Process for the production of electrode materials for lithium-based batteries, negative electrode and sulfur-based batteries

Abstract

Procedure comprising: Forming a precipitate (21) in an aqueous mixture by mixing a SiO x precursor (12) and an acid (14); Adding the precipitate (21) and a carbon material (19) to a base (17), thereby dissolving the precipitate (21) to form a solution containing the carbon material (19); Performing a hydrothermal synthesis using the solution, wherein nanostructure precursors (24) grow on the carbon material (19); and Annealing the nanostructure precursors (24) on the carbon material (19), thereby removing the carbon material (19) to form porous one-dimensional SiOx nanostructures (26, 26'), where 0 < x ≤ 2.

Description

BACKGROUNDSecondary or rechargeable lithium-ion batteries or lithium-sulfur batteries are frequently used in many stationary and portable devices, such as those found in consumer electronics, automotive aerospace industry. The class of lithium batteries has gained popularity for various reasons including relatively high energy density, non-memory as compared to other types of batteries, relatively low internal resistance, and low self-discharge rate when not in use. The ability of lithium batteries to undergo repeated cycles of energy over their useful life make them an attractive and reliable energy source.Active materials for lithium ion batteries with metal-based particles are disclosed in EP 2 936 586 B1. Further active materials for negative electrodes of lithium ion batteries are disclosed in EP 2 936 587 B1.CN 1 02 826 557 A discloses methods for producing silicon oxide nanotubes.A flexible composite electrode is described in CN 1 02 945 947 B.SUMMARYIn an example of a method disclosed herein, a precipitate is formed in an aqueous mixture by mixing an SiO x- precursor and an acid. The precipitate and a carbon material are added to a base, and the precipitate dissolves to form a solution in which the carbon material is contained. Hydrothermal synthesis is performed using the solution, and nanostructure precursors grow on the carbon material. The nanostructure precursors on the carbon material are annealed so that the carbon material is removed and porous one-dimensional SiO x(0 < x≤2) nanostructures are formed.Examples of the porous one-dimensional SiO x(0 < x≤2) nano-rods may be used as an additive in a positive electrode of a lithium-sulfur battery, as an active material in a lithium-sulfur battery when subjected to pre-lithography, or as an active material in a lithium-ion battery.BRIEF DESCRIPTION OF THE DRAWINGSFeatures and advantages of the examples of the present disclosure will become apparent by reference to the following detailed description and drawings, in which like reference numerals correspond to similar, though perhaps non-identical, components. For brevity, reference numerals or features having a previously described function may or may not be described in connection with other drawings in which they appear. FIGS. 1A through 1F are schematic fragmentary cross-sectional views collectively depicting several examples of the method of making the one-dimensional SiO x- nano-rods disclosed herein; FIG. 2 is a cross-sectional view of an example of a positive electrode on a current collector; FIG. 3 is a cross-sectional view of an example of a negative electrode on a current collector; FIG. 4 is a perspective schematic view of an example of a lithium ion battery including an example of the negative electrode disclosed herein; FIG. 5 is a perspective schematic view of an example of a lithium-sulfur battery including an example of the negative electrode disclosed herein; FIG. 6 is a transmission electron microscope ("TEM") photograph of examples of the porous one-dimensional SiO x- nano-rods formed by an example of the method disclosed herein using a scale bar of 2 μm; FIG. 7 is a TEM image using a scale bar of 2 μm, a view of the one-dimensional SiO x- nano-rods shown in FIG. 6 ; FIG. 8 shows the Raman spectra of an example of the porous one-dimensional SiO x- nano-rods and a comparative silicon wafer; and FIG. 9 is a graph depicting discharge capacity (mAh / g, left Y axis) and coulombic efficiency (%, right Y axis) versus cycle number for an exemplary lithium ion battery including a negative electrode with the porous one-dimensional SiO x- nano-rods as the active material.DETAILED DESCRIPTIONLithium-sulfur and lithium-ion batteries generally function by reversibly transferring lithium ions between a negative electrode (sometimes also called anode) and a positive electrode (sometimes also called cathode). The negative and positive electrodes are disposed on opposite sides of a porous polymer separator impregnated with an electrolyte solution suitable for conducting the lithium ions. Each of the electrodes is also connected to current collectors connected by an interruptible external circuit that allows an electric current to flow between the negative and positive electrodes.The life cycle of lithium-sulfur batteries may be limited by the migration, diffusion, or shuttle of lithium polysulfide intermediates (LiS x, where x equals 2<x<8) from the positive electrode through the porous polymer separator to the negative electrode during the process of battery discharge. The lithium polysulfide intermediates produced at the sulfur-based positive electrode are soluble in the electrolyte and can migrate to the negative electrode where they parasitically react with the negative electrode to form lower order lithium polysulfide intermediates. These lower order lithium polysulfide intermediates diffuse back to the positive electrode and regenerate the higher forms of the lithium polysulfide intermediates. As a result, a pendulum effect occurs. This effect results in reduced sulfur utilization, self-discharge, poorer cyclability, and reduced coulombic efficiency of the battery. Without being bound by any theory, it is believed that even a small amount of the lithium polysulfide intermediates form an insoluble end product, such as dilithium sulfide (Li 2 S), which can permanently bond to the negative electrode. This may result in parasitic loss of active lithium at the negative electrode, thereby preventing reversible electrode operation and reducing the life of the lithium-sulfur battery.As mentioned above, the pendulum effect leads to reduced sulfur utilization. This is due to the fact that the formation of the lithium polysulfide consumes intermediates of the sulfur in the positive electrode. A reduced amount of sulfur in the positive electrode means that less sulfur is available for use. Consuming sulfur also contributes to the limited life of sulfur-based batteries. It should be understood that the lithium polysulfide intermediates are referred to herein as polysulfides.In an example of the method disclosed herein, porous one-dimensional SiO 2- nano-rods may be prepared and added as an additive to a positive electrode. In another example of the method disclosed herein, porous one-dimensional SiO x( x<0<2) nano-rods may be prepared and added as active material to the negative electrode. It should be understood that SiO may be x silicon monoxide, silicon dioxide (in cases where it is particularly indicated that 0<x≤2), silicon suboxide, or combinations thereof. As used herein, the term "one-dimensional" means that the nanobar has a length (which may be up to a few microns) that is much larger than its diameter (ranging from 20 nm to 300 nm). Other structures that may be considered one-dimensional include nanowires, nanotubes, and nanofibers.In the example in which the SiO 2- nano-rods are mixed into the entire positive electrode, this additive is mixed with an active material, a binder, and a conductive filler. In this example, the porous one-dimensional SiO 2- nano-rods act as reservoirs for soluble polysulfide. Specifically, the soluble polysulfides formed in the positive electrode are trapped in the pores of the porous one-dimensional SiO 2- nano-rods. Since the polysulfides are trapped in the positive electrode, the polysulfides are unable to migrate to the negative electrode and react with the active material in the negative electrode. As a result, the porous one-dimensional SiO 2- nano-rods can mitigate the shuttle effect and increase the amount of sulfur for use in the positive electrode, and in turn improve the efficiency, life, and self-discharge of sulfur-based batteries.Moreover, the use of silicon as a negative electrode active material in lithium-based batteries is desirable due to the high theoretical capacity (e.g., 4200 mAh / g). However, it has been found that negative electrode active materials (e.g., silicon particles) having high specific capacities also have a large volume expansion and contraction during charging / discharging of the lithium-based battery. The large volume change (e.g., about 400%) experienced by the negative electrode active material during landing / discharge causes the negative electrode active material to crack, weaken, or otherwise mechanically degrade, resulting in loss of electrical contact and poor durability. Poor cycle performance often involves a large capacity fade resulting from the breakdown of contact between the negative electrode active material and the conductive filler in the negative electrode due to the large volume change.Some examples of the method disclosed herein form active silicon-based negative electrode materials that may improve cycle performance of various examples of the negative electrode. In one example, one-dimensional porous SiO x(0 < x<2) nano-rods may be made and used as the active material in the negative electrode of the lithium ion battery. In another example, porous one-dimensional silicide nano-rods may be prepared and lithium sulfur may be used as the negative electrode active material. The porous one-dimensional silicide nano-rods may be formed by pre-lithiating the porous one-dimensional SiO x(0 < x<2) nano-rods. In contrast to the porous one-dimensional SiO 2- nano-rods used as an additive in the positive electrode to trap polysulfides, the porous one-dimensional silicide nano-rods in the negative electrode are used as active materials to absorb and release lithium ions, and not to trap polysulfides.Several of the porous one-dimensional SiO x(0 < x≤2) nano-rods disclosed herein are collectively assembled to resemble a sea urchin. Each of the nano-rods is a small barbed extension extending from a central portion. The barbed extensions may have a decreasing diameter along the length of the nano-rods away from the central portion. Small spaces (i.e., spaces) may separate one nanorod