Rechargeable battery using an iron anode and a manganese oxide cathode

Abstract

Materials, designs, and methods of fabrication for iron-manganese oxide electrochemical cells are disclosed. In various embodiments, the negative electrode is comprised of a pelleted, briquette, or pressed iron-containing component containing metallic iron or an iron-based compound (iron oxide, hydroxide, sulfide, or a combination thereof), collectively referred to as an "iron negative electrode." In various embodiments, the positive electrode is comprised of a pelleted, briquette, or pressed manganese-containing component, including manganese(IV) oxide (MnO), manganese(III) oxide (MnO), manganese(III) oxyhydroxide (MnOOH), manganese(II) oxide (MnO), manganese(II) hydroxide (Mn(OH)), or a combination 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 a combination thereof. In various embodiments, the battery components are assembled in a prismatic or cylindrical shape.

Description

[Technical Field]

[0001] Related applications This application claims priority to U.S. Patent Provisional Application No. 62 / 879,153, entitled “Rechargeable Battery Using Iron Negative Electrode and Manganese Oxide Positive Electrode,” filed on 26 July 2019, and to U.S. Patent Provisional Application No. 63 / 021,267, entitled “Rechargeable Battery Using Iron Negative Electrode and Manganese Oxide Positive Electrode,” filed on 7 May 2020, the contents of both applications incorporated herein by reference for all purposes. Furthermore, this application claims priority to U.S. Patent Provisional Application No. 62 / 879,126, “Low Cost Metal Electrodes,” filed on 26 July 2019, and U.S. Patent Provisional Application No. 63 / 021,566, also “Low Cost Metal Electrodes,” filed on 7 May 2020, the contents of both applications being incorporated herein by reference for all purposes. Furthermore, this application claims priority to U.S. Patent Provisional Application No. 63 / 021,610, “Iron-Bearing Electrodes for Electrochemical Cells,” filed on 7 May 2020, the contents of which are incorporated herein by reference for all purposes. [Background technology]

[0002] Energy storage technologies are becoming increasingly important in power grids. At their most basic level, these energy storage assets provide smoothing to better match generation and demand in the distribution grid. The services performed by energy storage devices are beneficial to the power grid across multiple timescales, from milliseconds to years. Today, energy storage technologies exist that can support timescales from milliseconds to hours, but there is a need for long-term and ultra-long-term (collectively, >8 hours) energy storage systems. [Overview of the Initiative]

[0003] The materials, design, and manufacturing methods for an iron-manganese oxide electrochemical cell are disclosed. In various embodiments, the negative electrode consists of pelletized iron-containing components, briquette-containing iron-containing components, pressed iron-containing components, or sintered iron-containing components, which include metallic iron or iron-based compounds (oxides, hydroxides, sulfides, or combinations thereof), and are collectively referred to as the "iron negative electrode." In various embodiments, the positive electrode consists of pelletized manganese-containing components, briquette-containing manganese-containing components, pressed manganese-containing components, or sintered manganese-containing components, which include 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, and are collectively referred to as the "manganese oxide positive electrode." In various embodiments, the electrolyte consists of an aqueous alkali metal hydroxide containing lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), cesium hydroxide (CsOH), or a combination thereof. In various embodiments, the battery components are assembled in a prismatic or cylindrical shape. In various embodiments, a separator may be added.

[0004] The materials, design, and manufacturing methods for electrodes for electrochemical cells are disclosed. In various embodiments, the electrodes contain iron.

[0005] Various embodiments include a battery comprising a first electrode containing manganese oxide, an electrolyte, and a second electrode containing iron. In some embodiments, the iron comprises directly reduced iron (DRI). In some embodiments, the electrolyte is a liquid electrolyte. In some embodiments, the electrolyte comprises alkali metal hydroxides including lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), cesium hydroxide (CsOH), or mixtures thereof. In some embodiments, the electrolyte is lithium sulfide (Li2S) or polysulfide (Li2S) x (x=2~6), sodium sulfide (Na2S) or polysulfide (Na2S) x (x=2~6), potassium sulfide (K2S) or polysulfide (K2S) x (x=2~6), cesium sulfide (Cs2S) or polysulfide (Cs2S) x The second electrode consists of alkali metal sulfides or polysulfides containing x=2~6, or mixtures thereof. In some embodiments, the second electrode is pelletized and has a multimodal distribution. In some embodiments, the manganese oxide includes manganese(IV) oxide (MnO2), manganese(III) oxide (Mn2O3), manganese(III) oxyhydroxide (MnOOH), manganese(II) oxide (MnO), manganese(II) hydroxide (Mn(OH)2), or mixtures thereof. In some embodiments, the second electrode further includes iron oxides, hydroxides, sulfides, or mixtures thereof. In some embodiments, the second electrode further consists of one or more secondary phases containing silica (SiO2) or silicate, calcium oxide (CaO), magnesium oxide (MgO), or mixtures thereof. In some embodiments, the second electrode further comprises an inert conductive matrix containing carbon black, activated carbon, graphite powder, carbon steel mesh, stainless steel mesh, steel wool, nickel-coated carbon steel mesh, nickel-coated stainless steel mesh, nickel-coated steel wool, or a mixture thereof. In some embodiments, the second electrode further comprises one or more hydrogen evolution reaction inhibitors. In some embodiments, the specific surface area of ​​the first electrode is approximately 50 m². 2 It is less than / g. In some embodiments, the specific surface area of ​​the first electrode is approximately 1 m².2 It is less than / g. In some embodiments, the specific surface area of ​​the second electrode is approximately 5m². 2 It is less than / g. In some embodiments, the specific surface area of ​​the second electrode is approximately 1 m². 2 It is less than / g.

[0006] In some embodiments, the first electrode is made of a binder comprising polytetrafluoroethylene (PTFE), polyvinylidene difluoride (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 a combination thereof. In some embodiments, the first electrode is made of 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 a combination thereof. In some embodiments, a separator material is used between the first electrode and the second electrode. In some embodiments, the iron contains concentrated ore. 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, wustite, martite, goethite, limonite, siderite, pyrite, ilmenite, or spinel manganese ferrite. In some embodiments, the iron contains iron ore. In some embodiments, the iron ore contains at least 0.1% by mass of SiO2. In some embodiments, the iron ore contains at least 0.1% by mass of CaO. In some embodiments, the iron contains atomized iron powder. In some embodiments, the iron contains an iron lump product. In some embodiments, the average length of the iron lump product ranges from about 50 μm to about 50 mm. In some embodiments, the average internal porosity of the iron lump product ranges from about 10% by volume to about 90% by volume. In some embodiments, the average specific surface area of the iron lump product is about 0.1 m 2 / g to about 25 m 2The range is / g. In some embodiments, the electrolyte comprises molybdate anions and sulfide anions. In various embodiments, it may be included in a stack of one or more batteries in a bulk energy storage system. In some embodiments, the bulk energy storage system is a long-term energy storage (LODES) system. Various embodiments include a method for manufacturing a battery, the method comprising the steps of providing a first electrode containing manganese oxide, providing an electrolyte, and providing a second electrode containing iron. [Brief explanation of the drawing]

[0007] [Figure 1A] Figure 1A is a schematic diagram of a prismatic electrochemical cell according to various embodiments of the present disclosure. [Figure 1B] Figure 1B is a schematic diagram of a stack configuration based on the electrochemical cell disclosed in Figure 1A. [Figure 1C] Figure 1C is a schematic diagram of a stack configuration using a two-pole current collector to connect electrochemical repetitive units. [Figure 2A] Figure 2A is a schematic diagram of the hydrogen recombination electrode. [Figure 2B] Figure 2B is a schematic diagram of the hydrogen recombination electrode. [Figure 2C] Figure 2C is a schematic diagram of various arrangements of hydrogen recombination electrodes within the cell. [Figure 2D] Figure 2D is a schematic diagram of various arrangements of hydrogen recombination electrodes within the cell. [Figure 2E] Figure 2E is a schematic diagram of various arrangements of hydrogen recombination electrodes within the cell. [Figure 2F] Figure 2F is a schematic diagram of various arrangements of hydrogen recombination electrodes within the cell. [Figure 3A] Figure 3A is a schematic diagram of a proof-of-concept cell using approximately 1.3 g of iron powder as the negative electrode and approximately 0.8 g of positive electrode containing approximately 78 wt% MnO2. [Figure 3B] Figure 3B plots the cycle data (cell voltage vs. time) and capacitance curve (cell voltage vs. cell capacitance) for a selected cycle, using the proof-of-concept cell configuration shown in Figure 3A. [Figure 3C] Figure 3C plots the MnO2 discharge capacity (mAh / gMnO2) on the left Y-axis and the Coulomb efficiency on the right Y-axis for different cycles. [Figure 3D] Figure 3D is a plot of lifetime initial (BOL) polarization data (current density vs. positive electrode potential) using the proof-of-concept configuration of Figure 3A. [Figure 3E] Figure 3E shows the second cycle charge / discharge curve (total cell voltage vs. capacity) of the proof-of-concept EMD / DRI cell. [Figure 4A] Figure 4A is a schematic diagram of a stacked prismatic electrochemical cell using pelletized directly reduced iron (DRI) as the anode and a manganese compound-based cathode, based on the stack configuration of Figure 1B. [Figure 4B] Figure 4B is a schematic diagram of a cylindrical electrochemical cell according to various embodiments of the present disclosure, using pelletized direct reduced iron (DRI) as the anode and a manganese compound-based cathode. [Figure 5] Figure 5 shows negative electrodes according to various embodiments. [Figure 6A] Figure 6A shows an example of a discharge method. [Figure 6B] Figure 6B shows an embodiment of electrodes divided into horizontal layers housed in a larger container. [Figure 6C] Figure 6C shows an embodiment of electrodes divided into horizontal layers housed in a larger container. [Figure 6D] Figure 6D shows a metal fabric equipped with electrodes made of directly reduced iron pellets. [Figure 6E] Figure 6E shows an example of a porous mesh container. [Figure 6F] Figure 6F shows an example of a porous mesh container. [Figure 7] Figure 7 shows an example of a backing plate. [Figure 8] Figure 8 shows that the fastening rail can also function as a busbar. [Figure 9] Figure 9 shows a direct reduced iron (DRI) microbulb bed assembly. [Figure 10]Figure 10 shows a module consisting of rigid side walls. [Figure 11A] Figure 11A shows fastening techniques according to various embodiments. [Figure 11B] Figure 11B shows fastening techniques according to various embodiments. [Figure 12] Figure 12 shows the expandable material contained within the rigid iron electrode housing assembly. [Figure 13] Figure 13 shows thermal bonding. [Figure 14] Figure 14 shows the mechanical interactions of the pellets. [Figure 15] Figure 15 shows the pellet bed. [Figure 16] Figure 16 shows an example of a current collector. [Figure 17] Figure 17 shows mechanically processed pellets. [Figure 18] Figure 18 shows a comparison of the distribution of released products. [Figure 19] Figure 19 is a temperature plot. [Figure 20] Figure 20 shows an example of a method to avoid gaps. [Figure 21] Figure 21 shows an example of an additive holder configuration. [Figure 22] Figure 22 shows an example of an additive incorporation process. [Figure 23] Figure 23 shows the electrode formation process. [Figure 24] Figure 24 shows an example of a system in which one or more of the various embodiments can be used as part of a bulk energy storage system. [Figure 25] Figure 25 shows an example of a system in which one or more of the various embodiments can be used as part of a bulk energy storage system. [Figure 26] Figure 26 shows an example of a system in which one or more of the various embodiments can be used as part of a bulk energy storage system. [Figure 27] Figure 27 shows an example of a system in which one or more of the various embodiments can be used as part of a bulk energy storage system. [Figure 28] Figure 28 shows an example of a system in which one or more of the various embodiments can be used as part of a bulk energy storage system. [Figure 29] Figure 29 shows an example of a system in which one or more of the various embodiments can be used as part of a bulk energy storage system. [Figure 30] Figure 30 shows an example of a system in which one or more of the various embodiments can be used as part of a bulk energy storage system. [Figure 31] Figure 31 shows an example of a system in which one or more of the various embodiments can be used as part of a bulk energy storage system. [Figure 32] Figure 32 shows an example of a system in which one or more of the various embodiments can be used as part of a bulk energy storage system. [Modes for carrying out the invention]

[0008] The following examples are provided to illustrate various embodiments of the System and Method of the Invention. These examples are for illustrative purposes only, may be predictive, and should not be considered limiting, nor do they limit the scope of the Invention in any way.

[0009] Various embodiments will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings to refer to the same or similar parts. References to specific examples and implementations are for illustrative purposes only and are not intended to limit the scope of the claims. The following description of embodiments of the present invention is not intended to limit the invention to these embodiments, but rather to enable those skilled in the art to manufacture and use the invention. Unless otherwise noted, the accompanying drawings are not drawn to scale.

[0010] Where used herein, unless otherwise stated, room temperature is 25°C, and standard temperature and standard pressure are 25°C and 1 atm. Unless otherwise expressly stated, all tests, test results, physical properties, and values ​​that are temperature-dependent, pressure-dependent, or both are provided at standard ambient temperature and pressure.

[0011] Generally, the terms “approximately” and the symbol “~” as used herein, unless otherwise specified, mean to include a variation or range of ±10%, experimental error or instrument error associated with obtaining the stated values, preferably the greater of these.

[0012] Where used herein, unless otherwise specified, the enumeration of value ranges herein is intended merely as a simplified way of referring individually to each separate value that falls within the range. Unless otherwise indicated herein, each individual value within the range is incorporated herein as if it were individually enumerated herein.

[0013] As used herein, unless otherwise specified, the terms “%”, “weight%”, and “mass%” are used synonymously and refer to the weight of the first component as a percentage of the total weight of, for example, a formulation, mixture, particles, pellets, agglomerates, material, structure, or product. As used herein, unless otherwise specified, “volume%”, “% volume”, and similar terms refer to the volume of the first component as a percentage of the total volume of, for example, a formulation, mixture, particles, pellets, agglomerates, material, structure, or product.

[0014] The following examples are provided to illustrate various embodiments of the System and Method of the Invention. These examples are for illustrative purposes only, may be predictive, and should not be considered limiting, nor do they limit the scope of the Invention in any way.

[0015] It should be noted that it is not necessary to provide or express the theories underlying any novel, groundbreaking processes, materials, performances, or other beneficial features and properties that are the subject matter of or associated with embodiments of the present invention. Nevertheless, various theories are provided herein to further advance the art of the art. The theories presented herein do not in any way limit, restrict, or narrow the scope of protection granted to the inventions of the claims unless otherwise expressly stated. Such theories may not be necessary for the use of the present invention, nor may they be put into practice. Furthermore, it is understood that the present invention may be linked to new and previously unknown theories to describe the functional characteristics of embodiments of the methods, articles, materials, devices, and systems of the present invention. Such subsequently developed theories do not limit the scope of protection granted to the present invention.

[0016] The various embodiments of the systems, equipment, techniques, methods, activities, and operations shown herein can be used in various other activities and fields in addition to those shown herein. In addition, such embodiments can be used in conjunction with other equipment or activities that may be developed in the future, and with existing equipment or activities that may be partially modified based on the teachings herein. Furthermore, the various embodiments and examples shown herein can be used together, whole or in part, and in various different combinations. Accordingly, the configurations provided in the various embodiments herein can be used together. For example, the elements of the embodiment having A, A', and B, and the elements of the embodiment having A'', C, and D can be used together in various combinations according to the teachings herein, for example, A, C, D, and A, A'', C, D, etc. Accordingly, the scope of protection given to the present invention should not be limited to a particular embodiment, example, or a particular embodiment, configuration, or arrangement shown in a particular figure embodiment.

[0017] Where used herein, unless otherwise specified, the term “specific gravity,” also known as apparent density, should be given the broadest possible meaning and generally refer to the average weight per unit volume of a structure, such as the volumetric shape of a material. This property will include the internal porosity of the particles as part of their volume. This can be measured, among other techniques, with a low-viscosity fluid that wets the particle surface.

[0018] Where used herein, unless otherwise specified, the term “actual density,” sometimes also called true density, should be given the broadest possible meaning, generally referring to the weight per unit volume of a material when no voids are present in the material. This measurement and property essentially eliminates internal porosity from the material and does not include, for example, any voids in the material.

[0019] Therefore, the relationship between the three density properties can be explained using an aggregate of porous foam balls (e.g., Nerf® balls). The weight of the balls filling the container would be the bulk density of the balls:

[0020]

number

[0021] The weight of a single ball per unit spherical volume is likely its apparent density:

[0022]

number

[0023] The skeletal structure of the ball per unit volume of the remaining material, that is, the weight of the material constituting the ball after all void volume has been removed, would be the skeletal density.

[0024]

number

[0025] As used herein, unless otherwise specified, the terms agglomerates and aggregates should be given the broadest possible meaning, and generally refer to aggregates of particles in a powder.

[0026] Electrochemical cells, such as batteries, store electrochemical energy by utilizing the electrochemical potential difference created by the voltage difference between the positive and negative electrodes. This voltage difference generates an electric current if the electrodes are connected by a conductive element. In a battery, the negative and positive electrodes are connected in series by external and internal resistive elements. Generally, the external element conducts electrons, and the internal element (electrolyte) conducts ions. Since charge imbalance is not permitted between the negative and positive electrodes, these two flows must supply ions and electrons at the same rate. During operation, the flow of electrons can be used to drive external devices. Rechargeable batteries can be charged by applying a counter-voltage difference, and this counter-voltage difference manipulates the current and ion flow that flows in the opposite direction to the battery discharging during operation.

[0027] Embodiments of the present invention include apparatus, systems, and methods for long-term and ultra-long-term low-cost energy storage. In this specification, “long-term” and / or “ultra-long-term” refer to energy storage periods of 8 hours or longer, such as 8-hour energy storage periods, energy storage periods ranging from 8 to 20 hours, 20-hour energy storage periods, energy storage periods ranging from 20 to 24 hours, 24-hour energy storage periods, energy storage periods ranging from 24 hours to 1 week, and energy storage periods ranging from 1 week to 1 year (e.g., from several days to several weeks or several months). In other words, a “long-term” and / or “ultra-long-term” energy storage cell refers to an electrochemical cell that can be configured to store energy over several days, several weeks, or several seasons. For example, an electrochemical cell may be configured to store energy generated by a solar cell during the summer months when sunlight is abundant and solar power exceeds grid requirements, and to discharge the stored energy during the winter months when sunlight may be insufficient to meet grid requirements.

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

[0029] In other embodiments, the present invention includes devices, systems, and methods for storing energy for short durations of less than approximately eight hours. For example, an electrochemical cell may be configured to store energy generated by a photocell during a daytime cycle in which solar generation exceeds grid requirements at noon, and to release the stored energy in the evening or later when solar energy is deemed insufficient to meet grid requirements. Another example of the invention involves energy storage to be used as a backup power source when electricity supplied by the power grid is insufficient in facilities such as homes, commercial buildings, factories, hospitals, or data centers where the required discharge time varies from a few minutes to several days.

[0030] 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 certain embodiments, the electrolyte may be an alkaline solution (pH > 10). In certain embodiments, the electrolyte may be a nearly neutral solution (pH > 4).

[0031] According to various embodiments, the half-cell reaction on the negative electrode that occurs during discharge is as follows.

[0032] [ka]

[0033] [ka]

[0034] For example, the half-cell reaction on the negative electrode that occurs during discharge is Fe + 2OH - ∇Fe(OH)₂ + 2e₂ - and 3Fe(OH)2+2OH - ?Fe3O4+4H2O+2e - The theoretical capacity based on metallic iron following the negative electrode reaction in this example is 1276 mAh / gFe. During charging, the reverse reaction occurs.

[0035] According to various embodiments, the half-cell reactions that may occur on the positive electrode during discharge are as follows.

[0036] [ka]

[0037] [ka]

[0038] For example, the half-cell reaction on the positive electrode that occurs during discharge is MnO2+e -+H2O?MnOOH+OH - and MnOOH+e - +H2O?Mn(OH)2+OH - Therefore, the theoretical capacity based on MnO2 following the negative electrode reaction in this example is 616 mAh / g. MnO2 That's the case. The opposite reaction occurs during charging.

[0039] According to various embodiments, hydroxide anion (OH - ) are accelerating ions. In some embodiments, both hydroxide anions and alkali metal cations are accelerating ions. In other words, the ionic current is carried by the simultaneous migration of hydroxide anions and alkali metal cations along opposite directions.

[0040] In some embodiments, a significant negative electrode reaction occurs at Fe 0 When a reaction occurs between Fe(II) and Fe(II) (mechanism F1), and a significant positive electrode reaction occurs between Mn(IV) and Mn(III) (mechanism M1), the nominal cell voltage is approximately 1.2V. In some embodiments, when a significant negative electrode reaction occurs between Fe(II) and Fe(III) (mechanism F2), and a significant positive electrode reaction occurs between Mn(IV) and Mn(III) (mechanism M1), the nominal cell voltage is approximately 1.0V. In some embodiments, when a significant negative electrode reaction occurs between Fe 0 When a reaction occurs between Fe(II) and Fe(II) (mechanism F1), and a significant positive electrode reaction occurs between Mn(III) and Mn(II) (mechanism M2), the nominal cell voltage is approximately 0.8V. In some embodiments, when a significant negative electrode reaction occurs between Fe(II) and Fe(III) (mechanism F2), and a significant positive electrode reaction occurs between Mn(III) and Mn(II) (mechanism M2), the nominal cell voltage is approximately 0.6V. In certain embodiments, when both mechanisms F1 and F2 occur simultaneously or sequentially on the negative electrode, and both mechanisms M1 and M2 occur simultaneously or sequentially on the positive electrode, the nominal cell voltage is approximately 1.0V, or other values ​​between 1.2V and 0.6V. Any remaining cell resistance may further reduce the discharge cell voltage under load.

[0041] According to various embodiments, the primary side reaction on the negative electrode during charging is hydrogen evolution (HER). According to various embodiments, the primary side reaction on the positive electrode during charging is oxygen evolution (OER) or carbon oxidation (corrosion) reaction. One of the main advantages of Fe-MnO2 cells is these "self-balancing" side reactions, which significantly reduce concerns about thermal runaway if the negative and / or positive electrodes are damaged during charging or overcharging. In some embodiments, if the iron-based negative electrode material cannot be charged properly, the positive electrode reaction during charging is Mn(II) → Mn(III) and / or Mn(III) → Mn(IV), and the negative electrode reaction during charging is HER. In some embodiments, if the manganese-based positive electrode material cannot be charged properly, the negative electrode reaction during charging is Fe(III) → Fe(II) and / or Fe(II) → Fe 0 Therefore, the positive electrode reaction during charging is OER. In some embodiments, if the manganese-based positive electrode and iron-based negative electrode cannot be charged properly, the positive electrode reaction during charging is OER and the negative electrode reaction during charging is HER.

[0042] In some embodiments, the electrochemical cell comprises a negative electrode, a positive electrode, an electrolyte, and a separator positioned between the positive and negative electrodes (for example, as shown in Figure 1A). Figure 1A shows an electrochemical cell 100 comprising a negative electrode and an electrolyte 102 separated from the positive electrode and 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. Current collectors 107 may be attached to the negative electrode 102 and the positive electrode 103 respectively and supported by a polyethylene backing plate 106.

[0043] In some embodiments, the multiple electrochemical cells 100 shown in Figure 1A may be electrically connected in series to form a stack 120, for example, as shown in Figure 1B. For example, to connect one cell 100 to the next, the multiple cells 100 may be connected in series by metal bolts 122 passing through current collectors 107 secured by metal nuts 123 and polyethylene backing plates 106. In certain other embodiments, the multiple electrochemical cells 100 may be electrically connected in parallel. In certain other embodiments, the multiple electrochemical cells 100 are connected in a series-parallel mixed electrical configuration to preferentially combine the currents and voltages to be carried.

[0044] In some embodiments, multiple adjacent electrochemical cells 100 are physically and electrically connected using a set of metal bolts, nuts, and washers (e.g., bolt 122 and nut 123) as described above. In some embodiments, the metal bolts, nuts, and washers are stainless steel, carbon steel, aluminum, copper, or a combination thereof. In some embodiments, multiple adjacent electrochemical cells 100 are physically and electrically connected using metal tabs. In some embodiments, the metal tabs are connected by welding, brazing, or other common metal joining techniques. In some embodiments, multiple adjacent electrochemical cells, such as cell 131 in a stack 130, are electrically connected using bipolar current collectors 132, for example, as shown in Figure 1C. Cell 131 may be similar to cell 100, except that the current collector 132 may be a bipolar current collector and there may be no polyethylene backing plates 106 between each cell. In some embodiments, multiple adjacent electrochemical cells 100 in a stack 120 are electrically connected using monopolar current collectors 107, for example, as shown in Figure 1B.

[0045] In various embodiments, the cell architecture is prismatic, as shown, for example, in Figure 1A. In some embodiments, the cell is sealed. In some embodiments, the sealed cell is equipped with a ventilation opening for gas exchange. In non-limiting examples, the gas may be hydrogen generated on the negative electrode at the hydrogen evolution reaction potential. In some embodiments, the cell is covered with a removable lid.

[0046] In various embodiments, the cell architecture is cylindrical, as shown, for example, in Figure 1B. In some embodiments, the cell is sealed. In some embodiments, the sealed cell is equipped with a ventilation port for gas exchange. In non-limiting examples, the gas may be hydrogen generated on the negative electrode at the hydrogen evolution reaction potential. In some embodiments, the cell is covered with a movable lid.

[0047] In some embodiments, the hydrogen recombination electrode is placed near the negative electrode (for example, as shown in Figures 2A to 2F).

[0048] According to various embodiments, the negative electrode consists of a pelletized iron-containing compound, a briquette-containing iron-containing compound, a pressed iron-containing compound, or a sintered iron-containing compound. Such an iron-containing compound may contain one or more forms of iron ranging from highly reduced (more metallic) iron to highly oxidized (more ionic) iron. In various embodiments, the pellets may contain various iron compounds, such as iron oxide, iron hydroxide, iron sulfide, or combinations thereof. In various embodiments, the pellets may contain one or more secondary phases, such as silica (SiO2) or silicate, calcium oxide (CaO), or magnesium oxide (MgO). 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 can be used as the feed material for forming the sintered iron electrode. In some embodiments, the green body may further contain a binder, such as a polymer or an inorganic clay-like material. In various embodiments, agglomerated sintered iron pellets can be formed in furnaces such as continuous feed calcining furnaces, batch feed calcining furnaces, blast furnaces, rotary calcining furnaces, and rotary hearths. In various embodiments, the pellets may include in the form of a reducing and / or sintered iron-retaining precursor, and / or by-product material, known to those skilled in the art as directly reduced iron (DRI). Various embodiments may include processing the pellets containing the DRI pellets using electrical, electrochemical, mechanical, chemical, and / or thermal processes before introducing the pellets into an electrochemical cell.

[0049] Various embodiments of the use of directly reduced iron (DRI) as a material for batteries (or cells), as a component of batteries (or cells), and in combinations and variations thereof are considered. In various embodiments, DRI may be produced from a material obtained from the reduction of natural or processed iron ore without reaching the melting temperature of iron, or may be such a material. In various embodiments, the iron ore may be taconite, magnetite, hematite, goethite, etc. In various embodiments, DRI may be in the form of pellets that are spherical or substantially spherical. In various embodiments, DRI may be porous and may contain open and / or closed internal porosity. In various embodiments, DRI may include material that has been further processed by hot or cold briquetting. In various embodiments, DRI may be obtained by reducing iron ore pellets to iron metal (Fe 0DRI can be produced by forming more metallic (more reduced, less oxidized) materials such as wustite (FeO), or composite pellets containing iron metal and residual oxide phases. In various non-limiting embodiments, DRI may be reduced iron ore taconite, directly reduced ("DR") taconite, reduced "blast furnace (BF) grade" pellets, reduced "electric arc furnace (EAF) grade" pellets, "cold directly reduced iron (CDRI)" pellets, directly reduced iron ("DRI") pellets, hot briquette iron (HBI), or any combination thereof. In the iron and steel industry, DRI is sometimes called "sponge iron," and its use is common, particularly in India. Embodiments of iron materials, including exemplary embodiments of DRI materials for use in the various embodiments described herein, including use as electrode materials, may have one, more than one, or all of the material properties listed in Table 1 below. As used herein, including in Table 1, the following terms have the following meanings unless otherwise expressly stated: “Specific surface area” means the total surface area of ​​the material per unit mass, including the surface area of ​​pores in porous structures; “Carbon content” or “Carbon (weight %)” means the mass of total carbon as a percentage of the total mass of DRI; “Cementite content” or “Cementite (weight %)” means the mass of Fe3C as a percentage of the total mass of DRI; “Total Fe (weight %)” means the mass of all iron as a percentage of the total mass of DRI; “Metallic Fe (weight %)” means the mass of Fe3C as a percentage of the total mass of DRI. 0 It means the mass of iron in its state; "metallized" is the total mass of iron, Fe 0 It refers to the mass of iron in its state.

[0050] [Table 1]

[0051] *The specific surface area is preferably determined by the Brunauer-Emmett-Teller adsorption method ("BET"), more preferably BET as shown in ISO 9277 (this disclosure is incorporated herein by reference in its entirety); it is recognized that other tests, such as methylene blue (MB) staining, ethylene glycol monoethyl ether (EGME) adsorption, electrokinetic analysis of complex ion adsorption, and protein retention (PR) methods, can provide results that can be correlated with the BET results. ** 90% of the pore volume is d 孔、90%容積 It is the volume inside a hole with a larger diameter. *** 50% of the free surface area refers to the surface area inside holes with a diameter greater than 50% of the free surface area, i.e., holes with a diameter greater than d.

[0052] In addition, embodiments of iron materials, including, for example, embodiments of DRI materials, for use in the various embodiments described herein, including use as electrode materials, may have one or more of the following properties, features, or characteristics, as shown in Table 1A (note that a value in one row or column may exist together with values ​​in a different row or column).

[0053] [Table 1A]

[0054] The cold crush strength is preferably determined according to ISO 4700:20073, the entire disclosure of which is incorporated herein by reference. The cold crush strength distribution within the particle group is preferably determined according to ISO 4700:2007, the entire disclosure thereof being incorporated herein by reference.

[0055] Furthermore, the characteristics shown in Table 1 may be present in embodiments in addition to, or instead of, the characteristics in Table 1A. Larger and smaller values ​​of these characteristics may also be present in various embodiments.

[0056] In this embodiment, the specific surface area of ​​the pellet is approximately 0.05 m². 2 / g ~ approx. 35m 2 / g, approx. 0.1m 2 / g~about 5m 2 / g, approx. 0.5m 2 / g~about 10m 2 / g, approx. 0.2m 2 / g~about 5m 2 / g, approx. 1m 2 / g~about 5m 2 / g, approx. 1m 2 / g~about 20m 2 It may also be / g, which is about 1m 2 It can be larger than / g, or about 2m 2 It can be larger than / g, or about 5m 2 It may be less than / g, approximately 15m 2 It may be less than / g, approximately 20m 2 The values ​​may be less than / g, as well as combinations and variations thereof, and may be greater than or less than the specified value.

