Hard carbon materials and their preparation methods

Abstract

The present invention relates to the technical field of energy storage materials, and discloses a hard carbon material and a preparation method thereof. The hard carbon material involved includes a hard carbon body and a carbon film coated on the surface of the hard carbon body; the raw materials of the carbon film are CMC and nanowires. The preparation method of the hard carbon material involved includes the following steps: S1 Using biomass as the carbon-based raw material, the biomass is hydrothermally treated to obtain a primary carbonized body; S2 The primary carbonized body is treated with a silane coupling agent and reserved; S3 After CMC forms a CMC dispersion liquid, nanowires are added and blended to obtain a film-forming liquid; S4 After the film-forming liquid is coated on the surface of the primary carbonized body, it is dried and carbonized to obtain the hard carbon material. The hard carbon and its preparation method provided by the present invention obtain a material with high capacity and high initial efficiency by controlling the number of pores on the surface of the hard carbon material structure and enhancing its sodium storage active sites.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage materials, and more specifically, to hard carbon materials and their preparation methods. Background Art

[0002] Currently, as the core component of sodium-ion batteries, electrode materials directly determine the electrochemical performance of the batteries. Among the anode materials, hard carbon materials have been widely used due to their disordered structure and rich sources. However, although hard carbon has excellent reversible specific capacity, stable structure, and long service life, it has the problem of low initial Coulombic efficiency. This is because, during the first cycle, sodium ions are irreversibly adsorbed in some defects and pores of hard carbon and cannot be removed. Summary of the Invention

[0003] Technical problems to be solved by the present invention

[0004] To solve the problem of low initial Coulombic efficiency of hard carbon materials existing in the prior art.

[0005] Technical solutions adopted by the present invention

[0006] In view of the above technical problems, the object of the present invention is to provide hard carbon materials and their preparation methods.

[0007] The specific content is as follows:

[0008] First, the present invention provides a hard carbon material, including

[0009] a hard carbon body,

[0010] a carbon film coated on the surface of the hard carbon body; the raw materials of the carbon film are CMC and nanowires.

[0011] Second, the present invention provides a preparation method of the above-mentioned hard carbon material, including the following steps:

[0012] S1 Using biomass as the carbon-based raw material, the biomass is hydrothermally treated to obtain a primary carbonized body;

[0013] S2 The primary carbonized body is treated with a silane coupling agent and set aside;

[0014] S3 After CMC forms a CMC dispersion liquid, a nanowire dispersion liquid is added and blended to obtain a film-forming liquid;

[0015] S4 After the film-forming liquid is coated on the surface of the primary carbonized body, it is dried and carbonized to obtain the hard carbon material.

[0016] Beneficial effects achieved by the present invention

[0017] First, by loading a film layer on the surface of the carbonization precursor, as the carbonization precursor undergoes carbonization, CMC forms a carbonized layer that covers the surface of the hard carbon, thereby reducing the number of pores and defects on the surface of the hard carbon. Secondly, the formation of the carbonized layer by CMC can also effectively prevent structural damage caused by expansion due to volume change.

[0018] Second, the CMC film layer is interspersed with nanofibers, enabling the finally formed hard carbon material to have a nano-micro structure. Loaded on the surface of the hard carbon material through carbon fiber nano, it can utilize its micro-size, enabling a balanced packing between the specific surface area and defects, thereby improving the first Coulomb efficiency and rate performance.

[0019] Third, by first hydrothermally treating the biomass to form a pre-carbonized body, it is convenient to remove impurities in the biomass, control the disordered structure and adsorption sites in the hard carbon material, thereby enhancing the adsorption channel of Na + ; First hydrothermal treatment is also convenient for the subsequent complete coating of CMC. Specific Embodiments

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0021] Technical solutions

[0022] First, the present invention provides a hard carbon material, including

[0023] a hard carbon body,

[0024] a carbon film covering the surface of the hard carbon body; the raw materials of the carbon film are CMC and nanowires.

[0025] In the present invention, the hard carbon body is prepared from biomass as the raw material.

[0026] In the present invention, the biomass includes at least one of coconut shell, lotus stem, buckwheat shell, water hyacinth, water chestnut shell, coffee shell, and pinecone shell.

[0027] In the present invention, the nanowires include at least one of carbon nanowires and titanium dioxide nanowires.

[0028] Second, the present invention provides a preparation method of the aforementioned hard carbon material, including the following steps:

[0029] S1 Using biomass as the carbon-based raw material, the biomass is hydrothermally treated to obtain a primary carbonized body;

[0030] The S2 primary carbonized body is treated with a silane coupling agent and reserved for use;

[0031] After CMC forms a CMC dispersion liquid, a nanowire dispersion liquid is added for blending to obtain a film-forming liquid;

[0032] After the film-forming liquid is coated on the surface of the primary carbonized body, it is subjected to drying and carbonization treatments to obtain a hard carbon material.

