Closed-pore structure construction method of coal-based hard carbon material and application of closed-pore structure in sodium-ion battery

Abstract

The invention relates to the technical field of carbon materials and sodium-ion battery electrode materials, and provides a closed-pore structure construction method of a coal-based hard carbon material and application of the coal-based hard carbon material in a sodium-ion battery. CO2 generated by carbonate decomposition plays an activating role to form a large number of open pores, meanwhile, carbonate can react with aluminum oxide and silicon oxide in coal ash to form acid-soluble salt, more open pore structures are left after acid pickling and impurity removal, and the open pores are further directly converted into closed pores through high-temperature carbonization treatment subsequently, so that the open pores are formed. The coal-based hard carbon material with a closed pore structure and a disordered microcrystalline structure is obtained. By combining the activation effect of carbonate with ball milling and high-temperature secondary carbonization treatment, the construction of a closed-pore structure can be effectively realized, so that the carbon material shows high sodium storage capacity and coulombic efficiency. The method disclosed by the invention is simple in preparation process and low in cost, realizes high-added-value development and utilization of the coal-based hard carbon material, and has a good application and development prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of battery electrode materials, and in particular to a method for constructing a closed-pore structure of a coal-based hard carbon negative electrode material for a sodium ion battery and applications thereof. Background Art

[0002] As a secondary battery, sodium-ion batteries have the advantages of abundant resources, low cost, excellent low-temperature performance and environmental friendliness, and can be used for large-scale energy storage. Hard carbon has excellent electrochemical sodium storage performance, a wide range of sources and low cost, and is the most commercially advantageous sodium-ion battery negative electrode material. Common hard carbon precursors include biomass, resin, asphalt and coal precursors. Coal precursors have the advantages of high reserves, wide geographical distribution, low cost and high fixed carbon content, making them ideal precursors for preparing carbon negative electrode materials for sodium-ion batteries. Therefore, the development of low-cost and high-sodium storage performance coal-based hard carbon materials is the core competitive technology for achieving large-scale commercialization of sodium-ion batteries.

[0003] However, coal-based carbon materials tend to form highly graphitized microcrystalline structures during high-temperature carbonization, which inhibits the insertion and extraction of sodium ions, resulting in low sodium storage capacity. Furthermore, numerous defects form during pyrolysis, leading to low specific capacity and unsatisfactory first-cycle Coulombic efficiency. Furthermore, the presence of difficult-to-remove silicon-aluminum oxide ash in coal further limits its application in high-energy-density sodium-ion batteries.

[0004] Existing modification strategies for coal-based hard carbon materials, such as heteroatom doping, introduce heteroatoms such as nitrogen (Diamond & Related Materials, 2022, 130, 109481), sulfur (New Carbon Materials, 2024, 39, 297-307), and phosphorus (Journal of Alloys and Compounds, 2023, 946, 169384) into coal precursors. This can increase active sites by introducing defects, improve electrical conductivity, and help improve the sodium storage capacity and rate performance of coal-based hard carbon materials. However, the doping level and content are usually very low, the doping is uneven, and the initial efficiency is low. The commonly used alkali activation method to build open-pore secondary high-temperature carbonization or coating structure closed pores (Advanced Functional. Materials, 2022, 32, 2203725) can improve the initial efficiency and sodium storage capacity, but the use of strong alkali is costly and the steps are complicated. In addition, it is generally difficult to remove silicon and aluminum impurities from coal ash by hydrochloric acid pickling, and the removal by hydrofluoric acid cleaning is more complicated and relatively dangerous (Chemical Engineering Journal 2024, 493, 152389). Therefore, this work uses the high-temperature decomposition of carbonates to produce CO2 that reacts with carbon to form a developed pore structure. In addition, carbonates can react with impurities such as aluminum and silicon oxides that are difficult to remove in coal ash to form acid-soluble salts. After pickling, impurities and residual salt components are removed to form an open-pore structure. Subsequent direct high-temperature carbonization is performed to obtain a coal-based hard carbon material that is free of impurities and has a developed closed-pore structure. The closed-pore structure is conducive to improving the low-potential sodium storage capacity, thereby achieving an improvement in capacity and initial efficiency. Summary of the Invention

[0005] The purpose of the present invention is to provide a closed-pore structure construction method for coal-based hard carbon negative electrode materials for sodium ion batteries and its application, which achieves optimization of the preparation process of coal-based hard carbon materials, cost reduction and improvement of sodium storage performance.

