Preparation method of coal-based hard carbon negative electrode material and application thereof

Abstract

The application relates to a preparation method of a coal-based hard carbon negative electrode material and application thereof, and belongs to the field of secondary battery material preparation. The application aims at solving the problems that the coulomb efficiency and reversible charge-discharge specific capacity of the prepared hard carbon material are low after high-temperature treatment of the existing coal-based precursor, the operation of acid washing removal is relatively complex, and the used hydrofluoric acid is relatively dangerous. The preparation method comprises the following steps: one, descaling treatment; two, micro-arc oxidation treatment; and three, carbonization. Application: the application is used for preparing a secondary ion battery negative electrode material. The application is used for the preparation of the coal-based hard carbon negative electrode material and the application thereof.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of secondary battery material preparation. BACKGROUND

[0002] Solar energy, wind energy and other renewable energy generation have intermittency and instability, and the smooth and safe integration into the power grid requires the development of efficient and stable energy storage technology. Sodium resources are abundant in nature and low in price. In addition, sodium has a suitable redox potential (0.3V higher than Li + / Li), and the use of low-cost sodium-based raw materials and aluminum foil current collectors can significantly reduce costs. In this case, sodium-ion batteries can be applied to large-scale energy storage and other cost-focused rather than energy density fields.

[0003] The negative electrode material can be classified into the following categories through the electrochemical mechanism of storing Na + + ions: carbon-based materials, conversion-type materials, alloying-type materials, and organic materials. Carbon-based materials are low in cost and widely studied, but the specific sodium storage mechanism is not clear. Conversion / alloying reactions based on multi-electron transfer can provide higher theoretical specific capacity, but the material has large volume change during cycling, poor rate performance, and fast capacity decay. Organic materials have flexible structure and high theoretical specific capacity, but they will dissolve in the electrolyte and have low electrical conductivity.

[0004] Hard carbon precursor raw materials are abundant in source. Currently, the hard carbon precursors mainly include biomass, resin-based and petroleum-based materials. Resin-based hard carbon has obvious performance advantages, but is expensive and difficult to industrialize; petroleum-based precursors are low in cost, easy to obtain, and have high cost performance, but the performance is general; biomass precursors show higher reversible charge and discharge specific capacity and better cycle performance, but have low yield. According to different metamorphic degrees, coal can be divided into anthracite, bituminous coal, sub-bituminous coal and lignite. Coal-based materials have high carbon content and high yield.

[0005] In the prior art, the coal-based precursor after high-temperature treatment has low coulombic efficiency and reversible charge and discharge specific capacity of the prepared hard carbon material, and the ash in the raw material is generally removed by acid washing, and the silicon-containing impurities are often removed by hydrofluoric acid cleaning, which is relatively complex and the use of hydrofluoric acid is relatively dangerous. SUMMARY

[0006] The present application solves the problems of low coulombic efficiency and reversible charge and discharge specific capacity of the prepared hard carbon material, and the relatively complex operation of acid washing and the use of relatively dangerous hydrofluoric acid after high-temperature treatment of the existing coal-based precursor, and provides a preparation method of coal-based hard carbon negative electrode material and application thereof.

[0007] A preparation method of coal-based hard carbon negative electrode material, which is completed by the following steps:

[0008] I. Deashing treatment:

[0009] The raw coal is ground, sieved and dried to obtain dry coal powder, the dry coal powder is added into an aqueous hydrochloric acid solution and uniformly dispersed, then deashing treatment is performed, and finally filtration, water washing and vacuum drying are performed to obtain deashed coal powder;

[0010] II. Micro-arc oxidation treatment:

[0011] The deashed coal powder is subjected to micro-arc oxidation treatment to obtain an oxidation precursor;

[0012] III. Carbonization:

[0013] The oxidation precursor is uniformly mixed with a fluorine source powder to obtain a mixed powder, and then the mixed powder is subjected to carbonization treatment to obtain a coal-based hard carbon negative electrode material, thereby completing the preparation method of the coal-based hard carbon negative electrode material.

[0014] The coal-based hard carbon negative electrode material is used for preparing a secondary ion battery negative electrode material.

[0015] The coal-based hard carbon negative electrode material has the following beneficial effects:

[0016] (1) The present application utilizes the HF gas generated by the decomposition of the fluorine source in the carbonization process to react with the SiO2 impurities in the coal raw material, thereby combining the impurity removal step and the carbonization step into one, simplifying the preparation process and avoiding the use of hydrofluoric acid.

