Silicon-carbon composite fiber

Abstract

The composite fiber includes a porous silicon phase comprising elemental silicon and a porous carbon phase comprising elemental carbon. The silicon and carbon phases form an intertwined network in the composite fiber, with the silicon and carbon phases each interconnected and continuous throughout the composite fiber. The silicon and carbon phases together comprise at least 50 wt% of the composite fiber.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 240,135, entitled "Silicon-Carbon Composite Fiber," filed September 2, 2021, and U.S. Provisional Patent Application No. 63 / 242,525, entitled "Silicon-Carbon Composite Fiber," filed September 10, 2021, each of which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates to silicon-carbon composite fibers and methods of making and using same. [Background technology]

[0003] Lithium-ion batteries have grown rapidly in popularity over the past decade and are now the power source of choice for providing portable power for electronic devices, cordless devices, and automobiles. As technology becomes increasingly dependent on lithium-ion battery power, the lithium-ion battery industry has worked to expand the performance of the cells to provide maximum versatility to end users.

[0004] Graphite is commonly used in lithium-ion batteries because it can perform its function stably for hundreds of cycles with little or no capacity loss. Silicon has great potential as an anode material because it has a significantly higher capacity (4000 mAh / g) than the current industry standard graphite (372 mAh / g). However, silicon has a limitation: it swells by 350% upon lithiation. This swelling can cause severe destruction of the cell's internal structure, damaging cell components, shattering the anode itself, and ultimately losing electrical connectivity, resulting in rapid capacity loss. Therefore, there is a continuing need for improved silicon-containing anode materials and methods for preparing such silicon-containing anode materials. The prior art documents relevant to the invention of this application are as follows (including documents cited in the international phase after the international filing date and documents cited when the application entered the national phase in other countries). (Prior art document) (Patent document) (Patent Document 1) U.S. Patent Application Publication No. 2020 / 0152983 (Patent Document 2) U.S. Patent Application Publication No. 2020 / 0269207 (Patent Document 3) U.S. Patent Application Publication No. 2018 / 0269471 [Brief explanation of the drawings]

[0005] Various embodiments of the present disclosure will become more fully understood from the following detailed description and the accompanying drawings, in which like reference numbers may indicate identical or functionally similar elements. The embodiments are now described in detail with reference to the accompanying drawings, in which:

[0006] [Figure 1] FIG. 1 is an explanatory diagram illustrating the difference between fast and slow lithium ion transport on a composite fiber according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is an SEM image of a cross section of a porous silicon fiber template (PSFT) according to an embodiment of the present disclosure. [Figure 3] FIG. 3 shows two STEM images of a cross section of a Si—C composite fiber according to one embodiment of the present disclosure. [Figure 4] FIG. 4 is an elemental mapping of a cross section of a Si—C composite fiber by STEM-EELS according to one embodiment of the present disclosure. [Figure 5] FIG. 5 is a graph showing the relationship between 1st cycle specific lithiation capacity, 1st cycle coulombic efficiency (FCE), and carbon content (C wt %) for composite fibers according to embodiments of the present disclosure. [Figure 6] FIG. 6 is a graph showing the relationship between pore volume and crystalline silicon content in PSFT according to an embodiment of the present disclosure. [Figure 7] FIG. 7 is a graph showing the relationship between specific desorption capacity, FCE, and C% according to an embodiment of the present disclosure. [Figure 8] FIG. 8 is a graph showing the relationship between normalized capacity and C% according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0007] The following disclosure provides many different embodiments or examples. To simplify the disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to be limiting. Furthermore, the disclosure may repeat reference numerals and / or letters in various examples. This repetition is for the purposes of simplicity and clarity and does not, in itself, dictate a relationship between the various embodiments and / or configurations discussed.

