A high-first-efficiency pitch-based hard carbon composite material and its preparation method

Abstract

This invention discloses a high first-time efficiency asphalt-based hard carbon composite material and its preparation method. The preparation method includes: dissolving oxidized asphalt in an organic solvent, adding a heteroatom compound and dispersing it evenly, performing a hydrothermal reaction, and freeze-drying to obtain the hard carbon precursor material; adding Na2S2O3 to an organic solvent to prepare a solution, then adding the hard carbon precursor material, dispersing it evenly, spray-drying, heating and introducing a crosslinking gas, and then heating to 1000-1500℃ and holding for 1-6 hours to obtain the high first-time efficiency asphalt-based hard carbon composite material. This invention reduces the irreversible capacity of the hard carbon precursor material by depositing Na2S2O3 on its surface, thereby improving the first-time efficiency; it improves the specific capacity and power performance by creating pores through heteroatom doping; and it leverages the synergistic effect between the two to enhance the first-time efficiency and power performance of the material.

Description

Technical Field

[0001] This invention relates to the field of secondary battery material preparation technology, specifically providing a high initial efficiency pitch-based hard carbon composite material and its preparation method. Background Technology

[0002] Hard carbon, with its high degree of disorder, large interlayer spacing, and wide availability, is used in sodium-ion and lithium-ion batteries. However, oxygen-containing functional groups and defects growing along carbon edges or layers in hard carbon cause irreversible reactions during sodium-ion charging and discharging, resulting in lower initial coulombic efficiency and reduced battery energy density. Current measures to improve initial efficiency mainly include surface coating to reduce surface defects and irreversible capacity loss, or doping at defects to reduce irreversible capacity and improve initial efficiency.

[0003] Patent authorization number CN114639816B discloses a high first-efficiency hard carbon composite material and its preparation method. The composite material has a core-shell structure, with a core of hard carbon material, an intermediate layer of lithium carbonate composite layer covering the core, and an outer shell of amorphous carbon layer covering the intermediate layer. The lithium carbonate composite layer is composed of 95-99% lithium carbonate and 1-5% lithium flakes. Although the first-efficiency of the obtained material is improved, the specific capacity of the material will be reduced after coating. It is suitable for lithium-ion batteries, but has no effect on improving the first-efficiency of sodium-ion batteries. Summary of the Invention

[0004] To improve the first-time efficiency of hard carbon composite materials used in sodium-ion batteries, this invention provides a method for preparing high-first-time efficiency pitch-based hard carbon composite materials. The method improves the first-time efficiency by depositing Na2S2O3 on the surface of the hard carbon precursor to reduce its irreversible capacity, and by using heteroatom doping to create pores to improve specific capacity and power performance. The method also leverages the synergistic effect between the two methods to improve the first-time efficiency and power performance of the material.

[0005] On the one hand, the present invention provides the following technical solution:

[0006] A method for preparing a high-first-use efficiency pitch-based hard carbon composite material, the method comprising the following steps:

[0007] Step S1:

[0008] After dissolving oxidized asphalt in an organic solvent, a heteroatom compound is added and dispersed evenly. The mixture is then subjected to a hydrothermal reaction and freeze-dried to obtain the hard carbon precursor material.

[0009] Step S2:

[0010] Na2S2O3 was added to an organic solvent to prepare a solution, then a hard carbon precursor material was added and dispersed evenly. After spray drying, the temperature was raised and crosslinking gas was introduced. The temperature was then raised to 1000-1500℃ and held for 1-6 hours to obtain the high first-time efficiency asphalt-based hard carbon composite material.

[0011] This invention reduces the irreversible capacity of a hard carbon precursor by depositing Na2S2O3 on its surface, thereby improving the first-pass efficiency. It also improves the specific capacity and power performance by creating pores through heteroatom doping, and leverages the synergistic effect between the two to enhance the first-pass efficiency and power performance of the material.

[0012] Furthermore, in step S2, the mass ratio of Na2S2O3 to hard carbon precursor is 1-10:100, and the concentration of the Na2S2O3 organic solvent solution is 1-10 wt%.

[0013] Furthermore, in step S1, the mass ratio of oxidized asphalt, organic solvent, and heteroatom compound is 100:1000-2000:1-10.

