Preparation method of graphene double-coating-layer nanometer silicon negative electrode material

Abstract

The invention relates to the technical field of negative electrode materials, and discloses a preparation method of a graphene double-coating nanometer silicon negative electrode material, and the method comprises the following steps: step 1, crushing and grinding blocky metal silicon in a mortar to obtain silicon powder; step 2, carrying out vacuum drying on the ball-milled product; step 3, uniformly mixing the product obtained in the step 2 with flaky graphite and phenolic resin liquid according to a certain weight ratio; and 4, carrying out vacuum drying on the ball-milled product in the step 3, and then carrying out heat treatment in an inert atmosphere to obtain the graphene / double-coating-layer nano-silicon composite negative electrode material. The prepared modified nano silicon powder is used as a grinding aid, phenolic resin liquid is used as a graphite stripping aid, crystalline flake graphite can be effectively stripped into few-layer or multi-layer graphene by adopting a mechanical ball milling method, more importantly, the modified nano silicon in a final product is completely attached to the surface of the graphene, uniform compounding of the graphene and the nano silicon is realized, and the graphene / nano silicon composite material is prepared. The graphene / silicon composite negative electrode material is obtained.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of negative electrode materials, in particular to a preparation method of a graphene double-coating layer nanometer silicon negative electrode material. BACKGROUND

[0002] At present, the most commonly used preparation method of graphene / nano Si composite material is as follows: graphene oxide prepared by a Hummers method is mixed with nano Si in a solution through stirring, and graphene oxide / nano Si precursors are prepared through filtration, washing and drying treatment, and finally, the precursors are heat-reduced in an inert atmosphere to obtain graphene / nano Si composite material. The method for preparing graphene / nano Si composite material has obvious defects: 1. The graphene prepared by the Hummers method has a complex process, a relatively large environmental pollution risk, and a high defect density and poor conductivity; 2. In the graphene / nano Si composite material prepared by the method, only part of the nano Si is closely attached to the surface of graphene, and a considerable amount of nano Si is separated from graphene to form independent nano silicon aggregates, so that the electrochemical performance is far from expected; 3. In the graphene / silicon composite material prepared by the method, although the nano Si particles are attached to the surface of the graphene sheet, the nano Si particles are still in a surface exposed state and directly contact the electrolyte, and the SEI film is continuously formed in the cycle process, resulting in continuous capacity attenuation; In order to coat a carbon film protective layer on the surface of the nanometer silicon, the application provides a preparation method of a graphene double-coating layer nanometer silicon negative electrode material. SUMMARY

[0003] The application aims to provide a preparation method of a graphene double-coating layer nanometer silicon negative electrode material to solve the problems in the background art.

[0004] To achieve the above-mentioned purpose, the application provides the following technical scheme: a preparation method of a graphene double-coating layer nanometer silicon negative electrode material, which comprises the following steps: Step 1: crushing and grinding bulk metal silicon in a mortar to obtain silicon powder, then putting the silicon powder into a ball mill tank and adding a phenolic resin liquid, introducing inert gas to remove air in the ball mill tank, and then fixing the ball mill tank on a ball mill for ball milling treatment; Step 2: vacuum drying the product after ball milling, and then heat-treating in an inert atmosphere to form an amorphous carbon coating layer, so as to obtain nanometer silicon particles with a silicon monoxide / amorphous carbon double-coating layer; Step 3: mixing the product obtained in step 2 with flaky graphite and a phenolic resin liquid in a certain weight ratio, and uniformly placing the mixture in a ball mill tank for ball milling; Step 4, vacuum drying the ball-milling product in step 3, and then heat treating in an inert atmosphere to obtain a graphene / double-coated nanosilicon composite negative electrode material.

[0005] In step 1, the weight ratio of the mixture of silicon powder and phenolic resin liquid is 1:0.3-0.45.

[0006] In steps 1, 2 and 4, the inert gas is one of helium, neon and argon.

[0007] In step 1, the rotation speed of the ball mill is 450-500 rpm, the ball milling time is 20-24 h, and the temperature of the ball milling tank is controlled at 110-130 DEG C.

[0008] In step 2, the heat treatment temperature is 500-700 DEG C, and the heat treatment time is 3-4 h.

