Carbon nanotube-loaded silicon carbon material, preparation method thereof and application of carbon nanotube-loaded silicon carbon material in lithium ion battery

Abstract

According to the preparation method, the surface of the silica material is coated with the carbon layer by using the solid-phase carbon source, then the carbon nanotubes are grown on the surface of the carbon coating layer in situ by using chemical vapor deposition, the carbon nanotubes are uniformly distributed on the surface of the carbon coating layer and are tightly combined, and a three-dimensional conductive network constructed on the surface of the carbon layer by the carbon nanotubes not only greatly improves the conductivity of the material, but also improves the conductivity of the material. When the composite material is applied to the lithium ion battery, the rate capability and the cycle performance of the lithium ion battery are obviously improved; in addition, no catalyst is used during in-situ growth of the carbon nanotubes, so that the subsequent step of removing the catalyst can be omitted, and the preparation method is simple and low in cost.

Description

Technical Field

[0001] The present invention relates to a carbon nanotube-loaded silicon-carbon material, and in particular to a carbon nanotube-loaded silicon-carbon material, a preparation method thereof, and application thereof in lithium-ion batteries. Background Art

[0002] Silicon-carbon materials have gradually become the first choice for negative electrode materials of lithium-ion batteries due to their high theoretical gram capacity. Among them, silicon-oxygen materials, as a new generation of negative electrode materials, have a theoretical gram capacity of 2500mAh / g and have been successfully used in lithium-ion batteries. However, as a semiconductor, silicon material has worse electronic conductivity than graphite, which will cause lithium deposition on the surface of silicon-oxygen materials during fast charging. In addition, the volume of silicon-oxygen materials can expand by up to 180% during the process of lithium insertion and delithiation, which will cause the negative electrode material to pulverize during the cycle. In order to improve the electronic conductivity of silicon-oxygen materials, the most effective method is to carbon-coat the surface of silicon-oxygen materials.

[0003] Carbon coating of silicon oxide materials can not only inhibit the expansion of silicon oxide materials but also improve their conductivity. However, this carbon coating conducts electrons through point contact, and the degree of improvement in conductivity is limited. Therefore, in order to improve the rate performance and cycle performance of silicon oxide materials, battery factories often add carbon nanotubes during the homogenization process to increase the electronic conductivity of silicon oxide materials and improve the negative electrode conductive network. However, due to the large specific surface area of ​​carbon nanotubes, the viscosity of the slurry changes greatly during the homogenization process, and there is a problem of uneven dispersion of carbon nanotubes.

[0004] In order to solve the problem of carbon nanotube loading, in the existing technology, liquid phase coating and other means are often used to load carbon nanotubes on the surface of silicon oxide materials. For example, the silicon oxide material is mixed with a catalyst and then carbonized and screened to finally obtain the negative electrode material. Although this can also achieve the effect of improving the conductivity of the material, the catalyst needs to be post-processed and removed, which is costly. Summary of the Invention

[0005] In order to solve the technical problems existing in the background technology, the present invention proposes a silicon-carbon material loaded with carbon nanotubes, wherein the silicon-carbon material loaded with carbon nanotubes includes a silicon-carbon material and carbon nanotubes grown in situ on the surface of the silicon-carbon material, and the silicon-carbon material includes a silicon-oxygen material core and a carbon coating layer on the surface of the core.

[0006] In the present invention, when the carbon nanotubes are in-situ grown on the surface of the carbon coating layer, the three-dimensional conductive network constructed by the carbon nanotubes greatly improves the electrical conductivity and rate performance of the material.

[0007] The aspect ratio of the carbon nanotubes is 20-100, and the carbon nanotubes are ordinary carbon nanotubes or fluorine-containing carbon nanotubes;

[0008] Preferably, the carbon nanotubes are fluorine-containing carbon nanotubes.

