A nitrogen-doped carbon-coated spherical silicon-based negative electrode material and its preparation method and application

Abstract

The present invention belongs to the field of electrochemistry, and relates to the preparation of silicon-based negative electrode materials, and specifically to a nitrogen-doped carbon-coated spherical silicon-based negative electrode material, and a preparation method and application thereof. The preparation method includes high-temperature disproportionation of silicon oxide raw materials, sodium hydroxide etching, surface grafting amination, coating of a carbon source that forms a covalent bond with silicon oxygen, and high-temperature solid-phase reaction to form a nitrogen-doped carbon-coated spherical silicon-based negative electrode material. The preparation method provided by the present invention solves the shortcomings of the existing silicon-based negative electrode materials, such as the weak surface coating and low initial coulomb efficiency. The prepared nitrogen-doped carbon-coated spherical silicon-based negative electrode material has the advantages of high capacity, high initial charge and discharge efficiency, and good cycle performance after being prepared into a lithium-ion half-cell. Tested at a current density of 100mA / g, the initial charge specific capacity reached 1705mAh / g, the initial coulomb efficiency was 73.35%, and good cycle performance was shown when performing a constant current cycle performance test.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemistry and relates to the preparation of silicon-based negative electrode materials, and specifically relates to a nitrogen-doped carbon-coated spherical silicon-based negative electrode material and a preparation method and application thereof. Background Art

[0002] New energy vehicles are facing increasingly severe mileage anxiety. High-energy-density power battery technology will continue to develop at a high speed in the future, providing major opportunities for the development of power batteries while also putting forward higher requirements.

[0003] Graphite materials are the current mainstream negative electrode materials, but they are increasingly unable to meet the current requirements for high energy density batteries due to their low theoretical specific capacity (372mAh / g). In response to the requirements for higher energy density batteries, silicon-based materials have the advantages of high lithium deintercalation capacity, suitable potential, and good safety. They are expected to become the first choice for the next generation of negative electrode materials, with broad market prospects. Among them, silicon-based negative electrode materials have smaller volume expansion than nano-silicon and better cycle stability, making them silicon-based materials closer to industrial applications. However, the poor conductivity of silicon-oxygen negative electrode materials and low first efficiency have always restricted their industrial promotion. In order to promote the industrialization of silicon-oxygen negative electrode materials, solving the problems of cycle stability and low first efficiency from the perspective of material conductivity and surface carbon coating stability is currently the best choice.

[0004] Chinese patent CN201210446543.7 discloses a method for preparing a silicon-oxygen composite material for lithium-ion batteries, using sodium carboxymethyl cellulose as a binder, using liquid phase coating technology to carry out silicon-oxygen compounding, and simultaneously using spray drying technology to dry and granulate to prepare a negative electrode material with uniform particle size.

[0005] Chinese patent CN202111399973.3 discloses a method for preparing a modified silicon-based negative electrode pole piece, which improves the performance of the dry-process negative electrode pole piece by amminating the surface of the silicon-based negative electrode, strengthening the hydrogen bonding force between the binder and the negative electrode particles, and improving the bonding force between the two, thereby improving the battery performance.

[0006] However, the carbon coating force on the surface of silicon-based negative electrode materials prepared by the above schemes is weak, which is not enough to form a strong and uniform coating layer. It is difficult to improve the cycle stability and first coulomb efficiency of the prepared silicon-based negative electrode materials. Therefore, it is very necessary to develop a preparation method to improve the stability and conductivity of the surface coating structure of silicon-oxygen negative electrode materials. Summary of the invention

[0007] In view of the technical problems that the surface coating layer of silicon-oxygen negative electrode materials prepared by the prior art is not firm and the first coulombic efficiency is low, the present invention proposes a nitrogen-doped carbon-coated spherical silicon-based negative electrode material and its preparation method and application. The silicon-oxygen negative electrode material has a nitrogen-doped carbon-coated spherical structure, and the surface coating layer of the prepared nitrogen-doped carbon-coated spherical silicon-based negative electrode material is firm, and the conductivity and cycle stability of the material are improved.

[0008] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0009] A method for preparing a nitrogen-doped carbon-coated spherical silicon-based negative electrode material, comprising the following steps:

[0010] (1) The silicon oxide raw material with a D50 of 3 to 20 μm is subjected to high-temperature disproportionation in a protective atmosphere at a temperature range of 900 to 1400°C, a heating rate of 2 to 10°C / min, and a heat preservation time of 5 min to 8 h to obtain precursor I;

[0011] (2) Precursor I and a 4% to 20% sodium hydroxide solution are mixed and reacted for 4 min to 2 h, and then washed with deionized water to form precursor II;

[0012] (3) Precursor II was added to toluene to prepare a solution with a solid-liquid ratio of (0.5-1.5):30, stirred for 25-40 min, and then solvent A was added in a ratio of m(precursor II):V(solution A) = 3 g:(0.5-2) mL, and refluxed for 6-10 h to obtain precursor III;

[0013] (4) Ultrasonic dispersion of single-walled carbon nanotubes in deionized water for 10 min to 1 h, adding lithium carboxymethyl cellulose and then precursor III, stirring for 12 to 20 h, and spray drying to obtain precursor IV.

[0014] (5) Precursor IV is heat treated in a protective atmosphere at 600-850°C for 5 min-8 h at a heating rate of 2-10°C / min to obtain a nitrogen-doped carbon-coated spherical silicon-based negative electrode material.

