Silicon-carbon composite material with multi-level inner hole structure and preparation method and application thereof

Abstract

The application provides a silicon-carbon composite material with a multi-level inner hole structure and a preparation method thereof. The silicon-based component of the composite material is composed of two parts and has two types of holes. One hole is a nano-sized mesopore formed through a chemical etching step and finally remaining inside the silicon monoxide nanowire. The other hole is a networked mesopore formed between the silicon monoxide nanowire and the partially oxidized nanosilicon powder through a ball milling and sintering process. The two types of holes formed are beneficial to buffering volume expansion in the charge and discharge process. The conductive carbon-coated secondary particles can greatly reduce the overall volume expansion of the secondary particles due to the internal porosity. The conductive carbon shell can effectively avoid direct contact of the internal part with the electrolyte organic matter, only allowing lithium ions to be embedded and extracted, avoiding exposure of the silicon-based component, thereby effectively inhibiting repeated generation of the SEI film, and finally obtaining excellent negative electrode charge and discharge high capacity and stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of energy, and particularly relates to a silicon-carbon composite material with a multi-level inner pore structure and a preparation method and application thereof. BACKGROUND

[0002] The negative electrode is one of the important components of the core energy storage unit of a lithium ion battery together with the positive electrode and the separator and the electrolyte. The energy storage performance of the negative electrode is one of the key components that determine the energy storage performance of the battery. Therefore, the energy storage capacity of the energy storage active component used in the negative electrode is very important. The negative electrode material on the market at present is mainly graphite, including natural graphite and artificial graphite. Due to the continuous development of energy storage technologies such as power batteries, the development of lithium ion battery technologies with higher capacity requires further improvement of the capacity of the positive electrode and the negative electrode. The actual use capacity of graphite is already very close to its theoretical capacity (372 mAh / g), and its development space is exhausted. Therefore, the synthesis and design of new negative electrode materials with higher capacity are the focus of research and development investment in the industry in the past decade. Among the many negative electrode materials, silicon-based negative electrode materials have been initially applied. Silicon has a theoretical capacity of 4200 mAh / g, which is much higher than that of graphite negative electrodes. However, the silicon material expands too much (>300%) during charging and discharging, which causes the negative electrode to repeatedly expand and shrink in volume during the cycle charging and discharging process, resulting in particle fragmentation, pulverization and structural relaxation. The repeated growth of the SEI film leads to the continuous increase in the overall volume of the negative electrode and the consumption of a large amount of organic electrolyte, eventually causing the destruction of the conductive network in the negative electrode layer and the inability of the active silicon component to continue to participate in the electrochemical process, resulting in the quick failure of the battery. This problem is a key technical obstacle to the large-scale application of silicon-based batteries.

[0003] In view of the problem of structural instability caused by the large volume expansion of silicon-based negative electrode materials, a series of research progress and patent technologies have proposed various solutions in recent years. For example, the prior art reports that silicon nanowires can obtain stable reversible volume expansion without pulverization and fracture during charging and discharging, and the SEI layer can stably exist. In addition, the cross-linked network of the nanowire aggregate has a large number of inner pores, which provides a large amount of space for the volume expansion of the negative electrode active component, so that the space of the negative electrode active component can stably and reversibly charge and discharge, and the overall performance of the battery is excellent. However, the batch production of silicon nanowires currently faces the obstacles of high cost and low yield, and cannot be applied on a large scale in the short term.

[0004] For example, the prior art obtains a SiMxOy composite material by doping silicon with metal, the inner layer is silicon, the outer layer is metal oxide, and then the surface is wrapped with carbon particles. The obtained negative electrode material has a slowed SEI film formation due to the presence of metal oxide, and the carbon wrapping layer improves the conductivity, thereby effectively improving the initial coulombic efficiency and stability, but the capacity of the negative electrode cannot be effectively improved, and the high-capacity characteristics of the silicon-based negative electrode material are not fully utilized. For example, the prior art discloses a porous silicon-carbon negative electrode material and a preparation method thereof. The porous silicon-carbon negative electrode material is obtained by modulating the spatial dispersion of silicon through a porous graphene aggregate, combining an organic carbon source for carbonization, and strengthening the porous structure. The negative electrode material has good cycle stability and conductivity, but the comprehensive performance of the battery, such as high-capacity charging and discharging characteristics, is not improved, and the charging and discharging cycle stability period is not long, and other methods are still needed to further improve the cycle charging and discharging stability of the silicon-based negative electrode.

[0005] For example, the prior art discloses a silicon-carbon composite fiber wrapped with titanium dioxide to form an electrochemically stable layer with certain elasticity, avoid contact between silicon and electrolyte, and inhibit rapid growth of SEI film. Silicon nanoparticles are embedded inside the carbon nanofiber to further stabilize the spatial structure. However, this is achieved through electrospinning technology, which is costly and not suitable for large-scale production, and does not meet the requirements of low-cost production in large quantities by domestic and foreign production enterprises.

[0006] Therefore, in view of the social demand for low-cost mass production, it is necessary to develop a silicon-based negative electrode material with a special structure and a preparation process that meets the high-capacity power battery technology, to overcome the destruction of the conductive structure caused by repeated volume expansion and contraction of silicon during charging and discharging, and the uncontrollable growth of the SEI film caused by the exposure of new silicon surfaces, so as to have high charging and discharging initial efficiency, maintain high energy density and high cycle stability during long-term charging and discharging, and be essential for obtaining high-performance silicon-based lithium-ion batteries. SUMMARY

[0007] Therefore, the purpose of the present application is to provide a silicon-carbon composite material with a multi-level internal pore structure and a preparation method and application thereof. The silicon-carbon composite material provided by the present application has low preparation raw material and process cost, and is easy to produce in large quantities. When used as a negative active material to prepare a lithium-ion battery, it has good electrochemical performance.

[0008] The present application provides a silicon-carbon composite material with a multi-level internal pore structure, comprising:

[0009] A silicon-containing internal structure, the internal structure comprising: a nanowire unit and a core-shell structure unit;

[0010] A carbon layer wrapped on the surface of the silicon-containing internal structure.

[0011] Preferably, the nanowire unit is a silicon monoxide nanowire unit.

[0012] The core-shell structure unit comprises:

[0013] A silicon core;

[0014] A silicon monoxide shell disposed outside the silicon core.

[0015] Preferably, the silicon monoxide nanowire unit has a nanopore with a pore size < 5 nm.

[0016] Networked mesopores are formed between the nanowire units and the core-shell structure units, and / or networked mesopores are formed between the nanowire units and the nanowire units, the networked mesopores having a pore size of 2-100 nm.

[0017] Preferably, the silicon-carbon composite material with a multi-level internal pore structure has a porosity of 10-45% inside.

[0018] The present application provides a preparation method of a silicon-carbon composite material with a multi-level internal pore structure, comprising:

[0019] Mixing a porous silicon-based nanometer powder and a nanometer carbon source and sintering to obtain a silicon-carbon composite material with a multi-level internal pore structure.

[0020] Preferably, the preparation method of the porous silicon-based nanometer powder comprises:

[0021] Sintering a silicon-oxygen product, silicon powder and alkali metal salt to obtain a porous silicon-based nanometer powder.

[0022] Preferably, the preparation method of the silicon-oxygen product comprises:

[0023] Calcining halloysite, then acid washing and water washing to obtain a silicon-oxygen product.

