Modified silicon-based negative electrode material and preparation method and application thereof

Abstract

The invention provides a modified silicon-based negative electrode material as well as a preparation method and application thereof, and relates to the technical field of new energy battery negative electrodes. The preparation method provided by the invention comprises the following steps: dipping a boron-silicon substrate in a pre-lithium solution, evaporating a solvent to dryness, and calcining to obtain a modified substrate; growing silicon nitride nanowires on the surface of the modified matrix in situ to prepare a composite matrix; and reducing the composite matrix in a reducing atmosphere, and coating the surface with mesoporous carbon to prepare the modified silicon-based negative electrode material. The structure stability of the negative electrode material in the charging and discharging process can be effectively improved, the cycle performance reduction caused by the pulverization of the negative electrode material is avoided, and meanwhile, the first effect can be improved by performing pre-lithiation on the boron-silicon substrate.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode of new energy batteries, 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 economy and technology, energy and environmental problems are becoming increasingly severe. New energy technology has become one of the important research topics at present. Lithium-ion batteries, as the main branch of new energy technology, have attracted much attention. As people's demand for the energy and safety of lithium-ion batteries gradually increases, capacity issues and cycle performance issues have gradually received attention. In lithium-ion batteries, the capacity of positive and negative electrode materials determines the overall capacity of the battery. The capacity of the positive electrode material has reached a bottleneck and is difficult to break through. The theoretical specific capacity of the commonly used graphite negative electrode material is low. The overall capacity performance of the battery can be effectively improved by selecting the negative electrode material.

[0003] Among many materials, silicon-based materials have attracted extensive attention due to their ultra-high theoretical lithium storage capacity. However, there are still many problems in the application of silicon-based materials in lithium-ion batteries, such as poor electronic conductivity of silicon-based materials, severe polarization during charging and discharging, and huge volume changes during the cycle, resulting in poor stability, which hinders the development and large-scale application of silicon-based materials. At the same time, silicon-based materials consume more lithium ions during the initial formation of the SEI film, resulting in a low initial coulomb efficiency; the SEI film is constantly broken and regenerated during the repeated expansion and contraction of the silicon material, which consumes a large amount of lithium ions and seriously affects the service life of the lithium-ion battery.

[0004] Therefore, the prior art often performs pre-lithiation treatment on silicon-based negative electrode materials, pre-forming an SEI film on the surface of the negative electrode material to reduce the consumption of lithium ions in lithium-ion batteries, and can also protect the negative electrode material to a certain extent, preventing the material from pulverizing and falling off. For example, the Chinese invention patent with publication number CN115621425A provides a silicon-based negative electrode pre-lithiation method, which is obtained by short-circuiting the negative electrode plate and the lithium plate to obtain a pre-lithiation negative electrode. However, this requires separate treatment of the negative electrode material, which greatly increases the complexity of the processing steps, so 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 a preparation method and application thereof, 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 effect by pre-lithiation of the borosilicate matrix.

[0006] In a 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 calcining after evaporating the solvent 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 a borosilicate matrix, and 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, and 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, and at the same time can also increase the specific surface area and thus increase the loading amount of the 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] Optionally, 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.-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-containing atmosphere for 4 h to 6 h.

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

[0020] Optionally, the mass ratio of the silane solute in the silane solution to the borosilicate precursor 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 the 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] Optionally, the solvent is evaporated and then calcined under a protective atmosphere.

[0029] Optionally, when silicon nitride nanowires are grown in situ on the surface of a modified substrate to obtain a composite substrate, the method includes: depositing the modified substrate in a silicon source gas at 1000°C-1100°C for 10min-15min to obtain 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 comprises 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 also 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; Figure 2 A flowchart of a method for preparing a borosilicate substrate provided by the present invention. DETAILED DESCRIPTION

[0038] 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 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 understood by people with general skills in the field to which the present invention belongs. "Including" and similar words used in this article mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0039] See also Figure 1 The present invention provides a method for preparing a modified silicon-based negative electrode material, comprising the following steps: S1, immersing the borosilicate substrate in a pre-lithium solution, evaporating the solvent, and then calcining to obtain a modified substrate; S2, in-situ growing silicon nitride nanowires on the surface of the modified substrate to obtain a composite substrate; 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.

[0040] In fact, the preparation method provided by the present invention can effectively improve the uniformity of the dispersion of lithium solute in the borosilicate matrix by immersing the borosilicate matrix in a pre-lithium solution in step S1, and at the same time promote the combination stability of the three elements of boron, silicon and lithium after calcination, which is beneficial to ensure the position stability of lithium in the subsequent treatment process. Specifically, a Li-B-Si composite structure can be formed in the modified matrix by calcination, which is beneficial to improve the structural stability of the modified matrix.

