Silicon-carbon composite material with double-layer skeleton structure generated in situ, and preparation method and application thereof

Abstract

This invention relates to a silicon-carbon composite material with an in-situ generated double-layer framework structure, its preparation method, and its application. The silicon-carbon composite material includes: a porous carbon framework, silicon nanomaterials, a solid electrolyte framework, and a carbon coating layer. The silicon nanomaterials are dispersedly distributed on and between the surfaces of the porous carbon framework and the solid electrolyte framework. The solid electrolyte framework is attached to the surface and pore walls of the porous carbon framework. The silicon-carbon composite material is obtained by first depositing a solid electrolyte precursor sequentially on the surface and pore walls of a surface-activated porous carbon framework using atomic layer deposition technology, followed by silicon deposition and carbon coating treatment, and then calcination treatment. This allows the atoms of the precursor to migrate, diffuse, and undergo phase transformation to form a continuous phase layered solid electrolyte framework in situ. Applying the silicon-carbon composite material with the in-situ generated double-layer framework structure provided by this invention to lithium batteries can reduce the expansion rate of the electrode and improve the cycle performance of the lithium battery.

Description

Technical Field

[0001] This invention relates to the field of lithium battery materials technology, and in particular to a silicon-carbon composite material with an in-situ generated double-layer framework structure, its preparation method, and its application. Background Technology

[0002] Silicon-based anode materials, as a key pathway to improve the energy density of lithium-ion batteries, have long been constrained by structural collapse caused by drastic volume expansion during cycling, stripping of active materials, and continuous growth of the solid electrolyte interface (SEI), resulting in rapid capacity decay.

[0003] Traditional solutions, such as nano-silicon-carbon composites and porous buffer designs, still face three major technical bottlenecks: mismatch between ion / electron conduction networks, uncontrollable interfacial side reactions, and insufficient mechanical stability over long cycles.

[0004] Existing methods, such as mixing solid electrolytes with porous carbon and nano-silicon and then coating them with carbon, can improve the ionic and electronic conductivity of materials to some extent. However, the problem of poor interfacial stability still exists, which affects the stability of the material structure and thus the cycling performance.

[0005] Furthermore, depositing a solid electrolyte on the surface and pore walls of porous carbon before silicon deposition and carbon coating is a method that involves pre-depositing a solid electrolyte on the porous carbon surface and then undergoing a heating process for silicon deposition and carbon coating. This process causes repeated temperature rises and falls, leading to thermal stress and microcracks at the Si / solid electrolyte interface. After pre-crystallization, the surface of the solid electrolyte becomes passivated, hindering subsequent silicon / carbon interface bonding, resulting in poor interface stability. It also has limited ability to suppress silicon volume expansion, thus affecting cycle life and causing high energy consumption. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a silicon-carbon composite material with an in-situ generated double-layer skeleton structure, its preparation method, and its application.

[0007] This invention employs atomic layer deposition (ALD) technology to pre-deposit a solid electrolyte precursor on the surface and pore walls of a porous carbon framework. After silicon deposition and carbon coating, high-temperature calcination causes atomic migration and diffusion, and crystal phase transformation, resulting in the in-situ formation of a high-ionic-conducting solid electrolyte. This electrolyte forms covalent bonds with silicon in situ, replacing physical contact and reducing silicon volume expansion. Simultaneously, the carbon layer coating and dual-framework combination achieve both rigidity and flexibility, enabling dual electron / ion conduction. This silicon-carbon composite material effectively blocks the source of silicon expansion failure mechanisms, providing a negative electrode solution for next-generation lithium batteries that combines high energy density, long lifespan, and high safety.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a silicon-carbon composite material with an in-situ generated bilayer framework structure, the silicon-carbon composite material comprising: a porous carbon framework, silicon nanomaterials, a solid electrolyte framework, and an outermost carbon coating layer;

[0009] The silicon nanomaterials are dispersed on the surfaces of the porous carbon framework and the solid electrolyte framework, as well as between the porous carbon framework and the solid electrolyte framework; the solid electrolyte framework is attached to the surface and pore wall surface of the porous carbon framework.

[0010] The silicon-carbon composite material is obtained by first depositing the precursor of the solid electrolyte sequentially on the surface and pore walls of a porous carbon skeleton after surface activation treatment using atomic layer deposition technology, followed by silicon deposition, carbon coating treatment, and calcination treatment, so that the atoms of the precursor migrate, diffuse, and transform in situ to form a solid electrolyte skeleton.

[0011] The solid electrolyte framework is a continuous phase layered structure; the solid electrolyte in the solid electrolyte framework includes: oxide solid electrolyte and / or fluorine oxide solid electrolyte.

[0012] Preferably, the porous carbon framework comprises one or more of porous resin carbon, porous biomass carbon, porous pitch coke, or porous petroleum coke; the average particle size Dv50 of the porous carbon framework is 4 μm to 100 μm, the porosity is 50% to 85%, and the pore size is 1 nm to 50 nm; the specific surface area of ​​the porous carbon framework is 1000 m². 2 / g~3000m 2 / g, pore volume 0.5cm 3 / g~3cm 3 / g;

[0013] The silicon content in the silicon-carbon composite material is 5 wt% to 80 wt%.

[0014] Preferably, the thickness of the solid electrolyte framework is between 1 nm and 25 nm;

[0015] The oxide solid electrolyte specifically includes: garnet-type oxide solid electrolyte Li7Al3B12O 12 Perovskite oxide solid electrolyte Li 3x A2 2 / 3-x B2O3, NASICON-type oxide solid electrolyte Li 1+y A3 y B3 2-yOne or more of (PO4)3, wherein 0.01≤x≤0.5, 0.01≤y≤0.5; A1 is one or more of La, Ca, Sr, Ba, K, and B1 is one or more of Zr, Ta, Nb, Hf; A2 is one or more of La, Al, Mg, Fe, Ta, and B2 is one or more of Ti, Nb, Sr, Pr; A3 is one or more of Al, Y, Ga, Cr, In, Fe, Se, La, and B3 is one or more of Ti, Ge, Ta, Zr, Sn, Fe, V, Hf.

[0016] The fluoride oxide solid electrolyte specifically includes: Li 1.5 Al 0.5 Ge 1.5 (PO4) 2.9 F 0.1 Li 6.5 La3Zr 1.5 Ta 0.5 O 11.5 F 0.5 Li₂VO₂F, Li 1.2 Mn 0.8 Nb 0.2 O 1.6 F 0.4 Li m La n M1 a M2 b M3 c One or more of O6F; wherein, 1 < m + 3n < 5, 0 < m ≤ 2, 1 / 3 < n < 5 / 3; 0 ≤ a ≤ 2, 0 ≤ b ≤ 2, 0 ≤ c ≤ 2, a + b + c = 2, M1 is one or more of Zr, Ti, Hf, Si, Ge, Sn, M2 is one or more of Nb, Sb, Bi, V, Ta, and M3 is one or more of W, Cr, Mo, Mn.

[0017] In a second aspect, the present invention provides a method for preparing the in-situ coated silicon-carbon composite material described in the first aspect above, the method comprising:

[0018] The preparation of activated porous carbon framework includes: surface activation treatment of porous carbon framework to make the surface of porous carbon framework contain -OH bonds, thereby obtaining activated porous carbon framework;

[0019] A composite porous carbon framework is obtained by depositing a solid electrolyte precursor on the surface and pore walls of an activated porous carbon framework using atomic layer deposition (ALD) technology. The process includes: placing the activated porous carbon framework in a fluidized bed powder ALD apparatus, heating it to 150°C–350°C, sequentially introducing a gas containing one or more elements of a solid electrolyte precursor, and after each precursor is introduced, purging with an inert gas and intermittently introducing an oxidizing gas source to react with the precursor, causing different elements in the precursor to deposit on the surface of the porous carbon framework. The above deposition process is repeated 100–300 times to obtain a composite porous carbon framework.

[0020] The composite porous carbon framework was placed in a reaction apparatus for silicon deposition to obtain an intermediate material.

[0021] The intermediate material is carbon-coated to obtain a silicon-carbon composite material precursor.

[0022] The silicon-carbon composite material precursor is calcined to allow different elements deposited on the surface of the porous carbon skeleton to undergo atomic diffusion and crystal phase transformation, and then form a solid electrolyte skeleton with a continuous phase layer structure in situ, thus obtaining a silicon-carbon composite material with an in-situ double-layer skeleton structure.

[0023] The solid electrolyte in the solid electrolyte framework includes: oxide solid electrolyte and / or fluorine oxide solid electrolyte.

[0024] Preferably, the surface activation treatment is an acid activation treatment or an alkaline activation treatment;

[0025] The acid activation treatment includes: immersing a porous carbon framework in an acidic solution, stirring at 60℃ to 120℃ for 1 hour to 10 hours, washing with deionized water until neutral after the reaction, and drying at a low temperature of 60℃ to 80℃ to obtain an activated porous carbon framework with -OH bonds on its surface; the mass ratio of the porous carbon framework to the acidic solution is 10% to 50%; the acidic solution includes a nitric acid solution with a concentration of 20wt% to 70wt% and / or hydrogen peroxide;

[0026] The alkaline activation treatment includes: placing a porous carbon framework and potassium hydroxide powder in a ball mill at a ratio of 1-5:5-9, and ball milling at 500-1000 rpm for 2-8 hours under an inert atmosphere. Zirconia balls are used as the milling media. After ball milling, residual potassium ions are removed by washing with dilute hydrochloric acid with a molar concentration of 0.1 mol / L-1 mol / L. After drying at 60℃-100℃, an activated porous carbon framework with -OH bonds on its surface is obtained.

