Anthracite-based nitrogen-doped carbon material and preparation method and application thereof

Abstract

The present invention provides an anthracite-based nitrogen-doped carbon material and a preparation method and application thereof. The following steps are included: a. The crushed and screened anthracite and graphite phase carbon nitride are mixed uniformly by mechanical ball milling in a mass ratio of (5-1): 1 to obtain a mixture; b. The mixture is placed in a vacuum tube furnace, heated to 400-700°C in an argon atmosphere, and pyrolysis pretreatment is performed to obtain a pretreated mixture; c. After the pretreated mixture is cooled to room temperature, it is heated to 1000-1400°C in an argon atmosphere, and high-temperature carbonization is performed to obtain anthracite-based nitrogen-doped carbon material. The carbon material prepared by the present invention has low cost, easy raw materials, strong conductivity, stable structure, and can effectively improve the electrochemical performance of sodium ion batteries. At the same time, the present invention also provides a sodium ion battery based on anthracite-based nitrogen-doped carbon material as a negative electrode material, which exhibits a higher reversible specific capacity and superior cycle performance and rate performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a high-performance anthracite-based nitrogen-doped carbon material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have the advantages of high operating voltage, high energy density, and long cycle life, and have been widely used in portable electronic devices and electric vehicles. With the rapid consumption of limited lithium resources, it is urgent to find an alternative new energy source to meet people's growing needs.

[0003] As sodium is abundant in resources, has similar chemical properties to lithium, and has low cost, sodium-ion batteries are expected to become a new type of energy storage device with high economic benefits. However, commercial graphite anodes cannot support the reversible insertion and extraction of sodium ions due to their small interlayer spacing (0.3354nm) and the larger radius of sodium ions (0.102nm) than lithium ions (0.076nm), and exhibit low reversible capacity. Therefore, it is crucial to develop anode materials for sodium-ion batteries that are abundant in resources, low in cost, and have good performance. Summary of the invention

[0004] In view of this, the present invention provides an anthracite-based nitrogen-doped carbon material and a preparation method and application thereof.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing anthracite-based nitrogen-doped carbon material comprises the following steps:

[0007] a. The crushed and sieved anthracite and graphite phase carbon nitride were mixed uniformly by mechanical ball milling in a mass ratio of (5-1): 1 to obtain a mixture;

[0008] b. placing the mixture in a vacuum tube furnace, heating it to 400 to 700 ° C under an argon atmosphere, and performing pyrolysis pretreatment to obtain a pretreated mixture;

[0009] c. After the pretreated mixture is cooled to room temperature, it is heated to 1000-1400° C. in an argon atmosphere for high-temperature carbonization to obtain an anthracite-based nitrogen-doped carbon material.

[0010] Furthermore, in step b, the heating rate is 1 to 5°C / min, and the pyrolysis pretreatment time is 1 to 5h.

[0011] Furthermore, in step c, the heating rate is 2-10° C. / min, and the high-temperature carbonization time is 0.5-3 h.

[0012] Furthermore, the graphite phase carbon nitride is prepared by placing one or more of melamine, urea and thiourea in an argon atmosphere, heating to 550±50° C., and then reacting at this temperature.

[0013] Furthermore, the heating rate in preparing graphite phase carbon nitride is 1-3°C / min, and the heat preservation reaction time is 3-5h.

[0014] The anthracite-based nitrogen-doped carbon material prepared by the above method.

[0015] Furthermore, the anthracite-based nitrogen-doped carbon material is a three-dimensional network structure constructed by irregular block particles attached to carbon fibers, having a nano-scale mesoporous structure and an enlarged interlayer spacing, wherein the mesopore diameter is 2 to 3 nm, and the interlayer spacing is 0.370 to 0.395 nm.

[0016] Application of the above-mentioned anthracite-based nitrogen-doped carbon material in sodium ion batteries.

[0017] A sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte;

[0018] The negative electrode sheet is prepared from a negative electrode current collector and a negative electrode slurry disposed on the negative electrode current collector. The negative electrode slurry is mainly formed by mixing anthracite-based nitrogen-doped carbon material, a conductive agent, a binder and a solvent.

