CN109004203B

CN109004203B - Silicon-carbon composite negative electrode material and preparation method thereof

Info

Publication number: CN109004203B
Application number: CN201810873056.6A
Authority: CN
Inventors: 万水田
Original assignee: INNER MONGOLIA SANXIN INDUSTRIAL CO LTD
Current assignee: INNER MONGOLIA SANXIN INDUSTRIAL CO LTD
Priority date: 2018-08-02
Filing date: 2018-08-02
Publication date: 2020-12-01
Anticipated expiration: 2038-08-02
Also published as: CN109004203A

Abstract

The invention relates to a silicon-carbon composite negative electrode material and a preparation method thereof, belonging to the technical field of lithium ion battery materials. The preparation method of the silicon-carbon composite negative electrode material comprises the following steps: uniformly mixing a silane coupling agent and a porous carbon material in an organic solvent, and then performing spray drying to prepare a modified porous carbon material; the modified porous carbon material is subjected to heat preservation for 1-6h at the temperature of 1000-1200 ℃ in the presence of silane gas; then cooling to 600-800 ℃, and preserving the heat for 1-6h in the presence of a gas dopant to prepare a silicon-carbon material; the gas dopant is NH₃、N₂O、NO、N₂O₄One or a combination of several of them; the silicon-carbon material is subjected to heat preservation for 1-12h at the temperature of 900 ℃ in the presence of carbon source gas to obtain the silicon-carbon material. The silicon-carbon composite negative electrode material prepared by the invention has the characteristics of high specific capacity, strong conductivity and good cycle performance, and can be applied to lithium ion batteries with high specific energy density.

Description

Silicon-carbon composite negative electrode material and preparation method thereof

Technical Field

The invention relates to a silicon-carbon composite negative electrode material and a preparation method thereof, belonging to the technical field of lithium ion battery materials.

Background

According to the development and planning of new energy vehicles in China, the new energy vehicle industry puts higher requirements on the energy density of lithium ion batteries. For lithium ion batteries, the negative electrode material is an important component of the lithium ion battery and also an important factor influencing the energy density of the battery. At present, graphite materials are mainly used as the anode materials on the market, but the improvement of the energy density of the lithium ion battery is limited by the lower gram capacity of the graphite materials. The silicon cathode material is paid attention by researchers due to the advantages of high gram capacity, abundant resources and the like, and is applied to the fields of high-specific energy density lithium ion batteries and the like. However, the high expansion rate and poor conductivity of the silicon negative electrode material have been factors that have restricted their wide use.

The main methods for reducing the expansion of silicon materials at present are as follows: 1) the carbon material is coated on the surface of the nano silicon material, so that the conductivity of the nano silicon material is improved, and the expansion rate of the nano silicon material is reduced; 2) preparing a porous template, and embedding a silicon material into the holes to reduce the expansion rate of the silicon material; or preparing porous silicon material to reduce its expansion; 3) the material with low expansion rate and strong conductivity, such as graphene, carbon nanotube and other materials, is coated to reduce the expansion rate of the silicon material and improve the conductivity of the silicon material. However, although the above scheme improves the expansion of the silicon-carbon negative electrode material to a certain extent, the effect is not obvious, for example, the coating is uneven and the coating layer is thick, the nano silicon is easy to agglomerate to cause poor uniformity, the coating layer has poor conductivity, and the like, so that the specific capacity of the silicon-carbon composite material cannot be fully exerted, and meanwhile, the cycle performance and the rate capability are poor, so that the silicon-carbon composite material is difficult to popularize in a market.

For example, the chinese patent application publication No. CN107275590A discloses a porous silicon-carbon composite material and a preparation method thereof, wherein the material is prepared by firstly performing mechanical ball milling and acid etching on an iron-silicon alloy to obtain porous silicon, mixing the porous silicon with an organic carbon source, and performing spray pelletizing and high-temperature carbonization. Although the capacity, the first efficiency and the cycle performance of the material are improved to a certain extent, the expansion rate of the material is still high, the electronic conductivity is deviated, and the thickness of a carbon coating layer is thick, so that the energy density exertion of the material is influenced.

