CN115832254A

CN115832254A - Silicon-carbon composite negative electrode material and preparation method thereof

Info

Publication number: CN115832254A
Application number: CN202211578728.3A
Authority: CN
Inventors: 李胜; 刘双双; 王祥瑞; 黄绍丰; 李金武; 黄世强
Original assignee: Silver Silicon Ningbo Technology Co ltd
Current assignee: Silver Silicon Ningbo Technology Co ltd
Priority date: 2022-12-07
Filing date: 2022-12-07
Publication date: 2023-03-21
Anticipated expiration: 2042-12-07
Also published as: CN115832254B

Abstract

The invention belongs to the technical field of lithium battery electrode materials, and particularly discloses a silicon-carbon composite negative electrode material and a preparation method thereof. Mixing and grinding silicon and silicon dioxide to obtain a mixture with a small particle size, and then heating for reaction to generate silica vapor; synchronously condensing the silica vapor and the nano carbon material slurry, and introducing graphite to obtain a SiO @ C @ graphite composite material; and then introducing a gas carbon source, and forming a coating carbon layer on the surface of the obtained material to obtain the silicon-carbon composite anode material. According to the invention, the volume expansion is relieved through the nanocrystallization of the silicon oxide, and meanwhile, the specific inner and outer layer structures also provide a buffer layer for the expansion of the silicon oxide and form a double-carbon-layer conductive network, so that the cycle performance of the silicon-carbon composite negative electrode material is improved, and the rate performance of the silicon-carbon composite negative electrode material is also improved. The invention simplifies the process flow, improves the utilization rate of the silicon monoxide and greatly reduces the production cost.

Description

Silicon-carbon composite negative electrode material and preparation method thereof

Technical Field

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

Background

At present, graphite is taken as a main stream of a lithium ion battery negative electrode material, but the theoretical specific capacity of the graphite is only 372mAh/g, the gram capacity of the current carbon negative electrode material reaches 360mAh/g, the theoretical gram capacity is very close to the gram capacity, and the lifting space is not large. The theoretical specific capacity of silicon is 4200mAh/g, which is far larger than that of carbon. Therefore, silicon-based cathodes have entered the field of view of people in order to meet the demand for higher energy density batteries. In recent years, the demand of the industry for silicon-based negative electrodes has increased significantly.

However, there are some obstacles in commercialization and industrialization of silicon-based anode materials, and among them, the most important problem is the volume expansion of the silicon-based anode materials during charge and discharge. In the process of charging and discharging, the volume expansion of the silicon-based material reaches up to 300 percent, and the volume expansion can cause the silicon-based negative electrode material to generate cracks until pulverization, destroy the contact between the electrode material and a current collector, and cause the active material to be separated from a pole piece to cause the rapid attenuation of the battery capacity. And the expansion can generate great stress in the battery, so that the pole piece is extruded, and the pole piece is broken along with multiple cycles. In addition, such stress may also cause a decrease in the porosity inside the battery, decrease lithium ion moving channels, cause precipitation of lithium metal, and affect the safety of the battery.

Graphite is taken as a mainstream material of the current lithium ion battery cathode material, although the capacity is short, other performance advantages are obvious, and particularly the cycle performance, the low expansion and the like are realized. Therefore, the graphite and the silicon negative electrode are mixed for use, and the length of the two materials is taken as the silicon carbon negative electrode material. However, the conventional silicon-carbon negative electrode material is generally prepared by preparing a silicon/silicon oxide material and a graphite material respectively and then mixing the materials. The preparation method has the phenomenon of uneven mixing effect due to the complex and simple mixing steps. For example, patent CN 104103821a discloses a method for preparing silicon-carbon cathode, which directly uses a chemical vapor deposition method to prepare nano-scale Si-SiO _x Coating on the surface of carbon matrix realizes good dispersibility, but the Si-SiO of nanometer level _x The outer layer is not coated with a carbon layer, so that the Si-SiO of nanometer level _x The volume expansion of the silicon-carbon composite material is still large, the cycle performance of the silicon-carbon composite material is also influenced, the subsequent annealing and multiple pyrolysis processes are still required in the preparation method of the silicon-carbon composite material, and the process is relatively complex.

