A hard carbon material, its preparation method and application

Abstract

The present invention belongs to the technical field of battery material preparation, and specifically discloses a hard carbon material, a preparation method thereof and an application. The preparation method of the hard carbon material provided by the present invention impregnates the pore-filling carbon source mixed system into the large and small pores in the activated carbon under high temperature and high pressure. The pore-filling carbon source deposits into small molecule fragments in the pores of the activated carbon through a chemical reaction, and then rapidly raises the temperature to a specific temperature and keeps it warm, so that the pore-filling carbon source decomposes to form a carbon matrix to block the pores. Moreover, 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 broadening the interlayer spacing. The preparation method provided by the present invention greatly improves the fast charging performance of the hard carbon material when applied to the electrode sheet by reducing the closed pore volume and broadening the interlayer spacing.

Description

Technical Field

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

[0002] At present, the sodium storage mechanism of hard carbon is still controversial, but its charge-discharge curve mainly includes a sloping region above 0.1V and a plateau region below 0.1V. The high plateau capacity not only helps to achieve excellent total capacity but also can obtain excellent initial Coulomb efficiency (≥85%). This advantage also ensures the high energy density and long cycle life of the full battery system. However, the plateau capacity is mainly dominated by the graphite layer and closed pores of hard carbon, and the closed pores can provide more than 80% of the plateau capacity. Therefore, the current research on hard carbon materials mainly focuses on the design and regulation of the 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 advantage of the closed pores completely fails, resulting in poor fast charging performance of hard carbon. However, the current hard carbon synthesis methods will inevitably form a large number of closed pores. Therefore, it is very necessary to target the design of hard carbon without closed pores and only with an enlarged interlayer distance for achieving extremely fast charging. Summary of the Invention

[0004] In view of this, the present invention provides a hard carbon material, a preparation method thereof, and an application thereof. 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 broadening the interlayer distance.

[0005] To solve the above technical problems, the technical solution provided by the present invention is as follows:

[0006] The first aspect of the present invention provides a preparation method of a hard carbon material, comprising the following steps:

[0007] S1. Adding a pore-filling carbon source to an ethylene glycol aqueous solution to obtain a pore-filling carbon source mixed system;

[0008] S2. Adding activated carbon to the pore-filling carbon source mixed system, performing deposition at 6MPa - 9MPa and 120°C - 140°C, filtering by suction, washing, and drying to obtain an activated carbon mixture;

[0009] S3. Heating the activated carbon mixture to 1300°C - 1500°C at a rate of 300°C / s - 320°C / s for heat preservation to obtain a hard carbon material;

[0010] In S1, the pore-filling carbon source is a mixture of a polysaccharide substance and benzene.

[0011] Compared with the prior art, in the hard carbon material provided by the present invention, a mixture of a polysaccharide substance and benzene is selected as a carbon source. Under high temperature and high pressure, the molten polysaccharide substance will wrap benzene and enter the interior of the activated carbon pores. Benzene can also enter the extremely small pores of the activated carbon. Due to the high viscosity of the polysaccharide substance, it will fix benzene inside the small pores; the polysaccharide substance and benzene as pore-filling carbon sources will block the large and small pores of the activated carbon to the greatest extent. The conditions of high temperature and high pressure will cause the polysaccharide substance and benzene to deposit small molecule fragments in the activated carbon pores through chemical reactions, thereby facilitating the increase of the closed pore rate of the hard carbon and the widening of the layer spacing; further, the present invention limits the heating rate. 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 a specific heating rate can also cause a temperature difference between the inner and outer surfaces of the activated carbon. When heat preservation is carried out at a specific temperature, the thermal field gradient difference inside and outside the activated carbon can cause the disordered carbon atoms inside the activated carbon to preferentially nucleate, grow and rearrange to form a large number of graphite domains. At the same time, due to the difference in the nucleation energy barrier of carbon atoms at different positions, there will be a strong electrostatic repulsion force between the layers during the formation of the graphite domains, thereby widening the layer spacing.

[0012] The preparation method of the hard carbon material provided by the present invention deposits small molecule fragments by high-pressure impregnation of a pore-filling carbon source mixture system in the large and small pores of activated carbon, and then rapidly heats up to a specific temperature for heat preservation, so that the pore-filling carbon source decomposes 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 barrier of different carbon atoms, there is a strong electrostatic repulsion force between the layers, thereby widening the layer 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 layer spacing.

