A lignin graded porous carbon material with large-size micropores and its preparation method and application

Abstract

The present invention discloses a lignin graded porous carbon material with large-sized micropores, and its preparation method and application. The present invention first dissolves lignin in a water / organic solvent mixed solvent, separates and obtains organic solvent-insoluble lignin, then dissolves the lignin in a sodium hydroxide solution, adds sulfite and aldehydes, and dialyzes after heating reaction to obtain a sulfomethylated organic solvent-insoluble lignin solution. The sulfomethylated organic solvent-insoluble lignin, water-soluble potassium carboxylate and water-insoluble metal carbonate are prepared into a dispersion and uniformly mixed, poured into a high-speed stirred organic solvent, and a lignin / potassium salt / metal carbonate complex is prepared based on anti-solvent precipitation. The composite is carbonized at high temperature and acid-etched to obtain a lignin graded porous carbon material with large-sized micropores. The material has large-sized micropores and mesopores, can be used in the positive electrode of zinc ion hybrid capacitors, can provide storage sites and diffusion channels for hydrated zinc ions, and exhibits excellent capacitance performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of porous carbon materials, and in particular relates to a lignin graded porous carbon material with large-sized micropores, a preparation method and an application thereof. Background Art

[0002] Zinc-ion hybrid capacitors consist of a battery-type zinc negative electrode and a capacitor-type carbon positive electrode. They integrate the advantages of zinc-ion batteries and supercapacitors and have good application prospects in electric vehicles, portable and flexible devices, etc. However, commercial activated carbon as a carbon positive electrode currently has the problems of low specific capacitance and poor rate performance. It is difficult to match the battery-type zinc negative electrode in terms of energy storage kinetics, which limits the application of zinc-ion hybrid capacitors. Therefore, there is an urgent need to prepare high-specific capacitance carbon positive electrode materials for the construction of high-performance zinc-ion hybrid capacitors. The hierarchical porous structure helps to enhance the energy storage kinetics of the porous carbon positive electrode. The size of hexahydrated zinc ions is about 0.86nm. By constructing micropores with a size greater than 0.86nm and larger mesopores, storage sites and diffusion paths can be provided for hydrated zinc ions, thereby improving the zinc storage specific capacitance and rate performance of the porous carbon positive electrode.

[0003] Lignin is widely available, has a high carbon content, and is rich in conjugated benzene ring structures and active oxygen-containing functional groups. It is an ideal precursor for carbon materials. Porous carbon materials with high specific surface area can be prepared by chemical activation. Zhang et al. (J. Colloid. Interf. Sci. 2023, 635, 94-104) used K2CO3 and CaCl2 to activate lignin to prepare a porous carbon material with a specific surface area of ​​984 m 2 / g, with an average pore size of 3.9nm. Xue et al. (Chem. Eng. J. 2024, 480, 147994) used urea and potassium oxalate to activate lignin and prepared a porous carbon nanosheet with a specific surface area of ​​2276m 2 / g of microporous carbon material. The above method directly mixes lignin and a large amount of activating additives, which makes it difficult to evenly disperse the materials. As a result, there are a large number of micropores smaller than the size of hydrated zinc ions in the carbon material structure, and there are no large-sized mesopores, which is not conducive to the diffusion and transmission of zinc ions.

[0004] In order to improve the power of ion transmission, researchers used weakly corrosive metal salts as templates and prepared hierarchical porous carbon materials rich in mesopores through solution co-precipitation or assembly. Chinese patent CN201911111152.8 hydrothermally reacts lignin and basic carbonate to obtain a lignin / basic carbonate mixture, which is then carbonized at high temperature to prepare a high-mesoporous porous carbon material. The material contains fewer micropores larger than hydrated zinc ions and has a specific surface area of ​​only 485m 2 / g, and cannot be used as a zinc storage positive electrode; Chinese patent CN202111233499.7 co-precipitates lignin with soluble calcium salts and soluble carbonates to prepare a lignin / nano-CaCO3 composite, and prepares a high-specific-surface-area lignin hierarchical porous carbon by high-temperature carbonization. This material has excellent performance as an adsorbent, but there are few mesopores larger than 4nm in the structure, making it unsuitable as a high-rate zinc storage carbon positive electrode; Chinese patent CN202410852533.6 mixes organic zinc salts, potassium hydroxide, and lignin in an alcohol solution to prepare a lignin / nano-zinc oxide / organic potassium salt composite, and carbonizes it to prepare a lignin-based porous carbon material with high mesoporosity. Due to the poor complexing ability of lignin with organic zinc salts, a large amount of zinc salt is required in the preparation process, which increases the preparation cost; Chinese patent CN201811375772.8 prepares a composite by adding ethanol to a mixed dispersion of lignin sulfonate and metal oxalate, and prepares porous carbon nanosheets rich in mesopores by high-temperature carbonization. However, the weaker force causes the process to require 6 assembly steps, resulting in low preparation efficiency. Fu et al. (Chem. Eng. J. 2020, 392, 12372) used sodium lignin sulfonate solution to complex zinc ions and oxalate ions, and prepared sodium lignin sulfonate / zinc oxalate complexes by slowly adding ethanol, and prepared lignin carbon nanosheets by high-temperature carbonization. This process requires strict control of the ethanol drop rate, the process is time-consuming, and the precipitation rate of the lignin complex is low. Chen et al. (Angew. Chem. Int. Ed. 2024, 63, e202316116) used an antisolvent precipitation method to add an aqueous solution of ammonium citrate and sodium chloride to ethanol to obtain a composite salt assembly. A porous carbon material with rich large mesopores was prepared by carbonization, but the small molecule carbon source-ammonium citrate is easily decomposed by heat, and the carbon yield is only 8%, which is not conducive to large-scale preparation.

[0005] In summary, the following problems exist in the use of lignin porous carbon materials as positive electrodes for zinc ion hybrid capacitors:

[0006] (1) In terms of the preparation process of lignin precursors, direct mixing makes it difficult to evenly disperse lignin, activators, and templates, while the conventional solution assembly method has a weak driving force for lignin assembly, is time-consuming, and has poor efficiency, resulting in a low precipitation rate of the lignin composite precursor.

[0007] (2) In terms of the structural regulation of lignin porous carbon materials, the traditional activation method can prepare porous carbon materials with high specific surface area, but excessive activator introduces a large number of micropores whose sizes do not match the hydrated zinc ions, and the mesopores are sparse; using a single weakly corrosive metal salt such as basic carbonate, calcium carbonate or zinc oxalate as a template can prepare carbon materials rich in mesopores, but the micropores are few and the pore size is difficult to control.

[0008] (3) In terms of zinc storage performance, the proportion of micropores larger than 0.86 nm in lignin porous carbon materials is low, and the mesopore volume is small, resulting in low zinc storage specific capacitance and poor rate performance. Summary of the Invention

[0009] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide a method for preparing a lignin graded porous carbon material with large-sized micropores.

