Preparation method and application of carbon nanotube composite coke

Abstract

The invention discloses a preparation method and application of carbon nanotube composite coke, and belongs to the technical field of graphite negative electrode materials. The preparation method comprises the following steps: uniformly dispersing carbon nanotubes in residual oil or oil slurry, and coking to obtain the carbon nanotube composite coke. The prepared carbon nanotube composite coke is used for preparing a graphite negative electrode material. According to the carbon nano tube composite coke prepared by the preparation method provided by the invention, after the carbon nano tube is introduced to modify and graphitize the structure of the raw material coke, the hollow structure of the carbon nano tube provides a rapid transmission channel for lithium ions, and the tube wall defects of the carbon nano tube provide a path for diffusion of the lithium ions, so that the transmission and diffusion rates of the lithium ions are improved; therefore, compared with the traditional graphite negative electrode material prepared by graphitizing petroleum coke or needle coke raw materials, the graphite negative electrode material prepared from the carbon nanotube composite coke has higher rate capability and meets the requirement of the market on the fast charging performance of the graphite negative electrode material. The method is suitable for preparing the high-magnification graphite negative electrode material.

Description

Technical Field

[0001] The invention belongs to the technical field of graphite negative electrode materials and relates to a carbon nanotube composite coke, in particular to a preparation method and application of the carbon nanotube composite coke. Background Art

[0002] With the tremendous development of the electric vehicle market, higher requirements are placed on the fast charging capability of batteries. In lithium-ion batteries, graphite negative electrodes have the characteristics of slow lithium ion insertion / extraction and diffusion rates, and the graphite lithiation potential is close to the lithium metal potential (the difference is only about 0.1V), resulting in a high overpotential for lithium-ion batteries. During high-current charging, the high overpotential may cause lithium metal precipitation, generate lithium dendrites, and then pierce the diaphragm, causing the battery to short-circuit, and may cause spontaneous combustion and explosion in severe cases, greatly limiting the fast charging capability of lithium-ion batteries. Therefore, improving the fast charging capability of graphite negative electrode materials is one of the main ways to improve the safety of lithium-ion batteries. At present, common methods for improving the fast charging capability of graphite negative electrode materials include carbon nanotubes as conductive additives, reducing the particle size of graphite particles, and carbon coating.

[0003] However, these methods will have a negative impact on other properties of graphite negative electrode materials. For example, reducing the particle size of graphite particles will cause the product's tap compaction to be low and the oil absorption value to be high, affecting the processing performance of graphite negative electrode materials. In the formation stage, more electrolyte needs to be decomposed to form SEI, resulting in a low initial efficiency of lithium-ion batteries. At the same time, during the cycle process, due to the small particle size of graphite particles, graphite is easily stripped during the lithium ion embedding process, resulting in a decrease in the cycle stability of lithium-ion batteries. The carbon coating method requires a new carbonization process after graphitization. This process has high energy consumption and increases costs. In addition, the expansion of graphite during embedding will also cause the carbon coating layer to rupture, requiring continuous consumption of electrolyte to reform SEI, ultimately resulting in a decrease in battery cycle stability. Adding carbon nanotubes during slurry mixing can effectively improve the electronic conductivity of the electrode, but it does not change the intrinsic ion embedding / extraction kinetics of graphite, and has little improvement on the fast charging performance of graphite itself. Summary of the invention

[0004] The purpose of the present invention is to provide a preparation method and application of carbon nanotube composite coke to solve the problem of poor fast charging performance (poor rate performance) of graphite negative electrode materials.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for preparing carbon nanotube composite coke, which comprises uniformly dispersing carbon nanotubes in heavy oil and coking to obtain the carbon nanotube composite coke;

[0007] The heavy oil is residual oil or slurry oil.

[0008] As a limitation, the carbon nanotubes include multi-walled carbon nanotubes and / or single-walled carbon nanotubes; the diameter of the carbon nanotubes is 0.06-50 nm, and the length is 0.2-100 μm.

[0009] As a further limitation, the residual oil comprises at least one of atmospheric residual oil, vacuum residual oil and catalytic cracking residual oil;

[0010] Slurry oil includes catalytic cracking slurry oil.

[0011] As another limitation, the mass ratio of the carbon nanotubes to the heavy oil is 0.01-5:100.

[0012] As a further limitation, the coking temperature is 450-550° C. and the time is 18-48 hours.

[0013] The present invention also provides application of the carbon nanotube composite coke prepared by the preparation method, and the carbon nanotube composite coke is used to prepare graphite negative electrode material.

[0014] As a limitation, it specifically includes: grinding, shaping and graphitizing the carbon nanotube composite coke to obtain the graphite negative electrode material.