[0041] In some embodiments, see Figure 2 The method for preparing the borosilicate substrate used in step S1 comprises the following steps: S0-1, mixing boron oxide and silicon powder and calcining to obtain a borosilicate precursor; S0-2, calcining the borosilicate precursor in a nitrogen-containing atmosphere and then grinding it to obtain a borosilicate intermediate; S0-3, soaking the borosilicate intermediate in a silane solution and then drying it to obtain a borosilicate matrix.

[0042] In fact, by doping boron oxide into silicon materials, a boron-doped silicon matrix (boron silicon precursor) can be obtained. At the same time, the density of the boron silicon precursor can be effectively improved by calcination treatment, and the structural rigidity can be improved, thereby inhibiting the volume expansion of silicon. In addition, by calcining in a nitrogen-containing atmosphere, a nitride layer can be formed on the surface of the boron silicon precursor, which can improve the surface inertness and the integrity of the subsequent in-situ growth of silicon nitride nanowires, and further inhibit the expansion effect of the silicon material.

[0043] In some embodiments, when performing step S0-1, 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. In fact, adjusting the mixing ratio of the boron element and the silicon element is conducive to adjusting the proportion of the boron-silicon alloy phase in the formed boron-silicon intermediate and adjusting the structural strength of the boron-silicon skeleton in the boron-silicon intermediate, thereby framing the active silicon inside the skeleton.

[0044] In some embodiments, boron oxide and silicon powder can be ball-milled when executing step S0-1. This not only helps to promote the full 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.

[0045] In some embodiments, after mixing boron oxide and silicon powder during step S0-1, calcination is performed at 400-450°C in an inert atmosphere for 1-1.5 hours. In fact, at high temperature, the boron oxide can be partially melted and wrap the silicon powder and diffuse on the surface, thereby forming an amorphous boron-silicon interface layer, constructing a boron-silicon chemical bonding network, and improving structural stability.

[0046] 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-0.5 MPa. In fact, after calcination, the boron silicon precursor with a particle size of 0.1 μm-100 μm is obtained by cooling to room temperature and grinding, which is beneficial to increase the specific surface area, and further facilitates the nitrogen-containing atmosphere calcination treatment in step S0-2.

[0047] In some embodiments, the nitrogen-containing gas in the nitrogen-containing atmosphere used when performing step S0-2 includes one of methylamine, nitrogen, and ammonia. In addition, the borosilicate precursor can be calcined in a nitrogen-containing atmosphere at 1100°C-1300°C for 4h-6h, and a high-temperature nitridation reaction can be used to promote the formation of a mutually composite boron nitride or silicon nitride composite phase in the borosilicate precursor, and promote boron, silicon and nitrogen to combine to form a composite structure, and at the same time, a nitrided skeleton can be formed in the borosilicate intermediate, which is beneficial to improve the structural strength.

[0048] 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 nitridation 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 nitridation structure on the surface of the borosilicate precursor and the subsequent modification of silicon nitride nanowires.

[0049] In some embodiments, after executing step S0-2 to obtain the borosilicate intermediate, ball milling and screening are performed to obtain a borosilicate intermediate with a particle size of 10μm-100μm, which is beneficial to destroy the long-range ordered nitride structure in the borosilicate intermediate, and use the broken nitride structure to re-bond with boron and silicon, which is beneficial to improve the ion diffusion capacity, and then help improve the conductivity of the negative electrode material, and at the same time can increase the number of surface defects of the borosilicate intermediate.

[0050] 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, which is beneficial to the surface pre-lithiation in step S1.

[0051] 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 not to 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 the full mixing of the borosilicate intermediate and the silane solute. In addition, the solid-liquid mixing method commonly used in the art can be used during the mixing process, such as mechanical stirring, oscillation and / or ultrasonic treatment.

[0052] In some embodiments, when performing step S0-3, the mass ratio of silane solute to borosilicate precursor in the silane solution is (0.1-0.2): 1. In addition, the borosilicate intermediate can be soaked in the silane solution for 1 min-15 min. In fact, in order 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 soaking in the silane solution when performing step S0-3, the solid-liquid separation is performed and dried at 50°C-70°C.

