A dense silicon-carbon anode material and its preparation method

Abstract

This invention discloses a dense silicon-carbon anode material comprising core-shell structured particles, each particle including a core and a shell. The core is based on nano-silicon and silicate, with the nano-silicon dispersed within the silicate. The shell covering the core is a carbon coating layer. The invention also discloses its preparation method: Elemental silicon is mixed with silicon oxide and pressed into a blank, which is then heated and vaporized for deposition. Inorganic salt is introduced simultaneously to obtain the deposit, which is then crushed to obtain a micron-sized precursor material. This precursor material is then placed in an organic carbon source atmosphere for carbon deposition to obtain a carbon-coated mixed material. Finally, the material is washed, dried, depolymerized, and sieved to obtain the dense silicon-carbon anode material. This silicon-carbon anode material is a low-expansion, highly dense, and electrochemically stable material. Its structure contains finer nano-silicon particles, a silicate buffer layer, and uniform mesopores, effectively solving the expansion and first-efficiency problems encountered in silicon applications.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials, and more particularly to a dense silicon-carbon anode material and its preparation method. Background Technology

[0002] Lithium-ion batteries, as one of the three key components of new energy vehicles, offer higher driving range and longer lifespan due to their high energy density and long cycle life. Current lithium-ion batteries using traditional graphite have relatively low energy density, creating an urgent market need for novel anode materials. Silicon anodes, with their high capacity, low voltage, and abundant reserves, have become a hot research topic in the industry. Although silicon anodes can provide batteries with energy densities exceeding 300Wh / kg, their high overall expansion rate, low conductivity, and significant lithium intercalation side reactions lead to poor cycle performance and low initial efficiency, hindering the development and application of silicon anode materials.

[0003] Several solutions have been proposed to address the problems encountered in the application: preparing smaller nano-silicon particles, constructing more stable particle structures under electrochemical conditions, and combining with other materials to provide a smaller expansion rate. To improve initial charge / discharge efficiency and material cycle performance, patent document CN104247105A discloses a porous silicon oxide and linear carbon coated on its surface and in its pores. The pores in this material can cope with mechanical stress during volume changes while ensuring that conductivity does not decrease under internal crack conditions. However, this material has a large specific surface area and a relatively rough surface, resulting in an initial efficiency of only 72%.

[0004] Therefore, developing a silicon-carbon anode material with high initial efficiency, good cycle performance, dense structure that is not easily expanded, and electrochemically stable is a key issue for the industrialization of silicon anodes. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a dense silicon-carbon anode material with high initial efficiency, good cycle performance, and dense structure that is not easily expanded, as well as a method for preparing the same.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A dense silicon-carbon anode material includes core-shell structured particles, each particle comprising a core and a shell, wherein:

[0008] The core is based on nano-silicon and silicate, with the nano-silicon dispersed inside the silicate.

[0009] The outer shell covering the nucleus is a carbon coating layer;

[0010] The mass ratio of the nano-silicon, silicate, and coated carbon layer is (10-90):(5-90):(0.1-20).

[0011] Preferably, the coated carbon layer is a crystalline graphitic carbon layer with a coating thickness of 3-100 nm, and the interplanar spacing of the crystalline graphitic carbon layer can be controlled within 0.34-0.42 nm. The crystalline graphitic carbon layer is obtained by vapor deposition. The main process feature is that by adjusting the temperature, time, and gas source ratio, the carbon deposition rate is controlled to be sufficiently slow, allowing carbon atoms to arrange themselves layer by layer, thus depositing a graphitic structure. The interplanar spacing of the crystalline graphitic carbon layer of the present invention can be controlled within the range of 0.34-0.42 nm.

[0012] Preferably, the coated carbon layer is prepared by vapor-phase carbon deposition from an organic carbon source.

