can be added to their containers in a specific order to ensure optimal filling; for a non-limiting example, a layer of larger particles can be added first, followed by smaller particles to fill the spaces, then another layer of larger particles, and then another layer of smaller particles.

[0252] A method for reducing the size of iron pellets before battery pack assembly is disclosed as a solution to one or more losses in energy efficiency and specific capacity caused by pellet size. Reducing pellet size decreases the characteristic lengths of mass and electron transport within the pellet, thereby reducing polarization and potentially improving one or more of energy efficiency and specific capacity.

[0253] Reducing the size of pellets through a crushing process, such as jaw crushing (“crushing”), prior to assembly into a pellet bed has been shown to result in higher voltage efficiency. However, the crushing of pellets should lead to less interparticle contact on a per-particle basis (irregular particles achieve less contact than spherical particles), and more interfacial resistance per particle in a bed of given thickness. Furthermore, “rattlers,” in which particles have no electrical contact with their neighboring particles due to the geometry of the bed, are more likely to be polydisperse and irregular in shape compared to relatively monodisperse spheres. Therefore, it is presumed that the increase in voltage efficiency resulting from increased mass and electron transport within the pellets partially masks the increase in resistance-based voltage drop and the lack of electrically accessible material (and thus reduced capacity) due to the increased rattler portion.

[0254] In some implementations, the size of the pellets is reduced to half or less of their original size by crushing, which reduces the overpotential of the iron electrode by more than 10 mV.

[0255] Crushing of pellets can lead to a significant performance increase if a second conductive additive is added to the pellet bed to improve one or more of the conductivity between pellets or the conductivity from pellets to the current collector. This additive will increase conductivity by increasing the conductive surface area in contact with the pellets, thereby reducing the increased interfacial resistance in the pellet bed of crushed pellets. An additive is needed that does not inhibit mass transfer and results in a significant increase in the conductivity of the bed. Ideally, the additive should penetrate at a low volume fraction and possess high conductivity.

[0256] In some embodiments, the additive is one or more of carbon black or graphite, added to the crushed pellet bed at a volume fraction greater than 1%, such that the carbon black or graphite bridges the crushed pellets together. In some other embodiments, activated carbon or biochar, or materials with low to moderate conductivity, are used as low-cost alternatives to graphite.

[0257] In some implementations, the additive is a conductive mesh, such as stainless steel wire mesh.

[0258] In some implementations, the additive is a conductive rod, such as a stainless steel rod with a diameter smaller than the average pellet size.

[0259] Prior to nominal operation of the battery pack, additives that improve the performance of the iron electrode can be chemically incorporated into the iron electrode using various methods. These methods rely on intra-pellet mass transfer of chemicals from the electrolyte to the active iron sites within the porous structure of the pellets. Uniform penetration of the additive into the pellets is generally necessary to achieve the maximum desired performance enhancement effect. However, it is often difficult to uniformly penetrate certain liquid-soluble and solid-state additives into pellets typically produced by direct reduction processes, especially those with low solubility that react with direct reduced iron.

[0260] A method for reducing the size of iron pellets prior to battery assembly is disclosed as a means to achieve more uniform penetration of liquid-soluble and solid additives into the pellets during the additive incorporation process. Reducing the pellet size decreases the characteristic length of mass transfer within the pellet, thereby reducing the concentration gradient of the additives and enabling the additives to penetrate and be incorporated into the electrodes more uniformly.

[0261] In some implementations, the additive incorporation process is one or more of immersion in an electrolyte, electrochemical plating, and electrochemical cycling.

[0262] In some implementations, the additive is an initially liquid-soluble hydrogen evolution inhibitor that is incorporated into the solid electrode via an electrochemical or spontaneous chemical reaction.

[0263] In some implementations, the additive is an initial solid-state hydrogen evolution inhibitor that is further incorporated into the solid-state electrode via an electrochemical or chemical dissolution-reprecipitation reaction.

[0264] In some embodiments, the additives include one or more of the following: sodium thiosulfate, sodium thiocyanate, polyethylene glycol (PEG) 1000, trimethyl sulfoxide, zincate (by dissolving ZnO in NaOH), hexamethylenetetramine, decanethiol, sodium chloride, sodium permanganate, lead oxide (IV), lead oxide (II), magnesium oxide, sodium chlorate, sodium nitrate, sodium acetate, ferric phosphate, phosphoric acid, sodium phosphate, ammonium sulfate, ammonium thiosulfate, zinc barium white, magnesium sulfate, ferric acetylacetone (III), hydroquinone monomethyl ether, sodium metavanadate, sodium chromate, glutaric acid, dimethyl phthalate, methyl methacrylate, methylpentynol, adipic acid, allyl urea, citric acid, sulfur Malic acid, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, propylene glycol, divinylpropyltrimethoxysilane, aminopropyltrimethoxysilane, dimethyl ethynyl dicarboxylate (DMAD), 1,3-diethylthiourea, N,N'-diethylthiourea, aminomethylpropanol, methylbutynol, amino-modified organosilane, succinic acid, isopropanolamine, phenoxyethanol, dipropylene glycol, benzoic acid, N-(2-aminoethyl)-3-aminopropyl, behenamide, 2-phosphonobutane tricarboxylic acid, mipapyrate (mipa) borate), 3-methacryloyloxypropyltrimethoxysilane, 2-ethylhexanoic acid, isobutanol, tert-butylaminoethyl methacrylate, diisopropanolamine, propylene glycol n-propyl ether, sodium benzotriazole, pentasodium aminotrimethylenephosphonate, sodium cocoyl sarcosinate, dodecyl pyridine chloride, stearic acid trimethylammonium chloride, silachlorine, calcium lignite, quaternary ammonium salt-18 chloride, sodium hexametaphosphate, dicyclohexylamine nitrite, lead stearate, calcium dinonylnaphthalenesulfonate, ferrous(II) sulfide, sodium hydrosulfide, pyrite, sodium nitrite, complex alkyl phosphates (e.g., RHODAFAC® RA 600 emulsifier), 4-mercaptobenzoic acid, ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid salt (EDTA), 1,3-Propanediaminetetraacetic acid (PDTA), NTA, EDDS, DTPA and other aminopolycarboxylic acids (APC), 2-methylbenzenethiol, 1-octylthiol, bismuth sulfide, bismuth oxide, antimony(III) sulfide, antimony(III) oxide, antimony(V) oxide Bismuth selenide, antimony selenide, selenium sulfide, selenium oxide (IV), propargyl alcohol, 5-hexyn-1-ol, 1-hexyn-3-ol, N-allylthiourea, thiourea, 4-methylcatechol, trans-cinnamaldehyde, iron sulfide (III), calcium nitrate, hydroxylamine, benzotriazole, furfurylamine, quinoline, stannous chloride (II), ascorbic acid, tetraethylammonium hydroxide, calcium carbonate, magnesium carbonate, dialkyl dithiophosphate, potassium stannate, sodium stannate, tannic acid, gelatin, saponins, agar, 8-hydroxyquinoline, bismuth stannate, potassium gluconate, lithium molybdenum oxide, potassium molybdenum oxide, hydrogenated light petroleum, heavy cycloalkane petroleum (such as Ru) Stlick® 631 (for sale), antimony sulfate, antimony acetate, bismuth acetate, hydrogenated heavy naphtha (e.g., sold as WD-40®), tetramethylammonium hydroxide, sodium antimony tartrate, urea, D-glucose, C6Na2O6, potassium antimony tartrate, hydrazine sulfate, silica gel, triethylamine, potassium antimony trihydrate, sodium hydroxide, 1,3-di-o-tolyl-2-thiourea, 1,2-diethyl-2-thiourea, 1,2-diisopropyl-2-thiourea, N-phenylthiourea, N,N'-diphenylthiourea, sodium L-antimony tartrate, disodium rosinate, sodium selenide, potassium sulfide, and combinations thereof.

[0265] Figure 15 Example pellet beds 1501 and 1502 according to various embodiments are shown. Pellet beds 1501 and 1502 can be used in the negative electrode of the embodiments (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102). During operation of a battery pack with pellet bed electrodes, mass and electron transfer through the pellet bed may be difficult due to the total thickness of the pellet bed, resulting in polarization, which may reduce the energy efficiency of the battery pack by: (1) voltage drop during charging and discharging leading to lower voltage efficiency and (2) coulombic efficiency due to insufficient competition with the hydrogen evolution reaction during charging. The specific capacity of the resulting iron electrode is also reduced due to insufficient charging. For example, in some cases, polarization is partly due to mass transfer of hydroxide ions from the outside of the pellet bed to the center of the pellet bed. In other cases, polarization is partly due to electron transfer through the iron pellet network. Any of these polarization sources could generate a localized electrochemical potential within the pellet that favors hydrogen evolution during charging rather than the reduction reaction of the desired iron oxide species, which would reduce coulombic efficiency.

