Preparation method of metal-containing closed-pore-rich hard carbon nanofiber material and application of metal-containing closed-pore-rich hard carbon nanofiber material as sodium-ion battery negative electrode material

Abstract

The invention discloses a preparation method of a metal-containing closed-pore-rich hard carbon nanofiber material and application of the metal-containing closed-pore-rich hard carbon nanofiber material as a sodium-ion battery negative electrode material. The interior of the metal-containing hard carbon nanofiber material rich in closed pores contains metal, and the outer layer of the metal-containing hard carbon nanofiber material rich in closed pores is a carbon coating layer; the number of closed pores in the metal-containing hard carbon nanofiber material rich in closed pores is greater than the sum of the number of micropores and mesopores. The prepared metal-containing hard carbon nanofiber material rich in closed pores has sufficient sodium storage space, good sodium ion adsorption capacity and good electrolyte barrier property. The sodium storage capacity of the hard carbon negative electrode can be greatly improved, side reactions in the cycle process are inhibited, the cycle stability of the sodium-ion battery negative electrode is improved, and the performance is excellent. Meanwhile, the overall energy density of the battery can be further improved through the self-supporting integrated electrode structure design, and good application prospects are achieved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a method for preparing a metal-containing, closed-pore-rich hard carbon nanofiber material and its application as a negative electrode material for sodium-ion batteries. Background Technology

[0002] Sodium-ion batteries, due to their abundant reserves, hold promise as an important complementary technology to lithium-ion batteries and a crucial solution for the new energy industry to reduce its dependence on external resources. The anode material is one of the key factors affecting the performance of sodium-ion batteries. However, commercially available graphite, despite its mature technology, suffers from thermodynamic instability due to its low interlayer spacing (0.335 nm), making it unsuitable for sodium-ion batteries. Hard carbon materials, with their larger carbon interlayer spacing (0.37–0.42 nm), enable rapid sodium-ion insertion / extraction kinetics, and their abundant porosity enhances sodium storage capacity, making them the optimal anode material for sodium-ion batteries. However, achieving a balance between high specific capacity and high cycle stability in hard carbon materials remains a significant challenge.

[0003] Currently, hard carbon anode materials typically improve sodium storage capacity by introducing additional sodium-storing active sites and reducing ion diffusion resistance through heteroatom doping and the construction of porous nanostructures, thereby promoting sodium ion diffusion kinetics. However, these methods inevitably lead to high specific surface area, ultimately resulting in low coulombic efficiency and poor cycle stability. Furthermore, the theoretical specific capacity of hard carbon anodes is lower than that of metal anodes, failing to meet the ever-increasing energy density requirements.

[0004] Therefore, considering specific capacity, ion diffusion kinetics, and cycle stability, designing sub-nanopore structures that are inaccessible to the electrolyte to reduce specific surface area, while simultaneously modifying the sub-nanopores with metal elemental or single-atom sites possessing good sodium ion adsorption capacity, is an effective way for hard carbon materials to achieve a balance between high specific capacity and high cycle stability. However, the preparation of sub-nanopore-rich hard carbon materials with good sodium ion adsorption capacity remains quite difficult, and most hard carbon anodes require the addition of additional binders and conductive agents, thereby reducing battery energy density. Summary of the Invention

[0005] To address the problems in existing technologies, this invention proposes a method for preparing metal-containing, closed-pore-rich hard carbon nanofibers and their application as a negative electrode material for sodium-ion batteries. The metal-containing, closed-pore-rich hard carbon nanofibers prepared by this invention possess ample sodium storage space, excellent sodium ion adsorption capacity, and good electrolyte barrier properties. This significantly improves the sodium storage capacity of the hard carbon anode, suppresses side reactions during cycling, and enhances the cycle stability of the sodium-ion battery anode, exhibiting superior performance. Furthermore, the self-supporting integrated electrode structure design further improves the overall energy density of the battery, demonstrating promising application prospects.

[0006] One objective of this invention is to provide a metal-containing, closed-pore-rich hard carbon nanofiber material, wherein the metal-containing, closed-pore-rich hard carbon nanofiber material contains metal internally, and the outer layer of the metal-containing, closed-pore-rich hard carbon nanofiber material is a carbon coating layer; the number of closed pores in the metal-containing, closed-pore-rich hard carbon nanofiber material is greater than the sum of the number of micropores and mesopores.

[0007] Compared to carbon fiber materials that generally possess microporous (1-2 nm) and mesoporous (>2 nm) structures, the metal-containing, closed-pore-rich hard carbon nanofiber material of the present invention has abundant closed-pore (0.4-0.7 nm) structures, and the number of closed pores is greater than the sum of the number of micropores and mesopores.