The application publication number CN105355849A Chinese invention patent discloses a lithium battery cathode additive, which is in a core-shell structure, wherein the inner core is composed of nano silicon powder, a lithium powder compound and a hollow carbon sphere, the shell is mainly composed of a carbon nano tube, a surfactant and a doping agent, when in preparation, the nano silicon powder, the lithium powder compound and the hollow carbon sphere are firstly mixed uniformly to obtain a mixture A, the carbon nano tube and the surfactant are added into a solvent to be mixed uniformly to obtain a mixture B, then the mixture A and the mixture B are mixed uniformly and then are subjected to heat treatment at the temperature of 300-. The material is doped with more other components, so that the specific capacity of the silicon material is limited.

Disclosure of Invention

The invention aims to provide a preparation method of a silicon-carbon composite negative electrode material, which is used for improving the specific capacity of the silicon-carbon material.

The invention also aims to provide the silicon-carbon composite negative electrode material prepared by the method.

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

a preparation method of a silicon-carbon composite negative electrode material comprises the following steps:

1) uniformly mixing a silane coupling agent and a porous carbon material in an organic solvent, and then performing spray drying to prepare a modified porous carbon material;

2) the modified porous carbon material is subjected to heat preservation for 1-6h at the temperature of 1000-1200 ℃ in the presence of silane gas; then cooling to 600-800 ℃, and preserving the heat for 1-6h in the presence of a gas dopant to prepare a silicon-carbon material; the gas dopant is NH₃、N₂O、NO、N₂O₄One or a combination of several of them;

3) the silicon-carbon material is subjected to heat preservation for 1-12h at the temperature of 900 ℃ in the presence of carbon source gas to obtain the silicon-carbon material.

The preparation method comprises the steps of firstly soaking the porous carbon-based material in a silane coupling agent, drying, introducing silane gas and dopant gas to carry out primary deposition of silicon, then depositing on the surface of the porous carbon-based material by a vapor deposition method to generate carbon nano tubes for secondary deposition, and preparing the silicon-carbon composite material. The silane is cracked and deposited in the holes of the porous carbon-based material by using the vapor deposition method to reduce the expansion of silicon in the charging and discharging processes, meanwhile, the outer-layer carbon nano tube has the advantages of high mechanical strength, high conductivity and the like, and the vapor deposition method has the advantages of uniform doping, high consistency and the like, so that the finally prepared silicon-carbon composite negative electrode material has the characteristics of high specific capacity, high conductivity and good cycle performance, and can be applied to the lithium ion battery with high specific energy density.

In the step 1), the mass ratio of the silane coupling agent to the porous carbon material to the organic solvent is (0.1-1): (1-5): 100.

in the step 1), the silane coupling agent is one or a combination of more of gamma-aminopropyltriethoxysilane, gamma- (2, 3-epoxypropoxy) propyltrimethoxysilane, gamma- (methacryloyloxy) propyltrimethoxysilane, octyltriethoxysilane and dimethyldimethoxysilane.

In the step 1), the organic solvent is one or a combination of several of N-N-dimethylformamide, N-N-dimethylacetamide, N-N-diethylacetamide, N-methyl-2-pyrrolidone, gamma-butyrolactone and dimethyl sulfoxide.

The silane gas in the step 2) is monosilane (SiH)₄) Disilane (Si)₂H₆) One or a combination of both.

The carbon source gas in the step 3) is one or a combination of several of methane, acetylene, ethane and ethylene.

The silane coupling agent and the porous carbon material are uniformly mixed in the organic solvent, namely the silane coupling agent and the organic solvent are uniformly mixed, and then the porous carbon material is added and uniformly mixed.

In the step 2), the existence condition of the silane gas is that in a closed space, inert gas is firstly used for emptying, and then silane gas is introduced.

In the step 2), in the presence of a gas dopant, after heat preservation is carried out for 1-6h, the introduction of the gas dopant is stopped, and inert gas is introduced. And then cooling to room temperature, and crushing to obtain the silicon-carbon material.

And 3) the carbon source gas exists in the step 3) under the condition that the carbon source gas is firstly evacuated by inert gas and then introduced into the closed space.

And 3) after the temperature is maintained for 1-12h at the temperature of 700-900 ℃, stopping introducing the carbon source gas and introducing the inert gas. Then cooling to room temperature.