[0266] Increasing the bulk packing density of pellets is one way to address one or more losses in energy efficiency and specific capacity caused by the total thickness of the pellet bed. By increasing the bulk packing density, for a given electrode capacity, the thickness of the pellet bed is reduced, thereby reducing polarization across the bed and improving one or more of energy efficiency or specific capacity. For example, Figure 15 A pellet bed 1501 is shown, having porous pellets 1503 formed into spheres or marbles; and a pellet bed 1502, having porous pellet blocks 1505 formed by crushing spheres, marbles, or other shapes into blocks. The intra-particle transfer length t1 of the pellet bed 1501 can be greater than the intra-particle length t2 of the pellet bed 1502.

[0267] A method of processing pellets by a jaw crusher (“crushing”) prior to assembly into a pellet bed is disclosed as a way to increase bulk filling density and reduce polarization. In this way, crushing can produce pellet bed 1502 instead of pellet bed 1501. Prior to crushing, the pellets can be generally spherical and have a narrow size range. The crushing operation can break the pellets into multiple blocks with non-spherical shapes and a wider size distribution, resulting in a higher bulk filling density. For a fixed projected area and electrode material mass, the resulting higher bulk filling density reduces the thickness of the pellet bed, thereby reducing through-bed polarization and improving one or more of energy efficiency or specific capacity (e.g., comparing pellet bed 1502 and pellet bed 1501, when the material composition of porous pellets 1503 and porous pellet blocks 1505 is the same, pellet bed 1502 has reduced through-bed polarization and improved energy efficiency or specific capacity compared to pellet bed 1502). Figure 16 Pellet beds 1501 and 1502 with current collector 1601 attached are shown. The height h1 of the uncrushed pellet bed 1501 may be greater than the height h2 of the crushed pellet bed 1502, even if the same amount of pellet material may be present in pellet beds 1501 and 1502. Therefore, crushing can compress the size of the electrodes (e.g., negative electrode and electrolyte 102, negative electrode compartment 231, negative electrode 301, negative electrode 403, negative electrode 458, negative electrode 502, electrode 6102).

[0268] In some implementations, the pellets after the crushing operation are broken into blocks with serrated edges and a polydisperse size distribution, so that smaller blocks fall into the gaps between larger pellets, thereby increasing the packing density.

[0269] Certain performance properties of pellet bed electrodes may deteriorate due to time-dependent or charge production-dependent mechanisms during battery pack operation. Deteriorated performance properties may include, but are not limited to, specific capacity (mAh / g), electrode overpotential (mV), self-discharge rate (mAh / mo.), and coulombic efficiency (%). Several methods for restoring iron electrode performance by treating the battery pack after the start of battery life are disclosed here.

[0270] In some cases, the specific capacity of an electrode may decrease with battery cycling because cycle-dependent changes in the electrode's microstructure impede mass or electron transport, thus reducing the available capacity at a given polarization. More specifically, the pores within the pellets may become increasingly constricted with cycling as they fill with residual electrochemical discharge products, whose molar volume (per mole of iron) is larger than that of metallic iron. This progressive pore filling hinders mass transport of iron into these pores, potentially reducing the amount of iron within the pores and making electrochemical reactions less likely, thus lowering the specific capacity. In other cases, the resistance of certain iron sites may increase due to the contraction of the conductive pathways provided by the metallic network within the pellets. In still other cases, each pellet may contain an unreacted metallic core completely covered by a passivation layer.

[0271] Loss of accessible capacity due to battery pack use can be recovered by ex-situ processing of the pellets after the electrode capacity has decayed to a minimum threshold. Various embodiments include treating the used pellets with mechanical, chemical, electrochemical, and / or thermal processes (i.e., ex-situ processed pellets) before reintroducing them into the electrochemical cell to return the electrode to a state with improved chemical and physical properties. Improved chemical and physical properties may include higher content of desired impurities (e.g., hydrogen evolution reaction (HER) inhibitors), lower content of unwanted impurities (e.g., HER catalysts), higher specific surface area, higher total porosity, different pore size distributions (e.g., multi-peaked to reduce mass transfer resistance), different pellet size distributions (e.g., multi-peaked to enhance bed filling), different aspect ratios (e.g., for enhanced bed filling), etc. Mechanical processes applicable to ex-situ processing of the pellets may include crushing, grinding, and / or pulverizing, including but not limited to size reduction. Mechanical size reduction re-exposes the passivated metallic iron at the pellet core, making previously inaccessible iron accessible, thereby increasing capacity. Please note that the mechanical process of exposing the initially passivated iron at the pellet core may not be suitable before battery pack use, as more exposed metallic iron provides more sites where hydrogen evolution reactions may occur, either through Faraday parasitic reactions during charging or through spontaneous self-discharge reactions. However, extrinsic mechanical processes may be desirable as a method to recover and / or improve capacity resistance that has decreased due to battery pack use, where a larger portion of the iron is passivated and inaccessible, for example... Figure 17 As shown. Specifically, Figure 17 The image shows pellet 1702 after the battery pack has been used, which has been subjected to ex-situ processing, such as by crushing, grinding, etc., to expose the iron core 1703 in pellet 1702. Figure 17 A passivation layer 1705 is shown, which makes the core 1703 inaccessible before processing.

[0272] Ex-situ application of heat treatment to pellets may include treating the pellets at elevated temperatures in a reducing (e.g., hydrogen), oxidizing, and / or carburizing (e.g., carbon monoxide and / or carbon dioxide) atmosphere. In some embodiments, the reducing conditions are a gas mixture of 10% nitrogen, 30% carbon monoxide, 15% carbon dioxide, and 45% hydrogen at 800°C for 90 minutes. Ex-situ application of electrochemical processes to pellets may include reverse electroplating, electrochemical dissolution, etc. Ex-situ application of chemical processes to pellets may include acid etching, etc. In various embodiments, to increase the accessible capacity of the pellets during the discharge reaction, the pellets may be pretreated by immersion in an acid bath (e.g., concentrated HCl), which etches iron and enlarges the pores in the pellets, increasing the total porosity of the pellets compared to used pellets. In various embodiments, to increase the accessible capacity of the pellets during the discharge reaction, the pellets may be pretreated by immersion in a neutral or slightly alkaline bath to remove excess discharge products from the electrode. For example, one of the anticipated discharge products, ferrous(II) hydroxide, is typically unstable at pH < 8. Ferrous(II) hydroxide is preferentially removed by immersion in a bath at pH < 8, while metallic iron remains on the electrode. In a pH range of pH > 7 and pH < 8, the bath can be a diluted form of the electrolyte used during the electrochemical operation of the battery pack. After pretreatment, the etched and now more porous pellets can be reassembled into the negative electrode. The chemical treatment time can be optimized to increase the usable capacity of the pellets without losing excessive active material to the acid etching solution. Any of the above methods can be optimized to preferentially increase the pore size within the pellets. In some embodiments, the electrochemical process utilizes one or more large current pulses, which cause a non-uniform current distribution within the pellets, such that the current is concentrated on sharp and small physical features within the pellets, preferentially driving the electrochemical dissolution of these small physical features, thereby increasing the initial pore size. Any of the above processes can be performed prior to battery pack operation to improve the chemical and physical properties of the pellets relative to their unmodified, unused state.

[0273] The shape and size of the discharge products within the pores of iron pellets can affect performance in several ways. For example, a thin, uniform layer of discharge products can prevent pore blockage, which can improve capacity retention. On the other hand, a thin, uniform, non-porous layer of discharge products may passivate the underlying metallic iron, thereby hindering mass transfer of hydroxide ions through the discharge product layer during discharge and reducing the electrode's accessible capacity. In another example, non-uniform, high-surface-area porous discharge products can promote mass transfer through the discharge layer while increasing the effective surface area for the next discharge, both of which can increase the overall accessible capacity. Figure 18 compares the distribution of discharge products. Figure 18 The left side shows the discharge product 1803, which is unevenly distributed on the surface of the anode 1802. Figure 18 The right side shows discharge products 1804 as a uniform layer on the surface of anode 1802. The formation of discharge products can be mediated by electrolyte additives, anode additives, and / or a surface coating of anode 1802. Various methods for controlling the morphology of discharge products in an iron electrode are disclosed.