[0015] As a further limitation, after the grinding, the median particle size of the particle size volume distribution is 4-29 μm; after shaping, the median particle size of the particle size volume distribution is 5-30 μm; and the graphitization temperature is 2500-3200°C.

[0016] As another limitation, it specifically includes: grinding and shaping the carbon nanotube composite coke to obtain primary particles, mixing the primary particles with a binder and heating them to obtain secondary particles, and graphitizing the secondary particles to obtain the graphite negative electrode material.

[0017] As a further limitation, the binder includes at least one of asphalt, phenolic resin, epoxy resin, beta resin, gamma resin, polyethylene and polypropylene;

[0018] The mass ratio of the primary particles to the binder is 100:0.1-20;

[0019] The heating has a heating rate of 1-10°C / min, a final temperature of 650°C, and a holding time of 100-400min;

[0020] The median particle size of the secondary particles in the particle size volume distribution is 5-30 μm;

[0021] The graphitization temperature is 2500-3200°C.

[0022] Due to the adoption of the above technical solution, the present invention has the following technical advances compared with the prior art:

[0023] The present invention provides a method for preparing carbon nanotube composite coke, which has a simple process and is suitable for industrial production. The prepared carbon nanotube composite coke is prepared by modifying the structure of raw coke by introducing carbon nanotubes. After graphitization, the hollow structure of the carbon nanotubes can provide a fast transmission channel for lithium ions, and the wall defects of the carbon nanotubes can provide a path for the diffusion of lithium ions, thereby improving the transmission and diffusion rate of lithium ions. Therefore, compared with the graphite negative electrode material prepared by graphitizing traditional petroleum coke or needle coke raw materials, the graphite negative electrode material prepared by the carbon nanotube composite coke has higher rate performance, meeting the market's requirements for the fast charging performance of graphite negative electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a scanning electron microscope image of the graphite negative electrode material prepared in Example 4. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below by specific examples. It should be understood that the described examples are only used to explain the present invention, and are not intended to limit the present invention.

[0026] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art.

[0027] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0028] Example 1

[0029] This embodiment prepares a carbon nanotube composite coke, which specifically includes the following steps performed in sequence:

[0030] S1. 640 g of NMP solvent-dispersed multi-walled carbon nanotubes (the content of multi-walled carbon nanotubes is 5 wt%) are added to 60 kg of catalytic cracking oil slurry (the mass ratio of carbon nanotubes to oil slurry is about 0.05:100), and stirred at a speed of 2800 r / min for 30 min in a high-speed disperser to uniformly disperse the multi-walled carbon nanotubes to obtain a dispersion;

[0031] Among them, the diameter of multi-walled carbon nanotubes is 7-15nm and the length is 5-10μm;

[0032] S2. Inject the dispersion into a coking tower, raise the temperature to 500° C. and coke for 24 hours. After the reaction is completed, remove the coking tower to obtain the carbon nanotube composite coke A1.

[0033] Example 2

[0034] This embodiment prepares a carbon nanotube composite coke, which specifically includes the following steps performed in sequence:

[0035] S1. 200 g of single-walled carbon nanotubes (single-walled carbon nanotube content of 5 wt%) dispersed in NMP solvent were added to 100 kg of vacuum residue (the mass ratio of carbon nanotubes to residue was 0.01:100), and stirred at a speed of 2800 r / min for 30 min in a high-speed disperser to uniformly disperse the single-walled carbon nanotubes to obtain a dispersion;

[0036] Among them, the diameter of the multi-walled carbon nanotubes is 0.06-10nm, and the length is 0.2-10μm;

[0037] S2. Inject the dispersion into a coking tower, raise the temperature to 550° C. and perform coking for 18 hours. After the reaction is completed, remove the coking tower to obtain the carbon nanotube composite coke A2.

[0038] Example 3

[0039] This embodiment prepares a carbon nanotube composite coke, which specifically includes the following steps performed in sequence:

[0040] S1. Take 5 kg of carbon nanotubes (composed of a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes) and add them to 100 kg of mixed residual oil (the mass ratio of carbon nanotubes to residual oil is 5:100, and the mixed residual oil is obtained by mixing atmospheric residual oil and catalytic cracking residual oil in a mass ratio of 1:1), stir at a speed of 2800 r / min for 30 min in a high-speed disperser to uniformly disperse the multi-walled carbon nanotubes to obtain a dispersion;

[0041] Among them, the diameter of multi-walled carbon nanotubes is 40-50nm and the length is 95-100μm;

[0042] S2. Inject the dispersion into a coking tower, raise the temperature to 450° C. and perform coking for 48 hours. After the reaction is completed, remove the coking tower to obtain the carbon nanotube composite coke A3.