[0010] The method of the present invention utilizes sulfomethylated organic solvent-insoluble lignin as a carbon source, a water-soluble potassium carboxylate as an activator, and a water-insoluble metal carbonate as a template, and prepares a lignin hierarchical porous carbon material with large-sized micropores by rapid anti-solvent precipitation and high-temperature carbonization. First, lignin is dissolved in a water / organic solvent mixed solvent, and the filter residue is separated to obtain the organic solvent-insoluble lignin. The organic solvent-insoluble lignin is dissolved in a sodium hydroxide solution, sulfite and aldehyde are added, and the mixture is heated for reaction and then dialyzed to obtain a sulfomethylated organic solvent-insoluble lignin solution. The sulfomethylated organic solvent-insoluble lignin, water-soluble potassium carboxylate and water-insoluble metal carbonate are prepared into a dispersion and uniformly mixed, poured into a high-speed stirred organic solvent, allowed to stand, solid-liquid separation and drying to obtain a lignin / potassium salt / metal carbonate complex, which is then carbonized at high temperature and acid-etched to obtain a lignin hierarchical porous carbon material with large-sized micropores.

[0011] During the preparation process of the method of the present invention, lignin is dissolved in a water / organic solvent mixed solvent to obtain organic solvent-insoluble lignin, which is then subjected to sulfomethylation modification, effectively increasing the solubility difference of lignin in water and organic solvent, enhancing the assembly force between lignin, potassium carboxylate and metal carbonate during the anti-solvent precipitation process, significantly shortening the assembly time and improving the precipitation efficiency; during the carbonization process of the lignin / potassium carboxylate / metal carbonate composite, weak etching of the potassium carboxylate and gas released by pyrolysis of the metal carbonate can generate relatively large micropores, and metal oxides formed by pyrolysis of the metal carbonate can support the lignin carbon skeleton, generating mesopores with relatively large pore sizes, thereby forming a hierarchical porous carbon material with large micropores. The hierarchical porous carbon material is used as the positive electrode of a zinc ion hybrid capacitor, can provide storage sites and diffusion channels for hydrated zinc ions, and exhibits excellent capacitance performance.

[0012] Another object of the present invention is to provide a lignin graded porous carbon material with large-sized micropores prepared by the above method.

[0013] Another object of the present invention is to provide an application of the above-mentioned lignin graded porous carbon material with large-sized micropores in a positive electrode material for zinc ion batteries and / or a positive electrode material for zinc ion hybrid capacitors.

[0014] In the present invention, the specific surface area of ​​the lignin graded porous carbon material with large-sized micropores is not less than 1200 m2 / g, the proportion of micropores larger than 0.86nm is not less than 50% of the total micropores, and the mesoporosity is not less than 60%.

[0015] The purpose of the present invention is achieved through the following solutions:

[0016] A method for preparing a lignin graded porous carbon material with large-sized micropores, characterized by comprising the following steps:

[0017] (1) dissolving lignin in a water / organic solvent mixed solvent, filtering and drying the residue to obtain organic solvent-insoluble lignin;

[0018] (2) dissolving the organic solvent-insoluble lignin obtained in step (1) in a sodium hydroxide solution, controlling the solution pH to 10-12, adding sulfite and aldehyde, reacting at 80-100° C. for 2-4 hours, dialyzing and concentrating the reaction solution to obtain a lignin concentrate;

[0019] (3) mixing the lignin concentrate obtained in step (2) with a potassium carboxylate solution and a metal carbonate dispersion, and after sufficient stirring, pouring the mixture into a high-speed stirring organic solvent, stirring for 5 to 20 minutes, letting it stand, filtering, and drying the precipitate to obtain a lignin / potassium carboxylate / metal carbonate complex;

[0020] (4) carbonizing the lignin / potassium carboxylate / metal carbonate complex obtained in step (3) in an inert atmosphere, soaking the carbonized product in dilute acid, filtering, and drying to obtain a lignin hierarchical porous carbon material having large-sized micropores;

[0021] The mass ratio of the solute content in the lignin, sulfite, aldehyde, potassium carboxylate solution, and the metal carbonate content in the metal carbonate dispersion is 100:(30-120):(40-160):(100-300):(100-300).

[0022] Preferably, the mass ratio of the solute content in the lignin, sulfite, aldehyde, potassium carboxylate solution, and the metal carbonate content in the metal carbonate dispersion is 100:(60-80):(60-100):(150-200):(150-200);

[0023] The concentration of the potassium carboxylate solution and the metal carbonate dispersion is 20-200 g / L.

[0024] Preferably, in step (1), the organic solvent is one or more of acetone, ethanol, ethylene glycol, etc.; and the volume ratio of water to the organic solvent is 3:(5-10).

[0025] Preferably, in step (2), the sulfite is one or more of sodium sulfite, sodium bisulfite, etc.;

[0026] The aldehydes are one or more of formaldehyde, glyoxal, glutaraldehyde, etc.;

[0027] The dialysis refers to dialyzing the reaction solution in deionized water using a dialysis bag with a molecular weight cut-off of 1000Da for 20 to 30 hours;

[0028] The concentration refers to heating and concentrating the lignin concentrate at 80-100° C. until the mass concentration of the lignin concentrate is 30-50%.

[0029] Preferably, in step (3), the potassium carboxylate is one or more of potassium oxalate, potassium citrate, potassium acetate, and potassium tartrate;

[0030] The metal carbonate is one or more of basic zinc carbonate, basic magnesium carbonate, basic lead carbonate, and calcium carbonate;

[0031] The volume ratio of the mixed liquid to the organic solvent is 1:(2-6);

[0032] The organic solvent is one or more of ethanol, acetone, and ethylene glycol.

[0033] Preferably, in step (4), the carbonization temperature program is: heating to 200-350°C at 5-15°C / min, maintaining for 1-2 hours; then heating to 600-900°C at 1-10°C / min, maintaining for 2-4 hours, and then cooling;

[0034] The inert atmosphere is at least one of nitrogen and argon;

[0035] The dilute acid refers to one or more of nitric acid, sulfuric acid and hydrochloric acid with a concentration of 0.5 to 2 mol / L, and the soaking time is 12 to 24 hours.

[0036] Preferably, the lignin is at least one of bagasse alkali lignin, corncob alkali lignin, bamboo alkali lignin, wheat straw alkali lignin and enzymatically hydrolyzed lignin in a biorefining process.

[0037] Preferably, in step (1), the volume ratio of water to organic solvent is 3:7;

[0038] In step (2), the pH is adjusted to 11.5;

[0039] In step (3), the volume ratio of the mixed solution to the organic solvent is 1:3.5-4;

[0040] In step (4), the carbonization temperature program is as follows: heating to 250°C at 10°C / min and holding for 1 hour; then heating to 700°C at 5°C / min and holding for 2.5 hours; the concentration of the dilute acid is 1 mol / L;

[0041] The drying method in steps (1), (3) and (4) is at least one of infrared drying, blast drying, vacuum drying and freeze drying, the drying temperature is 50 to 200° C., and the drying time is 2 to 48 hours.

[0042] The method of the present invention prepares a lignin graded porous carbon material with large-sized micropores.

[0043] The invention relates to the use of the lignin graded porous carbon material with large-sized micropores in positive electrode materials for zinc ion batteries and / or positive electrode materials for zinc ion hybrid capacitors.

[0044] In step (1) of the present invention, a mixed solvent of acetone, ethanol, ethylene glycol, etc. and water is used to dissolve the lignin in order to separate and obtain organic solvent-insoluble lignin. In this step, the volume ratio of water to organic solvent must be controlled to be 3:(5-10), preferably 3:7. Excessively high or low water volume fractions are not conducive to the dissolution of the lignin, causing the lignin in step (3) to dissolve in the solvent, thereby reducing the assembly force.