[0027] Preferably, the volumetric flow rate of the gas precursor of the solid electrolyte is 50 sccm to 500 sccm;

[0028] The oxide solid electrolyte includes: garnet-type oxide solid electrolyte Li7Al3B12O 12 Perovskite oxide solid electrolyte Li 3x A2 2 / 3-x B2O3, NAS ICON type oxide solid electrolyte Li 1+y A3 y B3 2-y One or more of (PO4)3, wherein 0.01≤x≤0.5, 0.01≤y≤0.5; A1 is one or more of La, Ca, Sr, Ba, K, and B1 is one or more of Zr, Ta, Nb, Hf; A2 is one or more of La, Al, Mg, Fe, Ta, and B2 is one or more of Ti, Nb, Sr, Pr; A3 is one or more of Al, Y, Ga, Cr, In, Fe, Se, La, and B3 is one or more of Ti, Ge, Ta, Zr, Sn, Fe, V, Hf.

[0029] The fluoride solid electrolyte includes: Li 1.5 Al 0.5 Ge 1.5 (PO4) 2.9 F 0.1 Li 6.5 La3Zr 1.5 Ta 0.5 O 11.5 F 0.5 Li₂VO₂F, Li 1.2 Mn 0.8 Nb 0.2 O 1.6 F 0.4 Li m La n M1 a M2 b M3 c One or more of O6F; wherein, 1 < m + 3n < 5, 0 < m ≤ 2, 1 / 3 < n < 5 / 3; 0 ≤ a ≤ 2, 0 ≤ b ≤ 2, 0 ≤ c ≤ 2, a + b + c = 2, M1 is one or more of Zr, Ti, Hf, Si, Ge, Sn, M2 is one or more of Nb, Sb, Bi, V, Ta, and M3 is one or more of W, Cr, Mo, Mn;

[0030] The oxidation gas source includes O3 and / or H2O; the volumetric flow rate of the oxidation gas source is 50 sccm to 500 sccm.

[0031] The inert gas includes one or more of nitrogen, helium, or argon; the volumetric flow rate of the inert gas is 100 sccm to 1000 sccm.

[0032] Preferably, the silicon deposition specifically includes: placing the composite porous carbon framework in a reaction apparatus, heating it to 350°C to 550°C under a protective atmosphere, introducing silicon source gas into the reaction apparatus through the protective gas, maintaining the temperature for 2 to 6 hours, allowing the silicon elements decomposed by the silicon source gas to be deposited in the pores and on the surface of the composite porous carbon framework and grown into silicon nanomaterials, stopping the introduction of the silicon source gas, and obtaining the intermediate material;

[0033] The protective gas in the protective atmosphere includes nitrogen and / or argon; the flow rate of the protective gas is 1 L / min to 50 L / min.

[0034] The silicon source gas includes one or more gases selected from: metallic silicon vapor, silane, propane, dichlorosilane, trichlorosilane, and tetrachlorosilane; the flow ratio of the protective gas to the silicon source gas is 5:1 to 1:5.

[0035] The reaction equipment includes any one of a rotary kiln, a vapor deposition furnace, or a fluidized bed.

[0036] Preferably, the carbon coating treatment is gas phase carbon coating, specifically including: under a protective atmosphere, adjusting the temperature of the reaction equipment to 350℃~450℃, introducing carbon source gas into the reaction equipment, and keeping it at that temperature for 2 hours to 8 hours, so that the carbon elements decomposed by the carbon source gas are deposited on the surface of the intermediate material to form a carbon coating layer, thereby obtaining a silicon-carbon composite material precursor.

[0037] The protective atmosphere comprises nitrogen and / or argon; the flow rate of the protective gas is 1 L / min to 50 L / min; the carbon source gas comprises at least one of methane, acetylene, ethylene, and propylene; and the flow rate ratio of the protective gas to the carbon source gas is 20:1 to 1:1.

[0038] Preferably, when the solid electrolyte in the solid electrolyte framework is an oxide-based solid electrolyte, the calcination treatment specifically includes: heating the reaction equipment to 700℃~850℃ at a heating rate of 2℃ / min~10℃ / min under a protective atmosphere, and holding at that temperature for 2 hours~8 hours, so that different elements on the surface of the porous carbon framework undergo atomic diffusion and crystal phase transformation to form a continuous phase layered solid electrolyte framework in situ, thereby obtaining a silicon-carbon composite material with an in-situ generated double-layer framework structure; the protective gas in the protective atmosphere includes: nitrogen and / or argon; the flow rate of the protective gas is 1L / min~50L / min;

[0039] When the solid electrolyte in the solid electrolyte framework includes a fluorine oxide solid electrolyte, the calcination treatment specifically includes: switching the gas in the reaction equipment to a mixture of protective gas and fluorine source gas, heating to 350℃~700℃ at a heating rate of 2℃ / min~10℃ / min, holding at this temperature for 2 hours~8 hours for medium-temperature fluorination, and then heating to 700℃~850℃ at a heating rate of 2℃ / min~10℃ / min for high-temperature calcination treatment, so that different elements on the surface of the porous carbon framework and fluorine elements obtained by decomposition of the fluorine source gas undergo atomic diffusion and crystal phase transformation to form a solid electrolyte framework with a continuous phase layer structure in situ, thereby obtaining a silicon-carbon composite material with an in-situ generated double-layer framework structure;

[0040] The fluorine source gas includes one or more of the following: hydrogen fluoride (HF), sulfur tetrafluoride (SF4), nitrogen trifluoride (NF3), xenon difluoride (XeF2), and sulfur hexafluoride (SF6); the flow ratio of the fluorine source gas to the protective gas is 1:20 to 1:10.

[0041] Thirdly, the present invention provides a lithium battery comprising the silicon-carbon composite material with an in-situ generated double-layer skeleton structure as described in the first aspect above.

[0042] This invention provides an in-situ generated silicon-carbon composite material with a double-layer framework structure, its preparation method, and its application, which have the following technical effects:

[0043] This invention provides a method for preparing a silicon-carbon composite material with an in-situ bilayer framework structure. First, a porous carbon framework is activated to obtain an activated porous carbon framework with -OH bonds on its surface. Then, a solid electrolyte precursor is deposited on the surface and pore walls of the activated porous carbon framework using atomic layer deposition technology. Next, silicon deposition and carbon coating are performed sequentially. Finally, after high-temperature calcination, the different elements deposited on the surface of the activated porous carbon framework undergo atomic diffusion and crystal phase transformation to form a solid electrolyte framework with a continuous phase layer structure in situ, thus obtaining a silicon-carbon composite material with an in-situ bilayer framework structure.

[0044] The silicon-carbon composite material with an in-situ generated bilayer framework structure prepared by the preparation method provided by the present invention includes a porous carbon framework and an in-situ formed continuous phase layered solid electrolyte framework. The rigid solid electrolyte framework and the flexible porous carbon framework work together with the carbon coating layer to constrain the silicon nanomaterials. Furthermore, the rigid solid electrolyte framework transforms the silicon expansion stress from point-to-point concentration to area dispersion, which can better suppress the volume expansion of silicon. In addition, the layered solid electrolyte framework attached to the surface of the porous carbon framework can solve the problem of swelling or collapse of traditional porous carbon in electrolyte, thereby improving the stability of the material.

[0045] During the preparation process, different elements deposited on the surface of the activated porous carbon framework undergo atomic diffusion and crystal phase transformation to form a continuous layered solid electrolyte framework in situ. Compared with traditional blending and coating methods, the solid electrolyte framework forms covalent bonds with the porous carbon framework and silicon nanoparticles, which can effectively reduce interfacial impedance. In addition, the solid electrolyte has good ionic conductivity, and the porous carbon framework has good electrical conductivity, giving the silicon-carbon composite material of this invention high ionic and electronic conductivity and low sheet resistance. Furthermore, the calcination process can further shrink and compact the outermost carbon coating layer, increasing the density of the coating layer and helping to reduce side reactions.

[0046] Applying the silicon-carbon composite material with an in-situ generated double-layer skeleton structure provided by this invention to lithium batteries can reduce the expansion rate of the electrode and improve the cycle performance of lithium batteries. This solves the problems of short cycle life (caused by silicon volume expansion), poor interface stability (caused by continuous consumption of active lithium), and kinetic lag (low ionic conductivity and electronic conductivity) of existing silicon-based anode materials in lithium batteries. Attached Figure Description

[0047] Figure 1 A flowchart illustrating the preparation method of an in-situ generated bilayer skeleton structure silicon-carbon composite material provided in an embodiment of the present invention. Detailed Implementation

[0048] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0050] This invention provides an in-situ generated silicon-carbon composite material with a double-layer framework structure. The silicon-carbon composite material includes: a porous carbon framework, silicon nanomaterials, a solid electrolyte framework, and an outermost carbon coating layer.