[0057] Generally, iron ore pellets are produced by crushing, grinding, or milling iron ore into a fine powder form, and then concentrated by removing impurity phases (so-called "gangues") released during the grinding process. Generally, grinding the ore to a finer (smaller) particle size increases the purity of the resulting concentrate. The concentrate is then formed into pellets by a pelletizing or balling process (for example, using a drum or disc pelletizer). Generally, producing higher purity ore pellets requires more energy input. Iron ore pellets are generally commercially available in two main categories: blast furnace (BF) grade pellets and direct reduction (DR) grade (sometimes also called electric arc furnace (EAF) grade). The main difference is the SiO2 content, with other impurity phases being more abundant in BF grade pellets compared to DR grade pellets. Typical and important specifications for DR grade pellets or raw materials are that the total Fe content by mass percentage is in the range of 63 to 69% (e.g., 67% by mass), and the SiO2 content by mass percentage is less than 3% (e.g., 1% by mass). Typical and important specifications for BF grade pellets or raw materials are that the total Fe content by mass percentage is in the range of 60 to 67% (e.g., 63% by mass), and the SiO2 content by mass percentage is in the range of 2 to 8% (e.g., 4% by mass).

[0058] In certain embodiments, DRI can be produced by the reduction of "blast furnace" pellets, in which case the resulting DRI may have the material properties described in Table 2 below. The use of reduced BF grade DRI may be advantageous because it requires less input energy to produce the pellets, which in other words means a lower cost for the finished product.

[0059] [Table 2]

[0060] *The specific surface area is preferably determined by the Brunauer-Emmett-Teller adsorption method ("BET"), more preferably BET as described in ISO 9277 (the disclosures in this document are incorporated herein by reference in their entirety). It is recognized that other tests, such as methylene blue (MB) staining, ethylene glycol monoethyl ether (EGME) adsorption, electrokinetic analysis of complex ion adsorption, and protein retention (PR) methods, can provide results that can be correlated with BET results. ** 90% of the pore volume is d 孔、90%容積 It is the volume inside a hole with a larger diameter. *** 50% of the free surface area refers to the surface area inside holes with a diameter greater than 50% of the free surface area, i.e., holes with a diameter greater than d.

[0061] Furthermore, the characteristics shown in Table 2 may be present in embodiments in addition to, or instead of, the characteristics in Table 1 and / or Table 1A. Larger and smaller values ​​of these characteristics may also be present in various embodiments.

[0062] In certain embodiments, DRI can be produced by reducing DR-grade pellets, in which case the resulting DRI may have the material properties described in Table 3 below. The use of reduced DR-grade DRI may be advantageous because it has a higher Fe content in the pellets, thereby increasing the energy density of the battery.

[0063] [Table 3]

[0064] *The specific surface area is preferably determined by the Brunauer-Emmett-Teller adsorption method ("BET"), more preferably BET as described in ISO 9277 (the disclosures in this document are incorporated herein by reference in their entirety). It is recognized that other tests, such as methylene blue (MB) staining, ethylene glycol monoethyl ether (EGME) adsorption, electrokinetic analysis of complex ion adsorption, and protein retention (PR) methods, can provide results that can be correlated with BET results. ** 90% of the pore volume is d 孔、90%容積 It is the volume inside a hole with a larger diameter. *** 50% of the free surface area refers to the surface area inside holes with a diameter greater than 50% of the free surface area, i.e., holes with a diameter greater than d.

[0065] Furthermore, the characteristics shown in Table 3 may be present in embodiments in addition to, or instead of, the characteristics in Tables 1, 1A, and / or 2. Larger and smaller values ​​of these characteristics may also be present in various embodiments.

[0066] In various embodiments, the bed of conductive pellets constitutes an electrode in an energy storage system (e.g., it functions to provide an electrode, is a component of an electrode, forms an electrode, etc.). In this embodiment of the electrode, the pellets include iron-containing materials, reduced iron materials, unoxidized iron, highly oxidized iron, iron having valence states of 0 to 3+, and combinations and variations thereof. In this embodiment of the electrode, the pellets include iron having one or more of the features shown in Tables 1, 1A, 2, and 3. In embodiments, the pellets have porosity, e.g., an open pore structure, which may have pore sizes ranging from several nanometers to several microns. For example, embodiments may have pore sizes of about 5 nm to about 100 μm, about 50 nm to about 10 μm, about 100 nm to about 1 μm, greater than 100 nm, greater than 500 nm, less than 1 μm, less than 10 μm, less than 100 μm, and combinations and variations of such pore sizes, as well as larger and smaller pores. In some embodiments, the pellets include pellets of directly reduced iron (DRI). Embodiments of such electrodes in energy storage systems, particularly long-term energy storage systems, may have one or more of these features described above.

[0067] The filling of pellets creates macropores between individual pellets, such as openings, spaces, channels, or voids. These macropores facilitate ion transport across electrodes that, in some embodiments, have dimensions of several centimeters, still having very thick minimum dimensions compared to some other types of battery electrodes. The micropores within the pellets allow for contact between the active material and the electrolyte, enabling high surface area utilization of the active material. This electrode structure is particularly useful for improving the rate capacity of very thick electrodes for stationary, long-term energy storage, where thick electrodes may be required to achieve very high area capacities.

[0068] The pellets of these embodiments, in particular for use in electrode embodiments for long-term energy storage systems, may be of any volumetric shape, such as spheres, discs, packs, beads, tablets, pills, rings, lenses, plates, panels, cones, frustocones, square blocks, rectangular blocks, trusses, angles, channels, hollow sealed chambers, hollow spheres, blocks, sheets, films, fine particles, square timbers, rods, plates, cylinders, fibers, chemical fibers, tubes, cups, pipes, and various combinations thereof, as well as other more complex shapes. The electrode pellets may be the same shape or different shapes. The pellets in an electrode that is one of several electrodes in a long-term energy storage system may be the same as or different from the pellets in other electrodes in that storage system.

[0069] Pellet size refers to the maximum cross-sectional distance of the pellet, e.g., the diameter of the sphere, unless otherwise explicitly used. Pellets may be the same size or different sizes. It is recognized that the shape, size, and both of the pellets, and typically to a lesser extent, the shape and size of the container or housing that holds the pellets, determine the nature and size of the macropores of the electrode. Pellets may 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.

[0070] In this embodiment, the pellets that make up the electrode are approximately 3 g / cm³ 3 ~Approx. 6.5g / cm 3 Approximately 0.1 g / cm³ 3 ~Approx. 5.5g / cm 3 Approximately 2.3 g / cm³ 3 ~Approx. 3.5g / cm 3 3.2 g / cm³ 3 ~Approx. 4.9g / cm 3 Approximately 0.5 g / cm³ 3Larger than that, approximately 1 g / cm 3 Larger than that, approximately 2g / cm 3 Larger than that, approximately 3g / cm 3 It is possible to provide electrodes having bulk densities greater than, as well as combinations of these and various values, as well as larger and smaller values.

[0071] In certain embodiments, a mixture of reduced DR grade pellets and reduced BF grade pellets may be used together. In certain other embodiments, a combination of reducing material (DRI) and raw ore material (DR grade or BF grade) may be used.

[0072] In various embodiments, DRI may be produced using "artificial ore" or by-product form of iron oxide, such as waste. As one non-limiting example, mill scale is a mixture of iron oxides formed on the surface of hot-rolled steel, which in various embodiments is collected, crushed to form iron oxide powder, then agglomerated to form pellets, and then reduced to form DRI. Other waste streams may be similarly utilized 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 Fe-containing pickling solution may be neutralized with a base (such as potassium hydroxide or sodium hydroxide) to precipitate the iron oxide powder, which is then agglomerated to form pellets, and then reduced to form DRI.

[0073] In various embodiments, the precursor iron oxide is first reduced and then molded into pellets or other aggregates. In certain non-limiting embodiments, iron oxide powder derived from natural ore or artificial ore is reduced to iron metal powder in a reducing gas environment such as a linear hearth furnace with a hydrogen atmosphere in the range of 1% to 100% H2, at heating temperatures in the range of 700°C to 1400°C, 900°C to 1300°C, 900°C, 1000°C, and / or 1100°C. In embodiments using hydrogen as the reducing gas, the cementite (Fe3C) content of the DRI can be as low as 0% by weight.

[0074] In various embodiments, the precursor iron oxide is reduced under conditions that promote swelling or non-densification reduction. In certain non-limiting embodiments, iron oxide powder from natural ore or artificial ore is reduced to iron metal powder in a reducing gas environment such as a linear hearth furnace with a gas atmosphere such as a carbon monoxide mixture that promotes expansion of porosity by swelling, at heating temperatures in the range of 700°C to 1400°C, 900°C to 1300°C, 900°C, 1000°C, and / or 1100°C. In some embodiments, a precursor iron oxide containing a preferred pellet chemical to promote swelling may be selected, or additives such as limestone may be used.

[0075] In various embodiments, DRI pellets or agglomerates are formed from iron oxide powder in a single process using a rotary calcination furnace. The rotational motion of the furnace promotes the agglomeration of the powder into pellets or agglomerates, and the high-temperature reducing gas environment provides simultaneous reduction of iron oxide. In various other embodiments, a multi-stage rotary calcination furnace may be used, in which the agglomeration step and the reduction step can be independently controlled and optimized.

[0076] In various embodiments, the DRI has a non-spherical shape. In certain embodiments, the DRI may have a shape enclosed by substantially straight lines or a brick-like shape. In certain embodiments, the DRI may have a substantially cylindrical, rod-like, or disc-like shape. In certain embodiments, the DRI may have a substantially flat or sheet-like shape. In certain embodiments, the iron oxide powder is dry-formed by die-compression into a cylindrical shape or any other shape suitable for die pressing. In certain embodiments, the iron oxide powder is dry-formed into a sheet-like shape by roll pressing with calender rolls or a powder mill. In certain embodiments, the iron oxide powder is compounded with a binder such as clay or a polymer and dry-formed into a rod-like shape by extrusion. In certain embodiments, the iron oxide powder is compounded with a binder such as clay or a polymer and dry-formed into a sheet-like shape by roll pressing with calender rolls. The binder may consist of clay such as bentonite, or polymers such as corn starch, polyacrylamide, or polyacrylate. The binder may consist of a combination of one or more clays and one or more polymers. In certain embodiments, iron oxide powder is dispersed in a liquid to form a slurry, which is then used for wet molding into various shapes. In certain embodiments, the iron oxide slurry is slip-cast into a mold of substantially any shape. In certain embodiments, the iron oxide slurry is coated onto a sheet by a doctor blade method or other similar coating method.

[0077] In various embodiments, a bed of conductive microporous pellets constitutes the electrodes of an energy storage system. In some embodiments, the pellets include pellets of directly reduced iron (DRI). The filling of the pellets creates macropores between the individual pellets. The macropores facilitate ion transport across electrodes that, in some embodiments, have dimensions of several centimeters, still having very thick minimum dimensions compared to some other types of battery electrodes. The macropores can form less flexible pore spaces compared to micropores within the pellets. The micropores within the pellets allow for contact between the active material and the electrolyte due to the high surface area of ​​the pellets, enabling high utilization of the active material. This electrode structure is particularly useful for improving the rate capacity of very thick electrodes for stationary, long-term energy storage, where thick electrodes may be required to achieve very high area capacities.

[0078] In various embodiments, transient porosity-forming agents are incorporated during DRI production to increase the porosity of the resulting DRI. In one embodiment, the porosity of the DRI pellets is modified by incorporating a sacrificial porosity-forming agent, such as ice (solid H2O), which is later melted or sublimated under heat treatment, into the pelletizing process. In certain other embodiments, the transient porosity-forming agent includes naphthalene, which then sublimes to leave behind porosity. In other embodiments, the transient porosity-forming agent includes NH4CO3 (ammonium carbonate), which can also be introduced as a solid at various points in DRI production, decomposing under heat, leaving behind either gaseous or liquid species (NH3 + CO2 + H2O). In various other embodiments, the transient additive can perform additional functions in the cell (e.g., it may be an electrolyte component). In certain embodiments, the transient additive may be an alkali salt such as KOH, NaOH, or LiOH. In certain embodiments, the transient 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 transient additive may be a binder used to aggregate the iron ore powder into pellets or other shapes, such as sodium alginate or a carboxymethylcellulose binder.

[0079] In certain embodiments, the reducing gas used to form DRI is hydrogen (H2). In certain embodiments, hydrogen is produced by electrolyzing water from a renewable power source such as wind or solar energy. In certain embodiments, an electrolytic cell is connected to the energy storage system. In certain embodiments, the electrolytic cell is a proton exchange membrane (PEM) electrolytic cell. In certain embodiments, the electrolytic cell is an alkaline electrolytic cell. In embodiments using hydrogen as the reducing gas, the cementite (Fe3C) content of the DRI may be as low as 0% by weight.

[0080] In certain embodiments, natural gas (methane, CH4) is used as a reducing agent for producing DRI. In certain embodiments, methane is steam reformed (by reaction with water, H2O) to produce a mixture of carbon monoxide (CO) and hydrogen (H2) via the reaction CH4 + H2O → CO + 3H2. In certain embodiments, this reforming reaction occurs in an auxiliary reformer separate from the reactor where iron reduction occurs. In certain embodiments, the reforming occurs in situ in the reduction reactor. In certain embodiments, the reforming occurs in both the auxiliary reformer and the reduction reactor. In certain embodiments, coal is used as a reducing agent for producing DRI. In certain embodiments, coke is used as a reducing agent for producing DRI. In embodiments using carbon-containing reducing gas, the cementite (Fe3C) content of the DRI may be higher, up to 80% by weight.

[0081] In certain embodiments, a mixture of DRI produced using various reducing gases can be used to achieve beneficial combinations of composition and properties. In one non-limiting embodiment, a 50 / 50 mixture by mass of DRI produced from BF grade pellets reduced in natural gas and DRI produced from DR grade pellets reduced in hydrogen is used as the negative electrode of a battery. Other combinations of mass ratio, feedstock type (DR, BF, other artificial ores, etc.), and reducing medium (hydrogen, natural gas, coal, etc.) can be combined in other embodiments.

[0082] In various embodiments, the DRI pellets may be crushed, and the crushed pellets may constitute a bed (with or without added powder).

[0083] In various embodiments, additives beneficial to the electrochemical cycle, such as hydrogen evolution reaction (HER) inhibitors, may be added to the floor in solid form, for example, as powder or solid pellets.

[0084] In some embodiments, the metal electrode has a low initial specific surface area (e.g., about 5 m²). 2 Less than / g, preferably about 1m2 They may have a specific surface area (less than / g). Such electrodes tend to exhibit a low self-discharge rate in low-rate long-term energy storage systems. One example of a low specific surface area metal electrode is a bed of DRI pellets. In many typical and modern electrochemical cells, such as lithium-ion batteries or nickel-metal hydride batteries, a high specific surface area is desirable to facilitate high-rate capacity (i.e., high power). In long-term systems, the need for rate capacity is significantly reduced, so low specific surface area electrodes can meet the target rate capacity requirement while minimizing self-discharge.

[0085] In some embodiments, DRI pellets are processed by mechanical, chemical, electrical, electrochemical, and / or thermal methods before being used in an electrochemical cell. Such pretreatment can enable the achievement of superior chemical and physical properties, for example, by increasing the capacity available during the discharge reaction. The physical and chemical properties of DRI at the time of purchase (sometimes called "at receipt") may not be optimal for use as the anode in an electrochemical cell. Improved chemical and physical properties include the introduction of higher content of desirable impurities, such as HER inhibitors; achieving lower content of undesirable impurities (such as HER catalysts); achieving a higher specific surface area; achieving a higher total porosity; achieving a different pore size distribution from the initial DRI (such as a multimodal pore size distribution to reduce mass transport resistance); achieving a desired distribution of pellet size (such as a multimodal size distribution to enable pellets to be packed to a desired density); and modifying or selecting pellets to a desired aspect ratio (to achieve a desired bed packing density). Mechanical processing includes tumbling, milling, grinding, crushing, powdering, and pulverization. Chemical processing methods include acid etching. Chemical processing methods include immersing the pellet bed in an alkaline solution to create necking between the pellets, and roughening the micropores within the pellets. Thermal processing methods include processing the DRI at high temperatures in an inert atmosphere, a reducing atmosphere, an oxidizing atmosphere, and / or a carburizing atmosphere. In various embodiments, mechanical, chemical, electrical, electrochemical, and / or thermal methods for pre-processing the electrode-forming material, such as DRI pellets, can fuse the electrode-forming material to a bed, such as a bed of fused DRI pellets.

[0086] In some embodiments, the negative electrode may include an inert conductive matrix comprising carbon black, graphite powder, acetylene black, activated carbon, carbon steel mesh, stainless steel mesh, carbon steel wool, steel wool, nickel-coated carbon steel mesh, nickel-coated stainless steel mesh, nickel-coated steel wool, carbon steel expanded metal, nickel-coated carbon steel expanded metal, stainless steel expanded metal, nickel-coated stainless steel expanded metal, or a combination thereof.

[0087] According to various embodiments, the positive electrode consists of a manganese-containing compound comprising manganese(IV) oxide (MnO2), manganese(III) oxide (Mn2O3), manganese(III) oxyhydroxide (MnOOH), manganese(II) oxide (MnO), manganese(II) hydroxide (Mn(OH)2), or a combination thereof. In some embodiments, the positive electrode may contain one or more natural manganese oxide minerals such as barnesite, pylomanganite, black manganese, aftenskite, hollandite, ramsdelite, enstaite, spinel, hard manganese, todorokiite, iron manganese, vernadite, or a combination thereof. In some embodiments, the positive electrode may contain a manganese-containing compound having the structure of a manganese oxide mineral such as barnesite. In some embodiments, the positive electrode may contain manganese dioxide (EMD) as the electrolyte. In some embodiments, manganese dioxide is in the phases of α-MnO2, β-MnO2, γ-MnO2, δ-MnO2, ε-MnO2, λ-MnO2, or combinations thereof. In some embodiments, the positive electrode may include, but is not limited to, a manganese-containing compound having the structure of a manganese oxide mineral such as pylomanganite, ramsdelite, enstaite, hollandite, barnesite, or vernadite. In some embodiments, the positive electrode may include manganese(II) hydroxide (Mn(OH)2). In some embodiments, the positive electrode may include a manganese hydroxide mineral such as kimimanite. In some embodiments, the positive electrode may include a manganese-containing compound having the structure of a manganese hydroxide mineral such as kimimanite. In some embodiments, the positive electrode may include manganese(III) oxyhydroxide (MnOOH). In some embodiments, the positive electrode may include a manganese oxyhydroxide mineral such as hydromanganite, phytknechtite, groutite, or hydromanganite. In some embodiments, the positive electrode may contain a manganese-containing compound having the structure of a manganese oxyhydroxide mineral, such as hydromanganite.In various embodiments, the positive electrode includes an inert conductive matrix comprising carbon black, graphite powder, acetylene black, activated carbon, charcoal powder, coal powder, nickel-coated carbon steel mesh or expanded metal, nickel-coated stainless steel mesh or expanded metal, nickel-coated steel wool, or a combination thereof.

[0088] In this embodiment, the specific surface area of ​​the manganese-containing compound is approximately 0.05 m². 2 / g~about 50m 2 / g, approx. 0.5m 2 / g~about 5m 2 / g, as well as values ​​greater than or less than these values, are also possible.

[0089] In some embodiments, the positive electrode may contain one or more additives to enhance the capacity and cyclability of the positive electrode. In some embodiments, the additives of the positive electrode may include oxides, sulfides, and sulfoxides 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 of the positive electrode may include Li + kaNa + , K + Mg 2+ Ca 2+ Ba 2+ Co 2+ Cu 2+ Fe 2+ Fe 3+ , Bi 3+ Pb 2+ Zn 2+ Ni 2+The additives include metals or metal cations, such as, or combinations thereof. In some embodiments, the cathode additive(s) include carbon nanotubes, carbon nanofibers, graphene, nitrogen-doped carbon nanotubes, nitrogen-doped carbon nanofibers, nitrogen-doped graphene, or combinations thereof.

[0090] In some embodiments, the positive electrode may contain one or more binder compounds. In some embodiments, the binder compounds include polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVdF), polypropylene (PP), polyethylene (PE), fluorinated ethylene propylene (FEP), polyacrylonitrile, styrene-butadiene rubber, carboxymethylcellulose (CMC), sodium carboxymethylcellulose (Na-CMC), polyvinyl alcohol (PVA), polypyrrole (PPy), or combinations thereof.

[0091] In some embodiments, manganese oxide cathodes can be assembled in a "discharged" state. The "discharged" state is defined as Mn(III) (MnOOH, Mn2O3, etc.), Mn(II+III) (Mn3O4, etc.), and Mn(II) (Mn(OH)2, etc.). In some embodiments, sources of "discharged" manganese oxide or oxyhydroxide species include natural ores such as manganese hydrochloride, groutite, phytknechtite, manganese iron ore, kimimanite, manganese green ore, black ore, and nestaite. In other embodiments, the source of "discharged" manganese oxide species may be obtained from an installed primary alkaline cell (i.e., Zn / MnO2), where the "discharged" cathode of the primary alkaline cell may be reused in the assembly of a rechargeable manganese oxide cathode. In some embodiments, a “discharged” manganese oxide species may be incorporated into an additive(s) such as Bi2O3 or metallic bismuth, along with other electrode components, so that the electrical rechargeability of these “discharged” compounds can be returned to the “discharged” species of the desired phase (i.e., Mn(IV)). In some embodiments, the “discharged” cathode is joined to the “discharged” anode in a complete cell configuration for the first half of the cycle, which charges both the cathode and the anode. In other embodiments, the “discharged” cathode is joined to the charged anode in a complete cell configuration for the first half of the cycle, which charges the cathode with a hydrogen evolution reaction (HER) as the counter-electrode reaction.

[0092] In various embodiments, the amount of manganese-containing compound(s) loaded in the positive electrode is in the range of 50 to 90% by weight, based on the equivalent mass of MnO2. In various embodiments, the amount of conductive matrix loaded in the positive electrode is in the range of 5 to 40% by weight. In various embodiments, the amount of additive(s) loaded in the positive electrode is in the range of 0 to 20% by weight. In various embodiments, the amount of binder loaded in the positive electrode is in the range of 0 to 20% by weight.

[0093] In some embodiments, manganese-containing compounds(s) and additives(s) are combined through chemical reactions or, but not limited to, physical processes such as stirring, mixing, milling, compounding, or combinations thereof. In some embodiments, additives(s) are incorporated into the structure of manganese-containing compounds(s) through chemical, electrochemical, or thermal processes.

[0094] In some embodiments, the positive electrode, comprising manganese-containing compounds (one or more), additives (one or more), a conductive matrix, and a binder, is manufactured by a powder compression molding process such as a uniaxial press or calender rolling, but is not limited to these. In some embodiments, the compression molding is carried out dry or wet. In some embodiments, the positive electrode, comprising manganese-containing compounds (one or more), additives (one or more), a conductive matrix, and a binder, is manufactured by an extrusion process such as a screw or piston, but is not limited to these. In some embodiments, the compression molding is carried out dry or wet. In some embodiments, the positive electrode, comprising manganese-containing compounds (one or more), additives (one or more), a conductive matrix, and a binder, is manufactured by directly filling a mixed powder into a cell. In some embodiments, the mixed powder is filled in a dry state and expands by adding an 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, coating or printing processes such as doctor blades, screen printing, gravure coating, slot die coating, or comma coating are used to apply the mixed powder to the current collector, but are not limited to these.

[0095] In certain embodiments, a redox mediator can be used to facilitate electron transport in the redox reaction from MnO2 to MnOOH. In certain embodiments, the redox mediator can be used to facilitate electron transport in the redox reaction from MnO2 to Mn(OH)2. The requirements for the redox mediator are as follows: (1) facile and reversible redox kinetics; (2) a redox potential similar to that of the reaction it facilitates (i.e., MnO2?MnOOH or MnO2?Mn(OH)2); (3) stable in the presence of the electrolyte of interest (e.g., high-concentration alkaline). In some embodiments, the redox mediator is insoluble in the electrolyte. As non-limiting examples, redox mediators for rechargeable manganese dioxide electrodes are ferrocene, ferrocene derivatives, or combinations thereof. As another non-limiting example, the redox mediator is 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ). As another non-limiting example, the redox mediator is tetrathiafulvalene (TTF). In some embodiments, the redox mediator is soluble in the electrolyte. As non-limiting examples, redox mediators for rechargeable manganese dioxide electrodes are TEMPO, TEMPO derivatives, or combinations thereof. In certain embodiments, the redox mediator is LiI, NaI, KI, CsI, or combinations thereof.

[0096] In various embodiments, the electrolyte consists of an aqueous alkali metal hydroxide comprising lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), cesium hydroxide (CsOH), or combinations thereof. In some embodiments, the electrolyte is lithium sulfide (Li2S) or polysulfide (Li2S x , x = 2 to 6), sodium sulfide (Na2S) or polysulfide (Na2S x , x = 2 to 6), potassium sulfide (K2S) or polysulfide (K2S x , x = 2 to 6), cesium sulfide (Cs2S) or polysulfide (Cs2S xIt may contain alkali metal sulfides or polysulfides including x=2~6). In some embodiments, the electrolyte may contain a hydrogen evolution reaction (HER) inhibitor. In some embodiments, the HER inhibitor can be selected from the following non-restrictive set: sodium thiosulfate, sodium thiocyanate, polyethylene glycol (PEG) 1000, trimethylsulfoxonium iodide, zincate (by dissolving ZnO in NaOH), hexanethiol, decanethiol, sodium chloride, sodium permanganate, lead(IV) oxide, lead(II) oxide, magnesium oxide, sodium chlorate, sodium nitrate, sodium acetate, iron phosphate, phosphoric acid, sodium phosphate, ammonium sulfate, ammonium thiosulfate, Lithopone, magnesium sulfate, iron(III) acetylacetonate, hydroquinone monomethyl ether, sodium metavanadate, sodium chromate, glutaric acid, dimethyl phthalate, methyl methacrylate, methylpentinol, adipic acid, allylurea, citric acid, thiomalic acid, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, propylene glycol, trimethoxysilylpropyl diethylene, aminopropyltrimethoxysilane, dimethylacetylenedicarboxylate (DMAD), 1,3-diethylthiourea, N,N'-Diethylthiourea, aminomethylpropanol, methylbutynol, amino-modified organosilane, succinic acid, isopropanolamine, phenoxyethanol, dipropylene glycol, benzoic acid, N-(2-aminoethyl)-3-aminopropyl, behenamide, 2-phosphonobutanetricarboxylic acid, MIPA borate, 3-methacryloxypropyltrimethoxysilane, 2-ethylhexoic acid, isobutyl alcohol, t-butylaminoethyl methacrylate, diisopropanolamine, propylene glycol n-propyl ether, sodium benzotriazole, aminotrimethylene phosphate Pentasodium phosphate, sodium cocoyl sarcosinate, laurylpyridinium chloride, steartrimonium chloride, stearalkonium chloride, calcium montanaate, quaternium-18 chloride, sodium hexametaphosphate, dicyclohexylamine nitrite, lead stearate, calcium dinonylnaphthalene sulfonate, iron(II) sulfide, sodium hydrogen sulfide, pyrite, sodium nitrite, complex alkyl phosphate ester (e.g., RHODAFAC® RA600 emulsifier), 4-mercaptobenzoic acid, ethylenediaminetetraacetic acid, ethylenediaminetetraacetate (EDTA), 1,3-Propylenediamine tetraacetate (PDTA), nitrilotriacetate (NTA), ethylenediamine disuccinate (EDDS), diethylenetriamine pentaacetate (DTPA), and other aminopolycarboxylates (APC), diethylenetriaminepentaacetic acid, 2-methylbenzenethiol, 1-octanthiol, bismuth sulfide, bismuth oxide, antimony(III) sulfide, antimony(III) oxide, antimony(V) oxide, bismuth selenide, antimony selenide, selenium sulfide, selenium(IV) oxide, propargyl alcohol, 5-hexyn-1-ol, 1-hexyn-3-ol N-allylthiourea, thiourea, 4-methylcatechol, trans-cinnamaldehyde, iron(III) sulfide, calcium nitrate, hydroxylamine, benzotriazole, furfurylamine, quinoline, tin(II) chloride, ascorbic acid, tetraethylammonium hydroxide, calcium carbonate, magnesium carbonate, antimony dialkyldithiophosphate, potassium stannate, sodium stannate, tannic acid, gelatin, saponin, agar, 8-hydroxyquinoline, bismuth stannate, potassium gluconate, lithium molybdenum oxide, potassium molybdenum oxide, hydrogenated light oil, heavy naphthenic petroleum fractions (heavy Naphthenic petroleum oil (e.g., sold as Rustlick® 631), antimony sulfate, antimony acetate, bismuth acetate, hydrogenated heavy naphtha (e.g., sold as WD-40®), tetramethylammonium hydroxide, NaSb tartrate, urea, D-glucose, C6Na2O6, potassium antimony tartrate, hydrazine sulfate, silica gel, triethylamine, potassium antimonate trihydrate, sodium hydroxide, 1,3-di-o-tolyl-2-thiourea, 1,2-diethyl-2-thiourea, 1,2-diisopropyl-2-thiourea, N-phenylthiourea, N,N'-diphenylthiourea, sodium antimony tartrate, disodium rhizonate, sodium selenide, and combinations thereof.

[0097] In various embodiments, a separator that is impermeable to electrons and permeable to at least one alkali metal ion or hydroxide ion is in close contact between the negative electrode and the positive electrode. In some embodiments, the separator is a nonwoven fiber layer such as nylon or cellulose. In some embodiments, the separator is a porous polymer layer such as a polypropylene separator, polyethylene separator, or polybenzimidazole (PBI) separator. In some embodiments, the separator is a woven fabric layer such as a polypropylene mesh, polyethylene mesh, polyester mesh, or cotton gauze. In some embodiments, an anion exchange membrane that selectively conducts hydroxide ions is in close contact between the negative electrode and the positive electrode. In various embodiments, the separator is a size exclusion separator that selectively conducts hydroxide ions and alkali metal ions while preventing sulfide ions or polysulfide ions from passing from the negative electrode to the positive electrode. In various embodiments, the separator is a size exclusion separator that selectively conducts hydroxide ions while preventing sulfide ions or polysulfide ions from passing from the negative electrode to the positive electrode. 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 sulfide 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 sulfide 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 sulfide 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 sulfide ions.