[0024] Preferably, the preparation method of the nanometer carbon source comprises:

[0025] Sintering an organic matter and then grinding to obtain a nanometer carbon source.

[0026] The present application provides a lithium ion battery negative electrode, comprising: the silicon-carbon composite material with a multi-level internal pore structure according to the above technical solution; or the silicon-carbon composite material with a multi-level internal pore structure prepared by the method according to the above technical solution.

[0027] The present application provides a lithium ion battery, comprising: the lithium ion battery negative electrode according to the above technical solution.

[0028] The application provides a silicon-carbon composite material with a multi-level inner hole structure and a preparation method thereof, which can improve the initial coulomb efficiency of a lithium ion battery, buffer the volume expansion and contraction of a silicon component to the structural damage of a negative electrode active layer, thereby avoiding the exposure of a new surface caused by the volume expansion and contraction of the silicon component in the charging and discharging process, realizing the structural stability of an SEI film and a conductive network, and further obtaining a lithium ion battery negative electrode material with high capacity and high stability. The raw materials and process cost adopted by the application are low, and the active material obtained can be used as a component of a lithium ion battery negative electrode active material and matched with graphite in proportion, so that the balance matching of different requirements in cost and efficiency is met.

[0029] The application utilizes cheap halloysite and silicon powder as raw materials, and obtains a carbon-coated multi-level hole structure composite material through conventional physical and chemical treatment means, which has rich hole structures inside, and is beneficial to the structural stability of electrochemical charging and discharging. The halloysite and silicon powder are reacted and compounded, and the carbon-coated composite is further obtained, so that a multi-level hole structure composite material with structural stability and good conductivity is obtained, the construction of the porous structure and the compounding of high silicon content are realized under the condition of simple process, and the high capacity and high stability of the lithium ion battery negative electrode are ensured. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A process flow chart for preparing the silicon-carbon composite material of the embodiment of the application;

[0031] Figure 2 The cycle performance detection result of the silicon-carbon composite material prepared in Example 1 of the application;

[0032] Figure 3 The charge-discharge curve of the silicon-carbon composite material prepared in Example 1 of the application;

[0033] Figure 4 The XRD graph of the silicon-carbon composite material in Example 1 of the application;

[0034] Figure 5 The scanning electron microscope (SEM) image of the active Si / SiO prepared in Example 1 of the application;

[0035] Figure 6 The scanning electron microscope (SEM) image of the active Si / SiO prepared in Example 1 of the application;

[0036] Figure 7 The scanning electron microscope (SEM) image of the silicon-carbon composite material prepared in Example 1 of the application. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0038] The present application provides a silicon-carbon composite material with a multi-level inner pore structure, comprising:

[0039] A silicon-containing inner structure, the inner structure comprising: nanowire units and core-shell structure units;

[0040] A carbon layer coated on the surface of the silicon-containing inner structure.

[0041] In the present application, the silicon-carbon composite material with a multi-level inner pore structure has a carbon-coated outer shell and a porous silicon-based component (a silicon-containing inner structure) inside; the silicon-containing inner structure has a multi-level pore distribution.

[0042] In the present application, the nanowire units are preferably silicon monoxide nanowire units, and the silicon monoxide nanowire has a nanopore thereon, and the pore size of the nanopore is preferably <5 nm.

[0043] In the present application, the core-shell structure unit preferably comprises:

[0044] A silicon core;

[0045] A silicon monoxide shell arranged on the surface of the silicon core.

[0046] In the present application, a networked mesopore is formed between the nanowire units and the core-shell structure units, or between the nanowire units; the pore size of the networked mesopore is preferably 2-100 nm, more preferably 5-80 nm, more preferably 10-60 nm, more preferably 20-40 nm, and most preferably 30 nm. In the present application, a pore structure network is formed between the silicon monoxide nanowires and between the silicon monoxide nanowires and the surface silicon monoxide units in contact with the melt, and the pore size is between 2 nm and 100 nm.

[0047] In the present application, the carbon layer is preferably amorphous carbon.

[0048] In the present application, the particle size of the silicon-carbon composite material with a multi-level inner pore structure is preferably 2-20 μm, more preferably 5-15 μm, and most preferably 10 μm.

[0049] In the present application, the silicon-carbon composite material with multi-level inner pore structure is a micron-sized powder, the outer surface of which is wrapped with a dense carbon layer, and the inside of which is composed of two units of nanowire units of silicon monoxide and silicon monoxide / silicon core-shell units. The two units gradually react and fuse with each other to form a continuous body through the processes of ball milling and sintering of nanoporous silica and silicon powder, the continuous body has a multi-level nanopore structure as the internal silicon component of the micron-sized carbon-wrapped composite particles, the nanopore structure of silicon monoxide is initially formed after the nanorod of raw halloysite is sintered to transform the phase structure and chemically etched to remove the aluminum oxide component, the pore size is less than 5 nm, and is still preserved after the nanowire of silicon monoxide is formed through ball milling and sintering with silicon powder. The pore structure formed by the internal particles of the continuous body is due to the fact that the porous silica units and the silicon powder are combined through ball milling and then sintered, and the pore network between the two types of particles is still preserved during the fusion process. Sintering causes atomic migration, but a large number of pore structures formed by the non-fully dense contact between the particles of different morphologies are still preserved, and the pore size is between 2 nm and 100 nm.

[0050] The present application provides a preparation method of a silicon-carbon composite material with multi-level inner pore structure, comprising:

[0051] After the porous silicon-based powder and the carbon source are mixed and sintered, the silicon-carbon composite material with multi-level inner pore structure is obtained.

[0052] In the present application, the porous silicon-based powder is preferably a porous silicon-based nanopowder; the particle size of the porous silicon-based nanopowder is preferably 100-500 nm, more preferably 200-400 nm, and most preferably 300 nm.

[0053] In the present application, the preparation method of the porous silicon-based nanopowder preferably comprises:

[0054] The silicon-oxygen product, silicon powder and alkali metal salt are sintered to obtain the porous silicon-based nanopowder.

[0055] In the present application, the preparation method of the silicon-oxygen product comprises:

[0056] The halloysite is calcined and then subjected to acid washing and water washing to obtain the silicon-oxygen product.

[0057] In the present application, the halloysite is preferably in the form of nanofibers; the diameter of the nanofibers is preferably 5-30 nm, more preferably 10-25 nm, and most preferably 15-20 nm; the particle size of the halloysite is preferably 2500-3500 mesh, more preferably 2800-3200 mesh, and most preferably 3000 mesh.

[0058] In the present application, the calcination temperature is preferably 400-850℃, more preferably 500-800℃, and most preferably 600-800℃; the calcination temperature rising speed is preferably 8-12℃ / min, more preferably 10℃ / min; the calcination temperature holding time is preferably 1-3h, more preferably 2h; and the calcination is preferably followed by natural cooling to room temperature to obtain the silicon oxide.

[0059] In the present application, the acid pickling is preferably carried out by soaking in hydrochloric acid or sulfuric acid; the concentration of the sulfuric acid is preferably 1-3mol / L, more preferably 2mol / L; the acid pickling is preferably followed by centrifugal separation and then water washing, the stirring speed of the centrifugal separation is preferably 300-700rpm, more preferably 400-600rpm, and most preferably 500rpm, and the stirring time is preferably 5-10h, more preferably 6-8h; the water washing is preferably carried out by soaking in deionized water, and the water washing is preferably to neutral; the acid pickling and water washing are preferably repeated 2-4 times, more preferably 3 times; and the water washing is preferably followed by centrifugal separation and then drying; the drying temperature is preferably 60-150℃, more preferably 80-120℃, and most preferably 100℃; and the drying is preferably followed by grinding the obtained dried product into a dry powder. In the present application, the acid pickling and water washing remove the aluminum oxide component and other metal impurities.