[0009] In the present invention, carbon nanotubes with a suitable aspect ratio can form an effective three-dimensional conductive network on the surface of the carbon coating layer, which can meet the requirements of high current charging and discharging when applied to lithium-ion batteries;

[0010] When the carbon nanotubes are fluorinated carbon nanotubes, the fluorinated carbon nanotubes will combine with the carbon coating to produce CFC bonds, thereby making the combination of the fluorinated carbon nanotubes and the carbon coating stronger; the presence of fluorine atoms will also change the electronic structure of the carbon nanotubes and improve the conductivity.

[0011] The carbon coating layer has a thickness of 5-15 nm, and the silicon oxide material is silicon monoxide.

[0012] The present invention provides a method for preparing the above-mentioned carbon nanotube-loaded silicon-carbon material, comprising the following steps:

[0013] S1, mixing a solid carbon source and a silicon-oxygen material to obtain a mixed material;

[0014] S2, carbonizing the mixed material in step S1 under an inert atmosphere;

[0015] S3. Performing vapor deposition on the material carbonized in step S2 using a composite vapor-phase carbon source.

[0016] In the present invention, the composite gas-phase carbon source can in-situ grow carbon nanotubes on the surface of the carbon coating layer without a catalyst.

[0017] In step S1, the solid carbon source is one of high-temperature asphalt, coal asphalt, and petroleum asphalt, and the mass ratio of the solid carbon source to the silicon-oxygen material is 1-2:40.

[0018] In step S2, the carbonization temperature is 900-1100°C, the carbonization heating rate is 1-5°C / min, and the carbonization holding time is 3-5h.

[0019] The composite gaseous carbon source includes unsaturated hydrocarbons;

[0020] Preferably, the composite gaseous carbon source further comprises fluorocarbons, and the volume ratio of the unsaturated hydrocarbon to the fluorocarbon is 2-3:1.

[0021] Preferably, the unsaturated hydrocarbon is acetylene.

[0022] In the present invention, when the composite gas-phase carbon source includes a fluorocarbon, under high temperature conditions, the unsaturated hydrocarbon decomposes under the action of a catalyst to produce active species such as carbon atom free radicals. The fluorocarbon also generates fluorine-containing free radicals at high temperature. The carbon atom free radicals interact with the fluorine-containing free radicals, and the carbon atoms gradually aggregate to form a carbon nanotube structure, while the fluorine atoms are incorporated into the carbon nanotube lattice, thereby achieving in-situ growth of fluorine-containing carbon nanotubes. In the absence of a catalyst, when the fluorine content of the resulting fluorine-containing carbon nanotubes is low (3-10wt%), it is beneficial to improve the overall conductivity of the material.

[0023] In the composite gas-phase carbon source, the content of fluorinated hydrocarbons is lower than that of unsaturated hydrocarbons. Under this gas ratio, the in-situ grown fluorinated carbon nanotubes are evenly distributed and have a regular structure.

[0024] In step S3, the specific steps of the vapor deposition are as follows: placing the carbonized material in step S2 in a vapor deposition container, introducing an inert gas, heating the container from 25°C to 600°C at a heating rate of 5-15°C / min, and then heating the container from 600°C to 750°C-1000°C at a heating rate of 1-3°C / min, maintaining the temperature for 4-8 hours, and introducing a composite gas-phase carbon source;

[0025] Preferably, the total gas flow rate of the composite gaseous carbon source is 0.5-2.5 L / min;

[0026] Preferably, the inert gas is nitrogen, and the gas flow rate of the inert gas is 0.8-2.0 L / min;

[0027] Preferably, the vapor deposition container is a rotary furnace.

[0028] The present invention also provides an application of the carbon nanotube-loaded silicon-carbon material or the carbon nanotube-loaded silicon-carbon material prepared by the above preparation method in a lithium-ion battery.

[0029] Conductive carbon black, an adhesive and the silicon-carbon material loaded with carbon nanotubes are mixed evenly and then evenly distributed on the surface of a copper foil. The copper foil is dried and used as a negative electrode of a lithium-ion battery.

