Preparation method of nanosilicon-based composite material, nanosilicon-based composite material and application thereof

Abstract

The application provides a preparation method of a nano silicon-based composite material, the nano silicon-based composite material and application thereof, and belongs to the technical field of battery materials. The preparation method of the nano silicon-based composite material is as follows: a porous carrier is provided; molten silicon is permeated into the pores of the porous carrier to obtain a bulk silicon-based composite; the obtained bulk silicon-based composite is crushed and classified to obtain silicon-based composite particles with a median particle size d 50 of 1-50 microns; the obtained particles are surface-coated to obtain a silicon-based composite material; the silicon-based composite material is heated in an inert atmosphere, and is subjected to re-melting and rapid cooling and fine crystallization treatment; and the obtained powder is the nano silicon-based composite material. An electrode containing the nano silicon-based composite material exhibits good cycle stability in the charging and discharging process of a lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to the preparation method of nano-silicon-based composite materials, nano-silicon-based composite materials and their applications. Background Technology

[0002] Silicon possesses a theoretical lithium intercalation capacity far exceeding that of traditional carbon materials, forming a lithium-silicon alloy (Li) during the intercalation process. x The Si,x ratio can reach up to 4.4, corresponding to a theoretical lithium intercalation capacity of 4200 mAh / g. Therefore, silicon-based materials are the most promising anode materials for next-generation high-energy-density lithium-ion batteries. However, silicon-based materials face two problems in application: silicon volume expansion during lithium intercalation and poor silicon conductivity. During the charging and discharging process of lithium-ion batteries, silicon particles undergo significant volume effects due to lithium-silicon alloying / dealloying reactions, with volume expansion reaching up to 300% in the fully lithium-intercalated state. This leads to electrode structure damage, battery capacity decay, and reduced cycle efficiency. Controlling the size of silicon particles can alleviate the volume change of silicon during charging and discharging, and combining silicon with carbon materials can improve the conductivity of silicon-based materials. Nanoscale silicon-carbon composite materials can be prepared using chemical vapor deposition, in which silicon nanoparticles are loaded on the surface and / or within the pore structure of carbon materials. The pore structure of the carbon support can limit the size of the silicon particles, and the closed pores generated during the preparation process can alleviate the silicon particle lithium intercalation expansion. However, chemical vapor deposition (CVD) for preparing silicon-based materials has a serious problem: the silicon source used is usually silane gas, such as the most commonly used silane SiH4, which is a toxic and flammable gas and requires a trichlorosilane disproportionation reaction, resulting in extremely high production costs. Raw material costs and safety will be limiting factors for the large-scale industrialization of silicon-based composite materials prepared by CVD. Summary of the Invention

[0003] The main objective of this invention is to address the issues of raw material cost and safety in the preparation of nano-silicon-based composite materials by chemical vapor deposition in the prior art. The invention provides a method for preparing nano-silicon-based composite materials by using readily available and inexpensive silicon powder as the silicon source and a porous carrier with a ceramic oxide outer surface as the substrate. Silicon is then subjected to liquid-phase infiltration, crushed, coated with carbon, and subjected to high-temperature rapid cooling to refine the silicon crystals, thereby obtaining the nano-silicon-based composite material.

[0004] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a nano-silicon-based composite material is provided. The method specifically comprises: step S1, providing a porous support, wherein the porous support is a porous oxide ceramic and / or porous carbon with a nano-oxide ceramic layer on its surface; step S2, melting silicon powder at 900–1600°C and permeating the molten silicon into the pores of the porous support described in step S1 to obtain a bulk silicon-based composite; and step S3, crushing and classifying the bulk silicon-based composite obtained in step S2 to obtain a median particle size d.50 Silicon-based composite particles with a diameter of 1–50 μm are coated to obtain a silicon-based composite material. In step S4, the silicon-based composite material obtained in step S3 is heated in an inert atmosphere at a temperature of 1000–1400 °C for 0.5–5 h. Then, a cooling medium is introduced to reduce the temperature of the heated silicon-based composite material to 0–300 °C at an extremely rapid cooling rate, thereby obtaining a nano-silicon-based composite material.

[0005] According to another aspect of the present invention, a nano-silicon-based composite material is provided, wherein the nano-silicon-based composite material is prepared according to the above-described preparation method.

[0006] According to another aspect of the present invention, a high-temperature quenching apparatus is provided for heating materials and rapidly cooling them under the action of a cooling medium. The high-temperature quenching apparatus includes a heating device and a quenching device; wherein the heating device includes a feed inlet, a dynamic heating chamber, and a material insulation conduit; the feed inlet is located at the upper end of the dynamic heating chamber, and the material insulation conduit is located at the lower end of the dynamic heating chamber; the quenching device includes a quenching chamber, a cooling medium input pipe, an air inlet pipe, and a discharge outlet; the cooling medium input pipe is located on one side of the quenching chamber, the air inlet pipe is located at one end of the quenching chamber, and the discharge outlet is located at the other end of the quenching chamber; one end of the material insulation conduit is connected to the dynamic heating chamber, and the other end is connected to the quenching chamber, and is disposed on the side of the quenching chamber; the material enters the dynamic heating chamber through the feed inlet, is heated, flows out through the material insulation conduit, enters the quenching chamber, is cooled under the action of the cooling medium, and is then purged by gas from the air inlet pipe and discharged through the discharge outlet to obtain the material after high-temperature quenching.