[0045] In order to obtain sulfomethylated lignin with good water solubility and abundant ion binding sites in step (2), the mass ratio of lignin to sulfite and aldehydes needs to be controlled to be 100:30~120:40~160, preferably 100:(60~80):(60~100). If the weight ratio of lignin is too low, the grafting efficiency will be poor; if the weight ratio of lignin is too high, the degree of sulfomethylation will be low and the water solubility of lignin will be poor.

[0046] The reaction temperature of this step is 80-100°C and the reaction time is 2-4 hours. If the reaction temperature is too low or the reaction time is too short, it will not be conducive to sulfomethylation grafting; if the reaction temperature is too high or the reaction time is too long, it will cause lignin degradation and reduce the reaction yield.

[0047] This dialysis step is to remove residual sodium hydroxide, sulfites, and aldehydes, thereby improving the purity of the lignin concentrate. The dialysis bag used has a molecular weight cut-off of 1000 Da. If the molecular weight cut-off is too low, impurities will not be completely removed; if the molecular weight cut-off is too high, the yield of the lignin concentrate will be reduced.

[0048] The purpose of heating and concentrating the lignin solution in this step is to increase the concentration of the lignin solution. The mass fraction of the concentrated solution needs to be controlled at 30-50%. If the mass fraction of the concentrated solution is too low, the precipitation efficiency of step (3) will be reduced; if the mass fraction of the concentrated solution is too high, the lignin / potassium carboxylate / metal carbonate complex obtained in step (3) will be uneven.

[0049] Step (3) is to utilize the significant difference in solubility of sulfomethylated organic solvent-insoluble lignin in water and organic solvent, and to rapidly prepare a lignin / potassium carboxylate / metal carbonate complex based on anti-solvent precipitation.

[0050] This step requires controlling the concentrations of the potassium carboxylate solution and the metal carbonate dispersion. If the concentrations are too low, the lignin precipitation will be incomplete; if the concentrations are too high, the lignin, potassium carboxylate, and metal carbonate will be unevenly combined. The mixture must be thoroughly stirred to ensure a uniform dispersion of lignin, potassium carboxylate, and metal carbonate.

[0051] In this step, the mixed solution is poured into a high-speed stirring organic solvent. The stirring speed must be strictly controlled. If the stirring speed is too low, the materials will be unevenly dispersed. The stirring time is maintained for 5 to 20 minutes. If the stirring time is too short, the lignin, potassium carboxylate salt, and metal carbonate cannot be completely precipitated. If the stirring time is too long, the preparation efficiency is affected.

[0052] In this step, the volume ratio of the mixed liquid to the organic solvent needs to be controlled at 1:2 to 6, preferably 1:3.5 to 4. If the volume ratio of the organic solvent is too low, the solubility of lignin is large, the assembly force with the potassium carboxylate and the metal carbonate is weak, and the precipitation rate of the complex is low; if the volume ratio of the organic solvent is too high, the preparation cost is increased.

[0053] The inert atmosphere in step (4) can be nitrogen or argon or other inert gases. Carbonization is divided into two stages. The temperature of the first stage is required to be 200-350°C and the time is 1-2h. If the carbonization temperature is too low or the time is too short, it will not be conducive to the release of gas by the metal carbonate to activate the lignin. The second stage is required to be in the range of 600-900°C and the time is 2-4h. If the temperature or time is too short, the carbonization of the lignin and the activation of the potassium carboxylate salt will be incomplete, and the specific surface area of ​​the product will be low. If the temperature is too high or the time is too long, it will not only increase the production cost, but also cause the potassium carboxylate salt to be overactivated, resulting in the destruction of the pore structure and low product yield.

[0054] The concentration of the dilute acid solution in this step is required to be in the range of 0.5 to 2 mol / L, and the immersion time is controlled at 12 to 24 hours. If the acid concentration is too low or the immersion time is too short, metal impurities will remain and reduce the conductivity of the product; if the acid concentration is too high or the immersion time is too long, the microporous structure of the product will be destroyed.

[0055] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0056] (1) Compared with the lignin porous carbon material prepared by traditional chemical activation, the lignin graded porous carbon material with large-sized micropores prepared by the present invention has larger micropore diameter and mesoporosity, and the proportion of micropores larger than 0.86 nm is high, which can provide storage sites and diffusion paths for hydrated zinc ions, so that it has higher capacitance performance as a positive electrode material for zinc ion hybrid capacitors.

[0057] (2) The present invention uses potassium carboxylate as an activator and metal carbonate as a template, and uses an anti-solvent co-precipitation method to enhance the assembly force, thereby efficiently preparing a lignin composite precursor in one step, avoiding the use of highly corrosive reagents and shortening the preparation time, which is conducive to industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is a scanning electron microscope image of the lignin graded porous carbon with large-sized micropores obtained in Example 1 of the present invention.

[0059] Figure 2 These are the nitrogen adsorption / desorption isotherms and pore size distribution curves of the lignin graded porous carbon with large-sized micropores obtained in Example 1 of the present invention.

[0060] Figure 3 These are the charge and discharge curves of the electrode prepared from the lignin graded porous carbon with large-sized micropores obtained in Example 1 of the present invention at different current densities.

[0061] Figure 4 Specific capacitance of the lignin graded porous carbon with large-sized micropores obtained in Example 1 of the present invention at different current densities.

[0062] Figure 5 3 are the charge and discharge curves of the electrode prepared from the lignin porous carbon obtained in Comparative Example 3 of the present invention at different current densities.

[0063] Figure 6 Specific capacitance of the lignin porous carbon obtained in Comparative Example 3 of the present invention at different current densities. DETAILED DESCRIPTION

[0064] The present invention will be further described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

[0065] The materials involved in the following examples can be obtained from commercial channels.

[0066] Example 1

[0067] Weigh 100g of purified corn cob alkali lignin and add it to a mixed solution of 600ml water and 1400ml ethanol. After ultrasonic stirring, filter with water and place the filter residue in a 70℃ infrared drying oven to dry for 6h to obtain organic solvent-insoluble lignin; dissolve the organic solvent-insoluble lignin in 1000ml sodium hydroxide solution, adjust the pH to 11.5, then add 60g sodium bisulfite and 60g formaldehyde, and react at 85℃ for 3h under stirring. After the reaction is completed, the reaction solution is cooled to room temperature and dialyzed in deionized water using a dialysis bag with a molecular weight cutoff of 1000Da. After dialysis for 24h, the dialyzate is heated and evaporated at 85℃ to obtain 120ml of lignin concentrate with a mass concentration of 50%;

[0068] 150 g of potassium oxalate was dissolved in 1000 ml of water, and 150 g of basic zinc carbonate was dispersed in 1000 ml of water. The mixture was mixed with 120 ml of the above-mentioned lignin concentrate and stirred thoroughly for 2 h. The mixture was then poured into 8000 ml of ethanol solvent with high-speed stirring. After stirring for 10 min, the mixture was allowed to stand and separated to obtain a precipitate. The precipitate was placed in a 100°C forced air drying oven and dried for 12 h to obtain a solid powder of a lignin / potassium oxalate / basic zinc carbonate complex.