[0030] Beneficial effects of the present invention:

[0031] (1) By in-situ growing carbon nanotubes on the surface of silicon-carbon materials to construct a three-dimensional conductive network, not only the conductivity of the material is greatly improved, but also the rate performance and cycle performance of the battery are significantly improved when used in lithium-ion batteries;

[0032] (2) The present invention uses a composite gas-phase carbon source to grow carbon nanotubes in situ on the surface of the silicon-carbon material, which not only reduces the cost of raw materials but also avoids the subsequent step of removing the catalyst. DETAILED DESCRIPTION

[0033] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present disclosure.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0035] The technical solution of the present invention is described more clearly and completely below with reference to specific embodiments and comparative examples.

[0036] Example 1

[0037] This embodiment provides a silicon-carbon material loaded with carbon nanotubes, and the preparation method thereof is as follows:

[0038] (1) 4 kg of silicon oxide powder (D50: 6 μm) and 114 g of high-temperature asphalt (D50: 3 μm, residual carbon value 70%) were added to a VC mixer (VC-200) and mixed for 40 min at a speed of 500 rpm to obtain a mixture of silicon oxide and high-temperature asphalt;

[0039] (2) The mixed material was transferred into a box-type atmosphere furnace and carbonized and sintered in a nitrogen atmosphere. The carbonization curve was as follows: heating rate of 1.5°C / min, from 25°C to 950°C, and kept warm for 4 hours. The carbonized material was sieved through a 325-mesh sieve to obtain the carbonized undersize material.

[0040] (3) 3 kg of the above-mentioned carbonized undersize material was placed in a rotary kiln and introduced with nitrogen at a nitrogen flow rate of 0.8 L / min and a rotation speed of 20 r / min. The temperature curve of the rotary kiln was as follows: the temperature was raised from 25°C to 600°C at a heating rate of 8°C / min, and then raised from 600°C to 750°C at a heating rate of 3°C / min. When the temperature reached 750°C, acetylene gas was introduced at a gas flow rate of 0.8 L / min. The temperature was kept at 750°C for 4 h. After the heat preservation was completed, the acetylene gas was turned off. The material sintered in the rotary kiln was passed through a 325-mesh ultrasonic vibration sieve to obtain a silicon-carbon material loaded with carbon nanotubes.

[0041] Example 2

[0042] This embodiment provides a silicon-carbon material loaded with carbon nanotubes, and the preparation method thereof is as follows:

[0043] (1) 4 kg of silicon oxide powder (D50: 5 μm) and 171 g of high-temperature asphalt (D50: 4 μm, residual carbon value 60%) were added to a VC mixer (VC-200) and mixed for 40 min at a speed of 500 rpm to obtain a mixture of silicon oxide and high-temperature asphalt;

[0044] (2) The mixed material was transferred into a box-type atmosphere furnace and carbonized and sintered in a nitrogen atmosphere. The carbonization curve was as follows: heating rate of 1.5°C / min, from 25°C to 900°C, and holding temperature for 5 hours. The carbonized material was sieved through a 325-mesh sieve to obtain the carbonized undersize material.

[0045] (3) 3 kg of the above-mentioned carbonized undersize material was placed in a rotary kiln and introduced with nitrogen at a nitrogen flow rate of 0.8 L / min and a rotation speed of 20 r / min. The temperature curve of the rotary kiln was as follows: the temperature was raised from 25°C to 600°C at a heating rate of 8°C / min, and then raised from 600°C to 750°C at a heating rate of 3°C / min. When the temperature reached 750°C, acetylene gas was introduced at a gas flow rate of 0.8 L / min. The temperature was kept at 750°C for 4 h. After the heat preservation was completed, the acetylene gas was turned off. The material sintered in the rotary kiln was passed through a 325-mesh ultrasonic vibration sieve to obtain a silicon-carbon material loaded with carbon nanotubes.

[0046] Example 3

[0047] This embodiment provides a silicon-carbon material loaded with carbon nanotubes, and the preparation method thereof is as follows:

[0048] (1) 4 kg of silicon oxide powder (D50: 7 μm) and 114 g of high-temperature asphalt (D50: 5 μm, residual carbon value 70%) were added to a VC mixer (VC-200) and mixed for 40 min at a speed of 500 rpm to obtain a mixture of silicon oxide and high-temperature asphalt;

[0049] (2) The mixed material was transferred into a box-type atmosphere furnace and carbonized and sintered in an argon atmosphere. The carbonization curve was as follows: heating rate of 1.5°C / min, from 25°C to 1000°C, and heat preservation for 3 hours. The carbonized material was sieved through a 325-mesh sieve to obtain the carbonized undersize material.

