A high-capacity pitch-based hard carbon composite material and a method for preparing the same

Abstract

The application discloses a high-capacity asphalt-based hard carbon composite material and a preparation method thereof. The preparation method comprises the following steps: dissolving oxidized asphalt in an organic solvent, adding an organic cobalt salt and uniformly dispersing to obtain solution A; uniformly dispersing the solution A and sodium phosphate in a dopamine tetrahydrofuran solution, and uniformly dispersing through a hydrothermal reaction and vacuum drying to obtain a precursor material; and heating the precursor material under vacuum, carbonizing to obtain the high-capacity asphalt-based hard carbon composite material. In the carbonization process, gaseous organic cobalt gasification is used to realize pore formation of the carbon material, and in the sodium phosphate carbonization process, phosphorus doping is realized to improve the electronic conductivity of the material, and sodium doping is realized to reduce the defects on the surface of the material and improve the electronic conductivity of the material. The obtained composite material has the characteristics of high specific capacity, high initial efficiency and excellent power performance when applied to a sodium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary battery material preparation, and specifically provides a high-capacity asphalt-based hard carbon composite material and a preparation method thereof. Background Art

[0002] Asphalt is a porous carbon material with low graphitization degree and disordered structure in the short range and long range, and is used as the negative electrode material of sodium ion batteries. It has the advantages of wide material sources, low cost and high compaction density. However, it has defects such as low specific capacity (≤300mAh / g) and low first efficiency (90-92%). Its application in sodium ion batteries affects the improvement of its energy density.

[0003] Patent application number CN201810604519.9 discloses a novel method for asphalt-based spherical porous doped modified hard carbon negative electrode material, the preparation process of which is as follows: (1) cross-linking oxidation preparation: high-temperature coal-based asphalt is crushed and a cross-linking agent is added under N2 protection, the temperature is raised to melt the asphalt, and the asphalt and the cross-linking agent undergo a cross-linking reaction to prepare cross-linked asphalt, and then an oxidant is added, and O2 is introduced, and the reaction is stirred at a constant temperature to obtain cross-linked oxidized asphalt; (2) spray granulation; (3) carbonization of asphalt microspheres; (4) coating and graphitization of asphalt-based hard carbon, wherein the coating material is oil-based asphalt, etc. Although the specific capacity and compaction density of the obtained material are improved, there are defects such as low initial efficiency and low specific capacity at low voltage. Summary of the Invention

[0004] In order to address the defects of traditional materials such as low first efficiency and low specific capacity at low voltage, the present invention provides a high-capacity asphalt-based hard carbon composite material and a preparation method thereof. The first efficiency of the material is improved by doping cobalt salt into the asphalt-based hard carbon precursor to form pores and then carbonizing it with sodium phosphate, then doping with phosphorus and doping with sodium.

[0005] The reason for the above-mentioned defects in asphalt is that petroleum asphalt is mainly composed of oil, resin and asphaltenes, among which the oil is mainly saturated and aromatic. The saturated is a non-polar oil, mainly a mixture of straight-chain and branched alkanes and cycloalkanes, and the content of saturated in petroleum asphalt is generally 5-20%.

[0006] The content of aromatic components in petroleum asphalt is generally 40-65%. In the colloidal structure of petroleum asphalt, aromatic components and saturated components together constitute a continuous phase, allowing the colloid and asphaltene to be stably dispersed therein, and are the main part of the dispersion medium for the colloid-melting asphaltene. At the same time, the saturated components and low-polymerization aromatic components in petroleum asphalt are easily vaporized and lost during high-temperature processes to form glassy carbon. When these glassy carbons are used in sodium-ion batteries, sodium ions can enter their pores, but due to their closed pores, sodium ions cannot be intercalated or deintercalated, resulting in low coulombic efficiency. One way to improve the initial efficiency of asphalt-based hard carbon is to increase the pores and interlayer spacing of the material, and at the same time, doping with sodium elements reduces the loss of sodium ions during the initial charge and discharge process, thereby improving the initial efficiency.

[0007] On the one hand, the present invention provides the following technical solutions:

[0008] A method for preparing a high-capacity pitch-based hard carbon composite material, the preparation method comprising:

[0009] Step S1:

[0010] The oxidized asphalt is dissolved in an organic solvent, and an organic cobalt salt is added to disperse the mixture uniformly to obtain a solution A;

[0011] Step S2:

[0012] Dispersing the solution A and sodium phosphate in the dopamine tetrahydrofuran solution uniformly, performing a hydrothermal reaction, and vacuum drying to obtain a precursor material;

[0013] Step S3:

[0014] The precursor material is heated and carbonized under vacuum to obtain the high-capacity pitch-based hard carbon composite material.