[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 method for constructing a closed-pore structure of a coal-based hard carbon negative electrode material for a sodium ion battery and its application, comprising the following steps:

[0008] (1) Coal-based materials are mixed with carbonates and then subjected to high-temperature pretreatment and acid washing to remove impurities to form an open-pore structure, thereby obtaining a pretreated coal-based carbon material.

[0009] (2) The pretreated coal-based carbon material with an open-pore structure is subjected to high-energy ball milling treatment, and then subjected to high-temperature carbonization treatment to obtain a coal-based hard carbon material with a closed-pore structure.

[0010] The coal may be selected from any one of anthracite, bituminous coal, sub-bituminous coal and lignite;

[0011] The carbonate can be any one of calcium carbonate, magnesium carbonate, and sodium carbonate, and the mixing mass ratio of coal to carbonate is 1:3-3:1;

[0012] Preferably, the mixture ratio of coal to carbonate is 1:2-2:1;

[0013] The temperature of the high temperature activation pretreatment is 600-1000°C and the time is 1-3h;

[0014] Preferably, the heating rate for the high temperature activation pretreatment is 2-10°C / min;

[0015] The pickling conditions are as follows: using 2-4M hydrochloric acid, stirring mechanically at 200-400 rpm at 20-30°C for 6-12 hours, and then washing with deionized water until neutral;

[0016] The ball milling mixing conditions are as follows: a rotation speed of 200-600 r / min, a ball-to-material ratio of 1:1-50:1, and a duration of 4-24 hours.

[0017] The carbonization temperature of the activated ball-milled product under an inert atmosphere is 1200-1700° C., preferably 1300-1600° C., and the holding time is 1-3 hours.

[0018] The specific surface area of ​​the coal-based hard carbon material is 10-60m 2 g -1 ; The (002) crystal plane interlayer spacing of the coal-based hard carbon material is 0.35-0.38nm.

[0019] The coal-based hard carbon material is applied to the negative electrode material of sodium ion batteries.

[0020] The present invention provides a method for preparing a coal-based hard carbon material, comprising the following steps: mixing coal with carbonate, and performing high-temperature pretreatment under inert atmosphere conditions. During the process, CO2 generated by the decomposition of carbonate reacts with carbon at high temperature to activate the formation of a large number of open pores. At the same time, carbonate can react with impurities such as aluminum and silicon oxides that are difficult to remove in the coal ash to form acid-soluble salts. Subsequently, the carbon material with a developed open-pore structure can be removed by pickling with hydrochloric acid. The prepared open-pore structure carbon material is subjected to ball milling and then subjected to high-temperature secondary carbonization to further form a closed-pore structure coal-based hard carbon material. When the coal-based hard carbon material is used as the negative electrode of a sodium ion battery, its highly graphitized and small interlayer spacing carbon structure leads to a small number of sodium storage sites, exhibiting problems such as low specific capacity and poor first efficiency. In response to the problems existing in coal-based hard carbon materials, the present invention first pre-treats the coal and carbonate at high temperature after mixing, utilizes the high-temperature decomposition of carbonate to generate CO2 that reacts with carbon to form a developed pore structure, removes impurities and residual salt components after pickling to form an open-pore structure. Subsequently, high-energy mechanical ball milling treatment is performed and high-temperature carbonization is directly performed without the need for additional coating agents to obtain a coal-based hard carbon material free of impurities and having a developed closed-pore structure. The closed-pore structure is conducive to improving the low-potential sodium storage capacity, thereby achieving an increase in capacity and first efficiency. Compared with the coal-based hard carbon negative electrode material directly carbonized at high temperature, the electrochemical performance of the sodium ion battery negative electrode material described in the present invention is significantly improved. Experimental results show that when the coal-based hard carbon negative electrode material prepared by the preparation method provided by the present invention is used as a sodium ion battery negative electrode, its specific capacity can reach 252.6mAh g at a current density of 0.1C. -1 The coulombic efficiency in the first week was 75.5%, and the capacity retention rate was 93.3% after 100 cycles at a current density of 0.2C.