[0069] 10g of the above powder was placed in a tubular furnace and carbonized at high temperature under nitrogen atmosphere. The carbonization temperature was raised from room temperature to 250°C at a rate of 10°C / min and maintained for 1 hour; then raised to 700°C at a rate of 5°C / min and maintained for 2.5 hours. After carbonization, the temperature was cooled to room temperature to obtain a black powder. The black powder was soaked in 500ml of 1mol / L hydrochloric acid solution, stirred for 12 hours, filtered and washed with deionized water, and dried in a vacuum oven at 100°C for 24 hours to obtain a lignin-graded porous carbon material with large-sized micropores.

[0070] Example 2

[0071] Weigh 100g of purified alkali lignin from bamboo and add it to a mixed solution of 600ml of water and 1400ml of ethanol. After ultrasonic stirring, filter with water and place the filter residue in a 70℃ infrared drying oven to dry for 6h to obtain organic solvent-insoluble lignin; dissolve the organic solvent-insoluble lignin in 1000ml of sodium hydroxide solution, adjust the pH to 11.5, then add 60g of sodium bisulfite and 60g of glyoxal, and react at 85℃ for 3h under stirring. After the reaction is completed and the reaction solution is cooled to room temperature, the reaction solution is dialyzed in deionized water using a dialysis bag with a molecular weight cutoff of 1000Da. After dialysis for 24h, the dialyzate is heated and evaporated at 85℃ to obtain 200ml of lignin concentrate with a mass concentration of 30%;

[0072] 150 g of potassium citrate was dissolved in 1000 ml of water, and 200 g of basic zinc carbonate was dispersed in 1000 ml of water. The two were mixed with the above 200 ml of lignin concentrate and stirred thoroughly for 2 h. The mixture was then poured into 8000 ml of ethanol solvent with high-speed stirring. After stirring for 10 min, the mixture was allowed to stand and separated to obtain a precipitate. The precipitate was placed in a 100°C forced air drying oven and dried for 12 h to obtain a solid powder of a lignin / potassium citrate / basic zinc carbonate complex.

[0073] 10g of the above powder was placed in a tubular furnace and carbonized at high temperature under nitrogen atmosphere. The carbonization temperature was raised from room temperature to 250°C at a rate of 10°C / min and maintained for 1 hour; then raised to 800°C at a rate of 5°C / min and maintained for 3 hours. After carbonization, the temperature was cooled to room temperature to obtain a black powder. The black powder was soaked in 500ml of 1mol / L hydrochloric acid solution, stirred for 12 hours, filtered and washed with deionized water, and dried in a vacuum oven at 100°C for 24 hours to obtain a lignin-graded porous carbon material with large-sized micropores.

[0074] Example 3

[0075] Weigh 100g of purified wheat straw alkali lignin and add it to a mixed solution of 600ml water and 1400ml ethanol. After ultrasonic stirring, filter with water and place the filter residue in a 70℃ infrared drying oven to dry for 6h to obtain organic solvent insoluble lignin; dissolve the organic solvent insoluble lignin in 1000ml sodium hydroxide solution, adjust the pH to 11.5, then add 60g sodium bisulfite and 60g glutaraldehyde, and react at 85℃ for 3h under stirring. After the reaction is completed, the reaction solution is cooled to room temperature and dialyzed in deionized water using a dialysis bag with a molecular weight cutoff of 1000Da. After dialysis for 24h, heat the dialyzate at 85℃ to evaporate to obtain 150ml of lignin concentrate with a mass concentration of 40%;

[0076] Weigh 200 g of potassium acetate and dissolve it in 1000 ml of water. Weigh 200 g of basic magnesium carbonate and disperse it in 1000 ml of water. Mix the two with the above 150 ml of lignin concentrate and stir thoroughly for 2 hours. Then pour it into 8000 ml of ethanol solvent with high-speed stirring. Keep stirring for 10 minutes, let it stand and separate to obtain a precipitate. Place the precipitate in a 100°C forced air drying oven and dry it for 12 hours to obtain a solid powder of lignin / potassium acetate / basic magnesium carbonate complex.

[0077] 10g of the above powder was placed in a tubular furnace and carbonized at high temperature under nitrogen atmosphere. The carbonization temperature was raised from room temperature to 250°C at a rate of 10°C / min and maintained for 1 hour; then raised to 700°C at a rate of 5°C / min and maintained for 3 hours. After carbonization, the temperature was cooled to room temperature to obtain a black powder. The black powder was soaked in 500ml of 1mol / L hydrochloric acid solution, stirred for 12 hours, filtered and washed with deionized water, and dried in a vacuum oven at 100°C for 24 hours to obtain a lignin-graded porous carbon material with large-sized micropores.

[0078] Example 4

[0079] Weigh 100g of purified bagasse alkali lignin and add it to a mixed solution of 600ml water and 1400ml ethanol. After ultrasonic stirring, filter with water and place the filter residue in a 70℃ infrared drying oven to dry for 6h to obtain organic solvent insoluble lignin; dissolve the organic solvent insoluble lignin in 1000ml sodium hydroxide solution, adjust the pH to 11.5, then add 60g sodium bisulfite and 60g formaldehyde, and react at 85℃ for 3h under stirring. After the reaction is completed, the reaction solution is cooled to room temperature and dialyzed in deionized water using a dialysis bag with a molecular weight cutoff of 1000Da. After dialysis for 24h, the dialyzate is heated and evaporated at 85℃ to obtain 120ml of lignin concentrate with a mass concentration of 50%;

[0080] 150 g of potassium tartrate was dissolved in 1000 ml of water, and 150 g of basic lead carbonate was dispersed in 1000 ml of water. The mixture was mixed with 120 ml of the above-mentioned lignin concentrate and stirred thoroughly for 2 h. The mixture was then poured into 8000 ml of acetone solvent under high-speed stirring. The mixture was stirred for 10 min, and then allowed to stand and separate to obtain a precipitate. The precipitate was dried in a 100° C. forced air drying oven for 12 h to obtain a solid powder of a lignin / potassium tartrate / basic lead carbonate complex.

[0081] 10g of the above powder was placed in a tubular furnace and carbonized at high temperature under nitrogen atmosphere. The carbonization temperature was raised from room temperature to 250°C at a rate of 10°C / min and maintained for 1 hour; then raised to 700°C at a rate of 5°C / min and maintained for 4 hours. After carbonization, the temperature was cooled to room temperature to obtain a black powder. The black powder was soaked in 500ml of 1mol / L hydrochloric acid solution, stirred for 12 hours, filtered and washed with deionized water, and dried in a vacuum oven at 100°C for 24 hours to obtain a lignin-graded porous carbon material with large-sized micropores.

