Coal-based negative electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of batteries, and provides a coal-based negative electrode material and a preparation method and application thereof, and the negative electrode material comprises the following preparation raw materials: 7-9 parts of coal and 1-3 parts of a conductive agent. The method comprises the following steps: mixing coal and a solvent for acid leaching to obtain a coal-based sample; and forming the coal-based sample and the conductive agent, and performing electrolytic acid leaching to obtain the coal-based negative electrode material. The electrode material is prepared by using coal as a raw material, the use amount of hydrofluoric acid is reduced by 50% compared with that of a traditional hydrofluoric acid method, environmental protection is facilitated, the preparation cost is low, the method is simple, energy consumption is low, large-scale preparation is easy, impurities in coal are effectively removed, and the method can be applied to the field of sodium electricity.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a coal-based negative electrode material and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries (SIBs) have attracted attention due to their abundant raw material reserves, low price and high safety, and are considered to be a potential alternative to lithium-ion batteries. However, the negative electrode material of sodium-ion batteries has an important influence on the performance and cycle life of the battery. Since the radius of sodium ions is larger than that of lithium ions, the negative electrode material needs to provide enough space to accommodate the larger sodium ions while maintaining structural stability. At present, hard carbon materials are the first choice for the negative electrode of sodium-ion batteries because hard carbon has a large interlayer spacing and disorder, which is conducive to the insertion and extraction of sodium ions. In addition, the negative electrode material also needs to have a high purity to have good conductivity and structural stability to ensure efficient energy conversion and long-term recycling of the battery during charging and discharging.

[0003] Coal is the cheapest and most direct raw material for hard carbon materials, but it contains a large amount of impurities, the main impurity elements include silicon (Si), aluminum (Al), iron (Fe), calcium (Ca), magnesium (Mg), etc. These impurities usually exist in the form of oxides or sulfides, embedded in the coal surface and carbon layer, and tightly combined with the carbon matrix, making it difficult to separate and purify. The presence of impurities will affect the physical and chemical properties of coal, so it is not meaningful to directly apply coal to electrode materials, and it is not possible to obtain electrode materials with excellent performance.

[0004] Therefore, how to apply coal to battery materials has become an urgent problem that researchers need to solve. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects in the prior art and provide a coal-based negative electrode material and a preparation method and application thereof.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a coal-based negative electrode material, comprising the following raw materials in parts by weight:

[0008] 7 to 9 parts of coal and 1 to 3 parts of conductive agent.

[0009] Preferably, the conductive agent comprises one or more of graphite, conductive carbon black, chopped carbon fiber, carbon nanotube and graphene.

[0010] The present invention also provides a method for preparing the coal-based negative electrode material, comprising the following steps:

[0011] (1) Mixing coal and solvent for acid leaching to obtain a coal-based sample;

[0012] (2) The coal-based sample and the conductive agent are formed and then electrolytically acid-leached to obtain the coal-based negative electrode material.

[0013] Preferably, the solvent in step (1) comprises hydrochloric acid, hydrofluoric acid, sulfuric acid and water;

[0014] The volume ratio of the hydrochloric acid, hydrofluoric acid, sulfuric acid and water is 0.5-1.5:0.5-1.5:1-3:4-8.

[0015] Preferably, the mass ratio of coal to solvent in step (1) is 1:4-6.

[0016] Preferably, the acid leaching in step (1) is carried out at a temperature of 40 to 70° C. and for a time of 3 to 8 hours.

[0017] Preferably, the molding pressure in step (2) is 20 to 40 MPa.

[0018] Preferably, the electrolytic acid leaching solution in step (2) comprises hydrofluoric acid, sulfuric acid and water;

[0019] The volume ratio of hydrofluoric acid, sulfuric acid and water is 3-6:5-8:26-32;

[0020] The mass ratio of the mixture of the coal-based sample and the conductive agent to the electrolytic acid leaching solution is 1:4-10.

[0021] Preferably, the temperature of the electrolytic acid leaching in step (2) is 20 to 90°C, and the current density is 0.1 to 0.15 A / cm 2 , time is 2 to 150 hours.

