Low-expansion silicon-carbon negative electrode material, preparation method thereof and lithium ion battery

Abstract

The invention provides a low-expansion silicon-carbon negative electrode material, a preparation method thereof and a lithium ion battery, and relates to the field of lithium ion batteries. Mixing the MOF material, a graphite precursor, a pre-lithiation agent, an amphiphilic block copolymer, a first carbon source, a binder, a dispersant, nano silicon and an organic solvent, and performing ultrasonic treatment to obtain a first mixture; performing spray drying and first roasting on the first mixture to obtain a first roasted material; performing second mixing and first coating treatment on the first roasting material and a second carbon source to obtain a second mixture; performing second roasting on the second mixture to obtain a second roasted material; carrying out third mixing on the second roasted material and LiAlO2 nanoparticles to obtain a third mixture, and grinding the third mixture to obtain a ground material; performing fourth mixing and second coating treatment on the ground material and a third carbon source to obtain a fourth mixture; and performing third roasting to obtain the low-expansion silicon-carbon negative electrode material. The method has the advantages of easily available raw materials and simple operation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a low-expansion silicon-carbon negative electrode material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] With the progress of science and technology, various electronic devices and electric vehicles are emerging in an endless stream, and people have increasingly high demands on power supplies. Lithium batteries are widely used in intelligent devices and electric vehicles due to their high energy density, low self-discharge rate, no memory effect, long cycle life and other advantages.

[0003] At present, most commercial lithium ion batteries use graphite negative electrodes. Graphite negative electrodes are widely used due to their low lithium intercalation potential, stable structure and good charge-discharge reversibility. However, its theoretical specific capacity is only 372 mAh / g, which is difficult to meet the demand for high energy density batteries such as electric vehicles and high-end electronic products in the long term. Among the known negative electrode materials for lithium ion batteries, silicon has a theoretical specific capacity of up to 4200 mAh / g, which is a highly potential negative electrode material and can greatly improve the energy density of the battery.

[0004] However, during the lithium intercalation and deintercalation process, the volume change of silicon is as high as 300%-400%, which causes the structure of the electrode material to be damaged and the capacity to rapidly decay. In addition, the low electrical conductivity of silicon affects the charge-discharge efficiency of the battery. The existing silicon-carbon negative electrode material has a high expansion coefficient, poor structural stability, poor silicon particle dispersibility and low product purity.

[0005] Therefore, there is an urgent need to provide a preparation method of a silicon-carbon negative electrode material to solve the above problems. SUMMARY

[0006] The purpose of the present application is to provide a low-expansion silicon-carbon negative electrode material, a preparation method thereof and a lithium ion battery to solve the above problems.

[0007] To achieve the above purpose, the first aspect of the present application provides a preparation method of a low-expansion silicon-carbon negative electrode material, comprising: mixing MOF material, graphite precursor, pre-lithiation agent, amphiphilic block copolymer, first carbon source, binder, dispersant, nano-silicon and organic solvent to obtain a first mixture; and performing spray drying and first calcination on the first mixture to obtain a first calcined material; mixing the first calcined material and a second carbon source to obtain a second mixture; and performing second calcination on the second mixture under an inert atmosphere to obtain a second calcined material; mixing the second calcined material and LiAlO2 nanoparticles to obtain a third mixture, and performing grinding on the third mixture to obtain a ground material; carrying out fourth mixing on the ground material and a third carbon source, carrying out second coating treatment to obtain a fourth mixture; carrying out third roasting on the fourth mixture under an inert atmosphere to obtain the low-expansion silicon-carbon negative electrode material.

[0008] Optionally, the preparation method of the low-expansion silicon-carbon negative electrode material satisfies at least one of the following conditions: (1) the MOF material comprises ZIF-8; (2) the graphite precursor comprises natural graphite and / or artificial graphite; (3) the pre-lithiation agent comprises LiOH; (4) the amphiphilic block copolymer comprises one or more of polyethylene glycol block copolymer, polystyrene-polyacrylic acid, polylactic acid-polyethylene glycol-polylactic acid, and polyethylene oxide-polypropylene oxide; (5) the binder comprises one or more of sodium carboxymethyl cellulose, sodium alginate, and polyacrylic acid; (6) the dispersant comprises one or more of polyvinylpyrrolidone, polyethylene glycol, cetyltrimethylammonium bromide, and sodium dodecyl sulfate; (7) the first carbon source, the second carbon source, and the third carbon source each independently comprises one or more of phenolic resin, polyacrylonitrile, glucose, sucrose, coal tar pitch, petroleum pitch, carbon nanotube, and graphene; (8) the organic solvent comprises ethanol; (9) the LiAlO2 nanoparticles have a particle size of 50-200 nm.

[0009] Optionally, the preparation method of the low-expansion silicon-carbon negative electrode material satisfies at least one of the following conditions: (1) the mass ratio of the MOF material, the graphite precursor, the pre-lithiation agent, the amphiphilic block copolymer, the first carbon source, the binder, the dispersant, and the nano-silicon is 0.05-0.15:0.2-0.5:0.01-0.1:0.01-0.05:0.1-0.2:0.01-0.2:0.01-0.5:1; (2) the mass ratio of the first roasting material and the second carbon source is 1:0.03-0.07; (3) the mass ratio of the second roasting material and the LiAlO2 nanoparticles is 100:1-10; (4) the mass ratio of the ground material and the third carbon source is 1:0.1-1.

[0010] Optionally, the preparation method of the low-expansion silicon-carbon negative electrode material satisfies at least one of the following conditions: (1) the frequency of the ultrasound is 20-100 kHz, and the time is 30-60 min; (2) the inlet air temperature of the spray drying is 130-200 ℃, the rotation speed is 300-500 Hz, and the feeding pump speed is 20-35 rpm.

