Preparation method and application of fluorine-doped carbon material

Abstract

This invention discloses a method for preparing fluorine-doped carbon materials and their applications, belonging to the field of battery materials technology. Addressing the core bottlenecks of severe volume expansion and unstable SEI (Sediment Interface) in high-energy-density metal-ion batteries, this invention abandons the traditional approach of directly modifying the active material of the negative electrode. Instead, it proposes fluorine doping modification of any carbon component in the metal-ion battery negative electrode. Utilizing the fluorine transfer from the fluorine-doped carbon component to the active material interface during charge-discharge cycles, a stable SEI rich in metal fluorides and active material-fluorine bonds is induced, thereby improving the stability of the negative electrode interface and suppressing volume expansion. Directly coating the active material with a fluorine source results in severe HF etching of active materials such as silicon and tin. This invention achieves fluorine doping by mixing a fluorinated polymer with an HF-resistant carbon material, and then combining it with the active material, fundamentally avoiding the etching risk. Furthermore, the process is simple and cost-controllable, providing a novel approach for the control of the metal-ion battery negative electrode interface.

Description

Technical Field

[0001] This invention relates to the field of metal-ion battery electrode materials technology, specifically to a method for preparing fluorine-doped carbon materials based on fluorine transfer-regulated solid electrolyte interphase (SEI) and its application in the modification of solid electrolyte interphase in metal-ion batteries, particularly suitable for the preparation of silicon-based, carbon-based, tin-based and other negative electrodes for high energy density metal-ion batteries. Background Technology

[0002] With the rapid development of new energy vehicles, energy storage power stations, and artificial intelligence devices, the market demand for high-capacity, high-energy-density, and long-cycle-life metal-ion batteries is becoming increasingly urgent. For example, as the most mainstream energy storage system, silicon-based anodes in lithium-ion batteries possess extremely high theoretical capacity (3579 mAh g⁻¹). -1 With its low lithium intercalation voltage and abundant crustal reserves, it has become a core candidate material for improving energy density.

[0003] Sodium-ion batteries have excellent thermal stability, with an operating temperature range of -40℃ to 70℃, far exceeding the conventional range of lithium batteries. Sodium accounts for 2.3% of the abundance of crustal elements, hundreds of times that of lithium. It is widely distributed, not limited by geography, and can be extracted infinitely from seawater, which can solve resource monopolies and geopolitical risks. The manufacturing process is highly compatible with lithium batteries, and existing production lines can be quickly upgraded, reducing equipment investment.

[0004] Potassium-ion batteries (KIBs) have emerged as a highly attractive candidate, leveraging the Earth's abundant potassium resources (2.09% crustal abundance) and redox potentials comparable to lithium systems (-2 to 2.93 V vs. SHE). Furthermore, KIBs exhibit enhanced ion transport kinetics (Ki). + The Stokes radius in propylene carbonate is 3.6 Å, while that in Li is 4.8 Å, and its lower tendency to form dendrites makes it particularly suitable for high-power applications.

[0005] To mitigate the volume expansion problem, industry and academia have widely adopted the active material-carbon composite technology route. This involves introducing carbon components into the active material to construct a composite anode, utilizing the excellent conductivity, structural stability, and volume buffering properties of carbon materials to synergistically alleviate the volume expansion of the active material and improve the overall conductivity of the electrode. Silicon-carbon composites and carbon-tin composites have become the mainstream research and development direction for high-capacity anodes in metal-ion batteries.

[0006] Although carbon composite modification has improved the performance of anode materials to some extent, the stability of the SEI (Sediment Injection Layer) remains a core bottleneck restricting its cycle performance. Studies have shown that fluoride-rich SEIs possess high Young's modulus, a wide electrochemical window, and a low metal ion diffusion barrier, effectively suppressing electron tunneling, promoting uniform metal ion deposition, significantly improving the mechanical integrity and ionic conductivity of the SEI, and thus enhancing the electrochemical performance of the anode. Therefore, constructing a stable fluoride-rich SEI has become a core objective for interface control in metal-ion battery anodes. However, existing technologies are limited to directly doping the active material with fluorine for interface control, leading to the etching of the active material by the fluorine-containing precursor. The carbon component in metal-ion battery composite anodes exhibits high chemical stability and strong tolerance to HF, and is widely present in various composite anode systems, making it an essential component of the anode. Therefore, a method is needed that does not directly modify the anode active material, but instead modifies any carbon component commonly found in composite anodes with fluorine doping, and achieves precise control of the SEI at the active material interface through the fluorine transfer mechanism. This breaks the existing perception that "active materials must be directly modified", and provides a new direction for the interface modification of metal-ion battery anodes. It can be used for lithium-ion batteries and can also be extended to various metal-ion battery systems such as sodium-ion and potassium-ion batteries. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides an innovative strategy for regulating SEI by fluorine transfer. Fluorine-doped carbon is prepared by modifying the carbon component in the negative electrode of a metal-ion battery with fluorine doping, and the SEI of the negative electrode is stabilized by utilizing the fluorine transfer mechanism.

