Silicon-based electroactive material for sodium-ion battery pack and preparation method of silicon-based electroactive material

Abstract

A negative electrode of a battery circulating sodium ions includes a silicon-based electroactive material including a two-dimensional silicon layer having a hexagonal crystal structure. The silicon-based electroactive material is configured to embed sodium ions between the two-dimensional silicon layers and form an alloy of silicon and sodium during charging of the battery pack. 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 having a hexagonal crystal structure and spaced apart from each other by a planar monolayer of alkali metal ions and / or alkaline earth metal ions. Alkali metal ions and / or alkaline earth metal ions are extracted from the silicide precursor such that the hexagonal crystal structure of the two-dimensional silicon layer remains in the silicon-based electroactive material.

Description

Technical Field

[0001] The present disclosure relates to negative electrodes for cycling sodium ion batteries, and more particularly to silicon-based electroactive materials for negative electrodes and methods of making the same. Background Art

[0002] The information provided in this section is intended to generally introduce the background of the present disclosure. To the extent that the operations currently named as inventors are described in this section, and aspects of the specification that may not have been otherwise identified as prior art at the time of filing, are not admitted, either explicitly or implicitly, as prior art against the present disclosure.

[0003] The present disclosure relates to negative electrodes for cycling sodium ion batteries, and more particularly to silicon-based electroactive materials for negative electrodes and methods of making the same.

[0004] A sodium ion cycling battery generally includes a positive electrode, a negative electrode spaced apart from the positive electrode, and an ion-conducting electrolyte that provides a medium for the conduction of sodium ions between the positive electrode and the negative electrode during the discharge and charge process of the battery. Silicon is an ideal negative electrode material due to its relatively high specific capacity compared to graphite. Summary of the invention

[0005] According to one or more embodiments of the present disclosure, a sodium ion circulating battery includes a negative electrode including a silicon-based electroactive material, a positive electrode spaced apart from the negative electrode, and an electrolyte providing a medium for the conduction of sodium ions between the negative electrode and the positive electrode. The silicon-based electroactive material includes a two-dimensional silicon layer having a hexagonal crystal structure, and the two-dimensional silicon layer is configured to intercalate sodium ions between the two-dimensional silicon layers and form an alloy of silicon and sodium during the charging process of the battery. The positive electrode includes an electroactive positive electrode material.

[0006] The negative electrode may further include a polymer binder and optionally a conductive material.The negative electrode may have a thickness greater than or equal to about 30 microns and less than or equal to about 500 microns.

[0007] The silicon-based electroactive material may have a specific capacity of greater than or equal to about 950 mAh / g.

[0008] The negative electrode may be disposed on a major surface of the metal current collector.

[0009] The silicon-based electroactive material may be substantially free of crystalline silicon having a diamond, orthorhombic or cubic crystal structure.

[0010] A method for preparing a negative electrode for a battery pack for cycling 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 containing the silicon-based electroactive material on a metal substrate to form a negative electrode. The silicide precursor includes two-dimensional silicon layers having a hexagonal crystal structure and separated from each other by a planar monolayer 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 layer is retained in the silicon-based electroactive material.

[0011] The alkali metal ions or alkaline earth metal ions may be extracted from the silicide precursor by applying an acid solution to the silicide precursor.

[0012] The acid solution may include a hydrochloric acid (HCl) solution.

[0013] The alkali metal ions or alkaline earth metal ions may be extracted from the silicide precursor at ambient temperature or at a temperature less than or equal to about 0 degrees Celsius.

[0014] The silicide precursor may include calcium disilicide (CaSi2). In this case, the alkali metal ions or alkaline earth metal ions extracted from the silicide precursor may include calcium (Ca + )ion.

[0015] The silicon-based electroactive material may include a two-dimensional silicon layer having a hexagonal crystal structure. The two-dimensional silicon layer may be terminated by hydrogen ions, hydroxyl ions, or a combination thereof.

[0016] The method may also include preparing a slurry comprising a silicon-based electroactive material in a solvent, depositing the slurry on a metal substrate to form a precursor layer, and removing the solvent from the precursor layer to form a negative electrode.

[0017] The slurry may also include a polymer binder and optionally a conductive material.

[0018] The method may also include assembling the negative electrode into a battery including a positive electrode and an electrolyte providing a medium for conduction of sodium ions between the negative electrode and the positive electrode, the positive electrode containing sodium ions.

[0019] The method may further include 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.