[0015] Furthermore, in the step (1), the silicon dioxide raw material is prepared by using a ball mill, a crusher or a pulverizer to control the particle size and shape, and then screening and demagnetizing.

[0016] Furthermore, in the step (1), the silicon oxide raw material is crushed by a jaw roller combination and then air flow pulverized, and then sieved and demagnetized to obtain a D50 between 3 and 20 μm.

[0017] Furthermore, in the step (1), the silicon dioxide raw material particles are spherical in shape.

[0018] Furthermore, the concentration of sodium hydroxide in step (2) affects the structure formed on the surface of the silicon oxide material, and also affects the etching of silicon dioxide on the surface of silicon monoxide.

[0019] Furthermore, in step (2), the precursor II is washed with deionized water 3 to 5 times and vacuum dried to obtain a dry powder.

[0020] Furthermore, in the step (2), the cleaning endpoint is determined when the pH of the cleaning solution is neutral, and the surface of the precursor II has a rough structure formed by corrosion by sodium hydroxide.

[0021] Furthermore, in step (3), the solvent A is any one of or a combination of at least two of amino-containing organosilanes such as polydiallyldimethylammonium chloride, hexadecyltrimethylammonium bromide or 3-aminopropyltriethoxysilane.

[0022] Furthermore, the temperature of the reflux reaction in step (3) is preferably between 110°C and 130°C.

[0023] Furthermore, in step (4), the mass ratio of single-walled nanotubes to deionized water is 3 mg:40 g, and the mass ratio of single-walled carbon nanotubes to lithium carboxymethyl cellulose is (0.5-1):100.

[0024] Furthermore, in the step (4), after the lithium carboxymethyl cellulose is completely dissolved, the precursor III is added, and the mass ratio of the precursor III to the lithium carboxymethyl cellulose is 10:(0.5-1).

[0025] Furthermore, the spray drying conditions in step (4) are an inlet temperature of 180-350°C and an outlet temperature of 90-110°C.

[0026] Furthermore, in step (5), the inert atmosphere is any one of nitrogen, argon, helium or neon, or a combination of at least two of them.

[0027] Furthermore, the nitrogen-doped carbon-coated spherical silicon-based negative electrode material prepared by the above method has a spherical outer shape and a three-dimensional conductive structure interlaced with carbon nanotubes.

[0028] Furthermore, the nitrogen-doped carbon-coated spherical silicon-based negative electrode material is used as a negative electrode material for lithium-ion batteries.

[0029] The present invention has the following beneficial effects:

[0030] 1. The present invention first disproportionates the silicon-oxygen material at high temperature to form Si and SiO2, and forms a rough surface after sodium hydroxide etching treatment. On the one hand, the generation of silicon inside the material improves the initial efficiency and capacity of the material. On the other hand, the subsequent surface amination area is increased after sodium hydroxide etching treatment, which will increase more sites for forming covalent bonds with the carbon source. Secondly, lithium carboxymethyl cellulose can form a stable and uniform carbon source coating layer with the amination silicon-oxygen material, which will effectively improve the structural stability of the silicon-oxygen material surface. Then, by spray drying with carbon tubes to form spherical particles, followed by high-temperature treatment, not only the carbon source coating stability is improved, but also nitrogen doping improves conductivity. Thus, the spherical material has both firmly carbon-coated nitrogen-doped silicon-oxygen materials and carbon tubes interspersed in the three-dimensional conductive network, which provides a channel for the rapid transmission of electrons. At the same time, Si and SiO particles are buffered by carbon layers and carbon tubes, which promotes the formation of surface-stable SEI films and improves the material cycle stability.

[0031] 2. The nitrogen-doped carbon-coated spherical silicon-based negative electrode material prepared by the preparation method provided by the present invention has high first efficiency and high cycle stability when prepared into a lithium-ion half-cell. When tested at a current density of 100mA / g, the first charge specific capacity reached 1705mAh / g, and the first coulombic efficiency was 73.35%; and it showed good cycle performance when conducting a constant current cycle performance test. Therefore, the nitrogen-doped carbon-coated spherical silicon-based negative electrode material prepared by the present invention is suitable for power batteries and has broad market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 This is a scanning electron microscope image of the precursor II material prepared in Example 4 of the present invention at a magnification of 10.0k.

[0034] Figure 2 This is a scanning electron microscope image of the nitrogen-doped carbon-coated spherical silicon-based negative electrode material prepared in Example 4 of the present invention at a magnification of 10.0k.

[0035] Figure 3 This is a scanning electron microscope image of the nitrogen-doped carbon-coated spherical silicon-based negative electrode material prepared in Example 4 of the present invention at a magnification of 500x.

[0036] Figure 4The first cycle charge and discharge curves of the nitrogen-doped carbon-coated spherical silicon-based negative electrode material prepared in Example 4 of the present invention and the materials prepared in Comparative Examples 1 and 2.

[0037] Figure 5 Graph showing the cycling data of the nitrogen-doped carbon-coated spherical silicon-based negative electrode material prepared in Example 4 of the present invention and the materials prepared in Comparative Examples 1 and 2 in the first 50 weeks at 0.1C (3 weeks) and 0.3C (47 weeks). DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0039] In the following examples, a Hitachi S~3400N scanning electron microscope was used to measure the microscopic morphology of the prepared samples. The battery performance test was performed using a battery test system model LANHE CT2001A produced by Wuhan Landian Electronics Co., Ltd.

