A method for synthesizing corncob-based hard carbon

Abstract

This invention discloses a method for synthesizing corn cob-based hard carbon, comprising the following steps: weighing corn cobs, washing them with deionized water, and drying them; transferring the corn cobs to a graphite boat, placing them in an atmosphere furnace, and carbonizing them at a low temperature to obtain low-temperature carbonized corn cobs; pulverizing the low-temperature carbonized corn cobs using a pulverizer, transferring them to a grinder, adding a sodium-containing alkali, and grinding them; transferring the ground mixture to a graphite boat, placing it in an atmosphere furnace, and carbonizing it at a medium temperature under a nitrogen atmosphere to obtain a medium-temperature carbonized carbon material; taking the medium-temperature carbonized carbon material, washing it with deionized water until the filtrate is neutral, and neutralizing the filtrate with acid to neutral; transferring the material to an oven and drying it; taking the dried carbon material, grinding it with a grinder, adding a coated carbon source to form a mixed powder; transferring the mixed powder to a graphite boat, placing it in an atmosphere furnace, and carbonizing it at a high temperature to obtain hard carbon. This invention achieves wastewater-free synthesis of hard carbon, while also exhibiting high raw material utilization, simplified and efficient process, and good cycle stability.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and more specifically to a method for synthesizing corn cob-based hard carbon. Background Technology

[0002] Hard carbon, due to its high specific capacity, has become the most promising commercially viable anode material for sodium-ion batteries. Currently, there are many precursors for synthesizing hard carbon, including polymers, biomass, and fossil fuels. Polymers are too expensive to be widely accepted by the market. Biomass includes fruit shells, starch, and bamboo. Corn cobs, as an agricultural byproduct, are abundant and rich in hemicellulose, cellulose, and lignin, making them a potential precursor for hard carbon. However, there are currently few patents related to the synthesis of hard carbon using corn cobs, and the developed processes all have certain shortcomings. For example, patent CN202411942239.0 proposes a hard carbon composite material modified with antimony chloride, using corn cobs as a precursor. The process is complex, and the resulting hard carbon has a low specific capacity, only 100-150 mAh / g at 0.1C, which cannot meet the performance requirements of sodium-ion battery anode materials. Patent CN202411716093.8 proposes a corn cob-based hard carbon material, its preparation method, and its application. It involves mixing the material with monosaccharides and then carbonizing it. During carbonization, the monosaccharides decompose to form a porous structure, thereby improving the sodium storage capacity of the corn cob-based hard carbon material. However, due to the limited pore-forming ability of monosaccharides, the specific capacity of the resulting hard carbon is below 240 mAh / g. Patent CN202410491949.X selects corn cob as a hard carbon precursor, obtaining hard carbon through complex acid and alkali washing processes. Although the resulting hard carbon has good performance, the preparation process is complex, and the acid and alkali washing generates a large amount of wastewater. Patent CN202311769982.6 invented a method for preparing corn cob-based hard carbon anode material by hydrolyzing p-toluenesulfonic acid. This method also generates wastewater, and the extraction of cellulose (approximately 40%–50%), a key component of corn cob, through p-toluenesulfonic acid, along with the removal of lignin and hemicellulose, leads to the waste of most of the corn raw material and results in a very low hard carbon content. Patent CN202311769964.8 uses corn cobs as raw material for biomass hard carbon and thiourea as a nitrogen and sulfur source to synthesize hard carbon materials. Although no wastewater is generated, the specific capacity of the synthesized hard carbon is only about 200 mAh / g. In summary, for the synthesis of hard carbon from corn cobs, a preparation process that is free of wastewater pollution and has excellent performance needs to be developed. Summary of the Invention

[0003] This invention provides a method for synthesizing corn cob-based hard carbon, achieving wastewater-free synthesis of hard carbon while exhibiting high raw material utilization, simplified and efficient process, and good cycle stability.

[0004] In order to solve the above technical problems, the present invention provides a method for synthesizing corn cob-based hard carbon, comprising the following steps: (1) weighing corn cobs, washing them with deionized water, and drying them; (2) The dried corn cobs are transferred to a graphite boat and placed in an atmosphere furnace for low-temperature carbonization under a nitrogen atmosphere to obtain low-temperature carbonized corn cobs. (3) Crush the low-temperature carbonized corn cobs with a pulverizer, transfer them to a grinder, add sodium-containing alkali, and grind them thoroughly; (4) The ground mixture is transferred to a graphite boat and placed in an atmosphere furnace for medium-temperature carbonization under a nitrogen atmosphere to obtain medium-temperature carbonized carbon material. (5) Take medium-temperature carbonized material, wash it with deionized water until the filtrate is neutral, and neutralize the filtrate with acid until it is neutral; transfer the washed material to an oven and dry it; (6) Take the dried carbon material, grind it with a grinder, add the coated carbon source, and mix thoroughly to form a mixed powder; (7) Transfer the mixed powder to a graphite boat, place it in an atmosphere furnace, and carbonize it at high temperature under a nitrogen atmosphere to obtain hard carbon material.