[0008] This invention is primarily aimed at the mainstream silicon anode of lithium-ion batteries. This example is only used to illustrate the effectiveness of the strategy of this invention and does not constitute a limitation on the scope of application of this invention. This strategy can also be extended to metal-ion batteries with larger ionic radii, such as sodium and potassium ions, and various anode active material systems.

[0009] One objective of this invention is to provide a method for preparing a metal-ion battery anode with fluorine transfer-regulated solid electrolyte interphase (SEI), specifically comprising the following steps: (1) Preparation of fluorine-doped carbon components: Fluorine doping is performed on any carbon component in the negative electrode to obtain fluorine-doped carbon components; (2) Negative electrode assembly: The fluorine-doped carbon component is mixed with the negative electrode active material to prepare a negative electrode sheet and assemble it into a battery; (3) Fluorine transfer-induced SEI formation: During charge-discharge cycles, the fluorine-doped carbon component provides a fluorine source to the active material interface through fluorine transfer, inducing the formation of a stable SEI rich in metal fluorides and active material-fluorine bonds, thereby improving the stability of the negative electrode interface and suppressing volume expansion. The carbon component is selected from one or more of the following commonly used conductive carbons in negative electrodes (acetylene black, Super P, Ketjen black), graphite, graphene, and carbon nanotubes, wherein the conductive carbon is acetylene black, Super P, or Ketjen black.

[0010] Preferably, the carbon component is one or more of graphite, acetylene black AB, Super P, and Ketjen black KB.

[0011] The fundamental reason for choosing carbon components as the fluorine doping carrier is that carbon materials are resistant to HF corrosion and can withstand the corrosive gases generated by the pyrolysis of PVDF, while direct fluorination of active materials such as silicon and tin would be severely etched and destroyed.

[0012] Furthermore, in metal-ion batteries, this composite SEI can significantly improve mechanical strength and ionic conductivity, and suppress volume expansion and repeated SEI rupture.

[0013] The second objective of this invention is to provide a method for preparing a fluorine-doped carbon component for realizing the above-mentioned fluorine transfer strategy, using a fluorinated polymer as a fluorine source and any carbon component in the negative electrode of a metal-ion battery as a substrate, and preparing it by gel coating-high temperature carbonization or in-situ polymerization-carbonization method; In the fluorine-doped carbon component, fluorine is partially retained in the carbon layer in the form of CF bonds; The fluoropolymer is selected from one or more of PVDF, PTFE, PVF, and PCTFE; The carbon component is selected from one or more of graphite, acetylene black AB, Super P, and Ketjen black KB.

[0014] Furthermore, the gel coating-high temperature carbonization method specifically includes the following steps: (1) Add the fluoropolymer to N-methylpyrrolidone (NMP), heat to 40 ~ 100 ℃ and stir to dissolve to prepare a gel solution; the mass ratio of fluoropolymer to NMP is 1:100 ~ 1:20 to ensure that the viscosity of the gel solution is suitable for subsequent coating; (2) Add a base carbon material to the gel solution, wherein the mass ratio of the base carbon material to the fluoropolymer is 10:1 to 2:1, and spray at 500 to 800 r / min. -1 Stir at a rate of 10 ~ 24 h to ensure that the substrate carbon material is uniformly coated by the gel solution. After stirring, vacuum dry (80 ℃, 12 ~ 24 h) to obtain the gel composite. (3) The gel composite is placed in a quartz tube under an inert atmosphere and carbonized at high temperature to obtain fluorine-doped carbon material; the carbonization temperature is 550 ~ 650 ℃, preferably 600 ℃, and the heating rate is 1 ~ 10 ℃ min. -1The holding time is 1 to 3 hours. These process parameters ensure the preservation of CF bonds and uniform doping of fluorine.

