Fluorine-containing porous carbon, negative electrode material and preparation method thereof

Abstract

The application discloses fluorine-containing porous carbon, a negative electrode material and a preparation method thereof, and relates to the technical field of lithium ion battery negative electrode materials.The fluorinated modified porous carbon material is directly prepared by adopting the pulse plasma technology through a one-step method, a large number of complicated intermediate steps are omitted, and the preparation efficiency of the fluorine-containing porous carbon is greatly improved.When the fluorine-containing porous carbon is used as a lithium ion battery negative electrode, the strong C-F bond energy can provide additional pseudo-capacitance capacity, and in the subsequent charging and discharging process, a stable LiF interface layer can be more easily formed on the electrode surface, the side reaction in the cycle is effectively inhibited, and therefore the cycle stability and specific capacity of the battery are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, and more specifically, to a fluorine-containing porous carbon anode material and its preparation method. Background Technology

[0002] Porous carbon materials are widely used as anodes in lithium-ion batteries due to their high specific surface area, good conductivity, and structural tunability. However, the solid electrolyte interphase (SEI) film formed between the carbon material and the electrolyte is often unstable, leading to low initial coulombic efficiency (ICE) and rapid cycle decay. Fluorination modification can introduce strongly polar CF bonds into the porous carbon matrix, which not only enhances the adsorption and local enrichment of lithium ions, increasing lithium storage capacity, but also promotes the formation of stable LiF compounds on the electrode surface during subsequent charge and discharge processes. These compounds possess high interfacial energy, high ionic conductivity, high mechanical strength, and low solubility, making the SEI film more stable and dense, effectively suppressing side reactions and electrolyte decomposition, and significantly improving the material's initial coulombic efficiency (ICE). For example, in patent CN 120727802 A, a mixture of silicon-lithium composite material and fluorinated resin is calcined to obtain a silicon-carbon composite anode material with a core silicon and a lithium phosphate layer and a fluorinated carbon layer as double coating layers. When used as a lithium-ion anode material, it has an initial coulombic efficiency of over 88% and a reversible specific capacity of 2500 mAh / g. In patent CN 103708438 A, a fluorinated carbon source, a template agent, and an organic base are dissolved and mixed, and after template removal and high-temperature carbonization, a fluorinated mesoporous carbon material is obtained, which has a large specific surface area and good hydrophobicity. In patent CN 118702104 A, pre-activated carbon and a perfluoropolymer are carbonized at low temperature and then activated to obtain a fluorinated porous carbon material. The obtained material has a high pore volume and pore size.

[0003] However, traditional methods for preparing fluorinated porous carbon often require premixing the fluorine and carbon sources before co-carbonizing and activating them at high temperatures. This process is not only time-consuming and labor-intensive, but also complex and costly. Fluorination methods typically employ high-temperature blending or chemical vapor deposition (CVD), which still require high temperatures (>500 °C) and long reaction times, placing high demands on equipment and causing environmental pollution from the emitted fluorinated exhaust gases. Therefore, developing a room-temperature, rapid, controllable, and environmentally friendly method for preparing fluorinated porous carbon is of significant value.

[0004] Pulsed plasma technology is a novel non-destructive modification technique for nanomaterials, capable of surface modification or structural adjustment without sacrificing the material's inherent properties. Currently, there are reports of using pulsed plasma technology to prepare porous carbon. Patent CN 110339824 A describes the preparation of XAD-2 material with a high micro-mesopore ratio and highly functionalized surface using pulsed plasma technology. Compared to the original XAD-2 material, this material exhibits a higher specific surface area and pore volume, significantly enhancing its adsorption performance for PAHs. However, this patent focuses on the direct modification of the macroporous adsorption resin XAD-2 and requires complex pretreatment steps such as ultrasonic vibration, washing, and drying.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a fluorine-containing porous carbon, a negative electrode material, and a method for preparing the same to solve the above-mentioned technical problems.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides a method for preparing fluorine-containing porous carbon, comprising the following steps: A mixed gas is introduced into a reactor, where a discharge voltage is applied by a controlled pulsed plasma generator to generate pulsed plasma. After the reaction is carried out at 20~100℃, the reaction products are collected. The mixed gas includes carbon-containing gas, fluorine-containing gas, or a mixed gas including carbon-containing gas, fluorine-containing gas and dilution gas. The parameters of the pulsed plasma generator have at least one of the following characteristics: (1) The pulse frequency is 1~50kHz; (2) Duty cycle is 10-90%; (3) The discharge voltage is 10~30kV; (4) Power is 50~2000 W; (5) React for 2-30 min.

[0008] Secondly, the present invention also provides a fluorinated porous carbon material comprising: at least one fluorinated layer, wherein the fluorinated layer is prepared by the above-described method for preparing fluorinated porous carbon.

[0009] Thirdly, the present invention also provides a silicon-carbon anode material, wherein the carbon source of the silicon-carbon anode material is the aforementioned fluorine-containing porous carbon material or fluorine-containing porous carbon prepared by the aforementioned method.

[0010] Fourthly, the present invention also provides a battery comprising the above-described fluorine-containing porous carbon or the above-described silicon-carbon anode material, a conductive agent, and a binder.

