Boron-fluorine co-doped porous carbon material, preparation method thereof and silicon-carbon negative electrode material

Abstract

This invention provides boron-fluorine co-doped porous carbon materials, their preparation methods, and silicon-carbon anode materials, belonging to the field of anode materials. The preparation method of the boron-fluorine co-doped porous carbon material includes the following steps: pre-carbonizing a mixture of carbon, boron, and fluorine sources under an inert atmosphere to obtain a pre-carbonized product; performing high-temperature carbonization under an inert atmosphere to obtain the boron-fluorine co-doped carbon material; activating and creating pores to obtain the boron-fluorine co-doped porous carbon material; depositing nano-silicon in the pores of the boron-fluorine co-doped porous carbon material to obtain a silicon deposition intermediate; coating the surface of the silicon deposition intermediate with carbon using chemical vapor deposition to obtain a carbon-coated silicon-carbon material; and sieving to obtain the silicon-carbon anode material. This invention achieves bulk co-doping of boron and fluorine in the carbon framework by simultaneously mixing and carbonizing the fluorine source with the carbon and boron sources, rather than just surface modification. The coexistence of B-C and C-F bonds endows the carbon material with unique electronic structure and surface chemical properties.

Description

Technical Field

[0001] This invention belongs to the field of anode material technology, and specifically relates to boron-fluorine co-doped porous carbon materials and their preparation methods, as well as silicon-carbon anode materials. Background Technology

[0002] Depositing nanocrystalline silicon within a porous carbon framework is an effective strategy to mitigate volume expansion. The porous structure of carbon provides a buffer for silicon expansion, while the carbon framework acts as a conductive network to maintain electron transport. However, the interfacial bonding between porous carbon and silicon is weak (mainly physical adsorption), and silicon particles are prone to detach from the carbon framework during long-term cycling, leading to electrical contact failure.

[0003] To enhance the silicon-carbon interface bonding, researchers have attempted to dope porous carbon with heteroatoms (such as boron and nitrogen). Boron atoms, being electron-deficient, can form B-Si chemical bonds with silicon at high temperatures, "anchoring" silicon particles to the carbon framework. Patent CN118877872A discloses a method for preparing boron-doped porous carbon materials, which involves directly carbonizing a mixture of carbon source, boron source, and template agent, completing doping and pore formation in one step. However, this method has limited control over the degree of boron doping and pore structure.

[0004] On the other hand, fluorine exhibits a unique interfacial stabilizing effect in silicon-carbon anodes. The fluorine-containing layer can induce the formation of a highly stable LiF-rich SEI film on the silicon surface. This film possesses high mechanical strength and chemical inertness, effectively suppressing electrolyte side reactions and gas generation. Existing technologies, such as CN118645598A, disclose a fluorine-doped carbon-coated silicon-carbon anode material, but the fluorine exists only in the surface coating layer and fails to dope into the carbon framework phase.

[0005] Currently, there is no known technical solution that simultaneously incorporates boron and fluorine into a porous carbon framework in bulk, and utilizes their synergistic effect to enhance the silicon-carbon interface bonding and suppress gas generation. Therefore, developing a boron-fluorine co-doped porous carbon material and its preparation method is of great significance for improving the cycle stability of silicon-carbon anodes and suppressing gas generation. Summary of the Invention

[0006] In view of this, the present invention provides boron-fluorine co-doped porous carbon materials, their preparation methods, and silicon-carbon anode materials, aiming to solve at least one technical problem in the prior art.

[0007] This invention is implemented as follows: The first aspect of this invention provides a method for preparing boron-fluorine co-doped porous carbon materials, the method comprising the following steps: S1. The mixture of carbon source, boron source and fluorine source is pre-carbonized at 400℃-600℃ under an inert atmosphere to obtain the pre-carbonized product. S2. The pre-carbonized product is subjected to high-temperature carbonization treatment at 800℃-1050℃ under an inert atmosphere to obtain boron-fluorine co-doped carbon material. S3. The boron-fluorine co-doped carbon material is activated and pore-forming at 700℃-1000℃ to obtain a boron-fluorine co-doped porous carbon material.