[0098] In various embodiments, the battery components are assembled in a prismatic or cylindrical shape. In various embodiments, the current collectors include nickel, copper, aluminum, carbon steel, stainless steel, nickel-coated stainless steel, nickel-coated carbon steel, and nickel-coated steel wool, graphite, or combinations thereof. In various embodiments, the current collectors are metal plates, metal rods, metal tubes, expanded metal, perforated metal, metal mesh, graphite plates, graphite rods, graphite tubes, graphite foil, carbon powder-based plates, carbon powder-based rods, carbon powder-based tubes, carbon powder-based foil, or combinations thereof. In various embodiments, the current collectors are deposited in the form of a film or paste by techniques such as gravure coating or screen printing. In various embodiments, the battery housing material is polypropylene, high-density polyethylene, or polyvinyl chloride. In various embodiments, the electrolyte is in a static (non-circulating) mode or a fluid (circulating) mode.

[0099] In some embodiments, the current collector is a layer of conductive and electrolyte-impermeable barrier. In some embodiments, such a conductive and electrolyte-impermeable barrier comprises a carbon material and a hydrophobic binder. In some embodiments, the carbon material comprises carbon black, activated carbon, graphite, or a combination thereof. In some embodiments, the hydrophobic binder comprises polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVdF), polypropylene (PP), polyethylene (PE), fluorinated ethylene propylene (FEP), or a combination thereof. In prismatic cells, such current collectors are flat. In some embodiments, flat current collectors can be manufactured by a powder compression process, an extrusion process, a coating process, or a printing process. In some embodiments, flat current collectors and external structural components can be manufactured simultaneously by an extrusion process or a co-extrusion process. In cylindrical cells, such current collectors in the outer layer of the cell are hollow cylindrical or tubular in shape. In some embodiments, hollow cylindrical or tubular current collectors can be manufactured by an extrusion or co-extrusion process, or by bending or rolling a sheet material. In some embodiments, cylindrical current collectors and external structural components can be manufactured simultaneously by paste extrusion or co-extrusion processes.

[0100] In some embodiments, a layer of conductive and electrolyte impermeable barrier is placed between the electrode and the current collector. In some embodiments, such conductive and electrolyte impermeable barrier comprises a carbon material and a hydrophobic binder. In some embodiments, the carbon material comprises carbon black, activated carbon, graphite, or a combination thereof. In some embodiments, the hydrophobic binder comprises polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVdF), polypropylene (PP), polyethylene (PE), fluorinated ethylene propylene (FEP), or a combination thereof. In prismatic cells, the conductive and electrolyte impermeable barrier is flat. In some embodiments, a flat conductive and electrolyte impermeable barrier can be manufactured by a powder compression process, an extrusion process, a coating process, or a printing process. In cylindrical cells, the conductive and electrolyte impermeable barrier is hollow cylindrical or tubular. In some embodiments, a hollow cylindrical or tubular conductive and electrolyte impermeable barrier can be manufactured by an extrusion or co-extrusion process, or by folding or rolling a sheet material. In various embodiments, the current collector that contacts the conductive and electrolyte-impermeable barrier can be made of copper, aluminum, or carbon steel, and may be alkali-incompatible.

[0101] In some embodiments, the proton conductor is incorporated into the positive electrode to block sulfides from contacting the positive electrode surface and promote localized proton transfer. In some embodiments, the proton conductor is liquid and is applied to the positive electrode surface. In certain embodiments, the liquid proton conductor is a Nafion® solution. In some embodiments, the proton conductor is in a solid state and is mixed with other components of the positive electrode. In certain embodiments, the solid proton conductor is a Nafion® bead.

[0102] In various embodiments, the cell or stack is charged in current-controlled mode, voltage-controlled mode, or power-controlled mode, or a combination thereof. In various embodiments, the cell or stack is charged in constant current mode, constant voltage mode, constant power mode, or a combination thereof. In various embodiments, the cell or stack is discharged in constant current mode, constant voltage mode, constant power mode, or a combination thereof. In various embodiments, the cell or stack is discharged in current-controlled mode, voltage-controlled mode, or power-controlled mode, or a combination thereof.

[0103] In various embodiments, a sealed rechargeable Fe-MnO is used to catalyze the hydrogen oxidation reaction (HOR) that occurs on the negative electrode during cell charging. 2The cell is equipped with an auxiliary electrode. Such an auxiliary electrode is referred to as a hydrogen recombination electrode. The consumption of hydrogen as a by-reaction product not only mitigates hydrogen-related safety concerns but may also help maintain a balance in the charge state of the positive electrode. In various embodiments, the hydrogen recombination electrode comprises a catalyst core and a separator surrounding the core. The catalyst core provides the reaction site for HOR. The separator is ionic conductive and electrically insulating. In some embodiments, the catalyst core is a solid electrode, as shown, for example, in Figure 2A. Figure 2A shows a solid electrode which is a hydrogen recombination electrode 200 comprising a separator 202 and a catalyst core 203. In some embodiments, the catalyst core is a porous electrode, as shown, for example, in Figure 2B. Figure 2B shows a hydrogen recombination electrode 220 comprising a separator 202 and a porous catalyst core 221. In one example, the hydrogen recombination electrode 235 is placed in a negative electrode compartment, such as a negative electrode compartment 231 having an anode formed from DRI, as shown, for example, in Figure 2C. Figure 2C shows a specific example of an electrochemical cell 230 similar to the electrochemical cell 100 described above, where the anode may be formed from DRI and the cathode in the positive electrode compartment 232 may be formed from MnO2 / C. For example, the hydrogen recombination electrode 235 may be the hydrogen recombination electrode 200 or 220 described above. Hydrogen generated on the anode is consumed "in situ" by the hydrogen recombination electrode 235. The electrochemical cell 230 may be equipped with a threshold pressure vent 235. The threshold pressure of the vent may be higher than the threshold pressure of the vent in a cell where a hydrogen recombination electrode may not be present. In another example, the hydrogen recombination electrode 241 is placed between the anode and the cathode, as shown, for example, in Figure 2D, where the electrochemical cell 240 is equipped with a hydrogen recombination electrode 241 placed between the negative electrode compartment 231 and the positive electrode compartment 232. In this electrochemical cell 240 configuration, the polypropylene mesh 105 and the battery separator 104 may be replaced with a hydrogen recombination electrode 241, and therefore the hydrogen recombination electrode 241 may have a porous catalytic core, similar to the core of the hydrogen recombination electrode 220 described above. Hydrogen generated at the anode migrates through the pores of the anode and is consumed by the hydrogen recombination electrode 241. The hydrogen concentration gradient is the primary driving force for hydrogen mass transfer.In another exemplary configuration of electrochemical cell 250, the hydrogen recombination electrode 251 is located at the top of the anode in the upper part of the negative electrode compartment 231, as shown, for example, in Figure 2E. In such a configuration, the hydrogen recombination electrode 251 may be integrated with the vent. In another example, the hydrogen recombination electrode is identical to the cathode of cell 261, as shown, for example, in electrochemical cell 260 in Figure 2F. In other words, during charging, the primary electrochemical reaction on cathode 261 is the oxidation of manganese compounds (one or more), and the "auxiliary" electrochemical reaction on cathode 261 is HOR. The hydrogen concentration gradient is the primary driving force for hydrogen mass transfer from anode 231 to cathode 261 of cell 260.

[0104] In various embodiments, an auxiliary electrode, which functions as a rebalancing electrode, is placed on the positive electrode side. The main purpose of such an auxiliary electrode is to prevent overcharging of the positive electrode when HER is performed on the negative electrode side. In some embodiments, the auxiliary electrode is nickel oxyhydroxide. In some embodiments, the auxiliary electrode is the same manganese-based positive electrode with excess capacitance.

[0105] In various embodiments, the operating temperature is in the range of -20°C to 60°C. In some embodiments, the preferred operating temperature is in the range of 20°C to 40°C.

[0106] In a non-limiting example, a rechargeable Fe-MnO2 cell is prismatic in shape and comprises a MnO2-based positive electrode, a sintered iron negative electrode incorporating Bi2S3, a polypropylene separator, and a 15 wt% KOH + 15 wt% NaOH electrolyte. In this embodiment, the positive electrode comprises EMD (60-70 wt%), graphite (25-35 wt%), and PTFE (5-10 wt%), and includes a current collector made of nickel-coated steel mesh. The EMD, graphite, and PTFE powders are mixed in a wet process in the presence of isopropanol. The electrodes are manufactured by calendering the mixed powders and then drying them. The electrodes (one or more) and the nickel-coated steel mesh current collector are joined by hydraulic pressing. The thickness of the positive electrode is 1-10 mm. The thickness of the negative electrode is 1-10 mm. The target operating current density of the cell is 1-10 mA / cm². 2 That is the case.

[0107] In another non-limiting example, a rechargeable Fe-MnO2 cell is cylindrical and comprises a MnO2-based positive electrode, a DRI negative electrode incorporating Bi2S3, a polybenzimidazole (PBI) separator, and a 30 wt% KOH + 1 wt% LiOH electrolyte. In this embodiment, the positive electrode comprises EMD (70-80 wt%), carbon black (15-25 wt%), and PTFE (5-10 wt%), and includes a current collector of nickel-coated steel plate. The EMD, carbon black, and PTFE powders are mixed in a dry process and packed into a cylindrical cell in a dry state. In some embodiments, the positive electrode "pillar" is located in the center of the cylinder, while the negative electrode is arranged to surround the positive electrode "center". In some embodiments, the negative electrode "pillar" is located in the center of the cylinder, while the positive electrode is arranged to surround the negative electrode. A PBI separator sandwiched between two layers of polypropylene mesh is placed between the positive and negative electrodes.

[0108] In another non-limiting example, a rechargeable Fe-MnO2 cell is cylindrical and comprises a MnO2-based positive electrode, a DRI negative electrode incorporating Bi2S3, a polybenzimidazole (PBI) separator, and a 30 wt% KOH + 1 wt% LiOH electrolyte. In this embodiment, the positive electrode comprises EMD (70-80 wt%), carbon black (15-25 wt%), and PTFE (5-10 wt%). The EMD and carbon black powders are mixed in a ball mill before adding and mixing the PTFE dispersion. In some embodiments, additional processing aids are added. The mixture is then extruded through a circular die to form a tubular structure. The tube is then divided into appropriate lengths depending on the electrode height, and each division is rolled in a gravure coater to deposit a patterned copper paste current collector. In some embodiments, the positive electrode "pillar" is located in the center of the cylinder, while the negative electrode is positioned to surround the positive electrode "center". In some embodiments, the negative electrode "pillar" is positioned at the center of the cylinder, while the positive electrode is positioned to surround the negative electrode. A PBI separator, sandwiched between two layers of polypropylene mesh, is placed between the positive and negative electrodes.

[0109] In another non-restrictive example, proof-of-concept cell 300 was constructed according to Figure 3A. The working area of ​​cell 300 is approximately 1.5 cm². 2 The negative electrode 301 was iron powder weighing approximately 1.3 g. The positive electrode 302 was MnO2-based powder weighing approximately 0.8 g with a MnO2 content of approximately 78 wt%. The conductive matrix in this MnO2-based powder was carbon. The positive electrode 302 also had a perforated nickel wrap approximately 0.5 mm thick that served as a holder for the MnO2-based powder. A polypropylene battery separator 303 (Celgard 3501) was used between the negative electrode 301 and the positive electrode 302. The "negative electrode / separator / positive electrode" assembly (for example, a combination of negative electrode 301, separator 303, and positive electrode 302) was sandwiched between two stainless steel plates 304 that acted as current collectors. A spring clamp 305 was used to hold multiple cell components together. The contact between the spring clamp 305 and the current collector 304 was insulated by a layer of ethylene propylene diene monomer (EPDM) rubber 307, so that the cell 300 was compressed by a force 306 from the clamp onto the EPDM rubber 307. As shown on the right side of Figure 3A, the complete cell 300 (excluding the end of the current collector 304) was immersed in a plastic beaker 310 containing 5.5 M KOH + 0.5 M LiOH as solution 311. A mercury / mercury oxide (MMO) reference electrode 312 was placed in beaker 310 closer to the positive electrode 302, and the half-cell potential of the positive electrode was monitored. Assuming the positive electrode reaction is Mn(IV)-Mn(III), the total cell capacity is limited to the positive electrode 302 with an absolute capacity of approximately 100 mAh.

[0110] Figure 3B shows the proof-of-concept cell design, i.e., using cell 300 as shown in Figure 3A, with a reading of 6.4 mA / g MnO2 This corresponds to 2.7 mA / cm². 2shows the galvanostatic (constant current) cycles. In Figure 3B, there are 12 cycles with a total duration of >400 hours. During the 12 cycles, the average charge voltage is about 1.35 V and the average discharge voltage is about 0.80 V. As shown in the enlarged curve (full cell voltage vs capacity mAh), there are multiple flat regions related to the charge and discharge curves, indicating that the valence of iron and manganese-containing species is changing. Figure 3C summarizes the MnO2 capacity change (left Y-axis) and the Coulombic efficiency (right Y-axis) based on the graph shown in Figure 3B. The MnO2 capacity changes from 103 mAh / g MnO2 to 62 mAh / g MnO2 with an average decay rate of 3.3 mAh / g / cycle. The Coulombic efficiency changes from 90% at the beginning to 78% at the end. Figure 3D shows the initial life (beginning of life: BOL) half-cell positive electrode polarization curve using the proof-of-concept cell configuration, i.e., cell 300 shown in Figure 3A. Mercury / mercuric oxide (MMO) was used as the reference electrode. The apparent positive electrode area specific resistance (ASR) was about 20 Ω·cm 2 was.

[0111] In another non-limiting example, a proof-of-concept cell was constructed and tested using electrolyte manganese dioxide (EMD) as the positive electrode active material and direct reduced iron (DRI) as the negative electrode active material. The working area of the cell was about 9 cm 2 which was set from the area of the positive electrode. The negative electrode consisted of 6 DRI pellets with a total mass of 13.5 g, held in expanded nickel and also functioning as the current collector. The mass of the positive electrode was about 0.9 g, resulting in a MnO2 loading of 65 wt%. This MnO 2The conductive matrix and binder in the powder system were graphite and PTFE powders, respectively. The positive electrode also included a 20-mesh nickel gauze that functioned as a current collector. One PBI separator was used to wrap the positive electrode. The wrapped positive electrode was 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) was compressed between two acrylic end plates and secured with bolts, nuts, and washers. The entire cell, excluding the ends of the current collector, was immersed in a plastic beaker containing a 10 wt% KOH solution. A mercury / mercury oxide (MMO) reference electrode was placed in the beaker, and the half-cell potentials of both the positive and negative electrodes were monitored. Assuming the positive electrode reaction is Mn(IV)-Mn(III), the total cell capacity is limited by the positive electrode to approximately 170 mAh as a theoretical capacity.

[0112] Figure 3E shows the second cycle charge / discharge data for the proof-of-concept EMD / DRI cell as described in the paragraph above. The X axis represents the total cell capacity in mAh, and the Y axis represents the total cell voltage in V. Constant current-low voltage (CCCV) was used during charging. The cell was initially charged at 8.7 mA (corresponding to C / 20 based on the EMD capacity) until the positive electrode potential reached 0.5 V (relative to MMO). Subsequently, the cell was charged at a constant potential of 0.5 V (relative to MMO) until the charging current decayed to 0.87 mA. During discharge, a constant current of 8.7 mA (i.e., galvanostatic) was used until the positive electrode potential decreased to -0.2 V (relative to MMO). The theoretical cell capacity is approximately 170 mAh, which is 300 mAh / g EMD This corresponds to [the specified value]. 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 discharge voltage is 0.91 V. The Coulomb efficiency is 93.8%. The voltage efficiency is 74.6%. The energy efficiency is 70.0%. The charge-discharge curve has multiple flat / rising regions, which indicates that the valence of iron and manganese-containing species is changing.

[0113] In another non-limiting example, pelletized direct reduced iron (DRI) is used as the negative electrode. In some embodiments, electrochemical cells using DRI as the negative electrode and a manganese oxide-based positive electrode are prismatic cell configurations or stacked prismatic cell configurations, as shown in Figure 4A. For example, Figure 4A shows a prismatic stack 400 of six electrochemical cells 410 using pelletized DRI as the negative electrode 403 and a manganese compound-based positive electrode 407, similar to the stack configuration described above with reference to Figure 1B. Each cell 410 contains a negative electrode 403 immersed in an electrolyte 401 separated from the positive electrode 407 by a polypropylene mesh 405 and a battery separator 406. Bipolar current collectors 402 are positioned between each cell 410 and on the sides of the end cells 410 of the stack 400. Polyethylene backing plates 404 are positioned outside the two end cells 410 and the bipolar current collectors 402 in the stack, and polyethylene frames 408 support each cell 410. In some embodiments, an electrochemical cell 450 using DRI as the negative electrode 458 and a manganese oxide-based positive electrode 460 has a cylindrical cell configuration, as shown in Figure 4B. Figure 4B shows a side view of the cell 450 on the left side of the figure and a top view of the cell 450 on the right side of the figure, the top view shown in the figure with the polyethylene cover 454 removed. The negative electrode current collector 452 is at the center of the filled DRI that forms the negative electrode 458. The negative electrode 458 is supported within a polypropylene mesh 466 and immersed in the electrolyte 456. A battery separator 464 isolates the negative electrode 458 from the positive electrode 460 and the positive electrode electrolyte. The positive electrode current collector 468 surrounds the positive electrode 460. A polyethylene backing plate 462 forms the bottom of the cell 450, and a polyethylene cover 454 seals the top of the cell 450. As shown in the top view, the negative electrode 458 surrounds the negative electrode current collector 452, the separator 464 surrounds the positive electrode 460, the electrolyte 456, and the polypropylene mesh 466, the positive electrode 460 and its electrolyte surround the separator 464, and the positive electrode current collector 468 surrounds the positive electrode 460.

[0114] In another non-limiting example, the manganese-containing compound of the positive electrode is δ-MnO2 (barnesite) having a layered crystalline structure. The intermediate layer of δ-MnO2 may contain a metal cation. The metal cation is Li + kaNa + , K + Mg 2+ Ca 2+ Ba 2+ Cu 2+ Fe 2+ Fe 3+ , Bi 3+ Pb 2+ Zn 2+ , or a combination thereof. The intermediate layer of δ-MnO2 may contain protons. The intermediate layer of δ-MnO2 may contain water molecules. In some embodiments, δ-MnO2 is chemically produced from a water-soluble manganese precursor such as NaMnO4, KMnO4, MnSO4, MnCl2, Mn(NO3)2, Mn(II) acetate, or a combination thereof, before assembling the cell. In certain embodiments, δ-MnO2 is produced by mixing stoichiometric amounts of aqueous solutions of NaMnO4 and MnSO4 in the presence of 1 mol / L KCl, and then heat-treating the mixed solution at 90°C for 1 hour. In some embodiments, after assembling the cell using other phases of MnO2, such as α-MnO2, natural MnO2 (β-MnO2), electrolyte manganese oxide (EMD, γ-MnO2, ε-MnO2), or combinations thereof, δ-MnO2 is electrochemically generated in-situ during the cycle. In some embodiments, δ-MnO2 is generated in-situ during the first charge-discharge cycle. In some embodiments, δ-MnO2 is generated in-situ during the first few charge-discharge cycles.

[0115] In another non-limiting example, the manganese-containing compound in the cathode is α-MnO2, which has an open tunnel crystal lattice structure. The tunnels in α-MnO2 are Li + kaNa + , K + Mg 2+ Ca 2+ Ba 2+ Cu 2+ Fe 2+ Fe 3+ , Bi3+ Pb 2+ Zn 2+ The α-MnO2 tunnel may contain metal cations, or combinations thereof. The α-MnO2 tunnel may contain protons. The α-MnO2 tunnel may contain water molecules. In some embodiments, α-MnO2 is chemically produced from a water-soluble manganese precursor such as NaMnO4, KMnO4, MnSO4, MnCl2, Mn(NO3)2, Mn(II) acetate, or combinations thereof, before assembling the cell. In certain embodiments, but not limited to, an aqueous solution of KMnO4 and MnCl2 is mixed at an equimolar concentration of 0.2 mol / L, and then α-MnO2 is produced by a hydrohydric transition in an autoclave at a high temperature and pressure of 160°C for 6 hours. 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.

[0116] In another non-limiting example, the 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, barnesite, or a combination thereof. In some embodiments, the manganese-containing compound is natural manganese-containing ore, including, but not limited to, barnesite, soft manganese ore, black manganese ore, aftenskite, hollandite, ramsdelite, enstaite, spinel, hard manganese ore, todorokiite, iron manganese ore, vernadite, or a combination thereof. In certain embodiments, the natural manganese-containing ore is untreated. In certain embodiments, PTFE is added to the powder mixture before milling as a binder. In some embodiments, a conductive matrix, such as graphite, carbon black, activated carbon, nickel powder, or a combination thereof, is added to the powder mixture before milling. The milled powder mixture is combined with a metal or graphite current collector and used as the positive electrode in the assembled cell. In some embodiments, the assembled cell is a complete cell configuration using a DRI negative electrode. In some embodiments, the assembled cell is a complete cell configuration using a sintered iron negative electrode. In some embodiments, Bi-doped MnO2 is produced via a constant current cycle. In some embodiments, the cutoff potential during the reduction process is <-0.4V relative to the mercury / mercury oxide (MMO) reference electrode. In certain embodiments, the cutoff potential during the reduction process is -0.5V to -0.7V relative to the MMO reference electrode. In some embodiments, the cutoff potential during the oxidation process is >-0.3V relative to the MMO reference electrode. In certain embodiments, the cutoff potential during the reduction process is 0.1V to 0.3V relative to MMO. In some embodiments, the charge / discharge ratio is C / 24 to C / 1. In certain embodiments, the number of charge / discharge cycles is 1. In some embodiments, Bi-doped MnO2 is produced via a constant potential cycle. In some embodiments, the reduction potential is <-0.5V relative to the MMO reference electrode, and the oxidation potential is >0.1V relative to the MMO reference electrode. In some embodiments, Bi-doped MnO2 is generated via a constant power cycle.In some embodiments, Bi-doped MnO2 is generated via cyclic voltammetry. In certain embodiments, the upper limit potential of cyclic voltammetry is 0.1V to 0.3V relative to the MMO reference electrode. In certain embodiments, the lower limit potential of cyclic voltammetry is -0.5V to -0.7V relative to the MMO reference electrode. In some embodiments, the scanning speed is <100mV / s. In certain embodiments, the scanning speed is 0.1mV / s to 1.0mV / s. In some embodiments, the number of cycles is <100. In certain embodiments, the number of cycles is <10.

[0117] In another non-limiting example, based on the proposed electrode reaction, the rated current density is 15 mA / cm². 2An electrochemical cell was constructed with a rated cell voltage of 0.79V and a nominal discharge time of 1 hour. MnO2 powder and Bi2O3 powder are physically mixed and milled in the presence of graphite. According to various embodiments, the MnO2 powder is α-MnO2, natural MnO2 (β-MnO2), EMD, barnesite, or a combination thereof. In certain embodiments, PTFE is added to the powder mixture as a binder before milling. In certain embodiments, 30 wt% KOH solution is added to the powder mixture before milling. In certain embodiments, the MnO2 loading in the positive electrode is 65 wt%. The milled manganese-containing powder mixture is used as the positive electrode of the assembled cell. Iron-containing powder and Bi2S3 powder are physically mixed and milled in the presence of graphite. In some embodiments, the iron-containing powder is metallic iron such as DRI fine powder, DRI fragments, or a combination thereof. In some embodiments, the iron-containing powder is an iron-containing compound such as Fe(OH)2, Fe2O3, Fe3O4, or a combination thereof. In certain embodiments, PTFE is added to the powder mixture as a binder before milling. The milled iron-containing powder mixture is used as the negative electrode of the assembled cell. In some embodiments, the mixed positive electrode powder is applied to both sides of the current collector with a powder thickness of 200 microns on each side of the current collector. In some embodiments, the mixed negative electrode powder is applied to both sides of the current collector with a powder thickness of 200 microns on each side of the current collector. According to various embodiments, the current collector is nickel-coated carbon steel with a nickel coating thickness of less than 10 microns. In some embodiments, the thickness of the current collector is 100 microns. In some embodiments, a hydrophilic polypropylene battery separator, such as Celgard 3501, is placed between the positive and negative electrodes. In some embodiments, the porosity of the electrodes is 20% to 30%. In some embodiments, the working area of ​​the electrodes is 1000 cm². 2 In some embodiments, the cell-level energy density is higher than 50 Wh / L. In a particular embodiment, the cell-level energy density is 55 Wh / L. In a particular embodiment, the cell-level energy cost is 100$ / kWh.

[0118] In a non-limiting example, the manganese-containing cathode described can be coupled with an iron-containing anode as a static electrochemical energy storage system with a target duration of 24 hours. In some embodiments, Fe-MnO can be used as an energy storage system. 2 The target duration of the battery is 12 to 36 hours. In another non-limiting example, the manganese-containing positive electrode described can be coupled with an iron-containing negative electrode as a black starter with a target duration of 30 minutes. In some embodiments, the target duration of the Fe-MnO2 battery as a black starter is 1 to 60 minutes. In another non-limiting example, the manganese-containing electrode described can be provided as an auxiliary electrode in a large-scale long-duration energy storage system utilizing Fe-air chemistry. In this embodiment, the manganese-containing electrode(s) functioning as black starters are located on the positive electrode side of the Fe-air battery. In this embodiment, when the oxygen reduction reaction occurs at the main positive electrode, the manganese-containing auxiliary electrode(s) stop discharging. In this embodiment, the manganese-containing auxiliary electrode(s) are charged in the normal charging process of the Fe-air battery prior to or during the oxygen evolution reaction occurring at the main positive electrode.

[0119] In certain embodiments, the electrolyte is a nearly neutral aqueous solution with a pH of 4 to 10. In certain embodiments, the electrolyte is a sulfate or chloride solution such as Li2SO4, Na2SO4, K2SO4, CuSO4, NaCl, LiCl, KCl, CuCl2, or a combination thereof, dissolved in water.

[0120] Various embodiments may include a battery comprising a first electrode containing manganese oxide; an electrolyte; and a second electrode containing directly reduced iron. In some embodiments, the electrolyte is a liquid electrolyte. In some embodiments, the electrolyte consists of alkali metal hydroxides including lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), cesium hydroxide (CsOH), or mixtures thereof. In some embodiments, the electrolyte is lithium sulfide (Li2S) or polysulfide (Li2S) x (x=2~6), sodium sulfide (Na2S) or polysulfide (Na2S)x (x=2~6), potassium sulfide (K2S) or polysulfide (K2S) x (x=2~6), cesium sulfide (Cs2S) or polysulfide (Cs2S) x The second electrode consists of alkali metal sulfides or polysulfides containing x=2~6, or mixtures thereof. In some embodiments, the second electrode is pelletized and has a multimodal distribution. In some embodiments, the manganese oxide includes manganese(IV) oxide (MnO2), manganese(III) oxide (Mn2O3), manganese(III) oxyhydroxide (MnOOH), manganese(II) oxide (MnO), manganese(II) hydroxide (Mn(OH)2), or mixtures thereof. In some embodiments, the second electrode further includes iron oxides, hydroxides, sulfides, or mixtures thereof. In some embodiments, the second electrode further consists of one or more secondary phases containing silica (SiO2) or silicate, calcium oxide (CaO), magnesium oxide (MgO), or mixtures thereof. In some embodiments, the second electrode further comprises an inert conductive matrix containing carbon black, activated carbon, graphite powder, carbon steel mesh, stainless steel mesh, steel wool, nickel-coated carbon steel mesh, nickel-coated stainless steel mesh, nickel-coated steel wool, or a mixture thereof. In some embodiments, the second electrode further comprises one or more hydrogen evolution reaction inhibitors. In some embodiments, the specific surface area of ​​the first electrode is approximately 50 m². 2 It is less than / g. In some embodiments, the specific surface area of ​​the first electrode is approximately 1 m². 2 It is less than / g. In some embodiments, the specific surface area of ​​the second electrode is approximately 5m². 2 It is less than / g. In some embodiments, the specific surface area of ​​the second electrode is approximately 1 m². 2The amount is less than / g. In some embodiments, the first electrode consists of a binder comprising polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVdF), polypropylene (PP), polyethylene (PE), ethylene propylene fluoride (FEP), polyacrylonitrile, styrene-butadiene rubber, carboxymethylcellulose (CMC), sodium carboxymethylcellulose (Na-CMC), polyvinyl alcohol (PVA), polypyrrole (PPy), or a combination thereof. In some embodiments, the first electrode is composed of 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. In some embodiments, a separator material is used between the first and second electrodes. In some embodiments, the battery stack may include multiple batteries as described above. In some embodiments, the battery stack may include a current collector connecting two or more electrochemical repeating units of the same polarity. In some embodiments, the battery stack may include a bipolar current collector connecting two or more electrochemical repeating units of different polarities.

[0121] Various embodiments may provide a method for manufacturing a battery, comprising the steps of: providing a first electrode containing manganese oxide; providing a second electrode containing directly reduced iron; and providing an electrolyte located between the first and second electrodes. In some embodiments, the electrolyte is a liquid electrolyte.

[0122] Without being limited to any specific theory or model regarding the reactivity of iron electrodes, a possible scheme for the oxidation of iron electrodes in an alkaline electrolyte can proceed according to the following two reaction steps, Reaction 1 and Reaction 2. Additional or different reaction products are possible (one of which is described in Reaction 3 below), but the characteristics of the volume change after the reaction are common to all oxidation products of metallic iron. Reactions 1, 2, and 3 are as follows.

[0123] [ka]

[0124] [ka]

[0125] [ka]

[0126] Table 4 shows some key physical properties of selected iron-containing materials that may be used as negative electrode active materials (for example, in the negative electrodes 102, 231, 301, 403, and 458 described above) in alkali iron-based electrochemical cells such as batteries and metal-air batteries. The Pilling-Bedworth ratio is the ratio of the volume of the base cell of a metal oxide to the volume of the base cell of the corresponding metal (on which the oxide is formed), and is a measure of the net volume change in one step of the reaction. In Table 4, the Pilling-Bedworth ratio is calculated for the conversion from iron metal to specific iron-containing phases. Theoretical specific capacity is calculated based on the mass of Fe.

[0127] [Table 4]

[0128] Electrochemical cells using iron-based materials as the negative electrode (for example, cells 100, 131, 230, 240, 250, 260, 300, 410, and 450 mentioned above) are assembled in either a charged state, a discharged state, or an intermediate charged state. For example, if metallic iron is used as the active material in the cell during assembly, assembly will begin in a charged state. In contrast, if hematite (Fe2O3) is used to begin assembly in a discharged state. If Fe(OH)2 is used to begin assembly, an intermediate charged state is established.