[0011] The present invention has the following beneficial effects: This invention develops a room-temperature, rapid, controllable, and environmentally friendly method for preparing fluorinated porous carbon. It directly prepares fluorinated and modified porous carbon materials in one step. Compared with the traditional CVD method, the preparation method provided by this invention does not require high-temperature heating, has a short reaction time, and is pollution-free. The preparation and fluorination modification of porous carbon are carried out simultaneously in the reactor in one step, eliminating a large number of complicated intermediate steps, thereby improving or optimizing the current preparation process of fluorinated porous carbon and further improving its preparation efficiency.

[0012] The method provided by this invention allows for customization of the structure of the prepared fluorine-containing porous carbon. The distribution and concentration of fluorine in the obtained porous carbon can be precisely controlled by changing the concentration and flow rate of carbon-containing and fluorine-containing gases introduced at different times.

[0013] When the obtained fluorinated porous carbon is used as a negative electrode for lithium-ion batteries, the strong polar CF bonds can provide additional pseudocapacitive capacity. Furthermore, during subsequent charge and discharge processes, a stable LiF interface layer is more easily formed on the electrode surface, effectively suppressing side reactions during cycling, thereby significantly improving the cycle stability and specific capacity of the battery. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the specific structure of the pulsed plasma device used in this invention; In this context, 001 represents the reaction chamber, 002 represents the metal rod electrode, 003 represents the capillary needle electrode, 004 represents the power source, 005 represents the mixed gas channel, and 006 represents the fluorine-containing porous carbon obtained. Figure 2 Here is an HRTEM image of the fluorine-containing porous carbon prepared in Example 1; Figure 3 Here is a SEM-EDS image of the fluorine-containing porous carbon prepared in Example 1; Figure 4 Raman spectrum of fluorine-containing porous carbon prepared in Example 1 ( Figure 4 The horizontal axis represents the wavelength number, in centimeters. -1 ); Figure 5 The isothermal adsorption curve of the fluorine-containing porous carbon prepared in Example 1 (vertical axis is adsorbed capacity, horizontal axis is relative pressure (P / P0)). Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0017] In a first aspect, the present invention provides a method for preparing fluorine-containing porous carbon, comprising the following steps: A mixed gas is introduced into a reactor, where a discharge voltage is applied by a controlled pulsed plasma generator to generate pulsed plasma. After the reaction is carried out at 20~100℃, the reaction products are collected. The mixed gas includes carbon-containing gas, fluorine-containing gas, or a mixed gas including carbon-containing gas, fluorine-containing gas and dilution gas.

[0018] Compared with the traditional CVD method, the preparation method provided by this invention does not require high-temperature heating, has a short reaction time, is pollution-free, and the preparation and fluorination modification of porous carbon are carried out simultaneously in one step in the reactor, eliminating a large number of complicated intermediate steps and greatly improving the preparation efficiency of fluorinated porous carbon.

[0019] The method provided by this invention allows for customization of the structure of the prepared fluorine-containing porous carbon. The distribution and concentration of fluorine in the porous carbon can be precisely controlled by varying the concentration and flow rate of carbon- and fluorine-containing gases introduced at different times. The distribution of fluorine content in the fluorine-containing porous carbon can be adaptively controlled as needed, for example, configured as a layered structure with a gradient distribution of fluorine content at different depths.

[0020] In summary, the method for preparing fluorine-containing porous carbon developed in this invention has the technical advantages of being room temperature-controlled, rapid, controllable, and environmentally friendly.

[0021] The diluent gas in the mixed gas acts as a carrier gas. In one embodiment, the carrier gas may or may not be selected depending on the type of carbon- or fluorine-containing gas introduced. In pulsed plasma preparation of fluorine-containing porous carbon, the choice of diluent gas depends on the safety and functional requirements of the reaction system. When the fluorine-containing gas itself has mild chemical properties, low reaction power, and does not require physical bombardment, a diluent gas may not be needed to avoid introducing additional impurities and reduce process costs. When stable plasma discharge, enhanced gas dispersion, or regulation of fluorine-carbon particle energy is required, a carrier gas must be introduced. Argon, due to its excellent ionization properties and physical sputtering capabilities, is suitable for most deposition and etching processes; nitrogen can introduce functional nitrogen doping while diluting, improving the conductivity and interfacial stability of the material; hydrogen is used as a reducing atmosphere to adjust the stoichiometry of the fluorine-containing layer, but its concentration must be strictly controlled (usually mixed with argon) to ensure safety. By flexibly selecting the type and flow rate ratio (10-80%) of the carrier gas, precise control of the fluorine content gradient distribution, layer thickness, and pore structure can be achieved.

[0022] The pulsed plasma generator can be any commercially available pulsed plasma generator.

[0023] In a preferred embodiment of the present invention, the parameters of the pulsed plasma generator have at least one of the following characteristics: (1) The pulse frequency is 1~50kHz; (2) Duty cycle is 10-90%; (3) The discharge voltage is 10~30kV; (4) Power is 50~2000 W; (5) React for 2-30 minutes.

[0024] The pulse frequency is, for example, 1-10kHz, 5-15kHz, 15-25kHz, 20-30kHz, 25-45kHz, or 30-50kHz.

[0025] Duty cycle refers to the proportion of time that the plasma is actually in the "on" state within one pulse cycle.

[0026] For example, duty cycles of 10%, 11%, 12-20%, 15%-30%, 25%, 33%-45%, 46%-55%, 56%-60%, 62%-70%, 60%-90%, or 75%-90%.