[0008] Furthermore, the carbon source is selected from at least one of starch, cellulose, lignin, bulk phenolic resin, polyvinyl alcohol, sucrose, and glucose; The boron source is selected from at least one of boric acid, borax, boron oxide, and borate esters; The fluorine source is selected from at least one of ammonium fluoride, polytetrafluoroethylene, sodium fluoride, and potassium fluoride; The mass ratio of carbon source, boron source and fluorine source is (70-90): (5-20): (3-15).

[0009] Furthermore, the activated pore formation is achieved using at least one of steam activation and carbon dioxide activation.

[0010] Furthermore, the pre-carbonization treatment is carried out at a temperature of 450℃-550℃ for a time of 2h-4h.

[0011] Furthermore, the high-temperature carbonization treatment takes 1-6 hours; the activation and pore-forming process takes 2-10 hours.

[0012] This invention completely converts the boron source in the mixture into highly reactive boron trioxide (B2O3) during a high-temperature carbonization process at 800℃-1050℃, which undergoes a carbothermic reduction reaction with the carbon matrix. Studies have shown that when the carbonization temperature exceeds 600℃, boron can enter the six-membered ring framework of carbon, forming BC covalent bonds. Fluorine is introduced by mixing a fluorine source into the raw materials. During the pre-carbonization process at 400℃-600℃ and the subsequent high-temperature carbonization process at 800℃-1050℃, the fluorine source (such as NH4F) decomposes in situ and releases highly reactive fluorine species. The CF bonds formed during the pre-carbonization stage at 400℃-600℃, and the resulting carbon precursor framework, provide a preliminary fixation and enrichment environment for fluorine. Existing research indicates that CF bonds can be effectively preserved under pyrolysis conditions at 400℃-600℃. During high-temperature carbonization, the relatively stable carbon precursor framework further shrinks and densifies, forming a cage effect that encapsulates fluorine atoms within the carbon or in defects, significantly slowing down the rate of fluorine loss due to decomposition or volatilization. The two-step carbonization process of this invention ensures that fluorine atoms react with carbon atoms within a suitable temperature window, ultimately existing stably in the carbon framework as CF covalent bonds or semi-ionic bonds.

[0013] A second aspect of the present invention provides a boron-fluorine co-doped porous carbon material, wherein the boron-fluorine co-doped porous carbon material is prepared by the method for preparing the boron-fluorine co-doped porous carbon material.

[0014] Furthermore, the boron-fluorine co-doped porous carbon material has a specific surface area of ​​1500 m². 2 / g-2500m 2 / g, boron content is 0.3wt%-2.5wt%, fluorine content is 0.1wt%-2.0wt%.

[0015] A third aspect of the present invention provides a silicon-carbon anode material, the silicon-carbon anode material comprising the boron-fluorine co-doped porous carbon material, nano-silicon particles deposited in the pores of the boron-fluorine co-doped porous carbon material, and a carbon coating layer.

[0016] Furthermore, the preparation method of the silicon-carbon anode material includes the following steps: Nano-silicon was thermally deposited in the pores of the boron-fluorine co-doped porous carbon material to obtain a silicon deposition intermediate. Carbon coating was performed on the surface of the silicon deposition intermediate using chemical vapor deposition to obtain carbon-coated silicon-carbon material. The carbon-coated silicon-carbon material is sieved to obtain a silicon-carbon anode material.

[0017] Furthermore, a LiF-rich solid electrolyte interface film is formed in situ on the surface of the silicon-carbon anode material during cycling.