The porous carbon material is prepared by adopting a method comprising the following steps: performing crosslinking reaction on the oxidized asphalt, carbon disulfide, aluminum chloride and carbon tetrachloride at the temperature of 80-100 ℃, and performing solid-liquid separation to obtain a precursor; sintering the precursor for 1-3h at 1000-1200 ℃ in an inert atmosphere to obtain the porous carbon material.

The time of the crosslinking reaction is 1.5-2 h.

50-150g of oxidised bitumen is used per 1L of carbon disulphide.

1-5g of aluminium chloride is used per 50-150g of oxidised bitumen.

10-15g of carbon tetrachloride is used per 50-150g of the oxidized asphalt.

The crosslinking reaction of asphalt oxide, carbon disulfide, aluminum chloride and carbon tetrachloride at 80-100 deg.c is carried out by mixing asphalt oxide and carbon disulfide, heating to 80-100 deg.c and adding aluminum chloride and carbon tetrachloride for crosslinking reaction.

The oxidized asphalt and the carbon disulfide are evenly mixed and stirred at the rotating speed of 50-200 rpm. Stirring for 30 min.

Sintering at 1000-1200 ℃ for 1-3h, cooling, crushing and screening to obtain the porous carbon material. And cooling to room temperature.

The silicon-carbon composite negative electrode material prepared by the method is of a core-shell structure, the core is a nano silicon/porous carbon composite material, and the shell is a carbon nano tube. In the silicon-carbon composite negative electrode material, the mass percentage of silicon is 1-30%.

The invention has the beneficial effects that:

aiming at the problems of high expansion rate, small tap density, poor conductivity and the like of silicon-carbon cathode materials in the prior art, the silicon material is deposited inside the porous carbon material by a vapor deposition method, the carbon nano tube is deposited on the outer layer of the porous carbon material, and the silicon-carbon composite cathode material with low expansion rate, high consistency, good conductivity and high tap density is prepared by two times of deposition. According to the invention, the surface of the porous carbon material is doped with the silane compound, and the silane gas is cracked by a chemical vapor method to deposit silicon on the surface of the material and inside the porous carbon material, so that the deposition uniformity of the silicon is improved, the agglomeration of the silicon is avoided, meanwhile, the silane compound has a good bonding effect with the porous carbon and the silicon deposit, the bonding force between the silicon/porous carbon composite material can be improved, the tap density of the material is finally improved, and the expansion of the material is reduced. And nitrogen source dopant gas is introduced, so that the conductivity of the inner core of the porous silicon/carbon composite can be improved, and the compatibility of the silicon/porous carbon and the electrolyte can be improved. The carbon nano tube is coated on the surface of the core material, so that the silicon material is prevented from being directly contacted with the electrolyte, and the occurrence probability of side reaction is reduced.

Drawings

Fig. 1 is an SEM image of the silicon carbon composite anode material prepared in example 1.

Detailed Description

The technical solution of the present invention is further illustrated by the following specific examples.

Example 1

The preparation method of the silicon-carbon composite anode material comprises the following steps:

1) 100g of oxidized asphalt and 1000mL of carbon disulfide are added into a reaction kettle, and the mixture is rapidly stirred for 30min at the rotating speed of 100rpm, so that the oxidized asphalt and the carbon disulfide are uniformly mixed. Then the temperature is raised to 90 ℃, and 3g of AlCl is added₃And 12g of CCl₄Carrying out crosslinking reaction for 1h, then filtering, heating the obtained solid composite material to 1100 ℃ in an argon atmosphere, and preserving heat for 2 h; and then cooling to room temperature, and crushing and grading to obtain the porous carbon material.

2) Adding 0.5g of gamma-aminopropyltriethoxysilane into 100mL of N, N-dimethylformamide, uniformly dispersing, adding 3g of the porous carbon material, uniformly mixing, and spray-drying at an inlet temperature of 150 ℃ to obtain the modified porous carbon material.

3) Transferring the modified porous carbon material into a tubular furnace, firstly introducing nitrogen to discharge air in the tube, then introducing monosilane gas, after nitrogen is exhausted, continuously introducing and heating to 1100 ℃, preserving heat for 3 hours, then stopping introducing monosilane gas, cooling to 700 ℃, introducing ammonia gas as a gas dopant, preserving heat for 3 hours, then stopping introducing the ammonia gas dopant, introducing argon gas, naturally cooling to room temperature, and crushing to obtain the silicon-carbon material.