[0060] In the present application, the particle size of the silicon powder is preferably 30-5000nm, more preferably 100-4000nm, more preferably 100-3000nm, more preferably 100-2000nm, and most preferably 200-500nm.

[0061] In the present application, the alkali metal salt is preferably selected from one or more of the chlorides, sulfates and phosphates of alkali metals; the alkali metal is preferably selected from Li, Mg, Al, etc.; and the alkali metal salt is preferably LiCl or NaCl.

[0062] In the present application, the mass ratio of the silicon oxide product to the silicon powder is preferably (0.2-5) : 1, more preferably (0.5-4) : 1, and most preferably (0.8-1.5) : 1; and the mass of the alkali metal salt is preferably 5-90% of the mass of the porous silicon-based nanopowder (or the total mass of the silicon oxide product, the silicon powder and the alkali metal salt), more preferably 10-80%, more preferably 20-60%, more preferably 20-50%, and most preferably 20-40%.

[0063] In the present application, the sintering of the silicon-oxygen product, silicon powder and alkali metal salt is preferably carried out in an inert atmosphere, more preferably in an argon atmosphere; the temperature of the sintering is preferably 800-1600℃, more preferably 1000-1400℃, and most preferably 1200℃; the temperature rising rate of the sintering is preferably 1-3℃ / min, and more preferably 2℃ / min; the holding time of the sintering is preferably 2-6h, more preferably 3-5h, and most preferably 4h.

[0064] In the present application, the sintering is preferably followed by:

[0065] The obtained sintered product is washed with water to remove the alkali metal salt, and a porous silicon-based nanometer powder is obtained.

[0066] In the present application, the water washing is preferably centrifugal washing, and the number of times of the water washing is preferably 2-4, and more preferably 3; the water washing is preferably followed by drying to obtain a porous silicon-based nanometer powder; the drying is preferably oven drying, and the drying is preferably carried out in a vacuum oven; the temperature of the drying is preferably 40-80℃, more preferably 50-70℃, and most preferably 60℃.

[0067] In the present application, the components of the porous silicon-based nanometer powder preferably include silicon and silicon monoxide.

[0068] In the present application, the carbon source is preferably a nanometer carbon source; the particle size of the nanometer carbon source is preferably 10-100nm, more preferably 20-80nm, more preferably 30-60nm, and most preferably 40-50nm.

[0069] In the present application, the preparation method of the nanometer carbon source includes:

[0070] The organic matter is ground after sintering to obtain a nanometer carbon source.

[0071] In the present application, the organic matter is preferably selected from one or more of glucose, maltose, chitosan, polyvinylpyrrolidone, polyvinyl alcohol, etc.

[0072] In the present application, the sintering of the organic matter is preferably carried out in an inert atmosphere, more preferably in an argon atmosphere, and a powder with reactivity is obtained after sintering; the temperature rising rate of the sintering is preferably 1-3℃ / min, and more preferably 2℃ / min; the temperature of the sintering is preferably 200-400℃, more preferably 250-350℃, and most preferably 300℃; the holding time of the sintering is preferably 2-6h, more preferably 3-5h, and most preferably 4h.

[0073] In the present application, the grinding is preferably by nano sand mill to nano size carbon source; the grinding ball used in the grinding process is preferably zirconium ball, the diameter of the grinding ball is preferably 0.1-0.3mm, more preferably 0.2mm; the mass ratio of the organic matter and the grinding ball is preferably (18-22):1, more preferably 20:1; the grinding medium is preferably ethanol, more preferably anhydrous ethanol; the mass of the grinding medium is preferably 70-90% of the mass of the organic matter, more preferably 75-85%, most preferably 80%; the rotation speed in the grinding process is preferably 1500-2500rpm, more preferably 1800-2200rpm, most preferably 2000rpm; the temperature of the grinding is preferably 15-25℃, more preferably 20℃; the grinding is preferably followed by evaporation of the grinding medium.

[0074] In the present application, the mass ratio of the porous silicon-based powder and the carbon source is preferably (1-2):(1-5), more preferably (1.2-1.8):(2-4), most preferably (1.6-1.8):3.

[0075] In the present application, the mixing of the porous silicon-based nanopowder and the nanocarbon source is preferably ball milling; the ball milling time is preferably 1-30min, more preferably 2-20min, more preferably 2-10min, most preferably 2-5min; ethanol is preferably used as the dispersant in the ball milling process, more preferably anhydrous ethanol; in the ball milling process, the nanocarbon source is added to the porous silicon-based nanopowder dispersion (dispersant is ethanol) under rapid stirring, followed by low-speed stirring, then rapid stirring, and finally evaporation of ethanol; the speed of the rapid stirring is preferably 800-1200rpm, more preferably 1000rpm; the speed of the low-speed stirring is preferably 100-300rpm, more preferably 200rpm; the time of the low-speed stirring is preferably 20-40min, more preferably 30min; the time of the rapid stirring is preferably 20-40min, more preferably 30min.

[0076] In the present application, the sintering of the porous silicon-based nanopowder and the nanocarbon source is preferably carried out in an inert atmosphere, more preferably in an argon atmosphere; the sintering temperature is preferably 600-1400℃, more preferably 800-1000℃, most preferably 900℃; the heating rate of the sintering is preferably 1-3℃ / min, more preferably 2℃ / min; the holding time of the sintering is preferably 2-6h, more preferably 3-5h, most preferably 4h.

[0077] In the present application, the preparation method of the silicon-carbon composite material with multi-level pore structure is as shown in Figure 1 The preparation method preferably comprises the following steps:

[0078] 1) Nanoporous silica is obtained by calcination, acid washing, water washing and other steps from halloysite;

[0079] 2) The silicon-oxygen product obtained in step 1) is sintered with silicon powder and alkali metal salt at high temperature under an inert atmosphere, and the alkali metal salt is removed by water washing to obtain a porous silicon-based nanopowder, which is composed of silicon and silicon monoxide;

[0080] 3) The organic matter is pre-sintered at low temperature under an inert atmosphere to obtain a powder with reactivity, and the carbon source is ground to nanometer size by a nanometer sand mill;

[0081] 4) The porous silicon-based nanopowder obtained in step 2) and the pre-processed nanometer carbon source are uniformly mixed in a short time;

[0082] 5) The mixture of step 4) is co-sintered under an inert atmosphere to obtain the final product.

[0083] In the present application, the silicon-based component of the silicon-carbon composite material with a multi-level internal pore structure is composed of two parts with two types of pores. One type of pore is a nanometer-sized mesopore formed by a chemical etching step and finally remaining inside the silicon monoxide nanowire, with a pore size less than 5 nanometers. The other type of pore is a networked mesopore formed between the silicon monoxide nanowire and the partially oxidized nanometer silicon powder obtained through ball milling and sintering process, with a pore size in the range of 2 nanometers to 100 nanometers, which is closed inside the composite particles after the final carbon coating treatment. The two types of pores formed are beneficial to buffering the volume expansion during the charge and discharge process. In addition to the internal porosity, which can greatly reduce the overall volume expansion of the secondary particles, the conductive carbon shell can effectively prevent the internal part from directly contacting the electrolyte organic matter, allowing only lithium ions to be inserted and extracted, avoiding the exposure of the silicon-based component, thereby effectively inhibiting the repeated formation of the SEI film, and finally obtaining excellent negative electrode charge and discharge capacity and stability.