[0009] In step 3, the weight ratio of the mixture of nanosilicon particles with silicon monoxide / amorphous carbon double-coated layers, flaky graphite and phenolic resin liquid is 1:2.8-3:5.5-6.

[0010] In step 3, the ball milling time is 5-8 h, and the rotation speed is 600-800 rpm.

[0011] In step 4, the heat treatment temperature is 600-700 DEG C, and the heat treatment time is 1.5-3 h.

[0012] The phenolic resin liquid is a silicon surface modifier, and under the action of mechanical force and heat: active oxygen atoms are generated by decomposition and react with silicon to form a silicon monoxide interface layer, and a continuous amorphous carbon outer layer is formed by thermal polymerization.

[0013] In step 2, the particle size of the nanosilicon particles is in the range of 50-200 nm.

[0014] Compared with the prior art, the present application has the following beneficial effects: The present application uses a simple two-step mechanical ball milling method, with the aid of a specially prepared silicon surface modifier (phenolic resin liquid), which can efficiently convert inexpensive metallic silicon into nanosilicon and simultaneously achieve surface coating modification of the nanosilicon, forming a uniform silicon monoxide / amorphous carbon double-coated layer on the surface.

[0015] The present application uses a mechanical ball milling method to effectively exfoliate flaky graphite into few-layer or multi-layer graphene, and more importantly, the modified nanosilicon is attached to the surface of the graphene in the final product, achieving uniform compounding of graphene and nanosilicon, and obtaining a graphene / silicon composite negative electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 TEM images of the graphene / double-coated nanosilicon composite negative electrode material prepared in the present application. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be apparently and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0018] The present application will be further described in detail below with reference to the embodiments and drawings.

[0019] Referring to the drawings Figure 1 , Figure 1 TEM images of the graphene / double-coated nanosilicon composite negative electrode material prepared in the present application, Figure 1 Fig. (a) is a low-magnification morphology image of the graphene / double-coated nanosilicon composite negative electrode material, graphene / cracked carbon continuous phase (alternating light and dark stripes), proving the uniformity of ball milling dispersion, and the composite particles are uniformly dispersed in the graphene matrix; Fig. (b) is a medium-magnification interface image of the graphene / double-coated nanosilicon composite negative electrode material, which can be seen as a double-coated layer; Fig. (c) is a high-resolution silicon lattice image of the graphene / double-coated nanosilicon composite negative electrode material, and the 0.31 nm lattice spacing and the fuzzy transition zone verify the gradient silicon monoxide layer; Fig. (d) is a high-resolution graphene composite image of the graphene / double-coated nanosilicon composite negative electrode material, which has graphene / double-coated layer, and the few-layer graphene (1-3 layers) tightly coats the particles. Embodiment 1

[0020] A preparation method of a graphene double-coated nanosilicon negative electrode material, the method comprising the following steps: Step 1, crushing and grinding the bulk metal silicon in a mortar to obtain silicon powder, then putting the silicon powder into a ball mill jar and adding a phenolic resin liquid, the mixing weight ratio of the silicon powder and the phenolic resin liquid is 1:0.3, introducing helium to remove air in the ball mill jar, then fixing the ball mill jar on a ball mill, the rotation speed of the ball mill is 450 rpm, the ball milling time is 20 h, and the temperature of the ball mill jar is controlled at 120℃, the phenolic resin liquid is a silicon surface modifier, under the action of the ball milling mechanical force and heat: decomposing to generate active oxygen atoms and reacting with silicon to form a silicon monoxide interface layer, and heat polymerization to form a continuous amorphous carbon outer layer; Step 2, vacuum drying the product after ball milling, and then heat treatment in a helium atmosphere, the heat treatment temperature is 600℃, the heat treatment time is 3h, forming an amorphous carbon coating layer, obtaining nano-silicon particles with silicon monoxide / amorphous carbon double coating layers; Step 3, mixing the nano-silicon particles with silicon monoxide / amorphous carbon double coating layers obtained in step 2 with flaky graphite and phenolic resin liquid according to a weight ratio of 1:2.8:5.5, placing them in a ball mill tank for ball milling at a speed of 700rpm for 6h; Step 4, vacuum drying the ball-milled product in step 3, and then heat treatment in a helium atmosphere, the heat treatment temperature is 650℃, the heat treatment time is 2h, obtaining a graphene / double-coated nano-silicon composite negative electrode material. Example 2