[0051] Among them, silicon nanomaterials are dispersed on the surface of porous carbon framework and solid electrolyte framework, as well as between porous carbon framework and solid electrolyte framework; solid electrolyte framework is attached to the surface and pore wall surface of porous carbon framework.

[0052] Silicon-carbon composite materials are obtained by first depositing a solid electrolyte precursor onto the surface and pore walls of a porous carbon framework that has undergone surface activation treatment using atomic layer deposition technology, followed by silicon deposition, carbon coating treatment, and calcination treatment, so that the atoms of the precursor can migrate, diffuse, and transform in situ to form a solid electrolyte framework.

[0053] Porous carbon frameworks include one or more of the following: porous resin carbon, porous biomass carbon, porous pitch coke, or porous petroleum coke.

[0054] The average particle size Dv50 of the porous carbon framework is 4μm to 100μm, and can be any value within this range, such as: 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, 22μm, 24μm, 26μm, 28μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0055] The porosity of the porous carbon framework is 50% to 85%, and can be any value within this range, such as 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0056] The pore size of the porous carbon framework is 1nm to 50nm, which can be any value within this range, such as: 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] The specific surface area of ​​the porous carbon framework is 1000 m². 2 / g~3000m 2 / g can be any value within this range, for example: 1000m 2 / g、1200m 2 / g, 1400m 2 / g, 1600m 2 / g、1800m 2 / g、2000m 2 / g、2200m 2 / g、2400m2 / g、2600m 2 / g、2800m 2 / g、3000m 2 / g, etc., but not limited to the listed values; other unlisted values ​​within this range also apply.

[0058] The porous carbon framework has a pore volume of 0.5 cm³. 3 / g~3cm 3 / g can be any value within this range, for example: 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.2cm 3 / g, 1.4cm 3 / g, 1.6cm 3 / g, 1.8cm 3 / g, 2.0cm 3 / g, 2.2cm 3 / g, 2.4cm 3 / g, 2.6cm 3 / g, 2.8cm 3 / g, 3.0cm 3 / g, etc., but not limited to the listed values; other unlisted values ​​within this range also apply.

[0059] The solid electrolyte framework is a continuous layered structure; the thickness of the solid electrolyte framework is between 1 nm and 25 nm, and can be any value within this range, such as: 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0060] Solid electrolytes in the solid electrolyte framework include: oxide solid electrolytes and / or fluorine oxide solid electrolytes.

[0061] Specifically, oxide solid electrolytes include: garnet-type oxide solid electrolyte Li7Al3B12O 12 Perovskite oxide solid electrolyte Li 3x A2 2 / 3-xB2O3, NASICON-type oxide solid electrolyte Li 1+y A3 y B3 2-y One or more of (PO4)3, wherein 0.01≤x≤0.5 and 0.01≤y≤0.5; A1 is one or more of La, Ca, Sr, Ba, and K; B1 is one or more of Zr, Ta, Nb, and Hf; A2 is one or more of La, Al, Mg, Fe, and Ta; B2 is one or more of Ti, Nb, Sr, and Pr; A3 is one or more of Al, Y, Ga, Cr, In, Fe, Se, and La; and B3 is one or more of Ti, Ge, Ta, Zr, Sn, Fe, V, and Hf.

[0062] Fluoride oxide solid electrolytes specifically include: Li 1.5 Al 0.5 Ge 1.5 (PO4) 2.9 F 0.1 Li 6.5 La3Zr 1.5 Ta 0.5 O 11.5 F 0.5 Li₂VO₂F, Li 1.2 Mn 0.8 Nb 0.2 O 1.6 F 0.4 Li m La n M1 a M2 b M3 c One or more of O6F; wherein, 1 < m + 3n < 5, 0 < m ≤ 2, 1 / 3 < n < 5 / 3; 0 ≤ a ≤ 2, 0 ≤ b ≤ 2, 0 ≤ c ≤ 2, a + b + c = 2, M1 is one or more of Zr, Ti, Hf, Si, Ge, Sn, M2 is one or more of Nb, Sb, Bi, V, Ta, and M3 is one or more of W, Cr, Mo, Mn.

[0063] The silicon content in silicon-carbon composite materials is 5wt% to 80wt%, and can be any value within this range, such as: 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, 70wt%, 80wt%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0064] In this invention, particle size Dv50 refers to the volumetric median particle size of the material, representing the particle size corresponding to 50% of the material's volume distribution, a meaning known in the art. The particle size Dv50 of the porous carbon skeleton provided in this embodiment can be determined using instruments and conventional methods known in the art. Specifically, 1g of material sample is weighed and added to 20ml of deionized water, followed by 50ul of a 1% (w / w) aqueous solution of ethyl phenyl polyethylene glycol dispersant. The mixture is sonicated for 5 minutes, and then the dispersion is added to a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd. for particle size determination. The Dv50 value is then read.

[0065] In this invention, the porosity, specific surface area, pore size, and pore volume of the porous carbon framework are tested using a gas adsorption method, employing a specific surface area analyzer (model: Micromeritics ASAP2460). The sample is first sieved through a 200-mesh sieve; then, degassing is performed, typically by placing the sample in a vacuum and heating it at 200°C for several hours (up to 6 hours). Next, nitrogen gas is introduced under a constant low temperature (-196°C), and the nitrogen pressure is controlled to allow the sample to adsorb and desorb at different pressures, obtaining isothermal adsorption-desorption curves. Based on these isothermal adsorption-desorption curves, the specific surface area is calculated using BET fitting, and the pore size and pore volume are calculated using a t-plot model.

[0066] In this invention, the silicon content in the silicon-carbon composite material can be determined by a combination of thermogravimetric analysis (TGA) and inductively coupled plasma mass spectrometry (ICP-MS), and can be further verified by X-ray fluorescence spectrometry (XRF).

[0067] This invention provides a method for preparing the above-mentioned in-situ coated silicon-carbon composite material, such as... Figure 1 As shown, the preparation method specifically includes the following steps.

[0068] Step 110, preparing an activated porous carbon framework, includes: performing surface activation treatment on the porous carbon framework to make the surface of the porous carbon framework contain -OH bonds, thereby obtaining an activated porous carbon framework.

[0069] The porous carbon framework includes one or more of the following: porous resin carbon, porous biomass carbon, porous pitch coke, or porous petroleum coke; the average particle size Dv50 of the porous carbon framework is 4μm to 100μm, the porosity is 50% to 85%, and the pore size is 1nm to 50nm; the specific surface area of ​​the porous carbon framework is 1000m². 2 / g~3000m 2 / g, pore volume 0.5cm 3 / g~3cm 3 / g.

[0070] The surface activation treatment is either acid activation treatment or alkaline activation treatment.

[0071] Specifically, the acid activation treatment includes: immersing the porous carbon framework in an acidic solution, stirring at 60℃~120℃ for 1 hour to 10 hours, washing with deionized water until neutral after the reaction, and drying at low temperature at 60℃~80℃ to obtain an activated porous carbon framework with -OH bonds on its surface; the mass ratio of the porous carbon framework to the acidic solution is 10%~50%; the acidic solution includes a nitric acid solution with a concentration of 20wt%-70wt% and / or hydrogen peroxide.

[0072] The alkaline activation treatment includes: placing a porous carbon framework and potassium hydroxide powder in a ball mill at a ratio of 1-5:5-9, and ball milling at 500-1000 rpm for 2-8 hours under an inert atmosphere. Zirconia balls are used as the milling media. After ball milling, residual potassium ions are removed by washing with dilute hydrochloric acid with a molar concentration of 0.1 mol / L-1 mol / L. After drying at 60℃-100℃, an activated porous carbon framework with -OH bonds on its surface is obtained.

[0073] Step 120: A solid electrolyte precursor is deposited on the surface and pore walls of the activated porous carbon framework using atomic layer deposition technology to obtain a composite porous carbon framework.

[0074] Specifically, the process involves placing an activated porous carbon framework in a fluidized bed powder atomic layer deposition apparatus, heating it to 150°C–350°C, and sequentially introducing a gas containing one or more elements of a solid electrolyte. After each precursor is introduced, the mixture is purged with an inert gas after deposition, and an oxidizing gas source is introduced intermittently to allow the oxidizing gas source to react with the precursor, causing different elements in the precursor to deposit on the surface of the porous carbon framework. This deposition process is repeated 100–300 times to obtain a composite porous carbon framework.

[0075] The fluidized bed powder atomic layer deposition equipment used in this step combines atomic layer deposition (ALD) technology with a laboratory-grade fluidized bed reactor. With its uniquely designed fluidized bed reactor, it introduces atomic layer deposition technology into the powder materials industry, enabling atomic-level ultra-uniform deposition on the surfaces of micron and nanomaterials.

[0076] Solid electrolytes include: oxide solid electrolytes and / or fluorine oxide solid electrolytes.