[0084] The present application provides a lithium ion battery negative electrode, comprising: the silicon-carbon composite material with a multi-level internal pore structure as described in the above technical solution; or the silicon-carbon composite material with a multi-level internal pore structure prepared by the method as described in the above technical solution.

[0085] In the present application, the preparation method of the lithium ion battery negative electrode preferably comprises:

[0086] The silicon-carbon composite material with a multi-level internal pore structure, ketjen black, sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) are mixed to obtain a slurry;

[0087] The slurry is coated on a carbon-coated copper foil and dried to obtain an electrode sheet (lithium ion battery negative electrode).

[0088] In the present application, the Ketjen black is preferably Ketjen black CE-300j.

[0089] In the present application, the mass ratio of the silicon-carbon composite material with multi-level pore structure, Ketjen black, sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) is preferably (7-9):(0.8-1.2):(0.4-0.6):(0.4-0.6), more preferably 8:1:0.5:0.5.

[0090] In the present application, the drying is preferably vacuum drying; the drying is preferably carried out in a vacuum drying oven; the temperature of the drying is preferably 60-80℃, more preferably 70℃; the time of the drying is preferably 2-6h, more preferably 3-5h, most preferably 4h.

[0091] The present application provides a lithium ion battery, comprising: the lithium ion battery negative electrode of the above technical solution.

[0092] In the present application, the lithium ion battery is preferably a button half cell such as a CR2025 type button half cell; the lithium ion battery preferably further comprises: a counter electrode, an electrolyte, a separator.

[0093] In the present application, the counter electrode is preferably a lithium metal sheet; the electrolyte in the electrolyte is preferably LiPF6; the solvent of the electrolyte preferably comprises: EC, DEC and DMC; the volume ratio of the EC, DEC and DMC is preferably 1:(0.8-1.2):(0.8-1.2), more preferably 1:1:1; the separator is preferably a polypropylene microporous membrane.

[0094] In the present application, the preparation method of the lithium ion battery preferably comprises:

[0095] The counter electrode, the electrolyte, the separator and the lithium ion battery negative electrode are assembled into a battery in an Ar-filled glove box.

[0096] In the present application, the porous silicon nanowires are formed by co-sintering silicon powder and porous nanosilica to obtain silicon-based nanopowder, and then mixing and sintering the silicon-based nanopowder with a pretreated nanocarbon source. The porous nanosilica is obtained by removing aluminum oxide components and other impurities from halloysite through acid washing and high-temperature sintering. In the sintering process of the silicon-based nanopowder and the silicon powder, an appropriate amount of alkali metal salt is added as a structure change buffer. The carbon coating of the silicon-carbon composite material with a multi-level internal pore structure is limited to the external surface of the silicon-based nanopowder aggregate, and the silicon-based nanopowder is interwoven with each other to form secondary particles through the carbon coating process, with pores existing in the middle and being supported by the interlaced nanopowder. The porosity of the secondary particles of the nanoporous silicon-carbon composite material is adjustable in the range of 10-45%. In the charging and discharging process of the lithium ion battery, the silicon-carbon composite material with a multi-level internal pore structure can use the nanoporous structure to reserve space to offset the volume expansion and contraction caused by the charging and discharging of the silicon-based active component in the structure, without causing overall expansion and contraction and stress concentration, thereby stabilizing the performance of the battery negative electrode and obtaining a highly reversible charging and discharging capacity, which has important value in the field of power batteries.

[0097] The present application is further illustrated by the following examples without limiting the application to the examples described. In the following examples, the experimental methods not specified are selected according to the conventional methods and conditions or according to the instructions of the commercial products. The following are typical but non-limiting examples of the present application.

[0098] The various raw materials used in the embodiments of the present application are commercially available unless otherwise specified.

[0099] Example 1

[0100] The silicon-carbon composite material is prepared according to the following steps:

[0101] (1) Preparation of porous SiO2: Take 10 g of halloysite raw ore powder with a particle size of 3000 mesh, and heat it to 600℃ at a heating rate of 10℃ / min. After keeping the temperature at 600℃ for 2h, it is naturally cooled to room temperature. Then, 200ml of 2mol / L sulfuric acid is prepared, and the halloysite powder is added to the sulfuric acid solution while stirring. After the addition is completed, the stirring is maintained at a speed of 500rpm for 8h. The dispersion is centrifuged and washed with deionized water until it is neutral. The above steps are repeated three times to remove metal impurities. The obtained halloysite wet powder is dried in an oven at 60℃ to obtain nanoporous silica.

[0102] (2) Preparation of active Si / SiO material: 5 g of the above nanoporous SiO2 was weighed, 5 g of 200 nm silicon powder (mass ratio of porous SiO2: silicon powder = 1:1) was added, and 2.5 g of LiCl was weighed and mixed uniformly; the powder was placed in a crucible, heated to 1200°C at a rate of 2°C / min in an argon atmosphere, and kept at 1200°C for 4 h to obtain a solid powder; the solid powder was washed and centrifuged with 100 ml of water, repeated three times to remove any excess salt components, and dried in a vacuum oven at 60°C to obtain an active Si / SiO material.

[0103] (3) Preparation of organic-derived carbon: 20 g of glucose was weighed and placed in a corundum crucible, heated to 300°C at a rate of 2°C / min in an argon atmosphere, and kept at 300°C for 4 h to obtain a blackish-brown bulk material; the bulk was crushed and 0.2 mm zirconium balls were added to the nanoceramic bead mill at a solid mass ratio of 20:1, and 80% anhydrous ethanol was added as a grinding medium, the grinding was carried out at 2000 rpm for 5 min, the grinding temperature was 20°C, after grinding the ethanol was evaporated to obtain carbonaceous powder.

[0104] (4) Preparation of silicon-based composite material precursor: 4 g of active Si / SiO material in (2) was weighed, dispersed with 200 ml of anhydrous ethanol, and 6 g of organic-derived carbon (carbonaceous powder in step (3)) was added under rapid stirring at a speed of 1000 rpm, the mixed dispersion was ball milled in a ball mill tank at 200 rpm for 30 min, and after 30 min of rapid stirring the anhydrous ethanol was evaporated to obtain a precursor.

[0105] (5) Preparation of silicon-carbon composite material: the above precursor was placed in a corundum crucible, heated to 1200°C at a rate of 2°C / min in an argon atmosphere, and kept at 1200°C for 4 h to obtain a silicon-carbon composite material solid powder.

[0106] The XRD detection results of the silicon-carbon composite material prepared in Example 1 are shown in Figure 4 , the SEM detection results are shown in Figure 5 , Figure 6 , Figure 7 , Figure 5 , and Figure 6 are the internal structures of the silicon-carbon material, which include nanowires and core-shell structures, wherein the core-shell particles are attached to the nanowires, and the nanowires have continuous pores with a diameter of about 100 nm; Figure 7 is the electron micrograph of the final carbon-coated silicon-carbon negative electrode material, which presents an irregular block shape.

