Method for preparing lignin hard carbon negative electrode material by Joule thermal flash evaporation

Abstract

The invention discloses a method for preparing a lignin hard carbon negative electrode material through Joule thermal flash evaporation, and belongs to the technical field of negative electrode material preparation. The method mainly comprises the following steps: (1) reacting lignin with alkali liquor, adding acid, washing with water, and drying to obtain dried lignin; (2) preheating the dried lignin in a tubular furnace to obtain a hard carbon precursor; and (3) putting the hard carbon precursor into a graphite mold, and carbonizing through Joule heat flash evaporation to obtain the lignin-based hard carbon negative electrode material. According to the method, rapid temperature rise is realized by Joule heating, and the method is short in reaction time and high in reaction temperature. Compared with a radiation cooling mode of a traditional high-temperature furnace, black-body radiation can release most heat within milliseconds. Under the action of an electric field, lignin is recombined and stacked into a vortex layer carbon layer, and a three-dimensional continuous carbon network is formed. The ultrafast method can relieve the carbon layer accumulation phenomenon in the lignin pyrolysis process.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode material preparation, and in particular relates to a method for preparing a lignin hard carbon negative electrode material by Joule heat flash evaporation. Background Art

[0002] The rechargeable secondary battery industry has experienced explosive growth over the past decade. Battery anodes are typically derived from the pyrolysis of carbon sources with aromatic topologies. Common precursors include natural graphite, biomass-derived, resin-based, coal-based, and organic polymers. Compared to the high cost of organic materials and the non-renewable nature of coal-based materials, the energy abundance and low cost of biomass materials offer significant advantages in battery anode materials.

[0003] Lignin is the only aromatic polymer in nature with a three-dimensional network structure, and its carbon content is as high as 60%. In recent years, great progress has been made in the application of lignin in negative electrode materials. However, due to the heterogeneity of lignin itself and the cohesiveness of its aromatic ring structure, the changes in lignin during heating are complex. During the carbonization process, the carbon layers tend to stack in an orderly manner and graphitize, which is not conducive to the storage of sodium ions.

[0004] To address these issues, one potential solution is to increase the heating rate. However, achieving rapid heating in a high-temperature furnace is costly. When heated in a high-temperature furnace, the small gaseous molecules produced are easily carried away by the flowing protective gas, reducing overall yield. Furthermore, slow annealing can exacerbate the accumulation of carbon layers, and the direct pyrolysis of carbon materials has suboptimal electrical conductivity, making them incapable of meeting high-rate charge and discharge requirements. Summary of the Invention

[0005] [Technical Issues]

[0006] The present invention aims to solve the problem that when preparing negative electrode materials with lignin, the cost is high and the total output is low when using a high-temperature furnace to achieve rapid heating of lignin during the carbonization process, and slow annealing may aggravate the accumulation of carbon layers. The electrical conductivity of the carbon material directly pyrolyzed is not ideal and cannot meet the requirements of high-rate charging and discharging.

[0007] [Technical solution]

[0008] To address these issues, the present invention provides a method for preparing lignin hard carbon anode materials via Joule flash evaporation. This method utilizes Joule heating to achieve rapid temperature rise, resulting in a fast reaction time and high reaction temperature. Under the influence of an electric field, the lignin reorganizes and stacks into vortex-like carbon layers, forming a three-dimensional continuous carbon network. This ultrafast method can mitigate the carbon layer accumulation phenomenon during lignin pyrolysis.

[0009] The present invention provides a method for preparing a lignin hard carbon negative electrode material by Joule heat flash evaporation, which mainly comprises the following steps:

[0010] (1) reacting lignin with alkali solution, adding acid, washing and drying to obtain dry lignin;

[0011] (2) preheating the dried lignin obtained in step (1) in a tube furnace to obtain a hard carbon precursor;

[0012] (3) The hard carbon precursor obtained in step (2) is placed in a graphite mold and carbonized by Joule heat flash evaporation to obtain a lignin hard carbon negative electrode material.

[0013] In one embodiment of the present invention, in step (1), the lignin is one or more of alkali lignin, enzymatic lignin, organic solvent lignin, and sulfate lignin.

[0014] In one embodiment of the present invention, in step (1), the mass concentration of the alkali in the alkali solution is 10-30%, and the alkali is one or more of NaOH and KOH.

[0015] In one embodiment of the present invention, in step (1), the acid is one or more of HCl and H2SO4, and the mass concentration of the acid is 5-20%.