[0050] (3) 3 kg of the above-mentioned carbonized undersize material was placed in a rotary kiln and nitrogen was introduced at a nitrogen flow rate of 1.2 L / min and a rotation speed of 20 r / min. The temperature curve of the rotary kiln was as follows: the temperature was raised from 25°C to 600°C at a heating rate of 8°C / min, and then from 600°C to 750°C at a heating rate of 3°C / min. When the temperature reached 750°C, acetylene gas was introduced at a gas flow rate of 1.6 L / min. The temperature was kept at 750°C for 4 h. After the heat preservation was completed, the acetylene gas was turned off. The material sintered in the rotary kiln was passed through a 325-mesh ultrasonic vibration screen to obtain a silicon-carbon material loaded with carbon nanotubes.

[0051] Example 4

[0052] This embodiment provides a silicon-carbon material loaded with carbon nanotubes, and the preparation method thereof is as follows:

[0053] (1) 4 kg of silicon oxide powder (D50: 5 μm) and 171 g of coal tar pitch (D50: 4 μm, residual carbon value 55%) were added to a VC mixer (VC-200) and mixed for 40 min at a speed of 500 rpm to obtain a mixture of silicon oxide and coal tar pitch;

[0054] (2) The mixed material was transferred into a box-type atmosphere furnace and carbonized and sintered in a nitrogen atmosphere. The carbonization curve was as follows: heating rate of 1.5°C / min, from 25°C to 950°C, and kept warm for 4 hours. The carbonized material was sieved through a 325-mesh sieve to obtain the carbonized undersize material.

[0055] (3) 3 kg of the above-mentioned carbonized undersize material was placed in a rotary kiln and nitrogen was introduced at a nitrogen flow rate of 1.0 L / min and a rotation speed of 20 r / min. The temperature curve of the rotary kiln was as follows: the temperature was raised from 25°C to 600°C at a heating rate of 8°C / min, and then raised from 600°C to 900°C at a heating rate of 3°C / min. When the temperature reached 900°C, a mixed gas of ethylene and trifluoroethylene (the volume ratio of ethylene to trifluoroethylene was 2:1) was introduced at a gas flow rate of 0.8 L / min. The mixture was kept at 900°C for 4 h. After the end of the heat preservation, the introduction of the mixed gas of ethylene and trifluoroethylene was stopped. The material sintered in the rotary kiln was passed through a 325-mesh ultrasonic vibration sieve to obtain a silicon-carbon material loaded with carbon nanotubes.

[0056] Example 5

[0057] This embodiment provides a silicon-carbon material loaded with carbon nanotubes, and the preparation method thereof is as follows:

[0058] (1) 4 kg of silicon oxide powder (D50: 5 μm) and 171 g of high-temperature asphalt (D50: 4 μm, residual carbon value of 55%) were added to a VC mixer (VC-200) and mixed for 40 min at a speed of 500 rpm to obtain a mixture of silicon oxide and high-temperature asphalt;

[0059] (2) The mixed material was transferred into a box-type atmosphere furnace and carbonized and sintered in a nitrogen atmosphere. The carbonization curve was as follows: heating rate of 1.5°C / min, from 25°C to 950°C, and kept warm for 4 hours. The carbonized material was sieved through a 325-mesh sieve to obtain the carbonized undersize material.

