A nitrogen-fluorine dual-element doped porous carbon material, a silicon-carbon negative electrode material and a preparation method thereof

Abstract

The application provides a nitrogen-fluorine dual-element doped porous carbon material, a silicon-carbon negative electrode material and a preparation method of the silicon-carbon negative electrode material, and the preparation method of the porous carbon material comprises the following steps: mixing porous carbon with ammonium fluoride and / or ammonium bifluoride, and then performing gas phase deposition coating or liquid phase coating; and calcining the coated porous carbon material in a closed environment under an inert atmosphere, so that the nitrogen-fluorine dual-element doped porous carbon material is obtained. The application utilizes the characteristics of nanoscale micropores and super-large specific surface area of the porous carbon, simultaneously utilizes the low melting point and low boiling point properties of the ammonium fluoride and the ammonium bifluoride, adopts the method of gas phase deposition or liquid phase coating, obtains a uniform coated layer of the ammonium fluoride and the ammonium bifluoride, and then utilizes high-temperature calcination treatment to obtain the porous carbon material, which can simultaneously retain the characteristics of high specific surface area and nanoscale micropores, greatly reduces the expansion of the silicon-carbon negative electrode material when the silicon-carbon negative electrode material is prepared, guarantees the cycle performance of the material, and improves the rate performance of the obtained silicon-carbon negative electrode material.

Description

Technical Field

[0001] This invention belongs to the field of anode material technology, and particularly relates to a nitrogen and fluorine dual-element doped porous carbon material, a silicon-carbon anode material, and their preparation methods. Background Technology

[0002] To address the volume expansion problem of silicon-based anode materials, researchers have developed various strategies, among which vapor deposition (VCD) for preparing porous silicon-carbon anode materials is considered effective. This method utilizes porous carbon as a silicon source carrier, introducing silane gas into the pores of the porous carbon under high-temperature conditions, causing the silicon source to deposit within the carbon channels to form a silicon-carbon composite material. The porous structure of the carbon provides a buffer space for silicon expansion, effectively suppressing silicon particle pulverization. However, existing silicon-carbon materials still have some problems, such as poor electronic conductivity, insufficient pressure resistance, poor fast-charging performance, and low initial efficiency.

[0003] To further improve the performance of silicon-carbon anode materials, researchers have begun exploring new strategies. Nitrogen and fluorine doping is considered an effective method. Nitrogen atoms can improve the electronic conductivity and ion diffusion rate of the material, thereby enhancing its rate performance; while fluorine atoms can induce lithium ions to combine with fluorine to form a lithium fluoride SEI film. The lithium fluoride SEI film can reduce breakage and regeneration during cycling, thus extending the battery's cycle life. However, how to uniformly distribute nitrogen and fluorine atoms within the porous carbon framework and achieve their functionality remains a problem to be solved.

[0004] For example, in the published patent CN115275141A, ammonium fluoride, silicon powder, amino acids, and asphalt are subjected to high-energy ball milling and then calcined. Although nitrogen-fluorine doped silicon-carbon anode material is obtained, this method is a solid-phase mixing method, which has poor uniformity and consistency. Even if nitrogen and fluorine atoms can be doped, it is difficult to distribute them evenly in the silicon-carbon anode material skeleton. At the same time, the silicon particles obtained by ball milling are large in size, and the cycle performance of the silicon-carbon anode material obtained by this method is also poor. Summary of the Invention

[0005] Based on the aforementioned technical problems, this invention provides a nitrogen-fluorine dual-element doped porous carbon material, a silicon-carbon anode material, and their preparation methods. Utilizing the nanoscale micropores and ultra-large specific surface area of ​​porous carbon, and taking advantage of the low melting and boiling points of ammonium fluoride and ammonium bifluoride, a uniformly coated layer of ammonium fluoride and ammonium bifluoride approximately 10 nm thick is obtained using vapor-phase deposition or liquid-phase coating. This is followed by high-temperature calcination to obtain the nitrogen-fluorine dual-element doped porous carbon material. This porous carbon material retains both its high specific surface area and nanoscale micropores. When this porous carbon material is used to prepare a silicon-carbon anode material, the silicon particle size can be limited to 1-5 nm, thus significantly reducing the expansion of the silicon-carbon anode material, ensuring its cycle performance while improving its rate performance.