[0015] Furthermore, in the dopamine tetrahydrofuran solution in step S2, the solute is dopamine, the solvent is tetrahydrofuran, and the concentration is 1 to 10 wt%.

[0016] Furthermore, in step S1, the mass ratio of oxidized asphalt, organic solvent, and organic cobalt salt is 100:1000-5000:1-5.

[0017] Furthermore, in step S2, the mass ratio of solution A, sodium phosphate, and dopamine is 1000-5000:1-10:1-10.

[0018] Furthermore, the temperature of the hydrothermal reaction in step 2 is 100-200° C., the reaction time is 1-6 h, and the pressure is 1-5 MPa;

[0019] The vacuum drying temperature is 80° C. and the reaction time is 24 h.

[0020] Furthermore, the preparation process of the oxidized asphalt in step S1 is as follows:

[0021] Mix asphalt, absorber and binder in a mass ratio of 100:1 to 10:10 and press them into a block structure.

[0022] Then, the mixture is transferred to a microwave oven under an air atmosphere, heated at a power of 500 to 1000 W and a heating time of 10 to 120 seconds to obtain oxidized asphalt.

[0023] Furthermore, the absorber is ferrosoferric oxide, and the binder is starch, sodium cellulose or cellulose.

[0024] Furthermore, the organic solvent in step S1 is n-hexane, xylene, carbon disulfide or carbon tetrachloride.

[0025] Furthermore, in step S1, the organic cobalt salt is cobalt acetate, cobalt octoate, cobalt naphthenate or cobalt oxalate.

[0026] In another aspect of the present invention, a high-capacity pitch-based hard carbon composite material is provided, wherein the high-capacity pitch-based hard carbon composite material is prepared based on any one of the above methods.

[0027] Compared with the prior art, the high-capacity pitch-based hard carbon composite material and the preparation method thereof of the present invention have the following outstanding beneficial effects:

[0028] 1) The method of the present invention uniformly mixes asphalt, organic cobalt salt, and sodium phosphate through a hydrothermal reaction, and uniformly disperses the organic cobalt salt in the asphalt. During the carbonization process, gaseous cobalt can form pores in the carbon material and the gaseous cobalt is discharged along with the flowing protective gas, thereby partially reconstructing the hard carbon structure and generating a large number of closed pores, thereby improving the sodium storage performance of the material and the sodium storage performance and initial efficiency of the sodium ion battery.

[0029] 2) Vacuum microwave heating is used to prepare oxidized asphalt, and an absorber is added, which has high heating efficiency, fast oxidation rate, and high oxidation depth, so that more hydroxyl / carboxyl chemical groups are formed on the surface or inside the material, thereby improving the self-pore function of the material and its binding force with organic cobalt salts and sodium phosphate, thereby increasing the tap density.

[0030] 3) During the sodium phosphate carbonization process, phosphorus doping is achieved to improve the electronic conductivity of the material, and sodium doping is achieved to reduce defects on the surface of the material to improve the electronic conductivity of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a SEM image of the hard carbon composite material of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0033] Preparation method of oxidized asphalt:

[0034] 100g of asphalt, 5g of ferroferric oxide and 10g of starch were mixed evenly and pressed into a block structure. Then, they were transferred to a microwave oven under an air atmosphere at a power of 800W and a heating time of 60S to obtain oxidized asphalt.

[0035] Example 1

[0036] Step S1:

[0037] 100 g of oxidized asphalt was dissolved in 3000 g of n-hexane organic solvent, and then 3 g of cobalt acetate was added and dispersed evenly to obtain solution A;

[0038] Step S2:

[0039] 5 g of sodium phosphate was added to 3000 g of solution A and dispersed evenly, and then 100 g of a 5 wt% dopamine tetrahydrofuran solution was added and dispersed evenly, and the mixture was subjected to a hydrothermal reaction at a temperature of 150° C. and a pressure of 3 MPa for 3 h, and then vacuum dried at 80° C. for 24 h to obtain a precursor material;

[0040] Step S3:

[0041] The precursor material was transferred into a vacuum reactor, heated to 900° C. and carbonized for 3 h under a vacuum degree of 50 KPa to obtain a hard carbon composite material.

[0042] Example 2

[0043] Step S1:

[0044] 100 g of oxidized asphalt was dissolved in 1000 g of xylene organic solvent, and then 1 g of cobalt octoate was added and dispersed evenly to obtain solution A;

[0045] Step S2:

[0046] 1 g of sodium phosphate was added to 1000 g of solution A and dispersed evenly, and then added to 100 g of a 1 wt% dopamine tetrahydrofuran solution and dispersed evenly, and subjected to a hydrothermal reaction at a pressure of 1 MPa, a temperature of 100°C for 6 h, and vacuum dried at 80°C for 24 h to obtain a precursor material;

[0047] Step S3:

[0048] The precursor material was transferred into a vacuum reactor, heated to 700° C. and carbonized for 6 h under a vacuum degree of 10 KPa to obtain a hard carbon composite material.

