A nitrogen-doped carbon material, a preparation method and application thereof

Abstract

The application relates to the technical field of ion batteries, and discloses a nitrogen-doped carbon material and a preparation method and application thereof, wherein the preparation method of the nitrogen-doped carbon material comprises the following steps: (1) adding an acidic solution into papermaking black liquor to obtain alkali lignin; (2) dissolving the alkali lignin in a mixed solution of ammonia water and an organic solvent to obtain an alkali lignin solution; (3) carrying out hydrothermal reaction on the alkali lignin solution to obtain a pre-nitrogenation product; and (4) mixing the pre-nitrogenation product with calcium chloride, drying and pyrolyzing to obtain the nitrogen-doped carbon material; the pyrolysis temperature is 400-800 DEG C, and the pyrolysis time is 3-5 h. The nitrogen-doped carbon material is prepared by taking papermaking black liquor as a biomass raw material, efficient utilization of waste is realized, nitrogen elements in the nitrogen-doped carbon material are uniformly distributed in a carbon skeleton, the nitrogen content and the specific surface area of the nitrogen-doped carbon material can be accurately controlled through a pyrolysis process, and the adsorption and storage behaviors of the nitrogen-doped carbon material for potassium can be quantitatively controlled.

Description

Technical Field

[0001] This invention relates to the field of ion battery technology, and in particular to a nitrogen-doped carbon material, its preparation method, and its application. Background Technology

[0002] In recent years, lithium-ion batteries have been widely used due to their high energy density and safety, especially in portable mobile devices and electric vehicles. However, the relatively limited lithium resources and rapidly rising price have significantly limited the long-term application of lithium batteries. Therefore, there is an urgent need to develop new energy storage batteries with more abundant reserves and lower prices to supplement and replace lithium-ion batteries. Potassium-ion batteries, due to their low cost and high energy density, have become a potential supplement and alternative to lithium-ion batteries. Potassium ions can be intercalated into graphite structures to form intercalation compounds with a theoretical capacity of up to 279 mAh / g, thus carbon materials are considered the most promising anode materials for potassium-ion batteries. However, compared with lithium ions, the larger size of potassium ions leads to significant volume expansion of graphite materials during charge and discharge, and the reaction kinetics are slower.

[0003] In contrast, non-graphite carbon materials with less graphite structure generally exhibit better potassium storage capacity, attributed to their abundant defect structures and large specific surface area, which provide adsorption behavior in addition to intercalation. Introducing nitrogen atoms into the carbon framework can effectively increase the disorder of carbon materials, increase active sites, and thus improve their potassium storage performance. Currently, the conventional method for preparing biomass-based nitrogen-doped carbon materials is to mix biomass with nitrogen-containing compounds and then perform pyrolysis. Although this physical mixing method can successfully prepare nitrogen-doped carbon materials, it suffers from uneven nitrogen atom distribution. Furthermore, precise control of nitrogen content and specific surface area also faces challenges, making it difficult to quantitatively analyze the impact of these two key factors on potassium storage performance. Summary of the Invention

[0004] In view of this, the present invention provides a nitrogen-doped carbon material, its preparation method and its application in potassium-ion batteries, to solve the problems of uneven nitrogen atom distribution in existing nitrogen-doped carbon material preparation methods, and the difficulty in quantitatively analyzing the effects of nitrogen content and specific surface area on potassium storage performance in existing nitrogen-doped carbon material preparation methods.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] On one hand, the present invention provides a method for preparing nitrogen-doped carbon materials, comprising the following steps:

[0007] (1) Adding an acidic solution to papermaking black liquor yields alkali lignin;

[0008] (2) Dissolve the alkali lignin in a mixed solution of ammonia and organic solvent to obtain an alkali lignin solution;

[0009] (3) The alkali lignin solution is subjected to a hydrothermal reaction to obtain a pre-nitrided product;

[0010] (4) The pre-nitrided product is mixed with calcium chloride, dried and pyrolyzed to obtain nitrogen-doped carbon material;

[0011] The pyrolysis temperature is 400-800℃, and the pyrolysis time is 3-5h.