[0040] The silicon oxide negative electrode material, conductive agent and binder prepared by the present invention are slurried in a mass ratio of 8:1:1, uniformly coated on copper foil and dried to obtain a pole piece, wherein the binder is PAA. A LiPF6 electrolyte with a concentration of 1.0 mol / L is used, wherein the volume ratio of the solvent components EC:DEC:DMC is 1:1:1, and 10% FEC is added. A microporous polypropylene diaphragm is selected, and a lithium sheet is used as a counter electrode to assemble a CR2025 button half-cell. The first cycle test uses a current density of 100mA / g and a voltage range of 0.005~2.0V. The constant current cycle performance test is carried out at 25°C, with a current density of 300mA / g and a voltage range of 0.005~2V.

[0041] Example 1

[0042] This embodiment is a method for preparing a nitrogen-doped carbon-coated spherical silicon-based negative electrode material, and the steps are as follows:

[0043] (1) Weigh 5 g of silicon dioxide raw material with a D50 of 3 μm and place it in a corundum boat. In a tube furnace, introduce nitrogen at a rate of 100 mL / min, heat the temperature to 900°C at a rate of 2°C / min and keep the temperature for 5 min. After cooling in the furnace, the precursor I is obtained.

[0044] (2) Prepare a 4% sodium hydroxide solution, take 30 mL of the solution, add precursor I, stir and react with a magnetic stirrer at 200 r / min for 4 min, use suction filtration, use deionized water to wash the reactant 3 times, measure the pH of the washing solution to be neutral, transfer to a vacuum oven at 60°C and dry for 12 h to obtain precursor II;

[0045] (3) Weigh 3 g of precursor II and add it to 180 mL of toluene. After stirring with a magnetic stirrer at 200 r / min for 25 min, add 0.5 mL of solvent 3-aminopropyltriethoxysilane. Reflux the mixture at 110 °C for 8 h and dry to obtain precursor III.

[0046] (4) Ultrasonic dispersion of 3 mg of single-walled carbon nanotubes in 40 g of deionized water for 10 min, adding 0.3 g of lithium carboxymethyl cellulose, and adding 3 g of precursor III after complete dissolution. Stirring with a magnetic stirrer at 200 r / min for 12 h, a two-fluid spray dryer was used, and the spray drying conditions were an inlet temperature of 180 °C and an outlet temperature of 90 °C, and the precursor IV was obtained by spray drying.

[0047] (5) Precursor IV was placed in a corundum boat, nitrogen was introduced into a tubular furnace at a rate of 100 mL / min, the temperature was raised to 600°C at a rate of 2°C / min and kept at that temperature for 5 min. After cooling in the furnace, a nitrogen-doped carbon-coated spherical silicon-based negative electrode material was obtained.

[0048] The obtained silicon oxide material was prepared into a slurry, coated and assembled into a lithium-ion half-cell and tested at a current density of 100 mA / g. The first charge specific capacity reached 1605.7 mAh / g and the first efficiency was 76.2%, with good cycle and rate performance.

[0049] Example 2

[0050] This embodiment is a method for preparing a nitrogen-doped carbon-coated spherical silicon-based negative electrode material, and the steps are as follows:

[0051] (1) 15 g of silicon dioxide raw material with a D50 of 20 μm was weighed and placed in a corundum boat. Nitrogen was introduced into a tube furnace at a rate of 100 mL / min, and the temperature was raised to 1400°C at a rate of 10°C / min and kept at that temperature for 8 h. After cooling in the furnace, precursor I was obtained.

[0052] (2) Prepare a 20% sodium hydroxide solution, take 90 mL of the solution, add precursor I, stir and react with a magnetic stirrer at 200 r / min for 2 h, use suction filtration, use deionized water to wash the reactant 5 times, and measure the pH of the washing solution to be neutral. Transfer to a vacuum oven at 60°C and dry for 12 h to obtain precursor II;

[0053] (3) Weigh 12 g of precursor II and add it to 240 mL of toluene. After stirring with a magnetic stirrer at 200 r / min for 40 min, add 8 mL of solvent polydiallyldimethylammonium chloride. Reflux the mixture at 110 °C for 8 h and dry to obtain precursor III.

[0054] (4) Ultrasonic dispersion of 3 mg of single-walled carbon nanotubes in 40 g of deionized water for 10 min, adding 0.6 g of lithium carboxymethyl cellulose, and adding 12 g of precursor III after complete dissolution. Stirring with a magnetic stirrer at 200 r / min for 12 h, using a two-fluid spray dryer, spray drying conditions with an inlet temperature of more than 210 °C and an outlet temperature of 90 °C, spray drying to obtain precursor IV;

[0055] (5) Precursor IV was placed in a corundum boat, argon gas was introduced into a tubular furnace at a rate of 100 mL / min, the temperature was raised to 850°C at a rate of 10°C / min and kept for 8 h. After cooling in the furnace, a nitrogen-doped carbon-coated spherical silicon-based negative electrode material was obtained.

[0056] The obtained silicon oxide material was prepared into a slurry, coated and assembled into a lithium-ion half-cell, and tested at a current density of 100mA / g. The first charge specific capacity reached 1750.7mAh / g, the first efficiency was 75%, and it had good cycle and rate performance.