[0005] Furthermore, the corn cob in step (1) is a white corn cob or a red corn cob.

[0006] Furthermore, the low-temperature carbonization temperature in step (2) is 300℃-750℃, and the carbonization time is 1h-20h.

[0007] Further, the sodium-containing alkali in step (3) is at least one of sodium hydroxide, sodium carbonate and sodium bicarbonate, and the amount added is 0.1-5 times that of the carbon material after low-temperature carbonization.

[0008] Furthermore, the medium-temperature carbonization temperature in step (4) is 750-1000℃, and the carbonization time is 1-20h.

[0009] Furthermore, the acid used in step (5) is hydrochloric acid with a concentration of 0.1-12 mol / L.

[0010] Further, the carbon source for coating in step (6) is at least one of resin, sucrose, glucose, chitosan, and pitch, and the amount added is 0.1%-20% of the carbon material after medium-temperature carbonization and drying.

[0011] Furthermore, the high-temperature carbonization temperature in step (7) is 1100-1500℃, and the carbonization time is 1-20h.

[0012] The beneficial effects of this invention are: 1. Achieving wastewater-free synthesis: The filtrate after washing with sodium alkali is neutralized with hydrochloric acid to generate non-toxic and harmless sodium chloride, which completely solves the wastewater pollution problem of traditional processes; 2. High raw material utilization: No complex purification or component separation is required, making full use of hemicellulose, cellulose and lignin in corn cobs and avoiding raw material waste; 3. Simplified and efficient process: Corn cobs have a high density and retain their integrity and become brittle after low-temperature carbonization, making them easy to crush and process. No additional curing agent is required during the synthesis process. 4. Excellent sodium storage performance: Sodium-containing alkali etching forms a porous structure, and coating the carbon source further forms closed pores. The specific capacity of hard carbon 0.1C can reach 285-302 mAh / g, which is significantly better than products prepared by existing technologies. 5. Good cycle stability: The coating layer formed by coating the carbon source protects the porous structure and effectively improves the cycle stability of hard carbon materials; 6. Strong process adaptability: The performance fluctuates little within the range of low-temperature carbonization temperature (500-700℃) and high-temperature carbonization temperature (1300-1450℃). The best results are achieved when sodium hydroxide is preferred as the sodium alkali and resin is preferred as the carbon source for coating. It is also compatible with different types of corn cob raw materials. Attached Figure Description

[0013] Figure 1 This is the corn cob raw material used in Example 1 of the present invention.

[0014] Figure 2 This is the corn cob after low-temperature carbonization according to the present invention.

[0015] Figure 3 This is a SEM image of the hard carbon HC-1 synthesized in Example 1 of the present invention.

[0016] Figure 4 These are the electrochemical performance test results of the hard carbon synthesized in the embodiments and reference proportions of the present invention. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments are not intended to limit the present invention.

[0018] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0019] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0020] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0021] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0022] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0023] Reference Figures 1 to 4As shown, the present invention provides a method for synthesizing corn cob-based hard carbon, comprising the following steps: (1) weighing corn cobs, washing them with deionized water, and drying them; (2) transferring the dried corn cobs to a graphite boat, placing them in an atmosphere furnace, and carbonizing them at low temperature under a nitrogen atmosphere to obtain low-temperature carbonized corn cobs; (3) crushing the low-temperature carbonized corn cobs with a pulverizer, transferring them to a grinder, adding sodium-containing alkali, and grinding them thoroughly; (4) transferring the ground mixture to a graphite boat, placing it in an atmosphere furnace, and carbonizing it at medium temperature under a nitrogen atmosphere to obtain medium-temperature carbonized carbon material; (5) taking the medium-temperature carbonized carbon material, washing it with deionized water until the filtrate is neutral, and neutralizing the filtrate with acid to neutral; transferring the washed material to an oven and drying it; (6) taking the dried carbon material, grinding it with a grinder, adding a coated carbon source, and mixing it thoroughly to form a mixed powder; (7) transferring the mixed powder to a graphite boat, placing it in an atmosphere furnace, and carbonizing it at high temperature under a nitrogen atmosphere to obtain hard carbon.