[0006] The present invention proposes a method for preparing a nitrogen-fluorine dual-element doped porous carbon material, comprising the following steps:

[0007] S1. After mixing porous carbon with ammonium fluoride and / or ammonium bifluoride, vapor phase deposition or liquid phase coating is performed to obtain porous carbon material coated with ammonium fluoride and / or ammonium bifluoride.

[0008] S2. The coated porous carbon material is calcined in a closed environment under an inert atmosphere to form nitrogen and fluorine doping, thereby obtaining the nitrogen and fluorine dual-element doped porous carbon material.

[0009] Preferably, in step S1, the porous carbon has an average pore size of 1.5-5 nm and a specific surface area of ​​1200-2400 m². 2 / g, pore volume is 0.6-1.1g / mL;

[0010] Preferably, the mass ratio of the porous carbon to ammonium fluoride and / or ammonium hydrogen fluoride is 20-100:1.

[0011] Preferably, in step S1, the vapor deposition coating involves placing a mixture of porous carbon and ammonium fluoride and / or ammonium bifluoride in a sealed environment, heating it to vaporize the ammonium fluoride and / or ammonium bifluoride, and then depositing the mixture.

[0012] Preferably, the heating temperature is 250-300℃ and the heating time is 1-3h.

[0013] In this invention, due to the large specific surface area and abundant pores of porous carbon, it can adsorb the vaporized ammonium fluoride / or ammonium bifluoride into the pores. Therefore, by controlling the vapor deposition coating pretreatment, ammonium fluoride / ammonium bifluoride is uniformly dispersed into the porous carbon.

[0014] Preferably, in step S1, the liquid phase coating involves adding a mixture of porous carbon and ammonium fluoride and / or ammonium bifluoride to water to form a slurry, and then spray drying to remove the moisture from the slurry.

[0015] Preferably, the slurry has a solid content of 10-35 wt%.

[0016] Preferably, in step S1, before mixing the porous carbon with ammonium fluoride and / or ammonium bifluoride, the process further includes: coupling the porous carbon with an aminosilane coupling agent to graft amino groups into the porous carbon pores, and then imidizing it with formylphenylboronic acid to modify the porous carbon pores with phenylboronic acid.

[0017] Preferably, the mass ratio of the porous carbon to the aminosilane coupling agent and formylphenylboronic acid is 60-150:1-5:1.

[0018] In this invention, amino groups are introduced by hydroxyl condensation of amino silane coupling agent on the surface of porous carbon. Subsequently, the amino groups on the surface of porous carbon undergo Schiff base condensation reaction with formylphenylboronic acid, thereby modifying the inner surface of the porous carbon channels with phenylboronic acid groups. These groups can form strong electrostatic adsorption with ammonium bifluoride, thereby enabling more ammonium bifluoride to be anchored more uniformly inside the pores of the porous carbon, improving the nitrogen and fluorine doping efficiency, and further improving the rate performance and cycle stability of the porous carbon material.

[0019] Preferably, in step S2, the calcination temperature is 800-1200℃ and the time is 2-4 hours;

[0020] Preferably, the inert atmosphere is at least one of nitrogen, argon, or helium.

[0021] Preferably, in step S2, the pressure vessel of the sealed environment is one of a stainless steel bottle, a glass tube, or a quartz tube.

[0022] This invention also proposes a nitrogen-fluorine dual-element doped porous carbon material, which is prepared by the above-mentioned preparation method.

[0023] The present invention also proposes a method for preparing a silicon-carbon anode material, comprising: first performing silicon vapor deposition on the above-mentioned nitrogen-fluorine dual-element doped porous carbon material under a silicon source atmosphere, and then performing carbon vapor deposition under a carbon source atmosphere to obtain the silicon-carbon anode material.

[0024] Preferably, the silicon source atmosphere comprises silane and an inert gas; the carbon source atmosphere comprises alkane and an inert gas.

