A sandwich structure MCMB@Si@C silicon-carbon negative electrode material and a preparation method and application thereof

Abstract

This invention provides a sandwich structure MCMB@Si@C silicon-carbon anode material, its preparation method, and its application. The preparation method includes: (1) preparing mesophase carbon microspheres using pitch as raw material, and using the solid-liquid interface driving force during the growth process of the mesophase carbon microspheres, achieving uniform adhesion of nano-silicon on the surface of the mesophase carbon microspheres through a one-step self-assembly method, thus obtaining an MCMB@Si silicon-carbon anode material with mesophase carbon microspheres as the core. (2) coating the surface of the above silicon-carbon anode material with a layer of carbon material to construct an MCMB@Si@C silicon-carbon anode material with a sandwich structure. Using a liquid phase coating process, after high-temperature carbonization treatment, a dense carbon layer is formed on the outermost layer, which can play the dual role of buffer layer and conductive layer. This invention is composed of a core mesophase carbon microsphere, a middle layer of nano-silicon, and an outermost dense carbon layer. This sandwich buffer structure effectively improves the anode volume change during the lithium insertion / extraction process, endows the sandwich structure silicon-carbon anode material with excellent cycle stability and rate performance, and is conducive to the formation of a more stable solid electrolyte membrane.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a silicon-carbon anode material, its preparation method, and its application. Background Technology

[0002] In recent years, with the rapid development of new energy vehicles and various electronic products, the application requirements for the performance of lithium-ion batteries have become increasingly stringent. Among them, lithium-ion battery anode materials, as an important component of lithium-ion batteries, have always been a focus of research. Silicon-carbon anode materials, which combine the advantages of traditional carbon anode materials and silicon-based anode materials, can effectively improve the energy density of anode materials and enhance cycle performance and rate performance, and have thus become an increasingly important research focus.

[0003] Among numerous carbon anode materials, mesophase carbon microspheres (MCMBs) stand out due to their spherical shape and unique layered structure, which facilitates the insertion and extraction of lithium ions in different directions and exhibits minimal volume change during charge and discharge. However, compared to artificial and natural graphite, mesophase carbon microspheres have relatively lower capacity. Furthermore, mesophase carbon microspheres prepared using traditional processes exhibit high surface density and graphitization under high-temperature heat treatment, hindering rapid lithium insertion and extraction reactions and affecting the rate performance and high / low temperature performance of the anode material. Silicon-based anode materials, on the other hand, possess higher specific capacity, effectively improving battery energy density, but suffer from significant volume change and poor cycle performance during charge and discharge. Based on these issues, researchers proposed combining these two materials to prepare MCMB-Si composite materials and fully leveraging their synergistic effect through rational structural design. Current research results have confirmed the feasibility of this method.

[0004] However, current MCMB-Si silicon-carbon anode materials still have some problems: First, the material preparation process is complex. Second, the bonding force between MCMB and silicon-based materials is poor, resulting in poor stability during charge and discharge. To solve this problem, Chinese patent CN117525357 A proposes a silicon-carbon anode material for lithium-ion batteries and its preparation method. This method uses a spray-bonding-stripping-stacking technique to construct a multilayer silicon-carbon composite material, achieving overall optimization of electrochemical performance and solving the problem of significant capacity reduction in silicon-carbon composite materials with increasing cycle count. It also greatly alleviates the volume change of silicon during cycling and maintains the integrity of the electrode. Chinese patent CN 113193183 A proposes a method for preparing a double-carbon-layer silicon-carbon composite material. This invention uses loose, porous pyrolytic carbon as the intermediate carbon layer to coat nano-silicon, and dense pyrolytic carbon as the outer carbon layer, forming a double-carbon-layer structure coating nano-silicon. This structure effectively improves the volume change during charge and discharge, giving the material high specific capacity, high initial coulombic efficiency, and long cycle life. However, the intermediate carbon layer is easily damaged during electrode processing, resulting in poor conductivity. Furthermore, while the invention uses hot compaction to improve the contact tightness between the silicon and carbon phases, the interaction between the two phases remains weak. Chinese patent CN109659514 A proposes a silicon-carbon anode material based on mesophase carbon microspheres and its preparation method. This invention uses mesophase carbon microspheres as the core, with an outermost layer of amorphous carbon. Combining tetraethyl orthosilicate hydrolysis and magnesothermic reduction, a silicon-carbon anode material with uniformly encapsulated mesophase carbon microspheres of nano-silicon is prepared. This material exhibits excellent lithium storage characteristics when used as a lithium-ion battery anode material. However, the material preparation process of this invention is too complex, making industrial-scale production difficult.

