Ultra-microporous fluorine-doped hard carbon anode material and its preparation method

Abstract

The present invention provides a super-microporous fluorine-doped hard carbon negative electrode material and a preparation method thereof. Among them, the preparation method of the super-microporous fluorine-doped hard carbon negative electrode material includes: providing a precursor mixture, the precursor mixture including fluorinated cotton material and graphene oxide; freeze-drying the precursor mixture to obtain a precursor material; subjecting the precursor material to vacuum sintering to obtain a super-microporous hard carbon material; and performing fluorination treatment on the super-microporous hard carbon material in a fluorine gas atmosphere to obtain a super-microporous fluorine-doped hard carbon negative electrode material. The super-microporous fluorine-doped hard carbon negative electrode material prepared in the present invention has high initial efficiency, high sodium storage capacity and rate performance, and the preparation method is simple and low in cost, and to a certain extent, it can significantly improve the technical problem of low performance of the negative electrode material of sodium ion batteries existing in the related technical fields.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon materials, and particularly relates to a super-microporous fluorinated hard carbon negative electrode material and a preparation method thereof. Background Art

[0002] With the growth of energy demand and the urgent need for carbon dioxide emission reduction, low-cost and high-performance electrochemical energy storage systems have received extensive attention. Among them, sodium ions are recognized as the most promising to replace lithium-ion batteries as the next-generation new product system due to their low price, rich reserves, and suitable sodium chemical potential.

[0003] Since the ionic radius of sodium ions is larger than that of lithium ions, and the diffusion kinetics of sodium ion negative electrode materials is slower, the graphite material used for the negative electrode of lithium batteries has a reversible capacity of only 35 mAhg in sodium ion batteries -1 , therefore, developing high-performance and low-cost negative electrode materials is the key to promoting the commercialization of sodium ion batteries. Summary of the Invention

[0004] Embodiments of the present invention provide a super-microporous fluorinated hard carbon negative electrode material and a preparation method thereof, which can improve the technical problem of low performance of the negative electrode material of sodium ion batteries.

[0005] In a first aspect, embodiments of the present invention provide a preparation method of a super-microporous fluorinated hard carbon negative electrode material, including the following steps:

[0006] Provide a precursor mixture, where the precursor mixture includes fluorinated cotton material and graphene oxide;

[0007] Freeze-dry the precursor mixture to obtain a precursor material;

[0008] Vacuum sinter the precursor material to obtain a super-microporous hard carbon material;

[0009] Under a fluorine gas atmosphere, fluorinate the super-microporous hard carbon material to obtain a super-microporous fluorinated hard carbon negative electrode material.

[0010] In some embodiments of the present invention, the fluorination degree of the fluorinated cotton material is 2-10%, and the mass ratio of graphene oxide to the fluorinated cotton material in the precursor mixture is 1-6:20.

[0011] In some embodiments of the present invention, the temperature for freeze-drying the precursor mixture is -10 to -70 °C, and the time is 10 to 48 h.

[0012] In some embodiments of the present invention, the vacuum degree for vacuum sintering the precursor material is 50 Pa to 300 Pa.

[0013] In some embodiments of the present invention, the step of subjecting the precursor material to vacuum sintering to obtain the ultra-microporous hard carbon material includes:

[0014] Sinter the precursor material at 300-600 °C for 1-3 h, and then sinter it at 800-1200 °C for 2-8 h with a heating rate of 1-5 °C / min to obtain the ultra-microporous hard carbon material.

[0015] In some embodiments of the present invention, the temperature for fluorination treatment of the ultra-microporous hard carbon material is 600-1000 °C, and the fluorination time is 2-5 h.

[0016] In some embodiments of the present invention, the preparation method of the fluorinated cotton material includes:

[0017] Place the cotton material in a fluorine-containing acidic solution and soak it for fluorination for 0.5-5 h to obtain the fluorinated cotton material.

[0018] In some embodiments of the present invention, the cotton material includes one or more of absorbent cotton, cotton thread or sponge.

[0019] In some embodiments of the present invention, before the step of subjecting the ultra-microporous hard carbon material to fluorination treatment in a fluorine gas atmosphere to obtain an ultra-microporous fluorine-doped hard carbon negative electrode material, it further includes:

[0020] Subject the ultra-microporous hard carbon material to ball milling treatment in an inert gas atmosphere. The time of the ball milling treatment is 1-12 h, the ball-to-material ratio is 1:2-20:1, and the rotation speed is 100-800 r / min.