[0057] Example 3

[0058] This embodiment is a method for preparing a nitrogen-doped carbon-coated spherical silicon-based negative electrode material, and the steps are as follows:

[0059] (1) 5 g of silicon dioxide raw material with a D50 of 10 μm was weighed and placed in a corundum boat. Argon gas was introduced into a tube furnace at a rate of 100 mL / min, and the temperature was raised to 950°C at a rate of 5°C / min and kept for 1 h. After cooling in the furnace, precursor I was obtained;

[0060] (2) Prepare a 10% sodium hydroxide solution, take 30 mL of the solution, add precursor I, stir and react with a magnetic stirrer at 200 r / min for 1 h, use suction filtration, use deionized water to wash the reactant 5 times, and measure the pH of the washing solution to be neutral. Transfer to a vacuum oven at 60°C and dry for 12 h to obtain precursor II;

[0061] (3) Weigh 3 g of precursor II and add it to 90 mL of toluene. After stirring with a magnetic stirrer at 200 r / min for 30 min, add 1 mL of solvent hexadecyltrimethylammonium bromide. Reflux the mixture at 110 °C for 8 h and dry to obtain precursor III.

[0062] (4) Ultrasonic dispersion of 3 mg of single-walled carbon nanotubes in 40 g of deionized water for 1 h, adding 0.3 g of lithium carboxymethyl cellulose, and adding 3 g of precursor III after complete dissolution. Stirring with a magnetic stirrer at 200 r / min for 12 h, a two-fluid spray dryer was used, and the spray drying conditions were an inlet temperature of 350 °C and an outlet temperature of 110 °C, and the precursor IV was obtained by spray drying.

[0063] (5) Precursor IV was placed in a corundum boat, nitrogen was introduced into a tubular furnace at a rate of 100 mL / min, the temperature was raised to 750°C at a rate of 6°C / min and kept for 2 h. After cooling in the furnace, a nitrogen-doped carbon-coated spherical silicon-based negative electrode material was obtained.

[0064] The obtained silicon oxide material was prepared into a slurry, coated and assembled into a lithium-ion half-cell, and tested at a current density of 100mA / g. The first charge specific capacity reached 1570.5mAh / g, the first efficiency was 76%, and it had good cycle and rate performance.

[0065] Example 4

[0066] This embodiment is a method for preparing a nitrogen-doped carbon-coated spherical silicon-based negative electrode material, and the steps are as follows:

[0067] (1) Weigh 5 g of silicon dioxide raw material with a D50 of 5 μm and place it in a corundum boat. In a tube furnace, introduce nitrogen at a rate of 100 mL / min, heat the temperature to 1000°C at a rate of 5°C / min and keep the temperature for 5 min. After cooling in the furnace, the precursor I is obtained.

[0068] (2) Prepare a 5% sodium hydroxide solution, take 30 mL of the solution, add precursor I, stir and react with a magnetic stirrer at 200 r / min for 15 min, use suction filtration to wash the reactant 5 times with deionized water, and measure the pH of the washing solution to be neutral. Transfer to a vacuum oven at 60°C and dry for 12 h to obtain precursor II;

[0069] (3) Weigh 3 g of precursor II and add it to 90 mL of toluene. After stirring with a magnetic stirrer at 200 r / min for 30 min, add 1 mL of solvent 3-aminopropyltriethoxysilane. Reflux the mixture at 110 °C for 8 h and dry to obtain precursor III.

[0070] (4) Ultrasonic dispersion of 3 mg of single-walled carbon nanotubes in 40 g of deionized water for 1 h, adding 0.3 g of lithium carboxymethyl cellulose, and adding 3 g of precursor III after complete dissolution. Stirring with a magnetic stirrer at 200 r / min for 12 h, a two-fluid spray dryer was used, and the spray drying conditions were an inlet temperature of 185 °C and an outlet temperature of 91 °C, and the precursor IV was obtained by spray drying.

[0071] (5) Precursor IV was placed in a corundum boat, nitrogen was introduced into a tubular furnace at a rate of 100 mL / min, the temperature was raised to 750°C at a rate of 5°C / min and kept for 2 h. After cooling in the furnace, a nitrogen-doped carbon-coated spherical silicon-based negative electrode material was obtained.

[0072] Figure 1 This is a scanning electron microscope image of the second precursor material prepared in this example at a magnification of 10.0k. It can be seen from the image that after being etched with sodium hydroxide, uneven pits are formed on the surface of the material, which can increase the surface area of ​​the grafted amino group.

[0073] Figure 2 This is a scanning electron microscope image of the nitrogen-doped carbon-coated spherical silicon-based negative electrode material prepared in this example at a magnification of 10.0k. The image shows bright edges and a relatively flat surface with fine carbon tube distribution, indicating that the coating material may have good conductivity and uniform carbon tube distribution.

[0074] Figure 3 This is a scanning electron microscope image of the nitrogen-doped carbon-coated spherical silicon-based negative electrode material prepared in this example at a magnification of 500x. As can be seen from the image, the material finally prepared has excellent spherical effect and uniform particle size.

[0075] The obtained silicon-oxygen material was prepared into a slurry, coated and assembled into a lithium-ion half-cell, and tested at a current density of 100 mA / g. Figure 4 The first cycle charge and discharge curves of the nitrogen-doped carbon-coated spherical silicon-based negative electrode material prepared in this embodiment and the materials prepared in comparative examples 1 and 2. Figure 4 It can be seen that the first charge specific capacity reaches 1705mAh / g, and the first efficiency is 73.35%.

[0076] Figure 5 The data of the nitrogen-doped carbon-coated spherical silicon-based negative electrode material prepared in this embodiment and the materials prepared in comparative examples 1 and 2 at 0.1C (3 weeks) and 0.3C (47 weeks) for the first 50 cycles are shown in FIG. Figure 5 It can be seen that the charging capacity in the first week at 0.1C is 1700mAh / g, and the charging capacity remains stable after 3 weeks of cycling; after continuing to cycle at 0.3C for 47 weeks, the charging capacity is 1500mAh / g, with good cycle and rate performance.

