A coal-based hard carbon anode material, its preparation method and application

Abstract

This invention provides a coal-based hard carbon anode material, its preparation method, and its applications. The preparation method includes the following steps: introducing industrial waste gas into raw coal, sequentially performing pre-carbonization and pore-forming, followed by high-temperature carbonization to obtain the coal-based hard carbon anode material. The preparation method provided by this invention uses extremely low-cost industrial waste gas to perform pore-forming treatment on the raw coal material, greatly reducing the preparation cost, and the resulting coal-based hard carbon anode material has high capacity and excellent performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and relates to a coal-based hard carbon anode material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries are considered a reliable energy storage technology that complements existing lithium-ion batteries and will be applied to large-scale energy storage, two-wheeled vehicles, low-speed electric vehicles and other scenarios. Different scenarios have different requirements for battery capacity and power. At present, the price of sodium-ion battery anode materials with hard carbon as the mainstream is still high. How to prepare high-performance and low-cost hard carbon materials is a problem facing the industry.

[0003] Coal, as the most abundant and cheapest natural carbon source, possesses an initial aromatic macromolecular structure that provides a structural basis for the functional design of carbon materials. Coal has a high carbon content and abundant oxygen-containing functional groups, making coal-based hard carbon one of the main anode materials for sodium-ion batteries. However, due to the large ionic radius of sodium ions, coal tends to soften and carbonize at high temperatures, resulting in a small interlayer spacing and low sodium storage capacity. Currently, commercially available coal-based hard carbon has a capacity of only 200–220 mAh / g, which is almost insufficient to meet the sodium storage requirements of sodium-ion batteries.

[0004] CN111293309A discloses a method for improving the performance of coal-based sodium-ion battery anode materials and its application. The method involves mixing coal-based materials with soft carbon precursors, then treating them at low temperatures and then carbonizing them at high temperatures to obtain amorphous carbon materials, which are the anode materials for sodium-ion batteries.

[0005] CN114335522A discloses a coal-based carbon anode material, its preparation method and application, and a battery containing the material. The coal-based raw material is subjected to pretreatment, low-temperature heat treatment and high-temperature heat treatment in sequence to obtain the coal-based carbon anode material.

[0006] The preparation methods provided in the aforementioned literature are complex, have significantly increased costs, and offer limited improvement in the performance of hard carbon.

[0007] Therefore, how to reduce the preparation cost of hard carbon anode materials in sodium-ion batteries while improving their electrochemical performance is an urgent technical problem to be solved. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a coal-based hard carbon anode material, its preparation method, and its applications. The preparation method provided by this invention utilizes extremely low-cost industrial waste gas to perform pore-forming treatment on raw coal materials, significantly reducing preparation costs. Furthermore, the resulting coal-based hard carbon anode material exhibits high capacity and excellent performance.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing a coal-based hard carbon anode material, the method comprising the following steps:

[0011] Industrial waste gas is introduced into the raw coal, and pre-carbonization and pore formation are carried out in sequence, followed by high-temperature carbonization to obtain coal-based hard carbon anode material.

[0012] It should be noted that the industrial waste gas provided in this invention is waste gas generated by chemical plants, coking plants, pharmaceutical plants, etc., and these waste gases typically contain gaseous compounds such as carbon oxides (CO, CO2), sulfur oxides, and nitrogen oxides; among which, under normal circumstances, the CO2 content (mass concentration mg / m³) is... 3 (The same below) is 40% to 50%, CO, NO x (X is 1 or 2), SO2 content is 40% to 50%, O2 content is less than 5%, and the remainder is other gases; the types and contents of the above gases may vary to different degrees depending on the type of industrial waste gas.