[0033] In the present invention, a hard carbon body prepared from biomass as a raw material is selected because it has the advantages of rich sources, easy availability, and environmental friendliness, and also because of its hollow structure, large number of pores in the structure, and the presence of nitrogen elements. Applying these to the battery field can improve the sodium storage performance of hard carbon.

[0034] In order to obtain a controllable carbonized body structure to obtain rich sodium storage sites, and to solve the problems of low initial Coulomb efficiency and slightly poor rate performance existing in the existing application process.

[0035] Therefore, the biomass is first subjected to hydrothermal treatment to obtain a primary carbonized body. The conditions for hydrothermal treatment are as follows: the aforementioned biomass is broken and then put into a polytetrafluoroethylene hydrothermal reaction kettle together with deionized water for reaction. The reaction time is 6 - 14 h, and the reaction temperature is 150 - 250 °C. After the reaction is completed, the obtained product is subjected to suction filtration, washing, and drying to obtain the primary carbonized body. Preferably, the reaction temperature can be 150 - 180 °C, 150 - 200 °C, 180 - 250 °C, 180 - 200 °C, 200 - 250 °C. The particle size of the primary carbonized body is 6 - 10 μm.

[0036] In the present invention, in S2, the primary carbonized body is treated with a silane coupling agent to facilitate the coating of the film-forming liquid on its surface.

[0037] The silane coupling agent includes at least one of γ-aminopropyltriethoxysilane (KH 550), γ-methacryloxypropyltrimethoxysilane (KH 570), and γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH560). Preferably, the silane coupling agent is γ-aminopropyltriethoxysilane (KH550).

[0038] Preferably, in order to improve the storage active sites of the hard carbon material, oxygen-containing functional groups are introduced into the primary carbonized body before it is treated with the silane coupling agent.

[0039] Specifically, the primary carbonized body is acidified to obtain a primary carbonized body containing oxygen-containing functional groups. The acidifying reagent includes at least one of concentrated sulfuric acid, concentrated nitric acid, and concentrated hydrochloric acid. The acidifying conditions are 30 - 45 °C and the time is 3 - 6 h. Preferably, it is 30 - 40 °C and the time is 4 - 5 h.

[0040] After this treatment, the primary carbonized body is further treated with a silane coupling agent, that is, ball-milled with the silane coupling agent. A solvent is added during the ball milling process for treatment. The solvent is toluene or isopropyl alcohol. The ball milling time is 0.2 - 0.5 h. The mass ratio of the primary carbonized body to the silane coupling agent is 1:0.02 - 0.06.

[0041] In the present invention, in S3, the concentration of the CMC dispersion is 0.08 - 0.12 wt%. The concentration of the nanowire dispersion is 5 - 10 mg / mL. The medium of the above-mentioned dispersions is deionized water.

[0042] In the present invention, in S3, the volume ratio of the CMC dispersion to the nanowire dispersion is 1 - 10:40 - 100. Preferably, the volume ratio of the two is 2 - 7:40 - 80.

[0043] In the present invention, in S3, the CMC dispersion and the nanowire dispersion are subjected to co-blending treatment by ultrasonic means.

[0044] In the present invention, in S4, the primary carbonized body is placed in the coating solution. After coating and forming (by means of vacuum suction), it is taken out and placed in an oven at 70 - 90 °C for drying for 5 - 10 h to obtain a coated body, and the coated body is subjected to carbonization treatment.

[0045] In the present invention, in S4, the conditions for carbonization treatment are as follows: under a N2 atmosphere, the temperature is raised to 600 - 1300 °C at a heating rate of 1 - 10 °C / min, and the carbonization time is 2 - 5 h.

[0046] Preferably, the heating rate can be selected as 2 - 6 °C / min, specifically, it can be selected as 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min.

[0047] Preferably, the heating temperature can be selected as 600 - 900 °C, 900 - 1100 °C, 1100 - 1300 °C, 900 - 1300 °C.

[0048] <Example>

[0049] Example 1

[0050] A hard carbon material and its preparation method include the following:

[0051] Using coconut shell as the carbon-based raw material, after crushing the coconut shell, it is put into a hydrothermal reaction kettle together with deionized water. The material of the hydrothermal reaction kettle is polytetrafluoroethylene, and the reaction is carried out. After being treated at 220 °C for 10 h, the obtained product is subjected to suction filtration, washing, and drying treatments to obtain a primary carbonized body. The particle size of the primary carbonized body is 6 - 10 μm.

[0052] Mix the previously obtained primary carbonized body with concentrated sulfuric acid and heat it in a water bath to 35 °C for 4 h. After treatment, wash and dry it, and then ball mill it (0.5 h) with toluene and KH 550 to obtain a primary carbonized body with oxygen-containing groups after coupling treatment. Among them, the mass ratio of the primary carbonized body to KH 550 is 1:0.04.

[0053] Immerse the primary carbonized body with silane-oxygen-containing groups obtained from the above treatment in the film-forming solution.

[0054] The preparation method of the film-forming solution is as follows: CMC and carbon nanotubes form a CMC dispersion (0.1 wt%) and a carbon nanotube dispersion (8 mg / mL) respectively, and mix the above two dispersions, and the volume ratio is 5:50.