[0013] Preferably, in S1, the mass ratio of the polysaccharide substance to benzene in the pore-filling carbon source is 1:(1 - 2).

[0014] Preferably, in S1, the polysaccharide substance is at least one of oligopeptide, oligosaccharide, oligonucleotide or cellulose.

[0015] By further limiting the specific components of the polysaccharide substance in the pore-filling carbon source and the proportion range of the polysaccharide substance and benzene, the present invention can fully utilize the high viscosity of the polysaccharide substance to block benzene in the small pores of the activated carbon, thereby reducing the closed pore volume and improving the fast charging ability of the hard carbon material.

[0016] When the content of benzene is on the high side and the content of the polysaccharide substance is too low, the polysaccharide substance cannot completely block benzene in the small pores, resulting in an increase in the closed pore volume and thus reducing the fast charging ability of the hard carbon material; when the content of benzene is on the low side and the polysaccharide substance is on the high side, the polysaccharide substance completely encloses benzene and makes 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.

[0017] Preferably, in S1, the mass-volume ratio of the hole-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%.

[0018] Preferably, in S2, the mass ratio of the hole-filling carbon source to the activated carbon is (3 - 5) : (2 - 4).

[0019] By limiting the ratio of the hole-filling carbon source to the activated carbon, it can ensure that the hole-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 charging ability of the hard carbon material.

[0020] Preferably, in S2, the deposition time is 3 h - 4 h.

[0021] The present invention further limits the deposition time, which can fully fill the substances in the hole-filling carbon source mixture into the activated carbon, thereby reducing the closed pore volume of the hard carbon material and improving the fast charging ability of the hard carbon material.

[0022] Preferably, in S3, the heat preservation time is 3 h - 4 h.

[0023] The preferred heat preservation time is beneficial to further broaden the layer spacing and improve the fast charging ability of the hard carbon material.

[0024] The second aspect of the present invention provides a hard carbon material prepared by the above-mentioned preparation method of the hard carbon material.

[0025] The third aspect of the present invention provides the application of the above-mentioned hard carbon material in a sodium-ion battery.

[0026] Using the hard carbon material provided by the present invention to prepare an electrode sheet can significantly improve the fast charging ability of the battery. Description of the Drawings

[0027] Figure 1 It is the SEM diagram of the hard carbon material prepared in Example 1 of the present invention. Detailed Embodiments

[0028] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and the 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.

[0029] Example 1

[0030] This example provides a preparation method of a hard carbon material, including the following steps:

[0031] S1. Add 5 g of pore-filling carbon source to 50 mL of ethylene glycol aqueous solution to obtain a pore-filling carbon source mixed system. Among them, the pore-filling carbon source is a mixture of oligopeptide and benzene with a mass ratio of 1:2, and the volume content of ethylene glycol in the ethylene glycol aqueous solution is 45%;

[0032] S2. Add 2 g of activated carbon to the pore-filling carbon source mixed system, deposit for 3 h at 9 MPa and 120 °C, filter by suction, wash, and dry at 80 °C for 12 h to obtain an activated carbon mixture;

[0033] S3. Heat the activated carbon mixture to 1500 °C at a rate of 320 °C / s and hold for 3 h to obtain a hard carbon material.

[0034] Example 2

[0035] This example provides a method for preparing a hard carbon material, including the following steps:

[0036] 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. Among them, the pore-filling carbon source is a mixture of oligosaccharide and benzene with a mass ratio of 1:1, and the volume content of ethylene glycol in the ethylene glycol aqueous solution is 55%;

[0037] S2. Add 4 g of activated carbon to the pore-filling carbon source mixed system, deposit for 4 h at 6 MPa and 140 °C, filter by suction, wash, and dry at 80 °C for 12 h to obtain an activated carbon mixture;

[0038] S3. Heat the activated carbon mixture to 1300 °C at a rate of 300 °C / s and hold for 4 h to obtain a hard carbon material.