[0107] Example 2

[0108] The silicon-carbon composite material is prepared according to the following steps:

[0109] (1) Preparation of porous SiO2: take 10 g of halloysite raw powder with a particle size of 3000 mesh, and prepare 200 ml of 2 mol / L sulfuric acid, add the halloysite powder into the sulfuric acid solution, stir while adding, and keep stirring at a speed of 500 rpm for 8 h after adding, centrifuge the dispersion liquid and wash with deionized water until neutral; the above steps are repeated three times to remove metal impurities, and the obtained halloysite wet powder is dried in an oven at 60°C; the halloysite is ground into dry powder again, and heated to 600°C at a heating rate of 10°C / min, and then kept at 600°C for 2 h, and then naturally cooled to room temperature to obtain nano-porous SiO2.

[0110] (2) Preparation of active Si / SiO material: take 5 g of the above nano-porous SiO2, add 5 g of 200 nm silicon powder (mass ratio of porous SiO2: silicon powder = 1:1), and take 2.5 g of LiCl, and mix them evenly; the powder is placed in a crucible, heated to 1200°C at a heating rate of 2°C / min in an argon atmosphere, and kept at 1200°C for 4 h to obtain a solid powder; the solid powder is washed and centrifuged with 100 ml of water, repeated three times to remove any excess salt components, and dried in a vacuum oven at 60°C to obtain an active Si / SiO material.

[0111] (3) Preparation of organic-derived carbon: take 20 g of glucose and place it in a corundum crucible, heat to 300°C at a rate of 2°C / min in an argon atmosphere, and keep the temperature constant at 300°C for 4 h to obtain a blackish-brown block material; after crushing the block, 0.2 mm zirconium balls are added to the nanoceramic sand mill at a solid mass ratio of 20:1, and 80% anhydrous ethanol is added as a grinding medium, and the mixture is ground at 2000 rpm for 5 min, the grinding temperature is 20°C, and after grinding, the ethanol is evaporated to obtain carbon powder.

[0112] (4) Preparation of silicon-based composite material precursor: take 4 g of the active Si / SiO material in (2), and disperse it in 200 ml of anhydrous ethanol, and then add 6 g of organic-derived carbon (carbon powder in step (3)) under rapid stirring at a speed of 1000 rpm, mix the dispersion liquid in a ball mill tank at 200 rpm for 30 min, and then evaporate the anhydrous ethanol after rapid stirring for 30 min to obtain a precursor.

[0113] (5) Preparation of silicon-carbon composite material: place the above precursor in a corundum crucible, heat to 1200°C at a rate of 2°C / min in an argon atmosphere, and keep the temperature constant at 1200°C for 4 h to obtain a silicon-carbon composite material solid powder.

[0114] Example 2 differs from Example 1 in that the thermal treatment is performed prior to the acid washing in step (1), and the structure of the silicon-carbon composite material prepared is the same as that of Example 1.

[0115] Example 3

[0116] The silicon-carbon composite material is prepared according to the following steps:

[0117] (1) Preparation of porous SiO2: Take 10 g of halloysite raw powder with a particle size of 3000 mesh, and heat it to 600°C at a heating rate of 10°C / min. Keep the temperature at 600°C for 2 h, and then naturally reduce it to room temperature. Prepare 200 ml of 2 mol / L sulfuric acid, and add the halloysite powder into the sulfuric acid solution while stirring. After the addition is completed, keep the stirring speed at 500 rpm for 8 h. Centrifuge the dispersion liquid and wash it with deionized water until it is neutral. Repeat the above steps three times to remove metal impurities. Dry the obtained wet halloysite powder in an oven at 60°C to obtain nano-porous silicon dioxide.

[0118] (2) Preparation of active Si / SiO material: Take 5 g of the above nano-porous SiO2, and add 10 g of 200 nm silicon powder (mass ratio of porous SiO2: silicon powder = 1:2). Take 2.5 g of LiCl, and mix the three together. Place the powder in a crucible, and heat it to 1200°C at a heating rate of 2°C / min in an argon atmosphere. Keep the temperature at 1200°C for 4 h to obtain a solid powder. Wash and centrifuge the solid powder with 100 ml of water, repeat three times to remove any excess salt components, and dry it in a vacuum oven at 60°C to obtain the active Si / SiO material.

[0119] (3) Preparation of organic-derived carbon: Take 20 g of glucose and place it in a corundum crucible. Heat it to 300°C at a heating rate of 2°C / min in an argon atmosphere, and keep the temperature at 300°C for 4 h to obtain a blackish-brown block material. Crush the block, and add 0.2 mm zirconium balls to a nano-ceramic bead mill at a solid mass ratio of 20:1. Add anhydrous ethanol as a grinding medium at a mass fraction of 80%, and grind at 2000 revolutions / min for 5 min. The grinding temperature is 20°C. After the grinding is completed, evaporate the ethanol to obtain carbonaceous powder.

[0120] (4) Preparation of silicon-based composite material precursor: Take 4 g of the active Si / SiO material in (2), and disperse it in 200 ml of anhydrous ethanol. Add 6 g of organic-derived carbon (carbonaceous powder in step (3)) under rapid stirring at a speed of 1000 rpm. Mix the dispersion liquid in a ball mill jar at 200 revolutions / min for 30 min. After 30 min of rapid stirring, evaporate the anhydrous ethanol to obtain the precursor.

[0121] (5) Preparation of silicon-based composite material: the precursor is placed in a corundum crucible, and heated to 1200°C at a heating rate of 2°C / min in an argon atmosphere, and kept at 1200°C for 4h to obtain a silicon-carbon composite material solid powder.

[0122] Example 3 differs from Example 1 in that the Si:SiO2 in step (2) is 2:1, and the structure of the silicon-carbon composite material prepared in Example 3 is the same as that of Example 1.

[0123] Example 4

[0124] The silicon-carbon composite material is prepared according to the following steps:

[0125] (1) Preparation of porous SiO2: 10g of halloysite raw powder with a particle size of 3000 mesh is heated to 600°C at a heating rate of 10°C / min, and kept at 600°C for 2h, and then naturally cooled to room temperature; 200ml of 2mol / L sulfuric acid is prepared, the halloysite powder is added to the sulfuric acid solution, and stirred while adding, and after adding, the stirring speed is kept at 500rpm for 8h, the dispersion is centrifuged and washed with deionized water until neutral; the above steps are repeated three times to remove metal impurities, and the obtained wet halloysite powder is dried in an oven at 60°C to obtain nano-porous silicon dioxide.

[0126] (2) Preparation of active Si / SiO material: 5g of the above nano-porous SiO2 is weighed, 5g of 200nm silicon powder (mass ratio of porous SiO2:silicon powder = 1:1) is added, and 2.5g of NaCl is weighed and mixed evenly; the powder is placed in a crucible, heated to 1200°C at a heating rate of 2°C / min in an argon atmosphere, and kept at 1200°C for 4h to obtain a solid powder; the solid powder is washed and centrifuged with 100ml of water, repeated three times to remove any excess salt components, and dried in a vacuum oven at 60°C to obtain an active Si / SiO material.

[0127] (3) Preparation of organic-derived carbon: 20g of glucose is weighed and placed in a corundum crucible, heated to 300°C at a heating rate of 2°C / min in an argon atmosphere, and kept at 300°C for 4h to obtain a blackish-brown block material; the block is crushed and 0.2mm zirconium balls are added to a nanoceramic bead mill at a solid mass ratio of 20:1, and 80% anhydrous ethanol is added as a grinding medium, and ground at 2000r / min for 5min, the grinding temperature is 20°C, after grinding, the ethanol is evaporated to obtain carbonaceous powder.