[0053] In some embodiments, the lithium solute in the pre-lithium solution used in step S1 includes lithium acetate. In fact, after the borosilicate substrate is soaked in the pre-lithium solution and the solvent of the pre-lithium solution is evaporated, lithium acetate can be uniformly precipitated and attached to the surface pores of the borosilicate substrate, and the stability of lithium acetate on the surface of the borosilicate substrate can be improved after calcination.

[0054] In some embodiments, when performing step S1, the mass ratio of the borosilicate substrate to the lithium element in the pre-lithium 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 can not only play a structural buffering role, but also improve the density and uniformity when forming the SEI film.

[0055] In some embodiments, after ultrasonically impregnating the borosilicate substrate in the pre-lithium solution during step S1, the solvent is evaporated at 80° C.-100° C. In fact, by performing ultrasonic treatment during the impregnation process, the ultrasonic cavitation effect can be effectively utilized to eliminate tiny bubbles attached to the surface of the borosilicate substrate, and the grain size of lithium acetate during crystallization can be reduced, thereby improving the adhesion uniformity of lithium acetate on the surface of the borosilicate substrate.

[0056] In some embodiments, after the solvent in the lithium solution is evaporated during step S1, the modified substrate is obtained by calcining in a protective atmosphere at 800°C-1000°C for 0.5h-1h and then cooling to room temperature. In fact, the protective gas in the protective atmosphere used includes one of argon, helium, and neon, which is conducive to maintaining the structural stability of the substrate during the calcination and sintering process to avoid oxidative collapse. At the same time, the lithium element can be anchored on the surface of the borosilicate substrate and the structural density can be improved.

[0057] 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 10min-15min to obtain 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. In fact, by high-temperature cracking of the silicon source gas, silicon atoms can be adsorbed on the surface of the modified substrate and form a silicon coating layer, which can not only coat the modified substrate inside, but also serve as a directional nucleus for silicon nitride nanowires. When cracking and depositing in the silicon nitrogen gas, silicon nitride nanowires are directional formed on the surface of the modified substrate through gas-solid growth, and the interwoven nanowires can play a good protective and volume buffering role.

[0058] In some embodiments, the silicon source gas used in step S2 includes one of silane and silicon tetrachloride, the silicon nitrogen gas used includes silicon source gas and nitrogen source gas, and the concentration of silicon source gas in 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 of 0.1MPa-1MPa.

[0059] In some embodiments, the hydrogen concentration in the reducing atmosphere used when performing step S3 is 70%-100%. In fact, when performing reduction treatment in the reducing atmosphere, the reducing gas can penetrate into the silicon nitride nanowires and contact with the lithium compound on the surface of the borosilicate substrate to generate lithium nanoparticles by in-situ reduction, and the lithium nanoparticles are locked on the surface of the borosilicate substrate. In addition, the reducing atmosphere can also include an inert carrier gas, such as argon.

[0060] In some embodiments, the composite matrix can be reduced in a reducing atmosphere of 0.5MPa-1.5MPa when performing step S3. In fact, the reduction treatment in a high-pressure atmosphere is conducive to the reduction gas penetrating the silicon nitride nanowire coating layer into the interior of the borosilicate matrix. In addition, the composite matrix can also be reduced in a reducing atmosphere of 200°C-300°C for 2h-5h to control the content of lithium nanoparticles generated on the surface of the borosilicate matrix.

[0061] In some embodiments, after performing the reduction treatment in the reducing atmosphere in step S3 and cooling to room temperature, the modified silicon-based negative electrode material can be obtained by immersing in a mesoporous carbon suspension, separating and drying, and the solvent used in the mesoporous carbon suspension includes one of petroleum ether, chloroform, and dichloromethane. In fact, by immersing in the mesoporous carbon suspension, a mesoporous carbon coating layer can be formed on the surface of the substrate, which effectively improves the performance of the negative electrode material and protects the silicon nitride nanowires inside.

[0062] In some embodiments, the particle size of the mesoporous carbon in the mesoporous carbon suspension is 50nm-100nm, and the small-particle mesoporous carbon is dispersed on the surface of the substrate to achieve overall uniform coating. In addition, an active agent and a dispersant may be dissolved in the mesoporous carbon suspension to improve the suspension stability of the mesoporous carbon in the mesoporous carbon suspension and avoid agglomeration and sedimentation of the mesoporous carbon suspension.

[0063] 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 is conducive to the uniform attachment of the mesoporous carbon to the surface silicon nitride nanowires and the formation of a relatively dense mesoporous carbon coating layer. In addition, the concentration of mesoporous carbon in the mesoporous carbon suspension is 0.1g / mL-0.2g / mL, which is conducive to the uniform dispersion of the mesoporous carbon and the matrix in the suspension.