[0025] Preferably, the silane is at least one of silane, disilane, dichlorosilane, or chlorosilane; the alkane is at least one of methane, ethane, acetylene, ethylene, or propylene.

[0026] Preferably, the volume ratio of the silane to the inert gas is 1:2-6; the volume ratio of the alkane to the inert gas is 1:1-3.

[0027] Preferably, the temperature for silicon vapor deposition is 400-500℃ and the time is 2-4 hours, and the temperature for carbon vapor deposition is 500-600℃ and the time is 2-4 hours.

[0028] This invention also proposes a silicon-carbon anode material, which is prepared by the above-mentioned preparation method.

[0029] Compared with the prior art, the present invention has the following technical effects:

[0030] (1) This invention achieves uniform distribution of nitrogen and fluorine in the porous carbon framework by coating the surface of the porous carbon framework with ammonium fluoride and ammonium hydrogen fluoride, utilizing the low boiling point of ammonium hydrogen fluoride, and performing high-temperature heat treatment. This effectively solves the problem of uneven doping of nitrogen and fluorine atoms in the prior art and improves the electronic conductivity and ion diffusion rate of the porous carbon material.

[0031] (2) The nitrogen and fluorine dual-element doped porous carbon material of the present invention can significantly improve the rate performance of silicon-carbon anode material, effectively solve the problem of poor fast charging performance of silicon-carbon material in the prior art, and meet the requirements of high energy density lithium-ion battery for rate performance.

[0032] (3) By introducing fluorine atoms, the present invention promotes the combination of lithium ions and fluorine atoms to form a stable lithium fluoride SEI film, which effectively reduces the rupture and regeneration during the cycle, significantly extends the cycle life of the battery, and solves the problem of the instability of solid electrolyte membranes in the prior art. Attached Figure Description

[0033] Figure 1 The image shows a SEM image of the nitrogen-fluorine dual-element doped porous carbon material described in Example 1.

[0034] Figure 2 This is a TEM image of the ammonium bifluoride-coated porous carbon material described in Example 1;

[0035] Figure 3 This is a TEM image of the nitrogen and fluorine dual-element doped porous carbon material described in Example 1;

[0036] Figure 4 The above are the magnification data of the nitrogen and fluorine dual-element doped porous carbon material described in Example 1 and the resin-based carbon material described in Comparative Example 1. Detailed Implementation

[0037] The present invention will now be described in detail through specific embodiments. However, these embodiments are clearly provided for illustrative purposes and are not intended to limit the scope of the present invention.

[0038] Example 1

[0039] This embodiment presents a nitrogen-fluorine dual-element doped porous carbon material, which is prepared by the following method:

[0040] (1) Porous carbon (average pore size of 1.8 nm, specific surface area of ​​2000 m²) 2 / g) and ammonium bifluoride are added to a VC mixer at a mass ratio of 50:1 and mixed evenly. The resulting mixture is first placed in a sealed glass tube, and nitrogen gas is introduced to fill the glass tube. Then, the glass tube is heated under a nitrogen atmosphere to melt the glass and seal it. The glass tube is placed in a tube furnace and heated to 280°C at a heating rate of 2°C / min. After maintaining the temperature for 2 hours, it is naturally cooled to room temperature to obtain ammonium bifluoride coated porous carbon material.

[0041] (2) The glass tube containing the porous carbon material coated with ammonium bifluoride is placed in a tube furnace and heated to 1000°C at a heating rate of 5°C / min under a nitrogen atmosphere. After being kept at a constant temperature for 3 hours, it is naturally cooled to room temperature to obtain the nitrogen and fluorine dual-element doped porous carbon material.