[0077] Example 5

[0078] This embodiment is a method for preparing a nitrogen-doped carbon-coated spherical silicon-based negative electrode material, and the steps are as follows:

[0079] (1) 5 g of silicon dioxide raw material with a D50 of 10 μm was weighed and placed in a corundum boat. Nitrogen was introduced into a tube furnace at a rate of 100 mL / min, and the temperature was raised to 1100°C at a rate of 5°C / min and kept for 5 h. After cooling in the furnace, precursor I was obtained;

[0080] (2) Prepare a 5% sodium hydroxide solution, take 30 mL of the solution, add precursor I, stir and react with a magnetic stirrer at 200 r / min for 2 h, use suction filtration, use deionized water to wash the reactant 5 times, and measure the pH of the washing solution to be neutral. Transfer to a vacuum oven at 60°C and dry for 12 h to obtain precursor II;

[0081] (3) Weigh 3 g of precursor II and add it to 90 mL of toluene. After stirring with a magnetic stirrer at 200 r / min for 30 min, add 0.5 mL of solvent 3-aminopropyltriethoxysilane. Reflux the mixture at 110 °C for 8 h and dry to obtain precursor III.

[0082] (4) Ultrasonic dispersion of 3 mg of single-walled carbon nanotubes in 40 g of deionized water for 1 h, adding 0.3 g of lithium carboxymethyl cellulose, and adding 3 g of precursor III after complete dissolution. Stirring with a magnetic stirrer at 200 r / min for 12 h, a two-fluid spray dryer was used with spray drying conditions of an inlet temperature of 190 °C and an outlet temperature of 90 °C to obtain precursor IV.

[0083] (5) Precursor IV was placed in a corundum boat, argon gas was introduced into a tubular furnace at a rate of 100 mL / min, the temperature was raised to 650°C at a rate of 2°C / min and kept at that temperature for 5 h. After cooling in the furnace, a nitrogen-doped carbon-coated spherical silicon-based negative electrode material was obtained.

[0084] The obtained silicon oxide material was prepared into a slurry, coated and assembled into a lithium-ion half-cell and tested at a current density of 100 mA / g. The first charge specific capacity reached 1480.2 mAh / g, the first efficiency was 75%, and it had good cycle and rate performance.

[0085] Example 6

[0086] This embodiment is a method for preparing a nitrogen-doped carbon-coated spherical silicon-based negative electrode material, and the steps are as follows:

[0087] (1) Weigh 5 g of silicon dioxide raw material with a D50 of 5 μm and place it in a corundum boat. In a tube furnace, introduce nitrogen at a rate of 100 mL / min, heat the temperature to 1200°C at a rate of 10°C / min and keep the temperature for 5 min. After cooling in the furnace, the precursor I is obtained.

[0088] (2) Prepare a 10% sodium hydroxide solution, take 30 mL of the solution, add precursor I, stir and react with a magnetic stirrer at 200 r / min for 15 min, use suction filtration, use deionized water to wash the reactant 5 times, measure the pH of the washing solution to be neutral, transfer to a vacuum oven at 60°C and dry for 12 h to obtain precursor II;

[0089] (3) Weigh 3 g of precursor II and add it to 90 mL of toluene. After stirring with a magnetic stirrer at 200 r / min for 30 min, add 1 mL of solvent polydiallyldimethylammonium chloride. Reflux the mixture at 110 °C for 8 h and dry to obtain precursor III.

[0090] (4) Ultrasonic dispersion of 3 mg of single-walled carbon nanotubes in 40 g of deionized water for 1 h, adding 0.3 g of lithium carboxymethyl cellulose, and adding 3 g of precursor III after complete dissolution. Stirring with a magnetic stirrer at 200 r / min for 12 h, a two-fluid spray dryer was used, and the spray drying conditions were an inlet temperature of 185 °C and an outlet temperature of 90 °C, and the precursor IV was obtained by spray drying.

[0091] (5) Precursor IV was placed in a corundum boat, nitrogen was introduced into a tubular furnace at a rate of 100 mL / min, the temperature was raised to 850°C at a rate of 10°C / min and kept for 2 h. After cooling in the furnace, a nitrogen-doped carbon-coated spherical silicon-based negative electrode material was obtained.

[0092] The obtained silicon oxide material was prepared into a slurry, coated and assembled into a lithium-ion half-cell, and tested at a current density of 100mA / g. The first charge specific capacity reached 1560mAh / g, the first efficiency was 78%, and it had good cycle and rate performance.

[0093] Example 7

[0094] This embodiment is a method for preparing a nitrogen-doped carbon-coated spherical silicon-based negative electrode material, and the steps are as follows:

[0095] (1) Weigh 5 g of silicon dioxide raw material with a D50 of 9 μm and place it in a corundum boat. In a tube furnace, introduce nitrogen at a rate of 100 mL / min, heat the temperature to 900°C at a rate of 2°C / min and keep the temperature for 8 h. After cooling in the furnace, a precursor 1 is obtained.

