Hard carbon material and preparation method and application thereof

Abstract

The invention belongs to the technical field of battery material preparation, and particularly discloses a hard carbon material and a preparation method and application thereof. According to the preparation method of the hard carbon material provided by the invention, the pore-filling carbon source mixed system is impregnated in large and small pores in the activated carbon at high temperature and high pressure, the pore-filling carbon source is deposited into small molecular fragments in the pores of the activated carbon through chemical reaction, and the temperature is further rapidly increased to a specific temperature for heat preservation; the pore-filling carbon source is decomposed to form a carbon matrix to block a pore channel, disordered carbon atoms in the activated carbon can also form a large number of graphite domains, and due to nucleation energy barrier differences of different carbon atoms during formation of the graphite domains, a strong electrostatic repulsion effect exists between layers, so that the interlayer spacing is widened. According to the preparation method provided by the invention, by reducing the closed pore volume and widening the interlayer spacing, the fast charging performance of the hard carbon material applied to the electrode plate is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery material preparation, and in particular to a hard carbon material and a preparation method and application thereof. Background Art

[0002] At present, the sodium storage mechanism of hard carbon is still controversial, but its charge and discharge curve mainly includes the slope area above 0.1V and the platform area below 0.1V. The high platform capacity not only helps to achieve excellent total capacity but also obtain excellent first coulomb efficiency (≥85%). This advantage also ensures the high energy density and long cycle life of the full battery system. However, the platform capacity is mainly dominated by the hard carbon graphite layer and closed pores, and the closed pores can provide more than 80% of the platform capacity. Therefore, the current research on hard carbon materials mainly focuses on the design and regulation of closed pore size, quantity and volume.

[0003] However, the storage of sodium ions in the closed pores of hard carbon is a slow process. When charging and discharging rapidly at high rates, the closed pore advantage is completely lost, resulting in the problem of poor fast charging performance of hard carbon. However, the current hard carbon synthesis method will inevitably form a large number of closed pores, so the targeted design of hard carbon without closed pores and only with an enlarged interlayer distance is very necessary to achieve extremely fast charging. Summary of the invention

[0004] In view of this, the present invention provides a hard carbon material and a preparation method and application thereof. The preparation method provided by the present invention greatly improves the fast charging performance of the hard carbon material applied to electrode sheets by reducing the closed pore volume and widening the interlayer spacing.

[0005] In order to solve the above technical problems, the technical solution provided by the present invention is: The first aspect of the present invention provides a method for preparing a hard carbon material, comprising the following steps: S1, adding a pore-filling carbon source to an ethylene glycol aqueous solution to obtain a pore-filling carbon source mixed system; S2, adding activated carbon to the pore-filling carbon source mixed system, depositing at 6MPa-9MPa and 120°C-140°C, filtering, washing, and drying to obtain an activated carbon mixture; S3, heating the activated carbon mixture to 1300°C-1500°C at a rate of 300°C / s-320°C / s and keeping the temperature to obtain a hard carbon material; In S1, the pore-filling carbon source is a mixture of polysaccharides and benzene.

[0006] Compared with the prior art, the hard carbon material provided by the present invention selects a mixture of polysaccharides and benzene as a carbon source. Under high temperature and high pressure, the molten polysaccharide will wrap benzene and enter the pores of the activated carbon. Benzene can also enter the extremely small pores of the activated carbon. Due to its high viscosity, the polysaccharide will fix the benzene inside the small pores. The polysaccharide and benzene as pore-filling carbon sources will block the large and small pores of the activated carbon to the greatest extent. The high temperature and high pressure conditions will cause the polysaccharide and benzene to deposit small molecular fragments in the pores of the activated carbon through a chemical reaction, which is beneficial to improving the hard carbon. The closed porosity is improved and the interlayer spacing is widened; further, the present invention limits the heating rate, and the rapid heating process can decompose the pore-filling carbon source inside the activated carbon pores and form a carbon matrix to block the pores, and the specific heating rate can also form a temperature difference between the inner and outer surfaces of the activated carbon. When the activated carbon is kept warm at a specific temperature, the thermal field gradient difference inside and outside the activated carbon can make the disordered carbon atoms inside the activated carbon preferentially nucleate, grow and rearrange to form a large number of graphite domains. At the same time, due to the difference in nucleation energy barriers of carbon atoms at different positions, there will be a strong electrostatic repulsion between layers when the graphite domain is formed, thereby widening the interlayer spacing.

