Nitrogen-doped carbon sphere material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of sodium ion battery negative electrode materials, and particularly relates to a nitrogen-doped carbon sphere material as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) uniformly mixing thiourea and melamine, and calcining at high temperature to obtain a sulfur-doped graphite phase carbon nitride precursor; (2) mixing the precursor with metal powder to obtain a metal precursor mixture, and calcining at high temperature to obtain black powder; and (3) carrying out acid leaching, water washing and drying to obtain the nitrogen-doped carbon sphere material. The precursor graphite phase carbon nitride is subjected to heteroatom doping, and high-temperature calcination is performed under the catalysis of metal powder, so that the finally obtained nitrogen-doped carbon spheres are stable in morphology and uniform in distribution.

Description

Technical Field

[0001] The present invention belongs to the technical field of anode materials for sodium-ion batteries, and particularly relates to a nitrogen-doped carbon sphere material, a preparation method thereof, and an application thereof. Background Art

[0002] Due to the widespread distribution of sodium on the earth and the increasing cost associated with lithium in lithium-ion batteries, sodium-ion batteries have become the best candidates to replace lithium-ion batteries, especially in the field of large-scale energy storage. However, the relatively low redox potential of Na + / Na (only -2.71 V) and the relatively large sodium ion radius (about 0.102 nm) make it still face significant challenges for sodium-ion batteries to completely replace lithium-ion batteries. Currently, the widely studied anode materials for sodium-ion batteries include alloys, metal oxides, and carbonaceous materials. Compared with the first two materials, carbonaceous materials have the advantages of excellent electrical conductivity and good cycle stability, and are currently promising anode materials for sodium-ion batteries. Doping with heteroatoms (B, N, S, and P) can effectively expand the interlayer spacing of carbon materials and create abundant defect sites, which greatly enhances the sodium storage capacity of carbon materials. Therefore, heteroatom doping is considered the most effective measure to improve the sodium storage capacity of carbon materials. Among them, nitrogen doping is currently the most promising measure to improve carbonaceous materials because it can provide abundant nitrogen configurations (pyridine nitrogen, graphitic nitrogen, and pyrrole nitrogen).

[0003] Graphitic carbon nitride has a layered structure similar to graphite, but has an ultra-high nitrogen content (57.1 at.%). Although graphitic carbon nitride has attracted extensive attention in electrochemical energy storage, the instability of its structure and low conductivity during charge and discharge limit its application in sodium storage. The nitrogen-doped carbon materials derived from graphitic carbon nitride have improved the above disadvantages and enable them to play a role in the energy storage field. High-nitrogen-doped carbon materials can be synthesized by calcining metal as a catalyst and graphitic carbon nitride as a precursor in a non-oxidizing atmosphere at high temperature, and it has been proven that they have certain application value in anode materials for sodium-ion batteries.

[0004] The sodium storage performance of the high-nitrogen carbon materials obtained by simply mixing and calcining graphitic carbon nitride and metal powder is not excellent, and it is necessary to modify graphitic carbon nitride to further improve the rate performance of the high-nitrogen carbon materials. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the sodium storage performance of the high-nitrogen carbon materials obtained by simply mixing and calcining graphitic carbon nitride and metal powder is not excellent. To overcome the above-mentioned deficiencies and defects in the background art, the present invention provides a nitrogen-doped carbon sphere material, a preparation method thereof, and an application thereof.

[0006] To solve the above technical problem, the technical solution proposed by the present invention is as follows: A preparation method of a nitrogen-doped carbon sphere material, comprising the following steps: (1) Mix thiourea and melamine evenly and calcine at high temperature to obtain a sulfur-doped graphitic carbon nitride precursor; (2) Mix the precursor obtained in step (1) with metal powder to obtain a metal precursor mixture, and calcine at high temperature to obtain a black powder; (3) Acid-leach, wash with water and dry the black powder obtained in step (2) to obtain a nitrogen-doped carbon sphere material.

[0007] Mixing thiourea and melamine and then calcining can obtain a sulfur-doped graphitic carbon nitride precursor. The precursor is catalytically decomposed at high temperature into a nitrogen-containing carbonaceous material, and carbon sphere materials grow on the metal powder. The sulfur-doped precursor has a larger specific surface area and more defects compared with pure graphitized carbon nitride, and the finally synthesized carbon sphere materials are more uniform and complete.

[0008] Preferably, in step (1), the mass ratio of thiourea to melamine is 1:1 to 1:50, the calcination time is 2 to 8 h, and the calcination atmosphere is at least one of static air, nitrogen or argon.

