A fluorinated porous carbon material, a preparation method and application and a lithium ion capacitor

Abstract

The application provides a fluorinated porous carbon material, a preparation method and application and a lithium ion capacitor, and belongs to the technical field of capacitor electrode materials. Heavy oil byproducts are mixed with an activating agent through ball milling to obtain a mixed precursor; the mixed precursor is subjected to calcination and carbonization treatment in a protective atmosphere to obtain a porous carbon material; the porous carbon material is subjected to thermal reduction treatment in a reducing atmosphere to obtain a reduced porous carbon material; and the reduced porous carbon material is subjected to fluorination treatment in a fluorine-containing atmosphere to obtain a fluorinated porous carbon material. The fluorinated porous carbon material provided by the application has a high specific surface area, a developed pore structure, and introduced fluorine electron defects, and the ion adsorption active sites and interface stability are increased, so that when the fluorinated porous carbon material is used as a lithium ion capacitor positive electrode material, the lithium ion capacitor has a high charge storage capacity and a high stable working potential, and the energy density and power density of the lithium ion capacitor are improved.

Description

Technical Field

[0001] This invention relates to the field of capacitor electrode materials technology, and in particular to a fluorinated porous carbon material, its preparation method and application, and lithium-ion capacitors. Background Technology

[0002] In recent years, the large-scale use of non-renewable fuels such as coal and oil has exacerbated the energy crisis and environmental problems. In fact, besides fossil fuels, the Earth possesses various renewable energy sources, including geothermal, wind, hydro, and solar power, which can be converted into usable electricity. However, due to the uncertainty and intermittency of power generation from these renewable energy sources, efficient energy storage systems (EES) are needed to construct renewable energy-coupled power grids to facilitate their use, thereby meeting the needs of modern society and reducing its dependence on fossil fuels.

[0003] Electrochemical energy storage systems are among the fastest-growing types of electrical energy storage systems. Among these, lithium-ion-based energy storage devices, such as lithium-ion batteries (LIBs) and lithium-ion capacitors (LICs), hold a crucial position in the new energy industry. Lithium-ion capacitors are assembled from electrodes with different charge storage mechanisms. The positive electrode kinetics rely on the adsorption and desorption of anions, while the negative electrode kinetics rely on the insertion and extraction of lithium ions to complete charge storage. Therefore, lithium-ion capacitors combine the high energy density of lithium-ion batteries with the excellent rate capability and cycle performance of supercapacitors (SCs).

[0004] Improving the electrochemical performance of cathode materials is one of the important ways to enhance the electrochemical performance of lithium-ion capacitors. Porous carbon materials have attracted widespread attention from researchers due to their high specific surface area. Theoretically, the electrochemical double-layer capacitance and specific surface area of ​​cathode materials for lithium-ion capacitors are linearly correlated. When the specific surface area reaches a certain value (approximately 3500 nm), the capacitance increases significantly. 2 When the surface area is / g), the electrochemical double layer capacitance will reach a limit, and an excessively high specific surface area will cause serious surface side reactions and electrode instability under high operating potential conditions.

[0005] Introducing electronic defects into porous carbon materials can provide additional electrochemical double-layer capacitance, further improving charge storage capacity. For example, introducing oxygen-containing electronic defects into porous carbon materials is beneficial to improving their charge storage capacity, but at high operating potentials (approximately 4.5V), they will undergo redox reactions with electrolyte molecules or electrolyte ions, resulting in poor stability. Summary of the Invention

[0006] The purpose of this invention is to provide a fluorinated porous carbon material, its preparation method, its application, and a lithium-ion capacitor. The fluorinated porous carbon material provided by this invention has a high specific surface area and a well-developed pore structure. It also introduces fluorine electron defects, which increases the ion adsorption active sites and interface stability. When used as a positive electrode material for lithium-ion capacitors, it can avoid the problems of severe surface side reactions and electrode instability under high operating potential caused by excessively high specific surface area. It has both high charge storage capacity and a high stable operating potential.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing fluorinated porous carbon materials, comprising the following steps:

[0009] Heavy oil by-products and an activator are ball-milled and mixed to obtain a mixed precursor; the active groups in the heavy oil by-products include one or more of hydroxyl, carboxyl, aldehyde, carbonate, amide, mercapto, carbonyl, and imine groups; the activator is KOH or NaOH;

[0010] The mixed precursor was calcined and carbonized in a protective atmosphere to obtain a porous carbon material.