Therefore, how to provide a silicon-carbon composite negative electrode material and a preparation method thereof, which reduce the volume expansion of the silicon-carbon composite negative electrode material, improve the cycle stability of the battery, simplify the preparation process of the silicon-carbon composite negative electrode material, and reduce the preparation cost is a difficult problem to be solved in the field.

Disclosure of Invention

In view of the above, the invention provides a silicon-carbon composite negative electrode material and a preparation method thereof, so as to solve the problems of large volume expansion and potential safety hazard of the traditional silicon-based negative electrode and solve the problem of complex preparation process of the silicon-carbon composite negative electrode material.

In order to achieve the purpose, the invention adopts the following technical scheme:

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

1) Mixing and grinding silicon and silicon dioxide, and then heating for reaction to generate silicon-oxygen steam;

2) Synchronously condensing the silica vapor and the nano carbon material slurry, and introducing graphite to obtain a SiO @ C @ graphite composite material;

3) And introducing a gas carbon source, and forming a coating carbon layer on the surface of the SiO @ C @ graphite composite material to obtain the silicon-carbon composite negative electrode material.

Preferably, the reaction temperature in the step 1) is 1000-1600 ℃, the reaction pressure is less than or equal to 0.1torr, and the reaction time is 2-8 h.

Preferably, the mass ratio of silicon to silicon dioxide is 0.8to 1.2:0.8 to 1.2, and the particle size after grinding is 5to 100 meshes.

Preferably, the temperature for condensation in the step 2) is 600-900 ℃.

Preferably, the nanocarbon material slurry in step 2) includes one or more of a graphene solution, a carbon nanotube solution and a conductive carbon black solution.

Preferably, the particle size D10 of the graphite in the step 2) is 4 to 8 μm, the particle size D50 is 10 to 16 μm, and the particle size D90 is 25 to 35 μm.

Preferably, the mass ratio of the nanocarbon material to the silica vapor in the nanocarbon material slurry in the step 2) is 0.5 to 3:100, respectively;

the mass ratio of graphite to silica vapor in the step 2) is 100: 5to 15.

Preferably, the temperature for forming the coated carbon layer in the step 3) is 600 to 900 ℃, and the time for forming the coated carbon layer is 1to 3 hours.

Preferably, the gaseous carbon source comprises acetylene and/or methane.

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

According to the technical scheme, compared with the prior art, the invention has the following beneficial effects:

1. the invention realizes that the nano-scale silicon monoxide is directly and uniformly coated on the surface of the graphite matrix, and the nanocrystallization relieves the volume expansion of the silicon monoxide; meanwhile, the surface of the silicon oxide is provided with a double-coating layer with an inner layer of high-conductivity nano carbon material and an outer layer of amorphous carbon layer, so that a buffer layer is provided for the expansion of the silicon oxide, and the conductivity of the silicon oxide is improved. The cycle performance of the silicon monoxide can be obviously improved, and the cycle life of the whole silicon-carbon composite anode material is further prolonged.

2. The graphite is added in the preparation process of the silicon oxide, so that the silicon oxide can be directly deposited on the surface of the graphite, the processes of separately preparing massive or granular silicon oxide firstly, and then performing multi-stage crushing, grading and the like in the conventional technology are avoided, the process flow is simplified, the utilization rate of the silicon oxide is improved, and the production cost of the silicon-carbon composite cathode material is greatly 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 embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

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

Detailed Description

The invention provides a preparation method of a silicon-carbon composite negative electrode material, which comprises the following steps:

In the invention, the reaction temperature in the step 1) is 1000-1600 ℃, specifically 1100 ℃, 1200 ℃, 1300 ℃, 1400 ℃ and 1500 ℃; the pressure of the reaction is less than or equal to 0.1torr, specifically, 0.01torr, 0.02torr, 0.05torr, 0.06torr, 0.08torr; the reaction time is 2-8 h, and specifically can be 3h, 4h, 5h, 6h and 7h.

In the present invention, the mass ratio of silicon to silicon dioxide is 0.8to 1.2:0.8 to 1.2, preferably 0.85 to 1.15:0.85 to 1.15, more preferably 0.9 to 1.1:0.95 to 1.05, and preferably 1:1; the particle size after grinding is 5-100 meshes, specifically 10 meshes, 20 meshes, 40 meshes, 50 meshes, 60 meshes and 80 meshes.