[0008] This invention relates to a hard carbon fiber material for sodium-ion battery anodes and its preparation method. The main body of the metal-containing, closed-pore-rich hard carbon nanofiber material of this invention is hard carbon material, which encapsulates carbon nanofibers containing metal single atoms or elemental metals, with a small amount of soft carbon material serving as a carbon coating layer. When used as a sodium-ion battery anode, the hard carbon fiber material's internal closed-pore structure can block electrolyte penetration, reduce side reactions during cycling, and provide space for sodium storage within the fibers. Furthermore, the metal single atoms or elemental metals within the hard carbon fiber material have good sodium ion adsorption capacity, which helps to preferentially store sodium within the carbon fibers and reduces the risk of sodium metal precipitation on the carbon fiber surface. Simultaneously, the zinc-containing, closed-pore-rich hard carbon nanofiber material of this invention can serve as a self-supporting integrated electrode. Compared to other traditional hard carbon anodes, it does not require the addition of additional binders and conductive agents, thus significantly increasing the energy density of the sodium battery.

[0009] In the metal-containing, closed-pore-rich hard carbon nanofiber material of the present invention, preferably,

[0010] The metal exists within the hard carbon nanofiber material in at least one form: a single metal atom, an elemental metal, or an alloy; and / or,

[0011] The metal is selected from at least one of zinc, tin, and silver; and / or,

[0012] The metal-containing, closed-pore-rich hard carbon nanofiber material contains 0.5 to 5 wt% metal; for example, 0.5%, 1%, 2%, 3%, 4%, or 5%.

[0013] In the metal-containing, closed-pore-rich hard carbon nanofiber material of the present invention, preferably,

[0014] The diameter of the metal-containing, closed-pore-rich hard carbon nanofiber material is 0.002–2 μm; for example: 0.002 μm, 0.01 μm, 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm; and / or,

[0015] The closed pore is a closed-pore structure with a size of 0.4–0.7 nm; and / or,

[0016] In the aforementioned metal-containing, closed-pore-rich hard carbon nanofiber material, based on the total number of pores, the proportion of closed-pore structures is 95%–99%; for example: 95%, 96%, 97%, 98%, 99%; and / or,

[0017] The specific surface area of ​​the metal-containing, closed-pore-rich hard carbon nanofiber material, as determined by nitrogen adsorption-desorption testing, ranged from 2 to 20 m². 2 g -1 ; and / or,

[0018] The specific surface area of ​​the metal-containing, closed-pore-rich hard carbon nanofiber material, as determined by carbon dioxide adsorption-desorption tests, ranged from 140 to 390 m². 2 g -1 .

[0019] A second objective of this invention is to provide a method for preparing a metal-containing, closed-pore-rich hard carbon nanofiber material, comprising the following steps:

[0020] S1) Dissolve the metal acetate and the fiber-forming polymer in an amide solvent to form a metal acetate precursor solution and a fiber-forming polymer precursor solution, respectively;

[0021] S2) The two precursor solutions obtained in step S1) are mixed to obtain a spinning solution, and the spinning solution is made into a thin film material composed of micro and nano fibers by electrospinning.

[0022] S3) The thin film material obtained in step S2) is subjected to high-temperature annealing under a protective atmosphere to obtain a metal-containing porous hard carbon nanofiber material.

[0023] S4) Dissolve asphalt in a polar solvent to form an asphalt coating agent solution;

[0024] S5) Mix the metal-containing porous hard carbon nanofiber material obtained in step S3) with the asphalt coating agent solution obtained in step S4) evenly, dry it, and then carbonize the dried mixture at high temperature under a protective atmosphere to obtain a metal-containing closed-pore hard carbon nanofiber material.

[0025] One of the objectives of this invention is to prepare the metal-containing, closed-pore-rich hard carbon nanofiber material preferably using the method described above.

[0026] In the preparation method of the metal-containing, closed-pore-rich hard carbon nanofiber material of the present invention, preferably,

[0027] In step S1),

[0028] The metal acetate is at least one of zinc, tin, and silver; preferably, when using two metal acetates, the molar ratio of the two metal acetates is 0.5:9.5 to 9.5:0.5; for example: 0.5:9.5, 1:9, 1.5:8.5, 2:8, 2.5:7.5, 3:7, 3.5:6.5, 4:6, 4.5:5.5, 5:5, 5.5:4.5, 6:4, 6.5:3.5, 7:3, 7.5:2.5, 8:2, 8.5:1.5, 9:1, 9.5:0.5; and / or,

[0029] In the metal acetate precursor solution, the mass fraction of metal acetate is 0.2% to 4%, preferably 0.5% to 2%; for example: 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%; and / or,

[0030] The fiber-forming polymer is selected from at least one of polyacrylonitrile or polyvinylpyrrolidone; and / or

[0031] The amide solvent is selected from at least one of N,N-dimethylformamide or N,N-dimethylacetamide; and / or

[0032] The mass fraction of the fiber-forming polymer in the fiber-forming polymer precursor solution is 0.5% to 5%; for example: 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%.