[0011] The porous carbon material is subjected to thermal reduction treatment in a reducing atmosphere to obtain a reduced porous carbon material.

[0012] The reduced porous carbon material is fluorinated in a fluorine-containing atmosphere to obtain fluorinated porous carbon material.

[0013] Preferably, the heavy oil by-products include one or more of petroleum coke, ethylene tar, catalytic slurry, and petroleum pitch.

[0014] Preferably, the mass ratio of the heavy oil by-product to the activator is 1:(2-8).

[0015] Preferably, the ball milling mixing speed is 300-600 rpm and the time is 1-6 hours.

[0016] Preferably, the calcination and carbonization treatment is carried out at a temperature of 450–1250°C and a holding time of 30–120 min.

[0017] Preferably, the temperature of the thermal reduction treatment is 400–700°C, and the holding time is 30–180 min; the reducing atmosphere includes an inert gas and a reducing gas, and the volume fraction of the reducing gas in the reducing atmosphere is 0.5–10%.

[0018] Preferably, the fluorination treatment temperature is 200–450°C, and the holding time is 30–180 min; the fluorine-containing atmosphere includes an inert gas and a fluorine-containing gas, and the volume fraction of the fluorine-containing gas in the fluorine-containing atmosphere is 0.5–20%.

[0019] This invention provides a fluorinated porous carbon material prepared by the preparation method described above, which is a porous carbon material with fluorine electron defects; the specific surface area of ​​the fluorinated porous carbon material is ≥3000 m². 2 / g, micropore porosity ≥1.2cm 3 / g, with a fluorine content of 0.8–4.0 wt%.

[0020] This invention provides the application of the fluorinated porous carbon material described in the above technical solution as a positive electrode material for lithium-ion capacitors.

[0021] This invention provides a lithium-ion capacitor, using the fluorinated porous carbon material described in the above technical solution as the positive electrode material.

[0022] This invention provides a method for preparing fluorinated porous carbon materials, comprising the following steps: ball milling and mixing heavy oil by-products with an activator to obtain a mixed precursor; the active groups in the heavy oil by-products include one or more of hydroxyl, carboxyl, aldehyde, carbonate, amide, mercapto, carbonyl, and imine groups; the activator is KOH or NaOH; calcining and carbonizing the mixed precursor in a protective atmosphere to obtain a porous carbon material; thermally reducing the porous carbon material in a reducing atmosphere to obtain a reduced porous carbon material; and fluorinating the reduced porous carbon material in a fluorine-containing atmosphere to obtain a fluorinated porous carbon material. The fluorinated porous carbon material provided by this invention has a high specific surface area and a well-developed pore structure, and introduces fluorine electron defects, increasing ion adsorption active sites and interfacial stability. When used as a positive electrode material for lithium-ion capacitors, it exhibits both high charge storage capacity and a high stable operating potential, thereby improving the energy density and power density of lithium-ion capacitors. Specifically, this invention uses heavy oil by-products as a carbon source, which are ball-milled and mixed with an activator. The activator complexes with the active groups in the heavy oil by-products, promoting the etching of the carbon matrix formed by the heavy oil by-products during subsequent calcination and carbonization processes, thus forming a porous structure conducive to ion adsorption and rapid transport. Thermal reduction treatment removes excess oxygen-containing active groups from the porous carbon material, making it easier for fluorine functional groups to graft onto the surface of the porous carbon material during fluorination. Fluorination introduces fluorine into the reduced porous carbon material, altering the charge distribution around the carbon atoms and creating fluorine electron defects. This provides more adsorption active sites, resulting in higher specific capacity. Furthermore, fluorine passivates the surface of the reduced porous carbon material, enhancing the interfacial stability between the electrode and the electrolyte, enabling the electrode to operate stably under high-voltage conditions. The test results show that using the fluorinated porous carbon material provided by this invention as the positive electrode material to assemble lithium-ion capacitors achieves stable operation with long cycle life (10,000 cycles), high energy density (231Wh / kg), and high voltage window (0-5.0V).

