Preparation method of anti-oxidation nano-silicon slurry and application thereof

Abstract

The application discloses a kind of preparation methods of anti-oxidation nano silicon slurry, comprising the following steps: (1) oxidation inhibitor is added in alcohol solvent, stirring dissolves;(2) the silicon powder of D50 5-10um is dispersed in above-mentioned solution, and stirring is matched into the silicon slurry of solid content 10%-20%;(3) silicon slurry is ground by sand mill wet, and grinding is carried out in two stages, first using coarse grinding sand mill grinding 2-4h, then switching fine grinding sand mill grinding 15-30h.The application is by adding organic weak acid as oxidation inhibitor in sand mill solvent, so that the oxidation phenomenon of prepared nano silicon slurry is reduced.In addition, the addition of organic weak acid also helps to improve the dispersion performance of slurry, improve the fluidity of slurry, improve sand mill efficiency, and thus greatly improve the electrochemical performance of prepared silicon powder.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for preparing anti-oxidation nano-silicon. Background Technology

[0002] Lithium-ion batteries have become the preferred power supply device for 3C products, power machinery, energy storage devices, and other fields due to their high energy density, long cycle life, lack of memory effect, and environmental friendliness. Currently, commercially available lithium-ion battery anodes mainly use graphite-based materials. However, the capacity development of graphite materials is already very close to the theoretical capacity of 372 mAh / g; moreover, graphite materials are limited by their low potential plateau, making them prone to lithium metal deposition during high-current charging and discharging.

[0003] Si-based materials, as a new generation of lithium-ion battery anode materials, have a theoretical capacity of up to 4200 mAh / g, far exceeding the theoretical capacity of graphite, and are considered to have great potential to replace graphite as an anode material. However, Si still has many problems in practical applications. The most important one is that Si undergoes huge volume changes during charge and discharge, which damages the material's structure, making the electrode sheets prone to pulverization and detachment, ultimately leading to material failure and severely affecting the material's cycle performance.

[0004] To address these issues, the primary method currently employed is to nanoscale Si particles. This reduces internal stress caused by volume changes, mitigating material pulverization. Furthermore, this method can shorten the diffusion paths of lithium ions and electrons, thereby increasing the electrochemical reaction rate. The preparation of nanoscale Si particles commonly employs mechanical wet grinding, utilizing the strong shear forces between the grinding media to break Si particles to the nanoscale. However, grinding Si particles to the nanoscale exposes other problems: firstly, nanoscale Si has a high surface energy, making it prone to agglomeration and affecting grinding efficiency; secondly, nanoscale Si has high chemical reactivity and is easily oxidized during high-energy grinding, leading to a reduction or loss of electrochemical activity.

[0005] Chinese patent CN 111180719 A discloses a method for preparing nano-silicon through a three-stage grinding process. This method first involves pre-dispersing high-purity silicon powder, solvent, and dispersant in a dispersion tank. The dispersed slurry is then sequentially ground in a first-stage mill to below 1000 nm, a second-stage mill to below 100 nm, and a third-stage mill to below 50 nm, before drying to obtain nano-silicon powder. This preparation method is complex and requires cumbersome process conditions. Prolonged grinding significantly increases the oxidation degree of Si particles. Secondly, the three-stage grinding process places extremely high demands on the performance of the mills, making industrialization difficult. Thirdly, the dispersant added during grinding only reduces slurry viscosity and improves Si particle dispersibility; it does not effectively inhibit Si particle oxidation, ultimately leading to a sharp decline in the sample's reversible capacity and initial efficiency.

[0006] Chinese patent CN 110289400 A discloses a method for dispersing nano-silicon. This method first involves pulverizing coarse silicon powder with an airflow to an average particle size of 3-5 μm. Then, the coarse silicon powder is dissolved in a polar solvent, and hexadecyltrimethylammonium bromide is added as a dispersant. Finally, a wet ball milling process is used to obtain nano-silicon powder. While this method can effectively improve the flowability and dispersibility of the slurry, hexadecyltrimethylammonium bromide enhances the dispersion performance of Si particles through electrostatic repulsion, but it does not effectively inhibit the oxidation of Si particles, ultimately leading to a sharp decline in the reversible capacity and initial efficiency of the sample. Summary of the Invention

[0007] To address the shortcomings of the existing technology, this invention provides a method for preparing an anti-oxidation nano-silica slurry, comprising the following steps:

[0008] (1) Add the oxidation inhibitor to the alcohol solvent and stir to dissolve;

[0009] (2) Disperse silicon powder with a D50 of 5-10 μm in the above solution and stir to prepare a silicon slurry with a solid content of 10%-20%;

[0010] (3) The silicon slurry is wet-milled using a sand mill. The milling is carried out in two stages. First, a coarse sand mill is used for milling for 2-4 hours, and then a fine sand mill is used for milling for 15-30 hours.