[0013] The method for preparing coal-based hard carbon provided by this invention involves creating pores in raw coal (hard carbon precursor material) using industrial waste gas. The raw material is pre-carbonized before the pore-forming process, and the raw material and preparation steps work synergistically. The oxygen-containing functional groups in the industrial waste gas undergo redox reactions with carbon, while small-molecule gases can also penetrate the interior of the raw coal. This results in a hard carbon anode material with uniform particle size distribution, abundant pore structure, and excellent specific surface area, powder compaction density, and tap density. It exhibits structural stability and rich pore structures both internally and on the surface, effectively improving the capacity and initial efficiency of the hard carbon anode material. Furthermore, the use of low-cost industrial waste gas significantly reduces the preparation cost.

[0014] In this invention, without the addition of industrial waste gas, the purpose of activation and pore formation cannot be achieved, thus failing to improve the capacity contribution of hard carbon in sodium-ion batteries; similarly, without pre-carbonization before pore formation, hard carbon with rich pore structure cannot be obtained.

[0015] Preferably, the volatile matter content of the raw coal is 20% to 40%, for example, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, or 40%.

[0016] In this invention, volatiles escape from the coal-based precursor to form a carbon conductive network, which improves the conductivity and stability of hard carbon. If the volatiles in the raw coal are less than 20%, the conductive network structure formed by the precursor is not good and cannot provide more channels for sodium ion transport and storage. If there are too many, it will result in an excessively large specific surface area and an excessive number of macropores in the hard carbon precursor after carbonization, which will reduce the initial coulombic efficiency of the sodium-ion battery.

[0017] Preferably, the ash content of the raw coal is 3% to 7%, for example, 3%, 4%, 5%, 6% or 7%.

[0018] The raw coal selected in this invention has high volatile matter and low ash content, and is inexpensive, making it the raw material for the hard carbon anode material of this invention.

[0019] Preferably, the raw coal includes any one or a combination of at least two of coking coal, fat coal, or gas coal.

[0020] Preferably, the raw coal is crushed to obtain coal powder.

[0021] Preferably, the D50 of the pulverized coal is 4 to 8 μm, such as 4 μm, 5 μm, 6 μm, 7 μm or 8 μm.

[0022] Preferably, the inlet flow rate of the industrial waste gas is 2 to 10 L / min, such as 2 L / min, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min or 10 L / min.

[0023] In this invention, if the flow rate of the industrial waste gas is too low, less than 2L / min, it will not be conducive to the low degree of pore formation of hard carbon by the industrial waste gas, and the purpose of activation and capacity improvement will not be achieved; if it exceeds 10L / min, it will lead to the hard carbon having too rich a pore structure, resulting in an excessively large specific surface area and a low initial efficiency of the battery.

[0024] Preferably, the heating rates for pre-carbonization and pore formation are each independently 2 to 10 °C / min, for example 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min or 10 °C / min, etc.

[0025] Preferably, the pre-carbonization insulation temperature is 400-600℃, such as 400℃, 450℃, 500℃, 550℃ or 600℃.

[0026] In this invention, if the insulation temperature during the pre-carbonization stage is too low, it will not be conducive to the release of volatiles from the coal base; if the insulation temperature is too high, it will result in excessive energy consumption.

[0027] Preferably, the pre-carbonization holding time is 2 to 4 hours, such as 2 hours, 3 hours, or 4 hours.

[0028] Preferably, the heat preservation temperature for creating the hole is 800-1000℃, such as 800℃, 850℃, 900℃, 950℃ or 1000℃.

[0029] Preferably, the heat preservation time for creating the hole is 6 to 8 hours, such as 6 hours, 7 hours or 8 hours.

[0030] Preferably, the pre-carbonization and pore-forming are carried out in a rotary kiln.

[0031] The present invention employs a dynamic sintering method in the pre-carbonization and pore-forming stages, resulting in more uniform mixing and more thorough sintering.

[0032] Preferably, the rotary kiln has an inclination of 3 to 5%, such as 3, 4 or 5, and a rotation speed of 0.5 to 1.5 r / min, such as 0.5 r / min, 0.6 r / min, 0.7 r / min, 0.8 r / min, 0.9 r / min or 1 r / min.