[0019] Furthermore, the sodium ion battery has a first-week discharge capacity of up to 371.3 mAh / g. After 3,000 cycles, the capacity retention rate is as high as 91.5%. When the current density rises to 10.0 A / g, the capacity can be maintained at 295.8 mAh / g.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The anthracite-based nitrogen-doped carbon material prepared by the present invention uses anthracite as a precursor, which is rich in resources, low in cost and high in carbon yield. A two-step pyrolysis method is adopted. First, pyrolysis pretreatment helps to eliminate some small molecular impurities, enhance the interaction between materials, and stabilize the nitrogen content, thereby achieving high nitrogen doping during high-temperature carbonization; secondly, during the high-temperature carbonization process, regulating the nitrogen doping content helps to regulate the microstructure of the carbon material and the carbon interlayer spacing. The locally graphitized amorphous area, the enlarged interlayer spacing and the abundant defects can not only improve the conductivity of the material, but also provide more active sites for sodium ion storage. Although high disorder and large interlayer spacing are conducive to the insertion and storage of sodium, the material has poor conductivity, resulting in poor sodium ion transmission power and cycle capacity, while high graphitization and small interlayer spacing lead to higher electron conduction rate and lower reversible capacity.

[0022] (2) The present invention utilizes graphite phase carbon nitride to provide a rich nitrogen source, and forms a one-dimensional carbon fiber during a high-temperature carbonization process, which is easy to construct an efficient three-dimensional conductive network and a flexible skeleton, enhances the conductivity and structural stability of the material, and effectively improves the electrochemical performance of the sodium ion battery.

[0023] (3) The anthracite-based nitrogen-doped carbon material prepared by the present invention has a pore size of 2 to 3 nm, a nitrogen doping content of 1.0 to 5.0 at%, and an interlayer spacing of 0.370 to 0.395 nm. As a negative electrode material for sodium ion batteries, the first-week discharge capacity can be as high as 371.3 mAh / g, and after 3000 cycles, the capacity retention rate is as high as 91.5%; even if the current density rises to 10.0 A / g, the capacity can be maintained at 295.8 mAh / g. Compared with undoped anthracite, the reversible specific capacity, cycle performance and rate performance of the nitrogen-doped carbon material after graphite phase carbon nitride modification have been greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Figure a is a scanning electron microscope observation image of the anthracite-based nitrogen-doped carbon material provided in Example 1, and Figure b is a scanning electron microscope observation image of the anthracite-based carbon material provided in Comparative Example 1;

[0025] Figure 2 Figure a in the middle is a picture of the anthracite-based nitrogen-doped carbon material provided in Example 1 observed under a high-resolution transmission electron microscope, and Figure b is a picture of the anthracite-based carbon material provided in Comparative Example 1 observed under a high-resolution transmission electron microscope. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with specific embodiments so that those skilled in the art can understand the present invention more clearly.

[0027] Sources and physical and chemical parameters of key test materials:

[0028] The anthracite raw material is produced in Shizuishan, Ningxia, and its physical and chemical parameters are: volatile matter 6.55%, ash content 2.80%, and moisture content 0.87%.

[0029] The present invention does not describe specific raw materials, which are all existing materials and can be directly purchased from the market.

[0030] Example 1

[0031] This embodiment provides a method for preparing anthracite-based nitrogen-doped carbon material, comprising the following steps:

[0032] a. Take 1.0 g of crushed and sieved anthracite and 1.0 g of graphite carbon nitride and mix them evenly by mechanical ball milling to obtain a mixture;

[0033] The graphite phase carbon nitride is obtained by using melamine as raw material, heating to 550°C at a rate of 2°C / min in an argon atmosphere, and keeping the temperature for 4 hours.

[0034] b. Place the mixture in a vacuum tube furnace, raise the temperature to 600°C at a rate of 2°C / min in an argon atmosphere, and keep the temperature for 1 hour for pyrolysis pretreatment to obtain a pretreated mixture.