[0027] The discharge voltage is, for example, 10, 15, 12-22, 20, 25 or 30 kV.

[0028] The power ratings are 50-100, 100-200, 200-300, 300-500, 500-800, 800-1000, 1000-1500 or 1100-2000 W.

[0029] The reaction time is 2-10 min, 5-15 min, 5-20 min or 5-30 min.

[0030] The above preparation process has the technical advantages of being fast, efficient, operating at room temperature, controllable, and environmentally friendly.

[0031] In a preferred embodiment of the present invention, a layered structure in which the fluorine content is gradient distributed at different depths inside the fluorine-containing porous carbon material is constructed by controlling the concentration and flow rate of carbon-containing and fluorine-containing gases and the gas flow sequence.

[0032] The thickness and fluorine content of the fluorine-containing layer can be adjusted by controlling the concentration and flow rate of carbon- and fluorine-containing gases. Specifically, the concentration and flow rate of carbon- and fluorine-containing gases, as well as the gas flow sequence, are controlled to construct a layered structure (i.e., a "fluorine gradient layer") with a gradient distribution of fluorine content at different depths within the fluorine-containing porous carbon material. (a) Concentration / flow gradient control: During deposition or processing, the volume ratio of the fluorine-containing gas to the carbon-containing gas introduced into the reaction chamber is controlled in a segmented or continuous manner to be (10~1):1, and the dilution gas accounts for 10~80% of the total gas flow rate, so as to control the yield and flux of fluorine-carbon active particles in the plasma. (b) Pulse parameter gradient control: During deposition or processing, the pulse frequency of the pulsed plasma is controlled in a segmented or continuous manner from a first frequency range of 1 to 50 kHz to a second frequency range, or its duty cycle is controlled from a first proportional range of 10% to 90% to a second proportional range, in order to control the degree of plasma dissociation and the distribution of fluorocarbon particles. (c) Ventilation sequence and time gradient control: A multi-stage ventilation procedure is adopted, including: in the first stage, a mixture of fluorine-containing gas and dilution gas is preferentially or only introduced to form a first fluorinated layer; in the second stage, a mixture of carbon-containing gas, fluorine-containing gas and dilution gas is introduced and the gas ratio is adjusted to form a second fluorinated layer on the first fluorinated layer, and so on.

[0033] The spatial position of the fluorinated layer in the fluorinated porous carbon can be adjusted by controlling the gas flow sequence. For example, if a carbon-containing gas without fluorine is first introduced, and then a mixture of fluorinated gas and carbon-containing gas is introduced, the fluorinated layer in the fluorinated porous carbon material can be located on the outer layer, and the inner layer can be a fluorine-free layer.

[0034] A "sandwich" structure for the fluorine-containing layer can be achieved by first passing a carbon-containing gas without fluorine, then passing a mixture of a fluorine-containing gas and a carbon-containing gas, and finally passing a carbon-containing gas without fluorine.

[0035] In a preferred embodiment of the present invention, the carbon-containing gas is selected from at least one of alkanes such as methane and ethane, alkenes such as ethylene and propylene, alkynes such as acetylene and propyne, and aromatic compounds such as benzene, toluene, and xylene; the fluorine-containing gas is selected from at least one of alkanes such as tetrafluoromethane, hexafluoroethane, and octafluoropropane, and aromatic compounds such as hexafluorobenzene and trifluorotoluene; and the diluent gas is at least one of hydrogen, nitrogen, and argon.

[0036] In a preferred embodiment of the present invention, the preparation method includes: first preparing porous carbon without a fluorine layer, and then preparing fluorine-containing porous carbon according to the method described above; or, first preparing fluorine-containing porous carbon, and then preparing porous carbon without a fluorine layer. In other embodiments, the above steps can be repeated, that is, the "preparation of porous carbon without a fluorine layer and preparation of fluorine-containing porous carbon" can be repeated to form a multilayered "porous carbon without fluorine layer - fluorine-containing porous carbon - porous carbon without fluorine layer - fluorine-containing porous carbon" structure.

[0037] In one embodiment, when the number of fluorinated porous carbon layers is two or more, the fluorine content of the fluorinated porous carbon in different layers is independent of each other. For example, the fluorine content can be gradually decreased, or it can be decreased first and then increased, or it can be increased first and then decreased, or the fluorine content can be gradually decreased and then kept constant. Those skilled in the art can make variations, and are not limited to the above-described embodiments.

[0038] In a preferred embodiment of the present invention, the preparation method includes the following steps: S1: Carbon-containing gas and dilution gas are introduced into the reactor. Pulsed plasma is generated in the reactor by applying a discharge voltage through a controlled pulsed plasma generator. After the reaction is carried out at 20~100 °C, porous carbon without a fluorine layer is obtained. S2: Switch the mixed gas to prepare fluorine-containing porous carbon and obtain fluorine-containing porous carbon material with a "fluorine-free layer-fluorine-containing layer" double-layer structure.