[0011] In this invention, the oxidation inhibitor in step (1) is an organic weak acid, and is more preferably one or two of humic acid, citric acid, stearic acid, and ascorbic acid.

[0012] In this invention, the amount of oxidation inhibitor added in step (1) is 1%-10% of the mass of silicon powder, more preferably 5%-7%;

[0013] In this invention, the alcohol solvent used in step (1) is either ethanol or isopropanol;

[0014] In this invention, the coarse grinding mill in step (3) uses zirconium beads with a diameter range of 0.2-0.6 mm, and the fine grinding mill uses zirconium beads with a diameter range of 0.05-0.3 mm.

[0015] On the other hand, the present invention also provides nano-silicon powder prepared by the preparation method described above.

[0016] Furthermore, this invention provides a method for preparing a graphite / nano-silicon composite material, comprising the following steps:

[0017] (1) Take finely ground nano-silicon slurry and mix it with artificial graphite and binder at high speed, and add an appropriate amount of ethanol to adjust the solid content of the slurry.

[0018] (2) The above slurry is spray-dried to obtain spherical secondary particles of Si / graphite / binder composite.

[0019] (3) The spray-dried powder is placed in a box furnace and carbonized in an argon atmosphere to carbonize the binder and citric acid, thereby obtaining amorphous carbon-bonded graphite / nano-silicon composite material.

[0020] In this invention, the median particle size of the artificial graphite in step (1) is 5-10 μm;

[0021] In this invention, the mass ratio of silicon powder: graphite powder: glucose in step (1) is 3-7:93-97:3-5;

[0022] In this invention, the slurry in step (1) has a solid content of 20%-30%;

[0023] In this invention, the binder in step (2) is preferably glucose;

[0024] In this invention, the inlet air temperature of the spray drying step (2) is 120-180℃, the exhaust air temperature is 60-80℃, and the atomizer speed is 30-50Hz.

[0025] In this invention, the carbonization temperature in step (3) is 800-1000℃, the carbonization time is 2-5h, and the heating rate is 3-5℃ / min.

[0026] The beneficial effects of this invention are:

[0027] (1) The reaction between elemental Si and H2O in the macroscopic state is extremely weak and is generally considered non-reactive. The chemical equation for the reaction is Si + 4H2O → H4SiO4 + 2H2. However, when Si particles are ground to the nanoscale, the high specific surface area and increased active sites of nanomaterials further promote the reaction. Using oxidized Si particles as electrode materials leads to a decrease in the specific capacity and a decline in electrochemical activity. In addition, the reaction is accompanied by the generation of H2, which not only affects the performance of the product but may also endanger the production process. We adjust the pH of the slurry to the range of 4-6 by adding a weak organic acid to the sand milling solvent. On the one hand, this can inhibit the hydrolysis of silicic acid and slow down the forward reaction between Si and H2O; on the other hand, it can form a coating layer on the surface of nano-Si and a protective layer at the interface between Si particles and H2O, further inhibiting the reaction between Si and H2O; thus greatly reducing the oxidation degree of the prepared nano-silicon slurry.

[0028] (2) The addition of organic weak acid can form a protective layer on the surface of Si particles, prevent Si particles from agglomerating, reduce the particle size coarsening phenomenon during the sand milling process, improve the dispersion performance of the slurry, enhance the fluidity of the slurry, and thus improve the sand milling efficiency.

[0029] (3) Organic weak acids can be transformed into amorphous carbon layers during the later sintering process, which can improve the conductivity of silicon particles and thus greatly improve the electrochemical performance of the prepared silicon powder. Attached Figure Description

[0030] The invention will be further described below with reference to the accompanying drawings.

[0031] Figure 1 The image shows the XRD pattern of the nano-silicon powder prepared in Example 1 of this invention.

[0032] Figure 2 This is a SEM image of the nano-silicon powder prepared in Example 1 of the present invention; Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments.

