CN116281941B - A kind of nitrogen-doped hollow defect carbon sphere and its preparation method and application - Google Patents

Abstract

The invention discloses a nitrogen-doped hollow defect carbon sphere and a preparation method and application thereof, and belongs to the technical field of preparation of negative electrode materials of sodium ion batteries. The preparation method of the invention comprises the following steps: step 1) preparing a template melamine-formaldehyde resin ball by adopting a self-assembly method; 2) Coating the prepared MF spheres by dopamine hydrochloride, adding 1,3, 5-trimethylbenzene and triblock copolymer F127 to form micelles, and then inducing the micelles to self-assemble and place on a template under alkaline conditions; 3) Washing the product with alcohol to form defects on the surface; 4) And carrying out heat treatment on the prepared MF@MMPDA defect spheres to decompose the MF spheres at high temperature to obtain the nitrogen-doped hollow defect carbon spheres. The invention has the advantages of simple formula, simple and convenient operation, good repeatability, high purity product, good stability, environmental protection and high capacity as a cathode material.

Description

A kind of nitrogen-doped hollow defect carbon sphere and its preparation method and application

Technical field

The invention belongs to the technical field of nano-negative electrode materials, and specifically relates to a nitrogen-doped hollow defect carbon sphere and its preparation method and application.

Background technique

A large number of non-carbonaceous materials with different sodium storage mechanisms have been developed as anodes for sodium-ion batteries, including metal oxides/sulfides (such as TiO ₂ , SnS ₂ , MoS ₂ ) and metals/alloys (such as Sn, NiSe ₂ ). Overall, these materials still undergo severe volume changes upon Na ⁺ insertion, resulting in reduced cycling stability. On the contrary, reasonable design and convenient synthesis of non-noble metal materials have high requirements for sodium-ion batteries. Carbon materials with low price and simple fabrication have been widely studied as negative electrodes of sodium-ion batteries. However, shortcomings such as low theoretical specific capacity and unsatisfactory rate performance hinder the practical application of well-structured graphite in high-energy-density sodium-ion batteries. In addition, other carbon materials, including porous carbon, heteroatom-doped carbon and carbon with different structures, are also used as negative electrode materials to improve the energy and power density of rechargeable secondary batteries. Nitrogen-doped hollow defect carbon sphere materials prepared using MF spheres as templates. Since nitrogen and carbon have similar covalent radii, nitrogen can effectively adjust the electronic structure and charge density distribution when doped into carbon-containing materials, and in During the carbon sphere preparation process, the structure is controlled to form defects, both of which can improve the ability to store sodium.

As mentioned above, cleverly combining the structural design of carbon electrodes with the interlayer expansion of carbon hosts to accommodate more inserted sodium ions is one of the most effective ways to improve the sodium storage capacity of carbon electrodes. Therefore, it is still very necessary to develop carbon-based anodes for high-performance sodium-ion batteries.

Contents of the invention

The purpose of the present invention is to provide a nitrogen-doped hollow defect carbon sphere and its preparation method and application. Nitrogen-doped hollow defect carbon spheres with controllable morphological structure can be obtained for use as sodium-ion battery negative electrode materials and improve the energy of the negative electrode materials. Density, rate performance and specific capacity.

In order to achieve the above objectives, the present invention provides a method for preparing nitrogen-doped hollow defect carbon spheres, which includes the following steps:

(1) Use self-assembly method to prepare template MF balls

After mixing melamine and formaldehyde solution, add formic acid solution under heating conditions to continue the reaction. After the reaction is completed, centrifuge to collect the sample. After washing and drying, the template MF ball is obtained;

(2) The prepared template MF spheres are coated with dopamine hydrochloride (PDA), and 1,3,5-trimethylbenzene (TMB) and triblock copolymer are added to form micelles, which are then prepared under alkaline conditions. Obtain micellar mixed solution (MF@MMPDA, black solution);

(3) Collect the sample after centrifuging the micelle mixed solution, add alcohol and sonicate, wash repeatedly with alcohol and deionized water, and dry at constant temperature to prepare defective spheres (MF@MMPDA, brown powder);

(4) Heat treatment of defective spheres to prepare nitrogen-doped hollow defective carbon spheres (black powder).

Preferably, the triblock copolymer is F127, that is, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol).

Further, in step (1), the proportional relationship between formaldehyde solution, melamine and formic acid solution is: 6-10mL: 2-3g: 0.1-0.2mL, the concentration of formaldehyde solution is 35-40wt.%, and the volume fraction of formic acid solution is is 85-90%.

