Preparation method of melamine-modified acrylic resin hard carbon material

Abstract

The present invention discloses a preparation method of a melamine-modified acrylic resin hard carbon material. By using the -NH2 of melamine and the -COOH of acrylic resin for a chemical bond synthesis reaction, dehydration condensation occurs to generate amide bonds to connect them into a three-dimensional network structure. Specifically, it includes the following steps: Step 1, element doping; Step 2, low-temperature curing; Step 3, high-temperature carbonization: Then a loose and porous sponge-like melamine-modified acrylic resin hard carbon material can be obtained. The present invention uses an acrylic resin with a carboxyl functional group as the hard carbon precursor material, and uses the -NH2 of melamine and the -COOH of acrylic resin for a chemical bond synthesis reaction, and dehydration condensation generates amide bonds to connect them into a three-dimensional network structure; hydrothermal treatment generates sponge-like amorphous carbon, and low-temperature curing reduces the generation of pores and defects, greatly improving the initial efficiency; high-temperature carbonization changes the pores from macropores to micropores, increases the number of closed pores, enhances the sodium-ion battery platform capacity, and improves the cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of anode materials for sodium-ion batteries, and specifically to a preparation method of a melamine-modified acrylic resin hard carbon material. Background Art

[0002] Most of the resin precursors of the hard carbon materials for the anodes of sodium-ion batteries are mainly phenolic resins. However, the preparation process of phenolic resins is too cumbersome. It is necessary to mix formaldehyde and benzene in a certain proportion, and at the same time, an acid / alkaline solution needs to be added as a catalyst, and the polycondensation time needs to be strictly controlled. Secondly, formaldehyde monomers are toxic, and special attention needs to be paid to safety during the production and preparation process. Formaldehyde has a certain degree of harm to production workers and the environment. Finally, free phenol and free aldehyde gases will inevitably be volatilized during the transportation of the resin in high-temperature weather.

[0003] As the main anode material for sodium-ion batteries, phenolic resin hard carbon has basic problems such as low initial efficiency and poor cycle performance. The main reason is that the hard carbon has a short-range ordered and long-range disordered internal structure, which makes the potential barrier large when sodium ions are embedded, the ion migration impedance large, and the thermodynamic performance unstable. In addition, the electron state around the carbon atoms of the hard carbon itself is not conducive to the embedding of sodium ions, resulting in poor kinetic performance.

[0004] Acrylic resin is a type of thermoplastic resin made by polymerizing acrylic acid, methacrylic acid and their derivatives (esters, nitriles, amides), and can be repeatedly softened by heating and solidified by cooling. Generally, it is a linear polymer compound, which can be a homopolymer or a copolymer. It has excellent physical and mechanical properties, weather resistance, chemical resistance, water resistance and high light and color retention. By modifying acrylic resin with melamine, the internal part of the cross-linked resin-based hard carbon material is graphitized, increasing the number of closed pores and improving the capacity of the cross-linked resin-based hard carbon material. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a melamine-modified acrylic resin hard carbon material to solve the problems of low initial efficiency and poor cycle performance of existing phenolic resin hard carbon as the main anode material for sodium-ion batteries.

[0006] To achieve the above purpose, the present invention provides the following technical solution: A preparation method of a melamine-modified acrylic resin hard carbon material, which uses the -NH 2 of melamine and the -COOH of acrylic resin to carry out a chemical bond synthesis reaction, and dehydration condensation generates an amide bond to connect them into a three-dimensional network structure. The specific steps are as follows:

[0007] Step 1. Element doping: Dissolve melamine in a mixed solution of ethanol and deionized water, then add acrylic resin. After stirring evenly, transfer it to a hydrothermal reaction to form a spongy melamine-modified resin precursor;

[0008] Step 2. Low-temperature curing: Place the above-mentioned spongy melamine-modified resin precursor in a muffle furnace for heating to obtain a completely cured melamine-modified resin precursor;

[0009] Step 3. High-temperature carbonization: Perform two-stage heat treatment on the completely cured melamine-modified resin precursor obtained in Step 2 in a nitrogen atmosphere. The first stage is to maintain a constant temperature of 500 °C for 10 h, and the second stage is to maintain a constant temperature of 1400 °C for 2 h. After the second-stage heat treatment is completed, a porous spongy melamine-modified acrylic resin hard carbon material can be obtained.