[0082] Example 5

[0083] Weigh 100g of purified enzymatic lignin and add it to a mixed solution of 600ml water and 1400ml ethanol. After ultrasonic stirring, filter with water and place the filter residue in a 70℃ infrared drying oven to dry for 6h to obtain organic solvent-insoluble lignin; dissolve the organic solvent-insoluble lignin in 1000ml sodium hydroxide solution, adjust the pH to 11.5, then add 60g sodium bisulfite and 60g formaldehyde, and react at 85℃ for 3h under stirring. After the reaction is completed, the reaction solution is cooled to room temperature and dialyzed in deionized water using a dialysis bag with a molecular weight cutoff of 1000Da. After dialysis for 24h, heat the dialyzate at 85℃ to evaporate to obtain 200ml of lignin concentrate with a mass concentration of 30%;

[0084] 150 g of potassium oxalate was dissolved in 1000 ml of water, and 200 g of basic zinc carbonate was dispersed in 1000 ml of water. The mixture was mixed with 200 ml of the above-mentioned lignin concentrate and stirred thoroughly for 2 h. The mixture was then poured into 8000 ml of ethylene glycol solvent with high-speed stirring. After stirring for 10 min, the mixture was allowed to stand and separated to obtain a precipitate. The precipitate was placed in a 100°C forced air drying oven and dried for 12 h to obtain a solid powder of a lignin / potassium oxalate / basic zinc carbonate complex.

[0085] 10g of the above powder was placed in a tubular furnace and carbonized at high temperature under nitrogen atmosphere. The carbonization temperature was raised from room temperature to 250°C at a rate of 10°C / min and maintained for 1 hour; then raised to 600°C at a rate of 5°C / min and maintained for 3 hours. After carbonization, the temperature was cooled to room temperature to obtain a black powder. The black powder was soaked in 500ml of 1mol / L hydrochloric acid solution, stirred for 12 hours, filtered and washed with deionized water, and dried in a vacuum oven at 100°C for 24 hours to obtain a lignin-graded porous carbon material with large-sized micropores.

[0086] Example 6

[0087] Weigh 100g of purified corn cob alkali lignin and add it to a mixed solution of 600ml water and 1400ml ethanol. After ultrasonic stirring, filter with water and place the filter residue in a 70℃ infrared drying oven to dry for 6h to obtain organic solvent-insoluble lignin; dissolve the organic solvent-insoluble lignin in 1000ml sodium hydroxide solution, adjust the pH to 11.5, then add 60g sodium bisulfite and 60g glyoxal, and react at 85℃ for 3h under stirring. After the reaction is completed, the reaction solution is cooled to room temperature and dialyzed in deionized water using a dialysis bag with a molecular weight cutoff of 1000Da. After dialysis for 24h, heat the dialyzate at 85℃ to evaporate to obtain 120ml of lignin concentrate with a mass concentration of 50%;

[0088] 200 g of potassium citrate was dissolved in 1000 ml of water, and 150 g of basic zinc carbonate was dispersed in 1000 ml of water. The mixture was mixed with 120 ml of the above-mentioned lignin concentrate and stirred thoroughly for 2 h. The mixture was then poured into 8000 ml of ethanol solvent with high-speed stirring. The mixture was stirred for 10 min, and then allowed to stand and separate to obtain a precipitate. The precipitate was placed in a 100°C forced air drying oven and dried for 12 h to obtain a solid powder of a lignin / potassium citrate / basic zinc carbonate complex.

[0089] 10g of the above powder was placed in a tubular furnace and carbonized at high temperature under nitrogen atmosphere. The carbonization temperature was raised from room temperature to 250°C at a rate of 10°C / min and held for 1 hour; then raised to 900°C at a rate of 5°C / min and held for 2 hours. After carbonization, the temperature was cooled to room temperature to obtain a black powder. The black powder was immersed in 500ml of 1mol / L hydrochloric acid solution, stirred for 12 hours, filtered and washed with deionized water, and dried in a vacuum oven at 100°C for 24 hours to obtain a lignin-graded porous carbon material with large-sized micropores.

[0090] Comparative Example 1 (Compared with Example 1, lignin was not extracted using a water-ethanol mixed solvent)

[0091] Weigh 100g of purified corncob alkali lignin and dissolve it in 1000ml of sodium hydroxide solution. Adjust the pH to 11.5, then add 60g of sodium bisulfite and 60g of formaldehyde. Stir and react at 85°C for 3h. After the reaction is completed and the reaction solution is cooled to room temperature, it is dialyzed in deionized water using a dialysis bag with a molecular weight cutoff of 1000Da. After dialysis for 24h, the dialyzate is heated and evaporated at 85°C to obtain 120ml of lignin concentrate with a mass concentration of 50%.

[0092] 150 g of potassium oxalate was dissolved in 1000 ml of water, and 150 g of basic zinc carbonate was dispersed in 1000 ml of water. The mixture was mixed with 120 ml of the above-mentioned lignin concentrate and stirred thoroughly for 2 h. The mixture was then poured into 8000 ml of ethanol solvent with high-speed stirring. After stirring for 10 min, the mixture was allowed to stand and separated to obtain a precipitate. The precipitate was placed in a 100°C forced air drying oven and dried for 12 h to obtain a solid powder of a lignin / potassium oxalate / basic zinc carbonate complex.

[0093] 10g of the above powder was placed in a tubular furnace and carbonized at high temperature under nitrogen atmosphere. The carbonization temperature was raised from room temperature to 250°C at a rate of 10°C / min and maintained for 1 hour; then raised to 700°C at a rate of 5°C / min and maintained for 3 hours. After carbonization, the temperature was cooled to room temperature to obtain a black powder. The black powder was soaked in 500ml of 1mol / L hydrochloric acid solution, stirred for 12 hours, filtered and washed with deionized water, and dried in a vacuum oven at 100°C for 24 hours to obtain a lignin-graded porous carbon material with large-sized micropores.

[0094] Comparative Example 2 (Compared with Example 1, sulfomethylation reaction was not carried out using sodium bisulfite and formaldehyde)

[0095] Weigh 100g of purified corncob alkali lignin and add it to a mixed solution of 600ml water and 1400ml ethanol. After ultrasonic stirring, filter with water and dry the filter residue in a 70°C infrared drying oven for 6 hours to obtain organic solvent-insoluble lignin. Dissolve the organic solvent-insoluble lignin in 1000ml of sodium hydroxide solution, adjust the pH to 11.5, and dialyze the solution in deionized water using a dialysis bag with a molecular weight cutoff of 1000Da. After dialysis for 24 hours, heat the dialyzate at 85°C to evaporate and obtain 120ml of lignin concentrate with a mass concentration of 50%.

[0096] 150 g of potassium oxalate was dissolved in 1000 ml of water, and 150 g of basic zinc carbonate was dispersed in 1000 ml of water. The mixture was mixed with 120 ml of the above-mentioned lignin concentrate and stirred thoroughly for 2 h. The mixture was then poured into 8000 ml of ethanol solvent with high-speed stirring. After stirring for 10 min, the mixture was allowed to stand and separated to obtain a precipitate. The precipitate was placed in a 100°C forced air drying oven and dried for 12 h to obtain a solid powder of a lignin / potassium oxalate / basic zinc carbonate complex.

[0097] 10g of the above powder was placed in a tubular furnace and carbonized at high temperature under nitrogen atmosphere. The carbonization temperature was raised from room temperature to 250°C at a rate of 10°C / min and maintained for 1 hour; then raised to 700°C at a rate of 5°C / min and maintained for 3 hours. After carbonization, the temperature was cooled to room temperature to obtain a black powder. The black powder was soaked in 500ml of 1mol / L hydrochloric acid solution, stirred for 12 hours, filtered and washed with deionized water, and dried in a vacuum oven at 100°C for 24 hours to obtain a lignin-graded porous carbon material with large-sized micropores.

