SODIUM ION CYCLING BATTERY AND METHOD FOR MANUFACTURING SAME

Abstract

A negative electrode of a sodium ion cycling battery contains a silicon-based electroactive material comprising two-dimensional silicon layers with a hexagonal crystal structure. The silicon-based electroactive material is configured to sandwich sodium ions between the two-dimensional silicon layers during battery charging, forming an alloy of silicon and sodium. The silicon-based electroactive material is prepared by extracting alkali metal ions and / or alkaline earth metal ions from a silicide precursor comprising two-dimensional silicon layers with a hexagonal crystal structure spaced apart by planar monolayers of alkali metal ions and / or alkaline earth metal ions.The alkali metal ions and / or alkaline earth metal ions are extracted from the silicide precursor so that the hexagonal crystal structure of the two-dimensional silicon layers in the silicon-based electroactive material is preserved.

Description

INITIATIONThe information included in this subsection serves to generally illustrate the context of the disclosure.The present disclosure relates to negative electrodes for batteries that cycle sodium ions, and more particularly to silicon-based electroactive materials for negative electrodes and methods of making the same.Batteries that cycle sodium ions generally include a positive electrode, a negative electrode spaced from the positive electrode, and an ion conductive electrolyte that provides a medium for conducting sodium ions between the positive and negative electrodes during discharge and charging of the batteries. Silicon is a desirable material for negative electrodes because of its relatively high specific capacity compared to graphite.KR 10 2021 0 128 516 A discloses a two-dimensional structure for storing sodium ions comprising a siloxane compound.SUMMARYThe present invention relates to a battery that cycles sodium ions according to claim 1 and a method for manufacturing a negative electrode for a battery according to claim 3.A battery that cycles sodium ions according to one or more embodiments of the present disclosure includes a negative electrode comprising a silicon-based electroactive material, a positive electrode spaced apart from the negative electrode, and an electrolyte providing a medium for conducting sodium ions between the negative electrode and the positive electrode. The silicon-based electroactive material comprises two-dimensional silicon layers having a hexagonal crystal structure, wherein the two-dimensional silicon layers are terminated with alkoxy groups and have the formula Si 6 H 3( OCH 3)3 or Si 6 H 3( OC 2 H 5)3 and is configured to insert sodium ions between the two-dimensional silicon layers and form an alloy of silicon and sodium during charging of the battery. The positive electrode comprises an electroactive positive electrode material.The negative electrode may further comprise a polymer binder and optionally an electrically conductive material. The negative electrode may have a thickness of greater than or equal to about 30 micrometers and less than or equal to about 500 micrometers.The silicon-based electroactive material may have a specific capacity greater than or equal to about 950 milliampere hours per gram.The negative electrode may be disposed on a main surface of a metal current collector.The silicon-based electroactive material may be substantially free of crystalline silicon having a diamond-like, orthorhombic, or cubic crystal structure.A method of manufacturing a negative electrode for a battery that cycles sodium ions is disclosed. The method includes extracting alkali metal ions or alkaline earth metal ions from a silicide precursor to form a silicon-based electroactive material, and depositing a continuous layer comprising the silicon-based electroactive material on a metal substrate to form the negative electrode. The silicide precursor comprises two-dimensional silicon layers having a hexagonal crystal structure separated from each other by planar monolayers of alkali metal ions or alkaline earth metal ions. The alkali metal ions or alkaline earth metal ions are extracted from the silicide precursor so that the hexagonal crystal structure of the two-dimensional silicon layers is maintained in the silicon-based electroactive material, wherein a nonaqueous HCl solution with alcohol as a solvent is applied to the silicide precursor to form two-dimensional silicon layers terminated with alkoxy groups and having the formula Si 6 H 3( OCH 3)3 or Si 6 H 3( OC 2 H 5)3.The alkali metal ions or alkaline earth metal ions may be extracted from the silicide precursor at ambient temperature or at a temperature of about 0 degrees Celsius or below.The silicide precursor may include calcium disilicide (CaSi 2). In this case, the alkali metal ions or alkaline earth metal ions extracted from the silicide precursor may contain calcium (Ca +) - ions.The silicon-based electroactive material may include two-dimensional silicon layers having a hexagonal crystal structure. The two-dimensional silicon layers may be terminated with