[0039] Example 3

[0040] This example provides a method for preparing a hard carbon material, including the following steps:

[0041] S1. Add 4 g of pore-filling carbon source to 60 mL of ethylene glycol aqueous solution to obtain a pore-filling carbon source mixed system. Among them, the pore-filling carbon source is a mixture of oligonucleotide and benzene with a mass ratio of 1:1.5, and the volume content of ethylene glycol in the ethylene glycol aqueous solution is 50%;

[0042] S2. Add 3 g of activated carbon to the pore-filling carbon source mixed system, deposit for 3.5 h at 8 MPa and 130 °C, filter by suction, wash, and dry at 80 °C for 12 h to obtain an activated carbon mixture;

[0043] S3. Heat the activated carbon mixture to 1400 °C at a rate of 310 °C / s and hold for 3.3 h to obtain a hard carbon material.

[0044] Example 4

[0045] This example provides a method for preparing a hard carbon material, including the following steps:

[0046] S1. Add 4.5 g of the 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 with a mass ratio of 1:1.8, and the volume content of ethylene glycol in the ethylene glycol aqueous solution is 52%.

[0047] S2. Add 3.5 g of activated carbon to the pore-filling carbon source mixed system, deposit at 7 MPa and 135 °C for 3.2 h, perform suction filtration, washing, and dry at 80 °C for 12 h to obtain an activated carbon mixture.

[0048] S3. Heat the activated carbon mixture to 1450 °C at a rate of 315 °C / s and hold for 3.4 h to obtain a hard carbon material.

[0049] Example 5

[0050] This example provides a method for preparing a hard carbon material. Compared with Example 1, the difference is:

[0051] Increase the amount of benzene used. Among them, the pore-filling carbon source is a mixture of oligopeptide and benzene with a mass ratio of 1:3.

[0052] Other components, as well as the preparation method, are the same as those in Example 1.

[0053] Example 6

[0054] This example provides a method for preparing a hard carbon material. Compared with Example 1, the difference is:

[0055] Reduce the amount of benzene used. Among them, the pore-filling carbon source is a mixture of oligopeptide and benzene with a mass ratio of 1:0.5.

[0056] Other components, as well as the preparation method, are the same as those in Example 1.

[0057] Comparative Example 1

[0058] This comparative example provides a method for preparing a hard carbon material. Compared with Example 1, the difference is: Replace the oligopeptide with an equal amount of benzene.

[0059] Other components, as well as the preparation method, are the same as those in Example 1.

[0060] Comparative Example 2

[0061] This comparative example provides a method for preparing a hard carbon material. Compared with Example 1, the difference is:

[0062] Replace benzene with an equal amount of oligopeptide.

[0063] Other components, as well as the preparation method, are the same as those in Example 1.

[0064] Comparative Example 3

[0065] This comparative example provides a method for preparing a hard carbon material. Compared with Example 1, the difference lies in:

[0066] The oligopeptide is replaced with an equal amount of urea;

[0067] Other components, as well as the preparation method, are the same as those in Example 1.

[0068] Comparative Example 4

[0069] This comparative example provides a method for preparing a hard carbon material. Compared with Example 1, the difference lies in:

[0070] Benzene is replaced with acetonitrile;

[0071] Other components, as well as the preparation method, are the same as those in Example 1.

[0072] Comparative Example 5

[0073] This comparative example provides a method for preparing a hard carbon material. Compared with Example 1, the difference lies in:

[0074] Only the deposition temperature of S2 is restricted, and the pressure condition is changed. Specifically:

[0075] S2. Add 2 g of activated carbon to the pore-filling carbon source mixed system, deposit for 3 h at 5 MPa and 120 °C, filter by suction, wash, and dry at 80 °C for 12 h to obtain an activated carbon mixture;

[0076] Other components, as well as the preparation method, are the same as those in Example 1.

[0077] Comparative Example 6

[0078] This comparative example provides a method for preparing a hard carbon material. Compared with Example 1, the difference lies in:

[0079] The heating rate in S3 is changed. Specifically:

[0080] S3. Heat the activated carbon mixture to 1500 °C at a rate of 200 °C / s and hold for 3 h to obtain a hard carbon material;

[0081] Other components, as well as the preparation method, are the same as those in Example 1.