from another nanorod in the assembly. The morphology of the porous one-dimensional SiO x(0 < x ≤ 2) nano-rods (i.e., lithium ion battery active material) and the porous one-dimensional silicide nano-rods (i.e., lithium sulfur battery active material) provides space that can absorb the volume expansion of the silicon, and thus can reduce the stress on the silicon. It is believed that the spacing between individual porous one-dimensional SiO x(0 < x≤2) nano-rods and between individual porous one-dimensional silicide nano-rods contributes to a reduction in breakage, weakening or mechanical degradation, which would otherwise result in a capacity shrinkage during the charging and discharging process.Referring now to Figures 1A-1F, examples of the method for making the porous one-dimensional SiO x(0 < x ≤ 2) nano-rods will be discussed. In one example, the method includes, in part, hydrothermal synthesis to form the porous one-dimensional SiO x(0 < x≤2) nano-rods.Referring to FIG. 1A, an aqueous solution 16 is formed by mixing deionized water, the SiO x precursor 12, and an acid 14 into a container 18. The SiO x precursor 12 may be sodium metasilicate (NaSi 3) or hydrous sodium metasilicate (NaSiO 3 ·6H 2 O). The acid 14 may be hydrochloric acid (HCl) (e.g., 1 M HCl), H 2 SO 4, HNO 3, H 2 PO 4 or any other suitable acid.After the SiO x precursor 12 is added to the deionized water in the container 18, the SiO x precursor 12 may be thoroughly dissolved by stirring to form the solution 16. In one example, the solution 16 may be stirred for a time ranging from about 5 minutes to about 2 hours. Solution 16 may be mixed with a magnetic stirring bar, a hand stirring bar, or any other suitable means known to those skilled in the art. The acid 14 is then added to the solution 16 until a white precipitate 21 is formed in the solution 16. In addition, in the solution 16, a salt (for example, NaCl, Na 2 SO 4 etc.) is formed as a by-product of the reaction of the SiO x precursor 12 with the acid 14 (note that the salt is not shown in FIG. 1A ). The salt byproduct is soluble in the solution 16, and therefore the salt byproduct is dissolved in the solution 16. In addition, the salt is removed when the precipitate 21 is separated off.An example of the precipitate 21 that forms is Si(OH) 4. Si(OH) 4 is silica (a water insoluble acid) which in the examples disclosed herein is a white gel-like precipitate formed in solution 16. In one example, the Si(OH) 4 may be obtained from a reaction of hydrous Na 2 SiO 3 and 1M HCl. The precipitate 21 formed may be in the form of nanoparticles (i.e., particles having an average diameter in the range of about 1 nm to about 100 nm).The precipitate 21 formed in the solution 16 may be removed from the solution 16 using any suitable separation technique. For example, the precipitate 21 may be removed by vacuum filtration, centrifugal force, or any other suitable means. The precipitate 21 may be washed several times with deionized water during and / or after separation of the precipitate 21 from the solution 16. It may be desirable to wash the precipitate with deionized water before it is used in the hydrothermal synthesis.After the precipitate 21 is separated from the solution 16 and washed, the precipitate 21 may be dried at a temperature of about 60° C. to about 80° C. for a period of about 12 to about 24 hours.Referring to Figure 1B, in another container 18', an aqueous mixture 22 is formed by mixing deionized water, the precipitate 21, a carbon material 19, and a base 17. As mentioned above, the precipitate 21 is a water insoluble acid but will react with the base 17 to form a water soluble product (e.g., Na 2 SiO 4), which dissolves in the deionized water. The hollow carbon (hollow carbon) 19 may be suspended or dispersed in the deionized water. As such, the aqueous mixture 22 is also referred to herein as the aqueous mixture 22 in which the carbon material 19 is contained.Any carbon material 19 that can provide the heterogeneous nucleation sites for SiO x and is inert during hydrothermal synthesis can be used. In one example, the carbon material 19 is hollow carbon or graphite. Hollow carbon can be produced by thermal oxidation of carbon black. Some examples of suitable commercially available carbon black particles include VULCAN® XC72 (Cabot Corp.), KETJENBLACK® (Akzo Nobel), and Black Pearl (BP2000) (Cabot Corp.). In one example, for each 1 gram of the precipitate 21 contained in the solution, 0.01 g of the carbon material 19 may be added.The carbon material 19 provides heterogeneous nucleation sites during hydrothermal synthesis of the aqueous mixture 22, thus facilitating the nucleation and growth process of a nanostructure precursor 24 (see FIG. 1D ). It is believed that by providing heterogeneous nucleation sites during hydrothermal synthesis, the carbon material 19 increases the yield of the nanostructure precursor 24, and thus ultimately the porous one-dimensional SiO x- nano-rods. The edges and / or depressions of the carbon material 19 provide the nucleation sites for the growth of the nanostructure precursor 24.Moreover, it is believed that the carbon material 19 may act as a reducing agent to reduce SiO 2 to SiO x or SiO x to an even further reduced form of SiO x during a heat treatment (referred to as "2" between FIGS. 1D and 1F ) that may occur subsequent to the hydrothermal synthesis. This heat treatment 2 is discussed below with reference to FIG. 1F. It should be appreciated that the carbon material 19 does not react with the base 17 or the precipitate 21 during the hydrothermal synthesis or the formation of the aqueous mixture 22. As such, the carbon material 19 provides a substrate for the growth of the nanostructure precursor 24, but does not interfere with the growth of the nanostructure precursor 24.The base 17 is also contained in the aqueous mixture 22. The base 17 changes the pH of the aqueous mixture 22 (which may be initially very acidic, pH<5) to a pH in the range of about 5 to about 7 (i.e., less acidic or neutral). Some examples of base 17 include sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide (NH 4 OH), or other base suitable for adjusting the pH to the desired value. The base 17 not only adjusts the pH of the aqueous mixture 22, but also reacts with the precipitate 21 before hydrothermal synthesis. the reaction between the precipitate 21 and the base 17 forms a water-soluble product, and thus the base helps dissolve the precipitate 21. As such, the deionized water, the precipitate 21, and the base 17 may be mixed together to dissolve the precipitate 21 and form a solution, and then the carbon material 19 may be added to form the aqueous mixture 22. The reaction between the base and the precipitate 21 is discussed below with reference to Figures 1C-1D.The aqueous mixture 22 is mixed using any suitable technique as described above with reference to FIG. 1A. For example, the aqueous mixture 22 may be mixed for a period of about 5 minutes to about 2 hours. In one example, the aqueous mixture 22 is mixed for about 30 minutes.Turning now to FIG. 1C, after mixing the aqueous mixture 22, the aqueous mixture 22 may be added to a closed system 20. In one example, the closed system 20 is an autoclave. Some examples of the autoclave include a polytetrafluoroethylene-lined (e.g., TEFLON® lined) or copper-lined stainless steel autoclave. An TEFLON® lined autoclave is used at temperatures below 200°C. A copper-lined autoclave is used at temperatures at or above 200°C.The hydrothermal synthesis is performed in the closed system 20 as shown in FIG. 1C. In particular, the aqueous mixture 22 is exposed to heat and vapor pressure within the enclosed system 20 for a period of time. The temperature of the heat is in the range of about 150°C to about 200°C. The vapor pressure is in the range of about 700 psi to about 1380 psi. The heat and vapor pressure are applied for a period ranging from about 24 hours to about 48 hours. In one example, the enclosed system 20 may be heated to a temperature of about 200° C. for about 24 hours. It is believed that the vapor pressure in the closed system 20 may be about 1000 psi.As mentioned above, the aqueous mixture 22 subjected to hydrothermal synthesis contains a water-soluble product formed from the reaction of the precipitate 21 and the base 17. Application of heat and vapor pressure forms a nanostructure precursor 24 from the water-soluble product in the closed system 20. A plurality of nanostructure precursors 24 are bonded to the carbon material 19 and together the nanostructure precursors 24 form a sea urchin-like nanostructure. This sea urchin-like nanostructure has many solid SiO x- nano-rods grown radially and outward from the seeds of the carbon material 19.Generally, during the initial mixing of the aqueous mixture 22, the cation of the base 17 (e.g., Na of NaOH) is believed to be involved in a reaction with the precipitate 21 (Si(OH) 4) and thus the water soluble product (e.g.. Na 2 forms SiO 4). During hydrothermal synthesis, nucleation of a SiO x nanostructure precursor 24 from the water soluble product initiates at preferred sites (e.g., edges and depressions) on the carbon material 19. As the hydrothermal synthesis proceeds, the SiO x nanostructure precursor 24 continues to grow. It will be appreciated that during hydrothermal synthesis, a small amount of the cation from the water soluble product (and thus from base 17) is incorporated into the nanostructure precursors 24.As shown in FIG. 1D, after hydrothermal synthesis, a plurality of SiO x nanostructure precursors 24 are grown on a single particle of the carbon material 19. It is assumed that, as shown in FIG. 1D, at least a part of the nanostructure precursors 24 formed during hydrothermal synthesis are bonded to the hollow carbon 19. From the same preferred site, multiple SiO x nanostructure precursors 24 may also grow and thus may be associated with other SiO x nanostructure precursors 24. At least some of the nanostructure precursors 24 formed during hydrothermal synthesis are not associated with hollow carbon 19. In these examples, the SiO x nanostructure precursors 24 separate from the surfaces of the carbon material as the SiO x nanostructure precursors 24 grow. After the SiO x nanostructure precursors 24 separate from the surfaces of the carbon material 19, the SiO x nanostructure precursors 24 continue to grow to the sea urchin-like nanostructures.After hydrothermal synthesis, the nanostructure precursors 24 and the carbon material 19 are removed from the closed system 20 (FIG. 1D ) and an ion exchange process is performed (not shown). Ion exchange may be performed between