[0021] Second, in an embodiment of the present invention, there is provided an ultra-microporous fluorine-doped hard carbon negative electrode material, and the ultra-microporous fluorine-doped hard carbon negative electrode material is prepared by using any of the preparation methods of the ultra-microporous fluorine-doped hard carbon negative electrode material.

[0022] In some embodiments of the present invention, the fluorine doping rate of the ultra-microporous fluorine-doped hard carbon negative electrode material is 5-10%.

[0023] Advantageous effects of the embodiments of the present invention:

[0024] In the embodiments of the present invention, after obtaining the loose and porous precursor material, the ultra-microporous hard carbon material is obtained by subjecting the loose and porous precursor material to vacuum sintering. Then, in a fluorine gas atmosphere, the ultra-microporous hard carbon material is further subjected to fluorination treatment. The obtained ultra-microporous fluorine-doped hard carbon negative electrode material has high initial efficiency, high sodium storage capacity and rate performance, and the preparation method is simple and the cost is low. To a certain extent, it can significantly improve the technical problem of low performance of the negative electrode material of sodium ion batteries existing in the related technical field. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0026] Figure 1 is a schematic flow chart of a method for preparing a super-microporous fluorine-doped hard carbon negative electrode material provided by an embodiment of the present invention;

[0027] Figure 2 is a scanning electron microscope image of a super-microporous fluorine-doped hard carbon negative electrode material provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention. In the present invention, unless otherwise stated, the orientation terms such as "upper" and "lower" usually refer to the upper and lower in the actual use or working state of the device, specifically the drawing direction in the drawings; and "inner" and "outer" refer to the outline of the device.

[0029] Hard carbon composed of interlaced graphite microcrystals, abundant micropores and defects is considered to play an important role in the future commercialization of sodium-ion batteries due to its large interlayer spacing, large capacity and stable cycling performance. However, the high specific surface area and abundant defects of hard carbon materials will cause continuous reactions between the electrolyte and the electrode interface, generating a solid electrolyte interface film (SEI), resulting in a low first-cycle Coulombic efficiency of the negative electrode.

[0030] Research shows that through reasonable process technologies, hard carbon materials with controllable crystallinity or controllable micro-morphological structures, or doping on the surface of negative electrode materials, can effectively improve the first efficiency and fast charging performance of the negative electrode. Therefore, the capacity and Coulombic efficiency of hard carbon are affected by the micro-structure. It is reported that by constructing nanotubes, nanowires, carbon quantum dots, porous structures, hierarchical structures, etc. to change the particle size and micro-morphological structure of hard carbon, the electrochemical performance of electrode materials can be improved. At present, the commonly used atmospheric pressure inert atmosphere sintering regulation carbonization method, including carbonization temperature, temperature change rate, carbonization method, etc., is used to adjust the micro-structure of hard carbon.

[0031] However, the limited active sites of hard carbon will limit the adsorption of sodium ions, reducing its capacity and rate performance. By introducing heteroatom doping into hard carbon, the microproperties such as the interlayer spacing, surface wettability, and electronic conductivity of hard carbon materials can be optimized, thereby improving the sodium storage performance of hard carbon. However, the anode materials prepared by related technologies are limited by micropores, macropores / poreless structures, and a large number of defects caused during the doping process, resulting in low yield and difficulty in mass production of the prepared anode materials. Therefore, it is very important to develop a high initial efficiency, high capacity, and fast charging anode material.

[0032] As Figure 1 shown, the present invention provides a method for preparing a super-microporous fluorine-doped hard carbon anode material, which includes the following steps:

[0033] S1. Provide a precursor solution, and the precursor mixture includes a fluorinated cotton material and graphene oxide;

[0034] S2. Freeze-dry the precursor mixture to obtain a precursor material;

[0035] S3. Vacuum sinter the precursor material to obtain a super-microporous hard carbon material;

[0036] S4. Under a fluorine gas atmosphere, perform fluorination treatment on the super-microporous hard carbon material to obtain a super-microporous fluorine-doped hard carbon anode material.