[0015] The main function of step (1) is to construct a fluorine source carrier, convert the solid fluorinated polymer into a liquid or colloidal state, so that it has fluidity and coating ability, and ensure that the fluorine source can be uniformly attached to the surface of the carbon material to avoid agglomeration.

[0016] The main function of step (2) is to achieve precursor composite. Through physical stirring, the polymer solution / colloid encapsulates carbon particles, and the solvent is removed by drying to form a "core-shell" precursor. This establishes a close contact between the fluorine source and the carbon substrate, laying the physical foundation for element transfer and bonding during subsequent carbonization.

[0017] The main function of step (3) is structural transformation and fluorine doping. The polymer is pyrolyzed and carbonized to form a conductive carbon layer. At the same time, some CF bonds break and recombine, "locking" fluorine atoms in the carbon lattice or surface, transforming the insulating polymer into conductive fluorine-doped carbon, and retaining active fluorine species for transfer during battery cycling.

[0018] The fluorine-doped carbon components prepared by the above method have a specific surface area of ​​200~800 m². 2 g -1 The surface contains semi-ionic and covalent CF bonds. This structure can ensure the effective dissociation of fluorine species and their directional transfer to the active material interface during charging and discharging, thus meeting the core requirement of fluorine transfer regulation of SEI.

[0019] The fluorine-doped carbon component provided by this invention can also be one of the following: an electrode conductive agent, an additive, or a component of a composite electrode material.

[0020] The third objective of this invention is to provide a metal-ion secondary battery, comprising a positive electrode, a negative electrode prepared by the above method, a polypropylene membrane, and a corresponding metal-ion electrolyte. The specific preparation method includes the following steps: (1) Preparation of working electrode sheet: The negative electrode active material, fluorine-doped carbon component and binder are mixed and a dispersion medium is added and stirred to obtain a viscous slurry. The slurry is uniformly coated on the copper foil current collector, vacuum dried and sliced ​​to obtain the negative electrode sheet; (2) Battery assembly: Using the negative electrode as the working electrode and the metal sheet as the counter electrode, the working electrode, polypropylene separator, and metal counter electrode are sequentially installed into the CR2016 battery case, the corresponding metal ion electrolyte is injected and sealed to obtain a metal ion secondary battery.

[0021] Furthermore, the active material, fluorine-doped carbon component, and binder are mixed in a mass ratio of 60~75 : 15~20 : 10~20; The fluorine-doped carbon component accounts for 15-20 wt% of the total mass of the electrode material; The dispersion medium is NMP or deionized water, and the stirring rate after adding the dispersion medium is 500-800 rmin. -1 The stirring time is 10 to 24 hours. The binder is polyacrylic acid (PAA, molecular weight 100,000 to 500,000) or sodium carboxymethyl cellulose (CMC, degree of substitution 0.7 to 1.2). The solid content of the viscous slurry is 40-60 wt%; The vacuum drying temperature is 80 ~ 120 ℃, and the drying time is 12 ~ 24 h; The counter electrode metal sheet has a thickness of 0.5 to 2 mm and a diameter of 10 to 20 mm.

[0022] Furthermore, the electrochemical testing temperature of the metal ion secondary battery is 25 °C. When the metal ion is lithium ion, the battery electrolyte is a 1 M LiPF6 EC / DEC solution; when the metal ion is sodium ion / potassium ion, the battery electrolyte is a hexafluorophosphate organic electrolyte corresponding to the metal ion.

[0023] The metal-ion secondary battery provided by this invention can be a lithium-ion battery, a sodium-ion battery, or a potassium-ion battery. Because a stable metal-rich fluoride SEI is formed on the negative electrode, the cycle stability, rate performance, and volume compatibility of this battery are significantly improved.

[0024] For silicon anodes in lithium-ion batteries, fluorine species transfer and react with Li + The fluorine species combine to form LiF, which in turn forms corresponding Si-F bonds with the active material; for the tin anode of sodium-ion batteries, the fluorine species transfer and react with Na. + NaF is formed, which then forms a corresponding Sn-F bond with the active material; for the graphite anode of potassium-ion batteries, fluorine species are transferred and then react with K. + They combine to form KF, which in turn forms corresponding CF bonds with the active material.

[0025] Compared with the prior art, the present invention has the following significant advantages: (1) This invention utilizes the high tolerance of conductive agents, graphite and other carbon components in the negative electrode of metal-ion batteries to HF, and uses fluorinated polymers as fluorine sources to modify any carbon component with fluorine doping to prepare fluorine-doped carbon components; after assembling the negative electrode containing the fluorine-doped carbon components into a battery, during the charge and discharge cycle, the fluorine species in the fluorine-doped carbon components can be directionally transferred to the interface of the active material, combine with metal ions in the electrolyte to form metal fluorides, and at the same time form active material-fluorine bonds with the active material, inducing the formation of a stable SEI rich in metal fluorides and active material-fluorine bonds, synergistically improving interface stability and suppressing volume expansion.