Preferably, the concentration of the formaldehyde solution is 37 wt.%, and the volume fraction of the formic acid solution is 88%.

Further, the heating temperature in step (1) is 75-90°C, the reaction time after adding the formic acid solution is 100-150min; the reaction time of melamine and formaldehyde solution is 2-4min, the drying temperature is 75-90°C, and the drying The time is 10-15h.

Further, step (2) specifically includes the following steps:

Ultrasonically disperse 0.08-0.12g template MF balls in a mixed solution of alcohol and water, and then add 0.12-0.18g triblock copolymer, 0.45-0.55mL 1,3,5-trimethylbenzene and 0.12-trimethylbenzene into the mixed solution. 0.18g dopamine hydrochloride was sonicated for 15-30 min, and magnetically stirred at a speed of 200-500 r/min for 25-35 min. Then 0.3-0.4 mL ammonia solution was added and stirred continuously for 2-3 h to obtain a micellar mixed solution.

Preferably, step (2) specifically includes the following steps:

Disperse 0.1g of template MF balls in a mixed solution of alcohol and water by ultrasonic, then add 0.15g of triblock copolymer, 0.5mL of 1,3,5-trimethylbenzene and 0.15g of dopamine hydrochloride into the mixed solution and sonicate for 15 minutes. Stir magnetically at a speed of 300 r/min for 30 min, then add 0.375 mL ammonia solution, and stir continuously for 2 h to obtain a micellar mixed solution.

Further, in the mixed solution of alcohol and water, the volume fraction of alcohol is 99.0-99.9%, and the volume fraction of ammonia solution is 25-30%.

Preferably, the volume fraction of alcohol is 99.7% and the volume fraction of ammonia solution is 28%.

Further, the centrifugation speed in step (3) is 10000r/min, and the centrifugation time is 10-15min.

Further, the temperature of constant temperature drying in step (3) is 75-90°C, and the time of constant temperature drying is 10-15 hours.

Further, the heat treatment process of step (4) includes: in a protective gas atmosphere, the temperature is raised to 750-850°C at a heating rate of 1-2°C/min, and the defective sphere is calcined for 1-3 hours to obtain nitrogen-doped spheres. Hollow defective carbon spheres.

The invention also provides nitrogen-doped hollow defect carbon spheres prepared by the above preparation method of nitrogen-doped hollow defect carbon spheres.

The invention also provides the application of the above nitrogen-doped hollow defect carbon spheres in the preparation of button batteries, specifically:

Nitrogen-doped hollow defective carbon spheres, acetylene black and binder PVDF were added to the mortar at a mass ratio of 8 (80wt%): 1 (10wt%): 1 (10wt%), and then N-methylpyrrolidone was added. Grind until mixed; then apply the slurry on copper foil and transfer to a vacuum drying oven at 60°C for 12 hours;

The electrolyte consists of 1M sodium perchlorate dissolved in ethylene carbonate/diethylene carbonate (volume ratio 1:1);

And make it into a button cell in an argon-filled glove box;

Perform constant current charge and discharge tests on the NEWARE battery test system. The cut-off voltage of sodium-ion batteries is 0.01V to 3.0V;

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed on the VersasTAT workstation with a voltage range of 0.01V to 3.0V and a scan rate of 0.1mVs ^-1 ;

ESI is obtained by applying a sine wave with an amplitude of 5mV in the frequency range from 100kHz to 0.01Hz.

All tests were performed at room temperature.

To sum up, the present invention has the following advantages:

1. The present invention adopts a simple coating method to prepare the precursor MF@MMPDA. Because of the amphiphilic nature of F127, when F127, TMB, and PDA are added to the cosolvent solution, they can regularly aggregate under alkaline stirring conditions to form F127/TMB/PDA micelles, and then under appropriate stirring due to the Self-polymerization of multiple micelles self-assembled and coated the surface of MF spheres to obtain MF@MMPDA. After centrifugation and collection, TMB, which stabilizes the mesoporous structure, was removed by alcohol cleaning to generate defects. Finally, carbonization was performed to obtain nitrogen-doped hollow defect carbon spheres. And used as negative electrode material for sodium-ion batteries. Here, under constant TMB conditions, the amount of ammonia used can control the polymerization speed of PDA in micelle assembly, and the amount of MF also determines the size of the hollow structure. In addition, too fast stirring speed and stirring time will also cause Excessive polymerization causes defects to be filled and even hollow carbon spheres are formed. Therefore, the material obtained has a unique structure, abundant surface defects, and is simple to prepare. The material structure can be controlled by adjusting the amount of MF and ammonia water and controlling the stirring speed and stirring time. It has good stability and has high capacity and good rate performance as an anode material.