[0129] This invention describes materials, systems, and methods for using various iron-containing materials, starting from a discharged or partially discharged state in an alkaline electrochemical cell such as an Fe-Ni battery, Fe-MnO2 battery, or Fe-air battery. In certain embodiments of this invention, the iron-containing material includes certain iron-containing minerals also known as iron ore. In certain examples, Mn-rich ore is referred to as "manganiferous ore." Table 5 lists non-limiting examples of various common mineral formations of iron-containing materials, according to their mineral name, commonly corresponding chemical formula, and typical weight percentage of iron. Iron ore may include one or more such iron-containing minerals, as well as any other natural mineral formations containing iron.

[0130] [Table 5]

[0131] Iron ore may contain iron-containing materials such as mineral formations listed in Table 5 (but not limited to these), along with impurity phases such as SiO2, Al2O3, TiO2, CaO, MgO, and other impurity phases. These impurity phases are collectively referred to as "gange" phases in this art. Iron ore is mined and, if necessary, concentrated or beneficiated to produce high-Fe content material (generally >60 wt% Fe) for subsequent processing, including, but not limited to, reduction in a blast furnace, direct reduction processes (shaft furnace reduction, rotary hearth, linear hearth, rotary kiln, or fluidized bed reduction, etc.). The main stages of processing or classification before reduction include: (1) mining of ore. The ore is generally classified according to its iron content, and may be classified into low grade, medium grade, or high grade; (2) direct shipment of ore; (3) beneficiation of ore ("concentrate" or "pellet supply"); (4) pelletization (aggregation process). In this specification, general output may be referred to as direct reduction grade (DR grade) and blast furnace grade (BR grade). In this specification, the term "ore" may be used to refer to the mined material. The term "concentrate" may be used to refer to processed ore from which gangue facies have been preferentially removed in order to increase the iron weight fraction. These concentrates are generally (but not always) in powder or slurry form. Typical compositions of various iron ores and concentrates are shown in Table 6.

[0132] [Table 6]

[0133] Ore sources are sometimes named according to their composition (e.g., "hematite" or "magnetite"), or according to their specific geological formation. For example, one common iron ore source in the United States is called "taconite," which is a relatively low-grade iron ore containing the mineral forms of magnetite, hematite, chert, siderite, greenalite, minnesotaite, and stilpnomelane. Taconite is typically mined with an iron content of 20-35% by weight. Due to its low iron content, taconite is usually beneficulated (the iron content increases by removing gangue facies). Taconite beneficiation involves crushing and grinding the ore into a fine powder, then separating it by flotation or magnetic separation to form "concentrates" with a higher iron content by weight than the raw taconite ore. This powder is then mixed with a binder such as bentonite clay and aggregated into pellets. Depending on the amount of residual gangue contained in the pellets, the pellets may be classified as blast furnace grade (BF grade) or direct reduction grade (DR grade). A typical composition of DR grade pellets is shown in Table 7.

[0134] [Table 7]

[0135] Table 8 shows a typical composition of BF grade pellets.

[0136] [Table 8]

[0137] High-quality iron ore has a high Fe content at the time of mining and may not require ore dressing. These are called "direct-shipment ore."

[0138] Another aspect of the present invention is the use of iron ore material in electrochemical cells such as cells 100, 131, 230, 240, 250, 260, 300, 410, and 450. Another aspect of the present invention is the use of purified mineral as an active substance in electrochemical cells such as cells 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 cells such as cells 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 cells such as cells 100, 131, 230, 240, 250, 260, 300, 410, and 450. Another aspect of the present 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, and 450. According to aspects of the present invention, iron ore materials are usefully used as redox active electrodes in electrochemical cells, including primary (also known as "disposable") or secondary (also known as "rechargeable") type batteries.

[0139] In another aspect of the present invention, the iron ore material may be processed in a manner that preferentially promotes the presence of an iron-containing phase that optimizes performance in electrochemical devices. Performance indicators that can be improved in this way include, but are not limited to, specific capacity (measured in mAh / g), dynamic overpotential, Coulomb efficiency, cycle life, and calendar life. As an example, the iron ore pellets described above (both BF and DR grades) are generally processed in a manner that promotes the presence of hematite, since such pellets are produced primarily for use in steelmaking. The iron ore material is beneficulated as described above to produce concentrates containing both magnetite and hematite. After mixing with a binder and agglomerating to form pellets, these pellets are subjected to a heat treatment process called "hardening," which serves to: 1) sinter the pellets to improve their mechanical strength; and 2) convert magnetite to hematite. Time, temperature, and atmosphere are selected to promote phase conversion according to a process optimized for use in steelmaking (e.g., in a blast furnace or in a direct reduction process). However, hematite is far less conductive than magnetite, and hematite is thought to be more difficult to reduce electrochemically than magnetite. In one embodiment of the present invention, these heat treatment steps are eliminated to allow for an increase in the magnetite fraction; such unhardened pellets are sometimes referred to in the art as "green pellets" or "green bodies." In another embodiment, the treatment conditions are selected to sinter the pellets, but in a manner that maximizes the phase fraction of magnetite. In a particular embodiment, the hardening step includes exposure to oxygen so that magnetite oxidizes to hematite. The partial pressure of the oxidation step may be controlled to remain in the magnetite region without entering the hematite region. In a particular embodiment, the time and temperature are selected to promote sintering but minimize coarsening of the iron ore grains, so that the primary particle size remains fine. In a particular embodiment, the primary particle size of the magnetite grains is 500 microns (micron = 10⁻¹⁰ -6 It is less than m, or less than 100 microns, or less than 50 microns.

[0140] In certain embodiments, the iron ore is then processed into electrodes by thermochemical reduction. In some embodiments, the reduction may be continued to nearly complete the reduction from iron oxide to metallic iron. Nearly complete reduction from iron oxide to metallic iron is the goal of many industrial thermochemical reduction processes of iron.

[0141] In other embodiments, iron ore is incompletely reduced to metallic iron. There are several reasons why such incompletely reduced products are particularly useful in iron batteries. Firstly, some oxide phases formed during the reduction of iron are semiconducting and therefore may be useful as electron conductors in iron electrode materials. For example, magnetite is remarkably conductive at or near room temperature. Wustite is less conductive than magnetite, but still more conductive than most oxides. In some embodiments, the semiconductivity of wustite and magnetite may be used to form battery electrodes that may be composites with metallic iron. Partially reduced products may also be more electrochemically active. The inventors have found that in some situations wustite is more electrochemically active than metallic iron. Because wustite is in a higher oxidation state than metallic iron, it may be less costly to reduce thermochemically. Therefore, wustite may be cheaper and more efficient than metallic iron as a component of battery electrodes. In one embodiment, the positive electrode of an alkali iron battery may be formed from an infusible pellet consisting of hematite, which has conventionally been subjected to direct reduction or blast furnace processes. The pellets may be reduced in a vertical shaft furnace via a suitable mixture of hydrocarbons and other reducing gases known in the art of direct reduction of iron. The reduction process may be terminated when a metallization rate of up to 95% is achieved (metallization rate is a term used in the art of direct reduction of iron and represents the percentage of iron atoms that are completely metallic in the oxidized state). In some examples, a lower metallization rate may be preferred, and a metallization rate as low as 0% yields large quantities of magnetite or wustite as an alternative input material for batteries. The resulting partially reduced pellets, lumps, fragments, or particles may be packed into a particle bed for use as an iron electrode material. The electrode material may consist solely of iron oxide or may mainly consist of a mixture of magnetite and wustite.

[0142] The iron ore materials constituting the electrodes, devices, and systems of the present invention may have a wide range of purities, and in fact may have relatively high impurity concentrations compared to iron-containing materials synthesized from refined iron sources. Table 9 lists relatively common impurities in iron ore and typical concentration ranges in weight percent of impurities. In some embodiments of the present invention, the iron ore material may contain such natural impurities alone or in combination in at least minimal amounts.

[0143] [Table 9]

[0144] The non-limited advantages of using iron ore for such applications are low cost and the widespread 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 (such as refined ore, BF grade pellets, and DR grade pellets).

[0145] In certain embodiments, in an electrochemical cell using an alkaline electrolyte, the presence of a specific impurity phase is preferentially increased to obtain further performance advantages. For example, the alkaline electrolyte reacts with carbon dioxide (CO2) to form carbonate anions (CO3). 2- ) is formed, but this is a well-known mechanism of electrolyte degradation in the art. CaO reacts with water to form Ca(OH)2 according to CaO + H2O → Ca(OH)2. Ca(OH)2 is converted into CO3 2- It reacts with the carbonate, capturing it as CaCO3, and the hydroxide ion OH - It is known that this releases carbonate. Thus, the presence of CaO in the iron material creates a carbonate groove, scraping the carbonate from the alkaline electrolyte. Similar reactions are possible using MgO and BaO as well. In certain embodiments, the mass fraction of CaO is selected to be as high as possible to obtain the maximum carbonate capture capacity.

[0146] In various embodiments, the electrodes and devices of the present invention may include other materials in addition to iron ore. The electrodes of the present invention may consist of a composite that may include the iron ore, or ore mixed with relatively small metal particles such as DRI pellets and / or metal powder or shavings. For example, as shown in Figure 5, the negative electrode 502 may include spherical pellets 505 made of taconite and a composition 510 of relatively small metal particles made of a conductive material. The negative electrode 502 may be an example of the negative electrodes described above, such as negative electrodes 102, 231, 301, 403, and 458. By combining low-cost taconite pellets used as bulk iron supply material for pellets 505 with a conductive additive 510, the cost of forming conductive electrodes during battery assembly may be reduced. As another example, a composite metal electrode architecture may include a mixture of iron ore particles of different sizes, such as larger iron ore pellets (e.g., taconite, DRI, sponge iron, atomized iron, etc.) and smaller metal particle compositions such as fine metal powder or shavings (e.g., fine metal powder or shavings of DRI, taconite, sponge iron, atomized iron, etc.).

[0147] The iron ore used for the purposes of this specification may be selected or further processed or treated to improve certain physical properties. These properties include, but are not limited to, improved conductivity, improved reaction rates at surfaces or interfaces, and regulation of volume changes induced by electrochemical transformations during the cycle, which are at least partially characterized by the Pilling-Bedworth ratio shown in Table 4.

[0148] In some embodiments, the electrical conductivity of the metal electrodes is increased by adding conductive fibers, wires, meshes, or sheets to the pellets so that the conductive material is dispersed between the individual pellets. In one embodiment, the conductive fibers include copper or iron. In another embodiment, the fibers are chopped fibers. In yet another embodiment, the fibers are iron, and their diameter is selected to be greater than the thickness of the iron, which is reversibly oxidized and reduced as the battery discharges and charges. Thus, the interior of the fibers remains metallic iron as an electrode, and the fibers participate in the electrochemical reactions of the cell, maintaining the metallic conductive path within the electrode. In yet another embodiment, the fibers are sintered into iron ore when manufacturing the electrodes.

[0149] In other embodiments, a conductive additive is added to a mineral formation containing iron. The conductive additive may promote the electrochemical reactions of iron by providing an electron-conductive pathway for transporting electrons to and from redox-active iron moieties, without being bound by any particular scientific interpretation. The conductive additive may be, but is not limited to, almost any electron-conductive material, such as metals, metal carbides, metal nitrides, metal oxides, and allotropes of carbon such as carbon black, high-structure carbon black, graphite carbon, carbon fiber, carbon microfiber, vapor-grown carbon fiber 65 (VGCF), fullerene carbon such as "buckyballs," 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. Electronically conductive polymers include, but are not limited to, polyaniline or polyacetylene-based conductive polymers, or poly(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole, polythiophene, poly(p-phenylene), poly(triphenylene), polyazulene, polyfluorene, polynaphthalene, polyanthracene, polyfuran, polycarbazole, tetrathiafulvalene-substituted polystyrene, ferrocene-substituted polyethylene, carbazole-substituted polyethylene, polyoxyphenazine, polyacene, or poly(heterocene).

[0150] In some embodiments, the conductive additive comprises an ore or a metal salt. In some embodiments, the ore or metal salt is reduced thermochemically or electrochemically to a higher electron conductivity form. In some embodiments, the higher electron conductivity form comprises a metal salt such as a metal oxide or a metal. In some embodiments, the ore or metal salt that provides the conductive additive is selected such that the free energy of the negative electrode of the formation is less (i.e., more noble) than that of the iron ore or mineral or salt constituting the electrode, and may be preferentially reduced over the iron ore or mineral or salt. As a non-limiting example, the metal constituting the conductive additive may be formed from the starting ore or mineral form of the metal by thermochemical reduction to the metallic form. In some embodiments, the conductive additive comprises Ni, Co, Cu, Zn, Sn, brass, bronze, or Ag.

[0151] In certain embodiments, the conductive additive comprises copper, and is produced by adding copper ore to iron ore and then heating the mixture in a temperature and reducing gas environment, thereby reducing the copper ore to metallic copper. Optionally, the reducing environment may contain hydrogen gas. 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 so that the solid copper can then dewett the iron ore.

[0152] In another such embodiment, metal copper and iron ore, or copper ore and iron ore are heat-treated to co-sinter to produce a composite electrode having a high electron conductivity provided by the metal copper component.

[0153] In some embodiments, the conductive additive and the iron ore material are arranged in physical proximity, dimensionally adjusted, to improve the transport of electrons and ions to the redox active micro-regions of the electrode. In some embodiments, the conductive additive may form a continuous percolation network through the electrode. In other embodiments, the iron ore is in the form of particles and the conductive additive substantially coats the surface of the particles. In some embodiments, it is preferred that the combined volume of the iron ore and the conductive additive in the conductive additive is less than 20% by volume, preferably less than 10% by volume, and more preferably less than 5% by volume.

[0154] Even if the addition of the conductive additive improves the electron conductivity, other factors such as the particle size of the iron ore can affect the rate of the electrochemical reaction, and correspondingly, the charge and discharge rate and efficiency of the electrode may also be affected. Fine particles have a large surface area for electrochemical reactions and a small cross-sectional area dimension for electron or ion transport, which may improve the rate of the electrochemical reaction. However, fine particles are vulnerable to the influence of the passivation (i.e., electrical insulation) surface layer that may form during operation and may be more costly to form from the mined material. For the purposes of this discussion, the primary particle size is generally considered to be the size of a solid particle without internal voids, and the secondary particle size is considered to be the size of an aggregate of bonded primary particles. Thus, the pellets of the iron ore material mentioned above constitute secondary particles. In some embodiments, the average particle size of the iron ore primary particles or iron ore secondary particles constituting the electrodes, devices, and systems of the present invention corresponds to about a 325 mesh size (less than about 44 micrometers). In other embodiments, the average primary particle size of the iron ore particles is less than about 10 micrometers. In some embodiments, the primary particle size of the iron ore particles is greater than about 10 micrometers, preferably greater than about 15 micrometers, and more preferably greater than about 20 micrometers.

[0155] In general, the secondary particles constituting the iron ore electrode of the present invention, including the pelletized form of iron ore, may have considerable porosity for at least two reasons. Porosity allows for the penetration of the electrode secondary particles or pellets by the electrolyte of the electrochemical cell. Also, because it cycles between a discharge state (oxidation state) and a charge state (reduction state), this porosity is adapted to the volume change of the iron ore material. As shown in Table 4, the Pilling-Bedworth ratio of iron-containing minerals is 2 to 5 times. Therefore, the porosity of the electrode containing the conductive additive and iron ore material, excluding the volume change due to the subsequent electrochemical operation of the battery, is preferably 10% to 80%, more preferably 20% to 70%, and even more preferably 30% to 50% by volume. In some embodiments, at least 70%, preferably more than 80%, and even more preferably more than 90% of the porosity is filled with a liquid electrolyte.

[0156] In some embodiments, the conductive additive forms a porous structure having cavities in which iron ore particles reside, thereby allowing the free volume surrounding the iron ore particles to expand and contract, while the iron ore particles remain electrically connected to the continuous structure of the conductive additive. In some such structures, the cavities of the porous conductive structure are equiaxed. In other embodiments, the cavities are non-equixed and may be elongated in a tubular shape in one dimension, or elongated in two dimensions to form plate-like cavities of various aspect ratios.

[0157] In some embodiments, the electrode of the present invention is a composite comprising iron ore and an additive material that provides elastic compliance to the electrode, thereby enabling repeated expansion and contraction of redox active substances during discharge and charging. In some embodiments, the additive material is a polymer or a polymer binder. In some examples, the conductive additive is also the compliance material. Examples of polymer binders include: sodium carboxymethylcellulose (Na-CMC), lithium carboxymethylcellulose (Li-CMC), potassium carboxymethylcellulose (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, polythiophene, polypyrrole, poly(p-phenylene), polyaniline, poly(p-phenylene vinylene), and poly(3,4-ethylenedioxythiophene)polystyrene sulfonic acid (PEDOT:PSS).

[0158] Various embodiments may include a battery 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 a refined mineral. In some embodiments, the iron is at least one form selected from the group consisting of pellets, BF grade pellets, DR grade pellets, hematite, magnetite, wustite, maltite, goethite, limonite, siderite, pyrite, ilmenite, or spinel manganese ferrite. In some embodiments, the iron further contains at least 0.1 mass% SiO2. In some embodiments, the iron further contains at least 0.25 mass% SiO2. In some embodiments, the iron further contains at least 0.5 mass% SiO2. In some embodiments, the iron further contains at least 0.1 mass% CaO. In some embodiments, the iron further contains at least 0.25 mass% CaO. In some embodiments, the iron further contains at least 0.5 mass% CaO.

[0159] Electrochemical cells, such as batteries, store electrochemical energy by utilizing an electrochemical potential difference that creates a voltage difference between the positive and negative electrodes. This voltage difference generates an electric current if the electrodes are connected by a conductive element. In batteries, the negative and positive electrodes are connected in parallel by external and internal conductive elements. Generally, the external element conducts electrons, and the internal element (electrolyte) conducts ions. Since charge imbalance is not permitted between the negative and positive electrodes, these two flows must supply ions and electrons at the same rate. During operation, the flow of electrons can be used to drive external devices. Rechargeable batteries can be charged by applying a reverse voltage difference that drives the current and ion flow in the opposite direction to the battery that is discharging during operation.

[0160] Generally, but especially for long-term storage applications, electrodes and electrode materials that are low-cost and easy to manufacture are required. Manufacturing and / or processing processes may be evaluated and selected based on multiple criteria, including capital costs, material handling volume, operating costs, number of unit operations, number of material transports, number of material processing steps, required energy input, and the amount of waste and / or by-products generated.

[0161] Various embodiments of the use of metal agglomerates as components of a battery (or cell) (e.g., cells 100, 131, 230, 240, 260, 300, 410, 450) as materials for a battery (or cell), such as electrodes (e.g., negative electrodes 102, 231, 301, 403, 458, 502) and combinations and variations thereof. In various embodiments, the iron material may be iron powder such as gas atomized powder, water atomized powder, or spongy 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 internal voids in open and / or closed states. In various embodiments, the agglomerates may be composed of materials further treated by high-temperature briquetting or low-temperature briquetting. Embodiments of agglomerate materials for use in the various embodiments described herein as electrode materials may have one, two or more, or all of the material properties listed in Table 10 below. Where used herein, including in Table 10, the following terms have the following meanings unless expressly stated otherwise: “Specific surface area” means the total surface area of ​​the material per unit mass, including the surface area of ​​pores in a porous structure; “Total Fe (weight %)” means the mass percentage of total iron relative to the total mass of the agglomerate; “Metallic Fe (weight %)” means the mass percentage of Fe relative to the total mass of the agglomerate. 0 This refers to the mass percentage of iron in its state.

[0162] [Table 10]

[0163] *The specific surface area is preferably determined by the Brunauer-Emmett-Teller adsorption method ("BET"), more preferably BET as shown in ISO 9277 (this disclosure is incorporated herein by reference in its entirety); it is recognized that other tests, such as methylene blue (MB) staining, ethylene glycol monoethyl ether (EGME) adsorption, electrokinetic analysis of complex ion adsorption, and protein retention (PR) methods, can provide results that can be correlated with the BET results.

[0164] ** Skeleton density is preferably determined by the helium (He) gravity bottle method, more preferably as shown in ISO 12154 (the disclosures in this document are incorporated herein by reference in their entirety); it is recognized that other tests can be used to provide results that can be correlated with the results of the He gravity bottle method. Skeleton density may also be referred to in the art as “true density” or “actual density”.

[0165] *** The apparent density is determined by immersion in water, more preferably as shown in ISO 15968 (the disclosure in this document is incorporated herein by reference in its entirety). It is recognized that other tests can be used to provide results that can be correlated with the results of the He specific gravity bottle method. Porosity can be defined as the ratio of the apparent density to the actual density.

[0166]

number

[0167] #The total Fe (wt%) is preferably determined by dichromate titration, more preferably as shown in ASTM E246-10 (the disclosures in this document are incorporated herein by reference in their entirety); it is recognized that other tests, such as titration after tin(II) chloride reduction, titration after titanium(III) chloride reduction, and inductively coupled plasma (ICP) spectroscopy, can provide results that can be correlated with those obtained by dichromate titration.

[0168] ## Metallic Fe (wt%) is preferably determined by iron(III) chloride titration, more preferably as shown in ISO 16878 (the disclosures in this document are incorporated herein by reference in their entirety). It is recognized that other tests, such as bromine-methanol titration, can be used to provide results that can be correlated with those obtained by iron(III) chloride titration.

[0169] In this embodiment, the specific surface area of ​​the aggregate is approximately 0.05 m². 2 / g ~ approx. 35m 2 / g, approx. 0.1m 2 / g~about 5m 2 / g, approx. 0.5m 2 / g~about 10m 2 / g, approx. 0.2m 2 / g~about 5m 2 / g, approx. 1m 2 / g~about 5m 2 / g, approx. 1m 2 / g~about 20m 2 It may also be / g, which is about 1m 2 It can be larger than / g, or about 2m 2 It can be larger than / g, or about 5m 2 It may be less than / g, approximately 15m 2 It may be less than / g, approximately 20m 2 The values ​​may be less than / g, as well as combinations and variations thereof, and may also be larger or smaller values.

[0170] The packing of the agglomerates creates macropores, such as openings, spaces, channels, or voids, between the individual agglomerates. The macropores facilitate ion transport across the electrodes, which in some embodiments have a minimum dimension that is still very thick compared to some other types of battery electrodes that are several centimeters in dimension. The micropores within the agglomerates enable contact between the high surface area active material of the agglomerates and the electrolyte, allowing for a high level of utilization of the active material. This electrode structure is particularly useful for improving the rate capacity of very thick electrodes for stationary long-term energy storage, where thick electrodes may be required to achieve a very high areal capacity.

[0171] In various embodiments, the bed of the conductive microporous agglomerates constitutes the electrode of an energy storage system. In some embodiments, the agglomerates include agglomerates of direct reduced iron (DRI). The packing of the agglomerates creates macropores in the individual agglomerates. The macropores facilitate ion transport across the electrodes, which in some embodiments have a minimum dimension that is still very thick compared to some other types of battery electrodes that are several centimeters in dimension. The macropores can form a pore space with low tortuosity compared to the micropores of the agglomerates. The micropores within the agglomerates enable contact between the high surface area active material of the agglomerates and the electrolyte, allowing for a high level of utilization of the active material. This electrode structure is particularly useful for improving the rate capacity of very thick electrodes for stationary long-term energy storage, where thick electrodes may be required to achieve a very high areal capacity.

[0172] The aggregates of these embodiments, in particular for use in the embodiment of electrodes for long-term energy storage systems, may be of any volumetric shape, such as spheres, discs, packs, beads, tablets, pills, rings, lenses, plates, panels, cones, frustocones, square blocks, rectangular blocks, trusses, angles, channels, hollow sealed chambers, hollow spheres, blocks, sheets, films, microparticles, square bars, rods, angles, plates, cylinders, columns, fibers, chemical fibers, tubes, cups, pipes, and various combinations thereof, as well as other more complex shapes. The electrode aggregates may be the same shape or different shapes. The aggregate in an electrode that is one of several electrodes in a long-term energy storage system may be the same as or different from the aggregates of other electrodes in that storage system.

[0173] The size of an agglomerate refers to the maximum cross-sectional distance of the agglomerate, e.g., the diameter of a sphere, unless otherwise explicitly used. Agglomerates may be the same size or of different sizes. It is recognized that the shape, size, and both of the agglomerates, as well as typically to a lesser extent, the shape and size of the container or housing that holds the agglomerate, determine the properties and size of the macropores of the electrode. Agglomerates may 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.

[0174] In this embodiment, the aggregated material constituting the electrode is approximately 3 g / cm³ 3 ~Approx. 6.5g / cm 3 Approximately 0.1 g / cm³ 3 ~Approx. 5.5g / cm 3 Approximately 2.3 g / cm³ 3 ~Approx. 3.5g / cm 3 3.2 g / cm³ 3 ~Approx. 4.9g / cm 3 Approximately 0.5 g / cm³ 3Larger than that, approximately 1 g / cm 3 Larger than that, approximately 2g / cm 3 Larger than that, approximately 3g / cm 3 It is possible to provide electrodes having bulk densities greater than, as well as combinations of these and various values, as well as larger and smaller values.

[0175] In various embodiments, additives beneficial to the electrochemical cycle, such as hydrogen evolution reaction (HER) inhibitors, may be added to the floor in solid form, for example, as powder or solid pellets.

[0176] In some embodiments, the metal electrode has a low initial specific surface area (e.g., about 5 m²). 2 Less than / g, preferably about 1m 2 They may have a specific surface area (less than / g). Such electrodes tend to exhibit a low self-discharge rate in low-rate long-term energy storage systems. One example of a low specific surface area metal electrode is a bed of agglomerates. In many typical and modern electrochemical cells, such as lithium-ion batteries or nickel-metal hydride batteries, a high specific surface area is desirable to facilitate high-rate capacity (i.e., high power). In long-term systems, the need for rate capacity is significantly reduced, so low specific surface area electrodes can meet the target rate capacity requirement while minimizing self-discharge.

[0177] In another embodiment, desirable impurities or additives are incorporated into the agglomerate. If such impurities are solid, they can be incorporated by ball milling the powder additive together with the metal powder (for example, using a planetary ball mill or similar apparatus). In this case, the agglomerate itself acts as a milling medium. In this way, the powder additive is mechanically introduced into the pores or surface of the agglomerate. Alternatively, the agglomerate may be coated with beneficial additives, for example, by rotating or immersing it in a slurry containing the additives. Examples of such desirable impurities include alkali sulfides. Alkali sulfide salts have been demonstrated to significantly improve the availability of active materials at the Fe anode. In exactly the same way that soluble alkali sulfides can be added to the electrolyte, insoluble alkali sulfides can be added to the agglomerate, for example, by the method described above.

[0178] In various embodiments, the specific surface area of ​​the agglomerate is increased by three times or more, preferably five times or more, by techniques such as the Brunauer-Emmett-Teller gas adsorption method. In some embodiments, this surface area increase is achieved by using the agglomerate as an electrode in an electrochemical cell and electrochemically reducing it with an applied current.

[0179] The ratio of electrolyte to iron material, such as the cell aggregate, is approximately 0.5 mL. 電解質 :1g 鉄材料 ~about 5mL 電解質 :1g 鉄材料 Approximately 0.6 mL 電解質 :1g 鉄材料 ~about 3mL 電解質 :1g 鉄材料 Approximately 0.6 mL 電解質 :1g 鉄材料 , about 0.7mL 電解質 :1g 鉄材料 Approximately 0.8 mL 電解質 :1g 鉄材料 Approximately 1 mL 電解質 :1g 鉄材料 , as well as combinations and variations thereof, and larger and smaller ratios.

[0180] A packed bed of agglomerates can be a desirable configuration for iron-based electrodes because it provides an electron-conductive penetration pathway through the packed bed while leaving porosity available for the electrolyte to occupy, facilitating ion transport. In certain embodiments, the ratio of electrolyte volume to agglomerate volume may be in the range of 0.5 mL / g to 20 mL / g, such as 0.5 mL / g to 5 mL / g, or 0.6 mL / g or 1.0 mL / g. The agglomerates generally come into contact with surrounding agglomerates via a small contact area compared to their surface area, and in some cases, the contact can be considered a "point contact." Contact with a small cross-sectional area may result in constrictions in the flow of current, which may lead to relatively low electrical conductivity across the agglomerate bed, and consequently, high electrode overvoltage and low battery voltage efficiency.

[0181] In some embodiments, additives containing molybdate ions are used in alkaline batteries containing an iron anode. While not bound by any specific scientific interpretation, such additives can help suppress the hydrogen evolution reaction (HER) at the iron electrode and improve the battery's cycle efficiency. The concentration of the additive is selected to suppress HER while still allowing the desired iron charge / discharge process. As an example, molybdate ions may be added via a molybdate compound such as KMoO4. In one specific example, the electrolyte is used when the additive concentration is 10 mM (mM is millimoles, 10 -3 It contains molybdate anions at a concentration of molars / L. In other embodiments, the electrolyte contains molybdate anions at an additive concentration ranging from 1 to 100 mM.

[0182] In some embodiments, surfactants are used to control wetting and foaming during operation of metal-air batteries. During charging, at least two gas-evolving reactions can occur that lead to bubble formation. One is hydrogen evolution at the metal anode, which is a parasitic reaction that can contribute to poor Coulomb efficiency during battery cycling. The other is oxygen evolution, which is necessary for the function of the metal-air battery. Surfactant additives can mitigate the undesirable effects associated with both reactions. In the case of HER, hydrophobic surfactant additives can suppress the hydrogen evolution reaction at the metal anode by physically blocking water (HER reactant) from the metal anode during charging. In the case of ORR, surfactant additives can reduce the electrolyte surface tension and viscosity at the oxygen-evolving electrode, allowing for the generation of smaller, more uniform, and controllable bubbles during charging. In one non-limiting example, 1-octanthiol is added to the alkaline electrolyte at a concentration of 10 mM to mitigate both of these challenges.

[0183] In some embodiments, corrosion inhibitors used in the field of iron metallurgy to inhibit water corrosion are used as components of batteries having an iron anode for improved performance. In some embodiments, 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 such embodiments, the principles of corrosion science are used to prevent undesirable side reactions (e.g., hydrogen generation) under charging conditions, reduce the rate of spontaneous self-discharge during electrochemical retention, and maximize the availability of iron active materials during discharge. Generally, there are two types of corrosion inhibitors: interface inhibitors that react with the metal surface at the metal-environment interface to prevent corrosion, and environmental scavengers that inhibit corrosion by removing corrosive elements from the environment surrounding the metal surface. Under the broad protection of corrosion inhibitors, favorable performance characteristics in terms of the efficiency and capacity of the electrochemical cell can be achieved by adding inhibitors at appropriate concentrations. In the case of iron electrodes in metal-air batteries, one applicable common type of inhibitor is liquid-phase interface inhibitors. This category encompasses three main types of interfacial inhibitors: anode inhibitors, cathode inhibitors, and mixed inhibitors. Anode inhibitors create a passivation layer that inhibits the anodic metal dissolution reaction. Cathode inhibitors can reduce the rate of the reduction reaction (HER in the case of iron electrodes) or precipitate on the cathode active site to block the same reduction reaction. Mixed inhibitors can inhibit corrosion via one or both pathways and include, but are not limited to, molecules that can physically or chemically adsorb onto the metal surface to form a film that blocks the active site of the reduction reaction. Inhibitors can be added to the base electrolyte at any concentration.