[0023] Furthermore, the preparation method of fluorinated porous carbon material provided by this invention has low production cost and is a low-consumption and high-efficiency preparation process, which is suitable for large-scale commercial applications. Attached Figure Description

[0024] Figure 1 TEM image of the fluorinated porous carbon material prepared in Example 1;

[0025] Figure 2 The nitrogen adsorption-desorption curves are for the fluorinated porous carbon material prepared in Example 1.

[0026] Figure 3 XPS image of the fluorinated porous carbon material prepared in Example 1;

[0027] Figure 4 The charge-discharge curves of the fluorinated porous carbon material prepared in Example 1 are shown below.

[0028] Figure 5 A comparison chart of the rate performance of the fluorinated porous carbon material prepared in Example 1 and the carbon material prepared in Comparative Example 1;

[0029] Figure 6 The charge-discharge curves of the lithium-ion capacitor assembled using the fluorinated porous carbon material as the positive electrode in Example 1 are shown.

[0030] Figure 7 The charge-discharge curves of the lithium-ion capacitor assembled using carbon material as the positive electrode in Comparative Example 1 are shown.

[0031] Figure 8 The cycling curve of the lithium-ion capacitor assembled using the fluorinated porous carbon material as the positive electrode in Example 1 is shown.

[0032] Figure 9 The cycling curve of the lithium-ion capacitor assembled with carbon material as the positive electrode in Comparative Example 1 is shown.

[0033] Figure 10 The graph shows the energy density and power density of the lithium-ion capacitor assembled using the fluorinated porous carbon material as the positive electrode in Example 1. Detailed Implementation

[0034] This invention provides a method for preparing fluorinated porous carbon materials, comprising the following steps:

[0035] Heavy oil by-products and an activator are ball-milled and mixed to obtain a mixed precursor; the active groups in the heavy oil by-products include one or more of hydroxyl, carboxyl, aldehyde, carbonate, amide, mercapto, carbonyl, and imine groups; the activator is KOH or NaOH;

[0036] The mixed precursor was calcined and carbonized in a protective atmosphere to obtain a porous carbon material.

[0037] The porous carbon material is subjected to thermal reduction treatment in a reducing atmosphere to obtain a reduced porous carbon material.

[0038] The reduced porous carbon material is fluorinated in a fluorine-containing atmosphere to obtain fluorinated porous carbon material.

[0039] This invention involves ball milling heavy oil by-products with an activator to obtain a mixed precursor. In this invention, the active groups in the heavy oil by-products include one or more of hydroxyl, carboxyl, aldehyde, carbonate, amide, mercapto, carbonyl, and imine groups; preferably, the heavy oil by-products include one or more of petroleum coke, ethylene tar, catalytic slurry, and petroleum asphalt. In this invention, the activator is KOH or NaOH; the mass ratio of the heavy oil by-products to the activator is preferably 1:(2-8), more preferably 1:6. In this invention, the ball milling speed is preferably 300-600 rpm, more preferably 400 rpm; the time is preferably 1-6 hours, more preferably 3 hours.

[0040] This invention uses heavy oil by-products as a carbon source, which are ball-milled and mixed with an activator. The activator complexes with the active groups in the heavy oil by-products, promoting the etching of the carbon matrix formed by the heavy oil by-products during subsequent calcination and carbonization processes. This results in a porous structure that facilitates ion adsorption and rapid transport, yielding a porous carbon material with a high specific surface area and a well-developed pore structure. Preferably, this invention limits the mass ratio of heavy oil by-products to the activator to the aforementioned range and performs ball milling and mixing under the aforementioned conditions. By controlling the degree of reaction between the activator and the active groups in the heavy oil by-products, the activator achieves an ideal etching effect during subsequent calcination and carbonization processes, thus facilitating the production of a porous carbon material with a high specific surface area and a well-developed pore structure.

