A modified silicon-based negative electrode material and its preparation method and application

Abstract

The present invention provides a modified silicon-based negative electrode material, a preparation method, and an application thereof, and relates to the technical field of negative electrodes for new energy batteries. The preparation method provided by the present invention comprises: immersing a borosilicate substrate in a pre-lithiation solution, evaporating the solvent, and then calcining to obtain a modified substrate; in-situ growing silicon nitride nanowires on the surface of the modified substrate to obtain a composite substrate; and reducing the composite substrate in a reducing atmosphere and then coating the surface with mesoporous carbon to obtain a modified silicon-based negative electrode material. The present invention can effectively improve the structural stability of the negative electrode material during the charge and discharge process, avoid pulverization of the negative electrode material resulting in a decrease in cycle performance, and at the same time improve the first efficiency by pre-lithiation of the borosilicate substrate.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy battery negative electrodes, and in particular to a modified silicon-based negative electrode material and a preparation method and application thereof. Background Art

[0002] With the rapid development of the economy and technology, energy and environmental issues are becoming increasingly severe. New energy technologies have become one of the most important research topics. Lithium-ion batteries, as a major branch of new energy technologies, have attracted particular attention. As people's demand for the energy and safety of lithium-ion batteries gradually increases, capacity and cycle performance issues are gradually gaining attention. In lithium-ion batteries, the capacity of the positive and negative electrode materials determines the overall capacity of the battery. The capacity of the positive electrode material has currently reached a bottleneck and is difficult to break through. The theoretical specific capacity of the commonly used graphite negative electrode material is relatively low. By selecting the right negative electrode material, the overall capacity performance of the battery can be effectively improved.

[0003] Among many materials, silicon-based materials have attracted widespread attention due to their ultra-high theoretical lithium storage capacity. However, their application in lithium-ion batteries still faces numerous challenges, such as poor electronic conductivity, severe polarization during charge and discharge, and significant volume changes during cycling, leading to poor stability. This has hindered the development and large-scale application of silicon-based materials. Furthermore, silicon-based materials consume a large amount of lithium ions during the initial formation of the SEI film, resulting in a low initial coulombic efficiency. The SEI film constantly breaks and regenerates during the repeated expansion and contraction of the silicon material, consuming large amounts of lithium ions and severely impacting the lifespan of the lithium-ion battery.

[0004] Therefore, the existing technology often pre-lithiates silicon-based negative electrode materials to form an SEI film on the surface of the negative electrode material in advance to reduce lithium ion consumption in lithium-ion batteries. It can also provide a certain degree of protection for the negative electrode material and prevent the material from pulverizing and falling off. For example, Chinese invention patent publication number CN115621425A provides a silicon-based negative electrode pre-lithiation method, which is prepared by short-circuiting the negative electrode plate and the lithium plate to obtain a pre-lithiated negative electrode. However, this requires separate processing of the negative electrode material, which greatly increases the complexity of the processing steps. Therefore, it is urgent to provide a solution to improve this problem. Summary of the Invention

[0005] The purpose of the present invention is to provide a modified silicon-based negative electrode material and its preparation method and application, which can effectively improve the structural stability of the negative electrode material during the charging and discharging process, avoid the pulverization of the negative electrode material resulting in a decrease in cycle performance, and at the same time improve the initial efficiency by pre-lithiation of the borosilicate matrix.

[0006] In the first aspect, the present invention provides a method for preparing a modified silicon-based negative electrode material, comprising: immersing a borosilicate substrate in a pre-lithium solution and evaporating the solvent before calcining to obtain a modified substrate; in situ growing silicon nitride nanowires on the surface of the modified substrate to obtain a composite substrate; reducing the composite substrate in a reducing atmosphere and then coating the surface with mesoporous carbon to obtain a modified silicon-based negative electrode material.

[0007] The preparation method provided by the present invention can effectively reduce the lithium loss of the negative electrode during the first charge and discharge process by pre-lithiation in the borosilicate matrix. At the same time, the boron element can form a B-Si and B composite skeleton in the borosilicate matrix, thereby effectively inhibiting the volume expansion of silicon and improving the conductivity. In addition, the in-situ grown silicon nitride nanowires can well form an interconnected network, which can further inhibit the volume expansion of silicon and effectively prevent the pulverization of the negative electrode material, which is beneficial to improving the cycle performance. At the same time, it can also increase the specific surface area and thus increase the loading amount of mesoporous carbon, which can not only improve the rate performance but also protect the internal structure.