[0009] Preferably, in step (2), the metal powder is at least one of zinc powder, nickel powder, magnesium powder, cobalt powder or iron powder, and the mass ratio of the precursor to the metal powder is 0.1: -2:1.

[0010] Preferably, in step (2), the calcination temperature is maintained at a constant temperature of 600 to 900 °C for 1 h to 3 h, the heating rate is 1 to 5 °C / min, and the calcination atmosphere is at least one of nitrogen, argon or helium.

[0011] Preferably, in step (3), the acid leaching specifically includes: placing the black powder in an acid solution and magnetically stirring, the magnetic stirring speed is 200 to 800 rpm, and the stirring time is 5 to 20 h.

[0012] Preferably, the acid solution used for acid leaching in step (3) includes at least one of hydrochloric acid solution, nitric acid solution or sulfuric acid solution, and the concentration of the acid solution is greater than or equal to 1 mol / L.

[0013] Under the same technical concept, the present application also provides a nitrogen-doped carbon sphere material, which is prepared by the preparation method of the nitrogen-doped carbon sphere material, wherein the mass fraction ranges of C, N and O elements are: 60 to 80%, 10 to 30% and 2 to 10% respectively. Since the electronegativity of sulfur atoms is similar to that of nitrogen atoms, it is feasible to use sulfur atoms to replace nitrogen atoms in graphitic carbon nitride. Sulfur-doped graphitic carbon nitride will form defects related to nitrogen vacancies and increase the specific surface area of the material.

[0014] Preferably, the relative contents of pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen in the nitrogen configuration distribution on the surface of the nitrogen-doped carbon sphere material are 30-40%, 40-50%, and 10-20% respectively.

[0015] Under the same inventive concept, the present application also provides an application of the nitrogen-doped carbon sphere material, which is applied to the negative electrode of a sodium-ion battery.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention provides a nitrogen-doped carbon sphere material. By doping heteroatoms into the precursor graphitic carbon nitride and then performing high-temperature calcination under the catalysis of metal powder, the finally obtained nitrogen-doped carbon spheres have a stable morphology and uniform distribution. Compared with the graphitic carbon nitride without sulfur doping, the relative content of pyrrole nitrogen in the nitrogen-doped carbon spheres derived from sulfur-doped graphitic carbon nitride in the total nitrogen increases significantly, and the content of pyrrole nitrogen with p-orbital lone pair electrons increases significantly, resulting in an enhanced ability of the nitrogen-doped carbon sphere material to absorb sodium ions. (2) The nitrogen-doped carbon sphere material prepared by the present invention has better rate performance and cycle stability compared with commercial hard carbon materials. At a current density of 100 mA / g, the negative electrode material can provide a charge specific capacity of more than 340 mAh / g. After 1000 charge-discharge cycles at a current density of 500 mA / g, it can still maintain a discharge specific capacity of more than 175 mAh / g, and the capacity retention rate reaches 74.7%. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0018] Figure 1 SEM image of the sample prepared in Example 1; Figure 2 SEM image of the sample prepared in Comparative Example 1; Figure 3 XRD comparison chart of the samples prepared in Example 1 - Comparative Example 1; Figure 4 Raman comparison chart of the samples prepared in Example 1 - Comparative Example 1; Figure 5 High-resolution XPS spectrum of N 1s of the sample prepared in Example 1; Figure 6 High-resolution XPS spectrum of N 1s of the sample prepared in Comparative Example 1; Figure 7 Charge and discharge curve of the sample prepared in Example 1 at a current density of 100 mA / g; Figure 8 Rate performance comparison chart of the samples prepared in Example 1 - Comparative Example 1; Figure 9 Cycling performance graph of the sample prepared in Example 1 at a current density of 500 mA / g; Figure 10 Cycling performance graph of the sample prepared in Comparative Example 1 at a current density of 500 mA / g. Detailed implementation manners

[0019] To facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings of the specification and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0020] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0021] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or can be prepared by existing methods.

