A high-capacity pitch-based hard carbon material, its preparation method, and its application.

Abstract

This invention relates to the field of anode material technology, and discloses a high-capacity pitch-based hard carbon material, its preparation method, and its application. The preparation method includes the following steps: pitch is oxidized to obtain oxidized pitch; S2 oxidized pitch, a thiol crosslinking agent, and an organic sodium salt are crosslinked and heat-treated to obtain the hard carbon material. The hard carbon material provided in this application utilizes the nano- and micro-pores formed by the thiol crosslinking agent to enhance the sodium storage capacity of the material, and improves the specific capacity of the material through gas doping with phosphorus. The resulting composite material is applied to sodium-ion batteries to improve energy density and cycle performance.

Description

Technical Field

[0001] This invention relates to the field of negative electrode material technology, specifically to a high-capacity pitch-based hard carbon material, its preparation method, and its application. Background Technology

[0002] As market demands for higher energy density in sodium-ion batteries increase, the hard carbon used in sodium-ion battery anode materials requires high specific capacity and compaction density. Currently, commercially available hard carbon has a specific capacity of approximately 300 mAh / g and a compaction density of approximately 1.0 g / cm³. 3 This results in a low energy density in the material. Measures to improve the energy density of hard carbon mainly involve raw material selection, material doping, and processes such as pore formation to increase the specific capacity, while also considering the material's fast-charging performance. Under these circumstances, asphalt, as a negative electrode material, possesses advantages such as high isotropy, wide availability and high consistency of raw materials, high compaction density, and good kinetic properties. However, it suffers from drawbacks such as low specific capacity. Therefore, it is necessary to improve the sodium storage capacity of the material by oxidizing its surface to create nano- and micro-sized pores.

[0003] For example, patent CN115991467A discloses an oxidized asphalt-based hard carbon anode material for sodium-ion batteries and its preparation method. The preparation method involves using a fluidized bed to adjust the temperature and oxidize pulverized asphalt to obtain an oxidized precursor, followed by high-temperature carbonization to prepare the oxidized asphalt-based hard carbon anode material for sodium-ion batteries. The fluidized bed is used to oxidize and modify the asphalt, making the asphalt uniformly oxidized, deepening the oxidation degree, fully cross-linking the structure, increasing the interlayer spacing after carbonization, increasing the closed pores, and improving the specific capacity of the material. However, there are defects such as a small increase in specific capacity, deviation in power performance, and low initial efficiency, which limit the improvement of its energy density. Summary of the Invention

[0004] The technical problem solved by this invention:

[0005] This technology aims to address the issues of limited specific capacity improvement, power performance deviation, and low initial efficiency in existing anode materials.

[0006] The technical solution adopted in this invention is as follows:

[0007] To address the aforementioned technical problems, the present invention aims to provide a high-capacity asphalt-based hard carbon material, its preparation method, and its application. By adding a sulfur-based crosslinking agent and an organic sodium salt to oxidized asphalt, the degree of crosslinking of the material is improved, defects are reduced, the specific capacity and sodium ion diffusion rate of the material are increased, and the rate performance is enhanced.

[0008] The details are as follows:

[0009] First, the present invention provides a method for preparing a high-capacity pitch-based hard carbon material, comprising the following steps:

[0010] S1 asphalt is oxidized to obtain oxidized asphalt through oxidation treatment;

[0011] S1 includes the following features:

[0012] The mixture of oxygen and nitrogen is introduced into asphalt and then subjected to heat treatment. The oxygen mixture has a volume ratio of 9:1 and a flow rate of 10-100 L / h. The heat treatment process is carried out at a temperature of 150-250℃ for 1-6 hours.