[0008] The present disclosure provides silicon-carbon composite fibers ("Si-C composite fibers" or "composite fibers") having a silicon phase ("Si phase") and a carbon phase ("C phase"). The Si phase and C phase form an entangled network structure in the fiber, with each phase interconnected and continuous throughout the fiber. The Si phase comprises nanocrystalline or amorphous elemental silicon. The Si phase is present in the fiber in an amount ranging from 0 wt% to less than 100 wt%. The C phase comprises amorphous or crystalline carbon and is present in the fiber in an amount ranging from 0 wt% to less than 100 wt%. In some embodiments, the total amount of the Si phase and the C phase is in the range of 50 wt% to 100 wt%. In some embodiments, the C phase comprises at least 30 wt% of the fiber and / or the Si phase comprises at least 20 wt% of the fiber.

[0009] In some embodiments, the composite fiber has an amount of carbon of at least 29 wt%, at least 35 wt%, 37 wt%, at least 39 wt%, at least 40 wt%, at least 41 wt%, at least 42 wt%, at least 43 wt%, at least 44 wt%, at least 45 wt%, at least 46 wt%, 29-63 wt%, 37-63 wt%, 39-63 wt%, or 46-63 wt%.

[0010] When the content of carbon in the composite fiber is expressed as Xc (wt%, based on the total weight of the composite fiber) and the content of elemental silicon (excluding silica) in the composite fiber is expressed as Xsi (wt%, based on the total weight of the composite fiber), the composite fiber can be characterized by the following Equation 1 and Equation 2: Xsi / (100-Xc) Equation 1 0.3025 * Xc+3.70 * Xsi / (100-Xc)+57.97 Equation 2

[0011] In some embodiments, the bicomponent fibers have a value of Equation 1 of at least 0.62 or at least 0.69. In some embodiments, the bicomponent fibers have a value of Equation 2 of at least 70.3, at least 72.7, or at least 75.

[0012] In some embodiments, the composite fiber has all of the following characteristics: a carbon content of at least 29 wt%, a value of Equation 1 of at least 0.62, and a value of Equation 2 of at least 70.3. In some embodiments, the composite fiber has all of the following characteristics: a carbon content of at least 37 wt%, a value of Equation 1 of at least 0.69, and a value of Equation 2 of at least 72.7. In some embodiments, the composite fiber has all of the following characteristics: a carbon content of at least 39 wt%, a value of Equation 1 of at least 0.69, and a value of Equation 2 of at least 72.7. In some embodiments, the composite fiber has all of the following characteristics: a carbon content of at least 46 wt%, a value of Equation 1 of at least 0.69, and a value of Equation 2 of at least 75. When these conditions are met, the composite fiber can provide a high half-cell FCE (e.g., at least 70.5%, at least 73%, or at least 75%). Silicon generally has poor FCE, i.e., 1 stThe majority of lithium ions (1-FCE) transferred to silicon-containing electrodes during cycling are irreversible during the subsequent delithiation process. Improving the FCE of silicon active materials is important for increasing the energy density of lithium-ion battery cells containing silicon in one of the electrodes. When composite fibers are incorporated into a complete battery, this loss of active material occurs in both the anode (containing the composite fiber) and cathode. Once the active material is depleted, the battery must carry this deadweight for the remainder of its usable life. Therefore, increasing the FCE as much as possible is crucial for achieving good energy density, and even small improvements in FCE can result in significant improvements in battery performance (e.g., extended driving range for EVs).

[0013] In one or more embodiments, the composite fibers also contain amorphous or crystalline silicon oxide, SiO x (x≦2). The composite fibers may also contain aluminum (Al), magnesium (Mg), chlorine (Cl), sodium (Na), nitrogen (N), carbon oxides (CO x ) (x≦2), and / or other impurities such as hydrocarbon chains. In some embodiments, the composite fibers have 5 wt% or less, 4 wt% or less, 3 wt% or less, 2 wt% or less, or 1 wt% or less Al. In some embodiments, the composite fibers have 5 wt% or less, 4 wt% or less, 3 wt% or less, 2 wt% or less, or 1 wt% or less Mg. In some embodiments, the composite fibers have 40 wt% or less, 35 wt% or less, 30 wt% or less, 25 wt% or less, 20 wt% or less, 15 wt% or less, 10 wt% or less, or 5 wt% or less amorphous or crystalline silicon oxide, SiO x (x≦2).

