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

Abstract

The application provides a nitrogen-doped carbon material and a preparation method and application thereof. The method comprises the following steps: S1, purifying a coal raw material through acid washing, and then washing the coal raw material to neutral to obtain a coal-based precursor; S2, performing a hydrothermal reaction on the coal-based precursor and a saccharide compound in water, so that carboxyl functional groups of the coal-based precursor react with hydroxyl functional groups of the saccharide compound, and then drying the reaction product to obtain a composite precursor; S3, performing pyrolysis on the composite precursor to obtain a pyrolysis product; S4, performing nitrogen doping on the pyrolysis product to obtain a nitrogen-doped intermediate; and S5, performing carbonization on the nitrogen-doped intermediate to obtain the nitrogen-doped carbon material. The method provided by the application first washes the coal, then completes crosslinking of the coal and the saccharide compound in a hydrothermal process, then further stabilizes the structure in a subsequent pyrolysis stage, and then performs nitrogen doping and carbonization. The preparation method is simple, the prepared carbon material has few surface defects, and the reversible discharge specific capacity and the first coulombic efficiency are obviously improved.

Description

Technical Field

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

[0002] With the development of the new energy industry, lithium-ion batteries have been widely used in electric vehicles and other industries. However, their further development is constrained by a series of key issues, such as lithium resource reserves and the cost of lithium-ion batteries. Sodium-ion batteries have the advantages of low cost and abundant and widely distributed sodium reserves. Hard carbon, as the main negative electrode material for sodium-ion batteries, has a disordered amorphous structure that results in more defects and micropores in the material itself. These defects and micropores can serve as active sodium storage sites.

[0003] Sucrose has poor stability, and when hard carbon materials prepared by direct pyrolysis are used as anodes in sodium-ion batteries, they exhibit rapid capacity decay and low initial coulombic efficiency, failing to meet practical applications. This is mainly due to the formation of an SEI film over a large specific surface area and the irreversible intercalation of sodium ions into the material.

[0004] When using coal to prepare hard carbon materials, the impurity content of coal is relatively high and the surface contains a large number of functional groups. Hard carbon materials obtained by direct pyrolysis also have problems such as low sodium deintercalation / intercalation capacity and low initial coulombic efficiency.

[0005] Comparative document CN105185997B describes a method that mixes coal and hard carbon precursors, spray-dries them into pellets, and then pyrolyzes them at 400–600°C in an inert atmosphere, followed by carbonization at 1000–1600°C in an inert atmosphere. The problem with this method is that the direct mixing and spray-drying of the precursors results in low cross-linking between the coal and hard carbon precursors, poor stability during pyrolysis, high weight loss, and a higher specific surface area of ​​the pyrolysis products. This also makes it difficult to form closed-cell structures during subsequent carbonization.

[0006] The content of the background section is merely the technology known to the inventor and does not necessarily represent the prior art in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a nitrogen-doped carbon material and its preparation method. The method is simple and easy to operate, and the nitrogen-doped carbon material has the advantages of high reversible discharge specific capacity and high initial coulombic efficiency.

[0008] To achieve the above objectives, the first aspect of this application provides a nitrogen-doped carbon material, wherein the nitrogen content of the nitrogen-doped carbon material is 4-8 wt%, and the area ratio A of the amorphous carbon peak to the graphitized carbon peak is... D / A G The value is 2.2~2.5, and the closed-cell volume is 0.05~0.1cm³. 2 / g, with closed-pore diameters ranging from 0.1 to 4 nm.

[0009] The nitrogen-doped carbon material provided in this application has advantages such as high reversible discharge specific capacity and high initial coulombic efficiency.

[0010] In some embodiments of this application, the nitrogen-doped carbon material satisfies at least one of the following conditions:

[0011] a) The median particle size D of the nitrogen-doped carbon material 50 ≤10μm, optionally 5~7μm;

[0012] b) The carbon interlayer spacing d of the nitrogen-doped carbon material 002 ≥0.35nm, optionally 0.38~0.39nm;

[0013] c) The specific surface area of ​​the nitrogen-doped carbon material is ≤10 cm². 2 / g, optionally 4~5cm 2 / g;

[0014] d) The compaction density of the nitrogen-doped carbon material is ≥1.0 g / cm³. 3 The optional concentration is 1.25~1.30 g / cm³. 3 ;

[0015] e) The closed-pore volume of the nitrogen-doped carbon material is 0.065~0.085 cm³. 2 / g, with closed-pore diameter of 1~3nm.

[0016] The smaller particle size and higher compaction density of carbon materials are beneficial for improving their electrochemical performance. Their smaller specific surface area, fewer surface defects, and larger interlayer spacing provide more sodium storage sites.

[0017] The second method of this application provides a method for preparing nitrogen-doped carbon materials, including the following steps:

[0018] S1: After acid washing and purification of coal raw materials, the coal is washed with water until neutral to obtain coal-based precursors;

[0019] S2: The coal-based precursor is mixed with a carbohydrate compound and subjected to a hydrothermal reaction, so that the carboxyl functional group of the coal-based precursor reacts with the hydroxyl functional group of the carbohydrate compound. The reaction product is then dried to obtain a composite precursor.

[0020] S3: Pyrolyze the composite precursor to obtain pyrolysis products;

[0021] S4: The pyrolysis product is nitrogen-doped to obtain a nitrogen-doped intermediate; and

[0022] S5: Carbonize the nitrogen-doped intermediate to obtain the nitrogen-doped carbon material.

[0023] The method provided in this application first cleans the coal, then completes the cross-linking of coal and carbohydrate compounds in a hydrothermal process, further stabilizes the structure in a subsequent pyrolysis stage, and then performs nitrogen doping and carbonization. The preparation method is simple, and the resulting carbon material has fewer surface defects and significantly improved reversible discharge specific capacity and initial coulombic efficiency.

[0024] In some embodiments of this application, in step S1, the acid used for pickling includes one or more of hypochlorous acid, hydrochloric acid, hydrofluoric acid, and nitric acid;

[0025] And / or, the concentration of the acid used for pickling is 0.5~5 mol / L;

[0026] And / or, the acid used for pickling is a mixture of hypochlorous acid and nitric acid, wherein the volume ratio of hypochlorous acid to nitric acid is 1:(1~3).

[0027] And / or, the coal raw material includes one or more of bituminous coal, anthracite, and lignite.

[0028] This step, through acid washing and water washing, yields a coal-based precursor with high purity.

[0029] In some embodiments of this application, in step S2, the mass ratio of the coal-based precursor to the carbohydrate compound is 1:(1~2).

[0030] And / or, the temperature of the hydrothermal reaction is 150~200℃, and the reaction time is 18~24h;

[0031] And / or, the carbohydrate compound includes one or more of sucrose, glucose, maltose, fructose, and galactose;

[0032] And / or, the drying process is selected from any one of ambient temperature drying, freeze drying, and heat drying;

[0033] And / or, the drying is selected from heat drying, and the drying temperature is 80~100℃.

[0034] In this step, the carboxyl functional groups of coal react with the hydroxyl functional groups of carbohydrate compounds, thereby cross-linking them and improving the stability of the structure.

[0035] In some embodiments of this application, in step S3, the pyrolysis is carried out in a protective atmosphere, which is selected from one or more of argon, nitrogen, helium, and xenon.