[0007] According to another aspect of the invention, a negative electrode is provided, the negative electrode comprising a negative electrode active material, wherein the negative electrode active material comprises a nano-silicon-based composite material prepared according to the above preparation method, and / or the above-described nano-silicon-based negative electrode material.

[0008] According to another aspect of the present invention, a battery is provided, the battery comprising a positive electrode, a negative electrode, a separator, an electrolyte, and an aluminum-plastic film, wherein the negative electrode comprises a negative electrode active material, wherein the negative electrode active material comprises a nano-silicon-based composite material prepared according to the above preparation method, and / or the above-described nano-silicon-based negative electrode material.

[0009] By applying the technical solution of this invention, inexpensive and readily available non-toxic silicon powder is used directly as the silicon source and combined with a porous carrier to obtain nano-silicon-based composite materials, thus avoiding the problems of excessive cost and significant safety risks in the preparation of silicon-based composite materials by chemical vapor deposition. Attached Figure Description

[0010] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0011] Figure 1 This is a schematic diagram of the process for preparing nano-silicon-based composite materials.

[0012] Figure 2 This is a schematic diagram of a high-temperature rapid cooling device.

[0013] 1a—Feed inlet; 1b—Dynamic heating chamber; 1c—Material insulation conduit; 2a—Quick cooling chamber; 2b—Cooling medium input pipe; 2c—Air inlet pipe; 2d—Discharge outlet. Detailed Implementation

[0014] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0015] In a typical embodiment of this application, a method for preparing a nano-silicon-based composite material is provided. The method specifically comprises: Step S1, providing a porous support, wherein the porous support is a porous oxide ceramic and / or porous carbon with a nano-oxide ceramic layer on its surface; Step S2, melting silicon powder at 900–1600°C and permeating the molten silicon into the pores of the porous support described in Step S1 to obtain a bulk silicon-based composite; Step S3, crushing and classifying the bulk silicon-based composite obtained in Step S2 to obtain a median particle size d. 50 Silicon-based composite particles with a diameter of 1–50 μm are coated to obtain a silicon-based composite material. In step S4, the silicon-based composite material obtained in step S3 is heated in an inert atmosphere at a temperature of 1000–1400 °C for 0.5–5 h. Then, a cooling medium is introduced to rapidly reduce the temperature of the heated silicon-based composite material to 0–300 °C, thus obtaining a nano-silicon-based composite material. This preparation method is summarized as follows: Figure 1 middle.

[0016] The porous oxide ceramic or porous carbon in the porous support described in step S1 is preferably an oxide ceramic molecular sieve or a porous carbon molecular sieve. In some embodiments, the nano-oxide ceramic layer on the surface of the porous oxide ceramic and porous carbon in step S1 is one or more of Al2O3, SiO2, MgO, CaO, BaO, TiO2, ZnO, Y2O3, ZrO2, Nb2O5, La2O3, Ce2O3, and CeO2, and optionally one or more of Li2O, Na2O, K2O, B2O3, and P2O5. The porous oxide ceramic or the nano-oxide ceramic layer has a high lithium-ion conductivity. An appropriate amount of oxide ceramic in the composite material helps to improve its lithium-ion conductivity, thereby improving the rate performance of the anode material.

[0017] Porous oxide ceramics can be commercially available porous oxide ceramics, or can be prepared by various methods such as precipitation, hydrothermal, and microemulsion methods. Optionally, surfactants or pore-forming agents can be introduced during the preparation process to further regulate the pore structure of the porous oxide ceramics. The surfactants or pore-forming agents are one or more of the following: sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, polyethylene glycol, polyvinylpyrrolidone, polyethylene oxide-polypropylene oxide block copolymer, and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

[0018] For methods using porous carbon as a porous support, a nano-oxide ceramic layer needs to be added to the surface of the porous carbon. This nano-oxide ceramic layer on the porous carbon surface is indispensable in the composite material preparation process, serving to isolate the porous carbon from liquid silicon and prevent molten Si from chemically reacting with the porous carbon matrix at high temperatures to form inactive SiC. This problem does not exist when directly using porous ceramic oxides as a support for silicon infiltration. In some embodiments, the thickness of the nano-oxide ceramic layer on the porous carbon surface is 0.5–10 nm. The nano-oxide ceramic layer on the porous carbon surface can be prepared by various methods such as impregnation, deposition-precipitation, or atomic layer deposition (ALD).

[0019] The porous carrier, serving as the site for molten silicon infiltration, directly determines the ease of silicon infiltration, the volume of silicon it can accommodate, and the size and distribution of silicon particles in the composite material through its specific surface area, pore volume, and pore structure. In some embodiments, the specific surface area of ​​the porous carrier in step S1 is 50–3000 m². 2 / g, pore volume 0.2~3.0cm 3 / g, preferably, the specific surface area of ​​the porous carrier is 300-2000 m² / g. 2 / g, pore volume 0.5~1.5cm 3 / g; The porous carrier comprises micropores, mesopores and macropores, with their pore volumes accounting for 10-80%, 10-80% and 1-20% of the total pore volume, respectively.

[0020] Since liquid permeation involves capillary aggregation, the particle size of the porous support affects the transport of liquid-phase silicon to some extent, thus affecting the effectiveness of silicon permeation. In some embodiments, the median particle size of the porous support in step S1 is 2–50 μm, d max <1000μm. If the particle size is too small, the porous support is easily compressed by the liquid silicon and tends to stick together; if the particle size is too large, it is difficult for molten Si to penetrate into the pores of the porous support.