[0037] Specifically, in step S1, the provided precursor mixture is obtained by fluorinating cotton materials with a fluorine-containing acidic solvent. Preferably, the fluorination time is 0.5 - 5h to obtain a fluorinated cotton material. Thereafter, take a graphene oxide solution of 0.5 - 5mg / mL, ultrasonically disperse the graphene oxide solution for 1 - 4h, and then add the fluorinated cotton material to the graphene oxide solution to obtain the precursor mixture.

[0038] Among them, the cotton material is one or more of cotton wool, cotton thread, or sponge, and the fluorinated cotton material obtained by fluorinating the cotton material with the fluorine-containing acidic solvent is a partially fluorinated cotton material. The fluorine-containing acidic solvent is a diluted hydrogen fluoride solvent or ammonium fluoride solvent with a volume concentration ratio of 5 - 50%, or a mixed solvent of hydrogen fluoride and ammonium fluoride.

[0039] Understandably, in step S2, by freeze-drying the precursor mixture, the adsorption state of the graphene oxide material on the surface of the fluorinated cotton material can be maintained without change. Since the precursor material is doped with fluoride ions, and fluoride ions have a high electronegativity, under the molecular repulsion, the layer spacing of the carbon layer of the supermicroporous hard carbon material prepared in step S3 can be enlarged. Among them, by regulating the fluorination degree of the cotton material, controllable fluorine doping can be realized. That is, in this embodiment, by regulating the fluorination degree of the fluorinated cotton material in the precursor mixture, the layer spacing and the surface defect degree of the supermicroporous hard carbon negative electrode material can be further regulated, which is beneficial to improving the sodium storage capacity and rate performance.

[0040] Specifically, in step S3, the precursor material is subjected to vacuum sintering. Under vacuum conditions, the macropores of the precursor material are closed to form supermicropores. At the same time, during the sintering process, the graphene oxide material adsorbed on the fluorinated cotton material is reduced and bonded to the surface of the supermicroporous hard carbon material through F-C-O or F-C=O functional group chemical bonds. Since the functional groups of the precursor material are broken and atomic rearrangement occurs, the energy band gap of the precursor material is changed, introducing rich electronic defects, thereby improving the electronic conductivity of the supermicroporous hard carbon material and increasing the adsorption sites of sodium ions, and improving the sodium storage capacity and rate performance of the prepared supermicroporous hard carbon material.

[0041] Furthermore, through step S4, the supermicroporous hard carbon material is further fluorinated. Under high-temperature conditions, fluorine atoms are inserted into the carbon layer of the supermicroporous hard carbon material to realize the secondary adjustment of the microstructure of the supermicroporous hard carbon material, thereby obtaining the supermicroporous fluorine-doped hard carbon negative electrode material with high initial efficiency, high sodium storage capacity and rate performance, as Figure 2 shown, Figure 2 is the scanning electron microscope image of the supermicroporous fluorine-doped hard carbon negative electrode material.

[0042] In addition, it should be noted that the supermicroporous structure (<0.5 nm) of the supermicroporous fluorine-doped hard carbon negative electrode material itself can play the role of an ion sieve, reducing the diffusion of sodium ions and allowing unsolvated sodium ions to enter the pores, thereby reducing the interfacial contact between the electrolyte and the inner pores without sacrificing the diffusion kinetics and improving the initial efficiency of the supermicroporous fluorine-doped hard carbon negative electrode material.

[0043] According to the above analysis, in this embodiment, after obtaining the loose and porous precursor material, the ultra-microporous hard carbon material is obtained by subjecting the loose and porous precursor material to vacuum sintering. Subsequently, in a fluorine gas atmosphere, the ultra-microporous hard carbon material is further subjected to fluorination treatment, and the obtained ultra-microporous fluorine-doped hard carbon negative electrode material has high initial efficiency, high sodium storage capacity, and rate performance. Moreover, the preparation method is simple and the cost is low, which can significantly improve the technical problem of low performance of the negative electrode material of sodium-ion batteries in the related technical field to a certain extent.

[0044] Specifically, in this embodiment, the fluorination degree of the fluorinated cotton material is 2-10%, and the mass ratio of graphene oxide to the fluorinated cotton material in the precursor mixture is 1-6:20.