[0013] Preferably, the nano-silicon is a polycrystalline or amorphous phase, and the size of the nano-silicon is 1-20 nm; the silicate includes one or more of Li₂Si₂O₅, Li₂SiO₃, Na₄SiO₄, Mg₂SiO₄, Na₂MgSiO₄, K₄SiO₄, and K₂MgSiO₄. Preferably, the core contains a mesoporous structure, the internal porosity of the core is 0.1-10%, and the pore size is 0.1-10 nm; the particle size D50 of the dense silicon-carbon anode material is 3-20 μm, and the tap density is 0.8-1.4 g / cm³. 3 During the reaction, some gases (such as carbon dioxide) are generated and volatilize to form a mesoporous structure. At the same time, the final water washing step can wash away the unreacted salts and form a mesoporous structure. The mesoporous structure can reduce the effective lithium consumption during charging and discharging to a certain extent, providing high initial efficiency while also providing a buffer space for the overall expansion of silicon.

[0014] Based on the overall inventive concept, the present invention also provides a method for preparing a dense silicon-carbon anode material, comprising the following steps:

[0015] (1) Mix elemental silicon with silicon oxide and press it into a blank;

[0016] (2) The billet is heated and vaporized to deposit, while inorganic salt is introduced to obtain the deposited material;

[0017] (3) The deposited material is crushed to obtain micron-sized precursor material;

[0018] (4) The precursor material is placed in an organic carbon source atmosphere for carbon deposition to obtain a carbon-coated mixed material;

[0019] (5) The carbon-coated mixed material is washed with water, dried, depolymerized and sieved to obtain the dense silicon-carbon anode material.

[0020] Preferably, in step (1), the elemental silicon includes one or more of polycrystalline silicon, monocrystalline silicon, and amorphous silicon; the molar ratio of elemental silicon to silicon oxide is 1:(0.1 to 10).

[0021] Preferably, in step (2), the inorganic salt includes one or more of lithium carbonate, lithium hydroxide, lithium oxide, lithium phosphate, sodium carbonate, sodium hydroxide, and sodium phosphate; the mass ratio of the inorganic salt to the billet is 1:(0.1-50); the inorganic salt may also include one or more of potassium carbonate, potassium hydroxide, magnesium carbonate, and magnesium ingots. The role of lithium and magnesium is to convert silicon dioxide in the material into stable silicates, and the roles of sodium and potassium are the same.

[0022] Preferably, the heating temperature for the heated vaporization deposition is 1000-1300℃, the deposition time is 1-10h, and the inorganic salt is heated to a temperature of 500-800℃.

[0023] Preferably, in step (4), the organic carbon source includes one or more gases selected from methane, ethane, ethylene, acetylene, propylene, propane, butadiene, and benzene; the molar ratio of the organic carbon source to the carrier gas during carbon deposition is 1:(0.1-10); the carbon deposition temperature is 950-1000℃ and the time is 2-4h.

[0024] Preferably, the equipment used for pressing and molding in step (1) includes one or a combination of two-way pressing machine, single-sided pressing machine, cold isostatic press, and hot isostatic press; the equipment used for heating and vaporization deposition in step (2) includes one or a combination of vacuum vapor deposition furnace, vacuum melting furnace, vertical vacuum furnace, and microwave vacuum furnace; and the equipment used for carbon deposition in step (4) includes one of vapor deposition furnace, vacuum sintering furnace, rotary kiln, microwave vapor deposition furnace, and vapor fluidized bed.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. The high-density silicon-carbon anode material of the present invention is a low-expansion, high-density, and electrochemically stable silicon-carbon anode material. Its structure contains finer nano-silicon particles, a silicate buffer layer, and uniform mesopores, effectively solving the expansion and first-cycle efficiency problems in silicon applications. The small size of the nano-silicon grains in this structure effectively reduces volume expansion during the silicon lithium insertion / extraction process. The internally embedded silicate and mesoporous structure reduces effective lithium consumption during charging and discharging to a certain extent, providing high first-cycle efficiency while also providing buffer space for overall silicon expansion. The internal silicon is coated with lithium silicate salt, and the outer crystalline graphite-like carbon layer avoids direct contact between silicon and the electrolyte, while reducing effective lithium consumption in the electrolyte and ensuring stable SEI film formation, providing high first-cycle efficiency and long cycle performance for battery applications.