[0020] A method for preparing a negative electrode for a battery pack for cycling sodium ions is disclosed. The method comprises extracting calcium (Ca) from a calcium silicide precursor +) ions to form a silicon-based electroactive material, and depositing a continuous layer comprising the silicon-based electroactive material on a metal substrate to form a negative electrode. The calcium silicide precursor includes two-dimensional silicon layers having a hexagonal crystal structure and separated from each other by a planar monolayer of calcium ions. The calcium ions are extracted from the calcium silicide precursor so that the hexagonal crystal structure of the two-dimensional silicon layer is retained in the silicon-based electroactive material.

[0021] Calcium ions may be extracted from the calcium silicide precursor by applying an acid solution to the calcium silicide precursor, or by heating the calcium silicide precursor at a temperature greater than or equal to about 1420 degrees Celsius to release calcium gas therefrom.

[0022] The method may further include preparing a slurry comprising a silicon-based electroactive material, a polymer binder, and an optional conductive material in a solvent, depositing the slurry on a metal substrate to form a precursor layer, and removing the solvent from the precursor layer to form a negative electrode.

[0023] The method may also include assembling the negative electrode into a battery including a positive electrode and an electrolyte providing a medium for conduction of sodium ions between the negative electrode and the positive electrode, the positive electrode containing sodium ions.

[0024] The method may further include electrically coupling the negative electrode and the positive electrode to a power source such that sodium ions are released from the positive electrode and intercalated between the two-dimensional silicon layers of the silicon-based electroactive material of the negative electrode.

[0025] The present invention discloses the following scheme:

[0026] Solution 1. A circulating sodium ion battery pack, the battery pack comprising:

[0027] a negative electrode comprising a silicon-based electroactive material including a two-dimensional silicon layer having a hexagonal crystal structure, the silicon-based electroactive material being configured to intercalate sodium ions between the two-dimensional silicon layers and form an alloy of silicon and sodium during charging of the battery;

[0028] a positive electrode spaced apart from the negative electrode and comprising an electroactive positive electrode material; and

[0029] An electrolyte provides a medium for the conduction of sodium ions between the negative electrode and the positive electrode.

[0030] Option 2. A battery according to Option 1, wherein the negative electrode further comprises a polymer binder and an optional conductive material, and wherein the negative electrode has a thickness greater than or equal to about 30 microns and less than or equal to about 500 microns.

[0031] Option 3. A battery pack according to Option 1, wherein the silicon-based electroactive material has a specific capacity greater than or equal to about 950 mAh / g.

[0032] Option 4. The battery pack according to Option 1, wherein the negative electrode is disposed on a major surface of a metal current collector.

[0033] Option 5. A battery pack according to Option 1, wherein the silicon-based electroactive material is substantially free of crystalline silicon having a diamond, orthorhombic or cubic crystal structure.

[0034] Scheme 6. A method for preparing a negative electrode for a battery pack for cycling sodium ions, the method comprising:

[0035] extracting alkali metal ions or alkaline earth metal ions from a silicide precursor to form a silicon-based electroactive material, the silicide precursor comprising two-dimensional silicon layers having a hexagonal crystal structure and separated from each other by a planar monolayer of alkali metal ions or alkaline earth metal ions, wherein the alkali metal ions or alkaline earth metal ions are extracted from the silicide precursor such that the hexagonal crystal structure of the two-dimensional silicon layers is retained in the silicon-based electroactive material; and

[0036] A continuous layer comprising the silicon-based electroactive material is deposited on a metal substrate to form a negative electrode.

[0037] Option 7. The method according to Option 6, wherein the alkali metal ions or alkaline earth metal ions are extracted from the silicide precursor by applying an acid solution to the silicide precursor.

[0038] Option 8. A method according to Option 7, wherein the acid solution comprises a hydrochloric acid (HCl) solution.

[0039] Option 9. A method according to Option 7, wherein the alkali metal ions or alkaline earth metal ions are extracted from the silicide precursor at ambient temperature or a temperature less than or equal to about 0 degrees Celsius.

[0040] Option 10. The method according to Option 6, wherein the silicide precursor comprises calcium disilicide (CaSi2), and wherein the alkali metal ions or alkaline earth metal ions extracted from the silicide precursor comprise calcium (Ca + )ion.

[0041] Option 11. A method according to Option 6, wherein the silicon-based electroactive material comprises a two-dimensional silicon layer having a hexagonal crystal structure, and wherein the two-dimensional silicon layer is terminated by hydrogen ions, hydroxide ions or a combination thereof.

[0042] Solution 12. The method according to Solution 6 further includes:

[0043] preparing a slurry comprising a silicon-based electroactive material in a solvent;

[0044] depositing the slurry on a metal substrate to form a precursor layer; and

[0045] The solvent is removed from the precursor layer to form a negative electrode.