[0011] Optionally, the preparation method of the low-expansion silicon-carbon negative electrode material satisfies at least one of the following conditions: (1) the temperature of the first calcination is 600-1000 ℃, and the time is 1-6 h; (2) the temperature of the second calcination is 300-1400 ℃, and the time is 1-6 h; (3) the temperature of the third calcination is 300-1000 ℃, and the time is 1-6 h.

[0012] Optionally, the preparation method of the low-expansion silicon-carbon negative electrode material satisfies at least one of the following conditions: (1) the first coating treatment comprises third coating treatment, fourth coating treatment and fifth coating treatment performed in sequence; the temperature of the third coating treatment is 400-600 ℃, and the time is 20-40 min; the temperature of the fourth coating treatment is 600-800 ℃, and the time is 40-80 min; the temperature of the fifth coating treatment is 800-1000 ℃, and the time is 20-40 min; (2) the temperature of the second coating treatment is 60-220 ℃, the time is 4-12 h, and the stirring speed is 200-1000 rpm.

[0013] Optionally, the preparation method of the low-expansion silicon-carbon negative electrode material satisfies at least one of the following conditions: (1) the inert gas in the inert atmosphere comprises one or more of nitrogen, argon, neon, xenon and radon; (2) during the first calcination, the second calcination and the third calcination, the flow rate of the inert gas is independently 0.1-10 L / min; (3) the rotation speed of the grinding is 200-600 rpm, and the time is 1-6 h; (4) the concentration of the third carbon source is 10-30%.

[0014] The second aspect of the application provides a low-expansion silicon-carbon negative electrode material, comprising a core and a first carbon coating layer and a second carbon coating layer arranged on the surface of the core; obtained by the preparation method of the low-expansion silicon-carbon negative electrode material.

[0015] Optionally, the low-expansion silicon-carbon negative electrode material satisfies at least one of the following conditions: (1) the thickness of the first carbon coating layer is 5nm-50nm; (2) the thickness of the second carbon coating layer is 20nm-100nm.

[0016] The third aspect of the present application provides a lithium ion battery comprising the low-expansion silicon-carbon negative electrode material.

[0017] Compared with the prior art, the beneficial effects of the present application include: The preparation method of the low-expansion silicon-carbon negative electrode material provided by the present application first utilizes the hydrophilic groups in the amphiphilic block copolymer to form a core-shell type self-assembled micelle by hydrogen bonding with the hydroxyl groups on the surface of the MOF material, and the hydrophobic groups wrap the nanosilicon, and the mixed solution is subjected to ultrasonic treatment to break the MOF agglomerates and induce the ordered arrangement of the micelles to form a MOF-polymer layer on the surface of the nanosilicon. Then, through the first calcination, the MOF is carbonized to form a porous carbon skeleton to provide a buffer space for subsequent expansion; secondly, the first carbon coating layer is formed by second sintering to improve the structural stability, ensure the reaction stability, and improve the product purity, thereby effectively inhibiting the volume expansion of silicon, blocking the direct contact of silicon with electrolyte, and improving the electrochemical cycle performance, and then LiAlO2 is embedded into the defects of the first carbon coating layer by mechanical force to improve the material structure; then, a uniform and dense second carbon coating layer is further formed on the surface of the material by second coating treatment to optimize its electrochemical performance. The preparation method of the low-expansion silicon-carbon negative electrode material constructs a porous carbon skeleton, carries out two coating treatments in succession, embeds LiAlO2 to realize lithium source compensation, and finally provides a low-expansion silicon-carbon negative electrode material, which is easy to obtain raw materials and simple to operate.

[0018] The low-expansion silicon-carbon negative electrode material provided in the application is composed of a core, which is composed of nano-silicon particles, a MOF-derived porous carbon framework, a graphite precursor-derived carbon phase and Li2O generated in situ from a pre-lithiation agent, and the specific distribution is that the nano-silicon particles are uniformly dispersed in the pores of the MOF-derived porous carbon framework, a "core-shell" structure is formed by wrapping the hydrophobic groups of the amphiphilic block copolymer, and the agglomeration of the silicon particles is avoided; the graphite precursor-derived carbon phase is filled in the gaps of the porous carbon framework, and a continuous conductive network is formed with the porous carbon; the three-dimensional network structure of the porous carbon framework provides sufficient buffer space for the volume expansion of silicon and reduces the damage of expansion stress to the overall structure; the Li2O nanoparticles generated by the decomposition of the pre-lithiation agent are uniformly distributed in the interior of the carbon framework and serve as a buffer medium to fill part of the pores. The in-situ generation of Li2O can compensate for the loss of lithium during the lithium intercalation of silicon, and the synergistic effect of Li2O and the carbon framework further alleviates the volume change. The uniform distribution of the components of the core in the porous structure spatially disperses the stress generated by the expansion of silicon, avoids the material cracking caused by local stress concentration, and fundamentally inhibits the overall volume expansion. The LiAlO2 nanoparticles in the first coating layer are embedded in the defects of the carbon layer by mechanical grinding, part of the LiAlO2 nanoparticles are filled in the micropores of the first coating layer to form "supporting columns", and part of the LiAlO2 nanoparticles are adsorbed on the defect sites on the surface of the carbon layer to form chemical bonds with the carbon layer. The LiAlO2 embedded in the defects enhances the strength of the first coating layer through mechanical support to resist the outward thrust generated by the expansion of silicon, and the chemical bonding effect improves the interfacial compatibility of LiAlO2 and the carbon layer to avoid structural failure caused by interface separation during charging and discharging. The "defect filling-mechanical support" effect of LiAlO2 prevents the carbon layer from cracking or peeling off during the expansion of silicon, and the synergistic constraint effect of LiAlO2 and the carbon layer further limits the volume expansion of the core, thereby reducing the overall expansion rate. The lithium ion battery provided in the application has excellent stability and conductivity. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the application, and therefore should not be regarded as a limitation on the scope of the application.