[0008] Optionally, the preparation method of the borosilicate matrix includes: mixing boron oxide and silicon powder and calcining to obtain a borosilicate precursor; calcining the borosilicate precursor in a nitrogen-containing atmosphere and grinding to obtain a borosilicate intermediate; and soaking the borosilicate intermediate in a silane solution and drying to obtain the borosilicate matrix.

[0009] Optionally, the mass ratio of the boron element in the boron oxide to the silicon element in the silicon powder is (0.2-0.3):1.

[0010] Alternatively, boron oxide is mixed with silicon powder by ball milling.

[0011] Optionally, the mixture is calcined at 400°C-450°C after mixing.

[0012] Optionally, the mixture is calcined under an inert atmosphere.

[0013] Optionally, the mixture is calcined for 1 h to 1.5 h after mixing.

[0014] Optionally, the gas in the nitrogen-containing atmosphere includes one of methylamine, nitrogen and ammonia.

[0015] Optionally, the calcination is carried out in a nitrogen-containing atmosphere at 1100° C. to 1300° C.

[0016] Alternatively, the boron silicon precursor is calcined in a nitrogen-containing atmosphere at 800 sccm-1000 sccm.

[0017] Optionally, the particle size of the borosilicate intermediate is 10 μm-100 μm.

[0018] Optionally, calcination is carried out in a nitrogen atmosphere for 4 h to 6 h.

[0019] Optionally, the silane solute in the silane solution includes one of 3-piperazinylpropylmethyldimethoxysilane and N-(aminoethyl)-3-aminopropylmethyldimethoxysilane.

[0020] Optionally, the mass ratio of the silane solute to the borosilicate precursor in the silane solution is (0.1-0.2):1.

[0021] Optionally, the borosilicate precursor is immersed in the intermediate solution for 1 min to 15 min.

[0022] Optionally, the infiltration is followed by drying at 50°C-70°C.

[0023] Optionally, the lithium solute in the pre-lithium solution includes lithium acetate.

[0024] Optionally, the mass ratio of the borosilicate matrix to the lithium element in the pre-lithium solution is 1:(0.1-0.3).

[0025] Optionally, the borosilicate substrate is ultrasonically impregnated in a pre-lithium solution.

[0026] Optionally, the borosilicate substrate is immersed in a pre-lithium solution and then the solvent is evaporated at 80° C.-100° C.

[0027] Optionally, the solvent is evaporated and then calcined at 800°C-1000°C.

[0028] Alternatively, the solvent is evaporated and then calcined under a protective atmosphere.

[0029] Optionally, when in-situ growing silicon nitride nanowires on the surface of a modified substrate to prepare a composite substrate, the method includes: depositing the modified substrate in a silicon source gas at 1000°C-1100°C for 10min-15min to prepare an intermediate; generating the intermediate in a silicon nitrogen gas at 1000°C-1100°C for 30min-50min and then cooling to obtain a composite substrate.

[0030] Optionally, the hydrogen concentration in the reducing atmosphere is 70%-100%.

[0031] Optionally, the reduction is performed in a reducing atmosphere of 0.5 MPa-1.5 MPa.

[0032] Optionally, the reduction is performed in a reducing atmosphere at 200°C-300°C.

[0033] Optionally, the reduction treatment is carried out in a reducing atmosphere for 2 h to 5 h.

[0034] Optionally, after reduction and cooling, the material is immersed in a mesoporous carbon suspension, separated and dried to obtain a modified silicon-based negative electrode material, wherein the solvent of the mesoporous carbon suspension includes one of petroleum ether, chloroform and dichloromethane.

[0035] In the second aspect, the present invention also provides a modified silicon-based negative electrode material prepared by any of the above-mentioned optional preparation methods, comprising a borosilicate skeleton and lithium nanoparticles grown in situ within the borosilicate skeleton, a silicon nitride nanowire layer grown in situ on the outside of the borosilicate skeleton and a mesoporous carbon layer coated on the outside of the silicon nitride nanowire layer.