[0014] In one or more embodiments, the bicomponent fibers of the present disclosure have a length of greater than 0 to 20 m 2 / g, over 0~10m 2 / g, over 0~5m 2 / g, over 1~150m 2 / g, over 5~150m 2 / g, over 10~140m2 / g, over 20~130m 2 / g, over 30~120m 2 / g, or over 50 to 100m 2 / g BET specific surface area ("SSA").

[0015] In one or more embodiments, the bicomponent fiber is Bigger 0.3cm 3 / g, 0.01~0.3cm 3 / g、 0 Bigger 0.1cm 3 / g to , 0 Bigger 0.05cm 3 / g to , or 0.05 to 0.25 cm 3 / g of It has a pore volume.

[0016] In one or more embodiments, the bicomponent fibers have a median pore size of 5 to 30 nm or 10 to 20 nm.

[0017] In one or more embodiments, the bicomponent fibers have an average diameter of 0.1 to 10 microns, 0.5 to 6 microns, 1 to 8 microns, or 2 to 5 microns.

[0018] In one or more embodiments, the bicomponent fibers have an aspect ratio of fiber length to diameter of at least 3, at least 5, or at least 10.

[0019] The nanocrystalline silicon of the Si phase can have crystallites in the range of 1-100 nm, 1-50 nm, or 5-25 nm. In some embodiments, the Si phase has at least 50 wt%, at least 60 wt%, at least 70 wt%, or at least 80 wt% nanocrystalline silicon, based on the total weight of the Si phase. In other embodiments, the Si phase has at most 50 wt%, at most 40 wt%, at most 30 wt%, at most 20 wt%, or at most 10 wt% nanocrystalline silicon. In some embodiments, the Si phase has at most 50 wt%, at most 40 wt%, at most 30 wt%, at most 20 wt%, or at most 10 wt% amorphous or crystalline silicon oxide SiO x (x≦2). In other embodiments, the Si phase is at least 50 wt%, at least 60 wt%, at least 70 wt%, or at least 80 wt% amorphous or crystalline silicon oxide, SiO x (x≦2). In some embodiments, the Si phase consists of nanocrystalline silicon, amorphous silicon, and amorphous or crystalline silicon oxide SiO x (x≦2).

[0020] The C phase can have crystallites in the range of 1-100 nm, 1-50 nm, or 5-20 nm. In some embodiments, the C phase has at least 50 wt%, at least 60 wt%, at least 70 wt%, or at least 80 wt% crystalline carbon, based on the total weight of the C phase. In other embodiments, the C phase has at most 50 wt%, at most 40 wt%, at most 30 wt%, at most 20 wt%, or at most 10 wt% crystalline carbon. In some embodiments, the C phase has at most 50 wt%, at most 40 wt%, at most 30 wt%, at most 20 wt%, or at most 10 wt% amorphous carbon. In other embodiments, the C phase has at least 50 wt%, at least 60 wt%, at least 70 wt%, or at least 80 wt% amorphous carbon. In some embodiments, the C phase consists of crystalline and amorphous carbon.

[0021] In one or more embodiments, one of the Si phase or the C phase has a crystalline content greater than 50 wt% while the other of the Si phase or the C phase has a crystalline content less than 50 wt%, based on the weight of each phase. In some embodiments, one of the Si phase or the C phase has a crystalline content greater than 60 wt% and the other of the Si phase or the C phase has a crystalline content less than 40 wt%. In some embodiments, one of the Si phase or the C phase has a crystalline content greater than 70 wt% and the other of the Si phase or the C phase has a crystalline content less than 30 wt%.

