Silicon-carbon composite negative electrode material, preparation method thereof, lithium ion battery negative electrode sheet containing silicon-carbon composite negative electrode material and lithium ion battery

Abstract

The invention provides a silicon-carbon composite negative electrode material, a preparation method of the silicon-carbon composite negative electrode material, a lithium ion battery negative electrode plate containing the silicon-carbon composite negative electrode material and a lithium ion battery, and relates to the technical field of lithium ion batteries. The silicon-carbon composite negative electrode material comprises a porous carbon skeleton, silicon distributed in internal pores of the porous carbon skeleton, and a functional interface layer covering the outer surface of the skeleton, wherein no free silicon elementary substance exists on the outer surface of the porous carbon skeleton, and the functional interface layer comprises a metal fluoride passivation layer formed by reacting metal elements doped in the carbon skeleton with a fluorine-containing etching agent; and the hybrid electrolyte coating layer is formed by reacting an oxygen-containing or nitrogen-containing functional group grafted on the surface of the carbon skeleton with a fluorine-containing etching agent. According to the technical scheme, the stable interface layer with passivation protection and ion conduction functions can be constructed in situ while high-activity silicon on the surface is removed, so that the first coulombic efficiency, the cycling stability and the rate capability of the battery are remarkably improved, side reactions are reduced, and the safety of the battery is improved.

Description

Silicon-carbon composite anode materials and their preparation methods include lithium-ion battery anode sheets and lithium-ion batteries. Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a silicon-carbon composite anode material and its preparation method, as well as lithium-ion battery anode sheets and lithium-ion batteries containing the same. Background Technology

[0002] With the rapid development of portable electronic devices, electric vehicles, and large-scale energy storage systems, the market is demanding higher energy densities from lithium-ion batteries. Silicon, due to its extremely high theoretical specific capacity (approximately 4200 mAh / g, more than ten times that of traditional graphite anodes) and suitable lithium intercalation potential, is considered the most promising anode material for next-generation high-energy-density lithium-ion batteries. However, silicon undergoes significant volume expansion (up to 300%) during charging and discharging, leading to electrode material pulverization, detachment from the current collector, and continuous rupture and regeneration of the solid electrolyte interphase (SEI) film. This process irreversibly consumes the electrolyte and lithium source, ultimately causing rapid capacity decay and the end of cycle life.

[0003] To overcome the aforementioned bottlenecks, silicon-carbon composite materials have emerged. Chemical vapor deposition (CVD) can uniformly introduce silicon, generated from the decomposition of silicon source gas, into the pores of a porous carbon support, making it an effective method for preparing high-performance silicon-carbon composite materials. This method aims to utilize the excellent electrical conductivity and mechanical buffering effect of carbon materials to suppress the volume expansion of silicon and maintain the integrity of the electrode structure.

[0004] However, vapor deposition technology has an inherent drawback that has not yet been completely resolved: during the deposition process, silicon not only deposits within the internal pores of carbon materials but also inevitably deposits unintended on the outer surface. This surface-deposited silicon is highly reactive and comes into direct, large-area contact with the electrolyte during the first charge-discharge cycle, forming a thick and unstable SEI film, leading to a significant decrease in the initial coulombic efficiency. More importantly, this external silicon is subjected to unrestrained volume changes during cycling, making it highly susceptible to pulverization and detachment from the conductive carbon framework, becoming electrochemically inert "dead silicon" and blocking ion transport channels, thus drastically deteriorating the cycle stability of the battery.

[0005] To address the above problems, existing technologies mainly improve the technology from the following two dimensions, but both have obvious limitations: (1) Precursor design and deposition process optimization: By adjusting the pore size of the carbon carrier and improving deposition parameters (such as temperature and pressure), the distribution of silicon is attempted to be controlled. However, this can only reduce surface silicon to a certain extent and cannot achieve fundamental elimination, and it often comes at the cost of sacrificing the total silicon loading and internal filling rate; (2) Surface coating modification: A carbon layer or other buffer layer is coated on the surface of silicon-carbon materials. This method is a "passive protection" method. The newly added interface may increase the resistance to lithium-ion transport, and the coating layer may crack due to the expansion of silicon during long-term cycling, and the initial side reactions caused by surface silicon cannot be eliminated.

[0006] Therefore, it is essential and urgent to research and develop a silicon-carbon composite anode material and its processing method. This method can effectively and selectively remove harmful surface silicon formed by vapor deposition, while perfectly preserving the internal functional silicon. In the process of removal, a protective layer or solid electrolyte interphase (SEI) coating layer with excellent interfacial properties is constructed in situ, thereby improving the material's first coulombic efficiency, cycle stability, rate performance and volume expansion characteristics.

[0007] In view of this, the present invention is hereby proposed. Summary of the Invention

[0008] The primary objective of this invention is to provide a silicon-carbon composite anode material that achieves a synergistic balance between high capacity and high stability, thereby significantly improving the battery's initial coulombic efficiency, cycle life, rate performance, and safety.

[0009] The second objective of this invention is to provide a method for preparing a silicon-carbon composite anode material.

[0010] A third objective of this invention is to provide a lithium-ion battery negative electrode sheet.

[0011] The fourth objective of this invention is to provide a lithium-ion battery.