[0036] In a third aspect, the present invention further provides a use of any of the above-mentioned optional modified silicon-based negative electrode materials in a lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A flowchart of a method for preparing a modified silicon-based negative electrode material provided by the present invention;

[0038] Figure 2 This is a flowchart of a method for preparing a borosilicate substrate provided by the present invention. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meanings understood by people with ordinary skills in the field to which the invention belongs. The words "including" and similar words used in this article mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0040] See also Figure 1 The present invention provides a method for preparing a modified silicon-based negative electrode material, comprising the following steps:

[0041] S1, immersing the borosilicate substrate in a pre-lithium solution, evaporating the solvent, and then calcining to obtain a modified substrate;

[0042] S2, in situ growing silicon nitride nanowires on the surface of the modified substrate to prepare a composite substrate;

[0043] S3. The composite matrix is ​​reduced in a reducing atmosphere and then the surface is coated with mesoporous carbon to obtain a modified silicon-based negative electrode material.

[0044] In fact, the preparation method provided by the present invention can effectively improve the uniformity of the dispersion of lithium solute within the borosilicate matrix by immersing the borosilicate matrix in a pre-lithium solution in step S1. At the same time, after calcination, it can promote the binding stability of the three elements of boron, silicon, and lithium, which is beneficial to ensure the positional stability of lithium during subsequent processing. Specifically, the calcination treatment can form a Li-B-Si composite structure within the modified matrix, which is beneficial to improving the structural stability of the modified matrix.

[0045] In some embodiments, see Figure 2 The method for preparing the borosilicate substrate used in step S1 includes the following steps:

[0046] S0-1, mixing boron oxide and silicon powder and calcining them to obtain a borosilicate precursor;

[0047] S0-2, calcining the borosilicate precursor in a nitrogen atmosphere and then grinding it to obtain a borosilicate intermediate;

[0048] S0-3. The borosilicate intermediate is soaked in a silane solution and then dried to obtain a borosilicate matrix.

[0049] In practice, doping boron oxide into silicon creates a boron-doped silicon matrix (boron-silicon precursor). Calcination effectively increases the density and structural rigidity of the boron-silicon precursor, thereby suppressing silicon volume expansion. Furthermore, calcining in a nitrogen-containing atmosphere forms a nitride layer on the surface of the boron-silicon precursor, enhancing surface inertness and the integrity of subsequent in-situ silicon nitride nanowire growth, further suppressing silicon expansion.

[0050] In some embodiments, when performing step S0-1, the mass ratio of boron in boron oxide to silicon in silicon powder is (0.2-0.3):1. In practice, adjusting the mixing ratio of boron to silicon can help adjust the proportion of the boron-silicon alloy phase in the formed boron-silicon intermediate and adjust the structural strength of the boron-silicon skeleton in the boron-silicon intermediate, thereby facilitating the confinement of the active silicon within the skeleton.

[0051] In some embodiments, boron oxide and silicon powder can be ball-milled when executing step S0-1. This not only helps promote the sufficient mixing of boron oxide and silicon powder, but also reduces the particle size and increases the specific surface area, which is conducive to forming a borosilicate precursor with relatively uniform texture and composition during the calcination process.

[0052] In some embodiments, after mixing boron oxide and silicon powder during step S0-1, the mixture is calcined at 400°C-450°C in an inert atmosphere for 1-1.5 hours. In practice, the high temperature allows the boron oxide to partially melt, encapsulate the silicon powder, and diffuse onto the surface, thereby forming an amorphous boron-silicon interface layer and building a boron-silicon chemical bonding network, which helps improve structural stability.

[0053] In some embodiments, the inert atmosphere used in step S0-1 includes one of helium and argon, and the pressure of the inert atmosphere can be 0.1 MPa to 0.5 MPa. In practice, cooling to room temperature after calcination and grinding to obtain a borosilicate precursor with a particle size of 0.1 μm to 100 μm can help increase the specific surface area, thereby facilitating the nitrogen-containing atmosphere calcination in step S0-2.

[0054] In some embodiments, the nitrogen-containing gas in the nitrogen-containing atmosphere used in step S0-2 includes one of methylamine, nitrogen, and ammonia. Furthermore, the borosilicate precursor can be calcined in a nitrogen-containing atmosphere at 1100° C. to 1300° C. for 4 to 6 hours. This high-temperature nitridation reaction can promote the formation of a composite boron nitride or silicon nitride phase in the borosilicate precursor, promoting the combination of boron, silicon, and nitrogen to form a composite structure. Furthermore, a nitrided skeleton can be formed within the borosilicate intermediate, thereby improving structural strength.

[0055] In some embodiments, when executing step S0-2, the borosilicate precursor can be calcined in a nitrogen-containing atmosphere with a flow rate of 800sccm-1000sccm. This can ensure the saturation of the nitriding gas during the nitriding reaction, and at the same time enhance the mass transfer efficiency between the nitrogen-containing gas and the borosilicate precursor, which is beneficial to the formation of a nitrided structure on the surface of the borosilicate precursor and the subsequent modification of silicon nitride nanowires.