[0045] Since the fluorination degree of the fluorinated cotton material affects the microstructure of the prepared ultra-microporous fluorine-doped hard carbon negative electrode material, in this embodiment, preferably, the fluorinated cotton material with a fluorination degree of 2-10% is used. At the same time, since the mass ratio of graphene oxide to the fluorinated cotton material in the precursor mixture also affects the performance of the prepared ultra-microporous fluorine-doped hard carbon negative electrode material, preferably, the mass ratio of graphene oxide to the fluorinated cotton material is 1-6:20, that is, the adsorption amount of graphene oxide on the surface of the fluorinated cotton material in the precursor mixture accounts for 5-30% of the mass fraction of the fluorinated cotton material.

[0046] Furthermore, the temperature of freeze-drying the precursor mixture is -10 to -70 °C, and the time is 10 to 48 h.

[0047] In this embodiment, the temperature of freeze-drying the precursor mixture and the set vacuum degree affect the freeze-drying time. Under the condition that the content of the solvent in the precursor mixture is the same, if the freeze-drying temperature is lower and the vacuum degree is higher, the ice crystal size is smaller, and the pore size of the porous structure of the formed precursor material is also smaller. At the same time, the lower the vacuum degree, the higher the gasification rate of the solvent in the precursor mixture, and the shorter the freeze-drying time. On the contrary, if the freeze-drying temperature is higher and the vacuum degree is lower, the ice crystal size is larger, the pore size of the porous structure of the formed precursor material is larger, and at the same time, the lower the vacuum degree, the lower the gasification rate of the solvent in the precursor mixture, and the longer the freeze-drying time.

[0048] In an embodiment of the present invention, the vacuum degree of vacuum sintering of the precursor material is 50 Pa to 300 Pa.

[0049] In this embodiment, the ultra-microporous hard carbon material can be obtained by vacuum sintering the precursor material. Among them, the lower the set vacuum degree, the more accelerated the cleavage of functional groups and atomic rearrangement on the precursor material, thereby changing the energy band gap of the precursor material, introducing abundant electron defects, enhancing the electronic conductivity of the prepared ultra-microporous hard carbon material, and improving the fast charging performance of the prepared ultra-microporous hard carbon material. Preferably, the vacuum degree adopted is 50 Pa to 300 Pa.

[0050] Further, step S3 includes: sintering the precursor material at 300 to 600 °C for 1 to 3 h, and then sintering it at 800 to 1200 °C for 2 to 8 h, with a heating rate of 1 to 5 °C / min, to obtain the ultra-microporous hard carbon material.

[0051] In this embodiment, the ultra-microporous hard carbon material can be obtained after vacuum sintering. Among them, sintering includes low-temperature sintering and high-temperature sintering sequentially performed on the precursor material. Specifically, low-temperature sintering is carried out at a temperature of 300 to 600 °C, which can decompose the macromolecular groups on the surface of the precursor material to generate a first intermediate product. When the temperature rises to 800 to 1200 °C for high-temperature sintering, the small molecular groups on the surface of the first intermediate product continue to decompose. Due to the cleavage and rearrangement of chemical bonds between functional groups, the crystallinity of the prepared ultra-microporous hard carbon material becomes better, and the graphitization degree is improved, which is beneficial to the transport of electrons / ions, thereby improving the initial efficiency of the ultra-microporous hard carbon material.

[0052] Among them, if the temperature of low-temperature sintering is too high, it will lead to a decrease in the layer spacing of the first intermediate product, resulting in a decrease in the embeddable sodium ions, and further reducing the initial efficiency. If the temperature of high-temperature sintering is too high, it will lead to a decrease in the defects formed in the ultra-microporous hard carbon material, a reduction in the sites that can adsorb sodium ions, a decrease in the reversible capacity, and affect the cycle stability of the ultra-microporous hard carbon material.

[0053] In addition, the heating rate in the low-temperature sintering stage and the high-temperature sintering stage also needs to be controlled. If the heating rate is too high, that is, the heating is too fast, it will damage the pore structure of the ultra-microporous hard carbon material. If the heating rate is too low, that is, the heating is too slow, it will prolong the sintering time, which is not conducive to reducing the preparation cost. Preferably, the heating rate is 1 to 5 °C / min.

[0054] Further, the temperature for fluorination treatment of the ultra-microporous hard carbon material is 600 to 1000 °C, and the fluorination time is 2 to 5 h.