[0012] Preferably, the ratio of the alkali lignin and the mixed solution of ammonia and organic solvent in step (2) is (1-10) g: 100 mL.

[0013] Preferably, the volume ratio of ethanol to ammonia in the mixed solution of ammonia and organic solvent is 1:(2-4);

[0014] Preferably, the concentration of the ammonia water is 20-28%.

[0015] Preferably, the temperature of the hydrothermal reaction in step (3) is 100-120℃ and the time of the hydrothermal reaction is 6-12h.

[0016] Preferably, the mass ratio of calcium chloride to alkali lignin in step (4) is 1-3:1.

[0017] On the other hand, the present invention provides a nitrogen-doped carbon material prepared by any of the above-described preparation methods.

[0018] In addition, the present invention also provides a nitrogen-doped carbon material prepared by any of the above-described preparation methods, or the application of the above-described nitrogen-doped carbon material in a potassium-ion battery.

[0019] This invention provides a nitrogen-doped carbon material, its preparation method, and its applications. Compared with existing technologies, its advantages are as follows:

[0020] This invention utilizes the property of alkali lignin in papermaking black liquor. After adding an acidic solution to the papermaking black liquor, the alkali lignin precipitates and undergoes a hydrothermal reaction. After adding calcium chloride, it is pyrolyzed. During the pyrolysis process, the carbon material is catalyzed to graphitize and the carbon material is expanded to obtain nitrogen-doped carbon material.

[0021] The nitrogen element in the nitrogen-doped carbon material prepared by the method of this invention is uniformly distributed in the carbon framework through a hydrothermal grafting reaction. Furthermore, the nitrogen content and specific surface area of ​​the nitrogen-doped carbon material can be precisely controlled through the pyrolysis process, thereby quantitatively controlling the adsorption and storage behavior of the nitrogen-doped carbon material on potassium. In addition, this invention uses papermaking black liquor as a biomass raw material to prepare nitrogen-doped carbon material, realizing the efficient utilization of waste papermaking black liquor. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1 This is a graph showing the quantitative relationship between nitrogen content, specific surface area, and pyrolysis temperature of the nitrogen-doped carbon material of the present invention.

[0024] Figure 2 The image shows the SEM image of the nitrogen-doped carbon material of Example 1 of this invention.

[0025] Figure 3 This is a schematic diagram of the TEM mapping test results of the nitrogen-doped carbon material in Example 1 of the present invention;

[0026] Figure 4 This is a schematic diagram of the cycling performance of the nitrogen-doped carbon material of Example 1 of the present invention as a negative electrode material for a potassium-ion battery under the condition of 100 mA / g.

[0027] Figure 5 A schematic diagram of the cycling performance of the carbon-doped material prepared in Example 1 of this invention as a negative electrode material for a potassium-ion battery under 2000 mA / g conditions;

[0028] Figure 6 This is a schematic diagram of the cycling performance of the nitrogen-doped carbon material of Example 2 of the present invention as a negative electrode material for a potassium-ion battery under the condition of 100 mA / g.

[0029] Figure 7 This is a schematic diagram of the cycling performance of the nitrogen-doped carbon material of Example 5 of the present invention as a negative electrode material for a potassium-ion battery under the condition of 100 mA / g.

[0030] Figure 8 This is a schematic diagram of the cycling performance of nitrogen-doped carbon material as a potassium-ion battery anode material in Comparative Example 1 of the present invention under 100 mA / g conditions.

[0031] Figure 9This is a graph showing the relationship between the pyrolysis temperature and the discharge capacity and adsorption ratio of the nitrogen-doped carbon material in this invention.

[0032] Figure 10 This is a linear relationship between the ratio of nitrogen content to specific surface area and the adsorption ratio of the nitrogen-doped carbon material of the present invention. Detailed Implementation

[0033] The present invention will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments below are merely illustrative and do not limit the scope of the invention in any way. Furthermore, in the following embodiments, unless otherwise specified, the reagents and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the later embodiments, conditions and methods known in the art can be used for processing.

