CN115458729B

CN115458729B - Graphene-coated silicon material, and electric arc preparation method and application thereof

Info

Publication number: CN115458729B
Application number: CN202211330588.8A
Authority: CN
Inventors: 崔维国; 费鹏扬; 柳俊辰; 姜志国
Original assignee: Tianjin Pulan Nano Technology Co Ltd
Current assignee: Tianjin Pulan Nano Technology Co Ltd
Priority date: 2022-10-28
Filing date: 2022-10-28
Publication date: 2023-03-24
Anticipated expiration: 2042-10-28
Also published as: CN115458729A

Abstract

The invention relates to a graphene-coated silicon material, an electric arc preparation method and application thereof, relating to the field of lithium ion cathode materials and comprising the following steps: step S1, preparing a cathode and an anode: pressing graphite powder into a cathode; mixing graphite powder and a silicon-based material, then adding a binder, uniformly mixing, and pressing into an anode, wherein the weight ratio of the graphite powder, the silicon-based material and the binder in the anode is (1-4): (0.1 to 2.6): (0.125 to 0.4); s2, graphene in-situ coating: under a certain atmosphere and pressure, a certain voltage is applied between the cathode and the anode to generate arc discharge between the cathode and the anode, so that the generated graphene in situ coats the silicon material in the anode to obtain the graphene-coated silicon material. The graphene coated silicon material is generated in situ by adopting an arc method, and the generated graphene has good crystallinity and few defects, and has the advantages of complete coating and small using amount.

Description

Graphene-coated silicon material, and electric arc preparation method and application thereof

Technical Field

The invention relates to the field of lithium ion negative electrode materials, in particular to a graphene-coated silicon material, an electric arc preparation method and application thereof.

Background

At present, the development of new energy vehicles and energy storage industries is seriously hindered by the defects of low energy density, low power density, poor low-temperature performance, short cycle life, poor safety performance and the like of lithium ion batteries in the market. The defects of the lithium ion battery are usually caused by that the theoretical specific capacity of the graphite is only 375mAh/g, the lithium intercalation potential is close to the lithium precipitation potential, and the migration rate of lithium ions is low because of the graphite serving as a negative electrode material, so that the lithium ion battery taking the graphite as the negative electrode cannot meet the requirements of new energy industry on high energy density, high power density, high safety and long cycle life. Therefore, the development of a new high-specific-capacity anode material has a profound significance in promoting the development of new energy industry.

Silicon is considered to be the best material for replacing a graphite cathode because of its abundant earth reserves, low cost and large specific capacity. Silicon can form an alloy compound Li with lithium _x Si (0<x is less than or equal to 4.4), the highest theoretical specific capacity reaches 4200mAh/g, which is more than 11 times of that of a commercial graphite cathode, and the lithium intercalation potential of silicon is higher than the precipitation potential of lithium, so that the charging and discharging safety at high magnification and low temperature is improved. However, silicon materials have been studied for a long time on the negative electrode of lithium ion batteries, but the commercialization remains elusive for two reasons. Firstly, the volume change of the silicon material is very large (more than 300%) in the charging and discharging process, which causes the continuous rupture and reformation of the solid-liquid interface film, the decomposition of electrolyte, the easy pulverization of active substances and the deterioration of electric contact between the active substances and a current collector, and the basic reasons of the fast capacity attenuation and poor cycle performance of the lithium ion battery taking the silicon material as the negative electrode are adopted. Second, the silicon material is a semiconductor and is not as conductive as the graphite negative electrode, which limits its rate capability. Graphene is a two-dimensional single-layer nano material composed of carbon atoms, has the advantages of excellent mechanical properties, electrochemical stability, high conductivity and the like, and is the best choice for coating silicon materials, so that the defects of large volume change and poor conductivity of the graphene are overcome by coating silicon by graphene in the scientific community and the industrial community.

The current common method is to mechanically mix graphene and silicon material, which has the disadvantages of incomplete coating and large using amount, and can not completely solve the practical application problem of the silicon material, and increase the cost, for example, patent CN104916826A discloses a graphene-coated silicon negative electrode material and a preparation method thereof, which comprises the following steps: A. preparing a graphene oxide suspension; B. preparing a nano silicon particle suspension; C. preparing a graphene-coated silicon negative electrode material; although the graphene-coated silicon negative electrode material has high initial specific capacity, the cycling performance and the rate capability are poor, the first discharge specific capacity reaches 2746mAh/g under the current density of 0.01-1.2V and 200mA/g, the discharge specific capacity is kept at 803.8mAh/g after 50 cycles, and only 29.2% of the original capacity is kept. In view of this, in order to solve the problems of large dosage of toxic and harmful reagents, poor dispersibility and incomplete coating existing in the graphene-coated silicon material, the invention provides a graphene-coated silicon material, an electric arc preparation method and an application thereof.