[0007] The preparation method of the hard carbon material provided by the present invention is to deposit small molecular fragments by impregnating the pore-filling carbon source mixed system under high pressure in the large and small pores in the activated carbon, and then quickly heating it to a specific temperature for insulation, so that the pore-filling carbon source is decomposed to form a carbon matrix to block the pores, and the disordered carbon atoms in the activated carbon can also form a large number of graphite domains. During the formation of the graphite domains, due to the difference in the nucleation energy barriers of different carbon atoms, there is a strong electrostatic repulsion between the layers, thereby widening the interlayer spacing. The preparation method provided by the present invention greatly improves the fast charging performance of the hard carbon material applied to the electrode sheet by reducing the closed pore volume and widening the interlayer spacing.

[0008] Preferably, in S1, the mass ratio of the polysaccharide substance to benzene in the pore-filling carbon source is 1:(1-2).

[0009] Preferably, in S1, the polysaccharide substance is at least one of oligopeptides, oligosaccharides, oligonucleotides or cellulose.

[0010] By further limiting the specific composition of the polysaccharide in the pore-filling carbon source and the ratio range of the polysaccharide to benzene, the present invention can fully utilize the high viscosity of the polysaccharide to block benzene in the small pores of the activated carbon, thereby reducing the closed pore volume and improving the fast filling ability of the hard carbon material.

[0011] When the benzene content is too high, the polysaccharide content is too low, and the polysaccharide content cannot completely block benzene in the small pores, resulting in an increase in the closed pore volume, thereby reducing the fast charging ability of the hard carbon material; when the benzene content is too low, the polysaccharide content is too high, and the polysaccharide completely covers benzene, making it unable to be released in the small pores, thereby increasing the closed pore volume and reducing the fast charging ability of the hard carbon material.

[0012] Preferably, in S1, the mass volume ratio of the pore-filling carbon source to the ethylene glycol aqueous solution is (3-5) g: (50-70) mL, and the volume content of ethylene glycol in the ethylene glycol aqueous solution is 45%-55%.

[0013] Preferably, in S2, the mass ratio of the pore-filling carbon source to the activated carbon is (3-5): (2-4).

[0014] By limiting the ratio of the pore-filling carbon source to the activated carbon, it can be ensured that the pore-filling carbon source is completely filled in the activated carbon, thereby reducing the closed pore volume of the hard carbon material and improving the fast filling ability of the hard carbon material.

[0015] Preferably, in S2, the deposition time is 3h-4h.

[0016] The present invention further limits the deposition time, and can fully fill the substances in the pore-filling carbon source mixed system into the activated carbon, thereby reducing the closed pore volume of the hard carbon material and improving the fast filling ability of the hard carbon material.

[0017] Preferably, in S3, the insulation time is 3h-4h.

[0018] The optimal holding time is beneficial to further widen the interlayer spacing and improve the fast charging ability of the hard carbon material.

[0019] The second aspect of the present invention provides a hard carbon material prepared by the above-mentioned method for preparing the hard carbon material.

[0020] The third aspect of the present invention provides the use of the hard carbon material in a sodium ion battery.

[0021] The use of the hard carbon material provided by the present invention to prepare electrode sheets can significantly improve the fast charging capability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a SEM image of the hard carbon material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] Example 1 This embodiment provides a method for preparing a hard carbon material, comprising the following steps: S1. Add 5 g of a pore-filling carbon source to 50 mL of an ethylene glycol aqueous solution to obtain a pore-filling carbon source mixed system; wherein the pore-filling carbon source is a mixture of oligopeptides and benzene in a mass ratio of 1:2, and the volume content of ethylene glycol in the ethylene glycol aqueous solution is 45%; S2, adding 2 g of activated carbon to the pore-filling carbon source mixed system, depositing at 9 MPa and 120°C for 3 h, filtering, washing, and drying at 80°C for 12 h to obtain an activated carbon mixture; S3. The activated carbon mixture is heated to 1500°C at a rate of 320°C / s and kept at this temperature for 3 hours to obtain a hard carbon material.