[0016] In one embodiment of the present invention, in step (2), the preheating temperature of the tube furnace is 700-900°C.

[0017] In one embodiment of the present invention, in step (2), the preheating time in the tubular furnace is 1 to 4 hours; and the heating rate is 2 to 10° C. / min.

[0018] In one embodiment of the present invention, in step (3), the temperature for carbonization by Joule heat flash evaporation is 1000-1600° C.; the heating rate is 100-140° C. / min, and the time is 1-5 min.

[0019] In one embodiment of the present invention, in step (3), the voltage for Joule heat flash carbonization is 3-5V, the current is 300-500A, the output power is 1.5-4.5kW, and the pressure is 20-35MPa.

[0020] In one embodiment of the present invention, in step (3), the Joule heat flash evaporation is carried out for 2 to 6 carbonization cycles.

[0021] The present invention provides a lignin hard carbon negative electrode material prepared by the above method.

[0022] The present invention provides the use of the above-mentioned lignin hard carbon negative electrode material in a sodium ion battery.

[0023] [Beneficial Effects]

[0024] (1) The present invention utilizes the rich carbon content of lignin, removes the non-carbon components on the lignin through the Joule flash method, rebuilds and regulates the hard carbon structure of lignin, and forms a high-grade carbon material with strong crystallinity and structural order.

[0025] (2) The present invention regulates the carbon structure by regulating the number of Joule heating cycles, and the prepared lignin hard carbon negative electrode material is characterized by the regulation of the graphite order of the carbon layer.

[0026] (3) The present invention adjusts the carbon structure by the number of Joule heating cycles, and the reaction time is short, which is manifested as increased efficiency.

[0027] (4) This technology uses Joule heating to achieve rapid heating. This method has a fast reaction time and high reaction temperature. Compared with the radiation cooling method of traditional high-temperature furnaces, blackbody radiation can release most of the heat within milliseconds. Under the action of the electric field, lignin is reorganized and stacked into vortex carbon layers, forming a three-dimensional continuous carbon network. This ultrafast method can alleviate the carbon layer accumulation phenomenon during the lignin pyrolysis process. The lignin hard carbon negative electrode material prepared by Joule heat flash evaporation in the present invention can promote its application in energy conversion, opening up a new path for the high-value conversion of traditional fossil fuels. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a scanning electron microscope image of the lignin hard carbon negative electrode material of Example 1. DETAILED DESCRIPTION

[0029] Characterization of the material of the present invention:

[0030] The microstructure of the materials was observed using a transmission electron microscope (JEOL, JEM-2100).

[0031] The electrical conductivity was measured using a four-point probe meter (RM 3000+, Jandel Engineering, UK).

[0032] The preparation method of the lignin used in the present invention is as follows:

[0033] Alkali lignin extraction method: Add wood chips and 15% NaOH solution to a rotary cooker and heat at 160°C with stirring for 120 minutes. After the cooker cools to room temperature, remove the solid residue by filtration and wash with deionized water. The washings and filtrate are mixed and poured into 5000 mL of distilled acid water (pH = 2) to precipitate the lignin. Once the precipitate is separated, filter to obtain a solid. The precipitate is collected by filtration and washed with copious amounts of deionized water until the filtrate is neutral. The filtrate is then freeze-dried to obtain brown lignin.

[0034] The enzymatic lignin extraction method is as follows: 60g of enzymatic residue (purchased from Costeson Biotech, Enzymatic Lignin) was weighed and pulverized to 100 mesh using a micro-crusher and vacuum dried at 100°C for 12 hours. The residue was then added to a stainless steel autoclave, and 1.2L of 50% ethanol solution was added at a solid-to-liquid ratio of 1:20 (i.e., 1g of solid material was added to 20mL of solution). 6g of NaOH was added as a catalyst, and the mixture was mixed and heated to 220°C and reacted at 300 rpm for 2 hours. After the reaction was completed, the mixture was cooled to room temperature and filtered to separate the lignin solution from the insoluble matter. 5% by mass of H2SO4 was added to the filtrate to precipitate the solid. The separated filtrate was subjected to reduced pressure distillation to recover the ethanol. The solid was washed with water until neutral and then dried at 100°C to obtain lignin.

[0035] Organic solvent lignin extraction method: Add wood chips and ethanol solution (ethanol: water 7:3) into a rotary cooker and heat at 70°C with stirring for 120 minutes. The following steps are the same as the alkaline lignin extraction method.