[0022] In some embodiments, composite fibers are formed by infiltrating a carbon structure with silicon. For example, composite fibers can be formed by first preparing porous carbon fibers and then infiltrating the pore structure with silicon. Silicon infiltration can be achieved by a chemical vapor deposition (CVD) process using a silicon precursor gas, such as silane or trichlorosilane. The production of porous carbon fibers involves multiple steps. For example, synthetic polymer fibers are first prepared from polymers such as polyacrylonitrile (PAN), pitch, rayon, or resin. The synthetic polymer is then pyrolyzed to produce carbon fibers. To make carbon fibers porous, they must be subjected to activation or chemical exfoliation treatments. In activation methods, carbon fibers are heat-treated (e.g., at 700-1000°C) in an oxidizing atmosphere to form a porous structure. In chemical exfoliation methods, carbon fibers may be treated with a release agent such as acid and then subjected to an electric charge. Alternatively, a polymer blend, such as a mixture of PAN and polymethyl methacrylate (PMMA), may be fabricated into polymer fibers, which are then oxidized to cause phase separation. The PMMA is removed by pyrolysis, leaving behind porous carbon fibers.

[0023] In some embodiments, after the porous carbon fiber (C phase) is infiltrated with silicon (Si phase), the composite fiber may be further coated with a carbon material. The carbon coating may act to protect the exposed portions of the Si phase from solid electrolyte interphase (SEI) formation, as the SEI reduces the FCE. In some embodiments, at least 60%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or about 100% of the surface area of ​​the composite fiber may be coated with carbon.

[0024] In some embodiments, the porous carbon fibers (C phase) prior to infiltration with silicon (Si phase) have at least 50 wt%, at least 60 wt%, at least 70 wt%, or at least 80 wt% crystalline carbon. The porous carbon fibers have at most 50 wt%, at most 40 wt%, at most 30 wt%, at most 20 wt%, or at most 10 wt% amorphous carbon. The porous carbon fibers may have at most 15 wt%, at most 10 wt%, or at most 5 wt% impurities (components other than crystalline or amorphous carbon).

[0025] In some embodiments, porous carbon fibers are partially infiltrated with silicon and then infiltrated with carbon to form C—Si—C composite fibers. The carbon infiltration (C infiltration phase) may act to protect the Si phase from SEI formation. In some embodiments, the C—Si—C composite fibers contain at least 20 wt%, at least 30 wt%, or at least 40 wt% of the C phase, at least 20 wt%, at least 30 wt%, or at least 40 wt% of the Si phase, and at least 5 wt%, at least 10 wt%, or at least 20 wt% of the C infiltration phase, based on the total weight of the C—Si—C composite fiber. In the C—Si—C composite fibers, the C phase and the Si phase may be as described herein. The C infiltration phase may have the same properties as the C phase described herein and may include amorphous carbon, crystalline carbon, or a combination thereof. In some embodiments, the Si phase is substantially or completely covered by the C phase and / or the C infiltration phase. For example, at least 60%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or about 100% of the surface area of ​​the Si phase may be covered by the C phase and / or the C-infiltrated phase.

[0026] In some embodiments, composite fibers are formed by infiltrating a silicon structure with carbon. For example, composite fibers can be formed by first creating a porous silicon fiber template (PSFT) made of silicon metal and then infiltrating the pores with carbon. To create a PSFT, a fiber containing SiO2, i.e., a precursor fiber, is first created. This precursor fiber can be a silica fiber made by a sol-gel fiberization process or one made by acid leaching an oxide glass fiber.

[0027] The precursor fibers are reduced to metallic silicon-containing PSFT, for example, by magnesium thermal reduction. The PSFT is then infiltrated with carbon. For example, chemical vapor deposition (CVD) processes using a carbon source such as acetylene or other deposition processes such as physical vapor deposition, sputtering, or atomic layer deposition can be used. Alternatively, the porous fibers can be first infiltrated with a hydrocarbon polymer (e.g., a resin, polyvinyl acetate (PVA)) and then converted to carbon by pyrolysis.