[0034] Example 1

[0035] 30g of citric acid was dissolved in 2400g of ethanol. After dissolution, 600g of microsilica powder with a median particle size of 5µm was added and stirred to disperse, resulting in a silica slurry with a solid content of 20%. The silica slurry was then wet-milled using a sand mill in two stages: first, a coarse sand mill was used for 2 hours, followed by a fine sand mill for 15 hours. The coarse sand mill used a screen-type mill with 0.3-0.4mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear velocity of 14m / s. The fine sand mill used a dual-power screenless mill with 0.1mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear velocity of 15m / s. After fine milling, one drop of the nano-silica slurry was dispersed in 30ml of ethanol and sonicated for 5 minutes. The particle size distribution of the silica particles was then measured using a laser particle size analyzer, and the median particle size was found to be 94nm. 100g of finely ground nano-silicon slurry was dried in a vacuum oven at 60℃ for 12 hours. After the vacuum oven cooled naturally to room temperature, the dried nano-silicon powder was obtained. The oxygen content in the nano-silicon powder was measured to be 24 ppma using inert gas melting infrared spectroscopy.

[0036] Finely ground nano-silicon slurry was mixed with artificial graphite and glucose (median particle size 10 μm) at high speed. The ratio of silicon powder: graphite powder: glucose was 1:19:1. An appropriate amount of ethanol was added to adjust the slurry solid content to 20%. The slurry was then spray-dried at an inlet temperature of 140°C, an outlet temperature of 70°C, a rotary atomizing nozzle speed of 50 Hz, and a feed rate of 100 ml / min. Spray drying yielded spherical secondary particles with a median particle size of 25 μm. The spray-dried powder was then placed in a box furnace and carbonized at 900°C for 4 hours under an argon atmosphere at a heating rate of 5°C / min, allowing the glucose and citric acid to carbonize, resulting in an amorphous carbon-bonded graphite / nano-silicon composite material. The above-mentioned graphite / nano-silicon composite material was mixed evenly with conductive carbon black, thickener, and binder in a ratio of 90:7:1.5:1.5, and coated onto the surface of copper foil to form an electrode. This electrode was then assembled with a lithium-ion battery to form a coin cell. The half-cell capacity and initial efficiency were tested using a Blue Electric testing system. The half-cell capacity was 477.5 mAh / g, and the initial efficiency was 92.4%.

[0037] The following examples all use the same method as in Example 1 to prepare half-cells from the obtained nano-silicon slurry, and the specific capacity and initial efficiency of the half-cells are tested on the same equipment.

[0038] Example 2

[0039] 30g of stearic acid was dissolved in 2400g of ethanol. After dissolution, 600g of microsilica powder with a median particle size of 5µm was added and stirred to disperse, resulting in a silica slurry with a solid content of 20%. The silica slurry was then wet-milled using a sand mill in two stages: first, a coarse sand mill was used for 2 hours, followed by a fine sand mill for 15 hours. The coarse sand mill used a screen-type mill with 0.3-0.4mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear velocity of 14m / s. The fine sand mill used a dual-power screenless mill with 0.1mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear velocity of 15m / s. After fine milling, one drop of the nano-silica slurry was dispersed in 30ml of ethanol and sonicated for 5 minutes. The particle size distribution of the silica particles was then measured using a laser particle size analyzer, and the median particle size was found to be 96nm. 100g of finely ground nano-silicon slurry was dried in a vacuum oven at 60℃ for 12 hours. After the vacuum oven cooled naturally to room temperature, the dried nano-silicon powder was obtained. The oxygen content in the nano-silicon powder was measured to be 36 ppma using inert gas melting infrared spectroscopy.

[0040] A half-cell was fabricated from the nano-silicon slurry according to the method described in Example 1, and its electrochemical performance was tested. The half-cell capacity was 465.2 mAh / g, and the initial efficiency was 90.1%.

[0041] Example 3

[0042] 9g of humic acid was dispersed in 2700g of isopropanol, and then 300g of microsilica powder with a median particle size of 7µm was added. The mixture was stirred and dispersed to obtain a silica slurry with a solid content of 10%. The silica slurry was then wet-milled using a sand mill in two stages: first, a coarse sand mill was used for 4 hours, followed by a fine sand mill for 20 hours. The coarse sand mill used a screen-type mill with 0.2-0.3mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear velocity of 14m / s. The fine sand mill used a dual-power screenless mill with 0.05mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear velocity of 15m / s. After fine milling, one drop of the nano-silica slurry was dispersed in 30ml of ethanol and sonicated for 5 minutes. The particle size distribution of the silica particles was then measured using a laser particle size analyzer, and the median particle size was found to be 92nm. 100g of finely ground nano-silicon slurry was dried in a vacuum oven at 60℃ for 12 hours. After the vacuum oven cooled naturally to room temperature, the dried nano-silicon powder was obtained. The oxygen content in the nano-silicon powder was measured to be 30 ppma using inert gas melting infrared spectroscopy.

