Preparation method of carbon nitride / nano-hollow carbon sphere composite material and application of carbon nitride / nano-hollow carbon sphere composite material in fast sodium storage negative electrode

Abstract

The application relates to a preparation method of a carbon nitride / nano hollow carbon sphere composite material and application of the carbon nitride / nano hollow carbon sphere composite material in a fast sodium storage negative electrode. The carbon nitride / nano hollow carbon sphere composite material is prepared through an in-situ polymerization and heat treatment and deposition method. First, pyrrole monomers (Py) and cheap commercial polymethyl methacrylate (PMMA) template agents are uniformly dispersed into deionized water, and then an oxidizing agent is added to make the Py monomers perform in-situ polymerization and carbonization to obtain a polypyrrole derived nano hollow carbon sphere (PPy-HSC). Finally, heat treatment is adopted for modification, so that a carbon nitride (C3N4) inert layer is in-situ coated on the surface, the carbon yield of the preparation process is high, the raw material cost is easy to obtain, and the method is suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to the preparation of carbon anode materials, and particularly to high-rate sodium-ion storage and the controllable preparation of hollow carbon materials. Background Technology

[0002] Sodium-ion batteries (SIBs), with their abundant natural sodium reserves, are considered a more promising alternative energy storage system. Due to the large volume of sodium ions, the structural stability of the anode material is crucial for sodium ion insertion / extraction. Currently, research on hard carbon for sodium storage largely focuses on ether-based electrolytes. While these electrolytes exhibit superior sodium storage performance at low current densities, their high volatility and flammability significantly reduce battery safety. Furthermore, commonly used ether-based electrolytes have a narrow operating voltage range (approximately 3.6V vs. Na / Na). + This will limit the energy output of the battery in practical applications to some extent. However, carbon materials in ester electrolytes still face problems such as low capacity (<200mAh / g), poor rate performance, and poor cycle stability. Summary of the Invention

[0003] The purpose of this invention is to solve the problems of low specific capacity for sodium ion storage, short cycle life, and insufficient rate performance of carbon anode materials in ester electrolytes. A method for preparing carbon nitride / nano hollow carbon sphere composite materials and their application in rapid sodium storage anodes are proposed.

[0004] Hollow carbon spheres with a hollow structure possess advantages such as large specific surface area, structural stability, and high nitrogen content. The in-situ generated carbon nitride inert layer on the surface effectively shields oxygen-containing functional groups, thereby reducing side reactions between the material and the electrolyte during cycling. This induces a robust and uniformly thick solid electrolyte interphase (SEI) layer. Simultaneously, carbon nitride can accelerate the reaction of Na+... + Desolvation at the electrode interface improves electrochemical reaction kinetics. The prepared material exhibits excellent rate performance, high discharge capacity, and ultra-long cycle life.

[0005] The technical solution of this invention:

[0006] The preparation method of carbon nitride / hollow carbon nanospheres (HSC@CN) composite material includes the following preparation steps:

[0007] (1) Preparation of PPy / PMMA precursor: Pyrrole monomer (Py) and commercial polymethyl methacrylate (PMMA) template agent are mixed evenly in a solvent. After mixing for 2-4 hours, a precursor solution is obtained. Oxidant is added at a mass ratio of Py monomer to oxidant of 1:3.5-4. The reaction is carried out for 3-5 hours, and the polymerization temperature is maintained at 3-5℃. The mixture is washed multiple times by alternating filtration with deionized water and ethanol, and then dried in a forced-air drying oven at a drying temperature of 60-80℃ to obtain the PPy / PMMA precursor.

[0008] (2) Place the PPy / PMMA precursor obtained in step (1) into a tube furnace and heat-treat it at 600-800℃ for 2-3 hours in an inert gas environment to obtain polypyrrole-derived hollow carbon spheres (PPy-HSC).