[0056] In some embodiments, after executing step S0-2 to obtain a borosilicate intermediate, ball milling and screening are performed to obtain a borosilicate intermediate with a particle size of 10 μm-100 μm, which is beneficial to destroying the long-range ordered nitride structure in the borosilicate intermediate and using the broken nitride structure to rebond with boron and silicon, which is beneficial to improving the ion diffusion capacity, and thus is beneficial to improving the conductivity of the negative electrode material, and at the same time can increase the number of surface defects in the borosilicate intermediate.

[0057] In some embodiments, when performing step S0-3, the silane solute in the silane solution used includes one of 3-piperazinylpropylmethyldimethoxysilane and N-(aminoethyl)-3-aminopropylmethyldimethoxysilane. In fact, by modifying the surface of the borosilicate intermediate with silane, the surface active sites of the borosilicate intermediate can be increased, thereby facilitating the surface pre-lithiation in step S1.

[0058] In some embodiments, when performing step S0-3, the solvent in the silane solution used can be a chemical solvent commonly used in the art, and it is necessary that it does not react with the borosilicate intermediate and the silane solute. In fact, by treating the borosilicate intermediate in the silane solution, it is beneficial to promote sufficient mixing of the borosilicate intermediate and the silane solute. In addition, during the mixing process, solid-liquid mixing methods commonly used in the art can be used, such as mechanical stirring, oscillation, and / or ultrasonic treatment.

[0059] In some embodiments, the mass ratio of silane solute to borosilicate precursor in the silane solution during step S0-3 is (0.1-0.2):1. Furthermore, the borosilicate intermediate can be immersed in the silane solution for 1-15 minutes. In practice, to increase the silane modification rate, the borosilicate intermediate can be added to the silane solution and then ultrasonically treated at 40°C-50°C. In some further embodiments, after immersion in the silane solution during step S0-3, solid-liquid separation is performed and the intermediate is dried at 50°C-70°C.

[0060] In some embodiments, the lithium solute in the pre-lithium solution used in step S1 includes lithium acetate. In practice, immersing the borosilicate substrate in the pre-lithium solution and evaporating the solvent of the pre-lithium solution can promote the uniform precipitation of lithium acetate and its adhesion to the surface pores of the borosilicate substrate. Furthermore, after calcination, the stability of lithium acetate on the surface of the borosilicate substrate can be improved.

[0061] In some embodiments, when performing step S1, the mass ratio of the borosilicate substrate to the lithium element in the pre-lithiation solution is 1:(0.1-0.3). This is conducive to forming a stable pre-lithiation layer at the defect sites on the surface of the borosilicate substrate, and can be embedded in the borosilicate substrate to form a borosilicate-lithium composite structure, which not only acts as a structural buffer but also improves the density and uniformity of the SEI film when it is formed.

[0062] In some embodiments, during step S1, the borosilicate substrate is ultrasonically impregnated in a pre-lithium solution, and then the solvent is evaporated at 80°C-100°C. In practice, ultrasonic treatment during the impregnation process can effectively utilize the ultrasonic cavitation effect to eliminate tiny bubbles attached to the surface of the borosilicate substrate, while also reducing the grain size of lithium acetate during crystallization, thereby improving the uniformity of lithium acetate adhesion to the surface of the borosilicate substrate.

[0063] In some embodiments, after evaporating the solvent from the prelithium solution during step S1, the modified substrate is calcined in a protective atmosphere at 800°C-1000°C for 0.5-1 hour and then cooled to room temperature. In practice, the protective atmosphere used comprises a protective gas selected from argon, helium, and neon. This helps maintain the structural stability of the substrate during the calcination and sintering process, preventing oxidative collapse. It also anchors the lithium element on the surface of the borosilicate substrate, improving structural density.

[0064] In some embodiments, when executing step S2, the following sub-steps are included: depositing the modified substrate in a silicon source gas at 1000°C-1100°C for 10-15 minutes to produce an intermediate; and generating the intermediate in a silicon nitrogen gas at 1000°C-1100°C for 30-50 minutes, followed by cooling to produce a composite substrate. In practice, by pyrolyzing the silicon source gas at high temperature, silicon atoms can adsorb on the surface of the modified substrate and form a silicon coating layer, which not only coats the modified substrate within the modified substrate but also serves as a directional nucleus for silicon nitride nanowires. Subsequently, during pyrolysis and deposition in the silicon nitrogen gas, silicon nitride nanowires are directionally formed on the surface of the modified substrate through gas-solid growth, and the interwoven nanowires can provide excellent protection and volume buffering.