[0021] Silicon has a melting point of 1410℃. Due to the nanoscale effect, the melting point of nano-silicon may be lower to some extent. In step S2, silicon powder is melted at 900-1600℃, and the molten silicon is penetrated into the pores of the porous carrier described in step S1 to obtain a bulk silicon-based composite. Alternatively, molten Si can be directly penetrated into the pores of the porous carrier under high vacuum, or the porous carrier can be first mixed with nano- or micro-sized silicon particles, and a uniformly mixed porous carrier-silicon mixture at the submicron scale can be obtained through mechanical grinding and / or ball milling. Then, the mixture is subjected to vacuum and high-temperature treatment to allow the molten silicon particles to penetrate in situ into the pores of the porous carrier.

[0022] In some embodiments, step S2 specifically involves: melting silicon powder at 1400–1600°C, injecting the resulting liquid silicon into a preheated and high-vacuum porous carrier, maintaining it under a certain pressure for 0.5–10 h to obtain a bulk silicon-based composite, wherein the porous carrier is preheated at 900–1600°C for 0.5–5 h.

[0023] In some embodiments, step S2 specifically involves: mixing a porous carrier with nano- or micro-sized silicon particles, and obtaining a porous carrier-silicon mixture uniformly mixed at the submicron scale by means of mechanical grinding and / or ball milling; subjecting the obtained porous carrier-silicon mixture to high vacuum treatment, and then treating the porous carrier-silicon mixture at 900–1600°C for 0.5–10 h under an Ar and / or He atmosphere to obtain a bulk silicon-based composite in which liquid-phase silicon permeates within the pores of the porous carrier.

[0024] Bulk silicon-based composites are obtained through direct liquid-phase silicon infiltration, where the size of the silicon particles is determined by the pore size of the porous carrier. Silicon particles formed within mesopores and macropores remain relatively large and are prone to significant volume expansion during lithium intercalation, requiring rapid cooling and grain refinement. However, bulk silicon-based composites do not readily achieve sufficient contact with the cooling liquid, hindering effective grain refinement. Therefore, the silicon-based composites must first undergo a crushing process to obtain a median particle size d. 50The particles are silicon-based composite particles ranging from 1 to 50 μm, and the crushing method includes one or more combinations of mechanical grinding, ball milling, and air jet milling.

[0025] After crushing, some silicon particles are exposed, which can easily lead to the outflow of Si liquid during subsequent high-temperature melting. Therefore, it is necessary to perform surface coating treatment on the silicon-based composite particles. In some embodiments, the thickness of the surface coating layer is 2-300 nm, preferably 2-20 nm. In some embodiments, the surface coating is carbon coating. In some embodiments, the carbon coating is performed by chemical vapor deposition of a carbon precursor, specifically: the silicon-based composite particles obtained from crushing in step S3 are placed in a chemical vapor deposition furnace, a mixture of carbon precursor and inert gas (e.g., N2, Ar, He) is introduced, and the mixture is maintained at 550-1000°C for 0.5-5 h to obtain a silicon-based composite material. The carbon precursor includes, but is not limited to, CH4, C2H6, C2H4, C2H2, C3H8, C3H6, C4H 10 One or more of C4H8. In some embodiments, the volume concentration of the carbon precursor is 1-10%.

[0026] In some embodiments, prior to surface coating, the resulting silicon-based composite particles are acid-washed to remove some of the oxide ceramic, further creating pores, and controlling the oxide content within a suitable range. The oxide ceramic retained in the composite exists as a lithium-ion conductor.

[0027] After surface coating is completed in step S3, each silicon particle in the resulting silicon-based composite material has a thin coating layer around it. In the subsequent step S4, the silicon nanoparticles remain within the porous carrier channels after melting during the high-temperature melting process and are covered by the coating layer. Due to the nanoscale effect, the melting point of nano-silicon is somewhat reduced. In step S4, the silicon-based composite material obtained in step S3 is melted at 1000–1400°C and then subjected to rapid quenching to achieve a fine-grained transformation of crystalline Si, thus obtaining the nano-silicon-based composite material. The high-temperature melting and rapid quenching fine-grained transformation processes are carried out in a high-temperature rapid quenching device.

[0028] High-temperature melting is carried out in an inert atmosphere (Ar, He, N2) at 1000–1400°C. In some embodiments, silicon particles partially react with the surface carbon coating layer to form SiC during this process. In some embodiments, Ar or He is used as the carrier gas to generate a thin SiC coating layer; in some embodiments, N2 is used as the carrier gas to generate a composite coating layer of SiC and Si3N4. Both SiC and Si3N4 are chemically stable and have high strength. Therefore, the coating layer formed at high temperature can isolate silicon particles from the electrolyte in the application of nano-silicon-based composite materials, reduce side reactions, and help form a stable SEI film. It also has the function of binding expansion and improving material strength during silicon intercalation / deintercalation, thereby enhancing the structural stability of the composite electrode during charge-discharge cycles and improving the cycle stability of the material.

[0029] The rapid cooling and fine crystallization process involves using a cooling medium to cool the molten silicon-based composite material at a very rapid rate to 0–300°C. The molten silicon is retained at a low temperature as supercooled silicon, resulting in a nano-silicon-based composite material where silicon exists in an amorphous form. Electrodes containing this nano-silicon-based composite material exhibit isotropic volume expansion of the amorphous Si during lithium-ion battery charging and discharging, demonstrating excellent cycle performance. In some embodiments, the cooling medium in step S4 is one or a combination of liquid nitrogen (N2), liquid helium (He), liquid neon (Ne), liquid argon (Ar), liquid krypton (Kr), and liquid xenon (Xe). In some embodiments, the cooling rate is greater than 1000°C / s.