[0005] Therefore, how to simplify the process of preparing silicon-carbon anode materials from MCMB and silicon-based materials, making it easier to achieve industrial production and application, mitigating volume changes during lithium insertion / deintercalation, and improving the conductivity, cycle performance, and rate performance of silicon-carbon anode materials is an urgent industry problem to be solved. Summary of the Invention

[0006] Based on this, the present invention proposes a sandwich structure MCMB@Si@C silicon-carbon anode material, its preparation method, and its application. This preparation method is characterized by its simple process and ease of industrial production. The obtained silicon-carbon anode material can effectively mitigate volume changes during lithium insertion / extraction processes, improving its cycle stability and rate performance.

[0007] To achieve the above objectives, the technical solution of the present invention is implemented as follows: A method for preparing a sandwich structure MCMB@Si@C silicon-carbon anode material, comprising the following steps: (1) Mix and stir asphalt with nano-silicon and carry out thermal polymerization reaction to obtain thermally polymerized products containing mesophase carbon microspheres loaded with nano-silicon; (2) The thermal polymerization product obtained in step (1) is dissolved by stirring and heating with organic oil and filtered. The resulting filter cake is then repeatedly extracted with organic solvent as reflux liquid. The resulting insoluble matter is dried to obtain mesophase carbon microspheres with nano-silicon loaded on the surface, namely MCMB@Si material. (3) Mix the raw materials of MCMB@Si material and coated carbon material and perform liquid phase carbon layer coating treatment; after high temperature carbonization in an inert atmosphere, MCMB@Si@C silicon-carbon anode material with sandwich structure is obtained.

[0008] Preferably, the asphalt in step (1) is at least one of petroleum asphalt, coal tar pitch, modified coal tar pitch, coal tar, and secondary heavy petroleum oil; the nano-silicon is at least one of elemental silicon, silicon dioxide, and silicon monoxide, with a particle size of 50~200nm; and the mass ratio of asphalt to nano-silicon is 100:1~10.

[0009] Preferably, in the thermal polymerization reaction in step (1), the protective atmosphere is nitrogen and / or argon, the thermal polymerization reaction pressure is 0.1~2MPa, the reaction temperature is 350~450℃, the reaction time is 3~6h, and the stirring rate is 100~300rpm.

[0010] Preferably, in step (2), the mass ratio of organic oil to thermally polymerized product is 3~5:1, the heating and dissolving temperature is 80~120℃, the stirring rate during dissolution is 100~300rpm, and the stirring time is 0.5~3h.

[0011] Preferably, in step (2), the organic oil is wash oil or gasoline; the organic solvent is quinoline, ethanol or tetrahydrofuran; the drying temperature is 60~80 ℃, and the drying time is 6~24 h.

[0012] Preferably, the liquid phase carbon layer coating process in step (3) is either liquid phase physical coating or liquid phase in-situ chemical coating.

[0013] Preferably, the carbon coating material in step (3) is one or more of the following: asphalt, coated asphalt, phenolic resin, organic polymers such as polydopamine, graphite, and amorphous carbon, and the mass ratio of the carbon coating material to the MCMB@Si material is 30~100:100.

[0014] Preferably, in step (3), the high-temperature carbonization process is carried out at a temperature of 800~1400℃, a heating rate of 3~10℃ / min, and a holding time of 0.5~3h; the protective atmosphere is nitrogen and / or argon, with a gas flow rate of 30~100 mL / min. -1 .

[0015] Preferably, the sandwich structure MCMB@Si@C silicon-carbon anode material prepared by the method has a core of mesophase carbon microspheres, an intermediate layer of nano-silicon, and an outermost layer of dense carbon.

[0016] Preferably, the sandwich structure MCMB@Si@C silicon-carbon anode material is used in lithium-ion batteries.

[0017] The present invention has the following beneficial effects: (1) The present invention adopts a thermal polymerization reaction process. During the growth of mesophase carbon microspheres, there is a certain solid-liquid interface driving force. This driving force will cause the silicon particles in the system to move towards the surface of the mesophase carbon microspheres and then uniformly attach to the surface of the mesophase carbon microspheres, thus completing the self-assembly between the mesophase carbon microspheres and silicon particles in one step. Furthermore, the preparation of sandwich structure MCMB@Si@C silicon-carbon anode material is achieved through liquid phase coating.