[0020] Figure 1 SEM image of the low-expansion silicon-carbon negative electrode material provided for Example 1. DETAILED DESCRIPTION

[0021] First, the scheme provided in the application will be explained in more detail as follows: The first aspect of the application provides a preparation method of a low-expansion silicon-carbon negative electrode material, comprising: The MOF material, graphite precursor, pre-lithiation agent, amphiphilic block copolymer, first carbon source, binder, dispersant, nano-silicon and organic solvent are first mixed and ultrasonicated to obtain a first mixture; the first mixture is then spray-dried and first calcined to obtain a first calcined material. It should be noted that the pre-lithiation agent generates Li2O in situ, providing a buffer space for subsequent expansion; The first calcined material and the second carbon source are mixed and coated in a second manner to obtain a second mixture; the second mixture is then calcined in an inert atmosphere to obtain a second calcined material. The second calcined material and LiAlO2 nanoparticles are mixed in a third way to obtain a third mixture, which is then ground to obtain a ground material. It is worth noting that mechanical grinding of LiAlO2 nanoparticles induces LiAlO2 to embed into defects in the first carbon coating layer, forming a dual buffer structure of ion conduction channels and mechanical support. The ion conduction channels reduce lithium-ion migration resistance and improve the rate performance of the battery, while the mechanical support enhances the expansion resistance of the first carbon coating layer and limits the excessive expansion of the core silicon particles. Furthermore, LiAlO2 nanoparticles can also achieve lithium source compensation and improve conductivity. The ground material and the third carbon source are mixed in a fourth process and then coated in a second process to obtain a fourth mixture. The fourth mixture is then calcined in an inert atmosphere to obtain a low-expansion silicon-carbon anode material.

[0022] It is important to note that amphiphilic block copolymers can promote the uniform dispersion of graphite precursors. Graphite precursors are hydrophobic and prone to aggregation in water-ethanol mixtures. The hydrophobic groups of the amphiphilic block copolymers can bind to the hydrophobic surface of the graphite precursors through hydrophobic interactions. Simultaneously, the hydrophilic groups of the amphiphilic block copolymers interact with solvent molecules, imparting hydrophilicity to the graphite precursor surface, thus ensuring good compatibility with the solvent and preventing uneven dispersion caused by hydrophobic aggregation. Furthermore, the amphiphilic nature of the block copolymers can eliminate the interfacial tension between graphite and the micelle shell, achieving uniform mixing and improving compatibility.

[0023] In addition, when the first carbon source includes phenolic resin, the phenolic resin can bond with the hydrophilic groups of the amphiphilic block copolymer through hydrogen bonds, and the non-polar part contained in the phenolic resin molecular chain can interact with the hydrophobic groups of the amphiphilic block copolymer, so that the phenolic resin is evenly distributed inside and outside the micelles, laying the foundation for subsequent carbonization to form a continuous carbon layer.

[0024] When the pre-lithiation agent includes LiOH, LiOH is a polar compound that can bind to the hydrophilic groups of the amphiphilic block copolymer through hydrogen bonds, promoting the uniform dispersion of LiOH in the system, avoiding uneven distribution of Li2O generated during subsequent carbonization, and ensuring the uniformity of the buffer space.

[0025] During the first coating process, the second carbon source can penetrate into the pores (including micropores and mesopores) of the MOF porous carbon framework in the liquid phase. By filling the pores, the pore size distribution of the framework can be adjusted, providing a buffer space for the volume expansion of silicon and preventing structural collapse due to excessively large pores. At the same time, a uniform carbon layer is formed on the surface of the framework, improving conductivity. Carbon source molecules can diffuse into the defect sites of the framework and combine with the active groups on the surface of the framework, reducing the structural damage to the framework caused in the pretreatment and improving the mechanical strength of the porous carbon framework.

[0026] The mechanical force of grinding allows LiAlO2 nanoparticles to embed into defects in the porous carbon framework of MOFs. Once embedded, they act as "support points," enhancing the mechanical strength of the porous carbon framework and alleviating the volume expansion stress of silicon during subsequent charging and discharging, thus reducing framework collapse or deformation. Simultaneously, LiAlO2 possesses excellent lithium-ion conductivity; its embedding into defects connects the framework's pores, forming a through-channel lithium-ion transport pathway and improving ion transport efficiency within the framework. During the second coating process, LiAlO2 can combine with a third carbon source through polar interactions, causing the third carbon source to preferentially deposit on and near defects on the LiAlO2 surface, preventing localized carbon source aggregation and resulting in a more uniform second carbon coating layer. Furthermore, the second coating acts as a "bridge," connecting the porous carbon framework and the second carbon coating layer, forming a tighter interfacial bond between the second carbon coating layer, the porous carbon framework, and LiAlO2, reducing carbon layer shedding or cracking during charging and discharging.