the cation of the nanostructure precursor 24 and protons introduced into the nanostructure precursor 24. For example, and as described above, the cation of base 17 may initially react with precipitate 21 to form a water soluble product containing the cation and forming nanostructure precursor 24 during hydrothermal synthesis. Cation(s) that may have been introduced into the nanostructure precursor 24 may be exchanged with protons present in an acid, such as HCl (hydrochloric acid), introduced into the nanostructure precursors 24. For example, the nanostructure precursor 24 is removed from the closed system 20 and allowed to cool. The nanostructure precursor 24 is placed in a beaker and stirred while 1M HCl is added. Ion exchange takes place while the HCl is added. In this example, the HCl may be added until the pH reaches about 7.In a specific example of the method, NaSiO 3 ·6H 2 O is the SiO x precursor 12, and HCl is the acid 14. NaSiO 3 ·6H 2 O, and 1 M HCl are added to deionized water to form an example of solution 16. In one example, it is believed that the following reaction (I) occurs to form the precipitate 21: Na 2 SiO 3+ 2 HCl+H 2 O→Si(OH) 4( solid)+2NaCl (I)In this example, Si(OH) 4 is the precipitate 21 that is formed. The precipitate 21 is then removed from the solution 16 by vacuum filtration and washed with deionized water. The precipitate 21 can also be dried.After drying, the Si(OH) 4 precipitate 21 is added to deionized water along with NaOH as base 17 to form the aqueous mixture. When the Si(OH) 4 precipitate 21 is added along with the NaOH base 17, the components react to form the water soluble product. NaOH may be added to form a complete aqueous mixture 22 (i.e., no undissolved Si(OH) 4 precipitate 21 remains). When the Si(OH) 4 precipitate 21 is added to the base 17, the following reaction (II) occurs: Si(OH) 4+ 4 NaOH→Na 2 SiO 4( solution)+4H 2 O (II)The Na 2 SiO 4 is an example of the water-soluble product formed in the aqueous mixture 22 before the hydrothermal synthesis.In this example, hollow carbon is also added to the aqueous mixture 22 as carbon material 19. The carbon material 19 may be added prior to or after the addition or simultaneously with the precipitate 21 and / or the base 17. It should be understood that because the carbon material 19 does not react with the Si(OH) 4 precipitate 21, or the NaOH base 17, it may be added to the aqueous mixture 22 at any time during the formation of the aqueous mixture 22. After the Na 2 SiO 4 compound / water-soluble product is formed in the solution 22, the aqueous mixture 22 is introduced into the closed system 20, for example, an autoclave. Heat and vapor pressure are applied to the closed system 20 to effect the formation of the sea urchin-like SiO x- nanostructures as the nanostructure precursor 24 described above. In this particular example, HCl can be used for ion exchange to replace all cations from base 17 with protons.After the reaction(s) have occurred in the closed system 20 and the system has been used for ion exchange, it will be appreciated that the aqueous mixture 22 has been altered (indicated by reference numeral 22' in Figure 1D) and contains at least the nanostructure precursor 24 which has formed the sea urchin-like morphology as previously described. At least some deionized water is present in the aqueous mixture 22'. In some cases, other ions such as Na + or Cl - and K + or NH +, may also be present.After hydrothermal synthesis and ion exchange, the nanostructure precursor 24 may then be removed from the aqueous mixture 22' using any of the separation techniques described above with reference to FIG. 1A. After the nanostructure precursor 24 is washed, the nanostructure precursor 24 may be dried at a temperature in the range of about 60° C. to about 80° C. for a period of about 12 to about 24 hours.The dried nanostructure precursors 24 may then undergo various exemplary heat treatments to form the porous one-dimensional SiO 2- nano-rods 26 or the porous one-dimensional SiO x(0 < x<2) nano-rods 26'. The various examples of the heat treatments are labeled "1", "2", and "3" in FIGS. 1D, 1E, and / or 1F. It should be appreciated that the porous one-dimensional SiO 2- nano-rods 26 may be used as an additive in a positive electrode of a lithium-sulfur battery. Moreover, the porous one-dimensional SiO x(0 < x<2) nano-rods 26' may be used as an active material in a negative electrode of a lithium ion battery or as an active material in a pre-lithiated negative electrode of a lithium sulfur battery.Referring to FIG. 1E, in one example, a subsequent heat treatment (labeled "1") may be applied to the dried nanostructure precursors 24 (i.e., the SiO x sheets or solid nano-rods). The heat treatment 1 is a tempering process (i.e., heating followed by slow cooling of the furnace) that is performed in air or other oxygen-containing environment. The heat treatment 1 may be applied at a temperature in the range of about 250° C. to about 550° C. for a period of about 2 hours to about 5 hours. In one example, the heat treatment 1 is applied at 550 DEG C. for about 5 hours. During the heat treatment, the SiO 2- nano-rods 26 and the pores 28 are formed. In particular, the air acts as an oxidizing environment for the SiO x nanostructure precursors 24, and therefore the SiO x forms the SiO 2- nano-rods 26. Water evaporation creates three-dimensional interconnected pores 28 throughout the SiO 2- nano-rods 26. Additionally, during the heat treatment 1, the carbon material 19 is burned to leave the porous one-dimensional SiO 2- nano-rods 26 in a sea urchin-like configuration / morphology (see FIG. 6 ). The porous one-dimensional SiO 2- nano-rods 26 are connected at the center of the structure.In one example, during heat treatment 1, the following reactions (III, IV) occur between hollow carbon 19 and SiO x nanostructure precursors 24 to form porous one-dimensional SiO 2- nanostructures 26: SiO x+ O 2( from air)→SiO 2( III) C+O 2( from air)→CO 2 ≅ (IV)The SiO x nanostructure precursors 24 may be oxidized to form SiO 2 (Reaction III). As shown in the reaction (IV), the hollow carbon burns.The heat treatment 1 may be a more efficient way of obtaining SiO 2 than performing both treatments 2 and 3, for example.Referring to Figure 1F, in another example (labeled "2"), the dried nanobar precursors 24 are placed in an inert or reducing environment to prevent any undesirable side reactions with oxygen (not shown in Figure 1F). In one example, argon, nitrogen, or any other inert gas may be used to create the inert environment to avoid undesirable oxidation at elevated temperatures. As an example of a reducing environment, 10% H 2 is mixed with 90% argon or nitrogen to form a reducing environment.Once the nano-rod precursors 24 are in the inert or reducing environment, a heat treatment is applied to the nano-rod precursors 24 to form the porous one-dimensional SiO x(0 < x<2) nano-rods 26'. For example, when the inert environment is used, the carbon material 19 may act as a reducing agent during this heat treatment 2, and when the reducing environment is used, the carbon material 19 and the environment may act as a reducing agent during this heat treatment 2. In these examples, the SiO x- nanobar precursors 24 are further reduced. As such, the reaction in the inert or reducing environment results in the formation of the porous one-dimensional SiO x- nano-rods 26', where 0<x<2. The heat treatment 2 may be applied at a temperature of about 800° C. to about 1100° C. for a period of about 2 hours to about 5 hours. In one example, the heat treatment is applied at 1000° C. for 3 hours. It is believed that the following reduction reactions (V) and (VI) occur at temperatures of or above 1000°C: SiO 2+ 2 C → Si+2CO ≅ (V) SiO 2+ xC → SiO 2-x+ xCO ≅ (VI)In reactions (V) and (VI), X is 0<x<2. The carbon material 19 is the principal reducing agent in reactions (V) and (VI). The H 2- gas may in some cases participate in the reduction reactions.As mentioned above, in porous one-dimensional SiO x- nano-rods 26' 0<x<2. If it is desirable to form porous one-dimensional SiO 2- nano-rods 26 from the porous one-dimensional SiO x- nano-rods 26', an additional heat treatment 3 (from FIG. 1F to FIG. 1E ) may be performed in air or in another oxygen-containing environment. This additional heat treatment 3 in air or in another oxygen-containing environment may be performed as described hereinabove with reference to FIG. 1E. This will form the porous one-dimensional SiO 2- nano-rods 26.If the oxygen is not sufficient in the heat treatment 3, the following reaction (VII) may occur in which silicon (formed in the previous reduction step 2) is oxidized, but not enough to form porous one-dimensional SiO 2- nano-rods: 2Si + xO 2 → 2SiO x(0< x<2)(VII)It will be appreciated that x may not be stoichiometric if the O 2 is not sufficient. This results in the formation of silicon suboxide.Examples of the morphologies of the final porous one-dimensional SiO x- nano-rods 26' are shown in Figures 6 and 7. As shown in FIG. 6, a plurality of SiO x- nano-rods 26 are assembled into a sea urchin-like nanostructure. A description of how these nano-rods were formed is set forth in the Examples section. In addition, the porous one-dimensional SiO x- nano-rods 26' in the section of the examples will be further described with reference to FIG. 8. FIG. 8 illustrates the Raman spectroscopy results for the porous one-dimensional SiO x- nano-rods 26' and for a comparative example of silicon.In an example of the porous one-dimensional SiO x- nano-rods 26, 26' (0<x≤2), the three-dimensional pores 28 have a diameter within the porous one-dimensional SiO x- nano-rods 26, 26' (0<x≤2). In one example, the diameter of the pores 28 may range from about 2 nm to about 6 nm. When used in a positive electrode of a lithium-sulfur battery, the three-dimensional structure of the pores 28 substantially creates a polysulfide reservoir, thereby increasing the ability of the porous SiO 2- nano-rods 26 to trap the polysulfides in the positive electrode. When used in a negative electrode of a lithium-sulfur battery or a lithium-ion battery, the pores 28 of the porous, one-dimensional SiO x- nano-rods 26' (0<x<2) increase the mechanical strength of the active material by providing additional space that can accommodate volume expansion.FIGS. 1E and 1F show, schematically and correspondingly illustratively, porous one-dimensional SiO 2- nano-rods 26 and SiO x- nano-rods 26', respectively. Each of the porous nano-rods 26, 26' has a diameter of about 10 nm to about 100 nm. The length of each of the porous one-dimensional nano-rods 26, 26' is in