[0274] Additives and counterions in the electrolyte and / or electrodes can be used to control the morphology of discharge products. Additives and counterions can alter the porosity of the discharge layer and the accessibility of electrochemical active sites through the following mechanisms: Fe forms a two-layer discharge product with a relatively static Fe3O4 inner layer and a highly porous outer layer, which is strongly influenced by the electrolyte composition. Divalent cations tend to inhibit uniform discharge and contribute to the formation of a more porous outer layer. When monovalent cations are size-mismatched with Fe cations in the outer layer of the discharge product, they inhibit uniform discharge and produce a more porous outer layer. For example, lithium and cesium cations tend to produce more porous outer layers than sodium and potassium cations because lithium and cesium are less size-mismatched with iron cations. Additives and counterions used to control the morphology of discharge products include, but are not limited to, divalent sulfide ions (S2... - ), hydrosulfide (HS) - ), lithium cations (Li) + ), sodium cation (Na) + ), calcium cations (Ca2) + ), selenium ions (Se2) - ), cesium cation (Cs) + ) and barium cations (Ba2) + In some embodiments, sodium sulfide, lithium hydroxide, sodium hydroxide, calcium hydroxide, sodium selenide, and / or barium hydroxide are added to the electrolyte in various concentrations to provide soluble additives and counterions for controlling the morphology of discharge products.

[0275] In some embodiments, additives controlling the morphology of discharge products are initially contained within a solid-state electrode. These solid-state additives can be in the form of solid metal oxides and / or metal sulfides, which are introduced as solids into the iron electrode. Interesting metal sulfides and oxides include: FeS, FeS2, MnS, Bi2S3, Bi2O3, Sb2S3, FeAsS, PbS, SnS, HgS, AsS, Pb4FeSb6S 14 Pb3Sn4FeSb2S 14 SeS2, etc.

[0276] In some embodiments, additives for controlling the morphology of discharge products include one or more of the following: sodium thiosulfate, sodium thiocyanate, polyethylene glycol (PEG) 1000, trimethyl iodide sulfoxide, zincate (by dissolving ZnO in NaOH), hexamethylenetetramine, decanethiol, sodium chloride, sodium permanganate, lead oxide (IV), lead oxide (II), magnesium oxide, sodium chlorate, sodium nitrate, sodium acetate, ferric phosphate, phosphoric acid, sodium phosphate, ammonium sulfate, ammonium thiosulfate, zinc barium white, magnesium sulfate, ferric acetylacetone (III), hydroquinone monomethyl ether, sodium metavanadate, sodium chromate, glutaric acid, dimethyl phthalate, methyl methacrylate, methylpentynol, adipic acid, allyl urea, citric acid, thiocyanate, etc. Malic acid, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, propylene glycol, divinylpropyltrimethoxysilane, aminopropyltrimethoxysilane, dimethyl ethynyl dicarboxylate (DMAD), 1,3-diethylthiourea, N,N'-diethylthiourea, aminomethylpropanol, methylbutynol, amino-modified organosilane, succinic acid, isopropanolamine, phenoxyethanol, dipropylene glycol, benzoic acid, N-(2-aminoethyl)-3-aminopropyl, behenamide, 2-phosphonobutane tricarboxylic acid, mipapyrate (mipa) borate), 3-methacryloyloxypropyltrimethoxysilane, 2-ethylhexanoic acid, isobutanol, tert-butylaminoethyl methacrylate, diisopropanolamine, propylene glycol n-propyl ether, sodium benzotriazole, pentasodium aminotrimethylenephosphonate, sodium cocoyl sarcosinate, dodecyl pyridine chloride, stearic acid trimethylammonium chloride, silachlorine, calcium lignite, quaternary ammonium salt-18 chloride, sodium hexametaphosphate, dicyclohexylamine nitrite, lead stearate, calcium dinonylnaphthalenesulfonate, ferrous(II) sulfide, sodium hydrosulfide, pyrite, sodium nitrite, complex alkyl phosphates (e.g., RHODAFAC® RA 600 emulsifier), 4-mercaptobenzoic acid, ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid salt (EDTA), 1,3-Propanediaminetetraacetic acid (PDTA), NTA, EDDS, DTPA and other aminopolycarboxylic acids (APC), 2-methylbenzenethiophenol, 1-octylthiol, bismuth sulfide, bismuth oxide, antimony(III) sulfide, antimony(III) oxide, antimony(V) oxide Bismuth selenide, antimony selenide, selenium sulfide, selenium oxide (IV), propargyl alcohol, 5-hexyn-1-ol, 1-hexyn-3-ol, N-allylthiourea, thiourea, 4-methylcatechol, trans-cinnamaldehyde, iron sulfide (III), calcium nitrate, hydroxylamine, benzotriazole, furfurylamine, quinoline, stannous chloride (II), ascorbic acid, tetraethylammonium hydroxide, calcium carbonate, magnesium carbonate, dialkyl dithiophosphate, potassium stannate, sodium stannate, tannic acid, gelatin, saponins, agar, 8-hydroxyquinoline, bismuth stannate, potassium gluconate, lithium molybdenum oxide, potassium molybdenum oxide, hydrogenated light petroleum, heavy cycloalkane petroleum (such as Ru) Stlick® 631 (for sale), antimony sulfate, antimony acetate, bismuth acetate, hydrogenated heavy naphtha (e.g., sold as WD-40®), tetramethylammonium hydroxide, sodium antimony tartrate, urea, D-glucose, C6Na2O6, potassium antimony tartrate, hydrazine sulfate, silica gel, triethylamine, potassium antimony trihydrate, sodium hydroxide, 1,3-di-o-tolyl-2-thiourea, 1,2-diethyl-2-thiourea, 1,2-diisopropyl-2-thiourea, N-phenylthiourea, N,N'-diphenylthiourea, sodium L-antimony tartrate, disodium rosinate, sodium selenide, potassium sulfide, and combinations thereof.

[0277] Pretreatment involving electrochemical cycling can also be used to control the morphology of discharge products from the iron electrode. For example, the inventors observed that the compactness of the discharge products varies with temperature and current density. Pretreatment involving electrochemical cycling, performed at temperatures and current densities that are not necessarily the nominal operating conditions of the battery pack, can be used to form discharge product morphologies that contribute to high accessible capacity and persist after pretreatment when the operating conditions are set to nominal values. In various embodiments, the pretreatment consists of 100 cycles of deep electrochemical charge and discharge cycling at 10°C and a gravimetric current density of 25 mA / gFe.

[0278] The inventors have discovered that lowering the operating temperature of the iron electrode to below 30°C improves various performance properties, such as specific capacity, retention of specific capacity over many electrochemical cycles, and coulombic efficiency of the electrode. Various mechanisms may work simultaneously to produce these effects. For example, specific capacity can be increased at lower temperatures due to increased conductivity of the electrode material (including, but not limited to, iron and iron oxide discharge products). Increased conductivity of the electrode material enhances electron transfer to electrochemical reaction sites, leading to an increase in specific capacity at a given polarization limit of the electrode. In another example, lowering the temperature can slow the kinetics of undesirable electrolyte degradation or poisoning reactions that occur during the battery pack's lifespan, such as carbonate formation due to atmospheric carbon dioxide. For example, carbonate formation consumes OH- ions, reducing electrolyte conductivity, which lowers the solution's pH and leads to a decrease in specific capacity. Lowering the temperature slows these undesirable reactions and allows for better retention of the iron electrode's specific capacity throughout the battery pack's lifespan. In yet another example, lowering the temperature may slow the kinetics of undesirable hydrogen evolution reactions more than the iron reduction reactions required during charging of the battery pack, resulting in higher coulombic efficiency during charging. In various embodiments, the iron electrode is maintained at 20°C ± 5°C to improve electrode performance. In other embodiments, the iron electrode is maintained at 10°C ± 5°C to improve electrode performance. Figure 19 It is a temperature graph showing specific capacity and coulombic efficiency relative to the number of cycles.

[0279] Better electrochemical kinetics of charging (reduction) and discharging (oxidation) reactions at iron-based electrodes will improve the voltage efficiency and coulombic efficiency of the battery. Redox mediators can be used to improve the electrochemical kinetics of iron-based electrodes. Redox mediators are compounds that act as electron "shuttles" to mediate reduction or oxidation reactions. While commonly used in biocatalysis, redox mediators can also be used to promote desired oxidation and reduction reactions at iron-based electrodes. Requirements for redox mediators include (1) rapid and reversible redox kinetics; (2) redox potentials similar to the reactions they promote (including, but not limited to, Fe<>Fe(OH)2 and / or Fe(OH)2<>Fe3O4); and (3) stability in the presence of the electrolyte of interest. Redox mediators may be soluble or insoluble in the electrolyte of interest. In some embodiments, the redox mediator comprises one or more unsaturated bases, saturated bases, or combinations thereof. In some embodiments, the bases comprise electron-withdrawing functional groups, electron-donating functional groups, or combinations thereof. In some embodiments, the unsaturated bases include, but are not limited to, cyclopentyl-1,3-diene, benzene, 1H-pyrrole, pyridine, pyrazine, furan, 4H-pyrran, and 1,4-diphenyl ether. The saturated bases include, but are not limited to, cyclopentane, cyclohexane, 1,4-dithiene, 1-methyl-1H-pyrrole, or combinations thereof. In some embodiments, the saturated bases include, but are not limited to, cyclopentane, cyclohexane, 1,4-dioxane, tetrahydrofuran, tetrahydro-2H-pyrrole, 1,4-dithiene, tetrahydrothiophene, tetrahydro-2H-thiene, 1,4-dimethylpiperazine, and 1,3,5-trimethylpyrrole. Alkane (1,3,5-troxane), 1,3,5-trithiaane, or combinations thereof. In some embodiments, the electron-withdrawing functional group includes, but is not limited to, nitro, trichloro, cyano, carboxyl, fluorinated, hydroxyl, or combinations thereof. In some embodiments, the electron-donating functional group includes, but is not limited to, primary amine, secondary amine, tertiary amine, amide, methoxy, methyl, alkyl, alkenyl, alkynyl, phenyl, or combinations thereof. In one embodiment, the redox mediator for the iron-based negative electrode is a viologen-based compound. In some embodiments, the viologen-based compound includes, but is not limited to, methyl viologen, propyl viologen, hexyl viologen, octyl viologen, or combinations thereof.

