CN113594461B

CN113594461B - Carbon-silicon composite material and preparation method and application thereof

Info

Publication number: CN113594461B
Application number: CN202110846456.XA
Authority: CN
Inventors: 梁慧宇; 沈肖楠
Original assignee: Changzhou Enyuangu New Material Technology Co ltd
Current assignee: Changzhou Enyuangu New Material Technology Co ltd
Priority date: 2021-07-26
Filing date: 2021-07-26
Publication date: 2022-05-31
Anticipated expiration: 2041-07-26
Also published as: CN113594461A

Abstract

The embodiment of the invention discloses a preparation method of a carbon-silicon composite material, which comprises the steps of uniformly dispersing alkyl borane, nano-scale silicon powder and graphene, carrying out hydrothermal reaction at 100-200 ℃, drying a product, carbonizing the hydrothermal reaction product by using mixed gas of NH3 and inert gas, and introducing an inert gas-loaded conductive polymer monomer for reaction to obtain the carbon-silicon composite material. The composite material has a core-shell structure, the inner core is an aggregation forming body of nano-scale silicon powder, the inner core is doped with B element, and the shell is doped with N element and B element. According to the invention, boron is doped on the core nanoscale silicon powder in a hydrothermal mode to form a porous structure, so that the expansion of silicon in the charging and discharging processes can be reduced, the boron doping has the advantages of high uniformity, high consistency and the like, the specific capacity and the electronic conductivity of the material are improved, and a certain amount of boron and nitrogen are doped in the shell layer, so that the specific volume and the impedance of the composite material are improved.

Description

Carbon-silicon composite material and preparation method and application thereof

Technical Field

The invention belongs to the field of lithium ion batteries, and particularly relates to a carbon-silicon composite material as well as a preparation method and application thereof.

Background

The silicon carbon material is the preferred material of the high-energy-density cathode material due to the advantages of high energy density, wide source and the like, but the silicon carbon material has the defects of high expansion, even up to 200 percent, low conductivity and the like, so that the quick charge and low temperature performance of the silicon carbon material are influenced, and the application of the silicon carbon material is limited.

Under the same anode material, namely under the same N/P condition, the specific capacity of the cathode material is improved, on one hand, the surface density of the cathode pole piece can be reduced, the quick charging performance of the cathode pole piece is improved, and on the other hand, less silicon carbon material can be added under the high cathode specific capacity, so that the full-electricity expansion of the cathode pole piece can be reduced. Therefore, the silicon-carbon material is modified, the high-capacity and low-impedance silicon-carbon material is developed, the addition amount can be reduced, the expansion can be reduced, and the quick-charging and low-temperature performances can be improved.

In the prior art, different elements are doped into the silicon-carbon material to modify the silicon-carbon material, but the doping is generally completed by simple mixing, so that the silicon-carbon material is poorer in consistency and limited in performance improvement.

Disclosure of Invention

In order to solve the problems of low specific capacity and high impedance of silicon carbon materials in the prior art, the invention provides a carbon-silicon composite material, which is modified, and specific elements are doped in a special reaction mode, so that the specific capacity is greatly improved, the impedance is reduced, and a battery cathode material with excellent performance is obtained.

In order to achieve the technical purpose, the technical scheme adopted by the invention is as follows:

the technical purpose of the first aspect of the invention is to provide a preparation method of a carbon-silicon composite material, which comprises the following steps: adding alkyl borane, nano-scale silicon powder and graphene into an organic solvent, uniformly dispersing, carrying out hydrothermal reaction at 100-200 ℃, drying the product, and adding NH₃And carbonizing the hydrothermal reaction product and doping N into the hydrothermal reaction product by using mixed gas of inert gas, and introducing an inert gas-loaded conductive polymer monomer for reaction to obtain the composite material.

Further, the alkyl borane is selected from one of triphenylboron, diphenyl chloroborane, tetramethyl diboron and ferrocenyl dibromoborane; the weight ratio of the alkyl borane to the nano-silicon powder to the graphene is (1-10) to (1-3) 100.

Furthermore, the time of the hydrothermal reaction is 1-12 hours, and the pressure is 1-5 Mpa.

Further, NH₃The volume ratio of the inert gas to the mixed gas is (1-5): 10, and the flow rate of the mixed gas is 1-10 mL/min.

Further, the conductive polymer monomer is selected from at least one of aniline, thiophene and pyrrole. The volume ratio of the inert gas to the conductive polymer monomer is 10 (1-5), and the heat is preserved for 1-6 hours. Wherein the volume of the monomer of the conductive polymer is based on the volume of the conductive polymer after gasification under the reaction condition of carbonization.