[0030] In another typical embodiment of this application, a nano-silicon-based composite material is provided, wherein the nano-silicon-based composite material is prepared according to any of the above-described preparation methods. In some embodiments, the nano-silicon-based composite material contains 10% to 90% silicon by mass, 5% to 85% carbon by mass, and other elements by mass totaling 0.5% to 5%, wherein the other elements include oxygen. In some embodiments, the specific surface area of ​​the nano-silicon-based composite material is 0.1 to 50 m². 2 / g, total pore volume is 0.001~0.05cm³ 3 / g, preferably the specific surface area of ​​the composite material is 0.1 to 30 m² / g. 2 / g, total pore volume is 0.001~0.035cm³ 3 / g.

[0031] In another typical embodiment of this application, a high-temperature quenching device is provided, which is used to heat materials and quench them rapidly under the action of a cooling medium. The high-temperature quenching device includes a heating device and a quenching device. The heating device includes a feed inlet, a dynamic heating chamber, and a material insulation conduit. The feed inlet is located at the upper end of the dynamic heating chamber, and the material insulation conduit is located at the lower end of the dynamic heating chamber. The quenching device includes a quenching chamber, a cooling medium input pipe, an air inlet pipe, and a discharge port. The cooling medium input pipe is located on one side of the quenching chamber, the air inlet pipe is located at one end of the quenching chamber, and the discharge port is located at the other end of the quenching chamber. One end of the material insulation conduit is connected to the dynamic heating chamber, and the other end is connected to the quenching chamber, and is disposed on the side of the quenching chamber. The material enters the dynamic heating chamber through the feed inlet, is heated, flows out through the material insulation conduit, enters the quenching chamber, and is cooled under the action of the cooling medium. After being purged by gas through the air inlet pipe, it is discharged through the discharge port to obtain the material after high-temperature quenching.

[0032] Figure 2 A schematic diagram of a high-temperature quenching device is shown. The high-temperature quenching process is explained in detail with reference to the schematic diagram: The silicon-based composite material obtained in step S3 is added to the dynamic heating chamber 1b through the feed port 1a and heated under an inert atmosphere; the heated high-temperature silicon-based composite material flows out through the material insulation conduit 1c and enters the quenching chamber 2a, while the cooling medium enters the quenching chamber 2a through the cooling medium input pipe 2b; the quenching chamber 2a is pre-introduced with carrier gas through the air inlet pipe 2c. Under the action of the carrier gas flow, the high-temperature silicon-based composite material is fluidized and fully mixed with the cooling medium. The cooling medium instantly vaporizes and absorbs a large amount of heat from the high-temperature silicon-based composite material in contact with it, thereby rapidly reducing the temperature of the high-temperature silicon-based composite material to 0-300℃. At the same time, the carrier gas discharges the nano-silicon-based composite material from the discharge port 2d of the quenching chamber 2a, completing the high-temperature quenching fine crystallization process.

[0033] In another typical embodiment of this application, a negative electrode is provided, which comprises a negative electrode active material, wherein the negative electrode active material comprises a nano-silicon-based composite material prepared according to any of the above preparation methods, and / or any of the above nano-silicon-based negative electrode materials.

[0034] In another typical embodiment of this application, a battery is provided, the battery comprising a positive electrode, a negative electrode, a separator, an electrolyte, and an aluminum-plastic film, wherein the negative electrode comprises a negative electrode active material, wherein the negative electrode active material comprises a nano-silicon-based composite material prepared according to any of the above preparation methods, and / or any of the above nano-silicon-based negative electrode materials.

[0035] According to the technical solution provided by the present invention, the prepared nano-silicon-based composite material has the following beneficial effects:

[0036] (1) Molten Si is filled into the porous structure of a porous carrier by liquid-phase infiltration. The size of Si is limited by the porous structure of the carrier and is uniformly dispersed within the pores. After crushing, the exposed silicon particles are protected by a carbon coating layer. On this basis, high-temperature melting and rapid cooling fine crystallization are carried out. The silicon in the resulting silicon-based composite material exists in the form of nano-amorphous silicon. When used as a negative electrode material for lithium-ion batteries, the nano-amorphous silicon exhibits a small volume expansion during lithium intercalation, is isotropic, and has good structural reversibility and mechanical stability during charge and discharge, showing good cycle performance.

[0037] (2) The preparation process of nano-silicon-based composite materials forms a thin layer of SiC or a composite thin layer of SiC and Si3N4 on the surface of silicon particles, which can isolate silicon in the composite electrode from the electrolyte, reduce side reactions, and help form a stable SEI film; and has the effect of binding expansion and improving material strength during silicon insertion and extraction of lithium, so that the structural stability of the composite electrode is enhanced in charge and discharge cycle, thereby improving the cycle stability of the material.

[0038] The beneficial effects of this application are further illustrated below with reference to embodiments and comparative examples. The embodiments of this application should not be construed as limiting the scope of this application.

[0039] Example 1

[0040] Step S1: Provide porous Al2O3 ceramic with a specific surface area of ​​518 m². 2 / g, pore volume 0.72cm 3 / g; Porous Al2O3 ceramics contain micropores, mesopores and macropores, with their pore volumes accounting for 20%, 68% and 12% of the total pore volume, respectively.