[0042] The microstructure of the above nitrogen and fluorine dual-element doped porous carbon material is referenced. Figure 1 As shown; Figure 2 The above-mentioned ammonium bifluoride-coated porous carbon material is shown in the TEM image, with reference to... Figure 2 It can be seen that the porous carbon surface is coated with a layer of ammonium hydrogen fluoride, the coating thickness is about 10 nm, and there are a large number of ordered carbon lattices inside the porous carbon. Figure 3 The above TEM images show the nitrogen and fluorine dual-element doped porous carbon materials, for comparison. Figure 2 and Figure 3 It can be observed that after high-temperature treatment, the outer coating layer becomes thinner, and the ordered carbon lattice inside the porous carbon disappears. This is because the ammonium fluoride in the outer layer decomposes, and nitrogen and fluorine atoms are doped into the porous carbon layer, destroying the ordered carbon lattice structure inside. This destruction of the structure can increase the migration rate of lithium ions in the anode material, thereby improving the rate performance of the material.

[0043] This embodiment also presents a silicon-carbon anode material, which is prepared by the following method:

[0044] The above-mentioned nitrogen and fluorine dual-element doped porous carbon material was placed in a fluidized bed vapor deposition apparatus, and a mixture of silane (SiH4) and argon (the volume ratio of silane to argon was 1:4) was introduced. Vapor deposition was carried out at 460°C for 3 hours. The apparatus was then flushed with argon for 30 minutes, and a mixture of acetylene and argon (the volume ratio of acetylene to argon was 1:2) was introduced. Vapor deposition was carried out at 570°C for 3 hours to obtain the silicon-carbon anode material.

[0045] Example 2

[0046] This embodiment presents a nitrogen-fluorine dual-element doped porous carbon material, which is prepared by the following method:

[0047] (1) Porous carbon (average pore size of 1.8 nm, specific surface area of ​​2000 m²) 2 / g) and ammonium bifluoride were added to a VC mixer at a mass ratio of 30:1 and mixed evenly. The resulting mixture was added to deionized water and stirred for 3.5 hours to obtain a slurry with a solid content of 20wt%. The slurry was first stirred at 50°C for 1.5 hours, and then spray-dried to remove the water in the slurry to obtain ammonium bifluoride coated porous carbon material.

[0048] (2) The above-mentioned ammonium bifluoride-coated porous carbon material is filled into a stainless steel bottle and sealed. Then the stainless steel bottle is placed in a tube furnace, and the atmosphere inside the bottle is replaced with argon gas. The temperature is raised to 1100°C at a heating rate of 5°C / min. After maintaining the temperature for 2.5 hours, it is naturally cooled to room temperature to obtain the nitrogen and fluorine dual-element doped porous carbon material.

[0049] This embodiment also proposes a silicon-carbon anode material, which is prepared by the method for preparing silicon-carbon anode material described in Example 1. The difference is that the nitrogen-fluorine dual-element doped porous carbon material described in this embodiment is used instead of the nitrogen-fluorine dual-element doped porous carbon material described in Example 1.

[0050] Example 3

[0051] This embodiment presents a nitrogen-fluorine dual-element doped porous carbon material, which is prepared by the following method:

[0052] (1) Porous carbon (average pore size of 1.8 nm, specific surface area of ​​2000 m²) 2 / g) and ammonium fluoride were added to a VC mixer at a mass ratio of 50:1 and mixed evenly. The resulting mixture was added to a coating reactor and heated to 280°C at a heating rate of 5°C / min under a nitrogen atmosphere. After maintaining the temperature for 2.5 hours, it was naturally cooled to room temperature to obtain ammonium bifluoride coated porous carbon material.

[0053] (2) The above-mentioned ammonium bifluoride coated porous carbon material is filled into a stainless steel bottle and sealed. Then the stainless steel bottle is placed in a tube furnace, and the atmosphere inside the bottle is replaced with nitrogen. The temperature is raised to 1200°C at a heating rate of 2°C / min. After being kept at a constant temperature for 4 hours, it is naturally cooled to room temperature to obtain the nitrogen and fluorine dual-element doped porous carbon material.

[0054] This embodiment also proposes a silicon-carbon anode material, which is prepared by the method for preparing silicon-carbon anode material described in Example 1. The difference is that the nitrogen-fluorine dual-element doped porous carbon material described in this embodiment is used instead of the nitrogen-fluorine dual-element doped porous carbon material described in Example 1.