[0026] (2) Unlike direct fluorination or plasma fluorine doping methods, this invention uses fluoropolymers as the fluorine source and constructs a fluorine-doped carbon layer on the surface of the carbon component through gel coating-high temperature carbonization or in-situ polymerization-carbonization processes. Utilizing the thermal decomposition characteristics of fluoropolymers, the controllable retention of fluorine and the construction of a conductive carbon layer are achieved simultaneously in a single process. The resulting fluorine-doped carbon component possesses both excellent conductivity and fluorine transfer function, and can directly replace the conventional carbon component in the negative electrode without changing the existing electrode preparation process. Due to the high tolerance of carbon components to HF, the fluorine doping modification target is changed from the active material to the carbon component, completely avoiding the problem of HF etching of active materials such as silicon and tin during the modification of fluorine-containing precursors, thus achieving a unity of functional modification and material protection.

[0027] (3) This invention abandons the inherent idea of ​​"directly modifying the anode active material" in the prior art, focuses on the carbon component that is commonly found in the anode of metal-ion batteries and performs fluorine doping modification, providing a new strategy for fluorine transfer to regulate SEI, which is suitable for various composite anode systems, does not require changing the existing anode preparation framework, and is easy to promote industrially; the fluorine doping of the conductive agent is only an example, the core protection is the universal idea that "any carbon component can be fluorinated to regulate SEI", and has a wide range of applications.

[0028] (4) The SEI formed by fluorine-doped carbon components through fluorine transfer is rich in metal fluorides and active material-fluorine bonds. The high Young's modulus of the metal fluorides gives the SEI excellent mechanical strength and can effectively suppress electrode volume expansion. The active material-fluorine bonds can stabilize the surface of the active material, suppress electrolyte decomposition, and significantly improve the metal ion conduction efficiency. The stability and functional integrity of this composite SEI are significantly better than those of the traditional negative electrode SEI.

[0029] (5) The spatial support effect of the fluorine-doped carbon component, combined with the high-strength SEI induced by it, achieves synergistic suppression of the volume expansion of the negative electrode. Taking the lithium-ion battery negative electrode prepared by the fluorine-doped conductive agent and porous nano-silicon in the example of this invention as an example, the capacity retention rate after 100 cycles is 91.8%, and the volume expansion rate after 50 cycles is 36.8%. In contrast, the electrode without the fluorine-doped conductive agent has a capacity retention rate of only 81.2% after 100 cycles and a volume expansion rate of 78.2% after 50 cycles. The fluorine-doped carbon component effectively avoids the collapse of the electrode structure and the shedding of the active material.

[0030] (6) The fluoropolymers and carbon components used in this invention are all industrially mass-produced products. The preparation process is simple and the cost is controllable. There is no need to make substantial adjustments to the existing battery production process. It can be directly integrated into the existing production line. In addition to the mainstream lithium-ion battery silicon anode system, this strategy can also be extended to the metal-ion battery system of potassium ion and sodium ion with larger ionic radii. It is compatible with various anode active materials such as tin and graphite, and has a wide range of industrial applications.

[0031] It should be clarified that the choice of fluorine doping of the conductive agent is only an exemplary scheme. The core innovation of this invention lies in providing a universal methodological approach—that is, any carbon component in the composite negative electrode can be used as a fluorine doping carrier, and SEI regulation can be achieved through fluorine transfer. Attached Figure Description

[0032] Figure 1 TEM images of CFAB: basic morphology (a) and (c); magnified HRTEM lattice fringes (b); TEM-mapping images of each element: (d) carbon; (e) oxygen; (f) fluorine.

[0033] Figure 2 The XPS F1s fine spectra of CFAB and AB are shown.

[0034] Figure 3 For electrodes using CFAB conductive agent at 1 A g -1 Cyclic stability and coulombic efficiency at current density.

[0035] Figure 4 Electrodes of Example 1 and Comparative Example 1 before and at 1 A g -1 Impedance spectrum after 50 charge-discharge cycles.