[0046] Option 13. The method according to Option 12, wherein the slurry further comprises a polymer binder and an optional conductive material.

[0047] Solution 14. The method according to Solution 12 further includes:

[0048] The negative electrode is assembled into a battery including a positive electrode and an electrolyte that provides a medium for the conduction of sodium ions between the negative electrode and the positive electrode, the positive electrode containing sodium ions.

[0049] Solution 15. The method according to Solution 14 further includes:

[0050] The negative electrode and the positive electrode are electrically coupled 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.

[0051] Scheme 16. A method for preparing a negative electrode for a battery pack for cycling sodium ions, the method comprising:

[0052] Extraction of calcium (Ca) from calcium silicide precursor + ) ions to form a silicon-based electroactive material, the calcium silicide precursor comprising two-dimensional silicon layers having a hexagonal crystal structure separated from each other by a planar monolayer of calcium ions, wherein the calcium ions are extracted from the calcium silicide precursor such that the hexagonal crystal structure of the two-dimensional silicon layers is retained in the silicon-based electroactive material; and

[0053] A continuous layer comprising the silicon-based electroactive material is deposited on a metal substrate to form a negative electrode.

[0054] Embodiment 17. The method according to embodiment 16, wherein the calcium ions are extracted from the calcium silicide precursor by:

[0055] applying an acid solution to the calcium silicide precursor; or

[0056] The calcium silicide precursor is heated at a temperature greater than or equal to about 1420 degrees Celsius to release calcium gas therefrom.

[0057] Solution 18. The method according to Solution 16, further comprising:

[0058] preparing a slurry comprising a silicon-based electroactive material, a polymer binder, and optionally a conductive material in a solvent;

[0059] depositing the slurry on a metal substrate to form a precursor layer; and

[0060] The solvent is removed from the precursor layer to form a negative electrode.

[0061] Solution 19. The method according to Solution 18, further comprising:

[0062] The negative electrode is assembled into a battery including a positive electrode and an electrolyte that provides a medium for the conduction of sodium ions between the negative electrode and the positive electrode, the positive electrode containing sodium ions.

[0063] Solution 20. The method according to Solution 19, further comprising:

[0064] The negative electrode and the positive electrode are electrically coupled to a power source such that sodium ions are released from the positive electrode and intercalated between the two-dimensional silicon layers of the silicon-based electroactive material of the negative electrode.

[0065] 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 to be illustrative only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The present disclosure will be more fully understood through the detailed description and accompanying drawings, in which:

[0067] Figure 1 is a schematic perspective view of a motor vehicle powered by a battery pack including a plurality of battery modules.

[0068] Figure 2 yes Figure 1 A schematic cross-sectional view of a portion of one of the battery modules of FIG. 1 , the battery module including a plurality of circulating sodium ion electrochemical cells or batteries.

[0069] Figure 3 is a schematic cross-sectional view of a circulating sodium ion battery stack including a positive electrode, a negative electrode, a porous separator, and an electrolyte that permeates the positive and negative electrodes and the porous separator.

[0070] Among the drawings, reference numerals may be repeated to identify similar and / or identical elements. DETAILED DESCRIPTION

[0071] The silicon-based electroactive materials disclosed herein can be used in negative electrodes of batteries that circulate sodium ions to provide the negative electrode with a relatively high specific capacity compared to hard carbon (e.g., graphite). The silicon-based electroactive materials disclosed herein comprise a stack of spaced-apart silicon layers. The arrangement of the silicon layers in the silicon-based electroactive materials allows sodium ions to be intercalated between the silicon layers during the charging process of the battery, and then to alloy with the silicon in the layers and form a silicon-sodium alloy throughout the bulk of the silicon-based electroactive material.

[0072] Figure 1 A motor vehicle 2 is depicted that is powered by an electric motor 4 that draws power from a battery pack 6 that includes one or more battery modules 8. The battery modules 8 may be electrically coupled together in a series and / or parallel arrangement to meet the desired capacity and power requirements of the electric motor 4. The vehicle 2 may be an all-electric vehicle and may be powered solely by the electric motor 4, or the vehicle 2 may be a hybrid electric vehicle and may be powered by both the electric motor 4 and an internal combustion engine (not shown).