4) And transferring the silicon-carbon material into a tubular furnace, introducing argon gas to discharge air in the tube, then introducing methane gas, heating to 800 ℃, preserving the heat for 6 hours, stopping introducing the methane gas, introducing the argon gas, and naturally cooling to room temperature to obtain the silicon-carbon composite anode material.

The silicon-carbon composite negative electrode material of the embodiment has a core-shell structure, the core is a nano-silicon/porous carbon composite material, the shell is a carbon nano tube, and the mass percentage of a silicon oxide compound in the silicon-carbon composite negative electrode material is 33%.

Example 2

1) 50g of oxidized asphalt and 1000mL of carbon disulfide are added into a reaction kettle, and the mixture is rapidly stirred for 30min at the rotating speed of 50rpm, so that the oxidized asphalt and the carbon disulfide are uniformly mixed. Then the temperature is raised to 80 ℃, 5g of AlCl is added₃And 15g of CCl₄Carrying out crosslinking reaction for 2h, then filtering, heating the obtained solid composite material to 1200 ℃ in an argon atmosphere, and preserving heat for 1 h; and then cooling to room temperature, and crushing and grading to obtain the porous carbon material.

2) Adding 0.1g of gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane into 100mL of N-N-dimethylacetamide, uniformly dispersing, adding 5g of the porous carbon material, uniformly mixing, and performing spray drying at the inlet temperature of 100 ℃ to obtain the modified porous carbon material.

3) Transferring the modified porous carbon material into a tubular furnace, firstly introducing nitrogen to exhaust air in the tube, then introducing disilane gas, after nitrogen is exhausted, continuously introducing and heating to 1000 ℃, preserving heat for 6 hours, then stopping introducing disilane gas, cooling to 800 ℃, introducing nitrous oxide as a gas dopant, preserving heat for 6 hours, then stopping introducing the gas dopant, introducing nitrogen gas, then naturally cooling to room temperature, and crushing to obtain the silicon-carbon material.

4) And transferring the silicon-carbon material into a tubular furnace, introducing nitrogen gas to discharge air in the tube, introducing acetylene gas, heating to 700 ℃, preserving the heat for 1h, stopping introducing the acetylene gas, introducing the nitrogen gas, and naturally cooling to room temperature to obtain the silicon-carbon composite anode material.

The silicon-carbon composite negative electrode material of the embodiment has a core-shell structure, the core is a nano-silicon/porous carbon composite material, the shell is a carbon nano tube, and the mass percentage of silicon oxide in the silicon-carbon composite negative electrode material is 35%.

Example 3

1) 150g of oxidized asphalt and 1000mL of carbon disulfide are added into a reaction kettle, and the mixture is rapidly stirred for 30min at the rotating speed of 200rpm, so that the oxidized asphalt and the carbon disulfide are uniformly mixed. Then the temperature is raised to 100 ℃, 1g of AlCl is added₃And 10g of CCl₄Carrying out crosslinking reaction for 0.5h, then filtering, heating the obtained solid composite material to 1000 ℃ in an argon atmosphere, and preserving heat for 3 h; and then cooling to room temperature, and crushing and grading to obtain the porous carbon material.

2) Adding 1g of dimethyl dimethoxysilane into 100mL of gamma-butyrolactone, uniformly dispersing, adding 1g of the porous carbon material, uniformly mixing, and performing spray drying at the inlet temperature of 120 ℃ to obtain the modified porous carbon material.

3) Transferring the modified porous carbon material into a tubular furnace, firstly introducing argon to discharge air in the tube, then introducing monosilane gas, after nitrogen is exhausted, continuously introducing and heating to 1200 ℃, preserving heat for 1h, then stopping introducing monosilane gas, cooling to 600 ℃, introducing dinitrogen tetroxide serving as a gas dopant, preserving heat for 1h, then stopping introducing the gas dopant, introducing argon gas, naturally cooling to room temperature, and crushing to obtain the silicon-carbon material.

4) And transferring the silicon-carbon material into a tubular furnace, introducing argon gas to discharge air in the tube, introducing ethylene gas, heating to 900 ℃, preserving the heat for 1h, stopping introducing the ethylene gas, introducing the argon gas, and naturally cooling to room temperature to obtain the silicon-carbon composite anode material.