[0077] Oxide solid electrolytes include: garnet-type oxide solid electrolyte Li7Al3B12O 12 Perovskite oxide solid electrolyte Li3x A2 2 / 3-x B2O3, NASICON-type oxide solid electrolyte Li 1+y A3 y B3 2-y One or more of (PO4)3, wherein 0.01≤x≤0.5 and 0.01≤y≤0.5; A1 is one or more of La, Ca, Sr, Ba, and K; B1 is one or more of Zr, Ta, Nb, and Hf; A2 is one or more of La, Al, Mg, Fe, and Ta; B2 is one or more of Ti, Nb, Sr, and Pr; A3 is one or more of Al, Y, Ga, Cr, In, Fe, Se, and La; and B3 is one or more of Ti, Ge, Ta, Zr, Sn, Fe, V, and Hf.

[0078] Fluoride oxide solid electrolytes include: Li 1.5 Al 0.5 Ge 1.5 (PO4) 2.9 F 0.1 Li 6.5 La3Zr 1.5 Ta 0.5 O 11.5 F 0.5 Li₂VO₂F, Li 1.2 Mn 0.8 Nb 0.2 O 1.6 F 0.4 Li m La n M1 a M2 b M3 c One or more of O6F; wherein, 1 < m + 3n < 5, 0 < m ≤ 2, 1 / 3 < n < 5 / 3; 0 ≤ a ≤ 2, 0 ≤ b ≤ 2, 0 ≤ c ≤ 2, a + b + c = 2, M1 is one or more of Zr, Ti, Hf, Si, Ge, Sn, M2 is one or more of Nb, Sb, Bi, V, Ta, and M3 is one or more of W, Cr, Mo, Mn.

[0079] The volumetric flow rate of the gas precursor for the solid electrolyte is 50 sccm to 500 sccm.

[0080] The oxidizing gas source includes O3 and / or H2O; the volumetric flow rate of the oxidizing gas source is 50 sccm to 500 sccm.

[0081] The inert gas includes one or more of nitrogen, helium, or argon; the volumetric flow rate of the inert gas is 100 sccm to 1000 sccm.

[0082] Step 130: Place the composite porous carbon framework in a reaction apparatus for silicon deposition to obtain an intermediate material.

[0083] Specifically, silicon deposition includes: placing a composite porous carbon framework in a reaction apparatus, heating it to 350℃~550℃ under a protective atmosphere, introducing silicon source gas into the reaction apparatus through a protective gas, holding it at this temperature for 2 hours to 6 hours, allowing the silicon elements decomposed from the silicon source gas to deposit in the pores and on the surface of the composite porous carbon framework and grow into silicon nanomaterials, stopping the introduction of silicon source gas, and obtaining an intermediate material;

[0084] The protective gases for the protective atmosphere include nitrogen and / or argon; the flow rate of the protective gases is 1 L / min to 50 L / min.

[0085] The silicon source gas includes one or more of the following: metallic silicon vapor, silane, propane, dichlorosilane, trichlorosilane, and tetrachlorosilane; the flow ratio of the protective gas to the silicon source gas is 5:1 to 1:5.

[0086] The reaction equipment includes any one of the following: a rotary kiln, a vapor deposition furnace, or a fluidized bed;

[0087] The silicon nanomaterials deposited in this step include, but are not limited to: silicon nanocrystals, island-shaped silicon nanomaterials composed of closely packed silicon nanocrystals, or linear silicon nanomaterials composed of closely packed silicon nanocrystals.

[0088] The average particle size of the nano-silicon grains is between 0.5nm and 3nm, and can be any value within this range, such as: 0.5nm, 0.6nm, 0.7nm, 0.8nm, 0.9nm, 1nm, 1.1nm, 1.2nm, 1.3nm, 1.4nm, 1.5nm, 1.6nm, 1.7nm, 1.8nm, 1.9nm, 2nm, 2.1nm, 2.2nm, 2.3nm, 2.4nm, 2.5nm, 2.6nm, 2.7nm, 2.8nm, 2.9nm, 3.0nm, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0089] The average size of island-shaped or wire-shaped silicon nanomaterials is between 1 nm and 100 nm, and can be any value within this range, such as 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0090] Step 140: Carbon coating is applied to the intermediate material to obtain a silicon-carbon composite material precursor.

[0091] The carbon coating process is gas phase carbon coating, which specifically includes: under a protective atmosphere, adjusting the temperature of the reaction equipment to 350℃~450℃, introducing carbon source gas into the reaction equipment, and keeping it at that temperature for 2 hours to 8 hours, so that the carbon elements decomposed by the carbon source gas are deposited on the surface of the intermediate material to form a carbon coating layer, thereby obtaining a silicon-carbon composite material precursor.

[0092] The protective atmosphere includes nitrogen and / or argon; the flow rate of the protective gas is 1 L / min to 50 L / min; the carbon source gas includes at least one of methane, acetylene, ethylene, and propylene; and the flow rate ratio of the protective gas to the carbon source gas is 20:1 to 1:1.

[0093] Step 150: The silicon-carbon composite material precursor is calcined to allow different elements deposited on the surface of the porous carbon skeleton to undergo atomic diffusion and crystal phase transformation, thereby forming a solid electrolyte skeleton with a continuous phase layer structure in situ, resulting in a silicon-carbon composite material with an in-situ double-layer skeleton structure.

[0094] When the solid electrolyte in the solid electrolyte framework is an oxide-based solid electrolyte, the calcination treatment specifically includes: heating the reaction equipment to 700℃~850℃ at a heating rate of 2℃ / min~10℃ / min under a protective atmosphere, and holding it at that temperature for 2 hours~8 hours, so that different elements on the surface of the porous carbon framework undergo atomic diffusion and crystal phase transformation to form a continuous phase layered solid electrolyte framework in situ, thereby obtaining a silicon-carbon composite material with an in-situ generated double-layer framework structure; the protective gas in the protective atmosphere includes nitrogen and / or argon; the flow rate of the protective gas is 1L / min~50L / min.

[0095] When the solid electrolyte in the solid electrolyte framework includes a fluorine oxide solid electrolyte, the calcination treatment specifically includes: switching the gas in the reaction equipment to a mixture of protective gas and fluorine source gas, heating to 350℃~700℃ at a heating rate of 2℃ / min~10℃ / min, holding at this temperature for 2 hours~8 hours for medium-temperature fluorination, and then heating to 700℃~850℃ at a heating rate of 2℃ / min~10℃ / min for high-temperature calcination treatment. This allows different elements on the surface of the porous carbon framework and fluorine elements obtained from the decomposition of the fluorine source gas to undergo atomic diffusion and crystal phase transformation, forming a continuous phase layered solid electrolyte framework in situ, thus obtaining a silicon-carbon composite material with an in-situ generated double-layer framework structure.

[0096] The fluorine source gas includes one or more of the following: hydrogen fluoride (HF), sulfur tetrafluoride (SF4), nitrogen trifluoride (NF3), xenon difluoride (XeF2), and sulfur hexafluoride (SF6); the flow ratio of the fluorine source gas to the protective gas is 1:20 to 1:10.

[0097] In this invention, the solid electrolyte framework deposited on the surface and pore walls of the porous carbon framework by ALD is preferably a fluorine oxide solid electrolyte Li. m La n M1 a M2 b M3 c O6F, where 1 < m + 3n < 5, 0 < m ≤ 2, 1 / 3 < n < 5 / 3; 0 ≤ a ≤ 2, 0 ≤ b ≤ 2, 0 ≤ c ≤ 2, a + b + c = 2, M1 is one or more of Zr, Ti, Hf, Si, Ge, Sn, M2 is one or more of Nb, Sb, Bi, V, Ta, and M3 is one or more of W, Cr, Mo, Mn.

[0098] This is because the fluorine oxide solid electrolyte Li m La n M1 a M2 b M3 c O6F solid electrolytes possess high density, high purity, high volumetric energy density, low internal resistance, and excellent ion conductivity. Furthermore, Li... m La n M1 a M2 b M3 c O6F solid electrolyte possesses a rigid framework structure with tunable elemental composition. The introduction of diverse coordination environments through multivalent cation doping facilitates the formation of open channels conducive to lithium-ion transport. Simultaneously, fluorine doping further enhances the material's polarity and interfacial wettability, improving interfacial contact with the electrolyte and electrodes and reducing interfacial impedance. This invention forms a continuous layered Li-type structure in situ on the surface and pore walls of a porous carbon framework. m La n M1 a M2 b M3 c The O6F solid electrolyte framework gives the resulting silicon-carbon composite material excellent ionic conductivity and interfacial stability.

[0099] Li m La n M1 a M2 b M3 cPreferred precursors for O6F solid electrolytes include tris(2,2,6,6-tetramethyl-3,5-heptanedione)lanthanum (La(thd)3), niobium pentaethoxy (Nb(OEt)5), lithium bis(trimethylsilyl)amino (LiN(SiMe3)2), and hydrofluoric acid gas (HF).