[0017] (2) The micro-arc oxidation method is used to introduce more oxygen-containing functional groups into the precursor, thereby promoting the intermolecular crosslinking reaction in the carbonization process and generating more pore structures.

[0018] (3) The HF gas generated by the decomposition of the fluorine source at high temperature reacts with the SiO2 impurities in the coal raw material, thereby introducing part of the pores in the process of removing impurities and further improving the performance of the material.

[0019] (4) The present application uses in-situ impurity removal and pore formation and in-situ crosslinking methods to introduce pore structures into the coal during carbonization, and the coal-based hard carbon material prepared according to the method of the present application has high sodium storage capacity, first coulombic efficiency and rate performance as a sodium ion battery negative electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 SEM image of the coal-based hard carbon negative electrode material prepared in Example 2;

[0021] Figure 2 X-ray diffraction pattern of the coal-based hard carbon negative electrode material prepared in Example 2 and Comparative Example 1;

[0022] Figure 3The charge-discharge curve of the sodium ion battery prepared by using the coal-based hard carbon negative electrode material of Example 2 and Comparative Example 1;

[0023] Figure 4 The cycle performance graph of the sodium ion battery prepared by using the coal-based hard carbon negative electrode material of Example 2 and Comparative Example 1. DETAILED DESCRIPTION

[0024] Specific embodiment one: the preparation method of a coal-based hard carbon negative electrode material in this embodiment is completed according to the following steps:

[0025] I. Deashing treatment:

[0026] The raw material coal is ground, sieved and dried to obtain dry coal powder, the dry coal powder is uniformly dispersed in an aqueous hydrochloric acid solution, then deashing treatment is performed, and finally filtration, water washing and vacuum drying are performed to obtain deashed coal powder;

[0027] II. Micro-arc oxidation treatment:

[0028] The deashed coal powder is subjected to micro-arc oxidation treatment to obtain an oxidation precursor;

[0029] III. Carbonization:

[0030] The oxidation precursor is uniformly mixed with a fluorine source powder to obtain a mixed powder, and then the mixed powder is subjected to carbonization treatment to obtain a coal-based hard carbon negative electrode material, thereby completing the preparation method of the coal-based hard carbon negative electrode material.

[0031] The beneficial effects of this embodiment are:

[0032] (1) The present embodiment utilizes the HF gas generated by the decomposition of the fluorine source during the carbonization process to react with the SiO2 impurities in the coal raw material, thereby combining the impurity removal step and the carbonization step into one, simplifying the preparation process and avoiding the use of hydrofluoric acid.

[0033] (2) By means of micro-arc oxidation, more oxygen-containing functional groups are introduced into the precursor, promoting the intermolecular crosslinking reaction during carbonization and generating more pore structures.

[0034] (3) By means of the reaction between the HF gas generated by the decomposition of the fluorine source at high temperature and the SiO2 impurities in the coal raw material, part of the pores are introduced during the removal of impurities, further improving the performance of the material.

[0035] (4) By means of in-situ impurity removal and pore creation and in-situ crosslinking, the coal is introduced with pore structures during carbonization, and the coal-based hard carbon material prepared according to the method of the present application has high sodium storage capacity, first coulombic efficiency and rate performance as a negative electrode material for sodium ion batteries.

[0036] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the raw coal in step 1 is one or a combination of bituminous coal, sub-bituminous coal and lignite. Other aspects are the same as specific embodiment 1.

[0037] Specific embodiment 3: This embodiment differs from either specific embodiment 1 or 2 in that the ball milling in step 1 is performed at a rotation speed of 300-400 rpm for 2-5 hours, and the sieving in step 1 is performed through a 100-mesh sieve. Other steps are the same as those in specific embodiments 1 or 2.

[0038] Specific embodiment 4: This embodiment differs from one of specific embodiments 1 to 3 in that the concentration of the hydrochloric acid aqueous solution in step 1 is 3 mol / L to 5 mol / L; and the volume ratio of the dry coal powder to the hydrochloric acid aqueous solution in step 1 is 1 g: (10 to 30) mL. Other aspects are the same as specific embodiments 1 to 3.

[0039] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the deashing treatment in step 1 is carried out at a temperature of 25°C to 40°C and a rotation speed of 500 rpm to 700 rpm for 10 to 15 hours. Other aspects are the same as specific embodiments 1 to 5.

[0040] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the vacuum drying in step 1 is carried out at a temperature of 70° C. to 90° C. for 20 to 24 hours. Other aspects are the same as specific embodiments 1 to 5.