[0039] In a preferred embodiment of the present invention, the preparation method includes: first preparing porous carbon without a fluorine layer, then preparing fluorine-containing porous carbon according to the aforementioned method; and then preparing another porous carbon without a fluorine layer; the method includes the following steps: S1: Carbon-containing gas and dilution gas are introduced into the reactor. Pulsed plasma is generated in the reactor by applying a discharge voltage through a controlled pulsed plasma generator. After the reaction is carried out at 20~100 °C, porous carbon without a fluorine layer is obtained. S2: Switch the mixed gas to prepare fluorine-containing porous carbon and obtain fluorine-containing porous carbon material with a "fluorine-free layer-fluorine-containing layer" double-layer structure; S3: Carbon-containing gas and dilution gas are introduced into the reactor, and the reaction is carried out to obtain a fluorine-containing porous carbon material with a three-layer structure of "fluorine-free layer-fluorine-free layer".

[0040] Secondly, the present invention also provides a fluorinated porous carbon material, comprising: at least one fluorinated layer, wherein the fluorinated layer is prepared by the above-described method for preparing fluorinated porous carbon.

[0041] Fluorine-containing porous carbon materials include: fluorine-containing layers and fluorine-free layers spaced apart; In a preferred embodiment of the present invention, the number of fluorine-containing layers is 1-1000 layers, and the number of non-fluorine-containing layers is 1-1000 layers. In a preferred embodiment of the present invention, the thickness of the fluorinated layer in the fluorinated porous carbon material is 1~3000 nm; the fluorine content of the fluorinated layer is 1~50 wt%. In a preferred embodiment of the present invention, the fluorine-containing porous carbon has at least one of the following characteristics: Fluorine-containing porous carbon has a specific surface area of ​​500~1600 m². 2 / g; Fluorine-containing porous carbon has a pore volume of 0.2–1.5 cm³. 3 / g; The pore size of fluorinated porous carbon is 1~3 nm; The mesoporous content of fluorinated porous carbon is 5-80%; Raman spectra of fluorine-containing porous carbon I D / I G The ratio is 0.1 to 3.0.

[0042] In a preferred embodiment of the present invention, the fluorine content in the fluorine-containing porous carbon material is distributed in a layered structure at different depths within the fluorine-containing porous carbon material in a gradient manner. To achieve a layered structure in which the fluorine content inside fluorine-containing porous carbon materials exhibits a gradient distribution along the depth direction, this can be controlled through pulsed plasma processing. First, the porous carbon substrate is placed in a reaction chamber, and a mixture of carbon-containing gas, fluorine-containing gas (volume ratio 1:10~10:1), and dilution gas is introduced. The reaction is carried out for 2~30 minutes under the following conditions: pulse frequency 1~50kHz, duty cycle 10~90%, discharge voltage 10~30kV, and power 50~2000W. The key is to employ a multi-stage gas flow procedure. In the first stage, fluorine-containing gas and dilution gas are preferentially introduced to form an internal low-fluorine transition layer. In the second stage, a mixture of carbon-containing and fluorine-containing gas is introduced, and the fluorine content is increased to construct a high-fluorine surface layer. Alternatively, the pulse power and gas flow rate can be linearly adjusted in segments (e.g., high-power etching followed by low-power diffusion deposition) to obtain a layered structure with a continuous gradient or stepwise gradient distribution of fluorine content that gradually decreases (or increases) from the outer surface to the inner surface.

[0043] This gradient fluorination design gives fluorinated porous carbon the dual advantages of surface functionalization and internal stability: the high-fluorine outer layer forms a dense hydrophobic interface, enhancing chemical inertness and catalyzing the formation of a stable SEI film, suppressing side reactions, and improving initial coulombic efficiency and cycle life; the low-fluorine inner layer maintains the high conductivity and mechanical strength of the carbon skeleton; the continuous transition of fluorine content avoids stress concentration at heterogeneous interfaces and maintains structural integrity under charge-discharge and thermal shock; at the same time, the gradient fluorination layer acts as a molecular sieving barrier to prevent macromolecular poisoning, achieving a synergistic gain of high activity and long life in the fields of catalysis, separation, and energy storage.

[0044] Thirdly, the present invention also provides a silicon-carbon anode material, wherein the carbon source of the silicon-carbon anode material is the aforementioned fluorine-containing porous carbon material or fluorine-containing porous carbon prepared by the aforementioned method.

[0045] Electrochemical performance tests show that when the fluorinated porous carbon prepared by the method of this invention is directly used as the anode of a lithium-ion battery, its initial coulombic efficiency (ICE) can reach 76.8%, which is much higher than that of the fluorine-free porous carbon prepared under the same conditions (ICE is 64.3%). After 100 cycles at a current density of 0.5C, the capacity retention rate of the fluorinated porous carbon is as high as 92%, while that of the fluorine-free porous carbon is only 68%, demonstrating the significant improvement in cycle stability brought about by the stable LiF interface layer formed by the fluorinated porous carbon.

[0046] Fourthly, the present invention also provides a battery comprising the above-mentioned fluorine-containing porous carbon material or the above-mentioned silicon-carbon anode material, a conductive agent, and a binder.

[0047] The fluorinated porous carbon material provided by this invention exhibits excellent initial coulombic efficiency and long-term cycle stability when used as a silicon-carbon anode material. It shows promising application prospects in batteries, particularly lithium-ion batteries.