[0098] Comparative Example 3 (Compared with Example 1, no anti-solvent co-precipitation was used, and the mixed solution of lignin concentrate, potassium oxalate and basic zinc carbonate was directly evaporated)

[0099] Weigh 100g of purified corn cob alkali lignin and add it to a mixed solution of 600ml water and 1400ml ethanol. After ultrasonic stirring, filter with water and place the filter residue in a 70℃ infrared drying oven to dry for 6h to obtain organic solvent-insoluble lignin; dissolve the organic solvent-insoluble lignin in 1000ml sodium hydroxide solution, adjust the pH to 11.5, then add 60g sodium bisulfite and 60g formaldehyde, and react at 85℃ for 3h under stirring. After the reaction is completed, the reaction solution is cooled to room temperature and dialyzed in deionized water using a dialysis bag with a molecular weight cutoff of 1000Da. After dialysis for 24h, the dialyzate is heated and evaporated at 85℃ to obtain 120ml of lignin concentrate with a mass concentration of 50%;

[0100] 150 g of potassium oxalate was dissolved in 1000 ml of water, and 150 g of basic zinc carbonate was dispersed in 1000 ml of water. The two mixtures were mixed with 120 ml of the above lignin concentrate and stirred thoroughly for 2 h. The water was then evaporated at 85°C to obtain a precipitate. The precipitate was placed in a forced air drying oven at 100°C for 12 h to obtain a solid powder of a lignin / potassium oxalate / basic zinc carbonate complex.

[0101] 10g of the above powder was placed in a tubular furnace and carbonized at high temperature under nitrogen atmosphere. The carbonization temperature was raised from room temperature to 250°C at a rate of 10°C / min and maintained for 1 hour; then raised to 700°C at a rate of 5°C / min and maintained for 3 hours. After carbonization, the temperature was cooled to room temperature to obtain a black powder. The black powder was soaked in 500ml of 1mol / L hydrochloric acid solution, stirred for 12 hours, filtered and washed with deionized water, and dried in a vacuum oven at 100°C for 24 hours to obtain a lignin-graded porous carbon material with large-sized micropores.

[0102] Comparative Example 4 (compared with Example 1, potassium hydroxide was used instead of potassium oxalate)

[0103] Weigh 100g of purified corn cob alkali lignin and add it to a mixed solution of 600ml water and 1400ml ethanol. After ultrasonic stirring, filter with water and place the filter residue in a 70℃ infrared drying oven to dry for 6h to obtain organic solvent-insoluble lignin; dissolve the organic solvent-insoluble lignin in 1000ml sodium hydroxide solution, adjust the pH to 11.5, then add 60g sodium bisulfite and 60g formaldehyde, and react at 85℃ for 3h under stirring. After the reaction is completed, the reaction solution is cooled to room temperature and dialyzed in deionized water using a dialysis bag with a molecular weight cutoff of 1000Da. After dialysis for 24h, the dialyzate is heated and evaporated at 85℃ to obtain 120ml of lignin concentrate with a mass concentration of 50%;

[0104] Weigh 150g of potassium hydroxide and dissolve it in 1000ml of water. Weigh 150g of basic zinc carbonate and disperse it in 1000ml of water. Mix the two with the above 120ml of lignin concentrate and stir thoroughly for 2h. Then pour it into 8000ml of ethanol solvent with high-speed stirring. Keep stirring for 10min, let it stand and separate to obtain a precipitate. Dry the precipitate in a 100°C forced air drying oven for 12h to obtain a solid powder of lignin / potassium hydroxide / basic zinc carbonate complex.

[0105] 10g of the above powder was placed in a tubular furnace and carbonized at high temperature under nitrogen atmosphere. The carbonization temperature was raised from room temperature to 250°C at a rate of 10°C / min and maintained for 1 hour; then raised to 700°C at a rate of 5°C / min and maintained for 3 hours. After carbonization, the temperature was cooled to room temperature to obtain a black powder. The black powder was soaked in 500ml of 1mol / L hydrochloric acid solution, stirred for 12 hours, filtered and washed with deionized water, and dried in a vacuum oven at 100°C for 24 hours to obtain a lignin-graded porous carbon material with large-sized micropores.

[0106] Comparative Example 5 (compared with Example 1, only potassium oxalate was used as an activator)

[0107] Weigh 100g of purified corn cob alkali lignin and add it to a mixed solution of 600ml water and 1400ml ethanol. After ultrasonic stirring, filter with water and place the filter residue in a 70℃ infrared drying oven to dry for 6h to obtain organic solvent-insoluble lignin; dissolve the organic solvent-insoluble lignin in 1000ml sodium hydroxide solution, adjust the pH to 11.5, then add 60g sodium bisulfite and 60g formaldehyde, and react at 85℃ for 3h under stirring. After the reaction is completed, the reaction solution is cooled to room temperature and dialyzed in deionized water using a dialysis bag with a molecular weight cutoff of 1000Da. After dialysis for 24h, the dialyzate is heated and evaporated at 85℃ to obtain 120ml of lignin concentrate with a mass concentration of 50%;

[0108] 150 g of potassium oxalate was weighed and dissolved in 1000 ml of water. The mixture was mixed with 120 ml of the above lignin concentrate and stirred thoroughly for 2 h. The mixture was then poured into 8000 ml of ethanol solvent with high-speed stirring. The mixture was stirred for 10 min, and then allowed to stand and separate to obtain a precipitate. The precipitate was placed in a forced air drying oven at 100°C for 12 h to obtain a lignin / potassium oxalate complex solid powder.

[0109] 10g of the above powder was placed in a tubular furnace and carbonized at high temperature under nitrogen atmosphere. The carbonization temperature was raised from room temperature to 250°C at a rate of 10°C / min and maintained for 1 hour; then raised to 700°C at a rate of 5°C / min and maintained for 3 hours. After carbonization, the temperature was cooled to room temperature to obtain a black powder. The black powder was soaked in 500ml of 1mol / L hydrochloric acid solution, stirred for 12 hours, filtered and washed with deionized water, and dried in a vacuum oven at 100°C for 24 hours to obtain a lignin-graded porous carbon material with large-sized micropores.

[0110] Comparative Example 6 (Compared with Example 1, only basic zinc carbonate was used as a template)

[0111] Weigh 100g of purified corn cob alkali lignin and add it to a mixed solution of 600ml water and 1400ml ethanol. After ultrasonic stirring, filter with water and place the filter residue in a 70℃ infrared drying oven to dry for 6h to obtain organic solvent-insoluble lignin; dissolve the organic solvent-insoluble lignin in 1000ml sodium hydroxide solution, adjust the pH to 11.5, then add 60g sodium bisulfite and 60g formaldehyde, and react at 85℃ for 3h under stirring. After the reaction is completed, the reaction solution is cooled to room temperature and dialyzed in deionized water using a dialysis bag with a molecular weight cutoff of 1000Da. After dialysis for 24h, the dialyzate is heated and evaporated at 85℃ to obtain 120ml of lignin concentrate with a mass concentration of 50%;

[0112] 150 g of basic zinc carbonate was dispersed in 1000 ml of water, mixed with 120 ml of the above lignin concentrate, and stirred thoroughly for 2 h. The mixture was then poured into 8000 ml of ethanol solvent under high-speed stirring and stirred for 10 min. The mixture was allowed to stand and separated to obtain a precipitate, which was then dried in a forced air drying oven at 100°C for 12 h to obtain a solid powder of a lignin / basic zinc carbonate complex.