[0041] After obtaining the mixed precursor, the present invention calcines and carbonizes the mixed precursor in a protective atmosphere to obtain a porous carbon material. In the present invention, the calcination and carbonization temperature is preferably 450–1250°C, more preferably 600–1200°C, and even more preferably 800–1000°C; the heating rate to the required temperature for calcination and carbonization is preferably 2–10°C / min, more preferably 3–5°C / min; the holding time for calcination and carbonization is preferably 30–120 min, more preferably 90–120 min. The present invention does not limit the type of protective gas providing the protective atmosphere; any protective gas well known to those skilled in the art can be used, specifically nitrogen. The present invention preferably performs the calcination and carbonization treatment under the above conditions, which is beneficial for the heavy oil by-product to form a porous carbon material with a high specific surface area and well-developed pore structure under the etching action of the activator.

[0042] After the calcination and carbonization treatment, the obtained material is preferably cooled and then washed and dried sequentially to obtain a porous carbon material. In this invention, the cooling is preferably natural cooling to room temperature; in an embodiment of this invention, the room temperature is specifically 25°C. In this invention, the washing reagent is preferably hydrochloric acid, and the concentration of the hydrochloric acid is preferably 1 wt%; the washing is specifically performed until neutral. In this invention, the drying temperature is preferably 70–90°C, more preferably 80°C; the drying time is based on ensuring the material is fully dried.

[0043] After obtaining the porous carbon material, the present invention performs a thermal reduction treatment on the porous carbon material in a reducing atmosphere to obtain a reduced porous carbon material. In the present invention, the temperature of the thermal reduction treatment is preferably 400–700°C, more preferably 500–650°C, and even more preferably 550–600°C; the heating rate to the required temperature for the thermal reduction treatment is preferably 2–10°C / min, more preferably 5°C / min; the holding time of the thermal reduction treatment is preferably 30–180 min, more preferably 60–90 min. In the present invention, the reducing atmosphere preferably includes an inert gas and a reducing gas, and the volume fraction of the reducing gas in the reducing atmosphere is preferably 0.5–10%, more preferably 1–8%, and even more preferably 3–5%. In the present invention, the inert gas is preferably argon, and the reducing gas preferably includes CO, H2, or CH4. By performing a thermal reduction treatment on the porous carbon material in a reducing atmosphere, the present invention can remove excess oxygen-containing active groups from the porous carbon material, thereby making it easier for fluorine functional groups to be grafted onto the surface of the porous carbon material during the fluorination process.

[0044] After obtaining the reduced porous carbon material, the present invention fluorinates the reduced porous carbon material in a fluorine-containing atmosphere to obtain a fluorinated porous carbon material. In the present invention, the fluorination treatment temperature is preferably 200–450°C, more preferably 250–400°C, and even more preferably 300–350°C; the present invention preferably cools the material obtained after thermal reduction treatment to the fluorination treatment temperature, and then holds it at that temperature for fluorination treatment, preferably by natural cooling; the holding time for fluorination treatment is preferably 30–180 min, more preferably 60–90 min. In the present invention, the fluorine-containing atmosphere preferably includes an inert gas and a fluorine-containing gas, and the volume fraction of the fluorine-containing gas in the fluorine-containing atmosphere is preferably 0.5–20%, more preferably 1–10%, and even more preferably 2–5%. In the present invention, the inert gas is preferably argon, and the fluorine-containing gas preferably includes NF3 or CF4. This invention introduces fluorine into the reduced porous carbon material by fluorinating it in a fluorine-containing atmosphere. This alters the charge distribution around the carbon atoms, leading to the formation of fluorine electron defects, which increases the number of ion adsorption active sites and results in a higher specific capacity. Simultaneously, fluorine passivates the surface of the reduced porous carbon material, enhancing the interfacial stability between the electrode and the electrolyte, enabling stable operation of the electrode under high-voltage conditions (0–5.0 V). The fluorine-containing gas used in this invention is preferably NF3 or CF4. This fluorine-containing gas can reconstruct the carbon material without causing a phase transition (solid to gaseous) and escaping of carbon elements, thereby improving the residual carbon yield.