[0184] In various embodiments, inhibitors that form a passivation layer on a metal surface are paired with additives that depassivate the iron surface. If the concentrations are correct, an optimal balance between corrosion inhibition and active substance utilization can be achieved. In one specific embodiment, when directly reduced iron is used as the negative electrode, an alkaline electrolyte consisting of 5.5 M potassium hydroxide or sodium hydroxide is used, with 10 mM molybdate anion as a passivating agent and 10 mM sulfide anion as a depassivating agent. Specific examples of electrolyte compositions include 5.5M KOH + 0.5M LiOH + 10mM Na2S + 10mM 1-octanethol; 5.95M NaOH + 50mM LiOH + 50mM Na2S + 10 mM 1-octanethol; 5.95M NaOH + 50mM LiOH + 50mM Na2S + 10mM 1-octanethol + 10mM K2MoO4; and 5.95M NaOH + 50mM LiOH + 50mM Na2S + 10mM K2MoO4. However, this disclosure is not limited to any specific concentration of the above additives in the electrolyte. For example, one or more of the above additives may be included in the electrolyte at concentrations ranging from about 2mM to about 200mM, such as about 5mM to about 50mM or about 5mM to about 25mM.

[0185] In the case of physically adsorbed (chemisorbed or physisorbed) inhibitors, the interaction with the metal surface is often strongly dependent on temperature.

[0186] In one embodiment, an inhibitor is used that may desorb well from the iron surface at temperatures lower than the normal operating temperature. During charging, the inhibitor forms a film that suppresses hydrogen generation at the electrode. During discharge, raising or lowering the cell temperature can cause the inhibitor to desorb from the metal surface, exposing the active substance and improving the electrode's usability. During the next charge, the cell temperature may be returned to the normal operating temperature to modify the film and suppress HER. This process may be repeated to increase the charging efficiency and discharge usability of the iron electrode. In a non-limiting example, octanethol may be used as an inhibitor that can be physically or chemically adsorbed onto a metal anode (e.g., Fe, Ni). When the electrochemical cell is heated to a maximum of 60°C, the physically adsorbed octanethol desorbs, exposing more active sites that can be oxidized during discharge. The free octanethol in the electrolyte then physically adsorbs onto the anode again upon cooling. At higher temperatures (>60°C), octanethol may chemically adsorb onto the electrode, forming a continuous, uniform film across the entire surface. These chemisorbed species may desorb more effectively at low temperatures (<100°C).

[0187] To enable operation at higher temperatures, organic film formation inhibitors having oxygen, sulfur, silicon, or nitrogen functional groups are used to form a continuous chemisorbent film on the iron particle electrode, thereby replicating the depassivation behavior of sulfides while resisting decomposition or oxidation.

[0188] In one embodiment, 1 to 10 mM octanthiol is added to the electrolyte. During charging, the system is heated to a temperature outside of normal operating conditions (e.g., >50°C) to facilitate the formation of a more complete and uniform chemisorbed octanthiol film over the entire active site of the iron nanoparticle electrode, preventing hydrogen generation on the surface. During discharge, the system is cooled, causing a portion of the chemisorbed film to detach from the surface, revealing new active sites for discharge. The remaining octanthiol depassivates the electrode, promoting a more complete discharge. Figure 6A shows an example of a method to promote such a complete discharge. For example, Figure 6A shows electrodes 6102 (e.g., electrodes 102, 231, 301, 403, 458, 502) in a discharged state at the top of the figure. During discharge, a site 6104 where hydrogen generation (HER) is possible is formed, where the octanthiol film detaches from the surface of electrode 6102. In the next step of the method shown in the center of Figure 6A, 1–10 mM octanethol is added to the electrolyte 6103. During charging, the system is heated to a temperature outside of normal operating conditions (e.g., >50°C) to facilitate the formation of a more complete and uniform chemisorbed octanethol film over the entire active site of the iron nanoparticle electrode 6102, preventing hydrogen generation on the surface of electrode 6102 as the octanethol film is trapped in potential HER sites 6104. During discharge, the system is cooled, causing a portion of the chemisorbed film to desorb from the surface, revealing new active sites for discharge, such as the HER sites 6104. The remaining octanethol depassivates electrode 6102, promoting a more complete discharge.

[0189] During electrochemical quiescence, it is desirable to minimize corrosion of the metal electrodes. One type of corrosive medium for iron metal electrodes in aqueous electrolytes is dissolved oxygen. During electrochemical quiescence, dissolved oxygen can come into contact with the iron electrode, corroding the active material and causing the iron electrode to discharge.

[0190] 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 shutdown to reduce the concentration of dissolved oxygen in the electrolyte and prevent discharge of the iron electrode.

[0191] In one embodiment, an anode inhibitor (e.g., K2MoO4) is added to the electrolyte at a concentration of 1-10 mM before electrochemical cessation to form a passivation film that shields the metal surface from the corrosive medium in the electrolyte and prevents self-discharge. If it is necessary to discharge the electrodes after electrochemical cessation, aggressive ions (e.g., SO4) are added to the electrolyte. 2- , CrO4 - NO3 - By adding (), the active substance is exposed, the usability of the active substance is increased, and self-discharge is reduced.

[0192] In certain embodiments, other electrolyte additives are incorporated into the electrolyte. The electrolyte additives may be selected from the following non-restrictive set: sodium thiosulfate, sodium thiocyanate, polyethylene glycol (PEG) 1000, trimethylsulfoxonium iodide, zincate (by dissolving ZnO in NaOH), hexanethiol, decanethiol, sodium chloride, sodium permanganate, lead(IV) oxide, lead(II) oxide, magnesium oxide, sodium chlorate, sodium nitrate, sodium acetate, iron phosphate, phosphoric acid, sodium phosphate, ammonium sulfate, ammonium thiosulfate, lithopone Magnesium sulfate, iron(III) acetylacetonate, hydroquinone monomethyl ether, sodium metavanadate, sodium chromate, glutaric acid, dimethyl phthalate, methyl methacrylate, methylpentinol, adipic acid, allylurea, citric acid, thiomalic acid, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, propylene glycol, trimethoxysilylpropyl diethylene, aminopropyltrimethoxysilane, dimethylacetylenedicarboxylate (DMAD), 1,3-diethylthiourea, N,N'-Diethylthiourea, aminomethylpropanol, methylbutynol, amino-modified organosilane, succinic acid, isopropanolamine, phenoxyethanol, dipropylene glycol, benzoic acid, N-(2-aminoethyl)-3-aminopropyl, behenamide, 2-phosphonovopropyl(2-phosphonobutanetricarboxylic acid), MIPA borate, 3-methacryloxypropyltrimethoxysilane, 2-ethylhexoic acid, isobutyl alcohol, t-butylaminoethyl methacrylate, diisopropanolamine, propylene glycol n-propyl ether, sodium benzotriazole, aminotrimethylene phosphate Pentasodium sulfonate, sodium cocoyl sarcosinate, laurylpyridinium chloride, steartrimonium chloride, stearalkonium chloride, calcium montanoate, quaternium-18 chloride, sodium hexametaphosphate, dicyclohexylamine nitrite, lead stearate, calcium dinonylnaphthalene sulfonate, iron(II) sulfide, sodium hydrogen sulfide, pyrite, sodium nitrite, complex alkyl phosphate ester (e.g., RHODAFAC® RA600 emulsifier), 4-mercaptobenzoic acid, ethylenediaminetetraacetic acid, ethylenediaminetetraacetate (EDTA), 1,3-Propylenediamine tetraacetate (PDTA), nitrilotriacetate (NTA), ethylenediamine disuccinate (EDDS), diethylenetriamine pentaacetate (DTPA), and other aminopolycarboxylates (APC), diethylenetriamine pentaacetic acid, 2-methylbenzenethiol, 1-octanthiol, manganese dioxide, manganese(III) oxide, manganese(II) oxide, manganese oxyhydroxide, manganese(II) hydroxide, manganese(III) hydroxide, 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(III) sulfide, calcium nitrate, hydroxylamine, benzotriazole, furfurylamine, quinoline, tin(II) chloride, ascorbic acid, 8-hydroxyquinoline, pyrogallol, tetraethylammonium hydroxide, calcium carbonate, magnesium carbonate, antimony dialkyldithiophosphate, potassium stannate, sodium stannate, tannic acid, gelatin, saponin, agar, 8-hydroxyquinoline, bismuth stannate, potassium gluconate, lithium molybdenum oxide, potassium molybdenum oxide, hydrogenated light oil, heavy naphthenic petroleum fractions (heavy Naphthenic petroleum oil (e.g., sold as Rustlick® 631), antimony sulfate, antimony acetate, bismuth acetate, hydrogenated heavy naphtha (e.g., sold as WD-40®), tetramethylammonium hydroxide, NaSb tartrate, urea, D-glucose, C6Na2O6, potassium antimony tartrate, hydrazine sulfate, silica gel, triethylamine, potassium antimonate trihydrate, sodium hydroxide, 1,3-di-o-tolyl-2-thiourea, 1,2-diethyl-2-thiourea, 1,2-diisopropyl-2-thiourea, N-phenylthiourea, N,N'-diphenylthiourea, sodium antimony tartrate, disodium rhizonate, sodium selenide, potassium sulfide, and combinations thereof.

[0193] Additional additives may include SiO2-containing minerals, which can have beneficial effects on electrochemical performance by incorporating carbonates from the electrolyte or electrode. Additives containing such functional groups may be usefully incorporated into iron electrode materials. The specific mineral properties of the ore and other factors may strictly determine which SiO2-containing material to add, but examples of such SiO2-containing additives include silica, cristobalite, sodium silicate, calcium silicate, magnesium silicate, and other alkali metal silicates.

[0194] In certain embodiments, electrode agglomerates are prepared by agglomerating metal powder, such as iron-containing powder, into substantially spherical agglomerates. In various embodiments, agglomeration is carried out at room temperature, ambient outdoor temperature, or high temperature. In various embodiments, agglomeration is carried out in a rotary sintering furnace that simultaneously agglomerates and sintersects the powder. In certain embodiments, iron powders such as atomized iron powder, spongy iron powder, iron shavings, mill scale, carbonyl iron powder, electrolytic iron powder, and combinations or variations thereof are used as feedstock. In various embodiments, the heat treatment process is carried out at temperatures of approximately 700°C to approximately 1200°C, for example, approximately 800°C to approximately 1000°C. In various embodiments, the gas environment is inert (containing N2 or Ar), reducing (containing H2, CO2, CO, etc.), or a combination thereof. In various embodiments, the heat treatment process aggregates the powder and completely or partially sintersects it to form an agglomerate. In various embodiments, the size of the agglomerate is 1 μm (μm = 10⁻¹⁰ -6 m) ~ 1cm (cm = 10 -2 The range is m), for example, 10 μm, 100 μm, or 1 mm (mm = 10 -3 m)

[0195] In certain embodiments, the raw material supplied is a material known in the art, such as pig iron, granulated pig iron, nodular reduced iron, scrap iron, and / or scrap steel.

[0196] In various embodiments, fine iron powder, which is a large aggregate of powder particles less than 44 microns (often written as ~325 mesh because such particles can pass through a 325 mesh sieve), may be used as part of the supply material or may constitute the entirety of the supply material.

[0197] In certain embodiments, electrodes are fabricated by electrochemical deposition of iron from an aqueous solution. In certain embodiments, the deposition solution is acidic, with a pH less than about 4, e.g., about 3 or about 2. In certain embodiments, the solution is nearly neutral, with a pH of about 4 to about 10, e.g., about 5, about 7 or about 9. In certain embodiments, the electrolyte contains a salt such as NaCl, LiCl, or KCl. In certain embodiments, the liquid electrolyte is agitated by stirring, shaking, mixing, or turbulence to promote a non-uniform deposition rate and porous structure. In certain embodiments, the liquid electrolyte is gas-injected or aerated to introduce gas bubbles into the liquid during the deposition process.

[0198] In certain embodiments, iron powder is prepared by an electrometallurgical process to form porous iron. The iron-containing metal is processed from the molten material to spray, bubble, or mold onto a substrate or in a mold to form a low-cost, high-surface-area iron product. In certain embodiments, these powders may then be agglomerated in a rotary calcination furnace or by other means and then assembled into electrodes. In certain embodiments, the powder is assembled directly into electrodes without an intermediate agglomeration process. In certain embodiments, a mixture or combination of agglomerated and non-agglomerated powders is used for the electrodes. In certain embodiments, agglomerated and / or non-agglomerated powders formed by an electrometallurgical method are combined with other metals to process the electrodes.

[0199] Electrochemically formed metals, especially when the metal is in a liquid state, present unique opportunities for forming high-surface-area materials. In such cases, the resulting liquid product is cooled in various ways to achieve the desired properties. For example, iron formed by high-temperature electrometallurgy can be cooled directly in a high-surface-area mold, atomized into particles, or dispersed in a cooling medium.

[0200] In certain embodiments, the metal electrode is prepared directly by an electrometallic process such as molten oxide electrolysis. In certain embodiments, the porous electrode is formed by intentionally passing or injecting a gas into a molten oxide electrolysis cell. In certain embodiments, the gas is an inert gas such as N2 or Ar.

[0201] In certain embodiments, molten metal obtained from an electrometallurgical process is sprayed, bubbled, or molded onto a substrate or into a mold to form a low-cost, high-surface-area metal electrode. In certain embodiments, the metal is substantially iron.

[0202] In a non-limiting example, iron ore containing Fe2O3, Fe3O4, and mixtures thereof is dissolved in an electrolyte containing SiO2, Al2O3, MgO, and CaO in weight ratios of 60 wt%, 20 wt%, 10 wt%, and 10 wt%, respectively. This mixture is heated to a high temperature of approximately 1600°C. Metallic iron is electrochemically reduced from the molten oxide mixture and accumulates in the cathode. The molten metal is transported to a shot tower via tubes and valves, quenched in vacuum, and molten metal with an average diameter of 50 μm (μm = 10⁻¹⁰). -6 Fine iron powder of size m is generated. Subsequently, this iron powder is passed through a rotary firing furnace operating at 900°C in a nitrogen (N2, 100%) atmosphere to form aggregates with an average diameter of 2 mm, which are then assembled by filling metal electrodes.

[0203] In certain embodiments, the electrode may be fabricated from the thermochemical reduction of iron oxide. In some embodiments, the reduction may proceed to a near-complete reduction of iron oxide to metallic iron. Near-complete reduction of iron oxide to metallic iron is the goal of many industrial thermochemical reduction processes of iron. However, there are many potential reasons why such incompletely reduced products might be particularly useful for the formation of iron batteries. Firstly, some oxide phases formed during the reduction of iron are semiconducting and therefore may be useful as electron conductors in iron electrode materials. For example, magnetite is remarkably conductive at or near room temperature. Wustite is less conductive than magnetite but still more conductive than most oxides. In some embodiments, the semiconductivity of wustite and magnetite may be utilized to form battery electrodes that may be composites with metallic iron. Partially reduced products may also be more electrochemically active. We have observed that in some situations, wustite is more electrochemically active than metallic iron. Because wustite has a higher oxidation state than metallic iron, it may be less costly to reduce thermochemically. Therefore, wustite may be cheaper and more efficient than iron as a component of battery electrodes. In one embodiment, the positive electrode of an alkali iron battery may be produced from an infusible pellet consisting of carbon hematite, which has conventionally been subjected to direct reduction or blast furnace processes. The pellet may be reduced in a vertical shaft furnace via a suitable mixture of hydrocarbons and other reducing gases known in the art of direct reduction of iron. The reduction process may be terminated when a metallization rate of up to 95% is achieved (metallization rate is a term used in the art of direct reduction of iron, representing the percentage of iron atoms that are completely metallic in their oxidation state). In some examples, a lower metallization rate may be preferred, and a metallization rate as low as 0% may yield large quantities of magnetite or wustite as an alternative input material for batteries. The resulting partially reduced pellets, lumps, fragments, or particles may be packed into a particle bed for use as an iron electrode material. The electrode material may consist solely of iron oxide, or it may mainly consist of a mixture of magnetite and wustite.

[0204] In some cases, porous iron electrode materials may suffer from high electrical resistance when assembled into a bed. Thus, the performance of iron electrode materials inside a battery may be enhanced by methods to reduce resistance to charge transfer between particulate materials and by methods for collecting current from electrode active materials. This section describes methods for promoting charge transfer to current collectors in a filled bed.

[0205] Through experimentation, the inventors discovered that the performance of porous iron electrodes can potentially be enhanced by applying compressive force to the anode bed during the battery cycle. For example, applying a uniaxial compressive stress of 0.01 MPa or higher can reduce the contact resistance between porous particulate materials by more than an order of magnitude. If the compressive stress is too high, the electrode material may be locally fractured due to material cracking (and thus potentially leading to a localized decrease in conductivity), densification may occur due to deformation of the porous iron electrode material without cracking (which may then lead to a reduction in pore space available for the formation of discharge products, or a reduction in mass transport within the pore space), or other mechanical failure modes may occur. By applying a compressive stress that exceeds the stress required to reduce contact resistance without causing material fracture, the performance of the porous iron electrode material during the electrochemical cycle may be improved. Within this range, further increases in compressive stress or different configurations of compressive stress may be used to enhance the conductivity of the bed within the system and improve performance at stresses of approximately 0.1 to 10 MPa. As the applied stress (and therefore force) increases, the requirements for a mechanical enclosure capable of effectively applying such stress become more stringent, and generally the cost of the enclosure increases. Therefore, in one embodiment, a mechanical structure capable of simultaneously collecting and compressing a porous iron electrode material under stresses of 0.1 to 10 MPa is a particularly useful means for housing the iron electrode material in an electrochemical cell.

[0206] In various embodiments, it is beneficial for the current collector to perform multiple functions within the cell, including acting as a structural member. In one example, the current collector may structurally support the electrode by passing through the center of a packing bed of particulate material. In some embodiments, the packing bed may have current collectors on both sides in addition to a central current collector. In some embodiments, the central current collector of the packing bed may be fabricated from an unperforated sheet, while the outer current collectors may be perforated or otherwise contain holes to facilitate ion migration to the electrode active material. In various embodiments, air electrodes or other positive electrode materials may be positioned adjacent to the iron electrode material on both sides so that ions do not need to flow through the electrode material over the entire depth within the electrode, which can be achieved, for example, by ensuring symmetrical surfaces for migration. Thus, the absence of perforations in the current collector contained in the center of the bed may beneficially reduce the cost of the central current collector sheet while having little or no impact on migration within the system. The iron electrode material may be mounted on or compressed toward a combination of structural support and current collector provided in the center of the packing bed. Additional functions performed by the current-collecting component of iron electrodes include: anode placement / mounting, improved current collection, isolation of adjacent cells, and voltage stacking.

[0207] The degree to which the resistance of a porous electrode can be reduced to achieve a predetermined level of electrochemical performance is a function of the current collection method and material properties. When current is collected from more surfaces or when the total path length to the current collector is short, the final voltage drop is smaller, which may allow the battery to operate efficiently through high-resistance paths. Thus, the compression strategy and current collection strategy of the porous iron electrode can be beneficially optimized together to obtain the system with the lowest total cost for a given level of performance. Below, a set of techniques and designs for current collection from a porous electrode bed and compression of the porous electrode bed may be used in combination or separately to produce high-performance porous battery electrodes at low cost.

[0208] The current collector material can be any material used in the art to collect current in an alkaline battery at a potential to which the anode of an alkaline iron battery may be exposed. The composition of the electrolyte, the specific potential used during the battery cycle, and other process variables (e.g., temperature) determine the degree to which various current collector materials are stable. These materials include nickel, nickel-plated stainless steel, copper, copper-plated stainless steel, iron of sufficient thickness, carbon fiber and other carbon-based materials, and iron coated with cobalt ferrite.

[0209] In one embodiment, a reactor containing porous iron electrodes (e.g., electrodes 102, 231, 301, 403, 458, 502, 6102) may be divided into horizontal layers contained in a larger vessel. Figures 6B and 6C show exemplary embodiments of an embodiment in which the larger vessel 6202 is divided into horizontal layers 6203–6207. The larger vessel 6202 itself may act as the negative electrode (e.g., electrodes 102, 231, 301, 403, 458, 502, 6102). Referring to Figures 6B and 6C, these horizontal layers (e.g., 6203–6207) may also be referred to as packets. In each of these horizontal layers (e.g., 6203–6207), an anode, such as particulate anode material 6212, may be compressed by any method applicable to the compression and inclusion of particulate material. In this case, the current-collecting partition 6210 between packets may be inserted into a larger container 6202 that holds the packets (e.g., 6203-6207). A tab 6215 or other corresponding conductive mechanism on the partition 6210 may be used to hold the compression forcer (e.g., partition 6210) for the packets (e.g., 6203-6207) in place while also functioning as a current collector. This is shown in Figures 6B and 6C. The partition 6210 may also be provided with an optional capture lip 6216 on its side.

[0210] In one embodiment, the current collector may be a metal or other conductive fabric. For example, a mesh woven from nickel, copper, or graphite fibers. The current collector may surround or laminate the electrode material. The current collector fabric may surround a bed of directly reduced iron (DRI) pellets as electrodes, as shown below. The fabric may tighten, fasten, or otherwise mechanically tightly contact the electrode material to facilitate sufficient electrical contact with the electrode material. Figure 6D shows an example illustrating the case of a metal fabric 6402 with electrodes made of directly reduced iron pellets 6403 (e.g., electrodes 102, 231, 301, 403, 458, 502, 6102, 6202). The metal fabric 6402 may be a mesh or screen that wraps around the DRI pellets 6403, applies a compressive force or load 6404 to the DRI pellets 6403, presses multiple DRI pellets 6403 together within the mesh of the metal fabric 6402, and establishes close contact between the metal fabric 6402 and the DRI pellets 6403. The current 6405 may be collected by the metal fibers 6402.

[0211] In another embodiment, a conductive mesh pouch or bag can be used as a means for simultaneously compressing the electrode material and collecting current. More specifically, the mesh pouch or bag may be filled with fine-particle iron electrode material, and the bag may be fastened via a belt, string, wire, or other fastening mechanism, or otherwise reduced in volume to apply compression to the anode material. The fine-particle iron electrode material may be filled into a conductive mesh tube, and axial tension may be applied to the conductive mesh tube to compress the electrode material. In such a case, the weave of the mesh may be optimized so that the mesh tube is substantially compressed when axial tension is applied. This can be understood by analogy to a Chinese finger trap, where stretching a woven tube axially reduces the diameter of the tube. The amount of compression applied to the fine-particle iron material may be adjusted by the thickness of the threads in the weave, the density of the threads in the weave, and the amount of axial force / stretch applied to the weave. In some examples, the porous iron electrode material may consist of directly reduced iron pellets. In some examples, the porous iron electrode material may consist of crushed directly reduced iron pellets. In some cases, it may be beneficial to include a binder in the fine iron particle material to promote pellet adhesion.

[0212] In some embodiments, the porous mesh container and particulate active material may be arranged in a geometric configuration similar to that of a tea bag and tea leaves, for example, as shown in Figures 6E and 6F. Figure 6E shows a single fastening configuration 6500 in which the porous mesh bag 6501 is secured by a current collector 6502 at a single fastening point 6503. Configuration 6500 may also have negative electrodes (e.g., electrodes 102, 231, 301, 403, 458, 502, 6102). Figure 6F shows a two-point fastening configuration 6600 in which the porous mesh bag 6501 is secured by a current collector 6502 at a first fastening point 6503 and a second fastening point 6602. The two-point fastening configuration 6600 may also have negative electrodes (e.g., electrodes 102, 231, 301, 403, 458, 502, 6102). The tea bag container (e.g., 6501) may be conductive and function as a current collector. In some embodiments, the tea bag container (e.g., 6501) may have a current collector positioned inside the tea bag container packaging. The tea bag container (e.g., 6501) may have compression-promoting bands, including a band not positioned at the top of the tea bag container (e.g., 6501), such as a second fastening band 6602 or other positioned fastening bands. The tea bag container (e.g., 6501) may also have a band at the top of the container to retain the active material inside the container. In another embodiment, the tea bag container (e.g., 6501) may be non-conductive, and current collection may occur only through a current collector positioned inside the packaging of the tea bag container.

[0213] In another embodiment, an unrestrained, flexible conductive sheet may be loosely attached at its ends to a backing plate that may or may not be rigid, thereby forming a pouch. Fasteners, such as wires inserted through the flexible sheet and backing plate, open to fill the pouch with pellet or powdered anode material. The fasteners may be pulled closed to compress the anode and used for current collection. The fastening wires may be conductive and function as additional current collectors distributed throughout the pouch. The pouch may also be attached in a rigid manner (e.g., by welding) or by a connection that is rigid for one mode of motion and flexible for other modes of motion (e.g., a hinged connection). In some examples, current collection may be performed from one side such that neither the backing plate nor the pouch collects current, but in other examples, it may be advantageous to collect current from both sides of the pouch structure. An example of a fastening structure 700 having a backing plate 702 is shown in Figure 7 as a non-limiting example, which can show a configuration for negative electrodes (e.g., electrodes 102, 231, 301, 403, 458, 502, 6102). In some embodiments, the backing plate 702 may be used to rigidly support the pouch 705 shown in Figure 7 on both sides, where fastening wires 704 span the backing plate 702 and the pouch 705. Electrode material may be poured into the pouch 705 through an opening, which may then be closed by fastening or welding to form a closure 703.

[0214] In another embodiment, particulate electrode material may be compressed within a perforated sheet. The sheet may be conductive to serve both as a means for compressing the electrode material and as a means for collecting current from the electrode material. The holes in the sheet may be selected to be smaller than the characteristic size of the particulate material, and therefore less likely to escape from the cage formed by the perforated sheet.

[0215] In various embodiments, the electrode material may be a particulate material. To facilitate 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, for example, because it is difficult to create very fine perforations, particulate materials with particle sizes finer than porous or perforated materials are required. When particles finer than porous or perforated materials are required, the electrode material may be aggregated with a binder to form secondary particles consisting of a large number of primary particles. Thus, the primary particle size may be finer than the perforations, while the secondary particle size may be coarser. Such coarse particles may have difficulty passing through the pores or perforations of the current collector or other compression material, potentially allowing for more effective compression. In one embodiment, the aggregates may be bound using a polymer stable under alkaline conditions, such as poly(ethylene) or poly(tetrafluoroethylene). In another embodiment, the polymer may be introduced onto the surface of the primary particles, then thermally decomposed to form a conductive binder on the surface of the primary particles, thereby binding the primary particles together. In yet another embodiment, a polymer binder that is only partially stable under conditions suitable for the electrode may be introduced between the primary particles. The binder allows the electrode to be cycled in sufficient quantity, for example, through several electrochemical charge-discharge cycles, so that electrochemical bonds are formed between the various primary particles prior to the disintegration or degradation of the polymer. In another embodiment, the shape of the pores or perforations in the structure compressing the electrode material may be designed to hold the electrode material within the structure but to maximize ion transport through the perforations or pores. As a non-limiting example, elongated slits may be introduced into the perforated sheet to prevent particles from escaping through the slits, but the amount of area open to mass transport increases compared to the amount present when multiple perforations are equiaxed. In one embodiment, the particulate electrode material may consist of direct reduced iron, and the perforated sheet may consist of stainless steel. In another embodiment, the particulate electrode material may consist of direct reduced iron that has been crushed to a particle size several times smaller than the original pellet size, and the perforations in the current collector may be sized so that the crushed fragments do not escape from the compression cage.

[0216] In one embodiment, the bed of particles is vibrated, shaken, agitated, or moved so that the particles settle more tightly than when they were first filled. This method may be used periodically throughout the lifespan of the system to encourage new contact angles or arrangements between particles in response to changes in the shape or size of the particles. In the case of a container that provides pockets for particles, its orientation may be changed, for example, by rotating a wheel-shaped containment container.

[0217] In another embodiment, additives may be incorporated to promote conduction through electrodes between current collectors, or added to the base of the electrode material. It may be useful to concentrate the additives in key areas of the electrode structure. In one embodiment, the particulate anode material is bonded to the current collector using a conductive adhesive. This current collector may be of any shape, such as round or hollow sphere, and may have particulates on both sides. The conductive adhesive may contain a stable binder in an intended environment such as an alkaline electrolyte, conductive particles such as metal, conductive particles such as iron, fillers such as steel mill scrap, or powder. The binder may include, for example, poly(ethylene) or poly(tetrafluoroethylene). The conductive adhesive may further contain additives useful for battery performance, such as sulfide salt additives, or additives intended for bonding 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 relatively large resistances in the electrochemical system, forming a conductive bond between the electrode particulate material and the current collector can effectively promote battery performance at a low additional cost. The composition of the conductive adhesive is 10 to 80% by volume of conductive additives, with the remainder comprising a binder, optional additives, and possible co-solvents or tackifiers.

[0218] In another embodiment, current collection may be performed by forming a bond between each particulate material and a conductive rod. When the particulate material is attached to the current collector by a conductive bond, compressive stress does not need to be applied. The particulate material may be attached to the rod along the length of the rod. The anode mass may extend beyond the end of the rod. The anode mass may be attached via sintering, welding, or other metal bonding techniques, or by attachment using wires, or by deposition onto the rod from a solution or slurry via magnetic or solvent evaporation. The rod may be used to collect current from the anode. To facilitate the assembly of the composite anode, this rod-type anode may be snap-fitted into a flexible, slotted ring-shaped fastening mechanism. This fastening rail also functions as a busbar. This is schematically shown in Figure 8, where a rod 802 with iron particulate material 805 attached is fitted into a busbar 803. The rod 802 may have any cross-section, such as circular or straight, and does not need to be straight, but rather may be conceivable in a shape such as a coil to reinforce the packaging and limit the required volume of the busbar 803. A single rod 802, or multiple rods 802, may be combined to form the negative electrode (for example, electrodes 102, 231, 301, 403, 458, 502, 6102).

[0219] In another embodiment, for example, current collection and compression may be performed simultaneously through a pouch, which is processed from a crimped or welded sheet of metal and has an open top. The pouch may be filled with fine particulate iron electrode material, and the top of the pouch may be rolled down to compress the fine particulate material. Compression and rolling may be performed using a horizontal rod located inside the rolled portion. The pouch may be formed of a conductive material particularly suitable for current collectors in alkaline battery environments with iron cathodes. Current may be collected from the end(s) of the rod(s). The pouch may be porous or perforated to allow ion transport within the pouch, such as a nickel metal mesh.