[0018] B-Si and / or F-Si chemical bonds exist at the interface between the nano-silicon particles and the boron-fluorine co-doped porous carbon material. The formation of B-Si bonds between boron and silicon at high temperatures has a strong theoretical basis. When boron atoms come into contact with silicon, due to the difference in electronegativity between boron (approximately 2.04) and silicon (approximately 1.90), polar covalent bonds are easily formed. First-principles calculations show that the formation energy of a B-Si bond is approximately -0.8 eV, indicating that this bonding is thermodynamically favorable. This invention employs a thermal deposition method for silicon deposition at a high temperature (e.g., 520°C), providing sufficient thermodynamic driving force for the diffusion of boron and fluorine atoms from the carbon framework to the interface. Once the atoms diffuse to the fresh silicon surface, thermodynamically, the formation of B-Si and F-Si bonds is favored.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention achieves bulk co-doping of boron and fluorine in the carbon framework by simultaneously mixing and carbonizing fluorine sources with carbon and boron sources, rather than just surface modification. The coexistence of BC and CF bonds endows carbon materials with unique electronic structure and surface chemical properties.

[0020] 2. The boron atoms doped in this invention can form B-Si covalent bonds with the subsequently deposited nano-silicon after high-temperature carbonization, and the fluorine atoms doped can form F-Si bonds with silicon. The double chemical bonds firmly anchor the silicon particles to the carbon skeleton, significantly enhancing the interfacial bonding force and inhibiting silicon shedding.

[0021] 3. The fluorine-doped carbon layer formed in this invention can induce the formation of a stable LiF-rich SEI film during electrochemical cycling. This film possesses high mechanical strength and chemical inertness, effectively resisting damage caused by silicon volume expansion, reducing electrolyte side reactions, and suppressing gas generation at the source. Boron doping further enhances the conductivity and mechanical strength of the carbon framework, and the synergistic effect of both significantly improves cycling stability.

[0022] 4. The process of this invention has good compatibility. The method is based on conventional carbonization equipment, requires no special reactor, and has a wide range of raw material sources, making it suitable for large-scale production. Attached Figure Description

[0023] Figure 1 This is a SEM image of the silicon-carbon anode material prepared in Example 1 of the present invention.

[0024] Figure 2 This is the SEM energy dispersive spectroscopy (EDS) image of the silicon-carbon anode material prepared in Example 1 of this invention.

[0025] Figure 3 The voltage-to-capacity curve of the silicon-carbon anode material prepared in Example 1 of this invention is shown. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] Example 1 A method for preparing boron-fluorine co-doped porous carbon materials includes the following steps: (1) Raw material mixing: weigh starch, boric acid and ammonium fluoride in a mass ratio of 80:12:8, place them in a planetary ball mill, and ball mill at 300 rpm for 60 min to obtain mixed powder.

[0028] (2) Pre-carbonization: The mixed powder is carbonized at low temperature, kept at 500℃ for 2 hours, and then cooled naturally to obtain the pre-carbonized product.

[0029] (3) Crushing and grading: The pre-carbonized products are crushed by an air jet mill and then graded by a classifier.

[0030] (4) High-temperature carbonization: The above powder is carbonized at high temperature, kept at 950℃ for 2 hours, and then naturally cooled to obtain boron-fluorine co-doped carbon material.

[0031] (5) Activation and pore formation: The boron-fluorine co-doped carbon material is placed in an activation furnace, heated to 900°C, steam is introduced, and the temperature is maintained for 6 hours. Then, the atmosphere is switched back to N2 and the material is cooled naturally to obtain the boron-fluorine co-doped porous carbon material, denoted as B / F-PC, with D50≈10 μm.

[0032] The specific steps for fabricating silicon-carbon anode materials from the above boron-fluorine co-doped porous carbon materials include: (6) Silicon deposition: B / F-PC is placed in a fluidized bed CVD equipment, with silane as the silicon source and argon as the carrier gas, and nano-silicon is deposited at 520℃. The amount of silicon deposited is about 48 wt%, and a silicon deposition intermediate is obtained.