[0041] Step S2: Provide d 50 For 100nm, d max Silicon particles <500μm were mixed with porous Al2O3 ceramic and ball milled to obtain a porous Al2O3 ceramic-silicon mixture that was uniformly mixed at the submicron scale. The obtained porous Al2O3 ceramic-silicon mixture was subjected to high vacuum treatment and then treated at 1200℃ under Ar atmosphere for 5h to obtain a bulk silicon-based composite material infiltrated by liquid phase silicon in the porous Al2O3 ceramic channels.

[0042] Step S3: The bulk silicon-based composite obtained in step S2 is crushed and classified using an air jet mill to obtain the median particle size d. 50Silicon-based composite particles with a diameter of 12 μm were obtained. The silicon-based composite particles were acid-washed and dried. The resulting particles were then placed in a tube furnace and heated to 700 °C at a rate of 2 °C / min in a N2 atmosphere. The temperature was changed to a 5% C2H2-N2 mixture and held at 700 °C for 2 h. The mixture was then naturally cooled to room temperature in a N2 atmosphere to obtain a silicon-based composite material with a carbon coating layer thickness of 5 nm.

[0043] Step S4: The silicon-based composite material obtained in step S3 is subjected to high-temperature quenching treatment in a high-temperature quenching device. Specifically, the silicon-based composite material enters the dynamic heating chamber 1b through the feed port 1a and is heated to 1200℃ in an N2 atmosphere for 2 hours. Then, the heated high-temperature silicon-based composite material is carried into the quenching chamber 2a through the material insulation conduit 1c. At the same time, liquid argon is transported to the quenching chamber 2a through the cooling medium input pipe 2b, with liquid argon as the cooling medium. The quenching chamber 2a is pre-introduced with carrier gas through the gas inlet pipe 2c. Under the action of the carrier gas, the liquid argon and the 1200℃ silicon-based composite material are fully contacted in the quenching chamber 2a, causing its temperature to drop rapidly to 0℃, thus obtaining nano-silicon-based composite material, which is discharged through the discharge port 2d.

[0044] Example 2

[0045] Step S1: Provide porous Al2O3 ceramic with a specific surface area of ​​563 m². 2 / g, pore volume 0.24cm 3 / g; Porous Al2O3 ceramics contain micropores, mesopores and macropores, with their pore volumes accounting for 80%, 19% and 1% of the total pore volume, respectively.

[0046] Step S2: Same as step S2 in Example 1.

[0047] Step S3: Same as step S3 in Example 1.

[0048] Step S4: Same as step S4 in Example 1.

[0049] Example 3

[0050] Step S1: Provide a porous SiO2 molecular sieve with a specific surface area of ​​834 m². 2 / g, pore volume 1.52cm 3 / g; Porous SiO2 molecular sieves contain micropores, mesopores and macropores, with their pore volumes accounting for 14%, 82% and 4% of the total pore volume, respectively.

[0051] Step S2: Melt commercially available silicon powder at 1450℃ to obtain liquid silicon; preheat the porous SiO2 molecular sieve obtained in step S1 at 1000℃ and hold for 0.8h; then inject the obtained liquid silicon into the porous SiO2 molecular sieve under high vacuum and hold for 0.8h under normal pressure to obtain bulk silicon-based composite.

[0052] Step S3: Same as step S3 in Example 1.

[0053] Step S4: The silicon-based composite material obtained in step S3 is subjected to high-temperature rapid cooling treatment in a high-temperature rapid cooling device. Specifically, it is heated in a dynamic heating chamber in an N2 atmosphere at a heating temperature of 1100℃ for 0.5h; liquid argon is used as the cooling medium to make full contact with the silicon-based composite material at 1100℃ in the rapid cooling chamber, so that the temperature of the silicon-based composite material is rapidly reduced to 50℃, thereby obtaining nano-silicon-based composite material.

[0054] Example 4

[0055] Step S1: Provide porous MgO ceramic with a specific surface area of ​​566 m². 2 / g, pore volume 1.35cm 3 / g; Porous MgO ceramics contain micropores, mesopores and macropores, with their pore volumes accounting for 12%, 28% and 60% of the total pore volume, respectively.

[0056] Step S2: Melt commercially available silicon powder at 1500℃ to obtain liquid silicon; preheat the porous MgO ceramic obtained in step S1 at 1200℃ for 1.5h; then inject the obtained liquid silicon into the porous MgO ceramic under high vacuum and keep it under normal pressure for 4h to obtain bulk silicon-based composite.

[0057] Step S3: Same as step S3 in Example 1.

[0058] Step S4: Same as step S4 in Example 1.

[0059] Example 5

[0060] Step S1: Commercially available porous carbon is provided, and porous carbon with a nano-Al2O3 ceramic layer on the surface is obtained by impregnation method. The thickness of the nano-Al2O3 ceramic layer is 5 nm. The resulting porous carrier is denoted as porous carbon-Al2O3(5)-1. The specific surface area of ​​porous carbon-Al2O3(5)-1 is 545 m². 2 / g, pore volume is 0.61cm 3 / g; Porous carbon-Al2O3(5)-1 contains micropores, mesopores and macropores, and their pore volumes account for 26%, 64% and 10% of the total pore volume, respectively.

[0061] Step S2: Provide d50 For 100nm, d max <500μm silicon particles were mixed with porous carbon-Al2O3(5)-1 and silicon particles, and ball milled to obtain a mixture of porous carbon-Al2O3(5)-1-silicon that was uniformly mixed at the submicron scale. The obtained mixture of porous carbon-Al2O3(5)-1-silicon was subjected to high vacuum treatment, and then treated at 1200℃ under Ar atmosphere for 5h to obtain a bulk silicon-based composite material infiltrated by liquid phase silicon in the pores of porous carbon-Al2O3(5)-1.