[0100] When the solid electrolyte in the formed solid electrolyte framework is the aforementioned Li m La n M1 a M2 b M3 c In O6F, the formation process and principle are as follows:

[0101] (1) Solid electrolyte Li was deposited on the surface and pore walls of the activated porous carbon framework, respectively. m La n M1 a M2 b M3 c O6F precursors were deposited intermittently, followed by oxidative origin deposition and purging with a protective gas to form CO-La-O, CO-Nb2O5, and CO-Li on the surface and pore walls of the porous carbon framework.

[0102] (2) During silicon deposition, CO-La-O, CO-Nb2O5, and CO-Li, which are highly adhered to the porous carbon framework, undergo atomic diffusion and phase transformation at high temperatures, causing the diffused La, Li, M1, M2, M3, and O elements to react and form a tetragonal Li phase. m La n M1 a M2 b M3 c O6, and the active silicon atoms from the silicon source decomposition react with the tetragonal Li. m La n M1 a M2 b M3 c The La-O and Nb-O groups on the O6 surface react to form covalent bonds.

[0103] (3) During the calcination process, the low-temperature deposited carbon layer (carbon coating layer) in the previous carbon coating process can indeed retain nanopores (2nm~5nm), which are much larger than the molecular size of the fluorine source gas (about 0.25nm). Moreover, the porosity of the low-temperature deposited carbon layer is as high as 35% or more. Therefore, fluorine atoms decomposed after the fluorine source material undergoes medium-temperature fluorination can diffuse through the carbon layer pores and freely diffuse to the Li on the surface of the porous carbon framework. m La n M1 a M2 b M3 c In the tetragonal phase structure of O6, Li at high temperaturesm La n M1 a M2 b M3 c Oxygen vacancy activity is maximized in the tetragonal phase of O6, and fluoride ions fill Li. m La n M1 a M2 b M3 c Oxygen vacancies in the O6 lattice promote a cubic phase transformation. Pre-formed Si-O-La, Si-O-M1, Si-O-M2, or Si-O-M3 bonds remain stable during fluorination. Under continuous high-temperature calcination, the nanopores in the carbon coating collapse, forming a dense layer, and the pores shrink, creating a "soft armor." Simultaneously, the high-temperature treatment drives the Si-Li... m La n M1 a M2 b M3 c O6F-C three-phase crosslinking: Si-O-La / M1 / M2 / M3…OC forms a covalent network, which improves the "silicon volume expansion", "ion conduction" and "cycle life" of silicon-carbon composite materials.

[0104] The silicon-carbon composite material with an in-situ generated double-layer framework structure prepared by the above-described preparation method provided in this invention can be used as a negative electrode active material to prepare a negative electrode sheet, which can be used to assemble lithium batteries. Applying the silicon-carbon composite material with an in-situ generated double-layer framework structure provided by this invention to lithium batteries can reduce the expansion rate of the electrode sheet, improve the cycle performance of the lithium battery, and solve the problems of short cycle life (caused by the volume expansion of silicon), poor interface stability (caused by the continuous consumption of active lithium), and kinetic lag (low ionic and electronic conductivity) of existing silicon-based negative electrode materials in lithium batteries.

[0105] To better understand the technical solution provided by the present invention, the following uses several specific examples to illustrate the preparation process and characteristics of the silicon-carbon composite material with in-situ generated double-layer skeleton structure according to the present invention.

[0106] Example 1

[0107] This invention provides a method for preparing a silicon-carbon composite material with an in-situ generated double-layer framework structure, which specifically includes the following steps.

[0108] (1) Preparation of activated porous carbon framework, comprising: placing 1 kg of porous carbon framework and 1 kg of potassium hydroxide powder into a planetary ball mill, and ball milling at 600 rpm for 6 hours under an argon atmosphere. Zirconia balls were used as the milling media. After milling, residual potassium ions were removed by washing with 0.5 mol / L dilute hydrochloric acid, and then dried at 80°C to obtain an activated porous carbon framework with -OH bonds on its surface. The porous carbon matrix is ​​porous biomass carbon with a specific surface area of ​​1800 m². 2 / g, pore size 40nm, pore volume 2.5cm³ 3 / g.

[0109] (2) The activated porous carbon framework is placed in a fluidized bed powder atomic layer deposition equipment and deposited once by atomic layer deposition technology. The deposition temperature is 200℃. The specific details of the first deposition process are as follows.

[0110] S1: A La(thd)3 gas with a flow rate of 100 sccm is introduced with a pulse duration of 1 s. The mixture is then purged with nitrogen gas at a flow rate of 200 sccm for 30 s. Next, an oxidizing gas source O3 with a flow rate of 100 sccm is introduced with a pulse duration of 0.5 s. This process is followed by purging with nitrogen gas at a flow rate of 200 sccm for 20 s, resulting in the formation of CO-La-O on the surface of the porous carbon matrix. The chemical equation for this process is:

[0111] C-OH+La(thd)3→CO-La(thd)2+Hthd↑;

[0112] CO-La(thd)2+O3→CO-La-O+4CO2↑+2CH3COCH3↑;

[0113] S2: Nb(OEt)₅ gas with a flow rate of 100 sccm is introduced with a pulse duration of 1 s, followed by purging with nitrogen gas at a flow rate of 200 sccm for 30 s. Then, H₂O gas with a flow rate of 100 sccm is introduced with a pulse duration of 0.5 s, followed by purging with nitrogen gas at a flow rate of 200 sccm for 20 s. CO-Nb₂O₅ is formed on the surface of the porous carbon matrix. The reaction process in this step is as follows:

[0114] C-OH+Nb(OEt)5→CO-Nb(OEt)4+EtOH↑;

[0115] CO-Nb(OEt)4+H2O→CO-Nb(OH)4→CO-Nb2O5;

[0116] S3: A LiN(SiMe3)2 gas with a volumetric flow rate of 100 sccm is introduced with a pulse duration of 2 s, followed by purging with nitrogen gas at a volumetric flow rate of 200 sccm for 40 s, forming CO-Li bonds on the surface of the porous carbon matrix; the reaction process in this step is as follows:

[0117] C-OH+LiN(SiMe3)2→CO-Li+HN(SiMe3)2↑;

[0118] S4: Continue the above deposition process for a total of 150 times to obtain a composite porous carbon framework.

[0119] (3) The composite porous carbon framework is placed in a chemical vapor deposition furnace and heated to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere. Silane with a flow rate of 5L / min is introduced into the chemical vapor deposition furnace through nitrogen gas with a flow rate of 5L / min. The furnace is kept at this temperature for 4 hours, allowing the silicon elements decomposed from the silane to be deposited in the pores and on the surface of the composite porous carbon framework and grown into silicon nanomaterials. The flow of silane is then stopped, and the intermediate material is obtained.

[0120] During the silicon deposition process in this step, CO-La-O, CO-Nb2O5, and CO-Li attached to the porous carbon framework undergo atomic diffusion and phase transformation at high temperature, causing the diffused La, Nb, Li, and O elements to react and form a tetragonal Li phase. 1.25 La 0.58 Nb₂O₆, and the active silicon atoms from the decomposition of silane react with the tetragonal Li₂. 1.25 La 0.58 The La-O and Nb-O groups on the surface of Nb2O6 react to form covalent bonds.

[0121] (4) Under a nitrogen atmosphere, the temperature of the chemical vapor deposition furnace is adjusted to 400℃. Methane with a flow rate of 5L / min is introduced into the chemical vapor deposition furnace through nitrogen with a flow rate of 5L / min. The furnace is kept at the temperature for 6 hours, so that the carbon elements decomposed by methane are deposited on the surface of the intermediate material to form a carbon coating layer, thus obtaining the silicon-carbon composite material precursor.

[0122] (5) The gas in the chemical vapor deposition furnace was switched to a mixture of nitrogen at a flow rate of 5 L / min and hydrogen fluoride at a flow rate of 0.5 L / min. The temperature was increased to 350°C at a heating rate of 5°C / min and held for 6 hours for medium-temperature fluorination to decompose HF and obtain F ions. Then, the temperature was increased to 800°C at a heating rate of 4°C / min for high-temperature calcination to fill Li with F ions. 1.25 La 0.58 Nb₂O₆ lattice oxygen vacancies facilitate the in-situ formation of a continuous layered solid electrolyte framework, Li, after cubic phase transformation. 1.25 La 0.58Nb2O6F was used to obtain a silicon-carbon composite material with an in-situ double-layer framework structure.

[0123] The silicon-carbon composite material prepared in Example 1 was tested for ionic conductivity, electronic conductivity, and surface resistivity, as detailed below.