[0010] Among them, in Step 1, the volume ratio of ethanol to deionized water in the mixed solution is 1:1 - 5.

[0011] Among them, in Step 1, the mass ratio of melamine to acrylic resin is 1:1 - 10.

[0012] Among them, in Step 1, the temperature of the hydrothermal reaction is 100 - 150 °C, and the time is 1 - 10 h.

[0013] Among them, in Step 2, the specific conditions for heating in the muffle furnace are: the heating rate is 0.1 - 8 °C / min, and a constant temperature of 100 - 300 °C is maintained for 1 - 5 h.

[0014] Among them, the protective gas introduced during the heating process is one or more of nitrogen, argon, and helium, and its flow rate is 4 - 400 mL / min.

[0015] Among them, the ventilation flow rate of nitrogen in the high-temperature carbonization is 6 - 350 mL / min.

[0016] Among them, the heating rate during the two-stage heat treatment process can be 0.5 - 10 °C / min.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] The present invention uses acrylic resin with a carboxyl functional group as a hard carbon precursor material, and utilizes the -NH of melamine 2A chemical bond synthesis reaction is carried out with the -COOH of the acrylic resin, and dehydration condensation occurs to generate amide bonds to connect it into a three-dimensional network structure; among them, melamine is both a cross-linking agent for the acrylic resin and a doping agent for N element. While improving the structural stability, N element is incorporated to improve the conductivity of the overall material and the active sites for sodium storage; hydrothermal treatment generates sponge-like amorphous carbon, and low-temperature curing reduces the generation of pores and defects, greatly improving the initial efficiency; high-temperature carbonization changes the pores from macropores to micropores, increases the number of closed pores, improves the platform capacity of the sodium-ion battery, and improves the cycling performance. Brief Description of the Drawings

[0019] Figure 1 This is the SEM image of the melamine-modified acrylic resin hard carbon material of the present invention. Detailed Embodiments

[0020] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0021] Example 1

[0022] A preparation method of a melamine-modified acrylic resin hard carbon material, which can be used as the negative electrode material of a sodium-ion battery. Using the -NH 2 of melamine and the -COOH of the acrylic resin to carry out a chemical bond synthesis reaction, and dehydration condensation occurs to generate amide bonds to connect it into a three-dimensional network structure. The specific steps are as follows:

[0023] Step 1. Element doping: Dissolve 4 g of melamine in a mixed solution of 100 ml of ethanol and 200 ml of deionized water, then add 20 g of acrylic resin and stir evenly, and then transfer it to a hydrothermal reaction kettle and keep it at a constant temperature of 120 °C for 5 h to form a sponge-like melamine-modified resin precursor.

[0024] Step 2. Low-temperature curing: Place the above sponge-like melamine-modified resin precursor in a muffle furnace under a nitrogen atmosphere and heat it. Heat it from room temperature to 150 °C at a rate of 1 °C / min and keep it for 2 h to obtain a completely cured melamine-modified resin precursor.

[0025] Step 3. High-temperature carbonization: Grind the completely cured melamine-modified resin precursor obtained in Step 2 into powder, and conduct two-stage heat treatment in a nitrogen atmosphere. The first stage is to heat up to 500 °C at a rate of 2 °C / min for 10 h of low-temperature pre-carbonization heat treatment; the second stage is to heat up to 1400 °C for 3 h of high-temperature heat treatment; after the second-stage heat treatment is completed, a porous sponge-like melamine-modified acrylic resin hard carbon material can be obtained.