[0012] To achieve the above-mentioned objectives of this invention, the following technical solution is adopted: This invention provides a silicon-carbon composite anode material, which includes: a porous carbon framework, silicon distributed in the pores of the porous carbon framework, and a functional interface layer covering the outer surface of the porous carbon framework, wherein: no free silicon exists on the outer surface of the porous carbon framework; the functional interface layer includes: a metal fluoride passivation layer generated in situ by reacting a metal element doped in the porous carbon framework with a fluorine-containing etchant; or, a solid electrolyte interface (SEI) precursor layer generated in situ by reacting oxygen- or nitrogen-containing functional groups grafted on the surface of the porous carbon framework with a fluorine-containing etchant.

[0013] Furthermore, the thickness of the functional interface layer is 1~5nm.

[0014] Furthermore, the fluorinated etchant is selected from one or more of the following combinations: (a) a fluorinated acid solution, the fluorinated acid solution comprising an aqueous solution of hydrofluoric acid, a mixed acid of hydrofluoric acid and nitric acid, or a buffered oxide etchant (BOE); wherein the volume percentage concentration of HF in the fluorinated acid solution is 0.1% to 2%; (b) an acidic mixture, the acidic mixture being aqua regia or a mixed acid composed of nitric acid and hydrofluoric acid; (c) a fluorine-based plasma etching gas, including at least one of CF4, SF6, NF3, and C2F6; (d) gaseous hydrogen fluoride, the gaseous hydrogen fluoride comprising anhydrous hydrogen fluoride gas or a mixture of hydrogen fluoride and an inert gas; and (e) a synergistic atmosphere of water vapor and hydrogen fluoride.

[0015] This invention provides a method for preparing the aforementioned silicon-carbon composite anode material, the method comprising: S1: providing a porous carbon framework, performing chemical vapor deposition on the porous carbon framework to deposit silicon in its outer surface and internal pores, obtaining a silicon deposition precursor; S2: modifying the surface of the silicon deposition precursor to give its surface active sites that can chemically bond with a fluorine-containing etchant or its reaction intermediates; the active sites include: metal atoms doped in the porous carbon framework, or oxygen- or nitrogen-containing functional groups grafted onto the surface of the porous carbon framework; S3: subjecting the product obtained in step S2 to fluorine-containing etching treatment, removing silicon from the outer surface of the porous carbon framework while the active sites react with the fluorine-containing etchant to generate a functional interface layer covering the outer surface of the porous carbon framework in situ, thereby obtaining the silicon-carbon composite anode material.

[0016] Furthermore, when the active site is a metal atom doped in the porous carbon framework, the metal atom is selected from at least one of Al, Zr, Ti, Mg, Ca, La, and Ce.

[0017] Furthermore, when the active site is an oxygen- or nitrogen-containing functional group grafted onto the surface of a porous carbon framework, the functional group is selected from at least one of hydroxyl (–OH), amino (–NH2), or imino (=NH).

[0018] Furthermore, in step S1, the chemical vapor deposition is performed using a silane / nitrogen mixed gas at a temperature of 400–600°C.

[0019] Furthermore, the step of post-processing the silicon-carbon composite anode material obtained in step S3 includes: repeatedly washing the silicon-carbon composite anode material with deionized water until neutral, and then vacuum drying it.

[0020] The present invention provides a lithium-ion battery negative electrode sheet, the active material of which includes the above-mentioned silicon-carbon composite negative electrode material.

[0021] The present invention provides a lithium-ion battery comprising the above-mentioned lithium-ion battery negative electrode sheet.

[0022] Compared with existing technologies, the beneficial effects of this invention are as follows: The silicon-carbon composite anode material provided by this invention overcomes the limitations of existing technologies that can only perform overall material processing or passive coating. It achieves precise identification and differentiated processing of beneficial silicon (internal silicon) and harmful silicon (surface silicon) in the silicon-carbon composite material, thereby selectively removing the surface silicon that leads to performance degradation while retaining the internal silicon that contributes to capacity. This solves the fundamental contradiction of the difficulty in achieving both high capacity and high stability from the material design perspective. Simultaneously, a high-performance functional interface layer is constructed in situ while removing surface silicon. Therefore, the silicon-carbon composite anode material of this application achieves a synergistic unity of high capacity (internal silicon retention) and high stability (surface silicon removal and in-situ construction of an interface layer). Verification has shown that it significantly improves the battery's initial coulombic efficiency, cycle life, rate performance, and safety.

[0023] The present invention provides a method for preparing silicon-carbon composite anode materials. The method involves simultaneously loading silicon onto the outer surface and internal pores of a porous carbon skeleton via chemical vapor deposition, followed by surface modification to introduce metal atoms or oxygen / nitrogen-containing functional groups as active sites. Finally, a fluorine-containing etchant is used to selectively remove free silicon from the outer surface while triggering chemical bonding between the active sites and etching reaction intermediates, thereby generating a functional interface layer covering the outer surface of the carbon skeleton in situ. This integrates silicon removal and film formation into a single controllable reaction step, avoiding problems such as weak interface bonding, complex processes, and structural damage caused by the separation of etching and coating in traditional processes.