In the invention, the condensation temperature in the step 2) is 600-900 ℃, and specifically can be 650 ℃, 700 ℃, 750 ℃, 800 ℃ and 850 ℃.

In the invention, the nano-carbon material slurry in the step 2) comprises one or more of a graphene solution, a carbon nanotube solution and a conductive carbon black solution.

In the present invention, the solvent of the nanocarbon material slurry includes one or more of deionized water, heavy water, sodium Dodecyl Sulfate (SDS), and Sodium Dodecyl Benzene Sulfonate (SDBS).

In the present invention, the mass concentration of the nanocarbon material slurry may be 1to 5%, specifically 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%.

In the invention, the direction of the introduced nano carbon material slurry is different from the condensation direction of the silica vapor; after the nano carbon material slurry is introduced, the solvent can be instantly vaporized, and then the nano carbon material can form a coating layer on the surface of the silicon oxide in the condensation descending process.

In the present invention, the graphite in the step 2) is artificial graphite having a secondary granulated structure.

In the invention, the particle size D10 of the graphite in the step 2) is 4-8 μm, the particle size D50 is 10-16 μm, and the particle size D90 is 25-35 μm; d10 may be specifically 5 μm, 6 μm, or 7 μm; d50 may be specifically 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm; the D90 may specifically be 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm.

In the present invention, the mass ratio of the nanocarbon material to the silica vapor in the nanocarbon material slurry in the step 2) is 0.5 to 3:100, specifically, may be 0.6: 100. 0.8: 100. 1: 100. 1.2: 100. 1.4: 100. 1.5: 100. 1.6: 100. 1.8: 100. 2: 100. 2.2: 100. 2.4: 100. 2.6: 100. 2.8:100.

the mass ratio of graphite to silica vapor in the step 2) is 100: 5to 15, specifically 100: 6. 100, and (2) a step of: 7. 100, and (2) a step of: 8. 100: 9. 100: 10. 100: 11. 100, and (2) a step of: 12. 100, and (2) a step of: 13. 100, and (2) a step of: 14.

in the present invention, the preparation of the silicon-carbon composite anode material is preferably carried out in a vacuum rotary furnace.

In the present invention, the rotation frequency of the vacuum rotary kiln in the step 2) is preferably 10 to 30Hz, and specifically may be 12Hz, 15Hz, 18Hz, 20Hz, 22Hz, 24Hz, 26Hz, and 28Hz.

In the present invention, the temperature of the coated carbon layer formed in the step 3) is 600 to 900 ℃, and specifically, may be 650 ℃, 700 ℃, 750 ℃, 800 ℃, 850 ℃; the time for forming the coated carbon layer is 1to 3 hours, and specifically may be 1.2 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.5 hours, 2.6 hours, and 2.8 hours.

In the present invention, the gaseous carbon source comprises acetylene and/or methane.

In the present invention, when the gaseous carbon source is introduced, it is preferable to simultaneously introduce the shielding gas, wherein the volume ratio of the gaseous carbon source to the shielding gas is preferably 1: 2to 3; the protective gas can be one or more of nitrogen, helium, neon and argon.

The invention also provides the silicon-carbon composite anode material prepared by the preparation method.

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.

Example 1

Mixing silicon and silicon dioxide according to a mass ratio of 1:1, mixing and grinding to obtain a mixture with the particle size of 10-40 meshes, placing the mixture in a vacuum rotary furnace, adjusting the pressure in the furnace to be 0.1torr and the temperature to be 1200 ℃, and carrying out heat preservation reaction for 5 hours (no rotation is needed in the process) to generate silica vapor;

then silica vapor is condensed at 680 ℃, and simultaneously, a graphene aqueous solution (2 wt.%) is introduced in the opposite direction to the direction in which silica vapor is condensed, wherein the mass ratio of the graphene-containing mass of the solution to the silica vapor is 2:100, instantly vaporizing and volatilizing the solvent in the nano carbon material slurry to form a carbon coating layer on the surface of the silicon oxide, and simultaneously introducing graphite (D10 is 5 microns, D50 is 15 microns, D90 is 28 microns, the mass ratio of the graphite to the silica vapor is 100);

and then keeping 680 ℃ and introducing acetylene and nitrogen mixed gas (acetylene: nitrogen/v: v = 1:2), and forming a coating carbon layer on the surface of the SiO @ C @ graphite composite material after 2h to obtain the silicon-carbon composite negative electrode material.