[0073] like Figure 2 As shown in , each battery module 8 includes one or more electrochemical cells or batteries 10 that circulate sodium ions. In practice, the batteries 10 in the battery module 8 are often assembled as a stack of layers, which include a negative electrode layer 12, a negative electrode collector 13, a positive electrode layer 14, a positive electrode collector 15, and a separator layer 16. Each battery 10 is defined by a negative electrode layer 12 and a positive electrode layer 14, and the negative electrode layer 12 and the positive electrode layer 14 are separated from each other by a separator layer 16. In practice, the separator layer 16 can be impregnated with an electrolyte that provides a medium for the conduction of sodium ions between the negative electrode layer 12 and the positive electrode layer 14, or the separator layer 16 itself can act as an electrolyte. The negative electrode layer 12 is disposed on the negative electrode collector 13 and is electrically connected to the negative electrode collector 13, and the positive electrode layer 14 is disposed on the positive electrode collector 15 and is electrically connected to the positive electrode collector 15. As shown Figure 2 As shown in , for efficiency, these layers can be stacked so that some negative electrode current collectors 13 and some positive electrode current collectors 15 are double-sided and include negative electrode layers 12 or positive electrode layers 14 on both sides thereof, respectively. In this arrangement, adjacent negative electrode layers 12 and positive electrode layers 14 share a single negative electrode current collector 13 or positive electrode current collector 15, respectively.

[0074] Figure 3 An electrochemical cell or battery 20 that circulates sodium ions is depicted. The battery 20 can generate an electrical current during discharge that can be used to power a load device (e.g., the motor 4), and can be recharged by connection to a power source. Figure 1 and Figure 2 , in various aspects, the battery pack 20 can be used to power the electric motor 4 of the motor vehicle 2. Additionally or alternatively, the battery pack 20 can be used in other transportation applications (e.g., motorcycles, boats, tractors, buses, motorbikes, mobile homes, campers, tanks, and aircraft), and can be used to power fixed and / or portable electronic devices, components, and devices used in various other industries and applications (including, as non-limiting examples, industrial, residential and commercial buildings, consumer products, industrial equipment and machinery, agricultural or farm equipment, and heavy machinery).

[0075] The battery 20 includes a negative electrode 22, a positive electrode 24, a separator 26, and an electrolyte 28, which provides a medium for the conduction of sodium ions between the negative electrode 22 and the positive electrode 24. The negative electrode 22 is disposed on a major surface of a negative electrode current collector 30 and the positive electrode 24 is disposed on a major 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 coupled to a power source or load 34 (e.g., a motor 4) via an external circuit 36. The negative electrode 22 and the positive electrode 24 are configured so 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 the discharge process of the battery 20, the electrochemical potential established between the negative electrode 22 and the positive electrode 24 drives the spontaneous reduction and oxidation (redox) reactions within the battery 20 and the release of sodium ions and electrons at the negative electrode 22. The released sodium ions travel from the negative electrode 22 to the positive electrode 24 through the separator 26 and the electrolyte 28, while electrons travel from the negative electrode 22 to the positive electrode 24 via the external circuit 36, thereby generating an electric current. After the negative electrode 22 has been partially or completely depleted of sodium, the battery 20 may be charged by connecting the negative electrode 22 and the positive electrode 24 to a power source 34, which drives a non-spontaneous redox reaction within the battery 20 and releases sodium ions and electrons from the positive electrode 24. Repeated discharge and charging of the battery 20 may be referred to herein as a "cycle," wherein a full charge event followed by a full discharge event is considered a complete cycle.

[0076] The negative electrode 22 is configured to store and release sodium ions to facilitate charging and discharging of the battery 20, respectively. The negative electrode 22 may be in the form of a continuous material layer disposed on a major 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.

[0077] The negative electrode 22 includes an electrochemically active (electroactive) material that can store and release sodium ions by undergoing a reversible redox reaction with sodium during the charge and discharge process of the battery 20. In various aspects, the negative electrode 22 may include a polymer binder and an optional conductive material. In this case, the electroactive material of the negative electrode 22 may be a particulate material and the particles of the electroactive material may be mixed with the polymer binder and the optional conductive material. The electroactive material may constitute 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 by weight.

[0078] The electroactive material of negative electrode 22 includes a silicon-based electroactive material. The silicon-based electroactive material may constitute 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% by weight of the electroactive material of negative electrode 22.

