A nanometer silicon / mesocarbon microbead composite material, a preparation method and application thereof

Abstract

The application belongs to the technical field of secondary battery negative electrode materials, and particularly relates to a nano-silicon / mesocarbon microsphere composite material and a preparation method and application thereof. The preparation method of the nano-silicon / mesocarbon microsphere composite material provided by the application comprises the following steps: mixing nano-silicon and a carbon conductive agent to obtain a composite powder; mixing the composite powder and a first carbon source, and performing a first heat polycondensation reaction under a protective atmosphere and in a stirring state, and crushing to obtain a primary composite mesophase powder; mixing the primary composite mesophase powder and a second carbon source, and performing a second heat polycondensation reaction under a protective atmosphere and in a stirring state to obtain a secondary coated nano-silicon / mesocarbon microsphere precursor; pre-oxidizing and carbonizing the secondary coated nano-silicon / mesocarbon precursor to obtain the nano-silicon / mesocarbon microsphere composite material; the nano-silicon / mesocarbon microsphere composite material can effectively buffer the expansion stress of nano-silicon, inhibit the dissolution of nano-silicon, and has excellent charge and discharge cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery anode material technology, specifically relating to a nano-silicon / mesophase carbon microsphere composite material, its preparation method, and its application. Background Technology

[0002] With the rapid development of industries such as electric vehicles that place higher demands on rechargeable batteries, graphite-based anodes, currently the most widely used commercial anode in the lithium-ion battery industry, are limited by the theoretical specific capacity of carbon-based materials (LiC6, 372 mAh / g), and their energy density can no longer meet the demand for increased cell energy density. Silicon-based anode materials, on the other hand, have a theoretical specific capacity of up to 3579 mAh / g at room temperature, showing great potential to break through the energy density limitations of traditional anode materials. They also offer advantages such as lower risk of lithium plating during charging, greater safety, and abundant reserves, making them a promising candidate for the next generation of high-energy-density lithium-ion battery anode materials.

[0003] However, silicon undergoes significant volume expansion and contraction (>300%) during lithium insertion / extraction, leading to silicon particle pulverization, electrode structure damage, electrochemical performance failure, and rapid capacity decay. Mesophase carbon microspheres, a relatively mature graphite-based anode material, are widely used in the lithium-ion battery industry, exhibiting a reversible specific capacity between 300 and 340 mAh / g and possessing excellent carbon layer structure and lithium insertion / extraction performance. Existing technologies include methods for combining mesophase carbon microspheres with silicon materials to alleviate silicon volume expansion and improve the reversible specific capacity and cycle performance of silicon-carbon anode materials, but there is still room for improvement. For example, existing technologies disclose a silicon-carbon anode material based on mesophase carbon microspheres. However, this requires modification of the mesophase carbon microspheres with inorganic acids during preparation, increasing costs and polluting the environment. Furthermore, simply coating the surface of the mesophase carbon microspheres with a layer of nano-silicon particles limits the silicon content that can be loaded. A magnesothermic reduction reaction is also required after coating the amorphous carbon, making the process complex. Moreover, this silicon-carbon anode material, compared to single mesophase carbon microspheres, only increases the reversible capacity by 150-600 mAh / g, which translates to a maximum reversible capacity of approximately 950 mAh / g, failing to break the 1000 mAh / g limit. Existing technologies also disclose a method for preparing silicon mesophase carbon microspheres for lithium-ion batteries using a pitch thermal polycondensation reaction. This method simply involves uniformly mixing pitch and silicon, followed by thermal polycondensation and carbonization. If used to prepare materials with high silicon content, this method would affect the melting and growth of the pitch-polymerized mesophase. Simultaneously, silicon particles are easily unevenly dispersed within the mesophase carbon microspheres, and some silicon particles may be exposed on the particle surface and undergo dissolution reactions with the electrolyte, affecting the cycle life of the battery material. The prior art also discloses a shell-structured silicon / mesophase carbon microsphere composite material, which first organically coats nano-silicon, then blends it with mesophase pitch under heat, and then granulates it into spheres in a silicone oil medium using a suspension high-temperature process. The composite material is obtained after subsequent processing. The process is complex and difficult to control, making it difficult to prepare on a large scale. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a nano-silicon / mesophase carbon microsphere composite material, its preparation method, and its application. The preparation of a silicon-carbon anode material is achieved by using two thermal polycondensation reactions to uniformly embed nano-silicon / carbon conductive agent into the mesophase carbon microsphere structure. The process is simple and applicable to the preparation of high silicon loading composite materials. It can effectively buffer the expansion stress of nano-silicon and inhibit the dissolution of nano-silicon. The resulting nano-silicon / mesophase carbon microsphere composite material has excellent charge-discharge cycle performance.

[0005] To this end, the present invention provides the following technical solution.

[0006] In a first aspect, the present invention provides a method for preparing a nano-silicon / mesophase carbon microsphere composite material, comprising the following steps: S1: Mix nano-silicon and carbonaceous conductive agent to obtain composite powder; S2: Mix the composite powder and the first carbon source, carry out the first thermal condensation reaction under a protective atmosphere and stirring, and then crush to obtain a primary composite intermediate phase powder. S3: Mix the primary composite mesophase powder with the second carbon source, and carry out a second thermal polycondensation reaction under a protective atmosphere and stirring. Separate the mixture to obtain a secondary coated nano-silicon / mesophase microsphere precursor. S4: The secondary coated nano-silicon / mesophase precursor is pre-oxidized and carbonized to obtain a nano-silicon / mesophase carbon microsphere composite material.