[0035] c. After the pretreated mixture was cooled to room temperature, the temperature was raised to 1200°C at a rate of 5°C / min in an argon atmosphere and kept at that temperature for 1 hour for high-temperature carbonization to obtain an anthracite-based nitrogen-doped carbon material.

[0036] Example 2

[0037] This embodiment provides a method for preparing anthracite-based nitrogen-doped carbon material. The raw materials and method are basically the same as those in Example 1, except that the high-temperature carbonization temperature in step c is 1000°C.

[0038] Example 3

[0039] This embodiment provides a method for preparing anthracite-based nitrogen-doped carbon material. The raw materials and method are basically the same as those in Example 1, except that the high-temperature carbonization temperature in step c is 1400°C.

[0040] Example 4

[0041] This embodiment provides a method for preparing anthracite-based nitrogen-doped carbon material, comprising the following steps:

[0042] a. Take 3.0 g of crushed and sieved anthracite and 1.0 g of graphite carbon nitride and mix them evenly by mechanical ball milling to obtain a mixture;

[0043] The graphite carbon nitride is obtained by using urea as raw material, heating to 550°C at a rate of 1°C / min in an argon atmosphere, and keeping the temperature for reaction for 3 hours.

[0044] b. The mixture was placed in a vacuum tube furnace, heated to 400°C at a rate of 1°C / min in an argon atmosphere, and kept warm for 3 hours for pyrolysis pretreatment to obtain a pretreated mixture.

[0045] c. After the pretreated mixture is cooled to room temperature, it is heated to 1000°C at a rate of 2°C / min in an argon atmosphere and kept at this temperature for 0.5h for high-temperature carbonization to obtain anthracite-based nitrogen-doped carbon material.

[0046] Example 5

[0047] This embodiment provides a method for preparing anthracite-based nitrogen-doped carbon material, comprising the following steps:

[0048] a. Take 5.0 g of crushed and sieved anthracite and 1.0 g of graphite carbon nitride and mix them evenly by mechanical ball milling to obtain a mixture;

[0049] The graphite phase carbon nitride is obtained by using urea and thiourea as raw materials, heating to 550°C at a rate of 3°C / min in an argon atmosphere, and keeping the temperature for 5 hours.

[0050] b. The mixture was placed in a vacuum tube furnace, heated to 700°C at a rate of 5°C / min in an argon atmosphere, and kept at this temperature for 5 hours for pyrolysis pretreatment to obtain a pretreated mixture.

[0051] c. After the pretreated mixture was cooled to room temperature, it was heated to 1400°C at a rate of 10°C / min in an argon atmosphere and kept at this temperature for 3 hours for high-temperature carbonization to obtain anthracite-based nitrogen-doped carbon material.

[0052] Comparative Example 1

[0053] This comparative example provides a method for preparing anthracite-based carbon material, and its raw materials and method are basically the same as those in Example 1, except that: no graphite phase carbon nitride is added in step a.

[0054] Comparative Example 2

[0055] This comparative example provides a method for preparing anthracite-based nitrogen-doped carbon material. The raw materials and method are basically the same as those in Example 1, except that: in step a, the anthracite is 20.0 g.

[0056] Comparative Example 3

[0057] This comparative example provides a method for preparing an anthracite-based nitrogen-doped carbon material. Its raw materials and methods are basically the same as those in Example 1, except that: the pyrolysis pretreatment step of step b in Example 1 is omitted, and the following steps are performed to replace step b and step c in Example 1: the mixture is placed in a vacuum tube furnace, and in an argon atmosphere, the temperature is increased to 1200°C at a rate of 5°C / min, and the temperature is kept for 1 hour for high-temperature carbonization to obtain an anthracite-based nitrogen-doped carbon material.

[0058] Application performance testing:

[0059] Based on the above research, the carbon materials prepared in Examples 1-5 and Comparative Examples 1-3 are further used to prepare sodium ion batteries, including the following steps:

[0060] Add appropriate amount of deionized water to the carbon material, carbon nanotubes and sodium alginate in a mass ratio of 7:2:1, stir for at least 6 hours, and mix well to obtain a uniform slurry.