[0036] Kraft lignin extraction method: Wood chips and a cooking solution composed of 18% sodium hydroxide (Na2O), 20% sodium sulfide, and deionized water are placed in a cooking pot, which is then placed in a rotary cooking pot for cooking. The following steps are the same as for alkali lignin extraction.

[0037] The Joule heating device was from Hefei In-Situ Technology Co., Ltd., CIS-JH3.2.

[0038] Example 1

[0039] (1) Weigh 10 g of alkali lignin and place it in a three-necked flask. Add 50 mL of deionized water, adjust the pH to 10 with 20 wt% sodium hydroxide solution, stir at 75°C until the lignin is completely dissolved, adjust the pH to 2 with 10 wt% hydrochloric acid, wash with deionized water three times, and freeze-dry to obtain dry lignin;

[0040] (2) heating the dried lignin obtained in step (1) at 800° C. in a tube furnace at a heating rate of 5° C. / min for 2 h to obtain a lignin carbon precursor;

[0041] (3) The lignin carbon precursor (5.2 g) obtained in step (2) was placed in a graphite mold and carbonized in a Joule heating device at a carbonization temperature of 1200°C; a heating rate of 120°C / min, a holding time of 3 min, a Joule heating voltage of 5 V, a current of 350 A, an output power of 3.5 kW, and a pressure of 25 MPa; the Joule heat carbonization cycle was repeated 3 times. Figure 1Scanning electron microscopy shows that the carbon layer is dispersed and there is little accumulation, which shows that the method of preparing lignin hard carbon materials by Joule heating flash evaporation can effectively improve heating efficiency, reduce carbon layer accumulation and thus increase conductive efficiency (conductivity is 3.45×10^3S / m).

[0042] Example 2

[0043] (1) Weigh 10 g of enzymatically hydrolyzed lignin and place it in a three-necked flask. Add 50 mL of deionized water, adjust the pH to 10 with 15 wt% potassium hydroxide solution, stir at 75°C until the lignin is completely dissolved, adjust the pH to 3 with 10 wt% hydrochloric acid, wash twice with deionized water, and freeze-dry to obtain dry lignin.

[0044] (2) heating the dried lignin obtained in step (1) in a tube furnace at 700° C. at a heating rate of 5° C. / min for 3 h to obtain a lignin carbon precursor;

[0045] (3) The lignin carbon precursor (5.4 g) obtained in step (2) was placed in a graphite mold and subjected to Joule heating carbonization at a carbonization temperature of 1000°C; a heating rate of 130°C / min, a holding time of 4 min, a Joule heating voltage of 5 V, a current of 350 A, an output power of 3.5 kW, and a pressure of 30 MPa; and the Joule heating carbonization cycle was repeated 3 times.

[0046] Example 3

[0047] (1) Weigh 10 g of organic solvent lignin and place it in a three-necked flask. Add 50 mL of deionized water, adjust the pH to 10 with 15 wt% sodium hydroxide solution, stir at 75°C until the lignin is completely dissolved, adjust the pH to 2 with 15 wt% sulfuric acid, wash with deionized water four times, and freeze-dry to obtain dry lignin;

[0048] (2) heating the dried lignin obtained in step (1) at 900° C. in a tube furnace at a heating rate of 8° C. / min for 3 h to obtain a lignin carbon precursor;

[0049] (3) The lignin carbon precursor (5.0 g) obtained in step (2) was placed in a graphite mold and subjected to Joule heating carbonization at a carbonization temperature of 1400°C; a heating rate of 120°C / min, a holding time of 4 min, a Joule heating voltage of 5 V, a current of 400 A, an output power of 4.5 kW, and a pressure of 30 MPa; and the Joule heating carbonization cycle was repeated 5 times.

[0050] Example 4

[0051] (1) Weigh 10 g of kraft lignin and place it in a three-necked flask. Add 50 mL of deionized water, adjust the pH to 10 with 15 wt% sodium hydroxide solution, stir at 75°C until the lignin is completely dissolved, adjust the pH to 3 with 10 wt% hydrochloric acid, wash with deionized water 5 times, and freeze-dry to obtain dry lignin;

[0052] (2) The dried lignin obtained in step (1) was heated in a tubular furnace at 800° C. at a heating rate of 6° C. / min for 4 h to obtain a lignin carbon precursor.