[0018] (2) The sandwich-structured silicon-carbon anode material of the present invention is composed of mesophase carbon microspheres, nano-silicon, and a dense carbon layer from the inside out. The core mesophase carbon microspheres have strong lithium storage capacity, and their large specific surface area gives the nano-silicon good dispersion effect. The outermost dense carbon layer can play a dual role as a buffer layer and a conductive layer. These factors work together to give the sandwich-structured silicon-carbon anode material excellent cycle stability and rate performance, which can effectively improve the volume change phenomenon during lithium delithiation / lithiation process and is conducive to the formation of a more stable solid electrolyte membrane.

[0019] (3) The process for preparing MCMB@Si@C silicon-carbon anode material in this invention is simple, highly operable, and easy to industrialize. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 The image shows the SEM images of the MCMB@Si material in Example 1 of this invention. Figure ad shows the SEM images at different magnifications.

[0022] Figure 2 The image shows a SEM image of the MCMB@Si@C silicon-carbon anode material with an outermost phenolic resin coating in Example 1 of this invention (e.g., Figure 2 (as shown in Figure (a)) and EDS diagram (as shown in Figure (a)) Figure 2 As shown in (b), (c), and (d), where Figure 2 (b) is the EDS diagram of silicon and carbon. Figure 2 (c) is the EDS diagram of carbon in the MCMB@Si@C silicon-carbon anode material. Figure 2 (d) is the EDS diagram of silicon in MCMB@Si@C silicon-carbon anode material. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] The raw materials used in this invention, such as asphalt and nano-silicon, are all commercially available products; the asphalt, coated asphalt, phenolic resin, polydopamine, graphite, and amorphous carbon used are either commercially available products or prepared in the laboratory.

[0025] Example 1 A method for preparing a sandwich structure MCMB@Si@C silicon-carbon anode material, comprising the following steps: 70g of natural petroleum asphalt was weighed, crushed, and mixed with 1g of nano-silicon (elemental silicon with a particle size of 150nm). The mixture was then placed in a high-temperature, high-pressure reactor. After sealing, high-purity nitrogen was introduced to displace the air from the reactor. Nitrogen was then injected into the reactor, maintaining a system pressure of 1.0 MPa. The temperature was increased to 410℃ at a specific rate and held for 4 hours at a stirring rate of 200 rpm. After the reaction, the mixture was allowed to cool naturally to approximately 200℃. The reactor was then depressurized and opened, allowing the asphalt to flow out in a molten state, yielding a thermally polymerized product containing MCMB@Si material. This thermally polymerized product was mixed with wash oil at a mass ratio of 1:3, heated to 80℃, and stirred for 2 hours at a stirring rate of 100 rpm. While still hot, the mixture was filtered and collected by vacuum filtration. The resulting filter cake was crushed and placed in a cellulose filter paper wick. The filter paper wick was then placed in a Soxhlet extractor and repeatedly washed with quinoline as the reflux liquid until the reflux liquid became colorless. The material was then extracted using anhydrous ethanol as the reflux solution. The resulting material was vacuum dried at 80°C for 24 h, and the resulting brown powder was the MCMB@Si material.

[0026] Figure 1 The image shows a SEM image of the MCMB@Si material in this embodiment. As can be seen from the image, nano-silicon was successfully loaded and dispersed on the surface of the mesophase carbon microspheres, forming a silicon-carbon material with the mesophase carbon microspheres as the core. The particle size of the MCMB@Si microspheres is 5-15 μm.

[0027] Weigh 10 g of the obtained MCMB@Si material and 0.6 g of hexadecyltrimethylammonium bromide and mix them in 200 mL of deionized water. Sonicate for 30 min to mix thoroughly. Then, while heating and stirring in a 40 °C water bath, add 2 g of resorcinol, 1 mL of formaldehyde, and 15 mL of ammonia water sequentially, and react for 6 h. Stop stirring and age overnight. Centrifuge the solution and wash the product several times with water and ethanol. Spin the product at 5 °C for 1 min... -1 The material was carbonized at 800℃ for 3 hours to obtain MCMB@Si@C-RF silicon-carbon anode material.

[0028] Figure 2 Image (a) shows the SEM image of the MCMB@Si@C silicon-carbon anode material with a sandwich structure in this embodiment, where the outermost layer is coated with phenolic resin. As can be seen from the image, after coating with phenolic resin, the resulting silicon-carbon anode material has a smooth surface without any small spheres adhering to it. The image was obtained via EDS scanning (…). Figure 2 (b), (c), and (d)) confirm that the outermost layer is a dense carbon layer formed after coating with phenolic resin.

