A hard carbon material with a three-dimensional network structure, and a preparation method and application thereof

Abstract

This invention belongs to the field of new energy and discloses a three-dimensional network structure hard carbon material, its preparation method, and its application. The method involves using PMAA containing hydrophilic carboxyl groups and BzMA containing hydrophobic benzene rings as templates, which are induced to polymerize via a RAFT reaction to form block copolymer rod-shaped micelles. Aniline monomer (ANI) is added, and the blocks are bonded together through electrostatic attraction between the carboxyl groups on the copolymer and the amino groups of the aniline. Subsequently, polymerization is initiated under the action of ammonium persulfate to form a precursor, which is then carbonized at high temperature in a tube furnace to obtain a three-dimensional cross-linked network structure hard carbon material. This network structure not only possesses a certain degree of stability, mitigating the volume expansion caused by sodium ion insertion and extraction, reducing electrode stress and cracking risk, but also contains numerous pores, providing more active sites for sodium ions, shortening the ion diffusion distance, and increasing the adsorption and release rates of sodium ions. This contributes to improving the battery's discharge capacity and charging speed.

Description

Technical Field

[0001] This invention belongs to the field of new energy, and specifically relates to a hard carbon material with a three-dimensional network structure using block copolymer rod micelles as templates and polyaniline as a precursor, as well as its preparation method and application. Background Technology

[0002] With societal development, energy resource shortages and environmental problems caused by fossil fuels have drawn significant attention, making the development of new energy storage materials an urgent priority. Lithium-ion batteries, due to their high energy density, have become the preferred renewable energy storage material and have experienced rapid development. However, the limited abundance of lithium in the Earth's crust can no longer meet the demand for energy. Sodium, the sixth most abundant element on Earth, is distributed globally. Sodium and lithium belong to the same group, share similar chemical properties, and are widely distributed in the Earth's crust. If sodium could replace lithium as a new type of energy storage material, it would undoubtedly have broad application prospects.

[0003] Carbon materials, as anode materials for sodium-ion batteries, possess advantages such as high tunability and good stability, and have great application potential. Carbon-based materials include graphite, graphene, soft carbon, and hard carbon. Among them, hard carbon materials have high sodium storage capacity and low sodium intercalation potential, attracting great attention from researchers. However, ordinary hard carbon materials have limited sodium storage active sites, resulting in low specific capacitance, energy density, and poor cycle performance as anode materials for sodium-ion batteries. This is an important problem that still needs to be solved. Summary of the Invention

[0004] To address the shortcomings and deficiencies in the existing technologies and improve the sodium storage capacity, cycling performance, and rate performance of hard carbon, the primary objective of this invention is to provide a method for preparing a three-dimensional network structured hard carbon material. This method uses block copolymer rod micelles as templates and polyaniline as a precursor, and controls the morphology and structure of the hard carbon material.

[0005] Another objective of this invention is to provide a hard carbon material with a three-dimensional network structure prepared by the above-described preparation method.

[0006] Another object of the present invention is to provide the application of the above-mentioned three-dimensional network structure of hard carbon materials.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing a three-dimensional network structured hard carbon material comprises the following steps: Poly(PMAA) methacrylate (PMAA) and benzyl methacrylate (BzMA) are induced to polymerize via a RAFT reaction to form rod-shaped micelles of a diblock copolymer PMAA-PBzMA, wherein the rod-shaped micelles of PMAA-PBzMA include a PBzMA core and an outer shell of PMAA; the rod-shaped micelles are dissolved in water to form a 1 wt% aqueous solution, then hydrochloric acid solution is added and stirred until homogeneous; aniline monomer is then added and stirred, allowing the aniline monomer to be adsorbed onto the surface of the rod-shaped micelles through electrostatic forces; subsequently, an initiator is added to initiate aniline polymerization, yielding a precursor with polyaniline (PANI) as the shell and PMAA-PBzMA as the core; finally, the precursor is carbonized at a high temperature of 600-1800℃ to obtain the three-dimensional network structured hard carbon material.