[0033] In the preparation method of the metal-containing, closed-pore-rich hard carbon nanofiber material of the present invention, preferably,

[0034] In step S2),

[0035] The volume ratio of the metal acetate precursor solution to the fiber-forming polymer precursor solution is 1:1 to 1:9; for example: 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9; and / or,

[0036] The operating voltage for electrospinning is 10–25 kV, preferably 15–20 kV; for example: 10 kV, 12 kV, 15 kV, 18 kV, 20 kV, 22 kV, 25 kV; and / or,

[0037] The electrospinning temperature is 25–70°C; for example: 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C; and / or,

[0038] The electrospinning collection distance is 10–25 cm; for example: 10 cm, 12 cm, 15 cm, 18 cm, 20 cm, 22 cm, 25 cm; and / or,

[0039] The spinning solution is used to prepare thin film materials composed of micro-nano fibers with diameters of 0.002 to 2 μm; for example: 0.002 μm, 0.01 μm, 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm.

[0040] In the preparation method of the metal-containing, closed-pore-rich hard carbon nanofiber material of the present invention, preferably,

[0041] In step S3),

[0042] The high-temperature annealing temperature is 300–1200℃, preferably 1000–1200℃; for example: 300℃, 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃; and / or,

[0043] The high-temperature annealing time is 1 hour to 4 hours, preferably 2 to 3 hours; for example: 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours; and / or,

[0044] The protective atmosphere is selected from at least one of nitrogen or an inert gas; preferably, the inert gas is at least one of argon or helium.

[0045] In the preparation method of the metal-containing, closed-pore-rich hard carbon nanofiber material of the present invention, preferably,

[0046] In step S4),

[0047] The polar solvent is selected from at least one of tetrahydrofuran, dichloromethane, and dimethyl sulfoxide; and / or,

[0048] The asphalt is at least one of low-temperature asphalt or high-temperature asphalt; preferably, the softening point of the asphalt is in the range of 70–300℃, more preferably 240–300℃; for example: 70℃, 100℃, 130℃, 160℃, 190℃, 220℃, 250℃, 280℃, 300℃; and / or,

[0049] The asphalt coating agent solution contains asphalt at a concentration of 5–20 mg / mL; for example: 5 mg / mL, 7.5 mg / mL, 10 mg / mL, 12.5 mg / mL, 15 mg / mL, 17.5 mg / mL, 20 mg / mL.

[0050] In the preparation method of the metal-containing, closed-pore-rich hard carbon nanofiber material of the present invention, preferably,

[0051] In step S5),

[0052] The mass ratio of the asphalt coating agent solution to the metal-containing porous hard carbon fiber material is 100:1 to 2:1; preferably 80:1 to 5:1; for example, 100:1, 80:1, 50:1, 25:1, 10:1, 5:1, 2:1 and / or.

[0053] The drying process is at least one of rotary evaporation drying, oven drying, or natural air drying; and / or,

[0054] The protective atmosphere is selected from at least one of nitrogen or an inert gas; preferably, the inert gas is at least one of argon or helium; and / or,

[0055] The high-temperature carbonization temperature is 900–1500℃, preferably 1000–1400℃; for example: 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, 1450℃, 1500℃; and / or,

[0056] The high-temperature carbonization time is 1 to 20 hours, preferably 2 to 12 hours; for example: 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours.

[0057] A third objective of this invention is to provide a metal-containing, closed-pore-rich hard carbon nanofiber material as described in one objective of this invention, or a metal-containing, closed-pore-rich hard carbon nanofiber material prepared by the method described in another objective of this invention, for use as a battery anode material, preferably for use as a sodium-ion battery anode material.

[0058] The fourth objective of this invention is to provide a sodium-modified hard carbon fiber-based composite anode material, comprising the following preparation method:

[0059] The metal-containing, closed-pore-rich hard carbon nanofiber material is used as the negative electrode and sodium is used to form a half-cell. The half-cell is then subjected to sodium deposition by discharging the metal-containing, closed-pore-rich hard carbon nanofiber material negative electrode to obtain the sodium-modified hard carbon fiber-based composite negative electrode material.