[0027] In addition, the common coated carbon is amorphous carbon, that is, the carbon layers are arranged in a disordered stacked structure. In this structure, the outer core and shell are dense coated carbon layers without pores. Its crystal planes are similar to graphite. The graphite-like crystal planes are obtained by vapor deposition. The main process feature is that by adjusting the temperature, time and gas source ratio, the carbon deposition rate is controlled to be slow enough so that the carbon atoms are arranged layer by layer to form a graphite-like structure. This structure can not only improve the conductivity of the particles, but also resist the volume expansion stress of the particles and avoid the pulverization of particles due to strain during the lithium insertion and extraction process, ultimately improving the cycle performance of the battery.

[0028] 2. The preparation method of the present invention is simple to operate and low in cost. The present invention adds inorganic salts containing lithium, sodium, potassium or magnesium to perform metallization pretreatment on the material. The resulting material structure contains silicon dioxide. Through heating and vaporization deposition treatment, the silicon dioxide is directly converted into reversible capacity silicate, which can improve the first efficiency of silicon anode. It is equivalent to occupying a part of the irreversible site. At the same time, the silicate at this site can provide reversible capacity, further improving the first efficiency of the material.

[0029] Using a liquid-phase molten state method can yield a uniformly distributed silicate structure, avoiding the problem of particle expansion and uneven stress caused by uneven distribution, which can lead to cracking. At the same time, a dense layer of carbon can be prepared by simple gas-phase control. The method is simple, effective and has a high yield, which can provide a basis for the large-scale production of high-performance silicon anodes. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the 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 based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the dense silicon-carbon anode material constructed according to the present invention;

[0032] Figure 2 This is the XRD pattern of the silicon-carbon anode prepared in Example 1 of the present invention;

[0033] Figure 3 This is a TEM image of the silicon-carbon anode coating layer prepared in Example 1 of the present invention;

[0034] Figure 4 This is the XRD pattern of the silicon-carbon anode prepared in Comparative Example 1 of this invention. Detailed Implementation

[0035] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0036] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0037] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods.

[0038] Example 1:

[0039] A dense silicon-carbon anode material is a core-shell structured particle, wherein: the core comprises silicate (Li₂SiO₃) and uniformly distributed nano-silicon (5.3 nm in size) embedded within the silicate, wherein the silicate mass ratio is 45.04%, the nano-silicon mass ratio is 53.09%, and the carbon content is 1.87%. The core contains a uniformly distributed mesoporous structure with an internal porosity of 2% and a pore size of 5.5 nm; the shell is a dense, non-porous carbon coating layer with a coating thickness of 15 nm; the tap density is 1.22 g / cm³. 3 .

[0040] Its preparation method is as follows:

[0041] (1) Weigh 5000g of metallurgical micron silicon with D50 = 10μm and 5000g of silicon dioxide with D50 = 200nm, mix them at 1500rpm for 2h to form a homogeneous mixture; place 500g of the mixture in batches into a biaxial pressing molding machine, press it at 50 tons of pressure for 10min, and the diameter of the billet is... The height is 40mm;

[0042] (2) The pressed block material is placed in a PVD deposition equipment and heated and vaporized for deposition at a temperature of 1150℃ for 10 hours and an internal pressure of 10Pa. 200g of lithium carbonate is heated to 730℃ and introduced into the deposition chamber. The temperature of the deposition chamber is controlled at 700℃. After cooling, the deposited block material is obtained. The silicon content in the deposited material is 56%, the lithium silicate content is 44%, and the pH value is 9.

[0043] (3) Take 1000g of sediment block material and coarsely crush it into 3mm coarse particles by using a wheel mill at 500rpm for 2h. Adjust the air crusher equipment, the classifier frequency of the air crusher equipment is 180Hz, the feeding frequency is 5Hz, and the torque is adjusted by 20%-30% to obtain micron-level precursor material with D50=3μm.

[0044] (4) Take 1000g of precursor material and place it in a CVD deposition equipment. Introduce a mixture of acetylene and methane with a volume ratio of 1 / 3. The deposition temperature is 950℃ for 4h, the flow rate of the mixed gas is 5L / min, and the flow rate of the carrier gas is 13L / min. After deposition, carbon-coated mixed material is obtained.