Further, the specific operating conditions of carbonization and N doping are as follows: heating to 700-1000 ℃ at a heating rate of 1-5 ℃/min and keeping the temperature for 1-12 hours.

Further, the product after the hydrothermal reaction is frozen and dried at low temperature in vacuum to obtain a solid, and the specific conditions are as follows: the temperature is-60 ℃ to-20 ℃, the vacuum degree of the drying chamber is 0Pa to 100Pa, and the vacuum freeze drying time is 1 h to 48 h.

Further, the dispersion medium of the alkyl borane, the nano-scale silicon powder and the graphene is selected from at least one of carbon tetrachloride, N-methyl pyrrolidone, tetrahydrofuran and cyclohexane, wherein the mass concentration of the graphene is 0.08-1 wt%, and preferably 0.08-0.5 wt%.

As one specific embodiment, the carbon-silicon composite material is prepared by the following steps:

dispersing at least one alkyl borane selected from triphenylboron, diphenyl chloroborane, tetramethyl diboron and ferrocenyl dibromoborane, nano-silicon powder and graphene in an organic solvent according to the weight ratio of (1-10): 100, (1-3), carrying out hydrothermal reaction at 100-200 ℃ and under the pressure of 1-5 Mpa for 1-12 h, and carrying out vacuum freeze drying on the product to obtain a solid product;

introducing NH into the solid product₃Heating the mixed gas and inert gas in a volume ratio of (1-5) to 10 to 700-1000 ℃ at a heating rate of 1-5 ℃/min, and preserving the heat for 1-12 hours;

and keeping the temperature, switching the conductive polymer monomer loaded by inert gas to be introduced into the solid product, and keeping the temperature for 1-6 hours to obtain the composite material.

The technical purpose of the second aspect of the invention is to provide the carbon-silicon composite material prepared by the method.

The carbon-silicon composite material prepared by the method has a core-shell structure, the inner core is an aggregated formed body of nano-scale silicon powder, the inner core is doped with B element, and the outer shell is doped with N element and B element. The thickness of the shell layer of the material prepared by the method is 5-500 nm, preferably 10-100 nm; the thickness ratio of the inner core to the outer shell is 100 (5-20). The doping amount of the B element accounts for 0.5-5 percent of the total weight of the composite material, preferably 1-3 percent; the doping amount of the N element accounts for 0.5-5%, preferably 1-3%.

The technical purpose of the third aspect of the invention is to provide the application of the carbon-silicon composite material as a battery negative electrode material.

The carbon-silicon composite material of the invention is formed by doping N, B elements with carbon and silicon, and has higher specific volume and lower crater resistance.

The embodiment of the invention has the following beneficial effects:

(1) the carbon-silicon material prepared by the invention has a core-shell structure, the core nano-scale silicon powder is doped with boron, and the shell layer is doped with a certain amount of boron and nitrogen, so that the specific volume of the composite material is improved and the impedance is reduced.

(2) In the preparation process of the composite material, under the hydrothermal reaction condition, the hydrocarbyl borane has boron and carbon free radicals, is more easily combined with the nano-scale silicon powder structure, and forms a porous structure, so that the composite material has the advantages of high doping uniformity, high consistency and the like, the porous structure formed by the nano-scale silicon powder can reduce the self expansion in the charging and discharging process, and the uniform and high-consistency doping of boron improves the specific capacity and the electronic conductivity of the material; the doping of nitrogen and boron in the outer layer forms lattice defects in the carbon layer, so that the electron cloud fluidity can be improved, the anti-lithium storage reaction barrier can be reduced, the lithium storage binding sites can be increased, the interlayer spacing of graphite carbon can be increased, the lithium ion migration speed can be greatly improved, and the impedance can be reduced.

(3) The preparation process is simple and easy to operate, complex carrier ball milling and etching treatment processes are not needed, and the nano-scale silicon powder of the nuclear layer forms a porous structure through the selection of a boron source and the doping process of hydrothermal treatment, so that the full-electricity expansion of the composite material is reduced.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Wherein:

FIG. 1 is a flow chart of the preparation steps for examples 1-3;

fig. 2 SEM image of carbon silicon composite material prepared in example 1.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In examples 1-3, a carbon-silicon composite material was prepared according to the procedure shown in fig. 1, as follows:

example 1

S1: uniformly mixing 5g of triphenylboron with 100g of nano-scale silicon powder with the average particle size of 100nm, adding the mixture into 200mL of carbon tetrachloride solution with the graphene mass concentration of 1 wt%, then adding 1000mL of carbon tetrachloride organic flux, and performing ultrasonic dispersion uniformly. Performing hydrothermal reaction on the mixture at 160 ℃, 3Mpa and 6h, filtering, and performing vacuum freeze drying at-40 ℃ and 10pa for 24h to obtain a product, namely E1;

s2: the above product was transferred to a tube furnace, after which NH was introduced₃/Ar (volume ratio of3: 10) controlling the flow of the mixed gas to be 5mL/min, heating the tube furnace to 800 ℃ at the heating rate of 3 ℃/min, and preserving the temperature for 6 hours;

s3: stopping NH introduction₃Introducing Ar loaded and gasified aniline monomer (the volume ratio is 10: 3) as reaction gas, keeping the temperature for 3 hours, stopping introducing the reaction gas, and cooling to room temperature to obtain the silicon-carbon composite material.

Example 2

S1: 1g of diphenyl chloroborane and 100g of the same nano-scale silicon powder in the example 1 are uniformly mixed, added into 200mL of N-methyl pyrrolidone solution with the graphene mass concentration of 0.5 wt%, and then 1000mL of N-methyl pyrrolidone organic flux is added, and uniformly dispersed by ultrasonic. Performing hydrothermal reaction on the mixture at 100 ℃ and 1Mpa for 12h, filtering, and performing vacuum freeze drying at-20 ℃ and a vacuum degree of 100pa for 48h at a low temperature to obtain a product, which is marked as E2;

s2: the above product was transferred to a tube furnace, after which NH was introduced₃Controlling the flow rate of mixed gas/Ar (the volume ratio is 1: 10) to be 1mL/min, heating the tube furnace to 700 ℃ at the heating rate of 1 ℃/min, and preserving the temperature for 12 hours;

s3: stop to supply NH₃Introducing Ar loaded and gasified thiophene monomer (the volume ratio is 10: 1) as reaction gas, keeping the temperature for 1 hour, stopping introducing the reaction gas, and cooling to room temperature to obtain the silicon-carbon composite material.

Example 3

S1: uniformly mixing 10g of ferrocenyl dibromoborane with 100g of nano-scale silicon powder, adding the mixture into 60mL of tetrahydrofuran solution with the graphene mass concentration of 5 wt%, then adding 1000mL of tetrahydrofuran organic flux, and performing ultrasonic dispersion uniformly. Performing hydrothermal reaction on the mixture at 200 ℃, 5Mpa and 12h, filtering, and performing vacuum freeze drying at-60 ℃ and 10pa for 48h at low temperature to obtain a product, namely E3;

s2: the above product was transferred to a tube furnace, after which NH was introduced₃The flow rate of the mixed gas/Ar (volume ratio of 5: 10) is controlled to be 10mL/min, and the tube is heated at a heating rate of 5 ℃/minHeating to 1000 deg.C and maintaining for 1 hr;

s3: stopping NH introduction₃And introducing Ar loaded and gasified pyrrole monomer (the volume ratio is 10: 5) as reaction gas, keeping the temperature for 6 hours, stopping introducing the reaction gas, and cooling to room temperature to obtain the silicon-carbon composite material.

Comparative example 1

Adding 100g of nanoscale silicon powder same as that in example 1 into 1000mL of tetrahydrofuran solution, transferring the mixture into a ball mill, carrying out ball milling for 48h, drying the mixture at 60 ℃ for 48h to obtain a product F1, transferring the product F1 into a tube furnace, passing methane gas through the tube furnace under an inert atmosphere, heating the tube furnace to 800 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 1 h, stopping introducing carbon source gas, introducing argon gas, and naturally cooling to room temperature to obtain the silicon-carbon composite material.

Comparative example 2

The same procedure as in example 1 was repeated except that 5g of triphenylboron was replaced with 5g of boron oxide in S1. The product obtained in S1 was designated F2.

Comparative example 3

After 5g of boron oxide, 100g of the same nanoscale silicon powder as in example 1 and 2g of graphene were mixed uniformly, the mixture was granulated to obtain a product, denoted as F3. The subsequent operations were the same as those of S2 and S3 of example 1.

Performance testing of the materials prepared in the above examples and comparative examples:

(1) SEM test

The composite material prepared in S3 of example 1 was subjected to SEM test, and the test results are shown in fig. 2.

It can be seen that the composite material prepared in example 1 has uniform particle size distribution, the particle size of the particles is between 5 and 10 μm, and a small number of pore structures are formed among the materials.