[0028] The silicon metal-containing PSFT acts as a template matrix for incorporating carbon to form composite fibers. The silicon metal-containing fibers have a median pore diameter ranging from 3 to 50 nm and a pore size ranging from 0.1 to 1.5 cm. 3 / g range of pore volume, and 10 to 500 m 2 The PSFT has a specific surface area in the range of 1 / g. The PSFT can have a crystalline silicon content (Si%) of 50-95 wt% and a silicon crystallite size of 5-30 nm. In some embodiments, the PSFT has an elemental silicon content (Si%) of about 50-90 wt%, about 60-90 wt%, or at least about 69 wt%. In some embodiments, the PSFT has silicon crystallites (Si crystallite size) of about 6-26 nm, at least about 7 nm, at least about 8 nm, or about 8-25 nm. In some embodiments, the PSFT has a specific surface area in the range of about 120-400 nm. 2 / g, about 150~400m 2 / g, approx. 170~395m 2 / g, or approximately 200-350m 2 In some embodiments, the PSFT has a median pore diameter (pore size) of about 9-30 nm, about 10-30 nm, or about 11-29 nm. In some embodiments, the PSFT has a specific surface area (SSA) of about 0.45-0.95 cm. 3 / g, or approximately 0.5-0.9 cm 3 / g pore volume.

[0029] In some embodiments, the PSFT before carbon infiltration has at least 50 wt%, at least 60 wt%, at least 70 wt%, or at least 80 wt% crystalline silicon (nanocrystalline silicon). The PSFT has at most 50 wt%, at most 40 wt%, at most 30 wt%, at most 20 wt%, or at most 10 wt% amorphous or crystalline silicon oxide. The PSFT may be composed of at most 15 wt%, at most 10 wt%, or at most 5 wt% impurities (components other than silicon or silicon oxide).

[0030] Material properties can be controlled, for example, through the design of the reduction recipe, the firing temperature program, post-heat treatment, and / or the design of the calciner. For example, crystalline silicon content (Si%), Si crystallite size, pore volume, and pore diameter generally increase with the Mg / SiO2 ratio of the raw materials. On the other hand, specific surface area (SSA) is related to both Si% and crystallite size. Specifically, SSA increases with Si% but decreases with increasing Si crystallite size. Both Si% and Si crystallite size are affected by the recipe, particularly the Mg / SiO2 ratio. Si crystallite size, SSA, pore volume, and pore diameter can be further varied by adjusting the temperature and amount of moderator used. The heat generated during the reaction of SiO2 and Mg is absorbed by the moderator in the batch. A decrease in the ratio of moderator to Mg increases the batch temperature rise during the exothermic reaction, promoting Si crystallite growth and sintering, and decreasing SSA and pore volume. Increasing the batch holding temperature has a similar effect on crystallite size, SSA, and pore volume as the moderator.

[0031] In one or more embodiments, the PSFT is infiltrated with carbon to form a composite fiber. In such embodiments, the Si-C composite fiber can have a carbon content of 25-65 wt%, at least 29 wt%, at least 35 wt%, at least 37 wt%, at least 39 wt%, at least 46 wt%, 29-63 wt%, 39-63 wt%, or 46-63 wt%, and exhibits a carbon content of 100% or less in half-cell testing. stCycle coulombic efficiency (FCE) of 60-85%, 1 st The specific desorption capacity (1SDC) of the cycle is 800-2200mAh / g.

[0032] In one or more embodiments, the majority of elements in the composite fiber are Si, C, and oxygen (O), for example, at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, at least 95 wt%, at least 99 wt%, or at least 99.5 wt%.

[0033] According to embodiments of the present disclosure, composite Si-C fibers can provide superior properties compared to simple mixtures of Si fibers and carbon materials (e.g., carbon black or graphite). Without being bound by theory, this is believed to be due, at least in part, to improved transport and diffusion rates of electrons and lithium ions due to the interconnected carbon network within the fibers. Electrons and lithium ions have higher diffusivities in carbon than in silicon. The interconnected carbon network within the composite fibers facilitates the transport of electrons and lithium ions from the outer surface of the composite fiber to the interior of the composite fiber, or from the interior of the composite fiber to the outer surface of the composite fiber. Therefore, the number and transport rates of electrons and lithium ions increase with increasing carbon content in the fiber.