[0048] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0049] Example 1 This embodiment provides a method for preparing fluorine-containing porous carbon, the specific steps of which are as follows: Acetylene was used as the carbon-containing gas, tetrafluoromethane as the fluorine-containing gas, and argon as the diluent gas, with a total gas flow rate of 300 sccm. The volume ratio of carbon-containing gas to fluorine-containing gas was set to 8:1, and the diluent gas accounted for 50% of the total gas flow rate. Then, the pulsed plasma generator was turned on (see schematic diagram). Figure 1The power supply (shown) was set with the following parameters: pulse frequency 20 kHz, duty cycle 40%, discharge voltage 20 kV, and power 300 W. The mixed gas was introduced into the reactor, and after reacting at room temperature (30 ℃) for 10 minutes, the power and gas supply were turned off. Black powder was collected from the inner wall of the reactor, yielding a fluorinated porous carbon material, denoted as FPC-1.

[0050] Figure 2 The HRTEM image of the fluorine-containing porous carbon prepared in Example 1 shows short-range, tortuous graphite streaks. Figure 3 The SEM-EDS image of the fluorine-containing porous carbon prepared in Example 1 shows a clear distribution of fluorine. Figure 4 The image shows the Raman spectrum of the fluorine-containing porous carbon prepared in Example 1. I D / I G = 1.2; Figure 5 The isotherm diagram of the fluorine-containing porous carbon prepared in Example 1 shows an adsorption isotherm with a specific surface area of ​​1250 m². 2 / g, pore volume 0.85 cm³ 3 / g.

[0051] Example 2 This embodiment provides a method for preparing fluorine-containing porous carbon. Compared with Example 1, the difference lies in adjusting the volume ratio of carbon-containing gas to fluorine-containing gas to 4:1, while keeping other conditions unchanged. The resulting material is designated as FPC-2.

[0052] Example 3 This embodiment provides a method for preparing fluorinated porous carbon. Compared with Example 1, the difference is that the reaction time is adjusted to 20 minutes, while other conditions remain unchanged. The resulting material is designated as FPC-3.

[0053] Example 4 This embodiment provides a method for preparing fluorinated porous carbon. Compared with Example 1, the difference lies in that the carbon-containing gas is adjusted to methane, the fluorine-containing gas is hexafluoroethane, the volume ratio of carbon-containing gas to fluorine-containing gas is 6:1, the diluent gas is hydrogen, accounting for 30% of the total flow rate, the pulse frequency is adjusted to 10kHz, the duty cycle is 60%, the power is 150W, and the reaction time is 15 minutes. The obtained material is designated as FPC-4.

[0054] Example 5 This embodiment prepared a fluorinated porous carbon material with a layered structure, demonstrating the adjustability of its spatial arrangement and fluorine content. A stepwise aeration method was employed. First stage (preparation of fluorine-free layer): Only acetylene and argon gas (argon flow rate accounts for 50% of the total flow rate) are introduced, and the reaction is carried out for 5 minutes at a frequency of 20 kHz, a duty cycle of 40%, and a power of 300 W.

[0055] Second stage (preparation of fluorine-containing layer): switch the mixed gas and introduce acetylene, tetrafluoromethane and argon (the volume ratio of acetylene to tetrafluoromethane is 4:1, and the dilution gas is 50%), keep other parameters unchanged, and react for 5 minutes.

[0056] Third stage (preparation of another fluorine-free layer): switch back to a mixed gas of only acetylene and argon (argon flow rate accounts for 50% of the total flow rate), and react for 5 minutes.

[0057] Collection: After the reaction is complete, the product is collected to obtain a fluorine-containing porous carbon material with a three-layer structure of "fluorine-free layer-fluorine-free layer", which is designated as FPC-5.

[0058] Example 6 This embodiment prepared a fluorinated porous carbon material with a gradient structure consisting of a fluorinated layer, a first fluorinated layer, a second fluorinated layer, and a third fluorinated layer.

[0059] The first fluorinated layer and the second fluorinated layer have different fluorine contents and thicknesses, and the specific steps include the following: Step S1: Deposit the first fluorine-free layer (bottom layer) The reactor was evacuated to a background vacuum of 5 × 10⁻⁶. -3 Torr is introduced with carbon-containing gas acetylene (C2H2) and diluent gas argon (Ar). The acetylene flow rate is 40 sccm, and the argon flow rate is 60 sccm (the diluent gas accounts for 60%). The pulsed plasma generator is turned on, with the pulse frequency set to 15 kHz, duty cycle 30%, discharge voltage 18 kV, and power 250 W. The reaction is carried out at room temperature (30 ℃) for 8 minutes. The power and gas supply are then turned off, and black powder is collected on the inner wall of the reactor, which is the first fluorine-free layer (approximately 200 nm thick).

[0060] Step S2: Deposit the first fluorine-containing layer Maintaining a vacuum in the reactor, the mixed gas was switched to a carbon-containing gas (acetylene), a fluorine-containing gas (tetrafluoromethane (CF4),) and a dilution gas (argon). The volume ratio of acetylene to tetrafluoromethane was set to 6:1, and argon accounted for 50% of the total gas flow rate (i.e., acetylene flow rate 30 sccm, tetrafluoromethane flow rate 5 sccm, argon flow rate 35 sccm). The pulse frequency was set to 20 kHz, the duty cycle to 40%, the discharge voltage to 20 kV, and the power to 300 W. The reaction was carried out at 35 ℃ for 12 minutes. The power supply and gas source were then turned off, yielding the first fluorine-containing layer (fluorine content approximately 12 wt%, thickness approximately 150 nm).