[0024] In step (1), the corn cob is white or red; in step (2), the low-temperature carbonization temperature is 300℃-750℃ and the carbonization time is 1h-20h; in step (3), the sodium-containing alkali is at least one of sodium hydroxide, sodium carbonate and sodium bicarbonate, and the amount added is 0.1-5 times that of the carbon material after low-temperature carbonization; in step (4), the medium-temperature carbonization temperature is 750-1000℃ and the carbonization time is 1-20h; in step (5), the acid is hydrochloric acid, and the concentration of hydrochloric acid is 0.1-12mol / L; in step (6), the coating carbon source is at least one of resin, sucrose, glucose, chitosan and asphalt, and the amount added is 0.1%-20% of the carbon material after medium-temperature carbonization and drying; in step (7), the high-temperature carbonization temperature is 1100-1500℃ and the carbonization time is 1-20h.

[0025] The following are specific embodiments and reference proportions: Example 1: Step (1): Weigh white corn cobs, wash them with deionized water, and dry them at 80℃ for 10 hours. Step (2): Transfer them to a graphite boat, place them in an atmosphere furnace, and heat them at 3℃ / min to 700℃ for 2 hours under nitrogen atmosphere to obtain low-temperature carbonized corn cobs. Step (3): Crush the low-temperature carbonized corn cobs into particles with a particle size of 3mm using a pulverizer, transfer them to a grinder, add sodium hydroxide powder (3 times the mass of the carbon material after low-temperature carbonization), and grind them at 600rpm for 0.5 hours. Step (4): Transfer them to a graphite boat, place them in an atmosphere furnace, and heat them at 3℃ / min to 950℃ for 2 hours under nitrogen atmosphere to obtain medium-temperature carbonized carbon material. Step (5): Take the medium-temperature carbonized carbon material, wash it with deionized water until the filtrate is neutral, and neutralize the filtrate with hydrochloric acid to avoid generating toxic and harmful wastewater. Transfer the washed material to an oven and dry it at 100℃ for 5 hours. Step (6): Take the dried carbon material and grind it to a particle size of D50=5μm using a grinder. Then add resin powder (D50=2μm, mass is 10% of the mass of the carbon material after medium-temperature carbonization and drying) and mix thoroughly to form a mixed powder. Step (7): Transfer the mixed powder to a graphite boat, place it in an atmosphere furnace, and heat it to 1425℃ at a nitrogen atmosphere for 4 hours to obtain hard carbon HC-1.

[0026] Example 2: Step (1): Weigh red corn cobs, wash them with deionized water, and dry them at 80℃ for 10 hours. Step (2): Transfer them to a graphite boat, place them in an atmosphere furnace, and heat them at 3℃ / min to 650℃ for 3 hours under nitrogen atmosphere to obtain low-temperature carbonized corn cobs. Step (3): Crush the low-temperature carbonized corn cobs into particles with a particle size of 3mm using a pulverizer, transfer them to a grinder, add sodium hydroxide powder (3 times the mass of the carbon material after low-temperature carbonization), and grind them at 500rpm for 1 hour. Step (4): Transfer them to a graphite boat, place them in an atmosphere furnace, and heat them at 3℃ / min to 900℃ for 4 hours under nitrogen atmosphere to obtain medium-temperature carbonized carbon material. Step (5): Take the medium-temperature carbonized carbon material, wash it with deionized water until the filtrate is neutral, and neutralize the filtrate with hydrochloric acid to avoid generating toxic and harmful wastewater. Transfer the washed material to an oven and dry it at 100℃ for 5 hours. Step (6): Take the dried carbon material and grind it to a particle size of D50=5μm using a grinder. Then add resin powder (D50=5μm, mass is 10% of the mass of the carbon material after medium-temperature carbonization and drying) and mix thoroughly to form a mixed powder. Step (7): Transfer the mixed powder to a graphite boat, place it in an atmosphere furnace, and heat it to 1400℃ at 3℃ / min for 4 hours under nitrogen atmosphere to obtain hard carbon HC-2.