[0036] And / or, the flow rate of the protective atmosphere gas during the pyrolysis process is 100~1000 mL / min;

[0037] And / or, the pyrolysis temperature is 400~600℃;

[0038] And / or, the pyrolysis time is 2~6 hours;

[0039] And / or, the heating rate before the pyrolysis treatment is 1~10℃ / min;

[0040] And / or, the composite precursor has a weight loss rate of 15-30% during the pyrolysis process, and the specific surface area of ​​the pyrolysis product is 100-400 cm². 2 / g.

[0041] Through this step, the carbohydrates are pyrolyzed into gases and released, and the carbohydrates are carbonized. This allows the coal and carbohydrates to cross-link better, improving the stability of the structure.

[0042] In some embodiments of this application, step S4 includes:

[0043] The pyrolysis product is heat-treated under a nitrogen-containing atmosphere to obtain the nitrogen-doped intermediate; or

[0044] The pyrolysis product is mixed with a solid or liquid nitrogen source and then subjected to heat treatment to obtain the nitrogen-doped intermediate.

[0045] Optionally, the heat treatment temperature is 700~900℃, the time is 2~4h, and the heating rate is 2~7℃ / min;

[0046] And / or, the flow rate of the nitrogen-containing atmosphere is 200~600 mL / min;

[0047] And / or, the nitrogen-containing atmosphere includes ammonia;

[0048] And / or, the nitrogen-containing atmosphere includes a protective gas selected from one or more of argon, nitrogen, helium, and xenon; and / or

[0049] The solid nitrogen source includes one or more of urea, melamine, and dicyandiamide; and / or,

[0050] The liquid nitrogen source includes one or more of ethylenediamine, dopamine, aniline, triethanolamine, and triethylenetetraethylamine.

[0051] This step completes the nitrogen doping process.

[0052] In some embodiments of this application, in step S5, the carbonization is carried out in a protective atmosphere selected from one or more of argon, nitrogen, helium, and xenon.

[0053] And / or, the flow rate of the protective atmosphere gas during the carbonization process is 100~1000 mL / min;

[0054] And / or, the carbonization temperature is 1200~1400℃;

[0055] And / or, the carbonization time is 2-4 hours;

[0056] And / or, the heating rate before carbonization is 1~10℃ / min.

[0057] This step involves the final carbonization of the coal to ultimately produce nitrogen-doped carbon materials.

[0058] A third aspect of this application provides a negative electrode sheet comprising the nitrogen-doped carbon material described above or a nitrogen-doped carbon material prepared by the above preparation method.

[0059] A fourth aspect of this application provides a sodium-ion battery comprising the aforementioned negative electrode.

[0060] The sodium-ion battery provided in this application exhibits superior performance in terms of initial coulombic efficiency and reversible discharge specific capacity. This application comprehensively improves the performance of the finished battery.

[0061] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0062] The accompanying drawings, which form part of this disclosure, are used to provide a further understanding of this disclosure. The illustrative embodiments of this disclosure and their descriptions are used to explain this disclosure and do not constitute an undue limitation of this disclosure.

[0063] Figure 1 This is a process flow diagram for preparing nitrogen-doped carbon materials according to an embodiment of this application;

[0064] Figure 2 This is a SEM image of the nitrogen-doped carbon material provided in Example 1 of this application, with a magnification of 5000×; and

[0065] Figure 3 This is another SEM image of the nitrogen-doped carbon material provided in Example 1 of this application, with a magnification of 30000×. Detailed Implementation

[0066] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0067] The following disclosure provides many different embodiments or examples for implementing the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0068] Furthermore, unless otherwise specified, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It will also be understood that terms, such as those defined in common dictionaries, shall be interpreted as having the same meaning as they have in the context of the relevant technology and the invention, and shall not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0069] Taking into account the measurements discussed and the errors associated with the measurement of a particular quantity (i.e., limitations of the measurement system), as used herein, “about” or “approximately” includes the stated value and means within an acceptable range of deviation from the particular value as determined by a person skilled in the art. For example, “about” may mean within one or more standard deviations, or within ±30%, ±20%, ±10%, or ±5% of the stated value.

[0070] The specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings and examples, so as to better understand the solution of the present invention and its advantages in various aspects. However, the specific embodiments and examples described below are for illustrative purposes only and are not intended to limit the present invention.

[0071] The nitrogen-doped carbon material provided in this application has a nitrogen content of 4-8 wt%, and the area ratio A of the amorphous carbon peaks to the graphitized carbon peaks is... D / A G The value is 2.2~2.5, and the closed-cell volume is 0.05~0.1cm³. 2 / g, with closed-pore diameters ranging from 0.1 to 4 nm. The nitrogen-doped carbon material provided in this application has advantages such as high reversible discharge specific capacity and high initial coulombic efficiency.

[0072] In some specific embodiments, the nitrogen content of the nitrogen-doped carbon material can be 4 wt%, 5 wt%, 6 wt%, 7 wt%, or 8 wt%. In some specific embodiments, the area ratio A of the amorphous carbon peak to the graphitized carbon peak is... D / A GIt can be 2.2, 2.25, 2.3, 2.35, 2.4, 2.45 or 2.5.

[0073] In some specific embodiments, the closed-pore volume of the nitrogen-doped carbon material is 0.065~0.085 cm³. 2 / g, for example, 0.065cm 2 / g, 0.07cm 2 / g, 0.075cm 2 / g, 0.08cm 2 / g or 0.085cm 2 / g. In some specific embodiments, the closed-pore diameter of the nitrogen-doped carbon material is 1~3nm, for example 1nm, 1.5nm, 2nm, 2.5nm or 3nm.

[0074] Optionally, the median particle size D of the nitrogen-doped carbon material 50 ≤10μm, and more preferably 5~7μm. In some specific embodiments, D 50 The particle size can be 5 μm, 5.2 μm, 5.4 μm, 5.6 μm, 5.8 μm, 6.0 μm, 6.2 μm, 6.4 μm, 6.6 μm, 6.8 μm, or 7 μm. The smaller particle size of nitrogen-doped carbon materials is beneficial for improving their electrochemical performance.

[0075] Optionally, the carbon layer spacing d of the nitrogen-doped carbon material 002 ≥0.35nm, and more preferably 0.38~0.39nm. In some specific embodiments, d 002 The nanometers can be 0.38nm, 0.382nm, 0.384nm, 0.386nm, 0.388nm, or 0.39nm. Nitrogen-doped carbon materials have larger carbon interlayer spacing, which can provide more sodium storage sites, resulting in sodium-ion batteries with better performance.

[0076] Optionally, the specific surface area of ​​the nitrogen-doped carbon material is ≤10 cm². 2 / g, and optionally 4~6cm 2 / g. In some specific embodiments, the specific surface area can be 4cm². 2 / g, 4.2cm 2 / g, 4.4cm 2 / g, 4.6cm 2 / g, 4.8cm 2 / g, 5cm 2 / g, 5.2cm 2 / g, 5.4cm 2 / g, 5.6cm 2 / g, 5.8cm 2 / g or 6cm 2 / g. Nitrogen-doped carbon materials have a smaller specific surface area and fewer surface defects, which can provide more sodium storage sites.