[0055] It should be noted that the fluorine gas atmosphere mentioned in step S4 refers to a mixed atmosphere of fluorine gas and an inert gas, and the concentration of fluorine gas is 5-20%. The inert gas is one of nitrogen, helium or argon. And the fluorine doping rate of the prepared ultra-microporous fluorine-doped hard carbon negative electrode material is 5-10%.

[0056] Furthermore, in this embodiment, before step S4, the step of fluorinating the ultra-microporous hard carbon material in a fluorine gas atmosphere to obtain an ultra-microporous fluorine-doped hard carbon negative electrode material further includes:

[0057] The ultra-microporous hard carbon material is ball-milled in an inert gas atmosphere. The ball-milling time is 1-12 h, the ball-to-material ratio is 1:2-20:1, and the rotation speed is 100-800 revolutions per minute.

[0058] In the present invention, there is also provided an ultra-microporous fluorine-doped hard carbon negative electrode material, which is prepared by using any of the preparation methods of the ultra-microporous fluorine-doped hard carbon negative electrode materials.

[0059] Among them, the fluorine doping rate of the ultra-microporous fluorine-doped hard carbon negative electrode material is 5-10%.

[0060] The following further explains the preparation method of an ultra-microporous fluorine-doped hard carbon negative electrode material of the present invention through specific examples:

[0061] Example 1

[0062] Take an appropriate amount of cotton, soak it in 10 mol / L hydrofluoric acid for pretreatment. After soaking for 2 h, wash it clean and set aside. Take 200 mL of 2 mg / mL graphene oxide solution, ultrasonically disperse it for 2 h, and soak the above-prepared fluorinated cotton in the graphene oxide solution. After soaking for 1 h, a precursor mixture is obtained;

[0063] The precursor mixture is freeze-dried for 24 h (freezing temperature: -70 °C, vacuum degree: 5 Pa) to obtain a precursor material;

[0064] The precursor material is sintered at a heating rate of 2 °C / min under a vacuum degree of 100 Pa. First, it is heated to 350 °C and sintered for 2 h, and then it is heated to 1000 °C at a heating rate of 2 °C / min and sintered for 4 h to obtain an ultra-microporous hard carbon material;

[0065] The ultra-microporous hard carbon material is ball-milled (ball-milling time 8 h, ball-to-material ratio 1:5, rotation speed 400 revolutions per minute) to obtain an ultra-microporous hard carbon powder material, and it is fluorinated. The experimental conditions are: 10% fluorine / argon mixed gas, heated to 800 °C at a heating rate of 2 °C / min, and kept warm for 2 h to obtain a 5% fluorine-doped ultra-microporous fluorine-doped hard carbon negative electrode material.

[0066] Example 2

[0067] Take an appropriate amount of cotton, soak it in 10 mol / L hydrofluoric acid for pretreatment. After soaking for 2 h, wash it clean and set it aside. Take 200 mL of graphene oxide solution with a concentration of 2 mg / mL, ultrasonically disperse it for 2 h, and soak the above-prepared fluorinated cotton in the graphene oxide solution. After soaking for 1 h, a precursor mixture is obtained;

[0068] Freeze-dry the precursor mixture for 24 h (freezing temperature: -70 °C, vacuum degree: 5 Pa) to obtain a precursor material;

[0069] Under a vacuum degree of 100 Pa, heat the precursor material at a heating rate of 2 °C / min. First, heat it to 350 °C and sinter for 2 h, and then heat it to 1000 °C at a heating rate of 2 °C / min and sinter for 4 h to obtain a super-microporous hard carbon material;

[0070] Perform ball milling on the super-microporous hard carbon material (ball milling time: 8 h, ball-to-material ratio: 1:5, rotation speed: 400 r / min) to obtain a super-microporous hard carbon powder material, and perform fluorination treatment on it. The experimental conditions are as follows: 10% fluorine / argon mixed gas, heat it to 800 °C at a heating rate of 2 °C / min, and keep it warm for 2.5 h to obtain a 6% fluorine-doped super-microporous fluorine-doped hard carbon anode material.