[0034] In one aspect of the invention, a method for preparing nitrogen-doped carbon materials is provided, comprising the following steps:

[0035] (1) Add an acidic solution to the black liquor of papermaking to obtain alkali lignin.

[0036] In some embodiments of the present invention, this step specifically involves continuously adding an acidic solution to the papermaking black liquor under stirring conditions until the pH is less than 3, at which point the alkali lignin in the papermaking black liquor is fully precipitated. Experiments have shown that the yield of alkali lignin precipitation reaches its peak when the pH reaches 3.

[0037] In some embodiments of the present invention, the papermaking black liquor from which alkali lignin is precipitated is filtered to obtain a filter cake. The filter cake is washed with deionized water to remove salts and then dried in a forced-air drying oven to obtain alkali lignin. In some embodiments of the present invention, the drying temperature is 105-120℃, for example, 105℃, 110℃, 115℃, 120℃, etc., and the drying time is 12-48h, for example, 12h, 18h, 24h, 32h, 48h, etc.

[0038] In some embodiments of the present invention, the acidic solution is added to the papermaking black liquor while it is being stirred. The acidic solution can be hydrochloric acid, sulfuric acid, etc. Since the acidic solution is only used to adjust the pH value, there are no special limitations on the type and concentration of the acidic solution; adjustments can be made according to the actual situation.

[0039] Papermaking black liquor is a type of waste biomass generated during the papermaking process. It contains a large amount of alkali lignin, is produced in large quantities annually, is concentrated in certain areas, and lacks effective treatment methods. Therefore, this invention uses papermaking black liquor as a biomass raw material and a precursor for the preparation of non-graphite carbon, achieving efficient utilization of this waste. In the embodiments of this invention, the papermaking black liquor used is wastewater from a paper mill, and its main components are alkali and alkali lignin. Since the primary objective of this invention is to precipitate alkali lignin from the papermaking black liquor, other components of the black liquor are not specifically limited.

[0040] (2) Dissolve the alkali lignin in a mixed solution of ammonia and organic solvent to obtain an alkali lignin solution.

[0041] In some embodiments of the present invention, the ratio of the mixed solution of alkali lignin, ammonia, and organic solvent is (1-10) g:100 mL, for example, 1 g:100 mL, 2 g:100 mL, 5 g:100 mL, 8 g:100 mL, 10 g:100 mL, etc. In some embodiments of the present invention, the volume ratio of organic solvent to ammonia in the mixed solution is 1:(2-4), for example, 1:2, 1:3, 1:4, etc. The concentration of ammonia is 20-28%, for example, 20%, 22%, 24%, 26%, 28%, etc. The present invention uses the mixed solution of ammonia and organic solvent as the solvent for alkali lignin, wherein the role of ammonia is to undergo a grafting reaction with alkali lignin, providing a nitrogen source for nitrogen doping; the organic solvent can be ethanol, acetone, etc., as a co-solvent to accelerate the dissolution of alkali lignin.

[0042] (3) The alkali lignin solution undergoes a hydrothermal reaction to obtain a pre-nitrided product.

[0043] In some embodiments of the present invention, this step specifically involves transferring the alkali lignin solution to a stainless steel high-pressure reactor for hydrothermal reaction. It should be noted that the hydrothermal reaction process utilizes the pressure generated by the hydrothermal process itself; no additional pressurization is required.

[0044] In some embodiments of the present invention, the temperature of the hydrothermal reaction is 100-120°C, for example, 100°C, 110°C, 120°C, etc.; the time of the hydrothermal reaction is 6-12h, for example, 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc.

[0045] (4) The pre-nitrided product is mixed with calcium chloride, dried and pyrolyzed to obtain nitrogen-doped carbon material.