[0007] The method for preparing nano-silicon / mesophase carbon microsphere composite material provided by the present invention typically, but not limited to, includes a step of sieving the nano-silicon / mesophase carbon microsphere composite material; the sieving method includes sieving, and the particle size range of the nano-silicon / mesophase carbon microsphere composite material obtained by sieving is 1~25μm.

[0008] In one optional embodiment, in S1, the mass ratio of nano-silicon to carbonaceous conductive agent is 100:0.1~3.

[0009] In one optional embodiment, in step S2, the mass ratio of the composite powder to the first carbon source is 0.5~6.5:10.

[0010] In one optional embodiment, in step S3, the mass ratio of the primary composite mesophase powder to the second carbon source is 1 to 4:10.

[0011] In one optional embodiment, in S2, the temperature of the first thermal polycondensation reaction is 300~450℃, the holding time is 1~10h, and the pressure is 0.1~10MPa; typically, without limitation, the heating rate of the first thermal polycondensation reaction is 1~5℃ / min.

[0012] In one optional embodiment, during the first thermopolymerization reaction in S2, the stirring rate is 1000~1500 r / min.

[0013] In one optional embodiment, the particle size of the primary composite mesophase powder is 1~30μm. In S3, the method for pulverizing to obtain the primary composite mesophase powder is not specifically specified; pulverization to the target particle size range is sufficient. Typically, and not limited to this, the pulverization method includes one or a combination of air jet milling, mechanical grinding, ball milling, sieving, and air classification.

[0014] In an optional embodiment, step S2 includes the following steps: mixing the composite powder and a first carbon source, stirring at 1500-2500 r / min for 0.5-1 h at 120-240°C to ensure uniform dispersion, thereby obtaining a composite melt; heating the composite melt to 380-450°C under a protective atmosphere and a pressure of 0.1-10 MPa, and stirring at 1000-1500 r / min for 2-10 h to carry out a first thermal polycondensation reaction; cooling and then pulverizing to obtain a primary composite mesophase powder. In this step, the first carbon source is not mesophase asphalt.

[0015] In an optional embodiment, step S2 includes the following steps: mixing the composite powder and a first carbon source, heating to 300-380°C under a protective atmosphere and a pressure of 0.1-10 MPa, stirring at a speed of 1000-1500 r / min for 1-2 hours to disperse the mixture evenly, performing a first thermal polycondensation reaction, cooling, and pulverizing to obtain a primary composite mesophase powder. In this step, the first carbon source is mesophase pitch. The mesophase pitch includes, but is not limited to, at least one of pitch or other polycyclic aromatic hydrocarbon thermal polycondensation products, with a softening point of 180-280°C.

[0016] In one optional embodiment, in step S3, the temperature of the second thermal polycondensation reaction is 350~430℃, the holding time is 1~5h, and the pressure is 0.1~10MPa; typically, without limitation, the heating rate of the second thermal polycondensation reaction is 1~5℃ / min.

[0017] In one optional embodiment, during the second thermopolymerization reaction in S3, the stirring rate is 500~1000 r / min.

[0018] In one optional embodiment, in step S4, the pre-oxidation is carried out in an oxidizing atmosphere at a temperature of 200-350°C, a heating rate of 1-5°C / min, and a holding time of 0.5-4h. Typically, and not limited to this, the gas source for the oxidizing atmosphere includes, but is not limited to, one or more combinations of dry air, oxygen, and an oxygen-inert gas mixture, with a gas flow rate of 0.1-2 L / min.

[0019] In one optional embodiment, in step S4, carbonization is carried out in a protective atmosphere, the carbonization temperature is 700~1000℃, the heating rate is 1~5℃ / min, and the holding time is 1~5h.

[0020] In an optional embodiment, in S1, the method of mixing the nano-silicon and the carbonaceous conductive agent includes dispersion.

[0021] In one alternative embodiment, S2, after the second thermal polycondensation reaction, further includes a step of separating the secondary coated nano-silicon / mesophase microsphere precursor from the carbon source.

[0022] In one alternative embodiment, the dispersion method includes at least one of ball milling, ultrasonication, and sand milling.

[0023] In one alternative implementation, the dispersion time is 1 to 3 hours.

[0024] In one alternative implementation, the separation method includes extraction with an organic solvent, or solid-liquid separation.

[0025] In one optional embodiment, the organic solvent includes at least one selected from tetrahydrofuran, toluene, pyridine, quinoline, dichloromethane, and trichloroethylene. Typically, but not limited to, the organic solvent may also be a common product used in asphalt separation, such as asphalt wash oil. The main organic solvent used and the resulting extraction waste liquid can be recycled and reused in a closed loop, resulting in low pollutant emissions and an environmentally friendly process.

[0026] In one alternative embodiment, the solid-liquid separation method includes at least one of filtration, sedimentation, and centrifugation.

[0027] In one alternative embodiment, the nano-silicon includes at least one of elemental silicon, porous silicon, and silicon suboxide.

[0028] In one alternative embodiment, the average particle size of the nano-silicon ranges from 10 to 150 nm.

[0029] In one optional embodiment, the porous silicon has an average particle size range of 100-150 nm, an average pore size of 0.7-5 nm, and a specific surface area of ​​50-150 m². 2 / g.