[0029] Lithium-ion battery assembly and performance A suitable amount of sandwich-structured MCMB@Si@C-RF silicon-carbon anode material, polyvinylidene fluoride, and acetylene black, along with a suitable amount of N-methylpyrrolidone, were weighed according to a mass ratio of 8:1:1. After ball milling at 150 rpm for 2 h, copper foil was uniformly coated onto the mixture, and the mixture was vacuum dried at 80℃ for 12 h to obtain the battery electrode. Using the obtained battery electrode as the working electrode and a lithium sheet as the counter electrode, a lithium-ion button cell was assembled in a glove box. The current density was 200 mA g. -1 Under these conditions, the initial discharge specific capacity is 707.2 mA hg. -1 The initial coulomb efficiency was 83%, and the capacity retention rate after 1000 cycles was 85%. At 0.1 A g... -1 0.2 A g -1 0.4 A g -1 0.8 A g -1 and 1.6 A g -1 At current densities of 803 mAh g -1 681 mAh g -1 593 mAh g -1 536 mAh g -1 487 mAh g -1 435mAh g -1 The reversible capacity was observed, and upon recovery of current density, the reversible capacity recovered to 654 mAh g. -1 It exhibits excellent rate performance and cycle stability.

[0030] Example 2 A method for preparing a sandwich structure MCMB@Si@C silicon-carbon anode material, comprising the following steps: 70g of natural petroleum asphalt was weighed, crushed, and mixed with 1g of nano-silicon (elemental silicon with a particle size of 150nm). The mixture was then placed in a high-temperature, high-pressure reactor. After sealing, high-purity nitrogen was introduced to displace the air in the reactor. Nitrogen was then injected into the reactor, and the system pressure was maintained at 1.0 MPa. The temperature was increased to 410℃ at a certain rate and held for 4 hours at a stirring rate of 200 rpm. After the reaction, the mixture was allowed to cool naturally to approximately 200℃. The reactor was then depressurized and opened to allow the asphalt to flow out in a molten state, yielding a thermally polymerized product containing MCMB@Si material. This thermally polymerized product was mixed with wash oil at a mass ratio of 1:3, heated to 80℃, and stirred for 2 hours at a stirring rate of 100 rpm. While still hot, the mixture was filtered, and the resulting filter cake was collected. The filter cake was crushed and placed in a cellulose filter paper wick. The filter paper wick was then placed in a Soxhlet extractor and repeatedly washed with quinoline as the reflux liquid until the reflux liquid became colorless. The material was then extracted using anhydrous ethanol as the reflux solution. The resulting material was vacuum dried at 80°C for 24 h, and the resulting brown powder was the MCMB@Si material.

[0031] Weigh 10g of the MCMB@Si material obtained above and disperse it in 75 mL of 10 mmol L. -1 After homogeneous mixing with Tris-HCl buffer solution (pH = 8.5), 5 g of dopamine hydrochloride was added, and the mixture was stirred overnight at room temperature. The mixture was centrifuged, washed several times with deionized water, and dried under vacuum at 80 °C for 12 h to obtain the carbon precursor. The above material was then placed in a tube furnace and heated at 5 °C for 1 min under an argon atmosphere. -1 The material was heated to 800℃ and carbonized for 3 hours to obtain a sandwich structure MCMB@Si@C-PDA silicon-carbon anode material.

[0032] Lithium-ion battery assembly and performance A suitable amount of sandwich structure MCMB@Si@C-PDA silicon-carbon anode material, polyvinylidene fluoride, and acetylene black, along with a suitable amount of N-methylpyrrolidone, were weighed according to a mass ratio of 8:1:1. After ball milling at 150 rpm for 2 h, copper foil was uniformly coated onto the mixture, and the mixture was vacuum dried at 80℃ for 12 h to obtain the battery electrode. Using the obtained battery electrode as the working electrode and a lithium sheet as the counter electrode, a lithium-ion button cell was assembled in a glove box. The current density was 200 mA g. -1 The first reversible specific capacity is 914 mA hg. -1 The initial coulomb efficiency was 65%, and the capacity retention rate after 1000 cycles was 71%. At 0.1 A g... -10.2 A g -1 0.4 A g -1 0.8 A g -1 and 1.6 A g -1 At current densities of 895 mAh g -1 591 mAh g -1 523 mAh g -1 486 mAh g -1 407 mAh g -1 355mAh g -1 It exhibits reversible capacity, which recovers to 594 mAh g⁻¹ upon current density recovery. It also demonstrates good rate performance and cycle stability.