[0036] Figure 5 For Example 1 (a, before cycling; c, after cycling); Comparative Example 1 (b, before cycling; d, after cycling), the electrode was at 1 Ag -1 Scanning electron microscope (SEM) cross-sectional images before and after the next 50 charge-discharge cycles.

[0037] Figure 6XPS fine spectra of Example 1 and Comparative Example 1: (a) Example 1 F1s; (b) Comparative Example 1 F1s; (c) Example 1 Si2p; (d) Comparative Example 1 Si2p.

[0038] Figure 7 Optical photographs (a), XRD patterns (b), thermogravimetric curves (c), and XPS patterns (d) of PVDF / EnSi composites, EnSi, and CF with different mass ratios. Detailed Implementation 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. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0039] Unless otherwise specified, experimental methods in the following examples are generally performed under standard conditions or as recommended by the manufacturer. In this invention, "room temperature" and "normal pressure" refer to the temperature and pressure of the operating room, typically 25°C and one atmosphere.

[0040] The batteries designed in the following examples and comparative examples are CR2016 batteries.

[0041] Example 1: Application of fluorine-doped conductive agent CFAB in lithium-ion battery silicon anode (1) Add 1 g PVDF and 20 g NMP to a 250 mL beaker, stir and heat continuously until PVDF is completely dissolved to obtain a transparent gel solution. Then add 0.3 g acetylene black AB to the gel solution and stir overnight. Then dry in a vacuum oven at 80 °C for 12 h. Finally, dry the mixture at 2 °C for 1 min under an argon atmosphere. -1 The heating rate was increased from room temperature to 600 °C, and carbonization was carried out at this temperature for 2 h. The final product obtained was the fluorine-doped conductive agent CFAB.

[0042] in, Figure 1 Its TEM characterization image, Figure 1 (a) and (c) are the basic morphological diagrams of CFAB. Figure 1 (b) is the TEM-mapping diagram of each element. Figure 1 (d) represents carbon. Figure 1 (e) represents oxygen. Figure 1 (f) represents fluorine, indicating that fluorine is uniformly doped into the carbon material.

[0043] Figure 2 The XPS F1s fine spectra of CFAB and AB show that there are semi-ionic CF and covalent CF bonds on the surface of CFAB.

[0044] Figure 3 For electrodes using CFAB conductive agent at 1 A g -1 Cyclic stability and coulombic efficiency at current density.

[0045] (2) Preparation of working electrode sheet for lithium-ion half-cell: Porous nano-silicon was selected as the active material for the working electrode, sodium carboxymethyl cellulose (CMC) was used as the binder, and deionized water was used as the dispersion medium; the mass ratio of porous nano-silicon, CFAB, and CMC was 75:15:10. CMC was first dispersed separately in deionized water and stirred for 6 h until it was completely dissolved. Then, porous nano-silicon and CFAB were added and stirred at 800 r / min. -1 The mixture was mechanically stirred at a high speed for 16 h to obtain a uniform and viscous slurry. The slurry was then uniformly coated onto a copper foil current collector, vacuum dried at 100 °C for 18 h, and sliced ​​to obtain the working electrode sheet for a lithium-ion half-cell.

[0046] (3) Preparation of counter electrode for lithium-ion half-cell: Commercially available lithium metal discs with a thickness of 0.5 ~ 1 mm, a diameter of 15 mm, and no oxide layer on the surface are used directly as counter electrodes.

[0047] (4) Assembly of lithium-ion half-cell: In a glove box (water oxygen content < 0.1 ppm), the working electrode sheet, polypropylene separator and lithium metal counter electrode prepared in step (2) are sequentially loaded into the CR2016 battery case. The injected electrolyte is a 1 M LiPF6 EC / DEC mixed solution (volume ratio 1:1). The lithium-ion half-cell is encapsulated and tested at 25 ℃.

[0048] Example 2: Application of fluorine-doped conductive agent CFAB in tin anode of sodium-ion battery (1) The preparation of fluorine-doped conductive agent CFAB in the tin negative electrode of sodium battery follows the process of Example 1.

[0049] (2) Preparation of tin working electrode for sodium-ion battery: Porous nano tin active material, CFAB and CMC are mixed in a mass ratio of 70:20:10, and deionized water is used as the dispersion medium. The mixture is mechanically stirred for 16 h to obtain a uniform viscous slurry with a solid content of 50 wt%. The slurry is uniformly coated on a copper foil current collector and vacuum dried at 100 ℃ for 18 h. The slices are cut into 14 mm diameter round pieces to obtain the tin working electrode sheet for sodium-ion battery.

