Si-C-g-C3N4 material as well as preparation method and application thereof

Abstract

The invention discloses a Si (at) C (at) g-C3N4 material, which is characterized in that the surface of nano silicon is coated with a carbon layer, and the carbon layer is Si (at) C particles; the surfaces of the Si (at) C particles are coated with porous g-C3N4 layers, and part of the Si (at) C particles are distributed in pores of the g-C3N4 layers. The invention also discloses a preparation method of the Si-C-g-C3N4 material, which comprises the following steps: uniformly mixing Si-C particles, a first solvent and urea, heating and stirring to remove the first solvent, and calcining to obtain the Si-C-g-C3N4 material. The invention also discloses an application of the Si (at) C (at) g-C3N4 material in a negative electrode material. The Si (at) C (at) g-C3N4 material can relieve volume expansion of silicon, and when the Si (at) C (at) g-C3N4 material is used as a lithium ion negative electrode material, the Si (at) C (at) g-C3N4 material can show good rate capability and cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials, and in particular to a Si@C@g-C3N4 material and a preparation method and application thereof. Background Art

[0002] Silicon negative electrode materials have excessive volume expansion during the process of cyclic lithium insertion and extraction, which makes their structure prone to collapse during the cycle. From a macroscopic perspective, the incompleteness of the structure makes the electrode film prone to cracks after a certain number of cycles, and excessive membrane expansion easily causes the electrode film to pulverize and the active material to fall off the current collector, all of which have a very adverse effect on the cycle life. In addition, the silicon negative electrode material is exposed to the electrolyte environment for a long time, and the substances produced by the decomposition of the electrolyte in the electrolyte are easily deposited on the surface of Si. The huge volume change during the cycle causes the SEI on the surface to be repeatedly destroyed and formed. The continuous vicious cycle greatly reduces the efficiency of Si, which is not conducive to Si exerting excellent electrochemical properties. Finally, as a semiconductor material, Si's poor electronic conductivity and ionic conductivity also severely limit its ability to exhibit good rate performance. Summary of the Invention

[0003] Based on the technical problems existing in the background technology, the present invention proposes a Si@C@g-C3N4 material and its preparation method and application. The Si@C@g-C3N4 material of the present invention can alleviate the volume expansion of silicon. When used as a lithium-ion negative electrode material, it can exhibit good rate performance and cycle performance.

[0004] The present invention proposes a Si@C@g-C3N4 material, in which a carbon layer is coated on the surface of nano-silicon, which is Si@C particles; a porous g-C3N4 layer is coated on the surface of the Si@C particles, and some Si@C particles are distributed in the pores of the g-C3N4 layer.

[0005] Preferably, the particle size of the nano-silicon is 50-200 nm.

[0006] Preferably, the particle size of the Si@C particles is 1-5 μm.

[0007] Preferably, the thickness of the porous g-C3N4 layer is 5-20 nm.

[0008] The above-mentioned carbon layer is an amorphous carbon layer.

[0009] The present invention also proposes a method for preparing the above-mentioned Si@C@g-C3N4 material, comprising the following steps: uniformly mixing Si@C particles, a first solvent, and urea, heating and stirring to remove the first solvent, and calcining to obtain the Si@C@g-C3N4 material.

[0010] Preferably, the first solvent is ethanol.

[0011] Preferably, the weight ratio of Si@C particles to urea is 10:0.1-0.9.

[0012] Preferably, after stirring at room temperature for 30-60 min, the temperature is raised to 60-80° C. and heated with stirring until the solvent is removed.

[0013] Preferably, calcination is carried out in an inert gas atmosphere.

[0014] Preferably, the calcination is carried out at 500-600° C. for 50-70 min.

[0015] Preferably, the temperature is increased to 500-600°C at a rate of 5-10°C / min.

[0016] Preferably, nano-silicon is mixed with a carbon source and a second solvent, spray-dried, carbonized, and crushed to obtain Si@C particles.

[0017] Preferably, the weight ratio of nano-silicon to carbon source is 1:0.5-1.

[0018] Preferably, the carbon source is medium-temperature asphalt.

[0019] Preferably, the second solvent is an ethanol aqueous solution.

[0020] Preferably, the volume ratio of ethanol to water is 1:1.5-2.5.

[0021] Preferably, the carbonization is carried out in an inert gas atmosphere.

[0022] The above-mentioned inert gases are all argon.

[0023] Preferably, carbonization is performed at 800-900° C. for 2-4 hours, followed by cooling to 250-350° C. at a rate of 5-10° C. / min, and then naturally cooling to room temperature.