[0124] Test 1: Ionic conductivity and sheet resistance tests. Specifically, the ionic conductivity test was performed using electrochemical impedance spectroscopy (EIS) on an electrochemical workstation. The specific steps were as follows: First, the silicon-carbon composite material from Example 1 was placed in the test mold and continuously pressurized into a sheet material, which was then connected to the electrochemical workstation. To ensure the accuracy of the test, the test cell was placed in a temperature-controlled chamber. In the EIS test, the frequency range was set from 0.01 Hz to 1 MHz, and the amplitude voltage was set to 10 mV to accurately measure the material's resistance. Next, through analysis of the Nyquist impedance spectrum, the ionic conductivity of the material could be calculated using the following formula: In the determination of ionic conductivity, d in the formula represents the thickness of the sheet-like material of the silicon-carbon composite, R is the impedance value of the electrolyte read from the Nyquist impedance diagram of EIS, and S represents the effective contact area between the sheet-like material and the stainless steel inert electrode. To ensure the accuracy of the measurement, when testing the ionic conductivity at different temperatures, the constant temperature chamber needs to be set to the target temperature and maintained for half an hour to allow the test sample to reach thermal equilibrium. This step ensures the stability of the test environment, thereby allowing for accurate measurement of the ionic conductivity of the silicon-carbon composite at various temperatures. The ionic conductivity tests of this invention were all conducted at 25±2℃ and humidity less than 50%. Detailed test data are shown in Table 1.

[0125] Test 2, Electronic Conductivity Test: Similarly, the silicon-carbon composite material from Example 1 was placed in the test mold, continuously pressurized into a sheet, connected to an electrochemical workstation, and the CA program was imported. The potential U was controlled at 1V, and the time was 30 minutes. The test was started, and the time-current curve was obtained. The electronic conductivity formula is: Where d is the compacted thickness of the material, R = U / I, and I is the steady-state current. S is the effective contact area between the sheet material and the stainless steel inert electrode of the testing equipment. The calculation results of electronic conductivity are detailed in Table 1.

[0126] Test 3, Surface resistivity test: First, a coin cell half-cell of "silicon-carbon composite electrode | separator | lithium metal" was assembled using conventional methods. Specifically, the negative electrode material and conductive agent Super prepared in this embodiment were taken in a mass ratio of 8:1:1. P and the binder sodium carboxymethyl cellulose (CMC) are added to a mortar for preliminary grinding, then deionized water is added and the mixture is transferred to a pulper and stirred to form a slurry. The obtained slurry is then coated onto a copper foil current collector. After drying in a vacuum oven at 80°C for 12 hours, the dried electrode is rolled once at a pressure of 14 MPa. The rolled electrode is then cut into 14 mm diameter discs to serve as silicon-carbon composite electrode for a coin cell. The silicon-carbon composite electrode is assembled into a coin cell using conventional methods in an argon-filled glove box. The electrolyte used in the coin cell is a non-aqueous electrolyte, with lithium salt being 1 mol / L lithium hexafluorophosphate (LiPF6). The electrolyte solvent is ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), with a volume ratio of EC, DEC, and DMC of 1:1:1. A polyethylene (PE) membrane is used as the separator.

[0127] The assembled coin cell was connected to an electrochemical workstation. In the EIS test, the frequency range was set to 0.01 Hz to 1 MHz, and the amplitude voltage was set to 10 mV. Then, by analyzing the Nyquist impedance spectrum, R1 was read, and the surface resistance Rsurface = R1 × S, where S is the effective area of ​​the silicon-carbon composite electrode.

[0128] Test 4, Cyclic Performance Test and Negative Electrode Expansion Rate Test, specifically: To test the cycle stability of the full battery composed of the electrolyte, lithium iron phosphate (LFP) was used as the positive electrode active material to prepare the LFP positive electrode, and the silicon-carbon composite material prepared in Example 1 was used as the negative electrode active material. The batteries were assembled using conventional methods into a "LFP positive electrode | PE separator | silicon-carbon composite negative electrode" pouch battery. A Blue Electric tester was used to perform 500 cycles at a 1C current density, and the capacity retention rate was calculated and recorded. The test results are detailed in Table 1.

[0129] Electrode expansion rate test method: First, measure the thickness of the prepared silicon-carbon composite negative electrode sheet before cycling, denoted as D1. Discharge at 0.1C rate. After discharge, disassemble the battery in a glove box, remove the electrode sheet, and measure the thickness of the silicon-carbon composite negative electrode sheet after 500 cycles, denoted as D2. Calculate the initial expansion rate using the formula: Expansion rate of silicon-carbon composite negative electrode sheet.

[0130] = (D2-D1) / D1×100%. See Table 1 for detailed test data.

[0131] Example 2

[0132] This invention provides a method for preparing a silicon-carbon composite material with an in-situ bilayer framework structure. The method differs from Example 1 in step (1): 1 kg of porous carbon framework and 0.2 kg of potassium hydroxide powder are placed in a planetary ball mill and milled for 4 hours at 800 rpm under a nitrogen atmosphere. Zirconia balls are used as the milling media. After milling, residual potassium ions are removed by washing with 1 mol / L dilute hydrochloric acid, and then dried at 70°C to obtain an activated porous carbon framework with -OH bonds on its surface. Other preparation processes are the same as in Example 1.

[0133] The silicon-carbon composite material prepared in this embodiment was tested for ionic conductivity, electronic conductivity and sheet resistance. The silicon-carbon composite material prepared in this embodiment was also used to assemble a full cell for cycle performance and electrode expansion rate testing. The method was the same as in Example 1. The test data are detailed in Table 1.

[0134] Example 3

[0135] This invention provides a method for preparing a silicon-carbon composite material with an in-situ bilayer framework structure. The difference from Example 1 is in step (2) S4: continuing the cyclic deposition process for a total of 300 times to obtain a composite porous carbon framework. The other preparation processes are the same as in Example 1.

[0136] The silicon-carbon composite material prepared in this embodiment was tested for ionic conductivity, electronic conductivity and sheet resistance. The silicon-carbon composite material prepared in this embodiment was also used to assemble a full cell for cycle performance and electrode expansion rate testing. The method was the same as in Example 1. The test data are detailed in Table 1.

[0137] Example 4

[0138] This invention provides a method for preparing an in-situ bilayer framework structure of silicon-carbon composite material. The difference from Example 1 lies in the silicon nanomaterial deposition process in step (3): the composite porous carbon framework is placed in a chemical vapor deposition furnace and heated to 450°C at a rate of 3°C / min under a nitrogen atmosphere. Metallic silicon vapor with a flow rate of 3L / min is introduced into the chemical vapor deposition furnace through nitrogen gas at a flow rate of 9L / min. The furnace is held at this temperature for 3 hours, allowing the silicon elements from the decomposition of the metallic silicon vapor to deposit in the pores and on the surface of the composite porous carbon framework and grow into silicon nanomaterials. The introduction of metallic silicon vapor is then stopped, yielding an intermediate material. All other preparation processes are the same as in Example 1.

[0139] The silicon-carbon composite material prepared in this embodiment was tested for ionic conductivity, electronic conductivity and sheet resistance. The silicon-carbon composite material prepared in this embodiment was also used to assemble a full cell for cycle performance and electrode expansion rate testing. The method was the same as in Example 1. The test data are detailed in Table 1.

[0140] Example 5

[0141] This invention provides a method for preparing a silicon-carbon composite material with an in-situ generated bilayer framework structure. The method differs from Example 1 in step (2), where the gas introduction time, purging time, and number of cycles are different. Specifically:

[0142] S1: A La(thd)3 gas with a flow rate of 100 sccm is introduced with a pulse duration of 3 s. The mixture is then purged with nitrogen gas at a flow rate of 200 sccm for 50 s. Next, an oxidizing gas source O3 with a flow rate of 100 sccm is introduced with a pulse duration of 3 s, followed by purging with nitrogen gas at a flow rate of 200 sccm for 60 s. This process forms CO-La-O on the surface of the porous carbon matrix. The chemical equation for this process is:

[0143] S2: Nb(OEt)₅ gas with a flow rate of 100 sccm is introduced with a pulse duration of 3 s, followed by purging with nitrogen gas at a flow rate of 200 sccm for 50 s. Then, H₂O gas with a flow rate of 100 sccm is introduced with a pulse duration of 3 s, followed by purging with nitrogen gas at a flow rate of 200 sccm for 60 s. CO-Nb₂O₅ is formed on the surface of the porous carbon matrix. The chemical equation for this process is:

[0144] S3: A LiN(SiMe3)2 gas with a volumetric flow rate of 100 sccm is introduced, with a pulse duration of 3 s. Nitrogen gas with a volumetric flow rate of 200 sccm is then used to purge for 60 s, forming CO-Li bonds on the surface of the porous carbon matrix. The chemical equation for this process is:

[0145] S4: Continue the above deposition process for a total of 200 times to obtain a composite porous carbon framework.

[0146] The other preparation processes are the same as in Example 1.

[0147] The silicon-carbon composite material prepared in this embodiment was tested for ionic conductivity, electronic conductivity and sheet resistance. The silicon-carbon composite material prepared in this embodiment was also used to assemble a full cell for cycle performance and electrode expansion rate testing. The method was the same as in Example 1. The test data are detailed in Table 1.

[0148] Example 6

[0149] This invention provides a method for preparing an in-situ bilayer framework structure of silicon-carbon composite material, which differs from Example 1 in step (4): Under an argon atmosphere, the intermediate material is placed in a rotary kiln rotating at 0.8 rpm and heated to 450°C. Methane with a flow rate of 10 L / min is introduced into a chemical vapor deposition furnace through argon gas at a flow rate of 50 L / min. The furnace is held at this temperature for 4 hours, allowing the carbon elements from the decomposition of methane to deposit on the surface of the intermediate material to form a carbon coating layer, thus obtaining the silicon-carbon composite material precursor. Subsequent step (5) is also carried out in a rotary kiln. Other preparation processes are the same as in Example 1.