[0060] or,

[0061] A full cell is formed by using the metal-containing, closed-pore-rich hard carbon nanofiber material as the negative electrode and the sodium-containing positive electrode material. During charging, the sodium released from the positive electrode is stored in the metal-containing, closed-pore-rich hard carbon nanofiber material negative electrode, thus obtaining a sodium-modified hard carbon fiber-based composite negative electrode material.

[0062] According to an embodiment of the present invention, the sodium ion content of the sodium-modified hard carbon fiber-based composite anode material is 5-30 wt%.

[0063] According to embodiments of the present invention, the half-cell or full-cell further includes an electrolyte. The electrolyte is selected from carbonate electrolytes or ether electrolytes; preferably, the electrolyte is a carbonate electrolyte. Exemplarily, the carbonate electrolyte includes ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0064] Preferably, the electrolyte further contains a sodium salt. Exemplarily, the sodium salt includes at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium bis(fluorosulfonyl)imide (NaFSI), sodium trifluoromethanesulfonate (NaCF3SO3), etc., preferably NaPF6.

[0065] The electrolyte can be prepared using ratios commonly used by those skilled in the art. For example, the electrolyte comprises EC, DMC, and EMC in a volume ratio of 2:1:2. For example, the molar concentration of the sodium salt in the electrolyte is 0.5–2.5 mol / L. -1 Preferably 1.5 mol / L -1 .

[0066] According to an embodiment of the present invention, sodium treatment in step S6) refers to discharging the half-cell to below 0V and then continuing to discharge it. Preferably, the cutoff condition can be the half-cell capacity, discharge voltage, or discharge time, etc.

[0067] According to an embodiment of the present invention, when a full cell is composed of a metal-containing, closed-pore-rich hard carbon nanofiber material and a positive electrode material, the capacity value of the positive electrode material is 101-500% of the theoretical sodium intercalation capacity of the hard carbon fiber-based negative electrode material.

[0068] According to an embodiment of the present invention, the charging condition is to charge at 0.1-1C to 3.5-5V (e.g., 4.1V) to remove sodium from the positive electrode.

[0069] According to an embodiment of the present invention, the sodium-modified hard carbon fiber-based composite anode material comprises sodium, zinc, and hard carbon fibers, wherein the sodium is stored within the nano-confined space of the porous hard carbon fiber-based anode material; the sodium exists primarily in the form of NaC. x They exist in the form of atoms or small clusters within the nano-confined space of the porous hard carbon fiber-based anode material. Preferably, the nano-confined space is 0.34–2 nm.

[0070] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In the following, various technical solutions can, in principle, be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0071] Beneficial effects:

[0072] Using the zinc-rich, closed-pore hard carbon nanofiber material of this invention as the negative electrode for sodium-ion batteries exhibits excellent conductivity. The nanoscale pores composed of disordered carbon within the material provide a unique confined space for the reversible storage of sodium, effectively reducing the reaction between the electrolyte and metallic sodium and significantly improving the cycle stability of the negative electrode. Simultaneously, the metal single atoms or elemental metals within the hard carbon fiber material possess good sodium-ion adsorption capacity, facilitating preferential sodium storage within the carbon fiber and reducing the risk of sodium metal deposition on the carbon fiber surface. Furthermore, the hard carbon fiber negative electrode material itself provides excellent support, effectively reducing volume changes during repeated charge-discharge cycles, stabilizing the SEI on the negative electrode surface, and reducing sodium and electrolyte consumption. Moreover, compared to other hard carbon-based sodium-ion battery negative electrodes, the metal-containing, closed-pore hard carbon fiber negative electrode of this invention can serve as a self-supporting integrated electrode, eliminating the need for additional binders and conductive agents, thereby improving the overall energy density of the battery. Attached Figure Description

[0073] Figure 1A field emission scanning electron microscope (FEM) image of the porous hard carbon fiber material containing zinc metal in Embodiment 1 of the present invention is shown.

[0074] Figure 2 The images show (a) field emission scanning electron microscope (SEM) image and (b) transmission electron microscope (TEM) image of the zinc-containing, closed-pore-rich hard carbon nanofiber material of Example 1 of the present invention.

[0075] Figure 3 The XRD pattern of the zinc-containing, closed-pore-rich hard carbon nanofiber material of Example 1 of the present invention is shown.

[0076] Figure 4 The diagram shows the pore size distribution of the zinc-containing, closed-pore-rich hard carbon nanofiber material of Example 1 of the present invention based on nitrogen adsorption-desorption testing.

[0077] Figure 5 The diagram shows the pore size distribution of the zinc-containing, closed-pore-rich hard carbon nanofiber material of Example 1 of the present invention, based on a carbon dioxide gas adsorption-desorption test.