[0030] In one optional embodiment, the size of the carbonaceous conductive agent can be a conventional size in the art, such as the original average particle size of granular carbonaceous conductive agent ≤1μm; the average tube diameter of strip-shaped carbonaceous conductive agent ≤100nm; the average length of strip-shaped carbonaceous conductive agent ≤15μm; and strip-shaped carbonaceous conductive agents include, but are not limited to, fibrous carbonaceous conductive agents and tubular carbonaceous conductive agents.

[0031] In one optional embodiment, the size of the carbonaceous conductive agent can be a conventional size in the art, such as a particle size of granular carbonaceous conductive agent ≤10μm, a tube diameter of strip-shaped carbonaceous conductive agent ≤1μm, and a length of strip-shaped carbonaceous conductive agent ≤15μm.

[0032] In one optional embodiment, the first carbon source and the second carbon source comprise asphalt, wherein the softening point of the asphalt is 60~280℃.

[0033] In one optional embodiment, the first carbon source and the second carbon source each independently include at least one of coal tar pitch, petroleum pitch, impregnated pitch, mesophase pitch, naphthalene-based pitch, and ethylene tar.

[0034] In one optional embodiment, the protective atmosphere includes at least one of a nitrogen atmosphere, a helium atmosphere, and an argon atmosphere.

[0035] In one optional embodiment, the preparation method of the nano-silicon / mesophase carbon microsphere composite material provided by the present invention includes the following steps: (1) Mix nano-silicon and carbon conductive agent in a mass ratio of 100:0.1~3, disperse for 1~3h to depolymerize nano-silicon, and fully mix nano-silicon and carbon conductive agent to obtain composite powder.

[0036] (2) The composite powder and the first carbon source are mixed at a mass ratio of 0.5~6.5:10, heated to 120~240℃ to melt the first carbon source, and stirred at 1500~2500r / min for 0.5~1h to disperse it evenly, thus obtaining a composite melt. Under a protective atmosphere and a pressure of 0.1~10MPa, the composite melt is stirred at a rate of 1000~1500r / min, and the temperature is increased to 380~450℃ at a rate of 1~5℃ / min. The temperature is held for 2~10h to carry out the first thermal polycondensation reaction. After cooling, the mixture is pulverized to obtain a primary composite mesophase powder, which is then sieved to a particle size range of 1~30μm. In this step, the first carbon source is not mesophase pitch.

[0037] (3) The primary composite mesophase powder and the second carbon source are mixed at a mass ratio of 1~4:10. Under a protective atmosphere and a pressure of 0.1~10MPa, the mixture is stirred at a rate of 500~1000r / min and heated to 350~430℃ at a rate of 1~5℃ / min. The mixture is kept at this temperature for 1~5h to carry out the second thermal polycondensation reaction. The mixture after the reaction is extracted with an organic solvent until it is colorless. The solid-liquid separation yields the secondary coated nano-silicon / mesophase microsphere precursor.

[0038] (4) In an oxidizing atmosphere, the secondary coated nano-silicon / mesophase precursor is heated to 200-350℃ at 1-5℃ / min and held for 0.5-4h for pre-oxidation; then it is transferred to a protective atmosphere and heated to 700-1000℃ at 1-5℃ / min and held for 1-5h for carbonization to obtain nano-silicon / mesophase carbon microsphere composite material.

[0039] In one optional embodiment, the preparation method of the nano-silicon / mesophase carbon microsphere composite material provided by the present invention includes the following steps: (1) Mix nano-silicon and carbon conductive agent at a mass ratio of 100:0.1~3, disperse for 1~3h to depolymerize nano-silicon, and fully mix nano-silicon and carbon paper conductive agent to obtain composite powder.

[0040] (2) The composite powder and the first carbon source are mixed at a mass ratio of 0.5~6.5:10. Under a protective atmosphere and a pressure of 0.1~10MPa, the mixture is heated to 300~380℃ to melt the first carbon source. The mixture is stirred at a rate of 1000~1500r / min for 1~2h to disperse it evenly, and the first thermal polycondensation reaction is carried out. After cooling and pulverizing, a primary composite mesophase powder is obtained, and the particle size is sieved to a range of 1~30μm. In this step, the first carbon source is mesophase pitch. The mesophase pitch includes, but is not limited to, at least one of pitch or other polycyclic aromatic hydrocarbon thermal polycondensation products, with a softening point of 180~280℃.

[0041] (3) The primary composite mesophase powder and the second carbon source are mixed at a mass ratio of 1~4:10. Under a protective atmosphere and a pressure of 0.1~10MPa, the mixture is stirred at a rate of 500~1000r / min and heated to 350~430℃ at a rate of 1~5℃ / min. The mixture is kept at this temperature for 1~5h to carry out the second thermal polycondensation reaction. The mixture after the reaction is extracted with an organic solvent until it is colorless. The solid-liquid separation yields the secondary coated nano-silicon / mesophase microsphere precursor.

[0042] (4) In an oxidizing atmosphere, the secondary coated nano-silicon / mesophase precursor is heated to 200-350℃ at 1-5℃ / min and held for 0.5-4h for pre-oxidation; then it is transferred to a protective atmosphere and heated to 700-1000℃ at 1-5℃ / min and held for 1-5h for carbonization to obtain nano-silicon / mesophase carbon microsphere composite material.

[0043] Secondly, the present invention also provides a nano-silicon / mesophase carbon microsphere composite material prepared by the above preparation method.