[0071] Example 3

[0072] Take an appropriate amount of cotton, soak it in 10 mol / L hydrofluoric acid for pretreatment. After soaking for 2 h, wash it clean and set it aside. Take 200 mL of graphene oxide solution with a concentration of 2 mg / mL, ultrasonically disperse it for 2 h, and soak the above-prepared fluorinated cotton in the graphene oxide solution. After soaking for 1 h, a precursor mixture is obtained;

[0073] Freeze-dry the precursor mixture for 24 h (freezing temperature: -70 °C, vacuum degree: 5 Pa) to obtain a precursor material;

[0074] Under a vacuum degree of 100 Pa, heat the precursor material at a heating rate of 2 °C / min. First, heat it to 350 °C and sinter for 2 h, and then heat it to 1000 °C at a heating rate of 2 °C / min and sinter for 4 h to obtain a super-microporous hard carbon material;

[0075] Perform ball milling on the super-microporous hard carbon material (ball milling time: 8 h, ball-to-material ratio: 1:5, rotation speed: 400 r / min) to obtain a super-microporous hard carbon powder material, and perform fluorination treatment on it. The experimental conditions are as follows: 10% fluorine / argon mixed gas, heat it to 800 °C at a heating rate of 2 °C / min, and keep it warm for 3 h to obtain a 7% fluorine-doped super-microporous fluorine-doped hard carbon anode material.

[0076] Example 4

[0077] Take an appropriate amount of cotton, soak and pretreat it with 10 mol / L hydrofluoric acid. After soaking for 2 h, wash it clean and set it aside. Take 200 mL of graphene oxide solution at 2 mg / mL, ultrasonically disperse it for 2 h, and soak the above-prepared fluorinated cotton in the graphene oxide solution. After soaking for 1 h, a precursor mixture is obtained;

[0078] Freeze-dry the precursor mixture for 24 h (freezing temperature: -70 °C, vacuum degree: 5 Pa) to obtain a precursor material;

[0079] Under a vacuum degree of 100 Pa, heat the precursor material at a heating rate of 2 °C / min. First, heat it to 350 °C and sinter for 2 h, then heat it to 1000 °C at a heating rate of 2 °C / min and sinter for 4 h to obtain a super-microporous hard carbon material;

[0080] Perform ball milling on the super-microporous hard carbon material (ball milling time: 8 h, ball-to-material ratio: 1:5, rotation speed: 400 r / min) to obtain a super-microporous hard carbon powder material, and perform fluorination treatment on it. The experimental conditions are as follows: 10% fluorine / argon mixed gas, heat it to 800 °C at a heating rate of 2 °C / min, and keep it at a constant temperature for 3.5 h to obtain an 8% fluorine-doped super-microporous fluorine-doped hard carbon negative electrode material.

[0081] Example 5

[0082] Take an appropriate amount of cotton, soak and pretreat it with 10 mol / L hydrofluoric acid. After soaking for 2 h, wash it clean and set it aside. Take 200 mL of graphene oxide solution at 2 mg / mL, ultrasonically disperse it for 2 h, and soak the above-prepared fluorinated cotton in the graphene oxide solution. After soaking for 1 h, a precursor mixture is obtained;

[0083] Freeze-dry the precursor mixture for 24 h (freezing temperature: -70 °C, vacuum degree: 5 Pa) to obtain a precursor material;

[0084] Under a vacuum degree of 100 Pa, heat the precursor material at a heating rate of 2 °C / min. First, heat it to 350 °C and sinter for 2 h, then heat it to 1000 °C at a heating rate of 2 °C / min and sinter for 4 h to obtain a super-microporous hard carbon material;

[0085] Perform ball milling on the super-microporous hard carbon material (ball milling time: 8 h, ball-to-material ratio: 1:5, rotation speed: 400 r / min) to obtain a super-microporous hard carbon powder material, and perform fluorination treatment on it. The experimental conditions are as follows: 10% fluorine / argon mixed gas, heat it to 800 °C at a heating rate of 2 °C / min, and keep it at a constant temperature for 4 h to obtain a 9% fluorine-doped super-microporous fluorine-doped hard carbon negative electrode material.