[0027] In some embodiments, the method for preparing the low-expansion silicon-carbon anode material satisfies at least one of the following conditions: (1) The MOF material includes ZIF-8; (2) The graphite precursor includes natural graphite and / or artificial graphite; (3) The pre-lithiation agent includes LiOH; (4) The amphiphilic block copolymer includes one or more of polyethylene glycol block copolymers, polystyrene-polyacrylic acid, polylactic acid-polyethylene glycol-polylactic acid, and polyethylene oxide-polypropylene oxide; It is important to note that amphiphilic block copolymers can adapt to the interfacial compatibility requirements of multi-component systems. The raw material system of this application contains hydrophobic components (such as nano-silicon, graphite precursors) and hydrophilic components (such as MOF materials, pre-lithiation agent LiOH, binders, etc.), and the dispersion medium is a water-ethanol mixed solvent. Amphiphilic block copolymers possess both hydrophilic groups (such as hydroxyl and carboxyl groups) and hydrophobic groups (such as alkyl and benzene rings), allowing them to adapt to complex systems through their inherent compatibility. Furthermore, the hydrophobic groups of the amphiphilic block copolymers can encapsulate nano-silicon particles to form a "core-shell" structure, preventing silicon particle aggregation. The hydrophilic groups bind to the hydroxyl groups on the surface of the MOF material, inducing the MOF particles to arrange themselves orderly around the "silicon-polymer" micelles under ultrasonic treatment. After calcination, a porous carbon framework encapsulates the silicon particles, providing ample buffer space for silicon expansion. The amphiphilic nature of the amphiphilic block copolymers can eliminate interfacial tension between the graphite precursor and micelles, and between the carbon source and silicon, improving the compatibility of each phase. This reduces the direct contact between the electrolyte and silicon during charging and discharging, reduces volume instability caused by side reactions (such as repeated rupture / regeneration of the SEI film), and indirectly suppresses overall expansion.

[0028] (5) The adhesive includes one or more of sodium carboxymethyl cellulose, sodium alginate, and polyacrylic acid; (6) The dispersant includes one or more of polyvinylpyrrolidone, polyethylene glycol, hexadecyltrimethylammonium bromide, and sodium dodecyl sulfate; (7) The first carbon source, the second carbon source and the third carbon source each independently include one or more of phenolic resin, polyacrylonitrile, glucose, sucrose, coal tar pitch, petroleum pitch, carbon nanotubes and graphene; (8) The organic solvent includes ethanol; (9) The particle size of the LiAlO2 nanoparticles is 50-200 nm.

[0029] Optionally, the particle size of LiAlO2 nanoparticles can be any value between 50nm, 100nm, 150nm, 200nm, or 50-200nm.

[0030] In some embodiments, the method for preparing the low-expansion silicon-carbon anode material satisfies at least one of the following conditions: (1) The mass ratio of the MOF material, the graphite precursor, the pre-lithiation agent, the amphiphilic block copolymer, the first carbon source, the binder, the dispersant, and the nano-silicon is 0.05-0.15:0.2-0.5:0.01-0.1:0.01-0.05:0.1-0.2:0.01-0.2:0.01-0.5:1; Optionally, the mass ratio of MOF material, graphite precursor, pre-lithiation agent, amphiphilic block copolymer, first carbon source, binder, dispersant, and nano-silicon can be 0.05:0.2:0.01:0.01:0.1:0.01:0.01:1, 0.1:0.2:0.01:0.01:0.1:0.01:0.01:1, 0.15:0.2:0.01:0.01:0.1:0.01:0.01:1, 0.05:0 0.3:0.01:0.01:0.1:0.01:0.01:1、0.05:0.5:0.01:0.01:0.1:0.01:0.01:1、0.05:0.2:0.05:0.01:0.1:0.01:0.01:1、0.05:0.2:0.1:0.01:0.1:0.01:0.01:1、0.05:0.2:0.01:0.025:0.1:0.01:0 0.01:1, 0.05:0.2:0.01:0.05:0.1:0.01:0.01:1, 0.05:0.2:0.01:0.01:0.15:0.01:0.01:1, 0.05:0.2:0.01:0.01:0.2:0.01:0.01:1, 0.05:0.2:0.01:0.01:0.1:0.015:0.01:1, 0.05:0.2:0.01:0 Any value between 0.01:0.1:0.05:0.01:1, 0.05:0.2:0.01:0.01:0.01:0.01:0.025:1, 0.05:0.2:0.01:0.01:0.1:0.01:0.05:1, or 0.05-0.15:0.2-0.5:0.01-0.1:0.01-0.05:0.1-0.2:0.01-0.2:0.01-0.5:1; (2) The mass ratio of the first roasting material to the second carbon source is 1:0.03-0.07; Optionally, the mass ratio of the first roasting material to the second carbon source can be any value between 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, or 1:0.03-0.07. (3) The mass ratio of the second calcined material to the LiAlO2 nanoparticles is 100:1-10; Optionally, the mass ratio of the second calcined material to the LiAlO2 nanoparticles can be any value between 100:1, 100:2, 100:4, 100:6, 100:8, 100:10 or 100:1-10; (4) The mass ratio of the ground material to the third carbon source is 1:0.1-1.

[0031] Optionally, the mass ratio of the ground material to the third carbon source can be any value between 1:0.1, 1:0.5:1:1, or 1:0.1-1.

[0032] In some embodiments, the method for preparing the low-expansion silicon-carbon anode material satisfies at least one of the following conditions: (1) The frequency of the ultrasound is 20kHz-100kHz and the duration is 30-60min; Optionally, the frequency of the ultrasound can be any value between 20kHz, 40kHz, 60kHz, 80kHz, 100kHz or 20kHz-100kHz, and the duration can be any value between 30min, 40min, 50min, 60min or 30-60min. (2) The inlet air temperature of the spray dryer is 130℃-200℃, the rotation speed is 300Hz-500Hz, and the feed pump speed is 20rpm-35rpm.

[0033] Optionally, the inlet air temperature of the spray dryer can be any value between 130℃, 150℃, 180℃, 200℃ or 130℃-200℃, the rotation speed can be any value between 300Hz, 400Hz, 500Hz or 300Hz-500Hz, and the feed pump speed can be any value between 20rpm, 25rpm, 30rpm, 35rpm or 20rpm-35rpm.