[0027] Example 3: Step (1): Weigh white corn cobs, wash them with deionized water, and dry them at 80℃ for 10 hours. Step (2): Transfer them to a graphite boat, place them in an atmosphere furnace, and heat them at 3℃ / min to 600℃ for 4 hours under nitrogen atmosphere to obtain low-temperature carbonized corn cobs. Step (3): Crush the low-temperature carbonized corn cobs into particles with a particle size of 3mm using a pulverizer, transfer them to a grinder, add sodium hydroxide powder (4 times the mass of the carbon material after low-temperature carbonization), and grind them at 400rpm for 2 hours. Step (4): Transfer them to a graphite boat, place them in an atmosphere furnace, and heat them at 3℃ / min to 850℃ for 6 hours under nitrogen atmosphere to obtain medium-temperature carbonized carbon material. Step (5): Take the medium-temperature carbonized carbon material, wash it with deionized water until the filtrate is neutral, and neutralize the filtrate with hydrochloric acid to avoid generating toxic and harmful wastewater. Transfer the washed material to an oven and dry it at 100℃ for 5 hours. Step (6): Take the dried carbon material and grind it to a particle size of D50=5μm using a grinder. Then add sucrose powder (D50=3μm, mass is 10% of the mass of the carbon material after medium-temperature carbonization and drying) and mix thoroughly to form a mixed powder. Step (7): Transfer the mixed powder to a graphite boat, place it in an atmosphere furnace, and heat it to 1375℃ at 3℃ / min for 4 hours under a nitrogen atmosphere to obtain hard carbon HC-3.

[0028] Example 4: Step (1): Weigh white corn cobs, wash them with deionized water, and dry them at 80℃ for 10 hours. Step (2): Transfer them to a graphite boat, place them in an atmosphere furnace, and heat them at 3℃ / min to 550℃ for 6 hours under nitrogen atmosphere to obtain low-temperature carbonized corn cobs. Step (3): Crush the low-temperature carbonized corn cobs into particles with a particle size of 3mm using a pulverizer, transfer them to a grinder, add sodium hydroxide powder (3 times the mass of the carbon material after low-temperature carbonization), and grind them at 300rpm for 3 hours. Step (4): Transfer them to a graphite boat, place them in an atmosphere furnace, and heat them at 3℃ / min to 850℃ for 8 hours under nitrogen atmosphere to obtain medium-temperature carbonized carbon material. Step (5): Take the medium-temperature carbonized carbon material, wash it with deionized water until the filtrate is neutral, and neutralize the filtrate with hydrochloric acid to avoid generating toxic and harmful wastewater. Transfer the washed material to an oven and dry it at 100℃ for 5 hours. Step (6): Take the dried carbon material and grind it to a particle size of D50=5μm using a grinder. Then add glucose powder (D50=5μm, mass is 15% of the mass of the carbon material after medium-temperature carbonization and drying) and mix thoroughly to form a mixed powder. Step (7): Transfer the mixed powder to a graphite boat, place it in an atmosphere furnace, and heat it to 1350℃ at a nitrogen atmosphere for 4 hours to obtain hard carbon HC-4.

[0029] Example 5: Step (1): Weigh white corn cobs, wash them with deionized water, and dry them at 80℃ for 10 hours. Step (2): Transfer them to a graphite boat, place them in an atmosphere furnace, and heat them at 3℃ / min to 500℃ for 8 hours under nitrogen atmosphere to obtain low-temperature carbonized carbon material. Step (3): Crush the low-temperature carbonized carbon material into particles with a particle size of 3mm using a pulverizer, transfer them to a grinder, add sodium hydroxide powder (twice the mass of the carbon material after low-temperature carbonization), and grind at 300rpm for 3 hours. Step (4): Transfer them to a graphite boat, place them in an atmosphere furnace, and heat them at 3℃ / min to 900℃ for 4 hours under nitrogen atmosphere to obtain medium-temperature carbonized carbon material. Step (5): Take the medium-temperature carbonized carbon material, wash it with deionized water until the filtrate is neutral, and neutralize the filtrate with hydrochloric acid to avoid generating toxic and harmful wastewater. Transfer the washed material to an oven and dry it at 100℃ for 5 hours. Step (6): Take the dried carbon material and grind it to a particle size of D50=5μm using a grinder. Then add chitosan (D50=5μm, mass is 10% of the mass of the carbon material after medium-temperature carbonization and drying) and mix thoroughly to form a mixed powder. Step (7): Transfer the mixed powder to a graphite boat, place it in an atmosphere furnace, and heat it to 1350℃ at a nitrogen atmosphere for 4 hours to obtain hard carbon HC-5.