[0065] In some embodiments, the silicon source gas used in step S2 includes one of silane and silicon tetrachloride, the silicon-nitrogen gas used includes a silicon source gas and a nitrogen source gas, and the concentration of the silicon source gas in the silicon-nitrogen gas is 20%-30%, and the nitrogen source gas used includes one of ammonia, hydrazine, and methylamine. In some further embodiments, when step S2 is performed, the modified substrate can be surface deposited in a gas environment at 0.1 MPa-1 MPa.

[0066] In some embodiments, the hydrogen concentration in the reducing atmosphere used during step S3 is 70%-100%. In practice, during the reduction treatment in the reducing atmosphere, the reducing gas can penetrate into the silicon nitride nanowires and contact the lithiation on the surface of the borosilicate substrate, thereby in situ reducing the silicon nitride nanowires to generate lithium nanoparticles. The lithium nanoparticles are then locked onto the surface of the borosilicate substrate. Furthermore, the reducing atmosphere may also include an inert carrier gas, such as argon.

[0067] In some embodiments, during step S3, the composite substrate can be reduced in a reducing atmosphere at 0.5 MPa to 1.5 MPa. In practice, performing the reduction treatment in a high-pressure atmosphere facilitates the penetration of the reducing gas through the silicon nitride nanowire coating into the borosilicate substrate. Furthermore, the composite substrate can be reduced in a reducing atmosphere at 200°C to 300°C for 2 to 5 hours to control the content of lithium nanoparticles formed on the surface of the borosilicate substrate.

[0068] In some embodiments, after performing reduction treatment in a reducing atmosphere in step S3 and cooling to room temperature, the modified silicon-based negative electrode material can be prepared by immersing the substrate in a mesoporous carbon suspension, separating and drying the substrate, and using a solvent selected from petroleum ether, chloroform, and dichloromethane. In practice, immersion in the mesoporous carbon suspension forms a mesoporous carbon coating on the substrate surface, effectively improving the performance of the negative electrode material and protecting the silicon nitride nanowires within.

[0069] In some embodiments, the mesoporous carbon particles in the mesoporous carbon suspension range from 50 nm to 100 nm. By dispersing the small-sized mesoporous carbon particles on the substrate surface, uniform coating can be achieved. Furthermore, an active agent and a dispersant may be dissolved in the mesoporous carbon suspension to improve the suspension stability of the mesoporous carbon and prevent agglomeration and sedimentation of the mesoporous carbon suspension.

[0070] In some embodiments, the mass ratio of the composite matrix after reduction treatment to the mesoporous carbon in the mesoporous carbon suspension is 1:(0.5-0.7), which facilitates uniform adhesion of the mesoporous carbon to the surface silicon nitride nanowires and forms a relatively dense mesoporous carbon coating. Furthermore, the concentration of mesoporous carbon in the mesoporous carbon suspension is 0.1 g / mL-0.2 g / mL, which facilitates uniform dispersion of the mesoporous carbon and the matrix in the suspension.

[0071] In some embodiments, before the surface is coated with mesoporous carbon, the composite substrate after the reduction treatment can be pre-activated. For example, the composite substrate after the reduction treatment can be preheated in a vacuum environment at 50°C-80°C and then added to a mesoporous carbon suspension in an argon environment for mesoporous carbon coating. In addition, the composite substrate after the reduction treatment can also be surface treated with a commonly used non-ionic surfactant. In practice, after performing step S3 of surface coating with mesoporous carbon, the composite substrate is dried at 700°C-800°C in a vacuum environment for 3h-5h and then cooled.

[0072] The present invention also provides a modified silicon-based negative electrode material prepared by the preparation method provided in any of the above embodiments, comprising a borosilicate skeleton and lithium nanoparticles grown in situ within the borosilicate skeleton, a silicon nitride nanowire layer grown in situ on the outside of the borosilicate skeleton and a mesoporous carbon layer coated on the outside of the silicon nitride nanowire layer.