[0022] The present invention also provides application of the coal-based negative electrode material in a sodium battery.

[0023] The present invention provides a coal-based negative electrode material, comprising the following raw materials: 7 to 9 parts of coal and 1 to 3 parts of a conductive agent. The present invention mixes coal and a solvent for acid leaching to obtain a coal-based sample; the coal-based sample and the conductive agent are formed and then electrolytically acid-leached to obtain the coal-based negative electrode material. In the above steps, the main principle of step (1) is to acid-wash coal with mixed acid to dissolve inorganic minerals and part of the sulfide in the coal to generate easily soluble chlorides, sulfates and fluorosilicic acid, etc., so as to achieve the purpose of preliminary impurity removal. The main principle of step (2) is to ionize the composite acid by applying a voltage so that it is embedded in the carbon layer, causing the carbon layer to expand, and the intercalation force of a large number of anions, water molecules and bubbles will strongly act on the expanded carbon layer, thereby removing insoluble impurities. In addition, the introduction of the conductive agent can improve the conductivity of the hard carbon negative electrode.

[0024] The present invention uses coal as a raw material to prepare electrode materials, and the amount of hydrofluoric acid used is reduced by 50% compared with the traditional hydrofluoric acid purification method, which is beneficial to environmental protection, has low preparation cost, simple method, low energy consumption, is easy to prepare on a large scale, effectively removes impurities in coal, and can be applied to the field of sodium electricity. DETAILED DESCRIPTION

[0025] The present invention provides a coal-based negative electrode material, comprising the following raw materials in parts by weight:

[0026] 7 to 9 parts of coal and 1 to 3 parts of conductive agent.

[0027] In the present invention, the mass fraction of coal is preferably 7.5 to 8.5 parts, more preferably 7.6 to 8.4 parts, and even more preferably 7.8 to 8.2 parts.

[0028] In the present invention, the mass fraction of the conductive agent is preferably 1.5 to 2.5 parts, more preferably 1.6 to 2.4 parts, and even more preferably 1.8 to 2.2 parts.

[0029] In the present invention, the conductive agent comprises one or more of graphite, conductive carbon black, chopped carbon fiber, carbon nanotube and graphene.

[0030] The present invention also provides a method for preparing the coal-based negative electrode material, comprising the following steps:

[0031] (1) Mixing coal and solvent for acid leaching to obtain a coal-based sample;

[0032] (2) The coal-based sample and the conductive agent are formed and then electrolytically acid-leached to obtain the coal-based negative electrode material.

[0033] In the present invention, the coal needs to be fully dried before use, and the next step is carried out after it is dried to a constant weight.

[0034] In the present invention, the solvent in step (1) comprises hydrochloric acid, hydrofluoric acid, sulfuric acid and water.

[0035] In the present invention, the concentration of the hydrochloric acid is preferably 10-14 mol / L, more preferably 11-13 mol / L, more preferably 11.5-12.5 mol / L; the concentration of the hydrofluoric acid is preferably 20-25 mol / L, more preferably 21-24 mol / L, more preferably 22-23 mol / L; the concentration of the sulfuric acid is preferably 15-20 mol / L, more preferably 16-19 mol / L, more preferably 17-18 mol / L.

[0036] In the present invention, the volume ratio of hydrochloric acid, hydrofluoric acid, sulfuric acid and water is preferably 0.5-1.5:0.5-1.5:1-3:4-8, more preferably 0.6-1.4:0.6-1.4:1.5-2.5:5-7, and more preferably 0.8-1.2:0.8-1.2:1.8-2.2:5.5-6.5.

[0037] In the present invention, the mass ratio of coal to solvent in step (1) is preferably 1:4-6, more preferably 1:4.5-5.5, and even more preferably 1:4.8-5.2.

[0038] In the present invention, the acid leaching temperature in step (1) is preferably 40-70°C, more preferably 45-65°C, more preferably 50-60°C; the time is preferably 3-8h, more preferably 4.5-7.5h, more preferably 5-7h; the ultrasonic frequency is preferably 40-60HZ, more preferably 45-55HZ, more preferably 48-52HZ.