[0021] A method for preparing a graphene double-coated nano-silicon negative electrode material, the method comprising the following steps: Step 1, crushing and grinding bulk metal silicon in a mortar to obtain silicon powder, then placing the silicon powder into a ball mill tank and adding phenolic resin liquid, the mixing weight ratio of the silicon powder and the phenolic resin liquid is 1:0.45, introducing helium to remove air in the ball mill tank, and then fixing the ball mill tank on a ball mill, the rotation speed of the ball mill is 450rpm, the ball milling time is 20h, and the temperature of the ball mill tank is controlled at 120℃, the phenolic resin liquid is a silicon surface modifier, under the action of mechanical force and heat: decomposing to generate active oxygen atoms and reacting with silicon to form a silicon monoxide interface layer and a continuous amorphous carbon outer layer; Step 2, vacuum drying the product after ball milling, and then heat treatment in a helium atmosphere, the heat treatment temperature is 600℃, the heat treatment time is 3h, forming an amorphous carbon coating layer, obtaining nano-silicon particles with silicon monoxide / amorphous carbon double coating layers; Step 3, mixing the nano-silicon particles with silicon monoxide / amorphous carbon double coating layers obtained in step 2 with flaky graphite and phenolic resin liquid according to a weight ratio of 1:2.8:5.5, placing them in a ball mill tank for ball milling at a speed of 700rpm for 6h; Step 4, vacuum drying the ball-milled product in step 3, and then heat treatment in a helium atmosphere, the heat treatment temperature is 650℃, the heat treatment time is 2h, obtaining a graphene / double-coated nano-silicon composite negative electrode material. Example 3

[0022] A method for preparing a graphene double-coated nano-silicon negative electrode material, the method comprising the following steps: Step 1, break and grind the bulk metal silicon in a mortar to obtain silicon powder, then put the silicon powder into a ball mill tank, and add a phenolic resin liquid, the mixing weight ratio of the silicon powder and the phenolic resin liquid is 1:0.3, helium is introduced to remove air in the ball mill tank, then the ball mill tank is fixed on a ball mill for ball milling treatment, the rotating speed of the ball mill is 450 rpm, the ball milling time is 20 h, and the temperature of the ball mill tank is controlled at 120℃, the phenolic resin liquid is a silicon surface modifier, under the action of ball milling mechanical force and heat: active oxygen atoms are generated by decomposition to react with silicon to form a silicon monoxide interface layer and a continuous amorphous carbon outer layer formed by thermal polymerization; Step 2, vacuum drying the product after ball milling, and then heat treatment in a helium atmosphere, the heat treatment temperature is 600℃, the heat treatment time is 3h, forming an amorphous carbon coating layer, obtaining nano-silicon particles with silicon monoxide / amorphous carbon double coating layers; Step 3, mix the nano-silicon particles with silicon monoxide / amorphous carbon double coating layers obtained in step 2 with flaky graphite and a phenolic resin liquid according to a weight ratio of 1:3:6, and place them in a ball mill tank for ball milling for 6h at a rotating speed of 700rpm; Step 4, vacuum drying the ball milling product in step 3, and then heat treatment in a helium atmosphere, the heat treatment temperature is 650℃, the heat treatment time is 2h, obtaining a graphene / double-coated nano-silicon composite negative electrode material. Example 4

[0023] A preparation method of a graphene double-coated nano-silicon negative electrode material, the method comprising the following steps: Step 1, break and grind the bulk metal silicon in a mortar to obtain silicon powder, then put the silicon powder into a ball mill tank, and add a phenolic resin liquid, the mixing weight ratio of the silicon powder and the phenolic resin liquid is 1:0.45, helium is introduced to remove air in the ball mill tank, then the ball mill tank is fixed on a ball mill for ball milling treatment, the rotating speed of the ball mill is 450 rpm, the ball milling time is 20 h, and the temperature of the ball mill tank is controlled at 120℃, the phenolic resin liquid is a silicon surface modifier, under the action of ball milling mechanical force and heat: active oxygen atoms are generated by decomposition to react with silicon to form a silicon monoxide interface layer and a continuous amorphous carbon outer layer formed by thermal polymerization; Step 2, vacuum drying the product after ball milling, and then heat treatment in a helium atmosphere, the heat treatment temperature is 600℃, the heat treatment time is 3h, forming an amorphous carbon coating layer, obtaining nano-silicon particles with silicon monoxide / amorphous carbon double coating layers; Step 3, mix the nano-silicon particles with silicon monoxide / amorphous carbon double coating layers obtained in step 2 with flaky graphite and a phenolic resin liquid according to a weight ratio of 1:3:6, and place them in a ball mill tank for ball milling for 6h at a rotating speed of 700rpm; Step 4, vacuum drying the ball-milling product in step 3, and then heat treatment in a helium atmosphere, the heat treatment temperature is 650℃, the heat treatment time is 2h, to obtain the graphene / double-coated nano-silicon composite negative electrode material.