[0033] Example 3 A method for preparing a sandwich structure MCMB@Si@C silicon-carbon anode material, comprising the following steps: 70g of natural petroleum asphalt was weighed, crushed, and mixed with 1g of nano-silicon (elemental silicon with a particle size of 150nm). The mixture was then placed in a high-temperature, high-pressure reactor. After sealing, high-purity nitrogen was introduced to displace the air in the reactor. Nitrogen was then injected into the reactor, and the system pressure was maintained at 1.0 MPa. The temperature was increased to 410℃ at a certain rate and held for 4 hours at a stirring rate of 200 rpm. After the reaction, the mixture was allowed to cool naturally to approximately 200℃. The reactor was then depressurized and opened to allow the asphalt to flow out in a molten state, yielding a thermally polymerized product containing MCMB@Si material. This thermally polymerized product was mixed with wash oil at a mass ratio of 1:3, heated to 80℃, and stirred for 2 hours at a stirring rate of 100 rpm. While still hot, the mixture was filtered, and the resulting filter cake was collected. The filter cake was crushed and placed in a cellulose filter paper wick. The filter paper wick was then placed in a Soxhlet extractor and repeatedly washed with quinoline as the reflux liquid until the reflux liquid became colorless. The material was then extracted using anhydrous ethanol as the reflux solution. The resulting material was vacuum dried at 80°C for 24 h, and the resulting brown powder was the MCMB@Si material.

[0034] Weigh 10g of the obtained MCMB@Si material and mix it with 5g of coated bitumen. Disperse the mixture in a tetrahydrofuran solution, heat to 40°C, and stir at 100 rpm until the tetrahydrofuran solvent is completely evaporated. Then transfer the mixture to a tube furnace and heat it under an argon atmosphere at a gas flow rate of 30 mL / min. -1 , at 5℃ min -1 The sandwich structure MCMB@Si@C-CP silicon-carbon anode material was obtained by heating to 800℃ and carbonizing for 3 hours.

[0035] Lithium-ion battery assembly and performance A suitable amount of sandwich-structured MCMB@Si@C-CP silicon-carbon anode material, polyvinylidene fluoride, and acetylene black, along with a suitable amount of N-methylpyrrolidone, were weighed according to a mass ratio of 8:1:1. After ball milling at 150 rpm for 2 h, copper foil was uniformly coated onto the mixture, and the mixture was vacuum dried at 80℃ for 12 h to obtain the battery electrode. Using the obtained battery electrode as the working electrode and a lithium sheet as the counter electrode, lithium-ion button batteries were assembled in a glove box. The current density was 200 mA g. -1 The first reversible specific capacity is 732 mA hg. -1 The initial coulombic efficiency was 80%, and the capacity retention after 1000 cycles was 83%. At 0.1 A g... -1 0.2 A g -1 0.4 A g -1 0.8 A g -1 and 1.6 A g -1 At current densities of 643 mAh g -1 501 mAh g -1 473 mAh g -1 420 mAh g -1 362 mAh g -1 299 mAh g -1 The reversible capacity was observed, and upon recovery of current density, the reversible capacity recovered to 483 mAh g⁻¹. -1 It exhibits excellent rate performance and cycle stability.

[0036] Example 4 A method for preparing a sandwich structure MCMB@Si@C silicon-carbon anode material, comprising the following steps: 70g of natural petroleum asphalt was weighed, crushed, and mixed with 1g of nano-silicon (elemental silicon with a particle size of 150nm). The mixture was then placed in a high-temperature, high-pressure reactor. After sealing, high-purity nitrogen was introduced to displace the air in the reactor. Nitrogen was then injected into the reactor, and the system pressure was maintained at 2.0 MPa. The temperature was increased to 350℃ at a certain rate and held for 6 hours at a stirring rate of 100 rpm. After the reaction, the mixture was allowed to cool naturally to approximately 200℃. The reactor was then depressurized and opened to allow the asphalt to flow out in a molten state, yielding a thermally polymerized product containing MCMB@Si material. This thermally polymerized product was mixed with gasoline at a mass ratio of 1:4, heated to 100℃, and stirred for 1 hour at a stirring rate of 100 rpm. While still hot, the mixture was filtered and collected by vacuum filtration. The resulting filter cake was crushed and placed in a cellulose filter paper spool. The filter paper spool was then placed in a Soxhlet extractor and repeatedly washed with quinoline as the reflux liquid until the reflux liquid became colorless. The material was then extracted using anhydrous ethanol as the reflux solution. The resulting material was vacuum dried at 60°C for 18 h, and the resulting brown powder was the MCMB@Si material.