[0078] Figure 6 The example 1 shows a closed-cell-rich hard carbon fiber / sodium half-cell discharging 500 mAh g. -1 The curve.

[0079] Figure 7 The sodium half-cell based on a zinc-containing closed-pore hard carbon fiber electrode and a zinc-containing porous hard carbon fiber electrode shown in Example 1 operates at 1 mA cm⁻¹. -2 Comparison of coulombic efficiency at current densities.

[0080] Figure 8 A high-magnification transmission electron microscope image of the zinc-containing, closed-cell hard carbon fiber negative electrode from Test Example 1 after 100 cycles is shown.

[0081] Figure 9 A high-magnification transmission electron microscope image of the porous hard carbon fiber negative electrode containing zinc metal in Test Example 1 after 100 cycles is shown. Detailed Implementation

[0082] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0083] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the various possible combinations will not be described separately in this invention.

[0084] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0085] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0086] Example 1

[0087] Preparation of zinc-containing, closed-pore-rich hard carbon nanofiber materials:

[0088] Zinc acetate and polyacrylonitrile were separately dispersed in N,N-dimethylformamide. The two precursor solutions were mixed to obtain the spinning solution, in which the mass fractions of zinc acetate and polyacrylonitrile were 1% and 3%, respectively; the volume ratio of the metal acetate precursor solution to the fiber-forming polymer precursor solution was 1:1. The electrospinning process was carried out at a working voltage of 18 kV, a temperature of 35 °C, and a collection distance of 20 cm. The spinning solution was then used to prepare a thin film material composed of micro / nano fibers with diameters of 0.4–2 μm. The thin film material was then placed in a tube furnace and subjected to high-temperature annealing at 1000 °C under a nitrogen atmosphere for 2 hours, resulting in a porous hard carbon fiber material containing zinc metal. Its field emission scanning electron microscope (SEM) image is shown below. Figure 1 As shown.

[0089] Asphalt (softening point 280℃) is dissolved in tetrahydrofuran solvent to form an asphalt coating agent solution; the asphalt content in the asphalt coating agent solution is 5 mg / mL.

[0090] Zinc-containing porous hard carbon nanofibers were uniformly mixed with the obtained asphalt coating agent solution, wherein the mass ratio of the asphalt coating agent solution to the zinc-containing porous hard carbon nanofibers was 10:1. After rotary evaporation drying, the mixture was subjected to high-temperature carbonization under a nitrogen atmosphere at a temperature of 1000℃ for 2 hours. A zinc-containing, closed-pore-rich hard carbon nanofiber material was obtained, and its field emission scanning electron microscope image is shown below. Figure 2 As shown in (a), the transmission electron microscope image is as follows: Figure 2 As shown in (b), the XRD pattern is as follows: Figure 3 As shown.

[0091] Example 2

[0092] Preparation of tin-containing, closed-pore-rich hard carbon nanofiber materials:

[0093] Tin acetate and polyacrylonitrile were separately dispersed in N,N-dimethylformamide. The two precursor solutions were mixed to obtain the spinning solution, in which the mass fractions of zinc acetate and polyacrylonitrile were 1.5% and 2%, respectively. The volume ratio of the metal acetate precursor solution to the fiber-forming polymer precursor solution was 1:1. The working voltage applied during the electrospinning process was 17kV, the temperature was 40℃, and the collection distance was 18cm. The spinning solution was then used to form a thin film material composed of micro-nano fibers with a diameter of 0.8-1.5μm. The thin film material was then placed in a tube furnace and heated to 1000℃ under a nitrogen atmosphere for high-temperature annealing treatment for 2 hours, thus obtaining a porous hard carbon fiber material containing tin metal.

[0094] Asphalt (softening point 280℃) is dissolved in tetrahydrofuran solvent to form an asphalt coating agent solution; the asphalt content in the asphalt coating agent solution is 5 mg / mL.

[0095] The porous hard carbon nanofiber material containing tin metal was mixed evenly with the obtained coating agent solution, wherein the mass ratio of asphalt to porous hard carbon fiber material containing tin metal in the asphalt coating agent solution was 10:1; after rotary evaporation drying, the mixture was heated to 1000℃ under a nitrogen atmosphere for high-temperature annealing treatment, and the high-temperature carbonization time was 2h; thus, a tin metal-containing closed-pore hard carbon nanofiber material was obtained.