[0053] (3) The lignin carbon precursor (5.1 g) obtained in step (2) was placed in a graphite mold and subjected to Joule heating carbonization at a carbonization temperature of 1000°C; a heating rate of 140°C / min, a holding time of 3 min, a Joule heating voltage of 5 V, a current of 350 A, an output power of 2.5 kW, and a pressure of 20 MPa; and the Joule heating carbonization cycle was repeated twice.

[0054] Example 5

[0055] (1) Weigh 10 g of alkali lignin and place it in a three-necked flask. Add 50 mL of deionized water, adjust the pH to 10 with 20 wt% sodium hydroxide solution, stir at 75°C until the lignin is completely dissolved, adjust the pH to 2 with 10 wt% hydrochloric acid, wash with deionized water three times, and freeze-dry to obtain dry lignin;

[0056] (2) heating the dried lignin obtained in step (1) at 800° C. in a tube furnace at a heating rate of 5° C. / min for 2 h to obtain a lignin carbon precursor;

[0057] (3) The lignin carbon precursor (5.2 g) obtained in step (2) was placed in a graphite mold and subjected to Joule heating carbonization at a carbonization temperature of 1300°C; a heating rate of 130°C / min, a holding time of 2 min, a Joule heating voltage of 5 V, a current of 350 A, an output power of 3.5 kW, and a pressure of 25 MPa; and the Joule heating carbonization cycle was repeated twice.

[0058] Example 6

[0059] (1) Weigh 10 g of alkali lignin into a three-necked flask, add 50 mL of deionized water, adjust the pH to 10 with 20 wt% sodium hydroxide solution, and stir at 75°C until the lignin is completely dissolved. Adjust the pH to 2 with 10 wt% hydrochloric acid, wash three times with deionized water, and freeze-dry to obtain dry lignin.

[0060] (2) The dried lignin obtained in step (1) was heated in a tubular furnace at 800° C. at a heating rate of 5° C. / min for 2 h to obtain a lignin carbon precursor.

[0061] (3) The lignin carbon precursor (5.2 g) obtained in step (2) was placed in a graphite mold and subjected to Joule heating carbonization at a carbonization temperature of 1400°C; a heating rate of 140°C / min, a holding time of 5 min, a Joule heating voltage of 5 V, a current of 350 A, an output power of 3.5 kW, and a pressure of 25 MPa; and the Joule heating carbonization cycle was repeated 5 times.

[0062] The embodiments provided above are not intended to limit the scope of the present invention, nor are the steps described to limit their execution order. Any obvious improvements to the present invention made by those skilled in the art in combination with existing common knowledge shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a lignin hard carbon negative electrode material, characterized in that: The main steps are as follows: (1) reacting lignin with alkali solution, adding acid, washing and drying to obtain dry lignin; (2) preheating the dried lignin obtained in step (1) in a tube furnace to obtain a hard carbon precursor; (3) The hard carbon precursor obtained in step (2) is placed in a graphite mold and carbonized by Joule heat flash evaporation to obtain a lignin hard carbon negative electrode material.

2. The method according to claim 1, characterized in that In step (1), the lignin is one or more of alkali lignin, enzymatic lignin, organic solvent lignin, and sulfate lignin.

3. The method according to claim 1, characterized in that In step (1), the mass concentration of the alkali in the alkali solution is 10-30%, and the alkali is one or more of NaOH and KOH.

4. The method according to claim 1, wherein In step (1), the acid is one or more of HCl and H2SO4, and the mass concentration of the acid is 5-20%.

5. The method according to claim 1, wherein In step (2), the preheating temperature of the tubular furnace is 700-900° C., the preheating time is 1-4 h, and the heating rate is 2-10° C. / min.

6. The method according to claim 1, wherein In step (3), the temperature for carbonization by Joule heat flash evaporation is 1000-1600°C; the heating rate is 100-140°C / min, and the time is 1-5 minutes.

7. The method according to claim 1, characterized in that In step (3), the voltage of the Joule heat flash carbonization is 3 to 5 V, the current is 300 to 500 A, the output power is 1.5 to 4.5 kW, and the pressure is 20 to 35 MPa.

8. The method according to claim 1, characterized in that In step (3), Joule heat flash evaporation is carried out for carbonization cycles 2 to 6 times.

9. The lignin hard carbon negative electrode material prepared by the method according to any one of claims 1 to 8.

10. Use of the lignin hard carbon negative electrode material according to claim 9 in sodium ion batteries.

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