[0033] Preferably, the product after pore formation is acid-washed.

[0034] In this invention, the acid washing process removes the ash from the coal itself, preventing excessive ash from reducing the battery cell capacity and causing safety issues due to the introduction of foreign matter. On the other hand, it can also wash away a small amount of impurities introduced into the hard carbon from industrial waste gas.

[0035] Preferably, the concentration of acid in the pickling process is 2 to 4 mol / L, such as 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, or 4 mol / L.

[0036] Preferably, the acid used in the pickling includes at least two of HCl, H2SO4, HF, and HNO3.

[0037] Preferably, the ash content of the pickled material is ≤0.1%.

[0038] Preferably, the carbonization atmosphere during high-temperature carbonization is a protective atmosphere.

[0039] Preferably, the heating rate of the high-temperature carbonization is 2 to 5°C / min, for example, 2°C / min, 3°C / min, 4°C / min or 5°C / min.

[0040] Preferably, the carbonization temperature of the high-temperature carbonization is 1100-1300℃, such as 1100℃, 1150℃, 1200℃, 1250℃ or 1300℃.

[0041] Preferably, the carbonization time of the high-temperature carbonization is 6 to 12 hours, such as 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours.

[0042] As a preferred technical solution, the preparation method includes the following steps:

[0043] The raw coal with volatile matter of 20-40% and ash content of 3-7% is crushed to obtain coal powder with D50 of 4-8μm;

[0044] Industrial waste gas with a flow rate of 2-10 L / min is introduced into the pulverized coal, and the temperature is raised to 400-600℃ at a heating rate of 2-10℃ / min for pre-carbonization for 2-4 hours. Then, the temperature is raised to 800-1000℃ at a heating rate of 2-10℃ / min for pore formation for 6-8 hours.

[0045] The product after pore formation is acid-washed, and the ash content of the acid-washed material is ≤0.1%.

[0046] The acid-washed material is carbonized at high temperature under a protective atmosphere to obtain coal-based hard carbon anode material.

[0047] In a second aspect, the present invention provides a coal-based hard carbon anode material, wherein the coal-based hard carbon anode material is prepared by the preparation method described in the first aspect; the coal-based hard carbon anode material is a porous material.

[0048] Preferably, the pore volume of the CO2 desorption HK model of the coal-based hard carbon anode material is 0.10–0.15 cm³. 3 / g, for example, 0.1cm 3 / g, 0.11cm 3 / g, 0.12cm 3 / g, 0.13cm 3 / g, 0.14cm 3 / g or 0.15cm 3 / g etc.

[0049] Preferably, the specific surface area of ​​the coal-based hard carbon anode material DR model is 600-800 m². 2 / g, for example 600m 2 / g、650m 2 / g、700m 2 / g、750m 2 / g or 800m 2 / g etc.

[0050] Preferably, the powder compaction density of the coal-based hard carbon anode material is 0.9–1.2 cm³. 3 / g, for example, 0.9cm 3 / g, 1cm 3 / g, 1.1cm 3 / g or 1.2cm 3 / g etc.

[0051] Preferably, the tap density of the coal-based hard carbon anode material is 0.9–1.2 g / cm³. 3 For example, 0.9 g / cm 3 1g / cm 3 1.1g / cm 3Or 1.2g / cm 3 wait.

[0052] The hard carbon anode material provided by this invention has a uniform particle size distribution, rich pore structure, and excellent specific surface area, powder compaction density, and tap density. It has a stable structure and improved capacity and first-efficiency performance.