[0039] In the present invention, the suspension obtained by acid leaching in step (1) is filtered, the solid is collected, and dried to constant weight to obtain a coal-based sample.

[0040] In the present invention, the molding pressure in step (2) is preferably 20 to 40 MPa, more preferably 25 to 35 MPa, and even more preferably 28 to 32 MPa.

[0041] In the present invention, the solution for electrolytic acid leaching in step (2) comprises hydrofluoric acid, sulfuric acid and water.

[0042] In the present invention, the volume ratio of hydrofluoric acid, sulfuric acid and water is preferably 3-6: 5-8: 26-32, more preferably 3.5-5.5: 5.5-7.5: 27-31, and more preferably 4-5: 6-7: 28-30.

[0043] In the present invention, the concentration of the hydrofluoric acid is preferably 20-25 mol / L, more preferably 21-24 mol / L, more preferably 22-23 mol / L; the concentration of the sulfuric acid is preferably 15-20 mol / L, more preferably 16-19 mol / L, more preferably 17-18 mol / L.

[0044] In the present invention, the mass ratio of the mixture of the coal-based sample and the conductive agent to the electrolytic acid leaching solution is preferably 1:4-10, more preferably 1:6-9, and even more preferably 1:7-8.

[0045] In the present invention, the formed mixture is the positive electrode, and the platinum sheet is the negative electrode.

[0046] In the present invention, the temperature of the electrolytic acid leaching in step (2) is preferably 20 to 90°C, more preferably 30 to 80°C, and more preferably 40 to 70°C; the current density is preferably 0.1 to 0.15 A / cm 2 , more preferably 0.11 to 0.14 A / cm 2 , more preferably 0.12 to 0.13 A / cm 2 The voltage is preferably 1 to 5 V, more preferably 2 to 4 V, and more preferably 2.5 to 3.5 V; the time is preferably 2 to 150 h, more preferably 40 to 110 h, and more preferably 70 to 80 h.

[0047] In the present invention, after the electrolytic acid leaching in step (2) is completed, the solid is filtered, collected, and dried to a constant weight to obtain a coal-based negative electrode material.

[0048] The present invention also provides application of the coal-based negative electrode material in a sodium battery.

[0049] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0050] Example 1

[0051] Take 9 parts of coal and 1 part of conductive carbon black.

[0052] After the coal is fully dried, it is mixed with a solvent in a mass ratio of 1:5. The volume ratio of hydrochloric acid (12 mol / L), hydrofluoric acid (22.5 mol / L), sulfuric acid (18.5 mol / L) and water in the solvent is 1:1:2:4. The coal is acid-leached at 50°C and 50 Hz for 3 hours, the suspension is filtered, the solid is collected and dried to obtain a coal-based sample.

[0053] The coal-based sample and conductive carbon black were mixed and pressed at 30 MPa to form the positive electrode. The platinum sheet was used as the negative electrode. The electrolytic acid leaching solution contained hydrofluoric acid (22.5 mol / L), sulfuric acid (18.5 mol / L) and water in a volume ratio of 3:5:26. The mass ratio of the positive electrode to the electrolytic acid leaching solution was 1:4. The temperature was 20 °C, the voltage was 2 V, and the current density was 0.12 A / cm 2 After the electrolysis, the solid was collected by filtration and dried to constant weight to obtain a coal-based negative electrode material.

[0054] Example 2

[0055] Take 8 parts coal and 2 parts graphite.

[0056] After the coal is fully dried, it is mixed with a solvent in a mass ratio of 1:4. The volume ratio of hydrochloric acid (11 mol / L), hydrofluoric acid (23 mol / L), sulfuric acid (16 mol / L) and water in the solvent is 1:1.2:3:6. The coal is acid-leached at 40°C and 50 Hz for 4 hours, the suspension is filtered, the solid is collected and dried, and a coal-based sample is obtained.