The silicon-carbon composite negative electrode material of the embodiment is of a core-shell structure, the core is a nano-silicon/porous carbon composite material, the shell is a carbon nano tube, and the mass percentage of silicon in the silicon-carbon composite negative electrode material is 32%.

Comparative example

The silicon-carbon cathode in the comparative example is a silicon-carbon cathode material with the model number of S-500A purchased from Shenzhen City fibrate Rui New energy materials GmbH. Wherein the content of the silicon-oxygen compound is 30 percent.

Test examples

(1) SEM test

The silicon-carbon composite anode material prepared in example 1 was subjected to SEM test, and the test results are shown in fig. 1.

As can be seen from the figure, the silicon-carbon composite anode material in the embodiment 1 has a particle structure, the particle size is about 5-15 μm, and the size distribution is uniform and reasonable.

(2) Physical and Electrical Performance testing

According to the method in the national standard GBT 243358-2009 graphite cathode material for lithium ion batteries, the specific surface area, tap density, specific capacity (tested by a button cell) and conductivity (tested by a four-probe method) of the silicon-carbon material in the examples 1-3 and the comparative example are tested, and the rate capability and the cycle performance of the button cell are simultaneously tested.

Multiplying power performance test conditions: respectively charging at a multiplying power of 10C and discharging at 1C; the voltage range is 0.05-2V; the temperature is 25 +/-3 ℃.

Cycle performance test conditions: 1C charging and 1C discharging, wherein the voltage range is 0.05-2V, and the temperature is 25 +/-3 ℃; the number of cycles was 100.

And (4) under the condition of electricity deduction test:

negative electrode sheets were prepared from the negative electrode active materials of the silicon carbon materials of examples 1 to 3 and comparative example, respectively (formulation: silicon carbon material: CMC: SBR: SP: H)₂O95: 2.5:1.5:1:150) and a lithium sheet are taken as positive electrode sheets, and LiPF is adopted as electrolyte₆The volume ratio of the electrolyte solvent EC to DEC is 1:1, the diaphragm adopts a composite film of polyethylene PE, polypropylene PP and polyethylene propylene PEP, and the button cell is assembled in a glove box filled with hydrogen. And finally assembling the button cells A1, A2, A3 and B. The electrochemical performance is carried out on a Wuhan blue electricity CT2001A type battery tester, the charging and discharging voltage range is controlled to be 0.005-2.0V, and the charging and discharging multiplying power is 0.1C.

The results of the snap-on B test of button cells a1, a2, A3 are compared to comparative example 1 in table 1 below.

TABLE 1 comparison of the Properties of the silicon carbon materials in the examples and comparative examples

	Example 1	Example 2	Example 3	Comparative example
					Tap density (g/cm)³)	1.11	1.18	1.09	0.71
Specific capacity (mAh/g)	838.6	829.4	838.5	645.6
					First efficiency (%)	87.5	86.5	86.1	82.4
Resistivity (omega m)	3×10^-4	8×10^-4	9×10^-4	5×10^-3
					Specific surface area (g/m)²)	65.4	67.8	68.3	8.3
Multiplying factor (10C/1C,%)	90.1	88.6	86.2	80.1
					Circulation (100 times,%)	83.6	81.8	80.3	72.1

It can be seen from table 1 that the specific capacity and the first efficiency of the material prepared by the present invention are significantly superior to those of the comparative example because the nano silicon compound is uniformly deposited on the porous carbon material and is uniformly dispersed, the expansion of the material is reduced, the gram volume performance of the material is improved, and the conductivity of the material is improved because the surface of the material is coated with the carbon nanotube. The porous carbon material can increase the specific surface area of the composite material, is favorable for improving the liquid absorption and retention capacity of the material, and further improves the electrochemical performance of the material.

(3) Pouch cell testing

Taking the silicon-carbon materials in the examples 1-3 and the comparative examples as negative active materials, taking CMC/SBR as a binder, taking super carbon black SP as a conductive agent, taking secondary distilled water as a solvent, carrying out slurry mixing and coating to prepare a negative pole piece, and taking lithium iron phosphate as a positive active material to prepare a positive pole piece. In the electrolyte, a solvent EC/DEC/PC (EC: DEC: PC ═ 1:1:1) is used as the electrolyteThe solute is LiPF₆. Celgard 2400 membrane was used as the separator. Separately, 5Ah pouch cells C1, C2, C3 and D1 were prepared.