[0079] The silicon-based electroactive material includes a stack of polyanionic two-dimensional silicon layers having a hexagonal crystal structure. The silicon layers may be referred to as silicene, a two-dimensional allotrope of silicon having a bent or folded hexagonal crystal structure (space group P63mc, 186). The silicon-based electroactive material is configured to store and release sodium ions by intercalating sodium ions between the two-dimensional silicon layers during the charging process of the battery pack 20 and deintercalating the sodium ions during the discharging process of the battery pack 20. More specifically, the two-dimensional silicon layers are spaced apart from each other by a sufficient distance to allow sodium ions to be intercalated or inserted therebetween during the charging process of the battery pack 20. Thus, when the battery pack 20 is at least partially charged, the silicon layers are formed by the sodium (Na + ) ions are spaced apart from each other. Once the sodium ions have been inserted between the two-dimensional silicon layers and in close contact with the silicon ions defining the silicon layers, the sodium ions can alloy with the silicon ions, for example by forming covalent bonds therewith, and form a silicon-sodium (Si-Na) alloy. As such, the silicon-based electroactive material can have a specific capacity greater than or equal to about 950 milliampere hours per gram (mAh / g). In various aspects, the silicon-based electroactive material can have a specific capacity of about 954 mAh / g, which is the maximum theoretical sodium storage capacity of silicon.

[0080] The silicon-based electroactive material of the negative electrode 22 may be substantially free of crystalline silicon having a diamond, orthorhombic or cubic crystal structure. Specifically, the silicon-based electroactive material may be substantially free of the following silicon allotropes: DC-Si having a diamond crystal structure (space group Fd-3m, 227); Si having an orthorhombic crystal structure (space group Cmcm, 63); 24 ; Si with cubic crystal structure (space group Pm-3n, 223) 46 ; Si with cubic crystal structure (space group Fd-3m, 227) 136 In various embodiments, the silicon-based electroactive material of negative electrode 22 may be substantially free of amorphous silicon.

[0081] Silicon-based electroactive materials include two-dimensional silicon layers with a hexagonal crystal structure. However, when other crystalline forms of silicon (e.g., DC-Si, Si 24 、Si 46 or Si 136) is used as an electroactive material in the negative electrode 22 of a battery that circulates sodium ions, the high activation energy required for the diffusion of sodium ions into bulk crystalline silicon inhibits the sodium ions from alloying with the crystalline silicon and prevents silicon from reaching its theoretical sodium storage capacity of 954 mAh / g by forming a Si-Na alloy. In other words, the layered arrangement of the two-dimensional silicon layers in the silicon-based electroactive material allows sodium ions to be intercalated therebetween and, in turn, allows the formation of a Si-Na alloy during the charging process of the battery 20.

[0082] The polymer binder is electrochemically inert and may be included in the negative electrode 22 to provide structural integrity to the negative electrode 22 and / or to help the negative electrode 22 adhere to the main surface of the negative electrode current collector 30. Examples of polymer binders include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), ethylene propylene diene rubber (EPDM), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), nitrile 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.

[0083] The optional conductive material is electrochemically inert and can be included in the negative electrode 22 to provide sufficient conductivity to the negative electrode 22 to support the penetration of electrons therethrough. Examples of conductive materials include carbon-based materials, metals (e.g., nickel), and / or conductive polymers. Examples of conductive carbon-based materials include carbon black (CB) (e.g., acetylene black), graphite, graphene (e.g., graphene nanosheets, GNPs), graphene oxide, carbon nanotubes (CNTs), and / or carbon fibers (e.g., carbon nanofibers). Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, and / or polypyrrole. When included in the negative electrode 22, the optional 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 by weight.

[0084] The positive electrode 24 is configured to store and release sodium ions during the discharge and charge process of the battery 20. The positive electrode 24 can be in the form of a continuous porous layer disposed on the major surface of the positive electrode current collector 32. The positive electrode 24 includes an electroactive positive electrode material, a polymer binder, and an optional conductive material. In various aspects, the electroactive material of the positive electrode 24 can be a particulate material, and the particles of the electroactive material of the positive electrode 24 can be mixed with the polymer binder and the optional conductive material.

[0085] The electroactive material of the positive electrode 24 can store and release sodium ions by undergoing a reversible redox reaction with sodium at a higher electrochemical potential than the electroactive material of the negative electrode 22 (such that there is an electrochemical potential difference between the negative electrode 22 and the positive electrode 24). The electroactive material of the positive electrode 24 may include a material that can intercalate and deintercalate sodium or a material that can undergo a conversion reaction with sodium. In aspects where the electroactive material of the positive electrode 24 comprises an intercalation matrix material that can reversibly insert or intercalate sodium ions, the electroactive material of the positive electrode 24 may comprise a sodium transition metal oxide.

[0086] The same polymer binders and / or conductive materials disclosed above with respect to negative electrode 22 may be included in positive electrode 24 in substantially the same amounts for substantially the same reasons.

[0087] The separator 26 physically separates and electrically isolates the negative electrode 22 and the positive electrode 24 from each other while allowing sodium ions to pass therethrough. The separator 26 has an open microporous structure and may include organic and / or inorganic materials. For example, the separator 26 may include a polymer or a combination of polymers. For example, the separator 26 may include one or more polyolefins, such as 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 include a laminate of polymers, such as a laminate of PE and PP.