[0096] (2) Prepare 8% sodium hydroxide solution, take 30 mL of the solution, add precursor I, stir and react with a magnetic stirrer at 200 r / min for 20 min, use suction filtration, use deionized water to wash the reactant 5 times, measure the pH of the washing solution to be neutral, transfer to a vacuum oven at 60°C and dry for 12 h to obtain precursor II;

[0097] (3) Weigh 3 g of precursor II and add it to 90 mL of toluene. After stirring with a magnetic stirrer at 200 r / min for 30 min, add 1 mL of solvent 3-aminopropyltriethoxysilane. Reflux the mixture at 110 °C for 8 h and dry to obtain precursor III.

[0098] (4) Ultrasonic dispersion of 3 mg of single-walled carbon nanotubes in 40 g of deionized water for 1 h, adding 0.3 g of lithium carboxymethyl cellulose, and adding 3 g of precursor III after complete dissolution. Stirring with a magnetic stirrer at 200 r / min for 12 h, a two-fluid spray dryer was used with spray drying conditions of an inlet temperature of 190 °C and an outlet temperature of 90 °C to obtain precursor IV.

[0099] (5) Precursor IV was placed in a corundum boat, nitrogen was introduced into a tubular furnace at a rate of 100 mL / min, the temperature was raised to 750°C at a rate of 10°C / min and kept for 2 h. After cooling in the furnace, a nitrogen-doped carbon-coated spherical silicon-based negative electrode material was obtained.

[0100] The obtained silicon oxide material was prepared into a slurry, coated and assembled into a lithium-ion half-cell, and tested at a current density of 100mA / g. The first charge specific capacity reached 1560mAh / g, the first efficiency was 75%, and it had good cycle and rate performance.

[0101] Example 8

[0102] This embodiment is a method for preparing a nitrogen-doped carbon-coated spherical silicon-based negative electrode material, and the steps are as follows:

[0103] (1) Weigh 5 g of silicon dioxide raw material with a D50 of 10 μm and place it in a corundum boat. In a tube furnace, introduce nitrogen at a rate of 100 mL / min, heat the temperature to 900 °C at a rate of 10 °C / min and keep the temperature for 1 h. After cooling in the furnace, the precursor I is obtained.

[0104] (2) Prepare a sodium hydroxide solution with a concentration of 12%, take 30 mL of the solution, add precursor I, stir and react with a magnetic stirrer at 200 r / min for 1 h, use suction filtration, use deionized water to wash the reactant 5 times, and measure the pH of the washing solution to be neutral. Transfer to a vacuum oven at 60°C and dry for 12 h to obtain precursor II;

[0105] (3) Weigh 3 g of precursor II and add it to 90 mL of toluene. After stirring with a magnetic stirrer at 200 r / min for 30 min, add 0.8 mL of solvent 3-aminopropyltriethoxysilane. Reflux the mixture at 110 °C for 8 h and dry to obtain precursor III.

[0106] (4) Ultrasonic dispersion of 3 mg of single-walled carbon nanotubes in 40 g of deionized water for 1 h, adding 0.3 g of lithium carboxymethyl cellulose, and adding 3 g of precursor III after complete dissolution. Stirring with a magnetic stirrer at 200 r / min for 12 h, a two-fluid spray dryer was used with spray drying conditions of inlet temperature 180 °C and outlet temperature 90 °C to obtain precursor IV.

[0107] (5) Precursor IV was placed in a corundum boat, nitrogen was introduced into a tubular furnace at a rate of 100 mL / min, the temperature was raised to 750°C at a rate of 8°C / min and kept for 5 h. After cooling in the furnace, a nitrogen-doped carbon-coated spherical silicon-based negative electrode material was obtained.

[0108] The obtained silicon oxide material was prepared into a slurry, coated and assembled into a lithium-ion half-cell, and tested at a current density of 100mA / g. The first charge specific capacity reached 1600.6mAh / g, the first efficiency was 75.2%, and it had good cycle and rate performance.

[0109] Example 9

[0110] This embodiment is a method for preparing a nitrogen-doped carbon-coated spherical silicon-based negative electrode material, and the steps are as follows:

[0111] (1) Weigh 5 g of silicon dioxide raw material with a D50 of 3 μm and place it in a corundum boat. In a tube furnace, introduce nitrogen at a rate of 100 mL / min, heat the temperature to 1300°C at a rate of 6°C / min and keep the temperature for 4 h. After cooling in the furnace, the precursor I is obtained.

[0112] (2) Prepare a sodium hydroxide solution with a concentration of 16%, take 30 mL of the solution, add precursor I, stir and react with a magnetic stirrer at 200 r / min for 40 min, use suction filtration, use deionized water to wash the reactant 3 times, measure the pH of the washing solution to be neutral, transfer to a vacuum oven at 60°C and dry for 12 h to obtain precursor II;

[0113] (3) Weigh 3 g of precursor II and add it to 90 mL of toluene. After stirring with a magnetic stirrer at 200 r / min for 32 min, add 0.9 mL of a mixed solution of 3-aminopropyltriethoxysilane and polydiallyldimethylammonium chloride (the volume ratio of 3-aminopropyltriethoxysilane to polydiallyldimethylammonium chloride is 1:2). The mixture is refluxed at 110 °C for 6 h and dried to obtain precursor III.

[0114] (4) 2.4 mg of single-walled carbon nanotubes were ultrasonically dispersed in 40 g of deionized water for 40 min, and 0.3 g of lithium carboxymethyl cellulose was added. After complete dissolution, 5 g of precursor III was added. The mixture was stirred at 200 r / min with a magnetic stirrer for 15 h. A two-fluid spray dryer was used for spray drying. The spray drying conditions were an inlet temperature of 260 °C and an outlet temperature of 100 °C. Precursor IV was obtained by spray drying.