[0055] Example 4

[0056] This embodiment presents a nitrogen-fluorine dual-element doped porous carbon material, which is prepared by the following method:

[0057] (1) Porous carbon (average pore size of 1.8 nm, specific surface area of ​​2000 m²) 2 / g) was added to ethanol and dispersed evenly. 5wt% of 3-aminopropyltriethoxysilane was added to the porous carbon. The mixture was heated to 60°C under a nitrogen atmosphere and stirred for 6 hours. After filtration, washing with alcohol, and drying, the obtained aminated porous carbon was added back to ethanol and dispersed evenly. 2wt% of 3-acetylphenylboronic acid was added to the porous carbon. The mixture was heated to 55°C and stirred for 3 hours. After filtration, washing with alcohol, and drying, porous carbon modified with phenylboronic acid was obtained.

[0058] (2) The above-mentioned porous carbon modified with phenylboronic acid and ammonium bifluoride are added to a VC mixer at a mass ratio of 50:1 and mixed evenly. The resulting mixture is first placed in a glass tube with a cap, and nitrogen gas is introduced to fill the glass tube. Then, the glass tube is heated under a nitrogen atmosphere to melt the glass and seal it. The glass tube is placed in a tube furnace and heated to 280°C at a heating rate of 2°C / min. After maintaining the temperature for 2 hours, it is naturally cooled to room temperature to obtain ammonium bifluoride coated porous carbon material.

[0059] (3) Place the glass tube containing the ammonium bifluoride-coated porous carbon material into a tube furnace, and heat it to 1000°C at a heating rate of 5°C / min under a nitrogen atmosphere. After holding the temperature constant for 3 hours, it is naturally cooled to room temperature to obtain the nitrogen and fluorine dual-element doped porous carbon material.

[0060] This embodiment also proposes a silicon-carbon anode material, which is prepared by the method for preparing silicon-carbon anode material described in Example 1. The difference is that the nitrogen-fluorine dual-element doped porous carbon material described in this embodiment is used instead of the nitrogen-fluorine dual-element doped porous carbon material described in Example 1.

[0061] Comparative Example 1

[0062] This comparative example presents a resin-based carbon material, which is prepared by the following method:

[0063] (1) Add resorcinol and oxalic acid to deionized water at a molar ratio of 1:0.01, heat to 50°C, and slowly add 37wt% formaldehyde aqueous solution with a stirring speed of 200r / min. After 1 hour, the addition is completed and the molar ratio of formaldehyde to resorcinol is 1.5:1 to obtain the prepolymer solution.

[0064] (2) A 4 wt% potassium hydroxide aqueous solution was slowly added dropwise to the above prepolymer solution with a stirring speed of 800 r / min. After 1 h, the addition was completed. Then, a 37 wt% formaldehyde aqueous solution was slowly added dropwise. After 30 min, the addition was completed. The molar ratio of formaldehyde to resorcinol was 0.5:1. The mixture was heated to 70 °C and kept warm for 8 h to carry out the crosslinking reaction and obtain a gel. The gel was then dried at 100 °C to obtain the dried material.

[0065] (3) The dried material is carbonized at 700°C for 3 hours under a nitrogen atmosphere, and carbon dioxide and nitrogen are introduced (the volume ratio of carbon dioxide and nitrogen is 1:5). The temperature is raised to 800°C and activated for 5 hours. Then it is cooled to room temperature, ground, graded, shaped and sieved to obtain the resin-based carbon material (particle size D50 is about 6.5 μm).

[0066] This comparative example also presents a silicon-carbon anode material, which is prepared by the method for preparing silicon-carbon anode material described in Example 1. The difference is that the resin-based carbon material described in this comparative example is used instead of the nitrogen-fluorine dual-element doped porous carbon material described in Example 1.

[0067] Comparative Example 2

[0068] This comparative example directly presents a silicon-carbon anode material, which is prepared by the following method:

[0069] (1) Add silicon powder, pitch powder, amino acids and ammonium fluoride into a ball mill jar in a mass ratio of 10:1:1:0.2, add ethanol until the solid-liquid mass ratio is 1:2, ball mill for 12 hours, and dry at 60°C to obtain a composite precursor;

[0070] (2) The above composite precursor was heated to 700°C and calcined for 3 hours under a nitrogen atmosphere to obtain a mixture;

[0071] (3) The above mixture is added to a 5wt% hydrofluoric acid solution at a liquid-to-solid ratio of 20mL / kg and soaked for 3h. Then it is washed 3 times with deionized water and dried at 60℃ for 6h to obtain the silicon-carbon anode material.