[0024] The present invention also proposes the application of the above-mentioned Si@C@g-C3N4 material in negative electrode materials.

[0025] The present invention mixes nano-silicon with a carbon source, coats an amorphous carbon layer on the surface of the nano-silicon through spray drying and high-temperature carbonization, then mixes the nano-silicon with urea, and coats the surface of Si@C particles with a porous g-C3N4 layer (graphene-phase carbon nitride) through heating, stirring and calcination. Some Si@C particles are embedded in the pores of the g-C3N4 layer. This specific microstructure can make the Si@C@g-C3N4 material uniformly dispersed, alleviate the volume expansion of silicon, and reduce the problem of active material and electrode crushing. When used as a lithium ion negative electrode material, it can exhibit relatively stable rate performance and cycle performance. DETAILED DESCRIPTION

[0026] Hereinafter, the technical solutions of the present invention will be described in detail through specific embodiments. However, it should be clearly stated that these embodiments are provided for illustration only and are not to be construed as limiting the scope of the present invention.

[0027] Example 1

[0028] A method for preparing Si@C@g-C3N4 material comprises the following steps:

[0029] Industrial nano-silicon with a particle size of 100 nm (D50) and medium-temperature asphalt were mixed in a weight ratio of 1:1, and then an ethanol-water solution (ethanol to water volume ratio of 1:2) was added. The mixture was stirred for 1 hour to form a uniform slurry, which was then spray-dried and transferred to a tube furnace protected by high-purity argon. The mixture was kept at 800°C for 4 hours, then cooled to 300°C at a rate of 5°C / min, and naturally cooled to room temperature. The mixture was ground and sieved to obtain Si@C particles with a particle size of 3 μm (D50).

[0030] 10 g of Si@C particles were added to 50 ml of ethanol and ultrasonically stirred for 60 minutes to uniformly disperse them. Then 0.1 g of urea was added and stirred at room temperature for 60 minutes. Then, the mixture was stirred at 80°C until the ethanol was completely evaporated and removed. The mixture was then placed in an alumina crucible with a lid and heated to 550°C at a rate of 5°C / min in a tube furnace under an argon atmosphere. The mixture was kept at 550°C for 60 minutes to obtain Si@C@g-C3N4 material.

[0031] After testing, the above-mentioned Si@C@g-C3N4 material is composed of Si@C particles coated with an amorphous carbon layer on the surface of nano-silicon; a porous g-C3N4 layer is coated on the surface of the Si@C particles, and some Si@C particles are distributed in the gaps of the g-C3N4 layer. The thickness of the porous g-C3N4 layer is 12nm.

[0032] Example 2

[0033] A method for preparing Si@C@g-C3N4 material comprises the following steps:

[0034] Industrial nano-silicon with a particle size of 50 nm (D50) and medium-temperature asphalt were mixed in a weight ratio of 1:0.5, and then an ethanol-water solution (ethanol to water volume ratio of 1:2) was added and stirred for 1 hour to form a uniform slurry. The slurry was then spray-dried and transferred to a tube furnace protected by high-purity argon. The slurry was kept at 850°C for 3.5 hours, then cooled to 350°C at a rate of 6°C / min, and naturally cooled to room temperature. The slurry was ground and sieved to obtain Si@C particles with a particle size of 1.5 μm (D50).

[0035] 10 g of Si@C particles were added to 50 ml of ethanol and ultrasonically stirred for 60 minutes to uniformly disperse them. Then 0.5 g of urea was added and stirred at room temperature for 60 minutes. Then, the mixture was stirred at 60°C until the ethanol was completely evaporated and removed. The particles were then placed in an alumina crucible with a lid and heated to 600°C at a rate of 6°C / min in a tube furnace under an argon atmosphere. The particles were kept at 600°C for 50 minutes to obtain Si@C@g-C3N4 material.

[0036] Example 3

[0037] A method for preparing Si@C@g-C3N4 material comprises the following steps:

[0038] Industrial nano-silicon with a particle size of 70 nm (D50) and medium-temperature asphalt were mixed in a weight ratio of 1:1, and then an ethanol-water solution (ethanol to water volume ratio of 1:2) was added and stirred for 1 hour to form a uniform slurry. The slurry was then spray-dried and transferred to a tube furnace protected by high-purity argon gas, kept at 900°C for 4 hours, and then cooled to 250°C at a rate of 5°C / min. The slurry was naturally cooled to room temperature and ground and sieved to obtain Si@C particles with a particle size of 5 μm (D50).