[0044] Thirdly, the present invention also provides the application of the above-mentioned nano-silicon / mesophase carbon microsphere composite material as a negative electrode material for secondary batteries.

[0045] In one alternative embodiment, the secondary battery comprises a lithium-ion battery.

[0046] The technical solution of this invention has the following advantages: The preparation method of the nano-silicon / mesophase carbon microsphere composite material provided by the present invention includes the following steps: S1: Mixing nano-silicon and carbonaceous conductive agent to obtain composite powder; S2: Mixing the composite powder and a first carbon source, and performing a first thermal condensation reaction under a protective atmosphere and stirring, followed by pulverization to obtain a primary composite mesophase powder; S3: Mixing the primary composite mesophase powder with a second carbon source, and performing a second thermal condensation reaction under a protective atmosphere and stirring to obtain a secondary coated nano-silicon / mesophase microsphere precursor; S4: Pre-oxidizing and carbonizing the secondary coated nano-silicon / mesophase precursor to obtain the nano-silicon / mesophase carbon microsphere composite material. The preparation method provided by this invention has a short process, widely available raw materials, low cost, and is easy to scale up. It uses a primary composite mesophase powder containing nano-silicon, carbonaceous conductive agent, and a first carbon source obtained by primary thermal polycondensation as the core, and prepares a nano-silicon / mesophase carbon microsphere composite material with a mesophase carbon layer coating and a nano-silicon / carbonaceous conductive agent uniformly embedded in the mesophase carbon microsphere structure through an in-situ secondary thermal polycondensation reaction. The conductivity and mechanical properties of the material are further enhanced, which can effectively buffer the expansion stress of nano-silicon, inhibit the dissolution of nano-silicon, and have excellent charge-discharge cycle performance.

[0047] Using a two-stage thermal polycondensation reaction, a higher and more uniform silicon loading distribution can be achieved in the nano-silicon / mesophase carbon microsphere composite material. This high silicon loading and uniform distribution results in a higher and more stable reversible specific capacity. Furthermore, it leads to a superior spherical structure, resulting in a more uniform and consistent particle size distribution of the nano-silicon / mesophase carbon microspheres. The first thermal polycondensation achieves uniform composite formation of the mesophase carbon source, nano-silicon, and carbonaceous conductive agent. The initial stage of the second thermal polycondensation provides a flow medium for the primary composite mesophase powder, softening it and causing it to shrink into spheres under surface tension, thus obtaining the primary composite mesophase microspheres. The later stage of the second thermal polycondensation achieves secondary carbon coating with the primary composite mesophase microspheres as the core. This process has better compatibility than a simple heterogeneous nucleation process, forming a more uniform secondary carbon coating structure and effectively suppressing the secondary dissolution reaction between silicon and the electrolyte. The addition of the carbonaceous conductive agent improves the conductivity of the nano-silicon / mesophase carbon microsphere composite material while significantly enhancing its mechanical properties, providing a superior buffer structure for silicon volume expansion. In nano-silicon / mesophase carbon microsphere composite materials, nano-silicon particles and carbonaceous conductive agent particles are uniformly combined to form an excellent conductive network, which can significantly improve the rate performance of the material. Attached Figure Description

[0048] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0049] Figure 1 This is a SEM image of the nano-silicon / mesophase carbon microsphere composite material obtained in Example 1 of this invention; Figure 2 This is a SEM image of the carbon microsphere material obtained in Comparative Example 1 of this invention; Figure 3 This is a SEM image of the carbon microsphere material obtained in Comparative Example 4 of this invention; Figure 4 This is the first charge-discharge curve of the corresponding half-cell of the final product obtained in Embodiment 1 of the present invention. Detailed Implementation

[0050] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0051] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0052] Example 1 This embodiment provides a nano-silicon / mesophase carbon microsphere composite material and its preparation method, including the following steps: (1) Take nano-silicon (nano-silicon powder with an average particle size of 80nm) and carbonaceous conductive agent (conductive carbon black with an average particle size of 25nm, the same below) at a mass ratio of 100:1, and ball mill them at a high speed of 600r / min for 1h to depolymerize the nano-silicon and carbonaceous conductive agent to form nano-silicon-carbonaceous conductive agent composite powder.

[0053] (2) The composite powder and the first carbon source (medium-temperature coal tar pitch, softening point 90℃) were mixed at a mass ratio of 2:10. The mixture was heated to 150℃ in a high-temperature reactor to melt the first carbon source. The mixture was stirred at 1800 r / min for 0.5 h to obtain a composite melt. Under an argon protective atmosphere and a pressure of 0.1 MPa, the composite melt was stirred at a rate of 1000 r / min and heated to 420℃ at a rate of 2℃ / min. The temperature was held for 3 h to carry out the first thermal polycondensation reaction. The mixture was then cooled, pulverized, and a primary composite mesophase powder was obtained. The powder was sieved to obtain a particle size range of 1~18 μm.

[0054] (3) The primary composite mesophase powder and the second carbon source (medium-temperature coal tar pitch, softening point 90℃) were mixed at a mass ratio of 1:10 and placed in a high-temperature reactor. Under an argon protective atmosphere and a pressure of 0.1MPa, the mixture was stirred at a rate of 600r / min and heated to 400℃ at a rate of 2℃ / min. The mixture was kept at this temperature for 4h to carry out the second thermal polycondensation reaction. Tetrahydrofuran was used as the organic solvent, and the mixture after the reaction was extracted to colorless using a Soxhlet extractor. The mixture was then filtered to obtain the secondary coated nano-silicon / mesophase microsphere precursor.