[0072] Comparative Example 3

[0073] This comparative example presents a nitrogen-fluorine dual-element doped porous carbon material, which is prepared by the following method:

[0074] Porous carbon (average pore size 1.8 nm, specific surface area 2000 m²) was used. 2 / g) and ammonium bifluoride are added to a VC mixer at a mass ratio of 50:1 and mixed evenly. The resulting mixture is first placed in a sealed glass tube, and nitrogen gas is introduced to fill the glass tube. Then, the glass tube is heated under a nitrogen atmosphere to melt the glass and seal it. The tube is then placed in a tube furnace and heated to 1000°C at a heating rate of 5°C / min under a nitrogen atmosphere. After maintaining the temperature for 3 hours, it is naturally cooled to room temperature to obtain the nitrogen and fluorine dual-element doped porous carbon material.

[0075] This comparative example also presents a silicon-carbon anode material, which is prepared by the method for preparing silicon-carbon anode material described in Example 1. The difference is that the nitrogen-fluorine dual-element doped porous carbon material described in this comparative example is used instead of the nitrogen-fluorine dual-element doped porous carbon material described in Example 1.

[0076] Comparative Example 4

[0077] This comparative example presents a nitrogen-fluorine dual-element doped porous carbon material, which is prepared by the following method:

[0078] (1) Porous carbon (average pore size of 1.8 nm, specific surface area of ​​2000 m²) 2 / g) and ammonium bifluoride were added to ethanol at a mass ratio of 50:1 until the solid-liquid mass ratio was 1:2. The mixture was ball-milled for 12 hours and dried at 60°C to obtain the composite precursor.

[0079] (2) The above composite precursor is placed in a tube furnace and heated to 1000°C at a heating rate of 5°C / min under a nitrogen atmosphere. After being kept at a constant temperature for 3 hours, it is naturally cooled to room temperature to obtain the nitrogen and fluorine dual-element doped porous carbon material.

[0080] This comparative example also presents a silicon-carbon anode material, which is prepared by the method for preparing silicon-carbon anode material described in Example 1. The difference is that the nitrogen-fluorine dual-element doped porous carbon material described in this comparative example is used instead of the nitrogen-fluorine dual-element doped porous carbon material described in Example 1.

[0081] Comparative Example 5

[0082] A nitrogen-fluorine dual-element doped porous carbon material is prepared by the following method:

[0083] (1) Porous carbon (average pore size of 1.8 nm, specific surface area of ​​2000 m²) 2 / g) was added to ethanol and dispersed evenly. Then, 5wt% of 3-aminopropyltriethoxysilane (by weight of porous carbon) was added. The mixture was stirred and reacted under a nitrogen atmosphere for 12 hours. After filtration, washing with alcohol, and drying, aminated porous carbon was obtained.

[0084] (2) The above-mentioned aminated porous carbon and ammonium bifluoride are added to a VC mixer at a mass ratio of 50:1 and mixed evenly. The resulting mixture is first placed in a glass tube with a cap, and nitrogen gas is introduced to fill the glass tube. Then, the glass tube is heated under a nitrogen atmosphere to melt the glass and seal it. The glass tube is placed in a tube furnace and heated to 280°C at a heating rate of 2°C / min. After maintaining the temperature for 2 hours, it is naturally cooled to room temperature to obtain ammonium bifluoride coated porous carbon material.

[0085] (3) Place the glass tube containing the ammonium bifluoride-coated porous carbon material into a tube furnace, and heat it to 1000°C at a heating rate of 5°C / min under a nitrogen atmosphere. After holding the temperature constant for 3 hours, it is naturally cooled to room temperature to obtain the nitrogen and fluorine dual-element doped porous carbon material.