[0128] (4) Preparation of silicon-based composite precursor: 4 g of active Si / SiO material in (2) was dispersed with 200 ml of anhydrous ethanol, and 6 g of organic-derived carbon (carbonaceous powder in step (3)) was added under rapid stirring at a rotation speed of 1000 rpm. The mixed dispersion was ball-milled in a ball-milling tank at 200 rpm for 30 min, and then anhydrous ethanol was evaporated after rapid stirring for 30 min to obtain the precursor.

[0129] (5) Preparation of silicon-based composite material: the precursor was placed in a corundum crucible, and heated to 1200°C at a heating rate of 2°C / min in an argon atmosphere, and kept at 1200°C for 4 h to obtain a silicon-carbon composite material solid powder.

[0130] Example 4 is different from Example 1 in that 2.5 g of NaCl was added in step (2), and the structure of the silicon-carbon composite material prepared in Example 4 is the same as that of Example 1.

[0131] Example 5

[0132] The silicon-carbon composite material was prepared according to the following steps:

[0133] (1) Preparation of porous SiO2: 10 g of halloysite raw powder with a particle size of 3000 mesh was heated to 600°C at a heating rate of 10°C / min, and kept at 600°C for 2 h, and then naturally cooled to room temperature. 200 ml of 2 mol / L sulfuric acid was prepared, and the halloysite powder was added to the sulfuric acid solution while stirring, and the stirring was maintained at a rotation speed of 500 rpm for 8 h after the addition was completed. The dispersion was centrifuged and washed with deionized water until neutral. The above steps were repeated three times to remove metal impurities, and the obtained halloysite wet powder was dried in an oven at 60°C to obtain nano-porous silica.

[0134] (2) Preparation of active Si / SiO material: 5 g of the above nano-porous SiO2 was weighed, 10 g of 200 nm silicon powder (mass ratio of porous SiO2: silicon powder = 1:2) was added, and 2.5 g of NaCl was weighed and mixed evenly; the powder was placed in a crucible and heated to 1200°C at a heating rate of 2°C / min in an argon atmosphere, and kept at 1200°C for 4 h to obtain a solid powder; the solid powder was washed and centrifuged with 100 ml of water, and the excess salt components were removed by repeating the washing and centrifugation three times, and then dried in a vacuum oven at 60°C to obtain the active Si / SiO material.

[0135] (3) Preparation of organic derived carbon: 20 g of glucose was placed in a corundum crucible and heated to 300 °C at a rate of 2 °C / min under an argon atmosphere, and kept at 300 °C for 4 h to obtain blackish-brown bulk material; the bulk was crushed and 0.2 mm zirconium balls were added to the nanoceramic bead mill at a solid mass ratio of 20:1, and 80% anhydrous ethanol was added as a grinding medium, and the mixture was ground at 2000 rpm for 5 min, the grinding temperature was 20 °C, and after grinding, the ethanol was evaporated to obtain carbon powder.

[0136] (4) Preparation of silicon-based composite material precursor: 4 g of active Si / SiO material in (2) was weighed, and 200 ml of anhydrous ethanol was added to disperse it thoroughly, and 6 g of organic derived carbon (carbon powder in step (3)) was added under rapid stirring at a speed of 1000 rpm, and the mixed dispersion was ball milled in a ball mill tank at 200 rpm for 30 min, and after 30 min of rapid stirring, the anhydrous ethanol was evaporated to obtain the precursor.

[0137] (5) Preparation of silicon-based composite material: the precursor was placed in a corundum crucible and heated to 1200 °C at a rate of 2 °C / min under an argon atmosphere, and kept at 1200 °C for 4 h to obtain silicon-carbon composite material solid powder.

[0138] Example 5 differs from Example 1 in that the Si:SiO2 ratio in step (2) is 2:1, and 2.5 g of NaCl is added in step (2); the structure of the silicon-carbon composite material prepared in Example 5 is the same as that of Example 1.

[0139] Example 6

[0140] The silicon-carbon composite material was prepared according to the following steps:

[0141] (1) Preparation of porous SiO2: 10 g of halloysite raw powder with a particle size of 3000 mesh was heated to 600 °C at a rate of 10 °C / min, and kept at 600 °C for 2 h, then naturally cooled to room temperature; 200 ml of 2 mol / L sulfuric acid was prepared, and the halloysite powder was added to the sulfuric acid solution while stirring, and after the addition was completed, the stirring was continued at a speed of 500 rpm for 8 h, and the dispersion was centrifuged and washed with deionized water until neutral; the above steps were repeated three times to remove metal impurities, and the obtained halloysite wet powder was dried in an oven at 60 °C to obtain nano-porous silicon dioxide.

[0142] (2) Preparation of active Si / SiO material: 5 g of the above nanoporous SiO2 was weighed, 5 g of 200 nm silicon powder (mass ratio of porous SiO2: silicon powder = 1:1) was added, 2.5 g of LiCl was weighed and the three were mixed uniformly; the powder was placed in a crucible, heated to 1200°C at a rate of 2°C / min in an argon atmosphere, kept at 1200°C for 4 h, and a solid powder was obtained; the solid powder was washed and centrifuged with 100 ml of water, repeated three times to remove any excess salt components, and dried in a vacuum oven at 60°C to obtain the active Si / SiO material.

[0143] (3) Preparation of organic-derived carbon: 20 g of chitosan was weighed and placed in a corundum crucible, heated to 300°C at a rate of 2°C / min in an argon atmosphere, and kept at 300°C for 4 h to obtain a blackish-brown bulk material; the bulk was crushed and 0.2 mm zirconium balls were added to the nanoceramic bead mill at a solid mass ratio of 20:1, and 80% anhydrous ethanol was added as a grinding medium, ground at 2000 rpm for 5 min, the grinding temperature was 20°C, and after grinding, the ethanol was evaporated to obtain carbonaceous powder.

[0144] (4) Preparation of silicon-based composite material precursor: 4 g of active Si / SiO material in (2) was weighed, dispersed with 200 ml of anhydrous ethanol, and 6 g of organic-derived carbon (carbonaceous powder in step (3)) was added under rapid stirring at a speed of 1000 rpm, the mixed dispersion was ball milled in a ball mill tank at 200 rpm for 30 min, and after 30 min of rapid stirring, the anhydrous ethanol was evaporated to obtain the precursor.

[0145] (5) Preparation of silicon-based composite material: the above precursor was placed in a corundum crucible, heated to 1200°C at a rate of 2°C / min in an argon atmosphere, kept at 1200°C for 4 h, and a silicon-carbon composite material solid powder was obtained.

[0146] Example 6 differs from Example 1 in that the organic material in step (3) is chitosan.

[0147] Example 7

[0148] The silicon-carbon composite material was prepared according to the following steps:

[0149] (1) Preparation of porous SiO2: Take 10 g of halloysite raw powder with a particle size of 3000 mesh, and heat it to 600°C at a heating rate of 10°C / min. Keep the temperature at 600°C for 2 hours, and then naturally reduce it to room temperature. Prepare 200 ml of 2 mol / L sulfuric acid, and add the halloysite powder into the sulfuric acid solution while stirring. After adding, keep the stirring speed at 500 rpm for 8 hours. Centrifuge the dispersion liquid and wash it with deionized water until it is neutral. Repeat the above steps three times to remove metal impurities. Dry the obtained halloysite wet powder in an oven at 60°C to obtain nano-porous silicon dioxide.