hydrogen ions, hydroxyl ions, or a combination thereof.The method may further include preparing a slurry containing the silicon-based electroactive material in a solvent, depositing the slurry on the metal substrate to form a precursor layer, and removing the solvent from the precursor layer to form the negative electrode.The slurry may further comprise a polymer binder and optionally an electrically conductive material.The method may further include incorporating the negative electrode into a battery comprising a positive electrode and an electrolyte providing a medium for conducting sodium ions between the negative electrode and the positive electrode, wherein the positive electrode contains sodium ions.The method may further comprise electrically coupling the negative electrode and the positive electrode to a power source such that sodium ions are released from the positive electrode and electrochemically intercalated between the two-dimensional silicon layers of the silicon-based electroactive material of the negative electrode.A method of manufacturing a negative electrode for a battery that cycles sodium ions is disclosed. The method includes extracting calcium (Ca +) - ions from a calcium silicide precursor to form a silicon-based electroactive material, and depositing a continuous layer comprising the silicon-based electroactive material on a metal substrate to form the negative electrode. The calcium silicide precursor comprises two-dimensional silicon layers having a hexagonal crystal structure separated by planar monolayers of calcium ions. The calcium ions are extracted from the calcium silicide precursor, so that the hexagonal crystal structure of the two-dimensional silicon layers is maintained in the silicon-based electroactive material.The calcium ions may be extracted from the calcium silicide precursor by applying an acidic solution to the calcium silicide precursor or heating the calcium silicide precursor to a temperature of 1420 degrees Celsius or above to release calcium gas therefrom.The method may further comprise preparing a slurry containing the silicon-based electroactive material, a polymer binder, and optionally an electrically conductive material in a solvent, depositing the slurry on the metal substrate to form a precursor layer, and removing the solvent from the precursor layer to form the negative electrode.The method may further include incorporating the negative electrode into a battery comprising a positive electrode and an electrolyte providing a medium for conducting sodium ions between the negative electrode and the positive electrode, wherein the positive electrode contains sodium ions.The method may further comprise electrically coupling the negative electrode and the positive electrode to a power source such that sodium ions are released from the positive electrode and are intercalated between the two-dimensional silicon layers of the silicon-based electroactive material of the negative electrode.Further areas of applicability of the present disclosure will become apparent from the detailed description, claims and drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.BRIEF DESCRIPTION OF THE DRAWINGSThe present disclosure will become more fully understood from the detailed description and the accompanying drawings, in which: FIG. 1 is a schematic perspective view of an automobile powered by a battery pack having multiple battery modules. FIG. 2 is a schematic cross-sectional view of a portion of one of the battery modules of FIG. 1, wherein the battery module includes multiple electrochemical cells or batteries that cycle sodium ions. FIG. 3 is a schematic cross-sectional view of a battery that cycles sodium ions, the battery including a positive electrode, a negative electrode, a porous separator, and an electrolyte infiltrating the positive and negative electrodes and the porous separator.In the drawings, reference numerals may be used repeatedly to identify similar and / or identical elements.DETAILED DESCRIPTIONThe silicon-based electroactive materials presented herein may be used in negative electrodes of batteries that cycle sodium ions to impart a relatively high specific capacity to the negative electrodes compared to that of hard carbon (e.g., graphite). The silicon-based electroactive materials presented herein are comprised of stacks of spaced apart silicon layers. The arrangement of the silicon layers in the silicon-based electroactive materials allows sodium ions to become sandwiched between the silicon layers during charging of the batteries and again to alloy with the silicon in the layers and form a Si-Na alloy throughout the bulk of the silicon-based electroactive material.FIG. 1 illustrates a motor vehicle 2 powered by an electric motor 4 that draws current from a battery pack 6 having one or more battery modules 8. The battery modules 8 may be electrically connected in series and / or in parallel to meet the desired capacity and power requirements of the electric motor 4. The vehicle 2 may be a pure electric vehicle and may be propelled solely by the electric motor 4, or the vehicle 2 