[0280] In electrochemical cells with iron electrodes, the addition of sulfur unlocks the utilization of the iron electrode. However, sulfur is a known catalyst poison, so in electrochemical cell implementations with a catalyst cathode, a high sulfur concentration around the iron electrode and a low sulfur concentration at the catalyst electrode may be optimal.

[0281] In one embodiment, sulfur can be concentrated at the iron electrode by immersing it in a high-concentration sulfur solution before it enters the electrochemical cell. Furthermore, if the iron electrode undergoes a single formation cycle of charging and discharging, sulfur will be electrochemically added to the structure of the iron electrode. Then, upon addition to the desired electrochemical cell, it will remain concentrated near the anode.

[0282] In some embodiments, the iron electrode is immersed in an electrolyte with a high concentration of divalent sulfur ions (i.e., >50 mM) and then circulated in an electrolyte with a lower concentration of divalent sulfur ions (i.e., 50 mM).

[0283] In some embodiments, the porous iron electrode is immersed in an electrolyte bath containing any alkali metal or transition metal sulfides (Na2S, K2S, Bi2S3, SbS3, etc.) to increase the presence of sulfides.

[0284] In some implementations, the electrode is immersed in an electrolyte with a high concentration of divalent sulfur ions before cycling to incorporate divalent sulfur ions, after which the positive electrode is inserted into the full cell, wherein the initial concentration of divalent sulfur ions can be in the range of 10-250 mM (1.4-33.8 mgS / gFe) or higher.

[0285] In a non-limiting example, the porous iron electrode described above comprises a bed of DRI pellets.

[0286] Incorporating divalent sulfur ions or other beneficial additives uniformly or controllably into porous iron electrodes is challenging. One method for uniformly incorporating additives into porous materials is vacuum infiltration, in which the substrate is exposed to a vacuum (<1 atm) to evacuate pores, and then exposed to a liquid or molten additive to fill any vacancies in the material.

[0287] In various embodiments, the substrate is exposed to a vacuum sufficient to evacuate the pores. Figure 20 An exemplary method for cavitating holes is shown. In the first step, substrate 2000 is exposed to a high vacuum to cavitate holes 2001.

[0288] In one embodiment, the evacuated substrate is then exposed in a second step to an aqueous electrolyte formulation containing the previously described additive at a temperature of 0 to 250°C, such that the pores are completely or partially filled with additive 2002. After a certain period of time, such as less than 48 hours, the substrate 2000 may be rinsed or centrifuged in a third step to remove excess electrolyte.

[0289] In one embodiment, the evacuated substrate is then exposed to an additive in liquid or molten form at a temperature of 25°C to 250°C or 250°C to 2000°C, wherein the additive is one of those previously described in section ## (e.g., octyl mercaptan, FeS) that can be identified by those skilled in the art as compatible with the melting process. After a specific time of less than 48 hours, the substrate may be rinsed or centrifuged to remove excess liquid or molten material.

[0290] In one embodiment, the evacuated substrate is then exposed to a gaseous additive (e.g., H2S, H2Se, CS2 (greater than 50°C), PH3). After a certain time, such as less than 48 hours, the substrate can be cleaned with an inert gas or under vacuum to remove excess gaseous additive.

[0291] In a non-limiting example, a solution containing sodium sulfide is vacuum-permeated into the pores of a porous iron electrode prior to cycling to enhance permeation. Better permeation of divalent sulfur ions into the anode can improve overall performance capacity.

[0292] In a non-limiting example, sodium thiosulfate is heated until it melts (>45°C) before cycling and vacuum permeates into the pores of the porous iron electrode.

[0293] Additional methods for concentrating divalent sulfur ions into the iron particle electrode include isolating sulfide additives within or adjacent to the electrode in a variable-permeability retainer. In this way, controlled amounts of sulfide can be added to the iron particle electrode via passive or active electrochemical or chemical dissolution.

[0294] In one embodiment, the additive may be contained in a fully permeable or semi-permeable retainer, wherein the retainer is made of a plastic (e.g., polypropylene, polyethylene) that is stable in alkaline solutions.

[0295] In one embodiment, the additive may be contained in a retainer behind the ion-selective membrane, which allows the electrolyte to flow into the retainer and allows the additive to diffuse slowly into the solution.

[0296] In one embodiment, the additive may be contained in a conductive material (e.g., a conductive polymer mesh, a metal wire mesh).

[0297] In one embodiment, the retainer may be made of a layer of porous oxide (e.g., silicon dioxide).

[0298] In one embodiment, the additive retainer may be in physical contact, electrical contact, or both physical and electrical contact with the iron particle material electrode.

[0299] In one embodiment, the additive retainer can be in contact with the electrolyte and contact the iron particle material electrode solely through ion transfer in the electrolyte.

[0300] In one embodiment, the additive retainer may be immersed in a separate electrolyte container to provide a constant source of divalent sulfur ions. The electrolyte in contact with the iron particle material electrode is then replaced with the electrolyte in contact with the additive retainer.

[0301] In one embodiment, the additive holder may be in electrical contact with a potentiostat or system that holds the holder at a potential that prevents the additive from dissolving in the holder. Figure 21 An exemplary additive retainer construction is illustrated. Figure 21 In the configuration shown at the top, the package 2104 containing the additive can contact the iron particulate material 2103 placed in the electrolyte 2100 between the current collectors 2102. Figure 21 In the configuration shown at the bottom, the package 2104 containing the additive can be suspended in the electrolyte 2100, separated from the iron particulate material 2103 and the current collector 2102, for example, via an optional electrical connection 2110.

[0302] Divalent sulfur ions in electrolyte solutions have been shown to increase the available capacity and cycle life of iron electrodes in alkaline secondary battery packs. However, the concentration of divalent sulfur ions in the electrolyte decreases with cycle count and time, which may reduce the positive impact of dissolved sulfides on anode performance. One approach to improve performance throughout the entire lifespan is to directly incorporate sulfur-containing compounds into the iron electrode material.

[0303] In one embodiment, elemental sulfur is directly introduced into a porous iron anode by melting and diffusing sulfur into the porous metal. The sulfur is then introduced into the anode in solid form and comes into close contact with the active metal anode material, promoting positive interactions and thereby improving available capacity and cycle life.

[0304] In another embodiment, a metal sulfide is introduced as a solid into the iron anode. Metal sulfides of interest include: FeS, FeS2, MnS, Bi2S3, Sb2S3, FeAsS, PbS, SnS, HgS, AsS, and Pb4FeSb6S. 14 Pb3Sn4FeSb2S 14 Examples of metal sulfides include SeS2, etc. Cations in metal sulfides may contribute to the battery capacity (i.e., Fe), be inert to the charge / discharge reaction (i.e., Mn), or hinder the hydrogen evolution reaction (i.e., Pb, Sb, Hg, As, Bi).

[0305] In a non-limiting example, metal sulfides are incorporated into a bed of direct reduced iron (DRI) pellets.

[0306] Methods for incorporating sulfur-containing substances into iron electrodes include, but are not limited to: (1) incorporating bulk solid particles, powders, or agglomerates into the gaps between materials in the electrode bed; (2) incorporating metal sulfides (i.e., Bi2S3) with melting points lower than the melting point of iron metal by diffusion into the electrode pores; (3) incorporating metal sulfide powder by mixing it into oxidized ore pellets (i.e., iron flint pellets) during granulation (in this embodiment, the metal sulfides will be retained in the pellets through a reduction process, producing pellets containing metallic iron, metal sulfides, and impurities); (4) incorporating metal sulfides into pellets containing only metal sulfides and binders. In a non-constraint example, these pellets may be directly incorporated into the pellet bed of DRI with DRI pellets in a specific ratio; (5) incorporating metal sulfide powder by using mixing, grinding, or rolling equipment such as a ball mill.