[0088] The electrolyte 28 is ionically conductive and provides a medium for the conduction of sodium ions between the negative electrode 22 and the positive electrode 24. The electrolyte 28 includes an organic solvent and a sodium salt in the organic solvent. The organic solvent may include a non-aqueous aprotic organic solvent. The sodium salt is soluble in the organic solvent and provides a passage for the sodium ions to pass through the electrolyte 28. The sodium salt may include an inorganic sodium salt, an organic sodium salt, or a combination thereof.

[0089] The negative electrode current collector 30 and the positive electrode current collector 32 are conductive and provide electrical connections between the external circuit 36 ​​and the negative electrode 22 and the positive electrode 24, respectively. In various aspects, the negative electrode current collector 30 and the positive electrode current collector 32 can be made of metal and can be in the form of a non-porous metal foil, a perforated metal foil, a porous metal mesh, or a combination thereof. The negative electrode current collector 30 can be made of copper, nickel, or alloys thereof, stainless steel, or other suitable conductive materials. The positive electrode current collector 32 can be made of aluminum (Al) or other suitable conductive materials.

[0090] method

[0091] The silicon-based electroactive material of the negative electrode 22 can be prepared from a silicide precursor. The silicide precursor may include an alkali metal silicide, an alkaline earth metal silicide, or a combination thereof. For example, the silicide precursor may include 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 various embodiments, the alkali metal and / or alkaline earth metal in the silicide precursor may have an ionic radius greater than or equal to that of sodium. In various embodiments, the silicide precursor may include calcium silicide (CaSi2). Similar to the silicon-based electroactive material of the negative electrode 22, the silicide precursor includes a stack 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 a planar monolayer of alkali metal ions, alkaline earth metal ions or a combination thereof. In embodiments where the silicide precursor comprises calcium silicide, the two-dimensional silicon layers are separated from each other by a planar monolayer 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 .

[0092] Extracting alkali metal ions and / or alkaline earth metal ions 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 chemical etching techniques and / or by thermally treating the silicide precursor.

[0093] In the embodiment in which chemical etching technology is used to extract alkali metal ions and / or alkaline earth metal ions from the silicide precursor, an acid solution can be applied to the silicide precursor so that the alkali metal ions and / or alkaline earth metal ions are dissolved in the acid solution and deintercalated from the silicide precursor without changing the hexagonal crystal structure (topological chemical deintercalation) of the two-dimensional silicon layer. The acid solution may include an aqueous solution containing water as a solvent or a non-aqueous solution containing an alcohol (e.g., methanol, ethanol, etc.) as a solvent. The acid solution may be a concentrated solution of an acid or a saturated solution of an acid. In various 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 acid solution may be applied to the silicide precursor at a temperature less than or equal to about 0°C, or optionally less than or equal to about -30°C. After applying the liquid acid solution to the silicide precursor for a sufficient duration to extract alkali metal ions and / or alkaline earth metal ions therefrom and form a 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.

[0094] In various embodiments, the acid solution applied to the silicide precursor may include a hydrochloric acid (HCl) solution. In some embodiments, the HCl aqueous solution may be applied to the silicide precursor at a temperature of less than or equal to about 30 degrees Celsius (°C) to form a hydrogen-terminated two-dimensional silicon layer having the formula Si6H6(silane). In other embodiments, the HCl aqueous solution may be applied to the silicide precursor at a temperature of about 0°C to form a two-dimensional silicon layer terminated by hydrogen ions and / or hydroxyl (-OH) ions and having the formula Si6(OH)6 and / or Si6H x (OH) 6-x In various embodiments, a non-aqueous HCl solution may be applied to a silicide precursor to form a two-dimensional silicon layer terminated by alkoxy groups and having the formula Si6H3(OCH3)3 or Si6H3(OC2H5)3 (alkoxysilane).

[0095] In embodiments where heat treatment is used to extract alkali metal ions and / or alkaline earth metal ions from the silicide precursor, the silicide precursor may be heated to a temperature greater than or equal to the boiling point of the alkali metal ions and / or alkaline earth metal ions in the silicide precursor. The boiling point of calcium at about 1 atmosphere is about 1420 degrees Celsius (° C.). Thus, in embodiments where the silicide precursor includes calcium disilicide, the silicide precursor may be heated to a temperature greater than or equal to about 1420° C. to release calcium gas therefrom.