may be a hybrid electric vehicle and may be propelled by the electric motor 4 and an internal combustion engine (not shown).As shown in FIG. 2, each battery module 8 includes one or more electrochemical cells or batteries 10 that cycle sodium ions. In practice, the batteries 10 in the battery module 8 are often assembled as a stack of layers including negative electrode layers 12, negative electrode current collectors 13, positive electrode layers 14, positive electrode current collectors 15, and separator layers 16. In practice, the separator layer 16 may be infiltrated with an electrolyte that provides a medium for conducting sodium ions between the negative electrode layer 12 and the positive electrode layer 14, or the separator layer 16 itself may function as an electrolyte. The negative electrode layers 12 are disposed on and in electrical communication with the negative electrode current collectors 13, and the positive electrode layers 14 are disposed on and in electrical communication with the positive electrode current collectors 15. As shown in FIG. 2, for efficiency, the layers may be stacked such that some of the negative electrode current collectors 13 and some of the positive electrode current collectors 15 are double-sided and have negative electrode layers 12 or positive electrode layers 14 on both sides, respectively. In this arrangement, adjacent negative electrode layers 12 and positive electrode layers 14 share a single negative electrode current collector 13 or a positive electrode current collector 15, respectively.FIG. 3 illustrates an electrochemical cell or battery 20 in which sodium ions are cyclized. The battery 20 may generate an electric current during discharge that may be used to supply power to a load device (e.g., an electric motor 4), and may be charged by connecting to a power source. Like the batteries 10 illustrated in FIGS. 1 and 2, in some cases, the battery 20 may be used to supply power to an electric motor 4 of a motor vehicle 2. Additionally or alternatively, the battery 20 may also be used in other transportation applications (e.g., motorcycle, boat, tractor, bus, motorcycle, recreational vehicle, recreational vehicle, tank and plane) and used to power stationary and / or portable electronic devices, components and devices used in a variety of other industries and applications, such as industrial, residential and commercial buildings, consumer goods, industrial plants and machines, agricultural and agricultural equipment, as well as heavy machines, without being limited to these examples.The battery 20 includes a negative electrode 22, a positive electrode 24, a separator 26, and an electrolyte 28 that provides a medium for conducting sodium ions between the negative electrode 22 and the positive electrode 24. The negative electrode 22 is disposed on a main surface of a negative electrode current collector 30, and the positive electrode 24 is disposed on a main surface of a positive electrode current collector 32. In practice, the negative electrode current collector 30 and the positive electrode current collector 32 are electrically connected to a power source or load 34 (e.g., the electric motor 4) via an external circuit 36. The negative electrode 22 and the positive electrode 24 are configured such that an electrochemical potential difference is established between the negative electrode 22 and the positive electrode 24 when the battery 20 is at least partially charged. During discharge of the battery 20, the electrochemical potential developed between the negative electrode 22 and the positive electrode 24 results in spontaneous reduction and oxidation reactions (redox reactions) within the battery 20 and release of sodium ions and electrons at the negative electrode 22, and the released sodium ions migrate from the negative electrode 22 to the positive electrode 24 through the separator 26 and the electrolyte 28, while the electrons migrate from the negative electrode 22 to the positive electrode 24 via the external electric circuit 36 that generates an electric current. After the sodium of the negative electrode 22 is partially or fully depleted, the battery 20 may be charged by connecting the negative electrode 22 and the positive electrode 24 to the power source 34, causing non-spontaneous redox reactions within the battery 20 and the release of the sodium ions and electrons from the positive electrode 24. Repeated discharging and charging of the battery 20 may be referred to herein as "cycling," where a full charge followed by a full discharge is considered a full cycle.The negative electrode 22 is configured to store and release sodium ions to facilitate charging and discharging of the battery 20. The negative electrode 22 may have the shape of a continuous material layer disposed on a main surface of the negative electrode current collector 30. The negative electrode 22 may have a thickness of greater than or equal to about 30 micrometers (μm), optionally greater than or equal to about 50 μm, optionally greater than or equal to about 70 μm, or optionally greater than or equal to about 100 μm and