[0013] S2 oxidized asphalt, mercapto crosslinking agent, and organic sodium salt are crosslinked and heat-treated to obtain hard carbon material;

[0014] S2 includes the following features:

[0015] The thiol crosslinking agent includes at least one of 4-mercaptobenzoic acid, 3-mercaptoglutamate, ethyl 3-mercaptopropionate, 2-mercaptobenzoic acid, 2-mercaptobenzothiazole, and ethyl 2-mercaptopropionate; the organic sodium salt includes at least one of sodium valproate, sodium pyruvate, sodium acetate, sodium hydroxybenzenesulfonate, and sodium ascorbate.

[0016] The mass ratio of oxidized asphalt, mercapto crosslinking agent, and organic sodium salt is 100:10~30:1~10.

[0017] Heat treatment 2: Temperature 1200~1500℃, time 1~6h; Phosphine mixed gas is introduced into heat treatment 2; Phosphine mixed gas: volume ratio of phosphine to argon is 0.5~5:10, flow rate is 10~100ml / min.

[0018] Second, the present invention provides a hard carbon material obtained by the aforementioned preparation method.

[0019] Third, the present invention provides an application of the aforementioned hard carbon material in sodium-ion batteries.

[0020] The technical effects achieved by this invention are as follows:

[0021] (1) The abundant hydroxyl and carboxyl chemical groups on the surface of oxidized asphalt are cross-linked with sulfur-based cross-linking agents to form a porous structure, which can enhance the sodium storage function of the material. At the same time, organic sodium salts are doped and carbonized to obtain sodium-doped amorphous carbon, which improves the insertion and extraction rate of sodium ions during charging and discharging, and improves the rate performance.

[0022] (2) By introducing reducing phosphine gas, a chemical reaction occurs with the oxidizing chemical groups on the surface of the material, PH3+O2=P+H2O, thereby achieving phosphorus doping on the surface of the material and forming more pores on the surface of the material to improve the specific capacity of the material. Attached Figure Description

[0023] Figure 1 The image shows a SEM image of the hard carbon material prepared in Example 1. Detailed Implementation

[0024] 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0025] <Example>

[0026] Example 1

[0027] This embodiment provides a method for preparing pitch-based hard carbon material, including the following steps:

[0028] Step S1: Add asphalt to a rotary furnace and introduce an oxygen-nitrogen mixture (volume ratio, oxygen:nitrogen = 9:1) at a rate of 50 L / h, and heat to 200°C for 3 hours to obtain oxidized asphalt.

[0029] Step S2: Mix 100g of oxidized asphalt, 20g of 4-mercaptobenzoic acid and 5g of sodium valproate evenly, and crosslink and cure at 500℃ for 3h. Then raise the temperature to 1300℃ and introduce a reducing phosphine mixed gas (volume ratio, phosphine:argon = 2:10, flow rate 50ml / min) for carbonization for 3h to obtain hard carbon material.

[0030] Example 2

[0031] This embodiment provides a method for preparing pitch-based hard carbon material, including the following steps:

[0032] Step S1: Add asphalt to a rotary furnace and introduce an oxygen-nitrogen mixture (volume ratio, oxygen:nitrogen = 9:1) at a rate of 10 L / h, heat to 150°C, and introduce for 6 hours to obtain oxidized asphalt.

[0033] Step S2: Mix 100g of oxidized asphalt, 10g of 3-mercaptoglutamate and 1g of sodium pyruvate evenly, and crosslink and cure at 400℃ for 6h. Then raise the temperature to 1200℃ and introduce a reducing phosphine mixed gas (volume ratio, phosphine:argon = 0.5:10, flow rate 100ml / min) for carbonization for 6h to obtain hard carbon material.

[0034] Example 3

[0035] This embodiment provides a method for preparing pitch-based hard carbon material, including the following steps:

[0036] Step S1: Add asphalt to a rotary furnace and introduce an oxygen-nitrogen mixture (volume ratio, oxygen:nitrogen = 9:1) at a rate of 100 L / h, heat to 250°C, and introduce for 1 hour to obtain oxidized asphalt.