the range of about 80 nm to about 3 micrometers. The diameter of the nanorod 26, 26' may decrease along its length so that the nanorod terminates at one point or has a barbed structure. It is understood that each of the porous one-dimensional nano-rods 26, 26' has a diameter much smaller than its length, thereby becoming one-dimensional. The one-dimensional structure of the nano-rods 26, 26' has a larger surface area than a metal oxide nanoparticle (which can be assumed to be zero-dimensional because it is essentially a point). In one example, the surface area of each of the porous one-dimensional nano-rods 26, 26' is in the range of about 130 m 2 / g to about 200 m 2 / g. In comparison, nanoparticles generally have a surface area in the range of greater than 0 m 2 / g to about 100 m 2 / g. As an additive in the positive electrode, the larger surface area in the examples disclosed herein provides an increased area for capture of polysulfides or transition metal cations.Additionally, and as mentioned above, the seagele-like morphology of the porous one-dimensional SiO 2 and SiO x- nano-rods 26 and 26' provides a larger void between the individual nano-rods. As such, the sea urchin-like composite porous one-dimensional SiO x- nano-rods 26' are capable of absorbing volume expansion during lithiating to reduce mechanical degradation of the active material in the negative electrode. In some cases, the porous one-dimensional nano-rods 26' may increase the mechanical strength of the negative electrode compared to a negative electrode made with metal oxide nano-particles.During the fabrication of the positive or negative electrode, some of the porous one-dimensional nano-rods 26, 26' may fragment from the sea urchin-like nanostructure into individual nano-rods. When this occurs, the coating quality of a mixture containing the one-dimensional nano-rods 26, 26' can be improved because at least some of the nano-rods 26, 26' can deposit laterally over a surface of a current collector to which the mixture is applied during electrode formation. This alignment increases the mechanical strength of the resulting electrode.In some cases, the porous one-dimensional nano-rods 26 26' may be doped. Doping may be undesirable when a stiffer structure is desired. In one example, the dopant may be added by a subsequent hydrothermal synthesis process. Alternatively, the dopant may be added to the solution 22 during the initial hydrothermal synthesis. In this example, a subsequent hydrothermal synthesis process would not be used. As an example of the subsequent hydrothermal synthesis process, the porous nano-rods 26, 26' are added to an acid or deionized water containing the dopant. This mixture is sealed in the closed system 20, such as a TEFLON® lined stainless steel autoclave. The mixture is then subjected to a further hydrothermal treatment at a temperature in the range of about 150° C. to about 200° C. for a period in the range of about 12 hours to about 24 hours.In one example, the dopant is present in the acid or water in an amount ranging from about 0.01 mol % to about 1 mol %. The dopant is selected from the group consisting of chromium ions, vanadium ions, zirconium ions, niobium ions, yttrium ions, silicon ions and lanthanum ions. It is believed that adding a dopant to the porous one-dimensional nano-rods 26, 26' increases electrical conductivity and further stabilizes the structure of the porous one-dimensional nano-rods 26, 26'.After obtaining the porous one-dimensional SiO 2- nano-rods 26, the porous one-dimensional SiO 2- nano-rods 26 may be added as an additive to a positive electrode composition of a lithium-sulfur battery. The positive electrode composition contains at least one active material. This will be described in more detail with reference to Fig. 2.An example of the method for manufacturing a positive electrode 40' of a lithium-sulfur battery 500 (see FIG. 5 ) will now be discussed with reference to FIG. 2. FIG. 2 shows an example of a positive electrode 40' including a sulfur-based active material 31, a binder 32, a conductive filler 34, and the porous one-dimensional SiO 2- nano-rods 26 as an additive on a support 38.In the examples for manufacturing the positive electrode 40', the one-dimensional SiO 2- nano-rods 26 are selectively mixed with other positive electrode components in deionized water or an organic solvent depending on the binder 32 to form a dispersion or mixture. It should be understood that the one-dimensional SiO 2- nano-rods 26 are not embedded within the other positive electrode components.The sulfur-based active material 31 may be any material that sufficiently alloys and dealloys lithium with aluminum or other suitable current collector that functions as the positive end of the lithium-sulfur battery 500. An example of the sulfur-based active material 31 may be a sulfur-carbon composite. In one example, the amount of sulfur in the sulfur-carbon composite ranges from about 20% to about 95% by weight.As mentioned above, the sulfur-based active material 31 may be mixed with the binder 32 and the conductive filler 34. Suitable binders 32 include carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), styrene butadiene rubber carboxymethyl cellulose (SBR CMC), polyacrylic acid (PAA), cross-linked polyacrylic acid-polyethyleneimine, polyvinyl alcohol (PVA), polyimide, poly(acrylamide-co-diallyl dimethyl ammonium chloride), sodium alginate, polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), an ethylene propylene diene monomer (EPDM) rubber, or other water soluble or organic solvent based binders.The binder 32 structurally holds the sulfur-based active material 31 and the conductive filler 34 together.An example of the conductive filler 34 is a high surface area carbon such as acetylene black or activated carbon. Other examples of suitable conductive fillers 34 include graphene, graphite, carbon nanotubes, and / or carbon nanofibers. The conductive filler 34 provides electron conduction between the positive-side current collector 38 and the sulfur-based active material 31 in the positive electrode 40'. In one example, the positive electrode 40' may also be encapsulated in hollow carbon.In one example, the porous one-dimensional SiO 2- nano-rods 26 are mixed with the binder 32, the conductive filler 34, and the sulfur-based active material 31. All components can be mixed manually by dry milling. After all the components have been milled together, water or organic solvent (depending on the binder used 32) is added to the milled components to form the dispersion / mixture. In one example, the solvent is a polar aprotic solvent. Examples of suitable polar aprotic solvents are dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO) or another Lewis base or combinations thereof. When a water soluble binder such as sodium alginate is used, the solvent may be water. The dispersion / mixture can be mixed by milling. Milling aids in the conversion of the dispersion / mixture to a spreadable slurry. Low shear milling or high shear milling may be used to mix the dispersion / mixture. The milling time of the dispersion / mixture ranges from about 10 minutes to about 20 hours depending on the shear rate. In one example, a rotor mixer is used for about 20 minutes at about 2000 revolutions per minute to grind the dispersion / mixture.In an example of the dispersion / mixture, the amount of sulfur-based active material 31 is in the range of about 50% to about 95% by weight (based on total solids % by weight in the dispersion / mixture), and the amount of conductive filler 34 is in the range of about 5% to about 20% by weight (based on total solids % by weight in the dispersion / mixture), the amount of binder 32 in the range of about 5 wt % to about 20 wt % (based on the total solids wt % in the dispersion / mixture) and the amount of porous one-dimensional SiO 2- nano-rods 26 in the range of more than 0 wt % to about 2 wt % (based on the total solids wt % in the dispersion / mixture).The slurry is then applied to the support 38. In one example, the carrier 38 is the positive side current collector. It should be appreciated that the carrier 38 may be formed of aluminum or other suitable electrically conductive material known to those skilled in the art. The carrier 38 that is selected should be capable of collecting free electrons and moving them from and to an external circuit connected thereto.The slurry may be deposited using any suitable technique. For example, the slurry may be poured onto the surface of the support 38, or may be spread on the surface of the support 38, or may be coated on the surface of the support 38 using a slot die.The deposited slurry may be subjected to a drying process to remove any remaining solvent. Drying may be carried out using any suitable technique. For example, drying is carried out at ambient conditions (i.e., at room temperature about 18°C to 22°C and 1 atmosphere). Drying may be carried out at an elevated temperature in the range of about 50°C to about 80°C. In some examples, vacuum may also be used to speed the drying process. As an example of the drying process, the deposited slurry may be exposed to ambient drying for about 12 to about 24 hours, followed by vacuum drying at about 70° C. for about 20 minutes to about 1 hour.The drying process results in a coating formed on the surface of the support 38. This coating is the positive electrode 40'. In one example, the thickness of the dried slurry (i.e., the positive electrode 42) is in the range of about 5 μm to about 200 μm. In another example, the thickness of the dried slurry (i.e., positive electrode 40') is in the range of about 10 μm to about 100 μm.During the formation of the positive electrode 40', the water and / or the organic solvent(s) is / are removed and so the resulting positive electrode 50 comprises from about 50 wt % to about 95 wt % (based on the total wt % of the positive electrode 40') of the active material(s) 31, from about 5 wt % to 20 wt % (based on the total wt % of the positive electrode 40') of the conductive filler 34, from about 5 wt % up to 20 wt % (based on the total wt % of the positive electrode 40') of the binder 32, and from greater than 0 wt % up to about 2 wt % (based on the total wt % of the positive electrode 40') of the porous one-dimensional SiO 2- nano-rods 26.Referring to FIG. 3, the porous one-dimensional SiO x(0< x<2) nano-rods 26', which may optionally contain a dopant 30, may be added as an active material to a negative electrode composition of a lithium ion battery 400 (shown in FIG. 4) or a lithium sulfur battery 500 (shown in FIG. 5). It should be appreciated that the