less than or equal to about 500 μm.The negative electrode 22 comprises an electrochemically active (electroactive) material capable of storing and releasing sodium ions by undergoing a reversible redox reaction with sodium upon charging and discharging of the battery 20. In some cases, the negative electrode 22 may include a polymer binder and optionally an electrically conductive material. In this case, the electroactive material of the negative electrode 22 may be a particulate material, and the particles of electroactive material may be blended with the polymer binder and the optional electrically conductive material. The electroactive material may constitute, by weight, greater than or equal to about 50%, optionally greater than or equal to about 60%, or optionally greater than or equal to about 70%, and less than or equal to about 95%, optionally less than or equal to about 90%, or optionally less than or equal to about 80%, of the negative electrode 22.The negative electrode electroactive material 22 comprises a silicon-based electroactive material. The silicon-based electroactive material may constitute, by weight, greater than or equal to about 5%, optionally greater than or equal to about 10%, optionally greater than or equal to about 20%, or optionally greater than or equal to about 50%, and less than or equal to about 90%, optionally less than or equal to about 80%, or optionally less than or equal to about 70%, of the negative electrode electroactive material 22.The silicon-based electroactive material includes stacks of polyanionic two-dimensional silicon layers having a hexagonal crystal structure. The silicon layers may be referred to as silicons that is a two-dimensional allotrope of the silicon having a curved or undulated hexagonal crystal structure (space group P63mc, 186). The silicon-based electroactive material is configured to insert and release sodium ions between the two-dimensional silicon layers during charging of the battery 20, and deintercalate sodium ions during discharging of the battery 20. More specifically, the two-dimensional silicon layers are spaced apart a sufficient distance to allow sodium ions to be deposited or inserted therebetween during charging of the battery 20. When the battery 20 is at least partially charged, the silicon layers are spaced apart from each other by sodium ions (Na +) disposed therebetween. Once the sodium ions have been inserted between the two-dimensional silicon layers and are in close contact with the silicon ions defining the silicon layers, the sodium ions may alloy with the silicon ions, e.g., by forming covalent bonds with them, and form a silicon-sodium alloy (Si-Na). Thus, the silicon-based electroactive material may have a specific capacity greater than or equal to about 950 milliampere hours per gram (mAh / g). In some aspects, the silicon-based electroactive material may have a specific capacity of about 954 mAh / g, the maximum theoretical sodium storage capacity of silicon.The silicon-based electroactive material of the negative electrode 22 may be substantially free of crystalline silicon having a diamond-like, orthorhombic, or cubic crystal structure. Specifically, the silicon-based electroactive material may be substantially free from the following silicon allotropes: DC-Si having a diamond crystal structure (space group Fd-3m, 227); Si 24 having an orthorhombic crystal structure (space group Cmcm, 63); Si 46 having a cubic crystal structure (space group Pm-3n, 223); Si 136 having a cubic crystal structure (space group Fd-3m, 227). In embodiments, the silicon-based electroactive material of the negative electrode 22 may be substantially free of amorphous silicon.The silicon-based electroactive material includes two-dimensional silicon layers having a hexagonal crystal structure. However, when other crystalline forms of silicon (e.g., DC-Si, Si 24, Si 46 or Si 136) are used as the electroactive material in a negative electrode 22 of a battery that cycles sodium ions, the high activation energy that requires sodium ions to diffuse into the crystalline silicon prevents the sodium ions from alloying with the crystalline silicon and prevents the silicon from achieving its theoretical sodium storage capacity of 954 mAh / g by forming a Si-Na alloy. In other words, the lamination of the two-dimensional silicon layers in the silicon-based electroactive material enables the interposition of sodium ions therebetween, and thus the formation of a Si-Na alloy during the charging of the battery 20.The polymeric binder is electrochemically inactive and may be included in the negative electrode 22 to provide structural integrity to the negative electrode 22 and / or to assist the negative electrode 22 in adhering to the major surface of the negative electrode current collector 30. Examples of polymeric binders are polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), ethylene propylene diene monomer (EPDM) rubber, styrene butadiene rubber (SBR), carboxymethylcellulose (CMC), nitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), styrene ethylene butylene styrene copolymer (SEBS), polyacrylates, alginates, polyacrylic acid, and combinations thereof. The polymer binder may constitute greater than or equal to about 1%, or optionally greater than or equal to about 5%, and less than or equal to about 10% of the negative electrode 22 by weight.The optional electrically conductive material is electrochemically inactive and may be included in the negative electrode 22 to provide sufficient electrical conductivity to the negative electrode 22 to aid in the percolation of electrons therethrough. Examples of electrically conductive materials include carbon-based materials, metals (e.g., nickel), and / or electrically conductive polymers. Examples of carbon-based electrically conductive materials are carbon black (CB) (e.g., acetylene black), graphite, graphene (e.g., graphene nanoplatelets, GNP), graphene oxide, carbon nanotubes (CNT), and / or carbon fibers (e.g., carbon nanofibers). Examples of electrically conductive polymers include polyaniline, polythiophene, polyacetylene and / or polypyrrole. When included in the negative electrode 22, the optional electrically conductive material may constitute greater than 0%, optionally greater than or equal to about 1%, or optionally greater than or equal to about 5%, and less than or equal to about 10% of the negative electrode 22.The positive electrode 24 is configured to store and release sodium ions when the battery 20 is discharged and charged. The positive electrode 24 may have the shape of a continuous porous layer disposed on the main surface of the positive electrode current collector 32. The positive electrode 24 is comprised of an electroactive positive electrode material, a polymeric binder, and optionally an electrically conductive material. In some cases, the positive electrode electroactive material 24 may be a particulate material, and positive electrode electroactive material particles 24 may be mixed with the polymer binder and the optional electrically conductive material.The positive electrode electroactive material 24 may store and release sodium ions by performing a reversible redox reaction with sodium at a higher electrochemical potential than the negative electrode electroactive material 22 such that there is an electrochemical potential difference between the negative electrode 22 and the positive electrode 24. The positive electrode electroactive material 24 may include a material capable of depositing and de-depositing sodium or a material capable of performing a conversion reaction with sodium. In cases where the positive electrode electroactive material 24 comprises an intercalation host material that allows for the reversible insertion or intercalation of sodium ions, the positive electrode electroactive material 24 may comprise a sodium transition metal oxide.The same polymeric binders and / or electrically conductive materials described above with respect to the negative electrode 22 may be included in the positive electrode 24 in substantially equal amounts for substantially the same reasons.The separator 26 physically separates and electrically isolates the negative electrode 22 and the positive electrode 24 while allowing sodium ions to pass therethrough. The separator 26 has an open microporous structure and may comprise an organic and / or inorganic material. The separator 26 may comprise, for example, a polymer or a combination of polymers. The separator 26 may include, for example, one or more polyolefins, e.g., polyethylene (PE), polypropylene (PP), polyamide (PA), poly(tetrafluoroethylene) (PTFE), polyvinylidene fluoride (PVDF), and / or poly(vinyl chloride) (PVC). In one form, the separator 26 may comprise a polymeric laminate, e.g., a laminate of PE and PP.The electrolyte 28 is ionically conductive and provides a medium for conducting sodium ions between the negative electrode 22 and the positive electrode 24. The electrolyte 28 is composed of an organic solvent and a sodium salt in the organic solvent. The organic solvent may comprise a non-aqueous aprotic organic solvent. The sodium salt is soluble in the organic solvent and allows sodium ions to pass through the electrolyte 28.The negative electrode current collector 30 and the positive electrode current collector 32 are electrically conductive and provide an electrical connection between the external circuit 36 and the negative electrode 22 and the positive electrode 24, respectively. In some cases, the negative electrode current collector 30 and the positive electrode current collector 32 may be made of metal and may be in the form of nonporous metal foils, perforated metal foils, porous metal fabrics, or a combination thereof. The negative electrode current collector 30 may be made of copper, nickel or their alloys, stainless steel, or other suitable electrically conductive material. The positive electrode current collector 32 may be made of aluminum (Al) or another suitable electrically conductive material.MethodThe silicon-based electroactive material of the negative electrode 22 may be made of a silicide precursor. The silicide precursor may comprise an alkali metal silicide, an alkaline