[0037] Weigh 10 g of the obtained MCMB@Si material and 3 g of graphite and disperse them in 200 mL of ethanol. Then heat and stir at 40 °C and 100 rpm until all the ethanol solvent has evaporated. Transfer the mixture to a tube furnace and heat under an argon atmosphere at a gas flow rate of 80 mL / min. -1 The product was heated at 3℃ for 3 min. -1 The material was carbonized at 800℃ for 3 hours to obtain MCMB@Si@C-graphite silicon carbon anode material.

[0038] Lithium-ion battery assembly and performance Appropriate amounts of the above-mentioned sandwich structure MCMB@Si@C-graphite silicon-carbon anode material, polyvinylidene fluoride, and acetylene black, along with an appropriate amount of N-methylpyrrolidone, were weighed according to a mass ratio of 8:1:1. After ball milling at 150 rpm for 2 h, copper foil was uniformly coated onto the mixture, and the battery electrode was obtained after vacuum drying at 80℃ for 12 h. Using the obtained battery electrode as the working electrode and a lithium sheet as the counter electrode, lithium-ion button batteries were assembled in a glove box. The current density was 200 mA g. -1 The first reversible specific capacity is 680mA hg. -1 The initial coulomb efficiency was 80%, and the capacity retention rate after 1000 cycles was 78%, at 0.1 Ag. -1 0.2 A g -1 0.4 A g -1 0.8 A g -1 and 1.6 A g -1 At current densities of 565 mAh g -1 434 mAh g -1 411 mAh g -1 355mAh g -1 302 mAh g -1 255mAh g -1 The reversible capacity was observed, and upon recovery of current density, the reversible capacity recovered to 435 mAh g⁻¹. -1 It exhibits excellent rate performance and cycle stability.

[0039] Example 5 A method for preparing a sandwich structure MCMB@Si@C silicon-carbon anode material, comprising the following steps: 70g of natural petroleum asphalt was weighed, crushed, and mixed with 10g of nano-silicon (elemental silicon with a particle size of 150nm). The mixture was then placed in a high-temperature, high-pressure reactor. After sealing, high-purity nitrogen was introduced to displace the air in the reactor. Nitrogen was then injected into the reactor, and the system pressure was maintained at 0.1MPa. The temperature was increased to 450℃ at a certain rate and held for 3 hours at a stirring rate of 300 rpm. After the reaction, the mixture was allowed to cool naturally to approximately 200℃. The reactor was then depressurized and opened to allow the asphalt to flow out in a molten state, yielding a thermally polymerized product containing MCMB@Si material. This thermally polymerized product was mixed with gasoline at a mass ratio of 1:3, heated to 120℃, and stirred for 0.5 hours at a stirring rate of 200 rpm. While still hot, the mixture was filtered and collected by vacuum filtration. The resulting filter cake was crushed and placed in a cellulose filter paper tube. The filter paper tube was then placed in a Soxhlet extractor and repeatedly washed with quinoline as the reflux liquid until the reflux liquid became colorless. The material was then extracted using anhydrous ethanol as the reflux solution. The resulting material was vacuum dried at 70°C for 10 hours, and the resulting brown powder was the MCMB@Si material.

[0040] Weigh 10 g of the obtained MCMB@Si material and 10 g of coated asphalt, and disperse them in tetrahydrofuran. Heat to 40 °C and stir at 100 rpm until the tetrahydrofuran solvent is completely evaporated. Then transfer it to a tube furnace and heat under an argon atmosphere at a gas flow rate of 100 mL / min. -1 The product was heated at 10℃ for 1 min. -1 The temperature was raised to 1400℃ and carbonized for 1.5 hours to obtain MCMB@Si@C-coated pitch silicon-carbon anode material.

[0041] Lithium-ion battery assembly and performance Appropriate amounts of the above-mentioned sandwich structure MCMB@Si@C-CP silicon-carbon anode material, polyvinylidene fluoride, and acetylene black, along with an appropriate amount of N-methylpyrrolidone, were weighed at a mass ratio of 8:1:1. After ball milling at 150 rpm for 2 h, copper foil was uniformly coated onto the mixture, and the mixture was vacuum dried at 80 °C for 12 h to obtain the battery electrode. Using the obtained battery electrode as the working electrode and a lithium sheet as the counter electrode, lithium-ion button batteries were assembled in a glove box. The current density was 200 mA g. -1 The first reversible specific capacity is 852 mA hg. -1 The initial coulomb efficiency was 89%, and the capacity retention rate after 1000 cycles was 88%. At 0.1 A g... -1 0.2 A g -1 0.4 A g -1 0.8 A g -1 and 1.6 A g -1 At current densities of 796 mAh g -1 651 mAh g-1 615mAh g -1 572 mAh g -1 511mAh g -1 445mAh g -1 The reversible capacity was observed, and upon recovery of current density, the reversible capacity recovered to 714 mAh g. -1 It exhibits excellent rate performance and cycle stability.