(2) Determination of pore volume and specific surface area of intermediate product

The intermediates E1, E2, E3, F1, F2 and F3 prepared in the examples and comparative examples were subjected to pore volume and specific surface area measurements: the test equipment adopts a specific surface area tester, the test method is carried out according to GBT _245332009 graphite cathode materials of lithium ion batteries, and the results are shown in Table 1.

Table 1.

As can be seen from the data in Table 1, the doping manner of B in examples 1-3 can form a porous structure on the silicon surface, increase the pore volume and the specific surface area, and have an advantage in reducing the full-electric expansion rate of the composite material.

(3) Button cell test

The composites of the examples and comparative examples were assembled into button cells a1, a2, A3, B1, B2, and B3, respectively. The assembling method comprises the following steps: and adding a binder, a conductive agent and a solvent into the negative electrode material, stirring and pulping, coating the mixture on copper foil, and drying and rolling to obtain the negative electrode plate. The binder used was LA132 binder, the conductive agent was conductive carbon black SP, the negative electrode material was the composite material in examples and comparative examples, respectively, and the solvent was N-methylpyrrolidone (NMP). The proportion of each component is as follows: and (3) anode material: SP: LA 132: NMP 95 g: 1 g: 4 g: 220 mL; the electrolyte is LiPF₆/EC+DEC(LiPF₆The concentration of (b) is 1.3mol/L, the volume ratio of EC to DEC is 1:1), a metal lithium sheet is used as a counter electrode, and a polypropylene (PP) film is used as a diaphragm. The button cell is assembled in a glove box filled with argon, and the electrochemical performance test is carried out on a Wuhan blue CT2001A type battery tester, wherein the charging and discharging voltage range is 0.005V-2.0V, and the charging and discharging multiplying power is 0.1C. According to the standard test of GBT-245319 graphite cathode materials of lithium ion batteries, the test results are shown in Table 2.

TABLE 2

As can be seen from the data in Table 2, the specific capacity and the first efficiency of the silicon-carbon composite negative electrode material prepared in the embodiments 1-3 of the invention are obviously superior to those of the comparative example after the material is prepared into a battery. The core material of the negative electrode material is prepared by a hydrothermal method, and the porous nano silicon structure is obtained by doping boron, so that on one hand, the specific capacity and the electronic conductivity of the material can be improved by doping boron, and on the other hand, the expansion of nano silicon in the charge-discharge process can be reduced by the porous structure, thereby improving the first efficiency and the specific capacity of the material. Meanwhile, the hydro-thermal doping by using the alkyl borane has the advantages of high doping uniformity and good consistency, the structural stability of the composite material is improved, and the gram volume performance of the material is further improved.

(4) Pouch cell testing

And (3) taking the composite materials in the examples and the comparative examples as negative electrode materials to prepare the negative electrode piece. With ternary material (Li (Ni)_0.6Co_0.2Mn_0.2)O₂) As the positive electrode, LiPF₆Solution (solvent EC + DEC, volume ratio 1:1, LiPF)₆Concentration of 1.3mol/L) is electrolyte, celegard2400 is a diaphragm, and 5Ah soft package batteries C1, C2, C3, D1, D2 and D3 are respectively prepared.

Testing liquid suction capacity and liquid retention rate

Liquid absorption capacity: and (3) adopting a 1mL burette, sucking the electrolyte VmL, dripping a drop on the surface of the pole piece, timing until the electrolyte is completely absorbed, recording the time t, and calculating the liquid absorption speed V/t of the pole piece. The test results are shown in table 3.

And (4) testing the liquid retention rate: calculating the theoretical liquid absorption amount m of the pole piece according to the pole piece parameters₁Weighing the weight m of the pole piece₂Then, the pole piece is placed in electrolyte to be soaked for 24 hours, and the weight of the pole piece is weighed to be m₃Calculating the amount m of the pole piece liquid absorption₃-m₂And is calculated according to the following formula: retention rate ═ m₃-m₂)*100％/m₁. The test results are shown in table 3.

TABLE 3

As can be seen from Table 3, the liquid absorbing and retaining capabilities of the silicon-carbon composite negative electrode materials obtained in examples 1-3 are significantly higher than those of the comparative examples. Experimental results show that the silicon-carbon composite negative electrode material provided by the invention has high liquid absorption and retention capacity. The silicon-carbon composite negative electrode material provided by the invention is of a porous structure, has a high specific surface area, and improves the liquid absorption and retention capacity of the material.

Second, testing the resistivity and rebound rate of the pole piece

Testing the resistivity of the pole piece: the resistivity of the pole piece was measured using a resistivity tester and the results are shown in table 4.