[0073] Preparation Example 1

[0074] This preparation example 1 provides a method for preparing a borosilicate substrate, comprising the following steps:

[0075] S0-1. Boron oxide and pure silicon powder are mixed in a mass ratio of 9:14 and then ball-milled in a ball mill to obtain a ball-milled mixture. The ball-milled mixture is placed in the hearth of an atmosphere furnace. The atmosphere furnace is replaced with argon gas, and then the temperature is raised to 450°C at a rate of 10°C / min under an argon atmosphere, and then kept at this temperature for 1 hour. The mixture is then cooled to room temperature in the furnace to obtain a borosilicate precursor.

[0076] S0-2. Placing the borosilicate precursor in the hearth of an atmosphere furnace, replacing the atmosphere furnace with nitrogen and adjusting the nitrogen pressure in the atmosphere furnace to 0.3 MPa and the nitrogen flow rate to 80 sccm, heating the atmosphere furnace to 1200° C. at a rate of 10° C. / min, and then calcining at this temperature for 5 h. After cooling to room temperature with the furnace, the borosilicate precursor was ball-milled in a vacuum environment and sieved to obtain a borosilicate intermediate;

[0077] S0-3. Add the borosilicate intermediate to the silane solution (the silane solute is 3-piperazinepropylmethyldimethoxysilane, and the ratio of the silane solute to the borosilicate precursor is 0.2:1) at a solid-liquid ratio of 0.08 g / mL, keep it in a 45°C water bath for 10 minutes, filter it and separate it, then dry it in a vacuum drying oven at 60°C for 30 minutes and cool it to room temperature to obtain a borosilicate matrix.

[0078] Preparation Example 2

[0079] Preparation Example 2 provides a method for preparing a borosilicate substrate. The difference from Preparation Example 1 is that step S0-3 is not performed, and the borosilicate substrate is prepared in step S0-2.

[0080] Preparation Example 3

[0081] Preparation Example 3 provides a method for preparing a borosilicate substrate. The difference from Preparation Example 1 is that steps S0-2 and S0-3 are not performed, and the borosilicate substrate is prepared in step S0-1.

[0082] Preparation Example 4

[0083] Preparation Example 4 provides a method for preparing a borosilicate matrix, which differs from Preparation Example 1 in that step S0-2 is not performed, and the borosilicate precursor prepared in step S0-1 is ball-milled and sieved before step S0-3 is performed to prepare the borosilicate matrix.

[0084] Example 1

[0085] This embodiment 1 provides a method for preparing a modified silicon-based negative electrode material, comprising the following steps:

[0086] S1. The borosilicate matrix prepared in Preparation Example 1 was added to a saturated aqueous solution of lithium acetate (the mass ratio of borosilicate matrix to lithium was 1:0.2) at 80°C for ultrasonic dispersion, and then heated in an oil bath at 100°C to evaporate the water solvent. The mixture was then transferred to the hearth of an atmosphere furnace, and the atmosphere furnace was replaced with argon gas. The temperature was then raised to 900°C at a rate of 10°C / min and kept at this temperature for 45 minutes. The modified matrix was then cooled to room temperature and ground and pulverized to obtain the modified matrix.

[0087] S2. The modified substrate is transferred to a vapor deposition furnace (maintaining the pressure in the furnace at 0.5 MPa with a fluctuation of no more than 10%) and heated to 1100°C. After deposition in silane gas at a flow rate of 500 sccm for 10 minutes, an intermediate is obtained. Ammonia gas is then introduced to adjust the silane gas concentration in the deposition furnace to 25%, and surface growth is performed on the intermediate for 30 minutes. The composite substrate is then cooled to room temperature after being kept in a vacuum environment for 1 hour to obtain a composite substrate.

[0088] S3. Place the composite matrix in the hearth of an atmosphere furnace, replace the atmosphere furnace with pure hydrogen, and then adjust the hydrogen pressure in the atmosphere furnace to 1 MPa. Heat the atmosphere furnace to 300°C at a rate of 10°C / min and keep it warm for 3 hours. Cool the furnace to room temperature to obtain a reduced matrix. Add the reduced matrix to a mesoporous carbon suspension with a concentration of 0.2 g / mL (the mass ratio of the reduced matrix to the mesoporous carbon is 1:0.5, the average particle size of the mesoporous carbon is 75 nm, and the solvent is petroleum ether) for ultrasonic mixing. Keep it warm in a 70°C water bath environment for 2 hours, filter and separate, dry it in a vacuum environment at 800°C for 3 hours, and then cool it to room temperature to obtain a modified silicon-based negative electrode material.