[0049] Example 3

[0050] Step S1:

[0051] 100 g of oxidized asphalt was dissolved in 5000 g of carbon tetrachloride organic solvent, and then 5 g of cobalt oxalate was added and dispersed evenly to obtain solution A;

[0052] Step S2:

[0053] 10 g of sodium phosphate was added to 5000 g of solution A and dispersed evenly, and then added to 100 g of a 10 wt% dopamine tetrahydrofuran solution and dispersed evenly, and subjected to a hydrothermal reaction at a temperature of 200° C. and a pressure of 5 MPa for 1 h, and then vacuum dried at 80° C. for 24 h to obtain a precursor material;

[0054] Step S3:

[0055] The precursor material was transferred into a vacuum reactor, heated to 1000° C. and carbonized for 1 h under a vacuum degree of 100 KPa to obtain a hard carbon composite material.

[0056] Comparative Example 1:

[0057] The difference from Example 1 is that sodium phosphate is not added, and the other steps are the same as Example 1.

[0058] Comparative Example 2:

[0059] The difference from the embodiment is that cobalt acetate is not added, and the rest is the same as in embodiment 1

[0060] Performance Testing

[0061] (1) SEM test

[0062] The hard carbon composite negative electrode composite material prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown. Figure 1 It can be seen that the composite material has a uniform size distribution and slight adhesion, and the particle size is between 1-3μm.

[0063] (2) Physical and chemical performance test

[0064] The specific surface area, tap density, particle size, and powder conductivity of the hard carbon composite materials of the examples and comparative examples were tested in accordance with the national standard GB / T-24533-2019 "Graphite-based negative electrode materials for lithium-ion batteries." The diffusion coefficient of the materials was tested using GITT. The test results are shown in Table 1.

[0065] Table 1

[0066]

[0067] As can be seen from Table 1, the hard carbon negative electrode composite materials obtained in Examples 1-3 are significantly better than those in Comparative Examples 1-2 in terms of specific surface area and tap density parameters. The reason is that gaseous cobalt can form pores in the carbon material and the gaseous cobalt is discharged along with the flowing protective gas, and the hard carbon structure is partially reconstructed to generate a large number of closed pores, thereby improving the sodium storage performance of the material, and its porous structure improves the diffusion coefficient of the material.

[0068] (3) Button battery test

[0069] The hard carbon composite materials in Examples 1-3 and Comparative Examples 1-2 were used as negative electrode materials for lithium-ion batteries and assembled into button batteries. The specific preparation method of the negative electrode material was as follows: hard carbon composite material: CMC: SBR: SP: H2O were mixed in a mass ratio of 95:2.5:1.5:1:150 to prepare a negative electrode sheet; lithium sheet was used as the counter electrode; NaPF6 (solvent is EC:DEC:PC:propylene glycol polyoxypropylene ether = 1:2:1:0.05, concentration 1.3 mol / L) was used as the electrolyte; the diaphragm was a composite film of polyethylene PE, polypropylene PP and polyethylene propylene PEP. The button battery was assembled in an argon-filled glove box. The electrochemical performance was tested at Wuhan Landian.

[0070] The battery was tested on a CT2001A battery tester over a voltage range of 0.00V to 2.0V at a charge / discharge rate of 0.1C. The battery's initial discharge capacity and efficiency, DCR, cycle performance (0.5C / 0.5C, 100 cycles), and rate capability (2C / 0.1C) were measured. The test results are detailed in Table 2.

[0071] Table 2

[0072]

[0073] As can be seen from Table 2, the cycle performance and rate performance of the button batteries made using the hard carbon negative electrode composite materials of Examples 1-3 are significantly higher than those of the comparative examples. The reason is that the materials of the present invention have high powder conductivity, which reduces DCR and improves rate performance. At the same time, the specific surface area of ​​the example materials is larger, which improves the liquid retention performance of the materials and improves the cycle performance.

[0074] (4) Liquid absorption capacity, liquid retention rate test, rate performance test

[0075] The hard carbon composite materials in Examples 1-3 and Comparative Examples 1-2 were mixed and coated to prepare negative electrode sheets. 1 / 3 Mn 1 / 3 Ni 1 / 3O2) as the positive electrode and NaPF6 (solvent is EC:DEC:PC:propylene glycol polyoxypropylene ether = 1:2:1:0.05, concentration 1.3 mol / L) as the electrolyte to prepare 5Ah soft-pack batteries. The results are shown in Tables 3 and 4, respectively.