The SEM image of the silicon-carbon composite negative electrode material prepared in this example is shown in fig. 1, and it can be seen from fig. 1 that the silicon-carbon composite negative electrode material prepared by the present invention has a uniform size, only a few small particles of silicon monoxide are dispersed among graphite particles, and most of the silicon monoxide is deposited on the graphite surface or between graphite gaps, and no large blocks, large particles, or rod-like silicon monoxide is present, and the prepared negative electrode material can be directly used without multiple processes of pulverization and classification.

Example 2

Mixing silicon and silicon dioxide according to a mass ratio of 1:1, mixing and grinding to obtain a mixture with the particle size of 60-80 meshes, placing the mixture in a vacuum rotary furnace, adjusting the pressure in the furnace to be 0.05torr and the temperature to be 1000 ℃, and carrying out heat preservation reaction for 7 hours (no rotation is needed in the process) to generate silica vapor;

then the silica vapor was condensed at 600 ℃, while an aqueous graphene solution (3 wt.%) was fed in the opposite direction to the condensation of silica vapor, where the mass ratio of graphene-containing mass to silica vapor in the solution was 3:100, instantly vaporizing and volatilizing the solvent in the nano carbon material slurry to form a carbon coating layer on the surface of the silicon oxide, and simultaneously introducing graphite (D10 is 4 microns, D50 is 12 microns, D90 is 26 microns, the mass ratio of the graphite to the silica vapor is 100);

and then adjusting the temperature to 750 ℃, introducing acetylene and nitrogen mixed gas (acetylene: nitrogen/v: v = 1:2), and forming a coated carbon layer on the surface of the SiO @ C @ graphite composite material after 2.5 hours to obtain the silicon-carbon composite negative electrode material.

Example 3

Mixing silicon and silicon dioxide according to a mass ratio of 1.1:1, mixing and grinding to obtain a mixture with the particle size of 10-30 meshes, placing the mixture in a vacuum rotary furnace, adjusting the pressure in the furnace to be 0.8torr and the temperature to be 1600 ℃, and carrying out heat preservation reaction for 2 hours (no rotation is needed in the process) to generate silica vapor;

then the silicon dioxide vapor is condensed at 900 ℃, and simultaneously, a carbon nanotube solution (solvent is sodium dodecyl sulfate, 5 wt.%) and the silicon dioxide vapor are introduced in the opposite direction of condensation decrease, wherein the mass ratio of the carbon nanotubes in the solution to the silicon dioxide vapor is 1:100, instantly vaporizing and volatilizing the solvent in the nano carbon material slurry to form a carbon coating layer on the surface of the silica oxide, and simultaneously introducing graphite (D10 is 6 micrometers, D50 is 16 micrometers, D90 is 35 micrometers, and the mass ratio of the graphite to silicon-oxygen steam is 100;

then regulating the temperature to 600 ℃, introducing acetylene and nitrogen mixed gas (acetylene: helium/v: v = 1:3), and forming a coating carbon layer on the surface of the SiO @ C @ graphite composite material after 1h to obtain the silicon-carbon composite anode material.

Example 4

Silicon and silicon dioxide are mixed according to the mass ratio of 1:1.2, mixing and grinding to obtain a mixture with the particle size of 20-50 meshes, placing the mixture in a vacuum rotary furnace, adjusting the pressure in the furnace to be 0.6torr and the temperature to be 1300 ℃, and carrying out heat preservation reaction for 8 hours (no rotation is needed in the process) to generate silica vapor;

then the silica vapor was condensed at 800 ℃ while a conductive carbon black solution (solvent sodium dodecylbenzenesulfonate, 5 wt.%) containing a mass of conductive carbon black to silica vapor in a mass ratio of 2.5:100, instantly vaporizing and volatilizing the solvent in the nano carbon material slurry to form a carbon coating layer on the surface of the silicon oxide, and simultaneously introducing graphite (D10 is 4 microns, D50 is 11 microns, D90 is 30 microns, the mass ratio of the graphite to the silica vapor is 100;

then keeping 800 ℃, introducing mixed gas of methane and nitrogen (methane: argon/v: v = 1:3), and forming a coating carbon layer on the surface of the SiO @ C @ graphite composite material after 1.5h to obtain the silicon-carbon composite negative electrode material.