[0055] (4) In dry air (oxidizing atmosphere, airflow rate 0.2 L / min), the secondary coated nano-silicon / mesophase precursor was heated to 250℃ at 2℃ / min and held for 4 h for pre-oxidation; then transferred to an argon protective atmosphere and heated to 800℃ at 2℃ / min and held for 3 h for carbonization to obtain nano-silicon / mesophase carbon microsphere composite material. After being classified through a 300-mesh sieve, the sieved material was used to obtain nano-silicon / mesophase carbon microsphere composite material that can be used as silicon-carbon anode material.

[0056] The obtained nano-silicon / mesophase carbon microsphere composite material was observed using scanning electron microscopy. The resulting images are shown below. Figure 1 It can be seen that the material has a regular microsphere structure, the surface of the microsphere has a complete carbon layer structure, there are no exposed nano-silicon particles, and the nano-silicon is embedded in the interior of the mesophase carbon microspheres and its surface is relatively rough.

[0057] Example 2 This embodiment provides a nano-silicon / mesophase carbon microsphere composite material and its preparation method, including the following steps: (1) Take nano-silicon (nano-silicon powder with an average particle size of 100nm) and carbon conductive agent (carbon nanotubes with an average diameter of 10nm and an average length of 10μm, the same below) at a mass ratio of 100:1. In a ball mill jar, ball mill at a speed of 600r / min for 1h to depolymerize the nano-silicon and carbon conductive agent to form nano-silicon-carbon conductive agent composite powder.

[0058] (2) The composite powder and the first carbon source (medium-temperature coal tar pitch, softening point 90℃) were mixed at a mass ratio of 3:10. The mixture was heated to 180℃ in a high-temperature reactor to melt the first carbon source. The mixture was stirred at 2000 r / min for 0.5 h to obtain a composite melt. Under an argon protective atmosphere and a pressure of 0.1 MPa, the composite melt was stirred at a rate of 1200 r / min and heated to 400℃ at a rate of 2℃ / min. The temperature was held for 5 h to carry out the first thermal polycondensation reaction. The mixture was then cooled, pulverized, and a primary composite mesophase powder was obtained. The powder was sieved to obtain a particle size range of 1~25 μm.

[0059] (3) The primary composite mesophase powder and the second carbon source (medium-temperature coal tar pitch, softening point 90℃) were mixed at a mass ratio of 2:10 and placed in a high-temperature reactor. Under an argon protective atmosphere and a pressure of 0.1MPa, the mixture was stirred at a rate of 800r / min and heated to 420℃ at a rate of 2℃ / min. The mixture was kept at this temperature for 3h to carry out the second thermal polycondensation reaction. Tetrahydrofuran was used as the organic solvent, and the mixture after the reaction was extracted to colorless using a Soxhlet extractor. The mixture was then filtered to obtain the secondary coated nano-silicon / mesophase microsphere precursor.

[0060] (4) In dry air (oxidizing atmosphere, airflow rate 0.2 L / min), the secondary coated nano-silicon / mesophase precursor was heated to 280℃ at 5℃ / min and held for 2h for pre-oxidation; then transferred to an argon protective atmosphere and heated to 900℃ at 2℃ / min and held for 2h for carbonization to obtain nano-silicon / mesophase carbon microsphere composite material. After being classified through a 300-mesh sieve, the sieved material was used to obtain nano-silicon / mesophase carbon microsphere composite material that can be used as silicon-carbon anode material.

[0061] Example 3 This embodiment provides a nano-silicon / mesophase carbon microsphere composite material and its preparation method, including the following steps: (1) Take nano-silicon (nano-silicon powder with an average particle size of 120nm) and carbon conductive agent at a mass ratio of 100:2. The carbon conductive agent is conductive carbon black and carbon nanotubes at a mass ratio of 1:1. In a ball mill jar, ball mill at a high speed of 800r / min for 1h to depolymerize the nano-silicon and carbon conductive agent to form a nano-silicon-carbon conductive agent composite powder.

[0062] (2) The composite powder and the first carbon source (medium-temperature coal tar pitch, softening point 90℃) were mixed at a mass ratio of 4:10. The mixture was heated to 180℃ in a high-temperature reactor to melt the first carbon source. The mixture was stirred at 2000 r / min for 1 h to obtain a composite melt. Under an argon protective atmosphere and a pressure of 0.1 MPa, the composite melt was stirred at a rate of 1200 r / min and heated to 380℃ at a rate of 2℃ / min. The temperature was maintained for 6 h to carry out the first thermal polycondensation reaction. The mixture was then cooled, pulverized, and a primary composite mesophase powder was obtained. The powder was sieved to obtain a particle size range of 1~25 μm.

[0063] (3) The primary composite mesophase powder and the second carbon source (medium-temperature coal tar pitch, softening point 90℃) were mixed at a mass ratio of 3:10 and placed in a high-temperature reactor. Under an argon protective atmosphere and a pressure of 0.1MPa, the mixture was stirred at a rate of 800r / min and heated to 420℃ at a rate of 2℃ / min. The mixture was kept at this temperature for 2h to carry out the second thermal polycondensation reaction. Tetrahydrofuran was used as the organic solvent, and the mixture after the reaction was extracted to colorless using a Soxhlet extractor. The mixture was then filtered to obtain the secondary coated nano-silicon / mesophase microsphere precursor.