[0042] Example 6 A sandwich structure MCMB@Si@C silicon-carbon anode material and its preparation method are as follows: 70g of natural petroleum asphalt was weighed, crushed, and mixed with 1g of nano-silicon (silica with a particle size of 150nm). The mixture was then placed in a high-temperature, high-pressure reactor. After sealing, high-purity nitrogen was introduced to displace the air from the reactor. Nitrogen was then injected into the reactor, maintaining a system pressure of 1.0 MPa. The temperature was increased to 410℃ at a specific rate and held for 4 hours at a stirring rate of 200 rpm. After the reaction, the mixture was allowed to cool naturally to approximately 200℃. The reactor was then depressurized and opened, allowing the asphalt to flow out in a molten state, yielding a thermally polymerized product containing MCMB@Si material. This thermally polymerized product was mixed with wash oil at a mass ratio of 1:3, heated to 80℃, and stirred for 2 hours at a stirring rate of 100 rpm. While still hot, the mixture was filtered and collected by vacuum filtration. The resulting filter cake was crushed and placed in a cellulose filter paper spool. The filter paper spool was then placed in a Soxhlet extractor and repeatedly washed with quinoline as the reflux liquid until the reflux liquid became colorless. The material was then extracted using tetrahydrofuran as the reflux solution. The resulting material was vacuum dried at 80°C for 6 hours, and the resulting brown powder was the MCMB@Si material.

[0043] Weigh 10 g of the obtained MCMB@Si material and 6 g of coated bitumen, mix them, and disperse them in a tetrahydrofuran solution. Heat to 40°C and stir at 100 rpm until the tetrahydrofuran solvent is completely evaporated. Then transfer it to a tube furnace and heat under an argon atmosphere at a gas flow rate of 50 mL / min. -1 The product was heated at 5℃ for 5 min. -1 The material was carbonized at 1000℃ for 2 h to obtain MCMB@Si@C-amorphous carbon silicon carbon anode material.

[0044] Lithium-ion battery assembly and performance Appropriate amounts of the above-mentioned sandwich structure MCMB@Si@C-CP silicon-carbon anode material, polyvinylidene fluoride, and acetylene black, along with an appropriate amount of N-methylpyrrolidone, were weighed at a mass ratio of 8:1:1. After ball milling at 150 rpm for 2 h, copper foil was uniformly coated onto the mixture, and the mixture was vacuum dried at 80 °C for 12 h to obtain the battery electrode. Using the obtained battery electrode as the working electrode and a lithium sheet as the counter electrode, lithium-ion button batteries were assembled in a glove box. The current density was 200 mA g. -1 The first reversible specific capacity is 760mA hg. -1 The initial coulomb efficiency was 84%, and the capacity retention rate after 1000 cycles was 82%, at 0.1 Ag. -1 0.2 A g -1 0.4 A g -1 0.8 A g -1 and 1.6 A g -1 At current densities of 665 mAh g -1 523 mAh g -1 488mAh g -1 432 mAh g -1 392mAh g -1 326mAh g -1 It exhibits reversible capacity, which recovers to 515 mAh g⁻¹ upon current density recovery. It also demonstrates excellent rate performance and cycle stability.

[0045] Comparative Example 1 This comparative example provides an MCMB@Si material and its preparation method. The difference from Example 1 is that the MCMB@Si composite material surface is not carbon-coated. The steps are as follows: 70g of natural petroleum asphalt was weighed, crushed, and mixed with 1g of nano-silicon, and then placed together in a high-temperature and high-pressure reactor. After sealing, high-purity nitrogen was introduced to displace the air in the reactor. Nitrogen was then injected into the reactor to maintain a system pressure of 1.0 MPa. The temperature was increased to 410℃ at a certain rate and held for 4 hours at a stirring rate of 200 rpm. After the reaction, the mixture was allowed to cool naturally to approximately 200℃. The pressure was released, and the reactor was opened to allow the asphalt to flow out in a molten state, yielding a thermally polymerized product containing MCMB@Si material. The above thermally polymerized product and wash oil were mixed at a mass ratio of 1:3, heated to 80℃, and stirred for 2 hours at a stirring rate of 100 rpm. While hot, the mixture was filtered, and the resulting filter cake was collected. The filter cake was crushed and placed in a cellulose filter paper tube. The filter paper tube was then placed in a Soxhlet extractor and repeatedly washed with quinoline as the reflux liquid until the reflux liquid was colorless. Extraction was then performed using anhydrous ethanol as the reflux liquid. The obtained material was vacuum dried at 80℃ for 24 h, and the resulting brown powder was the MCMB@Si material.