[0021] The method of the present invention has a simple preparation process, realizes the high-value-added development and utilization of low-cost coal, and has good application development prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a scanning electron microscope (SEM) image of the hard carbon material prepared in Example 1 of the present invention;

[0023] Figure 2 This is an X-ray diffraction (XRD) pattern of the hard carbon material prepared in Example 1 of the present invention;

[0024] Figure 3 This is a high-resolution transmission electron microscopy (HRTEM) image of the hard carbon material prepared in Comparative Example 1 of the present invention;

[0025] Figure 4 Isothermal adsorption curves of the carbon material and the hard carbon material prepared by pretreatment in Comparative Example 1 of the present invention;

[0026] Figure 5 The charge and discharge curves of the sodium ion battery prepared in Comparative Example 1 of the present invention at the 1st, 2nd and 3rd cycles are shown;

[0027] Figure 6 The charge and discharge curves of the sodium ion battery prepared in Application Example 1 of the present invention in the 1st, 2nd and 3rd cycles are shown;

[0028] Figure 7 This is a cycle performance diagram of the sodium ion battery prepared in Application Example 1 of the present invention;

[0029] Figure 8 The charge and discharge curves of the sodium ion battery prepared in Example 2 of the present invention in the 1st, 2nd and 3rd cycles are shown;

[0030] Figure 9 These are the charge and discharge curves of the 1st, 2nd and 3rd cycles of the sodium ion battery prepared in Example 3 of the present invention.

[0031] Figure 10 These are the charge and discharge curves of the 1st, 2nd and 3rd cycles of the sodium ion battery prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0032] The technical solution provided by the present invention is further clearly and completely described below by way of specific embodiments.

[0033] The present invention provides a method for preparing a coal-based hard carbon material, comprising the following steps:

[0034] (1) Coal-based materials are mixed with carbonates and then subjected to high-temperature pretreatment and acid washing to remove impurities to form an open-pore structure, thereby obtaining a pretreated coal-based carbon material.

[0035] (2) The pretreated coal-based carbon material with an open-pore structure is ball-milled and subsequently subjected to high-temperature carbonization treatment to obtain a coal-based hard carbon material with a closed-pore structure.

[0036] In the present invention, unless otherwise specified, all raw materials for preparation are commercially available products well known to those skilled in the art. The coal can be selected from any one of the following.

[0037] In the present invention, the coal can be selected from any one of anthracite, bituminous coal, sub-bituminous coal, and lignite. The carbonate can be selected from any one of calcium carbonate, magnesium carbonate, and sodium carbonate. The mass ratio of the coal to the carbonate is 1:3-3:1.

[0038] In the present invention, the carbonate and the coal-based material only need to be simply mixed, and the carbonate melts and etches the coal-based material during the high-temperature activation process to form a rich pore structure, thereby increasing the specific surface area and disorder of the coal-based material; the temperature of the high-temperature activation pretreatment is preferably 600-1000°C, more preferably 800-900°C; the heating rate to the high-temperature activation treatment is preferably 2-10°C / min; the high-temperature activation pretreatment is carried out under an inert atmosphere; the activated product should be pickled after the high-temperature activation treatment, then washed to neutrality and then dried; the pickling conditions are such that Use hydrochloric acid with a concentration of 2-4M and mechanically stir at 200-400rpm at 20-30℃ for 6-12h; the ball milling mixing conditions are a rotation speed of 200-600r / min, a ball-to-material ratio of 1:1-50:1, and a duration of 4-24h, more preferably 15-24h; the carbonization temperature of the activated ball milled product is preferably 1200-1700℃, more preferably 1200-1600℃, and the holding time is 1-3h; the heating rate to the high-temperature carbonization treatment temperature is 2-10℃ / min; the atmosphere of the high-temperature carbonization treatment is an inert atmosphere. In the present invention, when the carbonization temperature and time are within the above ranges, and the ball milling time and rotation speed are within the above ranges, the pore structure of the activated product can be fully closed to obtain the coal-based closed-pore hard carbon material. The cooling, washing, filtration, and drying steps involved in the present invention are not particularly limited, and the processes well known to those skilled in the art can be used.