[0034] In some embodiments, the method for preparing the low-expansion silicon-carbon anode material satisfies at least one of the following conditions: (1) The temperature of the first calcination is 600℃-1000℃ and the time is 1-6h; Optionally, the temperature of the first roasting can be any value between 600℃, 700℃, 800℃, 900℃, 1000℃ or 600℃-1000℃, and the time can be any value between 1h, 2h, 4h, 6h or 1-6h. (2) The second roasting temperature is 300℃-1400℃ and the time is 1-6h; Optionally, the temperature of the second roasting can be any value between 300℃, 600℃, 900℃, 1200℃, 1400℃ or 300℃-1400℃, and the time can be any value between 1h, 2h, 4h, 6h or 1-6h. (3) The temperature of the third roasting is 300℃-1000℃ and the time is 1-6h.

[0035] Optionally, the temperature of the third roasting can be any value between 300℃, 600℃, 900℃, 1000℃ or 300℃-1000℃, and the time can be any value between 1h, 2h, 4h, 6h or 1-6h.

[0036] In some embodiments, the method for preparing the low-expansion silicon-carbon anode material satisfies at least one of the following conditions: (1) The first coating process includes a third coating process, a fourth coating process and a fifth coating process performed sequentially; The third coating treatment is performed at a temperature of 400℃-600℃ for 20-40 minutes. Optionally, the temperature of the third coating treatment can be any value between 400℃, 500℃, 600℃ or 400℃-600℃, and the time can be any value between 20min, 30min, 40min or 20-40min. The fourth coating treatment is performed at a temperature of 600℃-800℃ for a time of 40-80 minutes. Optionally, the temperature of the fourth coating treatment can be any value between 600℃, 700℃, 800℃ or 600℃-800℃, and the time can be any value between 40min, 50min, 60min, 70min, 80min or 40-80min. The fifth coating treatment is performed at a temperature of 800℃-1000℃ for a time of 20-40 minutes. Optionally, the temperature of the fifth coating treatment can be any value between 800℃, 900℃, 1000℃ or 800℃-1000℃, and the time can be any value between 20min, 30min, 40min or 20-40min. It is important to note that the decomposition and carbonization rates of carbon sources differ at different temperature stages. In the low temperature stage (400℃-600℃), the carbon source is initially softened and begins to decompose. At this time, the lower protective gas flow rate can reduce material disturbance and allow the carbon source to be uniformly attached to the surface of silicon particles and the pores of MOF-derived porous carbon skeleton, avoiding local aggregation of silicon particles due to airflow impact. In the medium temperature stage (600℃-800℃), moderately increasing the flow rate can promote the formation of a uniform network structure of the carbon layer and enhance the mechanical strength of the skeleton. In the high temperature stage (800℃-1000℃), the carbon source is completely carbonized to form a rigid carbon layer. The higher gas flow rate can promptly remove the small molecule byproducts generated by carbonization, preventing the byproducts from accumulating locally and hindering the dispersion of silicon particles, ultimately making the silicon particles more uniformly distributed in the carbon matrix. Dynamically adjusting the protective gas flow rate under the coating temperature gradient helps to distribute silicon particles evenly, improve the material structure, alleviate volume expansion, and improve its electrochemical performance. (2) The temperature of the second coating treatment is 60-220℃, the time is 4h-12h, and the stirring speed is 200-1000rpm.

[0037] Optionally, the temperature of the second coating treatment can be any value between 60℃, 100℃, 150℃, 200℃, 220℃ or 60-220℃, the time can be any value between 4h, 8h, 12h or 4h-12h, and the stirring speed can be any value between 200rpm, 400rpm, 600rpm, 800rpm, 1000rpm or 200-1000rpm.

[0038] In some embodiments, the method for preparing the low-expansion silicon-carbon anode material satisfies at least one of the following conditions: (1) The inert gas in the inert atmosphere includes one or more of nitrogen, argon, neon, xenon, and radon; (2) During the first calcination, the second calcination and the third calcination, the flow rate of the inert gas is 0.1-10 L / min for each of them independently; Optionally, during the first, second, and third calcination processes, the flow rate of the inert gas can be independently set to 0.1 L / min, 1 L / min, 5 L / min, 10 L / min, or any value between 0.1 and 10 L / min. (3) The grinding speed is 200-600 rpm and the time is 1-6 h; Optionally, the grinding speed can be any value of 200rpm, 400rpm, 600rpm or 200-600rpm, and the time can be any value between 1h, 2h, 3h, 4h, 5h, 6h or 1-6h; (4) The concentration of the third carbon source is 10-30%.

[0039] Optionally, the concentration of the third carbon source can be any value between 10%, 20%, 30%, or 10-30%.

[0040] A second aspect of this application provides a low-expansion silicon-carbon anode material, comprising a core and a first carbon coating layer and a second carbon coating layer disposed on the surface of the core; It is prepared by the aforementioned method for preparing low-expansion silicon-carbon anode material.

[0041] In some embodiments, the low-expansion silicon-carbon anode material satisfies at least one of the following conditions: (1) The thickness of the first carbon coating layer is 5nm-50nm; Optionally, the thickness of the first carbon coating layer (first coating layer) can be any value between 5nm, 10nm, 20nm, 30nm, 40nm, 50nm or 5nm-50nm; (2) The thickness of the second carbon coating layer is 20nm-100nm.

[0042] Optionally, the thickness of the second carbon coating layer (second coating layer) can be any value between 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm or 20nm-100nm.

[0043] A third aspect of this application provides a lithium-ion battery, including the aforementioned low-expansion silicon-carbon anode material.