[0043] Finely ground nano-silicon slurry was mixed with artificial graphite with a median particle size of 10 μm and glucose at a high-speed dispersion ratio of silicon powder: graphite powder: glucose = 1:19:1. An appropriate amount of isopropanol was added to adjust the slurry solid content to 20%. The slurry was then spray-dried at an inlet air temperature of 140℃, an outlet air temperature of 70℃, a rotary atomizing nozzle speed of 50 Hz, and a feed rate of 100 ml / min. Spray drying yielded spherical secondary particles with a median particle size of 25 μm. The spray-dried powder was then placed in a box furnace and carbonized at 900℃ for 4 hours under an argon atmosphere at a heating rate of 5℃ / min, allowing the glucose and citric acid to carbonize, resulting in an amorphous carbon-bonded graphite / nano-silicon composite material. The above-mentioned graphite / nano-silicon composite material was mixed with conductive carbon black, thickener, and binder in a ratio of 90:7:1.5:1.5 to form an electrode. This mixture was then coated onto the surface of copper foil and assembled with lithium-ion cells to form a coin cell. The half-cell capacity and initial efficiency were tested using a Blue Electric testing system. The half-cell capacity was 469.3 mAh / g, and the initial efficiency was 91.2%.

[0044] Example 4

[0045] 60g of ascorbic acid was dissolved in 2400g of ethanol. After dissolution, 600g of microsilica powder with a median particle size of 10µm was added and stirred to disperse, resulting in a silica slurry with a solid content of 20%. The silica slurry was then wet-milled using a sand mill in two stages: first, a coarse sand mill was used for 4 hours, followed by a fine sand mill for 30 hours. The coarse sand mill used a screen-type mill with 0.2-0.3mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear velocity of 14m / s. The fine sand mill used a dual-power screenless mill with 0.1mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear velocity of 15m / s. After fine milling, one drop of the nano-silica slurry was dispersed in 30ml of ethanol and sonicated for 5 minutes. The particle size distribution of the silica particles was then measured using a laser particle size analyzer, and the median particle size was found to be 87nm. 100g of finely ground nano-silicon slurry was dried in a vacuum oven at 60℃ for 12 hours. After the oven cooled to room temperature, the dried nano-silicon powder was obtained. The oxygen content in the nano-silicon powder was measured to be 40 ppma using inert gas melting infrared spectroscopy.

[0046] A half-cell was fabricated from the nano-silica slurry according to the method described in Example 1, and its electrochemical performance was tested. The half-cell capacity was 455.9 mAh / g, and the initial efficiency was 90.7%.

[0047] Example 5

[0048] 4.5g of citric acid was dissolved in 2550g of ethanol. After dissolution, 450g of microsilica powder with a median particle size of 5µm was added and stirred to disperse, resulting in a silica slurry with a solid content of 15%. The silica slurry was then wet-milled using a sand mill in two stages: first, a coarse sand mill was used for 3 hours, followed by a fine sand mill for 20 hours. The coarse sand mill used a screen-type mill with 0.4-0.6mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear speed of 14m / s. The fine sand mill used a dual-power screenless mill with 0.3mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear speed of 15m / s. After fine milling, one drop of the nano-silica slurry was dispersed in 30ml of ethanol and sonicated for 5 minutes. The particle size distribution of the silica particles was then measured using a laser particle size analyzer, and the median particle size was found to be 103nm. 100g of finely ground nano-silicon slurry was dried in a vacuum oven at 60℃ for 12 hours. After the oven cooled naturally to room temperature, the dried nano-silicon powder was obtained. The oxygen content in the nano-silicon powder was measured to be 57 ppma using inert gas melting infrared spectroscopy.

[0049] A half-cell was fabricated from the nano-silica slurry according to the method described in Example 1, and its electrochemical performance was tested. The half-cell capacity was 453.7 mAh / g, and the initial efficiency was 89.9%.