[0039] The present invention does not specifically limit the application method of the coal-based closed-pore carbon material, and the application method of carbon materials in sodium ion battery negative electrode materials well known to those skilled in the art can be adopted.

[0040] The following detailed description of the method for preparing a coal-based closed-pore hard carbon material provided by the present invention is based on examples. These examples are only some of the embodiments of the present invention and do not include all of the embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on these embodiments without inventive effort are considered within the scope of protection of the present invention.

[0041] Example 1

[0042] (1) 1.00 g of anthracite powder and 1.00 g of calcium carbonate were mixed, heated to 900 °C at a heating rate of 5 °C / min under argon atmosphere, kept at this temperature for 2 h, and cooled to obtain a mixed product;

[0043] (2) The mixed product in (1) was immersed in 120 mL of hydrochloric acid (3 mol / L) and stirred, and the mixed solution was then vacuum filtered and washed with deionized water until the solution was neutral. The product was dried in a conventional oven at 80°C for 12 h to obtain an activated product;

[0044] (3) The activated product obtained in (2) was ball-milled in a high-energy ball mill at a speed of 500 r / min and a ball-to-material ratio of 30:1 for 15 h to obtain a ball-milled product;

[0045] (4) The ball-milled product obtained in (3) was heated to 1500° C. at a heating rate of 5° C. / min under argon atmosphere, kept at this temperature for 2 h, and cooled to obtain the coal-based closed-pore hard carbon material of Example 1;

[0046] The coal-based closed-cell hard carbon material of Example 1 was subjected to an electron microscope scanning test, and the test results are as follows: Figure 1 As shown. Figure 1 It can be seen that the microstructure of the coal-based closed-pore hard carbon material in Example 1 is composed of irregular block particles with a particle size of 2 to 30 μm, and there is no pore structure on the surface of the block particles.

[0047] The coal-based closed-cell hard carbon material prepared in Example 1 was tested using an X-ray diffractometer, and the XRD pattern was as follows: Figure 2 As shown. Figure 2 The XRD pattern shows that the angle corresponding to the (002) peak is 25.36°, and the interplanar spacing calculated according to the Bragg formula is 0.3508nm.

[0048] The hard carbon material prepared in Example 1 was subjected to high-resolution transmission electron microscopy scanning test, and the test results are as follows: Figure 3 As shown by Figure 3 It can be seen that the graphite lattice stripes in Example 1 are disordered and a large number of closed-pore structures are distributed.

[0049] The activated carbon material of Example 1 and the final synthesized hard carbon material were subjected to isothermal nitrogen adsorption test. The test results are as follows: Figure 4 As shown. Figure 4 It can be seen that the specific surface area of ​​the activated carbon material in Example 1 is 58.1 m 2 g -1 , the pore volume reaches 0.2454cm 3 g -1 , and the specific surface area of ​​the final synthesized hard carbon material is 37.0 m 2 g -1 , the pore volume is 0.0997cm 3 g -1 .

[0050] Application Example 1

[0051] The coal-based hard carbon material prepared in Example 1 was mixed with sodium carboxymethyl cellulose at a mass ratio of 95:5 to form a slurry. The slurry was then evenly coated onto a current collector copper foil to produce a hard carbon electrode. In a glove box, CR2025 button cells were assembled using sodium metal as the counter electrode and a 1M NaClO₄ solution in ethylene carbonate and diethyl carbonate as the electrolyte.