[0009] The three-dimensional mesh structure is a topological structure formed by cross-connection of 30-50nm carbon fibers, and each carbon fiber unit is hollow inside.

[0010] The rod-shaped micelles of the diblock copolymer PMAA-PBzMA have a PBzMA core containing a benzene ring, which is an oleophilic and hydrophobic end, and a PMAA shell containing a carboxyl group, which is a hydrophilic and oleophobic end.

[0011] The rod-shaped micelles of the diblock copolymer PMAA-PBzMA are obtained by molecularly induced polymerization self-assembly of poly(PMAA) methacrylate and benzyl methacrylate (BzMA) in a co-solvent of organic solvent and water. The organic solvent is one or more of ethanol, methanol, propanol, acetone, N-methylformamide and dimethyl sulfoxide, and the volume ratio of organic solvent to water is 1:(1-10).

[0012] The precursor is prepared by electrostatic attraction between the amino groups on the aniline (ANI) monomer and the carboxyl groups on the diblock copolymer, followed by polymerization under the action of an initiator to form a network structure of polyaniline PANI, resulting in a precursor with polyaniline PANI as the shell and PMAA-PBzMA as the core; the initiator is one or more of potassium persulfate, ammonium persulfate, ferric chloride and hydrogen peroxide.

[0013] Specifically, the carbonization process involves placing the precursor in a tube furnace and heating it to 600-1800℃ at a rate of 2-10℃ / min under a nitrogen or argon atmosphere, holding it at that temperature for 1-12 hours to obtain a hard carbon material with a three-dimensional network structure.

[0014] A hard carbon material with a three-dimensional network structure prepared by the above-described preparation method.

[0015] The above-mentioned three-dimensional network structure of hard carbon material is used in the anode material of sodium-ion secondary batteries.

[0016] A three-dimensional network structure of hard carbon material, conductive agent acetylene black, and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 8:1:1, ground in a mortar, and N-methylpyrrolidone (NMP) is added to make a slurry. The slurry is then coated on copper foil, dried, and cut into electrode sheets to obtain the negative electrode sheet for sodium-ion secondary batteries.

[0017] The present invention has the following advantages and effects compared with the prior art:

[0018] (1) In this invention, poly(PMAA) containing hydrophilic carboxyl groups and poly(benzyl methacrylate) containing hydrophobic benzene rings are induced to polymerize via a RAFT reaction. The resulting rod-shaped micelles are used as templates, and aniline monomer (ANI) is added. The molecules are bonded together by electrostatic attraction between the carboxyl groups on the block copolymer and the amino groups of aniline. Subsequently, polymerization is initiated under the action of ammonium persulfate (APS) to form polyaniline (PANI). The polymer is then placed in a tube furnace and carbonized under a nitrogen atmosphere. During the high-temperature carbonization process, the PMAA-PBzMA template undergoes thermal decomposition, yielding a hard carbon material with a three-dimensional cross-linked network structure. This network structure not only has a certain degree of stability, mitigating the volume expansion caused by sodium ions during insertion and extraction, reducing electrode stress and cracking risk, but also has a large number of pores, which can provide more active sites for sodium ions, shorten the diffusion distance of ions, improve the adsorption and release rate of sodium ions, and improve the discharge capacity and charging speed of the battery.

[0019] (2) The mesh structure hard carbon material of the present invention is applied to the negative electrode of sodium-ion secondary battery, which is beneficial to improving the specific capacity, cycle stability and rate performance of sodium-ion secondary battery, and provides a new possibility for the large-scale and industrialized development of sodium-ion secondary battery. Attached Figure Description

[0020] Figure 1 These are SEM images of the hard carbon materials obtained in Example 1 and Comparative Example 1 of this invention.

[0021] Figure 2 The hard carbon materials obtained in Example 1 and Comparative Example 1 of this invention are at 100 mAg -1 The first three charge-discharge cycle curves are shown below.