[0045] (5) Take 1000g of the deposited material and place it in a 5L beaker. Add 3L of deionized water to soak and filter, repeating the soaking process three times. After filtration using a filter press, place the material in a box furnace at 105℃ for 12 hours to dry. Use a universal crusher to depolymerize and sieve the dried material to obtain a dense silicon-carbon anode material with a D50 of 5μm. The structure is as follows: Figure 1 As shown.

[0046] XRD characterization diagram as follows Figure 2 As shown, the TEM characterization image is as follows: Figure 3 As shown, by Figure 2 It can be seen that the prepared silicon-carbon anode material contains silicate (Li2SiO3), and the nano-silicon size is calculated to be 5.3 nm; from Figure 3 As can be seen, the outer coating layer is a graphite-like layered carbon coating. TEM data shows that its interlayer spacing is 0.35 nm, and the coating thickness is approximately 15 nm, exhibiting good coating uniformity. The advantages of controlling these parameters are twofold: firstly, it forms a protective layer on the silicon surface, preventing silicon exposure and ensuring the formation of a stable SEI film, while also mitigating silicon expansion; secondly, a certain coating thickness can improve the material's conductivity, as excessive thickness would reduce the material's initial coulombic efficiency. The crystalline graphite-like carbon layer is obtained through vapor deposition. The main process characteristics are achieved by adjusting the temperature to 950℃-1000℃, the reaction time to 2-4 hours, and the volume ratio of carbon gas source to carrier gas source to less than 50%, thereby controlling the carbon deposition rate sufficiently slowly to allow carbon atoms to arrange themselves layer by layer, thus depositing a graphite-like structure. The intergranular spacing of the crystalline graphite-like carbon layer in this invention can be controlled within the range of 0.34-0.42 nm.

[0047] Example 2:

[0048] A dense silicon-carbon anode material is a core-shell structured particle, wherein: the core comprises silicate (Li₂Si₂O₅) and uniformly distributed nano-silicon (4.75 nm in size) embedded within the silicate, wherein the silicate mass percentage is 28.56%, the nano-silicon mass percentage is 63.68%, and the carbon content is 7.76%. The core contains a uniformly distributed mesoporous structure with an internal porosity of 3.6% and a pore size of 3.5 nm; the shell is a dense, non-porous carbon coating layer with a coating thickness of 50 nm; the tap density is 1.23 g / cm³. 3 .

[0049] Its preparation method is as follows:

[0050] (1) Weigh 5000g of P-doped micron silicon with D50 = 6μm and 400g of silicon dioxide and place them in a VC mixer. Mix them at 1000rpm for 1 hour to obtain a homogeneous mixture. Place the mixture in batches in a biaxial pressing molding machine and mold it at 200t for 2 minutes. The diameter of the block is... The height is 40mm;

[0051] (2) The pressed block material is placed in a PVD deposition equipment and heated and vaporized for deposition at a temperature of 1050℃ for 6 hours, with an internal pressure of 10Pa. At the same time, 300g of lithium hydroxide is weighed, heated to 460℃ to melt, and introduced into the deposition chamber to obtain the deposited block material.

[0052] (3) Take 1000g of sediment material and coarsely crush it into 3mm coarse particles by using a rotary mill at 500rpm for 2h. Adjust the air crusher equipment, the classifier frequency of the air crusher equipment is 115Hz, the feeding frequency is 5Hz, and the torque is adjusted to 30%-35% to obtain the precursor material with D50=5μm.

[0053] (4) Take 1000g of precursor material and place it in a CVD deposition equipment. Introduce a mixed gas with a volume ratio of acetylene and methane of 1 / 1. The deposition temperature is 1000℃ for 2h, the flow rate of the mixed gas is 10L / min, and the flow rate of the carrier gas is 20L / min. After deposition, carbon-coated mixed material is obtained.

[0054] (5) Take 1000g of the deposited material and place it in a 5L beaker. Add 3L of deionized water and disperse it using an electric stirrer. Filter the material repeatedly three times using a filter. After filtration, place the material in a forced-air drying oven at 100℃ for 12 hours to dry. Depolymerize the dried material using a depolymerizer at a frequency of 30Hz. After depolymerization, sieve to obtain micron-sized silicon-carbon anode material with D50 = 7μm. The structure is as follows: Figure 1 As shown.