[0061] The uniform slurry is coated on the aluminum foil current collector, vacuum dried and cut into negative electrode sheets.

[0062] The prepared negative electrode sheet, a metal sodium sheet, a glass fiber separator and an electrolyte (a mixed solution of 1.0 mol NaPF6 dissolved in 1 L of ethylene glycol dimethyl ether) were assembled into a CR2032 button cell in a vacuum glove box filled with Ar atmosphere to obtain a sodium ion battery.

[0063] The physical and chemical parameters of the carbon materials prepared in each embodiment and comparative example were measured, and constant current charge and discharge tests were performed on the eight sodium ion batteries prepared. The details are as follows:

[0064] 1. Microstructure observations were performed using scanning electron microscopy and high-resolution transmission electron microscopy. The results are as follows: Figure 1 and 2 shown.

[0065] Depend on Figure 1 It can be seen from the scanning electron microscope image that the material prepared in Implementation 1 is macroscopically irregular block particles attached to a three-dimensional network structure constructed by carbon fibers, which enhances the conductivity and structural stability of the material and improves the electrochemical performance of the sodium ion battery; while the material prepared in Comparative Example 1 is mainly a block structure with irregular size and rough surface.

[0066] Figure 2 The high-resolution transmission electron microscope image further reveals its microstructure: the microstructure of the material prepared in Example 1 is composed of turbine-shaped graphite domains and amorphous regions; the microstructure of the negative electrode material prepared in Comparative Example 1 is a highly ordered graphite structure. The partially graphitized amorphous structure and the enlarged interlayer spacing are conducive to the rapid insertion and extraction of sodium ions, accelerating the transmission of ions and electrons, and improving the electrochemical performance of sodium ion batteries.

[0067] 2. The specific surface area and pore size distribution of the carbon materials prepared in each embodiment and comparative example were tested by nitrogen adsorption-desorption method, and the carbon interlayer spacing was calculated by Digital Micrograph software. The results are shown in Table 1.

[0068] Table 1 Parameters of carbon materials prepared in various embodiments and comparative examples

[0069]

[0070] It can be seen from Table 1 that compared with Comparative Example 1, the specific surface area, total pore volume and interlayer spacing of the anthracite-based nitrogen-doped carbon material in the embodiment are all greater than those in Comparative Example 1, indicating that the nitrogen-doped carbon material after modification of graphite phase carbon nitride has a superior structure, a larger specific surface area and an enlarged interlayer spacing, which is beneficial to increase the contact area between the electrode and the electrolyte, shorten the transmission distance of sodium ions, and accelerate the transmission of ions and electrons, thereby improving the electrochemical performance of the sodium ion battery.

[0071] Compared with Comparative Example 2, the specific surface area, total pore volume and interlayer spacing of the anthracite-based nitrogen-doped carbon material in the embodiment are all greater than those in Comparative Example 2, indicating that an appropriate mass ratio of anthracite and graphite phase carbon nitride is beneficial to improving the material structure.

[0072] Compared with Comparative Example 3, the specific surface area, total pore volume, interlayer spacing and nitrogen doping content of the anthracite-based nitrogen-doped carbon material in the embodiment are all greater than those in Comparative Example 3, indicating that the method of pyrolysis pretreatment followed by high-temperature carbonization is beneficial to increasing the nitrogen doping content and optimizing the material structure.

[0073] 3. Constant current charge and discharge test: The test voltage range is 0-2.5V, the current density is 0.05A / g, and the first week coulomb efficiency and reversible specific capacity of each sodium ion battery are obtained; the current density is 0.05, 0.1, 0.2, 0.5, 1, 2, 5 and 10A / g, and the rate performance of each sodium ion battery is obtained; at a current density of 0.5A / g, the charge and discharge cycle is 3000 weeks, and the reversible specific capacity retention rate of each sodium ion battery is obtained. The test results are shown in Table 2 below.