[0082] Comparative Example 7

[0083] This comparative example provides a method for preparing a hard carbon material. Compared with Example 1, the difference lies in:

[0084] The heating rate in S3 is changed. Specifically:

[0085] S3. Heat the activated carbon mixture to 1500 °C at a rate of 400 °C / s and hold for 3 h to obtain a hard carbon material;

[0086] The other components, preparation method are the same as those in Example 1.

[0087] Comparative Example 8

[0088] This comparative example provides a preparation method of a hard carbon material. Compared with Example 1, the difference lies in:

[0089] Changing the heat preservation temperature in S3. Specifically:

[0090] S3. Heat the activated carbon mixture at a rate of 320 °C / s to 1600 °C and keep it for 3 h to obtain the hard carbon material;

[0091] The other components, preparation method are the same as those in Example 1.

[0092] The interlayer distances (d 002 ) of the hard carbon materials prepared in Examples 1-6 and Comparative Examples 1-8 were respectively tested and applied to the preparation of sodium ion batteries. The sodium ion platform capacity and the fast charging ability at 5 A / g were tested. The specific operations are as follows:

[0093] The hard carbon materials prepared in Examples 1-6 and Comparative Examples 1-8 were respectively ground and mixed with acetylene black and sodium alginate according to a mass ratio of 8:1:1, and water was added and mixed evenly to obtain a mixed slurry (solid content 85%); the mixed slurry was coated on the surface of copper foil, and the coating amount was 2.5 g / cm 3 , and vacuum dried at 80 °C for 12 h to obtain a coated material; the coated material was cut into small round pieces with a diameter of 12 mm to obtain a negative electrode sheet; the negative electrode sheet was assembled into a battery, with a sodium metal sheet as the counter electrode, a glass fiber as the separator, and an electrolyte of 1 mol / L NaPF6 EC / DEC to obtain a sodium ion battery;

[0094] The assembled mock-up battery was placed on a Land CT2001A battery test system for electrochemical performance testing. The test temperature was 25 °C, the test electrochemical window was 0 V to 2.5 V, and the test current densities were 30 mA / g and 5 A / g;

[0095] Closed pore volume: The true density (ρ) of the prepared sample was tested, and then according to the formula: V 闭孔 = 1 / ρ - 1 / 2.26, where 2.26 is the true density of graphite.

[0096] The specific test results are shown in Table 1:

[0097] Table 1

[0098]

[0099] From the detection data of applying the hard carbon material provided in the embodiment of the present invention to the battery, the hard carbon material provided by the present invention has excellent fast charging performance.

[0100] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. 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 method for preparing a hard carbon material, characterized in that, It includes the following steps: S1. Add the pore-filling carbon source to the ethylene glycol aqueous solution to obtain a pore-filling carbon source mixed system; S2. Add activated carbon to the pore-filling carbon source mixed system, carry out deposition at 6 MPa - 9 MPa and 120°C - 140°C, perform suction filtration, washing, and drying to obtain an activated carbon mixture; S3. Heat the activated carbon mixture to 1300°C - 1500°C at a rate of 300°C / s - 320°C / s for heat preservation to obtain a hard carbon material; In S1, the pore-filling carbon source is a mixture of a polysaccharide substance and benzene with a mass ratio of 1:(1 - 2).

2. The preparation method of the hard carbon material according to claim 1, characterized in that, The polysaccharide substance is at least one of oligopeptide, oligosaccharide, oligonucleotide, or cellulose.

3. The preparation method of the hard carbon material according to claim 1, characterized in that 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%.

4. The preparation method of the hard carbon material according to claim 1, wherein, In S2, the mass ratio of the pore-filling carbon source to the activated carbon is (3 - 5):(2 - 4).

5. The preparation method of the hard carbon material according to claim 1, characterized in that, In S2, the deposition time is 3 h - 4 h.

6. The preparation method of the hard carbon material according to claim 1, characterized in that, In S3, the heat preservation time is 3 h - 4 h.

7. A hard carbon material, characterized in that, It is prepared by the preparation method of the hard carbon material according to any one of claims 1 - 6.

8. Application of the hard carbon material prepared by the preparation method of the hard carbon material according to any one of claims 1 - 6 or the hard carbon material according to claim 7 in a sodium-ion battery.

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