[0046] Lithium-ion battery assembly and performance A suitable amount of sandwich-structured MCMB@Si silicon-carbon anode material, polyvinylidene fluoride, and acetylene black, along with a suitable amount of N-methylpyrrolidone, were weighed at a mass ratio of 8:1:1. After ball milling at 150 rpm for 2 h, copper foil was uniformly coated onto the mixture, and the mixture was vacuum dried at 80℃ for 12 h to obtain the battery electrode. Using the obtained battery electrode as the working electrode and a lithium sheet as the counter electrode, a lithium-ion button cell was assembled in a glove box. The current density was 200 mA g. -1 The first reversible specific capacity is 663.8 mA hg. -1 The initial coulomb efficiency was 79%, the capacity retention rate after 1000 cycles was 65%, and the capacity retention rate after 1000 cycles was 85%. At 0.1 Ag... -1 0.2 A g -1 0.4 A g -1 0.8 Ag -1 and 1.6 A g -1 At current densities of 625 mAh g -1 413 mAh g -1 265 mAh g -1 223 mAh g -1 201 mAh g -1 187mAh g -1 The reversible capacity was observed, and upon recovery of current density, the reversible capacity recovered to 310 mAh g. -1 It exhibits good rate performance and cycle stability.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a sandwich structure MCMB@Si@C silicon-carbon anode material, characterized in that, The steps are as follows: (1) Mix and stir asphalt with nano-silicon and carry out thermal polymerization reaction to obtain thermally polymerized products containing mesophase carbon microspheres loaded with nano-silicon; (2) The thermally polymerized product obtained in step (1) is dissolved by stirring and heating with organic oil and then filtered. The resulting filter cake is repeatedly extracted with organic solvent as reflux liquid. The resulting insoluble matter is dried to obtain mesophase carbon microspheres with nano-silicon loaded on the surface, i.e., MCMB@Si material. The organic oil is wash oil or gasoline. The organic solvent is quinoline, ethanol or tetrahydrofuran. The mass ratio of organic oil to thermally polymerized product is 3~5:

1. The heating and dissolving temperature is 80~120℃ and the dissolving time is 0.5~3h. (3) Mix the raw materials of MCMB@Si material and coated carbon material and perform liquid phase carbon layer coating treatment; after high temperature carbonization in an inert atmosphere, MCMB@Si@C silicon-carbon anode material with sandwich structure is obtained; In step (3), the liquid phase carbon layer coating process is either liquid phase physical coating or liquid phase in-situ chemical coating. In step (3), the carbon coating material is one or more of asphalt, coated asphalt, phenolic resin, polydopamine, graphite and amorphous carbon, and the mass ratio of the carbon coating material to the MCMB@Si material is 3~10:

10. In step (3), the high-temperature carbonization process is carried out at a temperature of 800~1400℃, with a heating rate of 3~10℃ / min and a constant temperature of 0.5~3h; the inert atmosphere is nitrogen and / or argon.

2. The method for preparing the sandwich structure MCMB@Si@C silicon-carbon anode material according to claim 1, characterized in that: The asphalt in step (1) is at least one of petroleum asphalt, coal tar pitch, modified coal tar pitch, coal tar, and secondary heavy petroleum oil; the nano-silicon is at least one of elemental silicon, silicon dioxide, and silicon monoxide, with a particle size of 50~200nm; the mass ratio of asphalt to nano-silicon is 100:1~10.

3. The method for preparing the sandwich structure MCMB@Si@C silicon-carbon anode material according to claim 1, characterized in that: In step (1), the protective atmosphere for the thermal polymerization reaction is nitrogen and / or argon, the thermal polymerization reaction pressure is 0.1~2MPa, the reaction temperature is 350~450℃, the reaction time is 3~6h, and the stirring rate is 100~300rpm.

4. The method for preparing the sandwich structure MCMB@Si@C silicon-carbon anode material according to claim 1, characterized in that: The drying temperature in step (2) is 60~80℃, and the drying time is 6~24h.

5. The sandwich-structured MCMB@Si@C silicon-carbon anode material prepared by the method according to any one of claims 1-4, characterized in that: The core of the sandwich structure MCMB@Si@C silicon-carbon anode material is mesophase carbon microspheres, the middle layer is nano-silicon, and the outermost layer is a dense carbon layer.

6. The application of the sandwich structure MCMB@Si@C silicon-carbon anode material as described in claim 5 in lithium-ion batteries.

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