[0024] The present invention provides a lithium-ion battery negative electrode sheet, which includes the silicon-carbon composite negative electrode material described in this application. Due to the performance of the silicon-carbon composite negative electrode material, the lithium-ion battery made from the silicon-carbon composite negative electrode material has comprehensive electrochemical advantages such as high initial coulombic efficiency, good cycle stability, excellent rate performance, and high safety. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 shows the XPS spectra of Example 1 and Comparative Example 1 provided in Experimental Example 1 of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] According to one aspect of the present invention, a silicon-carbon composite anode material is provided, the silicon-carbon composite anode material comprising: a porous carbon framework, silicon distributed in the pores inside the porous carbon framework, and a functional interface layer covering the outer surface of the porous carbon framework, wherein: no free silicon element exists on the outer surface of the porous carbon framework; the functional interface layer comprises: a metal fluoride passivation layer generated in situ by reacting a metal element doped in the porous carbon framework with a fluorine-containing etchant; or, a solid electrolyte interface precursor layer generated in situ by reacting oxygen- or nitrogen-containing functional groups grafted on the surface of the porous carbon framework with a fluorine-containing etchant.

[0029] The silicon-carbon composite anode material provided by this invention achieves precise identification and differentiation of beneficial silicon (internal silicon) and harmful silicon (surface silicon) in silicon-carbon composite materials, thereby selectively removing the surface silicon that leads to performance degradation, while retaining the internal silicon that contributes to capacity. This solves the fundamental contradiction of high capacity and high stability from the material design perspective. While removing the surface silicon, a high-performance functional interface layer is constructed in situ.

[0030] For systems doped with metal elements, the functional interface layer is a metal fluoride nanopassivation layer, which can protect the carbon skeleton from damage in real time during the etching process and form a pre-existing stable interface as a lithium-ion conductor. For systems grafted with oxygen- or nitrogen-containing functional groups, the functional interface layer is a hybrid electrolyte coating layer, which is generated by the reaction of etching byproducts and functional groups. It is firmly bonded and can pre-construct the substrate of the ideal SEI film before the start of battery cycling, actively guiding the formation of a highly efficient and stable SEI.

[0031] Therefore, the functional interface layer generated in situ in this application is something that cannot be achieved by conventional surface coating or electrolyte additives in the prior art. It has been verified that the silicon-carbon composite anode material of this application can achieve comprehensive electrochemical performance improvements such as a significant increase in initial coulombic efficiency, a significant enhancement in cycle stability, excellent rate performance, a reduction in side reactions, and improved safety.

[0032] In a preferred embodiment of the present invention, the thickness of the functional interface layer is 1 to 5 nm, for example, it can be 1 nm, 2 nm, 3 nm, 4 nm or 5 nm, or any value in the range of 1 to 5 nm (such as 1.3 nm, 2.7 nm, 3.9 nm, 4.5 nm, etc.).

[0033] In a preferred embodiment of the present invention, the fluorinated etchant is selected from one or more of the following: (a) a fluorinated acid solution, the fluorinated acid solution comprising an aqueous solution of hydrofluoric acid, a mixed acid of hydrofluoric acid and nitric acid, or a buffered oxide etchant (BOE); wherein the volume percentage concentration of HF in the fluorinated acid solution is 0.1% to 2%; (b) an acidic mixture, the acidic mixture being aqua regia or a mixed acid composed of nitric acid and hydrofluoric acid; (c) a fluorine-based plasma etching gas, including at least one of CF4, SF6, NF3, and C2F6; (d) gaseous hydrogen fluoride, the gaseous hydrogen fluoride comprising anhydrous hydrogen fluoride gas or a mixture of hydrogen fluoride and an inert gas; and (e) a synergistic atmosphere of water vapor and hydrogen fluoride.

[0034] According to one aspect of the present invention, a method for preparing the above-mentioned silicon-carbon composite anode material is provided, the method comprising: S1: providing a porous carbon framework, performing chemical vapor deposition on the porous carbon framework to deposit silicon in its outer surface and internal pores, thereby obtaining a silicon deposition precursor; S2: modifying the surface of the silicon deposition precursor to give its surface active sites capable of chemically bonding with a fluorinated etchant or its reaction intermediate; the active sites comprising: metal atoms doped in the porous carbon framework, or oxygen- or nitrogen-containing functional groups grafted onto the surface of the porous carbon framework; S3: subjecting the product obtained in step S2 to fluorinated etching treatment, thereby removing silicon from the outer surface of the porous carbon framework while the active sites react with the fluorinated etchant to generate a functional interface layer covering the outer surface of the porous carbon framework in situ, thereby obtaining the silicon-carbon composite anode material.

[0035] The present invention provides a method for preparing silicon-carbon composite anode materials. The method involves simultaneously loading silicon onto the outer surface and internal pores of a porous carbon skeleton via chemical vapor deposition, followed by surface modification to introduce metal atoms or oxygen / nitrogen-containing functional groups as active sites. Finally, a fluorine-containing etchant is used to selectively remove free silicon from the outer surface while triggering chemical bonding between the active sites and etching reaction intermediates, thereby generating a functional interface layer covering the outer surface of the carbon skeleton in situ. This integrates silicon removal and film formation into a single controllable reaction step, avoiding problems such as weak interface bonding, complex processes, and structural damage caused by the separation of etching and coating in traditional processes.

[0036] In a preferred embodiment of the present invention, when the active site is a metal atom doped in a porous carbon framework, the metal atom is selected from at least one of Al, Zr, Ti, Mg, Ca, La, and Ce.