[0050] (3) Preparation of counter electrode for sodium-ion half cell: In a glove box (H2O, O2 < 0.1 ppm), the bulk sodium metal is rolled into a thin sheet and cut into sodium metal discs with a thickness of 0.5 ~ 1 mm and a diameter of 15 mm with no oxide layer on the surface, which are used as counter electrodes.

[0051] (4) Sodium-ion half-cell assembly: In a glove box (H2O, O2 < 0.1 ppm), the working electrode, polypropylene separator, and sodium metal sheet were sequentially loaded into the CR2016 battery case, and the electrolyte was injected as EC / DEC solution of 1 M NaPF6. The sodium-ion half-cell was then encapsulated and tested at 25 ℃.

[0052] Example 3: Fluorine-doped Ketjenblack (CFKB) and its application in graphite anodes for potassium-ion batteries (1) The preparation of fluorine-doped Ketjen black (CFKB) follows the same process as the preparation of CFAB in Example 1, except that AB is replaced with an equal mass of Ketjen black KB.

[0053] (2) Preparation of graphite working electrode for potassium-ion battery: Graphite active material, CFKB and CMC are mixed in a mass ratio of 70:20:10, and deionized water is used as the dispersion medium. The mixture is mechanically stirred for 16 h to obtain a uniform viscous slurry with a solid content of 50 wt%. The slurry is uniformly coated on a copper foil current collector and vacuum dried at 100 ℃ for 18 h. The slices are cut into 14 mm diameter round pieces to obtain the graphite working electrode sheet for potassium-ion battery.

[0054] (3) Preparation of counter electrode for potassium ion half cell: In a glove box (H2O, O2 < 0.1 ppm), blocky potassium metal is rolled into a thin sheet and cut into potassium metal discs with a thickness of 0.5 ~ 1 mm and a diameter of 15 mm with no oxide layer on the surface, which are used as counter electrodes.

[0055] (4) Assembly of potassium-ion half-cell: In a glove box (H2O, O2 < 0.1 ppm), the working electrode, polypropylene separator, and metal potassium sheet were sequentially loaded into the CR2016 battery case, and the electrolyte was injected as EC / DEC solution of 1 M KPF6. The potassium-ion half-cell was then encapsulated and tested at 25 ℃.

[0056] Comparative Example 1 The comparative example is completely identical to Example 1 in battery structure, preparation process, and raw materials, except that the conductive agent CFAB is replaced with an equal mass of acetylene black (AB), and all other parameters remain unchanged.

[0057] Comparative Example 2 The battery structure, preparation process, and raw materials of this comparative example are completely consistent with those of Example 2, except that the conductive agent CFAB is replaced with an equal mass of acetylene black (AB), and all other parameters remain unchanged.

[0058] Comparative Example 3 The comparative example is completely identical to Example 3 in battery structure, preparation process, and raw materials, except that CFKB is replaced with an equal mass of ordinary Ketjen Black (KB), and all other parameters remain unchanged.

[0059] Comparative Example 4 This comparative example does not perform carbon doping treatment on the fluoropolymer PVDF gel, but directly uses PVDF gel to coat the silicon material anode (EnSi) with coating ratios of 1:1 and 10:3.

[0060] Performance test results: (1) In 1 A g -1 The lithium-ion half-cells of Example 1 and Comparative Example 1 were subjected to cycle performance tests at current density, and the results are as follows: Example 1 (CFAB conductive agent) had an initial discharge capacity of 2835 mAh g. -1 After 100 cycles, the capacity retention rate was 91.8%, and after 50 cycles, the volume expansion rate was 36.8%; Comparative Example 1 (AB conductive agent) had an initial discharge capacity of 2924 mAhg. -1 After 100 cycles, the capacity retention rate was only 81.2%, while after 50 cycles, the volume expansion rate was as high as 78.2%, indicating that CFAB can significantly suppress volume expansion.

[0061] (2) At 0.5 A g -1 Cyclic performance tests were conducted on the sodium-ion half-cells of Example 2 and Comparative Example 2 at various current densities. The results are as follows: Example 2 (CFAB conductive agent) had an initial discharge capacity of 782 mAh g. -1 After 100 cycles, the capacity retention rate was 86.5%, and after 50 cycles, the volume expansion rate was 28.2%; Comparative Example 2 (AB conductive agent) had an initial discharge capacity of 775 mAhg. -1 After 100 cycles, the capacity retention rate was only 48.3%, while after 50 cycles, the volume expansion rate was as high as 62.5%, indicating that CFAB can significantly suppress volume expansion.