[0220] In another embodiment, a rigid container may be formed. The rigid container may have at least one conductive wall, may be made of a material suitable for use in alkaline electrolytes, and may further be suitable for use in iron cathode current collectors. The rigid container may be filled with particulate electrode material and compressed via a piston or plunger mechanism. In one exemplary embodiment, anode pellets (or powder) are filled into a welded can having a bottom and an outer perimeter, and compressed from above using a plunger mechanism. The faces of the rigid container may be made of a rigid but ion-permeable material, such as perforated sheet metal or an expandable sheet. In one embodiment, an expandable sheet metal constituted the side walls of the rigid container. The platen or face used by the plunger has tabs or other suitable mechanisms which mechanically engage with features on the side walls of the rigid container, so that the plunger only needs to provide the compressive force for assembly. Thus, the mechanically engaging features allow the piston to be used for initial compression but can be removed thereafter. The compressive load in this embodiment and other embodiments may be applied via any means common in the art for applying compressive loads, such as bolts, hydraulics, weights, threaded rods, cable ties, and rivets, but are not limited to these. Figure 9 shows an exemplary embodiment of compressing iron electrode material 903 in a rigid anode container 905 using a perforated press 902. In this case, the iron electrode material 903 may be directly reduced iron pellets called DRI sphere beds. Figure 9 is an exploded view on the left and an assembled view on the right. In the figure, the assembled anode container 905 in which the iron electrode material 903 is compressed may be a negative electrode (e.g., electrodes 102, 231, 301, 403, 458, 502, 6102).

[0221] In another embodiment, the iron microparticle material may be sandwiched between two sheets of a suitable conductive material, such as a metal fabric, and riveted around the edges so as to be fastened for compression. In some examples, the suitable conductive material may be intermittently riveted, fastened, or otherwise subjected to volume reduction over the entire area of ​​the electrodes to compress more uniformly.

[0222] In another embodiment, a suitable sheet or mesh may be used in combination with a rigid sidewall to simultaneously perform compression, current collection, and containment. More specifically, in an exemplary embodiment as shown in Figure 10, a module 1002 consisting of a rigid sidewall 1004 may be slightly overfilled with iron electrode material 1005 having a metal mesh top plate and bottom plate 1003, and the whole is sealed with fasteners 1006 (e.g., bolts, threaded rods, cable ties, rivets, etc.). Module 1002 may also be a negative electrode (e.g., electrodes 102, 231, 301, 403, 458, 502, 6102). Since the sidewall 1004 may be slightly overfilled with spheres (e.g., DRI spheres as iron electrode material 1005), the mesh 1003 applies a compressive load to the iron electrode material 1005 when the fasteners 1006 are tightened. The mesh 1003 may function as a current collector. The mesh 1003 may allow for good circulation or diffusion of the electrolyte to the iron electrode material 1005. The fastener 1006 may be used in combination with other elements to hold the iron electrode material 1005 in place and apply a clamping load. In some embodiments, the fastener 1006 may also function as a current collector. The mesh 1003 may be a corrosion-resistant wire mesh, a perforated plate, i.e., nickel, stainless steel, etc. The side wall 1004 may be any rigid material that is suitably stable in the electrochemical environment of the iron electrode 1005, i.e., plastic, several metals, etc. The resulting assembly of the iron electrode material 1005 and the current collector may be a module component or may be permanently connected to an electrochemical energy storage system.

[0223] In another embodiment, a gasket-like material, which is a suitable material, may be used, and iron microparticle electrode material may be incorporated into several surfaces. Depending on the localized fit and / or filling of the floor, the suitable material allows for variable displacement of the force-applying elements of the design. In one example, the suitable gasket surrounds a cylindrical cell, and conductive current-collecting perforated plates are formed at both ends of the cylindrical cell. Multiple plates are forcibly connected at various points along the circumference of the cell, for example, via bolts that penetrate the silicone gasket. The gasket may be formed from a suitable alkali-resistant material, such as ethylene propylene diene monomer (EPDM) rubber or related materials. In some examples, the gasket needs to be highly suitable, in which case a foam of a polymer material, such as EPDM foam, may be useful.

[0224] In another embodiment, the current collector may have divots or other positioning or contact features on its surface. These features may function to increase the contact area between the current collector and the particulate iron material and / or to position the particulate material, thereby making filling more efficient as a result of mold formation provided by the surface of the current collector. In one example, the current collector may have a series of divots sized and positioned so that a set of spherical particles, such as those obtained from a direct reduction process, are tightly packed adjacent to the surface. Other molds are also possible, such as body-centered cubic molds. In particulate materials with an axis of symmetry, such as rods, mold formation may have an axis of symmetry such as divots, which are cylindrical depressions. Divots may be introduced by machining, sheet metal dimple processing, or other deformation processes, or may include perforations or through-holes of a suitable size in the current collector. The current collector may be shaped to optimally compress multiple particulate materials relative to each other; for example, in the case of rod-shaped particulate material, the current collector may have sheets compressed so as to be cylindrically wound around a cylindrical aggregate and limiting the diameter of the cylinder.

[0225] To reduce electrical resistance caused by current collection, the current collector may be designed so that current is collected more uniformly across the entire filled bed electrode by introducing the current collecting component throughout the entire thickness of the electrode, or by allowing the current collecting component to penetrate moderately throughout the entire thickness of the electrode.

[0226] In certain embodiments, the current collector may feature spikes, rods, tabs, or other high-aspect-ratio features that may protrude into the electrode bed from other boundaries of the current collector sheet or filled bed electrode. These high-aspect-ratio features may be sized and shaped to contact a number of electrode material particles in the bed that would not be contacted by a simple, flat sheet current collector. In certain embodiments, a sheet metal current collector is used, having tabs that protrude into a space filled with particulate material. In another embodiment, an expanded sheet metal is used as a current collector, with several supports within the sheet cut and bent inward to function as tabs that protrude into a space filled with active material.

[0227] In certain embodiments, a conductive brush or a series of wires is attached to the current collector. The wires flexibly protrude into a space filled with iron electrode material. The wires make contact with the material due to the spring constant of the wires, and this contact may be improved by utilizing compressive pressure.

[0228] In many embodiments, fasteners or other compression-providing elements are desired to hold multiple current collectors in a position that compresses them relative to one another. Hereafter, the term fastener is understood to mean any element of a mechanical assembly that provides a fastening or compression function by using an additional part that mechanically engages with other parts of the assembly. The performance of an iron cathode consisting of individual pellets is improved by applying a sustained compressive load before the cell is operated. However, maintaining the load using metal fasteners such as stainless steel bolts is disadvantageous because it increases both the number of parts and assembly time, and the design becomes more complex and the number of parts can increase because the bolts must be electrically isolated from the current collectors to suppress hydrogen generation reactions (undesirable parasitic side reactions that reduce Coulomb efficiency) that occur on the bolts. Thus, while fasteners are desirable from a mechanical standpoint, metal fasteners are disadvantageous. Below, we consider several ways to replace metal fasteners in other ways.

[0229] In some embodiments, non-metallic fasteners may be used instead of metal fasteners. In one exemplary embodiment, two clamping current collector plates may surround an iron electrode bed. The current collector plates can be formed to apply compressive force to the anode bed via fasteners formed from electrically insulating non-metallic materials that are resistant to degradation in the alkaline environment of the electrolyte. The electrically insulating and non-metallic properties of the fasteners prevent electrons from being transported to the electrolyte-exposed surface of the fasteners, thus preventing undesirable hydrogen evolution reactions from occurring on the exposed surface of the fasteners. Reducing the HER rate means that more electrons are supplied to the desired anode reduction reaction, i.e., the Coulomb efficiency is higher. In certain embodiments, the fasteners are bolts and nuts. In certain embodiments, the fasteners are formed from one or more of acrylic, polytetrafluoroethylene, polyethylene, low-density polyethylene, high-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, or polyetheretherketone. In another exemplary embodiment, two clamping current collector plates surrounding the anode bed can be formed to apply compressive force to the anode bed via fasteners that reduce assembly time by using a “snap-in” mechanism rather than a screw mechanism requiring rotation of the fasteners. In a particular embodiment, the fastener is a dual-lock snap-in support of appropriate length. The fastening techniques described above may be optionally combined to perform compression while avoiding the use of metal fasteners. Figures 11A and 11B illustrate some fastening techniques. Figures 11A and 11B show embodiments that may be used to fasten the negative electrodes (e.g., electrodes 102, 231, 301, 403, 458, 502, 6102) in various embodiments. The explanatory diagram in Figure 11A shows an electrically insulating nut 1103 clamping two current collector sheets 1105 toward an iron electrode material 1100 labeled “anodic active material” in Figure 11A. The nut 1103 fastens onto the bolt 1102, pulling together multiple sheets 1105 and thereby compressing the anode active material 1100. A second example of a snap-in compression feature, such as a snap-in support 1110, is shown in Figure 11B, where the snap-in support 1110 replaces the bolt 1102 and nut 1103 in Figure 11A and operates in a similar manner to the bolt 1102 and nut 1103.

[0230] In some embodiments, it is beneficial to use a conforming mechanism that can apply a large, distributed load to the current collector or compression platen. In one example, the end face structure of a rectangular columnar box for housing the anode is a leaf spring mechanism that compresses and houses the pellet anode and then springs back after anode loading. The current collector itself may be a conforming mechanism such that the load is distributed throughout the entire system by applying the load to a relatively small number of points (like a leaf spring).

[0231] The application of compressive stress may be by alternative means other than compression applied through mechanical fastening of the structure. In certain examples, the iron electrode material may be housed in a rigid body (e.g., a prismatic cell with current collectors or other mechanical supports on all faces), but the application of compressive load during assembly is not required by using an expandable material covering one face of the anode housing. The expandable material may be expanded after the assembly of the cell, thus applying a compressive load to the anode bed after the cell has been filled with electrolyte. In certain embodiments, the expandable material may be placed between the iron electrode material and one of the small faces of the iron electrode material housing. In certain embodiments, the expandable material is an expandable hydrogel that swells upon contact with an aqueous electrolyte, thereby applying a compressive load to the anode active material when the electrolyte is filled. In certain embodiments, the expandable material is an inflatable plastic balloon with a port for introducing air, thus applying a compressive load to the anode active material once air is introduced. The plastic balloon may be composed of poly(ethylene), poly(propylene), or similar polymers, which are flexible and resistant to degradation in alkaline solutions. Figure 12 shows an example of an embodiment of the expandable material 1200 housed within a rigid iron electrode housing assembly 1202. The left side of Figure 12 shows the unexpanded state, and the right side of Figure 12 shows the expanded state of the expandable material 1200 compressing the anode active material 1202 within the anode housing assembly 1202. The rigid iron electrode housing assembly 1202 may be the negative electrode (e.g., electrodes 102, 231, 301, 403, 458, 502, 6102).

[0232] In another embodiment, the container of iron electrode material is not rigid, but like some metal fabrics, it maintains its volume or has a maximum volume within a reasonable approximation range under stresses of less than about 10 MPa—this may be called a flexible cage. In such an example, an expandable material may be placed inside the flexible cage, and compression may be imparted by the expansion of the expandable material inside the flexible cage. The expandable material obtained above may be used in the same way. The flexible cage is conductive and serves both as a current collector and as a means of compressing the filled iron electrode material.

[0233] In another embodiment, the iron electrode material may exhibit a substantial magnetic moment in the presence of a magnetic field. The iron electrode material may be ferromagnetic, as is the case with iron. Therefore, a magnetic field may be induced in the iron electrode material toward a rigid wall using one or more permanent magnets or electromagnets, thereby applying a compressive load to the anode active material.

[0234] In another embodiment, a pump present in the system, such as a pump intended to transfer electrolytes, is used for suction of the microparticle bed. Suction by the pump pulls the microparticle bed together, bringing multiple microparticles into contact with each other. A screen or mesh with an opening smaller than the expected smallest microparticle prevents the microparticles from being drawn into the pump.

[0235] In another embodiment, phosphates (including iron phosphate), phosphoric acid, or similar phosphorescent additives may be beneficial to incorporate into iron electrode material to promote mechanical contact and bonding between particulate materials. Phosphate bases form phosphate bridges between metal oxide groups, thereby causing multiple particulate materials in the electrode bed to solidify together, forming an electrode with improved mechanical and electrical connectivity. Iron oxides, some of which (particularly magnetite and wustite) are semiconducting, can function as useful conductors. When the bonded oxides are electrochemically reduced to metal species, such metal species may be electrochemically sintered or otherwise bonded. Thus, such oxide bonding may improve electrochemical performance, even temporarily, over many cycles. To form such phosphate bonds, the electrode material may be pretreated with a phosphorus-containing solution before being placed in the electrolyte, or a phosphorus-containing compound may be introduced into the electrolyte. Phosphate bonds can occur in various metal oxide systems, including cadmium, magnesium, aluminum, and zinc. Phosphate additives are particularly beneficial in iron electrodes because they may also reduce the tendency for hydrogen to be generated on the iron surface during charging.

[0236] In some embodiments, it may be necessary to form conductive paths between the particles of the iron electrode material by metallurgical bonding of the particles before insertion into the electrolyte. Such metallurgical bonding may provide sufficient conductivity through the iron electrode material without requiring compression to achieve satisfactory electrochemical performance. Various methods for eliminating the need for compression of the iron electrode material are described below.

[0237] In one embodiment, the iron electrode material is thermally assembled by a high-temperature process such as sintering or brazing. In the thermal process for joining the iron electrode material to the current collector, similar metals may be fused together to reduce contact resistance between the particulate materials in order to strengthen the electrical connection. Although sintering has been considered for the manufacture of iron electrode materials, it has not been considered for some particulate iron materials due to their unique particulate structure. For example, direct reduced iron is an attractive raw material for iron electrode materials, but its coarse particle size makes it unsuitable as a reliable candidate for thermal joining by the sintering process. Direct reduced iron may be used directly in the sintering process, or it may be used in combination with other joining materials on the surface of the direct reduced iron to form a suitable metallurgical bond. The joining material may be painted, sprayed, or introduced onto the direct reduced iron or other particulate iron material to bond with other direct reduced iron particles during the heat treatment process. It may be beneficial to concentrate the joining material at the contact points between the direct reduced iron or other particulate materials as a means of obtaining maximum electrical contact with minimum additional cost. Examples of joining materials include materials with low sintering temperatures that may undergo metallurgical bonding during the sintering process, such as suspensions of carbonyl iron that are directly coated or sprayed onto reduced iron or other particulate materials. In a second example, the joining material may be melted by exposure to heat, or it may be fusion-welded or brazed. In a second example, a nickel brazing compound may be coated onto an iron electrode material, and then the material may be heated to an appropriate temperature to form a metallurgical bond. A thermal joining method is shown in Figure 13. Figure 13 shows a state in which a plurality of metal pellets 1300 are placed on an anode current collector 1302. Heat is applied to the pellets 1300 and the anode current collector 1302, and as a result, the pellets 1300 are fused to the current collector, as shown in Figure 13. In this way, the pellets 1300 may be formed into a negative electrode (e.g., electrodes 102, 231, 301, 403, 458, 502, 6102).

[0238] Possible manufacturing techniques for thermally bonded microparticle bed systems may involve a rolled sheet of steel acting as a furnace belt. This belt is unrolled from a coil and straightened to become a surface that moves horizontally within a continuous hydrogen furnace. At the furnace inlet, iron electrode material (such as directly reduced iron) accumulates on the belt via a hopper. This iron electrode material and belt sheet move through the furnace, maximizing the temperature at which the iron electrode material and belt are bonded. This iron electrode material and current collector sheet can then be cut into smaller pieces and used as anodes in the reactor.

[0239] In various embodiments, multiple particulate materials for iron electrodes make good contact with each other by forming a "plane" due to stress concentration at the contact points. In some examples, the electrode material does not need to be held with strong force throughout its service life; rather, the particulate materials may be pressed together during manufacturing to form flat areas, and then held with relatively small forces throughout its service life. To achieve this, the electrode cage may be supported under high load stress to form flat areas in the particulate material and reduce the contact resistance between particles. After partially releasing the force and removing the cage from the support structure, the electrode cage may be placed in the reactor under this weak compressive force, although the contact resistance was lower due to the application of strong compressive force. If the cage becomes disturbed or the cell resistance becomes excessive at any point during the service life, the cage can be removed, placed back into the support structure for recompression, and then the force can be released again to return the cage to the cell.

[0240] In various embodiments, the solubility of the iron intermediate in an alkaline medium may be utilized to form necks between particle materials in the iron electrode material constituting the packed bed. The iron electrode may be maintained within an appropriate pH, temperature, and optionally voltage range, so as shown in the figure below, at a sufficiently high concentration that the bonding between particles in the packed bed grows by a solution-precipitation reaction mediated by soluble species, HFeO2 -A soluble intermediate is formed, here referred to as a sphere. The bonds between particles may be called necks. Such neck formation may be performed in a pretreatment step or in-applied within an electrochemical cell for energy storage. Roughening may form necks between pellets to increase conductivity between pellets and reduce overpotential at the anode. In one embodiment of neck formation, the process includes immersing the pellet bed in an alkaline solution for >3 days, thereby allowing the soluble species to roughen the bed on a micron-to-millimeter scale, increasing contact between pellets. In another embodiment, an electrochemical cycle is employed to promote the deposition of soluble intermediate species. In a third embodiment, the pellets are coated with iron powder, such as atomized iron powder or sponge iron powder, to promote the formation of "necks" and reduce contact resistance between DRI pellets. As the cycle continues, the powder particles can be "sintered" into the host DRI pellets. Mechanistically, this is because, as shown in Figure 14, for example, the soluble intermediate Fe species (HFeO2) favors the deposition of discharge products at the interface between large and small particles. - This can occur due to mass transfer. Specifically, Figure 14 shows a state in which a bed 1400 is provided with individual DRI fragments 1402 (e.g., DRI spheres). By electrochemical and / or chemical reactions, the bed 1400 may be formed into a necked bed 1405 of multiple DRI fragments 1402 (e.g., spheres) joined together by a neck 1406 in between. In this way, the bed 1405 may be a solid mass of joined DRI fragments, in contrast to the original starting bed 1400 of separate fragments. In various embodiments, the necked bed 1405 may be used at the negative electrode (e.g., electrodes 102, 231, 301, 403, 458, 502, 6102).

[0241] In various embodiments, the particulate material may be joined by techniques common to welding metallic materials. In one embodiment, the particulate material may be resistance welded by passing a high current through the packing bed. The current may be applied by a compression roller assembly to bring multiple particles into contact before or simultaneously with the resistance welding process. In various embodiments, the particles may be mechanically deformed at high temperatures so that metallurgical bonds are formed at the contact points between the particles. In one example, a hot forming machine for hot forming or direct reduced iron may be operated at low compression pressure so that the particulate material deforms at the contact points to form metallurgical bonds. In the case of internally porous particulate material (such as direct reduced iron), compaction may utilize stress concentration at the contact points between particles to form metallurgical bonds between particles, although the internal porosity of the particulate material may hardly change away from the contact points. In various embodiments, the formation of metallurgical bonds may be carried out in an inert atmosphere to prevent oxidation of the iron electrode material. In various embodiments, the bed of particulate material may be ultrasonically compacted or compacted by other vibration means. Ultrasonic or vibration compaction may be accompanied by axial pressure. In various embodiments, multiple particulate materials may be fused together via any of the fusion welding techniques common in the art, such as tungsten inert gas welding, metal inert gas welding, and gas-metal arc welding, but not limited to these. In another embodiment, the materials may be explosively welded.

[0242] In various embodiments, conductive metal solder may be placed at the contact points between particulate materials to form metallic bonds between the materials. In one example, tin may be dip-coated onto a bed of particulate materials. In another example, copper may be dip-coated onto the particulate material. In yet another embodiment, a conductive liquid is passed through both a tube and a nozzle to deposit the coated particles. Precise control of the nozzle allows for precise positioning of individual particles, potentially optimizing the geometric arrangement of the electrodes. The deposited particles are then stacked to form a three-dimensional structure.

[0243] In various embodiments, the particulate material may be etched with one of a variety of acids and then mechanically deformed before being inserted into an electrochemical cell. The etching action may remove any surface oxides that would interfere with bonding, potentially enabling electrical contact between the anode materials. Acids such as hydrochloric acid, nitric acid, or any other acid used to strip iron oxide from metallic iron surfaces may be used. In some examples, compression may be performed while the particulate material is in the acid.

[0244] In various embodiments, the particulate material for the iron electrode may include a directly reduced iron material. The directly reduced iron material may be processed without using a cement coating to reduce sticking during the reduction process. These cements can inhibit charge transfer across the interface between pellets. In this way, the directly reduced iron material may have enhanced charge transfer properties for electrochemical cycles. In one example, a fluidized bed reduction process is used to enable the use of a directly reduced iron material that does not require a cement coating.

[0245] In various embodiments, the particulate material for constituting the iron electrode material may be compressed around the current-collecting mesh. The current-collecting mesh may then be heated (for example, by electrical resistance) and chicken wire may be welded to the particulate material surrounding the mesh. Multiple pellets may then be connected to each other by the mesh and welded together. The mesh may be relatively thick and coarse, like the fence material for chicken wire.

[0246] During operation of a battery using pellet bed electrodes, the size of the pellets can make mass and electron transport within the pellet difficult. As a result, polarization can occur, potentially reducing the battery's energy efficiency, due to (1) a decrease in voltage efficiency due to voltage drop during charging and discharging, and (2) a decrease in Coulomb efficiency due to insufficient competition with the hydrogen evolution reaction during charging. Insufficient charging also reduces the specific capacity of the resulting iron electrode. For example, in certain cases, polarization often occurs due to the transport of large amounts of hydroxide ions from the outside of the pellet through the pores to the iron reaction site in the center of the pellet. In other cases, polarization often occurs due to the transport of electrons from electrical contact points on the outside of the pellet to the center of the pellet through the internal network of iron material. Both of these causes of polarization lead to localized electrochemical potentials within the pellet, which can favor the hydrogen evolution reaction during charging over the desirable reduction reaction of iron oxide species, potentially reducing Coulomb efficiency.

[0247] In one embodiment, the size of the particles may be selected to improve packing. In a non-limiting example, the floor may consist of 50% particles greater than 5 mm in diameter, 25% particles between 5 mm and 1 mm in diameter, and 25% particles less than 1 mm in diameter, such that the smaller particles fill the spaces between the larger particles. Particles smaller than the original DRI size may be formed from the DRI in the manner detailed below. These particles may be placed in the containment in a specific order to ensure optimal packing, and in a non-limiting example, a layer of larger particles may be added first, followed by smaller particles to fill the spaces, followed by another layer of larger particles, and then another layer of smaller particles.

[0248] As a method to address one or more energy efficiency losses and specific capacity losses due to pellet size, we disclose reducing the size of iron pellets before battery assembly. Reducing the pellet size shortens the specific lengths of mass transport and electrical transfer within the pellet, reduces polarization, and may improve one or more of the energy efficiency and specific capacity.

[0249] It is known that reducing the size of pellets through crushing processes such as jaw crushing before assembly into a pellet bed improves voltage efficiency. However, pellet crushing should result in both reduced inter-particle contact within each particle (irregular particles have less contact than spherical particles) and increased interfacial resistance per particle in a bed of a given thickness. Furthermore, because the bed packing is geometric, "rattlers" where particles do not electrically contact adjacent particles are likely to be polydisperse irregular shapes rather than relatively monodisperse spheres. As a result, we surmise that the improved voltage efficiency due to enhanced mass transport and electrical transfer within the pellets partially masks the increased voltage drop due to electronic resistance and the loss of electrically contacting material (and thus reduced capacitance) due to the increased proportion of rattles.

[0250] In certain embodiments, crushing reduces the pellet size to less than half of the original size, resulting in a decrease in the overpotential of the iron electrode to more than 10 mV.

[0251] Adding secondary conductive additives to the pellet bed to improve one or more of the conductivity between pellets or from pellets to the current collector can lead to a substantial improvement in performance of pellet crushing. By increasing the conductive surface area in contact with the pellets, the additives increase conductivity and reduce the additional interfacial resistance of crushed pellets in the pellet bed. Additives that significantly increase the conductivity of the bed without inhibiting mass transfer are desired. The optimal additive is one that penetrates at a low volume fraction and is highly conductive.

[0252] In certain embodiments, the additive is one or more carbon black or graphite, added to the crushed pellet bed at a volume fraction of more than 1% so that the carbon black or graphite crosslinks with the crushed pellets. In certain other embodiments, low-to-medium conductive activated carbon or biochar is used as a low-cost alternative to graphite.

[0253] In certain embodiments, the additive is a piece of conductive mesh, such as stainless steel wire mesh.

[0254] In a particular embodiment, the additive is a conductive rod, such as a stainless steel rod, with a diameter smaller than the average pellet size.

[0255] Before the nominal operation of the battery, additives that improve iron electrode performance may be chemically incorporated into the iron electrodes through various processes that depend on the transport of chemical species from the electrolyte into the pellet's porous structure to the active iron moiety. To maximize the desired performance improvement effect of the additives, it is often necessary to uniformly impregnate the additives into the pellets. However, especially for low-solubility additives that react directly with reduced iron, it is often difficult to uniformly impregnate the pellets, which are typically liquid-soluble and solid, with specific additives.

[0256] As a method for more uniformly permeating liquid-soluble and solid additives into the pellets during the additive incorporation process, we disclose reducing the size of the iron pellets before battery assembly. Reducing the pellet size shortens the specific length of mass transport within the pellet and reduces the concentration gradient of the additive, thereby enabling more uniform permeation and incorporation of the additive into the electrodes.

[0257] In certain embodiments, the additive incorporation process is one or more of the following: immersion in an electrolyte, electrochemical plating, and electrochemical cycling.

[0258] In certain embodiments, the additive is an initially liquid-soluble hydrogen generation inhibitor, which is incorporated into a solid electrode via electrochemical or spontaneous chemical reactions.

[0259] In certain embodiments, the additive is initially a solid hydrogen evolution inhibitor, which is further incorporated into a solid electrode via an electrochemical or chemical dissolution-reprecipitation reaction.

[0260] In certain embodiments, the additives include one or more of the following: sodium thiosulfate, sodium thiocyanate, polyethylene glycol (PEG) 1000, trimethylsulfoxonium iodide, zincate (by dissolving ZnO in NaOH), hexanethiol, decanethiol, sodium chloride, sodium permanganate, lead(IV) oxide, lead(II) oxide, magnesium oxide, sodium chlorate, sodium nitrate, sodium acetate, iron phosphate, phosphoric acid, sodium phosphate, ammonium sulfate, ammonium thiosulfate, lithopone, magnesium sulfate, iron(III) acetylacetonate, hydroquinone monomethyl ether, sodium metavanadate, sodium chromate, glutaric acid, dimethyl phthalate, methyl methacrylate, methylpentinol, adipic acid, allylurea, citric acid, thiomalic acid, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, propylene glycol, trimethoxysilylpropyldiethylene, aminopropyltrimethoxysilane, dimethylacetyldicarboxylate (DMAD), 1,3-diethylthiourea, N,N'-Diethylthiourea, aminomethylpropanol, methylbutynol, amino-modified organosilane, succinic acid, isopropanolamine, phenoxyethanol, dipropylene glycol, benzoic acid, N-(2-aminoethyl)-3-aminopropyl, behenamide, 2-phosphonobutanetricarboxylic acid, MIPA borate, 3-methacryloxypropyltrimethoxysilane, 2-ethylhexoic acid, isobutyl alcohol, t-butylaminoethyl methacrylate, diisopropanolamine, propylene glycol n-propyl ether, sodium benzotriazole, aminotrimethylene phosphate Pentasodium phosphate, sodium cocoyl sarcosinate, laurylpyridinium chloride, steartrimonium chloride, stearalkonium chloride, calcium montanaate, quaternium-18 chloride, sodium hexametaphosphate, dicyclohexylamine nitrite, lead stearate, calcium dinonylnaphthalene sulfonate, iron(II) sulfide, sodium hydrogen sulfide, pyrite, sodium nitrite, complex alkyl phosphate ester (e.g., RHODAFAC® RA600 emulsifier), 4-mercaptobenzoic acid, ethylenediaminetetraacetic acid, ethylenediaminetetraacetate (EDTA), 1,3-Propylenediamine tetraacetate (PDTA), nitrilotriacetate (NTA), ethylenediamine disuccinate (EDDS), diethylenetriamine pentaacetate (DTPA), and other aminopolycarboxylates (APC), diethylenetriaminepentaacetic acid, 2-methylbenzenethiol, 1-octanthiol, bismuth sulfide, bismuth oxide, antimony(III) sulfide, antimony(III) oxide, antimony(V) oxide, bismuth selenide, antimony selenide, selenium sulfide, selenium(IV) oxide, propargyl alcohol, 5-hexyn-1-ol, 1-hexyn-3-ol N-allylthiourea, thiourea, 4-methylcatechol, trans-cinnamaldehyde, iron(III) sulfide, calcium nitrate, hydroxylamine, benzotriazole, furfurylamine, quinoline, tin(II) chloride, ascorbic acid, tetraethylammonium hydroxide, calcium carbonate, magnesium carbonate, antimony dialkyldithiophosphate, potassium stannate, sodium stannate, tannic acid, gelatin, saponin, agar, 8-hydroxyquinoline, bismuth stannate, potassium gluconate, lithium molybdenum oxide, potassium molybdenum oxide, hydrogenated light oil, heavy naphthenic petroleum fractions (heavy Naphthenic petroleum oil (e.g., sold as Rustlick® 631), antimony sulfate, antimony acetate, bismuth acetate, hydrogenated heavy naphtha (e.g., sold as WD-40®), tetramethylammonium hydroxide, NaSb tartrate, urea, D-glucose, C6Na2O6, potassium antimony tartrate, hydrazine sulfate, silica gel, triethylamine, potassium antimonate trihydrate, sodium hydroxide, 1,3-di-o-tolyl-2-thiourea, 1,2-diethyl-2-thiourea, 1,2-diisopropyl-2-thiourea, N-phenylthiourea, N,N'-diphenylthiourea, sodium antimony tartrate, disodium rhizonate, sodium selenide, potassium sulfide, and combinations thereof.

[0261] Figure 15 shows examples of pellet beds 1501 and 1502 according to various embodiments. Pellet beds 1501 and 1502 may be used in the negative electrodes of the embodiments (e.g., electrodes 102, 231, 301, 403, 458, 502, 6102). During operation of a battery using pellet bed electrodes, the entire thickness of the pellet bed may make mass and electron transport difficult, resulting in polarization that can reduce the energy efficiency of the battery due to (1) a decrease in voltage efficiency due to voltage drop during charging and discharging, and (2) a decrease in Coulomb efficiency due to insufficient competition with the hydrogen generation reaction during charging. As a result of insufficient charging, the specific capacity of the resulting iron electrode is also reduced. For example, in certain examples, the polarization is partly due to the mass transport of hydroxide ions from the outside of the pellet bed towards the center of the pellet bed. In other examples, the polarization is due to electron transport through the network of iron pellets. All of these causes of polarization can lead to localized electrochemical potentials within the pellet, which can favor hydrogen evolution during charging over the desired reduction reaction of iron oxide species, potentially reducing Coulomb efficiency.