[0050] Example 6

[0051] 42g of citric acid was dissolved in 2400g of ethanol. After dissolution, 600g of microsilica powder with a median particle size of 5µm was added and stirred to disperse, resulting in a silica slurry with a solid content of 20%. The silica slurry was then wet-milled using a sand mill in two stages: first, a coarse sand mill was used for 3 hours, followed by a fine sand mill for 15 hours. The coarse sand mill used a screen-type mill with 0.4-0.6mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear speed of 14m / s. The fine sand mill used a dual-power screenless mill with 0.2mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear speed of 15m / s. After fine milling, one drop of the nano-silica slurry was dispersed in 30ml of ethanol and sonicated for 5 minutes. The particle size distribution of the silica particles was then measured using a laser particle size analyzer, and the median particle size was found to be 93nm. 100g of finely ground nano-silicon slurry was dried in a vacuum oven at 60℃ for 12 hours. After the vacuum oven cooled naturally to room temperature, the dried nano-silicon powder was obtained. The oxygen content in the nano-silicon powder was measured to be 32 ppma using inert gas melting infrared spectroscopy.

[0052] A half-cell was fabricated from the nano-silicon slurry according to the method described in Example 3, and its electrochemical performance was tested. The half-cell capacity was 463.2 mAh / g, and the first-efficiency rating was 91.3%.

[0053] The addition of a weak organic acid can adjust the pH of the slurry to a weakly acidic state, inhibiting the forward reaction between nano-silicon and water. This increases the difficulty of oxidation reactions between nano-silicon and water, thus reducing the oxygen content in the nano-silicon powder after sand milling. On the other hand, the organic acid also acts as a dispersant, adsorbing onto the surface of silicon particles and preventing particle aggregation, thereby enhancing slurry stability and significantly improving milling efficiency. A comparison of Examples 1 and 2 shows that citric acid is more effective than stearic acid in inhibiting oxidation.

[0054] Based on the electrochemical data of the samples from Examples 1-6, and considering the influence of the organic weak acid on the median particle size and oxygen content, Example 1 exhibits the best electrochemical performance and the smallest Si particle size. Therefore, we determine Example 1 as the optimal example.

[0055] Comparative Example 1

[0056] 600g of microsilica powder with a median particle size of 5µm was added to 2400g of ethanol and stirred to disperse, resulting in a silica slurry with a solid content of 20%. The silica slurry was then wet-milled using a sand mill in two stages: first, a coarse sand mill was used for 2 hours, followed by a fine sand mill for 15 hours. The coarse sand mill used a screen-type mill with 0.3-0.4mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear velocity of 14m / s. The fine sand mill used a dual-power screenless mill with 0.1mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear velocity of 15m / s. After fine milling, one drop of the nano-silica slurry was dispersed in 30ml of ethanol and sonicated for 5 minutes. The particle size distribution of the silica particles was then analyzed using a laser particle size analyzer, and the median particle size was measured to be 255nm. 100g of finely ground nano-silicon slurry was dried in a vacuum oven at 60℃ for 12 hours. After the vacuum oven cooled naturally to room temperature, the dried nano-silicon powder was obtained. The oxygen content in the nano-silicon powder was measured to be 206 ppma using inert gas melting infrared spectroscopy.

[0057] A half-cell was fabricated from the nano-silica slurry according to the method described in Example 1, and its electrochemical performance was tested. The half-cell capacity was 420.7 mAh / g, and the initial efficiency was 85.2%.

[0058] Comparative Example 2

[0059] 30g of PVP K30 was dissolved in 2400g of ethanol. After dissolution, 600g of microsilica powder with a median particle size of 5µm was added and stirred to disperse, resulting in a silica slurry with a solid content of 20%. The silica slurry was then wet-milled using a sand mill in two stages: first, a coarse sand mill was used for 2 hours, followed by a fine sand mill for 15 hours. The coarse sand mill used a screen-type mill with 0.3-0.4mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear velocity of 14m / s. The fine sand mill used a dual-power screenless mill with 0.1mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear velocity of 15m / s. After fine milling, one drop of the nano-silica slurry was dispersed in 30ml of ethanol and sonicated for 5 minutes. The particle size distribution of the silica particles was then measured using a laser particle size analyzer, and the median particle size was found to be 126nm. 100g of finely ground nano-silicon slurry was dried in a vacuum oven at 60℃ for 12 hours. After the oven cooled to room temperature, the dried nano-silicon powder was obtained. The oxygen content in the nano-silicon powder was measured to be 175 ppma using inert gas melting infrared spectroscopy.