2. The raw materials selected in the present invention are all cheap and easy to obtain, and are environmentally friendly materials. The preparation method is simple, has good repeatability, and the prepared product has high purity.

Description of the drawings

Figure 1 is a scanning electron microscope picture and a transmission electron microscope picture of the nitrogen-doped hollow defect carbon sphere material in Example 1 of the present invention.

Figure 2 shows the 9000 cycles of the sodium-ion battery assembled with the nitrogen-doped hollow defect carbon ball material in Example 1 of the present invention at a current density of 5A g ^-1 and the charge and discharge of 100 cycles measured at a current density of 100mA g ^-1 Cycle graph.

Figure 3 shows the 8000 cycles of the sodium-ion battery assembled with the nitrogen-doped hollow defect carbon sphere material in Example 2 of the present invention measured at a current density of 5A g ^-1 and the charge and discharge of 180 cycles measured at a current density of 100mA g ^-1 Cycle graph.

Figure 4 shows the sodium-ion battery assembled with the nitrogen-doped hollow defect carbon ball material in Comparative Example 1 of the present invention, which measured 10,000 cycles at a current density of 5A g ^-1 and 200 cycles of charge and discharge measured at a current density of 100mA g ^-1 Cycle graph.

Figure 5 is a scanning electron microscope picture of the nitrogen-doped hollow defect carbon sphere material in Comparative Example 2 of the present invention.

Figure 6 shows the sodium-ion battery assembled with the nitrogen-doped hollow defect carbon ball material in Comparative Example 2 of the present invention, which measured 10,000 cycles at a current density of 5A g ^-1 and 200 cycles of charge and discharge measured at a current density of 100mA g ^-1 Cycle graph.

Detailed ways

The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. If the specific conditions are not specified in the examples, the conditions should be carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

Example 1

This embodiment provides a nitrogen-doped hollow defect carbon sphere MF@MMPDA, which is prepared by the following method:

(1) Use self-assembly method to prepare template melamine-formaldehyde resin balls (MF balls)

Mix 8 mL of formaldehyde solution (concentration: 37 wt.%) in 200 mL of deionized water at a speed of 150 r/min, and stir continuously for 2 minutes; then add 2 g of melamine to the mixed solution, and stir continuously for 2 min at a speed of 150 r/min; Add 0.2 mL of formic acid solution (volume fraction: 88%) at 80°C, and stir continuously for 2 hours at a speed of 150 r/min; after the stirring is completed, collect the sample by centrifugation at a speed of 10,000 r/min with a high-speed centrifuge, and use deionized water Wash with absolute ethanol several times, and finally place the sample in a constant-temperature vacuum oven at 80°C to dry for 12 hours; the white powder obtained is the template MF ball.

(2) Covering

0.1g MF balls were ultrasonically dispersed in a mixed solution of alcohol and water (5mL of alcohol (volume fraction: 99.7%) and 5mL of water respectively), and then 0.15g F127, 0.5mLLTMB, and 0.15gPDA were added to the mixed solution and ultrasonicated for 15 min, and at 300r Stir magnetically at a speed of /min for 30 min, then add 0.375 mL ammonia solution (volume fraction: 28%), stir continuously for 2 h, and obtain a black MF@MMPDA micelle mixed solution.

(3) Clean the MF@MMPDA ball with alcohol to form defects on the surface

Place an appropriate amount of the MF@MMPDA micelle mixed solution into a 10mL centrifuge tube, collect the samples by centrifugation at a speed of 10000r/min in a high-speed centrifuge, then add 7mL of alcohol and sonicate for 15min, and finally wash several times with alcohol and deionized water. , the sample was placed in a constant-temperature vacuum oven at 80°C for 12 h to obtain brown powder MF@MMPDA.

(4)Heat treatment

In an Ar2 atmosphere, the MF@MMPDA powder was calcined at 800°C for 2 hours at a heating rate of 1°C/min; the black powder obtained was nitrogen-doped hollow defect carbon spheres.