[0307] In another embodiment, the above-described incorporation method is used in conjunction with sulfur-containing additives, including but not limited to metal sulfides.

[0308] In another embodiment, sulfur-containing additives include, but are not limited to, metal sulfides, which are incorporated into the iron anode material through a drum screen screening process in the production of DRI, for example... Figure 22 As shown, DRI pellets 2200 in the mesh cylinder are injected with sulfur additives during production to produce DRI pellets 2202 with sulfur additives.

[0309] It is difficult to uniformly or controllably incorporate additives into preformed metal electrodes, which limits the effectiveness of the additives.

[0310] Various embodiments include selective precipitation using reactive counterions. In various embodiments, a metal is incorporated into a particulate iron material electrode in a neutral or oxidized state, and subsequently reacts with selected counterions. The concentration of the metal additive is determined by the solubility of the source compound or the final desired concentration of reactive counterions in the electrode. In some embodiments, the electrode is exposed to an electrolyte containing a reactive counterion source (e.g., Na₂S, K₂S, Na₂Se, Na₂Te) to form compounds (e.g., CdS, Bi₂S₃, Bi₂Se₃) in situ, wherein the location and concentration can be determined by the presence, concentration, and solubility of the added metal, reactive counterions, or the resulting compound. In some embodiments, the accessibility of these additives can be further tuned by using short-acting pore-forming agents. In some embodiments, the electrode is electrochemically cycled before or after exposure to an electrolyte containing a specific concentration of reactive counterions to control the uptake of the reactive counterions.

[0311] In an unconstrained example, 0.5–10 wt% Bi₂O₃ is incorporated into the electrode before electrochemical cycling to a potential sufficient to decrease to the formation of Bi(s). Exposure to an electrolyte containing 250 mM Na₂S may result in the formation of Bi₂S₃ distributed throughout the electrode, as shown below: In various embodiments, the additives of interest (e.g., Na2S, Na2Se, Na3PO4) that serve as sources of sulfur, selenium, tellurium, nitrogen, or phosphorus are incorporated into the electrode at a concentration determined by the solubility of the source compound or the final desired concentration of the final compound in the electrode.

[0312] In some embodiments, the electrode is exposed to a source containing reactive metals (e.g., Fe, Bi, Hg, As, Cd, Cu, Ni, In, Tl, Zn, Mn, Ag) or metal ions (e.g., Bi(NO3)3, NaAsO4, Cd(NO3)2, CuSO4). In an electrolyte containing xH2O, compounds (e.g., CdS, Bi2S3, Bi2Se3) are formed in situ, where the location and concentration can be determined by the presence, concentration, and solubility of the added metal, reactive counterions, or the resulting compound. The solubility of non-metallic additives may allow for the creation of local concentration gradients in the electrolyte, resulting in regions more conducive to precipitation. In some embodiments, the accessibility of these additives can be further tuned by using short-acting pore-forming agents. In some embodiments, the electrode is electrochemically cycled before or after exposure to an electrolyte containing a specific concentration of metal or metal-containing ions to control the uptake of metal or metal-containing ions.

[0313] In a non-limiting example, Na₂S can be incorporated into the metal electrode. Exposure to an electrolyte containing Bi(NO₃)₃ may result in the formation of Bi₂S₃ distributed throughout the electrode, as shown in the following reaction: In various embodiments, an additive of interest (e.g., S or Se metal) that is a source of sulfur, selenium, tellurium, nitrogen, or phosphorus but may not itself be an ion is incorporated into the electrode at a concentration determined by the solubility of the source compound or the final desired concentration of the final compound in the electrode.

[0314] In various embodiments, the electrode containing a non-reactive additive may be exposed to an electrolyte. In one embodiment, the electrolyte contains NaOH or KOH, and in another embodiment, the electrolyte undergoes electrochemical cycling to generate anion species (e.g., S2) at the anode or in the electrolyte. - S2 2- Polysulfide ions. These can react to form Bi₂S₃ on the surface or be isolated in the anode, such as... Figure 23 As shown. When counterion reactions occur, exposure of the anode to this electrolyte may increase the overall porosity, which may be beneficial to the overall available capacity.

[0315] Additives sensitive to water and air can decompose rapidly in aqueous alkaline electrolytes. For example, additives containing divalent sulfur ions (S...) 2- ) and hydrosulfide (HS) - Compounds containing sulfur, such as Na₂S or NaSH, decompose upon exposure to oxygen by forming sulfates or other sulfur-containing compounds (e.g., sulfites, thiosulfates, sulfur, polysulfides). It is advantageous to maintain the sulfur species in the electrode or electrolyte as divalent sulfide ions or hydrogen sulfide ions, because it is difficult to reduce sulfates or other oxidized sulfur-containing compounds to sulfides, disulfides or hydrogen sulfide.

[0316] In one implementation, based on the principles of Le Chatelier, a sufficient amount of oxidized sulfur species (e.g., Na2SO4, Na2S2O3, Na2SO3, metallized S (S metal)) is added to the electrolyte to reduce or completely inhibit the formation of oxidized sulfur species by shifting the balance toward the sulfur species that favor reduction.

[0317] In one embodiment, oxidized sulfur-containing compounds (e.g., Na₂SO₄, Na₂S₂O₃, Na₂SO₃, metallized S) are added to the electrode. Upon exposure to the electrolyte, these soluble additives may dissolve in the electrolyte, thereby increasing the porosity of the electrode and reducing or inhibiting the formation of oxidized sulfur compounds in the solution.

[0318] In one embodiment, sulfur-containing species (e.g., FeSO4, FeS2O3, FeSO3) that also contain metal cations are added to suppress the oxidation of reduced sulfur species and to suppress the dissolution of metal species from the iron electrode.

[0319] DRI-based iron anodes exhibit compatibility with a wide range of initial sulfide concentrations in the electrolyte. Furthermore, it has been shown that the initial sulfide concentration of gS / gFe is the driving factor, rather than the sulfide concentration in the electrolyte.

[0320] In some implementations, an initial divalent sulfur ion concentration of 1 mM Na2S (0.1 mgS / gFe) is sufficient to achieve stable capacity performance.

[0321] In some implementations, an initial divalent sulfide ion concentration of 10 mM Na2S (1.4 mgS / gFe) is sufficient to achieve stable capacity performance.

[0322] In some implementations, an initial divalent sulfide ion concentration of 50 mM Na2S (6.8 mgS / gFe) is sufficient to achieve stable capacity performance.

[0323] In some implementations, an initial divalent sulfide ion concentration of 175 mM Na2S (23.6 gS / gFe) is sufficient to achieve stable capacity performance.

[0324] In some implementations, an initial divalent sulfide ion concentration of >=250 mM Na2S (33.8 gS / gFe) is sufficient to obtain stable capacity performance.

[0325] Furthermore, incorporating divalent sulfur ions into the iron anode can be achieved through a variety of techniques.

[0326] In some implementations, sulfides are incorporated through an electrolyte with a high concentration of divalent sulfur ions within the full cell.

[0327] In some implementations, the sulfide is incorporated by immersion in an electrolyte with a high concentration of divalent sulfur ions prior to cycling, and the cycling can be carried out in an electrolyte that does not contain divalent sulfur ions (which may be beneficial to the positive electrode).

[0328] In some implementations, divalent sulfur ions are incorporated by immersion in a high divalent sulfur ion concentration electrolyte prior to cycling, after which the positive electrode is inserted into the full cell, wherein the divalent sulfur ion concentration can range from 10-250 mM (1.4-33.8 mgS / gFe) or higher.

[0329] Optimal incorporation of divalent sulfide ions can also be achieved through maintenance methods, including but not limited to: 1) periodically adding a solution or solid form with a high concentration of divalent sulfide ions; 2) continuously adding sulfides in solid or solution form, wherein the concentration of divalent sulfide ions can range from 10-250 mM (1.4-33.8 mgS / gFe) or higher.

[0330] In one embodiment, 325-mesh iron sponge powder with internal pores is thermally bonded by sintering to form the substrate of the iron electrode material. Bismuth oxide and iron sulfide are incorporated throughout the sintered electrode material, which is thermally bonded to the current-collecting perforated sheet, and the sintered connection between the current collector and the powder particles avoids the need for compression to achieve conduction. The alkaline electrolyte contains 80% potassium hydroxide, 15% sodium hydroxide, and 5% lithium hydroxide (molar amounts), with a total hydroxide concentration of 6 moles in the aqueous solution.

[0331] In one embodiment, the iron electrode material may comprise directly reduced iron pellets, and the electrolyte comprises six moles of potassium hydroxide, 0.1 moles of lithium hydroxide, and 0.05 moles of sodium sulfide. The iron electrode may further comprise 1 wt% bismuth sulfide finely distributed within the directly reduced iron pellets. The electrode material is compressed within a rigid cage comprising a nickel-plated current-collecting stainless steel plate. Uniaxial pressure is applied to compress the pellets within a rigid wall structure comprising poly(methyl methacrylate), and the current-collecting plate is secured in place by stainless steel bolts that are electrically isolated from the current collector. The bed thickness in this embodiment can range from 1 to 10 cm.