[0061] Step S3: Deposit the second fluorine-free layer Switch back to the gas ratio of step S1 (acetylene 40 sccm, argon 60 sccm), use the same pulse parameters (15 kHz, 30% duty cycle, 18 kV, 250 W), and react at room temperature (30 °C) for 10 minutes to obtain the second fluorine-free layer (approximately 250 nm thick).

[0062] Step S4: Deposit the second fluorine-containing layer The gas mixture was then switched again to acetylene, tetrafluoromethane, and argon, but the volume ratio of acetylene to tetrafluoromethane was adjusted to 4:1, while the argon content remained at 50% (acetylene 32 sccm, tetrafluoromethane 8 sccm, argon 40 sccm). The pulse frequency was set to 25 kHz, the duty cycle to 50%, the discharge voltage to 22 kV, and the power to 350 W. The reaction was carried out at 40 ℃ for 15 minutes to obtain a second fluorinated layer (fluorine content approximately 25 wt%, thickness approximately 120 nm).

[0063] Step S5: Deposit the third fluorine-free layer (outermost layer) Finally, switch back to the gas ratio of step S1 (acetylene 40 sccm, argon 60 sccm), use a pulse frequency of 12 kHz, a duty cycle of 25%, a discharge voltage of 16 kV, a power of 200 W, and react at 30 ℃ for 6 minutes to obtain the outermost fluorine-free layer (thickness of about 150 nm).

[0064] Finally, the black powder collected from the inner wall of the reactor yields a product with a "fluorine-free layer". First fluorine-containing layer Fluorine-free layer Second fluorine-containing layer A five-layer fluorine-containing porous carbon material without a fluorine layer is designated as FPC-6.

[0065] Comparative Example 1 This comparative example provides a method for preparing fluorine-free porous carbon.

[0066] The difference from Example 1 is that no fluorine-containing gas (tetrafluoromethane) is introduced into the gas mixture; it consists only of acetylene and argon. All other conditions are exactly the same as in Example 1. The resulting material is designated PC-1.

[0067] Comparative Example 2 This comparative example uses conventional chemical vapor deposition (CVD) to prepare fluorine-containing porous carbon.

[0068] First, following the method of Comparative Example 1, a fluorine-free porous carbon substrate PC-1 was prepared using pulsed plasma. Then, PC-1 was placed in a tube furnace under argon protection and heated to 600°C. After the temperature stabilized, the atmosphere was switched to a mixture of tetrafluoromethane and argon (volume ratio 1:4), and the mixture was kept at 600°C for 2 hours for fluorination modification. Subsequently, the temperature was lowered to room temperature under an argon atmosphere to obtain fluorinated porous carbon, denoted as FPC-CVD.

[0069] Experimental Example 1 The fluorine-containing porous carbon materials prepared in Examples 1-6 and Comparative Examples 1-2 were characterized structurally, and the performance testing methods involved are as follows: Pore ​​structure analysis: The specific surface area and pore volume of the material were determined by nitrogen adsorption-desorption (BET); the pore size distribution was calculated by nonlocal density functional theory (NLDFT).

[0070] Microstructure and structure: The morphology of the material was observed using scanning electron microscopy (SEM), and the layered structure was observed using transmission electron microscopy (TEM); Raman spectroscopy was used to test the material. I D / I G The value is used to assess the degree of graphitization.

[0071] The test results are shown in Table 1.

[0072] Table 1. Statistical table of performance test results of samples prepared in different embodiments and comparative examples.

[0073] As can be seen from the data in Table 1, the fluorine-containing porous carbons (FPC-1~FPC-6) prepared by the pulsed plasma method in this invention all have high specific surface areas (900~1450 m²). 2 / g) and pore volume (0.60~1.02 cm³) 3 / g). Among them, FPC-3 had the highest specific surface area and pore volume (1450 m²) due to the extended reaction time (20 min). 2 / g, 1.02 cm 3 / g), while FPC-4, due to the use of methane and hexafluoroethane, the replacement of argon with hydrogen, and lower power, has a relatively lower specific surface area and pore volume (900 m). 2 / g, 0.60cm 3 / g). Regarding fluorine content, by adjusting the volume ratio of carbon-containing to fluorine-containing gases, the fluorine content can be increased from 8.5% (FPC-1, 8:1) to 18.2% (FPC-2, 4:1). Furthermore, with increasing fluorine content, the specific surface area and pore volume decrease slightly (from 1250 to 1100 m²). 2The concentration of fluorine ( / g) indicates that excessive fluorine may partially block the pores. FPC-5 and FPC-6 successfully constructed a layered distribution of fluorine through stepwise aeration (FPC-5 consisted of three layers: "fluorine-free-fluorine-free", and FPC-6 consisted of a five-layer gradient), maintaining good specific surface area and pore volume (1180~1270 m³). 2 / g, 0.80~0.84 cm 3 / g). Comparative Example 1 (PC-1) was fluorine-free and had a pore structure similar to FPC-1, indicating that pulsed plasma deposition of carbon itself can achieve a high specific surface area. Comparative Example 2 (conventional CVD fluorination) had a significantly lower specific surface area and pore volume than the pulsed plasma sample (850 m²). 2 / g, 0.58 cm 3 The presence of fluorine content ( / g) indicates that traditional CVD high-temperature fluorination processes easily lead to pore collapse, and fluorine is only enriched on the surface, making it difficult to achieve uniform doping or gradient distribution in the bulk phase. In summary, the method of this invention can achieve flexible control of fluorine content and spatial distribution while maintaining excellent pore structure.