From the transmission electron microscope picture (TEM) and scanning electron microscope picture (SEM) in Figure 1, we can see the morphology of the prepared nitrogen-doped hollow defect carbon spheres.

This embodiment also provides the application of the above nitrogen-doped hollow defect carbon spheres in the preparation of button batteries, including the following steps:

Nitrogen-doped hollow defect carbon spheres (80wt%), acetylene black (10wt%) and polyvinylidene fluoride (PVDF) (10wt%) dissolved in N-methylpyrrolidone (NMP) were added to the mortar and ground. Mix until combined.

The slurry was then coated on copper foil and transferred to a vacuum oven at 60°C for 12 hours.

The electrolyte consisted of 1M sodium perchlorate dissolved in ethylene carbonate/diethylene carbonate (volume ratio 1:1). And made into a button battery in the glove box.

Galvanostatic charge and discharge tests were performed on the NEWARE battery test system. The cut-off voltage of the sodium-ion battery was 0.01V to 3.0V; cyclic voltammetry distribution (CV) and electrochemical impedance spectroscopy (EIS) were performed on the VersasTAT workstation. The voltage range was 0.01 V to 3.0V with a scan rate of 0.1mVs ^-1 ; ESI is obtained by applying a sine wave with an amplitude of 5mV in the frequency range from 100kHz to 0.01Hz.

All tests were performed at room temperature.

To test the electrochemical effect of the sodium-ion battery prepared in Example 1, set the cut-off voltage of the sodium-ion battery to 0.01V to 3.0V, and the current density to 100mA g ^-1 and 5A g ^-1 . The test results are shown in Figure 2.

As can be seen from Figure 2, the nitrogen-doped hollow defect carbon balls prepared in the present invention are made into button batteries and have excellent electrochemical performance. At a current density of 5A g ^-1 , the specific capacity remains at 205.56mAh g ^-1 after 9000 cycles. At a current density of 100mA g ^-1 , after 100 cycles, the specific capacity remains at 305.5mAh g ^-1 . The first Coulombic efficiency was 51%, mainly due to the decomposition of the electrolyte and the formation of SEI on the material surface, and then the Coulombic efficiency tended to stabilize.

Example 2

The difference between this embodiment and Example 1 is that the added amount of TMB is 0.4 mL.

The nitrogen-doped hollow defect carbon spheres of Example 2 were prepared into button batteries according to the method in Example 1, and relevant electrochemical tests were conducted under the same conditions.

The test results are shown in Figure 3. It can be seen from Figure 3 that the MF@MMPDA material made with a small amount of TMB is made into a button battery. At a current density of 5A g ^-1 , the specific capacity only remains at 61.66mAh after 8000 cycles. g ^-1 , while at a current density of 100mA g ^-1 , the specific capacity only remains at 132.13mAh g ^-1 after 180 cycles.

Comparative example 1

The preparation method of this comparative example is the same as that of Example 1, except that the amount of ammonia water (28%) provided as the source of alkaline conditions is changed to 0.45 mL, that is, more alkaline conditions are provided for the self-polymerization of PDA to affect the micelle formation process. The formation of its material defects. The remaining steps are the same as in Example 1.

The prepared active material was made into a button battery according to the standards and requirements of Example 1 and subjected to relevant electrochemical tests. The test results are shown in Figure 4. It can be seen from Figure 4 that the button battery assembled under this preparation scheme has a specific capacity of only 74.99mAh g ^-1 after 10,000 cycles at a current density of 5A g ^-1 , while at 100mA g At a current density of ^-1 , the specific capacity remains at 153.59mAh g ^-1 after 200 cycles. It has poor cycle stability and low capacity.

Comparative example 2

The preparation method is the same as Example 1, except that the amount of MF (0.05g) used in the process of coating MF with PDA/F127/TMB micelles is changed, that is, the amount of template relied on for the formation of the hollow structure is changed. The remaining steps are the same as in Example 1.