[0041] Specific embodiment seven: This embodiment differs from specific embodiments one to six in that the micro-arc oxidation treatment described in step two is specifically carried out at a power of 30kW to 60kW, a frequency of 800Hz to 1200Hz, a duty cycle of 30% to 50% and a current density of 8A / dm 2 ~12A / dm 2 Under the conditions of , the deashed pulverized coal is subjected to micro-arc oxidation treatment for 20 min to 50 min. Other steps are the same as those in the first to sixth embodiments.

[0042] Specific embodiment eight: This embodiment differs from any one of specific embodiments one to seven in that the fluorine source powder in step three is an organic fluorine source and an inorganic fluorine source or a mixture of both; the chemical formula of the organic fluorine source is (C a H b F c ) n , wherein a=1-4, b=0-6, c=1-6, n=1-10000; the general chemical formula of the inorganic fluorine source is MFm wherein M = Fe, Zn, Na, Li, NH4, Cr, Sb, Ti, Sn or V, m = 1-4; the mass percentage of the oxidation precursor in the mixed powder in step three is 70%-95%. The other aspects are the same as those in embodiments one to seven.

[0043] Embodiment nine: different from one of embodiments one to eight, the carbonization treatment in step three is specifically carried out at a temperature increasing rate of 1 ℃ / min-10 ℃ / min, and then the temperature is increased to 1000 ℃-1400 ℃, and then the carbonization treatment is carried out for 2 h-5 h under the conditions of inert atmosphere and temperature of 1000 ℃-1400 ℃; the inert atmosphere is argon or nitrogen. The other aspects are the same as those in embodiments one to eight.

[0044] Embodiment ten: application of the coal-based hard carbon negative electrode material, which is used for preparing a secondary ion battery negative electrode material.

[0045] The beneficial effects of the present application are verified by the following embodiments:

[0046] Embodiment one:

[0047] A preparation method of a coal-based hard carbon negative electrode material, which is completed according to the following steps:

[0048] I. desalination treatment:

[0049] The raw material coal is ball milled for 3 h under the condition of a rotation speed of 400 rpm, and then is passed through a 100-mesh screen and dried to obtain dry coal powder; the dry coal powder is uniformly dispersed in an aqueous hydrochloric acid solution, and then is desalinated for 12 h under the conditions of a temperature of 30 ℃ and a rotation speed of 600 rpm; after desalination, the desalinated coal powder is filtered, washed with water, and finally vacuum dried for 24 h under the condition of a temperature of 80 ℃.

[0050] The concentration of the aqueous hydrochloric acid solution is 3 mol / L; the mass of the dry coal powder to the volume of the aqueous hydrochloric acid solution is 1 g:20 mL.

[0051] II. micro-arc oxidation treatment:

[0052] The desalinated coal powder is subjected to micro-arc oxidation treatment for 30 min under the conditions of a power of 60 kW, a frequency of 1000 Hz, a duty cycle of 40%, and a current density of 10 A / dm 2 to obtain an oxidation precursor.

[0053] III. carbonization:

[0054] Mixing the oxidation precursor with the fluorine source powder to obtain a mixed powder, heating the mixed powder to 1200 DEG C at a heating rate of 5 DEG C / min under an argon atmosphere, and then carbonizing the mixed powder under an argon atmosphere at 1200 DEG C for 2 h to obtain the coal-based hard carbon negative electrode material.

[0055] The raw coal in step one is lignite; the lignite is lignite from the Zalai Nuoer mining area, wherein the mass percentage of ash is 7.64%, the mass percentage of moisture is 10.01%, the mass percentage of volatile matter is 35.72%, and the mass percentage of fixed carbon is 46.63%.

[0056] The fluorine source powder in step three is an organic fluorine source; the organic fluorine source is polytetrafluoroethylene; and the mass percentage of the oxidation precursor in the mixed powder in step three is 95%.

[0057] Example 2: Different from example 1, the mass percentage of the oxidation precursor in the mixed powder in step three is 85% in this example.

[0058] Example 3: Different from example 1, the mass percentage of the oxidation precursor in the mixed powder in step three is 70% in this example.

[0059] Example 4: Different from example 1, the heating rate in step three is 1 DEG C / min in this example.

[0060] Example 5: Different from example 1, the heating rate in step three is 10 DEG C / min in this example.

[0061] Example 6: Different from example 1, the carbonization temperature in step three is 1000 DEG C in this example.

[0062] Example 7: Different from example 1, the carbonization temperature in step three is 1400 DEG C in this example.