Disclosure of Invention

The invention aims to solve the technical problem of providing a graphene-coated silicon material, an electric arc preparation method and application thereof. The purpose is to provide the silicon anode material which can be completely coated in situ and is prepared by an arc method and coated by graphene, and the conductivity and the cyclicity of the silicon anode material are improved.

The technical scheme for solving the technical problems is as follows: an electric arc preparation method of a graphene-coated silicon material comprises the following steps:

step S1, preparing a cathode and an anode: pressing graphite powder into a cathode; mixing graphite powder and a silicon-based material, then adding a binder, uniformly mixing, and pressing into an anode, wherein the weight ratio of the graphite powder, the silicon-based material and the binder in the anode is (1-4): (0.1 to 2.6): (0.125 to 0.4);

s2, graphene in-situ coating: and applying voltage between the cathode and the anode to generate arc discharge between the cathode and the anode, so that the generated graphene in situ coats the silicon-based material in the anode, and washing with strong base to obtain the graphene-coated silicon negative electrode material. And washing the obtained anode product with a sodium hydroxide or potassium hydroxide solution to remove oxides on the surface of the silicon-based material, and further obtaining the graphene-coated silicon material cathode with a certain cavity structure, so that the volume expansion of the silicon material in the charging and discharging process is relieved.

The beneficial effects of the invention are: according to the method, graphite powder is used as a cathode, graphite powder, a silicon-based material and a binder are used as an anode, a silicon-based compound in a graphene-coated anode is generated in situ through arc discharge between the cathode and the anode under a certain voltage, and a graphene-coated silicon material is generated in situ by an arc method. The weight ratio of the raw materials is (1-4): (0.1 to 2.6): (0.125 to 0.4) the anode is formed by pressing graphite powder, a silicon-based material and a binder.

On the basis of the technical scheme, the invention can be improved as follows.

Further, the cathode and the anode are pressed into a rod shape in the step S1, and the weight ratio of the graphite powder, the silicon-based material and the binder in the anode is (1-2): (0.3 to 1.3): (0.125 to 0.2).

The beneficial effect of adopting the further scheme is that: the weight ratio of the graphite powder, the silicon-based material and the binder in the anode is (1 to 2): (0.3 to 1.3): (0.125-0.2), so that the performance of the silicon negative electrode material coated by the graphene is more excellent.

Further, in the step S1, graphite powder in the cathode and the anode is at least one of natural graphite and artificial graphite, and the particle size D50 of the graphite powder is 0.1 to 200 mu m; the silicon-based material in the anode is one or more of silicon powder, silicon dioxide powder and silica powder, and the particle size D50 of the silicon-based material is 0.01-100 mu m; the binder in the anode is one or more of phenolic resin, polyvinyl alcohol, polyacrylic acid, polyacrylonitrile, polyvinylidene fluoride and polytetrafluoroethylene.

The beneficial effect of adopting the further scheme is that: the raw materials of the graphene used in the invention are commercial natural graphite or/and artificial graphite, the used silicon materials are silicon powder, silicon monoxide and silicon dioxide which are produced in large scale, and all the raw materials are cheap and easy to obtain and have low cost; by adopting graphite powder with the particle size D50 of 0.1 to 200 mu m and silicon-based material with the particle size D50 of 0.01 to 100 mu m, the graphite and the silicon materials with the particle size are easy to gasify during arc discharge, so that the graphite and the silicon materials are easier to condense into nano-structured graphene and nano-silicon, too small particles are difficult to disperse, and too large particles are difficult to react.

Further, in the step S1, graphite powder in the cathode is artificial graphite, graphite powder in the anode is natural graphite, and the particle size of the graphite powder is 1-100 mu m; the particle size D50 of the silicon-based material is 0.1 to 10 mu m; the binder in the anode is one or a mixture of more than one of phenolic resin and polyvinyl alcohol.

Further, in the step S2, the atmosphere is nitrogen, argon, helium, a nitrogen-hydrogen mixture, an argon-hydrogen mixture, or a helium-hydrogen mixture, and the pressure of the atmosphere is 350 to 750torr. When the mixed gas is nitrogen-hydrogen mixed gas, argon-hydrogen mixed gas and helium-hydrogen mixed gas, the mixed gas can be mixed in any volume ratio.

The beneficial effect of adopting the further scheme is that: the silicon-based material is completely coated in situ by adopting the atmosphere of nitrogen, argon, helium, nitrogen-hydrogen mixed gas, argon-hydrogen mixed gas and helium-hydrogen mixed gas, and the pressure is 350 to 750Torr.

Further, in the step S2, the atmosphere is one of helium and a mixture of helium and hydrogen, and the pressure of the atmosphere is 500 to 600Torr.

Further, in the step S2, the voltage applied between the cathode and the anode is 5 to 50V.