[0062] Step S3: Same as step S3 in Example 1.

[0063] Step S4: Same as step S4 in Example 1.

[0064] Example 6

[0065] Step S1: Commercially available porous carbon is provided, and porous carbon with a nano-Al2O3 ceramic layer on the surface is obtained by impregnation method. The thickness of the nano-Al2O3 ceramic layer is 5 nm. The resulting porous carrier is denoted as porous carbon-Al2O3(5)-2. The specific surface area of ​​porous carbon-Al2O3(5)-2 is 1582 m². 2 / g, pore volume is 0.87cm 3 / g; Porous carbon-Al2O3(5)-2 contains micropores, mesopores and macropores, and their pore volumes account for 58%, 27% and 15% of the total pore volume, respectively.

[0066] Step S2: Same as step S2 in Example 5.

[0067] Step S3: Same as step S3 in Example 1.

[0068] Step S4: Same as step S4 in Example 1.

[0069] Example 7

[0070] Step S1: Commercially available porous carbon is provided, and porous carbon with a nano-Al2O3 ceramic layer on the surface is obtained by impregnation method. The thickness of the nano-Al2O3 ceramic layer is 5 nm. The resulting porous carrier is denoted as porous carbon-Al2O3(5)-3. The specific surface area of ​​porous carbon-Al2O3(5)-3 is 2159 m². 2 / g, pore volume 0.82cm 3 / g; Porous carbon-Al2O3(5)-3 contains micropores, mesopores and macropores, and their pore volumes account for 89%, 9% and 2% of the total pore volume, respectively.

[0071] Step S2: Same as step S2 in Example 5.

[0072] Step S3: Same as step S3 in Example 1.

[0073] Step S4: Same as step S4 in Example 1.

[0074] Example 8

[0075] Step S1: Same as step S1 in Example 6.

[0076] Step S2: Melt commercially available silicon powder at 1450℃ to obtain liquid silicon; preheat the porous carbon-Al2O3(5)-2 obtained in step S1 at 1450℃ and keep it at that temperature for 1 hour; then inject the obtained liquid silicon into the porous carbon-Al2O3(5)-2 in a high vacuum state and keep it at atmospheric pressure for 3 hours to obtain a bulk silicon-based composite.

[0077] Step S3: Same as step S3 in Example 1.

[0078] Step S4: Same as step S4 in Example 1.

[0079] Example 9

[0080] Step S1: Same as step S1 in Example 6.

[0081] Step S2: Melt commercially available silicon powder at 1450°C to obtain liquid silicon. Preheat the porous carbon-Al2O3(5)-2 obtained in step S1 at 1450°C for 1 hour. Then inject the obtained liquid silicon into the porous carbon-Al2O3(5)-2 under high vacuum and keep it at 1 MPa for 3 hours to obtain bulk silicon-based composite.

[0082] Step S3: Same as step S3 in Example 1.

[0083] Step S4: Same as step S4 in Example 1.

[0084] Example 10

[0085] Step S1: Commercially available porous carbon is provided, and a porous carbon with a nano-ZrO2 ceramic layer on the surface is obtained by impregnation method. The thickness of the nano-ZrO2 ceramic layer is 0.5 nm, and the resulting porous carrier is denoted as porous carbon-ZrO2(0.5). The specific surface area of ​​porous carbon-ZrO2(0.5) is 1425 m². 2 / g, pore volume is 0.98cm 3 / g; Porous carbon-ZrO2(0.5) contains micropores, mesopores and macropores, with their pore volumes accounting for 46%, 39% and 15% of the total pore volume, respectively.

[0086] Step S2: Provide d 50 For 100nm, d maxSilicon particles <500μm were mixed with porous carbon-ZrO2(0.5) and then ball-milled to obtain a uniformly mixed porous carbon-ZrO2(0.5)-silicon mixture at the submicron scale. The obtained porous carbon-ZrO2(0.5)-silicon mixture was subjected to high vacuum treatment. Then, the porous carbon-ZrO2(0.5)-silicon mixture was treated at 1200℃ for 10h under Ar atmosphere to obtain a bulk silicon-based composite material infiltrated by liquid phase silicon in the porous carbon-ZrO2(0.5) channels.

[0087] Step S3: The bulk silicon-based composite obtained in step S2 is crushed and classified using an air jet mill to obtain the median particle size d. 50 The silicon-based composite particles were 12 μm in size. The resulting particles were then placed in a tube furnace and heated to 700 °C at 2 °C / min in a He atmosphere. The temperature was then changed to a 5% C3H8-He mixture and held at 700 °C for 0.5 h. The mixture was then naturally cooled to room temperature in a He atmosphere to obtain the silicon-based composite material with a carbon coating thickness of 2 nm.

[0088] Step S4: The silicon-based composite material obtained in step S3 is subjected to high-temperature rapid cooling treatment in a high-temperature rapid cooling device. Specifically, it is heated in a dynamic heating chamber in an N2 atmosphere at a heating temperature of 1350℃ for 2.8 hours. Liquid argon is used as the cooling medium to make full contact with the silicon-based composite material at 1380℃ in the rapid cooling chamber, so that the temperature of the silicon-based composite material is rapidly reduced to 100℃, thereby obtaining nano-silicon-based composite material.