[0030] Example 6: Step (1): Weigh white corn cobs, wash them with deionized water, and dry them at 80℃ for 10 hours. Step (2): Transfer them to a graphite boat, place them in an atmosphere furnace, and heat them at 3℃ / min to 700℃ for 2 hours under nitrogen atmosphere to obtain low-temperature carbonized carbon material. Step (3): Crush the low-temperature carbonized carbon material into particles with a particle size of 3mm using a pulverizer, transfer them to a grinder, add sodium carbonate powder (3 times the mass of the low-temperature carbonized carbon material), and grind at 600rpm for 1 hour. Step (4): Transfer them to a graphite boat, place them in an atmosphere furnace, and heat them at 3℃ / min to 950℃ for 6 hours under nitrogen atmosphere to obtain medium-temperature carbonized carbon material. Step (5): Take the medium-temperature carbonized carbon material, wash it with deionized water until the filtrate is neutral, and neutralize the filtrate with hydrochloric acid to avoid generating toxic and harmful wastewater. Transfer the washed material to an oven and dry it at 100℃ for 5 hours. Step (6): Take the dried carbon material and grind it to a particle size of D50=5μm using a grinder. Then add resin powder (D50=2μm, mass is 10% of the mass of the carbon material after medium-temperature carbonization and drying) and mix thoroughly to form a mixed powder. Step (7): Transfer the mixed powder to a graphite boat, place it in an atmosphere furnace, and heat it to 1425℃ at a nitrogen atmosphere for 4 hours to obtain hard carbon HC-6.

[0031] Example 7: Step (1): Weigh white corn cobs, wash them with deionized water, and dry them at 80℃ for 10 hours. Step (2): Transfer them to a graphite boat, place them in an atmosphere furnace, and heat them at 3℃ / min to 700℃ for 2 hours under nitrogen atmosphere to obtain low-temperature carbonized carbon material. Step (3): Crush the low-temperature carbonized corn cobs into particles with a particle size of 3mm using a pulverizer, transfer them to a grinder, add sodium bicarbonate powder (3 times the mass of the low-temperature carbonized carbon material), and grind at 600rpm for 1 hour. Step (4): Transfer them to a graphite boat, place them in an atmosphere furnace, and heat them at 3℃ / min to 950℃ for 8 hours under nitrogen atmosphere to obtain medium-temperature carbonized carbon material. Step (5): Take the medium-temperature carbonized carbon material, wash it with deionized water until the filtrate is neutral, and neutralize the filtrate with hydrochloric acid to avoid generating toxic and harmful wastewater. Transfer the washed material to an oven and dry it at 100℃ for 5 hours. Step (6): Take the dried carbon material and grind it to a particle size of D50=5μm using a grinder. Then add resin powder (D50=2μm, mass is 10% of the mass of the carbon material after medium-temperature carbonization and drying) and mix thoroughly to form a mixed powder. Step (7): Transfer the mixed powder to a graphite boat, place it in an atmosphere furnace, and heat it to 1425℃ at a nitrogen atmosphere for 4 hours to obtain hard carbon HC-7.

[0032] Reference Example 1: The preparation method is basically the same as in Example 1, except that steps (3) to (5) are removed to obtain hard carbon HCC-1.

[0033] Reference Example 2: The preparation method is basically the same as in Example 1, except that step (6) is removed to obtain hard carbon HCC-2.

[0034] Reference Example 3: The preparation method is basically the same as in Example 1, except that steps (3) to (6) are removed to obtain hard carbon HCC-3.

[0035] Reference Example 4: The preparation method is basically the same as in Example 1, except that the medium-temperature carbonization temperature in step (4) is changed to 700°C to obtain hard carbon HCC-4.

[0036] Battery assembly and testing: The hard carbon material, conductive carbon black, and sodium carboxymethyl cellulose prepared in Example 1 and the reference ratio were mixed in a mass ratio of 90:5:5. Styrene-butadiene rubber and deionized water were added to prepare a slurry, which was stirred for 5 hours and then coated onto copper foil. The slurry was dried in a vacuum drying oven at 80°C for 10 hours. The resulting electrode was used as the negative electrode, and a sodium metal sheet was used as the positive electrode. The electrolyte was a 0.8M NaPF6 / DIGLYME (100 Vol%) solution, and the separator was a glass fiber separator (GF / D). The cells were assembled into CR2032 type button half-cells in an argon-filled glove box. Figure 4 The specific capacity data of the obtained battery at 0.1C and 1C rates, and the specific capacity data after 100 cycles at 1C.