[0076] (1) Liquid absorption capacity:

[0077] Using a 1mL burette, draw 1mL of electrolyte (V = 1mL) and drip one drop onto the electrode surface. The time is counted until the electrolyte is completely absorbed. The time t is recorded and the electrode absorption rate (V / t) is calculated. The test results are shown in Table 3.

[0078] (2) Liquid retention rate test:

[0079] According to the electrode parameters, the theoretical liquid absorption amount m1 of the electrode is calculated, and the weight of the electrode is weighed as m2. Then, the electrode is placed in the electrolyte and soaked for 24 hours. The weight of the electrode is weighed as m3, and the liquid absorption amount of the electrode is calculated as m3-m2. It is calculated according to the following formula: liquid retention rate = (m3-m2)*100% / m1. The test results are shown in Table 3.

[0080] Table 3

[0081] Serial number Liquid absorption speed (S) Fluid retention rate Example 1 54 90.1％ Example 2 61 88.7％ Example 3 48 92.1％ Comparative Example 1 88 84.9％ Comparative Example 2 96 82.1％

[0082] As can be seen from Table 3, the liquid absorption and retention capabilities of the negative electrodes prepared using the composite materials obtained in Examples 1-3 are significantly better than those of the comparative examples. The reason for this is that the hard carbon materials in the examples have a high specific surface area, which improves the liquid absorption and retention performance of the electrode.

[0083] (3) Rate performance test:

[0084] The rate performance of the soft-pack battery was tested with a charge and discharge voltage range of 1 to 4.0 V, a temperature of 25±3.0°C, charging at 1.0C and 3.0C, and discharging at 1.0C. The test results are shown in Table 4.

[0085] Table 4

[0086]

[0087] As can be seen from Table 4, the rate charging performance of the soft-pack batteries in Examples 1 to 3 is significantly better than that of the comparative example, that is, the charging time is shorter. The reason for this is that the doping of phosphorus during the carbonization of sodium phosphate improves the electronic conductivity of the material, and the sodium doping reduces the defects on the surface of the material, thereby improving the electronic conductivity of the material and improving the power performance of the material.

[0088] The embodiments described above are only preferred specific implementations of the present invention. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a high-capacity pitch-based hard carbon composite material, characterized in that: The implementation of the preparation method includes: Step S1: The oxidized asphalt is dissolved in an organic solvent, and an organic cobalt salt is added to disperse the mixture uniformly to obtain a solution A; Step S2: Dispersing the solution A and sodium phosphate in a tetrahydrofuran solution of dopamine uniformly, performing a hydrothermal reaction, and vacuum drying to obtain a precursor material; Step S3: heating and carbonizing the precursor material under vacuum to obtain the high-capacity pitch-based hard carbon composite material; In step S1, the organic cobalt salt is one of cobalt acetate, cobalt octoate, cobalt naphthenate or cobalt oxalate; The preparation process of oxidized asphalt in step S1 is as follows: Mix asphalt, absorber and binder in a mass ratio of 100:1 to 10:10 and press them into a block structure. Then, the mixture was transferred to a microwave oven under air atmosphere and heated at a power of 500-1000W for 10-120s to obtain oxidized asphalt. The wave absorbing agent is ferrosoferric oxide, and the binder is one of starch, sodium cellulose or cellulose.

2. The method for preparing a high-capacity pitch-based hard carbon composite material according to claim 1, characterized in that: In the tetrahydrofuran solution of dopamine in step S2, the solute is dopamine, the solvent is tetrahydrofuran, and the concentration is 1-10 wt%.

3. A method for preparing a high-capacity pitch-based hard carbon composite material according to claim 1 or 2, characterized in that: In step S1, the mass ratio of oxidized asphalt, organic solvent, and organic cobalt salt is 100:1000-5000:1-5.

4. The method for preparing a high-capacity pitch-based hard carbon composite material according to claim 3, characterized in that: In step S2, the mass ratio of solution A, sodium phosphate, and dopamine is 1000-5000:1-10:1-10.

5. The method for preparing a high-capacity pitch-based hard carbon composite material according to claim 4, characterized in that: The temperature of the hydrothermal reaction in step 2 is 100-200°C, the reaction time is 1-6 hours, and the pressure is 1-5 MPa; The vacuum drying temperature is 80° C. and the reaction time is 24 h.

6. The method for preparing a high-capacity pitch-based hard carbon composite material according to claim 1, characterized in that: The organic solvent in step S1 is one of n-hexane, xylene, carbon disulfide or carbon tetrachloride.

7. A high-capacity pitch-based hard carbon composite material, characterized in that: The high-capacity pitch-based hard carbon composite material is prepared based on any one of the methods of claims 1-6.

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