[0009] (3) The hollow carbon spheres PPy-HSC obtained in step (2) are thoroughly mixed and ground with the raw materials for preparing the carbon nitride inert layer at a mass ratio of 1:0.25-0.5. Then, the mixture is placed under vacuum and heat-treated at 400-500℃ for 2-3 hours to allow the carbon nitride generated by the pyrolysis of the raw materials for preparing the carbon nitride inert layer to coat the surface of the hollow carbon spheres in situ to form an inert layer, thus obtaining the carbon nitride / nano hollow carbon sphere HSC@CN composite material.

[0010] Specifically, in step (1), the mass ratio of polymethyl methacrylate (PMMA) to pyrrole monomer (Py) is 1:2 to 3, the oxidant is one of ammonium persulfate, sodium persulfate and potassium persulfate, the solvent is deionized water or ethanol, and the total concentration of Py monomer and PMMA template agent in the precursor solution is 7 g / L to 10 g / L.

[0011] In step (2), the inert gas can be nitrogen or argon.

[0012] In step (3), the raw material for preparing the carbon nitride inert layer can be one of dicyandiamide, urea, or melamine, and the heating rate of the heat treatment is 2 to 4 °C / min.

[0013] This invention also provides the application of HSC@CN in a fast sodium storage anode, the method of which is as follows:

[0014] Battery Assembly: The final target product, carbon nitride / nano-hollow carbon sphere HSC@CN composite material, conductive carbon black (super P), and polyvinylidene fluoride (PVDF), were mixed in N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1 for 1–2 hours until completely homogeneous to obtain a slurry. This slurry was then coated onto current collector aluminum foil to a thickness of 150–200 μm and dried in a forced-air drying oven at 120 °C for 8–10 hours to obtain the electrode. The electrode was cut into 10 mm diameter circular electrodes using a cutting machine, and then transferred into an argon-filled glove box. A CR2023 coin cell and a 12 mm diameter sodium metal sheet were used to form a two-electrode system to investigate the electrochemical performance under different conditions.

[0015] Advantages and beneficial effects of the present invention:

[0016] The preparation steps of this invention are simple, the raw materials are readily available, and the carbon yield is high, making it suitable for large-scale production and exhibiting excellent reproducibility. This invention also has significant advantages in carbonization conditions: when preparing sodium-storage hard carbon from biomass, a long carbonization time above 1000℃ is required, while the polypyrrole selected in this invention has a significantly lower carbonization temperature (carbonization can be achieved at temperatures above 550℃), making it more energy-efficient and environmentally friendly. Simultaneously, the use of PMMA templates, which have a low melting point and are inexpensive, allows for removal during the carbonization process, eliminating the need for repeated washing with strong acids and alkalis, thus reducing pollution and improving the safety of the preparation process. The in-situ generated carbon nitride inert protective layer on the surface has an ordered structure, which can both prevent the continuous occurrence of side reactions and promote Na+ production. + The desolvation process lays a solid foundation for ultra-long cycling and excellent rate performance. Attached Figure Description

[0017] Figure 1 Raman spectra of the prepared PPy-HSC and HSC@CN;

[0018] Figure 2 XRD pattern for HSC@CN;

[0019] Figure 3 To prepare TGA tests for HSC@CN;

[0020] Figure 4 TEM image of the prepared HSC@CN;

[0021] Figure 5 To assess the rate performance of the prepared HSC@CN;

[0022] Figure 6 The prepared HSC@CN was prepared at 20 A·g -1 Cyclic performance. Detailed Implementation

[0023] Example 1

[0024] In the preparation of carbon nitride / hollow carbon nanospheres (HSC@CN) composite materials, the size of the PMMA template can be 100–200 nm in the PPy / PMMA precursor preparation step. Before adding the Py monomer, the mass fraction of PMMA in the solvent does not exceed 50%.

[0025] (1) Preparation of PPy / PMMA precursor: 120g of pyrrole (Py) monomer and 20g of commercial polymethyl methacrylate (PMMA) template agent were mixed evenly in deionized water and kept for 2h to obtain the precursor solution; 420g of ammonium persulfate oxidant was added to the precursor solution and the reaction time was 3.5h, and the polymerization temperature was maintained at 4℃; the precursor was obtained by alternately filtering and washing with deionized water and ethanol and drying at 60℃.