[0060] (3) 3 kg of the above-mentioned carbonized undersize material was placed in a rotary kiln and nitrogen was introduced at a nitrogen flow rate of 1.2 L / min and a rotation speed of 20 r / min. The temperature curve of the rotary kiln was as follows: the temperature was raised from 25°C to 600°C at a heating rate of 8°C / min, and then raised from 600°C to 1000°C at a heating rate of 3°C / min. When the temperature reached 1000°C, a mixed gas of acetylene and difluorochloromethane (the volume ratio of acetylene to difluorochloromethane was 3:1) was introduced. The total gas flow rate of the mixed gas of acetylene and difluorochloromethane was 0.8 L / min. The mixture was kept at 1000°C for 4 h. After the heat preservation was completed, the mixed gas of acetylene and difluorochloromethane was turned off. The material sintered in the rotary kiln was passed through a 325-mesh ultrasonic vibration screen to obtain a silicon-carbon material loaded with carbon nanotubes.

[0061] Comparative Example 1

[0062] This comparative example proposes a silicon-carbon material, and its preparation method is the same as that of Example 1, except that steps (1) and (2) are omitted.

[0063] In Comparative Example 1, due to the lack of the solid-phase carbon coating process in steps (1) and (2), the gas-phase carbon source cannot directly grow complete carbon nanotubes in situ on the surface of silicon monoxide, and the resulting silicon-carbon material has extremely low electrical conductivity.

[0064] Comparative Example 2

[0065] This comparative example proposes a silicon-carbon material loaded with carbon nanotubes, and its preparation method is the same as that of Example 1, except that the step (3) of "when the temperature rises to 750°C, acetylene gas is passed through at a gas flow rate of 0.8 L / min" is changed to "when the temperature rises to 750°C, a mixed gas of methane and trifluoroethylene is passed through at a total gas flow rate of 0.8 L / min."

[0066] In Comparative Example 2, since the reaction activity of methane is lower than that of acetylene, fluorine-containing carbon nanotubes cannot be uniformly grown on the surface of the carbon coating layer in the absence of a catalyst, and the conductivity of the prepared silicon-carbon material loaded with carbon nanotubes is much lower than that of Example 1.

[0067] Comparative Example 3

[0068] This comparative example proposes a silicon-carbon material loaded with carbon nanotubes, and its preparation method is the same as that of Example 4, except that the step (1) of "taking 4 kg of silicon 2 oxide powder (D50: 5 μm) and 171 g of coal tar pitch (D50: 4 μm, residual carbon value of 55%)" is changed to "taking 4 kg of silicon 2 oxide powder (D50: 5 μm), 171 g of coal tar pitch (D50: 4 μm, residual carbon value of 55%) and 200 g of Ni powder with a median particle size D50 of 1 μm".

[0069] In Comparative Example 3, although nickel can be used as a catalyst to induce the in-situ growth of fluorine-containing carbon nanotubes on the surface of the carbon coating layer, the presence of the catalyst makes the fluorine content in the fluorine-containing carbon nanotubes too high. Excessive fluorine atoms destroy the conjugated structure of the carbon nanotubes, and the transmission channel of electrons in the carbon nanotubes is hindered, which in turn leads to a decrease in conductivity.

[0070] Performance Testing

[0071] The sample materials prepared in the above embodiments and comparative examples were assembled into button cells, and the specific assembly steps were as follows: the sample materials prepared above, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were stirred and mixed in a mass ratio of 91.5:2:6.5, wherein polyvinylidene fluoride was dissolved in N-methylpyrrolidone (the mass ratio of polyvinylidene fluoride to N-methylpyrrolidone was 1:8); the mixed slurry was evenly coated on a previously prepared copper foil, and dried in a vacuum drying oven at 110°C for 12 hours to obtain a positive electrode of the button cell. A metal lithium sheet was selected as the negative electrode, Celgard2400 was used as a diaphragm, and an electrolyte containing 1 mol / L LiPF6 was used. The solvent of the electrode liquid was a mixed solution of EC and DMC (the volume ratio of EC:DMC was 1:1). The button cell CR2016 was assembled in a deoxygenated and dehydrated glove box filled with argon;

[0072] The button batteries prepared from the sample materials of Examples 1-5 are denoted as P1-P5, and the button batteries prepared from Comparative Examples 1-3 are denoted as DP1-DP3. The button batteries P1-P5 and DP1-DP3 are subjected to charge and discharge cycles. The charge and discharge conditions are as follows: the charge and discharge voltage is 1.0 V, and the charge and discharge rate is 0.5C. The reversible capacity, the initial efficiency, and the number of cycles in which the capacity is maintained above 80% under the charge and discharge conditions of 0.5C / 0.5C of the button batteries are tested. The test results are shown in Table 1.