[0064] (4) In dry air (oxidizing atmosphere, airflow rate 0.2 L / min), the secondary coated nano-silicon / mesophase precursor was heated to 300℃ at 2℃ / min and held for 2h for pre-oxidation; then transferred to an argon protective atmosphere and heated to 900℃ at 2℃ / min and held for 2h for carbonization to obtain nano-silicon / mesophase carbon microsphere composite material. After being classified through a 300-mesh sieve, the sieved material was used to obtain nano-silicon / mesophase carbon microsphere composite material that can be used as silicon-carbon anode material.

[0065] Example 4 This embodiment provides a nano-silicon / mesophase carbon microsphere composite material and its preparation method, including the following steps: (1) Take nano-silicon suboxide (nano-silicon, average particle size of 150nm) and carbonaceous conductive agent at a mass ratio of 100:3. The carbonaceous conductive agent is conductive carbon black and nano-carbon fiber (average tube diameter of 100nm, average length of 10μm, the same below) at a mass ratio of 2:1. In a ball mill jar, ball mill at a speed of 800r / min for 1.5h to depolymerize the nano-silicon and carbonaceous conductive agent to form nano-silicon-carbonaceous conductive agent composite powder.

[0066] (2) The composite powder and the first carbon source (petroleum asphalt, softening point 80℃) were mixed at a mass ratio of 6.1:10. The mixture was heated to 150℃ in a high-temperature reactor to melt the first carbon source. The mixture was stirred at 2000 r / min for 1 h to obtain a composite melt. Under an argon protective atmosphere and a pressure of 0.2 MPa, the composite melt was stirred at a rate of 1200 r / min and heated to 380℃ at a rate of 2℃ / min. The temperature was held for 6 h to carry out the first thermal polycondensation reaction. The mixture was then cooled, pulverized, and a primary composite mesophase powder was obtained. The powder was sieved to obtain a particle size range of 1~20 μm.

[0067] (3) The primary composite mesophase powder and the second carbon source were mixed at a mass ratio of 3:10. The second carbon source was impregnated pitch powder (softening point 112℃) and ethylene tar at a mass ratio of 8:2. The mixture was placed in a high-temperature reactor and stirred at a rate of 800 r / min under an argon protective atmosphere and a pressure of 0.2 MPa. The temperature was increased to 400℃ at a rate of 2℃ / min and held for 2 h to carry out the second thermal polycondensation reaction. Tetrahydrofuran was used as the organic solvent and the mixture after the reaction was extracted to colorless using a Soxhlet extractor. The mixture was filtered and separated to obtain the secondary coated nano-silicon / mesophase microsphere precursor.

[0068] (4) In dry air (oxidizing atmosphere, airflow rate 0.2 L / min), the secondary coated nano-silicon / mesophase precursor was heated to 250℃ at 2℃ / min and held for 2h for pre-oxidation; then transferred to an argon protective atmosphere and heated to 900℃ at 2℃ / min and held for 2h for carbonization to obtain nano-silicon / mesophase carbon microsphere composite material. After being classified through a 300-mesh sieve, the sieved material was used to obtain nano-silicon / mesophase carbon microsphere composite material that can be used as silicon-carbon anode material.

[0069] Example 5 This embodiment provides a nano-silicon / mesophase carbon microsphere composite material and its preparation method, including the following steps: (1) Take nano-silicon (porous silicon, with an average particle size of 150 nm, an average pore size of 5 nm, and a specific surface area of ​​100 m²) at a mass ratio of 100:3. 2 / g), carbonaceous conductive agent, the carbonaceous conductive agent is conductive carbon black and carbon nanofiber in a mass ratio of 2:1, and is ball-milled at a high speed of 800 r / min for 1 h in a ball mill jar to depolymerize the nano-silicon and carbonaceous conductive agent to form nano-silicon-carbonaceous conductive agent composite powder.

[0070] (2) The composite powder and the first carbon source (intermediate phase pitch, softening point 180℃) are mixed at a mass ratio of 6.1:10. In a high-temperature reactor, under an argon protective atmosphere and a pressure of 0.1MPa, the mixture is heated to 330℃ to melt the first carbon source. The mixture is stirred at a rate of 1000r / min for 1.5h to carry out the first thermal polycondensation reaction. After cooling and crushing, a primary composite intermediate phase powder is obtained. The powder is then sieved to make its particle size range 1~20μm.

[0071] (3) The primary composite mesophase powder and the second carbon source (impregnated asphalt powder, softening point 112℃) were mixed at a mass ratio of 3:10 and placed in a high-temperature reactor. Under an argon protective atmosphere and a pressure of 0.1MPa, the mixture was stirred at a rate of 1000r / min and heated to 380℃ at a rate of 2℃ / min. The mixture was kept at this temperature for 2h to carry out the second thermal polycondensation reaction. Tetrahydrofuran was used as the organic solvent, and the mixture after the reaction was extracted to colorless using a Soxhlet extractor. The mixture was then filtered to obtain the secondary coated nano-silicon / mesophase microsphere precursor.

[0072] (4) In dry air (oxidizing atmosphere, airflow rate 0.2 L / min), the secondary coated nano-silicon / mesophase precursor was heated to 250℃ at 2℃ / min and held for 2h for pre-oxidation; then transferred to an argon protective atmosphere and heated to 850℃ at 2℃ / min and held for 2h for carbonization to obtain nano-silicon / mesophase carbon microsphere composite material. After being classified through a 300-mesh sieve, the sieved material was used to obtain nano-silicon / mesophase carbon microsphere composite material that can be used as silicon-carbon anode material.