[0052] Comparative Example 1

[0053] 1 g of anthracite was heated to 1500°C at a heating rate of 5°C / min under argon atmosphere and carbonized at constant temperature for 2 h to obtain a hard carbon material.

[0054] The coal-based hard carbon material prepared in Comparative Example 1 was mixed with sodium carboxymethyl cellulose at a mass ratio of 95:5 to form a slurry. The slurry was then evenly coated onto a current collector copper foil to produce a hard carbon electrode. In a glove box, CR2025 button cells were assembled using sodium metal as the counter electrode and a 1M NaClO₄ solution in ethylene carbonate and diethyl carbonate as the electrolyte.

[0055] Performance Testing

[0056] The battery prepared in Example 1 was subjected to charge and discharge performance tests under the following conditions: the current density was set to 0.1C (1C = 300mAg -1 ); the discharge cut-off voltage is 0.001V, and the charge cut-off voltage is 3V. The test results are as follows Figure 5 shown.

[0057] from Figure 5 The charge and discharge curve shows that its sodium storage capacity in the first week is 130.0mAg -1 , the coulombic efficiency in the first week was 71.2%, and the sodium storage capacity performance was poor.

[0058] The battery prepared in Example 1 was tested for charge and discharge performance. The test conditions were: the current density was set to 0.1C; the discharge cut-off voltage was 0.001V, and the charge cut-off voltage was 3V. The test results are as follows: Figure 6 and Figure 7 shown.

[0059] from Figure 6 The charge and discharge curve shows that its sodium storage capacity in the first week is 252.6mAg -1 , the first-week Coulomb efficiency is 75.5%, which has a high sodium storage capacity and good first-week Coulomb efficiency.

[0060] from Figure 7 It can be seen from the cycle curve that at a current density of 0.2C, after 100 cycles, its capacity retention rate reaches 93.3%, and the cycle stability is good.

[0061] Example 2

[0062] The carbonate in Example 1 is replaced by magnesium carbonate, and the remaining technical features are the same as those in Example 1 to obtain a hard carbon material.

[0063] Application Example 2

[0064] The coal-based hard carbon material prepared in Example 2 was mixed with sodium carboxymethyl cellulose at a mass ratio of 95:5 to form a slurry. The slurry was then evenly coated onto a current collector copper foil to produce a hard carbon electrode. In a glove box, CR2025 button cells were assembled using sodium metal as the counter electrode and a 1M NaClO₄ solution in ethylene carbonate and diethyl carbonate as the electrolyte.

[0065] Performance Testing

[0066] The battery prepared in Example 2 was tested for charge and discharge performance under the following conditions: current density was set to 0.1C; discharge cut-off voltage was 0.001V, and charge cut-off voltage was 3V. Figure 8 shown.

[0067] from Figure 8 The charge and discharge curve shows that its sodium storage capacity in the first week is 223.6mAg -1 The coulombic efficiency in the first week is 69.0%, which is significantly improved compared with comparative example 1.

[0068] Example 3

[0069] The ball-milled product in Example 1 was carbonized at a high temperature of 1400° C., and the remaining technical features were the same as those in Example 1 to obtain a hard carbon material.

[0070] Application Example 3

[0071] The coal-based hard carbon material prepared in Example 3 was mixed with sodium carboxymethyl cellulose at a mass ratio of 95:5 to form a slurry. The slurry was then evenly coated onto a current collector copper foil to produce a hard carbon electrode. In a glove box, CR2025 button cells were assembled using sodium metal as the counter electrode and a 1M NaClO₄ solution in ethylene carbonate and diethyl carbonate as the electrolyte.

[0072] The battery prepared in Example 3 was tested for charge and discharge performance. The test conditions were: current density was set to 0.1C; discharge cut-off voltage was 0.001V, and charge cut-off voltage was 3V. The test results are shown in the figure. Figure 9 shown.

[0073] from Figure 9 The charge and discharge curve shows that its sodium storage capacity in the first week is 201.3mAg-1 The coulombic efficiency in the first week is 72.9%, which is significantly improved compared with comparative example 1.