[0063] Example 8: Different from example 1, the fluorine source powder in step three is a mixture of an organic fluorine source and an inorganic fluorine source at a mass ratio of 100:50; the organic fluorine source is polytetrafluoroethylene; and the inorganic fluorine source is ammonium fluoride.

[0064] Example 9: Different from example 1, the fluorine source powder in step three is a mixture of an organic fluorine source and an inorganic fluorine source at a mass ratio of 100:100; the organic fluorine source is polytetrafluoroethylene; and the inorganic fluorine source is ammonium fluoride.

[0065] Example 10: This example is different from example 1 in that: the raw coal in step one is bituminous coal; the bituminous coal is from Hongshaquan mine area in Xinjiang, with ash content of 5%, moisture content of 7%, volatile content of 8%, and fixed carbon content of 80%; the fluorine source powder in step three is a mixture of organic fluorine source and inorganic fluorine source with a mass ratio of 100: 100; the organic fluorine source is polytetrafluoroethylene; and the inorganic fluorine source is ammonium fluoride. The others are the same as example 1.

[0066] Example 11: This example is different from example 1 in that: the raw coal in step one is sub-bituminous coal; the sub-bituminous coal is from Hongshaquan mine area in Xinjiang, with ash content of 6%, moisture content of 9%, volatile content of 22%, and fixed carbon content of 63%; the fluorine source powder in step three is a mixture of organic fluorine source and inorganic fluorine source with a mass ratio of 100: 100; the organic fluorine source is polytetrafluoroethylene; and the inorganic fluorine source is ammonium fluoride. The others are the same as example 1.

[0067] Example 12: This example is different from example 1 in that: the raw coal is ball milled for 3h under the condition of 300rpm in step one; the raw coal in step one is sub-bituminous coal; the sub-bituminous coal is from Hongshaquan mine area in Xinjiang, with ash content of 6%, moisture content of 9%, volatile content of 22%, and fixed carbon content of 63%; the fluorine source powder in step three is a mixture of organic fluorine source and inorganic fluorine source with a mass ratio of 100: 100; the organic fluorine source is polytetrafluoroethylene; and the inorganic fluorine source is ammonium fluoride. The others are the same as example 1.

[0068] Example 13: This example is different from example 1 in that: the raw coal is ball milled for 5h under the condition of 400rpm in step one; the raw coal in step one is sub-bituminous coal; the sub-bituminous coal is from Hongshaquan mine area in Xinjiang, with ash content of 6%, moisture content of 9%, volatile content of 22%, and fixed carbon content of 63%; the fluorine source powder in step three is a mixture of organic fluorine source and inorganic fluorine source with a mass ratio of 100: 100; the organic fluorine source is polytetrafluoroethylene; and the inorganic fluorine source is ammonium fluoride. The others are the same as example 1.

[0069] Example 14: The difference between this example and Example 1 is that: in step three, carbonization is carried out under nitrogen atmosphere; in step three, the fluorine source powder is a mixture of organic fluorine source and inorganic fluorine source with a mass ratio of 100:100; the organic fluorine source is polytetrafluoroethylene; and the inorganic fluorine source is ammonium fluoride. The others are the same as Example 1.

[0070] Comparative Example 1: The difference between this example and Example 1 is that: step two is omitted; and in step three, the fluorine source powder is omitted. The others are the same as Example 1.

[0071] Performance test:

[0072] (1) SEM test:

[0073] The coal-based hard carbon negative material prepared in Example 2 was subjected to SEM test, and the results are shown in Figure 1 . Figure 1 Figure is a SEM image of the coal-based hard carbon negative material prepared in Example 2; as can be seen from the figure, the material presents a granular structure with a particle size of 3-5 μm.

[0074] (2) X-ray test:

[0075] Figure 2 Figure is an X-ray diffraction pattern of the coal-based hard carbon negative material prepared in Example 2 and Comparative Example 1; as can be seen from the figure, the silicon impurities are removed after co-carbonization with polytetrafluoroethylene.

[0076] (3) Button cell test:

[0077] The coal-based hard carbon negative materials prepared in Examples 1-14 and Comparative Example 1 were assembled into button cells according to the following method:

[0078] The coal-based hard carbon negative materials prepared in Examples 1-14 and Comparative Example 1 were used as anodes, and button cells were assembled with sodium sheets, electrolyte and separators in a glove box with oxygen and water content of less than 0.1 ppm. The separator was glass fiber separator Whatman GF / D; the electrolyte was a solution of NaPF6, the concentration of NaPF6 in the electrolyte was 1 mol / L, and the solvent was diethylene glycol dimethyl ether (DIGLYME).