[0074] Table 2 Parameters of sodium ion batteries made of carbon materials prepared in various embodiments and comparative examples

[0075]

[0076] It can be seen from Table 2 above that compared with Comparative Example 1, the anthracite-based nitrogen-doped carbon material in the embodiment is used as the negative electrode material, and the prepared sodium ion battery exhibits a higher reversible specific capacity, especially the battery's cycle performance and rate performance are greatly improved. This shows that the macroscopic efficient conductive network structure of the nitrogen-doped carbon material and the microscopic locally graphitized amorphous structure and the enlarged interlayer spacing play a crucial role.

[0077] Compared with Comparative Example 2, the anthracite-based nitrogen-doped carbon material in the embodiment is used as the negative electrode material, and the prepared sodium ion battery exhibits higher reversible specific capacity, superior rate performance and cycle performance, indicating that the appropriate mass ratio of anthracite and graphite phase carbon nitride has a positive effect on the prepared sodium ion battery.

[0078] Compared with Comparative Example 3, the anthracite-based nitrogen-doped carbon material in the embodiment is used as the negative electrode material, and the prepared sodium ion battery shows a higher reversible specific capacity, excellent rate performance and cycle performance, indicating that the method of pyrolysis pretreatment followed by high-temperature carbonization has a positive effect on the prepared sodium ion battery.

[0079] At the same time, it can be seen from Table 2 above that the pyrolysis temperature in the preparation method of the anthracite-based nitrogen-doped carbon material of Examples 1 to 3 has a certain influence on the electrochemical performance of the prepared sodium ion battery.

[0080] Furthermore, the optimal pyrolysis temperature parameter range was determined to be around 1200°C through experiments, which is conducive to the preparation of sodium ion battery negative electrode materials with superior electrochemical properties.

[0081] The above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Application of an anthracite-based nitrogen-doped carbon material in a sodium ion battery, characterized in that: The preparation method of the anthracite-based nitrogen-doped carbon material comprises the following steps: a. The crushed and sieved anthracite and graphite phase carbon nitride were mixed uniformly by mechanical ball milling in a mass ratio of (5-1):1 to obtain a mixture; b. placing the mixture in a vacuum tube furnace, heating it to 400 to 700 ° C under an argon atmosphere, and performing pyrolysis pretreatment to obtain a pretreated mixture; c. After the pretreated mixture is cooled to room temperature, the temperature is raised to 1200-1400° C. in an argon atmosphere for high-temperature carbonization to obtain an anthracite-based nitrogen-doped carbon material; The graphite phase carbon nitride is prepared by placing one or more of melamine, urea, and thiourea in an argon atmosphere, heating to 550±50°C, and keeping the temperature for reaction; The heating rate of the graphite phase carbon nitride heat preservation reaction is 1-3°C / min, and the heat preservation reaction time is 3-5h.

2. The use according to claim 1, characterized in that: In step b, the heating rate is 1 to 5° C. / min, and the pyrolysis pretreatment time is 1 to 5 h.

3. The use according to claim 1, characterized in that: In step c, the heating rate of the mixture during high-temperature carbonization is 2 to 10° C. / min, and the high-temperature carbonization time is 0.5 to 3 h.

4. The use according to claim 1, characterized in that: The anthracite-based nitrogen-doped carbon material is a three-dimensional network structure in which irregular block particles are attached to carbon fibers, and has a nano-scale mesoporous structure and an enlarged interlayer spacing. The mesopore diameter is 2 to 3 nm, and the interlayer spacing is 0.370 to 0.395 nm.

5. A sodium ion battery, characterized in that: Including positive electrode sheet, negative electrode sheet, separator and electrolyte; The negative electrode sheet is prepared from a negative electrode current collector and a negative electrode slurry disposed on the negative electrode current collector, wherein the negative electrode slurry is mainly formed by mixing anthracite-based nitrogen-doped carbon material, a conductive agent, a binder and a solvent in the application of claim 1.

6. The sodium ion battery according to claim 5, characterized in that: The sodium ion battery has a discharge capacity of up to 371.3 mAh / g in the first cycle, and a capacity retention rate of up to 91.5% after 3000 cycles. When the current density rises to 10.0 A / g, the capacity can be maintained at 295.8 mAh / g.

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