[0089] Example 2

[0090] This embodiment 2 provides a method for preparing a modified silicon-based negative electrode material. The difference from embodiment 1 is that the borosilicate substrate prepared in preparation example 2 is used in step S1.

[0091] Example 3

[0092] This embodiment 3 provides a method for preparing a modified silicon-based negative electrode material. The difference from embodiment 1 is that the borosilicate substrate prepared in preparation example 3 is used in step S1.

[0093] Example 4

[0094] This embodiment 4 provides a method for preparing a modified silicon-based negative electrode material. The difference from embodiment 1 is that the borosilicate substrate prepared in preparation example 4 is used in step S1.

[0095] Comparative Example 1

[0096] This comparative example 1 provides a preparation method of a modified silicon-based negative electrode material, which is different from Example 1 in that no mesoporous carbon coating is performed in step S3, and the modified silicon-based negative electrode material is obtained by cooling to room temperature after reduction treatment.

[0097] Comparative Example 2

[0098] Comparative Example 2 provides a method for preparing a modified silicon-based negative electrode material, which differs from Example 1 in that no hydrogen reduction treatment is performed in step S3, and the composite matrix prepared in step S2 is added to the mesoporous carbon suspension.

[0099] Comparative Example 3

[0100] Comparative Example 3 provides a method for preparing a modified silicon-based negative electrode material, which is different from Example 1 in that step S2 is not performed, and the modified matrix prepared in step S1 is subjected to step S3.

[0101] Performance testing

[0102] The modified silicon-based negative electrode materials prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were used as active materials, mixed with LA133 (binder) and acetylene black (conductive agent) in a ratio of 8:1:1, coated on copper foil, vacuum dried, and rolled into a composite sheet. The composite sheet was cut into a negative electrode sheet with a diameter of 14 mm, metallic lithium was used as the counter electrode sheet, lithium hexafluorophosphate was used as the electrolyte, and a polypropylene microporous membrane was used as the separator. The battery was assembled into a button-type lithium battery in a glove box and the following tests were carried out: first coulomb efficiency, constant current discharge at a current density of 0.1C at room temperature To 0.01V, then discharge at a constant current density of 0.02C to 0.005V, and finally charge the device to 1.5V at a constant current density of 0.1C. The capacity when charged to 1.5V is measured as the first reversible specific capacity and the first coulombic efficiency is calculated. The results are shown in Table 1 below; for cycle performance, constant current charge and discharge are performed at room temperature at a current density of 0.1C, and the charge and discharge voltage is limited to 0.005V-1.5V. The charge specific capacity after 100 cycles is measured, and the capacity retention rate after 100 cycles is calculated. The results are shown in Table 1 below.

[0103] Table 1 Electrochemical performance test results of lithium batteries

[0104]

[0105] As can be seen from Table 1, in Example 2, when the borosilicate substrate is not subjected to surface silane treatment, the bonding strength to lithium acetate is reduced during the pre-lithiation process, thereby reducing the first reversible specific capacity of the negative electrode material, and the first coulombic efficiency is also reduced; in Example 3, the mixture after simple calcination of borosilicate is directly used to prepare the negative electrode material, resulting in a significant decrease in the structural strength of the borosilicate substrate, and then a decrease in the capacity retention rate; in Example 4, the borosilicate substrate is not subjected to nitriding treatment, resulting in a decrease in the bonding strength between the borosilicate substrate and the silicon nitride nanowires and a decrease in its own structural strength, thereby reducing the cycle performance; and in Comparative Example 1, the surface is not coated with mesoporous carbon, resulting in a decrease in the first efficiency and a decrease in the cycle performance, and in Comparative Example 2, hydrogen reduction is not performed, resulting in a decrease in the utilization rate of the lithium compound and a decrease in the bonding performance with borosilicate, and in Comparative Example 3, silicon nitride nanowires are not generated, resulting in a decrease in both the first efficiency and the cycle performance.

[0106] While the embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations of these embodiments are possible. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as set forth in the claims. Furthermore, the invention described herein is susceptible to other embodiments and may be practiced or implemented in a variety of ways.

Claims

1. A method for preparing a modified silicon-based negative electrode material, characterized in that: include: mixing boron oxide and silicon powder and calcining the mixture to obtain a borosilicate precursor; The boron silicon precursor is calcined in a nitrogen atmosphere and then ground to obtain a boron silicon intermediate; The borosilicate intermediate is soaked in a silane solution and then dried to obtain a borosilicate matrix; the borosilicate matrix is ​​soaked in a pre-lithium solution and the solvent is evaporated and then calcined to obtain a modified matrix; The modified matrix is ​​deposited in silicon source gas at 1000°C-1100°C for 10min-15min to obtain an intermediate; the intermediate is generated in silicon nitrogen gas at 1000°C-1100°C for 30min-50min and then cooled to obtain a composite matrix; the composite matrix is ​​reduced in a reducing atmosphere and then the surface is coated with mesoporous carbon to obtain a modified silicon-based negative electrode material.