[0045] This invention provides a fluorinated porous carbon material prepared by the preparation method described above, which is a porous carbon material with fluorine electron defects; the specific surface area of ​​the fluorinated porous carbon material is ≥3000 m². 2 / g, preferably 3000-3600m 2 / g, more preferably 3200~3570m 2 / g; micropore porosity ≥1.2cm 3 / g, preferably 1.6–2.2cm 3 / g, further preferably 1.7–2.0cm 3 / g; the fluorine content is 0.8-4.0wt%, preferably 1.0-3.5wt%, and more preferably 2.0-3.0wt%. The fluorinated porous carbon material provided by the present invention has a high specific surface area, well-developed pore structure, moderate fluorine electron defect concentration, and stable surface chemical properties.

[0046] This invention provides the application of the fluorinated porous carbon material described in the above-mentioned technical solution as a positive electrode material for lithium-ion capacitors. The fluorinated porous carbon material provided by this invention has a high specific surface area and a well-developed pore structure, which is beneficial for promoting ion transport within the electrode; the appropriate amount of fluorine electron defects in its structure is beneficial for providing more adsorption active sites; and its passivated material surface is beneficial for enhancing the interfacial stability between the electrode and the electrolyte. Lithium-ion capacitors assembled using the fluorinated porous carbon material provided by this invention as the positive electrode material can achieve an energy density of up to 231 Wh / kg under high voltage window conditions (0–5.0 V). -1 The capacity retention rate is higher than 95% after 10,000 cycles; moreover, the present invention uses fluorinated porous carbon material as the positive electrode material of lithium-ion capacitor, which has a high stable working potential, thereby avoiding the growth of lithium dendrites on the negative electrode and reducing the hidden dangers of short circuit, fire and explosion of lithium-ion capacitor.

[0047] This invention provides a lithium-ion capacitor using the fluorinated porous carbon material described in the above-mentioned technical solution as the positive electrode material. In this invention, the preparation method of the positive electrode of the lithium-ion capacitor preferably includes the following steps: mixing the fluorinated porous carbon material, acetylene black, PVDF, and a solvent to obtain a mixed slurry; coating the mixed slurry onto the surface of an aluminum foil, drying it, and then cutting it into a circular piece with a diameter of 16 mm to obtain the positive electrode of the lithium-ion capacitor. In this invention, the preferred mass ratio of the fluorinated porous carbon material, acetylene black, and PVDF is 8:1:1; the preferred solvent is N-methylpyrrolidone; the preferred drying temperature is 60°C, and the preferred drying time is 12 hours. In this invention, the preferred negative electrode of the lithium-ion capacitor is commercially available soft carbon pre-lithiated. In this invention, the electrolyte of the lithium-ion capacitor is preferably a mixture of LiPF6, ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC), the concentration of LiPF6 in the electrolyte is preferably 1.0 mol / L, and the volume ratio of EC, DEC, and DMC is preferably 1:1:1.

[0048] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0049] Example 1

[0050] 2g of petroleum coke and 12g of potassium hydroxide were placed in a ball mill jar and ball milled at 400 rpm for 3 hours to obtain a mixed precursor powder. The mixed precursor powder was then heated to 800°C from room temperature (25°C) at a heating rate of 3°C / min in a nitrogen atmosphere and held at that temperature for 2 hours for calcination and carbonization treatment. After that, it was naturally cooled to room temperature. The resulting material was washed with 1wt% hydrochloric acid until neutral and then dried at 80°C to obtain a porous carbon material.

[0051] The porous carbon material was subjected to thermal reduction treatment in a reducing atmosphere (provided by a mixture of Ar and CO, with CO volume fraction of 5%), heated from room temperature to 600°C at a heating rate of 5°C / min, and held at that temperature for 60 min. Afterward, it was naturally cooled to 350°C, and the reducing atmosphere was adjusted to a fluorine-containing atmosphere (provided by a mixture of Ar and NF3, with NF3 volume fraction of 2%), held at that temperature for 60 min, and then naturally cooled to room temperature to obtain fluorinated porous carbon material.

[0052] Example 2

[0053] Fluorinated porous carbon materials were prepared according to the method of Example 1, except that petroleum coke was replaced with ethylene tar.

[0054] Example 3

[0055] Fluorinated porous carbon materials were prepared according to the method of Example 1, except that petroleum coke was replaced with catalytic oil slurry.

[0056] Example 4

[0057] Fluorinated porous carbon materials were prepared according to the method of Example 1, except that petroleum coke was replaced with petroleum pitch and the holding temperature for calcination carbonization was 600°C.