[0022] Figure 3 The hard carbon materials obtained in Example 1 and Comparative Example 1 of this invention are in 1Ag -1 The following is a cycle curve (the number of cycles is 500).

[0023] Figure 4 This is a rate performance diagram of the hard carbon materials obtained in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0024] The following specific embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention.

[0025] Example 1

[0026] (1) Add methacrylic acid monomer MAA and thermal initiator in an aqueous solution at a molar ratio of 60:1. During heating and stirring in a nitrogen atmosphere, free radicals are generated to initiate the polymerization reaction. The reaction temperature is 60℃ and the reaction time is 4 hours to generate polymethacrylic acid PMAA.

[0027] (2) In a cosolvent of ethanol and water in a volume ratio of 1:5, poly(PMAA) methacrylate monomers (BzMA) and azodicyanovalerate initiator (ACVA) were added at a molar ratio of 4:100:1. The mixture was heated and stirred in a nitrogen atmosphere to carry out a reversible addition-fracture chain transfer (RAFT) copolymerization reaction at a reaction temperature of 90°C for 6 hours, resulting in rod-shaped micelles of the diblock copolymer PMAA-PBzMA.

[0028] (3) The rod-shaped micelles of the diblock copolymer PMAA-PBzMA obtained in step (2) were dissolved in deionized water at a mass ratio of 1:99 to obtain an aqueous solution of PMAA-PBzMA with a mass percentage concentration of 1%. 137.5 mL of the aqueous solution was taken and 25 mL of 0.1 mol / L hydrochloric acid solution was added and stirred evenly. Then 0.25 mL of ANI monomer (2.7 mmol) was added and stirred for 2 hours to obtain a mixed solution. Then 0.31 g of APS (1.35 mmol) was dissolved in 5 mL of water and slowly added dropwise to the above mixed solution. The reaction was continued at room temperature for 24 hours to generate the polymer PMAA-PBzMA@PANI. The polymer was placed in the freezer for 5-6 hours and then transferred to a freeze dryer for 48 hours to obtain a precursor with polyaniline PANI as the shell and PMAA-PBzMA as the core, abbreviated as P-PANI.

[0029] (4) The precursor obtained in step (3) is placed in a tube furnace and carbonized at 5°C / min to 600°C under a nitrogen atmosphere. After holding at the temperature for 2 hours, it is naturally cooled to room temperature to obtain a hard carbon material with a three-dimensional network structure.

[0030] Example 2

[0031] (1) Add methacrylic acid monomer MAA and thermal initiator in an aqueous solution at a molar ratio of 60:1. During heating and stirring in a nitrogen atmosphere, free radicals are generated to initiate the polymerization reaction. The reaction temperature is 60℃ and the reaction time is 4 hours to generate polymethacrylic acid PMAA.

[0032] (2) In a cosolvent of ethanol and water in a volume ratio of 1:5, poly(PMAA) methacrylate monomers (BzMA) and azodicyanovalerate initiator (ACVA) were added at a molar ratio of 4:100:1. The mixture was heated and stirred in a nitrogen atmosphere to carry out a reversible addition-fracture chain transfer (RAFT) copolymerization reaction at a reaction temperature of 90°C for 6 hours, resulting in rod-shaped micelles of the diblock copolymer PMAA-PBzMA.

[0033] (3) The rod-shaped micelles of the diblock copolymer PMAA-PBzMA obtained in step (2) were dissolved in deionized water at a mass ratio of 1:99 to obtain an aqueous solution of PMAA-PBzMA with a mass percentage concentration of 1%. 137.5 mL of the aqueous solution was taken and 25 mL of 0.1 mol / L hydrochloric acid solution was added and stirred evenly. Then 0.25 mL of ANI monomer (2.7 mmol) was added and stirred for 2 hours to obtain a mixed solution. Then 0.31 g of APS (1.35 mmol) was dissolved in 5 mL of water and slowly added dropwise to the above mixed solution. The reaction was continued at room temperature for 24 hours to generate the polymer PMAA-PBzMA@PANI. The polymer was placed in the freezer for 5-6 hours and then transferred to a freeze dryer for 48 hours to obtain a precursor with polyaniline PANI as the shell and PMAA-PBzMA as the core.