[0150] The silicon-carbon composite material prepared in this embodiment was tested for ionic conductivity, electronic conductivity and sheet resistance. The silicon-carbon composite material prepared in this embodiment was also used to assemble a full cell for cycle performance and electrode expansion rate testing. The method was the same as in Example 1. The test data are detailed in Table 1.

[0151] Example 7

[0152] This invention provides a method for preparing a silicon-carbon composite material with an in-situ bilayer framework structure. The difference from Example 1 lies in the intermediate-temperature fluorination step (5): the gas in the chemical vapor deposition furnace is switched to a mixture of nitrogen (35 L / min) and hydrogen fluoride (7 L / min), and the temperature is increased to 650°C at a rate of 3°C / min, held for 5 hours for intermediate-temperature fluorination, forming CF-Li on the surface of the porous carbon matrix (the equation for this process is CO-Li + HF → CF-Li + H2O↑). All other preparation processes are the same as in Example 1.

[0153] The silicon-carbon composite material prepared in this embodiment was tested for ionic conductivity, electronic conductivity and sheet resistance. The silicon-carbon composite material prepared in this embodiment was also used to assemble a full cell for cycle performance and electrode expansion rate testing. The method was the same as in Example 1. The test data are detailed in Table 1.

[0154] Example 8

[0155] This invention provides a method for preparing a silicon-carbon composite material with an in-situ bilayer framework structure. The method differs from Example 1 in step (5) high-temperature treatment: the temperature is raised to 850°C at a rate of 8°C / min for high-temperature calcination. This allows the La, Nb, Li, and F in CO-La-O, CO-Nb2O5, and CF-Li on the surface of the porous carbon framework to undergo atomic diffusion and crystal phase transformation, resulting in the in-situ formation of a continuous phase layered solid electrolyte framework, Li. 1.25 La 0.58 Nb2O6F was used to obtain a silicon-carbon composite material with an in-situ double-layer framework structure. All other preparation processes were the same as in Example 1.

[0156] The silicon-carbon composite material prepared in this embodiment was tested for ionic conductivity, electronic conductivity and sheet resistance. The silicon-carbon composite material prepared in this embodiment was also used to assemble a full cell for cycle performance and electrode expansion rate testing. The method was the same as in Example 1. The test data are detailed in Table 1.

[0157] Example 9

[0158] This invention provides a method for preparing a silicon-carbon composite material with an in-situ formed bilayer framework structure. The difference from Example 1 is that the solid electrolyte in the in-situ formed solid electrolyte framework is Li. 1.3 Al 0.3 Ti 1.7 (PO4)3(LATP) is prepared by the following steps.

[0159] (1) The process of preparing the activated porous carbon framework is the same as step (1) in Example 1.

[0160] (2) The activated porous carbon matrix was placed in a fluidized bed atomic layer deposition reactor and atomic layer deposition was carried out by atomic layer deposition technology. The deposition temperature was 200℃. The first deposition process is as follows.

[0161] S1: Introduce aluminum isopropoxide (Al(OC3H7)3) gas with a gas volume flow rate of 100 sccm for 1 s, purge with nitrogen gas with a gas volume flow rate of 200 sccm for 30 s, then introduce an oxidizing gas source O3 with a gas volume flow rate of 100 sccm for 0.5 s, purge with nitrogen gas with a gas volume flow rate of 200 sccm for 20 s, forming CO-Al bonds on the surface of the porous carbon matrix;

[0162] S2: Tetrabutyl titanate (Ti(OC4H9)4) gas with a gas volume flow rate of 100 sccm is introduced for a pulse time of 1 s. Nitrogen gas with a gas volume flow rate of 200 sccm is purged for 30 s. Then H2O gas with a gas volume flow rate of 100 sccm is introduced for a pulse time of 0.5 s. Nitrogen gas with a gas volume flow rate of 200 sccm is purged for 20 s. CO-Ti(OH)4 bonds are formed on the surface of the porous carbon matrix.

[0163] S3: Introduce lithium carbonate (Li2CO3) gas at a volume flow rate of 100 sccm for 2 s, and purge with nitrogen gas at a volume flow rate of 200 sccm for 40 s; finally, introduce ammonium dihydrogen phosphate (NH4H2PO4) gas at a volume flow rate of 100 sccm for 0.5 s, and purge with nitrogen gas at a volume flow rate of 200 sccm for 20 s to form CP-Li bonds on the surface of the porous carbon matrix;

[0164] S4: Continue the above deposition process for a total of 150 times to obtain a composite porous carbon precursor.

[0165] (4) Under a nitrogen atmosphere, the temperature of the chemical vapor deposition furnace is adjusted to 400℃. Methane with a flow rate of 5L / min is introduced into the chemical vapor deposition furnace through nitrogen with a flow rate of 5L / min. The furnace is kept at the temperature for 6 hours, so that the carbon elements decomposed by methane are deposited on the surface of the intermediate material to form a carbon coating layer, thus obtaining the silicon-carbon composite material precursor.

[0166] (5) The gas in the chemical vapor deposition furnace was switched to a mixture of nitrogen at a flow rate of 5 L / min and hydrogen fluoride at a flow rate of 0.5 L / min. The temperature was increased to 800℃ at a heating rate of 5℃ / min and held for 8 hours. This allowed Al, Ti, Li and P atoms in CO-Al, CO-Ti(OH)4 and CP-Li to diffuse and undergo phase transformation to form a solid electrolyte framework, Li. 1.3 Al 0.3 Ti 1.7 (PO4)3 was used to obtain a silicon-carbon composite material with an in-situ double-layer skeleton structure.

[0167] The silicon-carbon composite material prepared in this embodiment was tested for ionic conductivity, electronic conductivity and sheet resistance. The silicon-carbon composite material prepared in this embodiment was also used to assemble a full cell for cycle performance and electrode expansion rate testing. The method was the same as in Example 1. The test data are detailed in Table 1.

[0168] To better illustrate the effects of the embodiments of the present invention, a comparative example is provided to be made with the embodiments described above.

[0169] Comparative Example 1

[0170] This comparative example provides a preparation process for a silicon-carbon composite material, which involves silicon deposition and carbon coating of the porous carbon skeleton used in step (1) of Example 1. The silicon deposition and carbon coating process is the same as that in steps (3) and (4) of Example 1, and the silicon-carbon composite material is finally obtained.

[0171] The silicon-carbon composite material prepared in this comparative example was tested for ionic conductivity, electronic conductivity and sheet resistance. The silicon-carbon composite material prepared in this comparative example was also used to assemble a full cell for cycle performance and electrode expansion rate testing. The method was the same as in Example 1. The test data are detailed in Table 1.

[0172] Comparative Example 2

[0173] This comparative example uses solid electrolyte Li 1.25 La 0.58Nb2O6F was ball-milled with the porous carbon skeleton and nano-silicon particles of Example 1 at a ratio of 1:7:2 for 10 hours at 800 rpm. Then, carbon coating was performed using the same method as in Example 1 to obtain a silicon-carbon composite material.

[0174] The silicon-carbon composite material prepared in this comparative example was tested for ionic conductivity, electronic conductivity and sheet resistance. The silicon-carbon composite material prepared in this comparative example was also used to assemble a full cell for cycle performance and electrode expansion rate testing. The method was the same as in Example 1. The test data are detailed in Table 1.

[0175] Comparative Example 3

[0176] This comparative example uses the solid electrolyte Li from Example 9. 1.3 Al 0.3 Ti 1.7 (PO4)3 was ball-milled with the porous carbon skeleton and nano-silicon particles of Example 9 at a ratio of 1:7:2 for 10 hours at a speed of 800 rpm. Then, carbon coating treatment was performed in the same way as in Example 9 to obtain silicon-carbon composite material.

[0177] The silicon-carbon composite material prepared in this comparative example was tested for ionic conductivity, electronic conductivity and sheet resistance. The silicon-carbon composite material prepared in this comparative example was also used to assemble a full cell for cycle performance and electrode expansion rate testing. The method was the same as in Example 1. The test data are detailed in Table 1.

[0178] Table 1 summarizes the test data for Examples 1-9 and Comparative Examples 1-3.

[0179]

[0180] Table 1

[0181] As can be seen from the comparison of test data in Table 1, the ionic conductivity, electronic conductivity, and cycle retention of Examples 1-8 are much higher than those of Comparative Examples 1-2, while the sheet resistance and silicon anode expansion rate of Examples 1-8 are significantly lower than those of Comparative Examples 1-2. The ionic conductivity, electronic conductivity, and cycle retention of Example 9 are much higher than those of Comparative Example 3, while the sheet resistance and silicon anode expansion rate of Example 9 are significantly lower than those of Comparative Example 3.