[0057] The coal-based sample was mixed with graphite and pressed into shape at 25 MPa as the positive electrode. The platinum sheet was used as the negative electrode. The electrolytic acid leaching solution contained hydrofluoric acid (23 mol / L), sulfuric acid (16 mol / L) and water in a volume ratio of 6:6:30. The mass ratio of the positive electrode to the electrolytic acid leaching solution was 1:7. The temperature was 40 °C, the voltage was 3 V, and the current density was 0.14 A / cm 2 After electrolysis, the solid was collected by filtration and dried to constant weight to obtain a coal-based negative electrode material.

[0058] Example 3

[0059] Take 8 parts of coal and 2 parts of carbon nanotubes.

[0060] After the coal is fully dried, it is mixed with a solvent in a mass ratio of 1:5. The volume ratio of hydrochloric acid (13.5 mol / L), hydrofluoric acid (21 mol / L), sulfuric acid (19 mol / L) and water in the solvent is 0.8:1.1:2:7. The coal is acid-leached at 65°C and 50 Hz for 8 hours, the suspension is filtered, the solid is collected and dried to obtain a coal-based sample.

[0061] Coal-based samples and carbon nanotubes were mixed and pressed at 40 MPa to form the positive electrode. Platinum sheet was used as the negative electrode. The electrolytic acid leaching solution contained hydrofluoric acid (21 mol / L), sulfuric acid (19 mol / L) and water in a volume ratio of 4:5:28. The mass ratio of the positive electrode to the electrolytic acid leaching solution was 1:9. The temperature was 70 °C, the voltage was 5 V, and the current density was 0.11 A / cm 2 After the electrolysis, the solid was collected by filtration and dried to constant weight to obtain a coal-based negative electrode material.

[0062] Example 4

[0063] Take 8 parts coal and 2 parts chopped carbon fiber.

[0064] After the coal is fully dried, it is mixed with a solvent in a mass ratio of 1:6. The volume ratio of hydrochloric acid (10 mol / L), hydrofluoric acid (22 mol / L), sulfuric acid (19 mol / L) and water in the solvent is 1.4:0.7:1.5:6.4. The coal is acid-leached at 55°C and 50 Hz for 6 hours, the suspension is filtered, the solid is collected and dried to obtain a coal-based sample.

[0065] Coal-based samples and chopped carbon fibers were mixed and pressed at 28 MPa to form the positive electrode. Platinum sheet was used as the negative electrode. The electrolytic acid leaching solution contained hydrofluoric acid (22 mol / L), sulfuric acid (19 mol / L) and water in a volume ratio of 5.5:7.5:30. The mass ratio of the positive electrode to the electrolytic acid leaching solution was 1:6. The temperature was 45 °C, the voltage was 3 V, and the current density was 0.12 A / cm 2 After the electrolysis, the solid was collected by filtration and dried to constant weight to obtain a coal-based negative electrode material.

[0066] Comparative Example 1

[0067] Raw coal without any processing.

[0068] Comparative Example 2

[0069] The difference between Comparative Example 2 and Example 1 is that no electrochemical treatment is performed and only a coal-based sample is obtained.

[0070] The products of Examples 1 to 4 and Comparative Examples 1 and 2 were heated to 500°C at a heating rate of 5°C / min and kept at that temperature for 1 hour, then continued to be heated to 850°C and kept at that temperature for 1.5 hours, and the ash content was measured. The results are recorded in Table 1.

[0071] Table 1 Ash content determination results

[0072] Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Example 4 Ad% 73.9 94.3 95.5 97.5 98.4 99.6

[0073] As can be seen from Table 1, the coal purification method provided by the present invention has the advantages of low cost and low ash content compared with the traditional acid-washed coal method. The coal purification method provided by the present invention can improve the electrochemical performance of sodium ion batteries.