[0089] Example 11

[0090] Step S1: Commercially available porous carbon is provided, and porous carbon with a nano-TiO2 ceramic layer on the surface is obtained by impregnation method. The thickness of the nano-TiO2 ceramic layer is 10 nm, and the resulting porous carrier is denoted as porous carbon-TiO2 (10). The specific surface area of ​​porous carbon-TiO2 (10) is 1610 m². 2 / g, pore volume 0.79cm 3 / g; Porous carbon-TiO2(10) contains micropores, mesopores and macropores, and their pore volumes account for 68%, 24% and 8% of the total pore volume, respectively.

[0091] Step S2: Provide d 50 For 100nm, d max<500μm silicon particles, porous carbon-TiO2(10) and silicon particles are mixed, and a mixture of porous carbon-TiO2(10)-silicon with uniform mixing at the submicron scale is obtained by ball milling; the obtained mixture of porous carbon-TiO2(10)-silicon is subjected to high vacuum treatment; then the mixture of porous carbon-TiO2(10)-silicon is treated at 1600℃ for 3h under Ar atmosphere to obtain a bulk silicon-based composite material infiltrated by liquid phase silicon in the pores of porous carbon-TiO2(10).

[0092] Step S3: The bulk silicon-based composite obtained in step S2 is crushed and classified using an air jet mill to obtain the median particle size d. 50 The resulting silicon-based composite particles were 20 μm in diameter. The particles were then placed in a tube furnace and heated to 700 °C at 2 °C / min in an Ar atmosphere. The temperature was then changed to a 5% C2H2-Ar mixture and held at 700 °C for 10 h. The mixture was then naturally cooled to room temperature in an Ar atmosphere to obtain a silicon-based composite material with a carbon coating thickness of 50 nm.

[0093] Step S4: The silicon-based composite material obtained in step S3 is subjected to high-temperature rapid cooling treatment in a high-temperature rapid cooling device. Specifically, it is heated in a dynamic heating chamber in an N2 atmosphere at a heating temperature of 1400℃ for 3 hours. Liquid argon is used as the cooling medium to make full contact with the silicon-based composite material at 1400℃ in the rapid cooling chamber, so that the temperature of the silicon-based composite material is rapidly reduced to 300℃, thereby obtaining nano-silicon-based composite material.

[0094] Electrode and half-cell preparation and electrochemical performance testing methods:

[0095] CR2032 coin cells were fabricated using conventional methods with electrode sheets comprising the composite materials of each embodiment and comparative example, and their electrical performance was tested. The CR2032 coin cells were assembled in a glove box, using a lithium metal sheet as the counter electrode, a polypropylene microporous membrane as the separator, and LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC = 1:1), with a LiPF6 concentration of 1 mol / L. Charge-discharge tests were performed on the cells using a LAND battery testing system.

[0096] (1) Specific capacity and initial coulombic efficiency test: After the CR2032 coin cell was left to stand for 6 hours, it was discharged at 0.05C to 0.005V, and then discharged at 0.01C to 0.005V; after standing for 5 minutes, it was charged at a constant current of 0.05C to 1.5V; the ratio of the initial delithiation capacity to the initial lithium insertion capacity is the initial coulombic efficiency of the battery. After standing for 5 minutes, the above charge and discharge steps were repeated twice.

[0097] (2) Capacity retention rate test: After the CR2032 button cell completes the above specific capacity and initial coulombic efficiency tests, it is discharged to 0.005V at 0.25C; after standing for 5 minutes, it is charged to 1.5V at a constant current of 0.25C, and cycled 50 times. The capacity retention rate is calculated by dividing the specific capacity of the 50th cycle by the charging capacity of the 1st cycle by 100%.

[0098] The basic physical properties and electrochemical performance test results of the nano-silicon-based composite materials prepared according to the method in the examples are shown in Table 1.

[0099] Table 1

[0100]

[0101] Examples 1-4 use porous oxide ceramics as porous supports. Due to acid leaching to remove some oxide components, the silicon content is high, and the contents of other elements are also relatively high. Therefore, the electrodes containing the resulting nano-silicon-based composite material have very high specific capacity, all greater than 2400 mAh / g. However, the initial efficiency is relatively low, with an initial coulombic efficiency of less than 90% at 1.5V and a capacity retention rate of more than 80% after 50 cycles. Due to the high silicon content, while having high capacity, its cycle capacity retention rate is lower than that of nano-silicon-based composite materials using porous carbon with a nano-oxide ceramic layer on the surface as a support. Examples 5-11 use porous carbon with a nano-oxide ceramic layer on the surface as a porous support. The materials exhibit high specific capacity, all greater than 1900 mAh / g, an initial coulombic efficiency of more than 91% at 1.5V, and a capacity retention rate of more than 93% after 50 cycles.

[0102] As can be seen from the above description, the embodiments of this application achieve the following technical effects:

[0103] (1) The silicon powder, which is cheap, readily available and non-toxic in industry, is used directly as the silicon source and combined with a porous carrier to obtain nano-silicon-based composite materials, thus avoiding the problems of high cost and significant safety risks in the preparation of silicon-based composite materials by chemical vapor deposition.