[0096] Example 3

[0097] Preparation of zinc / silver-containing closed-pore hard carbon nanofiber materials:

[0098] Silver acetate, zinc acetate, and polyacrylonitrile were dispersed separately in N,N-dimethylformamide. The three precursor solutions were mixed to obtain the spinning solution, in which the mass fractions of silver acetate, zinc acetate, and polyacrylonitrile were 0.75%, 0.75%, and 2%, respectively; the volume ratio of the silver acetate precursor solution, the zinc acetate precursor solution, and the fiber-forming polymer precursor solution was 1:1:2; the working voltage applied during the electrospinning process was 20kV, the temperature was 35℃, and the collection distance was 18cm, thus forming a thin film material composed of micro-nano fibers with a diameter of 1-2μm. The thin film material was then placed in a tube furnace and heated to 1000℃ under a nitrogen atmosphere for high-temperature annealing treatment for 2 hours, resulting in a porous hard carbon fiber material containing zinc / silver metal.

[0099] Asphalt (softening point 280℃) is dissolved in tetrahydrofuran solvent to form an asphalt coating agent solution; the asphalt content in the asphalt coating agent solution is 5 mg / mL.

[0100] The porous hard carbon nanofiber material containing zinc / silver metal was mixed evenly with the obtained coating agent solution, wherein the mass ratio of asphalt to porous hard carbon fiber material containing zinc / silver metal in the asphalt coating agent solution was 10:1; after rotary evaporation drying, the mixture was heated to 1000℃ under a nitrogen atmosphere for high-temperature annealing treatment, and the high-temperature carbonization time was 2h; thus, a closed-pore-rich hard carbon nanofiber material containing zinc / silver metal was obtained.

[0101] Comparative Example 1

[0102] It adopts a preparation method that is basically the same as that in Example 1 of this invention, the only difference being that...

[0103] The steps of dissolving asphalt in a polar solvent to form an asphalt coating agent solution and mixing the metal-containing porous hard carbon nanofiber material obtained in step S3) with the asphalt coating agent solution obtained in step S4) uniformly, drying, and then carbonizing the mixture at high temperature under a protective atmosphere are not performed.

[0104] Comparative Example 2

[0105] It adopts a preparation method that is basically the same as that in Example 1 of this invention, the only difference being that...

[0106] No metal salts are added to the spinning solution.

[0107] Table 1 summarizes the metal content, closed-pore structure ratio, and specific surface area test data under nitrogen / carbon dioxide adsorption-desorption tests of the metal-containing closed-pore hard carbon nanofiber materials prepared in Examples 1-3 and the hard carbon nanofiber materials prepared in Comparative Examples 1-2.

[0108] Table 1. Parameter determination of metal-containing closed-pore hard carbon nanofiber materials

[0109]

[0110] As shown in Table 1, only the preparation method of this invention can yield metal-rich, closed-pore hard carbon nanofiber materials with a reduced specific surface area compared to existing hard carbon anode materials. Existing reported carbon nanofiber materials all possess numerous micropores and mesopores, resulting in large specific surface areas. During cycling, they cannot suppress electrolyte penetration, leading to severe side reactions. In contrast, the carbon fibers of this invention are largely free of micropores and mesopores, consisting mostly of closed pores with a diameter less than 0.8 nm. This unique closed-pore structure effectively prevents electrolyte penetration, significantly suppressing side reactions and providing space for sodium storage within the fibers. Furthermore, the metal single atoms or elemental metals within the hard carbon fiber material exhibit good sodium ion adsorption capacity, facilitating preferential sodium storage within the carbon fiber and reducing the risk of sodium metal deposition on the carbon fiber surface. Simultaneously, the metal-rich, closed-pore hard carbon nanofiber material of this invention can serve as a self-supporting integrated electrode. Compared to other traditional hard carbon anodes, it eliminates the need for additional binders and conductive agents, thereby significantly increasing the energy density of sodium batteries.

[0111] Test Example 1

[0112] The zinc-containing, closed-pore hard carbon nanofiber material prepared in Example 1 was subjected to nitrogen adsorption-desorption testing, and the characterization results are as follows: Figure 4 As shown. From Figure 4 The results show that nitrogen gas has difficulty penetrating the zinc-containing, closed-pore-rich hard carbon nanofiber material, indicating that the material has very few mesopores and larger micropores. Further carbon dioxide adsorption-desorption tests were conducted, and the characterization results are as follows: Figure 5 As shown. From Figure 5 The results show that carbon dioxide can easily enter the zinc-containing, closed-pore-rich hard carbon nanofiber material, and verify that the zinc-containing, closed-pore-rich hard carbon nanofiber material has a closed-pore structure of 0.4-0.7 nm in size, which can effectively prevent the penetration of electrolyte and thus reduce side reactions.