[0332] In one embodiment, the iron electrode material may include carbonyl iron powder, lead oxide, and iron sulfide. Lead oxide is added at 0.1% by weight of the total solids in the electrode, and iron sulfide is added at 1.5% by weight of the total solids in the electrode. The solids are lightly sintered to bind and agglomerate them, and then compressed in a nickel mesh fabric, which is compressed by the expansion of a polyethylene bulb. The electrolyte is 5 moles of sodium hydroxide, and the additives are 0.005 moles of sodium sulfide and 0.01 moles of octyl mercaptan.

[0333] In another embodiment, the direct reduced iron pellets are crushed to form particle sizes ranging from 1 to 6 mm. The pellets are mixed with 1% by weight of natural flake graphite with a particle size of 200 micrometers and 0.05% by weight of iron sulfide with a particle size of 100 micrometers. The electrolyte is an aqueous solution containing 6.5 mol of potassium hydroxide, 0.5 mol of lithium hydroxide, 0.25 mol of sodium sulfide, and 0.001 mol of octyl mercaptan. The solid mixture is packed into a nickel mesh bag with a mesh size of approximately 0.5 mm, and the bag is compressed by a tightening mechanism to slightly compress the solid material.

[0334] Various embodiments may include a battery pack comprising: a first electrode; an electrolyte; and a second electrode, wherein at least one of the first and second electrodes comprises atomized metal powder. Various embodiments may include a battery pack comprising: a first electrode; an electrolyte; and a second electrode, wherein at least one of the first and second electrodes comprises iron agglomerates. In some embodiments, the iron agglomerates have an average length ranging from about 50 μm to about 50 mm. In some embodiments, the iron agglomerates have an average internal porosity ranging from about 10% to about 90% by volume. In some embodiments, the iron agglomerates have a porosity ranging from about 0.1 μm... 2 / g to approximately 25m 2 / g average specific surface area. In some embodiments, the electrolyte permeates between the iron agglomerates. In some embodiments, the electrolyte contains 1-octylthiol. In some embodiments, the electrolyte contains molybdate anions and divalent sulfide anions. In some embodiments, the iron agglomerates are supported within a metal textile mesh, providing compressive force and current collection for the iron agglomerates. In some embodiments, the iron agglomerates are aggregated together and bound to the current collector.

[0335] Various embodiments include a method of manufacturing an electrode, comprising: electrochemically producing a metal powder; and forming the metal powder into an electrode. In some embodiments, electrochemically producing the metal powder includes at least partially using a molten salt electrochemical method to electrochemically produce the metal powder. In some embodiments, electrochemically producing the metal powder includes at least partially using a gas atomization method to electrochemically produce the metal powder. In some embodiments, electrochemically producing the metal powder includes at least partially using a water atomization method to electrochemically produce the metal powder.

[0336] In various embodiments, sacrificial pore-forming agents, convertible pore-forming agents, short-acting pore-forming agents, removable pore-forming agents, or techniques may be used. In these embodiments, the intermediate material still containing the pore-forming agent may have a total Fe content ranging from 20% to 90% by weight. The pore-forming agent may be partially removed before use as an electrode, completely removed before use as an electrode, or completely removed during use as an electrode, as well as combinations and variations thereof. In one embodiment, the intermediate may have a total Fe content of 25% to 50% by weight, and after removal of the pore-forming agent, an electrode with a total Fe content of 60% to 90% by weight is provided.

[0337] In embodiments, as described herein, iron materials can be processed, chemically modified, mechanically modified, or otherwise constructed to alter one or more of their characteristics. These methods are generally described herein as being performed on DRI materials. It will be understood that these methods can be used with other iron-containing materials, such as reduced iron materials, unoxidized iron, highly oxidized iron, iron with valence states of 0 to 3+, and combinations and variants thereof. In this way, iron-containing pellets are provided for use in electrode configurations of long-duration electrical storage cells having predetermined characteristics (e.g., those described herein).

[0338] In some embodiments, the DRI is mechanically manipulated to grind, abrade, or polish the surface and / or remove fine powder. In one embodiment, DRI pellets are tumbled in a drum screen to abrade the surface and remove fine powder / dust. This operation may have the beneficial effect of reducing the reactivity of the pelleted DRI, making it easier and safer to transport without the need for briquetting or other compaction operations. In another embodiment, DRI blocks or sheets are passed under a rotating brush to remove fine powder from the surface, with similar beneficial effects.

[0339] In one embodiment, porosity is increased by pretreating DRI in an acid bath (e.g., concentrated HCl), which etches the iron and creates larger pores, thereby increasing the total porosity. The etching time can be optimized to increase the total capacity of the DRI pellets without losing too much active material in the acidic etching solution.

[0340] In another embodiment, desired impurities or additives are incorporated into the DRI. When these impurities are solids, they can be incorporated using DRI pellets by ball milling (e.g., using a planetary ball mill or similar equipment) with powdered additives, the pellets acting as their own grinding media. In this way, the powdered additives are mechanically introduced into the pores or surface of the DRI pellets. The DRI can also be coated with beneficial additives, for example, by rolling or soaking in a slurry containing the additives. These desired impurities can include alkali metal sulfides. Alkali metal sulfide salts have been shown to significantly improve the utilization of active materials in Fe anodes. Just as soluble alkali metal sulfides can be added to the electrolyte, insoluble alkali metal sulfides can be added to the DRI, for example, by the methods described above.

[0341] In some embodiments, the surface area of ​​a material containing cementite or iron carbide (e.g., DRI pellets containing cementite or iron carbide) can be increased by using the material as the anode of an electrochemical cell and discharging it. In some embodiments, a specific current density can be 0.1-25 mA / g. This high surface area iron oxide can also be used in a variety of applications beyond electrochemical cells.

[0342] In various embodiments, to increase conductivity, the pellets can be mixed with powders that are more conductive but potentially more expensive to create a composite bed with higher conductivity. This powder can increase the areal capacity of the battery by filling the voids between the pellets. This can potentially reduce the electrolyte volume to DRI pellet ratio in a way that can be systematically modified and optimized. In one embodiment, the powder is used at current collection sites to increase the contact surface area, thereby reducing the interfacial resistivity between the current collector and the small contact area of ​​the spherical pellets, as described in more detail in the previous section. This ensures the ability to modify and control the effective current density at the pellets. Modifying the particle size in the composite bed can result in controllable cost and conductivity. In another example, the use of additional powder, wire, mesh, yarn, or flocked conductive materials makes it possible to use low-conductivity pellets (e.g., DR flint pellets) or under-metallized direct reduction pellets (sometimes referred to as "remet" in the industry) in the composite bed by increasing overall conductivity. In one embodiment, the conductive component may include DRI fines or other waste from the DRI process.

[0343] In one embodiment, the porous sintered iron electrode can be formed from DRI, the particle size of which can be reduced or can be made into powder, for example by crushing or grinding. Fine DRI powder or other waste can also be used to form the sintered iron electrode. The sintered electrode can be formed with a binder under heat and / or pressure, and then the binder can be burned off at a high temperature to sinter the green form. DRI pellets can also be directly melted together by sintering in a non-oxidizing atmosphere without a binder, optionally with pressure applied to create electrical and physical bonds between the pellets.

[0344] In various embodiments, porous negative electrodes can be formed by crushing, shredding, or grinding hot-pressed iron (HBI). In various embodiments, HBI may be preferred for transport and delivery due to its low surface area and reactivity, but the porosity of HBI may be too low for practical applications in thick electrodes due to limitations in ion transport. To achieve an optimal combination of transport and performance, DRI can be transported to the battery assembly or manufacturing site in briquettes, where it is crushed, ground, and / or shredded to increase the porosity of the resulting electrode.

[0345] DRI pellets packed into a bed can be an ideal configuration for iron-based electrodes because they provide an electron conduction permeation path through the packed bed while leaving pores available for electrolyte occupation, facilitating ion transport. In some embodiments, the electrolyte volume to DRI mass ratio can range from 0.5 mL / g to 5 mL / g, for example, 0.6 mL / g or 1.0 mL / g. Compared to the surface area of ​​the pellets, DRI pellets typically contact surrounding pellets through a small contact area, which in some cases can be considered a “point contact.” This small cross-sectional area of ​​contact can restrict current flow, potentially resulting in relatively low conductivity of the small pellet bed as a whole, which in turn leads to high electrode overpotentials and low voltage efficiency in the battery pack.