[0033] (7) Carbon coating: The silicon deposition intermediate is placed in a fluidized bed CVD equipment, acetylene is used as the carbon source and argon is used as the carrier gas, and carbon coating is carried out at 600℃ to obtain carbon-coated silicon-carbon materials.

[0034] (8) Screening: The carbon-coated silicon carbide material is passed through an ultrasonic vibrating screen and classified using 250-mesh and 325-mesh screens to collect products with a particle size range of 8μm-10μm, thus obtaining the finished silicon carbide anode material.

[0035] The SEM morphology image of the silicon-carbon anode material obtained in this embodiment is shown below. Figure 1 As shown; field emission scanning electron microscopy (SEM) was used (JSM) 7800F) Analysis of the EDS-Mapping elemental analysis spectrum of the finished silicon-carbon anode material, such as Figure 2 As shown, the energy peaks of boron and fluorine can be observed in the EDS-Mapping spectrum of SEM, proving that the element doping was successful.

[0036] The voltage-to-capacity curve of the silicon-carbon anode material obtained in this embodiment is as follows: Figure 3 As shown, Figure 3 The results show that the delithiation specific capacity at 1.5V is 1923mAh / g and the first-week coulombic efficiency is 95.3%, proving that the prepared material has good structural stability.

[0037] Example 2 The difference between this embodiment and Embodiment 1 is that cellulose is used instead of starch as the carbon source, while the other steps and conditions are the same as in Embodiment 1.

[0038] Example 3 The difference between this embodiment and Embodiment 1 is that lignin is used instead of starch as the carbon source, while the other steps and conditions are the same as in Embodiment 1.

[0039] Example 4 The difference between this embodiment and Embodiment 1 is that block phenolic resin is used instead of starch as the carbon source, while the other steps and conditions are the same as in Embodiment 1.

[0040] Example 5 The difference between this embodiment and Embodiment 1 is that polytetrafluoroethylene powder is used instead of ammonium fluoride for the fluorinated compound, while the other steps and conditions are the same as in Embodiment 1.

[0041] Example 6 The difference between this embodiment and Embodiment 1 is that carbon dioxide is used instead of water vapor in the pore-forming activation step, while the other steps and conditions are the same as in Embodiment 1.

[0042] Comparative Example 1 The difference between this comparative example and Example 1 is that boric acid and ammonium fluoride are not added, only starch is used, while the other steps and conditions are the same as in Example 1.

[0043] Comparative Example 2 The difference between this comparative example and Example 2 is that boric acid is not added, and only starch and ammonium fluoride are used in a mass ratio of 92:8. All other steps and conditions are the same as in Example 1.

[0044] Comparative Example 3 The difference between this comparative example and Example 1 is that ammonium fluoride is not added, and only starch and boric acid are used in a mass ratio of 88:12. All other steps and conditions are the same as in Example 1.

[0045] I. Physicochemical Tests The physicochemical properties of the porous carbon materials and silicon-carbon anode materials prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were tested, and the results are shown in Table 1.

[0046] Using German SPECTRO ICP The content of each element was analyzed by OES plasma atomic emission spectrometry; the particle size (μm) range of the material was tested using a Dandong Better Laser Particle Size Analyzer BT-9300ST; and the specific surface area of ​​the material was tested using a Quantachrome Autosorb IQ3 from the United States.

[0047] Table 1

[0048] II. Electrochemical Performance Testing The silicon-carbon anode materials prepared in Examples 1-6 and Comparative Examples 1-3 were mixed with conductive agent and binder respectively in a mass ratio of 95:1.5:3.5 and homogenized in pure water (solid content 48wt%) to obtain a slurry. The slurry was coated onto a copper foil current collector, vacuum baked at 100°C for 8 hours, pressed into shape, and punched to obtain anode sheets. A coin cell was assembled in an argon-filled glove box, with a lithium metal sheet as the counter electrode, PE as the separator, and 1 mol / L LiPF6 EC / DMC (Vol 1:1) as the electrolyte. The coin cell was subjected to charge-discharge tests, with the following procedure: 0.2C DC to 0V, 0.05C DC to 0V, 0V CV 50μA, 0.01C DC to 0V, 0V CV 20μA, Rest 10min, 0.2C CC to2V; among them, the testing equipment for button cells was the LAND battery testing system of Wuhan Landian Electronics Co., Ltd., and the test results are shown in Table 2.