[0262] One way to address one or more energy efficiency losses and / or specific capacity losses due to the overall thickness of the pellet bed is to increase the volumetric packing density of the pellets. By increasing the volumetric packing density, the thickness of the pellet bed relative to a given electrode capacity decreases, thereby reducing polarization across the bed and improving one or more of the energy efficiency or specific capacity. For example, Figure 15 shows a pellet bed 1501 having porous pellets 1503 formed as spheres or spheres, and a pellet bed 1502 having porous pellet fragments 1505 which may be formed by crushing spheres, spheres, or other shapes into multiple fragments. The in-pellet transport length t1 of pellet bed 1501 may be longer than the in-pellet fragment length t2 of pellet bed 1502.

[0263] As a method for increasing volumetric packing density and reducing polarization, a method of processing pellets by jaw crushing ("crushing") before assembling them into a pellet bed is disclosed. In this method, crushing may form a pellet bed 1502 instead of a pellet bed 1501. Before crushing, the pellets may be nearly spherical and have a narrow size range. In the crushing operation, the pellets may be cut into multiple non-spherical fragments with a wide size distribution, resulting in a higher volumetric packing density. The resulting high volumetric packing density reduces the thickness of the pellet bed and the mass of the electrode material relative to the fixed molded area, thereby reducing polarization across the bed and improving one or more of the energy efficiency or specific capacity (for example, when comparing pellet bed 1502 and pellet bed 1501, if the material composition of the porous pellets 1503 and porous pellet fragments 1505 is the same, pellet bed 1502 reduces the polarization of the bed and improves one or more of the energy efficiency or specific capacity compared to pellet bed 1501). Figure 16 shows pellet beds 1501 and 1502 to which current collectors 1601 are attached. Even if the same amount of pellet material is present in pellet beds 1501 and 1502, the height h1 of the uncrushed pellet bed 1501 may be greater than the height h2 of the crushed pellet bed 1502. Thus, crushing can reduce the size of the electrodes (e.g., electrodes 102, 231, 301, 403, 458, 502, 6102).

[0264] In a particular embodiment, the pellets after the crushing operation are cut into multiple fragments, which have sawtooth edges and a polydisperse size distribution such that smaller fragments fit into the gaps between larger pellets, thus increasing the packing density.

[0265] Certain performance attributes of pellet bed electrodes may deteriorate during battery operation due to time-dependent or charge-processing-dependent mechanisms. These deteriorated performance attributes include, but are not limited to, specific capacity (mAh / g), electrode overpotential (mV), self-discharge rate (mAh / mo), and Coulomb efficiency (%). Several methods for restoring iron electrode performance through treatment of batteries after the start of their life are disclosed herein.

[0266] In certain cases, cycle-dependent changes in the electrode microstructure that impede mass or electron transport may cause the electrode's specific capacity to decrease with battery cycling, thereby reducing the available capacity at a given polarization. More specifically, the pores within the pellet may gradually narrow with cycling as they are filled with residual electrochemical discharge products that have a larger molar volume (per mole of iron) than metallic iron. As the pores fill, mass transport to the iron within those pores is hindered, reducing the amount of iron in the pores, decreasing its availability for electrochemical reactions, and thus reducing the specific capacity. In other cases, the electrical resistance to certain iron regions may increase as the conductive paths provided by the metal network within the pellet narrow. In other cases, there may be an unreacted core of metallic iron within each pellet completely covered by a passivation layer.

[0267] Losses of usable capacity due to battery use may be recovered by ex-situ processing performed on the pellet after the electrode capacity has decayed to a minimum threshold. Various embodiments include processing the spent pellet with mechanical, chemical, electrochemical, and / or thermal processes (i.e., processing the pellet outside the apparatus) before reintroducing the pellet into the electrochemical cell to restore the electrodes to a state with better chemical and physical properties. Better chemical and physical properties include higher content of desirable impurities (e.g., hydrogen evolution reaction (HER) inhibitors), lower content of undesirable impurities (e.g., HER catalysts), higher specific surface area, higher total porosity, different pore size distributions (e.g., multimodal to reduce mass transport resistance), different pellet size distributions (e.g., multimodal to enhance bed filling), different aspect ratios (e.g., to enhance bed filling), etc. Mechanical processes that can be applied to the pellet outside the apparatus include, but are not limited to, crushing, grinding, and / or pulverization, which include size reduction. Mechanical size reduction re-exposes the passivated metallic iron in the pellet core, making previously unusable iron available and increasing capacity. It should be noted that performing the mechanical process to expose the initially passivated iron in the pellet core before battery use is undesirable because an increase in exposed metallic iron increases the number of areas where hydrogen generation reactions can occur, either through Faraday parasitic reactions during charging or spontaneous self-discharge reactions. However, mechanical processes performed outside the apparatus may be desirable as a method to restore and / or improve the reduced capacitance electrical resistance due to battery use. At this point, a larger fraction of iron is passivated and unusable, as shown, for example, in Figure 17. Specifically, Figure 17 shows a used pellet 1702 that has been subjected to external processing such as crushing and grinding to expose the iron core 1703 within the pellet 1702. Figure 17 shows the passivation layer 1705 that renders the core 1703 unusable even after processing.

[0268] Thermal processes applicable to pellets outside the apparatus may include treating pellets at high temperatures in a reducing (e.g., hydrogen), oxidizing, and / or carburizing (e.g., carbon monoxide and / or carbon dioxide) atmosphere. In certain embodiments, reducing conditions are a mixed gas of 10% nitrogen, 30% carbon monoxide, 15% carbon dioxide, and 45% hydrogen, at 800°C for 90 minutes. Electrochemical processes applicable to pellets outside the apparatus may include reverse electroplating, electrochemical dissolution, etc. Chemical processes applicable to pellets outside the apparatus may include acid etching, etc. In various embodiments, pellets may be pretreated by immersion in an acid bath (e.g., concentrated HCl) to increase the total porosity of the pellets compared to used pellets by etching the iron to enlarge the pores of the pellets and increase the usable capacity of the pellets during the discharge reaction. In various embodiments, pellets may be pretreated by immersion in a neutral or slightly basic bath to remove excess discharge products from the electrodes and increase the usable capacity of the pellets during the discharge reaction. For example, iron(II) hydroxide, one of the expected discharge products, is typically unstable at pH < 8. Immersion in a pH < 8 bath preferentially removes iron(II) hydroxide while preserving metallic iron in the electrode. In the pH range of pH > 7 and pH < 8, the bath may be a diluted form of the electrolyte used during the electrochemical operation of the battery. After pretreatment, the etched and porous pellet may be reassembled into the negative electrode. The chemical treatment time may be optimized to increase the usable capacity of the pellet without losing a significant amount of active material in the acid etching solution. Any of the processes described above may be optimized to preferentially enlarge the small pores in the pellet. In certain embodiments, the electrochemical process utilizes one or more large current pulses that result in a non-uniform current distribution within the pellet, thereby concentrating the current on sharp, small physical features within the pellet, preferentially promoting electrochemical dissolution at these small physical features, and enlarging the initially small pores. Additionally, any of the above treatments may be performed before battery operation to improve the chemical and physical properties of the pellet compared to its unmodified and unused state.

[0269] The shape and size of the discharge products within the pores of the iron pellet can affect performance in various ways. For example, a thin, uniform layer of discharge products may avoid pore clogging and improve capacity retention. On the other hand, a thin, uniform layer of non-porous discharge products may passivate the underlying metallic iron, thereby hindering the transport of hydroxide ions through the discharge product layer during discharge and reducing the usable capacity of the electrode. In another example, porous discharge products with a high surface area and uneven surface may increase the active surface area for the next discharge while promoting mass transport through the discharge layer, both of which may increase the total usable capacity. Figure 18 compares the distribution of discharge products. The left side of Figure 18 shows discharge products 1803 unevenly distributed on the surface of anode 1802. The right side of Figure 18 shows discharge products 1804 forming a uniform layer on the surface of anode 1802. The formation of discharge products may be mediated by electrolyte additives, anode additives, and / or surface coating agents of anode 1802. Various methods for controlling the morphology of discharge products in iron electrodes are disclosed.

[0270] To control the morphology of the discharge product, additives and counterions may be used in the electrolyte and / or electrodes. Additives and counterions can alter the porosity and available electrochemically active sites of the discharge layer, and this alteration is possible through the following mechanism: Fe forms a two-layer discharge product consisting of a relatively static inner layer of Fe3O4 and a highly porous outer layer, and this two-layer discharge product is strongly influenced by the electrolyte composition. Divalent cations tend to inhibit uniform discharge and promote the formation of a more porous outer layer. Monovalent cations inhibit uniform discharge and produce a more porous outer layer if their size does not sufficiently match that of the Fe cations contained in the outer layer of the discharge product. For example, lithium and cesium cations tend to produce a more porous outer layer compared to sodium and potassium cations because lithium and cesium do not match the size of iron cations very well. As additives and counterions for controlling the morphology of the discharge product, sulfides (S) 2- ), hydrosulfide (HS - ), lithium cation (Li +), sodium cation (Na + ), calcium cation (Ca 2+ ), selenide (Se 2- ), cesium cation (Cs + ), and barium cation (Ba 2+ This includes, but is not limited to, the following. In certain embodiments, sodium sulfide, lithium hydroxide, sodium hydroxide, calcium hydroxide, sodium selenide, and / or barium hydroxide are added to the electrolyte at various concentrations to provide soluble additives and counterions that act to control the morphology of the discharge product.

[0271] In certain embodiments, additives for controlling the morphology of the discharge product are initially contained within the solid electrode. The solid additive may be in the form of a solid metal oxide and / or metal sulfide introduced as a solid into the iron electrode. Examples of metal sulfides and oxides include: FeS, FeS2, MnS, Bi2S3, Bi2O3, Sb2S3, FeAsS, PbS, SnS, HgS, AsS, Pb4FeSb6S 14 Pb3Sn4FeSb2S 14 Examples include SeS2, etc.

[0272] In certain embodiments, additives for controlling the morphology of discharge products include one or more of the following: sodium thiosulfate, sodium thiocyanate, polyethylene glycol (PEG) 1000, trimethylsulfoxonium iodide, zincate (by dissolving ZnO in NaOH), hexanethiol, decanethiol, sodium chloride, sodium permanganate, lead(IV) oxide, lead(II) oxide, magnesium oxide, sodium chlorate, sodium nitrate, sodium acetate, iron phosphate, phosphoric acid, sodium phosphate, ammonium sulfate, ammonium thiosulfate Um, Lithopone, Magnesium Sulfate, Iron(III) Acetylacetonate, Hydroquinone Monomethyl Ether, Sodium Metavanadate, Sodium Chromate, Glutaric Acid, Dimethyl Phthalate, Methyl Methacrylate, Methylpentinol, Adipic Acid, Allylurea, Citric Acid, Thiomalic Acid, N-(2-Aminoethyl)-3-Aminopropyltrimethoxysilane, Propylene Glycol, Trimethoxysilylpropyl Diethylene, Aminopropyl Trimethoxysilane, Dimethyl Acetylene 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-phosphonobutanetricarboxylic acid, MIPA borate, 3-methacryloxypropyltrimethoxysilane, 2-ethylhexoic acid, isobutyl alcohol, t-butylaminoethyl methacrylate, diisopropanolamine, propylene glycol n-propyl ether, sodium benzotriazole, aminotrimethylene phosphate Pentasodium phosphate, sodium cocoyl sarcosinate, laurylpyridinium chloride, steartrimonium chloride, stearalkonium chloride, calcium montanaate, quaternium-18 chloride, sodium hexametaphosphate, dicyclohexylamine nitrite, lead stearate, calcium dinonylnaphthalene sulfonate, iron(II) sulfide, sodium hydrogen sulfide, pyrite, sodium nitrite, complex alkyl phosphate ester (e.g., RHODAFAC® RA600 emulsifier), 4-mercaptobenzoic acid, ethylenediaminetetraacetic acid, ethylenediaminetetraacetate (EDTA), 1,3-Propylenediamine tetraacetate (PDTA), nitrilotriacetate (NTA), ethylenediamine disuccinate (EDDS), diethylenetriamine pentaacetate (DTPA), and other aminopolycarboxylates (APC), diethylenetriaminepentaacetic acid, 2-methylbenzenethiol, 1-octanthiol, bismuth sulfide, bismuth oxide, antimony(III) sulfide, antimony(III) oxide, antimony(V) oxide, bismuth selenide, antimony selenide, selenium sulfide, selenium(IV) oxide, propargyl alcohol, 5-hexyn-1-ol, 1-hexyn-3-ol N-allylthiourea, thiourea, 4-methylcatechol, trans-cinnamaldehyde, iron(III) sulfide, calcium nitrate, hydroxylamine, benzotriazole, furfurylamine, quinoline, tin(II) chloride, ascorbic acid, tetraethylammonium hydroxide, calcium carbonate, magnesium carbonate, antimony dialkyldithiophosphate, potassium stannate, sodium stannate, tannic acid, gelatin, saponin, agar, 8-hydroxyquinoline, bismuth stannate, potassium gluconate, lithium molybdenum oxide, potassium molybdenum oxide, hydrogenated light oil, heavy naphthenic petroleum fractions (heavy Naphthenic petroleum oil (e.g., sold as Rustlick® 631), antimony sulfate, antimony acetate, bismuth acetate, hydrogenated heavy naphtha (e.g., sold as WD-40®), tetramethylammonium hydroxide, NaSb tartrate, urea, D-glucose, C6Na2O6, potassium antimony tartrate, hydrazine sulfate, silica gel, triethylamine, potassium antimonate trihydrate, sodium hydroxide, 1,3-di-o-tolyl-2-thiourea, 1,2-diethyl-2-thiourea, 1,2-diisopropyl-2-thiourea, N-phenylthiourea, N,N'-diphenylthiourea, sodium antimony tartrate, disodium rhizonate, sodium selenide, potassium sulfide, and combinations thereof.

[0273] Pretreatment involving electrochemical cycling also facilitates control over the morphology of the discharge products of the iron electrodes. For example, the inventors have observed that the compaction of the discharge products changes with temperature and current density. Pretreatment involving electrochemical cycling at temperatures and current densities that are not necessarily the nominal operating conditions of the battery may be used to form a discharge product morphology that persists when the operating conditions are set to nominal values ​​after pretreatment, leading to a high usable capacity. In various embodiments, pretreatment consists of 100 deep electrochemical charge-discharge cycles at 10°C and a gravimetric current density of 25 mA / gFe.

[0274] The inventors have found that lowering the operating temperature of the iron electrode to below 30°C improves various performance attributes, including specific capacity, retention of specific capacity over many electrochemical cycles, and the Coulomb efficiency of the electrode. Various mechanisms may be operated simultaneously to achieve these effects. For example, though not limited to, the conductivity of electrode materials containing discharge products of iron or iron oxide may increase, potentially improving specific capacity at low temperatures. Increased conductivity of the electrode material facilitates electrical transport to the electrochemical reaction site, resulting in increased specific capacity up to a predetermined polarization limit of the electrode. In another example, lowering the temperature may slow down the rate of undesirable electrolyte degradation and harmful reactions that occur during the battery's lifespan, such as carbonate formation due to carbon dioxide from the atmosphere. For example, carbonate formation is OH - Ion consumption reduces the conductivity of the electrolyte, lowers the pH of the solution, and leads to a decrease in specific capacity. Lowering the temperature slows down these undesirable reactions, improving the specific capacity retention rate of the iron electrode over the battery's lifespan. In another example, lowering the temperature may slow down the rate of the undesirable hydrogen evolution reaction compared to the desirable iron reduction reaction during battery charging, potentially resulting in higher Coulomb 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 shows temperature plots of specific capacity and Coulomb efficiency against the number of cycles.

[0275] Improving the electrochemical dynamics of charging (reduction) and discharging (oxidation) reactions in iron-based electrodes improves both the voltage efficiency and Coulomb efficiency of the cell. Redox mediators can be used to improve the electrochemical dynamics of iron-based electrodes. A redox mediator is a compound that acts as an electron "shuttle" and mediates reduction or oxidation reactions. While redox mediators are commonly used in the field of biocatalysis, they can also be used to promote desirable oxidation and reduction reactions in iron-based electrodes. Requirements for redox mediators include (1) fast and reversible redox dynamics; (2) a redox potential similar to the redox potential of the reaction being promoted (including, but not limited to, Fe·Fe(OH)2 and / or Fe(OH)2·Fe3O4); and (3) stability in the presence of the target electrolyte. The redox mediator may be soluble or insoluble in the target electrolyte. In some embodiments, the redox mediator includes one or more unsaturated base groups, saturated base groups, or combinations thereof. In some embodiments, the base group includes electron-withdrawing functional groups, electron-donating functional groups, or combinations thereof. In certain embodiments, unsaturated base groups include, but are not limited to, cyclopenta-1,3-diene, benzene, 1H-pyrrole, pyridine, pyrazine, furan, 4H-pyran, 1,4-dioxin, thiophene, 4H-thiopyran, 1,4-dithiine, 1-methyl-1H-pyrrole, or combinations thereof. In certain embodiments, saturated base groups include, but are not limited to, cyclopentane, cyclohexane, 1,4-dioxane, tetrahydrofuran, tetrahydro-2H-pyran, 1,4-dithiane, tetrahydrothiophene, tetrahydro-2H-thiopyran, 1,4-dimethylpiperazine, 1,3,5-troxane, 1,3,5-trithiane, or combinations thereof. In certain embodiments, electron-withdrawing functional groups include, but are not limited to, nitro, trichloro, cyano, carboxyl, fluoro, hydroxyl, or combinations thereof.In certain embodiments, the electron-donating functional group may be, but is not limited to, a primary amine, a secondary amine, a tertiary amine, an amide, a methoxy, a methyl, an alkyl, an alkenyl, an alkynyl, a phenyl, or a combination thereof. In one embodiment, the redox mediator of the iron-based anode is a viologen-based compound. In certain embodiments, the viologen-based compound may be, but is not limited to, a methyl viologen, a propyl viologen, a hexyl viologen, an octyl viologen, or a combination thereof.

[0276] In electrochemical cells equipped with iron electrodes, the iron electrodes can be used by adding sulfur to the cell. However, since sulfur is a known catalyst poison, in embodiments of electrochemical cells equipped with a catalytic cathode, it is considered optimal for the sulfur concentration around the iron electrode to be high and the sulfur concentration at the catalytic electrode to be low.

[0277] In one embodiment, immersing an iron electrode in a high-concentration sulfur solution before entering an electrochemical cell can cause sulfur to concentrate on the iron electrode. Furthermore, once the iron electrode undergoes a single formation cycle of "charging, then discharging," sulfur is electrochemically added to the structure of the iron electrode. When then added to the target electrochemical cell, the sulfur remains concentrated near the anode.

[0278] In certain embodiments, the iron electrode is immersed in an electrolyte with a higher sulfide concentration (i.e., >50 mM) before cycling in an electrolyte with a lower sulfide concentration (i.e., 50 mM).

[0279] In certain embodiments, a porous iron electrode is immersed in an electrolyte bath containing any alkali or transition metal sulfide (such as Na2S, K2S, Bi2S3, SbS3, etc.) to increase the presence of sulfides.

[0280] In a particular embodiment, sulfides are incorporated by immersion in a high-sulfide concentration electrolyte before cycling, and then the positive electrode is inserted into a full cell capable of having an initial sulfide concentration of 10-250 mM (1.4-33.8 mgS / gFe) or higher.

[0281] In one non-limiting example, the porous iron electrode described above includes a bed of DRI pellets.

[0282] It is difficult to uniformly or control the incorporation of sulfides or other beneficial additives into porous iron electrodes. One method for uniformly incorporating additives into porous materials is vacuum immersion, in which the substrate is exposed to a vacuum (<1 atmosphere) to empty the pores, and then exposed to a liquid or molten additive to fill the pores in the material.

[0283] In various embodiments, the substrate is exposed to a vacuum sufficient to empty the holes. Figure 20 shows one exemplary method for emptying the holes. In the first step, the substrate 2000 is exposed to a high vacuum to empty the holes 2001.

[0284] In one embodiment, in the second step, the empty substrate is then exposed to an aqueous electrolyte preparation containing the additive specified above at a temperature of 0 to 250°C, so that the pores are completely or partially filled with additive 2002. After a predetermined time, for example less than 48 hours, in the third step, the substrate 2000 may be rinsed or centrifuged to remove excess electrolyte.

[0285] In one embodiment, the empty substrate is then exposed to an additive in liquid or molten form, which is one of those specified in Section ## beforehand (e.g., octanthiol, FeS) that a person skilled in the art can identify as suitable for a melting process at temperatures of 25–250°C or 250–2000°C. After a predetermined time of less than 48 hours, the substrate may be rinsed or centrifuged to remove excess liquid or molten material.

[0286] In one embodiment, the empty substrate is then exposed to a gaseous additive (e.g., H2S, H2Se, CS2, and PH3 above 50°C). After a predetermined time, for example less than 48 hours, the substrate may be purged with an inert gas or under vacuum to remove any excess gaseous additive.

[0287] In a non-limiting example, before cycling, a solution containing sodium sulfide is vacuum-impregnated into the pores of the porous iron electrode 2000 to improve penetration. Good penetration of the sulfide into the anode can improve overall workability.

[0288] In a non-specific example, sodium thiosulfate is heated until melted (>45°C) and then vacuum-impregnated into the pores of a porous iron electrode before the cycle.

[0289] An additional method for localizing sulfides in a particulate material electrode includes the step of isolating the sulfide additive within the electrode or in a holder with variable permeability near the electrode. In this way, a controlled amount of sulfide can be added to the iron particulate electrode by passive or active electrochemical or chemical dissolution.

[0290] In one embodiment, the additive may be housed in a completely or semi-permeable holder, where the holder is made of a plastic (e.g., polypropylene, polyethylene) that is stable in an alkaline solution.

[0291] In one embodiment, the additive may be housed in a holder behind the ion-selective membrane, which allows the electrolyte to flow into the holder and slows the diffusion of the additive into the solution.

[0292] In one embodiment, the additive may be contained in a conductive material (e.g., a conductive polymer mesh, a metal wire mesh).

[0293] In one embodiment, the holder may be formed from a layer of porous oxide (e.g., silica).

[0294] In one embodiment, the additive holder may be in physical, electrical, or physicoelectric contact with the iron fine particle material electrode.

[0295] In one embodiment, the additive holder may be in contact with the electrolyte, or it may be in contact only with the iron nanoparticle material electrode via ion transport in the electrolyte.

[0296] In one embodiment, the additive holder may be immersed in another container of electrolyte to provide a constant sulfide source. The electrolyte in contact with the iron fine particle material electrode is then replaced with the electrolyte in contact with the additive holder.

[0297] In one embodiment, the additive holder may be electrically in contact with a constant potential device or system that maintains the holder at a potential that prevents the dissolution of the additive within the holder. Figure 21 shows an example of the configuration of the additive holder. In the configuration shown at the top of Figure 21, the additive containment bag 2104 may be in contact with the iron particulate material 2103 placed in the electrolyte 2100 that exists between the iron particulate material 2103 and the current collector 2102. In the configuration shown at the bottom of Figure 21, the additive containment bag 2104 may be suspended in the electrolyte 2100, separated from the iron particulate material 2103 and the current collector 2102, by an optional electrical connection part 2110 or the like.

[0298] Sulfide ions in the electrolyte have been proven to enhance the usable capacity and cycle life of iron electrodes in alkaline secondary batteries. However, it is known that the concentration of sulfide ions in the electrolyte decreases over time with the number of cycles, potentially reducing the beneficial effect of dissolved sulfides on anode performance. One way to enable performance improvements throughout the entire lifespan is to directly incorporate sulfur-containing species into the iron electrode material.

[0299] In one embodiment, elemental sulfur is directly introduced into a porous iron anode by melting and diffusing sulfur into a porous metal. Subsequently, the sulfur is introduced into the anode as a solid, bringing it into close contact with the active metal anode material and promoting favorable interactions that improve usable capacity and cycle life.

[0300] In another embodiment, a metal sulfide is introduced into the iron anode as a solid. Examples of target metal sulfides include: FeS, FeS2, MnS, Bi2S3, Sb2S3, FeAsS, PbS, SnS, HgS, AsS, and Pb4FeSb6S. 14 Pb3Sn4FeSb2S 14 Examples include SeS2, etc. The cations in the metal sulfide may contribute to the battery capacity (i.e., Fe), may be inert to the charge-discharge reaction (i.e., Mn), or may delay the hydrogen evolution reaction (i.e., Pb, Sb, Hg, As, Bi).

[0301] In one non-specific example, metal sulfides are directly incorporated into the reduced iron (DRI) pellet bed.

[0302] Methods for incorporating sulfur-containing species into iron electrodes include, but are not limited to, the following: (1) incorporating bulk solid particles, powders, or agglomerates into the voids between materials in the electrode bed; (2) incorporating metal sulfides (i.e., Bi2S3) with a melting point lower than that of iron metal into the electrode holes by melt diffusion; (3) incorporating metal sulfide powder into oxide ore pellets (i.e., taconite pellets) by mixing during the pelletizing process (in such embodiments, the metal sulfide remains in the pellets even after the reduction process, producing pellets containing metallic iron, metal sulfides, and impurities); (4) incorporating metal sulfides into pellets containing only metal sulfides and binders. In one example without binding, these pellets can be directly incorporated into a DRI pellet bed containing DRI pellets in a specific ratio; (5) incorporating metal sulfide powder using mixing, milling, or rotating equipment such as a ball mill.

[0303] In another embodiment, the above-described method of integration is used in conjunction with a sulfur-containing additive, including a metal sulfide, but is not limited to this method.

[0304] In another embodiment, as shown in Figure 22, a sulfur-containing additive including a metal sulfide is incorporated into the iron anode material by a trommel screening process step for DRI production, in which the sulfur additive is injected into the DRI pellet 2200 in a mesh cylinder during production, resulting in a DRI having sulfur additive pellet 2202.

[0305] It is difficult to uniformly or precisely incorporate additives into pre-formed metal electrodes, which limits the effectiveness of the additives.

[0306] Various embodiments involve selective precipitation with reactive counterions. In various embodiments, a metal is incorporated into a particulate iron material electrode in a neutral or oxidized state and then reacted with a selected counterion. 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 a particular embodiment, the electrode is exposed to an electrolyte containing a source of reactive counterions (e.g., Na2S, K2S, Na2Se, Na2Te) to form a compound (e.g., CdS, Bi2S3, Bi2Se3) in the apparatus. Here, the localization and concentration may be determined by the presence, concentration, and solubility of the additive metal, reactive counterions, or the resulting compound. In a particular embodiment, the availability of these additives can be further adjusted by using a transient pore-forming agent. In a particular embodiment, the electrode is electrochemically cycled before and after exposure to an electrolyte containing a specific concentration of reactive counterions to control the uptake of reactive counterions.

[0307] In the case where bonding does not occur, 0.5–10 wt% Bi₂O₃ is incorporated into the electrode before electrochemical cycling to a sufficiently reductive potential for Bi(s) formation. Exposure to an electrolyte containing 250 mM Na₂S may lead to the formation of Bi₂S₃ distributed throughout the electrode via the reaction described below.

[0308] [ka]

[0309] [ka]

[0310] In various embodiments, the target additive (e.g., Na2S, Na2Se, Na3PO4), which is a source of sulfur, selenium, tellurium, nitrogen, or phosphorus, is incorporated into the electrode at a concentration determined by the solubility of the source compound or the desired final concentration of the final compound in the electrode.

[0311] In certain embodiments, this electrode is composed of a reactive metal (e.g., Fe, Bi, Hg, As, Cd, Cu, Ni, In, Tl, Zn, Mn, Ag) or a metal-containing ion (e.g., Bi(NO3)3, NaAsO4, Cd(NO3)2, CuSO4) * x The electrode is exposed to an electrolyte containing a source of H2O to form a compound (e.g., CdS, Bi2S3, Bi2Se3) within the apparatus. Here, the localization and concentration may be determined by the presence, concentration, and solubility of the added metal, reactive counterions, or the resulting compound. The solubility of the nonmetallic additive creates a local concentration gradient in the electrolyte, resulting in regions where precipitation is more promoted. In certain embodiments, the availability of these additives may be further adjusted by using transient pore-forming agents. In certain embodiments, the electrode is electrochemically cycled before and 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.

[0312] In cases where bonding is not performed, Na2S may be incorporated into the metal electrode. When exposed to an electrolyte containing Bi(NO3)3, Bi2S3 distributed throughout the electrode may be formed by the reaction shown below.

[0313] [ka]

[0314] In various embodiments, an additive of a choice (e.g., S or Se metal) that is a source of sulfur, selenium, tellurium, nitrogen, or phosphorus, but does not have to be ionic itself, is incorporated into the electrode at a concentration determined by the solubility of the source compound or the final target concentration of the final compound in the electrode.

[0315] In various embodiments, the electrode containing a nonreactive additive may be exposed to an electrolyte, which in one embodiment may be an electrolyte containing NaOH or KOH, and in one embodiment, an anionic species (e.g., S2) may be added to the anode or electrolyte. - S2 2- The mixture is electrochemically cycled to produce polysulfides. As shown in Figure 23, these species may react to form Bi2S3 on the surface or be sealed within the anode. Exposing the anode to this electrolyte may increase the overall porosity as counterions react, which may be beneficial for the overall usable capacity.

[0316] Water and air-sensitive additives can degrade rapidly in aqueous alkaline electrolytes. For example, sulfides such as Na2S and NaSH (S 2- ) and disulfides (HS - Compounds containing ) degrade upon exposure to oxygen by forming sulfates or other sulfur-containing compounds (e.g., sulfites, thiosulfates, sulfur, polysulfides).

[0317] [ka]

[0318] [ka]

[0319] [ka]

[0320] [ka]

[0321] Since it is difficult to reduce sulfates or other sulfur oxide-containing compounds back to sulfides, disulfides, or hydrogen sulfide, it is preferable to maintain the sulfur species in the electrode or electrolyte as sulfides or disulfides.

[0322] In one embodiment, sulfur oxide-containing species (e.g., Na2SO4, Na2S2O3, Na2SO3, S metal) are added to the electrolyte in an amount sufficient to reduce or completely suppress the formation of sulfur oxide species by shifting the equilibrium in favor of reducing sulfur species, according to Le Chatelier's principle.

[0323] In one embodiment, sulfur oxide-containing species (e.g., Na2SO4, Na2S2O3, Na2SO3, S metal) are added to the electrode. Upon exposure to the electrolyte, these soluble additives dissolve in the electrolyte, potentially increasing the porosity of the electrode and reducing or suppressing the formation of sulfur oxide species in the solution.

[0324] In one embodiment, sulfur oxide-containing species (e.g., FeSO4, FeS2O3, FeSO3) including metal cations are added to suppress the oxidation of reducing sulfur species and to suppress the dissolution of metal species from the iron electrode.