[0053] Thirdly, the present invention also provides a sodium-ion battery, the sodium-ion battery comprising the coal-based hard carbon anode material as described in the second aspect.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] The method for preparing coal-based hard carbon provided by this invention involves creating pores in raw coal (hard carbon precursor material) using industrial waste gas. The raw material is pre-carbonized before the pore-forming process, and the raw material and preparation steps work synergistically. The oxygen-containing functional groups in the industrial waste gas undergo redox reactions with carbon, while small-molecule gases can also penetrate the interior of the raw coal. This results in a hard carbon anode material with uniform particle size distribution, abundant pore structure, and excellent specific surface area, powder compaction density, and tap density. The material exhibits structural stability and rich pore structures both internally and on the surface, effectively improving the capacity and initial efficiency of the hard carbon anode material. Furthermore, the use of inexpensive industrial waste gas significantly reduces the preparation cost. Attached Figure Description

[0056] Figure 1 This is a schematic flowchart of the preparation method of the coal-based hard carbon anode material provided in Example 1. Detailed Implementation

[0057] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0058] Example 1

[0059] This embodiment provides a coal-based hard carbon anode material, which has a porous structure, and the preparation method is as follows:

[0060] The specific preparation process is as follows: Figure 1 As shown:

[0061] 1000g of lump coking coal (volatile matter 20%, ash content 5%) is dried to a moisture content of less than 10%, then coarsely crushed into powder by a double roll crusher, and then the powdered coal is crushed by a mechanical mill to control the particle size Dv50 to 5μm to obtain powder A.

[0062] Powder A was placed in a rotary kiln for high-temperature pre-carbonization and pore formation. The rotary kiln had an inclination of 3% and a rotation speed of 1 r / min. Industrial waste gas was first introduced for 30 minutes to purge the air from the kiln. The industrial waste gas consisted of CO2, CO, and NO. x SO2:O2 = 48%:48%:2%; Under industrial waste gas atmosphere, the heating rate is 2℃ / min, the gas flow rate is 2L / min, the first stage pre-carbonization insulation temperature is 400℃, the insulation time is 4h, the second stage hole-forming insulation temperature is 800℃, the insulation time is 6h to obtain powder B.

[0063] Powder B was placed in 2 mol / L HCl solution and 3 mol / L HF solution for magnetic stirring and acid washing, respectively. After filtration and washing to neutralize (the ash content of powder B after acid washing was 0.1%), powder B was dried and then carbonized at high temperature in a high-temperature furnace at 1100℃ for 6 hours under a nitrogen atmosphere of 1 L / min and a heating rate of 2℃ / min. The mixture was then passed through a 200-mesh sieve. Coal-based hard carbon anode material C1 was obtained.

[0064] Example 2

[0065] This embodiment provides a coal-based hard carbon anode material, which has a porous structure, and the preparation method is as follows:

[0066] 1000g of lumpy coking coal (volatile matter 30%, ash content 7%) was dried to a moisture content of less than 10%, and then coarsely crushed into powder by a double-stage crusher. The powdered coal was then crushed by an air jet mill to control the particle size Dv50 to 6μm to obtain powder A.

[0067] Powder A was placed in a rotary kiln for high-temperature pre-carbonization and pore formation. The rotary kiln had an inclination of 5% and a rotation speed of 1.5 r / min. Industrial waste gas was first introduced for 30 minutes to purge the air from the kiln. The industrial waste gas consisted of CO2, CO, and NO. x SO2:O2 = 45%:47%:5%. Under an industrial waste gas atmosphere, the heating rate is 5℃ / min, the gas flow rate is 5L / min, the first stage pre-carbonization insulation temperature is 600℃, the insulation time is 4h, and the second stage hole-forming insulation temperature is 900℃, the insulation time is 7h to obtain powder B.

[0068] Powder B was placed in 3 mol / L H2SO4 solution and 3 mol / L HF solution respectively, and then magnetically stirred and acid-washed. After filtration and washing, the powder was neutralized (the ash content of powder B after acid washing was 0.1%). After drying, powder B was carbonized at high temperature in a high-temperature furnace at 1200℃ for 6 hours. The protective atmosphere was nitrogen with a flow rate of 1 L / min and a heating rate of 5℃ / min. The powder was then passed through a 200-mesh sieve to obtain coal-based hard carbon anode material C2.