[0043] Example 4

[0044] This embodiment provides an application of carbon nanotube composite coke, using the carbon nanotube composite coke to prepare a graphite negative electrode material, and testing the relevant properties of the graphite negative electrode, which specifically includes the following steps:

[0045] S1. Preparation of graphite negative electrode material

[0046] The carbon nanotube composite coke A1 prepared in Example 1 was taken and ground by a 70-meter mill to obtain a milled material with a medium particle size of 10.5 μm in the particle size volume distribution. The milled material was shaped by a shaping machine to obtain shaped particles with a medium particle size of 11.5 μm in the particle size volume distribution (experimentally verified, after grinding, the medium particle size of the particle size volume distribution was 4-29 μm; after shaping, the medium particle size of the particle size volume distribution was 5-30 μm, both of which can meet the requirements of graphite negative electrode materials). The shaped particles were placed in an Acheson graphitization furnace and graphitized at 3000° C. (experimentally verified, when the graphitization temperature range was 2500-3200° C., the capacity of the obtained graphite negative electrode material met the requirements), mixed and homogenized, and sieved with a 300-mesh sieve to obtain the graphite negative electrode material B1;

[0047] The graphite negative electrode material B1 was scanned by electron microscope, and the results are as follows Figure 1 As shown;

[0048] Depend on Figure 1 It can be seen that the presence of carbon nanotubes can be clearly seen on the surface of graphite, and the roots extend downward and grow inside the graphite, which can provide a favorable transport channel for the transmission of lithium ions.

[0049] S2. Preparation of comparative samples

[0050] 640 g of NMP solvent was added to 60 kg of catalytic cracking oil slurry, and stirred at a speed of 2800 r / min for 30 min in a high-speed disperser to obtain a dispersion, and the dispersion was injected into a coking tower, and the temperature was increased to 500° C. for coking for 24 h. After the reaction was completed, the coking tower was removed to obtain raw coke;

[0051] The raw coke was ground through a 70-mesh grinder to obtain a powder material having a median particle size of 10.5 μm in particle size volume distribution; the powder material was shaped through a shaping machine to obtain shaped particles having a median particle size of 11.5 μm in particle size volume distribution; the shaped particles were placed in an Acheson graphitization furnace, graphitized at 3000°C, mixed and homogenized, and sieved through a 300-mesh sieve to obtain a comparison sample.

[0052] S3. Test the performance of graphite negative electrode materials

[0053] Take 3.6g of graphite negative electrode material B1 and comparative sample respectively, add 0.45g of SP conductive additive and 0.45g of PVDF binder respectively, mix, add to 15g of NMP solvent and evenly disperse to obtain slurry, apply the slurry evenly on copper foil, use R&D scraper (30μm) for coating to obtain pole piece, then put the pole piece into oven at 100℃ for 2h, cut the dried pole piece into 14mm size, assemble into button lithium-ion battery in the order of negative electrode shell, spring, gasket, lithium sheet, diaphragm, negative electrode sheet and positive electrode shell, test the rate performance of battery at room temperature, 1C=372mAh / g, take the capacity at 0.3C as the benchmark, the capacity at other rates relative to it, the results are shown in Table 1:

[0054] Table 1 Battery rate performance test results

[0055] Sample name 0.3C 0.5C 1C 2C 3C 4C 5C 6C Graphite anode material B1 100％ 98％ 95％ 87％ 78％ 67％ 57％ 48％ Comparative samples 100％ 98％ 93％ 83％ 71％ 57％ 46％ 35％

[0056] As can be seen from Table 1, the capacity of the comparison sample gradually decreases with the increase of the test rate. At 6C, the capacity is only 35% of that at 0.3C. The graphite negative electrode material B1 prepared based on carbon nanotube composite coke shows a better rate performance, and still has a capacity retention rate of 48% at 6C. The results show that the introduction of carbon nanotubes can significantly improve the rate performance of graphite negative electrode materials.

[0057] Example 5

[0058] This embodiment provides an application of carbon nanotube composite coke, and the carbon nanotube composite coke is used to prepare a graphite negative electrode material, which specifically includes the following steps:

[0059] The carbon nanotube composite coke A2 prepared in Example 2 was ground by a 70-speed grinding mill to obtain a powdered material, and the powdered material was shaped by a shaping machine to obtain primary particles;

[0060] Take 100 kg of primary particles and add 0.1 kg of asphalt (the mass ratio of primary particles to binder is 100:0.1), mix them evenly under an inert atmosphere, put the materials into a granulation equipment, heat them to 650°C at a heating rate of 1°C / min under an inert atmosphere, keep them warm for 100 minutes, soften the binder, make the powders stick together, remove the volatile matter, and obtain secondary particles with a median particle size of 5.0 μm in particle size volume distribution;

[0061] The secondary particles were placed in a box-type graphitization furnace, graphitized at 3000° C., mixed and homogenized, and sieved with a 300-mesh sieve to obtain the graphite negative electrode material B2.