[0022] Example 1 A nitrogen-doped carbon sphere material, sulfur-doped graphitic carbon nitride, wherein the mass fraction ranges of C, N, and O elements are 66.33%, 19.64%, and 9.77% respectively. The nitrogen configuration distribution on the surface of the nitrogen-doped carbon sphere material, and the relative contents of pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen are 38.08%, 41.95%, and 19.97% respectively The preparation method of the nitrogen-doped carbon sphere material includes: (1) Weigh 2 g of thiourea and 10 g of melamine, stir and dissolve them in an aqueous solution at a rotation speed of 500 rpm; the water bath heating temperature is 80 °C, and stir until the solution is completely evaporated to obtain a homogeneous mixture of thiourea and melamine in a certain proportion; put the mixture into a covered corundum boat, and heat it at 550 °C for 6 h in a muffle furnace under static air, and the heating rate is 2 °C / min; (2) Take 5 g of the above sulfur-doped graphitic carbon nitride and 5 g of zinc powder, and mechanically grind them in a mortar for 30 min to obtain a metal precursor mixture; place the metal precursor mixture in a tubular furnace, and pass argon at a ventilation rate of 50 mL / min to maintain a non-oxidizing atmosphere in the tubular furnace, and maintain a heating rate of 2 °C / min until it reaches 800 °C and then calcine it at high temperature for 2 h to obtain a black powder; (3) Immerse the obtained black powder in 1 mol / L hydrochloric acid and stir magnetically for 12 h at a magnetic stirring speed of 600 rpm to remove the residual metal powder. After washing with water multiple times and drying in vacuum at 80 °C for 12 h, the nitrogen-doped carbon sphere material can be obtained, and the obtained nitrogen-doped carbon sphere material is named NS-Zn.

[0023] Uniformly disperse the prepared negative electrode material NS-Zn, conductive material acetylene black, and binder sodium carboxymethyl cellulose (average molecular weight of about 70,000) in deionized water for 8 h at a mass ratio of 8:1:1 to obtain the required slurry. Use a coater to uniformly coat the slurry on the rough surface of the copper foil, and set the coating thickness to 150 μm. After drying the electrode sheet in vacuum at 80 °C for 12 h, dry it in vacuum at 120 °C for 2 h, and then cut the electrode sheet into circular pieces with a diameter of 14 mm. In a glove box (maintaining the ppm of oxygen and water to be less than 0.01), orderly assemble the reference electrode sodium sheet, glass fiber separator, electrode sheet, positive and negative electrode shells, gaskets, and shrapnel into a sodium-ion button battery. The dropped electrolyte is a 1 mol / L NaClO4 solution, and the solvent is ethylene carbonate and dimethyl carbonate with a volume ratio of 1:1. Use a Wuhan Blue Electric CT2001A battery tester to test the rate performance and cycle stability of the assembled battery.

[0024] Comparative Example 1 It is basically the same as Example 1, except that the undoped graphitic carbon nitride obtained by directly pyrolyzing 10 g of melamine is used as the precursor, and it is calcined at 800 °C for 2 h under the catalysis of metal powder. The obtained black carbon material is named N-Zn.

[0025] Uniformly disperse the prepared negative electrode material N-Zn, conductive material acetylene black, and binder sodium carboxymethyl cellulose (average molecular weight of about 70,000) in deionized water for 8 h at a mass ratio of 8:1:1 to obtain the required slurry. Use a coater to uniformly coat the slurry on the rough surface of the copper foil, and set the coating thickness to 150 μm. After drying the electrode sheet in vacuum at 80 °C for 12 h, dry it in vacuum at 120 °C for 2 h, and then cut the electrode sheet into circular pieces with a diameter of 14 mm. In a glove box (maintaining the ppm of oxygen and water to be less than 0.01), orderly assemble the reference electrode sodium sheet, glass fiber separator, electrode sheet, positive and negative electrode shells, gaskets, and shrapnel into a sodium-ion button battery. The dropped electrolyte is a 1 mol / L NaClO4 solution, and the solvent is ethylene carbonate and dimethyl carbonate with a volume ratio of 1:1. Use a Wuhan Blue Electric CT2001A battery tester to test the rate performance and cycle stability of the assembled battery.

[0026] Performance Characterization Figure 1 It is the SEM image of the sample NS-Zn prepared in Example 1. Figure 2SEM image of the sample N-Zn prepared as Comparative Example 1. It can be seen that the carbon spheres formed by NS-Zn are more complete in morphology and more evenly distributed than those of N-Zn.

[0027] Figure 3 XRD comparison chart of the samples prepared in Example 1 - Comparative Example 1, indicating that the samples NS-Zn and N-Zn prepared in Example 1 and Comparative Example 1 are both amorphous carbon.

[0028] Figure 4 Raman comparison chart of the samples prepared in Example 1 - Comparative Example 1. Both NS-Zn and N-Zn have a characteristic D band of carbon material at 1330 cm-1 and a characteristic G band at 1580 cm-1.