[0069] Example 3

[0070] This embodiment provides a coal-based hard carbon anode material, which has a porous structure, and the preparation method is as follows:

[0071] 1000g of lump coal (volatile matter 40%, ash content 3%) is dried to a moisture content of less than 10%, then coarsely crushed into powder by a double roll crusher, and then the powdered coal is crushed by a mechanical mill to control the particle size Dv50 to 8μm to obtain powder A.

[0072] Powder A was placed in a rotary kiln for high-temperature pre-carbonization and pore formation. The rotary kiln had an inclination of 3% and a rotation speed of 1.5 r / min. Industrial waste gas was first introduced for 30 minutes to purge the air from the kiln. The industrial waste gas consisted of CO2, CO, and NO. x SO2:O2 = 47%:48%:3%. Under an industrial waste gas atmosphere, the heating rate is 8℃ / min, the gas flow rate is 8L / min, the first stage pre-carbonization insulation temperature is 600℃, the insulation time is 6h, and the second stage hole-forming insulation temperature is 1000℃, the insulation time is 4h to obtain powder B.

[0073] Powder B was placed in 3 mol / L HNO3 solution and 3 mol / L HF solution respectively, and then magnetically stirred and acid-washed. After filtration and washing, the powder was neutralized (the ash content of powder B after acid washing was 0.1%). After drying, powder B was carbonized at high temperature in a high-temperature furnace at 1300℃ for 6 hours. The protective atmosphere was nitrogen with a flow rate of 1 L / min and a heating rate of 8℃ / min. The coal-based hard carbon anode material C3 was obtained by passing it through a 200-mesh sieve.

[0074] Example 4

[0075] The difference between this embodiment and Embodiment 1 is that the raw coal in this embodiment is lean coal with 15% volatile matter and 5% ash.

[0076] The remaining preparation methods and parameters are consistent with those in Example 1.

[0077] Example 5

[0078] The difference between this embodiment and Embodiment 1 is that the raw coal in this embodiment is gas coal with 45% volatile matter and 5% ash.

[0079] The remaining preparation methods and parameters are consistent with those in Example 1.

[0080] Example 6

[0081] The difference between this embodiment and Embodiment 1 is that the flow rate of industrial waste gas in this embodiment is 1L / min.

[0082] The remaining preparation methods and parameters are consistent with those in Example 1.

[0083] Example 7

[0084] The difference between this embodiment and Embodiment 1 is that the flow rate of industrial waste gas in this embodiment is 15L / min.

[0085] The remaining preparation methods and parameters are consistent with those in Example 1.

[0086] Example 8

[0087] The difference between this embodiment and Embodiment 1 is that the pre-carbonization temperature in this embodiment is 300°C.

[0088] The remaining preparation methods and parameters are consistent with those in Example 1.

[0089] Example 8

[0090] The difference between this embodiment and Embodiment 1 is that the pre-carbonization temperature in this embodiment is 700℃.

[0091] The remaining preparation methods and parameters are consistent with those in Example 1.

[0092] Example 10

[0093] The difference between this embodiment and Embodiment 1 is that the heat preservation temperature for creating holes in this embodiment is 700℃.

[0094] The remaining preparation methods and parameters are consistent with those in Example 1.

[0095] Example 11

[0096] The difference between this embodiment and Embodiment 1 is that the heat preservation temperature for creating holes in this embodiment is 1400℃.

[0097] The remaining preparation methods and parameters are consistent with those in Example 1.

[0098] Comparative Example 1

[0099] The difference between this comparative example and Example 1 is that industrial waste gas was not introduced into this comparative example during the pre-carbonization stage, and nitrogen atmosphere was used for pre-carbonization treatment (i.e., nitrogen was used to replace industrial waste gas).

[0100] The remaining preparation methods and parameters are consistent with those in Example 1.