[0024] Comparative Example 1 A method for preparing a nano-silicon negative electrode material, the method comprising the following steps: Step 1, crushing and grinding bulk metal silicon in a mortar to obtain silicon powder, then placing the silicon powder into a ball mill tank, and adding deionized water, the weight ratio of the silicon powder and the deionized water is 1:0.3, purging helium to remove air in the ball mill tank, and then fixing the ball mill tank on a ball mill for ball milling treatment, the rotation speed of the ball mill is 450rpm, the ball milling time is 20h, and the temperature of the ball mill tank is controlled at 120℃; Step 2, vacuum drying the product after ball milling, and then heat treatment in a helium atmosphere, the heat treatment temperature is 600℃, the heat treatment time is 3h, to obtain nano-silicon particles; Step 3, mixing the nano-silicon particles obtained in step 2 with flaky graphite and deionized water according to a weight ratio of 1:2.8:5.5, placing in a ball mill tank for ball milling for 6h at a rotation speed of 700rpm; Step 4, vacuum drying the ball-milling product in step 3, and then heat treatment in a helium atmosphere, the heat treatment temperature is 650℃, the heat treatment time is 2h, to obtain the nano-silicon composite negative electrode material.

[0025] Comparative Example 2 A method for preparing a nano-silicon negative electrode material, the method comprising the following steps: Step 1, crushing and grinding bulk metal silicon in a mortar to obtain silicon powder, then placing the silicon powder into a ball mill tank, purging helium to remove air in the ball mill tank, and then fixing the ball mill tank on a ball mill for ball milling treatment, the rotation speed of the ball mill is 450rpm, the ball milling time is 20h, and the temperature of the ball mill tank is controlled at 120℃; Step 2, vacuum drying the product after ball milling, and then heat treatment in a helium atmosphere, the heat treatment temperature is 600℃, the heat treatment time is 3h, to obtain nano-silicon particles; Step 3, mixing the nano-silicon particles obtained in step 2 with flaky graphite according to a weight ratio of 1:2.8, placing in a ball mill tank for ball milling for 6h at a rotation speed of 700rpm; Step 4, vacuum drying the ball-milling product in step 3, and then heat treatment in a helium atmosphere, the heat treatment temperature is 650℃, the heat treatment time is 2h, to obtain the nano-silicon composite negative electrode material.

[0026] Experimental Example Test the specific capacity and cycle number of the composite negative electrode material: The lithium ion batteries were assembled by using the nano-silicon composite negative electrode materials in Examples 1-4 and Comparative Examples 1 and 2 as the negative electrode, metal sodium sheet as the positive electrode, and lithium battery electrolyte. The constant current charge-discharge test was carried out at a current density of 50 mA / g by using a LAND battery test system, and the test conditions and results are shown in Table 1. Table 1 First discharge capacity and first coulombic efficiency of lithium ion batteries

[0027] As can be seen from the above table, the lithium ion battery of the graphene / double-coated nano-silicon composite negative electrode material prepared in Example 4 has a high initial discharge capacity (more than 2000 mAh / g) and a first storage efficiency of more than 85%. The first discharge capacity of Comparative Example 1 is only 1020.5 mAh / g, and the first coulombic efficiency is 71.1%. The first discharge capacity of Comparative Example 2 is only 953.4 mAh / g, and the first coulombic efficiency is 54.1%. Therefore, the graphene / double-coated nano-silicon composite negative electrode material prepared in the present application has a high specific capacity. The graphene / double-coated nano-silicon composite negative electrode material can not only buffer the volume expansion problem of silicon-carbon materials during the charge-discharge process, but also provide a fast channel for the transmission of lithium ions between layers. The specific values are shown in Table 1.