[0074] Performance Testing

[0075] Based on the coal-based negative electrode material provided in the above embodiments and comparative examples, a negative electrode sheet was made and used as an anode. 3 V 2 (PO 4 ) 3 (NVP) was used to make the positive electrode, GF / D glass fiber was used as the separator, and 1M NaClO 4 (the solvent includes ethylene carbonate and diethyl carbonate in a volume ratio of 1:1) as the electrolyte to assemble a sodium ion full battery;

[0076] The preparation steps of the negative electrode plate include: mixing coal-based negative electrode material (80wt%), SuperP (10wt%), carboxymethyl cellulose (2wt%) and styrene-butadiene rubber (8wt%) to form a slurry, coating it on a copper foil, and drying it in a vacuum drying oven at 100°C for 12h to obtain a negative electrode plate, wherein the active material loading of the negative electrode plate is greater than 3mg·cm-2 . Except for the slurry composition of 8:1:1 by mass Na 3 V 2 (PO 4 ) 3 Except for , SuperP and polyvinylidene fluoride, the manufacturing process of the positive electrode is the same as that of the negative electrode.

[0077] The electrochemical performance of the sodium ion battery prepared above was tested.

[0078] The test conditions for charge and discharge performance are: voltage range 0~2V, current density 30mA·g -1 Charge and discharge tests were carried out under the conditions to obtain the reversible capacity and initial efficiency.

[0079] The test conditions for the cycle performance are: voltage range 0~2V, current density 30mA·g -1 and 50mA·g -1 After 5 cycles at 100 mA g -1 The current density was used for long cycle performance test, and the capacity retention rate was calculated after 100 cycles. The test results are shown in Table 2.

[0080] Table 2 Electrochemical performance test results

[0081]

[0082] It can be seen from Table 2 that the first coulombic efficiency of the coal-based negative electrode material provided by the present invention is excellent, which is significantly improved compared with the untreated coal-based material, and after 100 cycles, the reversible capacity retention rate can still reach 92.3%, which is a low-cost and excellent performance negative electrode material.

[0083] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A coal-based negative electrode material, characterized in that: Contains the following raw materials by weight: 7 to 9 parts of coal and 1 to 3 parts of conductive agent.

2. The coal-based negative electrode material according to claim 1, characterized in that: The conductive agent comprises one or more of graphite, conductive carbon black, chopped carbon fiber, carbon nanotube and graphene.

3. The method for preparing the coal-based negative electrode material according to claim 1 or 2, characterized in that: It includes the following steps: (1) Mixing coal and solvent for acid leaching to obtain a coal-based sample; (2) The coal-based sample and the conductive agent are formed and then electrolytically acid-leached to obtain the coal-based negative electrode material.

4. The method for preparing a coal-based negative electrode material according to claim 3, characterized in that: The solvent in step (1) comprises hydrochloric acid, hydrofluoric acid, sulfuric acid and water; The volume ratio of the hydrochloric acid, hydrofluoric acid, sulfuric acid and water is 0.5-1.5:0.5-1.5:1-3:4-8.

5. The method for preparing a coal-based negative electrode material according to claim 4, characterized in that: In step (1), the mass ratio of coal to solvent is 1:4-6.

6. The method for preparing a coal-based negative electrode material according to any one of claims 3 to 5, characterized in that: The acid leaching temperature in step (1) is 40-70° C. and the time is 3-8 hours.

7. The method for preparing a coal-based negative electrode material according to claim 6, characterized in that: The molding pressure in step (2) is 20 to 40 MPa.

8. The method for preparing a coal-based negative electrode material according to claim 7, characterized in that: The electrolytic acid leaching solution in step (2) comprises hydrofluoric acid, sulfuric acid and water; The volume ratio of hydrofluoric acid, sulfuric acid and water is 3-6:5-8:26-32; The mass ratio of the mixture of the coal-based sample and the conductive agent to the electrolytic acid leaching solution is 1:4-10.

9. The method for preparing a coal-based negative electrode material according to claim 8, characterized in that: The temperature of the electrolytic acid leaching in step (2) is 20-90°C, and the current density is 0.1-0.15A / cm 2 , time is 2 to 150 hours.

10. Use of the coal-based negative electrode material according to claim 1 or 2 in sodium batteries.

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