[0037] In a preferred embodiment of the present invention, when the active site is an oxygen- or nitrogen-containing functional group grafted onto the surface of a porous carbon framework, the functional group is selected from at least one of hydroxyl (–OH), amino (–NH2), or imino (=NH).

[0038] Preferably, the preparation method of the silicon-carbon composite anode material (the functional interface layer is a fluoride-based inorganic layer) includes: (a1) providing a porous carbon framework, wherein the porous carbon framework is doped with at least one element selected from Al, Zr, Ti, Mg, Ca, La, Ce; (b1) performing chemical vapor deposition of silicon on the porous carbon framework to obtain a silicon-deposited porous carbon framework, wherein the silicon is distributed on the outer surface and internal pores of the porous carbon framework to obtain a silicon-carbon composite precursor A; (c1) selectively etching the silicon-carbon composite precursor A to remove the silicon on the outer surface of the porous carbon framework while retaining the silicon in its internal pores, and generating a functional interface layer covering the outer surface of the porous carbon framework in situ during the etching process.

[0039] Preferably, the preparation method of the silicon-carbon composite anode material (the functional interface layer is a fluorine-doped silicon-based hybrid layer) includes: (a2) providing a porous carbon framework, performing chemical vapor deposition of silicon on the porous carbon framework to obtain a silicon-deposited porous carbon framework, wherein the silicon is distributed on the outer surface and internal pores of the porous carbon framework; (b2) grafting surface-activated functional groups onto the silicon-deposited porous carbon framework, grafting functional groups containing amino, imino, or hydroxyl groups to obtain a silicon-carbon composite precursor B; (c2) selectively etching the silicon-carbon composite precursor B to remove the silicon on the outer surface of the porous carbon framework while retaining the silicon in its internal pores, and generating a functional interface layer covering the outer surface of the porous carbon framework in situ during the etching process.

[0040] Preferably, the preparation method of the silicon-carbon composite anode material (the functional interface layer is formed by the co-formation of fluoride and fluorine-doped silicon-based hybrid) includes: (a3) ​​providing a porous carbon framework, wherein the porous carbon framework is doped with at least one element selected from Al, Zr, Ti, Mg, Ca, La, and Ce; (b3) performing chemical vapor deposition of silicon on the porous carbon framework to obtain a silicon-deposited porous carbon framework, wherein the silicon is distributed on the outer surface and internal pores of the porous carbon framework to obtain a silicon-carbon composite precursor C; (c3) grafting surface-activated functional groups onto the silicon-carbon composite precursor C, wherein the grafted functional groups contain amino, imino, or hydroxyl groups. (d3) Selective etching is performed on the silicon-carbon composite precursor D to remove silicon from the outer surface of the porous carbon skeleton while retaining silicon in its internal pores, and a functional interface layer covering the outer surface of the porous carbon skeleton is generated in situ during the etching process; In a preferred embodiment of the present invention, the temperature of chemical vapor deposition in step S1 is 400~600℃, for example, it can be 400℃, 450℃, 500℃, 550℃ or 600℃, or any value in the range of 400~600℃ (such as 425℃, 480℃, 530℃, 575℃, etc.).

[0041] In a preferred embodiment of the present invention, the step of post-processing the silicon-carbon composite anode material obtained in step S3 includes: repeatedly washing the silicon-carbon composite anode material with deionized water until neutral, and then vacuum drying it.

[0042] According to one aspect of the present invention, a lithium-ion battery negative electrode sheet is provided, wherein the active material comprises the aforementioned silicon-carbon composite negative electrode material.

[0043] The present invention provides a lithium-ion battery negative electrode sheet, which includes the silicon-carbon composite negative electrode material described in this application. Due to the performance of the silicon-carbon composite negative electrode material, the lithium-ion battery made from the silicon-carbon composite negative electrode material has comprehensive electrochemical advantages such as high initial coulombic efficiency, good cycle stability, excellent rate performance, and high safety.

[0044] According to one aspect of the present invention, a lithium-ion battery comprises the aforementioned lithium-ion battery negative electrode.

[0045] The technical solution of the present invention will be further described below with reference to the embodiments.

[0046] Example 1 Al-doped carbon support and HF dynamic passivation treatment: A method for preparing a silicon-carbon composite anode material, including the following steps: (1) Providing a porous carbon skeleton: The porous carbon skeleton has a BET specific surface area of ​​1637 m² / g, an average pore size of 1.8 nm, and a total pore volume of 0.66 cm³ / g.

[0047] (2) Al doping modification: The porous carbon framework was immersed in 0.1M Al(NO3)3 aqueous solution, stirred for 12h, centrifuged and dried, and then annealed at 800℃ for 2h in argon to obtain a porous carbon framework with an Al doping amount of about 0.8 wt%.