[0049] Table 2

[0050] Table 2 shows that the coin cell assembled from the silicon-carbon anode material prepared by boron-fluorine co-doped porous carbon material has significantly higher electrical performance than that of undoped or boron / fluorine single-doped materials.

[0051] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing boron-fluorine co-doped porous carbon materials, characterized in that, The preparation method includes the following steps: S1. The mixture of carbon source, boron source and fluorine source is pre-carbonized at 400℃-600℃ under an inert atmosphere to obtain the pre-carbonized product. S2. The pre-carbonized product is subjected to high-temperature carbonization treatment at 800℃-1050℃ under an inert atmosphere to obtain boron-fluorine co-doped carbon material. S3. The boron-fluorine co-doped carbon material is activated and pore-forming at 700℃-1000℃ to obtain a boron-fluorine co-doped porous carbon material.

2. The method for preparing boron-fluorine co-doped porous carbon material according to claim 1, characterized in that, The carbon source is selected from at least one of starch, cellulose, lignin, bulk phenolic resin, polyvinyl alcohol, sucrose, and glucose; The boron source is selected from at least one of boric acid, borax, boron oxide, and borate esters; The fluorine source is selected from at least one of ammonium fluoride, polytetrafluoroethylene, sodium fluoride, and potassium fluoride; The mass ratio of carbon source, boron source and fluorine source is (70-90): (5-20): (3-15).

3. The method for preparing boron-fluorine co-doped porous carbon material according to claim 1, characterized in that, The activated pore formation is achieved by at least one of steam activation and carbon dioxide activation.

4. The method for preparing boron-fluorine co-doped porous carbon material according to claim 1, characterized in that, The pre-carbonization treatment is carried out at a temperature of 450℃-550℃ for 2-4 hours.

5. The method for preparing boron-fluorine co-doped porous carbon material according to claim 1, characterized in that, The high-temperature carbonization treatment lasts for 1-6 hours; the activation and pore-forming process lasts for 2-10 hours.

6. A boron-fluorine co-doped porous carbon material, characterized in that, The boron-fluorine co-doped porous carbon material is prepared by the method for preparing boron-fluorine co-doped porous carbon material according to any one of claims 1 to 5.

7. The boron-fluorine co-doped porous carbon material according to claim 6, characterized in that, The boron-fluorine co-doped porous carbon material has a specific surface area of ​​1500 m². 2 / g-2500m 2 / g, boron content is 0.3wt%-2.5wt%, fluorine content is 0.1wt%-2.0wt%.

8. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material includes the boron-fluorine co-doped porous carbon material as described in claim 6 or 7, nano-silicon particles deposited in the pores of the boron-fluorine co-doped porous carbon material, and a carbon coating layer.

9. The silicon-carbon anode material according to claim 8, characterized in that, The preparation method of the silicon-carbon anode material includes the following steps: Nano-silicon was thermally deposited in the pores of the boron-fluorine co-doped porous carbon material to obtain a silicon deposition intermediate. Carbon coating was performed on the surface of the silicon deposition intermediate using chemical vapor deposition to obtain carbon-coated silicon-carbon material. The carbon-coated silicon-carbon material is sieved to obtain a silicon-carbon anode material.

10. The silicon-carbon anode material according to claim 8, characterized in that, During cycling, a LiF-rich solid electrolyte interface film is formed in situ on the surface of the silicon-carbon anode material.

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