[0074] Experimental Example 2 This preparation example provides a synthesis procedure for silicon-carbon anode materials using CVD, as follows: Step S1: Weigh 5.0 g of the fluorine-containing porous carbon powder prepared in Example FPC-1, place it in a chemical vapor deposition reactor, introduce high-purity argon gas (200 sccm), heat to 150 ℃ at 5 ℃ / min and hold for 1 hour to remove gas from the pores, then heat to 600 ℃ at 10 ℃ / min. After holding at this temperature for 30 minutes, introduce silane (SiH4, purity 99.999%), controlling the volume ratio of argon to silane at 4:1 (argon 80 sccm, silane 20 sccm), and deposit at 600 ℃ for 2 hours, maintaining a slight positive pressure (200 sccm) in the reaction chamber. (300 Pa). After deposition, the silane was turned off, and argon gas was kept purging. The mixture was allowed to cool naturally to room temperature to obtain a composite material of fluorine-containing porous carbon-supported nano-silicon. Step S2: The above FPC was then... Si 1. Heat to 800 °C at 10 °C / min and hold for 30 minutes. Then, introduce a mixture of acetylene (C2H2) and argon gas with a volume ratio of 2:7 (acetylene 40 sccm, argon 140 sccm). Deposit at 800 °C for 1 hour to allow pyrolytic carbon to be uniformly deposited on the particle surface and at the pore openings, forming a layer approximately 5 mm thick. A dense carbon coating layer of 10 nm was formed. After shutting off the acetylene, the material was naturally cooled to room temperature under an argon atmosphere to obtain the silicon-carbon anode material.

[0075] The fluorinated porous carbon materials prepared in Examples 1-6 and Comparative Examples 1-2 were used to prepare silicon-carbon anode materials according to the methods described in the above examples, namely Preparation Example 1, Preparation Example 2, Preparation Example 3, Preparation Example 4, Preparation Example 5, Preparation Example 6, Comparative Example 1, and Comparative Example 2. Then, electrodes were prepared. After being assembled into batteries, the electrochemical performance of the batteries was tested.

[0076] The electrochemical performance testing methods are as follows: (1) Electrode preparation: The active material (fluorine-containing porous carbon or silicon-carbon anode material), conductive carbon black (Super P) and binder (polyacrylic acid, PAA) are mixed in a mass ratio of 8:1:1, and an appropriate amount of deionized water is added to form a slurry. The slurry is coated on copper foil, vacuum dried and then cut into electrode sheets.

[0077] (2) Battery assembly: Using lithium metal sheet as counter electrode, polypropylene microporous membrane (Celgard 2400) as separator, 1 MLiPF6 dissolved in ethylene carbonate / diethyl carbonate / methyl ethyl carbonate (EC / DEC / EMC, volume ratio 1:1:1) as electrolyte, CR2032 button half cell was assembled in argon glove box.

[0078] (3) Test conditions: Constant current charge and discharge tests were conducted using the Blue Battery Test System at 25 ℃, with a voltage window of 0.01V~3.0V (vs. Li / Li + The initial coulombic efficiency (ICE) is calculated from the initial charge capacity / initial discharge capacity. Cycle performance was tested for 100 cycles at a current density of 0.5C.

[0079] Table 2. Statistical table of performance test results of silicon-carbon samples prepared in different embodiments and comparative examples.

[0080] As shown in Table 2, the FPC-6 silicon-carbon anode with a gradient layered structure exhibits the best initial coulombic efficiency (91.2%), capacity retention after 100 cycles at 0.5C (95.3%), and 5C rate performance (82.5%). Its gradient fluorine distribution stabilizes the SEI film and buffers silicon expansion. In contrast, the fluorine-free PC-1, lacking fluorine doping, has significantly lower initial efficiency (82.3%) and cycle retention (71.5%). The traditional CVD surface-fluorinated sample (FPC-CVD), although containing fluorine (84.8%), is only enriched on the surface and cannot form an internal gradient, resulting in a cycle retention of only 78.2%. The uniformly high-fluorine FPC-2, due to its excessive fluorine content, is prone to side reactions, resulting in a cycle retention (85.6%) lower than the gradient design. In terms of capacity, FPC-3 has the largest specific surface area (1450 m²). 2 / g), highest pore volume (1.02 cm³). 3The initial discharge capacity reached 1920 mAh / g, but its cycle stability (92.0%) was slightly inferior to FPC-6. In summary, the gradient layered fluorine distribution can better balance interfacial stability, stress buffering, and electron / ion transport, resulting in the best overall electrochemical performance.