[0346] In various embodiments, the conductivity of the DRI pellet bed can be increased in a variety of ways. In some embodiments, the conductivity of the DRI pellet bed can be increased by using an additional conductive material, which may surround, be embedded within, surround the entire pellet bed, or penetrate the pellet bed. The conductive material may be one or more of a metal, metal oxide, metal carbide, metal nitride, semiconductor, carbon, conductive polymer, or a composite material containing at least one of these electronically conductive materials. The conductive material may be in the form of powder, wire, mesh, or sheet. In some embodiments, the conductive material itself may participate in the electrochemical reactions in the battery pack, including but not limited to providing storage capacity. In some other embodiments, the conductive material is substantially non-electrochemically active. In one embodiment, the conductive material is a powder, and the powder fills or partially fills the space between pellets or between pellets and current collectors to improve inter-pellet or pellet-to-current collector conductivity. For example, the conductive powder may contain DRI “fine powder,” a powdered waste product of the direct reduction process, with a composition similar to DRI. In this case, the powder can be used to increase the conductivity of the bed and increase the storage capacity of the anode. In another embodiment, the conductive material is a powder, and the powder is applied to the surface of the pellets to form a coating. This coating provides a larger area for electrical contact between the pellets.

[0347] In various embodiments, a conductive coating is applied to low-conductivity pellets to enable their use in electrodes. In some embodiments, low-conductivity pellets, such as flint particles or unmetallized direct reduction particles (sometimes referred to in the industry as "remet"), may be coated. The coating may be conductive to reduce the resistance from the current collector to the flint pellets during the initial reduction step. The coating may or may not be removed during or after the reduction step. In one embodiment, the coating is a thin conformal metal layer, such as stainless steel, surrounding each pellet. In another embodiment, the coating is a thin layer of lead, which is applied to the exterior of each pellet using a directional deposition technique, such as sputtering, evaporation, or other physical vapor deposition technique. In some embodiments, the coating is applied by rolling the DRI and coating material together in a rotating container. In some embodiments, the DRI in the rotating container is substantially spherical.

[0348] In another embodiment, some or all of the individual pellets in the pellet bed are wrapped with conductive wire, foil, or sheet. In some embodiments, a fastening mechanism (e.g., a sieve) is used to apply tension to the wire, foil, or sheet. Optionally, this current collector surrounding the individual pellets can be connected to the gathered wire or to a larger current collector. In another example, a conductive mesh, yarn, or flock is distributed in the spaces between the DRI pellets to increase electrical connectivity. In various embodiments, the conductive material is a mesh with an opening (net size) chosen to be smaller than the pellets so that the pellets do not pass through the mesh. In this case, the conductive material can be stainless steel, nickel, or other metals and metal alloys. In another example, the DRI pellets are directly connected to each other by conductive wires passing through or surrounding the individual pellets. For example, the wires can be passed through holes in the DRI pellets, similar to forming a string of beads, resulting in electrical contact not only between the pellets but also within the pellets. Optionally, a string of balls can be kept in contact using an electrical terminal or a "stopper," where tension is optionally applied to the line. The electrical terminal can optionally be electrically connected to a larger current-collecting fixture, such as a plate.

[0349] In another embodiment, the conductivity of the pellet bed is improved by applying a compressive load to the anode of the DRI pellet bed to increase the inter-pellet forces and / or pellet-to-pellet or pellet-to-current collector contact area, thereby reducing contact resistance and improving electrochemical performance. Typical DRI pellets are approximately spherical in shape, have internal porosity, and can elastically deform to >5% linear strain before yielding. Applying a compressive load to the DRI bed increases the effective contact area at the interfaces between pellets and between pellets and the current collector. It is advantageous to use pellets with yield strain, which allows deformation to achieve the desired increase in conductivity without fracture. In one embodiment, pellets having a compressive strength of 700 to 2500 psi are used in the pellet bed electrode to which a compressive load is applied. Furthermore, a mechanical assembly providing the compressive load on the pellet bed can also serve as the current collector. The resistance of such a pellet bed, measured in a dry state before any filling with liquid electrolyte, can be reduced by two to 100 times or more by applying a compressive load. In some embodiments, the applied load can range from 0.1 psi to 1000 psi, for example, 50 psi or 100 psi. In some embodiments, the applied load can range from 0.1 psi to 10 psi, for example, 1 psi or 5 psi. In one example, metal plates on opposite faces of the pellet bed are used to provide both current collection and compressive load on the pellet bed. Optionally, one or more plates can be replaced with macroporous current collectors (e.g., metal mesh) to facilitate ion transport throughout the electrode. Preferably, connecting opposite current collectors so that they are at the same potential advantageously makes the electrochemical reaction rate more uniform throughout the electrode. In another example, the container containing the pellet bed serves as both the current collector and the method of applying compressive load. In another embodiment, an array of conductive pillars (or rods) connected to a common, bottom-facing current collector is implemented. Thus, numerous areas of current collection can be placed throughout the pellet bed. This approach also reduces the effective transport length within the electrode from the total thickness of the pellet bed to the inter-pillar spacing. In addition, these columns can be used to fix mechanical clamping mechanisms, such as plates or perforated plates on top of the pellet bed, thereby concentrating the downward force on the pellet bed, while also serving as current collection elements.

[0350] In some implementations, the compressive load can be provided partially or entirely by magnetic force. For example, a force can be applied using permanent magnets located on one or more sides of the bed, causing the pellets in the bed to be attracted by the magnets. For DRI pellet beds that are primarily metallic iron, the pellet bed is expected to be primarily ferromagnetic, and the pellet bed will be attracted by the magnets. Magnets may also be embedded in other fixtures around the pellet bed. The magnets and fixtures are used to hold the pellet bed in place and provide compressive stress, thereby improving the electrical contact between the pellets and between the pellets and the current collector as described above.

[0351] In some implementations, the inter-pellet contact resistance in the pellet bed can be reduced by applying a pretreatment to the pellet bed prior to battery pack assembly and / or operation. Several such pretreatment processes are described in the following paragraphs.

[0352] In some embodiments, whole DRI pellets are packed into a bed and sintered in an inert or reducing (i.e., non-oxidizing) atmosphere, optionally with mechanical pressure applied during sintering, for example using a material stable at the sintering temperature and atmosphere. The sintering temperature can range from 600 to 1100°C. The non-oxidizing atmosphere can consist partially or entirely of inert gases such as nitrogen or argon. The non-oxidizing atmosphere may also include a mixture of gases that tend to reduce iron, such as CO and CO2, and H2 and H2O. The precise composition of the mixture can be optimized according to the Ellingham diagram to ensure that the oxidation of iron is thermodynamically unfavorable. In one embodiment, a synthesis gas (5% H2, 95% N2) is used at sintering temperatures of about 600°C to about 1100°C, for example, 600°C to about 850°C, 850°C, about 850°C to about 1100°C, etc., to provide non-oxidizing conditions. The combination of high temperature and a non-oxidizing atmosphere may promote atomic diffusion and particle coarsening at the pellet contact points, leading to pellet bonding. The result is a DRI pellet bed molten together with low inter-pellet contact resistance. The same process can also be used to melt the pellets into the current collector.

[0353] In another embodiment, the pellets are joined using a heat treatment employing a flux or sintering aid to significantly reduce the heat treatment temperature required to form sintered necks between the pellets. Examples of fluxes or sintering aids include one or more metals with melting points lower than iron, such as zinc, tin, copper, aluminum, bismuth, and lead, or metals that alloy with iron with melting temperatures lower than iron, such as eutectic liquids exhibiting lower melting points. Other examples of sintering aids include one or more glass-forming compositions, including but not limited to silicates, borates, and phosphates.

[0354] In another embodiment, the pellets can be electrofused together through a process such as welding. In some such embodiments, welding is accomplished by passing an electric current through a pellet bed. In some such embodiments, this current is transmitted by discharging a capacitor.

[0355] In various embodiments, the anode electrode is an ordered array of spheres. In some embodiments, the spheres are arranged as cylinders. In some embodiments, the spheres are arranged as plates. In some embodiments, the spheres are arranged as disks. In some embodiments, the spheres are arranged as rectangular prisms. In some embodiments, the spheres are arranged as hexagonal prisms. In some embodiments, the spheres are arranged into arbitrary volumes.

[0356] In various embodiments, an electrolyte management system may be provided in which different electrolyte additives or formulations are added to the battery pack when switching between operating states. The optimal electrolyte formulation for operation of the battery pack in the charging, discharging, and idle states may differ significantly. The electrolyte management system of various embodiments can improve the capacity utilization of the iron electrode, reduce battery self-discharge, and suppress the hydrogen evolution reaction (HER). One or more of these benefits can be achieved simultaneously. In one embodiment of such an electrolyte management system, any number of different electrolyte formulation reservoirs are provided, each reservoir connected to the electrochemical cell using a separate flow controller. At different operating stages, each electrolyte formulation flows into the cell in a different relative amount based on the optimal concentration of the composition for the instantaneous operating mode (charging, discharging, idle). The electrolyte management system can be configured to adjust the electrolyte composition based on the instantaneous state of charge of the battery pack.