porous one-dimensional SiO x(0 < x<2) nano-rods 26' formed by the methods disclosed herein can be used individually or in combination as the active material in the negative electrodes 50, 50', respectively. When used in the negative electrode 50 of the lithium ion battery 400, the porous one-dimensional SiO x(0 < x<2) nano-rods 26' may be used as formed in the methods disclosed herein. When used in the negative electrode 50 of the lithium-sulfur battery 500, the negative electrode 50 (and thus the porous one-dimensional SiO x(0 < x<2) nano-rods 26') may be subjected to pre-lithography to form porous one-dimensional silicide nano-rods 26". Fig. 3 illustrates an example of the negative electrode 50' containing the active material 26', the binder 32, and the conductive filler 34 on the support 36, and an example of the negative electrode 50 containing the active material 26", a binder 32, and a conductive filler 34 on a support 36.In the examples for making the negative electrode 50', the active material 26' and / or 26" is mixed with other negative electrode components to form a dispersion or slurry. Examples of the other negative electrode components may include the binder 32 and the conductive filler 34.Examples of the binder 32 and the filler 34 include those materials previously disclosed herein with reference to FIG. 2 for the positive electrode 40' of the lithium-sulfur battery 500. The porous one-dimensional SiO x(0 < x<2) nano-rods 26' may be mixed as the active material with the binder 32 and the conductive filler 34 using the same method as disclosed hereinabove with reference to FIG. 2 for the positive electrode 40' of the lithium-sulfur battery 500.In an example of the dispersion / mixture, the amount of active material 26' is in the range of about 50% to about 95% by weight (based on total solid weight % of the dispersion / mixture), conductive filler 34 from about 5% to 20% by weight (based on total solid weight % of the dispersion / mixture), and binder 32 from about 5% to 20% by weight (based on total solid weight % of the dispersion / mixture).The slurry is then deposited onto the support 36. In one example, the carrier 36 is the negative side current collector. It should be appreciated that the carrier 36 may be formed of copper or any other suitable electrically conductive material known to those skilled in the art. The selected carrier 36 should be capable of collecting free electrons and moving them to and from an external circuit.The slurry is applied and dried by the same methods as disclosed hereinabove with reference to Figure 2 for the positive electrode 40' of the lithium-sulfur battery 500.The drying process results in a coating formed on the surface of the carrier 36. This coating is the negative electrode 50'. In one example, the thickness of the dried slurry (i.e., the negative electrode 50') is in the range of about 5 μm to about 200 μm. In another example, the thickness of the dried slurry (i.e., the negative electrode 50') is in the range of about 10 μm to about 100 μm.During formation of the negative electrode 50', the water and / or organic solvent(s) is / are removed and thus the resulting negative electrode 50' comprises from about 50 wt % to about 95 wt % (based on the total wt % of the positive electrode 50') of the active material(s) 26', from about 5 wt % to 20 wt % (based on the total wt % of the positive electrode 50') of the conductive filler 34, and from about 5 wt % to 20 wt % (based on the total wt % of the positive electrode 50') of the binder 32.The negative electrode 50' can be used as is in the lithium ion battery 400, or it can be prelithiated as described below with reference to the negative electrode 50.The negative electrode 50 is particularly suitable for the lithium-sulfur battery 500 because the negative electrode 50 is subjected to the pre-lithography that converts the porous one-dimensional SiO x(0 < x<2) nano-rods 26' (which is an additive capable of capturing polysulfides) into porous one-dimensional silicide nano-rods 26" (which is an active material that can improve the ion transport). The porous one-dimensional silicide nano-rods 26" are believed to have a faster lithium ion diffusion rate compared to active silicon materials having a zero-dimensional particle morphology. This is believed to be due in part to the one-dimensional morphology with a shorter diffusion length.The negative electrode 50 can be prepared using the i) techniques described above for the negative electrode 50', ii) binder 34 and conductive filler 32 and iii) amounts.Prior to use as the negative electrode 50' in the lithium-sulfur battery 500 (FIG. 5), the example of the negative electrode 50 disclosed herein is prelithiated to convert the porous one-dimensional SiO x(0 < x<2) nano-rods 26' into the active material 26". In one example, the active material 26" that is formed includes porous one-dimensional silicide nano-rods 26". An example of the silicide nano-rods 26" is lithium silicide (Li 4,4 Si) nano-rods 26". It is believed that during lithiating, a series of phase transitions occur to form the silicide nano-rods 26". It is assumed that amorphous Li x Si may be formed first during these phase transitions. Then, while further lithium is added during the pre-lithiating, amorphous Li x Si crystallizes to form Li 22 Si 5( i.e., Li 4,4 Si).In one example, the negative electrode 50 is pre-lithiated using a lithium-silicon (Li-Si) half-cell process. More specifically, the Li-Si half cell is assembled using the silicon-based negative electrode 50. The Li-Si half cell is impregnated in a prelithiated electrolyte.Examples of the prelithiated electrolyte include lithium metal or a lithium salt dissolved in a solvent or solvent mixture. For example, the lithium salt may be LiPF 6, LiB 4, LiClO 4, LiN(SO 2 CF 3)2( LiTFSI, or (lithium bis(trifluoromethanesulfonyl)imide)), LiB(C 2 O 4)2( LiBO), LiF 2( C 2 O 4) ( LiODFB), LiPF 4( C 2 O 4) ( LiFOP), LiNO 3, LiN(SO 2 F) 2( LiFSI), LiPF 3( C 2 F 5)3( LiFAP), LiPF 4( CF3)2, LiPF3(CF3)3, and combinations thereof. In one example, the lithium salt in the electrolyte for pre-lithiating is 1M LiPF6.In one example, the lithium salt or lithium metal is dissolved in a solvent mixture of dimethoxyethane (DME) and fluoroethylene carbonate (FEC). The volume ratio of solvents (DME FEC) is in the range of 10 to 1 to 1 to 10. In one example, the volume ratio of DME to FEC is 3 to 1. it was found that the use of FEC as a co-solvent during the pre-lithiating process forms a desirable solid electrolyte intermediate phase layer (SEI) (not shown in FIG. 4 ) on the exposed surface(s) of the silicon-based negative electrode 50. The FEC is active and easily decomposes during the pre-lithiating to form the SEl layer. In another example, diethylene glycol (DEC) and FEC may be used as a solvent mixture to dissolve the lithium metal. The volume ratio of these solvents (DEC FEC) is also in the range of 10 to 1 to 1 to 10.A voltage potential is applied to the half cell, which decomposes at least some components in the electrolyte. The decomposition product deposits on the exposed surface(s) of the negative electrode 50 to form the SEl layer. The decomposition product may be LiF, Li 2 CO 3, Li x PF y O z, F-substituted lithium ethylene dicarbonate (F-LEDC), an unsaturated polyolefin, etc. The voltage potential is applied for a time sufficient to form the SEl layer. In one example, the application time may be shorter when a higher current is used. Similarly, the application time may be shorter when a lower current is used. The SEI layer may have a thickness of about 10 nm or less.In another example, the negative electrode 50' can be prelithiated by briefly shorting lithium and silicon with the previously described prelithiated electrolyte therebetween. This can be accomplished for a period of time ranging from about 1 hour to about 24 hours.During the pre-lithiating, lithium ions are dissolved (or ablated) from the lithium metal and are capable of diffusing into the negative electrode 50, thereby lithiating the negative electrode 50. The lithium ions can react with the porous one-dimensional SiO x(0 < x<2) nano-rods 26' to form porous one-dimensional silicide nano-rods 26". When the pre-lithiating is completed, the lithiated negative electrode 50 may be rinsed to remove any remaining pre-lithiated electrolyte, and then used in the lithium-sulfur battery 500 (FIG. 5 ).Referring to FIG. 4, the lithium ion battery 400 is illustrated. The lithium ion battery 400 in FIG. 4 includes the negative electrode 50' wherein the porous one-dimensional SiO x(0 < x<2) nano-rods 26' are the active material.As shown in FIG. 4, the lithium ion battery 400 includes, in addition to the negative electrode 50' and the negative-side current collector 36, a positive electrode 40, a positive-side current collector 38, and a porous separator 42 positioned between the negative electrode 50' and the positive electrode 40.In FIG. 4, the positive electrode 40 may be formed of any lithium-based active material that can sufficiently in- and out-deposit lithium, while aluminum or other suitable current collector 38 functions as the positive end of the lithium-ion battery 400. A common class of known lithium-based materials suitable for positive electrode 40 includes layered lithium transition metal oxides. Some specific examples of the lithium-based active materials include lithium manganese oxide spinel (LiMn 2 O 4), lithium cobalt oxide (LiCoO 2), nickel manganese spinel [Li(Ni 0,5 Mn 1,5) O 2], a layered nickel manganese cobalt oxide [Li(Ni x Mn y Co z) O 2 or Li(Ni x Mn y Co z) O 4 or a lithium iron polyanion oxide such as lithium iron phosphate (LiFePO 4) or lithium iron fluorophosphate (Li 2 FePO4F). Other lithium-based active materials may also be used, such as LiNi x M 1-x O 2( M is comprised of any ratio of Al, Co, and / or Mg), aluminum-stabilized lithium manganese oxide spinel (Li x Mn 2x Al y O 4), lithium vanadium oxide (LiV 2 O 5), Li 2 MSiO4(M is comprised of any ratio of Co, Fe, and / or Mn), xLi 2 MnO 3-(1-x) LiMO 2( M is composed of any ratio of Ni, Mn and / or Co) and any other highly efficient nickel-manganese-cobalt material. By "any ratio" is meant that each element may be present in any amount. For example, M could be Al with or without Co and / or Mg, or any other combination of the stated elements.The lithium-based positive electrode active material 40 may be mixed with the polymeric binder 34 and the high surface area carbon (i.e., the conductive filler 32). Some examples of suitable binders are polyvinylidene fluoride (PVDF), an ethylene propylene diene monomer (EPDM) rubber, water-based