[0048] (3) Chemical vapor deposition (CVD) for silicon loading: The Al-doped porous carbon framework obtained in step (2) was placed in a CVD reactor, and a silane / nitrogen mixed gas (SiH4:N2=1:9) was introduced. Silicon deposition was carried out at a temperature of 500℃ to obtain a silicon-carbon composite material with a silicon content of 42.00%; (4) Fluorine etching and in-situ interface construction: The silicon-carbon composite material was slowly added to a 1.0 wt% hydrofluoric acid aqueous solution, and the mixture was kept at a constant temperature of 25℃ and continuously magnetically stirred at a speed of 250 rpm for 60 minutes. The mixture was centrifuged for 5 minutes using a high-speed centrifuge, and the supernatant was removed. Subsequently, the mixture was repeatedly centrifuged and washed with deionized water until the supernatant was neutral. The mixture was then vacuum dried to obtain a silicon-carbon composite anode material coated with ALF3.

[0049] Example 2 Mg-doped carbon support and HF dynamic passivation treatment A method for preparing a silicon-carbon composite negative electrode material, including the following steps: (1) Providing a porous carbon skeleton: Same as in Example 1; (2) Al doping modification: The porous carbon skeleton is immersed in 0.1M Mg(NO3)2 aqueous solution, stirred for 12h, centrifuged and dried, and then annealed at 800℃ for 2h in argon to obtain a porous carbon skeleton with Mg doping of about 0.8 wt%.

[0050] (3) Chemical vapor deposition (CVD) loaded silicon: The Mg-doped porous carbon framework powder obtained in step (2) was placed in a CVD reactor, and a silane / nitrogen mixed gas (SiH4:N2=1:9) was introduced. Silicon deposition was carried out at a temperature of 500℃ to obtain a silicon-carbon composite material with a silicon content of 42.00%; (4) Fluorine etching and in-situ interface construction: The silicon-carbon composite material was added to an aqueous solution containing NH4F+HF, where HF was 1.0 wt%. The mixture was kept at a constant temperature of 25℃ and continuously magnetically stirred at a speed of 250 rpm for 60 minutes. The mixture was centrifuged for 5 minutes using a high-speed centrifuge and the supernatant was removed. Subsequently, the mixture was repeatedly centrifuged and washed with deionized water until the supernatant was neutral. The mixture was then vacuum dried to obtain a silicon-carbon composite anode material coated with MgF2.

[0051] Example 3: A method for preparing a silicon-carbon composite anode material by La-doped carbon support and HF dynamic passivation treatment, including the following steps: (1) Providing a porous carbon skeleton: Same as in Example 1; (2) Al doping modification: The porous carbon skeleton is immersed in 0.1M La(NO3)2 aqueous solution, stirred for 12h, centrifuged and dried, and then annealed at 800℃ for 2h in argon to obtain a porous carbon skeleton with a Mg doping amount of about 0.8 wt%.

[0052] (3) Chemical vapor deposition (CVD) loaded silicon: The La-doped porous carbon framework powder obtained in step (2) was placed in a CVD reactor, and a silane / nitrogen mixed gas (SiH4:N2=1:9) was introduced. Silicon was deposited at a temperature of 500℃ to obtain a silicon-carbon composite material with a silicon content of 42.00%; (4) Fluorine etching and in-situ interface construction: The silicon-carbon composite material was laid flat in a quartz boat and sent to the isothermal zone of a horizontal tube furnace. After sealing the tube furnace, the mechanical pump was started to draw the pressure inside the furnace to 0.5 Pa. Then, NF3 gas diluted with high-purity argon (NF3 volume concentration of 10%) was introduced at a flow rate of 50 sccm. The gas flow rate was maintained, and the furnace temperature was raised to 200℃ at a rate of 10℃ / min and held at this temperature for 10 minutes. Stop heating, continue to purge the furnace tube with pure argon gas (100 sccm) until room temperature, remove the sample, and obtain silicon-carbon composite anode material with LaF3 coating on the surface.

[0053] Example 4 - A method for preparing a silicon-carbon composite anode material by grafting OH functional groups onto a carbon support and synthesizing SEI coating layer in situ with HF, comprising the following steps: (1) Providing a porous carbon skeleton: same as in Example 1; (2) Chemical vapor deposition (CVD) of silicon: The porous carbon skeleton powder is placed in a CVD reactor, and a silane / nitrogen mixed gas (SiH4:N2=1:9) is introduced, and silicon deposition is carried out at a temperature of 500℃ to obtain a silicon-carbon composite precursor.

[0054] (3) Grafting of surface hydroxyl (–OH) functional groups: The silicon-carbon composite precursor is placed in the reaction chamber, and after vacuuming, gaseous ethylene glycol vapor is introduced to obtain a silicon-carbon composite precursor with -OH grafted on the surface.

[0055] (4) Fluorine-containing etching and in-situ SEI coating construction: The silicon-carbon composite precursor was slowly added to a 1.0 wt% hydrofluoric acid aqueous solution and magnetically stirred continuously at 250 rpm for 60 minutes at a constant temperature of 25°C. The mixture was centrifuged for 5 minutes using a high-speed centrifuge, and the supernatant was removed. Subsequently, the mixture was repeatedly washed with deionized water by centrifugation until the supernatant was neutral. The mixture was then vacuum dried to obtain a silicon-carbon composite anode material with a silicon-oxygen-fluorine inorganic SEI coating layer with high ionic conductivity on its surface.