[0037] Step S2: Mix 100g of oxidized asphalt, 30g of ethyl 3-mercaptopropionate and 10g of sodium acetate evenly, and crosslink and cure at 600℃ for 1h. Then raise the temperature to 1500℃ and introduce a reducing phosphine mixed gas (volume ratio, phosphine:argon = 2:10, flow rate 10ml / min) for carbonization for 1h to obtain hard carbon material.

[0038] <Comparative Example>

[0039] Comparative Example 1

[0040] The difference from Example 1 is that asphalt is used instead of oxidized asphalt, otherwise it is the same as Example 1.

[0041] Comparative Example 2

[0042] Unlike Example 1, 4-mercaptobenzoic acid was not added; otherwise, it was the same as Example 1.

[0043] Comparative Example 3

[0044] Unlike Example 1, sodium valproate was not added; otherwise, it was the same as Example 1.

[0045] Comparative Example 4

[0046] Unlike Example 1, phosphine gas was not introduced; only argon gas was introduced. Otherwise, the process was the same as in Example 1.

[0047] <Experimental Example>

[0048] SEM test

[0049] The hard carbon material prepared in Example 1 was subjected to SEM testing, and the results are as follows: Figure 1 As shown.

[0050] Depend on Figure 1 It can be seen that the material has a granular structure with slight granulation, and the particle size is between 10-15μm.

[0051] Physicochemical performance testing

[0052] The powder conductivity, powder OI value, specific surface area, and particle size of the hard carbon materials in Examples 1-3 and Comparative Examples 1-4 were tested according to the test methods in standard GB / T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries". At the same time, the grain size La was tested by XRD. The test results are shown in Table 1.

[0053] Table 1 Test Results

[0054]

[0055]

[0056] As can be seen from Table 1, the OI value, powder conductivity and grain size of the hard carbon materials prepared in Examples 1-3 are significantly better than those in Comparative Examples 1-4. The reason may be that organic sodium salts are doped in the materials of the examples, and sodium-doped amorphous carbon is obtained after carbonization, which increases the insertion and extraction rate of sodium ions during charging and discharging, thereby increasing the electronic conductivity of the material. Furthermore, phosphorus doping on its surface increases the pore structure of the material, thereby increasing the specific surface area of ​​the material and reducing the grain size.

[0057] Button test

[0058] The hard carbon materials obtained in Examples 1-3 and Comparative Examples 1-4 were assembled into coin cells according to the following methods.

[0059] The hard carbon materials prepared in Examples 1-3 and Comparative Examples 1-4 were used as negative electrodes and assembled into coin cells with sodium sheets, electrolytes, and separators in a glove box with argon and water contents both below 0.1 ppm. The separator was Celegard 2400; the electrolyte was a NaPF6 solution with a NaPF6 concentration of 1.1 mol / L, and the solvent was a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DMC) in a 1:1 weight ratio.

[0060] The prepared coin cells were labeled A-1, B-1, C-1, D-1, E-1, F-1, and G-1, respectively. The performance of the coin cells was then tested using a blue electric tester. The test conditions were: 0.1C charge-discharge rate, voltage range of 0.005-2V, and 3 cycles. The rate performance (1C / 0.1C) and cycle performance (0.5C / 0.5C, 100 cycles) of the coin cells were tested simultaneously. The test results are shown in Table 2.

[0061] Table 2 Test Results

[0062]

[0063] As can be seen from Table 2, the coin cells made using the hard carbon materials of Examples 1-3 have significantly higher discharge capacity and efficiency than those of Comparative Examples 1-4. Experimental results show that doping with sodium salts in the materials of this invention improves the rate of sodium ion insertion / extraction during charge / discharge, thus improving the rate capability and initial efficiency; simultaneously, phosphorus doping enhances the specific capacity of the material.