[0086] Example 6

[0087] Take an appropriate amount of cotton, soak it in 10 mol / L hydrofluoric acid for pretreatment. After soaking for 2 h, wash it clean and set aside. Take 200 mL of 2 mg / mL graphene oxide solution, ultrasonically disperse it for 2 h, and soak the above-prepared fluorinated cotton in the graphene oxide solution. After soaking for 1 h, a precursor mixture is obtained;

[0088] Freeze-dry the precursor mixture for 24 h (freezing temperature: -70 °C, vacuum degree: 5 Pa) to obtain a precursor material;

[0089] Under a vacuum degree of 100 Pa, heat the precursor material at a heating rate of 2 °C / min. First, heat it to 350 °C and sinter for 2 h, then heat it to 1000 °C at a heating rate of 2 °C / min and sinter for 4 h to obtain a super-microporous hard carbon material;

[0090] Perform ball milling on the super-microporous hard carbon material (ball milling time: 8 h, ball-to-material ratio: 1:5, rotation speed: 400 r / min) to obtain a super-microporous hard carbon powder material, and perform fluorination treatment on it. The experimental conditions are as follows: 10% fluorine / argon mixed gas, heat it to 800 °C at a heating rate of 2 °C / min, and keep it at this temperature for 5 h to obtain a 10% fluorine-doped super-microporous fluorine-doped hard carbon anode material.

[0091] Comparative Example 1

[0092] Take an appropriate amount of cotton, soak it in 10 mol / L hydrofluoric acid for pretreatment. After soaking for 2 h, wash it clean and set aside. Take 200 mL of 2 mg / mL graphene oxide solution, ultrasonically disperse it for 2 h, and soak the above-prepared fluorinated cotton in the graphene oxide solution. After soaking for 1 h, a precursor mixture is obtained;

[0093] Freeze-dry the precursor mixture for 24 h (freezing temperature: -70 °C, vacuum degree: 5 Pa) to obtain a precursor material;

[0094] Under a vacuum degree of 100 Pa, heat the precursor material at a heating rate of 2 °C / min. First, heat it to 350 °C and sinter for 2 h, then heat it to 1000 °C at a heating rate of 2 °C / min and sinter for 4 h to obtain a super-microporous hard carbon material;

[0095] Perform ball milling on the super-microporous hard carbon material (ball milling time: 8 h, ball-to-material ratio: 1:5, rotation speed: 400 r / min) to obtain a super-microporous hard carbon powder material.

[0096] Comparative Example 2

[0097] Take an appropriate amount of cotton, soak it in 10 mol / L hydrofluoric acid for pretreatment. After soaking for 2 h, wash it clean and set aside. Take 200 mL of 2 mg / mL graphene oxide solution, ultrasonically disperse it for 2 h, and soak the above-prepared fluorinated cotton in the graphene oxide solution. After soaking for 1 h, a precursor mixture is obtained;

[0098] Blast-dry the precursor material at a drying temperature of 100 °C for 24 h to obtain the dried precursor material;

[0099] Under a vacuum of 100 Pa, at a heating rate of 2 °C / min, first heat the precursor material to 350 °C and sinter for 2 h, then heat it to 1000 °C at a heating rate of 2 °C / min and sinter for 4 h to obtain a super-microporous hard carbon material;

[0100] Perform ball milling on the super-microporous hard carbon material (ball milling time 8 h, ball-to-material ratio 1:5, rotation speed 400 r / min) to obtain a super-microporous hard carbon powder material.

[0101] Furthermore, detect the performance of the materials prepared in Examples 1 to 6 and Comparative Examples 1 and 2. Among them, the detection process includes:

[0102] (1) Preparation of the electrode: Mix the materials prepared in Examples 1 to 6 and the materials prepared in Comparative Examples 1 and 2 with CMC (binder sodium carboxymethyl cellulose) and super P (conductive carbon black) in a ratio of 8:1:1, stir evenly, coat it on the surface of aluminum foil, and transfer it to a vacuum drying oven at 90 °C and dry for 12 h. Then, after cold pressing, die-cut it into circular electrodes with a diameter of 12 mm, and 8 circular electrodes are obtained. Among them, the circular electrodes corresponding to the materials prepared in Examples 1 to 6 are Samples 1 to 6, and the circular electrodes corresponding to the materials prepared in Comparative Examples 1 and 2 are Samples 7 and 8. The loading of the active material in Samples 1 to 8 prepared is 2.5 mg / cm 2 。