[0056] Example 5 - A method for preparing a silicon-carbon composite anode material by grafting NH2 functional groups onto a carbon support and synthesizing SEI coating layer in situ with HF, comprising the following steps: (1) Providing a porous carbon skeleton: same as in Example 1; (2) Chemical vapor deposition (CVD) of silicon: The porous carbon skeleton powder is placed in a CVD reactor, and a silane / nitrogen mixed gas (SiH4:N2=1:9) is introduced, and silicon deposition is carried out at a temperature of 500℃ to obtain a silicon-carbon composite precursor.

[0057] (3) Grafting of surface hydroxyl (–OH) functional groups: The silicon-carbon composite precursor is placed in the reaction chamber, and after evacuation, gaseous 3-aminopropyltriethoxysilane (KH550) vapor is introduced to obtain a silicon-carbon composite precursor with -NH2 grafted on the surface.

[0058] (4) Fluorine-containing etching and in-situ SEI coating construction: The surface-grafted -NH2 silicon-carbon composite precursor was laid flat in a quartz boat and placed in the isothermal zone of a horizontal tube furnace. After sealing the tube furnace, the mechanical pump was started to evacuate the furnace pressure to 0.5 Pa. Then, NF3 gas diluted with high-purity argon (NF3 volume concentration of 10%) was introduced at a flow rate of 50 sccm. The gas flow rate was maintained, and the furnace temperature was increased to 200℃ at a rate of 10℃ / min and held at this temperature for 10 minutes. Heating was stopped, and pure argon gas (100 sccm) was continued to purge the furnace tube to room temperature. The sample was then removed, yielding a silicon-carbon composite anode material with a silicon-nitrogen-fluorine inorganic SEI coating with high ionic conductivity on the surface.

[0059] Example 6 - A method for preparing a silicon-carbon composite anode material by in-situ synthesis of SEI coating layer with NH2 functional group grafted carbon support and HF, comprising the following steps: (1) Providing a porous carbon framework: same as in Example 1; (2) Al doping modification: the porous carbon framework is immersed in 0.1M Al(NO3)3 aqueous solution, stirred for 12h, centrifuged and dried, and then annealed at 800℃ for 2h in argon. Al-doped porous carbon support is obtained.

[0060] (3) Chemical vapor deposition (CVD) of silicon: Porous carbon framework powder is placed in a CVD reactor and a silane / nitrogen mixed gas (SiH4:N2=1:9) is introduced. Silicon is deposited at a temperature of 500℃ to obtain a silicon-carbon composite precursor with a silicon content of 42.00%; (4) Grafting of surface amino (–NH2) functional groups: The silicon-carbon composite precursor is placed in a reaction chamber, and after evacuation, gaseous 3-aminopropyltriethoxysilane (KH550) vapor is introduced to obtain a silicon-carbon composite precursor with surface grafted -NH2.

[0061] (5) Fluorine-based plasma etching and in-situ construction of bifunctional interface layer: The surface-grafted -NH2 silicon-carbon composite precursor was laid flat in a quartz boat and sent into the isothermal zone of a horizontal tube furnace. After sealing the tube furnace, the mechanical pump was started to evacuate the furnace pressure to 0.5 Pa. Then, NF3 gas diluted with high-purity argon (NF3 volume concentration of 10%) was introduced at a flow rate of 50 sccm. The gas flow rate was maintained, and the furnace temperature was increased to 200℃ at a rate of 10℃ / min and held at this temperature for 10 minutes. Heating was stopped, and pure argon gas (100 sccm) was continued to purge the furnace tube to room temperature. The sample was taken out to obtain silicon-carbon composite anode material with AlF3 and silicon-nitrogen-fluorine inorganic SEI bilayer coating.

[0062] The difference between Comparative Example 1 and Example 1 is that the silicon-carbon composite material obtained in steps (1) to (3) of Example 1 is used as the silicon-carbon composite negative electrode material, that is, after silicon deposition, the steps of fluorine etching and in-situ interface construction in step (4) are not performed.

[0063] Comparative Example 2: A method for preparing a silicon-carbon composite anode material without doping modification, comprising the following steps: (1) Providing a porous carbon framework: Same as Example 1; (2) Chemical vapor deposition (CVD) loading of silicon: The porous carbon framework is placed in a CVD reactor, and a silane / nitrogen mixed gas (SiH4:N2=1:9) is introduced. Silicon deposition is carried out at a temperature of 500℃ to obtain a silicon-carbon composite material, wherein the silicon content is 42.00%; (3) Fluorine etching and in-situ interface construction: The silicon-carbon composite material is slowly added to a 1.0 wt% hydrofluoric acid aqueous solution, and the mixture is kept at a constant temperature of 25℃ and continuously magnetically stirred at a speed of 250 rpm for 60 minutes. The mixture is centrifuged for 5 minutes using a high-speed centrifuge, and the supernatant is removed. Subsequently, the mixture is repeatedly centrifuged and washed with deionized water until the supernatant is neutral. The mixture is then vacuum dried to obtain the product.

[0064] Comparative Example 3: Except for step (4), in which a high-concentration HF (10wt%) solution was used to treat the silicon-carbon composite anode material for 60 minutes, the other steps were the same as in Example 1.

[0065] Experimental Example 1: To verify the technical effectiveness of the silicon-carbon composite anode material of the present invention, the samples prepared in Examples 1-6 and Comparative Examples 1-3 were uniformly tested using the following standardized method. All tests were performed under the same environment, equipment, and parameters.