[0046] In some embodiments of the present invention, before mixing the pre-nitrided product with the calcium chloride, the method further includes adjusting the pH value of the pre-nitrided product to be less than 7 to avoid the calcium chloride reacting to form calcium hydroxide. In some embodiments of the present invention, this step specifically involves transferring the pre-nitrided product to a beaker or similar container, adding an acidic solution to adjust the pH value to less than 7, then adding calcium chloride, dissolving it, and drying it in an oven. The dried pre-nitrided product is then placed in a tube furnace for pyrolysis to obtain nitrogen-doped carbon material.

[0047] In some embodiments of the present invention, the mass ratio of calcium chloride to alkali lignin is 1-3:1, for example, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, etc. By adding calcium chloride, the graphitization of carbon materials can be catalyzed during pyrolysis, and more mesopores can be formed.

[0048] In some embodiments of the present invention, the drying temperature is 105-120℃, for example, 105℃, 110℃, 115℃, 120℃, etc., and the drying time is 12-24h, for example, 12h, 15h, 20h, 24h, etc.

[0049] In some embodiments of the present invention, the pyrolysis temperature is 400-800℃, and the pyrolysis time is 3-5 hours. The pyrolysis temperature can be, for example, 400℃, 500℃, 600℃, 700℃, 800℃, etc., and the pyrolysis time can be, for example, 3 hours, 4 hours, 5 hours, etc. By adjusting the pyrolysis temperature, the nitrogen content and specific surface area of ​​the nitrogen-doped carbon material can be precisely controlled, thereby allowing quantitative control over the potassium adsorption and storage behavior of the nitrogen-doped carbon material.

[0050] The present invention does not have a particular limitation on the heating rate to the pyrolysis temperature, and it can be any rate. In the embodiments of the present invention, the heating rate is 5°C / min.

[0051] In some embodiments of the present invention, after the pyrolysis is completed, the following steps are further included: washing and drying the pyrolysis product. The washing may be performed using deionized water and ethanol 3-5 times, for example, 3, 4, or 5 times. The drying temperature is 105-120℃, for example, 105℃, 110℃, 115℃, 120℃, etc., and the drying time is 12-24 hours, for example, 12 hours, 15 hours, 20 hours, 24 hours, etc.

[0052] On the other hand, the present invention provides a nitrogen-doped carbon material prepared by any of the above-described preparation methods. Since this nitrogen-doped carbon material is prepared using the methods described above, it possesses all the features and advantages of the methods described above, which will not be repeated here.

[0053] In this invention, the nitrogen content of the nitrogen-doped carbon material is 4-10%.

[0054] In addition, the present invention also provides a nitrogen-doped carbon material prepared by any of the above-described preparation methods, or the application of the above-described nitrogen-doped carbon material in a potassium-ion battery.

[0055] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. The embodiments of this application are only examples, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] Example 1

[0057] This embodiment provides a method for preparing nitrogen-doped carbon materials, which is carried out according to the following steps:

[0058] (1) Take 100 mL of papermaking black liquor and place it in a beaker. Add concentrated hydrochloric acid continuously at a speed of 800 rpm until the pH value is less than 3, and alkali lignin is fully precipitated. Filter the papermaking black liquor from which alkali lignin is precipitated to obtain a filter cake. Wash the filter cake with deionized water and then dry it in a 110℃ forced-air drying oven for 24 h to obtain alkali lignin.

[0059] (2) Add 5g of the alkali lignin obtained in step (1) to a mixed solution of 20mL ethanol and 80mL concentrated ammonia, and stir continuously until completely dissolved to obtain an alkali lignin solution.

[0060] (3) Transfer the alkali lignin solution to a stainless steel high-pressure reactor and keep it at 120°C for 12 hours to carry out a hydrothermal reaction to obtain the pre-nitrided product.

[0061] (4) Transfer the pre-nitrided product to a beaker, continuously add concentrated hydrochloric acid to the beaker until the pH value is less than 7, then add 10g of calcium chloride, dissolve it, and place it in an oven to dry at 120℃ for 48h.