[0034] (4) The precursor obtained in step (3) is placed in a tube furnace and carbonized at 900°C at 5°C / min under a nitrogen atmosphere. After holding at the temperature for 2 hours, it is naturally cooled to room temperature to obtain a hard carbon material with a three-dimensional network structure.

[0035] Example 3

[0036] (1) Add methacrylic acid monomer MAA and thermal initiator in an aqueous solution at a molar ratio of 60:1. During heating and stirring in a nitrogen atmosphere, free radicals are generated to initiate the polymerization reaction. The reaction temperature is 60℃ and the reaction time is 4 hours to generate polymethacrylic acid PMAA.

[0037] (2) In a cosolvent of ethanol and water in a volume ratio of 1:5, poly(PMAA) methacrylate monomers (BzMA) and azodicyanovalerate initiator (ACVA) were added at a molar ratio of 4:100:1. The mixture was heated and stirred in a nitrogen atmosphere to carry out a reversible addition-fracture chain transfer (RAFT) copolymerization reaction at a reaction temperature of 90°C for 6 hours, resulting in rod-shaped micelles of the diblock copolymer PMAA-PBzMA.

[0038] (3) The rod-shaped micelles of the diblock copolymer PMAA-PBzMA obtained in step (2) were dissolved in deionized water at a mass ratio of 1:99 to obtain an aqueous solution of PMAA-PBzMA with a mass percentage concentration of 1%. 137.5 mL of the aqueous solution was taken and 25 mL of 0.1 mol / L hydrochloric acid solution was added and stirred evenly. Then 0.25 mL of ANI monomer (2.7 mmol) was added and stirred for 2 hours to obtain a mixed solution. Then 0.31 g of APS (1.35 mmol) was dissolved in 5 mL of water and slowly added dropwise to the above mixed solution. The reaction was continued at room temperature for 24 hours to generate the polymer PMAA-PBzMA@PANI. The polymer was placed in the freezer for 5-6 hours and then transferred to a freeze dryer for 48 hours to obtain a precursor with polyaniline PANI as the shell and PMAA-PBzMA as the core.

[0039] (4) The precursor obtained in step (3) is placed in a tube furnace and heated to 1200°C at 5°C / min under a nitrogen atmosphere. After holding at the temperature for 2 hours, it is naturally cooled to room temperature to obtain a hard carbon material with a three-dimensional network structure.

[0040] Example 4

[0041] (1) Add methacrylic acid monomer MAA and thermal initiator in an aqueous solution at a molar ratio of 60:1. During heating and stirring in a nitrogen atmosphere, free radicals are generated to initiate the polymerization reaction. The reaction temperature is 60℃ and the reaction time is 4 hours to generate polymethacrylic acid PMAA.

[0042] (2) In a cosolvent of ethanol and water in a volume ratio of 1:5, poly(PMAA) methacrylate monomers (BzMA) and azodicyanovalerate initiator (ACVA) were added at a molar ratio of 4:100:1. The mixture was heated and stirred in a nitrogen atmosphere to carry out a reversible addition-fracture chain transfer (RAFT) copolymerization reaction at a reaction temperature of 90°C for 6 hours, resulting in rod-shaped micelles of the diblock copolymer PMAA-PBzMA.

[0043] (3) The rod-shaped micelles of the diblock copolymer PMAA-PBzMA obtained in step (2) were dissolved in deionized water at a mass ratio of 1:99 to obtain an aqueous solution of PMAA-PBzMA with a mass percentage concentration of 1%. 137.5 mL of the aqueous solution was taken and 25 mL of 0.1 mol / L hydrochloric acid solution was added and stirred evenly. Then 0.25 mL of ANI monomer (2.7 mmol) was added and stirred for 2 hours to obtain a mixed solution. Then 0.31 g of APS (1.35 mmol) was dissolved in 5 mL of water and slowly added dropwise to the above mixed solution. The reaction was continued at room temperature for 24 hours to generate the polymer PMAA-PBzMA@PANI. The polymer was placed in the freezer for 5-6 hours and then transferred to a freeze dryer for 48 hours to obtain a precursor with polyaniline PANI as the shell and PMAA-PBzMA as the core.