Comparative example 1

The present comparative example differs from example 1 only in that a pure aqueous solution is used instead of the aqueous graphene solution.

Comparative example 2

This comparative example differs from example 1 only in that no graphite is added.

Comparative example 3

This comparative example differs from example 1 only in that nitrogen is used instead of acetylene.

Experimental example 1

100 parts of the obtained silicon-carbon composite negative electrode material, 5 parts of carbon black conductive agent and 8 parts of polyvinylidene fluoride binder in examples 1to 4 and comparative examples 1to 3 are respectively mixed to obtain negative electrode slurry, the negative electrode slurry is coated on a current collector to obtain a negative electrode sheet, and a lithium cobaltate positive electrode and lithium hexafluorophosphate are adopted as electrolyte to assemble the lithium ion battery.

The lithium ion battery was subjected to electrochemical performance tests, and the test results are shown in table 1. Wherein the first discharge specific capacity test condition is 50 ℃, and 0.1C discharge is carried out; the capacity retention rate is tested under the test condition of 0.1C rate for 200 times of charge-discharge cycle test.

TABLE 1 electrochemical Performance test results

It can be seen from table 1 that after the silicon-carbon composite negative electrode material prepared by the invention is applied to a lithium battery, the discharge specific capacity and the capacity retention rate of the battery can be remarkably improved, and after 200 times of charging and discharging, the capacity can still reach over 95%, which proves that the silicon-based negative electrode material does not excessively expand and is not separated from a pole piece, and the rapid attenuation of the battery capacity is avoided. Comparative example 1 has slightly larger volume expansion and slightly poorer cycle and multiplying power, comparative example 2 has higher initial discharge specific capacity but poor cycle stability and larger expansion and worst comprehensive performance because the silicon material has larger proportion, and comparative example 3 has slightly larger volume expansion and slightly poorer cycle and multiplying power than comparative example 1. The reason is that the carbon nano material has better conductivity and can more effectively inhibit volume expansion.

In the present specification, the embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

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

3) And introducing a gas carbon source to form a coating carbon layer on the surface of the SiO @ C @ graphite composite material to obtain the silicon-carbon composite anode material.

2. The method for preparing the silicon-carbon composite anode material according to claim 1, wherein the reaction temperature in the step 1) is 1000-1600 ℃, the reaction pressure is less than or equal to 0.1torr, and the reaction time is 2-8 h.

3. The preparation method of the silicon-carbon composite anode material as claimed in claim 2, wherein the mass ratio of the silicon to the silicon dioxide is 0.8-1.2: 0.8to 1.2, and the particle size after grinding is 5to 100 meshes.

4. The method for preparing a silicon-carbon composite anode material according to any one of claims 1to 3, wherein the condensation temperature in the step 2) is 600 to 900 ℃.

5. The method for preparing the silicon-carbon composite anode material as claimed in claim 4, wherein the nano-carbon material slurry in the step 2) comprises one or more of a graphene solution, a carbon nanotube solution and a conductive carbon black solution.

6. The method for preparing the silicon-carbon composite anode material according to the claim 1, 2, 3 or 5, wherein the particle size D10 of the graphite in the step 2) is 4-8 μm, the D50 is 10-16 μm, and the D90 is 25-35 μm.

7. The method for preparing a silicon-carbon composite anode material according to claim 6, wherein the mass ratio of the nanocarbon material to the silicon oxygen vapor in the nanocarbon material slurry in the step 2) is 0.5 to 3:100, respectively;

the mass ratio of graphite to silica vapor in the step 2) is 100: 5to 15.

8. The method for preparing a silicon-carbon composite anode material according to claim 7, wherein the temperature for forming the coated carbon layer in the step 3) is 600-900 ℃, and the time for forming the coated carbon layer is 1-3 h.

9. The method for preparing the silicon-carbon composite anode material as claimed in claim 8, wherein the gaseous carbon source comprises acetylene and/or methane.

10. The silicon-carbon composite negative electrode material prepared by the preparation method of any one of claims 1to 9.