[0066] (I) The specific testing methods are as follows: 1. Resistivity test: The surface resistivity of the material is tested by the four-probe method to characterize the removal effect of surface silicon content; 2. Electrode, half-cell preparation and electrochemical performance test: The negative electrode materials prepared in the above examples and comparative examples are used as negative electrode active materials to prepare negative electrode sheets respectively. The negative electrode sheets are prepared into CR2032 coin cells by conventional methods, and the electrical performance of the cells is tested. The specific testing methods are as follows: (1) Half-cell assembly: CR2032 coin cells are assembled in a glove box, with lithium metal sheet as counter electrode, polypropylene microporous membrane as separator, and LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC=1:1), wherein the concentration of LiPF6 is 1mol / L. The cells are charged and discharged using the LAND battery testing system.

[0067] (2) Initial efficiency test: After the CR2032 coin cell was left to stand for 6 hours, it was discharged at 0.1C to 0.005V and the capacity was recorded as Q1; then it was discharged at a constant voltage of 0.005V until the current was cut off at 0.01C and the total capacity was recorded as Q2; after standing for 5 minutes, it was charged at a constant current of 0.1C to 1.5V; the ratio of the initial delithiation capacity to the initial lithium insertion capacity is the initial coulombic efficiency of the battery.

[0068] (3) Capacity retention rate test: After standing for 5 minutes, repeat the above charge and discharge steps twice; then discharge to 0.005V at 0.25C; after standing for 5 minutes, charge to 1.5V at a constant current of 0.25C, and cycle 50 times. The capacity retention rate is calculated by dividing the specific capacity of the 50th cycle by the charging capacity of the 1st cycle by 100%.

[0069] (4) Electrode expansion rate: After the CR2032 type button cell was left to stand for 6 hours, it was discharged to 0.005 V at 0.05 C, and then discharged to 0.005 V at 0.01 C. Then the button cell was disassembled in the glove box, the electrode was cleaned with DEC and the thickness of the electrode was measured. The expansion rate was calculated as: (thickness of electrode in the first fully charged state - thickness of fresh electrode) / thickness of fresh electrode × 100%.

[0070] (5) Electrochemical Impedance (ESI) Test: Electrochemical impedance spectroscopy is performed using an electrochemical workstation. The test frequency is set to 0.01-1000kHz, and the amplitude is set to 5mV. The impedance value of the electrode is tested after 50 cycles.

[0071] (6) Rate test: constant current charge and discharge. Cycle stably for 3 cycles at 0.2C, and record the average discharge capacity as the "100% baseline". Cycle for 3 cycles at 2C. Finally, return to 0.2C and record the discharge capacity.

[0072] 2C rate capacity retention rate: (high rate capacity / 0.2C reference capacity) × 100%.

[0073] (ii) The specific test results are shown in Table 1.

[0074] Table 1:

[0075] As shown in the table above, the silicon-carbon composite anode material and its preparation method provided by the present invention achieve precise structural control and synergistic performance improvement by pre-placing metal doping sites in the porous carbon framework or grafting oxygen- or nitrogen-containing functional groups onto the surface, and simultaneously triggering in-situ interface construction during fluorine etching.

[0076] The specific technical effects are as follows: (1) Significant effect of structural selectivity control: The surface resistivity of the materials obtained in Examples 1–6 is ≤21 Ω·m (Example 1: 10.3 ± 0.4 Ω·m) as tested by the four probe method, which meets the structural requirement of "no free silicon element on the outer surface of the porous carbon skeleton"; Figure 1 is the XPS spectrum of Example 1 and Comparative Example 1 provided in this experimental example.

[0077] As shown in Figure 1, the sample of Example 1 exhibits a essentially flat baseline within the range of 99.0–104.0 eV, with no detected silicon signal, indicating the absence of silicon on the outer surface and within a depth of 10 nm of the porous carbon framework. This aligns with the structural characteristic of "no free silicon on the outer surface" in this invention. In contrast, the sample of Comparative Example 1 shows significant elemental silicon (Si) at 99.4 eV. 0 Characteristic peaks appear at 103.2 eV, indicating the presence of silicon oxide (SiO₂). x The characteristic peaks indicate that a large amount of free silicon is exposed on the material surface, and there is also some naturally oxidized silicon oxide, which contrasts sharply with Example 1. ICP-OES analysis shows that its silicon content remains stable at 41.5~41.9 wt%.

[0078] (2) Significant improvement in initial coulombic efficiency: In CR2032 coin cells, the initial coulombic efficiency of Examples 1–6 was 85.1–86.7%, which was 6.8–8.4 percentage points higher than that of untreated Comparative Example 1 (78.3%) and 4.9–6.5 percentage points higher than that of Comparative Example 2 (80.2%) without active sites. This indicates that the effective removal of highly active silicon on the surface and the functional interface layer generated in situ together reduced the irreversible lithium loss during the first week of SEI film formation.

[0079] (3) Significantly enhanced cycling stability: After 50 cycles at a rate of 0.25C, the capacity retention of Examples 1–6 was 92.9–95.6%, which was significantly better than that of Comparative Example 1 (82.4%) and Comparative Example 2 (87.3%). The charge transfer impedance (Rct) was measured to be 31–47 Ω, which was much lower than that of Comparative Example 1 (103 Ω), confirming that the in-situ generated metal fluoride passivation layer or silicon-nitrogen / oxygen-fluorine hybrid electrolyte coating layer has excellent interfacial stability and ion transport kinetics performance.