[0055] Example 3:

[0056] A dense silicon-carbon anode material is a core-shell structured particle, wherein: the core comprises silicate (Na₂SiO₃) and uniformly distributed nano-silicon (2.05 nm in size) embedded within the silicate, with the silicate accounting for 64.11% by mass, the nano-silicon accounting for 25.89% by mass, and the carbon content being 10%. The core contains a uniformly distributed mesoporous structure with an internal porosity of 9% and a pore size of 2.1 nm; the shell is a dense, non-porous carbon coating layer with a coating thickness of 100 nm; the tap density is 1.26 g / cm³. 3 .

[0057] Its preparation method is as follows:

[0058] (1) Weigh 5000g of vapor-deposited silicon with D50 = 200um and 7000g of silicon dioxide with D50 = 100nm and place them in a VC mixer. Mix them at 1500rpm for 2 hours to obtain a homogeneous mixture. Take 500g of the above mixture in batches and place them in a unidirectional molding machine. Press them at 100t pressure for 5 minutes to form the block. The diameter of the block is... The height is 40mm;

[0059] (2) The pressed and shaped block material is placed in a PVD deposition equipment and heated and vaporized for deposition at a temperature of 1000℃ for 18 hours and an internal pressure of 100Pa. At the same time, 500g of sodium carbonate is weighed, heated to 850℃, and then introduced into the deposition vaporization chamber. After cooling, the deposited block material is obtained.

[0060] (3) Take 1000g of sediment material, and use a jaw crusher to crush the material into coarse particles of 3mm by adjusting the jaw plate width to 1mm; then feed the crushed material into a mechanical mill to obtain a precursor material with D50=5μm;

[0061] (4) Take 1000g of precursor material and place it in a CVD deposition equipment. Introduce a mixed gas with a molar ratio of acetylene and methane of 1 / 1. The deposition temperature is 1000℃ for 2h, the flow rate of the mixed gas is 10L / min, and the flow rate of the carrier gas is 20L / min.

[0062] (5) Take 1000g of the deposited material and place it in a 5L beaker. Add 3L of deionized water and disperse it by electric stirring. Filter it repeatedly 3 times using a filter. After filtration, place the material in a forced-air drying oven at 100℃ for 12h to dry it. Place the dried material in a universal crusher for depolymerization and sieving to finally obtain a micron-sized silicon anode material with D50=11μm.

[0063] Comparative Example 1:

[0064] Preparation of a silicon-carbon anode material:

[0065] (1) Weigh 5000g of metallurgical micron silicon with D50 = 10μm and 5000g of silicon dioxide with D50 = 200nm, mix them at 1500rpm for 2h to form a homogeneous mixture; place 500g of the mixture in batches into a biaxial pressing molding machine, press it under 50 tons of pressure for 10min, and the diameter of the block is... The height is 40mm;

[0066] (2) The pressed block material is placed in a PVD deposition equipment, heated and vaporized for deposition at a temperature of 1150℃ for 12 hours, with an internal pressure of 10Pa. The temperature of the cooling chamber is controlled at 500℃. After cooling to room temperature, the deposited block material is obtained.

[0067] (3) Take 1000g of sediment block material and coarsely crush it into 3mm coarse particles by using a wheel mill at 500rpm for 2h. Adjust the air crusher equipment, the classifier frequency of the air crusher equipment is 180Hz, the feeding frequency is 5Hz, and the torque is adjusted by 20%-30% to obtain the precursor material with D50=3μm.

[0068] (4) Take 1000g of precursor material and place it in a CVD deposition equipment. Introduce a mixture of acetylene and methane with a molar ratio of 1 / 3. The deposition temperature is 950℃ for 4h, the flow rate of the mixed gas is 5L / min, and the flow rate of the carrier gas is 13L / min. After deposition, carbon-coated mixed material is obtained.