[0039] 10 g of Si@C particles were added to 50 ml of ethanol and ultrasonically stirred for 60 minutes to uniformly disperse them. Then 0.9 g of urea was added and stirred at room temperature for 60 minutes. Then, the mixture was stirred at 70°C until the ethanol was completely evaporated and removed. The particles were then placed in an alumina crucible with a lid and heated to 500°C at a rate of 5°C / min in a tube furnace under an argon atmosphere. The particles were kept at 500°C for 70 minutes to obtain Si@C@g-C3N4 material.

[0040] Comparative Example 1

[0041] Industrial nano-silicon with a particle size D50 of 100nm.

[0042] Comparative Example 2

[0043] Take the Si@C particles prepared in Example 1.

[0044] Comparative Example 3

[0045] A method for preparing Si@g-C3N4 material comprises the following steps:

[0046] The “Si@C particles” were replaced with “industrial nano-silicon with a particle size D50 of 100 nm”, and the rest were the same as in Example 1.

[0047] The materials prepared in Examples 1-3 and Comparative Examples 1-3 were respectively used as negative electrode materials, and the negative electrode material, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were stirred and mixed in a weight ratio of 80:10:10, wherein the PVDF was dissolved with an appropriate amount of N-methylpyrrolidone to obtain a negative electrode slurry; the negative electrode slurry was evenly coated on a pre-punched copper foil, baked in a vacuum drying oven at 110° C. for 12 h, and weighed. It was used as the positive electrode of a simulated battery, the metal lithium sheet was used as the negative electrode, the separator was Celgard 2400, the electrolyte was 1 mol / L LiPF6 (the solvent was EC:DMC=1:1 v / v), and the battery was assembled into a button cell CR 2016 in a deoxygenated and dehydrated glove box filled with argon.

[0048] Each set of button cells was tested for capacity, initial efficiency, and cycling performance at 3C / 1C, 2C / 1C, and 1C / 1C cycles. The results are shown in Table 1.

[0049] Table 1 Test results

[0050]

[0051]

[0052] It can be seen from Table 1 that the Si@g-C3N4 material of the present invention has good rate performance and cycle performance.

[0053] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A Si@C@g-C3N4 material, characterized in that: The surface of nano-silicon is coated with a carbon layer, which is Si@C particles; the surface of Si@C particles is coated with a porous g-C3N4 layer, and some Si@C particles are distributed in the pores of the g-C3N4 layer.

2. The Si@C@g-C3N4 material according to claim 1, characterized in that The particle size of the nano-silicon is 50-200 nm; preferably, the particle size of the Si@C particles is 1-5 μm; preferably, the thickness of the porous g-C 3 N 4 layer is 5-20 nm.

3. A method for preparing the Si@C@g-C3N4 material according to claim 1 or 2, characterized in that: The method comprises the following steps: uniformly mixing Si@C particles, a first solvent and urea, removing the first solvent by heating and stirring, and calcining to obtain Si@C@g-C3N4 material.

4. The method for preparing the Si@C@g-C3N4 material according to claim 3, characterized in that: The first solvent is ethanol.

5. The method for preparing the Si@C@g-C3N4 material according to claim 3 or 4, characterized in that: The weight ratio of Si@C particles to urea is 10:0.1-0.

9.

6. The method for preparing the Si@C@g-C3N4 material according to any one of claims 3 to 5, characterized in that: After stirring at room temperature for 30-60 min, the temperature was raised to 60-80°C and heated with stirring until the solvent was removed.

7. The method for preparing the Si@C@g-C3N4 material according to any one of claims 3 to 6, characterized in that: Calcination is carried out in an inert gas atmosphere; preferably, calcination is carried out at 500-600° C. for 50-70 min; preferably, the temperature is increased to 500-600° C. at a rate of 5-10° C. / min.

8. The method for preparing the Si@C@g-C3N4 material according to any one of claims 3 to 7, characterized in that: The nano-silicon is mixed with a carbon source and a second solvent, spray-dried, carbonized, and crushed to obtain Si@C particles.

9. The method for preparing the Si@C@g-C3N4 material according to claim 8, characterized in that: The weight ratio of nano-silicon to carbon source is 1:0.5-1; preferably, the carbon source is medium-temperature asphalt; preferably, the second solvent is an ethanol-water solution; preferably, the volume ratio of ethanol to water is 1:1.5-2.5; preferably, carbonization is carried out in an inert gas atmosphere; preferably, carbonization is carried out at 800-900°C for 2-4h, then cooled to 250-350°C at a rate of 5-10°C / min, and naturally cooled to room temperature.

10. Use of the Si@C@g-C3N4 material according to claim 1 or 2 in anode materials.

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