[0104] (2) Molten Si is filled into the porous structure of a porous carrier by liquid-phase infiltration. The size of Si is limited by the pore structure of the porous carrier and is uniformly dispersed within the pores. After crushing, the exposed silicon particles are protected by a carbon coating layer. On this basis, high-temperature melting and rapid cooling fine crystallization treatment are carried out. The silicon in the resulting silicon-based composite material exists in the form of nano-amorphous silicon. When used as a negative electrode material for lithium-ion batteries, the nano-amorphous silicon exhibits a small degree of volume expansion during lithium intercalation and is isotropic. It also has good structural reversibility and mechanical stability during charge and discharge, showing good cycle performance.

[0105] (3) The preparation process of nano-silicon-based composite materials forms a thin layer of SiC or a composite thin layer of SiC and Si3N4 on the surface of silicon particles, which can isolate silicon in the composite electrode from the electrolyte, reduce side reactions, and help form a stable SEI film; and has the effect of binding expansion and improving the strength of the material during the silicon insertion and extraction process, so that the structural stability of the composite electrode is enhanced in charge and discharge cycles, thereby improving the cycle stability of the material.

[0106] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. 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 nano-silicon-based composite materials, characterized in that, The preparation method is specifically as follows: Step S1: Provide a porous support, wherein the porous support is porous carbon with a nano-oxide ceramic layer on its surface; Step S2: Melt silicon powder at 900~1600 °C and penetrate the molten silicon into the pores of the porous carrier described in step S1 to obtain a bulk silicon-based composite. Step S3: The bulk silicon-based composite obtained in step S2 is crushed and classified to obtain the median particle size. d 50 Silicon-based composite particles with a diameter of 1~50 μm were surface-coated to obtain silicon-based composite materials. Step S4: The silicon-based composite material obtained in step S3 is heated in an inert atmosphere at a temperature of 1000~1400 ℃ and held for 0.5~5 h. Then, a cooling medium is introduced to reduce the temperature of the heated silicon-based composite material to 0~300 ℃ at an extremely rapid cooling rate, thereby obtaining a nano-silicon-based composite material.

2. The method for preparing the nano-silicon-based composite material according to claim 1, characterized in that, The nano-oxide ceramic layer on the porous carbon surface in step S1 is selected from one or more of Al2O3, SiO2, MgO, CaO, BaO, TiO2, ZnO, Y2O3, ZrO2, Nb2O5, La2O3, Ce2O3, and CeO2, and optionally from one or more of Li2O, Na2O, K2O, B2O3, and P2O5.

3. The method for preparing the nano-silicon-based composite material according to claim 1, characterized in that, The porous carbon with a nano-oxide ceramic layer on its surface described in step S1 has a thickness of 0.5~10 nm.

4. The method for preparing the nano-silicon-based composite material according to claim 1, characterized in that, The specific surface area of ​​the porous carrier mentioned in step S1 is 50~3000 m². 2 / g, pore volume 0.2~3.0 cm³ 3 / g.

5. The method for preparing the nano-silicon-based composite material according to claim 1, characterized in that, Step S2 specifically involves melting silicon powder at 1400~1600 ℃, injecting the resulting liquid silicon into a porous carrier under high vacuum, and maintaining it under a certain pressure for 0.5~10 h to obtain a bulk silicon-based composite. The porous carrier is preheated at 900~1600 ℃ for 0.5~5 h. And / or: a porous carrier is mixed with nano- or micro-sized silicon particles, and a porous carrier-silicon mixture uniformly mixed at the submicron scale is obtained by mechanical grinding and / or ball milling; the obtained porous carrier-silicon mixture is subjected to high vacuum treatment, and then the porous carrier-silicon mixture is treated at 900~1600 °C for 0.5~10 h under Ar and / or He atmosphere to obtain a bulk silicon-based composite in which liquid-phase silicon permeates into the pores of the porous carrier.

6. The method for preparing the nano-silicon-based composite material according to claim 1, characterized in that, The thickness of the surface coating layer in step S3 is 2~300 nm.

7. The method for preparing the nano-silicon-based composite material according to claim 1, characterized in that, Step S3 involves acid washing the silicon-based composite particles before surface coating.

8. The method for preparing the nano-silicon-based composite material according to claim 1, characterized in that, The cooling medium in step S4 is one or more of liquid nitrogen, liquid helium, liquid neon, liquid argon, liquid krypton, and liquid xenon.

9. The method for preparing the nano-silicon-based composite material according to claim 1, characterized in that, The cooling rate described in step S4 is greater than 1000 ℃ / s.

10. A nano-silicon-based composite material, characterized in that, The nano-silicon-based composite material is a nano-silicon-based composite material prepared by the preparation method described in claim 1.

11. The nano-silicon-based composite material according to claim 10, characterized in that, In the nano-silicon-based composite material, the mass percentage of silicon is 10% to 90%, the mass percentage of carbon is 5% to 85%, and the mass percentage of other elements is 0.5% to 5%, including oxygen.

12. The nano-silicon-based composite material according to claim 10, characterized in that, The specific surface area of ​​the nano-silicon-based composite material is 0.1~50 m². 2 / g, total pore volume is 0.001~0.05 cm³ 3 / g.

13. The negative electrode, characterized in that, The negative electrode comprises a negative electrode active material, which comprises the nano-silicon-based composite material prepared by the preparation method of any one of claims 1 to 9, or the nano-silicon-based composite material as described in any one of claims 10 to 12.

14. A battery, characterized in that, The battery comprises a positive electrode, a negative electrode, a separator, an electrolyte, and an aluminum-plastic film. The negative electrode comprises a negative electrode active material, which comprises the nano-silicon-based composite material prepared by the preparation method of any one of claims 1 to 9, or the nano-silicon-based composite material as described in any one of claims 10 to 12.

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