[0069] (5) Take 1000g of the deposited material and place it in a 5L beaker. Soak it three times and filter it with a filter. Then dry it in a box furnace at 105℃ for 12h. The dried material is deagglomerated and sieved using a universal crusher to obtain a coating material D50=5μm.

[0070] XRD characterization diagram of silicon-carbon anode material as shown in the figure. Figure 4 As shown, with Figure 2 In contrast, it is evident that the prepared material does not contain silicates and exhibits amorphous silicon suboxide.

[0071] Comparative Example 2:

[0072] Preparation of a silicon-carbon anode material:

[0073] (1) Weigh 5000g of metallurgical micron silicon with D50 = 5μm and 6000g of silicon dioxide with D50 = 200nm, and mix them in a mixer at 1500rpm for 2 hours to form a mixture; place the mixture in batches in a biaxial pressing molding machine, and press it into shape under 50 tons of pressure for 10 minutes. The diameter of the block is... The height is 40mm;

[0074] (2) The pressed block material is placed in a PVD deposition equipment, heated and vaporized for deposition at a temperature of 1250℃ for 8 hours, with an internal pressure of 10Pa. The temperature of the cooling chamber is controlled at 800℃, and then cooled to room temperature to obtain the deposited block material.

[0075] (3) Take 1000g of sediment material and use a two-way roller press with a pressure of 50t to adjust the gap to 1mm to coarsely crush it into 3mm coarse particles; adjust the air crusher equipment, the air crusher classifier frequency is 180Hz, the feeding frequency is 5Hz, and the torque is adjusted by 20%-30% to obtain the precursor material with D50=6μm.

[0076] Comparative Example 3

[0077] (1) Weigh 5000g of silicon suboxide with D50 = 5μm and take 200g of lithium carbonate to form a homogeneous mixture by mixing in a VC mixer at 1500rpm for 30min;

[0078] (2) Take 2000g of the mixture and place it in a carbonization furnace. Sinter it at 850℃ for 4 hours at 5℃ / min to form a precursor material.

[0079] (3) In a CVD deposition apparatus containing 1000g of precursor material, a mixed gas of acetylene and methane in a volume ratio of 1 / 1 was introduced. The deposition temperature was 800℃ for 2 hours, the flow rate of the mixed gas was 10L / min, and the flow rate of the carrier gas was 20L / min. After deposition, a silicon-carbon anode material with a D50 of 6um was obtained. The carbon coating layer was amorphous loose carbon with a carbon layer thickness of 30nm.

[0080] The following method was used to test the coin cell performance of the silicon-carbon anode materials of Examples 1-3 and Comparative Examples 1-2: A slurry of silicon-carbon anode material:CMC:SBR = 7:2:1 was prepared, with the solid content of the slurry controlled at 45%. This slurry was then coated onto a copper foil current collector to obtain the anode sheet. The compaction density of the electrode sheet was controlled at 1.3-1.5 g / cm³. 3 A 2032 coin cell was assembled using lithium metal sheets as the counter electrode and 1 mol / L LiPF6 / EC+DMC electrolyte. The battery was tested using the LAND battery testing system under constant current charge-discharge conditions at 0.1C, with a voltage range of 0.001-1.5V. The test results are shown in Table 1 below.

[0081] Table 1: Characterization parameters of the silicon-carbon anode prepared in this invention

[0082]

[0083]

[0084] Table 1 shows that the first-efficiency of Examples 1-3 is nearly 30 percentage points higher than that of Comparative Example 2, indicating that the effective silicate structure and dense carbon coating structure in the examples can effectively avoid direct contact between silicon and electrolyte, greatly improving the first-efficiency of the material. The expansion rate of the materials in Examples 1-3 is 6-8 percentage points lower than that in Comparative Example 2, indicating that the internal mesopores and silicate system can effectively provide for the volume expansion of silicon, ensuring better subsequent cycle stability. The addition of inorganic salts does not affect the formation of nano-silicon. The formation of mesopores is related to the gaseous inorganic salts. The formation of mesopores mainly occurs during the reaction process when some gases (such as carbon dioxide) are generated and volatilize to form a mesoporous structure; simultaneously, the final water washing step can wash away unreacted salts, forming a mesoporous structure. Examples 1-3 have a higher tap density than Example 2, indicating that the dense structure constructed in this invention can effectively improve the tap density of the material, providing support for the stability of the material under electrochemical conditions.