[0062] (5) The dried product from step (4) is placed in a tube furnace for pyrolysis and carbonization. The temperature is increased from room temperature to pyrolysis temperature at a rate of 5℃ / min. The pyrolysis temperature is 600℃ and the pyrolysis time is 3h.

[0063] (6) The pyrolysis product of step (5) is washed three times each with deionized water and ethanol, and dried at 105°C for 12 hours to obtain nitrogen-doped carbon material.

[0064] Example 2

[0065] This embodiment is basically the same as embodiment 1, except that the pyrolysis temperature in step (5) is 400℃.

[0066] Example 3

[0067] This embodiment is basically the same as embodiment 1, except that the pyrolysis temperature in step (5) is 500℃.

[0068] Example 4

[0069] This embodiment is basically the same as embodiment 1, except that the pyrolysis temperature in step (5) is 700℃.

[0070] Example 5

[0071] This embodiment is basically the same as embodiment 1, except that the pyrolysis temperature in step (5) is 800℃.

[0072] Figure 1 The graph shows the quantitative relationship between nitrogen content and specific surface area of ​​nitrogen-doped carbon materials and pyrolysis temperature. It can be seen from the graph that under pyrolysis temperatures of 400℃, 500℃, 600℃, 700℃, and 800℃, the nitrogen content of the carbon materials is 9.36%, 7.82%, 6.33%, 4.78%, and 4.07%, respectively, and the specific surface area is 127 m². 2 / g、225m 2 / g、335m 2 / g、441m 2 / g、523m 2 / g. Both nitrogen content and specific surface area show a precise linear relationship with pyrolysis temperature, indicating that the nitrogen content and specific surface area of ​​nitrogen-doped carbon materials can be precisely controlled by adjusting the pyrolysis temperature using the method of this invention.

[0073] Figure 2 The image shows a SEM image of the nitrogen-doped carbon material obtained in Example 1. As can be seen from the image, the nitrogen-doped carbon material is composed of irregular carbon block agglomerations and has abundant morphological defects on its surface, which is beneficial to the improvement of battery performance.

[0074] Figure 3 The figure shows the mapping test results of the nitrogen-doped carbon material obtained in Example 1. As can be seen from the figure, the nitrogen element in the nitrogen-doped carbon material is uniformly distributed in the carbon framework.

[0075] Comparative Example 1

[0076] This comparative example is basically the same as Example 1, except that step (3) is omitted, that is, the alkali lignin solution is not subjected to hydrothermal reaction.

[0077] Application examples

[0078] The nitrogen-doped carbon materials prepared in Examples 1, 2, 5, and Comparative Example 1 were mixed with a conductive agent and polyvinylidene fluoride at a mass ratio of 8:1:1. Methylpyrrolidone was added and mixed to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After thorough drying, the slurry was punched into circular electrode sheets and assembled into coin cells in a glove box. The assembly conditions were as follows: potassium metal was used as the counter electrode; a 1 mol / L KN(SO₂F)₂ solution of ethylene carbonate and diethyl carbonate (volume ratio 1:1) was used as the electrolyte; glass fiber GF / D was used as the separator; and after standing for 1 hour, constant current charge-discharge tests were performed using a CT3001A blue battery testing system, with a voltage range of 0.01-3V.

[0079] Figure 4 The figure shows the cycling performance of the nitrogen-doped carbon material obtained in Example 1 as a negative electrode material for potassium-ion batteries under the condition of 100 mA / g. As can be seen from the figure, the nitrogen-doped carbon material can still achieve a discharge capacity of 467.3 mAh / g after 200 cycles, with a capacity retention rate of 97.95%.

[0080] Figure 5 The figure shows the cycling performance of the nitrogen-doped carbon material obtained in Example 1 as a negative electrode material for potassium-ion batteries under the condition of 2000 mA / g. As can be seen from the figure, the nitrogen-doped carbon material still has a discharge capacity of 183.7 mAh / g after 5000 cycles, with a capacity retention rate of 89.9%.