[0062] Example 6

[0063] This embodiment provides an application of carbon nanotube composite coke, and the carbon nanotube composite coke is used to prepare a graphite negative electrode material, which specifically includes the following steps:

[0064] The carbon nanotube composite coke A3 prepared in Example 3 was ground by a 70-speed grinding mill to obtain a ground material, and the ground material was shaped by a shaping machine to obtain primary particles;

[0065] Take 100 kg of primary particles and add 20 kg of epoxy resin (the mass ratio of primary particles to binder is 100:20), mix them evenly under an inert atmosphere, put the materials into a granulation equipment, heat them to 650°C at a heating rate of 10°C / min under an inert atmosphere, keep them warm for 400 minutes, soften the binder, make the powders bond together, remove volatiles, and obtain secondary particles with a median particle size of 30.0 μm in particle size volume distribution;

[0066] The secondary particles were placed in an Acheson graphitization furnace, graphitized at 3200° C., mixed and homogenized, and sieved with a 300-mesh sieve to obtain the graphite negative electrode material B3.

[0067] Example 7

[0068] This embodiment provides an application of carbon nanotube composite coke, and the carbon nanotube composite coke is used to prepare a graphite negative electrode material, which specifically includes the following steps:

[0069] The carbon nanotube composite coke A3 prepared in Example 3 was ground by a 70-speed grinding mill to obtain a powdered material, and the powdered material was shaped by a shaping machine to obtain primary particles;

[0070] Take 100 kg of primary particles and add 10 kg of phenolic resin (the mass ratio of primary particles to binder is 100:10), mix them evenly under an inert atmosphere, put the materials into a granulation device, heat them to 650° C. at a heating rate of 5° C. / min under an inert atmosphere, keep them warm for 300 minutes, soften the binder, make the powders bond together, remove volatiles, and obtain secondary particles with a median particle size of 17.0 μm in particle size volume distribution;

[0071] The secondary particles were placed in an Acheson graphitization furnace, graphitized at 2500° C., mixed and homogenized, and sieved with a 300-mesh sieve to obtain the graphite negative electrode material B4.

Claims

1. A method for preparing carbon nanotube composite coke, characterized in that: The carbon nanotube composite coke is obtained by uniformly dispersing the carbon nanotubes in heavy oil and coking the heavy oil. The heavy oil is residual oil or slurry oil.

2. The method for preparing carbon nanotube composite coke according to claim 1, characterized in that: The carbon nanotubes include multi-walled carbon nanotubes and / or single-walled carbon nanotubes; the diameter of the carbon nanotubes is 0.06-50 nm, and the length is 0.2-100 μm.

3. The method for preparing carbon nanotube composite coke according to claim 2, characterized in that: The residual oil comprises at least one of atmospheric residual oil, vacuum residual oil and catalytic cracking residual oil; Slurry oil includes catalytic cracking slurry oil.

4. A method for preparing carbon nanotube composite coke according to any one of claims 1 to 3, characterized in that: The mass ratio of the carbon nanotubes to the heavy oil is 0.01-5:

100.

5. The method for preparing carbon nanotube composite coke according to claim 4, characterized in that: The coking temperature is 450-550°C and the time is 18-48h.

6. An application of carbon nanotube composite coke prepared by the preparation method according to any one of claims 1 to 5, characterized in that: Carbon nanotube composite coke is used to prepare graphite negative electrode materials.

7. The use according to claim 6, characterized in that: Specifically include: The carbon nanotube composite coke is ground, shaped and graphitized to obtain the graphite negative electrode material.

8. The use according to claim 7, characterized in that: After the grinding, the median particle size of the particle size volume distribution is 4-29 μm; after shaping, the median particle size of the particle size volume distribution is 5-30 μm; and the graphitization temperature is 2500-3200° C.

9. The use according to claim 6, characterized in that: Specifically include: The carbon nanotube composite coke is ground and shaped to obtain primary particles, the primary particles are mixed with a binder and heated to obtain secondary particles, and the secondary particles are graphitized to obtain the graphite negative electrode material.

10. The use according to claim 9, characterized in that: The binder comprises at least one of asphalt, phenolic resin, epoxy resin, beta resin, gamma resin, polyethylene and polypropylene; The mass ratio of the primary particles to the binder is 100:0.1-20; The heating has a heating rate of 1-10°C / min, a final temperature of 650°C, and a holding time of 100-400min; The median particle size of the secondary particles in the particle size volume distribution is 5-30 μm; The graphitization temperature is 2500-3200°C.

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