[0060] A half-cell was fabricated from the nano-silica slurry according to the method described in Example 1, and its electrochemical performance was tested. The half-cell capacity was 436.2 mAh / g, and the initial efficiency was 86.5%.

[0061] Comparative Example 3

[0062] 30g of cetyltrimethylammonium bromide was dissolved in 2400g of ethanol. After dissolution, 600g of microsilica powder with a median particle size of 5µm was added and stirred to disperse, resulting in a silica slurry with a solid content of 20%. The silica slurry was then wet-milled using a sand mill in two stages: first, a coarse sand mill was used for 2 hours, followed by a fine sand mill for 15 hours. The coarse sand mill used a screen-type mill with 0.3-0.4mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear speed of 14m / s. The fine sand mill used a dual-power screenless mill with 0.1mm zirconium beads as the grinding media, a zirconium bead filling rate of 75%, and a mill linear speed of 15m / s. After fine milling, one drop of the nano-silica slurry was dispersed in 30ml of isopropanol and sonicated for 5 minutes. The particle size distribution of the silica particles was then measured using a laser particle size analyzer, and the median particle size was found to be 107nm. 100g of finely ground nano-silicon slurry was dried in a vacuum oven at 60℃ for 12 hours. After the oven cooled to room temperature, the dried nano-silicon powder was obtained. The oxygen content in the nano-silicon powder was measured to be 153 ppma using inert gas melting infrared spectroscopy.

[0063] A half-cell was fabricated from the nano-silica slurry according to the method described in Example 1, and its electrochemical performance was tested. The half-cell capacity was 440.8 mAh / g, and the initial efficiency was 86.9%.

[0064] Data from Examples 1-6 and Comparative Examples 1-3 are shown in Table 1.

[0065] Table 1

[0066]

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent substitutions, and improvements made by those skilled in the art to the above embodiments without departing from the scope of the present invention and based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a graphite / nano-silicon composite material, comprising the following steps: (a) Take nano-silicon slurry, artificial graphite, and binder and disperse and mix them at high speed, then add an appropriate amount of ethanol to adjust the solid content of the slurry; (b) The above slurry is spray-dried to obtain spherical secondary particles of Si / graphite / binder composite; (c) The spray-dried powder is placed in a box furnace and carbonized under an argon atmosphere. The temperature is increased to carbonize the binder and citric acid, resulting in an amorphous carbon-bonded graphite / nano-silicon composite material. The preparation method of the nano-silicon slurry includes the following steps: (1) Add the oxidation inhibitor to the alcohol solvent and stir to dissolve; (2) Disperse silicon powder with D50 of 5-10 μm in the solution obtained in step (1) and stir to prepare a silicon slurry with a solid content of 10%-20%. (3) The silicon slurry is wet-milled using a sand mill. The milling is carried out in two stages. First, a coarse sand mill is used for milling for 2-4 hours, and then a fine sand mill is used for milling for 15-30 hours. The oxidation inhibitor in step (1) is one or two of humic acid, citric acid, stearic acid, and ascorbic acid. The amount of oxidation inhibitor added in step (1) is 1%-10% of the silicon powder mass.

2. The preparation method according to claim 1, characterized in that, In step (1), the amount of oxidation inhibitor added is 5%-7% of the mass of silicon powder.

3. The preparation method according to claim 1, characterized in that, In step (1), the alcohol solvent is either ethanol or isopropanol.

4. The preparation method according to any one of claims 1-3, characterized in that, In step (3), the coarse grinding mill uses zirconium beads with a diameter range of 0.2-0.6 mm, and the fine grinding mill uses zirconium beads with a diameter range of 0.05-0.3 mm.

5. The preparation method according to any one of claims 1-3, characterized in that, In step (a), the median particle size of the artificial graphite is 5-10 μm.

6. The preparation method according to any one of claims 1-3, characterized in that, In step (a), the mass ratio of silicon powder: graphite powder: binder is 3-7:93-97:3-5.

7. The preparation method according to any one of claims 1-3, characterized in that, In step (a), the slurry has a solid content of 20%-30%.

8. The preparation method according to any one of claims 1-3, characterized in that, In step (b), the inlet air temperature for spray drying is 120-180℃, the exhaust air temperature is 60-80℃, and the atomizer speed is 30-50Hz; and / or, in step (c), the carbonization temperature is 800-1000℃, the carbonization time is 2-5h, and the heating rate is 3-5℃ / min.

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