[0025] Example 2 This embodiment provides a method for preparing a hard carbon material, comprising the following steps: S1. Add 3 g of pore-filling carbon source to 70 mL of ethylene glycol aqueous solution to obtain a pore-filling carbon source mixed system; wherein the pore-filling carbon source is a mixture of oligosaccharides and benzene in a mass ratio of 1:1, and the volume content of ethylene glycol in the ethylene glycol aqueous solution is 55%; S2, adding 4 g of activated carbon to the pore-filling carbon source mixed system, depositing at 6 MPa and 140° C. for 4 h, filtering, washing, and drying at 80° C. for 12 h to obtain an activated carbon mixture; S3. The activated carbon mixture is heated to 1300°C at a rate of 300°C / s and kept at this temperature for 4 hours to obtain a hard carbon material.

[0026] Example 3 This embodiment provides a method for preparing a hard carbon material, comprising the following steps: S1. Add 4 g of a pore-filling carbon source to 60 mL of an ethylene glycol aqueous solution to obtain a pore-filling carbon source mixed system; wherein the pore-filling carbon source is a mixture of oligonucleotide and benzene in a mass ratio of 1:1.5, and the volume content of ethylene glycol in the ethylene glycol aqueous solution is 50%; S2, adding 3 g of activated carbon to the pore-filling carbon source mixed system, depositing at 8 MPa and 130°C for 3.5 h, filtering, washing, and drying at 80°C for 12 h to obtain an activated carbon mixture; S3. The activated carbon mixture is heated to 1400°C at a rate of 310°C / s and kept at this temperature for 3.3 hours to obtain a hard carbon material.

[0027] Example 4 This embodiment provides a method for preparing a hard carbon material, comprising the following steps: S1. Add 4.5 g of a pore-filling carbon source to 65 mL of an ethylene glycol aqueous solution to obtain a pore-filling carbon source mixed system; wherein the pore-filling carbon source is a mixture of cellulose and benzene in a mass ratio of 1:1.8, and the volume content of ethylene glycol in the ethylene glycol aqueous solution is 52%; S2, adding 3.5 g of activated carbon to the pore-filling carbon source mixed system, depositing at 7 MPa and 135° C. for 3.2 h, filtering, washing, and drying at 80° C. for 12 h to obtain an activated carbon mixture; S3. The activated carbon mixture is heated to 1450°C at a rate of 315°C / s and kept at this temperature for 3.4 hours to obtain a hard carbon material.

[0028] Example 5 This embodiment provides a method for preparing a hard carbon material. Compared with Embodiment 1, the difference is that: Increasing the amount of benzene, wherein the pore-filling carbon source is a mixture of oligopeptide and benzene in a mass ratio of 1:3; The other ingredients and preparation method are the same as those in Example 1.

[0029] Example 6 This embodiment provides a method for preparing a hard carbon material. Compared with Embodiment 1, the difference is that: The amount of benzene used is reduced, wherein the pore-filling carbon source is a mixture of oligopeptide and benzene in a mass ratio of 1:0.5; The other ingredients and preparation method are the same as those in Example 1.

[0030] Comparative Example 1 This comparative example provides a method for preparing a hard carbon material, which is different from Example 1 in that: the oligopeptide is replaced with an equal amount of benzene; The other ingredients and preparation method are the same as those in Example 1.

[0031] Comparative Example 2 This comparative example provides a method for preparing a hard carbon material. Compared with Example 1, the difference is: Replace benzene with an equal amount of oligopeptide; The other ingredients and preparation method are the same as those in Example 1.

[0032] Comparative Example 3 This comparative example provides a method for preparing a hard carbon material. Compared with Example 1, the difference is: The oligopeptide was replaced with an equal amount of urea; The other ingredients and preparation method are the same as those in Example 1.

[0033] Comparative Example 4 This comparative example provides a method for preparing a hard carbon material. Compared with Example 1, the difference is: Replace benzene with acetonitrile; The other ingredients and preparation method are the same as those in Example 1.

[0034] Comparative Example 5 This comparative example provides a method for preparing a hard carbon material. Compared with Example 1, the difference is: Only limit the deposition temperature of S2 and change the pressure conditions, specifically: S2, adding 2 g of activated carbon to the pore-filling carbon source mixed system, depositing at 5 MPa and 120°C for 3 h, filtering, washing, and drying at 80°C for 12 h to obtain an activated carbon mixture; The other ingredients and preparation method are the same as those in Example 1.

[0035] Comparative Example 6 This comparative example provides a method for preparing a hard carbon material. Compared with Example 1, the difference is: Change the heating rate in S3, specifically: S3, heating the activated carbon mixture to 1500°C at a rate of 200°C / s and keeping the temperature for 3 hours to obtain a hard carbon material; The other ingredients and preparation method are the same as those in Example 1.