[0014] Furthermore, the hydrothermal reaction temperature is 100–200°C, the reaction time is 1–6 h, and the freeze-drying temperature is -40°C for 24 h.

[0015] Furthermore, the preparation process of oxidized asphalt in step S1 is as follows:

[0016] Asphalt is added to a reaction vessel, and air is introduced. The volume of air introduced is 10 times the volume of the asphalt. The pressure in the reaction vessel is 0.5 MPa, the temperature is 50-150℃, and the oxidation time is 1-6 hours to obtain oxidized asphalt.

[0017] Furthermore, the organic solvent in step S1 is benzene, toluene, or xylene.

[0018] Furthermore, in step S1, the heteroatom compound is phospholipid, urea, dopamine, or thiophene.

[0019] Furthermore, the organic solvent in step S2 is turpentine, diethyl ether, or methyl ether;

[0020] In step S2, after spray drying, the temperature is raised to 200-400°C and crosslinking gas is introduced, and then the temperature is raised to 1000-1500°C and held for 1-6 hours.

[0021] Furthermore, in step S2, the crosslinking gas is ethylene oxide, propylene oxide, 1,2-epoxybutane, or 1,4-epoxybutane.

[0022] In another aspect, the present invention provides a high first-efficiency pitch-based hard carbon composite material, which is prepared based on any of the methods described above.

[0023] Compared with the prior art, the present invention provides a high first-time efficiency pitch-based hard carbon composite material and its preparation method, which have the following outstanding advantages:

[0024] 1) This invention utilizes a liquid phase method to coat the surface of a hard carbon precursor with Na2S2O3, carbonize it, and then dope the defects with sulfur and coat it with sodium oxide. During the first charge and discharge process, sodium oxide provides sufficient sodium ions to reduce the sodium ions consumed by the material to form an SEI film, thereby improving the first efficiency. At the same time, sulfur doping on the surface of the material increases the number of active sites and improves the specific capacity of the material.

[0025] 2) By using cross-linking gas, the defects in the material are doped a second time, which reduces its irreversible capacity and improves the initial efficiency. Moreover, gas cross-linking has the advantages of better uniformity, significantly improved initial efficiency and higher efficiency compared with traditional liquid phase cross-linking. Attached Figure Description

[0026] Figure 1 This is a SEM image of the high first-time efficiency hard carbon composite material prepared in Example 1 of this invention. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0028] Preparation method of oxidized asphalt:

[0029] Asphalt is added to a reaction vessel, and air is introduced. The volume of air introduced is 10 times the volume of the raw asphalt. The pressure in the reaction vessel is 0.5 MPa, the temperature is 100℃, and the oxidation time is 3 hours to obtain oxidized asphalt. Example 1

[0030] Step S1:

[0031] 100g of oxidized asphalt was dissolved in 1500g of toluene organic solvent, and then 5g of phospholipid was added and dispersed evenly. The mixture was subjected to hydrothermal reaction at 150℃ for 3h, and then freeze-dried (-40℃, 24h) to obtain hard carbon precursor material.

[0032] Step S2:

[0033] 5g of Na2S2O3 was added to 100g of benzene organic solvent to prepare a 5wt% solution. Then, 100g of hard carbon precursor material was added, dispersed evenly, spray-dried, heated to 300℃ and ethylene oxide crosslinking gas was introduced, and then heated to 1200℃ and held for 3h to obtain a high first-time efficiency hard carbon composite material. Example 2

[0034] Step S1:

[0035] 100g of oxidized asphalt was dissolved in 1000g of toluene organic solvent, and then 1g of urea was added and dispersed evenly. The mixture was subjected to hydrothermal reaction at 100℃ for 6h, and then freeze-dried (-40℃, 24h) to obtain hard carbon precursor material.

[0036] Step S2:

[0037] 1g Na2S2O3 was added to 100g diethyl ether organic solvent to prepare a 1wt% solution. Then, 100g hard carbon precursor material was added, dispersed evenly, spray-dried, heated to 200℃ and propylene oxide crosslinking gas was introduced, and then heated to 1000℃ and held for 6h to obtain a high first-time efficiency hard carbon composite material. Example 3

[0038] Step S1:

[0039] 100g of oxidized asphalt was dissolved in 2000g of xylene organic solvent, and then 10g of dopamine was added and dispersed evenly. The mixture was subjected to hydrothermal reaction at 200℃ for 1h, followed by freeze drying (-40℃, 24h) to obtain hard carbon precursor material.