[0058] Example 5

[0059] Fluorinated porous carbon materials were prepared according to the method of Example 1, except that petroleum coke was replaced with petroleum pitch and the holding temperature for calcination carbonization was 1000°C.

[0060] Example 6

[0061] Fluorinated porous carbon materials were prepared according to the method of Example 1, except that petroleum coke was replaced with petroleum pitch, and the holding temperature for calcination carbonization was 1200°C. The fluorinated atmosphere during the fluorination process was provided by a mixture of Ar and F2 gas, with an F2 volume fraction of 2%.

[0062] Example 7

[0063] Fluorinated porous carbon materials were prepared according to the method of Example 1, except that petroleum coke was replaced with petroleum pitch and the volume fraction of NF3 in the Ar and NF3 mixed gas was 0.5%.

[0064] Example 8

[0065] Fluorinated porous carbon materials were prepared according to the method of Example 1, except that petroleum coke was replaced with petroleum pitch and the volume fraction of NF3 in the Ar and NF3 mixed gas was 5%.

[0066] Example 9

[0067] Fluorinated porous carbon materials were prepared according to the method of Example 1, except that petroleum coke was replaced with petroleum pitch and the volume fraction of NF3 in the Ar and NF3 mixed gas was 10%.

[0068] Comparative Example 1

[0069] Carbon materials were prepared according to the method of Example 1, except that the fluorine-containing atmosphere was replaced with an argon atmosphere, that is, the material obtained after thermal reduction was not fluorinated, but held at 350°C for 60 min in an argon atmosphere.

[0070] Comparative Example 2

[0071] Fluorinated porous carbon materials were prepared according to the method of Example 1, except that petroleum coke was replaced with petroleum pitch and the reducing atmosphere was replaced with argon atmosphere. That is, the porous carbon materials obtained after calcination and carbonization were not subjected to thermal reduction treatment, but were kept at 600°C for 60 min in argon atmosphere, and then fluorinated.

[0072] Comparative Example 3

[0073] Fluorinated porous carbon materials were prepared according to the method in Example 1, except that petroleum coke was replaced with petroleum pitch and potassium hydroxide was omitted. That is, the petroleum pitch was directly ball-milled and then subjected to subsequent calcination carbonization, thermal reduction and fluorination treatment.

[0074] Test Example 1

[0075] The specific surface area, micropore porosity, and fluorine content of the carbon materials prepared in Examples 1-9 and Comparative Examples 1-3 were tested, and the results are shown in Table 1.

[0076] Table 1. Index parameters of carbon materials prepared in Examples 1-9 and Comparative Examples 1-3

[0077]

[0078]

[0079] Figure 1 This is a TEM image of the fluorinated porous carbon material prepared in Example 1. Figure 1 It can be seen that the fluorinated porous carbon material prepared in Example 1 has an interconnected three-dimensional network structure, including an interconnected multilayer pore structure and an ultrathin carbon wall.

[0080] Figure 2 The nitrogen adsorption-desorption curves for the fluorinated porous carbon material prepared in Example 1 are shown below. Figure 2 It can be seen that the adsorption-desorption curve of the fluorinated porous carbon material prepared in Example 1 is a type IV isotherm, and it is within the low pressure range (P / P o The specific surface area (<0.1) shows a significant increase, and a hysteresis loop appears in the high-pressure range, which is characteristic of a typical hierarchical porous carbon structure. The specific surface area is 3563.5 m². 2 / g, micropore porosity 1.83cm 3 / g.

[0081] Figure 3 The XPS image of the fluorinated porous carbon material prepared in Example 1 is shown below. Figure 3 It can be seen that the XPS spectrum of the fluorinated porous carbon material prepared in Example 1 shows a characteristic peak of F element with a very high intensity at a position of about 690 eV.

[0082] Depend on Figures 1-3 As shown in Table 1, the fluorinated porous carbon material prepared in the embodiments of the present invention has a well-developed multilayer pore structure. Applying the fluorinated porous carbon material as a positive electrode material in lithium-ion capacitors helps to alleviate the limitation of PF6- diffusion inside the electrode and provides PF6- adsorption sites, thereby improving specific capacity and rate performance. Moreover, the surface of the fluorinated porous carbon material has abundant fluorine functional groups, which helps to provide more adsorption active sites and passivate the material surface, enhance the interfacial stability between the electrode and the electrolyte, and enable the electrode material to operate stably at high potentials.