[0150] (2) Preparation of active Si / SiO material: Take 5 g of the above nano-porous SiO2, and add 5 g of 200 nm silicon powder (mass ratio of porous SiO2: silicon powder = 1:1). Take 2.5 g of LiCl and mix them evenly. Put the powder in a crucible, and heat it to 1200°C at a heating rate of 2°C / min in an argon atmosphere. Keep the temperature at 1200°C for 4 hours to obtain a solid powder. Wash and centrifuge the solid powder with 100 ml of water, repeat three times to remove any excess salt components, and dry it in a vacuum oven at 60°C to obtain an active Si / SiO material.

[0151] (3) Preparation of organic-derived carbon: Take 20 g of glucose and put it in a corundum crucible. Heat it to 300°C at a heating rate of 2°C / min in an argon atmosphere, and keep the temperature at 300°C for 4 hours to obtain a blackish-brown block material. Crush the block, and add 0.2 mm zirconium balls to a nano-ceramic bead mill at a solid mass ratio of 20:1. Add 80% anhydrous ethanol as a grinding medium, and grind at 2000 revolutions / min for 5 minutes. The grinding temperature is 20°C. After grinding, evaporate the ethanol to obtain carbon powder.

[0152] (4) Preparation of silicon-based composite material precursor: Take 6 g of the active Si / SiO material in (2), and disperse it in 200 ml of anhydrous ethanol. Add 4 g of organic-derived carbon (carbon powder in step (3)) under rapid stirring at a speed of 1000 rpm. Mix the dispersion liquid in a ball mill tank at 200 revolutions / min for 30 minutes. After 30 minutes of rapid stirring, evaporate the anhydrous ethanol to obtain a precursor.

[0153] (5) Preparation of silicon-based composite material: Put the above precursor into a corundum crucible, and heat it to 1200°C at a heating rate of 2°C / min in an argon atmosphere. Keep the temperature at 1200°C for 4 hours to obtain a silicon-carbon composite material solid powder.

[0154] Example 7 differs from Example 1 in that the mass of the silicon-based material and the organic-derived carbon in step (4) are 6 g and 4 g, respectively, and the structure of the silicon-carbon composite material prepared in Example 7 is the same as that of Example 1.

[0155] Example 8

[0156] The silicon-carbon composite material is prepared according to the following steps:

[0157] (1) Preparation of porous SiO2: Take 10 g of halloysite raw powder with a particle size of 3000 mesh, and heat it to 600°C at a heating rate of 10°C / min. After keeping the temperature at 600°C for 2 h, it is naturally cooled to room temperature. Then, 200 ml of 2 mol / L sulfuric acid is prepared, and the halloysite powder is added to the sulfuric acid solution while stirring. After the addition is completed, the stirring is continued at a speed of 500 rpm for 8 h. The dispersion is centrifuged and washed with deionized water until it is neutral. The above steps are repeated three times to remove metal impurities. The obtained wet halloysite powder is dried in an oven at 60°C to obtain nano-porous silicon dioxide.

[0158] (2) Preparation of active Si / SiO material: Take 5 g of the above nano-porous SiO2, and add 5 g of 200 nm silicon powder (mass ratio of porous SiO2: silicon powder = 1:1). Then, take 2.5 g of LiCl and mix them evenly. The powder is placed in a crucible and heated to 1200°C at a heating rate of 2°C / min in an argon atmosphere. After keeping the temperature at 1200°C for 4 h, a solid powder is obtained. The solid powder is washed and centrifuged with 100 ml of water, and the process is repeated three times to remove any excess salt components. The material is dried in a vacuum oven at 60°C to obtain the active Si / SiO material.

[0159] (3) Preparation of organic-derived carbon: Take 20 g of chitosan and place it in a corundum crucible. Heat it to 300°C at a heating rate of 2°C / min in an argon atmosphere, and keep the temperature at 300°C for 4 h to obtain a block material. Crush the block material and add 0.2 mm zirconium balls to a nano-ceramic bead mill at a solid mass ratio of 20:1. Add anhydrous ethanol as a grinding medium at a mass fraction of 80%, and grind at 2000 revolutions / min for 5 min. The grinding temperature is 20°C. After grinding, evaporate the ethanol to obtain carbonaceous powder.

[0160] (4) Preparation of silicon-based composite material precursor: Take 6 g of the active Si / SiO material in step (2), and disperse it in 200 ml of anhydrous ethanol. Add 4 g of organic-derived carbon (carbonaceous powder in step (3)) under rapid stirring at a speed of 1000 rpm. Mix the dispersion in a ball mill tank at 200 revolutions / min for 30 min. After 30 min of rapid stirring, evaporate the anhydrous ethanol to obtain the precursor.

[0161] (5) Preparation of silicon-based composite material: The precursor was placed in a corundum crucible, and heated to 1200°C at a rate of 2°C / min in an argon atmosphere, and kept at 1200°C for 4h to obtain a silicon-carbon composite material solid powder.

[0162] Example 8 differs from Example 1 in that the organic matter in step (3) is chitosan; the mass of the silicon-based material and the organic matter-derived carbon in step (4) is 6g and 4g, respectively; and the structure of the silicon-carbon composite material prepared in Example 8 is the same as that of Example 1.

[0163] Performance detection

[0164] Structure and morphology characterization of silicon-carbon composite material

[0165] The XRD detection result of the silicon-carbon composite material prepared in Example 1 is shown in Figure 4 .

[0166] The SEM test result of the silicon / silicon dioxide composite material prepared in step (2) of Example 1 is shown in Figure 5 , Figure 6 and Figure 7 .

[0167] The cycle of the silicon-based composite material prepared in Example 1 under the condition of 0.2C charge-discharge rate was characterized, and the detection method was as follows: under the condition of 0.2C charge-discharge rate, the discharge capacity was obtained by discharging to 0.01V first, and then the charge capacity was obtained by charging to 2.0V, and the specific charge-discharge capacity was obtained by mass conversion, as shown in Figure 2 , the first charge-discharge capacity of the composite material was 1260.4mAh / g and 985.8mAh / g, respectively, the corresponding first cycle coulombic efficiency was 78.2%, and the capacity retention rate after 40 cycles was 75.9%, which was the best comprehensive cycle performance compared with other examples.

[0168] Figure 3 The charge-discharge curve of the silicon-carbon composite material prepared in Example 1 is shown in the following table, and the detection method was as follows: after standing for 12h, the discharge curve was obtained by discharging to 0.01V first under the condition of 0.2C charge-discharge rate, and then the charge curve was obtained by charging to 2.0V; the voltage sharply decreased before the capacity was 200mAh / g in the lithium intercalation stage, and the voltage tended to be constant after 400mAh / g; there was a weak hump near 1.25V, which corresponded to the beginning of SEI generation, and there was an obvious lithium intercalation platform between 0-0.2V, and the platform slope close to 0 indicated uniform lithium intercalation; there was no obvious platform in the whole range of the curve in the lithium extraction stage, which may be due to the capacity coupling of amorphous carbon and silicon material.

[0169] Mass fraction of silicon-based material and lithium storage performance

[0170] The electrochemical performance of the silicon-carbon composite material prepared in the examples was detected by assembling a CR2025 type button half-battery; the specific assembly method was as follows:

[0171] A metal lithium sheet with a thickness of 1 mm and a diameter of 16 mm was used as the counter electrode; 1 mol / L LiPF6 / EC:DEC:DMC (1:1:1) was used as the electrolyte; a polypropylene microporous membrane was used as the separator; the active material (the silicon-carbon composite material prepared in the examples), Ketjen black CE-300j, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were prepared into a slurry according to a mass ratio of 8:1:0.5:0.5, uniformly coated on a carbon-coated copper foil with a thickness of 10 μm, and placed in a vacuum drying oven for vacuum drying at 70°C for 4 h to prepare an electrode sheet with a thickness of about 40 μm; the battery was assembled in an Ar-filled glove box.