Further, the voltage applied between the cathode and the anode in the step S2 is 20 to 35V.

The second objective of the present invention is to provide a graphene-coated silicon material, which is prepared by the above-mentioned arc preparation method of the graphene-coated silicon material.

The beneficial effect who adopts above-mentioned scheme is: according to the invention, the graphene coated silicon material is generated in situ by adopting an arc method, and the generated graphene has good crystallinity and few defects, and has the advantages of complete coating and small using amount.

The third objective of the present invention is to provide an application of the graphene-coated silicon material, wherein the graphene-coated silicon material is used as a lithium ion battery material.

The beneficial effect who adopts above-mentioned scheme is: according to the invention, due to the adoption of in-situ coating of graphene, the volume change is relieved, the conductivity is improved, and the cycling performance of the graphene-coated silicon anode material prepared by the invention is relatively stable.

Drawings

Fig. 1 is a projection electron microscope photograph of a graphene-coated negative electrode silicon material prepared by an arc method in example 1 of the present invention;

fig. 2 is an x-ray diffraction pattern of the graphene-coated negative electrode silicon material prepared by the arc process in examples 1 to 3 of the present invention;

fig. 3 is a cycle curve of the graphene-coated negative electrode silicon material prepared by the arc process in examples 1 to 3.

Detailed Description

The principles and features of this invention are described below in conjunction with examples which are set forth to illustrate, but are not to be construed to limit the scope of the invention.

Example 1

The embodiment provides an electric arc preparation method of a graphene-coated silicon material, which comprises the following steps:

1) Taking natural graphite with D50 of 10 mu m, and pressing into a rod-shaped cathode; mixing 100g of natural graphite with the D50 of 5 microns and 65g of silicon powder with the D50 of 1 micron, adding 10g of phenolic resin, fully and uniformly mixing, and pressing into a rod-shaped anode;

2) Under the helium protective atmosphere, the pressure is adjusted to 550Torr, 28V voltage is applied to the anode and the cathode, arc discharge is generated between the two electrodes, and the graphene generated in situ in the arc discharge process coats the silicon material in the anode to obtain the graphene-coated silicon material.

Example 2

1) Taking artificial graphite with D50 of 35 mu m, and pressing into a rod-shaped cathode; mixing 150g of natural graphite with the D50 of 30 mu m and 90g of silicon monoxide with the D50 of 10 mu m, then adding 30g of phenolic resin, fully and uniformly mixing, and pressing into a rod-shaped anode;

2) And under the protection atmosphere of helium-hydrogen mixed gas, adjusting the pressure to be 600Torr, applying 30V voltage to the anode and the cathode to generate arc discharge between the two electrodes, and coating the silicon material in the anode by the graphene generated in situ in the arc discharge process to obtain the graphene-coated silicon material.

Example 3

1) Taking artificial graphite with D50 of 60 mu m, and pressing into a rod-shaped cathode; mixing 80g of natural graphite with the D50 of 25 mu m and 8g of silicon dioxide with the D50 of 2 mu m, then adding 10g of phenolic resin, fully and uniformly mixing, and pressing into a rod-shaped anode;

2) And under the protection atmosphere of helium-hydrogen mixed gas, adjusting the pressure to be 580 Torr, applying 35V voltage to the anode and the cathode to generate arc discharge between the two electrodes, and coating the silicon material in the anode by the graphene generated in situ in the arc discharge process to obtain the graphene-coated silicon material.

Examples of the experiments

The electrical property detection of the graphene-coated silicon material obtained in each embodiment mainly comprises the following steps:

1) Preparing an N-methyl pyrrolidone solution of polyvinylidene fluoride (PVDF) with 5% of solid content;

2) Weighing a certain amount of graphene-coated silicon material and a certain amount of a conductive agent Super-P (carbon black), grinding and uniformly mixing, then dropwise adding an N-methyl pyrrolidone solution of PVDF, continuously grinding and uniformly mixing to obtain slurry; wherein the weight ratio of the silicon material coated by the graphene, the conductive agent Super-P and the PVDF is 80: 10;

3) Coating the slurry on a copper foil, and preparing a pole piece through vacuum drying, rolling and cutting;

4) Lithium sheet is used as a counter electrode, the diaphragm is a polyethylene and polypropylene composite diaphragm, and 1.2 mol/L LiPF is used ₆ The three-component mixed solvent EC/DMC/EMC (the volume ratio of the three solvents is 1: 1) solution is used as electrolyte to assemble the button cell. The charging and discharging voltage is limited to 0.05-1.5V.

Fig. 1 is a projection electron microscope image of a graphene-coated silicon material generated in situ after arc discharge, and it can be seen from fig. 1 that silicon is nano-scale particles, is uniformly dispersed and is coated by graphene, and this structure not only solves the disadvantage of poor conductivity of silicon, but also alleviates severe volume change of silicon in the charging and discharging process through the coating of graphene. Therefore, the graphene coated silicon material prepared by the method is used as an anode and has great practical application value.