[0044] (4) The precursor obtained in step (3) is placed in a tube furnace and heated to 1500°C at 5°C / min under a nitrogen atmosphere. After holding at the temperature for 2 hours, it is naturally cooled to room temperature to obtain a hard carbon material with a three-dimensional network structure.

[0045] Comparative Example 1

[0046] Compared with Example 1, Comparative Example 1 provides a method for polymerization of aniline monomers directly without using a template.

[0047] (1) Dissolve 0.25 mL of ANI monomer (2.7 mmol) in 25 mL of 0.1 mol / L hydrochloric acid solution and stir for 2 hours. Then, dissolve 0.31 g of APS (1.35 mmol) in 5 mL of water and slowly add it dropwise to the above solution. Continue to react at room temperature for 24 hours to generate polymer PANI. Place it in the freezer for 5-6 hours and then transfer it to a freeze dryer to dry for 48 hours to obtain polyaniline PANI precursor.

[0048] (2) The precursor obtained in step (1) is placed in a tube furnace and carbonized at 5°C / min to 600°C under a nitrogen atmosphere. After holding at the temperature for 2 hours, it is naturally cooled to room temperature to obtain hard carbon material.

[0049] Example of effect

[0050] Preparation of hard carbon material electrode sheets: The hard carbon materials obtained in Examples 1-4 and Comparative Example 1 were mixed with acetylene black and binder (PVDF) at a mass ratio of 8:1:1 and ground evenly. An appropriate amount of N-methylpyrrolidone (NMP) was added to form a slurry, which was then evenly coated onto copper foil. After drying in a vacuum oven at 60°C for 12 hours, electrode sheets were obtained and then cut into pieces using a cutting machine. A round disc.

[0051] This example provides a sodium-ion battery half-cell. The electrode sheet obtained above is used as the negative electrode, a metallic sodium sheet as the counter electrode, glass fiber as the separator, and a 1 mol / L NaPF6 diethylene glycol dimethyl ether solution as the electrolyte. The cells are assembled into a coin cell in an argon-filled glove box. The battery is tested using a LAND battery testing system (CT2001A) with a charge / discharge voltage range of 0–3V. The parameters and sodium storage performance of the resulting battery are measured, and the results are shown in Table 1.

[0052] Table 1. Main parameters and sodium storage performance of batteries prepared from the hard carbon materials obtained in Examples 1-4 and Comparative Example 1.

[0053]

[0054] Figure 1 The images are SEM images of hard carbon materials. In (a), it can be seen that Example 1 P-PANI is a topological structure formed by cross-connection of 30-50nm carbon fibers. This network architecture not only has a certain degree of stability, which can alleviate the volume expansion caused by sodium ions during insertion and extraction, reduce the stress and cracking risk of the electrode, but also has a large number of pores, which can provide more active sites for sodium ions, shorten the diffusion distance of ions, and improve the adsorption and release rate of sodium ions. This helps to improve the discharge capacity and charging speed of the battery. In contrast, (b) shows that Comparative Example 1 PANI is an amorphous block and does not have the advantages of the structure of Example 1.

[0055] Figure 2 Figure 1 shows the charge-discharge curves of hard carbon materials. Figure 2(a) shows the material of Example 1 with a charge specific capacity of 259.8 mAh / g and an initial coulombic efficiency of 59% at a current density of 100 mA / g and a voltage range of 0-3V. Figure 3(b) shows that the material of Comparative Example 1 only shows a charge specific capacity of 156 mAh / g and an initial coulombic efficiency of 55% at a current density of 100 mA / g and a voltage range of 0-3V.