[0113] 10g of the above powder was placed in a tubular furnace and carbonized at high temperature under nitrogen atmosphere. The carbonization temperature was raised from room temperature to 250°C at a rate of 10°C / min and maintained for 1 hour; then raised to 700°C at a rate of 5°C / min and maintained for 3 hours. After carbonization, the temperature was cooled to room temperature to obtain a black powder. The black powder was soaked in 500ml of 1mol / L hydrochloric acid solution, stirred for 12 hours, filtered and washed with deionized water, and dried in a vacuum oven at 100°C for 24 hours to obtain a lignin-graded porous carbon material with large-sized micropores.

[0114] Example Effect Description

[0115] The structure of the lignin graded carbon materials obtained in the examples and comparative examples was characterized and their performance in the positive electrode materials of zinc ion hybrid capacitors was tested. The results are shown in Tables 1 and 2. Figures 1 to 6 .

[0116] The microstructure of the samples was characterized by scanning electron microscopy (SEM, Hitachi SU8220). The specific surface area and pore structure of the samples were measured using a fully automatic specific surface and porosity analyzer (Micromeritics ASAP 2020 instrument).

[0117] In zinc ion hybrid capacitor performance testing, the working electrode was prepared using the lignin-carbon material obtained in this invention, acetylene black, and polytetrafluoroethylene in a mass ratio of 8:1:1. A zinc sheet was used as the negative electrode, and 1M ZnSO₄ was used as the electrolyte. The capacitor was assembled into a button-type capacitor for electrochemical testing. The test window was 0.2 to 1.8 V, and the charge and discharge current density was 0.1 to 50 A / g.

[0118] Table 1 shows the pore structure parameters of lignin hierarchical porous carbon materials prepared in different embodiments and comparative examples.

[0119] Table 2 shows the specific capacitance of lignin graded porous carbon materials prepared in different embodiments and comparative examples.

[0120] Table 1 Pore structure characteristic parameters of lignin graded porous carbon materials

[0121]

[0122]

[0123] Table 2 Specific capacitance of lignin graded porous carbon materials

[0124]

[0125] Description of Table 1 and Table 2:

[0126] The specific surface areas of the lignin graded porous carbon materials prepared in Examples 1 to 6 all exceeded 1200 m 2 / g, the proportion of large-sized micropores is greater than 50%, and the proportion of mesopores is greater than 60%. The specific surface area of ​​Example 1 is as high as 1633m 2 / g, with a total pore volume of 1.68 cm 3 / g, a large-scale microporosity of 64.6%, and a mesoporosity of 65.4%. Its specific surface area is much higher than that of the lignin porous carbon material obtained in Comparative Example 1 without using a water-ethanol mixed solvent to extract lignin, the lignin porous carbon material obtained in Comparative Example 2 by sulfomethylation without using sodium bisulfite and formaldehyde, the lignin porous carbon material obtained by direct evaporation of the precursor in Comparative Example 3, the lignin porous carbon material obtained by activation with potassium oxalate alone in Comparative Example 5, and Comparative Example 6. The large-scale microporosity and mesoporosity are much higher than those of the lignin porous carbon material obtained by activation with potassium hydroxide in Comparative Example 4.

[0127] The zinc ion hybrid capacitor performance test results in Table 2 show that the lignin graded porous carbon obtained in Example 1 has excellent specific capacitance and capacitance retention. At a current density of 0.1 A / g, the specific capacitance is 445 F / g, and at a current density of 50 A / g, the specific capacitance remains at 180 F / g. These values ​​are much higher than those in Comparative Examples 1 to 6, indicating that the graded lignin porous carbon prepared by the present invention is superior to lignin porous carbon prepared by traditional methods.

[0128] Compared with Example 1, Comparative Example 1 does not use a water-ethanol mixed solvent to extract lignin, resulting in a high solubility of lignin in the ethanol solvent during the assembly process, low precipitation efficiency of lignin with potassium oxalate and basic zinc carbonate, uneven composite, weakened activation effect, and a specific surface area of ​​the obtained lignin porous carbon (850m 2 / g) and total pore volume (0.88 cm 3 / g) are significantly lower than those in Example 1, resulting in extremely poor specific capacitance and rate performance.

[0129] Compared with Example 1, Comparative Example 2 does not perform sulfomethylation reaction on lignin, resulting in weak assembly driving force, inability of lignin to be uniformly compounded with potassium oxalate and basic zinc carbonate, poor carbonization activation effect, and the specific surface area of ​​the obtained lignin porous carbon (922m 2 / g) and total pore volume (1.01 cm 3 / g) are significantly lower than those in Example 1, resulting in extremely poor specific capacitance and rate performance.

[0130] Compared with Example 1, in Comparative Example 3, no anti-solvent co-precipitation was used, and the mixture of lignin concentrate, potassium oxalate and basic zinc carbonate was directly evaporated, resulting in uneven mixing of the lignin / potassium oxalate / basic zinc carbonate complex, which weakened the activation effect of potassium oxalate and basic zinc carbonate. The specific surface area of ​​the obtained lignin porous carbon (1039m 2 / g), total pore volume (1.23cm 3 / g) and mesoporosity (48.8%) were lower than those in Example 1, resulting in poor specific capacitance and capacitance retention.

[0131] Compared with Example 1, Comparative Example 4 uses potassium hydroxide instead of potassium oxalate. Potassium hydroxide is highly corrosive and easily introduces a large number of micropores that do not match the size of hydrated zinc ions. Although the porous carbon material has a high specific surface area (1728m 2 / g), but the large-scale microporosity (32.5%) and mesoporosity (50.4%) are lower than those in Example 1, resulting in poor specific capacitance and capacitance retention.

[0132] Compared with Example 1, Comparative Example 5 only uses potassium oxalate as an activator. The activation efficiency of a single potassium salt is poor, and the lignin aggregation structure cannot be fully opened. The specific surface area of ​​the obtained lignin porous carbon (918m 2 / g), total pore volume (0.50cm 3 / g), large-size microporosity (36.7%) and mesoporosity (10.2%) are significantly lower than those of the sample obtained in Example 1, resulting in extremely poor specific capacitance and capacitance retention.

[0133] Compared with Example 1, Comparative Example 6 only uses basic zinc carbonate as a template, the activation effect is poor, the number of micropores of the obtained lignin porous carbon is insufficient, and the specific surface area (749m 2 / g) and large-size micropore volume (0.12 cm 3 / g) are lower than those of the sample obtained in Example 1, resulting in extremely poor specific capacitance and capacitance retention.

[0134] In summary, the anti-solvent precipitation method and the combined activation of potassium carboxylate and metal carbonate of the present invention can prepare lignin hierarchical porous carbon materials with high specific surface area and abundant large-sized micropores. As the positive electrode material of zinc ion hybrid capacitors, it shows significantly better performance than the lignin porous carbon materials prepared by traditional methods.

[0135] Figure 1 This is a scanning electron microscope image of the lignin graded porous carbon material prepared in Example 1 of the present invention. It can be seen that it presents an interconnected flaky porous carbon structure with an open skeleton and abundant pores.