[0081] In summary, this invention provides a method for preparing fluorine-containing porous carbon using pulsed plasma technology and the applications of the obtained product. This method is simple, operates under mild conditions (room temperature and pressure), reacts rapidly (within minutes), is environmentally friendly and pollution-free, and allows for precise control of the fluorine content and distribution of the product. The prepared fluorine-containing porous carbon material exhibits excellent electrochemical performance in lithium-ion batteries, particularly in high-energy-density silicon-carbon anodes, significantly improving the initial coulombic efficiency and cycle life of the battery. Therefore, this invention has extremely high industrial practical value and broad market application prospects.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing fluorine-containing porous carbon, characterized in that, It includes the following steps: A mixed gas is introduced into a reactor, where a discharge voltage is applied by a controlled pulsed plasma generator to generate pulsed plasma. After the reaction is carried out at 20~100 °C, the reaction products are collected. The mixed gas includes carbon-containing gas, fluorine-containing gas, or, the mixed gas includes carbon-containing gas, fluorine-containing gas and diluent gas. The parameters of the pulsed plasma generator have at least one of the following characteristics: (1) The pulse frequency is 1~50kHz; (2) Duty cycle is 10-90%; (3) The discharge voltage is 10~30kV; (4) Power is 50~2000 W; (5) React for 2-30 min.

2. The method for preparing fluorine-containing porous carbon according to claim 1, characterized in that, By controlling the concentration and flow rate of carbon- and fluorine-containing gases, as well as the gas flow sequence, a layered structure in which the fluorine content is gradient-distributed at different depths within the fluorine-containing porous carbon material is constructed. And / or, the volume ratio of the carbon-containing gas to the fluorine-containing gas is (10~1):1, and the dilution gas accounts for 10~80% of the total gas flow rate; And / or, adjust the pulse frequency of the pulsed plasma from a first frequency range of 1 to 50 kHz to a second frequency range, or adjust its duty cycle from a first proportional range of 10% to 90% to a second proportional range, in order to control the degree of plasma dissociation and the distribution of fluorocarbon particles.

3. The method for preparing fluorine-containing porous carbon according to claim 1, characterized in that, The carbon-containing gas is selected from at least one of alkanes, alkenes, alkynes, and aromatic compounds; The fluorine-containing gas is selected from at least one of alkanes and aromatic compounds; The diluting gas is at least one of hydrogen, nitrogen, and argon.

4. The method for preparing fluorine-containing porous carbon according to claim 1, characterized in that, The preparation method includes: first preparing porous carbon without a fluorine layer, and then preparing fluorine-containing porous carbon according to the method described in claim 1; or, first preparing fluorine-containing porous carbon, and then preparing porous carbon without a fluorine layer. And / or, the preparation method includes the following steps: S1: Carbon-containing gas and dilution gas are introduced into the reactor. Pulsed plasma is generated in the reactor by applying a discharge voltage through a controlled pulsed plasma generator. After the reaction is carried out at 20~100℃, porous carbon without fluorine layer is obtained. S2: Switch the mixed gas to prepare fluorine-containing porous carbon and obtain a fluorine-containing porous carbon material with a "fluorine-free layer-fluorine-containing layer" double-layer structure.

5. The method for preparing fluorine-containing porous carbon according to claim 1, characterized in that, The preparation method includes: first preparing porous carbon without a fluorine layer, then preparing fluorine-containing porous carbon according to the method described in claim 1; and then preparing another porous carbon without a fluorine layer; it includes the following steps: S1: Carbon-containing gas and dilution gas are introduced into the reactor. Pulsed plasma is generated in the reactor by applying a discharge voltage through a controlled pulsed plasma generator. After the reaction is carried out at 20~100℃, porous carbon without fluorine layer is obtained. S2: Switch the mixed gas to prepare fluorine-containing porous carbon and obtain a fluorine-containing porous carbon material with a "fluorine-free layer-fluorine-containing layer" double-layer structure; S3: Carbon-containing gas and dilution gas are introduced into the reactor to react and produce a fluorine-containing porous carbon material with a three-layer structure of "fluorine-free layer-fluorine-free layer".

6. A fluorine-containing porous carbon material, characterized in that, It includes: At least one fluorine-containing layer, wherein the fluorine-containing layer is prepared by the method for preparing fluorine-containing porous carbon according to any one of claims 1-5.

7. The fluorine-containing porous carbon material according to claim 6, characterized in that, The fluorine-containing porous carbon material includes: a fluorine-containing layer and a fluorine-free layer spaced apart; And / or, the number of fluorine-containing layers is 1-1000 layers, and the number of fluorine-free layers is 1-1000 layers; And / or, the thickness of the fluorine-containing layer in the fluorine-containing porous carbon material is 1~3000 nm; the fluorine content of the fluorine-containing layer is 1~50 wt%.

8. The fluorine-containing porous carbon material according to claim 7, characterized in that, The fluorine-containing porous carbon has at least one of the following characteristics: Fluorine-containing porous carbon has a specific surface area of ​​500~1600 m². 2 / g; The fluorine-containing porous carbon has a pore volume of 0.2~1.5 cm³. 3 / g; The fluorine-containing porous carbon has a pore size of 1~3 nm; The mesoporous content of the fluorinated porous carbon is 5-80%; Raman spectra of the fluorine-containing porous carbon I D / I G The ratio is 0.1 to 3.0; And / or, the fluorine content in the fluorine-containing porous carbon material is distributed in a layered structure at different depths within the fluorine-containing porous carbon material.

9. A silicon-carbon anode material, wherein the carbon source of the silicon-carbon anode material is the fluorine-containing porous carbon material according to any one of claims 6-8 or the fluorine-containing porous carbon prepared by the method according to any one of claims 1-5.

10. A battery, characterized in that, It includes the fluorine-containing porous carbon material as described in any one of claims 6-8 or the silicon-carbon anode material as described in claim 9, a conductive agent, and a binder.

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