[0103] (2) Performance detection: Using Samples 1 to 8 as the negative electrode and sodium sheet as the positive electrode, 1 M NaPF 6It is dissolved in a mixed solvent of diethylene glycol and dimethyl ether (the volume ratio of diethylene glycol to dimethyl ether is 1:1) as the electrolyte, and assembled into a CR2032 button battery for testing. Among them, the first Coulombic efficiency test and the rate performance test are both carried out on a LAND-CT2100A battery cabinet of Blue Energy. Specifically, the test conditions for the first Coulombic efficiency are: constant current charge and discharge are carried out at a current of 50 mA / g and a voltage of 0 - 2.5 V. The test conditions for the rate performance are: constant current charge and discharge tests are carried out at a voltage of 0 - 2.5 V with currents of 50 mA / g, 100 mA / g, 200 mA / g, 500 mA / g, 1000 mA / g, and 2000 mA / g respectively.

[0104] The results are shown in the following table

[0105]

[0106]

[0107] It can be clearly seen that the test results of the first Coulombic efficiency and the rate performance test of Samples 1 to 6 are both better than those of Samples 7 and 8. Therefore, the super-microporous fluorine-doped hard carbon negative electrode material prepared by the present invention has high initial efficiency, high sodium storage capacity and rate performance, and the preparation method is simple and the cost is low, which can significantly improve the technical problem of low performance of the negative electrode material of sodium ion batteries existing in the related technical fields.

[0108] Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those skilled in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A preparation method of a super-microporous fluorine-doped hard carbon anode material, characterized in that, it comprises the following steps: Provide a precursor mixture, the precursor mixture comprising a fluorinated cotton material and graphene oxide; Freeze-dry the precursor mixture to obtain a precursor material; wherein, the temperature for freeze-drying the precursor mixture is -10 to -70 °C, and the time is 10 to 48 h; Vacuum sinter the precursor material, sinter the precursor material at 300 to 600 °C for 1 to 3 h, and then, sinter it at 800 to 1200 °C for 2 to 8 h, and the heating rate is 1 to 5 °C / min to obtain a super-microporous hard carbon material; Under a fluorine gas atmosphere, perform fluorination treatment on the super-microporous hard carbon material to obtain a super-microporous fluorine-doped hard carbon anode material.

2. The preparation method of the super-microporous fluorine-doped hard carbon anode material according to claim 1, characterized in that, the fluorination degree of the fluorinated cotton material is 2 to 10%, and the mass ratio of graphene oxide to the fluorinated cotton material in the precursor mixture is 1 to 6:

20.

3. The preparation method of the super-microporous fluorine-doped hard carbon anode material according to claim 1, characterized in that, the vacuum degree for vacuum sintering the precursor material is 50 Pa to 300 Pa.

4. The preparation method of the super-microporous fluorine-doped hard carbon anode material according to claim 1, characterized in that, the temperature for fluorination treatment of the super-microporous hard carbon material is 600 to 1000 °C, and the fluorination time is 2 to 5 h.

5. The preparation method of the super-microporous fluorine-doped hard carbon anode material according to claim 1, characterized in that, the preparation method of the fluorinated cotton material comprises: Place the cotton material in a fluorine-containing acidic solution and soak it for fluorination for 0.5 - 5 h to obtain the fluorinated cotton material.

6. The preparation method of the super-microporous fluorine-doped hard carbon anode material according to claim 1, characterized in that, the cotton material comprises one or more of absorbent cotton, cotton thread or sponge.

7. The preparation method of the super-microporous fluorine-doped hard carbon anode material according to claim 1, characterized in that, before the step of performing fluorination treatment on the super-microporous hard carbon material under a fluorine gas atmosphere to obtain a super-microporous fluorine-doped hard carbon anode material, it further comprises: Under an inert gas atmosphere, perform ball milling treatment on the super-microporous hard carbon material, the time for the ball milling treatment is 1 to 12 h, the ball-to-material ratio is 1:2 to 20:1, and the rotation speed is 100 to 800 r / min.

8. A super-microporous fluorine-doped hard carbon anode material, characterized in that, it is prepared by using the preparation method of the super-microporous fluorine-doped hard carbon anode material according to any one of claims 1 - 7.

9. The super-microporous fluorine-doped hard carbon anode material according to claim 8, characterized in that, the fluorine doping rate of the super-microporous fluorine-doped hard carbon anode material is 5 to 10%.

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