[0115] (5) Precursor IV was placed in a corundum boat, nitrogen was introduced into a tubular furnace at a rate of 100 mL / min, the temperature was raised to 700°C at a rate of 4°C / min and kept at that temperature for 4 h. After cooling in the furnace, a nitrogen-doped carbon-coated spherical silicon-based negative electrode material was obtained.

[0116] Example 10

[0117] This embodiment is a method for preparing a nitrogen-doped carbon-coated spherical silicon-based negative electrode material, and the steps are as follows:

[0118] (1) Weigh 5 g of silicon dioxide raw material with a D50 of 3 μm and place it in a corundum boat. In a tube furnace, introduce nitrogen at a rate of 100 mL / min, heat the temperature to 1050°C at a rate of 5°C / min, and keep the temperature for 6 h. After cooling in the furnace, the precursor I is obtained.

[0119] (2) Prepare a 10% sodium hydroxide solution, take 30 mL of the solution, add precursor I, stir and react with a magnetic stirrer at 200 r / min for 1.5 h, use suction filtration, use deionized water to wash the reactant three times, and measure the pH of the washing solution to be neutral. Transfer to a vacuum oven at 60°C and dry for 12 h to obtain precursor II;

[0120] (3) Weigh 3 g of precursor II and add it to 75 mL of toluene. After stirring with a magnetic stirrer at 200 r / min for 38 min, add 1.2 mL of a mixed solution of polydiallyldimethylammonium chloride and hexadecyltrimethylammonium bromide (the volume ratio of polydiallyldimethylammonium chloride to hexadecyltrimethylammonium bromide is 1:1). The mixture is refluxed at 110 °C for 10 h and dried to obtain precursor III.

[0121] (4) 1.8 mg of single-walled carbon nanotubes were ultrasonically dispersed in 40 g of deionized water for 20 min, 0.3 g of lithium carboxymethyl cellulose was added, and after complete dissolution, 3.75 g of precursor III was added, and the mixture was stirred at 200 r / min with a magnetic stirrer for 20 h. A two-fluid spray dryer was used for spray drying under the conditions of an inlet temperature of 320 °C and an outlet temperature of 105 °C, and precursor IV was obtained by spray drying;

[0122] (5) Precursor IV was placed in a corundum boat, nitrogen was introduced into a tubular furnace at a rate of 100 mL / min, the temperature was raised to 600°C at a rate of 7°C / min and kept at that temperature for 6 h. After cooling in the furnace, a nitrogen-doped carbon-coated spherical silicon-based negative electrode material was obtained.

[0123] Comparative Example 1

[0124] This comparative example is a method for preparing the silicon-oxygen negative electrode material obtained by step (1) of Example 4, and the steps are as follows:

[0125] 5 g of silicon dioxide raw material with a D50 of 5 μm was weighed and placed in a corundum boat. Nitrogen was introduced into a tubular furnace at a rate of 100 mL / min, and the temperature was raised to 1000°C at a heating rate of 5°C / min and kept for 5 min. After cooling in the furnace, the silicon-oxygen negative electrode material was obtained.

[0126] The obtained silicon-oxygen material was prepared into a slurry, coated and assembled into a lithium-ion half-cell, and tested at a current density of 100 mA / g. Figure 4 It can be seen that the first charge specific capacity of comparative example 1 reaches 1307 mAh / g, and the first efficiency is 60.8%.

[0127] Depend on Figure 5 It can be seen that in comparative example 1, the first week charging capacity at 0.1C is 1300mAh / g, and the charging capacity after 3 weeks of cycling is about 900mAh / g; after continuing to cycle at 0.3C for 47 weeks, the charging capacity is 300mAh / g.

[0128] Comparative Example 2

[0129] This comparative example is a method for preparing a silicon-oxygen negative electrode material obtained by steps (1), (2), (4) and (5) of Example 4, and the steps are as follows:

[0130] (1) Weigh 5 g of silicon dioxide raw material with a D50 of 5 μm and place it in a corundum boat. In a tube furnace, introduce nitrogen at a rate of 100 mL / min, heat the temperature to 1000°C at a rate of 5°C / min and keep the temperature for 5 min. After cooling in the furnace, the precursor I is obtained.

[0131] (2) Prepare a 5% sodium hydroxide solution, take 30 mL of the solution, add precursor I, stir and react with a magnetic stirrer at 200 r / min for 15 min, use suction filtration to wash the reactant 5 times with deionized water, and measure the pH of the washing solution to be neutral. Transfer to a vacuum oven at 60°C and dry for 12 h to obtain precursor II;

[0132] (3) Ultrasonic dispersion of 3 mg of single-walled carbon nanotubes in 40 g of deionized water for 1 h, adding 0.3 g of lithium carboxymethyl cellulose, and adding 3 g of precursor II after complete dissolution. Stirring with a magnetic stirrer at 200 r / min for 12 h, a two-fluid spray dryer was used with spray drying conditions of inlet temperature 185 °C and outlet temperature 91 °C to obtain precursor III.

[0133] (4) Precursor III was placed in a corundum boat, nitrogen was introduced into a tubular furnace at a rate of 100 mL / min, the temperature was raised to 750°C at a rate of 5°C / min and kept for 2 h. After cooling in the furnace, a nitrogen-doped carbon-coated spherical silicon-based negative electrode material was obtained.