And testing the liquid absorption and retention capacity of the prepared negative plate and the cycle performance (1.0C/1.0C) of the lithium battery. The test method is carried out according to the national standard GB/T2433and 2009 graphite cathode material for lithium ion batteries; and meanwhile, calculating the mass energy density of the soft package lithium ion battery according to the discharge capacity and the mass of the lithium ion battery.

The test results are shown in tables 2-3 below.

TABLE 2 liquid-absorbing and liquid-retaining abilities of negative electrode sheet

	Imbibition speed (mL/min)	Liquid retention rate (24h electrolyte volume/0 h electrolyte volume)
			Example 1	3.8	95.1％
Example 2	3.6	94.3％
			Example 3	3.5	94.2％
Comparative example	1.2	83.1％

As can be seen from table 2, the liquid absorbing and retaining capabilities of the negative electrode tabs in examples 1 to 3 are all significantly better than those of the comparative examples, which may be due to: the silicon-carbon material has high specific surface area by adopting a vapor deposition method and adopting a porous carbon material, so that the liquid absorption and retention capability of the pole piece is improved, and meanwhile, the specific surface area of the carbon nano tube coated by the shell is large, so that the liquid absorption and retention capability of the pole piece can be further improved.

TABLE 3 cycling performance of pouch cells

As can be seen from table 3, the cycle performance of the pouch batteries in examples 1 to 3 is significantly better than that of the comparative example, and the analysis reason may be: the nano-silicon is uniformly deposited in porous carbon holes by adopting a vapor deposition method, so that the expansion of the nano-silicon in the charging and discharging processes is reduced, and meanwhile, the silane coupling agent has better binding force with the porous carbon and the nano-silicon, so that the binding force between materials is improved, and the cycle performance of the materials is improved.

Claims

1. The preparation method of the silicon-carbon composite negative electrode material is characterized by comprising the following steps of:

1) uniformly mixing a silane coupling agent and a porous carbon material in an organic solvent, and then performing spray drying to prepare a modified porous carbon material; the silane coupling agent is one or a combination of more of gamma-aminopropyltriethoxysilane, gamma- (2, 3-epoxypropoxy) propyltrimethoxysilane, gamma- (methacryloyloxy) propyltrimethoxysilane, octyltriethoxysilane and dimethyldimethoxysilane; the organic solvent is one or a combination of more of N-N-dimethylformamide, N-N-dimethylacetamide, N-N-diethylacetamide, N-methyl-2-pyrrolidone, gamma-butyrolactone and dimethyl sulfoxide; the mass ratio of the silane coupling agent to the porous carbon material to the organic solvent is (0.1-1): (1-5): 100, respectively;

2）the modified porous carbon material is subjected to heat preservation for 1-6h at the temperature of 1000-1200 ℃ in the presence of silane gas; then cooling to 600-800 ℃, and preserving the heat for 1-6h in the presence of a gas dopant to prepare a silicon-carbon material; the gas dopant is NH₃、N₂O、NO、N₂O₄One or a combination of several of them;

2. The method for preparing a silicon-carbon composite anode material according to claim 1, wherein: the silane gas in the step 2) is one or the combination of monosilane and disilane.

3. The method for preparing a silicon-carbon composite anode material according to claim 1, wherein: the carbon source gas in the step 3) is one or a combination of several of methane, acetylene, ethane and ethylene.

4. The method for producing a silicon-carbon composite anode material according to any one of claims 1 to 3, characterized in that: the porous carbon material in the step 1) is prepared by adopting a method comprising the following steps: performing crosslinking reaction on the oxidized asphalt, carbon disulfide, aluminum chloride and carbon tetrachloride at the temperature of 80-100 ℃, and performing solid-liquid separation to obtain a precursor; sintering the precursor for 1-3h at 1000-1200 ℃ in an inert atmosphere to obtain the porous carbon material.

5. The method for preparing a silicon-carbon composite anode material according to claim 4, wherein: the time of the crosslinking reaction is 1.5-2 h.

6. A silicon carbon composite anode material made by the method of claim 1.