[0034] The increased diffusion rate also helps to reduce the exposure time of the Si domain surface to tensile stress buildup during the deliting step, thereby avoiding cracking of the silicon domains (see the top left panel of Figure 1 compared to the top right panel). The increased rate also helps to reduce the exposure time of the fiber surface to tensile stress buildup during the deliting step, thereby avoiding cracking of the fiber surface (see the bottom left panel of Figure 1 compared to the bottom right panel).

[0035] In some embodiments, the composite fibers contain lithium and at least a portion of the silicon from the Si phase. xThe lithium-containing composite fiber may contain lithium, forming a Si alloy, where x is greater than 0 and equal to 4. In some embodiments, the lithium-containing composite fiber may further contain Li2SiO3. In some embodiments, the lithium-containing composite fiber may be prepared by preparing a nanoporous fibrous structure of either silicon or carbon, followed by infiltrating the other nanoporous fibrous structure of carbon or silicon, and then reacting the infiltrated structure with a lithium source to form Li x In other embodiments, lithium-containing composite fibers can be formed by creating a silicon nanoporous fibrous structure and then reacting the structure with a lithium source to form a Li x In yet another embodiment, lithium can be introduced into the Si-C composite fibers to form a Si alloy and finally infiltrate the structure with carbon. x By forming a Si alloy, lithium-containing composite fibers can be formed. [Example]

[0036] Example 1 After magnesium thermal reduction, acid washing was performed to remove undesired reaction products to form PSFT, which was analyzed as detailed below. Figure 2 shows an SEM image of a cross section of PSFT with metallic silicon. Pores measuring several tens of nanometers in diameter are observed. X-ray diffraction (XRD) analysis of the PSFT in Figure 2 also showed that it is composed of 50–95 wt% crystalline silicon and 5–50 wt% amorphous silicon oxide (SiOx) by Rietveld analysis. The amorphous silicon oxide in PSFT can be stoichiometric (SiO2) or non-stoichiometric (SiO x , x<2). [Example]

[0037] The PSFT of Example 1 was infiltrated with carbon and analyzed as detailed below. Figure 3 shows a STEM image of a Si-C composite fiber, showing an interconnected porous network of Si crystallites, carbon, and SiOx. XRD of the composite fiber shows that the carbon is mostly amorphous or exhibits a weakly ordered structure similar to carbon black. In some cases, chemical bonds are formed at the interface between Si and C; that is, SiC compounds (silicon carbide) may form at the interface.

[0038] Typical silicon crystallite sizes can range from 5 to 30 nm in diameter, as determined by Rietveld or Scherrer analysis of silicon X-ray diffraction peaks or by direct measurement of crystallites in STEM images. Figure 3 shows STEM images of a Si-C composite. The high-angle dark-field (HAADF) image shows the morphology of the crystal grains in the fibers, while the bright-field (BF) image shows periodic striations, indicating that the grains in the HAADF image are mostly single-crystal silicon, i.e., crystallites. When the shape of the silicon crystallites is irregular, the long axis of the particle is defined as the diameter.

[0039] Figure 4 shows elemental mapping of Si (top right) and C (bottom left) in Si-C composite fibers by STEM-EELS. As shown by the overlay of the elemental mapping images of Si and C (bottom right), Si and C are complementary in the fiber structure. This indicates that carbon penetrates the porous space of the Si fiber template and is in close contact with the Si crystallites. Silicon crystallites are interconnected through connections with neighboring silicon crystallites and amorphous silicon oxide. Therefore, the initial PSFT was confirmed to be a porous network in which silicon and silicon oxide are interconnected. [Example]