[0136] Figure 2 This is the nitrogen adsorption-desorption curve and pore size distribution curve of the lignin graded porous carbon material obtained in Example 1 of the present invention. The adsorption amount of its nitrogen adsorption-desorption curve increases significantly in the low-pressure region, indicating the presence of micropores. Obvious hysteresis loops appear in the medium-pressure region and the high-pressure region, indicating the presence of mesopores, so the material has graded porous properties. The pore size distribution curve shows that its micropore distribution is concentrated in 0.7-1.0nm and 1-2nm, the mesopore distribution is concentrated in 4-50nm, and the macropores are concentrated in 70nm. Its micropores and mesopores are attributed to the activation of gases released by the thermal decomposition of potassium oxalate and basic zinc carbonate and the etching effect of potassium compounds, while the macropores are related to the zinc oxide generated in situ.

[0137] Figure 3 These are the charge-discharge curves of the lignin graded porous carbon material prepared in Example 1 of the present invention as the positive electrode material for zinc ion hybrid capacitors at different current densities. All curves are triangular in shape, and there is no significant voltage drop at high current densities, indicating that the material has ideal capacitance properties.

[0138] Figure 4The lignin graded porous carbon material prepared in Example 1 of the present invention has a specific capacitance as a positive electrode material for zinc ion hybrid capacitors at different current densities, and its specific capacitance is 445F / g (0.1A / g), 369F / g (0.2A / g), 303F / g (0.5A / g), 270F / g (1.0A / g), 250F / g (2.0A / g), 227F / g (5.0A / g), 214F / g (10A / g), 200F / g (20A / g) and 180F / g (50A / g), showing excellent performance and good application potential.

[0139] Figure 5 and Figure 6 The charge and discharge curves and specific capacitance of the lignin porous carbon obtained in Comparative Example 3 of the present invention as the positive electrode material of the zinc ion hybrid capacitor at different current densities are as follows: the specific capacitance is 319F / g (0.1A / g), 277F / g (0.2A / g), 231F / g (0.5A / g), 212F / g (1.0A / g), 198F / g (2.0A / g), 184F / g (5.0A / g), 163F / g (10A / g), 118F / g (20A / g) and 78F / g (50A / g), which shows that the performance is significantly inferior to that of Example 1, indicating that the anti-solvent co-precipitation technology for preparing the lignin composite precursor proposed in the present invention is significantly better than the conventional evaporation technology.

Claims

1. A method for preparing a lignin-based hierarchical porous carbon material having large-sized micropores, characterized in that: The following steps are involved: (1) dissolving lignin in a water / organic solvent mixture, filtering and drying the residue to obtain organic solvent-insoluble lignin; (2) dissolving the organic solvent-insoluble lignin obtained in step (1) in a sodium hydroxide solution, controlling the solution pH to 10-12, adding sulfite and aldehyde, reacting at 80-100° C. for 2-4 hours, dialyzing and concentrating the reaction solution to obtain a lignin concentrate; (3) The lignin concentrate obtained in step (2) is mixed with a potassium carboxylate solution and a metal carbonate dispersion, and after sufficient stirring, the mixture is poured into a high-speed stirring organic solvent, stirred for 5 to 20 minutes, allowed to stand, filtered, and the precipitate is dried to obtain a lignin / potassium carboxylate / metal carbonate complex; (4) carbonizing the lignin / potassium carboxylate / metal carbonate complex obtained in step (3) in an inert atmosphere, soaking the carbonized product in dilute acid, filtering, and drying to obtain a lignin hierarchical porous carbon material having large-sized micropores; The mass ratio of the solute content in the lignin, sulfite, aldehyde, potassium carboxylate solution, and the metal carbonate content in the metal carbonate dispersion is 100:(30-120):(40-160):(100-300):(100-300).

2. The method for preparing a lignin graded porous carbon material with large-sized micropores according to claim 1, characterized in that: The mass ratio of the solute content in the lignin, sulfite, aldehyde, potassium carboxylate solution, and the metal carbonate content in the metal carbonate dispersion is 100: (60-80): (60-100): (150-200): (150-200); The concentration of the potassium carboxylate solution and the metal carbonate dispersion is 20-200 g / L.

3. The method for preparing a lignin graded porous carbon material with large-sized micropores according to claim 2, characterized in that: In step (1), the organic solvent is one or more of acetone, ethanol, and ethylene glycol; and the volume ratio of water to the organic solvent is 3:(5-10).

4. The method for preparing a lignin graded porous carbon material with large-sized micropores according to claim 3, characterized in that: In step (2), the sulfite is one or more of sodium sulfite and sodium bisulfite; The aldehydes are one or more of formaldehyde, glyoxal, and glutaraldehyde; The dialysis refers to dialyzing the reaction solution in deionized water using a dialysis bag with a molecular weight cut-off of 1000 Da for 20 to 30 hours; The concentration refers to heating and concentrating the lignin concentrate at 80-100° C. until the mass concentration of the lignin concentrate is 30-50%.

5. The method for preparing a lignin graded porous carbon material with large-sized micropores according to claim 4, characterized in that: In step (3), the potassium carboxylate is one or more of potassium oxalate, potassium citrate, potassium acetate, and potassium tartrate; The metal carbonate is one or more of basic zinc carbonate, basic magnesium carbonate, basic lead carbonate, and calcium carbonate; The volume ratio of the mixed liquid to the organic solvent is 1:(2-6); The organic solvent is one or more of ethanol, acetone, and ethylene glycol.

6. The method for preparing a lignin graded porous carbon material with large-sized micropores according to claim 5, characterized in that: In step (4), the carbonization temperature program is as follows: heating to 200-350°C at 5-15°C / min, maintaining for 1-2 hours; then heating to 600-900°C at 1-10°C / min, maintaining for 2-4 hours, and then cooling; The inert atmosphere is at least one of nitrogen and argon; The dilute acid refers to one or more of nitric acid, sulfuric acid and hydrochloric acid with a concentration of 0.5 to 2 mol / L, and the soaking time is 12 to 24 hours.

7. The method for preparing a lignin graded porous carbon material with large-sized micropores according to any one of claims 1 to 6, characterized in that: The lignin is at least one of bagasse alkali lignin, corncob alkali lignin, bamboo alkali lignin, wheat straw alkali lignin and enzymatic hydrolysis lignin in a biorefining process.

8. The method for preparing a lignin graded porous carbon material with large-sized micropores according to claim 7, characterized in that: In step (1), the volume ratio of water to organic solvent is 3:7; In step (2), the pH is adjusted to 11.5; In step (3), the volume ratio of the mixed solution to the organic solvent is 1:3.5-4; In step (4), the carbonization temperature program is as follows: heating to 250°C at 10°C / min and holding for 1 hour; then heating to 700°C at 5°C / min and holding for 2.5 hours; the concentration of the dilute acid is 1 mol / L; The drying method in steps (1), (3) and (4) is at least one of infrared drying, blast drying, vacuum drying and freeze drying, the drying temperature is 50-200°C and the drying time is 2-48h.

9. The lignin graded porous carbon material with large-sized micropores prepared by the method according to any one of claims 1 to 8.

10. Use of the lignin graded porous carbon material with large-sized micropores according to claim 9 in positive electrode materials for zinc ion batteries and / or positive electrode materials for zinc ion hybrid capacitors.

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