[0079] The button cells prepared were tested for performance using a new Wei tester, and the test conditions were: charging and discharging at a current density of 30 mA·g -1 , the voltage range was 0-2 V, and the cycle was stopped after 3 weeks, and the rate performance (300 mA·g -1 ) of the button cell was tested, and the test results are shown in Table 1. Figure 3 Figure is a charging and discharging curve of the sodium ion battery prepared using the coal-based hard carbon negative material of Example 2 and Comparative Example 1. Figure 4The cycle performance chart of sodium ion batteries prepared using the coal-based hard carbon negative electrode material of Example 2 and Comparative Example 1; it can be found that the capacity retention rate is improved from 84.1% to 96.9%.

[0080] Table 1

[0081]

[0082] As can be seen from Table 1, the discharge capacity and rate performance of the button cell prepared using the coal-based hard carbon negative electrode material of Examples 1-14 are higher than that of Comparative Example 1. The experimental results show that the introduction of pores in the material of the examples can improve the specific sodium storage capacity of the material, and the closed pore structure can improve the first coulombic efficiency.

Claims

1. A method for preparing a coal-based hard carbon negative electrode material, characterized in that It is completed according to the following steps: I. Deashing treatment: The raw coal is ground, sieved and dried to obtain dry coal powder, the dry coal powder is uniformly dispersed in an aqueous hydrochloric acid solution, then deashing treatment is performed, and finally filtration, water washing and vacuum drying are performed to obtain deashed coal powder; II. Micro-arc oxidation treatment: The deashed coal powder is subjected to micro-arc oxidation treatment to obtain an oxidation precursor; III. Carbonization: The oxidation precursor is uniformly mixed with a fluorine source powder to obtain a mixed powder, and then the mixed powder is subjected to carbonization treatment to obtain a coal-based hard carbon negative electrode material, thereby completing the preparation method of the coal-based hard carbon negative electrode material.

2. The method according to claim 1, characterized in that The raw coal in step I is one of bituminous coal, sub-bituminous coal and lignite, or a combination of several thereof.

3. The method for preparing a coal-based hard carbon negative electrode material according to claim 1, characterized in that The ball milling in step I is specifically performed at a rotation speed of 300 rpm to 400 rpm for 2 h to 5 h; and the sieving in step I is performed through a 100-mesh sieve.

4. The method according to claim 1, characterized in that The aqueous hydrochloric acid solution in step I has a concentration of 3 mol / L to 5 mol / L; and the mass of the dry coal powder to the volume of the aqueous hydrochloric acid solution in step I is 1 g to (10-30) mL.

5. The method for preparing a coal-based hard carbon negative electrode material according to claim 1, characterized in that The deashing treatment in step I is specifically performed at a temperature of 25°C to 40°C and a rotation speed of 500 rpm to 700 rpm for 10 h to 15 h.

6. The method for preparing a coal-based hard carbon negative electrode material according to claim 1, characterized in that The vacuum drying in step I is specifically performed at a temperature of 70°C to 90°C for 20 h to 24 h.

7. The method according to claim 1, characterized in that The micro-arc oxidation treatment in Step 2 is performed on the deashed coal powder under conditions of a power of 30 kW to 60 kW, a frequency of 800 Hz to 1200 Hz, a duty ratio of 30% to 50%, and a current density of 8 A / dm 2 2 A / dm 2 for 20 min to 50 min.

8. The method for preparing a coal-based hard carbon negative electrode material according to claim 1, characterized in that The fluorine source powder in step three is a mixture of one or both of an organic fluorine source and an inorganic fluorine source; the organic fluorine source has a general chemical formula of (C a H b F c ) n wherein a = 1-4, b = 0-6, c = 1-6, and n = 1-10000; the inorganic fluorine source has a general chemical formula of MF m wherein M = Fe, Zn, Na, Li, NH4, Cr, Sb, Ti, Sn, or V, and m = 1-4; the mass percentage of the oxidation precursor in the mixed powder in step three is 70%-95%.

9. The method for preparing a coal-based hard carbon negative electrode material according to claim 1, characterized in that The carbonization treatment in step III is specifically performed under an inert atmosphere at a temperature increasing rate of 1°C / min to 10°C / min, the temperature is increased to 1000°C to 1400°C, and then the carbonization treatment is performed under the inert atmosphere and at a temperature of 1000°C to 1400°C for 2 h to 5 h; the inert atmosphere is argon or nitrogen.

10. Use of a coal-based hard carbon negative electrode material prepared according to claim 1, characterized in that It is used for preparing a secondary ion battery negative electrode material.

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