[0028] The constant current charge-discharge test was carried out at a current density of 500 mA / g, and the graphene / double-coated nano-silicon composite negative electrode material prepared in Examples 1-4 had a good capacity retention rate (more than 90%) after 200 cycles, showing excellent cycle stability.

[0029] The capacity retention rates of Comparative Examples 1 and 2 were less than 60%. The specific values are shown in Table 2.

[0030] Table 2 Capacity retention rate of lithium ion batteries after 200 cycles

[0031]

[0032] In summary, the simple two-step mechanical ball milling method used in the present application can efficiently convert inexpensive metal silicon into nano-silicon with the help of a specially designed silicon surface modifier (phenolic resin solution), and at the same time, the surface of the nano-silicon is coated and modified to form a uniform silicon monoxide / amorphous carbon double-coated layer.

[0033] The application uses the prepared modified nano-silicon powder as a grinding aid and phenolic resin liquid as a graphite peeling aid to effectively peel flake graphite into few-layer or multi-layer graphene by mechanical ball milling.

[0034] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely divergences of the principles and spirit of the application and that numerous modifications, changes, substitutions, and alterations can be made thereto without departing from the spirit and scope of the application as defined by the appended claims and their equivalents.

Claims

1. A method for preparing a graphene-coated double-layer nano-silicon anode material, characterized in that, The method includes the following steps: Step 1: Crush and grind the blocky metallic silicon in a mortar to obtain silicon powder. Then, put the silicon powder into a ball mill jar, add phenolic resin liquid, pass in inert gas to remove air from the ball mill jar, and then fix the ball mill jar on a ball mill for ball milling. Step 2: Vacuum dry the ball-milled product, and then heat treat it in an inert atmosphere to form an amorphous carbon coating layer, thus obtaining nano-silicon particles with a silicon suboxide / amorphous carbon double coating layer. Step 3: Mix the product obtained in Step 2 with flake graphite and phenolic resin liquid in a certain weight ratio, and then place it in a ball mill jar for ball milling. Step 4: Vacuum dry the ball milling product from Step 3, and then heat treat it in an inert atmosphere to obtain a graphene / double-coated nano-silicon composite anode material.

2. The method for preparing a graphene-coated double-layer nano-silicon anode material according to claim 1, characterized in that: In step 1, the weight ratio of silicon powder and phenolic resin liquid is 1:0.3-0.

45.

3. The method for preparing a graphene-coated double-layer nano-silicon anode material according to claim 1, characterized in that: In steps 1, 2, and 4, the inert gas is one of helium, neon, or argon.

4. The method for preparing a graphene-coated double-layer nano-silicon anode material according to claim 1, characterized in that: In step 1, the ball mill rotates at 450-500 rpm, the milling time is 20-24 h, and the temperature of the mill jar is controlled at 110℃-130℃.

5. The method for preparing a graphene-coated double-layer nano-silicon anode material according to claim 1, characterized in that: In step 2, the heat treatment temperature is 500℃-700℃, and the heat treatment time is 3-4 hours.

6. The method for preparing a graphene-coated double-layer nano-silicon anode material according to claim 1, characterized in that: In step 3, the mixing weight ratio of nano-silicon particles with a silicon suboxide / amorphous carbon double coating, flake graphite, and phenolic resin liquid is 1:2.8-3:5.5-6.

7. The method for preparing a graphene-coated double-layer nano-silicon anode material according to claim 1, characterized in that: In step 3, the ball milling time is 5~8 hours and the rotation speed is 600~800 rpm.

8. The method for preparing a graphene-coated double-layer nano-silicon anode material according to claim 7, characterized in that: In step 4, the heat treatment temperature is 600℃-700℃ and the heat treatment time is 1.5-3 h.

9. The method for preparing a graphene-coated double-layer nano-silicon anode material according to claim 1, characterized in that: Phenolic resin liquid is a silicon surface modifier. Under the mechanical force and heat of ball milling, it decomposes to produce active oxygen atoms that react with silicon to form a silicon suboxide interface layer and thermally polymerizes to form a continuous amorphous carbon outer layer.

10. The method for preparing a graphene-coated double-layer nano-silicon anode material according to claim 1, characterized in that: In step 2, the particle size of the nano-silicon particles ranges from 50 to 200 nm.

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