[0077] Optionally, the compaction density of the nitrogen-doped carbon material is ≥1.0 g / cm³. 3 Further optionally, it is 1.25~1.30 g / cm³. 3 In some specific embodiments, the compaction density can be 1.25 g / cm³. 3 1.26 g / cm 3 1.27g / cm 3 1.28g / cm 3 1.29g / cm 3 Or 1.30g / cm 3 Nitrogen-doped carbon materials have a higher compaction density, which is beneficial for improving the electrochemical performance of the materials.

[0078] Figure 1 This application illustrates a method for preparing a nitrogen-doped carbon material according to an embodiment of the present application, comprising the following steps S1 to S5.

[0079] S1: After acid washing and purification of the coal raw material, it is washed with water until neutral to obtain the coal-based precursor.

[0080] Optionally, the coal raw material includes one or more of bituminous coal, anthracite, and lignite; more preferably, the coal raw material includes lignite. Optionally, the acid used for pickling includes one or more of hypochlorous acid, hydrochloric acid, hydrofluoric acid, and nitric acid. In some specific embodiments, the acid can be a mixed acid, such as a mixture of hypochlorous acid and nitric acid, or a mixture of hypochlorous acid and hydrochloric acid. In some specific embodiments, the concentration of hypochlorous acid can be 1-2 mol / L, the concentration of nitric acid can be 2-4 mol / L, and the volume ratio of hypochlorous acid to nitric acid is 1:(1-3). The coal raw material has a relatively high impurity content, which can be removed by pickling. This step, through pickling and water washing, yields a relatively clean coal-based precursor.

[0081] S2: The coal-based precursor is mixed with a carbohydrate compound and subjected to a hydrothermal reaction, which allows the carboxyl functional group of the coal-based precursor to react with the hydroxyl functional group of the carbohydrate compound. The reaction product is then dried to obtain a composite precursor.

[0082] Optionally, the carbohydrate compound includes one or more of sucrose, glucose, maltose, fructose, and galactose.

[0083] Coal contains a large number of carboxyl functional groups, while carbohydrates contain a large number of hydroxyl functional groups. During the hydrothermal reaction in water, the carboxyl and hydroxyl functional groups can react to crosslink the coal and carbohydrates.

[0084] Optionally, the hydrothermal reaction temperature is 150-200℃, and the reaction time is 18-24 hours. In some specific embodiments, the hydrothermal reaction temperature can be 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, or 200℃. In some specific embodiments, the hydrothermal reaction time can be 18 hours, 18.5 hours, 19 hours, 19.5 hours, 20 hours, 20.5 hours, 21 hours, 21.5 hours, 22 hours, 22.5 hours, 23 hours, 23.5 hours, or 24 hours. Carbohydrates undergo dehydration at 150-200℃, which promotes hydrogen bond formation and intermolecular interactions, improving the structural stability of the complex precursor.

[0085] At temperatures above 200℃, especially between 200 and 400℃, carbohydrate compounds rapidly lose weight due to intense dehydration, accompanied by adhesion and foaming processes, preventing them from cross-linking with coal-based precursors to form an interpenetrating network. Above 400℃, the carbohydrate compounds essentially complete the carbonization process.

[0086] Optionally, the mass ratio of coal-based precursor to carbohydrate compounds is 1:(1~2). In some specific embodiments, the mass ratio of coal-based precursor to carbohydrate compounds can be 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, or 1:2. Within this range, the coal-based precursor and carbohydrate compounds cross-link to form an interpenetrating network structure. Furthermore, the cross-linking of carbohydrate compounds with the groups in the coal reduces the gelatinization of carbohydrate compounds during subsequent processing. If the ratio is too high, the carbohydrate compounds will gelatinize during the subsequent high-temperature process, adhering to the surface of the coal-based precursor, which is detrimental to the pyrolysis of the coal. If the ratio is too low, it will not be able to reduce surface defects in the coal-based precursor.

[0087] Optionally, the drying process is selected from any one of ambient temperature drying, freeze drying, and heat drying;

[0088] Optionally, drying is selected from heat drying, and the drying temperature is 80~100°C. In some specific embodiments, the drying temperature is 80°C, 85°C, 90°C, 95°C, or 100°C. Drying temperatures below 100°C are only used to remove moisture from the composite precursor.

[0089] In this step, the carboxyl functional groups of coal react with the hydroxyl functional groups of carbohydrate compounds, thereby cross-linking them and improving structural stability. Furthermore, the dehydration reaction of the carbohydrate compounds during hydrothermal processing promotes hydrogen bond formation and intermolecular interactions.

[0090] This application utilizes a hydrothermal process at low temperatures, which can enhance the cross-linking degree between coal and sucrose. On one hand, this improves the structural stability of the composite precursor, preventing gelatinization of the sugar compounds and damage to the molecular structure during subsequent high-temperature pyrolysis. On the other hand, it facilitates pore shrinkage during the subsequent carbonization process, forming more closed-pore structures.

[0091] S3: Pyrolyze the composite precursor to obtain the pyrolysis product.

[0092] Optionally, the pyrolysis process is carried out in a protective atmosphere, which is selected from one or more of argon, nitrogen, helium, and xenon. Optionally, the gas flow rate of the protective atmosphere during pyrolysis is 100~1000 mL / min, the pyrolysis temperature is 400~600℃, the pyrolysis time is 2~6 h, and the heating rate is 1~10℃ / min. In some specific embodiments, the gas flow rate of the protective atmosphere during pyrolysis is 100 mL / min, 200 mL / min, 300 mL / min, 400 mL / min, 500 mL / min, 600 mL / min, 700 mL / min, 800 mL / min, 900 mL / min, or 1000 mL / min. In some specific embodiments, the pyrolysis temperature can be 400℃, 430℃, 450℃, 470℃, 500℃, 520℃, 540℃, 560℃, 580℃, or 600℃. In some specific embodiments, the pyrolysis time can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or 6h. In some specific embodiments, the heating rate is 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min.

[0093] The composite precursor experiences a weight loss of 15-30% during pyrolysis, and the specific surface area of ​​the pyrolysis products obtained after pyrolysis is 100-400 cm². 2 / g. In some specific embodiments, the weight loss rate of the composite precursor during pyrolysis is 15%, 17%, 19%, 21%, 23%, 25%, 27%, 29%, or 30%. In some specific embodiments, the specific surface area of ​​the pyrolysis product obtained after pyrolysis is 100 cm². 2 / g, 150cm 2 / g、200cm 2 / g、250cm 2 / g、300cm 2 / g, 350cm 2 / g or 400cm 2 / g.

[0094] Before the temperature rises to 400-600℃, for example, within the range of 200-400℃, carbohydrate compounds rapidly lose weight due to intense dehydration, accompanied by adhesion and foaming processes, thus better cross-linking with the coal. In this temperature range, the coal also undergoes partial pyrolysis, primarily thermoplastic pyrolysis. After heating to 400-600℃, the carbohydrate compounds are essentially carbonized, and the coal undergoes thermosetting pyrolysis.

[0095] Within this pyrolysis temperature range, the molecular structure of the cross-linked composite precursor can be stabilized, and secondary cross-linking of coal is beneficial. Furthermore, the pyrolysis of carbohydrates into organic gases releases, making the material structure more stable and enabling the formation of a porous structure within the material.