[0026] (2) The PPy / PMMA precursor obtained in step (1) is placed in a tube furnace and heat-treated at 700°C for 3 hours in an argon atmosphere to obtain polypyrrole-derived hollow carbon spheres (PPy-HSC).

[0027] (3) Mix 3g PPy-HSC and 0.9g urea thoroughly in step (2), place under vacuum, heat treat at 500℃ for 3h, with a heating rate of 2℃ / min, to obtain carbon nitride / nano hollow carbon sphere composite material (HSC@CN) anode composite material.

[0028] Example 2

[0029] (1) Preparation of PPy / PMMA precursor: 115g of pyrrole (Py) monomer and 25g of commercial polymethyl methacrylate (PMMA) template agent were mixed evenly in deionized water and kept for 3h to obtain the precursor solution; 431.5g of sodium persulfate oxidant was added to the precursor solution and the reaction time was 4h. The polymerization temperature was controlled at 3℃; the precursor was obtained by alternately filtering and washing with deionized water and ethanol and drying at 70℃.

[0030] (2) The PPy / PMMA precursor obtained in step (1) is placed in a tube furnace and heat-treated at 700°C for 2 hours in an inert gas environment to obtain polypyrrole-derived hollow carbon spheres (PPy-HSC).

[0031] (3) Mix 3g PPy-HSC and 1.05g dicyandiamide thoroughly in step (2), place under vacuum, heat treat at 450℃ for 2.5h, with a heating rate of 3℃ / min, to obtain carbon nitride / nano hollow carbon sphere composite material (HSC@CN) anode composite material.

[0032] Example 3

[0033] (1) Preparation of PPy / PMMA precursor: 140g of pyrrole (Py) monomer and 25g of commercial polymethyl methacrylate (PMMA) template agent were mixed evenly in a solvent and kept for 4h to obtain the precursor solution. 560g of potassium persulfate oxidant was added to the precursor solution, and the polymerization temperature was maintained at 5℃. The mixture was washed with deionized water and ethanol alternately by vacuum filtration, and dried at 80℃ to obtain the PPy / PMMA precursor.

[0034] (2) The PPy / PMMA precursor obtained in step (1) is placed in a tube furnace and heat-treated at 750°C for 2.5 h in an inert gas environment to obtain polypyrrole-derived hollow carbon spheres (PPy-HSC).

[0035] (3) Mix 3g PPy-HSC and 1.35g melamine thoroughly in step (2), place under vacuum, heat treat at 480℃ for 2h, with a heating rate of 2.5℃ / min, to obtain carbon nitride / nano hollow carbon sphere composite material (HSC@CN) negative electrode composite material.

[0036] Battery assembly

[0037] Example 4:

[0038] (1) Preparation of working electrode: The final target product HSC@CN composite material, conductive carbon black (super P) and polyvinylidene fluoride (PVDF) were mixed evenly in N-methylpyrrolidone at a mass ratio of 8:1:1 and stirred for 2 hours. After forming a uniform slurry, it was coated onto an aluminum foil current collector and dried in a 120℃ forced-air drying oven for 8 hours. Finally, the dried electrode was cut into round pieces with a diameter of 10 mm using a cutting machine.

[0039] (2) Battery assembly: The electrolyte was 5 mmol NaClO4 dissolved in 5 mL of a mixed solution of ethylene carbonate (EC) and propylene carbonate (PC) (volume ratio 1:1), with an additional 5 vol.% of fluoroethylene carbonate (FEC). A 16 mm diameter glass fiber was used as the separator, and a 12 mm diameter sodium metal sheet was used as the counter electrode. The entire assembly process of the CR2032 coin cell was carried out in an argon-filled glove box, and the voltage test range was 0.01–2.5 V.