[0073] Table 1 Performance test data of each embodiment and comparative example at 0.5C

[0074]

[0075]

[0076] 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 silicon-carbon material loaded with carbon nanotubes, characterized in that: The silicon-carbon material loaded with carbon nanotubes comprises a silicon-carbon material and carbon nanotubes grown in situ on the surface of the silicon-carbon material. The silicon-carbon material comprises a silicon-oxygen material core and a carbon coating layer on the surface of the core.

2. The carbon nanotube-loaded silicon-carbon material according to claim 1, characterized in that: The aspect ratio of the carbon nanotubes is 20-100, and the carbon nanotubes are ordinary carbon nanotubes or fluorine-containing carbon nanotubes; Preferably, the carbon nanotubes are fluorine-containing carbon nanotubes.

3. The carbon nanotube-loaded silicon-carbon material according to claim 1 or 2, characterized in that: The carbon coating layer has a thickness of 5-15 nm, and the silicon oxide material is silicon monoxide.

4. A method for preparing the carbon nanotube-loaded silicon-carbon material according to any one of claims 1 to 3, characterized in that: The steps include: S1, mixing a solid carbon source and a silicon-oxygen material to obtain a mixed material; S2, carbonizing the mixed material in step S1 under an inert atmosphere; S3. Performing vapor deposition on the material carbonized in step S2 using a composite vapor-phase carbon source.

5. A method for preparing the carbon nanotube-loaded silicon-carbon material according to claim 4, characterized in that: In step S1, the solid carbon source is one of high-temperature asphalt, coal asphalt or petroleum asphalt, and the mass ratio of the solid carbon source to the silicon-oxygen material is 1-2:

40.

6. A method for preparing the carbon nanotube-loaded silicon-carbon material according to claim 4 or 5, characterized in that: In step S2, the carbonization temperature is 900-1100°C, the carbonization heating rate is 1-5°C / min, and the carbonization holding time is 3-5h.

7. A method for preparing the carbon nanotube-loaded silicon-carbon material according to any one of claims 4 to 6, characterized in that: The composite gaseous carbon source includes unsaturated hydrocarbons; Preferably, the composite gaseous carbon source further comprises fluorocarbons, and the volume ratio of the unsaturated hydrocarbon to the fluorocarbon is 2-3:

1. Preferably, the unsaturated hydrocarbon is acetylene.

8. The method for preparing a silicon-carbon material loaded with carbon nanotubes according to any one of claims 4 to 7, characterized in that: In step S3, the specific steps of the vapor deposition are as follows: placing the carbonized material in step S2 in a vapor deposition container, introducing an inert gas, heating the container from 25°C to 600°C at a heating rate of 5-15°C / min, and then heating the container from 600°C to 750°C-1000°C at a heating rate of 1-3°C / min, maintaining the temperature for 4-8 hours, and introducing a composite gas-phase carbon source; Preferably, the total gas flow rate of the composite gaseous carbon source is 0.5-2.5 L / min; Preferably, the inert gas is nitrogen, and the gas flow rate of the inert gas is 0.8-2.0 L / min; Preferably, the vapor deposition container is a rotary furnace.

9. Use of the carbon nanotube-loaded silicon-carbon material according to any one of claims 1 to 3 or the carbon nanotube-loaded silicon-carbon material prepared by the preparation method according to any one of claims 4 to 8 in a lithium-ion battery.

10. Use of the carbon nanotube-loaded silicon-carbon material in lithium-ion batteries according to claim 9, characterized in that: Conductive carbon black, an adhesive and the silicon-carbon material loaded with carbon nanotubes are mixed evenly and then evenly distributed on the surface of a copper foil. The copper foil is dried and used as a negative electrode of a lithium-ion battery.

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