[0096] Optionally, this step can be performed in an inert gas, such as argon or helium.

[0097] Through this step, the carbohydrates are carbonized, the high molecular weight organic matter in the coal is released through pyrolysis, and the coal and carbohydrates can be better cross-linked together, improving the stability of the structure.

[0098] S4: Nitrogen doping of the pyrolysis products yields nitrogen-doped intermediates.

[0099] Optionally, in this step, the nitrogen source can be a gaseous nitrogen source, a solid nitrogen source, or a liquid nitrogen source.

[0100] When the nitrogen source is a gaseous nitrogen source, this step can be: heat-treating the pyrolysis product under a nitrogen-containing atmosphere to obtain a nitrogen-doped intermediate.

[0101] Optionally, the nitrogen-containing atmosphere includes ammonia. Further, the nitrogen-containing atmosphere also includes a protective gas selected from one or more of argon, nitrogen, helium, and xenon. In some specific embodiments, the volume ratio of ammonia to the protective gas in the nitrogen-containing atmosphere is 1:(1~3), for example, 1:1, 1:2, or 1:3.

[0102] Optionally, the flow rate of the nitrogen-containing atmosphere is 200–600 mL / min. In some specific embodiments, the flow rate of the nitrogen-containing atmosphere is 200 mL / min, 250 mL / min, 300 mL / min, 350 mL / min, 400 mL / min, 450 mL / min, 500 mL / min, 550 mL / min, or 600 mL / min. At this flow rate, more nitrogen can be incorporated into the pyrolysis products.

[0103] When the nitrogen source is a solid or liquid nitrogen source, this step may be as follows: The pyrolysis product is mixed with the solid or liquid nitrogen source and then subjected to heat treatment to obtain a nitrogen-doped intermediate. Optionally, the solid nitrogen source includes one or more of urea, melamine, and dicyandiamide. Optionally, the liquid nitrogen source includes one or more of ethylenediamine, dopamine, aniline, triethanolamine, and triethylenetetraethylamine.

[0104] Optionally, the heat treatment temperature in this step is 700~900℃, the time is 2~4h, and the heating rate is 2~7℃ / min. In some specific embodiments, the heating temperature can be 700℃, 720℃, 740℃, 760℃, 780℃, 800℃, 820℃, 840℃, 860℃, 880℃, or 900℃. In some specific embodiments, the heating time can be 2h, 2.5h, 3h, 3.5h, or 4h. In some specific embodiments, the heating rate can be 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min, 5.5℃ / min, 6℃ / min, 6.5℃ / min, or 7℃ / min. At the above temperatures and times, nitrogen doping is more favorable. Slow heating also facilitates the doping of more nitrogen.

[0105] This step completes nitrogen doping, with a doping amount of 4-8 wt%. Nitrogen doping in the pyrolysis products can increase the carbon interlayer spacing and improve the sodium ion transport rate.

[0106] S5: Carbonize the nitrogen-doped intermediate to obtain nitrogen-doped carbon materials.

[0107] Optionally, the carbonization process is carried out in a protective atmosphere, which is selected from one or more of argon, nitrogen, helium, and xenon. Optionally, the gas flow rate of the protective atmosphere during carbonization is 100~1000 mL / min, the carbonization temperature is 1200~1400℃, the carbonization time is 2~4 h, and the heating rate is 1~10℃ / min. In some specific embodiments, the gas flow rate of the protective atmosphere during carbonization is 100 mL / min, 200 mL / min, 300 mL / min, 400 mL / min, 500 mL / min, 600 mL / min, 700 mL / min, 800 mL / min, 900 mL / min, or 1000 mL / min. In some specific embodiments, the carbonization temperature may be 1200℃, 1220℃, 1240℃, 1260℃, 1280℃, 1300℃, 1320℃, 1340℃, 1360℃, 1380℃, or 1400℃. In some specific embodiments, the carbonization time may be 2h, 2.5h, 3h, 3.5h, or 4h. In some specific embodiments, the heating rate is 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min.

[0108] This step involves the final carbonization of the coal to obtain nitrogen-doped carbon material. After high-temperature carbonization, the pores inside the material shrink, and some pores become closed pores, which is beneficial for sodium ion storage. The closed-pore volume of the nitrogen-doped carbon material is 0.05~0.1 cm³. 2 / g, with closed-pore diameters ranging from 0.1 to 4 nm.

[0109] The method provided in this application first purifies the coal, then completes the cross-linking of coal and carbohydrate compounds in a hydrothermal process, further stabilizes the structure in a subsequent pyrolysis stage, and then performs nitrogen doping and carbonization. The preparation method is simple, and the resulting carbon material has fewer surface defects and significantly improved reversible discharge specific capacity and initial coulombic efficiency.

[0110] This application further provides a negative electrode, comprising the above-described nitrogen-doped carbon material or nitrogen-doped carbon material prepared by the above-described preparation method.

[0111] A negative electrode typically includes a negative current collector and a negative electrode film layer disposed on the negative current collector, wherein the negative electrode film layer may include the aforementioned nitrogen-doped carbon material.

[0112] The current collector can be a metal foil, such as aluminum foil or copper foil, with copper foil being preferred. The negative electrode film layer may also include binders and conductive agents. Binders can be, for example, styrene-butadiene rubber (SBR), polyvinylidene chloride (PVDF), polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC-Na), sodium alginate, etc. Conductive agents can be, for example, graphene, carbon nanotubes, Ketjen black, conductive carbon black (SP), etc. Optionally, the negative electrode film layer may also include other additives, such as dispersants (e.g., carboxymethyl cellulose (CMC)).

[0113] This application also provides a sodium-ion battery comprising the aforementioned negative electrode.

[0114] The sodium-ion battery described in this application is a secondary battery, meaning it can be reused after discharge by recharging to activate the active materials. Typically, a secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, serves as a barrier. The electrolyte, acting as a conductor of ions, separates the positive and negative electrodes.

[0115] The positive electrode may include a current collector and a positive electrode film. The current collector may be a metal foil, such as aluminum foil or copper foil. The specific type of active material in the positive electrode film is not limited and can be selected according to actual needs. This application also does not limit the types of separator and electrolyte, which can be selected according to actual needs.

[0116] The sodium-ion battery provided in this application exhibits superior performance in terms of initial coulombic efficiency and reversible discharge specific capacity. This application comprehensively improves the performance of the finished battery.

[0117] The present invention will now be described with reference to specific embodiments. The process conditions and values ​​used in the following embodiments and comparative examples are exemplary, and their possible ranges are as shown in the foregoing description of the invention. For process parameters not specifically noted, conventional techniques can be used. Unless otherwise specified, the reagents and instruments used in the technical solutions provided by the present invention can all be purchased from conventional channels or the market. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0118] Example 1

[0119] This embodiment prepares a nitrogen-doped carbon material, and the specific steps are as follows:

[0120] S1: Lignite is purified by acid washing with a mixture of hypochlorous acid and nitric acid, and then washed with water until neutral to obtain a coal-based precursor. The concentration of hypochlorous acid in the mixed acid is 1 mol / L, the concentration of nitric acid is 3 mol / L, and the volume ratio of hypochlorous acid to nitric acid is 1:1.