[0026] Example 2

[0027] A preparation method of a melamine-modified acrylic resin hard carbon material, which can be used as the negative electrode material of a sodium-ion battery. Using the -NH 2 of melamine and the -COOH of acrylic resin to carry out a chemical bond synthesis reaction, dehydrating and condensing to form an amide bond to connect them into a three-dimensional network structure, which specifically includes the following steps:

[0028] Step 1. Element doping: Dissolve 4 g of melamine in a mixed solution of 50 ml of ethanol and 250 ml of deionized water, then add 20 g of acrylic resin and stir evenly, and then transfer it to a hydrothermal reaction kettle and keep it at a constant temperature of 120 °C for 5 h to form a sponge-like melamine-modified resin precursor.

[0029] Step 2. Low-temperature curing: Place the above sponge-like melamine-modified resin precursor in a muffle furnace under a nitrogen atmosphere and heat it up at a rate of 1 °C / min to 150 °C and keep it for 2 h to obtain a completely cured melamine-modified resin precursor.

[0030] Step 3. High-temperature carbonization: Grind the completely cured melamine-modified resin precursor obtained in Step 2 into powder, and conduct two-stage heat treatment in a nitrogen atmosphere. The first stage is to heat up to 500 °C at a rate of 2 °C / min for 10 h of low-temperature pre-carbonization heat treatment; the second stage is to heat up to 1400 °C for 3 h of high-temperature heat treatment; after the second-stage heat treatment is completed, a porous sponge-like melamine-modified acrylic resin hard carbon material can be obtained.

[0031] Example 3

[0032] A preparation method of a melamine-modified acrylic resin hard carbon material, which can be used as the negative electrode material of a sodium-ion battery. Using the -NH 2 of melamine and the -COOH of acrylic resin to carry out a chemical bond synthesis reaction, dehydrating and condensing to form an amide bond to connect them into a three-dimensional network structure, which specifically includes the following steps:

[0033] Step 1. Element doping: Dissolve 2 g of melamine in a mixed solution of 100 ml of ethanol and 200 ml of deionized water, then add 20 g of acrylic resin and stir evenly. Then transfer it to a hydrothermal reaction kettle and keep it at a constant temperature of 120 °C for 5 h to form a spongy melamine-modified resin precursor;

[0034] Step 2. Low-temperature curing: Place the above spongy melamine-modified resin precursor in a muffle furnace under a nitrogen atmosphere and heat it. Raise the temperature to 150 °C at a rate of 1 °C / min and keep it for 2 h to obtain a completely cured melamine-modified resin precursor;

[0035] Step 3. High-temperature carbonization: Grind the completely cured melamine-modified resin precursor obtained in Step 2 into powder and carry out two-stage heat treatment in a nitrogen atmosphere. The first stage is to raise the temperature to 500 °C at a rate of 2 °C / min for low-temperature pre-carbonization heat treatment for 10 h; the second stage is to raise the temperature to 1400 °C for high-temperature heat treatment for 3 h. After the second-stage heat treatment is completed, a porous spongy melamine-modified acrylic resin hard carbon material can be obtained.

[0036] Example 4

[0037] A preparation method of a melamine-modified acrylic resin hard carbon material, which can be used as the negative electrode material of a sodium-ion battery. Using the -NH of melamine 2 and -COOH of acrylic resin to carry out a chemical bond synthesis reaction, dehydrating and condensing to form an amide bond to connect them into a three-dimensional network structure, specifically including the following steps:

[0038] Step 1. Element doping: Dissolve 4 g of melamine in a mixed solution of 100 ml of ethanol and 200 ml of deionized water, then add 20 g of acrylic resin and stir evenly. Then transfer it to a hydrothermal reaction kettle and keep it at a constant temperature of 120 °C for 5 h to form a spongy melamine-modified resin precursor;

[0039] Step 2. Low-temperature curing: Place the above spongy melamine-modified resin precursor in a muffle furnace under a nitrogen atmosphere and heat it. Raise the temperature to 300 °C at a rate of 1 °C / min and keep it for 2 h to obtain a completely cured melamine-modified resin precursor;