[0064] Soft-pack battery performance test

[0065] Using the hard carbon materials of Examples 1-3 and Comparative Examples 1-4 as negative electrode active materials, layered oxides (NaFe) 1 / 3M n1 / 3 Ni 1 / 3 O2 was used as the positive electrode material, electrolyte, and separator to assemble a 5Ah pouch battery. The separator was Celegard 2400, and the electrolyte was a NaPF6 solution (a 1:1 volume ratio mixture of EC and DEC, with a NaPF6 concentration of 1.3 mol / L). The fabricated pouch batteries were labeled A-2, B-2, C-2, D-2, E-2, F-2, and G-2, respectively. Their cycle and rate performance were tested under the following conditions:

[0066] Cyclic performance: The cycle performance of the battery was tested at a charge / discharge rate of 1C / 1C, a voltage range of 1.5V-3.95V, and a temperature of 25±3℃.

[0067] Rate performance: The battery is charged to 100% SOC at a rate of 1C using constant current + constant voltage mode (1C + 0.1C). Then the constant current ratio is calculated as constant current capacity / (constant current capacity + constant voltage capacity).

[0068] The test results are shown in Table 3.

[0069] Table 3 Test Results

[0070] Negative electrode material used in batteries Capacity retention rate (%) after 500 cycles Fast charging performance (constant current ratio) Example 1 96.18 95.2％ Example 2 96.99 94.1％ Example 3 95.34 96.2％ Comparative Example 1 91.17 92.7％ Comparative Example 2 90.54 91.3％ Comparative Example 3 87.32 89.4％ Comparative Example 4 88.54 90.5％

[0071] Table 3 compares the cycle performance and fast charging performance of the soft-pack batteries prepared with the obtained negative electrode materials. It can be seen that the cycle performance of the battery in the example is significantly better than that of the comparative example. The reason is that the material in the example has a lower OI value, which reduces expansion and improves cycle performance; at the same time, the sodium salt coating on the surface of the material in the example increases the number of sodium ions during charging and discharging, thus improving the rate performance.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A process for the preparation of high capacity pitch-based hard carbon material, characterized in that, The method comprises the following steps: S1: obtaining oxidized pitch by oxidizing pitch; S2: obtaining hard carbon material by cross-linking and heat treating the oxidized pitch, mercapto cross-linking agent and organic sodium salt; The second heat treatment is performed at a temperature of 1200-1500℃ for 1-6h, and phosphine mixed gas is introduced during the second heat treatment.

2. The production method according to claim 1, characterized by, S1 comprises feature (S1-1): (S1-1) introducing oxygen mixed gas into pitch and performing the first heat treatment to obtain.

3. The production method according to claim 2, characterized by, S1 comprises at least one of features (S1-1-1) to (S1-1-2): (S1-1-1) the oxygen mixed gas comprises oxygen and nitrogen at a volume ratio of 9:1; (S1-1-2) the oxygen mixed gas has a flow rate of 10-100L / h.

4. The production method according to claim 2, characterized by, S1 comprises feature (S1-1-3): (S1-1-3) the first heat treatment is performed at a temperature of 150-250℃ for 1-6h.

5. The production method according to any one of claims 1 to 4, characterized by, S2 comprises at least one of features (S2-1) to (S2-2): (S2-1) the mercapto cross-linking agent comprises at least one of 4-mercaptobenzoic acid, 3-mercapto glutamic acid, 3-mercapto propyl ethyl ester, 2-mercaptobenzoic acid, 2-mercaptobenzothiazole and 2-mercapto propyl ethyl ester; (S2-2) the organic sodium salt comprises at least one of sodium valproate, sodium pyruvate, sodium acetate, sodium hydroxybenzenesulfonate and sodium ascorbate.

6. The production method according to claim 5, wherein S2 comprises feature (S2-3): (S2-3) the mass ratio of the oxidized pitch, mercapto cross-linking agent and organic sodium salt is 100:10-30:1-10.

7. The preparation method according to claim 1, characterized in that, The phosphine mixed gas comprises phosphine and argon at a volume ratio of 0.5-5:10, and has a flow rate of 10-100ml / min.

8. A hard carbon material prepared by the method of any one of claims 1 to 7.

9. Use of the hard carbon material of claim 8 in a sodium ion battery.

Images