[0121] S2: A coal-based precursor and sucrose were mixed at a 1:1 mass ratio, and deionized water was added to carry out a hydrothermal reaction in a reactor. The reaction product was then dried to obtain a composite precursor. The hydrothermal reaction temperature was 200℃, and the reaction time was 18 hours. The drying temperature was 85℃.

[0122] S3: The composite precursor is pyrolyzed to obtain the pyrolysis product. The pyrolysis is carried out in argon gas at a temperature of 400℃ for 4 hours.

[0123] The pyrolysis products were tested, and the performance parameters are shown in Table 1.

[0124] S4: The pyrolysis products are heat-treated in a nitrogen-containing atmosphere to obtain a nitrogen-doped intermediate. The nitrogen-containing atmosphere is NH3 / N2 (v / v=1:1), the gas flow rate is 400 mL / min, the heat treatment temperature is 900℃, and the heat treatment time is 2 h.

[0125] S5: The nitrogen-doped intermediate is carbonized to obtain nitrogen-doped carbon material. The carbonization is carried out in argon gas at a temperature of 1300℃ for 2 hours.

[0126] The nitrogen-doped carbon material was analyzed, and its SEM image is shown below. Figure 2 and Figure 3 Other performance parameters are shown in Table 2.

[0127] The performance characterization methods for the carbon materials obtained in this embodiment, the following embodiments, and the comparative examples are as follows:

[0128] The specific surface area of ​​the material was obtained by performing adsorption-desorption experiments using BET; the median particle size (D) of the sample was measured using a laser particle size analyzer. 50 XRD was used to determine the carbon interlayer spacing (d) of the material. 002 Calculations were performed with an incident light wavelength of 1.54056 Å; Raman spectroscopy was used to determine the ratio A of the typical D and G peak areas to the amorphous carbon peak and the graphitized carbon peak. D / A G Calculations were performed; the nitrogen content in the material was determined using an organic elemental analyzer (EA). Small-angle X-ray scattering (SAXS) was used to determine the closed pore size of the material.

[0129] The compaction density of powder is tested using a compaction density meter. The principle is as follows: a certain amount of powder sample is placed in the measuring device, and pressure is applied to the powder sample through a pressure device to compact it. Under pressure, the volume of the powder sample decreases, and its density increases. The measuring device records the volume and density of the compacted sample and calculates the compaction density.

[0130] Example 2

[0131] This embodiment prepares a nitrogen-doped carbon material, and the specific steps are as follows:

[0132] S1: Lignite is purified by acid washing with a mixture of hypochlorous acid and nitric acid, and then washed with water until neutral to obtain a coal-based precursor. The concentration of hypochlorous acid in the mixed acid is 1 mol / L, the concentration of nitric acid is 3 mol / L, and the volume ratio of hypochlorous acid to nitric acid is 1:1.

[0133] S2: A coal-based precursor and glucose were mixed at a mass ratio of 1:2, and deionized water was added. A hydrothermal reaction was then carried out in a reactor. The reaction product was then dried to obtain the composite precursor. The hydrothermal reaction temperature was 180℃, and the reaction time was 20 hours. The drying temperature was 85℃.

[0134] S3: The composite precursor is pyrolyzed to obtain the pyrolysis product. The pyrolysis is carried out in argon gas at a temperature of 400℃ for 4 hours.

[0135] The pyrolysis products were tested, and the performance parameters are shown in Table 1.

[0136] S4: The pyrolysis product is heat-treated under a nitrogen-containing atmosphere to obtain a nitrogen-doped intermediate. The nitrogen-containing atmosphere is NH3 / Ar (v / v=1:1), the gas flow rate is 400 mL / min, the heat treatment temperature is 900℃, and the heat treatment time is 2 h.

[0137] S5: Carbonize the nitrogen-doped intermediate to obtain nitrogen-doped carbon material. The carbonization temperature is 1300℃ and the carbonization time is 2h.

[0138] The nitrogen-doped carbon material was tested, and the performance parameters are shown in Table 2.

[0139] Example 3

[0140] This embodiment prepares a nitrogen-doped carbon material, and the specific steps are as follows:

[0141] S1: Lignite is purified by acid washing with a mixture of hypochlorous acid and nitric acid, and then washed with water until neutral to obtain a coal-based precursor. The concentration of hypochlorous acid in the mixed acid is 1 mol / L, the concentration of nitric acid is 3 mol / L, and the volume ratio of hypochlorous acid to nitric acid is 1:1.

[0142] S2: A coal-based precursor and maltose were mixed at a 1:1 mass ratio, and deionized water was added to carry out a hydrothermal reaction in a reactor. The reaction product was then dried to obtain a composite precursor. The hydrothermal reaction temperature was 200℃, and the reaction time was 18 hours. The drying temperature was 85℃.

[0143] S3: The composite precursor is pyrolyzed to obtain the pyrolysis product. The pyrolysis is carried out in argon gas at a temperature of 600℃ for 2 hours.

[0144] The pyrolysis products were tested, and the performance parameters are shown in Table 1.

[0145] S4: The pyrolysis products are heat-treated in a nitrogen-containing atmosphere to obtain a nitrogen-doped intermediate. The nitrogen-containing atmosphere is NH3 / He (v / v=1:1), the gas flow rate is 200 mL / min, the heat treatment temperature is 900℃, and the heat treatment time is 2 h.

[0146] S5: Carbonize the nitrogen-doped intermediate to obtain nitrogen-doped carbon material. The carbonization temperature is 1300℃ and the carbonization time is 2h.

[0147] The nitrogen-doped carbon material was tested, and the performance parameters are shown in Table 2.

[0148] Example 4

[0149] This embodiment prepares a nitrogen-doped carbon material, and the specific steps are as follows:

[0150] S1: Lignite is purified by acid washing with a mixture of hypochlorous acid and nitric acid, and then washed with water until neutral to obtain a coal-based precursor. The concentration of hypochlorous acid in the mixed acid is 1 mol / L, the concentration of nitric acid is 3 mol / L, and the volume ratio of hypochlorous acid to nitric acid is 1:1.

[0151] S2: A coal-based precursor and sucrose were mixed at a 1:1 mass ratio, and deionized water was added to carry out a hydrothermal reaction in a reactor. The reaction product was then dried to obtain a composite precursor. The hydrothermal reaction temperature was 150℃, and the reaction time was 24 hours. The drying temperature was 85℃.

[0152] S3: The composite precursor is pyrolyzed to obtain the pyrolysis product. The pyrolysis is carried out in argon gas at a temperature of 400℃ for 4 hours.

[0153] The pyrolysis products were tested, and the performance parameters are shown in Table 1.

[0154] S4: The pyrolysis products are heat-treated in a nitrogen-containing atmosphere to obtain a nitrogen-doped intermediate. The nitrogen-containing atmosphere is NH3 / N2 (v / v=1:1), the gas flow rate is 400 mL / min, the heat treatment temperature is 700℃, and the heat treatment time is 4 h.

[0155] S5: Carbonize the nitrogen-doped intermediate to obtain nitrogen-doped carbon material. The carbonization temperature is 1300℃ and the carbonization time is 2h.

[0156] The nitrogen-doped carbon material was tested, and the performance parameters are shown in Table 2.