[0101] Comparative Example 2

[0102] The difference between this comparative example and Example 1 is that this comparative example does not undergo a pre-carbonization process, but directly heats up to 800°C to carry out the second stage of pore-forming and heat preservation.

[0103] The remaining preparation methods and parameters are consistent with those in Example 1.

[0104] (1) Parameter testing

[0105] The specific surface area, pore volume, powder compaction density, and tap density of the coal-based hard carbon anode materials provided in Examples 1-11 and Comparative Examples 1-2 were tested under the following conditions:

[0106] a. Specific surface area and pore volume: 800 mg of the hard carbon material from Examples 1 to 11 and Comparative Examples 1 to 2 was weighed and placed into a sample tube. The CO2 adsorption capacity of the sample was measured at different pre-set pressure points at 195 K using CO2 adsorption-desorption, and adsorption isotherms were obtained. The specific surface area and desorption pore volume were calculated from the adsorption isotherms using computer data processing.

[0107] b. Powder compaction density: Weigh 1000 mg of the hard carbon material from Examples 1 to 11 and Comparative Examples 1 to 2 above, and place it into a sample tube. Record the weight as m (grams). Slowly slide the gasket and top column down through the hole, and install them together with the gasket on the compaction density meter. Tighten the pressure control knob. Shake the pressure lever while observing the maximum value on the digital pressure gauge of the compaction density meter. Once the specified value of 2200 Ib is reached, start the stopwatch. After 30 seconds, release the pressure control knob to remove the pressure. The gasket will descend to a certain height. Tighten the pressure control knob again, and remove the top column, sleeve, and base plate together with the gasket. Place them on the digital thickness gauge and read the value on the digital thickness gauge within 10 seconds. Record this value as H (millimeters, mm). S is the cross-sectional area of ​​the top column (square centimeters, cm²). 2 The compaction density (g / cm) of the sample is calculated using the formula: ρ=10m / (S×H), which gives the powder compaction density.

[0108] c. Tap Density: Weigh 100±0.5g of the hard carbon material from Examples 1 to 11 and Comparative Examples 1 to 2 above and place it in a sample tube. For each measurement, two parallel samples are required. Accurately weigh the graduated cylinder and record the mass as m1. Place equal masses of graphite-based negative electrode material into the left and right graduated cylinders of the tap density meter, ensuring the powder surface is horizontal. Place the graduated cylinders on the vibration device and tighten them with clamps equipped with guide rods. Vibrate until the powder volume remains constant. Set the vibration device to an amplitude of 3mm and a vibration frequency of 100-300 times per minute for 1000 vibrations. If the powder surface is horizontal after tapping, the reading can be taken directly. If the powder surface is not horizontal after tapping, read the highest and lowest values ​​and calculate their average to obtain the tapped volume. When reading, use a 100cm... 2Use a graduated cylinder accurate to 0.5 cm. Remove the graduated cylinder and weigh the total mass m2 of the graduated cylinder and the sample after tapping. The tapped density of the sample is calculated according to the formula ρ=(m2-m1) / V, where V is the volume after tapping in milliliters (mL).

[0109] The specific test results of the above tests are shown in Table 1.

[0110] (II) Preparation and Performance Testing of Sodium-ion Batteries

[0111] Preparation of sodium-ion batteries: Coal-based hard carbon anode materials provided in Examples 1-11 and Comparative Examples 1-2

[0112] 9.65g of conductive carbon black (SP) and 0.15g of conductive carbon black (SP) were mixed in a homogenizer for 10 min. Then, 0.15g of carboxymethyl cellulose (CMC) and 14g of deionized water were added and mixed for 10 min. Finally, 0.1g of styrene-butadiene rubber (SBR) was added and mixed for another 5 min to obtain a uniformly dispersed slurry. The slurry was uniformly coated on copper foil using a 100μm thick scraper and dried at 80℃ for 12 h in a vacuum drying oven. The resulting negative electrode sheet was rolled, punched, and weighed to obtain a negative electrode disc (prepared from the hard carbon negative electrode materials provided in Examples 1-11 and Comparative Examples 1-2, respectively). In an argon glove box, the positive electrode shell, negative electrode disc, glass diaphragm, electrolyte, glossy sodium sheet, nickel foam, and negative electrode shell were assembled in sequence and sealed on a sealing machine. The electrolyte solute was 1mol / L NaPF6, and the solvent was ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1.