[0029] Figure 5 High-resolution XPS N 1s spectrum of the sample NS-Zn prepared in Example 1 Figure 6 High-resolution XPS N 1s spectrum of the sample N-Zn prepared as Comparative Example 1. The relative contents of pyrrolic nitrogen in NS-Zn and N-Zn accounting for the total nitrogen are 41.95% and 31.45% respectively, and the relative content of pyrrolic nitrogen in NS-Zn accounting for the total nitrogen is significantly higher than that of N-Zn.

[0030] Figure 7 Charge-discharge curve of the sample NS-Zn prepared in Example 1 at a current density of 100 mA / g. It can be seen that the initial charge specific capacity of NS-Zn at a current density of 100 mA / g is 351.2 mAh / g, and the discharge specific capacity is 426.7 mAh / g.

[0031] Figure 8 Rate performance comparison chart of the samples prepared in Example 1 - Comparative Example 1. It can be seen that the charge specific capacity of NS-Zn reaches 336.6 mAh / g at a current density of 100 mA / g, which is significantly better than 245.8 mAh / g of N-Zn. Even at a large current of 10 A / g, it still maintains at 103.9 mAh / g, which is better than 87.8 mAh / g of N-Zn. This is mainly attributed to the higher relative content of pyrrolic nitrogen in NS-Zn accounting for the total nitrogen and the complete morphology and uniform distribution of the formed carbon spheres.

[0032] Figure 9 Cycling performance of the sample NS-Zn prepared in Example 1 at a current density of 500 mA / g Figure 10 Cycling performance chart of the sample N-Zn prepared as Comparative Example 1 at a current density of 500 mA / g. After 1000 charge-discharge cycles of NS-Zn at a current density of 500 mA / g, it can still maintain a discharge specific capacity of 177 mAh / g, which is significantly better than 163.3 mAh / g of N-Zn.

[0033] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing nitrogen-doped carbon sphere material, characterized in that: The following steps are involved: (1) mixing thiourea and melamine evenly and calcining at high temperature to obtain a sulfur-doped graphite phase carbon nitride precursor; (2) mixing the precursor obtained in step (1) with metal powder to obtain a metal precursor mixture, and calcining at high temperature to obtain a black powder; (3) The black powder obtained in step (2) is acid-leached, water-washed, and dried to obtain a nitrogen-doped carbon sphere material.

2. The preparation method according to claim 1, characterized in that The mass ratio of thiourea to melamine in step (1) is 1:1-1:50, the calcination time is 2-8 hours, and the calcination atmosphere is at least one of static air, nitrogen or argon.

3. The preparation method according to claim 1, characterized in that: The metal powder in step (2) is at least one of zinc powder, nickel powder, magnesium powder, cobalt powder or iron powder, and the mass ratio of the precursor to the metal powder is 0.1:-2:

1.

4. The preparation method according to claim 1, characterized in that: The calcination temperature in step (2) is 600-900°C and maintained at a constant temperature for 1h-3h, the heating rate is 1-5°C / min, and the calcination atmosphere is at least one of nitrogen, argon or helium.

5. The preparation method according to claim 1, characterized in that: The acid leaching in step (3) specifically comprises: placing the black powder in an acid solution and magnetically stirring it, the magnetic stirring speed is 200 to 800 rpm, and the stirring time is 5 to 20 hours.

6. The preparation method according to claim 5, characterized in that: The acid solution used for acid leaching in step (3) includes at least one of hydrochloric acid solution, nitric acid solution or sulfuric acid solution, and the concentration of the acid solution is greater than or equal to 1 mol / L.

7. A nitrogen-doped carbon sphere material, characterized in that: The nitrogen-doped carbon sphere material is prepared by the preparation method according to any one of claims 1 to 6, wherein the mass fractions of C, N and O elements are in the ranges of 60-80%, 10-30% and 2-10%, respectively.

8. The carbon ball material according to claim 1, characterized in that: The nitrogen configuration distribution on the surface of the nitrogen-doped carbon ball material has relative contents of pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen of 30-40%, 40-50% and 10-20% respectively.

9. An application of nitrogen-doped carbon sphere material, characterized in that: The nitrogen-doped carbon sphere material as described in any one of claims 1 to 2 or the nitrogen-doped carbon sphere material prepared by the method as described in any one of claims 3 to 8 is used in the negative electrode of a sodium ion battery.

Images