[0113] A half-cell was constructed using the zinc-containing, closed-pore hard carbon nanofiber anode prepared in Example 1 and sodium. The electrolyte used in the half-cell was a mixed solution of EC, DMC, EMC, and NaPF6 (NaPF6 concentration 1.5M, volume ratio of EC, DMC, and EMC 2:1:2). The half-cell voltage was discharged below 0V, and the maximum capacity before the appearance of the overpotential for sodium nucleation was used as the cutoff condition. Figure 6 As shown, the maximum capacity in this embodiment is 500mAh g. -1 Subsequently at 1mA cm -2 Under a current density of 500 mAh g, the discharge specific capacity is 500 mAh g. -1 The charging voltage is cut off to 2V, such as Figure 7As shown, the sodium / hard carbon fiber half-cell can maintain a stable coulombic efficiency of approximately 99.3% for over 250 cycles. The comparison of cycle efficiency between the zinc-containing closed-pore hard carbon nanofiber material and the zinc-containing porous hard carbon nanofiber material in Example 1 demonstrates that the closed-pore structure exhibits superior reversibility compared to the porous structure with a higher specific surface area.

[0114] The zinc-containing, closed-pore-rich hard carbon nanofiber material prepared in Example 1 was used as a sodium support to assemble a symmetrical battery (both the positive and negative electrodes were sodium-loaded zinc-containing, closed-pore-rich hard carbon nanofibers; the metal-containing, closed-pore-rich hard carbon nanofiber negative electrode and sodium formed a half-cell; the sodium||hard carbon half-cell was sodium-modified by discharging to obtain the sodium-loaded zinc-containing, closed-pore-rich hard carbon nanofibers). The battery was used at a current density of 1 mA cm⁻¹. -2 (The electrolyte used in the symmetric battery was a mixed solution of EC, DMC, EMC, and NaPF6 (NaPF6 concentration was 1.5M, and the volume ratio of EC, DMC, and EMC was 2:1:2). After 100 charge-discharge cycles (each charging and discharging process lasted 1 hour), the battery was disassembled to obtain a high-magnification transmission electron microscope image of the cycled zinc-containing, closed-pore-rich hard carbon nanofiber material, as shown below.) Figure 8 As shown, the SEI layer thickness on the surface is relatively uniform after cycling, approximately 4-5 nm. Conversely, the porous hard carbon nanofiber material containing zinc metal prepared in Example 1, used as a sodium support, was assembled into a symmetrical battery at a current density of 1 mA cm⁻¹. -2 After 100 charge-discharge cycles, the battery was disassembled, yielding a high-magnification transmission electron microscope image of the cycled, zinc-containing porous hard carbon nanofiber material, as shown below. Figure 9 As shown, the SEI layer on the surface after cycling is relatively thick and unevenly distributed, approximately 12-18 nm.

[0115] In summary, the metal-containing, closed-pore-rich hard carbon nanofiber material prepared in this invention possesses ample sodium storage space, excellent sodium ion adsorption capacity, and good electrolyte barrier properties. It can significantly improve the sodium storage capacity of the hard carbon anode, suppress side reactions during cycling, and enhance the cycle stability of the sodium-ion battery anode, exhibiting superior performance. Furthermore, the self-supporting integrated electrode structure design can further improve the overall energy density of the battery, demonstrating promising application prospects.

[0116] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0117] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0118] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application’s filing, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0119] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

Claims

1. A metal-containing, closed-pore-rich hard carbon nanofiber material, characterized in that: The metal-containing, closed-pore-rich hard carbon nanofiber material contains metal inside, and the outer layer of the metal-containing, closed-pore-rich hard carbon nanofiber material is a carbon coating layer; the number of closed pores in the metal-containing, closed-pore-rich hard carbon nanofiber material is greater than the sum of the number of micropores and mesopores.

2. The metal-containing, closed-pore-rich hard carbon nanofiber material according to claim 1, characterized in that: The metal exists within the hard carbon nanofiber material in at least one form: a single metal atom, an elemental metal, or an alloy; and / or, The metal is selected from at least one of zinc, tin, and silver; and / or, The metal-containing, closed-pore-rich hard carbon nanofiber material contains 0.5–5 wt% metal.

3. The metal-containing, closed-pore-rich hard carbon nanofiber material according to claim 1, characterized in that: The diameter of the metal-containing, closed-pore-rich hard carbon nanofiber material is 0.002–2 μm; and / or, The closed pore is a closed-pore structure with a size of 0.4–0.7 nm; and / or, In the aforementioned metal-containing, closed-pore-rich hard carbon nanofiber material, based on the total number of pores, the proportion of closed-pore structures is 95%–99%; and / or, The specific surface area of ​​the metal-containing, closed-pore-rich hard carbon nanofiber material, as determined by nitrogen adsorption-desorption testing, ranged from 2 to 20 m². 2 g -1 ; and / or, The specific surface area of ​​the metal-containing, closed-pore-rich hard carbon nanofiber material, as determined by carbon dioxide adsorption-desorption tests, ranged from 140 to 390 m². 2 g -1 .