[0044] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0045] Example 1 This embodiment provides a low-expansion silicon-carbon anode material and its preparation method. The specific preparation steps are as follows: S1: ZIF-8, artificial graphite, LiOH, polystyrene-polyacrylic acid (amphiphilic block copolymer), phenolic resin, sodium carboxymethyl cellulose (binder), hexadecyltrimethylammonium bromide (dispersant), and nano-silica are mixed in a mass ratio of 0.1:0.2:0.05:0.05:0.1:0.2:0.01:1. The mixture is then dispersed in a water-ethanol solvent (volume ratio 3:1), with a mass ratio of the mixture to the water-ethanol solvent of 3:25. S2: Place the well-dispersed solution in an ultrasonic instrument, first sonicate at low frequency (20kHz) for 40 minutes, then sonicate at high frequency (100kHz) for 20 minutes to obtain silicon-carbon anode precursor slurry; S3: Set the spray drying inlet air temperature to 150℃, the rotation speed to 400Hz, and the pump speed to 30rpm. Use the spray drying equipment to dry the silicon-carbon anode precursor slurry to obtain the silicon-carbon anode material precursor material. S4: The silicon-carbon anode precursor material obtained by spraying is placed in a tube furnace under nitrogen protection for carbonization treatment. The carbonization temperature is set to 600℃, the holding time is set to 2h, and the nitrogen flow rate is controlled to be 0.25L / min. After carbonization is completed, the first carbonized material is obtained. S5: Place the first carbonized material and asphalt in the coating machine at a mass ratio of 1:0.05. Set the coating temperature for the first stage to 400℃, control the nitrogen flow rate to 50mL / min, and hold for 30min. Set the coating temperature for the second stage to 700℃, control the nitrogen flow rate to 300mL / min, and hold for 60min. Set the coating temperature for the third stage to 900℃, control the nitrogen flow rate to 500mL / min, and hold for 20min. Collect the material. S6: The material collected in step 5 is placed in a tube furnace under nitrogen protection for carbonization treatment. The carbonization temperature is set to 1000℃, the holding time is set to 4h, and the nitrogen flow rate is controlled to be 0.25L / min. After carbonization is completed, the second carbonized material is obtained. S7: Place the second carbonized material into a ball mill, add LiAlO2 nanoparticles (50nm particle size) at a mass ratio of 100:5 (second carbonized material: LiAlO2 nanoparticles mass ratio), set the ball mill speed to 300rpm, grind for 1h, and place the ground material into a vacuum drying oven to dry for 4h; place the dried material into a 10% asphalt solution (asphalt:NMP=1:10) to dissolve, and simultaneously turn on the ultrasonic instrument to sonicate for 30min to assist in uniform dispersion, place the dispersed solution into a reaction vessel, set the stirring speed to 600rpm, start stirring, and simultaneously introduce inert gas to remove air, maintain a slight positive pressure of 0.05~0.1MPa in the reaction vessel, set the temperature to 180℃, and stir for 10h to allow the asphalt to be uniformly adsorbed on the surface of the silicon carbon particles; S8: After the reaction is completed, allow the material to cool naturally to room temperature. Dry the obtained material in a vacuum drying oven at 80°C for 16 hours. Place the dried material in a tube furnace under nitrogen protection for carbonization treatment. Set the carbonization temperature to 1000°C and the holding time to 4 hours. Control the nitrogen flow rate to 0.25 L / min. After carbonization, crush the material and sieve it through a 200-mesh screen to obtain low-expansion silicon-carbon anode material.

[0046] SEM images of the low-expansion silicon-carbon anode material are shown below.Figure 1 As stated above.

[0047] Example 2 This embodiment provides a low-expansion silicon-carbon anode material and its preparation method. The specific preparation steps are as follows: S1: ZIF-8, artificial graphite, LiOH, polystyrene-polyacrylic acid, phenolic resin, sodium carboxymethyl cellulose, hexadecyltrimethylammonium bromide, and nano-silicon are mixed in a mass ratio of 0.05:0.3:0.01:0.05:0.1:0.2:0.01:1. The mixed material is then dispersed in a water-ethanol solvent (volume ratio 3:1), with a mass ratio of the mixed material to the water-ethanol solvent of 3:25. S2: Place the well-dispersed solution in an ultrasonic instrument, first sonicate at low frequency (20kHz) for 40 minutes, then sonicate at high frequency (100kHz) for 20 minutes to obtain silicon-carbon anode precursor slurry; S3: Set the spray drying inlet air temperature to 180℃, the rotation speed to 500Hz, and the pump speed to 20rpm. Use the spray drying equipment to dry the silicon-carbon anode precursor slurry to obtain the silicon-carbon anode material precursor material. S4: The silicon-carbon anode precursor material obtained by spraying is placed in a tube furnace under nitrogen protection for carbonization treatment. The carbonization temperature is set to 600℃, the holding time is set to 2h, and the nitrogen flow rate is controlled to be 0.25L / min. After carbonization is completed, the first carbonized material is obtained. S5: Place the first carbonized material and asphalt in the coating machine at a mass ratio of 1:0.05. Set the coating temperature for the first stage to 500℃, control the nitrogen flow rate to 65mL / min, and hold for 30min. Set the coating temperature for the second stage to 800℃, control the nitrogen flow rate to 450mL / min, and hold for 60min. Set the coating temperature for the third stage to 1000℃, control the nitrogen flow rate to 650mL / min, and hold for 20min. Collect the material. S6: The material collected in step 5 is placed in a tube furnace under nitrogen protection for carbonization treatment. The carbonization temperature is set to 1000℃, the holding time is set to 4h, and the nitrogen flow rate is controlled to be 0.25L / min. After carbonization is completed, the second carbonized material is obtained. S7: Place the second carbonized material into a ball mill, add LiAlO2 nanoparticles (50nm particle size) at a mass ratio of 100:3 (second carbonized material: LiAlO2 nanoparticles mass ratio), set the ball mill speed to 300rpm, grind for 1h, and place the ground material into a vacuum drying oven to dry for 4h; place the dried material into a 10% asphalt solution (asphalt:NMP=1:10) to dissolve, and simultaneously turn on the ultrasonic instrument to sonicate for 30min to assist in uniform dispersion, place the dispersed solution into a reaction vessel, set the stirring speed to 600rpm, start stirring, and simultaneously introduce inert gas to remove air, maintain a slight positive pressure of 0.05~0.1MPa in the reaction vessel, set the temperature to 190℃, and stir for 10h to allow the asphalt to be uniformly adsorbed on the surface of the silicon carbon particles; S8: After the reaction is completed, allow the material to cool naturally to room temperature. Dry the obtained material in a vacuum drying oven at 80°C for 16 hours. Place the dried material in a tube furnace under nitrogen protection for carbonization treatment. Set the carbonization temperature to 1000°C and the holding time to 4 hours. Control the nitrogen flow rate to 0.25 L / min. After carbonization, crush the material and sieve it through a 200-mesh screen to obtain low-expansion silicon-carbon anode material.