Testing the rebound rate of the pole piece: firstly, testing the average thickness of the pole piece to be D1 by using a thickness gauge, then placing the pole piece in a vacuum drying oven at 80 ℃ for drying for 48h, testing the thickness of the pole piece to be D2, and calculating according to the following formula: rebound resilience (D2-D1) 100%/D1. The test results are shown in table 4.

TABLE 4

As can be seen from the data in table 4, the negative electrode plate prepared by using the silicon-carbon composite negative electrode materials obtained in examples 1 to 3 has a significantly lower rebound ratio than the comparative example, that is, the negative electrode plate prepared by using the silicon-carbon composite negative electrode material of the present invention has a lower rebound ratio. The charge density of the material is improved by expansion and the resistivity of the pole piece is reduced by adding the alkyl borane into the material and forming a net structure with the nano silicon, and meanwhile, the surface coating layer in the material is doped with nitrogen elements to reduce the impedance and be beneficial to improving the electronic conductivity of the material, so that the resistivity of the pole piece is reduced.

Thirdly, testing the cycle performance

The cycle performance of the battery is tested at the temperature of 25 +/-3 ℃ with the charge-discharge multiplying power of 1C/1C and the voltage range of 2.8V-4.2V. The test results are shown in table 5.

TABLE 5

As can be seen from Table 5, the cycle performance of the battery prepared by the silicon-carbon composite anode material provided by the invention is obviously better than that of the comparative example. The electrode plate prepared from the silicon-carbon composite negative electrode material provided by the invention has a lower expansion rate, the structure of the electrode plate is more stable in the charging and discharging processes, and the cycle performance of the electrode plate is improved. In addition, the silicon-carbon composite negative electrode material has the characteristic of high lithium ion content, provides sufficient lithium ions in the charging and discharging process, and further improves the cycle performance of the battery.

The above disclosure is only for the purpose of illustrating the preferred embodiments of the present invention, and it is therefore to be understood that the invention is not limited by the scope of the appended claims.

Claims

1. A preparation method of a carbon-silicon composite material comprises the following steps:

adding alkyl borane, nano-scale silicon powder and graphene into an organic solvent, uniformly dispersing, carrying out hydrothermal reaction at 100-200 ℃, drying the product, and adding NH₃And carbonizing the hydrothermal reaction product and doping N into the hydrothermal reaction product by using mixed gas of inert gas, and introducing an inert gas-loaded conductive polymer monomer for reaction to obtain the composite material.

2. The production method according to claim 1, wherein the hydrocarbylborane is at least one member selected from the group consisting of triphenylboron, diphenylchloroborane, tetramethyldiboron and ferrocenyldibromoborane.

3. The preparation method according to claim 1, wherein the weight ratio of the alkyl borane to the nano-silicon powder to the graphene is 1-10: 100: 1-3.

4. The preparation method according to claim 1, wherein the hydrothermal reaction time is 1-12 h, and the pressure is 1-5 MPa.

5. The method of claim 1, wherein NH is₃The volume ratio of the inert gas to the mixed gas of the inert gas and the mixed gas is 1-5: 10, and NH is added₃The flow rate of the mixed gas with the inert gas is controlled to be 1-10 mL/min.

6. The production method according to claim 1, wherein the conductive polymer monomer is at least one selected from aniline, thiophene, and pyrrole.

7. The method according to claim 1, characterized in that the specific operating conditions of carbonization and N doping are: heating to 700-1000 ℃ at a heating rate of 1-5 ℃/min and preserving the heat for 1-12 hours.

8. The method of claim 1, comprising the steps of:

dispersing at least one alkyl borane selected from triphenylboron, diphenyl chloroborane, tetramethyl diboron and ferrocenyl dibromoborane, nano-scale silicon powder and graphene in an organic solvent according to the weight ratio of 1-10: 100: 1-3, carrying out hydrothermal reaction for 1-12 h at 100-200 ℃ and under the pressure of 1-5 Mpa, and carrying out vacuum freeze drying on the product to obtain a solid product;

introducing NH into the solid product₃Heating the mixed gas and inert gas in a volume ratio of 1-5: 10 to 700-1000 ℃ at a heating rate of 1-5 ℃/min, and preserving heat for 1-12 hours;

and keeping the temperature, switching a conductive polymer monomer loaded by inert gas to be introduced into the solid product, and keeping the temperature for 1-6 hours to obtain the composite material.

9. A carbon silicon composite material produced by the method of any one of claims 1 to 8.

10. Use of the carbon silicon composite material of claim 9 as a battery negative electrode material.