[0040] Step S2:

[0041] 10g Na2S2O3 was added to 100g dimethyl ether organic solvent to prepare a 10wt% solution. Then, 100g hard carbon precursor material was added, dispersed evenly, spray-dried, heated to 400℃ and 1,2-epoxybutane crosslinking gas was introduced, and then heated to 1500℃ and held for 1h to obtain a high first-time efficiency hard carbon composite material.

[0042] Comparative Example 1:

[0043] Unlike Example 1, no phospholipids were added; otherwise, they were the same as in Example 1.

[0044] Comparative Example 2:

[0045] Unlike Example 2, Na2S2O3 was not added; otherwise, it was the same as Example 1. The preparation process was as follows: the hard carbon precursor material from step S1 of Example 1 was used and transferred to a tube furnace, heated to 300°C and ethylene oxide crosslinking gas was introduced, and then heated to 1200°C and held for 3 hours to obtain a high first-time efficiency hard carbon composite material.

[0046] Performance testing

[0047] (1) SEM test

[0048] The high first-time efficiency hard carbon composite material prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown. By Figure 1 As can be seen from the data, the hard carbon composite material prepared in Example 1 is spherical with a particle size D50 between (5-10) μm.

[0049] (2) Physical and chemical properties and button cell testing

[0050] The high-initial-efficiency hard carbon composite materials prepared in Examples 1-3 and Comparative Examples 1-2 were tested for interlayer spacing (D002), specific surface area, tap density, particle size D50, and powder conductivity. The testing methods followed the national standard GB / T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries". The test results are shown in Table 1.

[0051] The hard carbon composite materials from Examples 1-3 and Comparative Examples 1-2 were used as negative electrode materials for lithium-ion batteries to assemble coin cells. The specific preparation method for the negative electrode material was as follows: a negative electrode sheet was prepared by mixing hard carbon composite material, CMC, SBR, SP, and H2O in a mass ratio of 94:2.5:1.5:2:150; a sodium sheet was used as the counter electrode; the electrolyte was NaPF6 (solvent: EC:DEC:PC:propylene glycol polyoxypropylene ether = 1:2:1:0.05, concentration 1.3 mol / L); the separator was a composite membrane of polyethylene (PE), polypropylene (PP), and polyethylene propylene (PEP). The coin cells were assembled in an argon-filled glove box. Electrochemical performance was tested using a Wuhan Landian CT2001A battery tester, with a charge / discharge voltage range of 0.00V to 2.0V and a charge / discharge rate of 0.1C. The initial discharge capacity and initial efficiency of the coin cells were tested. The test results are shown in Table 1.

[0052] Table 1

[0053] Example D002 (nm) Specific surface area (m² / g) Tap density (g / cm3) Particle size (D50, μm) Powder conductivity (S / cm) Initial discharge capacity (mAh / g) First-time efficiency (%) Example 1 0.388 7.4 0.85 6.7 38 356.2 92.5 Example 2 0.387 6.8 0.82 6.3 32 352.3 91.1 Example 3 0.385 7.6 0.87 6.9 41 361.7 92.4 Comparative Example 1 0.379 4.4 0.70 7.9 19 305.5 89.4 Comparative Example 2 0.372 5.1 0.73 7.7 23 322.4 87.2

[0054] As can be seen from Table 1, the hard carbon composite materials prepared in Examples 1-3 are superior to those in Comparative Examples 1-2 in terms of initial discharge capacity and initial efficiency. This is because phosphorus is used to create pores and provide more active sites to improve specific capacity, and crosslinking gas is used to dope the defects of the material a second time, reducing its irreversible capacity and improving initial efficiency.

[0055] (3) Soft-pack battery test:

[0056] The hard carbon composite materials from Examples 1-3 and Comparative Examples 1-2 were slurried and coated to prepare negative electrode sheets, using layered oxides (NaFe) 1 / 3 Mn 1 / 3 Ni 1 / 3A 5Ah soft-pack battery was prepared using O2 as the positive electrode and NaPF6 (solvent: EC:DEC:PC:propylene glycol polyoxypropylene ether = 1:2:1:0.05, concentration 1.3mol / L) as the electrolyte.