[0073] Comparative Example 1 This comparative example provides a carbon microsphere material and its preparation method. Compared with Example 3, the only difference is that step (1) is not performed, and composite powder is not added in step (2).

[0074] The carbon microsphere material was observed using a scanning electron microscope, and the resulting images are shown below. Figure 2 It can be seen that it is a relatively smooth mesophase carbon microsphere structure without the embedding of nano-silicon.

[0075] Comparative Example 2 This comparative example provides a carbon microsphere material and its preparation method. The only difference from Example 3 is that, in step (1), an equal mass of nano-silicon is used to replace the carbon conductive agent.

[0076] Comparative Example 3 This comparative example provides a carbon microsphere material and its preparation method. Compared with Example 3, the only difference is that in step (1), an equal mass of carbonaceous conductive agent is used to replace nano-silicon.

[0077] Comparative Example 4 This comparative example provides a carbon microsphere material and its preparation method. Compared with Example 3, the only difference is that in step (3), no second carbon source is added and no second thermal polycondensation reaction is performed. Instead, the first composite intermediate phase powder is directly taken, and the mixture after reaction is extracted to colorless using a Soxhlet extractor with tetrahydrofuran as the organic solvent.

[0078] The carbon microsphere material was observed using a scanning electron microscope, and the resulting images are shown below. Figure 3 It can be seen that its morphology is an irregular sphere, with some nano-silicon agglomeration units exposed on the surface of the mesophase carbon microspheres, and the outer layer is not covered by mesophase carbon, so the structure is not compact.

[0079] Comparative Example 5 This comparative example provides a carbon microsphere material and its preparation method. Compared with Example 3, the only difference is that step (2) is to mix the composite powder and green mesophase carbon microspheres (D50 is 6.5μm, softening point is 320℃) at a mass ratio of 4:10, heat to 350℃ in a high-temperature reactor to soften the green mesophase carbon microspheres, stir and mix at 200r / min for 1h to obtain a primary composite mesophase powder, and sieve it to make its particle size range 1~25μm.

[0080] Experimental Example 1 The final products obtained in the examples and comparative examples were tested using a laser particle size analyzer with reference to GB / T 19077-2024 Particle Size Analysis by Laser Diffraction Method. The results are shown in Table 1.

[0081] Table 1

[0082] As shown in Table 1, the final products obtained in the embodiments of this application have smaller differences in particle sizes D10, D50, and D90, and the particle size distribution is more uniform and concentrated. However, Comparative Example 4 did not undergo a second thermal polycondensation, and Comparative Example 5 used finished mesophase carbon microspheres as green balls to replace the first carbon source, which means that Comparative Example 5 did not undergo a first thermal polycondensation. The resulting products had larger differences in D10, D50, and D90, and poor particle size distribution consistency.

[0083] Experimental Example 2 The specific steps for assembling CR2032 coin cells using the final products obtained in the examples and comparative examples are as follows: Using a lithium metal sheet as the counter electrode, the active material (the final product obtained in the examples and comparative examples), conductive carbon black, and styrene-butadiene rubber (SBR) / carboxymethyl cellulose (CMC) (SBR:CMC mass ratio of 1:1) were dispersed in deionized water at a mass ratio of 8:1:1 to prepare a slurry with a solid content of 48%. This slurry was then uniformly coated onto a Cu foil, with a coating surface density of 1.4 mg / cm². 2The working electrode was prepared by vacuum drying; the electrolyte was 1 mol / L LiPF6, and the solvent used in the electrolyte was ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1. The electrolyte also contained 5% fluoroethylene carbonate (FEC) by volume. The separator was a Celgard 2400 polypropylene microporous membrane. The counter electrode, working electrode, separator, and electrolyte were assembled into a coin cell in a glove box.

[0084] The aforementioned coin cell half-cells were connected to the Xinwei testing system. Under the conditions of a charge / discharge current of 100 mAh / g and a charge / discharge cutoff voltage of 0.005~1.5V, the specific capacity of the first charge (lithiation removal) was measured as Q1, and the specific capacity of the first discharge (lithiation insertion) was measured as Q2. After 100 cycles, the specific capacity of the 100th charge (lithiation removal) was measured as Q3. The initial coulombic efficiency was calculated as Q1 / Q2×100%, and the capacity retention rate after 100 cycles was calculated as Q3 / Q1×100%. The data for the initial charge specific capacity, initial coulombic efficiency, and capacity retention rate after 100 cycles are shown in Table 2; the first-cycle charge / discharge curves of the corresponding half-cells of the final product obtained in Example 1 are shown in Table 2. Figure 4 .