4. A method for preparing a metal-containing, closed-pore-rich hard carbon nanofiber material, characterized in that, Includes the following steps: S1) Dissolve the metal acetate and the fiber-forming polymer in an amide solvent to form a metal acetate precursor solution and a fiber-forming polymer precursor solution, respectively; S2) The precursor solution obtained in step S1) is mixed to obtain a spinning solution, and the spinning solution is made into a thin film material composed of micro and nano fibers by electrospinning. S3) The thin film material obtained in step S2) is subjected to high-temperature annealing under a protective atmosphere to obtain a metal-containing porous hard carbon nanofiber material. S4) Dissolve asphalt in a polar solvent to form an asphalt coating agent solution; S5) Mix the metal-containing porous hard carbon nanofiber material obtained in step S3) with the asphalt coating agent solution obtained in step S4) evenly, dry it, and then carbonize the dried mixture at high temperature under a protective atmosphere to obtain a metal-containing closed-pore hard carbon nanofiber material. The metal-containing, closed-pore-rich hard carbon nanofiber material according to any one of claims 1-3 is preferably prepared using the method described above.

5. The method for preparing metal-containing, closed-pore-rich hard carbon nanofiber material according to claim 4, characterized in that: In step S1), The metal acetate is at least one of zinc, tin, and silver; preferably, when two metal acetates are used, the molar ratio of the two metal acetates is 0.5:9.5 to 9.5:0.5; and / or, In the metal acetate precursor solution, the mass fraction of metal acetate is 0.2% to 4%, preferably 0.5% to 2%; and / or, The fiber-forming polymer is selected from at least one of polyacrylonitrile or polyvinylpyrrolidone; and / or The amide solvent is selected from at least one of N,N-dimethylformamide or N,N-dimethylacetamide; and / or The mass fraction of the fiber-forming polymer in the fiber-forming polymer precursor solution is 0.5% to 5%.

6. The method for preparing metal-containing, closed-pore-rich hard carbon nanofiber material according to claim 4, characterized in that: In step S2), The volume ratio of the metal acetate precursor solution to the fiber-forming polymer precursor solution is 1:1 to 1:9; and / or, The operating voltage for electrospinning is 10–25 kV, preferably 15–20 kV; and / or, The temperature for electrospinning is 25–70°C; and / or, The electrospinning collection distance is 10–25 cm; and / or, The spinning solution was used to prepare a thin film material composed of micro-nano fibers with a diameter of 0.002 to 2 μm.

7. The method for preparing metal-containing, closed-pore-rich hard carbon nanofiber material according to claim 4, characterized in that: In step S3), The high-temperature annealing temperature is 300–1200℃, preferably 1000–1200℃; and / or, The high-temperature annealing treatment time is 1 hour to 4 hours, preferably 2 to 3 hours; and / or, The protective atmosphere is selected from at least one of nitrogen or an inert gas; preferably, the inert gas is at least one of argon or helium.

8. The method for preparing metal-containing, closed-pore-rich hard carbon nanofiber material according to claim 4, characterized in that: In step S4), The polar solvent is selected from at least one of tetrahydrofuran, dichloromethane, and dimethyl sulfoxide; and / or, The asphalt is at least one of low-temperature asphalt or high-temperature asphalt; preferably, the softening point of the asphalt is in the range of 70–300℃, more preferably 240–300℃; and / or, The asphalt coating agent solution contains 5–20 mg / mL of asphalt.

9. The method for preparing metal-containing, closed-pore-rich hard carbon nanofiber material according to claim 4, characterized in that: In step S5), The mass ratio of the asphalt coating agent solution to the metal-containing porous hard carbon fiber material is 100:1 to 2:1; preferably 80:1 to 5:1; and / or, The drying process is at least one of rotary evaporation drying, oven drying, or natural air drying; and / or, The protective atmosphere is selected from at least one of nitrogen or an inert gas; preferably, the inert gas is at least one of argon or helium; and / or, The high-temperature carbonization temperature is 900–1500℃, preferably 1000–1400℃; and / or, The high-temperature carbonization time is 1 to 20 hours, preferably 2 to 12 hours.

10. The application of a metal-containing, closed-pore-rich hard carbon nanofiber material as described in any one of claims 1-3 or a metal-containing, closed-pore-rich hard carbon nanofiber material prepared by the method described in any one of claims 4-9 as a battery anode material, preferably as a sodium-ion battery anode material.

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