Fig. 2 is an X-ray diffraction pattern of the graphene-coated silicon material prepared by the method, and it can be determined from fig. 2 that the crystal form of silicon is not changed in the preparation process.

Fig. 3 is a cycle performance diagram of the graphene-coated silicon material prepared by the present invention. The biggest defect of directly using silicon as the anode material of the lithium ion battery is that the cycle performance is extremely poor, and the active material is inactivated mainly because the volume change of the silicon is large in the charging and discharging process, so that the electrode is broken and peeled from a current collector. As can be seen from fig. 3, under the current density of 0.05-1.5 v and 100 mA/g, the button cell assembled by the graphene-coated silicon negative electrode material prepared in example 1 has the first discharge specific capacity of 895 mAh/g, and after 30 cycles, the discharge specific capacity is kept at 720 mAh/g, which keeps 80.4% of the original capacity; the button cell is assembled by the graphene-coated silicon negative electrode material prepared in the embodiment 2, the first discharge specific capacity of the button cell reaches 560 mAh/g, the discharge specific capacity is kept at 500 mAh/g after 50 cycles, and 89.3% of the original capacity is kept; the button battery is assembled by adopting the graphene-coated silicon negative electrode material prepared in the embodiment 3, the first discharge specific capacity of the button battery reaches 290 mAh/g, the discharge specific capacity is kept at 380 mAh/g after 50 cycles, and 100% of the original capacity is kept.

In conclusion, the graphene-coated silicon anode material prepared by the method has relatively stable cycle performance, and is mainly benefited from in-situ coating of graphene, so that the volume change is relieved, and the conductivity is improved.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims

1. An electric arc preparation method of a graphene-coated silicon material is characterized by comprising the following steps of:

step S1, preparing a cathode and an anode: pressing graphite powder into a cathode; mixing graphite powder and a silicon-based material, then adding a binder, uniformly mixing, and pressing into an anode, wherein the weight ratio of the graphite powder, the silicon-based material and the binder in the anode is (1-4): (0.1-2.6): (0.125-0.4);

s2, graphene in-situ coating: applying voltage between the cathode and the anode to generate arc discharge between the cathode and the anode, so that the generated graphene in situ coats a silicon-based material in the anode, and washing the silicon-based material by strong alkali to obtain a graphene-coated silicon negative electrode material; in the step S1, the graphite powder in the cathode and the anode is at least one of natural graphite and artificial graphite, and the particle size D50 of the graphite powder in the cathode and the anode is 0.1-200 mu m; the silicon-based material in the anode is one or more of silicon powder, silicon dioxide powder and silica powder, and the particle size D50 of the silicon-based material is 0.01-100 mu m; the binder in the anode is one or more of phenolic resin, polyvinyl alcohol, polyacrylic acid, polyacrylonitrile, polyvinylidene fluoride and polytetrafluoroethylene.

2. The arc preparation method of the graphene-coated silicon material according to claim 1, wherein the cathode and the anode are pressed into a rod shape in step S1, and the weight ratio of the graphite powder, the silicon-based material and the binder in the anode is (1-2): (0.3-1.3): (0.125-0.2).

3. The arc preparation method of graphene-coated silicon material according to claim 1 or 2, wherein in step S1, the graphite powder in the cathode is artificial graphite, the graphite powder in the anode is natural graphite, and the particle size D50 of the graphite powder in the cathode and the anode is 1-100 μm; the grain diameter D50 of the silicon-based material is 0.1-10 mu m; the binder in the anode is one or more of phenolic resin and polyvinyl alcohol.

4. The method of claim 1, wherein in step S2, a voltage is applied between the cathode and the anode in an atmosphere of nitrogen, argon, helium, a mixture of nitrogen and hydrogen, a mixture of argon and hydrogen, or a mixture of helium and hydrogen, and the pressure of the atmosphere is 350 to 750Torr.

5. The arc preparation method of graphene-coated silicon material according to claim 4, wherein the atmosphere in step S2 is helium or a mixture of helium and hydrogen, and the pressure of the atmosphere is 500-600 Torr.

6. The arc preparation method of graphene-coated silicon material according to claim 1, wherein the voltage applied between the cathode and the anode in step S2 is 5-50V.

7. The arc preparation method of graphene-coated silicon material according to claim 6, wherein the voltage applied between the cathode and the anode in step S2 is 20-35V.

8. A graphene-coated silicon material, characterized by being prepared by the arc preparation method of a graphene-coated silicon material according to any one of claims 1 to 7.

9. Use of a graphene-coated silicon material according to claim 8 as a lithium ion battery material.