[0086] This comparative example also presents a silicon-carbon anode material, which is prepared by the method for preparing silicon-carbon anode material described in Example 1. The difference is that the nitrogen-fluorine dual-element doped porous carbon material described in this comparative example is used instead of the nitrogen-fluorine dual-element doped porous carbon material described in Example 1.

[0087] The silicon-carbon anode materials prepared in each embodiment and each comparative example were used as anode materials to assemble batteries:

[0088] (1) Preparation of positive electrode sheet: The positive electrode active material lithium nickel cobalt manganese oxide (NCM811), conductive agent SuperP, carbon nanotubes, and binder polyvinylidene fluoride (PVDF) are mixed with N-methylpyrrolidone (NMP) in a mass ratio of 97:1:0.5:1.5 to prepare a positive electrode slurry (solid content of 70wt%). The obtained positive electrode slurry is coated on both sides of the current collector aluminum foil, dried at 100℃, and then cold-pressed at room temperature at 4MPa. Then, the edges are cut, the sheets are cut, the strips are slit, and the tabs are welded to make a positive electrode sheet.

[0089] (2) Preparation of negative electrode sheet: N-methylpyrrolidone (NMP) solvent and PVDF binder are stirred and mixed under nitrogen protection atmosphere, then SuperP conductive agent is added and stirred and mixed, then negative electrode active material is added and stirred and mixed thoroughly. The negative electrode active material, SuperP and binder are prepared into negative electrode slurry (solid content is 50wt%) in a mass ratio of 96:1.5:2.5. The negative electrode active material is obtained by mixing silicon-carbon negative electrode material and graphite prepared in each example and each comparative example with a specific capacity of 600mAh / g. The obtained negative electrode slurry is coated on both sides of the current collector copper foil, dried at 100°C, cold pressed at 4MPa at room temperature, then trimmed, cut into pieces, slit, and welded with tabs to make negative electrode sheet.

[0090] (3) Using a PE porous polymer film as a separator, the prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes, and wound to obtain a bare battery cell; the bare battery cell is placed in an aluminum-plastic shell package and subjected to a relative vacuum pressure of -0.95×10 5 At Pa, the cells are dried at 100°C until the moisture content is below 100ppm. The electrolyte is then injected into the dried bare cells. The electrolyte is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:DEC = 1:1:1, and LiPF6 (1.0M). The cells are then encapsulated, left to stand, formed (0.02C constant current charging for 2 hours, 0.1C constant current charging for 2 hours), shaped, and capacity tested (capacity grading) to produce a soft-pack liquid lithium-ion battery.

[0091] During battery assembly, five batteries were prepared for each test group, and a total of five sets of data were tested. The final performance was taken as the average of the five sets of data.

[0092] Battery cycle performance was tested on Xinwei equipment as follows: at 25℃, the battery was first discharged at 0.1C to 0.005V, then discharged at 0.08C to 0.001V, then at 0.05C to 0.001V, and then at 0.02C to 0.001V, and then left to stand for 10 minutes; then it was charged at 0.1C to 1.5V, left to stand for 10 minutes, and the charge and discharge capacity after the first cycle was recorded, and the initial coulombic efficiency was calculated; the battery was cycled 100 times in the above manner, and the charge and discharge capacity after 100 cycles was recorded, and the capacity retention rate after 100 cycles was calculated. The capacity retention rate after 1000 cycles was tested and calculated in the same way, and the test results are shown in Table 1 below.

[0093] Table 1. Performance results of the silicon-carbon anode materials described in the examples and comparative examples.

[0094]

[0095] As shown in Table 1 above, the examples exhibit better cycle stability and rate performance compared to the comparative examples. The performance results of Examples 1 and Comparative Example 3 indicate that the nitrogen and fluorine dual-element doping efficiency of the porous carbon material obtained by direct calcination without vapor deposition coating is relatively low. The cycle performance and rate performance of the material in Comparative Example 3 are significantly lower than those of Example 1, but slightly better than those of Comparative Example 1. The performance results of Examples 1 and Comparative Example 4 indicate that although nitrogen and fluorine dual-element doping can be achieved in the porous carbon material obtained by simple grinding and mixing, the doping effect is relatively poor. The performance results of Examples 4 and Comparative Example 5 indicate that simple amination modification of porous carbon cannot improve the nitrogen and fluorine doping efficiency, and its contribution to improving the rate performance and cycle stability of the obtained porous carbon material is basically zero.