[0325] DRI-based iron anodes exhibit compatibility across a wide range of initial sulfide concentrations in the electrolyte. Furthermore, it has been found that the initial sulfide concentration on the gS / gFe ratio, rather than the sulfide concentration in the electrolyte, is the driving factor.

[0326] In certain embodiments, an initial sulfide concentration of 1 mM Na2S (0.1 mgS / gFe) is sufficient for stable capacity performance.

[0327] In certain embodiments, an initial sulfide concentration of 10 mM Na2S (1.4 mgS / gFe) is sufficient for stable capacity performance.

[0328] In certain embodiments, an initial sulfide concentration of 50 mM Na2S (6.8 mgS / gFe) is sufficient for stable capacity performance.

[0329] In certain embodiments, an initial sulfide concentration of 175 mM Na2S (23.6 mgS / gFe) is sufficient for stable capacity performance.

[0330] In certain embodiments, an initial sulfide concentration of Na2S (33.8 gS / gFe) of ≥250 mM is sufficient for stable capacity performance.

[0331] Furthermore, the method for incorporating sulfides into the iron anode can be achieved using various technologies.

[0332] In a particular embodiment, sulfides are incorporated into the full cell via an electrolyte with a high sulfide concentration.

[0333] In certain embodiments, sulfides are incorporated via immersion in a high-sulfide concentration electrolyte before cycling, and this incorporation can be completed in a sulfide-free electrolyte (which may be beneficial for the cathode).

[0334] In a particular embodiment, sulfides are incorporated by immersion in a high-sulfide concentration electrolyte before cycling, and then the positive electrode is inserted into a full cell in which the sulfide concentration can be in the range of 10 to 250 mM (1.4 to 33.8 mgS / gFe) or higher.

[0335] Sulfide uptake can be optimally achieved by maintenance methods including, but are not limited to, the following: 1) periodic addition of high-concentration sulfide solutions or solids; and 2) continuous addition of sulfides in solid or solution form, where the sulfide concentration can be in the range of 10 to 250 mM (1.4 to 33.8 mgS / gFe) or higher.

[0336] In one embodiment, a 325-mesh iron sponge powder having pores opening inside the particles is thermally bonded by sintering to form the base of the iron electrode material. The sintered electrode material incorporates bismuth oxide and iron sulfide, and these materials are thermally bonded to a current-collecting perforated sheet. The sintered connection with the current collector and the sintered connection between the powder particles eliminate the need for compression for conductivity. The alkaline electrolyte consists of a mixture of 80% potassium hydroxide, 15% sodium hydroxide, and 5% lithium hydroxide in molar ratio, and the total hydroxide concentration in the aqueous solution is 6 moles.

[0337] In one embodiment, the iron electrode material may directly contain reduced iron pellets along with an electrolyte comprising 6 moles of potassium hydroxide, 0.1 moles of lithium hydroxide, and 0.05 moles of sodium sulfide. The iron electrode may further contain 1% by weight of bismuth sulfide finely dispersed in the directly reduced iron pellets. The electrode material may be compressed within a rigid cage comprising a nickel-plated stainless steel current collector plate that applies uniaxial pressure to compress the pellets within a rigid wall structure made of poly(methyl methacrylate), and the current collector plate may be held in place by stainless steel bolts electrically insulated from the current collector. The floor thickness of such embodiments may range from 1 to 10 centimeters.

[0338] In one embodiment, the iron electrode material may include carbonyl iron powder, lead oxide, and iron sulfide. Both lead oxide and iron sulfide may be present in amounts of 0.1% by weight and 1.5% by weight, respectively, relative to the total weight of the solids in the electrode. The multiple solids are lightly sintered to bond together into a mass, and then compressed in a nickel mesh fabric formed by inflating and compressing a polyethylene balloon. The electrolyte is 5 moles of sodium hydroxide, with 0.005 moles of sodium sulfide and 0.01 moles of octanthiol as additives.

[0339] In another embodiment, reduced iron pellets are directly crushed to a particle size in the range of 1 to 6 mm. These particles are mixed with 1% by weight of natural flake graphite with a particle size of 200 microns and 0.05% by weight of iron sulfide with a particle size of 100 microns relative to the solid mixture. The electrolyte is an aqueous solution containing 6.5 moles of potassium hydroxide, 0.5 moles of lithium hydroxide, 0.25 moles of sodium sulfide, and 0.001 moles of octanthiol. The solid mixture is loaded into a nickel mesh bag with a mesh size of approximately 0.5 mm, and the bag is compressed by a fastening mechanism to lightly compress the solid material.

[0340] Various embodiments may include a battery comprising a first electrode, an electrolyte, and a second electrode. Here, at least one of the first and second electrodes contains atomized metal powder. Various embodiments may include a battery comprising a first electrode, an electrolyte, and a second electrode. Here, at least one of the first and second electrodes contains an iron agglomerate. In some embodiments, the average length of the iron agglomerate is in the range of about 50 μm to about 50 mm. In some embodiments, the average internal porosity of the iron agglomerate is in the range of about 10 volume% to about 90 volume%. In some embodiments, the average specific surface area of ​​the iron agglomerate is about 0.1 m². 2 / g ~ approx. 25m 2 The range is / g. In some embodiments, the electrolyte permeates between the iron masses. In some embodiments, the electrolyte contains 1-octanthiol. In some embodiments, the electrolyte contains molybdate anions and sulfide anions. In some embodiments, the iron masses are supported within a metal fabric mesh that provides compressive force and current collection to the iron masses. In some embodiments, multiple iron masses are joined to each other and joined to a current collector.

[0341] Various embodiments are electrode manufacturing methods comprising the steps of electrochemically generating metal powder and forming the metal powder into an electrode. In some embodiments, the step of electrochemically generating metal powder includes a step of at least partially generating metal powder using a molten salt electrochemical substance. In some embodiments, the step of electrochemically generating metal powder includes a step of at least partially generating metal powder by gas spraying. In some embodiments, the step of electrochemically generating metal powder includes a step of at least partially generating metal powder by water spraying.

[0342] In various embodiments, sacrificial pore-forming agents, convertible pore-forming agents, transient pore-forming agents, removable pore-forming agents, or techniques can be utilized. In such embodiments, the intermediate material in which the pore-forming agent is still present may have a total Fe weight percentage in the range of 20% to 90% by weight. The pore-forming agent can be removed partially before use as an electrode, entirely before or during use as an electrode, and in combinations and variations thereof. In one embodiment, the intermediate may have a total Fe of 25% to 50% by weight, and removal of the pore-forming agent provides the electrode with a total Fe of 60% to 90% by weight.

[0343] In embodiments, as shown herein, iron materials can be processed, chemically modified, mechanically modified, or otherwise configured such that one or more of their characteristics are altered. Such methodologies are generally described herein as being implemented with DRI materials. It is understood that such methodologies can be applied to 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 variations thereof. Thus, iron-containing pellets having predetermined characteristics, for example, those shown herein, are provided for use in electrode configurations of long-term electrical storage cells.

[0344] In certain embodiments, DRI is subjected to mechanical operations for grinding, scraping, or polishing a surface and / or removing fine particles. In one embodiment, DRI pellets are rotated in a trommel sieve to scrape the surface and remove fine powder / dust from the surface. This operation can have the beneficial effect of reducing the reactivity of the DRI pellets, making shipment easier and safer without relying on briquetting or other compression operations. In another embodiment, a block or sheet of DRI is passed under a rotating brush to remove fine particles from the surface. This exhibits a similar beneficial effect.

[0345] In one embodiment, the porosity of DRI is increased by pretreatment with an acid bath (e.g., concentrated HCl). The acid bath etches the iron, creating larger pores and increasing the overall porosity. By optimizing the etching time, the total volume of the DRI pellet can be increased without excessive loss of active material into the acid etching solution.

[0346] In another embodiment, desirable impurities or additives are incorporated into the DRI. If such impurities are solid, they can be incorporated by ball milling the powder additive together with the DRI pellets (for example, using a planetary ball mill or similar apparatus). In this case, the pellets themselves act as a milling medium. In this way, the powder additive is mechanically introduced into the pores or surface of the DRI pellets. Alternatively, the DRI may be coated with beneficial additives, for example, by rotating or immersing it in a slurry containing the additives. Examples of such desirable impurities include alkali sulfides. Alkali sulfide salts have been shown to significantly improve the availability of active materials at the Fe anode. In exactly the same way that soluble alkali sulfides can be added to the electrolyte, insoluble alkali sulfides can be added to the DRI, for example, by the method described above.

[0347] In some embodiments, the surface area of ​​cementite or iron carbide-containing materials, such as DRI pellets containing cementite or iron carbide, is increased by using the material as the anode of an electrochemical cell and discharging it. In certain embodiments, the specific current density may be 0.1 to 25 mA / g. This high-surface-area iron oxide can also be used in various applications other than electrochemical cells.

[0348] In various embodiments, to increase electrical conductivity, pellets can be mixed with a more electrically conductive but potentially more expensive powder to produce a more highly conductive composite bed. This powder can increase the area capacity of the cells by filling the gaps between the pellets. This can reduce the ratio of electrolyte volume to DRI pellets in a manner that can be systematically varied and optimized. In one embodiment, as described in more detail in the previous section, this powder is used in the current collector to increase the contact surface area and reduce the interfacial resistivity between the current collector and the small contact area of ​​the spherical pellets. This ensures the ability to vary and control the effective current density of the pellets. By changing the particle size of the composite bed, cost and conductivity can be controlled. In another example, the use of additional conductive materials such as powder, wire, mesh, gauze, or wool increases the overall conductivity, making it possible to use low-conductivity pellets (sometimes referred to in the industry as "remet"), such as DR taconite pellets or poorly metallized direct reduction pellets, in the composite bed. In one embodiment, the conductive component may include DRI fine powder or other waste materials from the DRI process.

[0349] In one embodiment, the porous sintered iron electrode may be formed from DRI, the DRI whose particle size may be reduced by, for example, crushing or grinding, or which may be in powder form. Alternatively, the sintered iron electrode may be formed using DRI powder or other waste materials. The sintered electrode may be formed using a binder under heat and / or pressure, and then the binder may be burned off, and the raw form may be sintered at a high temperature. Alternatively, in order to create electrical and physical connectivity between the pellets, the DRI pellets may be directly fused together by sintering in a non-oxidizing atmosphere with optionally applied pressure without using a binder.

[0350] In various embodiments, the porous anode may be formed by crushing, shredding, or grinding hot briquette iron (HBI). In various embodiments, HBI may be preferred for shipping and transport due to its lower surface area and reactivity, however, the porosity of HBI may be too low for practical applications in thick electrodes due to limited ion transport. To achieve an optimal combination of transport and performance, DRI may be transported in briquette form to the cell assembly or manufacturing site, where it may be crushed, ground, and / or shredded to increase the porosity of the resulting electrode.

[0351] A DRI pellet bed can be a desirable configuration for iron-based electrodes because it provides an electronically conductive penetration pathway through the bed while leaving porosity available for the electrolyte to occupy, facilitating ion transport. In certain embodiments, the ratio of electrolyte volume to DRI mass may be in the range of 0.5 mL / g to 5 mL / g, such as 0.6 mL / g or 1.0 mL / g. DRI pellets generally come into contact with surrounding pellets via a small contact area compared to the surface area of ​​the pellets, and in some cases, the contact can be considered a "point contact." Small cross-sectional area contacts can result in constrictions in the flow of current, which may lead to relatively low electrical conductivity across the pellet bed, and consequently, high electrode overvoltage and low battery voltage efficiency.

[0352] In various embodiments, the electrical conductivity of a DRI pellet bed can be increased in several ways. In some embodiments, the electrical conductivity of a DRI pellet bed can be increased by using additional conductive material, which may surround individual pellets, be embedded within individual pellets, surround the entire pellet bed, or penetrate the pellet bed. The conductive material may be one or more of metals, metal oxides, metal carbides, metal nitrides, semiconductors, carbon, conductive polymers, or a composite containing at least one of such electronically conductive materials. The electronically conductive material may be in the form of a powder, wire, mesh, or sheet. In certain embodiments, the conductive material itself may contribute to the electrochemical reactions of the battery, including but not limited to providing storage capacity. In certain other embodiments, the electronically conductive material is substantially electrochemically inactive. In one embodiment, the conductive material is a powder, which fills or partially fills the spaces between pellets or between pellets and current collectors to improve electrical conductivity between pellets or between pellets and current collectors. For example, the conductive powder may consist of DRI "fine powder," which is a powder waste product of the direct reduction process and has a composition similar to DRI. In this case, the fine powder can serve both to increase the electrical conductivity of the bed and to increase the storage capacity of the anode. In another embodiment, the conductive material is a powder, which is applied to the surface of the pellets to form a coating. Such a coating provides a larger surface area for electrical contact between the pellets.

[0353] In various embodiments, a conductive coating is applied to low-conductivity pellets to enable their use as electrodes. In certain embodiments, low-conductivity pellets such as taconite pellets or insufficiently metallized direct reduction pellets (sometimes referred to in the industry as "remet") may be coated. The coating may be conductive to reduce the electrical resistance from the current collector to the taconite 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 metallic layer, such as stainless steel, that wraps around each pellet in a circumferential direction. In another embodiment, the coating is a thin layer of lead that coats the outside of each pellet using a directional deposition technique such as sputtering, vapor deposition, or other physical vapor deposition techniques. In certain embodiments, the coating is applied by rotating the DRI and the coating material together in a rotating vessel. In certain embodiments, the DRI in the rotating vessel is substantially spherical in shape.

[0354] In another embodiment, some or all of the individual pellets in the pellet bed are wrapped in electrically conductive wire, foil, or sheet. In some embodiments, a clamping mechanism such as a mesh is used to apply tension to the wire, foil, or sheet. Optionally, such current collectors surrounding individual pellets may be bundled together or attached to wires connected to a larger current collector. In another example, conductive mesh, gauze, or wool is scattered in the spaces between DRI pellets to increase electrical connectivity. In various embodiments, the conductive material is a mesh having openings (clear size) selected to be smaller than the pellets so that the pellets do not pass through the mesh. The conductive material in this case may 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 that pass through or around the individual pellets. For example, as in forming a string of beads, wires can be passed through holes in the DRI pellets to provide electrical contact not only between pellets but also within the pellets. Optionally, the string of pellets can maintain contact using electrical terminals or “stoppers” to which tension is optionally applied. The electrical terminals may optionally be electrically connected to a larger current collector or fixing device, such as a plate.

[0355] In another embodiment, the electrical conductivity of a pellet bed is improved by applying a compressive load to the DRI pellet bed anode to increase the inter-pellet force and / or the inter-pellet contact area or the contact area between the pellets and the current collector, thereby reducing contact resistance and enhancing electrochemical performance. Typical DRI pellets are approximately spherical in shape, have internal porosity, and can be elastically deformed to a linear strain of >5% before yielding. Applying a compressive load to the DRI bed can increase the effective contact area between pellets and at the interface between the pellets and the current collector. It is advantageous to use pellets with a yield strain that allows deformation to achieve the desired increase in conductivity without causing fracture. In one embodiment, pellets having a compressive strength of 700 to 2500 psi are used for pellet bed electrodes to which a compressive load is applied. In addition, the mechanical assembly that provides the compressive load to the pellet bed can also serve as a current collector. The electrical resistance of such a pellet bed, measured in a dry state before any liquid electrolyte is filled, can be reduced by half to one-hundredth or more by applying a compressive load. In certain embodiments, the applied load may be in the range of 0.1 psi to 1000 psi, such as 50 psi or 100 psi. In certain embodiments, the applied load may be in the range of 0.1 psi to 10 psi, such as 1 psi or 5 psi. In one example, a metal plate on the opposite surface of the pellet bed serves to provide both current collection and a compressive load to the pellet bed. Optionally, one or more of the plates may be replaced with a macroporous current collector (e.g., a metal mesh) to facilitate ion transport across the entire electrode. The opposing current collectors are preferably joined so that they are at the same potential, which is advantageous for more uniform electrochemical reaction rates across the entire electrode. In another example, the container containing the pellet bed serves both as a current collector and as a means of applying a compressive load. In another embodiment, an array of conductive posts (or rods) connected to a common downward current collector is implemented. Thus, a number of current collection areas can be arranged across the entire pellet bed.Furthermore, this method can reduce the effective transport length within the electrode from the total thickness of the pellet bed to the distance between posts. In addition, these posts can be used to attach a mechanical clamping mechanism, such as a plate or perforated plate, to the top of the pellet bed, which can then act as a current collector while incorporating a downward force on the pellet bed.

[0356] In some embodiments, the compressive load may be provided partially or entirely by magnetic force. For example, a force can be applied using permanent magnets placed on one or more sides of the floor so that the pellets in the floor are attracted to the magnets. In the case of a DRI pellet floor, which is mainly metallic iron, the pellet floor is expected to be mainly ferromagnetic and will be attracted to the magnets. The magnets may also be embedded in other fixtures surrounding the pellet floor. The magnets and fixtures serve to hold the pellet floor in place and provide compressive stress that results in improved electrical contact between pellets and between pellets and current collectors, as described above.

[0357] In some embodiments, the inter-pellet contact resistance of the pellet bed can be reduced by using pretreatment applied to the pellet bed before the battery is assembled and / or put into operation. Some of these pretreatment processes are described in the following paragraphs.

[0358] In some embodiments, the entire DRI pellet is packed into a bed and sintered under an inert or reducing (i.e., non-oxidizing) atmosphere, optionally using a material stable in the sintering temperature and atmosphere, and applying mechanical pressure during sintering. The sintering temperature may be in the range of 600 to 1100°C. The non-oxidizing atmosphere may consist partially or entirely of an inert gas such as nitrogen or argon. The non-oxidizing atmosphere may also contain a mixture of gases that tend to reduce iron, such as CO and CO2 and H2 and H2O. The exact composition of the mixture can be optimized according to the Ellingham diagram to ensure that oxidation of iron is thermodynamically unfavorable. In one embodiment, to provide non-oxidizing conditions, a forming gas (5% H2, 95% N2) is used at sintering temperatures of about 600°C to about 1100°C, such as 600°C to about 850°C, 850°C, or about 850°C to about 1100°C. The combination of high temperature and a non-oxidizing atmosphere can promote atomic diffusion and particle coarsening at the pellet contacts, causing the pellets to bond together. The result is a bed of DRI pellets that are fused together and have low inter-pellet contact resistance. The pellets can also be fused with current collectors using the same process.

[0359] In another embodiment, pellets are joined using a heat treatment in which a flux or sintering aid is used to substantially reduce the heat treatment temperature required to form a sintered neck between the pellets. Examples of fluxes or sintering aids include one or more metals with a lower melting point than iron, such as zinc, tin, copper, aluminum, bismuth, and lead, or metals that form iron alloys with a lower melting point than iron, such as those exhibiting a low-melting-point eutectic. Other examples of sintering aids include one or more glass-forming compositions, including but not limited to silicates, borates, and phosphates.

[0360] In another embodiment, the pellets may be electrically fused together by a process such as welding. In some such embodiments, welding is achieved by passing an electric current through the bed of pellets. In some such embodiments, such an electric current is delivered by discharging a capacitor.

[0361] In various embodiments, the anode electrode is a regular array of pellets. In certain embodiments, the pellets are arranged in a cylinder. In certain embodiments, the pellets are arranged in a plate. In certain embodiments, the pellets are arranged in a disk. In certain embodiments, the pellets are arranged in a rectangular prism. In certain embodiments, the pellets are arranged in a hexagonal prism. In certain embodiments, the pellets are arranged in an arbitrary volume.

[0362] In various embodiments, an electrolyte management system can be provided in which different electrolyte additives or formulations are added to the battery when switching operating states. The optimal electrolyte formulation for operation during charging, discharging, and idle states of the battery can vary considerably. Electrolyte management systems in various embodiments can improve the capacity utilization of iron electrodes, improve cell self-discharge, and suppress hydrogen evolution reactions (HER). One or more such benefits can be achieved simultaneously. In one embodiment of such an electrolyte management system, any number of separate electrolyte formulation reservoirs are provided, each connected to an electrochemical cell via a separate flow controller. During different stages of operation, different relative amounts of each electrolyte formulation are introduced into the cell based on the optimal concentrations of component species for the instantaneous operating mode (charging, discharging, idle). The electrolyte management system can be configured to adjust the electrolyte composition based on the instantaneous charge state of the battery.

[0363] Various embodiments can provide methods and apparatus for maintaining the liquid electrolyte level of a battery. A container containing water, when exposed to air, will experience evaporation until the partial pressure of water vapor in the air equals the vapor pressure of water at the system's temperature. Specifically, an electrochemical system in which an aqueous electrolyte is exposed to the environment will experience this same evaporation. Dehydration of the electrolyte can lead to problems resulting from a reduction in electrolyte volume, and changes in electrolyte concentration can alter electrochemical performance. To mitigate these problems, various embodiments can maintain the electrolyte level by continuously or intermittently supplying the electrolyte to the cell volume. Specifically, the electrolyte liquid level can be maintained by introducing the electrolyte into the container until it overflows from an overflow point. Since the liquid level cannot rise beyond this outflow point, this level can be maintained in a relatively controlled manner. Specifically, several volumes can be arranged in a cascade so that overflow from one chamber flows into the next chamber, establishing a "liquid communication" between cells. By connecting these cells in series, it becomes possible to supply liquid electrolyte to multiple cells simultaneously from a single source. The overflow from the last container can be recirculated to the first container. In systems using a shared electrolyte that flows in a cascade manner between cells, the properties of the electrolyte can be monitored and processed at a central location among the many cells. Electrolyte adjustments, such as compositional adjustments or addition of components to mitigate problems related to electrolyte carbonation and electrolyte dehydration, are beneficial to perform at such accumulation sources of circulating electrolytes.

[0364] Various embodiments can provide compositions and methods for adding beneficial additives to the electrolyte of an aqueous electrochemical cell. Electrolytic production of hydrogen during charging of an aqueous secondary battery can lead to Coulomb inefficiency, gas accumulation within the cell housing, safety concerns, and electrolyte consumption. Furthermore, metal electrode self-discharge can occur due to the spontaneous reaction of metals and electrolytes to form metal hydroxides, producing reactive hydrogen as a product. Certain solid-phase hydrogen generation inhibitors (e.g., Bi, Sb, As) can reduce these harmful effects, but incorporating solid-phase inhibitors into the porous metal electrodes of the battery can be costly and pose manufacturing challenges. Therefore, various embodiments provide compositions and methods for dissolving and adding ions of the desired additive (e.g., Bi 3+ Sb 3+ A...

Claims

1. It is a battery, A first electrode containing manganese oxide, Electrolytes, The second electrode contains iron, Equipped with, Herein, the first electrode and the second electrode are in contact with an electrolyte, and the iron of the second electrode is characterized by containing a packed bed of pellets having a multimodal size distribution.

2. The battery according to claim 1, characterized in that the iron includes directly reduced iron (DRI).

3. The battery according to claim 1, characterized in that the electrolyte is a liquid electrolyte.

4. The battery according to claim 3, characterized in that the electrolyte contains an alkali metal hydroxide comprising lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), cesium hydroxide (CsOH), or a mixture thereof.

5. The electrolyte is lithium sulfide (Li ２ S) or polysulfide (Li ２ Sx, x = 2 to 6), sodium sulfide (Na ２ S) or polysulfide (Na ２ Sx, x = 2 to 6), potassium sulfide (K ２ S) or polysulfide (K ２ Sx, x = 2 to 6), cesium sulfide (Cs ２ S) or polysulfide (Cs ２ The battery according to claim 4, characterized by containing an alkali metal sulfide or polysulfide comprising Sx (x = 2 to 6), or a mixture thereof.

6. The battery according to claim 1, characterized in that the second electrode is pelletized and has a multimodal distribution.

7. The manganese oxide is manganese(IV) oxide (MnO ２ ), manganese(III) oxide (Mn ２ O ３ ), manganese(III) oxyhydroxide (MnOOH), manganese(II) oxide (MnO), manganese(II) hydroxide (Mn(OH) ２ ), or a mixture thereof, and the battery according to claim 1 is characterized by this.

8. The battery according to claim 1, wherein the second electrode further comprises an iron oxide, hydroxide, sulfide, or a mixture thereof.

9. The battery according to claim 1, wherein 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-coated carbon steel mesh, nickel-coated stainless steel mesh, nickel-coated steel wool, or a mixture thereof.

10. The battery according to claim 1, wherein the second electrode further contains one or more hydrogen generation reaction inhibitors.

11. The specific surface area of ​​the first electrode is 50 m². ２ The battery according to claim 1, characterized in that it is less than / g.

12. The specific surface area of ​​the first electrode is 1 m² ２ The battery according to claim 1, characterized in that it is less than / g.

13. The specific surface area of ​​the second electrode is 5 m². ２ The battery according to claim 1, characterized in that it is less than / g.

14. The specific surface area of ​​the second electrode is 1 m². ２ The battery according to claim 1, characterized in that it is less than / g.

15. The battery according to claim 1, characterized in that the first electrode contains a binder comprising polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVdF), polypropylene (PP), polyethylene (PE), fluoroethylene propylene (FEP), polyacrylonitrile, styrene-butadiene rubber, carboxymethylcellulose (CMC), sodium carboxymethylcellulose (Na-CMC), polyvinyl alcohol (PVA), polypyrrole (PPy), or a combination thereof.

16. The first electrode is made of bismuth(III) oxide (Bi ２ O ３ ), bismuth(III) sulfide (Bi ２ S ３ ), barium oxide (BaO), barium sulfate (BaSO) ４ ), barium hydroxide (Ba(OH) ２ ), calcium oxide (CaO), calcium sulfate (CaSO4) ４ ), calcium hydroxide (Ca(OH) ２ ), magnesium oxide (MgO), magnesium hydroxide (Mg(OH) ２ The battery according to claim 1, characterized in that it has an additive material comprising carbon nanotubes, carbon nanofibers, graphene, nitrogen-doped carbon nanotubes, nitrogen-doped carbon nanofibers, nitrogen-doped graphene, or a combination thereof.

17. The battery according to claim 1, characterized in that a separator material is used between the first electrode and the second electrode.

18. The battery according to claim 1, characterized in that the iron includes a refined mineral.

19. The battery according to claim 1, characterized in that the iron comprises at least one form of iron selected from the group consisting of pellets, BF grade pellets, DR grade pellets, hematite, magnetite, wustite, maltite, goethite, limonite, siderite, pyrite, ilmenite, or spinel manganese ferrite.

20. The battery according to claim 1, characterized in that the iron includes iron ore.

21. The iron ore contains at least 0.1% by mass of SiO ２ The battery according to claim 20, characterized by including the following:

22. The battery according to claim 20, characterized in that the iron ore contains at least 0.1% by mass of CaO.

23. The battery according to claim 1, characterized in that the iron includes atomized iron powder.

24. The battery according to claim 1, characterized in that the iron includes iron ingots.

25. The battery according to claim 24, characterized in that the average length of the iron mass is in the range of 50 μm to 50 mm.

26. The battery according to claim 24, characterized in that the average internal porosity of the iron mass is in the range of 10 volume% to 90 volume%.

27. The average specific surface area of ​​the aforementioned iron mass is 0.1 m². ２ / g to 25m ２ The battery according to claim 24, characterized in that it is in the range of / g.

28. The battery according to claim 24, characterized in that the electrolyte comprises a molybdate anion and a sulfide anion.

29. A bulk energy storage system, A stack comprising one or more batteries, at least one of the one or more batteries is A first electrode containing manganese oxide, Electrolytes, The second electrode contains iron, Includes, Herein, the first electrode and the second electrode are in contact with an electrolyte, and the iron of the second electrode is characterized by containing a packed bed of pellets having a multimodal size distribution.

30. The bulk energy storage system according to claim 29, characterized in that the bulk energy storage system is a long-term energy storage (LODES) system.

31. The bulk energy storage system according to claim 30, characterized in that the iron includes directly reduced iron (DRI).

32. The bulk energy storage system according to claim 30, characterized in that the electrolyte is a liquid electrolyte.

33. The bulk energy storage system according to claim 32, characterized in that the electrolyte comprises an alkali metal hydroxide including lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), cesium hydroxide (CsOH), or a mixture thereof.

34. The electrolyte is lithium sulfide (Li ２ S) or polysulfide (Li ２ Sx, x = 2 to 6), sodium sulfide (Na ２ S) or polysulfide (Na ２ Sx, x = 2 to 6), potassium sulfide (K ２ S) or polysulfide (K ２ Sx, x = 2 to 6), cesium sulfide (Cs ２ S) or polysulfide (Cs ２ The bulk energy storage system according to claim 33, characterized by comprising an alkali metal sulfide or polysulfide containing Sx (x = 2 to 6), or a mixture thereof.

35. The bulk energy storage system according to claim 30, characterized in that the second electrode is pelletized and has a multimodal distribution.

36. The manganese oxide is manganese(IV) oxide (MnO ２ ), manganese(III) oxide (Mn ２ O ３ ), manganese(III) oxyhydroxide (MnOOH), manganese(II) oxide (MnO), manganese(II) hydroxide (Mn(OH) ２ The bulk energy storage system according to claim 30, characterized by comprising ), or a mixture thereof.

37. The second electrode further comprises an iron oxide, hydroxide, sulfide, or mixture thereof. A bulk energy storage system according to claim 30, characterized by the following:

38. The bulk energy storage system according to claim 30, wherein the second electrode further has an inert conductive matrix comprising carbon black, activated carbon, graphite powder, carbon steel mesh, stainless steel mesh, steel wool, nickel-coated carbon steel mesh, nickel-coated stainless steel mesh, nickel-coated steel wool, or a mixture thereof.

39. The bulk energy storage system according to claim 30, characterized in that the second electrode further contains one or more hydrogen generation reaction inhibitors.

40. The first electrode is made of bismuth(III) oxide (Bi ２ O ３ ), bismuth(III) sulfide (Bi ２ S ３ ), barium oxide (BaO), barium sulfate (BaSO) ４ ), barium hydroxide (Ba(OH) ２ ), calcium oxide (CaO), calcium sulfate (CaSO4) ４ ), calcium hydroxide (Ca(OH) ２ ), magnesium oxide (MgO), magnesium hydroxide (Mg(OH) ２ The bulk energy storage system according to claim 30, characterized in that it has additives including carbon nanotubes, carbon nanofibers, graphene, nitrogen-doped carbon nanotubes, nitrogen-doped carbon nanofibers, nitrogen-doped graphene, or a combination thereof.

41. The bulk energy storage system according to claim 30, characterized in that the iron includes iron ore.

42. The iron ore contains at least 0.1% by mass of SiO ２ A bulk energy storage system according to claim 41, characterized by including the following:

43. The bulk energy storage system according to claim 41, characterized in that the iron ore contains at least 0.1% by mass of CaO.

44. The bulk energy storage system according to claim 30, wherein the iron includes iron ingots.

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