[0080] (4) Excellent rate performance and volume stability: At a high rate of 2C, the capacity retention of Examples 1–6 reached 61–70%, which is more than 50% higher than that of Comparative Example 1 (40%); the electrode expansion rate was controlled at 69–77%, which is significantly lower than that of Comparative Example 1 (273%), indicating that the unobstructed ion transport channels were preserved and the effect of silicon volume expansion on the overall electrode structure was effectively suppressed.

[0081] (5) Improved process robustness and safety: All examples were completed at room temperature, with a mild HF concentration (1.0 wt%) or under controlled plasma conditions, and no material pulverization, swelling or violent decomposition of electrolyte was observed. Comparative Example 3 was treated with 10.0 wt% HF, which caused the silicon content to drop sharply to 35 wt%, which in turn confirms the key role of the concentration range of fluorine-containing etchant (0.1–2 wt%) and the in-situ passivation mechanism defined in this invention in ensuring process controllability and structural safety.

[0082] In summary, starting from the intrinsic structure of the material, this invention systematically solves the core bottlenecks of high-capacity silicon-based anodes, such as low initial efficiency, poor cycling performance, large expansion, and weak rate capability, through the synergistic mechanism of "selective removal of surface silicon" and "in-situ construction of functional interface layer", without sacrificing the capacity contribution of internal silicon. The technical effect is objective, verifiable, and significantly improved, possessing outstanding substantive features and significant progress.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon-carbon composite anode material, characterized in that, The silicon-carbon composite anode material comprises: a porous carbon framework, silicon distributed in the pores of the porous carbon framework, and a functional interface layer covering the outer surface of the porous carbon framework, wherein: no free silicon exists on the outer surface of the porous carbon framework; the functional interface layer comprises: a metal fluoride passivation layer generated in situ by reacting a metal element doped in the porous carbon framework with a fluorine-containing etchant; or, a solid electrolyte interface precursor layer generated in situ by reacting oxygen- or nitrogen-containing functional groups grafted on the surface of the porous carbon framework with a fluorine-containing etchant.

2. The silicon-carbon composite anode material according to claim 1, characterized in that, The thickness of the functional interface layer is 1~5nm.

3. The silicon-carbon composite anode material according to claim 1, characterized in that, The fluorinated etchant is selected from one or more of the following: (a) a fluorinated acid solution, which includes an aqueous solution of hydrofluoric acid, a mixed acid of hydrofluoric acid and nitric acid, or a buffered oxide etchant; wherein the volume percentage concentration of HF in the fluorinated acid solution is 0.1% to 2%; (b) an acidic mixture, which is aqua regia or a mixed acid composed of nitric acid and hydrofluoric acid; (c) a fluorine-based plasma etching gas, including at least one of CF4, SF6, NF3, and C2F6; (d) gaseous hydrogen fluoride, which includes anhydrous hydrogen fluoride gas or a mixture of hydrogen fluoride and an inert gas; and (e) a synergistic atmosphere of water vapor and hydrogen fluoride.

4. A method for preparing a silicon-carbon composite anode material according to any one of claims 1 to 3, characterized in that, The preparation method includes: S1: providing a porous carbon framework, performing chemical vapor deposition on the porous carbon framework to deposit silicon in its outer surface and internal pores, obtaining a silicon deposition precursor; S2: modifying the surface of the silicon deposition precursor to give its surface active sites that can chemically bond with a fluorine-containing etchant or its reaction intermediates; the active sites include: metal atoms doped in the porous carbon framework, or oxygen- or nitrogen-containing functional groups grafted onto the surface of the porous carbon framework; S3: performing fluorine-containing etching treatment on the product obtained in step S2, removing silicon from the outer surface of the porous carbon framework while the active sites react with the fluorine-containing etchant to generate a functional interface layer covering the outer surface of the porous carbon framework in situ, obtaining a silicon-carbon composite anode material.

5. The method for preparing the silicon-carbon composite anode material according to claim 4, characterized in that, When the active site is a metal atom doped in a porous carbon framework, the metal atom is selected from at least one of Al, Zr, Ti, Mg, Ca, La, and Ce.

6. The method for preparing the silicon-carbon composite anode material according to claim 4, characterized in that, When the active site is an oxygen- or nitrogen-containing functional group grafted onto the surface of a porous carbon framework, the functional group is selected from at least one of hydroxyl, amino, or imino groups.

7. The method for preparing the silicon-carbon composite anode material according to claim 4, characterized in that, In step S1, chemical vapor deposition is performed using a silane / nitrogen mixed gas at a temperature of 400–600°C.

8. The method for preparing the silicon-carbon composite anode material according to claim 4, characterized in that, The step of post-processing the silicon-carbon composite anode material obtained in step S3 includes: repeatedly washing the silicon-carbon composite anode material with deionized water until neutral, and then vacuum drying it.

9. A lithium-ion battery negative electrode sheet, characterized in that, Its active material comprises the silicon-carbon composite anode material as described in any one of claims 1 to 3.

10. A lithium-ion battery, characterized in that, It comprises the lithium-ion battery negative electrode sheet as described in claim 9.

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