[0040] Step 3. High-temperature carbonization: Grind the completely cured melamine-modified resin precursor obtained in Step 2 into powder and carry out two-stage heat treatment in a nitrogen atmosphere. The first stage is to raise the temperature to 500 °C at a rate of 2 °C / min for low-temperature pre-carbonization heat treatment for 10 h; the second stage is to raise the temperature to 1400 °C for high-temperature heat treatment for 3 h. After the second-stage heat treatment is completed, a porous spongy melamine-modified acrylic resin hard carbon material can be obtained.

[0041] Example 5

[0042] A preparation method of a melamine-modified acrylic resin hard carbon material, which can be used as the negative electrode material of a sodium-ion battery. Using the -NH of melamine 2 and the -COOH of acrylic resin to carry out a chemical bond synthesis reaction, dehydrating and condensing to generate amide bonds to connect them into a three-dimensional network structure, specifically including the following steps:

[0043] Step 1. Element doping: Dissolve 4 g of melamine in a mixed solution of 100 ml of ethanol and 200 ml of deionized water, then add 20 g of acrylic resin and stir evenly. Then transfer it to a hydrothermal reaction kettle and keep it at a constant temperature of 120 °C for 5 h to form a spongy melamine-modified resin precursor;

[0044] Step 2. Low-temperature curing: Place the above-mentioned spongy melamine-modified resin precursor in a muffle furnace under a nitrogen atmosphere and heat it. Raise the temperature to 150 °C at a rate of 2 °C / min and keep it for 2 h to obtain a completely cured melamine-modified resin precursor;

[0045] Step 3. High-temperature carbonization: Grind the completely cured melamine-modified resin precursor obtained in Step 2 into powder, and carry out two-stage heat treatment in a nitrogen atmosphere. The first stage is to raise the temperature to 500 °C at a rate of 2 °C / min for low-temperature pre-carbonization heat treatment for 10 h; the second stage is to raise the temperature to 1400 °C for high-temperature heat treatment for 3 h; after the heat treatment in the second stage is completed, a loose and porous spongy melamine-modified acrylic resin hard carbon material can be obtained.

[0046] Comparative Example 1

[0047] A preparation method of an N-doped acrylic resin hard carbon material, which can be used as the negative electrode material of a sodium-ion battery. The specific preparation method is as follows:

[0048] Step 1. Mix 4 g of melamine and 20 g of acrylic resin evenly to obtain a mixed resin precursor;

[0049] Step 2. Place the obtained mixed resin precursor in a muffle furnace under an argon atmosphere, raise the temperature to 500 °C at a rate of 2 °C / min and keep it for 10 h; then raise the temperature to 1400 °C at the same heating rate for high-temperature heat treatment for 3 h, and then a melamine-mixed acrylic resin hard carbon material can be obtained.

[0050] Comparative Example 2

[0051] A preparation method of an acrylic resin hard carbon material, which can be used as the negative electrode material of a sodium-ion battery. The specific preparation method is as follows:

[0052] Step 1: Disperse 4 g of ammonia water in a mixed solution of 100 ml of ethanol and 200 ml of deionized water. Then add 20 g of acrylic resin and mix evenly. Next, transfer it to a hydrothermal reactor and keep it at a constant temperature of 120 °C for 5 h to obtain a spongy melamine-modified resin precursor.

[0053] Step 2: Place the obtained melamine-modified resin precursor in a muffle furnace under a nitrogen atmosphere and heat it to 150 °C at a rate of 1 °C / min and keep it for 2 h to obtain a fully cured N-doped resin precursor.

[0054] Step 3: Grind the fully cured resin into powder, heat it to 500 °C at a rate of 2 °C / min under an argon atmosphere, first perform low-temperature pre-carbonization heat treatment for 10 h; then heat it to 1400 °C and perform high-temperature heat treatment for 3 h to obtain a melamine-modified acrylic resin hard carbon material.