[0074] Example 4

[0075] The calcium carbonate in Example 1 was replaced with magnesium carbonate, and the ball-milled product was carbonized at a high temperature of 1400° C. The remaining technical features were the same as those in Example 1 to obtain a hard carbon material.

[0076] Application Example 4

[0077] The coal-based hard carbon material prepared in Example 4 was mixed with sodium carboxymethyl cellulose at a mass ratio of 95:5 to form a slurry. The slurry was then evenly coated onto a current collector copper foil to produce a hard carbon electrode. In a glove box, CR2025 button cells were assembled using sodium metal as the counter electrode and a 1M NaClO₄ solution in ethylene carbonate and diethyl carbonate as the electrolyte.

[0078] Performance Testing

[0079] The battery prepared in Example 4 was tested for charge and discharge performance under the following conditions: current density was set to 0.1C; discharge cut-off voltage was 0.001V, and charge cut-off voltage was 3V. Figure 10 shown.

[0080] from Figure 10 The charge and discharge curve shows that its sodium storage capacity in the first week is 204.6mAg -1 The first-week Coulomb efficiency is 77.4%. Compared with comparative example 1, its capacity and first efficiency are improved.

[0081] The electrochemical test performances of the coal-based carbon materials of Examples (Comparative) 1-4 are summarized in Table 1 below.

[0082] Table 1 Electrochemical test performance of coal-based hard carbon materials in Example 1-4

[0083]

[0084] It can be seen from the above experimental test results that the coal-based closed-pore hard carbon material prepared by the present invention has excellent sodium storage capacity and coulombic efficiency.

[0085] 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 principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for constructing a closed-pore structure of a coal-based hard carbon material, characterized in that: The following steps are involved: (1) After coal and carbonate are mixed, they are pretreated at high temperature under an inert atmosphere. The gas generated by the decomposition of carbonate is used to form pores. The residual metal impurities are then removed by acid washing and the pores are expanded to obtain pretreated coal-based carbon materials. (2) The pretreated coal-based carbon material is subjected to high-energy ball milling, and then directly subjected to high-temperature carbonization treatment to obtain a coal-based hard carbon material with a closed-pore structure.

2. The method according to claim 1, wherein The coal in step (1) can be selected from any one of anthracite, bituminous coal, sub-bituminous coal and lignite.

3. The method according to claim 1, wherein The carbonate in step (1) can be any one of calcium carbonate, magnesium carbonate, sodium carbonate and potassium carbonate, and the mixing mass ratio of coal to carbonate is 1:3-3:

1.

4. The method according to claim 1, wherein The high-temperature pretreatment in step (1) is carried out under an inert atmosphere with a heating rate of 2-10°C / min, a high-temperature pretreatment temperature of 600-1000°C, and a constant temperature time of 1-3h. The gas of the inert atmosphere is any one of nitrogen, helium or argon, or a mixture of several thereof.

5. The method according to claim 1, wherein The acid washing conditions in step (1) are to use 2-4 M hydrochloric acid, mechanically stir at 200-400 rpm at 20-30° C. for 6-12 h, and then wash with deionized water until neutral.

6. The method according to claim 1, wherein The high-energy ball milling treatment conditions in step (2) are specifically as follows: a ball milling speed of 200-600 r / min, a ball-to-material ratio of 1:1-50:1, and a ball milling time of 4-24 h.

7. The method according to claim 1, wherein In step (2), the high-temperature carbonization temperature is 1200-1700° C. under an inert atmosphere, and the constant temperature time is 1-3 hours. The gas of the inert atmosphere is any one of nitrogen, helium or argon, or a mixture of several of them.

8. The coal-based hard carbon material prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The specific surface area of ​​the coal-based hard carbon material is 10-60m 2 g -1 ; The (002) crystal plane interlayer spacing of the coal-based hard carbon material is 0.36-0.39nm.

9. An application of a sodium ion battery, characterized in that: The coal-based hard carbon material according to claim 1 is used as a negative electrode material for sodium ion batteries.

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