[0056] Figure 3 The graph shows the cycling performance of the hard carbon material. It can be seen that compared with Comparative Example 1, Example 1 has better cycling stability. At a current density of 1000 mA / g, it still has 97% capacity retention after 500 cycles.

[0057] Figure 4 The graph shows the rate performance of the hard carbon material. It can be seen that Example 1 also has better rate performance compared to Comparative Example 1. After five cycles of testing at different current densities from 100 mA / g to 20000 mA / g, the sample of Example 1 still retains 96% of its capacity when the current density is returned to 1000 mA / g.

[0058] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a three-dimensional network structured hard carbon material, comprising the following steps: poly(PMAA) methacrylate (PMAA) and benzyl methacrylate (BzMA) are induced to polymerize via a RAFT reaction to form rod-shaped micelles of a diblock copolymer PMAA-PBzMA, wherein the rod-shaped micelles of the diblock copolymer PMAA-PBzMA include a PBzMA core and a PMAA shell encapsulating it; the rod-shaped micelles are dissolved in water to form a 1 wt% aqueous solution, then hydrochloric acid solution is added and stirred, and then aniline monomer is added and stirred to allow the aniline monomer to be adsorbed onto the surface of the rod-shaped micelles by electrostatic forces; then an initiator is added to initiate the polymerization of aniline to obtain a precursor with polyaniline (PANI) as the shell and PMAA-PBzMA as the core; finally, the precursor is carbonized at a high temperature of 600-1800℃ to obtain a three-dimensional network structured hard carbon material.

2. The method of claim 1, wherein: The three-dimensional mesh structure is a topological structure formed by cross-connection of 30-50nm carbon fibers, and each carbon fiber unit is hollow inside.

3. The method for preparing a three-dimensional network structured hard carbon material according to claim 1, characterized in that: The rod-shaped micelles of the diblock copolymer PMAA-PBzMA have a PBzMA core containing a benzene ring, which is an oleophilic and hydrophobic end, and a PMAA shell containing a carboxyl group, which is a hydrophilic and oleophobic end.

4. The method of claim 1, wherein: The rod-shaped micelles of the diblock copolymer PMAA-PBzMA are obtained by molecularly induced polymerization self-assembly of poly(PMAA) methacrylate and benzyl methacrylate (BzMA) in a co-solvent of organic solvent and water. The organic solvent is one or more of ethanol, methanol, propanol, acetone, N-methylformamide and dimethyl sulfoxide, and the volume ratio of organic solvent to water is 1:(1-10).

5. The method of claim 1, wherein: The precursor is prepared by electrostatic attraction between the amino groups on the aniline monomer and the carboxyl groups on the diblock copolymer, followed by polymerization initiated by an initiator to form a network structure of polyaniline PANI, resulting in a precursor with polyaniline PANI as the shell and PMAA-PBzMA as the core; the initiator is one or more of potassium persulfate, ammonium persulfate, ferric chloride and hydrogen peroxide.

6. The method of claim 1, wherein: Specifically, the carbonization process involves placing the precursor in a tube furnace and heating it to 600-1800℃ at a rate of 2-10℃ / min under a nitrogen or argon atmosphere, holding it at that temperature for 1-12 hours to obtain a hard carbon material with a three-dimensional network structure.

7. A hard carbon material with a three-dimensional network structure prepared by the preparation method according to any one of claims 1-6.

8. The application of the three-dimensional network structure hard carbon material according to claim 7 in the anode material of sodium-ion secondary batteries.

9. Use according to claim 8, characterized in that: A three-dimensional network structure of hard carbon material, conductive agent acetylene black, and polyvinylidene fluoride are mixed in a mass ratio of 8:1:1, ground in a mortar, and N-methylpyrrolidone is added to make a slurry. The slurry is then coated on copper foil, dried, and cut into electrode sheets to obtain the negative electrode sheet for sodium-ion secondary batteries.

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