[0081] Figure 6 The figure shows the cycling performance of the nitrogen-doped carbon material obtained in Example 2 as a negative electrode material for potassium-ion batteries under the condition of 100 mA / g. As can be seen from the figure, the nitrogen-doped carbon material still has a discharge capacity of 295.6 mAh / g after 200 cycles, with a capacity retention rate of 96.74%.

[0082] Figure 7 The figure shows the cycling performance of the nitrogen-doped carbon material obtained in Example 5 as a negative electrode material for potassium-ion batteries under the condition of 100 mA / g. As can be seen from the figure, the nitrogen-doped carbon material can still achieve a discharge capacity of 183.2 mAh / g after 200 cycles, with a capacity retention rate of 97.82%.

[0083] Figure 8 The figure shows the cycling performance of the undoped carbon material obtained in Comparative Example 1 as a negative electrode material for potassium-ion batteries under 100 mA / g conditions. As can be seen from the figure, after 200 cycles, the discharge capacity of this material is only 76.8 mAh / g, with a capacity retention of 56.63%. This indicates that nitrogen doping can effectively increase the defect sites in the material and improve its adsorption capacity for potassium ions.

[0084] Figure 9The graph shows the relationship between the pyrolysis temperature and the discharge capacity and adsorption ratio of the nitrogen-doped carbon material. As can be seen from the graph, with the increase of pyrolysis temperature, the adsorption ratio of the nitrogen-doped carbon material gradually decreases and shows a certain linear relationship. The intercalation capacity and adsorption capacity both show a trend of first increasing and then decreasing. The discharge capacity is optimal at a pyrolysis temperature of 600℃.

[0085] Figure 10 The graph shows a linear relationship between the ratio of nitrogen content to specific surface area and the adsorption ratio of the nitrogen-doped carbon material of the present invention, indicating that the present invention can quantitatively control the adsorption behavior of potassium ions.

[0086] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a nitrogen-doped carbon material, characterized in that, Includes the following steps: (1) Adding an acidic solution to papermaking black liquor yields alkali lignin; (2) Dissolve the alkali lignin in a mixed solution of ammonia and organic solvent to obtain an alkali lignin solution; (3) The alkali lignin solution is subjected to a hydrothermal reaction to obtain a pre-nitrided product; (4) The pre-nitrided product is mixed with calcium chloride, dried and pyrolyzed to obtain nitrogen-doped carbon material; The pyrolysis temperature is 400-800℃, and the pyrolysis time is 3-5h.

2. The method for preparing nitrogen-doped carbon material according to claim 1, characterized in that, The ratio of the alkali lignin and the mixed solution of ammonia and organic solvent in step (2) is (1-10) g: 100 mL.

3. The method for preparing nitrogen-doped carbon material according to claim 1, characterized in that, The volume ratio of organic solvent to ammonia in the mixed solution of ammonia and organic solvent is 1:(2-4).

4. The method for preparing nitrogen-doped carbon material according to any one of claims 1-3, characterized in that, The mass concentration of the ammonia water is 20-28%.

5. The method for preparing nitrogen-doped carbon material according to claim 1, characterized in that, The hydrothermal reaction in step (3) is carried out at a temperature of 100-120℃ for 6-12 hours.

6. The method for preparing nitrogen-doped carbon material according to claim 1, characterized in that, The mass ratio of calcium chloride to alkali lignin in step (4) is 1-3:

1.

7. The method for preparing nitrogen-doped carbon material according to any one of claims 1-6, characterized in that, Step (4) further includes adjusting the pH value of the pre-nitrided product to less than 7 before mixing the pre-nitrided product with the calcium chloride.

8. A nitrogen-doped carbon material prepared by the preparation method according to any one of claims 1-7.

9. The application of a nitrogen-doped carbon material prepared by the preparation method according to any one of claims 1-7 or the nitrogen-doped carbon material according to claim 8 in a potassium-ion battery.

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