[0055] The primary carbonized body immersed in the film-forming solution is then subjected to vacuum suction so that the film-forming solution coats the surface of the carbonized body to form a coated body, and the film-forming solution accounts for 8% of the mass of the entire coated body. Place it in an oven at 80 °C and dry for 6 h.

[0056] Carbonize the coated body obtained from the above treatment. Under a nitrogen atmosphere, heat it at a heating rate of 5 °C / min to 1100 °C, keep it warm for 3 h, and then cool it naturally to obtain a hard carbon material.

[0057] Example 2

[0058] The difference between this example and Example 1 is that the primary carbonized body is not treated with concentrated sulfuric acid.

[0059] Example 3

[0060] The difference between this example and Example 1 is that carbon nanotubes are not added to the coating solution.

[0061] Example 4

[0062] The difference between this example and Example 1 is that the primary carbonized body is not treated with KH 550 and film-forming coating.

[0063] Example 5

[0064] The difference between this example and Example 1 is that CMC and carbon nanotubes form a CMC dispersion (0.08 wt%) and a carbon nanotube dispersion (5 mg / mL) respectively.

[0065] Example 6

[0066] The difference between this example and Example 1 is that it is heated to 1000 °C at a heating rate of 3 °C / min and kept warm for 4 h.

[0067] Example 7

[0068] The difference between this embodiment and Embodiment 1 is that the temperature is raised to 1300°C at a heating rate of 6°C / min and held for 2 h.

[0069] <Comparative Example>

[0070] Comparative Example 1

[0071] The difference between this comparative example and Embodiment 1 is that the coconut shell is directly carbonized to obtain a carbonized body, and the carbonization conditions are the same as those in Embodiment 1.

[0072] <Test Example>

[0073] Using the hard carbon materials prepared in Embodiments 1 to 7 and Comparative Example 1 as samples, tests were conducted. The samples, carbon black, and PVDF were blended at a mass ratio of 80:10:10 to form a slurry, and then made into an electrode sheet. Then, a sodium sheet was used as the counter electrode, and 1 mol / L DMC was used as the electrolyte to prepare a button cell.

[0074] The initial Coulombic efficiency and reversible specific capacity of the aforementioned hard carbon samples were measured. The results are shown in Table 1. Among them, Embodiments are represented by E, and Comparative Examples are represented by C.

[0075] Table 1 Measurement Results of Hard Carbon Materials

[0076] Sample E1 E2 E3 E4 E5 E6 E7 C1 Reversible specific capacity (mAh / g) 501.3 479.6 483.1 421.6 492.4 486.4 480.9 410.6 Initial Coulombic efficiency (%) 90.2 87.4 87.9 80.3 89.1 88.2 87.1 77.6

[0077] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A hard carbon material, characterized in that, including a hard carbon body, a carbon film coated on the surface of the hard carbon body; the raw material of the carbon film is CMC and nanowires; the nanowires include at least one of carbon nanowires and titanium dioxide nanowires; a preparation method of the hard carbon material, comprising the following steps: S1 Using biomass as the carbon-based raw material, the biomass is hydrothermally treated to obtain a primary carbonized body; S2 The primary carbonized body is treated with a silane coupling agent and reserved; S3 After CMC forms a CMC dispersion, a nanowire dispersion is added and blended to obtain a film-forming solution; S4 After the film-forming solution is coated on the surface of the primary carbonized body, it is dried and carbonized to obtain the hard carbon material.

2. The hard carbon material according to claim 1, characterized in that, The hard carbon body is prepared from biomass as the raw material.

3. The hard carbon material according to claim 2, wherein The biomass includes at least one of coconut shell, lotus stem, buckwheat shell, water hyacinth, water chestnut shell, coffee shell, and pinecone shell.

4. The hard carbon material according to claim 1, wherein in S1, the conditions of the hydrothermal treatment are that after the biomass is crushed, it is put into a hydrothermal reaction kettle together with deionized water for reaction. The reaction time is 6-14 h, and the reaction temperature is 150-250 °C. After the obtained product is filtered, washed, and dried, the primary carbonized body is obtained.

5. The hard carbon material according to claim 1, wherein in S3, the concentration of the CMC dispersion is 0.08-0.12 wt%; the concentration of the nanowire dispersion is 5-10 mg / mL; the volume ratio of the CMC dispersion to the nanodispersion is 2-7:40-80.

6. The hard carbon material according to claim 1, wherein The primary carbonized body is put into the coating solution. After coating and forming, it is taken out and placed in an oven at 70-90 °C for drying for 5-10 h to obtain a coated body.

7. The hard carbon material according to claim 1, wherein in S4, the conditions of the carbonization treatment are that under a N2 atmosphere, it is heated to 600-1300 °C at a heating rate of 1-10 °C / min, and the carbonization time is 2-5 h.

8. The hard carbon material according to any one of claims 1, 4 to 7, characterized in that, Before S2, the primary carbonized body is acidified to obtain a primary carbonized body containing oxygen-containing functional groups.