[0040] Example 3 A number of samples were prepared from the same PSFT infiltrated with different amounts of carbon. Figure 5 shows the results of one of the samples. st The relationship between the cycling specific lithiation capacity, FCE, and C% is shown. The results show that for a given PSFT, the specific lithiation capacity tends to decrease as the C% increases. [Example]

[0041] Example 4 PSFT with various pore volumes was prepared and infiltrated with carbon to form composite fibers. The pore volume and Si% of PSFT are shown in Figure 6. The amount of carbon that can be infiltrated into PSFT is generally limited by the pore volume of PSFT, i.e., the void space accessible to carbon. The larger the pore volume, the more carbon can be infiltrated, resulting in a higher carbon content.

[0042] The composite fibers were then molded into half-cells and tested. The results are shown in Figures 7 and 8. As carbon or silicon infiltrates the PSFT or carbon fiber, the total volume of the formed Si-C composite remains unchanged relative to the original PSFT or carbon fiber template. However, the FCE is significantly improved (e.g., 40%–75%, as shown in Figure 7), and the charge / discharge volumetric capacity of a single fiber increases (as shown in the example in Figure 8). [Example]

[0043] Example 5 The properties of PSFT were measured by magnesium thermal reduction. The raw materials used for the reduction and the measurement results are summarized in Table 1 below. [Table 1]

[0044] The materials in Table 1 were infiltrated with carbon to form Si-C composite fibers. An electrode containing Si-C composite fibers was paired with a lithium metal electrode to form a half-coin cell, and the FCE and 1 st The cycle specific desorption capacity (1SDC) test was performed. The properties of the Si-C composite fiber and the results of the half-cell test are summarized in Table 2 below. [Table 2]

[0045] As described above, when a composite fiber had all of the following properties: a carbon content of at least 29 wt%, a Formula 1 value of at least 0.62, and a Formula 2 value of at least 70.3, the FCE was greater than 73%. Furthermore, when a composite fiber had all of the following properties: a carbon content of at least 37 wt%, a Formula 1 value of at least 0.69, and a Formula 2 value of at least 72.7, the FCE was greater than 73%. Furthermore, when a composite fiber had all of the following properties: a carbon content of at least 46 wt%, a Formula 1 value of at least 0.69, and a Formula 2 value of at least 75, the FCE was greater than 75%. Conversely, Comparative Example 5 had a Formula 1 value of 0.69 and a carbon content of 31.7 wt%, but only a Formula 2 value of 70.1. As a result, Comparative Example 5 achieved an FCE of only 63.8%.

[0046] While various embodiments have been shown and described, it will be understood that the present disclosure is not limited to such embodiments, but includes all modifications and variations that would be apparent to one skilled in the art. It is therefore to be understood that the present disclosure is not intended to be limited to the particular forms disclosed, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.

Claims

1. A composite fiber, a porous silicon phase having elemental silicon; a porous carbon phase having elemental carbon; and the silicon phase and the carbon phase form an entangled network structure in the composite fiber such that each of the silicon phase and the carbon phase is interconnected and continuous throughout the composite fiber; the silicon phase and the carbon phase together constitute at least 50 wt % of the composite fiber; the elemental carbon comprises at least 29 wt% of the composite fiber, based on the total weight of the composite fiber; Based on the total weight of the composite fiber, the wt% of elemental carbon in the composite fiber is represented by Xc and the wt% of elemental silicon in the composite fiber is represented by Xsi, and the following formula is used: Xsi / (100-Xc)≧0.62 9325 ＊ Xc+3.701 ＊ Xsi / (100-Xc)+57.97≧70.

3. and The bicomponent fibers (i) have a median pore size of 5 to 30 nm, or (ii) have an average diameter of 0.1 to 10 microns, with an aspect ratio of fiber length to diameter of at least 3.

2. 10. The composite fiber of claim 1, wherein the elemental carbon comprises at least 37 wt.% of the composite fiber, and ＊ Xc+3.70 ＊ A bicomponent fiber, wherein Xsi / (100-Xc)+57.97) is at least 72.