[0134] The obtained silicon-oxygen material was prepared into a slurry, coated and assembled into a lithium-ion half-cell, and tested at a current density of 100 mA / g. Figure 4 It can be seen that the first charge specific capacity of comparative example 2 reaches 1399 mAh / g, and the first efficiency is 68.9%.

[0135] Depend on Figure 5 It can be seen that in comparative example 2, the charging capacity at 0.1C in the first week is 1400mAh / g, and the charging capacity after 3 weeks of cycling is about 1300mAh / g; after continuing to cycle at 0.3C for 47 weeks, the charging capacity is 800mAh / g.

[0136] The silicon-oxygen negative electrode material prepared by Example 4 and Comparative Examples 1 and 2 Figure 4 , Figure 5 From the performance data, it can be seen that the capacity and cycle performance of the silicon-oxygen material of Comparative Example 1, which is only subjected to high-temperature disproportionation, are the worst. Comparative Example 2 shows that the electrical performance of the carbon-coated material after disproportionation is improved compared with Comparative Example 1, but compared with the embodiment, the capacity and cycle performance are poor. The reason is that the embodiment adopts a material surface roughening treatment to increase the surface area of ​​the material, which can carry more amino groups and carbon sources. Therefore, the spherical material has both firmly carbon-coated nitrogen-doped silicon-oxygen material and a three-dimensional conductive network with carbon tubes interspersed therein, which provides a channel for the rapid transmission of electrons. At the same time, the Si and SiO particles are buffered by the carbon layer and the carbon tubes, which promotes the formation of a surface-stable SEI film and improves the material cycle stability.

[0137] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a nitrogen-doped carbon-coated spherical silicon-based negative electrode material, characterized in that: Here are the steps: (1) High-temperature disproportionation: disproportionate the silicon dioxide raw material at high temperature under an inert atmosphere to obtain a precursor I; the inert atmosphere is nitrogen, the high-temperature disproportionation temperature is 900-1400°C, the high-temperature disproportionation time is 5 min-8 h, and the heating rate is 2-10°C / min; (2) Sodium hydroxide etching: The precursor I obtained in step (1) is mixed with a sodium hydroxide solution for reaction. After the reaction is completed, the precursor is washed with deionized water until it is neutral and then dried to obtain a precursor II. (3) Surface grafting amination: Precursor II obtained in step (2) is added to toluene to prepare a solution, and solvent A is added after stirring to carry out reflux reaction. After the reaction is completed, the surface grafting amination process is completed to obtain precursor III; the solvent A is any one of polydiallyldimethylammonium chloride, hexadecyltrimethylammonium bromide or ammonia-containing organosilane or a combination of at least two thereof, and the ammonia-containing organosilane is 3-aminopropyltriethoxysilane; the mass volume ratio of precursor II to solution A is 3g: (0.5~2)mL, and the reflux reaction time is 6~10h; (4) Carbon coating: Pre-treat the single-walled carbon nanotubes and mix them with lithium carboxymethyl cellulose. After the lithium carboxymethyl cellulose is completely dissolved, stir them with the precursor III obtained in step (3). After stirring, spray dry them. The inlet temperature of the spray dryer is 180-350°C and the outlet temperature is 90-110°C to obtain the precursor IV. (5) High temperature solid phase reaction: The precursor IV obtained in step (4) is subjected to a high temperature solid phase reaction under an inert atmosphere to obtain a nitrogen-doped carbon-coated spherical silicon-based negative electrode material.

2. The method for preparing the nitrogen-doped carbon-coated spherical silicon-based negative electrode material according to claim 1, characterized in that: The D50 of the silicon dioxide raw material in step (1) is 3-20 μm.

3. The method for preparing the nitrogen-doped carbon-coated spherical silicon-based negative electrode material according to claim 1, characterized in that: The concentration of the sodium hydroxide solution in step (2) is 4% to 20%, and the mixing reaction time is 4 minutes to 2 hours.

4. The method for preparing the nitrogen-doped carbon-coated spherical silicon-based negative electrode material according to claim 1, characterized in that: The solid-to-liquid ratio of the solution in step (3) is (0.5-1.5):30, and the stirring time is 25-40 min.

5. The method for preparing the nitrogen-doped carbon-coated spherical silicon-based negative electrode material according to claim 1, characterized in that: The pretreatment in step (4) is as follows: ultrasonically dispersing the single-walled carbon nanotubes in deionized water, wherein the mass ratio of the single-walled carbon nanotubes to the deionized water is 3 mg:40 g, and the ultrasonic dispersion time is 10 min to 1 h; the mass ratio of the single-walled carbon nanotubes to lithium carboxymethyl cellulose is (0.5-1):100; the mass ratio of the precursor III to lithium carboxymethyl cellulose is 10:(0.5-1), and the stirring time is 12 to 20 h.

6. The method for preparing the nitrogen-doped carbon-coated spherical silicon-based negative electrode material according to claim 1, characterized in that: In step (5), the inert atmosphere is any one of nitrogen, argon, helium or neon, or a combination of at least two of them; the temperature of the high-temperature solid-phase reaction is 600-850°C, the time of the high-temperature solid-phase reaction is 5 min-8 h, and the heating rate is 2-10°C / min.

7. A nitrogen-doped carbon-coated spherical silicon-based negative electrode material, characterized in that: The nitrogen-doped carbon-coated spherical silicon-based negative electrode material is prepared by the method according to any one of claims 1 to 6.

8. Use of the nitrogen-doped carbon-coated spherical silicon-based negative electrode material according to claim 7 as a negative electrode material for lithium-ion batteries in the preparation of lithium-ion batteries.

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