[0062] (3) At 0.5 A g -1 Cyclic performance tests were conducted on the potassium-ion half-cells of Example 3 and Comparative Example 3 at different current densities. The initial reversible capacity of Example 3 was 383 mAh g⁻¹. -1 After 100 cycles, the capacity retention was 85.8%, and after 50 cycles, the volume expansion was 34.2%. The initial reversible capacity of Comparative Example 3 was 379 mAh g⁻¹. -1 After 100 cycles, the capacity retention rate was only 58.7%, and after 50 cycles, the volume expansion rate was 82.1%.

[0063] Suppressing volume expansion can prevent the SEI from repeatedly breaking down and reconstructing during the cycle.

[0064] Figure 4 Initial (0th cycle) and 50th cycle EIS tests show that: the interfacial charge transfer impedance (R) of Example 1 is... ct) and SEI impedance (R SEI Both were significantly lower than the control group 1, and R SEI The stability after cycling demonstrates that the fluorinated SEI structure is robust and the interface is stable, effectively resisting volume expansion.

[0065] Figure 5 SEM side views of the electrodes before (a) and after (c) of Comparative Example 1 and before (b) and after (d) of Comparative Example 1 confirm that the fluorinated SEI inhibits volume expansion.

[0066] also, Figure 6 The fine XPS spectra showed that in Example 1, fluorine transfer occurred after charge-discharge cycles to form LiF and Si-F bonds, which is beneficial to the stability of the silicon anode interface.

[0067] (4) The product of directly coating EnSi with PVDF gel was characterized by XRD, thermogravimetric analysis and XPS. The results are as follows: Figure 7 As shown, where Figure 7 'a' is an optical photograph. Figure 7 b represents the XRD pattern. Figure 7 c represents the thermogravimetric curve. Figure 7 d represents the XPS spectrum.

[0068] As can be seen from the optical photographs, when the mass ratio of PVDF to EnSi is 1:1, the resulting product (CFSi) has an optical photograph similar to that of EnSi, both being fine brown powders, but with a darker color. When the mass ratio of PVDF to EnSi is 10:3, the product has a completely different appearance, presenting as a black crystalline powder, similar to the product (CF) obtained by direct carbonization of PVDF. This indicates that excessive PVDF gel may have etched EnSi during the carbonization process.

[0069] The XRD patterns show that the diffraction peaks of the product with a PVDF / EnSi ratio of 1:1 (CFSi) are not significantly different from those of EnSi, indicating that the PVDF-derived carbon is an amorphous structure. In contrast, the product with a ratio of 10:3 only shows broad peaks of amorphous carbon and cannot detect diffraction peaks of crystalline silicon. This preliminarily proves that EnSi has been completely etched or transformed into an amorphous state.

[0070] Thermogravimetric analysis results show that the product with a mass ratio of 10:3 loses more than 99% of its weight in air at 600 °C, while the product with a mass ratio of 1:1 (CFSi) loses 29%, corresponding to the combustion of amorphous carbon. Pure EnSi, on the other hand, shows almost no mass loss before 600 °C, and its mass increase above 800 °C is due to the oxidation of silicon.

[0071] The XPS spectra show that the 10:3 ratio product mainly contains C, O, and F elements, with almost no detectable Si 2s and Si 2p signal peaks. In contrast, the 1:1 ratio product (CFSi) shows obvious Si 2s and Si 2p peaks, with a significantly enhanced O 1s peak intensity, indicating that oxygen mainly originates from the oxide layer on the silicon surface. For comparison, EnSi exhibits stronger Si 2s and Si 2p peaks, with the highest O 1s peak intensity; its weak C 1s peak is mainly due to unavoidable XPS sample preparation contamination.

[0072] In summary, when PVDF is directly coated with silicon active materials, the HF generated by high-temperature pyrolysis will severely etch and damage the silicon materials. Although low-content PVDF can achieve partial composite, there is still a potential risk of etching and the effect is limited. However, the present invention adopts the technical solution of "PVDF coated with carbon, fluorine doped carbon and then mixed with active materials", which completely avoids etching and achieves efficient fluorine transfer and SEI control at the same time.