7.

3. 10. The composite fiber of claim 1, wherein the elemental carbon comprises at least 46 wt.% of the composite fiber, and ＊ Xc+3.70 ＊ Xsi / (100-Xc)+57.97) is at least 75.

4. 10. The composite fiber of claim 1, wherein the silicon phase has silicon crystallites having a size of 6 to 25 nm; and The silicon phase has at least 50 wt % crystalline silicon, based on the total weight of the silicon phase.

5. In the composite fiber according to claim 1, the composite fiber has a pore volume greater than 0 cm3 / g and up to 0.3 cm ３ / g, the composite fiber.

6. 10. The composite fiber of claim 1, wherein the composite fiber has a median pore size of 5 to 30 nm.

7. 10. The bicomponent fiber of claim 1, wherein the bicomponent fiber has an average diameter of 0.1 to 10 microns and an aspect ratio of fiber length to diameter of at least 3.

8. 10. The composite fiber of claim 1, wherein the carbon phase has crystallites in the range of 1 to 100 nm.

9. 9. The composite fiber of claim 8, wherein the carbon phase has at least 50 wt% crystalline carbon, based on the total weight of the carbon phase.

10. 10. The composite fiber of claim 1, further comprising lithium, wherein at least a portion of the silicon from the lithium and silicon phase is Li ｘ A composite fiber in which a Si alloy is formed and x is greater than 0 and up to 4.

11. 1. A method comprising: forming a porous fibrous template having one of elemental carbon or elemental silicon; infiltrating the porous fiber template with an infiltration phase having the other of elemental carbon or elemental silicon to form a composite fiber; the porous fibrous template phase and the infiltrating phase form an entangled network structure in the composite fiber such that each of the porous fibrous template phase and the infiltrating phase is interconnected and continuous throughout the composite fiber; the elemental silicon and the elemental carbon together constitute at least 50 wt% of the composite fiber; the elemental carbon comprises at least 29 wt% of the composite fiber, based on the total weight of the composite fiber; Based on the total weight of the composite fiber, the wt% of elemental carbon in the composite fiber is represented by Xc and the wt% of elemental silicon in the composite fiber is represented by Xsi, and the following formula is used: Xsi / (100-Xc)≧0.62 9325 ＊ Xc+3.701 ＊ Xsi / (100-Xc)+57.97≧70.

3. and The method wherein the bicomponent fibers (i) have a median pore size of 5 to 30 nm, or (ii) have an average diameter of 0.1 to 10 microns, with an aspect ratio of fiber length to diameter of at least 3.

12. The method of claim 11 , wherein the porous fibrous template comprises elemental carbon.

13. The method of claim 11 , wherein the porous fibrous template comprises elemental silicon.

14. 12. The method of claim 11, wherein the median pore size of the infiltrating phase is 0.1 to 5 nm smaller than the median pore size of the porous fibrous template.

15. 12. The method of claim 11, wherein the step of infiltrating the porous fiber template comprises chemical vapor deposition, physical vapor deposition, sputtering, atomic layer deposition, or pyrolysis.

16. 12. The method of claim 11, wherein the porous fibrous template comprises 50 to 95 wt % crystalline silicon or crystalline carbon, the crystalline silicon or crystalline carbon having a crystallite size of 6 to 25 nm.

17. 12. The method of claim 11, wherein the porous fiber template has a thickness of 150 to 400 mm. ２ / g BET specific surface area, 8-30 nm median pore diameter, and 0.5-0.9 cm ３ / g pore volume.

18. 12. The method of claim 11, The composite fibers are reacted with a lithium source to form Li ｘ forming a Si alloy, or If the porous fibrous template comprises elemental silicon, the porous fibrous template may be reacted with a lithium source to form Li prior to infiltration. ｘ A method for forming a Si alloy.

19. An electrode active material comprising the composite fiber according to claim 1 .

20. 20. An electrode comprising the electrode active material of claim 19.

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