[0096] For example, the silicon-based electroactive material can be assembled into a negative electrode, such as negative electrode 22, by depositing the silicon-based electroactive material on a metal substrate. In various embodiments, the metal substrate can be made of substantially the same material as the negative electrode current collector 30 and have substantially the same shape as the negative electrode current collector 30. The silicon-based electroactive material can be deposited on the metal substrate by preparing a slurry of particles of the silicon-based electroactive material in a solvent. Similar to the negative electrode 22, the slurry may also include a polymer binder and an optional conductive material. The slurry can be deposited on the metal substrate to form a precursor layer, and then the solvent can be removed from the precursor layer to form the negative electrode 22.

[0097] Thereafter, the negative electrode 22 can be assembled into a battery, such as the battery 20. During the charging process of the battery 20, the negative electrode 22 and the positive electrode 24 are electrically coupled to the power source 34, so that the sodium ions are released from the positive electrode 24 and electrochemically intercalated between the two-dimensional silicon layers of the silicon-based electroactive material of the negative electrode 22.

[0098] The foregoing description is essentially only exemplary and is absolutely not intended to limit the present disclosure, its application or use. The broad teachings of the present disclosure can be implemented in various forms. Therefore, although the present disclosure includes specific examples, the true scope of the present disclosure should not be limited thereto, because after studying the drawings, the specification and the appended claims, other modifications will become apparent. It should be understood that one or more steps in the method may be implemented in different orders (or simultaneously) without changing the principles of the present disclosure. In addition, although each embodiment is described above as having certain features, any one or more features described in any embodiment of the present disclosure may be implemented in any other embodiment and / or combined with the features of any other embodiment, even if the combination is not explicitly described. In other words, the embodiments are not mutually exclusive, and the mutual replacement of one or more embodiments is still within the scope of the present disclosure.

[0099] Various terms are used to describe the spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.), including "connected," "engaged," "coupled," "adjacent," "next to," "on top of," "on," "under," and "disposed." Unless explicitly described as "directly," when describing the relationship between a first element and a second element in the above disclosure, the relationship can be a direct relationship in which no other intermediate elements exist between the first element and the second element, or an indirect relationship in which one or more intermediate elements exist between the first element and the second element (spatially or functionally). The phrase "at least one of A, B, and C" used herein should be interpreted as meaning a logical (A or B or C) using a non-exclusive logical OR, and should not be interpreted as meaning "at least one A, at least one B, and at least one C." The term "and / or" used herein includes a combination of one or more of the associated listed items.

[0100] The terms used herein are only for the purpose of describing specific exemplary embodiments, and are not intended to be limiting. Unless the context clearly indicates otherwise, as used herein, the singular forms "a", "an" and "the" may be intended to also include plural forms. The terms "comprise", "include", "cover" and "have" are compatible, and therefore specify the presence of the features, elements, compositions, steps, integers, operations and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or their groups. Although the open term "comprising" should be understood as a non-limiting term for describing and claiming the various embodiments described herein, in some aspects, the term may be understood as alternatively being a more restrictive and limited term, such as "consisting of..." or "consisting essentially of..." Thus, for any given embodiment of a narration composition, material, assembly, element, feature, integer, operation and / or method step, the present disclosure also specifically includes an embodiment consisting of or essentially consisting of such narrated compositions, materials, assemblies, elements, features, integers, operations and / or method steps. In the case of “consisting of,” alternative embodiments exclude any additional compositions, materials, components, elements, features, integers, operations, and / or method steps, while in the case of “consisting essentially of,” any additional compositions, materials, components, elements, features, integers, operations, and / or method steps that materially affect the basic and novel characteristics are excluded from such embodiments, but any compositions, materials, components, elements, features, integers, operations, and / or method steps that do not materially affect the basic and novel characteristics may be included in the embodiments.

[0101] Any method step, process and operation described herein should not be interpreted as necessarily requiring them to be performed in the particular order discussed or illustrated, unless clearly determined as the execution order.It should also be understood that, unless otherwise stated, additional or alternative steps can be adopted.Although the terms first, second, third, etc. can be used to describe various steps, elements, components, regions, layers and / or sections in this article, unless otherwise stated, these steps, elements, components, regions, layers and / or sections should not be limited by these terms.These terms can only be used to distinguish a step, element, component, region, layer or section from another step, element, component, region, layer or section.Unless the context clearly indicates, terms such as "first", "second" and other numerical terms do not imply order or sequence when used in this article.Therefore, the first step, element, component, region, layer or section discussed below can be referred to as the second step, element, component, region, layer or section without departing from the teaching of exemplary embodiments.