[0073] Although the above embodiments have described the present invention and its implementation in detail, it should be noted that for those skilled in the art, any changes, modifications, substitutions, combinations, simplifications, etc., made to the corresponding conditions without departing from the technical principles of the present invention should be considered as equivalent substitutions, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a metal-ion battery anode containing fluorine-doped carbon material, characterized in that, Includes the following steps: (1) Preparation of fluorine-doped carbon materials: Fluorine doping is performed on any carbon material in the negative electrode to obtain fluorine-doped carbon materials; (2) Negative electrode assembly: The fluorine-doped carbon material is mixed with the negative electrode active material to prepare a negative electrode sheet and assemble it into a battery; (3) Fluorine transfer-induced SEI formation: During charge-discharge cycles, the fluorine-doped carbon material provides a fluorine source to the active material interface through fluorine transfer, inducing the formation of a stable SEI rich in metal fluorides and active material-fluorine bonds, thereby improving the stability of the negative electrode interface and suppressing volume expansion. The carbon material is selected from one or more of conductive carbon, graphite, graphene, and carbon nanotubes.

2. A method for preparing a fluorine-doped carbon material, used to prepare the fluorine-doped carbon material of claim 1, characterized in that, It is prepared by using fluoropolymers as fluorine sources and carbon materials as substrates, through gel coating-high temperature carbonization or in-situ polymerization-carbonization methods; In the fluorine-doped carbon material, fluorine is partially retained in the carbon layer in the form of CF bonds. The fluoropolymer is selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), or polychlorotrifluoroethylene (PCTFE).

3. The preparation method according to claim 2, characterized in that, The gel coating-high temperature carbonization method includes the following steps: (1) Preparation of gel solution: Dissolve the fluoropolymer in N-methylpyrrolidone, heat to 40~100℃ and stir to obtain gel solution; the mass ratio of the fluoropolymer to N-methylpyrrolidone is 1:100~1:20; (2) Gel coating: Carbon material is added to the gel solution, wherein the mass ratio of the carbon material to the fluoropolymer is 10:1 to 2:1, and the mixture is heated at 500 to 800 r·min. -1 Stir for 10-24 h, then vacuum dry to obtain the gel complex; (3) High-temperature carbonization: The gel composite is placed in an inert atmosphere and carbonized at 1~10℃·min. -1 Heat to 550~650℃ and hold for 1~3 h to obtain fluorine-doped carbon component; The inert atmosphere is argon gas with a purity of ≥99.99%.

4. A metal-ion secondary battery, characterized in that, It comprises a positive electrode, a negative electrode sheet prepared from the fluorine-doped carbon material as described in claim 1, a polypropylene separator, and a corresponding metal ion electrolyte.

5. The method for preparing a metal-ion secondary battery as described in claim 4, characterized in that, Includes the following steps: (1) Preparation of working electrode sheet: The negative electrode active material, fluorine-doped carbon material and binder are mixed and a dispersion medium is added and stirred to obtain a viscous slurry. The slurry is uniformly coated on the copper foil current collector, vacuum dried and sliced ​​to obtain the negative electrode sheet; (2) Battery assembly: Using the negative electrode as the working electrode and the metal sheet as the counter electrode, the working electrode, polypropylene separator, and metal counter electrode are sequentially installed into the CR2016 battery case, the corresponding metal ion electrolyte is injected and sealed to obtain a metal ion secondary battery.

6. The method for preparing a metal-ion secondary battery according to claim 5, characterized in that, The active material, fluorine-doped carbon material, and binder are mixed in a mass ratio of 60~75 : 15~20 : 10~20; The fluorine-doped carbon material accounts for 15-20 wt% of the total mass of the electrode material; The dispersion medium is NMP or deionized water, and the stirring rate after adding the dispersion medium is 500-800 r / min. -1 The stirring time is 10 to 24 hours. The binder is polyacrylic acid (PAA) with a molecular weight of 100,000 to 500,000, or sodium carboxymethyl cellulose (CMC) with a degree of substitution of 0.7 to 1.

2. The solid content of the viscous slurry is 40-60 wt%; The vacuum drying temperature is 80 ~ 120 ℃, and the drying time is 12 ~ 24 h; The counter electrode has a thickness of 0.5 to 2 mm and a diameter of 10 to 20 mm.

7. The method for preparing a metal-ion secondary battery according to claim 5, characterized in that, The specific surface area of ​​the fluorine-doped carbon material is 200~800 m². 2 g -1 The surface contains both semi-ionic CF bonds and covalent CF bonds.

8. The method for preparing a metal-ion secondary battery according to claim 5, characterized in that, The fluorine-doped carbon material can be one of the following: an electrode conductive agent, an additive, or a component of a composite electrode material.

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