[0083] Test Example 2

[0084] The electrochemical performance of the carbon materials prepared in Examples 1-9 and Comparative Examples 1-3 was tested, as follows:

[0085] The carbon materials prepared in Examples 1-9 and Comparative Examples 1-3 were mixed with acetylene black and PVDF at a mass ratio of 8:1:1 and dispersed in N-methylpyrrolidone solvent to obtain a mixed slurry.

[0086] The mixed slurry was uniformly coated onto aluminum foil and dried at 60°C for 12 hours. It was then cut into circular pieces with a diameter of 16 mm. In a nitrogen-filled glove box, a coin cell was formed using lithium foil as the counter electrode (the electrolyte used was a mixture of LiPF6, EC, DEC and DMC, with a LiPF6 concentration of 1.0 mol / L and a volume ratio of EC, DEC and DMC of 1:1:1). Constant current charge-discharge tests were then conducted under a current density of 0.1–20 A / g.

[0087] Figure 4 The charge-discharge curves are for the fluorinated porous carbon material prepared in Example 1. Figure 5 Table 2 shows a comparison of the rate performance of the fluorinated porous carbon material prepared in Example 1 and the carbon material prepared in Comparative Example 1. Specific data for each example and comparative example are shown in Table 2. It can be seen that the fluorinated porous carbon material prepared in Example 1, with its large specific surface area, well-developed pore structure, and fluorine functional groups on the surface, exhibits a specific capacity of 116.8 mAh / g (0.1 A / g) at high potential. Even when the current density increases to 0.5 A / g, 2.0 A / g, and 10.0 A / g, it still maintains specific capacities of 110.4 mAh / g, 103.3 mAh / g, and 89.3 mAh / g, respectively, which is much higher than that of Comparative Example 1. This indicates that fluorine electronic defects provide more adsorption sites and faster ion diffusion channels for PF6-, enabling the fluorinated porous carbon material prepared in Example 1 to simultaneously possess high specific capacity, high capacity retention, and fast ion transfer rate.

[0088] Table 2. Specific capacity of carbon materials prepared in Examples 1-9 and Comparative Examples 1-3 at different current densities.

[0089]

[0090]

[0091] Test Example 3

[0092] The carbon materials prepared in Examples 1-9 and Comparative Examples 1-3 were assembled into lithium-ion capacitors, and the electrochemical performance of the lithium-ion capacitors was tested as follows:

[0093] The carbon materials prepared in Examples 1-9 and Comparative Examples 1-3 were mixed with acetylene black and PVDF at a mass ratio of 8:1:1 and dispersed in N-methylpyrrolidone solvent to obtain a mixed slurry.

[0094] The mixed slurry was uniformly coated onto aluminum foil and dried at 60°C for 12 hours. It was then cut into circular pieces with a diameter of 16 mm. In a nitrogen-filled glove box, a button-type lithium-ion capacitor was constructed using pre-lithiated commercial soft carbon as the negative electrode (the electrolyte used was a mixture of LiPF6, EC, DEC and DMC, with a LiPF6 concentration of 1.0 mol / L and a volume ratio of EC, DEC and DMC of 1:1:1). A constant current charge-discharge test was then performed at a current density of 0.5 A / g, followed by cycling at a current density of 10 A / g.

[0095] Table 3 shows the capacity retention of lithium-ion capacitors assembled using carbon materials prepared in Examples 1-9 and Comparative Examples 1-3 as positive electrodes under a current density of 10 A / g. As can be seen from Table 3, the fluorinated porous carbon material prepared in Example 1 retains 95.4% of its capacity after 10,000 cycles at a high current density, which is much higher than that of Comparative Example 1. This indicates that the presence of fluorine functional groups on the surface of the porous carbon material plays a role in passivating the material surface, reducing the occurrence of side reactions between the surface and the electrolyte, enhancing interfacial stability, and thus improving cycle stability.