[0057] Test the liquid absorption capacity of the negative electrode.

[0058] Cyclic performance test: charge / discharge current 2.0C / 2.0C, voltage range 1-4.0V, number of cycles 500.

[0059] Rate performance testing: Testing the initial cycle DCR and constant current ratio under 2C charging conditions of the pouch battery.

[0060] The test results are shown in Table 2.

[0061] Table 2

[0062] project Aspiration rate (mL / min) Cycle retention rate (%) Cyclic charging DCR (mΩ) 2C constant current ratio (%) Example 1 5.9 97.6 21.7 93.4 Example 2 5.1 96.4 23.8 92.7 Example 3 6.5 96.9 20.9 94.8 Comparative Example 1 2.9 87.9 39.1 87.5 Comparative Example 2 2.3 89.8 33.6 89.1

[0063] As shown in Table 2, compared with the comparative example, the liquid absorption and retention capacity of the negative electrode sheets in Examples 1-3 are significantly better than those in the comparative example. The reason for this is that the materials in the examples have a high specific surface area, which increases the liquid absorption rate of the materials. At the same time, the cross-linking gas is used to dope the defects of the materials a second time, which reduces the irreversible capacity, reduces side reactions, and improves cycle performance.

[0064] The embodiments described above are merely preferred embodiments of the present invention. Ordinary variations and substitutions made by those skilled in the art within the scope of the technical solutions of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-first-use efficiency pitch-based hard carbon composite material, characterized in that, The method is implemented in the following steps: Step S1: After dissolving oxidized asphalt in an organic solvent, a heteroatom compound is added and dispersed evenly. The mixture is then subjected to a hydrothermal reaction and freeze-dried to obtain a hard carbon precursor material. Step S2: Na2S2O3 was added to an organic solvent to prepare a solution, then a hard carbon precursor material was added, dispersed evenly, spray-dried, heated and crosslinking gas was introduced, and then heated to 1000-1500℃ and held for 1-6 hours to obtain the high first-time efficiency asphalt-based hard carbon composite material. The preparation process of oxidized asphalt in step S1 is as follows: Asphalt is added to a reaction vessel, and air is introduced. The volume of air introduced is 10 times the volume of the asphalt. The pressure in the reaction vessel is 0.5 MPa, the temperature is 50-150℃, and the oxidation time is 1-6 hours to obtain oxidized asphalt.

2. The method for preparing a high first-pass efficiency pitch-based hard carbon composite material according to claim 1, characterized in that, In step S2, the mass ratio of Na2S2O3 to hard carbon precursor is 1-10:100, and the concentration of the Na2S2O3 organic solvent solution is 1-10 wt%.

3. A method for preparing a high first-pass efficiency 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 heteroatom compound is 100:1000-2000:1-10.

4. The method for preparing a high first-pass efficiency pitch-based hard carbon composite material according to claim 3, characterized in that, The hydrothermal reaction is carried out at a temperature of 100–200°C for 1–6 hours, and the freeze-drying is carried out at a temperature of -40°C for 24 hours.

5. The method for preparing a high first-pass efficiency pitch-based hard carbon composite material according to claim 3, characterized in that, The organic solvent in step S1 is benzene, toluene, or xylene.

6. The method for preparing a high first-pass efficiency pitch-based hard carbon composite material according to claim 3, characterized in that, The heteroatom compound in step S1 is phospholipid, urea, dopamine, or thiophene.

7. The method for preparing a high first-pass efficiency pitch-based hard carbon composite material according to claim 3, characterized in that, The organic solvent in step S2 is turpentine, diethyl ether, or methyl ether. In step S2, after spray drying, the temperature is raised to 200-400°C and crosslinking gas is introduced, and then the temperature is raised to 1000-1500°C and held for 1-6 hours.

8. The method for preparing a high first-pass efficiency pitch-based hard carbon composite material according to claim 3, characterized in that, In step S2, the crosslinking gas is ethylene oxide, propylene oxide, 1,2-epoxybutane, or 1,4-epoxybutane.

9. A high-first-use efficiency pitch-based hard carbon composite material, characterized in that, The high first-time efficiency pitch-based hard carbon composite material is prepared according to any one of claims 1-8.

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