[0064] In some embodiments, before the surface is coated with mesoporous carbon, the composite matrix after reduction treatment can be pre-activated. For example, the composite matrix after 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 matrix after reduction treatment can be surface treated with a commonly used non-ionic surfactant. In fact, after performing step S3, the surface is coated with mesoporous carbon, and then dried at 700°C-800°C in vacuum for 3h-5h and then cooled.

[0065] The present invention also provides a modified silicon-based negative electrode material obtained by the preparation method provided in any of the above embodiments, comprising a borosilicate skeleton and lithium nanoparticles grown in situ in 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.

[0066] Preparation Example 1

[0067] This preparation example 1 provides a method for preparing a borosilicate substrate, comprising the following steps: S0-1, boron oxide and pure silicon powder are mixed in a mass ratio of 9:14, and then mixed and ball-milled in a ball mill to obtain a ball-milled mixture, and the ball-milled mixture is placed in the furnace of an atmosphere furnace, and the atmosphere furnace is gas-replaced with argon gas, and then heated to 450°C at a rate of 10°C / min in an argon atmosphere, and then kept warm for 1 hour, and then cooled to room temperature with the furnace to obtain a borosilicate precursor; S0-2, placing the borosilicate precursor in the furnace 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 for 5 hours, cooling to room temperature with the furnace, and then ball milling and sieving in a vacuum environment to obtain a borosilicate intermediate; S0-3. Add the borosilicate intermediate to the silane solution (the silane solute is 3-piperazinepropylmethyldimethoxysilane, and the silane solute and the borosilicate precursor are 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 and separate it, dry it in a 60°C vacuum drying oven for 30 minutes and cool it to room temperature to obtain a borosilicate matrix.

[0068] Preparation Example 2

[0069] This Preparation Example 2 provides a method for preparing a borosilicate substrate, which is different from Preparation Example 1 in that step S0-3 is not performed, and the borosilicate substrate is prepared in step S0-2.

[0070] Preparation Example 3

[0071] This Preparation Example 3 provides a preparation method for a borosilicate substrate, which is different from Preparation Example 1 in that step S0-2 and step S0-3 are not performed, and the borosilicate substrate is prepared in step S0-1.

[0072] Preparation Example 4

[0073] This Preparation Example 4 provides a preparation method for a borosilicate matrix, which is different from Preparation Example 1 in that step S0-2 is not performed, and the borosilicate precursor obtained in step S0-1 is ball-milled and sieved before step S0-3 is performed to obtain the borosilicate matrix.

[0074] Example 1

[0075] This embodiment 1 provides a method for preparing a modified silicon-based negative electrode material, comprising the following steps: S1. Add the borosilicate matrix prepared in Preparation Example 1 into a saturated aqueous solution of lithium acetate (mass ratio of borosilicate matrix to lithium is 1:0.2) at 80°C for ultrasonic dispersion, heat in a 100°C oil bath environment to evaporate the water solvent, transfer to the furnace of an atmosphere furnace, replace the atmosphere furnace with argon gas, heat to 900°C at a rate of 10°C / min and keep warm for 45 minutes, cool to room temperature with the furnace, grind and pulverize to obtain a modified matrix; S2, transferring the modified substrate to a vapor deposition furnace (maintaining the gas pressure in the furnace at 0.5 MPa, with fluctuations not exceeding 10%) and heating it to 1100°C, depositing it in a silane gas with a flow rate of 500 sccm for 10 minutes to obtain an intermediate, then introducing ammonia gas to adjust the silane gas concentration in the atmosphere deposition furnace to 25%, and performing surface growth on the intermediate for 30 minutes; keeping the temperature in a vacuum environment for 1 hour, and then cooling it to room temperature to obtain a composite substrate; S3. Place the composite matrix in the furnace of an atmosphere furnace, replace the gas in the atmosphere furnace with pure hydrogen and 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, and then cool it to room temperature to obtain a reduced matrix; add the reduced matrix into 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.

[0076] Example 2

[0077] 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.

[0078] Example 3

[0079] 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.

[0080] Example 4

[0081] 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.

[0082] Comparative Example 1

[0083] This comparative example 1 provides a method for preparing 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 with the furnace after reduction treatment.

[0084] Comparative Example 2

[0085] This comparative example 2 provides a method for preparing a modified silicon-based negative electrode material, which is different 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.

[0086] Comparative Example 3

[0087] This 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 substrate prepared in step S1 is subjected to step S3.