sodium alginate and / or carboxymethylcellulose (CMC)). The polymeric binder 34 structurally holds the lithium-based active materials and the high surface area carbon together. An example of the high surface area carbon is acetylene black. The high surface area carbon ensures electron conduction between the positive-side current collector 38 and the positive-electrode active material particles 40.The positive side current collector 38 may be formed of aluminum or other suitable electrically conductive material known to those skilled in the art.The porous separator 42 in Fig. 4, which functions as both an electrical insulator and a mechanical support, is disposed between the negative electrode 50' and the positive electrode 40 to prevent the physical contact between the two electrodes 50', 40 and the occurrence of a short circuit. In addition to providing a physical barrier between the two electrodes 50', 40, the porous separator 42 ensures the passage of lithium ions (indicated by the black dots in Figure 4 and the open circles with a (+) charge) and associated anions (indicated by the open circles with a (-) charge in Figure 4) through an electrolyte solution filling its pores. This helps to ensure that the lithium ion battery 400 is functioning properly.The porous separator 42 may be a polyolefin membrane. The polyolefin may be a homopolymer (derived from a single monomer constituent) or a heteropolymer (derived from more than one monomer constituent) and may be either linear or branched. When a heteropolymer derived from two monomeric constituents is used, the polyolefin may take any copolymer chain arrangement including those of a block copolymer or a random copolymer. The same applies if the polyolefin is a heteropolymer derived from more than two monomer constituents. For example, the polyolefin membrane can be formed from polyethylene (PE), polypropylene (PP), a mixture of PE and PP or multilayer-structured porous films of PE and / or PP.In other examples, the porous separator 44 may be formed of another polymer selected from polyethylene terephthalate (PET), polyvinylidene fluoride (PVdF), polyamides (nylons), polyurethanes, polycarbonates, polyesters, polyetheretherketones (PEEK), polyethersulfones (PES), polyimides (PI), polyamideimides, polyethers, polyoxymethylene (e.g., acetal), polybutylene terephthalate, polyethyleneenaphthenate, polybutene, acrylonitrile-butadiene-styrene copolymers (ABS), polystyrene copolymers, polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polysiloxane polymers (such as polydimethylsiloxane (PDMS)), polybenzimidazole (PBI), polybenzoxazole (PBO), Polyphenylenes (e.g., ParmaxTM(Mississippi Polymer Technologies, Inc., Bay Saint Louis, Mississippi)), polyarylene ether ketones, polyperfluorocyclobutanes, polytetrafluoroethylene (PTFE), polyvinylidene fluoride copolymers and terpolymers, polyvinylidene chloride, polyvinyl fluoride, liquid crystalline polymers (e.g., VECTRANTM(Hoechst AG, Germany), ZENITE® (DuPont, Wilmington, DE), poly(p-hydroxybenzoic acid), polyaramides, polyphenylene oxide, and / or combinations thereof. In yet another example, the porous separator 42 may be selected from a combination of the polyolefin (such as PE and / or PP) and one or more of the polymers listed above.The porous separator 42 may include a single layer or a multilayer laminate made from either a dry or a wet process. For example, a single layer of polyolefin and / or other listed polymers may represent the entirety of the porous separator 42. However, as another example, multiple discrete layers of similar or dissimilar polyolefins and / or polymers may be assembled in the porous separator 42. In one example, a discrete layer of one or more of the polymers may be coated onto a discrete layer of the polyolefin to form the porous separator 42. Additionally, the polyolefin (and / or other polymer) layer and other optional polymer layers may be additionally provided in the porous separator 42 as a fiber layer to help provide the porous separator 42 with the appropriate structural and porosity characteristics. Still other suitable porous separators 42 include those having a ceramic layer affixed thereto and those having ceramic filler in the polymer matrix (i.e., an organic-inorganic composite matrix).Any suitable electrolyte solution that can conduct lithium ions between the negative electrode 50' and the positive electrode 40 can be used in the lithium ion battery 400. In one example, the electrolyte solution may be a non-aqueous liquid electrolyte solution containing a lithium salt dissolved in an organic solvent or a mixture of organic solvents. Those skilled in the art are aware of the many non-aqueous liquid electrolyte solutions that can be used in the lithium ion battery 400, as well as how they can be prepared or commercially purchased. Examples of lithium salts that may be dissolved in an organic solvent to form a non-aqueous liquid electrolyte solution include LiClO 4, LiAlCl 4, LiI, LiBr, LiSCN, LiF 4, LiB(C 6 H 5)4, LiCF 3 SO 3, LiN(FSO 2)2( LIFSI), LiN(CF 3 SO 2)2( LITFSI), LiAsF6, LiPF 6, LiB(C 2 O 4)2( LiBO), LiB 2( C 2 O 4) ( LiODFB), LiPF 4( C 2 O 4) ( LiFOP), LiNO 3 and mixtures thereof. These and other similar lithium salts can be dissolved in a variety of organic solvents, such as cyclic carbonates (ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate), linear carbonates (dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate), aliphatic carboxylic esters (methyl formate, methyl acetate, methyl propionate), γ-lactones (γ-butyrolactone, γ-valerolactone), chain structure ethers (1,2-dimethoxyethane, 1-2-diethoxyethane, ethoxymethoxyethane, tetraglyme), cyclic ethers (tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane), and mixtures thereof.As shown in FIG. 4, the lithium ion battery 400 also includes an interruptible external circuit 46 that connects the negative electrode 50' and the positive electrode 40. The lithium ion battery 400 may also support a load device 44 operatively connected to the external circuit 46. The load device 44 is supplied with electric energy from the electric current flowing through the external circuit 46 when the lithium ion battery 400 is discharged. While the load device 44 may be any number of known electrically powered devices, some specific examples of a power-consuming load device 44 include an electric motor for a hybrid vehicle or for a pure electric vehicle, a laptop, a cellular phone, and a cordless power tool. However, the load device 44 may be an electric current generating device that charges the lithium ion battery 400 to store energy. For example, the tendency of windmills and solar collectors to generate current variably and / or periodically often results in a need to store excess energy for later use.The lithium ion battery 400 may also include a variety of other components, which, although not shown herein, are nevertheless known to those skilled in the art. For example, the lithium-sulfur battery 100 may include a housing, gaskets, terminals, lids, and other desirable components or materials that may be disposed between or around the negative electrode 50' and the positive electrode 40 for performance or other practical purposes. Moreover, the size and shape of the lithium ion battery 400, as well as the design and chemical composition of its major components, may vary depending on the particular application for which it is designed. Battery-powered automobiles and portable electronic devices are, for example, two cases where the lithium ion battery 400 is most likely to be designed for various sizes, capacities, and power output specifications. The lithium ion battery 400 may also be connected in series and / or in parallel with other similar lithium ion batteries 400 to generate a higher output voltage and current (when connected in parallel) or a higher voltage (when connected in series) when the load device 44 so requires.The lithium ion battery 400 generally operates by reversibly transferring lithium ions between the negative electrode 50' and the positive electrode 40. In the fully charged state, the voltage of the battery 400 is at a maximum (typically in the range of 2.0V to 5.0V); whereas in the fully discharged state, the voltage of the battery 400 is at a minimum (typically in the range of 0V to 2.0V). The Fermi energy levels of the active materials in the positive and negative electrodes 40, 50' vary substantially in battery operation, as does the difference between the two, known as the battery voltage. The battery voltage decreases during discharge, with the Fermi levels getting closer and closer together. During charging, the reverse process occurs, with the battery voltage increasing as the Fermi levels are driven apart. During battery discharge, the external load device 44 allows an electric current to flow in the external circuit 46 in a direction such that the difference between the Fermi levels (and correspondingly the cell voltage) decreases. The reverse occurs during charging of the battery: the battery charger forces an electric current to flow in the external circuit 46 in a direction such that the difference between the Fermi levels (and correspondingly the cell voltage) increases.At the beginning of a discharge, the negative electrode 50' of the lithium ion battery 400 contains a high concentration of incorporated lithium, while the positive electrode 40 is relatively exhausted. If the negative electrode 50' contains a sufficiently higher relative amount of incorporated lithium, the lithium-ion battery 400 can generate a useful electrical current via reversible electrochemical reactions that occur when the external circuit 46 is closed to connect the negative electrode 50' and the positive electrode 40. The configuration of the external closed circuit will under such circumstances cause the extraction of intercalated lithium from the negative electrode 50'. The extracted lithium atoms are split into lithium ions (identified by the black dots and by the open circles with a (+) charge) and electrons (e -) while leaving the intercalation host at the negative electrode electrolyte interface.The chemical potential difference between the positive electrode 40 and the negative electrode 50' (in the range of about 2.0 V to about 5.0 V, depending upon the exact chemical composition of the electrodes 50', 40) drives the electrons (e -) produced by the oxidation of intercalated lithium at the negative electrode 50' through the external circuit 46 toward the positive electrode 40. The electrons (e -) flowing through the external circuit 46 and the lithium ions in the electrolyte solution migrating through