2. The preparation method according to claim 1, characterized in that The mass ratio of the boron element in the boron oxide to the silicon element in the silicon powder is (0.2-0.3):

1.

3. The preparation method according to claim 1, characterized in that Boron oxide and silicon powder are mixed by ball milling.

4. The preparation method according to claim 1, characterized in that After mixing, calcination is carried out at 400-450°C.

5. The preparation method according to claim 1, characterized in that After mixing, the mixture was calcined under an inert atmosphere.

6. The preparation method according to claim 1, characterized in that After mixing, calcine for 1h-1.5h.

7. The preparation method according to claim 1, characterized in that The gas in the nitrogen-containing atmosphere includes one of methylamine, nitrogen and ammonia.

8. The preparation method according to claim 1, characterized in that Calcination in a nitrogen atmosphere at 1100℃-1300℃.

9. The preparation method according to claim 1, characterized in that The boron silicon precursor is calcined in a nitrogen-containing atmosphere at 800 sccm-1000 sccm.

10. The preparation method according to claim 1, characterized in that The particle size of the borosilicate intermediate is 10 μm-100 μm.

11. The preparation method according to claim 1, characterized in that Calcinate in a nitrogen atmosphere for 4-6 hours.

12. The preparation method according to claim 1, characterized in that The silane solute in the silane solution includes 3-piperazinepropylmethyldimethoxysilane, N -One of the (aminoethyl)-3-aminopropylmethyldimethoxysilanes.

13. The preparation method according to claim 1, characterized in that The mass ratio of the silane solute to the borosilicate precursor in the silane solution is (0.1-0.2):

1.

14. The preparation method according to claim 1, characterized in that Immerse the borosilicate intermediate in the silane solution for 1 min-15 min.

15. The preparation method according to claim 1, characterized in that After infiltration, dry at 50℃-70℃.

16. The preparation method according to claim 1, characterized in that The lithium solute in the pre-lithium solution includes lithium acetate.

17. The preparation method according to claim 1, characterized in that The mass ratio of the borosilicate matrix to the lithium element in the pre-lithium solution is 1:(0.1-0.3).

18. The preparation method according to claim 1, characterized in that The borosilicate substrate is ultrasonically impregnated in the pre-lithium solution.

19. The preparation method according to claim 1, characterized in that The borosilicate substrate is immersed in the pre-lithium solution and then the solvent is evaporated at 80-100°C.

20. The preparation method according to claim 1, characterized in that After the solvent is evaporated, the mixture is calcined at 800-1000°C.

21. The preparation method according to claim 1, characterized in that After evaporating the solvent, the product was calcined under protective atmosphere.

22. The preparation method according to claim 1, characterized in that The hydrogen concentration in the reducing atmosphere is 70%-100%.

23. The preparation method according to claim 1, characterized in that The reduction is carried out in a reducing atmosphere of 0.5 MPa-1.5 MPa.

24. The preparation method according to claim 1, characterized in that The reduction is carried out in a reducing atmosphere at 200°C-300°C.

25. The preparation method according to claim 1, characterized in that Reduction treatment was carried out in a reducing atmosphere for 2h-5h.

26. The preparation method according to claim 1, characterized in that After reduction and cooling, the material is immersed in a mesoporous carbon suspension, separated and dried to obtain a modified silicon-based negative electrode material, wherein the solvent of the mesoporous carbon suspension includes one of petroleum ether, chloroform and dichloromethane.

27. A modified silicon-based negative electrode material obtained by the preparation method according to any one of claims 1 to 26, characterized in that: The invention comprises a borosilicate skeleton and lithium nanoparticles in situ grown in the borosilicate skeleton. A silicon nitride nanowire layer and a mesoporous carbon layer covering the outer side of the silicon nitride nanowire layer are in situ grown on the outer side of the borosilicate skeleton.

28. Use of the modified silicon-based negative electrode material prepared by the preparation method according to any one of claims 1 to 26 or the modified silicon-based negative electrode material according to claim 27 in a lithium-ion battery.

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