[0182] This is because Comparative Example 1 is a traditional silicon-carbon composite material that has not been coated with a solid electrolyte and has not formed a solid electrolyte framework structure. The ionic conductivity of Comparative Example 1 is many orders of magnitude lower than the electronic conductivity, making it difficult to detect. Furthermore, during cycling, the porous carbon framework has limited effect on inhibiting silicon expansion, resulting in a large volume expansion rate and thus a low cycle retention rate.

[0183] In contrast, Comparative Example 2 used a physical mixing method to coat the porous carbon framework, solid electrolyte, and nano-silicon particles. This resulted in insufficient contact between the particles, increased surface resistivity, and ineffective suppression of silicon expansion, leading to poor test data.

[0184] Similarly, Comparative Example 3 also involved the physical blending of porous carbon framework, solid electrolyte, and nano-silicon particles. However, insufficient contact between the particles resulted in increased surface resistivity, and silicon expansion was not effectively suppressed, leading to poor test data.

[0185] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing in-situ coated silicon-carbon composite material, characterized in that, The preparation method includes: The preparation of activated porous carbon framework includes: surface activation treatment of porous carbon framework to make the surface of porous carbon framework contain -OH bonds, thereby obtaining activated porous carbon framework; A composite porous carbon framework is obtained by depositing a solid electrolyte precursor on the surface and pore walls of an activated porous carbon framework using atomic layer deposition (ALD) technology. The process includes: placing the activated porous carbon framework in a fluidized bed powder ALD apparatus, heating it to 150°C–350°C, sequentially introducing a gas containing one or more elements of a solid electrolyte precursor, and after each precursor is introduced, purging with an inert gas and intermittently introducing an oxidizing gas source to react with the precursor, causing different elements in the precursor to deposit on the surface of the porous carbon framework. The above deposition process is repeated 100–300 times to obtain a composite porous carbon framework. The composite porous carbon framework was placed in a reaction apparatus for silicon deposition to obtain an intermediate material. The intermediate material is carbon-coated to obtain a silicon-carbon composite material precursor. The silicon-carbon composite material precursor is calcined to allow different elements deposited on the surface of the porous carbon skeleton to undergo atomic diffusion and crystal phase transformation, and then form a solid electrolyte skeleton with a continuous phase layer structure in situ, thus obtaining a silicon-carbon composite material with an in-situ double-layer skeleton structure. The solid electrolyte in the solid electrolyte framework includes: oxide solid electrolyte and / or fluoride oxide solid electrolyte; The volumetric flow rate of the gas precursor for the solid electrolyte is 50 sccm to 500 sccm; The oxide solid electrolyte includes: garnet-type oxide solid electrolyte Li7Al3B12O 12 Perovskite oxide solid electrolyte Li 3x A2 2 / 3-x B2O3, NASICON-type oxide solid electrolyte Li 1+y A3 y B3 2-y One or more of (PO4)3, wherein 0.01≤x≤0.5, 0.01≤y≤0.5; A1 is one or more of La, Ca, Sr, Ba, K, and B1 is one or more of Zr, Ta, Nb, Hf; A2 is one or more of La, Al, Mg, Fe, Ta, and B2 is one or more of Ti, Nb, Sr, Pr; A3 is one or more of Al, Y, Ga, Cr, In, Fe, Se, La, and B3 is one or more of Ti, Ge, Ta, Zr, Sn, Fe, V, Hf. The fluoride solid electrolyte includes: Li 1.5 Al 0.5 Ge 1.5 (PO4) 2.9 F 0.1 Li 6.5 La3Zr 1.5 Ta 0.5 O 11.5 F 0.5 Li₂VO₂F, Li 1.2 Mn 0.8 Nb 0.2 O 1.6 F 0.4 Li m La n M1 a M2 b M3 c One or more of O6F; wherein, 1 < m + 3n < 5, 0 < m ≤ 2, 1 / 3 < n < 5 / 3; 0 ≤ a ≤ 2, 0 ≤ b ≤ 2, 0 ≤ c ≤ 2, a + b + c = 2, M1 is one or more of Zr, Ti, Hf, Si, Ge, Sn, M2 is one or more of Nb, Sb, Bi, V, Ta, and M3 is one or more of W, Cr, Mo, Mn; The oxidation gas source includes O3 and / or H2O; the volumetric flow rate of the oxidation gas source is 50 sccm to 500 sccm. The inert gas includes one or more of nitrogen, helium, or argon; the volumetric flow rate of the inert gas is 100 sccm to 1000 sccm.

2. The production method according to claim 1, characterized by, The surface activation treatment is either an acidic activation treatment or an alkaline activation treatment; The acid activation treatment includes: immersing a porous carbon framework in an acidic solution, stirring at 60℃~120℃ for 1 hour~10 hours, washing with deionized water until neutral after the reaction, and drying at a low temperature of 60℃~80℃ to obtain an activated porous carbon framework with -OH bonds on its surface; the mass ratio of the porous carbon framework to the acidic solution is 10%~50%; the acidic solution includes a nitric acid solution with a concentration of 20wt%-70wt% and / or hydrogen peroxide; The alkaline activation treatment includes: placing a porous carbon framework and potassium hydroxide powder in a ball mill at a ratio of 1-5:5-9, and ball milling at 500-1000 rpm for 2-8 hours under an inert atmosphere. Zirconia balls are used as the milling media. After ball milling, residual potassium ions are removed by washing with dilute hydrochloric acid with a molar concentration of 0.1 mol / L-1 mol / L. After drying at 60℃-100℃, an activated porous carbon framework with -OH bonds on its surface is obtained.

3. The preparation method according to claim 1, characterized in that, The silicon deposition specifically includes: placing the composite porous carbon framework in a reaction apparatus, heating it to 350°C to 550°C under a protective atmosphere, introducing silicon source gas into the reaction apparatus through the protective gas, maintaining the temperature for 2 to 6 hours, allowing the silicon elements decomposed by the silicon source gas to be deposited in the pores and on the surface of the composite porous carbon framework and grown into silicon nanomaterials, stopping the introduction of the silicon source gas, and obtaining the intermediate material; The protective gas in the protective atmosphere includes nitrogen and / or argon; the flow rate of the protective gas is 1 L / min to 50 L / min. The silicon source gas includes one or more gases selected from: metallic silicon vapor, silane, propane, dichlorosilane, trichlorosilane, and tetrachlorosilane; the flow ratio of the protective gas to the silicon source gas is 5:1 to 1:

5. The reaction equipment includes any one of a rotary kiln, a vapor deposition furnace, or a fluidized bed.

4. The method of claim 1, wherein, The carbon coating process is gas phase carbon coating, specifically including: under a protective atmosphere, adjusting the temperature of the reaction equipment to 350℃~450℃, introducing carbon source gas into the reaction equipment, and keeping it at that temperature for 2 hours to 8 hours, so that the carbon elements decomposed by the carbon source gas are deposited on the surface of the intermediate material to form a carbon coating layer, thereby obtaining a silicon-carbon composite material precursor. The protective atmosphere comprises nitrogen and / or argon; the flow rate of the protective gas is 1 L / min to 50 L / min; the carbon source gas comprises at least one of methane, acetylene, ethylene, and propylene; and the flow rate ratio of the protective gas to the carbon source gas is 20:1 to 1:

1.

5. The preparation method according to claim 1, characterized in that, When the solid electrolyte in the solid electrolyte framework is an oxide-based solid electrolyte, the calcination treatment specifically includes: heating the reaction equipment to 700℃~850℃ at a heating rate of 2℃ / min~10℃ / min under a protective atmosphere, and holding at that temperature for 2 hours~8 hours, so that different elements on the surface of the porous carbon framework undergo atomic diffusion and crystal phase transformation to form a continuous phase layered solid electrolyte framework in situ, thereby obtaining a silicon-carbon composite material with an in-situ generated double-layer framework structure; the protective gas in the protective atmosphere includes: nitrogen and / or argon; the flow rate of the protective gas is 1L / min~50L / min; When the solid electrolyte in the solid electrolyte framework includes a fluorine oxide solid electrolyte, the calcination treatment specifically includes: switching the gas in the reaction equipment to a mixture of protective gas and fluorine source gas, heating to 350℃~700℃ at a heating rate of 2℃ / min~10℃ / min, holding at this temperature for 2 hours~8 hours for medium-temperature fluorination, causing the fluorine source gas to decompose into fluoride ions, and then heating to 700℃~850℃ at a heating rate of 2℃ / min~10℃ / min for high-temperature calcination treatment, so that different elements on the surface of the porous carbon framework and the fluorine element obtained from the decomposition of the fluorine source gas undergo atomic diffusion and crystal phase transformation to form a solid electrolyte framework with a continuous phase layer structure in situ, thereby obtaining a silicon-carbon composite material with an in-situ generated double-layer framework structure; The fluorine source gas includes one or more of the following: hydrogen fluoride (HF), sulfur tetrafluoride (SF4), nitrogen trifluoride (NF3), xenon difluoride (XeF2), and sulfur hexafluoride (SF6); the flow ratio of the fluorine source gas to the protective gas is 1:20 to 1:

10.

6. A lithium battery, characterized by The lithium battery comprises a silicon-carbon composite material with an in-situ generated double-layer skeleton structure prepared by any of the preparation methods described in claims 1-5.

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