[0040] Figure 1 The figures show the Raman spectra of PPy-HSC and HSC@CN. As can be seen from the figures, after being coated with an inert layer, the Ig of HSC@CN... D / I G The decrease in the ratio indicates that the disorder of the carbon layer in PPy-HSC decreased after heat treatment with urea.

[0041] Figure 2The XRD pattern of the prepared HSC@CN shows that the diffraction peaks at 2θ = 27.4° and 44.7° correspond to the characteristic peaks of C3N4, indicating that C3N4 is deposited on the surface of PPy-HSC.

[0042] Figure 3 The thermogravimetric curves for HSC@CN show that the C3N4 on the surface completely decomposes at around 700℃. The calculated mass fraction of C3N4 in HSC@CN is 2 wt.%.

[0043] Figure 4 The image shows the TEM morphology of HSC@CN. The prepared material has a distinct hollow structure, with carbon spheres having a diameter of approximately 180 nm. The overall structure is uniform, and the particle size distribution is even.

[0044] Figure 5 To assess the rate performance of the HSC@CN sodium-ion battery assembled with metallic sodium at different current densities, the results show that at a current density of 0.2 A·g -1 At that time, the reversible capacity can reach 250mAh·g -1 When the current density increases to 40 A·g -1 At that time, the reversible capacity can still be maintained at approximately 101 mAh·g. -1 ( Figure 5 middle).

[0045] Figure 6 The prepared HSC@CN was prepared at a current density of 20 A·g -1 The cycle life results show that the prepared electrode material exhibits excellent cycle stability; that is, after 40,000 cycles, the coulombic efficiency remains relatively stable, and the capacity can be maintained at approximately 120 mAh·g. -1 .

Claims

1. A method for preparing carbon nitride / hollow carbon nanospheres (HSC@CN) composite materials, comprising the following preparation steps: (1) Preparation of PPy / PMMA precursor: Pyrrole (Py) monomer and commercial polymethyl methacrylate (PMMA) template agent were dispersed and mixed evenly in a solvent to obtain a precursor solution. After mixing for 2-4 hours, an oxidant was added and the reaction was carried out for 3-5 hours. The polymerization temperature was controlled at 3-5℃. The precursor was obtained by alternately filtering and washing with deionized water and ethanol and drying at 60-80℃. (2) The PPy / PMMA precursor obtained in step (1) is placed in a tube furnace and heat-treated at 600-800℃ for 2-3 hours in an inert gas environment to obtain polypyrrole-derived hollow carbon spheres (PPy-HSC). (3) The PPy-HSC obtained in step (2) is thoroughly mixed with the raw material for preparing the carbon nitride inert layer at a mass ratio of 1:0.25 to 0.5, and then heat-treated at 400 to 500°C for 2 to 3 hours under vacuum to obtain carbon nitride / nano hollow carbon sphere composite material (HSC@CN).

2. The method for preparing the carbon nitride / nano-hollow carbon sphere composite material according to claim 1, characterized in that, In step (1), the mass ratio of polymethyl methacrylate (PMMA) to pyrrole Py monomer is 1:2-3, the total concentration of Py monomer and PMMA template agent in the precursor solution is 7g / L-10g / L, and the solvent is deionized water or ethanol.

3. The method for preparing the carbon nitride / nano-hollow carbon sphere composite material according to claim 1, characterized in that, The oxidant is one of ammonium persulfate, sodium persulfate, and potassium persulfate, and the mass ratio of Py monomer to oxidant is 1:3.5-4.

4. The method for preparing the carbon nitride / nano-hollow carbon sphere composite material according to claim 1, characterized in that, In step (2), the inert gas is nitrogen or argon.

5. The method for preparing the carbon nitride / nano-hollow carbon sphere composite material according to claim 1, characterized in that, In step (3), the raw material for preparing the carbon nitride inert layer is one of dicyandiamide, urea or melamine, and the heating rate of the heat treatment is 2 to 4 °C / min.

6. The application of the carbon nitride / nano-hollow carbon sphere composite material prepared by the method of any one of claims 1-5 in a fast sodium storage anode.

Images