[0048] Example 3 The difference from Example 1 is that the mass ratio of ZIF-8, artificial graphite, LiOH, amphiphilic block copolymer, phenolic resin, binder, dispersant, nano-silicon LiOH, polystyrene-polyacrylic acid, phenolic resin, sodium carboxymethyl cellulose, hexadecyltrimethylammonium bromide, and nano-silicon is 0.15:0.5:0.1:0.05:0.2:0.2:0.5:1.

[0049] Comparative Example 1 The difference from Example 1 is that ZIF-8, LiOH pre-lithiation agent, and polystyrene-polyacrylic acid are not added in step S1.

[0050] Comparative Example 2 The difference from Example 1 is that in step S5, no temperature gradient setting or protective gas flow rate control is made for the coating. The first carbonized material and asphalt are directly mixed and stirred for 110 minutes.

[0051] Comparative Example 3 The difference from Example 1 is that in step S7, LiAlO2 nanoparticles are not added, and the second carbonized material is directly dried and mixed with the asphalt solution.

[0052] Comparative Example 4 The difference from Example 1 is that in step S7, the asphalt solution is not coated, that is, the second coating layer is not set.

[0053] Comparative Example 5 The difference from Example 1 is that polystyrene-polyacrylic acid is not added in step S1.

[0054] Comparative Example 6 The difference from Example 1 is that in step S1, polystyrene-polyacrylic acid is replaced with polyethylene glycol monomethyl ether.

[0055] The silicon-carbon anode materials prepared in the above embodiments and comparative examples were respectively used to make coin cells. The specific process of making coin cells is as follows: A negative electrode slurry was prepared by mixing silicon-carbon negative electrode material, polyvinylidene fluoride (PVDF), and conductive agent (Super-P) in a mass ratio of 8:1:1. The obtained negative electrode slurry was coated on a current collector copper foil, placed in an oven, dried at 80°C for 12 hours, and then cut to obtain silicon-carbon negative electrode sheets. A polypropylene microporous membrane was used, a lithium sheet was used as the counter electrode, and 1 mol / L LiPF6 was used as the electrolyte. The obtained silicon-carbon negative electrode sheets were assembled into a coin cell in a glove box under an argon atmosphere.

[0056] The prepared battery was subjected to electrochemical performance testing. The data of the electrochemical performance testing are shown in Table 1. The expansion rate of the battery after cycling was measured with a micrometer.

[0057] Table 1 Electrochemical Performance Tests

[0058] analyze: The results above show that Comparative Example 1 lacks ZIF-8, the material has no porous structure, and stress concentration occurs when silicon particles expand, causing the electrode expansion rate to increase from 15.7% to 25.7%. At the same time, the absence of Li2O generated from the decomposition of LiOH as a buffer medium further exacerbates the volume expansion and cannot compensate for lithium loss. The lack of amphiphilic block copolymers leads to particle agglomeration, poor dispersibility, and decreased cycle stability. In Comparative Example 2, the removal of the temperature gradient and protective gas flow rate control in the first coating treatment resulted in uneven carbonization of the carbon source and localized aggregation, leading to poor silicon particle dispersion. The initial reversible specific capacity dropped to 1301 mAh / g, and the cycle retention rate was only 72%. In Comparative Example 3, without LiAlO2 nanoparticles to provide mechanical support, the carbon layer is prone to cracking when silicon expands, and the electrode expansion rate increases from 15.7% to 25.2%. At the same time, as LiAlO2 serves as a lithium-ion conduction channel, the absence of LiAlO2 increases the resistance to ion migration and reduces the rate performance. In Comparative Example 4, the absence of a second coating treatment exposes surface defects, exacerbates electrolyte erosion, reduces SEI film stability, lowers the initial coulombic efficiency to 74.3%, and results in a cycle retention rate of only 74%. The synergistic constraint of the dual coating layers disappears, and without the buffer of the outer carbon layer during silicon expansion, the electrode expansion rate rises to 29.6%. Comparative Example 5: Without the amphiphilic block copolymer, the material cannot form "core-shell" micelles, resulting in uneven dispersion of silicon particles, obstructed electron conduction, a decrease in the first reversible specific capacity, a cycle retention rate of 71%, the disappearance of its induction of ZIF-8 ordered arrangement, leading to disorder of the porous carbon skeleton after carbonization, insufficient buffer space, and an increase in expansion rate. Although polyethylene glycol monomethyl ether in Comparative Example 6 is amphiphilic, its hydrophobicity is poor, and it cannot effectively encapsulate silicon or induce ZIF-8 to arrange in an orderly manner. This leads to the aggregation of silicon particles and disorder of the porous carbon skeleton, resulting in a first reversible specific capacity of 1407 mAh / g and a cycle retention rate of 72%.