earth metal silicide, or a combination thereof. The silicide precursor may include, for example, a binary compound of silicon and an alkali metal (e.g., Li, Na, K, Rb, Cs, and / or Fr), an alkaline earth metal (e.g., Be, Mg, Ca, Sr, Ba, and / or Ra), or a combination thereof. In embodiments, the alkali metal and / or the alkaline earth metal in the silicide precursor may have an ionic radius greater than or equal to that of sodium. In embodiments, the silicide precursor may comprise calcium silicide (CaSi 2). Like the silicon-based electroactive material of the negative electrode 22, the silicide precursor also consists of stacks of polyanionic two-dimensional silicon layers having a hexagonal crystal structure. In the silicide precursor, the two-dimensional silicon layers are spaced apart from each other by planar monolayers of alkali metal ions or alkaline earth metal ions, or a combination thereof. In embodiments where the silicide precursors comprise calcium silicide, the two-dimensional silicon layers are spaced apart from each other by planar monolayers of calcium ions, and the calcium ions are extracted from the calcium silicide precursor to form the silicon-based electroactive material of the negative electrode 22.The alkali metal ions and / or the alkaline earth metal ions are extracted from the silicide precursor to form the silicon-based electroactive material. The alkali metal ions and / or alkaline earth metal ions may be extracted from the silicide precursor using a chemical etching technique and / or by applying a thermal treatment to the silicide precursor.In embodiments where a chemical etching process is used to extract the alkali metal ions and / or the alkaline earth metal ions from the silicide precursor, an acidic solution may be applied to the silicide precursor such that the alkali metal ions and / or the alkaline earth metal ions dissolve in the acidic solution and are deintercalated from the silicide precursor without altering the hexagonal crystal structure of the two-dimensional silicon layers (topochemical deintercalation). The acidic solution includes a nonaqueous solution with alcohol as a solvent (e.g., methanol, ethanol, etc.). The acid solution may be a concentrated solution of an acid or a saturated solution of an acid. In embodiments, the acid solution may be applied to the silicide precursor at ambient temperature, e.g., at a temperature of about 25 degrees Celsius (° C.). Alternatively, the acidic solution may be applied to the silicide precursor at a temperature of less than or equal to about 0°C, or optionally less than or equal to about -30°C. After the liquid phase acid solution is applied to the silicide precursor for a sufficient time to extract the alkali metal ions and / or the alkaline earth metal ions therefrom and form the solid phase silicon-based electroactive material, the silicon-based electroactive material may be separated from the liquid phase by filtration and washed to remove residual reaction byproducts therefrom.The acid solution applied to the silicide precursor comprises hydrochloric acid (HCl). A nonaqueous HCl solution with alcohol as solvent is applied to the silicide precursor to form two-dimensional silicon layers terminated with alkoxy groups and having the formula Si 6 H 3( OCH 3)3 or Si 6 H 3( OC 2 H 5)3 (alkoxysilane).The silicon-based electroactive material may be assembled into a negative electrode, such as negative electrode 22, by depositing the silicon-based electroactive material onto a metal substrate. In embodiments, the metal substrate may be made of substantially the same materials and have substantially the same shape as the negative electrode current collector 30. The silicon-based electroactive material may be deposited on the metal substrate by preparing a slurry comprising particles of the silicon-based electroactive material in a solvent. Like the negative electrode 22, the slurry may also contain a polymer binder and optionally an electrically conductive material. The slurry may be deposited on the metal substrate to form a precursor layer, and then the solvent may be removed from the precursor layer to form the negative electrode 22.Thereafter, the negative electrode 22 may be incorporated into a battery such as the battery 20. During charging of the battery 20, the negative electrode 22 and the positive electrode 24 are electrically coupled to the power source 34 such that sodium ions are released from the positive electrode 24 and are electrochemically intercalated between the two-dimensional silicon layers of the silicon-based electroactive material of the negative electrode 22.The foregoing description is for illustrative purposes only and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure may be practiced in a variety of forms. Therefore, while this disclosure includes specific examples, the true scope of the disclosure should not be so limited as other modifications will become apparent upon examination of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be performed in different orders (or concurrently) without altering the principles of the present disclosure. Although each of the above-described embodiments has particular features, one or more of these features described with respect to any embodiment of the disclosure may be implemented in and / or combined with features of any other embodiments, even if this combination is not expressly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure.Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described with various terms including "connected," "engaged," "coupled," "vbenabart," "next to," "top on," "over," "under," and "arranged.". Where a relationship between first and second elements is not expressly described as "direct" in the above disclosure, this relationship may be a direct relationship in which no other intervening elements are present between the first and second elements, but also an indirect relationship in which one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the term "A, B, and / or C" should be construed using a non-exclusive logical "OR" as being logical (A ORed with B ORed with C), and not as "at least one of A, at least one of B, and at least one of C.". As used herein, the term "and / or" includes combinations of one or more of the associated listed items.The terminology used herein is for the purpose of describing example embodiments only and is not to be taken as limiting. As used herein, the singular forms "a," "an," and "the" may also include the plural forms unless the context clearly indicates otherwise. The terms "comprises," "comprising," "including," and "having" are inclusive and therefore specify the presence of stated features, elements, compositions, steps, integers, operations, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Although the open terms "comprises," "comprising," "including," and "having" are to be understood as non-limiting terms that serve to describe and claim various embodiments set forth herein, in certain cases, the terms may alternatively be understood as more limiting and restrictive terms, such as "consisting of" or "consisting essentially of.". Therefore, for any given embodiment that specifies compositions, materials, components, elements, ingredients, features, integers, operations, and / or process steps, the present disclosure expressly also includes embodiments that consist of or consist essentially of such specified compositions, materials, components, elements, ingredients, features, integers, operations, and / or process steps. In the case of "consisting of", the alternative embodiment excludes any additional compositions, materials, components, elements, ingredients, features, integers, operations, and / or process steps, while in the case of "consisting essentially of", any additional compositions, materials, components, elements, ingredients, features, integers, operations, and / or process steps that significantly impact the basic and novel characteristics are excluded from such an embodiment, but any compositions, materials, components, elements, ingredients, features, integers, operations, and / or process steps that do not significantly impact the basic and novel characteristics may be included in the embodiment.All method steps, processes, and operations described herein are not to be construed as necessarily requiring execution in the order discussed or illustrated, unless expressly characterized as the order of execution. It will also be appreciated that additional or alternative steps may be employed, unless otherwise indicated. Although the terms "first," "second," "third," etc. may be used herein to describe various steps, elements, components, regions, layers, and / or sections, these steps, elements, components, regions, layers, and / or sections should not be limited by these terms unless otherwise specified. These terms may be used only to distinguish one step, element, component, region, layer, or portion from another step, element, component, region, layer, or portion. Terms such as "first / r", "second / r", and other numerical terms, when used herein, do not imply a sequence or order unless the context clearly indicates. Thus, a first step, element, component, region, layer, or portion discussed below could be referred to as a second step, element, component, region, layer, or portion without departing from the teachings of the embodiments.Throughout this disclosure, the numerical values represent approximate dimensions or limits for ranges and include minor deviations from the stated values and embodiments, such as those having the stated value, as well as those having exactly the stated value. Unlike the working examples at the end of the detailed description, all numerical values of parameters (e.g., amounts or conditions) in this specification are to be understood as being modified by the term "about" in all cases, regardless of whether or not "about" actually appears before the numerical value. Numerical values of parameters in the appended claims are to be understood as modified by the term "about" only if this term appears before the numerical value. "about" means that the numerical value indicated permits slight imprecision (with