[0157] Example 5

[0158] This embodiment prepares a nitrogen-doped carbon material, and the specific steps are as follows:

[0159] S1: Lignite is purified by acid washing with a mixture of hypochlorous acid and nitric acid, and then washed with water until neutral to obtain a coal-based precursor. The concentration of hypochlorous acid in the mixed acid is 1 mol / L, the concentration of nitric acid is 3 mol / L, and the volume ratio of hypochlorous acid to nitric acid is 1:1.

[0160] S2: A coal-based precursor and sucrose were mixed at a 1:1 mass ratio, and deionized water was added to carry out a hydrothermal reaction in a reactor. The reaction product was then dried to obtain a composite precursor. The hydrothermal reaction temperature was 200℃, and the reaction time was 18 hours. The drying temperature was 85℃.

[0161] S3: The composite precursor is pyrolyzed to obtain the pyrolysis product. The pyrolysis is carried out in argon gas at a temperature of 400℃ for 4 hours.

[0162] The pyrolysis products were tested, and the performance parameters are shown in Table 1.

[0163] S4: The pyrolysis products are heat-treated under a nitrogen-containing atmosphere to obtain a nitrogen-doped intermediate. The nitrogen-containing atmosphere is NH3 / N2 (v / v=1:1), the gas flow rate is 400 mL / min, the heat treatment temperature is 800℃, and the heat treatment time is 3 h.

[0164] S5: Carbonize the nitrogen-doped intermediate to obtain nitrogen-doped carbon material. The carbonization temperature is 1400℃ and the carbonization time is 2h.

[0165] The nitrogen-doped carbon material was tested, and the performance parameters are shown in Table 2.

[0166] Example 6

[0167] This embodiment prepares a nitrogen-doped carbon material, and the specific steps are as follows:

[0168] S1: Lignite is purified by acid washing with a mixture of hypochlorous acid and nitric acid, and then washed with water until neutral to obtain a coal-based precursor. The concentration of hypochlorous acid in the mixed acid is 1 mol / L, the concentration of nitric acid is 3 mol / L, and the volume ratio of hypochlorous acid to nitric acid is 1:1.

[0169] S2: A coal-based precursor and sucrose were mixed at a 1:1 mass ratio, and deionized water was added to carry out a hydrothermal reaction in a reactor. The reaction product was then dried to obtain a composite precursor. The hydrothermal reaction temperature was 200℃, and the reaction time was 18 hours. The drying temperature was 85℃.

[0170] S3: The composite precursor is pyrolyzed to obtain the pyrolysis product. The pyrolysis is carried out in argon gas at a temperature of 400℃ for 4 hours.

[0171] The pyrolysis products were tested, and the performance parameters are shown in Table 1.

[0172] S4: The pyrolysis products are heat-treated in a nitrogen-containing atmosphere to obtain a nitrogen-doped intermediate. The nitrogen-containing atmosphere is NH3 / N2 (v / v=1:1), the gas flow rate is 600 mL / min, the heat treatment temperature is 900℃, and the heat treatment time is 2 h.

[0173] S5: Carbonize the nitrogen-doped intermediate to obtain nitrogen-doped carbon material. The carbonization temperature is 1200℃ and the carbonization time is 4h.

[0174] The nitrogen-doped carbon material was tested, and the performance parameters are shown in Table 2.

[0175] Comparative Example 1

[0176] This comparative example prepares a nitrogen-doped carbon material, and the specific steps are as follows:

[0177] S1: Lignite is purified by acid washing with a mixture of hypochlorous acid and nitric acid, and then washed with water until neutral to obtain a coal-based precursor. The concentration of hypochlorous acid in the mixed acid is 1 mol / L, the concentration of nitric acid is 3 mol / L, and the volume ratio of hypochlorous acid to nitric acid is 1:1.

[0178] S2': The coal-based precursor is added to deionized water and subjected to a hydrothermal reaction in a reactor. The reaction product is then dried to obtain the composite precursor. The hydrothermal reaction temperature is 200℃, and the reaction time is 18 hours. The drying temperature is 85℃.

[0179] S3: The composite precursor is pyrolyzed to obtain the pyrolysis product. The pyrolysis is carried out in argon gas at a temperature of 400℃ for 4 hours.

[0180] The pyrolysis products were tested, and the performance parameters are shown in Table 1.

[0181] S4: The pyrolysis products are heat-treated in a nitrogen-containing atmosphere to obtain a nitrogen-doped intermediate. The nitrogen-containing atmosphere is NH3 / N2 (v / v=1:1), the gas flow rate is 400 mL / min, the heat treatment temperature is 900℃, and the heat treatment time is 2 h.

[0182] S5: Carbonize the nitrogen-doped intermediate to obtain nitrogen-doped carbon material. The carbonization temperature is 1300℃ and the carbonization time is 2h.

[0183] The nitrogen-doped carbon material was tested, and the performance parameters are shown in Table 2.

[0184] Comparative Example 2

[0185] This comparative example prepares a nitrogen-doped carbon material, and the specific steps are as follows:

[0186] S1: Lignite is purified by acid washing with a mixture of hypochlorous acid and nitric acid, and then washed with water until neutral to obtain a coal-based precursor. The concentration of hypochlorous acid in the mixed acid is 1 mol / L, the concentration of nitric acid is 3 mol / L, and the volume ratio of hypochlorous acid to nitric acid is 1:1.

[0187] S3': Coal-based precursors and sucrose are mixed at a mass ratio of 1:1 and then pyrolyzed to obtain pyrolysis products. The pyrolysis is carried out in argon atmosphere at a temperature of 400℃ for 4 hours.

[0188] The pyrolysis products were tested, and the performance parameters are shown in Table 1.

[0189] S4: The pyrolysis products are heat-treated in a nitrogen-containing atmosphere to obtain a nitrogen-doped intermediate. The nitrogen-containing atmosphere is NH3 / N2 (v / v=1:1), the gas flow rate is 400 mL / min, the heat treatment temperature is 900℃, and the heat treatment time is 2 h.

[0190] S5: Carbonize the nitrogen-doped intermediate to obtain nitrogen-doped carbon material. The carbonization temperature is 1300℃ and the carbonization time is 2h.

[0191] The nitrogen-doped carbon material was tested, and the performance parameters are shown in Table 2.

[0192] Comparative Example 3

[0193] This comparative example prepares a nitrogen-doped carbon material, and the specific steps are as follows:

[0194] S1: Lignite is purified by acid washing with a mixture of hypochlorous acid and nitric acid, and then washed with water until neutral to obtain a coal-based precursor. The concentration of hypochlorous acid in the mixed acid is 1 mol / L, the concentration of nitric acid is 3 mol / L, and the volume ratio of hypochlorous acid to nitric acid is 1:1.

[0195] S2: A coal-based precursor and sucrose were mixed at a 1:1 mass ratio, and deionized water was added to carry out a hydrothermal reaction in a reactor. The reaction product was then dried to obtain a composite precursor. The hydrothermal reaction temperature was 200℃, and the reaction time was 18 hours. The drying temperature was 85℃.

[0196] S4': The composite precursor is heat-treated in a nitrogen-containing atmosphere to obtain a nitrogen-doped intermediate. The nitrogen-containing atmosphere is NH3 / N2 (v / v=1:1), the gas flow rate is 400 mL / min, the heat treatment temperature is 900℃, and the heat treatment time is 2 h.