[0357] Various embodiments can provide methods and apparatus for maintaining liquid electrolyte levels in a battery pack. Containers containing water undergo evaporation when exposed to air until the partial pressure of water vapor in the air equals the vapor pressure of water at the system temperature. Specifically, electrochemical systems with aqueous electrolytes exposed to the environment will undergo the same evaporation. Dehydration of the electrolyte can lead to problems due to a reduction in electrolyte volume, and changes in electrolyte concentration can alter electrochemical performance. To mitigate this problem, in various embodiments, the electrolyte level can be maintained by allowing electrolyte to flow into the battery volume constantly or intermittently. Specifically, the electrolyte liquid level can be maintained by introducing electrolyte into the container until it overflows above an overflow point. Since the liquid level cannot rise above this overflow point, it can be maintained in a relatively controlled manner. Specifically, multiple containers can be arranged in a cascaded manner so that overflow from one chamber can flow into the next chamber, thus establishing "liquid connectivity" between the batteries. Connecting these batteries in series allows a single source to supply liquid electrolyte to multiple batteries simultaneously. The overflow from the last container can be recycled back to the first container. In systems using a shared electrolyte, the electrolyte flows in a cascaded manner between cells, and its properties can be monitored and managed at a central location across many cells. To mitigate problems associated with electrolyte carbonation and dehydration, electrolyte conditioning (e.g., adjusting composition or adding components) is advantageously performed at the collection source for circulating the electrolyte.

[0358] Various embodiments can provide compositions and methods for adding beneficial additives to electrolytes in aqueous electrochemical batteries. During the charging process of aqueous secondary battery packs, the electrolysis generating hydrogen gas leads to low coulombic efficiency, gas accumulation in the battery casing, safety issues, and electrolyte consumption. Furthermore, self-discharge of the metal electrode can occur through a spontaneous reaction between the metal and the electrolyte to form metal hydroxides, in which hydrogen gas is generated as a reaction product. Certain solid-phase hydrogen evolution inhibitors (e.g., Bi, Sb, As) can reduce these detrimental effects, but incorporating solid-phase inhibitors into the porous metal electrodes of the battery pack can be costly and present manufacturing challenges. Therefore, in various embodiments, a soluble salt of the desired hydrogen evolution inhibitor is added to the liquid electrolyte, which dissolves to provide solution ions of the desired additive (e.g., Bi). 3+ Sb 3+ As 3+ Additives are selected to induce inhibitory ions into the metal electroplating reaction (e.g., Bi). 3+ →Bi 0 The redox potential of the HER inhibitor occurs at a higher half-cell potential (measured vs. RHE, but at a lower cell potential) than the charging potential of the anolyte active material. Therefore, during the charging (reduction of the metal electrode) of the battery pack, the ionic form of the HER inhibitor is electrodeposited onto the surface of the metal electrode, providing a cost-effective and simple strategy for introducing the HER inhibitor into the electrolyte chemistry of the battery pack. The electrodeposited inhibitor suppresses the hydrogen evolution reaction on the electrode surface, which can be a porous electrode. During discharge mode, the deposit may dissolve back into the electrolyte. Salt additives are preferably selected so that they do not degrade the operation of the cathode during charging or discharging operations.

[0359] In another embodiment, the electrochemical cell includes an electrode on which a hydrogen oxidation reaction (HOR) is performed to recapture hydrogen generated during the hydrogen etherification (HER) side reaction, thereby mitigating the release of potentially hazardous hydrogen. Hydrogen bubbles generated during HER can be captured and exposed to the HOR electrode, which can be the working electrode of the battery cell unit or an additional electrode added to the system. In one embodiment, hydrogen is captured by arranging the battery electrodes such that buoyancy carries hydrogen bubbles to the HOR electrode. For example, the system can be tilted or include a funnel designed to facilitate this flow.

[0360] In various embodiments, the liquid electrolyte flows through an aggregate or bed of DRI pellets. For thick (up to several centimeters) battery electrode packs containing active material pellets, achieving adequate transport of reactants, reactant products, and additives through the thick bed on a timescale commensurate with the battery pack's operation (charging and discharging) timescale can be challenging. Insufficient transport rates in the electrolyte can have several adverse effects, including, but not limited to, increased overpotential losses in pellet-based electrodes and reduced utilization of active materials. In metal electrode battery packs with alkaline electrolytes, bubble formation and pH gradie...

Claims

1. A battery pack, comprising: The first electrode contains manganese oxide; Electrolyte; and The second electrode contains iron; The first electrode and the second electrode are each in contact with the electrolyte. The iron of the second electrode comprises a packed bed of pellets with a multi-peak size distribution, and the packed bed of pellets is subjected to a compressive stress of 0.1 MPa to 10 MPa.

2. The battery pack according to claim 1, wherein, The iron includes direct reduced iron (DRI).

3. The battery pack according to claim 1, wherein, The electrolyte is a liquid electrolyte.

4. The battery pack according to claim 3, wherein, The electrolyte contains an alkali metal hydroxide, including lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), cesium hydroxide (CsOH), or mixtures thereof.

5. The battery pack according to claim 1, wherein, The manganese oxides include manganese oxide (IV)(MnO2), manganese oxide (III)(Mn2O3), manganese hydroxy oxide (III)(MnOOH), manganese oxide (II)(MnO), manganese hydroxide (II)(Mn(OH)2), or mixtures thereof.

6. The battery pack according to claim 1, wherein, The second electrode also contains iron oxides, hydroxides, sulfides, or mixtures thereof.

7. The battery pack according to claim 1, wherein, The second electrode further comprises one or more second phases, the second phase comprising silicon dioxide (SiO2) or silicates, calcium oxide (CaO), magnesium oxide (MgO) or mixtures thereof.

8. The battery pack according to claim 1, wherein, The second electrode also comprises an inert conductive matrix, which includes carbon black, activated carbon, graphite powder, carbon steel mesh, stainless steel mesh, steel wool, nickel-plated carbon steel mesh, nickel-plated stainless steel mesh, nickel-plated steel wool, or mixtures thereof.

9. The battery pack according to claim 1, wherein, The second electrode also contains one or more hydrogen evolution reaction inhibitors.

10. The battery pack according to claim 1, wherein, The first electrode has a diameter of less than 50m 2 Specific surface area per g.

11. The battery pack according to claim 1, wherein, The first electrode has a diameter of less than 1m 2 Specific surface area per g.

12. The battery pack according to claim 1, wherein, The second electrode has a diameter of less than 5m. 2 Specific surface area per g.

13. The battery pack according to claim 1, wherein, The second electrode has a diameter of less than 1m. 2 Specific surface area per g.

14. The battery pack according to claim 1, wherein, The first electrode includes an adhesive comprising polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polypropylene (PP), polyethylene (PE), fluorinated ethylene propylene (FEP), polyacrylonitrile, styrene-butadiene rubber, carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (Na-CMC), polyvinyl alcohol (PVA), polypyrrole (PPy), or combinations thereof.

15. The battery pack according to claim 1, wherein, The first electrode contains additives, including bismuth(III) oxide (Bi₂O₃), bismuth(III) sulfide (Bi₂S₃), barium oxide (BaO), barium sulfate (BaSO₄), barium hydroxide (Ba(OH)₂), calcium oxide (CaO), calcium sulfate (CaSO₄), calcium hydroxide (Ca(OH)₂), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)₂), carbon nanotubes, carbon nanofibers, graphene, nitrogen-doped carbon nanotubes, nitrogen-doped carbon nanofibers, nitrogen-doped graphene, or combinations thereof.

16. The battery pack according to claim 1, wherein, An insulating material is used between the first electrode and the second electrode.

17. The battery pack according to claim 1, wherein, The iron includes iron concentrate.

18. The battery pack according to claim 1, wherein, The iron includes iron ore.

19. The battery pack according to claim 18, wherein, The iron ore contains at least 0.1% SiO2 by mass.

20. The battery pack according to claim 18, wherein, The iron ore contains at least 0.1% CaO by mass.

21. The battery pack according to claim 1, wherein, The iron comprises atomized iron powder.

22. The battery pack according to claim 1, wherein, The iron includes iron aggregates.

23. The battery pack according to claim 22, wherein, The iron agglomerates have an average length ranging from 50 μm to 50 mm.

24. The battery pack according to claim 22, wherein, The iron agglomerates have an average internal porosity ranging from 10% to 90% by volume.

25. The battery pack according to claim 22, wherein, The iron agglomerates have an average specific surface area ranging from 0.1 m². 2 / g to 25m 2 / g.

26. The battery pack according to claim 22, wherein, The electrolyte contains molybdate anions and divalent sulfide anions.

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