[0085] Table 2

[0086] As can be seen from Table 2, compared with the comparative examples, the final product obtained in this application has a superior cycle capacity retention rate, with a capacity retention rate of over 84.6% after 100 cycles; at the same time, the initial coulombic efficiency is also relatively excellent. Among them, the initial coulombic efficiency of Example 4 is relatively low, at 81.5%, because the nano-silicon used in Example 4 is silicon suboxide, and the coulombic efficiency of silicon suboxide is objectively low. Compared with Example 3, Comparative Example 1 does not add nano-silicon and carbonaceous conductive agent, but only carbon microspheres. Due to the absence of silicon-based materials and conductive agents, its initial coulombic efficiency and specific capacity are the lowest. Compared with Example 3, Comparative Example 2 does not add carbonaceous conductive agent; Comparative Example 3 does not add nano-silicon; the electrical properties of both are much worse than those of Example 3. Compared with Example 3, Comparative Example 4 does not add a second carbon source or perform a second thermal polycondensation. The final product is obtained by directly carbonizing the primary composite mesophase powder. Its initial coulombic efficiency and cycle capacity retention rate are relatively worse than those of Example 3. Compared with Example 3, Comparative Example 5 used finished mesophase carbon microspheres as green pellets to replace the first carbon source. The initial coulombic efficiency and specific capacity of the resulting product were worse than those of Example 3, and the cycle capacity retention rate was significantly reduced.

[0087] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a nano-silicon / mesophase carbon microsphere composite material, characterized in that, Includes the following steps: S1: Mix nano-silicon and carbonaceous conductive agent to obtain composite powder; S2: Mix the composite powder and the first carbon source, carry out the first thermal condensation reaction under a protective atmosphere and stirring, and then crush to obtain a primary composite intermediate phase powder. S3: Mix the primary composite mesophase powder with the second carbon source, and carry out a second thermal polycondensation reaction under a protective atmosphere and stirring to obtain a secondary coated nano-silicon / mesophase microsphere precursor. S4: The secondary coated nano-silicon / mesophase precursor is pre-oxidized and carbonized to obtain a nano-silicon / mesophase carbon microsphere composite material.

2. The preparation method according to claim 1, characterized in that, In S1, the mass ratio of nano-silicon to carbonaceous conductive agent is 100:0.1~3; And / or, in S2, the mass ratio of the composite powder to the first carbon source is 0.5~6.5:10; And / or, in S3, the mass ratio of the primary composite intermediate phase powder to the second carbon source is 1~4:10; And / or, in S2, the temperature of the first thermal polycondensation reaction is 300~450℃, the holding time is 1~10h, and the pressure is 0.1~10MPa; And / or, in S2, during the first thermopolymerization reaction under stirring, the stirring rate is 1000~1500 r / min; And / or, the particle size of the primary composite mesophase powder is 1~30μm.

3. The preparation method according to claim 2, characterized in that, The S2 includes the following steps: mixing the composite powder and the first carbon source, and stirring at 1500-2500 r / min for 0.5-1 h at 120-240°C to obtain the composite melt; Under a protective atmosphere and a pressure of 0.1~10MPa, the composite melt is heated to 380~450℃ and stirred at a speed of 1000~1500r / min for 2~10h to carry out the first thermal polycondensation reaction. After pulverization, a primary composite intermediate phase powder is obtained. Alternatively, S2 includes the following steps: mixing the composite powder and the first carbon source, heating to 300-380℃ under a protective atmosphere and a pressure of 0.1-10MPa, stirring at a speed of 1000-1500r / min for 1-2h to carry out the first thermal polycondensation reaction, pulverizing, and obtaining a primary composite mesophase powder.

4. The preparation method according to claim 1, characterized in that, In step S3, the temperature of the second thermal polycondensation reaction is 350~430℃, the holding time is 1~5h, and the pressure is 0.1~10MPa. And / or, in S3, during the second thermopolymerization reaction under stirring, the stirring rate is 500~1000 r / min; And / or, in S4, the pre-oxidation is carried out in an oxidizing atmosphere, the pre-oxidation temperature is 200~350℃, the heating rate is 1~5℃ / min, and the holding time is 0.5~4h; And / or, in S4, carbonization is carried out in a protective atmosphere, the carbonization temperature is 700~1000℃, the heating rate is 1~5℃ / min, and the holding time is 1~5h; And / or, in S1, the method of mixing nano-silicon and carbonaceous conductive agent includes dispersion; And / or, in S2, after the second thermal polycondensation reaction, the step of separating the secondary coated nano-silicon / mesophase microsphere precursor from the carbon source is also included.

5. The preparation method according to claim 4, characterized in that, In S1, the dispersion method includes at least one of ball milling, ultrasonication, and sand milling; And / or, in S1, the dispersion time is 1~3h; And / or, in S2, the separation method includes extraction with an organic solvent, or solid-liquid separation.

6. The preparation method according to claim 5, characterized in that, The organic solvent includes at least one of tetrahydrofuran, toluene, pyridine, quinoline, dichloromethane, and trichloroethylene; And / or, the solid-liquid separation method includes at least one of filtration, sedimentation, and centrifugation.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The nano-silicon includes at least one of elemental silicon, porous silicon, and silicon suboxide. And / or, the average particle size of the nano-silicon ranges from 10 to 150 nm; And / or, the carbonaceous conductive agent includes at least one of carbon nanotubes, graphene, conductive carbon black, carbon nanofibers, expanded graphite, and graphite powder. And / or, the first carbon source and the second carbon source include asphalt, wherein the softening point of the asphalt is 60~280℃; And / or, the protective atmosphere includes at least one of nitrogen atmosphere, helium atmosphere, and argon atmosphere.

8. The preparation method according to claim 7, characterized in that, The first carbon source and the second carbon source each independently include at least one of coal tar pitch, petroleum pitch, impregnated pitch, mesophase pitch, naphthalene-based pitch, and ethylene tar.

9. A nano-silicon / mesophase carbon microsphere composite material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the nano-silicon / mesophase carbon microsphere composite material as described in claim 9 as a negative electrode material for secondary batteries.

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