[0113] Performance testing: The testing system is the Blue Electric testing system, with a voltage window of 5mV to 3V;

[0114] The capacitor was discharged to 5mV at a rate of 0.1C (current density 30mA / g), then discharged to 5mV at a rate of 0.05C (current density 15mA / g), then discharged to 5mV at a rate of 0.01C (current density 3mA / g), and finally charged to 2V at a rate of 0.1C (current density 30mA / g). The charge and discharge capacity and the initial coulombic efficiency were recorded. The specific test results are shown in Table 1.

[0115] Table 1

[0116]

[0117]

[0118] As shown in Table 1:

[0119] The data from Examples 1, 4, and 5 show that if the volatile matter content of the raw coal is too low (below 20%), the hard carbon precursor will have a small pore volume after coal-based precarbonization, resulting in low specific surface area, powder compaction, and tap density. Conversely, if the volatile matter content is too high (exceeding 40%), the hard carbon precursor will have an excessively large pore volume after coal-based precarbonization, resulting in an overly rich pore structure and a low initial efficiency of the sodium battery.

[0120] The data results from Examples 1, 6, and 7 show that if the flow rate of industrial waste gas is too low, the coal-based precursor will not be able to form a large number of pores; while if the flow rate is too high, the coal-based precursor will form an excessively rich pore structure.

[0121] The data results from Examples 1, 8, and 9 show that if the pre-carbonization temperature is too low, it will make it difficult for the volatile matter in the coal to be discharged, resulting in a low number of micropores; while if the pre-carbonization temperature is too high, it will result in excessive energy consumption and waste of electricity resources.

[0122] The data results from Examples 1, 10, and 11 show that if the pre-carbonization temperature is too low, the hard carbon cannot form a stable carbon layer structure, resulting in low powder compaction and tap density, and low initial efficiency of sodium battery capacity; while if the temperature is too high, the hard carbon will close the pores, resulting in a reduction in pore volume and low sodium battery capacity.

[0123] The data from Example 1 and Comparative Example 1 show that without introducing industrial waste gas during the preparation process, the effective pore volume of hard carbon cannot be obtained, thus failing to solve the problem of excessively low capacity of coal-based hard carbon.

[0124] The data from Example 1 and Comparative Example 2 show that if the pore-forming process is carried out directly during the preparation process, and the pre-carbonization process is omitted, the problem of volatile matter escaping cannot be solved, the pore volume is still too small, and the sodium battery capacity cannot be improved.

[0125] In summary, the coal-based hard carbon preparation method provided by this invention uses industrial waste gas to create pores in the raw coal (hard carbon precursor material). The process involves pre-carbonization followed by pore-forming, with the raw material and preparation steps working in synergy. The oxygen-containing functional groups in the industrial waste gas undergo redox reactions with carbon, while small-molecule gases can penetrate the interior of the raw coal. This results in a hard carbon anode material with uniform particle size distribution, abundant pore structure, and excellent specific surface area, powder compaction density, and tap density. The material exhibits structural stability and rich pore structures both internally and on the surface, effectively improving the capacity and initial efficiency of the hard carbon anode material. Furthermore, the use of inexpensive industrial waste gas significantly reduces preparation costs.