[0096] Table 3 shows the capacity retention of lithium-ion capacitors assembled using the porous carbon materials prepared in Examples 1-9 and Comparative Examples 1-3 as positive electrodes at a current density of 10 A / g.

[0097]

[0098]

[0099] Figure 6 The charge-discharge curves are shown for the lithium-ion capacitor assembled using the fluorinated porous carbon material as the positive electrode in Example 1. Figure 7 The charge-discharge curves are shown for the lithium-ion capacitor assembled using carbon material as the positive electrode in Comparative Example 1. Figure 6 It can be seen that the lithium-ion capacitor assembled using the fluorinated porous carbon material as the positive electrode in Example 1 can be easily charged to 5V without voltage hysteresis or polarization, and has an energy density as high as 231Wh / kg; Figure 7 It can be seen that the lithium-ion capacitor assembled with carbon material as the positive electrode in Comparative Example 1 exhibits obvious voltage hysteresis and polarization, showing low coulombic efficiency.

[0100] Figure 8 This is a cycling curve of a lithium-ion capacitor assembled using the fluorinated porous carbon material as the positive electrode in Example 1. Figure 9 This is a cycling curve of a lithium-ion capacitor assembled using carbon material as the positive electrode in Comparative Example 1. Figure 8It can be seen that the lithium-ion capacitor assembled with fluorinated porous carbon material as the positive electrode in Example 1 retains 95.4% of its capacity after 10,000 cycles; while the lithium-ion capacitor assembled with carbon material as the positive electrode in Comparative Example 1 retains only 82.3% of its capacity after 2,000 cycles.

[0101] Figure 10 The graph shows the energy density and power density of the lithium-ion capacitor assembled using the fluorinated porous carbon material as the positive electrode in Example 1. Figure 10 It can be seen that the lithium-ion capacitor assembled with fluorinated porous carbon material as the positive electrode in Example 1 has an energy density of 161Wh / kg when the power density is 4165W / kg.

[0102] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a fluorinated porous carbon material, specifically comprising the following steps: Heavy oil by-products and an activator are ball-milled to obtain a mixed precursor. The active groups in the heavy oil by-products include one or more of hydroxyl, carboxyl, aldehyde, carbonate, amide, mercapto, carbonyl, and imine groups. The activator is KOH or NaOH. The heavy oil by-products include one or more of petroleum coke, ethylene tar, catalytic slurry, and petroleum pitch. The mass ratio of the heavy oil by-products to the activator is 1:

6. The ball milling speed is 300-600 rpm, and the time is 1-6 hours. The mixed precursor is calcined and carbonized in a protective atmosphere to obtain a porous carbon material; the calcination and carbonization temperature is 450~1250℃ and the holding time is 30~120min. The porous carbon material is subjected to thermal reduction treatment in a reducing atmosphere to obtain a reduced porous carbon material. The reduced porous carbon material was subjected to fluorination treatment in a fluorine-containing atmosphere to obtain fluorinated porous carbon material. The fluorination treatment is carried out at a temperature of 200~450℃ and a holding time of 30~180min; the fluorine-containing atmosphere includes an inert gas and a fluorine-containing gas, and the volume fraction of the fluorine-containing gas in the fluorine-containing atmosphere is 0.5~20%; the fluorine-containing gas includes NF3 or CF4. The fluorinated porous carbon material is a porous carbon material with fluorine electron defects; the specific surface area of ​​the fluorinated porous carbon material is 3000~3600 m². 2 / g, micropore porosity 1.6~2.2cm 3 / g, with a fluorine content of 0.8~4.0wt%.

2. The preparation method according to claim 1, characterized in that, The temperature of the thermal reduction treatment is 400~700℃, and the holding time is 30~180min; the reducing atmosphere includes an inert gas and a reducing gas, and the volume fraction of the reducing gas in the reducing atmosphere is 0.5~10%.

3. Fluorinated porous carbon material prepared by the preparation method according to claim 1 or 2.

4. The application of the fluorinated porous carbon material according to claim 3 as a positive electrode material for lithium-ion capacitors.

5. A lithium-ion capacitor, characterized in that, The fluorinated porous carbon material described in claim 3 is used as the positive electrode material.

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