the porous separator 42 finally coalesce to form intercalated lithium at the positive electrode 40. The electrical current flowing through the external circuit 46 may be conducted through the load device 44 and utilized until the level of incorporated lithium in the negative electrode 50' drops below a durable level or the need for electrical energy ends.The lithium ion battery 400 may be charged after partial or complete discharge of its available capacity. To charge the lithium ion battery 400, an external charger is connected to the positive and negative electrodes 40, 50' to drive the electrochemical reactions reverse to the battery discharge. During recharging, the electrons (e -) flow back through the external circuit 46 toward the negative electrode 50' and the lithium ions are carried by the electrolyte back through the porous separator 42 toward the negative electrode 50. The electrons (e -) and lithium ions are merged again at the negative electrode 50', thereby replenishing them with intercalated lithium for consumption during the next battery discharge cycle.The external battery charger that may be used to charge the lithium ion battery 400 may vary depending on the size, construction, and particularly the use of the lithium ion battery 400. Some suitable external chargers include a battery charger plugged into a power outlet and an automobile alternator.Referring to FIG. 5, the lithium-sulfur battery 500 includes the positive electrode 40' with the porous one-dimensional SiO 2- nano-rods 26 as an additive. The lithium-sulfur battery 500 also includes the negative electrode 50, the negative-side current collector 36, a positive-side current collector 38, and a porous separator 42 positioned between the negative electrode 50 and the positive electrode 40'.It should be appreciated that the porous separator 42 may be the same type of porous separator 42 used in a lithium ion battery 400 described herein. In addition, the negative current collector 36 and positive current collector 38 described herein for the lithium ion battery 400 may also be used in the lithium-sulfur battery 500.The electrolyte solution for the lithium-sulfur battery 500 includes an ether-based solvent and a lithium salt dissolved in the ether-based solvent. Examples of the ether-based solvent include cyclic ethers such as 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, and chain structure ethers such as 1,2-dimethoxyethane, 1-2-diethoxyethane, ethoxymethoxyethane, tetraethylene glycol dimethyl ether (TEGDME), polyethylene glycol dimethyl ether (PEGDME), and mixtures thereof. Examples of the lithium salt include LiClO 4, LiAlCl 4, LiI, LiBr, LiSCN, LiF 4, LiB(C 6 H 5)4, LiAsF 6, LiCF 3 SO 3, LiN(FSO 2)2( LIFSI), LiN(CF 3 SO2)2(LiTFSl), LiB(C 2 O 4)2( LiBO), LiF 2( C 2 O 4) ( LiODFB), LiPF 4( C 2 O 4) ( LiFOP), LiNO 3, LiPF 6 and mixtures thereof.The negative electrode 50 for the lithium-sulfur battery 500 may include any active material that provides a sufficient lithium source for lithium redox reactions and does not react with the current collector. In one example, the current collector may be copper or another suitable current collector that serves as the negative terminal of the lithium-sulfur battery 500. Examples of active materials include the porous, one-dimensional silicide nano-rods 26" (as shown in Figure 5), lithium metal (alone or encapsulated in carbon), or lithiated silicon. The other components for the negative electrode 50 have been described above with reference to FIG. 3.The positive and negative electrodes 40', 50 are in contact with the corresponding current collectors 38, 36, respectively. the negative-side current collector 36 collects and moves free electrons to and from the external circuit 46. the positive-side current collector 38 collects and moves free electrons to and from the external circuit 46.The lithium-sulfur battery 500 may support a load device 44, which may be operatively connected to the external circuit 46. The load device 44 receives supply of electric energy from the electric current flowing through the external circuit 46 when the lithium-sulfur battery 400 is discharged. While the load device 44 may be any number of known electrically powered devices, some specific examples of a power-consuming load device include an electric motor for a hybrid vehicle or for a fully electric vehicle, a laptop, a cellular phone, and a wireless electric tool. However, the load device 44 may also be an electric current generating device that charges the lithium-sulfur battery 500 for the purpose of storing energy. For example, the tendency of windmills and solar collectors to generate current variably and / or periodically often results in a need to store excess energy for later use.The lithium-sulfur battery 500 may include a variety of other components, which, although not shown herein, are nevertheless known to those skilled in the art. For example, the lithium-sulfur battery 500 may include a housing, gaskets, terminals, lids, and other desirable components or materials that may be disposed between or around the negative electrode 50 and the positive electrode 40' for performance or other practical purposes. Moreover, the size and shape of the lithium-sulfur battery 500, as well as the design and chemical composition of its major components, may vary depending on the particular application for which it is designed. Battery-powered automobiles and portable electronic devices are, for example, two cases where the lithium-sulfur battery 500 is most likely to be designed for various size, capacity, and power output specifications. The lithium-sulfur battery 500 may also be connected in series and / or in parallel with other similar lithium-sulfur batteries 500 to generate a higher output voltage and current (when connected in parallel) or a higher voltage (when connected in series) when the load device 44 so requires.The lithium-sulfur battery 500 may generate a useful electric current during discharge of the battery (shown by reference numeral 48 in FIG. 5 ). During discharge, the chemical processes in the battery 500 include dissolution of lithium (Li+) from the surface of the negative electrode 50 and incorporation of the lithium cations into alkali metal polysulfide salts (i.e., Li 2 S) into the positive electrode 40'. As such, polysulfides (sulfur is reduced) are sequentially formed on the surface of the positive electrode 40' while the battery 500 is discharged. The chemical potential difference between the positive electrode 40' and the negative electrode 50 (depending on the exact chemical structure of the electrodes 50, 40' in the range of about 1.5 to 3.0 volts) drives the electrons generated by the dissolution of lithium at the negative electrode 50 through the external circuit 46 to the positive electrode 40'. The resulting electrical current flowing through the external circuit 46 may be utilized and passed directly through the load device 44 until the lithium in the negative electrode 50 has been depleted and the capacity of the lithium-sulfur battery 500 has decreased.The lithium-sulfur battery 500 may be charged or re-energized at any time by applying an external power source to the lithium-sulfur battery 500 to reverse the electrochemical reactions occurring during the discharge of the battery. During the charging process (shown by the reference numeral 49 in FIG. 5), deposition of lithium occurs on the negative electrode 50 and sulfur formation occurs on the positive electrode 40'. The connection of an external power source to the lithium-sulfur battery 500 forces the otherwise non-spontaneous oxidation of lithium at the positive electrode 40' to produce electrons and lithium ions. The electrons flowing through the external circuit 46 back toward the negative electrode 50 and the lithium ions (Li+) carried by the electrolyte via the porous membrane 42 back toward the negative electrode 50 re-coalesce at the negative electrode 50 and fill it with lithium for consumption during the next battery discharge cycle. The external power source that can be used to charge the lithium-sulfur battery 500 may vary depending on the size, design, and particularly the end use of the lithium-sulfur battery 500. Some suitable external power sources include a battery charger plugged into a power outlet and an alternator of a motor vehicle.Examples are provided herein to further illustrate the present disclosure. It is to be understood that these examples are provided for purposes of illustration and are not to be taken as limiting the scope of the disclosure.EXAMPLESExample 1Porous SiO x- nano-rods are prepared according to an example disclosed herein. A precipitate of H 4 SiO 4 was prepared by adding Na 2 SiO 3 ·6H 2 O, and 1M HCl to deionized water. the H 2 SiO 3 precipitate was filtered, washed, and dried.About 3 grams of H 4 SiO 4- nanoparticles having an average diameter in the range of about 30 nm to about 200 nm are added to 20 ml of deionized water, 60 ml of 1 M NaOH, and 0.03 g of hollow carbon to form a solution having the hollow carbon dispersed therein. The solution is introduced into a TEFLON® lined stainless steel autoclave. The process parameters for hydrothermal synthesis include exposing the solution to a temperature of 200°C for about 24 hours. The pressure in the autoclave during hydrothermal synthesis is believed to be about 1000 psi. At the end of the 24 hour period, the reaction product is removed from the autoclave. Ion exchange is performed on the reaction product using a 1M HCl solution until a pH of about 7 is obtained. After ion exchange, the reaction product is filtered, washed and dried to obtain the nanostructure precursors, SiO x sheets / nano-rods. The nanostructure precursor includes the SiO x sheets / nano-rods assembled into a sea urchin-like nanostructure, wherein each SiO x sheet / SiO x nano-rod has an average length of 200 nm to about 5 μm and an average diameter of about 20 nm to about 200 nm.The sea urchin-like nanostructures with the hollow carbon composite are then subjected to annealing at 1000° C. for about 3 hours in a reducing environment of 10% H 2 and 90% Ar. During the heat treatment, the hollow carbon is removed, the SiO x sheets are further reduced to a form of SiO x where x<2. The removed hollow carbon is oxidized to form carbon monoxide, which is also produced as a byproduct in the heat treatment. The annealing reactions are shown in reactions (V) and (VI) described herein.However, the porous silicon or porous SiO x rods formed during annealing may not be heated in an oxygen-containing environment (e.g., air). During this treatment, the silicon or SiO x would