[0126] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

[0127] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0128] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a coal-based hard carbon anode material, characterized in that, The preparation method includes the following steps: Industrial waste gas is introduced into the raw coal, and pre-carbonization and pore formation are carried out in sequence. After acid washing, high-temperature carbonization is carried out in a protective atmosphere to obtain coal-based hard carbon anode material. The industrial waste gas includes CO2, CO, and NO. x SO2 and O2, where X is 1 or 2; With mass concentration mg / m 3 The CO2 content is estimated to be 40%~50%, with CO and NO content also present. x The total content of SO2 is 40%~50%, and the content of O2 is less than 5%; The volatile matter content of the raw coal is 20-40%; The heat preservation temperature for pre-carbonization is 400~600℃; The heat preservation temperature for the hole formation is 800~1000℃; The carbonization temperature for high-temperature carbonization is 1100~1300℃.

2. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The ash content of the raw coal is 3-7%.

3. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The raw coal includes any one or a combination of at least two of coking coal, fat coal, or gas coal.

4. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The raw coal is crushed to obtain coal powder.

5. The method for preparing the coal-based hard carbon anode material according to claim 4, characterized in that, The D50 of the pulverized coal is 4~8μm.

6. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The inlet flow rate of the industrial waste gas is 2~10L / min.

7. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The heating rates for pre-carbonization and pore formation are each 2~10℃ / min independently.

8. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The heat preservation time for pre-carbonization is 2-4 hours.

9. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The heat preservation time for the pore formation is 6-8 hours.

10. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The pre-carbonization and pore-forming are carried out in a rotary kiln.

11. The method for preparing the coal-based hard carbon anode material according to claim 10, characterized in that, The rotary kiln has an inclination of 3-5% and a rotation speed of 0.5-1.5 r / min.

12. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The concentration of acid in the pickling process is 2-4 mol / L.

13. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The acid used in the pickling includes at least two of the following: HCl, H2SO4, HF, and HNO3.

14. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The ash content of the pickled material is ≤0.1%.

15. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, The heating rate for high-temperature carbonization is 2~5℃ / min.

16. The method for preparing the coal-based hard carbon anode material according to any one of claims 1-15, characterized in that, The carbonization time for the high-temperature carbonization is 6~12 hours.

17. The method for preparing coal-based hard carbon anode material according to claim 1, characterized in that, The preparation method includes the following steps: The raw coal with volatile matter of 20-40% and ash content of 3-7% is crushed to obtain coal powder with D50 of 4-8μm; Industrial waste gas with a flow rate of 2-10 L / min is introduced into the pulverized coal, and the temperature is raised to 400-600℃ at a heating rate of 2-10℃ / min for pre-carbonization for 2-4 hours. Then, the temperature is raised to 800-1000℃ at a heating rate of 2-10℃ / min for pore formation for 6-8 hours. The product after pore formation is pickled, and the ash content of the pickled material is ≤0.1%; The acid-washed material is carbonized at high temperature under a protective atmosphere to obtain coal-based hard carbon anode material.

18. A coal-based hard carbon anode material, characterized in that, The coal-based hard carbon anode material is prepared by the preparation method according to any one of claims 1-17; the coal-based hard carbon anode material is a porous material.

19. The coal-based hard carbon anode material according to claim 18, characterized in that, The pore volume of the CO2 desorption HK model for the coal-based hard carbon anode material is 0.10~0.15 cm³. 3 / g.

20. The coal-based hard carbon anode material according to claim 18, characterized in that, The specific surface area of ​​the coal-based hard carbon anode material in the DR model is 600~800 m². 2 / g.

21. The coal-based hard carbon anode material according to claim 18, characterized in that, The powder compaction density of the coal-based hard carbon anode material is 0.9~1.2 g / cm³. 3 .

22. The coal-based hard carbon anode material according to claim 18, characterized in that, The tap density of the coal-based hard carbon anode material is 0.9~1.2 g / cm³. 3 .

23. A sodium-ion battery, characterized in that, The sodium-ion battery includes the coal-based hard carbon anode material as described in any one of claims 18-22.

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