[0197] S5: Carbonize the nitrogen-doped intermediate to obtain nitrogen-doped carbon material. The carbonization temperature is 1300℃ and the carbonization time is 2h.

[0198] The nitrogen-doped carbon material was tested, and the performance parameters are shown in Table 2.

[0199] Comparative Example 4

[0200] This comparative example prepares a carbon material, and the specific steps are as follows:

[0201] S1: Lignite is purified by acid washing with a mixture of hypochlorous acid and nitric acid, and then washed with water until neutral to obtain a coal-based precursor. The concentration of hypochlorous acid in the mixed acid is 1 mol / L, the concentration of nitric acid is 3 mol / L, and the volume ratio of hypochlorous acid to nitric acid is 1:1.

[0202] S2: A coal-based precursor and sucrose were mixed at a 1:1 mass ratio, and deionized water was added to carry out a hydrothermal reaction in a reactor. The reaction product was then dried to obtain a composite precursor. The hydrothermal reaction temperature was 200℃, and the reaction time was 18 hours. The drying temperature was 85℃.

[0203] S3: The composite precursor is pyrolyzed to obtain the pyrolysis product. The pyrolysis is carried out in argon gas at a temperature of 400℃ for 4 hours.

[0204] The pyrolysis products were tested, and the performance parameters are shown in Table 1.

[0205] S5': Carbonize the pyrolysis products to obtain carbon materials. The carbonization temperature is 1300℃ and the carbonization time is 2 hours.

[0206] The carbon materials were tested, and the performance parameters are shown in Table 2.

[0207] Comparative Example 5

[0208] This comparative example prepares a nitrogen-doped carbon material, and the specific steps are as follows:

[0209] S1: Lignite is purified by acid washing with a mixture of hypochlorous acid and nitric acid, and then washed with water until neutral to obtain a coal-based precursor. The concentration of hypochlorous acid in the mixed acid is 1 mol / L, the concentration of nitric acid is 3 mol / L, and the volume ratio of hypochlorous acid to nitric acid is 1:1.

[0210] S2: A coal-based precursor and sucrose were mixed at a 1:1 mass ratio, and deionized water was added to carry out a hydrothermal reaction in a reactor. The reaction product was then dried to obtain a composite precursor. The hydrothermal reaction temperature was 200℃, and the reaction time was 18 hours. The drying temperature was 85℃.

[0211] S3: The composite precursor is pyrolyzed to obtain the pyrolysis product. The pyrolysis is carried out in argon gas at a temperature of 400℃ for 4 hours.

[0212] The pyrolysis products were tested, and the performance parameters are shown in Table 1.

[0213] S4: The pyrolysis products are heat-treated in a nitrogen-containing atmosphere to obtain nitrogen-doped carbon materials. The nitrogen-containing atmosphere is NH3 / N2 (v / v=1:1), the gas flow rate is 400 mL / min, the heat treatment temperature is 900℃, and the heat treatment time is 2 h.

[0214] The nitrogen-doped carbon material was tested, and the performance parameters are shown in Table 2.

[0215] Experimental Example

[0216] The carbon materials obtained in Examples 1-6 and Comparative Examples 1-5 were respectively assembled into batteries. The specific steps are as follows:

[0217] According to the mass ratio of active material:SP:CMC:SBR=92:2:2:4, carbon material, SP, CMC and SBR were weighed and mixed evenly in deionized water to prepare a slurry; the evenly mixed slurry was coated on aluminum foil current collector, baked in an oven at 80℃ for 1 hour, and cooled to room temperature.

[0218] Adjust the roller spacing and roll the electrode sheets. Cut the rolled electrode sheets into small round pieces with a diameter of 14mm and weigh them as m1. Similarly, cut the aluminum foil current collector into aluminum foil round pieces with a diameter of 14mm and weigh them as m2. (m1-m2)×0.94 represents the mass of the active material, denoted as m3. Place the weighed round pieces in an 80℃ oven and vacuum dry for 12 hours.

[0219] The vacuum-dried small discs were transferred to a glove box, and sodium discs were used as the counter electrode and auxiliary electrode. The electrolyte was 1M NaPF6 / EC:DMC:DEC=2:2:1, and a glass fiber diaphragm was used as the separator. Sodium-ion button cells were assembled in a glove box where the oxygen and water content were both less than 0.01ppm.

[0220] The assembled button-type sodium-ion batteries were left to stand for 12 hours. The electrochemical performance of the standing button-type sodium-ion batteries was then tested under constant current using the Wuhan Landian Battery Testing System. Specific parameters are shown in Table 3.

[0221] Table 1 Performance parameters of pyrolysis products in Examples 1-6 and Comparative Examples 1-5

[0222]

[0223] Table 2 Performance parameters of carbon materials in Examples 1-6 and Comparative Examples 1-5

[0224]

[0225] Table 3 Electrochemical performance of sodium-ion batteries prepared from carbon materials in Examples 1-6 and Comparative Examples 1-5

[0226]

[0227] As shown in Table 1, pyrolysis of coal after hydrothermal synthesis only involves the cross-linking of the coal itself. The weight loss after pyrolysis is merely the volatilization of small-molecule organic matter in the coal, resulting in no significant increase in specific surface area. However, the product of pyrolysis of a mixture of coal and sugars, without hydrothermal cross-linking, exhibits a lower degree of cross-linking during pyrolysis, leading to significant weight loss of sugars and irreversible increase in specific surface area due to sugar gelatinization.

[0228] As can be seen from Table 2, the nitrogen doping content of the nitrogen-doped carbon material prepared in the embodiments of this application is approximately 4-8 wt%, A D / A G It is approximately 2.2~2.5, D 50 The wavelength is approximately 5–7 μm, the d(002) is approximately 0.38–0.39 nm, and the specific surface area is approximately 4–6 cm². 2 / g, compacted density is approximately 1.25~1.30 g / cm³. 3 The method provided in this application first cleans the coal, then completes the cross-linking of coal and carbohydrate compounds in a hydrothermal process, further stabilizes the structure in a subsequent pyrolysis stage, and then does nitrogen doping and carbonization. The preparation method is simple, and the resulting carbon material has fewer surface defects, a smaller specific surface area, and a significantly increased interlayer spacing, which is beneficial for improving the electrochemical performance of the material.

[0229] Furthermore, as shown in Table 2, the carbon materials prepared without sucrose, hydrothermal processes, pyrolysis processes, nitrogen doping processes, or carbonization processes exhibit poorer performance. In particular, the carbon materials prepared without hydrothermal processes and carbonization processes show very obvious surface defects and have a larger specific surface area compared to carbon materials prepared with hydrothermal and carbonization processes. Hydrothermal processes can increase the degree of cross-linking between coal and sucrose, improve the thermal stability of the prepared materials, and facilitate pore shrinkage during subsequent carbonization processes, forming more closed-cell structures.

[0230] As shown in Table 3, compared with Comparative Examples 1 to 5, the reversible discharge specific capacity and initial coulombic efficiency of the battery are significantly improved when the carbon material prepared in this application is used as the negative electrode.