[0036] Comparative Example 7 This comparative example provides a method for preparing a hard carbon material. Compared with Example 1, the difference is: Change the heating rate in S3, specifically: S3, heating the activated carbon mixture to 1500°C at a rate of 400°C / s and keeping the temperature for 3 hours to obtain a hard carbon material; The other ingredients and preparation method are the same as those in Example 1.

[0037] Comparative Example 8 This comparative example provides a method for preparing a hard carbon material. Compared with Example 1, the difference is: Change the insulation temperature in S3, specifically: S3, heating the activated carbon mixture to 1600°C at a rate of 320°C / s and keeping the temperature for 3 hours to obtain a hard carbon material; The other ingredients and preparation method are the same as those in Example 1.

[0038] The hard carbon materials prepared in Examples 1-6 and Comparative Examples 1-8 were tested for their interlayer distances (d 002 ), used to prepare sodium ion batteries, and tested the obtained sodium ion platform capacity and 5A / g fast charging capability. The specific operation is as follows: The hard carbon materials prepared in Examples 1-6 and Comparative Examples 1-8 were ground and mixed with acetylene black and sodium alginate in a mass ratio of 8:1:1, and water was added to mix evenly to obtain a mixed slurry (solid content 85%); the mixed slurry was coated on the surface of the copper foil at a coating amount of 2.5 g / cm 3, vacuum dried at 80°C for 12h to obtain a coating material; cut the coating material into small discs with a diameter of 12mm to obtain a negative electrode sheet; assemble the negative electrode sheet into a battery, with a sodium metal sheet as a counter electrode, a glass fiber as a separator, and an electrolyte of 1 mol / L NaPF6EC / DEC to obtain a sodium ion battery; The assembled mold battery was placed on the Land CT2001A battery test system for electrochemical performance testing. The test temperature was 25°C, the test electrochemical window was 0V~2.5V, and the test current density was 30mA / g and 5A / g. Closed pore volume: Test the true density (ρ) of the prepared sample, and then use the formula: V 闭孔 =1 / ρ-1 / 2.26, 2.26 is the true density of graphite.

[0039] The specific test results are shown in Table 1: Table 1

[0040] According to the test data of using the hard carbon material provided by the embodiment of the present invention in the battery, the hard carbon material provided by the present invention has excellent fast charging performance.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a hard carbon material, characterized in that: The steps include: S1, adding a pore-filling carbon source to an ethylene glycol aqueous solution to obtain a pore-filling carbon source mixed system; S2, adding activated carbon to the pore-filling carbon source mixed system, depositing at 6MPa-9MPa and 120°C-140°C, filtering, washing, and drying to obtain an activated carbon mixture; S3, heating the activated carbon mixture to 1300°C-1500°C at a rate of 300°C / s-320°C / s and keeping the temperature to obtain a hard carbon material; In S1, the pore-filling carbon source is a mixture of polysaccharides and benzene.

2. The method for preparing a hard carbon material according to claim 1, characterized in that: In S1, the mass ratio of the polysaccharide substance to benzene in the pore-filling carbon source is 1:(1-2).

3. The method for preparing a hard carbon material according to claim 1 or 2, characterized in that: The polysaccharide substance is at least one of oligopeptides, oligosaccharides, oligonucleotides or cellulose.

4. The method for preparing a hard carbon material according to claim 1, characterized in that: In S1, the mass volume ratio of the pore-filling carbon source and the ethylene glycol aqueous solution is (3-5) g: (50-70) mL, and the volume content of ethylene glycol in the ethylene glycol aqueous solution is 45%-55%.

5. The method for preparing a hard carbon material according to claim 1, characterized in that: In S2, the mass ratio of the pore-filling carbon source to the activated carbon is (3-5):(2-4).

6. The method for preparing a hard carbon material according to claim 1, characterized in that: In S2, the deposition time is 3h-4h.

7. The method for preparing a hard carbon material according to claim 1, characterized in that: In S3, the insulation time is 3h-4h.

8. A hard carbon material, characterized in that: The hard carbon material is prepared by the method for preparing the hard carbon material according to any one of claims 1 to 7.

9. Use of a hard carbon material prepared by the method for preparing a hard carbon material according to any one of claims 1 to 7 or the hard carbon material according to claim 8 in a sodium ion battery.

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