some approximation to the accuracy of the value, approximately or rather close to the value, fast). Where the imprecision given by "about" is not otherwise understood by this common meaning in the art, then "about" as used herein means at least modifications that may result from common methods of measuring and using such parameters. For example, "about" may comprise a deviation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%. Moreover, the disclosure of ranges includes the disclosure of all values and further divided ranges within the entire range, including the endpoints and the sub-ranges indicated for the ranges.As used herein, the terms "composition" and "material" are used interchangeably to refer generally to a substance that contains at least the preferred chemical components, elements or compounds, but which may also contain additional elements, compounds or substances, including traces of impurities, unless otherwise specified. An "X-based" composition or material generally refers to compositions or materials wherein "X" is the largest single component of the composition or material in weight percent (%). This may include both compositions or materials having a weight fraction of greater than 50% X and compositions or materials having a weight fraction of less than 50% X, as long as X is the largest single component of the composition or material based on its total weight. When a composition or material is referred to as being "substantially free" of a substance, the composition or material may contain less than 5%, optionally less than 3%, optionally less than 1%, or optionally less than 0.1% of the substance.As used herein, the term "metal" may refer to a pure elemental metal or an alloy of an elemental metal and one or more other metal or non-metal elements (referred to as "alloying elements"). The alloying elements can be selected to impart certain desirable properties to the alloy that the parent metal element does not have.

Claims

A battery that cycles sodium ions, the battery comprising: a negative electrode comprising a silicon-based electroactive material comprising two-dimensional silicon layers having a hexagonal crystal structure, the two-dimensional silicon layers terminated with alkoxy groups and having the formula Si 6 H 3( OCH 3)3 or Si 6 H 3( OC 2 H 5)3 wherein the silicon-based electroactive material sandwiches sodium ions between the two-dimensional silicon layers during charging of the battery and forms an alloy of silicon and sodium, wherein the silicon-based electroactive material comprises less than 5% of crystalline silicon with a diamond-shaped silicon, orthorhombic or cubic crystal structure; a positive electrode spaced from the negative electrode and comprising an electroactive material for the positive electrode; and an electrolyte providing a medium for conducting sodium ions between the negative electrode and the positive electrode.The battery of claim 1, wherein the negative electrode further comprises a polymer binder and optionally an electrically conductive material, wherein the negative electrode has a thickness of greater than or equal to 30 micrometers and less than or equal to 500 micrometers, and wherein the negative electrode is disposed on a major surface of a metal current collector.A method of manufacturing a negative electrode for a battery that cycles sodium ions, the method comprising: extracting calcium (Ca +) - ions from a calcium silicide precursor to form a silicon-based electroactive material, wherein the calcium silicide precursor comprises two-dimensional silicon layers having a hexagonal crystal structure and spaced apart from each other by planar monolayers of calcium ions, wherein the calcium ions are extracted from the calcium silicide precursor by applying a hydrochloric acid (HCl) solution such that the hexagonal crystal structure of the two-dimensional silicon layers is maintained in the silicon-based electroactive material, wherein a non-aqueous HCl solution is applied to the silicide precursor with alcohol as a solvent to form the two-dimensional silicon layers, wherein the two-dimensional silicon layers are terminated with alkoxy groups and have the formula Si 6 H 3( OCH 3)3 or Si 6 H 3( OC 2 H 5)3 ; and depositing a continuous layer comprising the silicon-based electroactive material on a metal substrate to form the negative electrode.The method of claim 3, wherein the calcium ions are extracted from the silicide precursor at ambient temperature or at a temperature of 0 degrees Celsius or below.The method of claim 3, further comprising: preparing a slurry containing the silicon-based electroactive material, a polymer binder, and optionally an electrically conductive material in a solvent; depositing the slurry on the metal substrate to form a precursor layer; and removing the solvent from the precursor layer to form the negative electrode.The method of claim 3, wherein the silicon-based electroactive material contains less than 5% of crystalline silicon having a diamond-shaped, orthorhombic, or cubic crystal structure.

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