[0096] Figure 4The magnification data for Example 1 and Comparative Example 1 are provided by... Figure 4 It can be seen that at low current rates of 0.1C / 0.2C / 0.33C, the charging capacity retention rates of the Example and the Comparative Example are not significantly different. However, at high current rates of 0.5C / 1C / 2C / 3C, the charging capacity retention rate of Example 1 is significantly better than that of Comparative Example 1.

[0097] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen-fluorine dual-element doped porous carbon material, characterized in that, Includes the following steps: S1. After mixing porous carbon with ammonium fluoride and / or ammonium bifluoride, vapor phase deposition or liquid phase coating is performed to obtain porous carbon material coated with ammonium fluoride and / or ammonium bifluoride. S2. The coated porous carbon material is calcined in a closed environment under an inert atmosphere to form nitrogen and fluorine doping, thereby obtaining the nitrogen and fluorine dual-element doped porous carbon material. In step S1, before mixing the porous carbon with ammonium fluoride and / or ammonium bifluoride, the process further includes: coupling the porous carbon with an aminosilane coupling agent to graft amino groups into the porous carbon pores, and then imidizing it with formylphenylboronic acid to modify the porous carbon pores with phenylboronic acid. The mass ratio of the porous carbon to the aminosilane coupling agent and formylphenylboronic acid is 60-150:1-5:

1.

2. The method for preparing nitrogen-fluorine dual-element doped porous carbon material according to claim 1, characterized in that, In step S1, the porous carbon has an average pore size of 1.5-5 nm and a specific surface area of ​​1200-2400 m². 2 / g, pore volume is 0.6-1.1g / mL; The mass ratio of the porous carbon to ammonium fluoride and / or ammonium bifluoride is 20-100:

1.

3. The method for preparing nitrogen-fluorine dual-element doped porous carbon material according to claim 1 or 2, characterized in that, In step S1, the vapor deposition coating involves placing a mixture of porous carbon and ammonium fluoride and / or ammonium bifluoride in a sealed environment, heating it to vaporize the ammonium fluoride and / or ammonium bifluoride, and then depositing the mixture. The heating temperature is 250-300℃, and the time is 1-3 hours.

4. The method for preparing nitrogen-fluorine dual-element doped porous carbon material according to claim 1 or 2, characterized in that, In step S1, the liquid phase coating involves adding a mixture of porous carbon and ammonium fluoride and / or ammonium bifluoride to water to form a slurry, and then spray drying to remove the water from the slurry. The slurry has a solid content of 10-35 wt%.

5. The method for preparing nitrogen-fluorine dual-element doped porous carbon material according to claim 1 or 2, characterized in that, In step S2, the calcination temperature is 800-1200℃ and the time is 2-4 hours; And / or the inert atmosphere is at least one of nitrogen, argon or helium.

6. A nitrogen-fluorine dual-element doped porous carbon material, characterized in that, It is prepared by the preparation method described in any one of claims 1-5.

7. A method for preparing a silicon-carbon anode material, characterized in that, include: The nitrogen-fluorine dual-element doped porous carbon material of claim 6 is subjected to silicon vapor deposition in a silicon source atmosphere, and then carbon vapor deposition is performed in a carbon source atmosphere to obtain the silicon-carbon anode material.

8. The method for preparing the silicon-carbon anode material according to claim 7, characterized in that, The silicon source atmosphere includes silane and an inert gas, and the carbon source atmosphere includes alkane and an inert gas; the silane is at least one of methane or ethyl silane, and the alkane is at least one of methane or ethane; The silicon vapor deposition temperature is 400-500℃ and the time is 2-4h; the carbon vapor deposition temperature is 500-600℃ and the time is 2-4h.

9. A silicon-carbon anode material, characterized in that, It is prepared by the preparation method described in claim 7 or 8.

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