be oxidized to form SiO x(0 < x≤2) (e.g., 2Si+xO 2 → 2SiO x(0< x≤2). When the porous one-dimensional SiO x- nano-rods are used as an active material in the negative electrode of a lithium-sulfur or lithium-ion battery, this heat treatment is undesirable because SiO x is a suitable active material. If the porous one-dimensional SiO x- nano-rods were used as an additive in the positive electrode, the SiO x would be oxidized until SiO 2 is formed. In this particular example, the resulting product was porous SiO x- nano-rods, where 0<x<2, and this product was not subjected to additional heating. Therefore, the porous one-dimensional SiO x- nano-rods were used as an active material in a negative electrode. The SiO x- nano-rods were confirmed by Raman spectroscopy.A TEM image of the porous SiO x- nano-rods 26' was taken. These are shown in Figures 6 and 7 and clearly illustrate the morphology of the porous one-dimensional nano-rods 26'. As shown in FIG. 6, the porous SiO x sheets / nano-rods 26' are joined together and resemble a sea urchin. The dimensions of the porous one-dimensional nano-rods 26' can be measured using the TEM image.Raman spectroscopy results were obtained for the porous one-dimensional SiO x- nano-rods 26' (labeled 1) and for comparison and for a pure silicon wafer (labeled 2). These results are shown in Fig. 8. FIG. 8 shows the diffraction intensity (number) (Y axis with the designation "L") versus the wave number (cm -1) ( X axis with the designation "cm -1"). The plot shows the presence of SiO x, as the line is shifted from the results for the pure silicon. The value of x in SiO x can be determined using neutron diffraction.Example 2The porous one-dimensional SiO x- nano-rods of Example 1 are integrated into a negative electrode as an active material. The example negative electrode contains about 60% of the active material, about 20% of a binder, and about 20% of a conductive filler.To form the example negative electrode, the respective components are mixed in deionized water to form a dispersion / mixture. More specifically, the dispersion / mixture contains about 120 mg of the porous one-dimensional SiO x- nano-rods as the active material, 40 mg sodium alginate as the binder, 40 mg of Super P®Li carbon black as the conductive filler, and 2.5 g (or 2.5 ml) of deionized water. The dispersions / mixtures are hand milled and then mixed with a rotor mixer at 2000 rpm for 20 minutes to form a coatable slurry. The slurry is coated on a copper current collector using a bar coater. The electrode coating is air dried overnight at room temperature and then dried in vacuoat about 60°C for about 30 minutes.The example negative electrode is used together with a lithium metal negative electrode to construct lithium ion battery half cells. Button cells (2032 hardware) are assembled in an Ar-filled glovebox. Microporous three-layer polypropylene (PP) and polyethylene (PE) polymer membranes (Celgard 2032 available from Celgard) are used as the separator. 1M LiPF 6 in a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1: 1, Novolyte, USA) with 10 wt % of fluoroethylene carbonate (FEC) as an additive was used as an electrolyte.The coin cells are maintained at 30°C to perform electrochemical cycle tests. The cycle tests are performed at a rate of C / 10 and run within the voltage window of 0.5 V to 1 V versus Li / Li + for at least 100 cycles.Figure 9 shows the discharge capacity (mAh / g) (Y axis labeled "C" on the left) versus cycle index (X axis labeled "#") for the button cell. Coulombic efficiency of the coin cell (%) (Y axis on the right side designated as "%") is also shown. The discharge capacity (solid circles) of the button cell with the sample negative electrode was over 500 mAh / g over 80 cycles. In addition, the coulombic efficiency (solid squares) of the button cell with the sample negative electrode is more than 75% over 80 cycles. These results show that the porous one-dimensional SiO x- nano-rods function as a suitable active material for a lithium ion battery.Reference throughout the specification to "one example," "another example," "an example," and so forth means that a particular element (e.g., feature, structure, and / or characteristic) described in connection with the example is included in at least one example described herein, and may or may not be present in the other examples. Moreover, it should be understood that the described elements for each example may be combined in any suitable manner in the various examples, unless the context clearly dictates otherwise.It is understood that the ranges set forth herein include the ranges set forth and any value or sub-range within the range set forth. For example, the range from about 30 nm to about 200 nm should be interpreted as including not only the expressly stated limits from about 30 nm to about 200 nm, but also including individual values such as 35 nm, 60 nm, 165.5 nm, etc. and including sub-ranges such as from about 40 nm to about 155 nm, etc. Moreover, when "about" is used to describe a value, it is understood that minor deviations (up to + / - 5%) of said value are included.In the specification and claims of the examples disclosed herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.While several examples have been described in detail, it will be apparent to those skilled in the art that the disclosed examples may be modified. Therefore, the foregoing description is to be considered as not restrictive.

Claims

A method comprising: forming a precipitate (21) in an aqueous mixture by mixing an SiO x precursor (12) and an acid (14); adding the precipitate (21) and a carbon material (19) to a base (17), thereby dissolving the precipitate (21) to form a solution in which the carbon material (19) is contained; performing hydrothermal synthesis using the solution, wherein nanostructure precursors (24) grow on the carbon material (19); and annealing the nanostructure precursors (24) on the carbon material (19), thereby removing the carbon material (19) to form porous one-dimensional SiOx nanostructures (26, 26'), wherein 0<x≤2.The method of claim 1, wherein the SiO x precursor is Si(OH) 4.The method of claim 1, wherein the hydrothermal synthesis comprises exposing the aqueous mixture to heat and vapor pressure in a closed system (20), causing the nanostructure precursors (24) to grow on the carbon material (19).The method of claim 1, wherein the annealing is performed in an inert or reducing environment such that the porous one-dimensional SiOx nano-rods (26, 26') have 0 < x < 2, and wherein the method further comprises: adding the porous one-dimensional SiO x- nano-rods (26, 26') to a negative electrode (50, 50') composition of a lithium ion battery as an active material; applying the negative electrode (50, 50') composition to a current collector to form a negative electrode (50, 50'); and pre-lithiating the negative electrode (50, 50'), thereby forming porous one-dimensional silicide nano-rods (26").The method of claim 1, wherein the annealing is performed in an oxygen-containing environment to form porous one-dimensional SiO 2- nano-rods (26, 26'), and wherein the method further comprises adding the porous one-dimensional SiO 2- nano-rods (26, 26') as an additive to the positive electrode (40, 40') composition of a lithium-sulfur battery (500).The method of claim 1, additionally comprising: removing the nanostructure precursor (24) and any liquid present after hydrothermal synthesis from a closed system (20) prior to annealing the nanostructure precursors (24); wherein annealing the nanostructure precursors (24) comprises: placing the nanostructure precursors (24) in an inert environment or in a reducing environment; and applying a heat treatment at a temperature in the range of 800°C to 1100°C for a time in the range of 2 hours to 5 hours, thereby forming the porous one-dimensional SiO x- nanostructures (26, 26'), where 0 < x < 2.The method of claim 6, additionally comprising: removing the porous one-dimensional SiO x- nano-rods (26, 26'), where 0 < x < 2, from the inert environment or the reducing environment and one of: i) adding the porous one-dimensional SiO x- nano-rods (26, 26') as an active material to a negative electrode (50, 50') composition of a lithium ion battery (400); or ii) adding the porous one-dimensional SiO x- nano-rods as an active material to a negative electrode (50, 50') composition of a lithium-sulfur battery (500) and pre-lithiating the negative electrode of the lithium-sulfur battery (500), thereby forming porous one-dimensional silicide nano-rods (26").The method of claim 1, wherein the annealing of the nanostructure precursors (24) occurs by applying a heat treatment in an oxygen-containing environment at a temperature in the range of 350°C to 700°C for a time in the range of 2 hours to 5 hours, thereby forming porous one-dimensional SiO 2- nano-rods (26, 26'), and wherein the carbon material (19) is hollow carbon or graphite.A negative electrode (50, 50') comprising: a binder; a conductive filler; and an active material mixed with the binder and the conductive filler throughout the negative electrode, wherein the active material is selected from the group consisting of porous one-dimensional SiOx nano-rods (26, 26'), where 0<x<2, or porous one-dimensional silicide nano-rods (26").The negative electrode (50, 50') according to claim 9, wherein the porous one-dimensional SiOx nano-rods, where 0 < x < 2, or the porous one-dimensional silicide nano-rods are not embedded in the binder or the conductive filler.The negative electrode (50, 50') of claim 9, wherein the porous one-dimensional SiOx nano-rods, where 0 < x < 2, or the porous one-dimensional silicide nano-rods are present in an amount of 60 wt% to 95 wt%, based on the total wt% of the negative electrode material, and wherein each of the porous one-dimensional SiOx nano-rods, where 0 < x < 2, or each of the porous one-dimensional silicide nano-rods has a diameter of 10 nm to 100 nm and a length of 80 nm to 3 micrometers, the diameter being smaller than the length.A sulfur-based battery comprising: a positive electrode (40, 40') including: a sulfur-based active material; a binder; a conductive filler; and porous one-dimensional SiO 2- nano-rods (26, 26') mixed with the sulfur-based active material, the binder, and the conductive filler throughout the positive electrode; a negative electrode (50, 50'); and a microporous polymer separator soaked in an electrolyte solution, wherein the microporous polymer separator is disposed between the positive electrode (40, 40') and the negative electrode (50, 50').

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