[0037] Referring to the attached diagram, Figure 1 The results show that corn cobs can maintain their integrity before and after low-temperature carbonization without foaming, but become more brittle, easier to crush, and easier to process, so there is no need to introduce a curing agent. Figure 3 The hard carbon synthesized in Example 1 exhibits an irregular polyhedral morphology. Comparison with Examples 1-5 reveals that using sodium hydroxide as the sodium-containing alkali allows for the synthesis of high-performance hard carbon regardless of whether resin, sucrose, glucose, or chitosan is used as the coating carbon source. The 0.1C specific capacity of the hard carbon is concentrated in the range of 285-302 mAh / g. The material using resin-based coating agents exhibits the best performance. Low-temperature carbonization at 500-700℃ and high-temperature carbonization at 1300-1450℃ have little impact on the performance of the hard carbon. Comparison with Examples 1, 6, and 7 shows that using sodium hydroxide as the sodium-containing alkali is superior to using sodium carbonate and sodium bicarbonate, because sodium hydroxide is more alkaline, resulting in more thorough etching and pore formation of the corn cob. Comparison with Examples 1 and Reference Examples 1-3 shows that removing either the sodium-containing alkali treatment step or the carbon source addition step with coating function leads to a decrease in the performance of the hard carbon. Comparing Example 1 and Reference Example 4, the hard carbon performance significantly decreased when the intermediate carbonization temperature was 700°C. This is because the temperature was too low to effectively induce the effect of the sodium-containing alkali. It is worth noting that this patent uses a sodium-containing alkali. After washing, the filtrate originally contained alkaline substances such as sodium hydroxide or sodium carbonate, but these were neutralized by adding hydrochloric acid to form sodium chloride. Sodium chloride is non-toxic and harmless, and there is no wastewater treatment issue.

[0038] The embodiments described above are merely preferred embodiments for fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for synthesizing corn cob-based hard carbon, characterized in that, Includes the following steps: (1) Weigh the corn cobs, wash them with deionized water, and dry them; (2) The dried corn cobs are transferred to a graphite boat and placed in an atmosphere furnace for low-temperature carbonization under a nitrogen atmosphere to obtain low-temperature carbonized corn cobs. (3) Crush the low-temperature carbonized corn cobs with a pulverizer, transfer them to a grinder, add sodium-containing alkali, and grind them thoroughly; (4) The ground mixture is transferred to a graphite boat and placed in an atmosphere furnace for medium-temperature carbonization under a nitrogen atmosphere to obtain medium-temperature carbonized carbon material. (5) Take medium-temperature carbonized material, wash it with deionized water until the filtrate is neutral, and neutralize the filtrate with acid until it is neutral; transfer the washed material to an oven and dry it; (6) Take the dried carbon material, grind it with a grinder, add the coated carbon source, and mix thoroughly to form a mixed powder; (7) Transfer the mixed powder to a graphite boat, place it in an atmosphere furnace, and carbonize it at high temperature under a nitrogen atmosphere to obtain hard carbon.

2. The method for synthesizing corn cob-based hard carbon as described in claim 1, characterized in that, The corn cob mentioned in step (1) is a white corn cob or a red corn cob.

3. The method for synthesizing corn cob-based hard carbon as described in claim 1, characterized in that, The low-temperature carbonization temperature in step (2) is 300℃-750℃, and the carbonization time is 1h-20h.

4. The method for synthesizing corn cob-based hard carbon as described in claim 1, characterized in that, The sodium-containing alkali in step (3) is at least one of sodium hydroxide, sodium carbonate and sodium bicarbonate, and the amount added is 0.1-5 times that of the carbon material after low-temperature carbonization.

5. The method for synthesizing corn cob-based hard carbon as described in claim 1, characterized in that, The medium-temperature carbonization temperature in step (4) is 750-1000℃, and the carbonization time is 1-20h.

6. The method for synthesizing corn cob-based hard carbon as described in claim 1, characterized in that, The acid used in step (5) is hydrochloric acid with a concentration of 0.1-12 mol / L.

7. The method for synthesizing corn cob-based hard carbon as described in claim 1, characterized in that, The carbon source for coating in step (6) is at least one of resin, sucrose, glucose, chitosan, and pitch, and the amount added is 0.1%-20% of the carbon material after medium-temperature carbonization and drying.

8. The method for synthesizing corn cob-based hard carbon as described in claim 1, characterized in that, The high-temperature carbonization temperature in step (7) is 1100-1500℃, and the carbonization time is 1-20h.

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