[0059] Comparative examples and comparative examples show that the low-expansion silicon-carbon anode material prepared by this application has a high initial reversible specific capacity, an initial coulombic efficiency of over 90%, and maintains a high capacity retention rate after 100 cycles at 0.1C, indicating good cycle stability. The electrode expansion rate is also low, which improves the volume expansion problem of silicon.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0061] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing a low-expansion silicon-carbon anode material, characterized in that, include: The MOF material, graphite precursor, pre-lithiation agent, amphiphilic block copolymer, first carbon source, binder, dispersant, nano-silicon and organic solvent are first mixed and ultrasonicated to obtain a first mixture; the first mixture is then spray-dried and first calcined to obtain a first calcined material. The first calcined material and the second carbon source are mixed and coated in a second manner to obtain a second mixture; the second mixture is then calcined in an inert atmosphere to obtain a second calcined material. The second calcined material and LiAlO2 nanoparticles are mixed in a third way to obtain a third mixture, which is then ground to obtain a ground material. The ground material and the third carbon source are mixed in a fourth process and then coated in a second process to obtain a fourth mixture. The fourth mixture is then calcined in an inert atmosphere to obtain a low-expansion silicon-carbon anode material.

2. The method for preparing the low-expansion silicon-carbon anode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The MOF material includes ZIF-8; (2) The graphite precursor includes natural graphite and / or artificial graphite; (3) The pre-lithiation agent includes LiOH; (4) The amphiphilic block copolymer includes one or more of polyethylene glycol block copolymers, polystyrene-polyacrylic acid, polylactic acid-polyethylene glycol-polylactic acid, and polyethylene oxide-polypropylene oxide; (5) The adhesive includes one or more of sodium carboxymethyl cellulose, sodium alginate, and polyacrylic acid; (6) The dispersant includes one or more of polyvinylpyrrolidone, polyethylene glycol, hexadecyltrimethylammonium bromide, and sodium dodecyl sulfate; (7) The first carbon source, the second carbon source and the third carbon source each independently include one or more of phenolic resin, polyacrylonitrile, glucose, sucrose, coal tar pitch, petroleum pitch, carbon nanotubes and graphene; (8) The organic solvent includes ethanol; (9) The particle size of the LiAlO2 nanoparticles is 50-200 nm.

3. The method for preparing the low-expansion silicon-carbon anode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The mass ratio of the MOF material, the graphite precursor, the pre-lithiation agent, the amphiphilic block copolymer, the first carbon source, the binder, the dispersant, and the nano-silicon is 0.05-0.15:0.2-0.5:0.01-0.1:0.01-0.05:0.1-0.2:0.01-0.2:0.01-0.5:1; (2) The mass ratio of the first roasting material to the second carbon source is 1:0.03-0.07; (3) The mass ratio of the second calcined material to the LiAlO2 nanoparticles is 100:1-10; (4) The mass ratio of the ground material to the third carbon source is 1:0.1-1.

4. The method for preparing the low-expansion silicon-carbon anode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The frequency of the ultrasound is 20kHz-100kHz and the duration is 30-60min; (2) The inlet air temperature of the spray dryer is 130℃-200℃, the rotation speed is 300Hz-500Hz, and the feed pump speed is 20rpm-35rpm.

5. The method for preparing the low-expansion silicon-carbon anode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The temperature of the first calcination is 600℃-1000℃ and the time is 1-6h; (2) The second roasting temperature is 300℃-1400℃ and the time is 1-6h; (3) The temperature of the third roasting is 300℃-1000℃ and the time is 1-6h.

6. The method for preparing the low-expansion silicon-carbon anode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The first coating process includes a third coating process, a fourth coating process and a fifth coating process performed sequentially; The third coating treatment is performed at a temperature of 400℃-600℃ for 20-40 minutes. The fourth coating treatment is performed at a temperature of 600℃-800℃ for a time of 40-80 minutes. The fifth coating treatment is performed at a temperature of 800℃-1000℃ for a time of 20-40 minutes. (2) The temperature of the second coating treatment is 60-220℃, the time is 4h-12h, and the stirring speed is 200-1000rpm.

7. The method for preparing the low-expansion silicon-carbon anode material according to any one of claims 1-6, characterized in that, At least one of the following conditions must be met: (1) The inert gas in the inert atmosphere includes one or more of nitrogen, argon, neon, xenon, and radon; (2) During the first calcination, the second calcination and the third calcination, the flow rate of the inert gas is 0.1-10 L / min for each of them independently; (3) The grinding speed is 200-600 rpm and the time is 1-6 h; (4) The concentration of the third carbon source is 10-30%.

8. A low-expansion silicon-carbon anode material, characterized in that, It includes a core and a first carbon coating layer and a second carbon coating layer disposed on the surface of the core; It is prepared by the method for preparing low-expansion silicon-carbon anode material according to any one of claims 1-7.

9. The low-expansion silicon-carbon anode material according to claim 8, characterized in that, At least one of the following conditions must be met: (1) The thickness of the first carbon coating layer is 5nm-50nm; (2) The thickness of the second carbon coating layer is 20nm-100nm.

10. A lithium-ion battery, characterized in that, Including the low-expansion silicon-carbon anode material as described in claim 8 or 9.

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