[0231] This application utilizes a hydrothermal process at low temperatures, which improves the stability of sucrose molecules and prevents gelatinization and molecular structure damage during subsequent high-temperature pyrolysis. Pyrolysis further enhances the material's structural stability. Subsequent nitrogen doping expands the interlayer spacing, providing more sodium storage sites. The carbon material prepared through hydrothermal synthesis, pyrolysis, nitrogen doping, and carbonization exhibits excellent properties.

[0232] from Figure 2 and Figure 3 It can be seen that the nitrogen-doped carbon material prepared in this application is uniform in size, with a particle size of about 5~7μm.

[0233] Obviously, the above embodiments are merely examples for clearly illustrating the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A nitrogen-doped carbon material, characterized in that, The nitrogen content in the nitrogen-doped carbon material is 4-8 wt%, and the area ratio A of the amorphous carbon peaks and the graphitized carbon peaks is... D / A G The value is 2.2~2.5, and the closed-cell volume is 0.05~0.1cm³. 2 / g, closed pore diameter is 0.1~4nm; The specific surface area of ​​the nitrogen-doped carbon material is ≤10 cm². 2 / g; The method for preparing the nitrogen-doped carbon material includes the following steps: S1: After acid washing and purification of coal raw materials, the coal is washed with water until neutral to obtain coal-based precursors; S2: The coal-based precursor is mixed with a carbohydrate compound and subjected to a hydrothermal reaction, so that the carboxyl functional group of the coal-based precursor reacts with the hydroxyl functional group of the carbohydrate compound. The reaction product is then dried to obtain a composite precursor. S3: Pyrolyze the composite precursor to obtain pyrolysis products; S4: The pyrolysis product is heat-treated under a nitrogen-containing atmosphere to obtain a nitrogen-doped intermediate; or, the pyrolysis product is mixed with a solid or liquid nitrogen source and then heat-treated to obtain a nitrogen-doped intermediate; and S5: Carbonize the nitrogen-doped intermediate to obtain the nitrogen-doped carbon material; The coal raw materials include one or more of bituminous coal, anthracite, and lignite; The pyrolysis temperature is 400~600℃; the pyrolysis time is 2~6h.

2. The nitrogen-doped carbon material according to claim 1, characterized in that, The nitrogen-doped carbon material satisfies at least one of the following conditions: a) The median particle size D of the nitrogen-doped carbon material 50 ≤10μm; b) The carbon interlayer spacing d of the nitrogen-doped carbon material 002 ≥0.35nm; c) The specific surface area of ​​the nitrogen-doped carbon material is 4-6 cm². 2 / g; d) The compaction density of the nitrogen-doped carbon material is ≥1.0 g / cm³. 3 ; e) The closed-pore volume of the nitrogen-doped carbon material is 0.065~0.085 cm³. 2 / g, with closed-pore diameter of 1~3nm.

3. The nitrogen-doped carbon material according to claim 1, characterized in that, The nitrogen-doped novel carbon material satisfies at least one of the following conditions: a) The median particle size of the nitrogen-doped carbon material is 5~7 μm; b) The carbon interlayer spacing d of the nitrogen-doped carbon material 002 The wavelength is 0.38~0.39 nm. c) The specific surface area of ​​the nitrogen-doped carbon material is 4-6 cm². 2 / g; d) The compaction density of the nitrogen-doped carbon material is 1.25~1.30 g / cm³. 3 ; e) The closed-pore volume of the nitrogen-doped carbon material is 0.065~0.085 cm³. 2 / g, with closed-pore diameter of 1~3nm.

4. A method for preparing a nitrogen-doped carbon material, characterized in that, Includes the following steps: S1: After acid washing and purification of coal raw materials, the coal is washed with water until neutral to obtain coal-based precursors; S2: The coal-based precursor is mixed with a carbohydrate compound and subjected to a hydrothermal reaction, so that the carboxyl functional group of the coal-based precursor reacts with the hydroxyl functional group of the carbohydrate compound. The reaction product is then dried to obtain a composite precursor. S3: Pyrolyze the composite precursor to obtain pyrolysis products; S4: The pyrolysis product is heat-treated in a nitrogen-containing atmosphere to obtain a nitrogen-doped intermediate; or, the pyrolysis product is mixed with a solid or liquid nitrogen source and then heat-treated to obtain a nitrogen-doped intermediate. as well as S5: Carbonize the nitrogen-doped intermediate to obtain the nitrogen-doped carbon material; The coal raw materials include one or more of bituminous coal, anthracite, and lignite; The pyrolysis temperature is 400~600℃; the pyrolysis time is 2~6h.

5. The preparation method according to claim 4, characterized in that, In step S1, the acid used for pickling includes one or more of hypochlorous acid, hydrochloric acid, hydrofluoric acid, and nitric acid. And / or, the concentration of acid used for pickling is 0.5~5 mol / L.

6. The preparation method according to claim 4, characterized in that, The acid used for pickling is a mixture of hypochlorous acid and nitric acid, wherein the volume ratio of hypochlorous acid to nitric acid is 1:(1~3).

7. The preparation method according to claim 4, characterized in that, In step S2, the mass ratio of the coal-based precursor to the carbohydrate compound is 1:(1~2). And / or, the temperature of the hydrothermal reaction is 150~200℃, and the time of the hydrothermal reaction is 18~24h; And / or, the carbohydrate compound includes one or more of sucrose, glucose, maltose, fructose, and galactose; And / or, the drying process is selected from any one of ambient temperature drying, freeze drying, and heat drying.

8. The preparation method according to claim 4, characterized in that, The drying process is selected from heat drying, and the drying temperature is 80~100℃.

9. The preparation method according to claim 4, characterized in that, In step S3, the pyrolysis is carried out in a protective atmosphere, which is selected from one or more of argon, nitrogen, helium, and xenon. And / or, the flow rate of the protective atmosphere gas during the pyrolysis process is 100~1000 mL / min; And / or, the heating rate before the pyrolysis treatment is 1~10℃ / min; And / or, the composite precursor has a weight loss rate of 15-30% during the pyrolysis process, and the specific surface area of ​​the pyrolysis product is 100-400 cm². 2 / g.

10. The preparation method according to claim 4, characterized in that, The heat treatment temperature is 700~900℃, the time is 2~4h, and the heating rate is 2~7℃ / min; And / or, the flow rate of the nitrogen-containing atmosphere is 200~600 mL / min; And / or, the nitrogen-containing atmosphere includes ammonia; And / or, the nitrogen-containing atmosphere includes a protective gas selected from one or more of argon, nitrogen, helium, and xenon; And / or, the solid nitrogen source includes one or more of urea, melamine, and dicyandiamide; And / or, the liquid nitrogen source includes one or more of ethylenediamine, dopamine, aniline, triethanolamine, and triethylenetetraethylamine.

11. The preparation method according to claim 4, characterized in that, In step S5, the carbonization is carried out in a protective atmosphere, which is selected from one or more of argon, nitrogen, helium, and xenon. And / or, the flow rate of the protective atmosphere gas during the carbonization process is 100~1000 mL / min; And / or, the carbonization temperature is 1200~1400℃; And / or, the carbonization time is 2-4 hours; And / or, the heating rate before carbonization is 1~10℃ / min.

12. A negative electrode sheet, characterized in that, It includes the nitrogen-doped carbon material according to any one of claims 1-3, or the nitrogen-doped carbon material prepared by any one of the preparation methods according to claims 4-11.

13. A sodium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 12.

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