[0102] Throughout this disclosure, numerical values ​​represent approximate measurements or range limits to cover slight deviations from given values ​​and embodiments having approximately the values ​​mentioned and embodiments having exactly the values ​​mentioned. Except in the working examples provided at the end of the detailed description, all numerical values ​​of (e.g., amounts or conditions) parameters in this specification (including the appended claims) should be understood to be modified by the term "about" in all cases, regardless of whether "about" actually appears before the numerical value. "About" means that the numerical value allows a certain slight imprecision (close to the exact value of the value to a certain extent; approximately or reasonably approximate the value; almost). If the imprecision provided by "about" is not otherwise understood in this ordinary sense in the art, then "about" as used herein refers to at least the deviation that can be caused by the common methods of measuring and using such parameters. For example, "about" may include 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 some aspects optionally less than or equal to 0.1% deviation. Furthermore, the disclosure of a range includes disclosure of all values ​​within the entire range and further subdivided ranges, including disclosure of endpoints and subranges given for that range.

[0103] As used herein, the terms "composition" and "material" are used interchangeably and refer generally to a substance that contains at least a preferred chemical constituent, element, or compound, but which may also contain additional elements, compounds, or substances, including trace impurities, unless otherwise specified. A composition or material "based on X" refers generally to a composition or material in which "X" is the single largest component of the composition or material by weight percentage (%). This can include compositions or materials having greater than 50 wt % X, as well as compositions or materials having less than 50 wt % X, as long as X is the single largest component of the composition or material based on its overall 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% by weight of the substance.

[0104] As used herein, the term "metal" may refer to a pure elemental metal or an alloy of an elemental metal with one or more other metals or nonmetallic elements (referred to as "alloying" elements). Alloying elements may be selected to impart certain desirable properties to the alloy that are not exhibited by the base metal alone.

Claims

1. A battery pack for circulating sodium ions, the battery pack comprising: a negative electrode comprising a silicon-based electroactive material, the silicon-based electroactive material comprising a two-dimensional silicon layer having a hexagonal crystal structure, the silicon-based electroactive material being configured to intercalate sodium ions between the two-dimensional silicon layers and form an alloy of silicon and sodium during charging of the battery, the silicon-based electroactive material being substantially free of crystalline silicon having a diamond, orthorhombic, or cubic crystal structure; a positive electrode spaced apart from the negative electrode and comprising an electroactive positive electrode material; and An electrolyte provides a medium for the conduction of sodium ions between the negative electrode and the positive electrode.

2. The battery of claim 1, wherein the negative electrode further comprises a polymer binder and optionally a conductive material, wherein the negative electrode has a thickness greater than or equal to about 30 microns and less than or equal to about 500 microns, and wherein the negative electrode is disposed on a major surface of a metal current collector.

3. A method for preparing a negative electrode for a battery pack for cycling sodium ions, the method comprising: Extraction of calcium (Ca) from calcium silicide precursor + ) ions to form a silicon-based electroactive material, the calcium silicide precursor comprising two-dimensional silicon layers having a hexagonal crystal structure separated from each other by a planar monolayer of calcium ions, wherein the calcium ions are extracted from the calcium silicide precursor such that the hexagonal crystal structure of the two-dimensional silicon layers is retained in the silicon-based electroactive material; and A continuous layer comprising the silicon-based electroactive material is deposited on a metal substrate to form a negative electrode.

4. The method of claim 3, wherein calcium ions are extracted from the calcium silicide precursor by applying an acid solution to the silicide precursor.

5. The method of claim 4, wherein calcium ions are extracted from the silicide precursor at ambient temperature or a temperature less than or equal to about 0 degrees Celsius.

6. The method of claim 3, wherein the calcium silicide precursor is heated at a temperature greater than or equal to about 1420 degrees Celsius to release calcium gas therefrom to extract calcium ions from the calcium silicide precursor.

7. The method according to claim 3, further comprising: preparing a slurry comprising a silicon-based electroactive material, a polymer binder, and optionally a conductive material in a solvent; depositing the slurry on a metal substrate to form a precursor layer; and The solvent is removed from the precursor layer to form a negative electrode.

8. The method according to claim 3, further comprising: The negative electrode is assembled into a battery including a positive electrode and an electrolyte that provides a medium for the conduction of sodium ions between the negative electrode and the positive electrode, the positive electrode containing sodium ions.

9. The method according to claim 3, further comprising: The negative electrode and the positive electrode are electrically coupled to a power source such that sodium ions are released from the positive electrode and intercalated between the two-dimensional silicon layers of the silicon-based electroactive material of the negative electrode.

10. The method of claim 3, wherein the silicon-based electroactive material is substantially free of crystalline silicon having a diamond, orthorhombic, or cubic crystal structure.

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