[0172] The model of the battery test system was LAND CT3002A, and the voltage range was 0.001-2.0 V.

[0173] The detection method of the mass fraction of Si in the silicon-carbon composite material was thermogravimetric testing: the testing temperature was 100-800°C, the testing atmosphere was air atmosphere, and the heating rate was 10°C / min. The silicon content was obtained by analyzing the mass of the residue.

[0174] The porosity of the silicon-carbon composite material was obtained by mercury intrusion porosimetry.

[0175] The mass fraction of Si, the lithium storage performance, and the porosity of the silicon-carbon composite material prepared in the examples were as follows:

[0176]

[0177] From the above table, it can be seen that heat treatment of the ore before acid washing is a necessary condition for preparing porous silicon dioxide; the method of acid washing first and then heat treatment in Example 2 is difficult to remove aluminum oxide compounds in the halloysite, and the pores are filled with aluminum oxide; the reason is that the acid and alkali resistant silicon dioxide covers the surface of the metal oxide layer, and it is difficult for H + to diffuse into the interior of the ore, so that the porosity of the finally prepared porous silicon dioxide is low; while the method of heat treatment first and then acid washing in Example 1 can prepare silicon dioxide with higher porosity, because the heat treatment removes the crystal water, eliminates the hydrogen bonding of the halloysite, and destroys the original structure, so that it is easy for H + to diffuse into the interior of the ore, and the strengthening of the etching effect leads to the change of the porosity of the ore; the composite material with higher porosity can accommodate the expansion of the silicon-based material, so that the electrochemical performance is improved; the silicon-carbon composite material prepared in Example 1 has the largest porosity, and has the best initial efficiency and cycle performance.

[0178] Meanwhile, the mass ratio of Si to SiO2 and the porous structure regulated by salt composition significantly affect the lithium storage performance of silicon-based composite materials: the mass ratio of Si to SiO2 regulates the oxygen content in the silicon-based material, thereby adjusting the final capacity. Oxygen plays a crucial role in forming a stable anode material; Examples 1 and 4, with higher oxygen content, exhibit higher capacity retention. Salt composition regulates the pore structure of the composite material. Compared to Examples 4 and 5, under the condition of using NaCl as a porosity regulator, Example 5 yields a material with more macropores, a lower proportion of micropores, and larger pores that facilitate lithium-ion diffusion and reserve space for volume expansion, ultimately improving the initial coulombic efficiency. However, the cycling performance deteriorates once the macropores are filled with SEI. Ultimately, the improvement in electrochemical performance depends on the control of various suitable conditions, rather than simply the regulation of salt composition.

[0179] In addition, amorphous carbon ( Figure 4 The broad peak near 20° in the middle section (proving the presence of amorphous carbon) significantly affects the lithium storage performance of the composite material. Amorphous carbon coating on the surface of precursor particles reinforces the gaps, resulting in a compact anode material with a smaller specific surface area. The SEI film formed by the amorphous carbon-coated material is more uniform, and the cycle stability is improved. In Examples 6 and 8, the organic carbon source used was chitosan, a natural polysaccharide that is abundant, inexpensive, and has abundant oxygen-loving functional groups. In the other examples, the organic carbon source used was glucose. The final results show that glucose is more suitable as an organic carbon for coating silicon-based materials, while the electrochemical performance of silicon-based materials coated with chitosan after heat treatment is worse overall.

[0180] Meanwhile, the lithium storage capacity, first-efficiency, and cycle stability of the silicon-carbon composite materials prepared with reference to the embodiments and comparative examples of the present invention are all limited by the material synthesis route.

[0181] This invention provides a silicon-carbon composite material with a multi-layered internal porous structure. This multi-layered internal porous structure refers to the presence of various pore structures, including nanopores within porous silicon suboxide nanowires, mesopores formed by the cross-linking of porous silicon suboxide nanowires, and mesopores formed between porous silicon suboxide nanowires and partially fused surface-oxidized silicon particles. All three types of pores exist within the internal space due to the carbon coating on the outermost layer of the composite powder particles. When the composite powder is used as a negative electrode in a lithium-ion battery for charging and discharging, the volume expansion of the silicon-containing components is partially offset by the pores, thus preventing damage to the macroscopic structure of the negative electrode and enabling stable charging and discharging. The multi-layered internal porous structure in this invention refers to the presence of various pores within the carbon-coated powder particles of the composite material, including nanopores inherent in the porous silicon suboxide nanowires themselves, mesopores formed by the cross-linking of porous silicon suboxide nanowires, and mesopores formed between the porous silicon suboxide nanowires and silicon particles.

[0182] While the application has been described and illustrated with reference to specific embodiments thereof, those skilled in the art will appreciate that various adaptations, changes, modifications, substitutions, developments, improvements, and permutations can be made in the specific embodiments described in this application without departing from the true spirit and scope of the application, as defined by the appended claims. All such modifications are intended to be within the scope of the claims. Although methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations can be combined, sub-divided, or re-ordered to form equivalent methods without departing from the teachings of the present application. Accordingly, unless specifically indicated herein, the order and grouping of operations are not a limitation of this application.

Claims

1. A silicon-carbon composite material with a multi-level inner pore structure, comprising: a silicon-containing inner structure, the inner structure comprising: nanowire units and core-shell structure units; a carbon layer coated on a surface of the silicon-containing inner structure; the nanowire units are silicon monoxide nanowire units; the core-shell structure units comprise: a silicon core; a silicon monoxide shell disposed outside the silicon core; networked mesopores are formed between the nanowire units and the core-shell structure units, or between the nanowire units, the networked mesopores having a pore size of 2-100 nm.

2. The silicon-carbon composite material having a multi-level pore structure according to claim 1, wherein the nanowire units have nanopores, the nanopores having a pore size of < 5 nm.

3. The silicon-carbon composite material having a multi-level pore structure according to claim 1, wherein the silicon-carbon composite material with the multi-level inner pore structure has a porosity of 10-45% inside. 4.A method for preparing the silicon-carbon composite material with the multi-level inner pore structure according to claim 1, comprising: mixing a porous silicon-based powder and a carbon source and then sintering to obtain the silicon-carbon composite material with the multi-level inner pore structure; the method for preparing the porous silicon-based powder comprises: sintering a silicon oxide product, silicon powder and an alkali metal salt to obtain the porous silicon-based powder; the method for preparing the silicon oxide product comprises: calcining halloysite, and then performing acid washing and water washing to obtain the silicon oxide product.

5. The method for preparing the silicon-carbon composite material with a multi-layered internal porous structure according to claim 4, characterized in that, the method for preparing the carbon source comprises: sintering an organic substance, and then grinding to obtain the carbon source.

6. A lithium-ion battery anode comprising: the silicon-carbon composite material with the multi-level inner pore structure according to claim 1; or the silicon-carbon composite material with the multi-level inner pore structure prepared by the method for preparing the silicon-carbon composite material with the multi-level inner pore structure according to claim 4.

7. A lithium-ion battery comprising: a lithium ion battery negative electrode according to claim 6.

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