From the scanning electron microscope picture (SEM) in Figure 5, it can be seen that the surface morphology of the prepared nitrogen-doped hollow defect carbon spheres was made into a button battery according to the standards and requirements of Example 1 and related electrochemical tests were performed. The test results are shown in Figure 6. From Figure 6, it can be seen that the button battery assembled under this preparation scheme has a specific capacity of only 40.27mAh g ^-1 after 10,000 cycles at a current density of 5Ag ^-1 , while at a current density of 100mAg ^-1 At a current density of 200 cycles, the specific capacity remained at 55.45mAh g ^-1 after 200 cycles. It also had poor cycle stability and low capacity. This is attributed to the fact that the amount of MF added is reduced when the amounts of other drugs remain unchanged during the material preparation process. At this time, TMB and PDA are relatively increased, which respectively leads to disordered micelle self-assembly and reduced defects, resulting in the assembled battery having unstable low capacity. . Similarly, the self-polymerization of PDA on the same MF template increases, resulting in repeated deintercalation of ions during the working process of the prepared battery, causing structural rupture. Therefore, the battery capacity increases during the relative activation process but is also accompanied by instability.

It can be seen from Figure 2, Figure 3, Figure 4, and Figure 6 that Figure 2 has the best electrochemical performance. This is attributed to the larger hollow structure and abundant defects shown in Figure 1. The material provides better electrochemical properties under a high specific surface area. There are many active sites for ion storage, and the hollow structure also allows ions to be deintercalated multiple times to stabilize the structure.

Although specific embodiments of the present invention have been described in detail, this should not be construed as limiting the scope of protection of the patent. Within the scope described in the claims, various modifications and transformations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims (7)

1. The preparation method of the nitrogen-doped hollow defect carbon sphere is characterized by comprising the following steps of:

(1) Template MF ball prepared by self-assembly method

After mixing melamine and formaldehyde solution uniformly, adding formic acid solution under heating condition to continue reaction, centrifuging after the reaction is finished, collecting a sample, washing and drying to obtain a template MF sphere;

(2) Coating the prepared template MF spheres by dopamine hydrochloride, adding 1,3, 5-trimethylbenzene and triblock copolymer to form micelles, and then preparing a micelle mixed solution under alkaline conditions; the method specifically comprises the following steps:

dispersing 0.08-0.12g of template MF balls in a mixed solution of alcohol and water by ultrasonic, adding 0.12-0.18g of triblock copolymer, 0.45-0.55mL of 1,3, 5-trimethylbenzene and 0.12-0.18g of dopamine hydrochloride into the mixed solution by ultrasonic for 15-30min, magnetically stirring for 25-35min at a rotating speed of 200-500r/min, then adding 0.3-0.4mL of ammonia water solution, and continuously stirring for 2-3h to obtain a micelle mixed solution; the triblock copolymer is F127;

(3) Centrifuging the micelle mixed solution, collecting a sample, adding alcohol, performing ultrasonic treatment, repeatedly cleaning with alcohol and deionized water respectively, and drying at constant temperature to obtain a defective sphere; the constant temperature drying temperature is 75-90 ℃, and the constant temperature drying time is 10-15h;

(4) Performing heat treatment on the defective sphere to obtain the nitrogen-doped hollow defective carbon sphere, wherein the heat treatment process comprises the following steps of: and in the atmosphere of protective gas, heating to 750-850 ℃ at a heating rate of 1-2 ℃/min, and calcining the defective sphere for 1-3 hours to obtain the nitrogen-doped hollow defective carbon sphere.

2. The method for preparing nitrogen-doped hollow defect carbon spheres according to claim 1, wherein in the step (1), the ratio of formaldehyde solution, melamine and formic acid solution is as follows: 6-10mL:2-3g:0.1-0.2mL, the concentration of the formaldehyde solution is 35-40wt.%, and the volume fraction of the formic acid solution is 85-90%.

3. The method for preparing nitrogen-doped hollow defective carbon spheres according to claim 1, wherein the heating temperature in the step (1) is 75-90 ℃, and the reaction time after adding formic acid solution is 100-150min;

the reaction time of melamine and formaldehyde solution is 2-4min, the drying temperature in the step (1) is 75-90 ℃, and the drying time in the step (1) is 10-15h.

4. The method for preparing nitrogen-doped hollow defective carbon spheres according to claim 1, wherein the volume fraction of alcohol in the mixed solution of alcohol and water is 99.0-99.9%, and the volume fraction of the aqueous ammonia solution is 25-30%.

5. The method for preparing the nitrogen-doped hollow defect carbon sphere according to claim 1, wherein the centrifugal speed in the step (3) is 10000r/min, and the centrifugal time is 10-15min.

6. The nitrogen-doped hollow defect carbon sphere prepared by the preparation method of the nitrogen-doped hollow defect carbon sphere according to any one of claims 1 to 5.

7. The use of the nitrogen-doped hollow defect carbon sphere according to claim 6 for preparing a button cell.