Claims

1. A method for preparing a dense silicon-carbon anode material, characterized in that, The dense silicon-carbon anode material comprises core-shell structured particles, each particle consisting of a core and a shell, wherein: The core is based on nano-silicon and silicate, with the nano-silicon dispersed inside the silicate; the core contains a mesoporous structure. The outer shell covering the nucleus is a carbon coating layer; the carbon coating layer is a crystalline graphite-like carbon layer. The mass ratio of the nano-silicon, silicate, and coated carbon layer is (10-90):(5-90):(0.1-20); The preparation method includes the following steps: (1) Mix elemental silicon with silicon oxide and press it into a blank; (2) The billet is heated and vaporized for deposition, while inorganic salt is introduced to obtain deposited material; the heating temperature for heating and vaporization deposition is 1000-1300℃, and the deposition time is 1-10h; the inorganic salt is lithium carbonate, lithium hydroxide or sodium carbonate. When the inorganic salt is lithium carbonate, it is heated to 730-800℃ before introduction; when the inorganic salt is lithium hydroxide, it is heated to 460℃ or 500-800℃ before introduction; when the inorganic salt is sodium carbonate, it is heated to 850℃ before introduction. (3) The deposited material is crushed to obtain micron-sized precursor material; (4) The precursor material is placed in an organic carbon source atmosphere for carbon deposition to obtain a carbon-coated mixed material; the organic carbon source includes one or more gases selected from methane, ethane, ethylene, acetylene, propylene, propane, butadiene, and benzene; the flow rate ratio of the organic carbon source to the carrier gas during carbon deposition is 1:(0.1-10); the carbon deposition temperature is 950-1000℃ and the time is 2-4h; (5) The carbon-coated mixed material is washed with water, dried, depolymerized and sieved to obtain the dense silicon-carbon anode material.

2. The method for preparing the dense silicon-carbon anode material according to claim 1, characterized in that, The coating thickness of the carbon layer is 3-100 nm, and the interplanar spacing of the crystalline graphite carbon layer can be controlled between 0.34-0.42 nm.

3. The method for preparing the dense silicon-carbon anode material according to claim 1, characterized in that, The coated carbon layer is prepared by vapor-phase carbon deposition from an organic carbon source.

4. The method for preparing the dense silicon-carbon anode material according to claim 1, characterized in that, The nano-silicon is a polycrystalline or amorphous phase, and the size of the nano-silicon is 1-20 nm; the silicate includes one or more of Li2Si2O5, Li2SiO3, Na4SiO4, Mg2SiO4, Na2MgSiO4, K4SiO4, and K2MgSiO4.

5. The method for preparing the dense silicon-carbon anode material according to claim 1, characterized in that, The core has an internal porosity of 0.1-10% and a pore size of 0.1-10 nm; the dense silicon-carbon anode material has a particle size (D50) of 3-20 μm and a tap density of 0.8-1.4 g / cm³. 3 .

6. The preparation method according to claim 1, characterized in that, In step (1), the elemental silicon includes one or more of polycrystalline silicon, monocrystalline silicon, and amorphous silicon, and the elemental silicon has a D50 of 0.01-20 μm; the silicon oxide is SiO2; and the molar ratio of elemental silicon to silicon oxide is 1:(0.1-10).

7. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the inorganic salt to the billet is 1:(0.1-50).

8. The preparation method according to any one of claims 1-7, characterized in that, The equipment used for pressing and molding in step (1) includes one or a combination of two-way pressing machine, single-sided pressing machine, cold isostatic press, and hot isostatic press; the equipment used for heating and vaporization deposition in step (2) includes one or a combination of vacuum vapor deposition furnace, vacuum melting furnace, vertical vacuum furnace, and microwave vacuum furnace; the equipment used for carbon deposition in step (4) includes one of vapor deposition furnace, vacuum sintering furnace, rotary kiln, microwave vapor deposition furnace, and vapor fluidized bed.

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