[0088] Performance Testing

[0089] The modified silicon-based negative electrode materials prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were used as active materials, respectively 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, and the composite sheet was cut into a negative electrode sheet with a diameter of 14 mm. Metal lithium was used as the counter electrode sheet, lithium hexafluorophosphate was used as the electrolyte, and a polypropylene microporous membrane was used as the diaphragm. The button-type lithium batteries were assembled in a glove box and the following tests were carried out: the 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.

[0090] Table 1 Electrochemical performance test results of lithium batteries

[0091]

[0092] As can be seen from Table 1, when the borosilicate substrate is not treated with silane on the surface in Example 2, 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 negative electrode material is directly made of a mixture of borosilicate simply calcined, which leads to 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 nitrided, 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; 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.

[0093] Although the embodiments of the present invention are described in detail above, it is obvious to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as described in the claims. Moreover, the present invention described herein may have other embodiments and may be implemented or realized in a variety of ways.

Claims

1. A method for preparing a modified silicon-based negative electrode material, characterized in that: include: The borosilicate substrate is immersed in a pre-lithium solution, the solvent is evaporated, and then calcined to obtain a modified substrate; Silicon nitride nanowires are in-situ grown on the surface of a modified substrate to obtain a composite substrate; the composite substrate 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 preparation method of the borosilicate matrix comprises: 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; soaking the borosilicate intermediate in a silane solution and drying to obtain a borosilicate matrix.

3. The preparation method according to claim 2, 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; and / or, the boron oxide and the silicon powder are ball-milled and mixed; and / or, after mixing, they are calcined at 400°C-450°C; and / or, after mixing, they are calcined in an inert atmosphere; and / or, after mixing, they are calcined for 1h-1.5h.

4. The preparation method according to claim 2, characterized in that: The gas in the nitrogen-containing atmosphere includes one of methylamine, nitrogen, and ammonia; and / or, calcination is performed in a nitrogen-containing atmosphere at 1100°C-1300°C; and / or, the borosilicate precursor is calcined in a nitrogen-containing atmosphere at 800sccm-1000sccm; and / or, the particle size of the borosilicate intermediate is 10μm-100μm; and / or, calcination is performed in a nitrogen-containing atmosphere for 4h-6h.

5. The preparation method according to claim 2, characterized in that: The silane solute in the silane solution includes 3-piperazinepropylmethyldimethoxysilane, N -(aminoethyl)-3-aminopropylmethyldimethoxysilane; and / or, the mass ratio of the silane solute to the borosilicate precursor in the silane solution is (0.1-0.2):1; and / or, the borosilicate intermediate is immersed in the silane solution for 1min-15min; and / or, after immersion, it is dried at 50℃-70℃.

6. The preparation method according to claim 1, characterized in that: The lithium solute in the pre-lithium solution includes lithium acetate; and / or, the mass ratio of the borosilicate substrate to the lithium element in the pre-lithium solution is 1:(0.1-0.3); and / or, the borosilicate substrate is ultrasonically impregnated in the pre-lithium solution; and / or, after the borosilicate substrate is impregnated in the pre-lithium solution, the solvent is evaporated at 80°C-100°C; and / or, after the solvent is evaporated, the substrate is calcined at 800°C-1000°C; and / or, after the solvent is evaporated, the substrate is calcined under a protective atmosphere.

7. The preparation method according to claim 1, characterized in that: When silicon nitride nanowires are grown in situ on the surface of a modified substrate to obtain a composite substrate, the process includes: depositing the modified substrate in a silicon source gas at 1000-1100°C for 10-15 minutes to obtain an intermediate; generating the intermediate in a silicon nitrogen gas at 1000-1100°C for 30-50 minutes and then cooling to obtain a composite substrate.

8. The preparation method according to claim 1, characterized in that: The hydrogen concentration in the reducing atmosphere is 70%-100%; and / or, the reduction is carried out in a reducing atmosphere of 0.5MPa-1.5MPa; and / or, the reduction is carried out in a reducing atmosphere of 200℃-300℃; and / or, the reduction treatment is carried out in a reducing atmosphere for 2h-5h; and / or, after reduction and cooling, it 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.

9. A modified silicon-based negative electrode material obtained by the preparation method according to any one of claims 1 to 8, 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 coated on the outside of the silicon nitride nanowire layer are in-situ grown on the outside of the borosilicate skeleton.

10. Use of the modified silicon-based negative electrode material obtained by the preparation method according to any one of claims 1 to 8 or the modified silicon-based negative electrode material according to claim 9 in a lithium-ion battery.

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