[0055] Experimental Example 1

[0056] SEM test: Perform SEM test on the loose and porous spongy melamine-modified acrylic resin hard carbon material prepared in Example 1, and the results are as Figure 1 shown. It can be seen from Figure 1 that the loose and porous spongy melamine-modified acrylic resin hard carbon material presents a porous sponge-like structure, with a large number of hole structures on the surface, and the particle size is between 20 - 30 μm.

[0057] Example 2

[0058] Method for testing the specific capacity per gram and the number of cycles of the sodium-ion battery anode material: Using the hard carbon materials in Examples 1 - 5 and Comparative Examples 1 - 2 as the anode, a sodium metal sheet as the cathode, and 1.0 mol / L LiPF6 / EC (ethylene carbonate) + DMC (dimethyl carbonate) + FEC (fluoroethylene carbonate) (volume ratio of EC, DMC, and FEC is 4.5:4.5:1) as the electrolyte, assemble CR2032 coin cells respectively in an argon glove box. Use a BlueTEC (LAND) battery test system to test constant current charge and discharge under a voltage window of 0 - 2 V, and the test conditions and results are shown in Table 1 below:

[0059] Table 1

[0060]

[0061] As can be seen from Table 1, the button battery was subjected to a constant current charge-discharge test at a current density of 500 mA / g, with a voltage range of 0 - 2 V and 100 cycles. The button half-cells of the melamine-modified resin hard carbon materials prepared in Examples 1 - 5 all had good cycle retention rates (greater than 90%), demonstrating excellent cycle stability. The capacity retention rates of Comparative Examples 1 and 2 were only about 60%. The specific values are shown in Table 2 (the capacity retention rates of the button half-cells of the electrode materials prepared in Examples 1 - 5 and Comparative Examples 1 - 2 after 100 cycles).

[0062] Table 2

[0063] Current density 500 mA / g Capacity retention rate of 100 cycles (%) Example 1 99.7 Example 2 98.7 Example 3 92.3 Example 4 94.2 Example 5 97.6 Comparative Example 1 62.7 Comparative Example 2 50.4

[0064] In summary, the present invention uses an acrylic resin with a carboxyl functional group as the hard carbon precursor material, and uses the -NH2 of melamine and the -COOH of the acrylic resin to carry out a chemical bond synthesis reaction, dehydrating and condensing to form amide bonds to connect them into a three-dimensional network structure; among them, melamine is both a cross-linking agent for the acrylic resin and an N element doping agent, doping the N element while improving the structural stability, improving the conductivity of the overall material and the active sites for sodium storage; hydrothermal treatment generates a sponge-like amorphous carbon, and low-temperature curing reduces the generation of pores and defects, greatly improving the initial efficiency; high-temperature carbonization changes the pores from macropores to micropores, increases the number of closed pores, improves the sodium-ion battery platform capacity, and improves the cycle performance.

[0065] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a melamine-modified acrylic resin hard carbon material, characterized in that: The -NH2 of melamine and the -COOH of acrylic resin are used for chemical bond synthesis reaction, and dehydration condensation generates amide bonds to connect them into a three-dimensional network structure, which specifically includes the following steps: Step 1, element doping: dissolving melamine in a mixed solution of ethanol and deionized water, wherein the volume ratio of ethanol to deionized water in the mixed solution is 1:1-5, and then adding acrylic resin, wherein the mass ratio of melamine to acrylic resin is 1:1-10, stirring evenly and transferring to a hydrothermal reaction, wherein the temperature of the hydrothermal reaction is 100-150°C, and the time is 1-10h, to form a sponge-like melamine-modified resin precursor; Step 2, low temperature curing: placing the sponge-like melamine-modified resin precursor in a muffle furnace for heating, the specific conditions of heating in the muffle furnace are: a heating rate of 0.1-8°C / min, a constant temperature of 100-300°C for 1-5h, and the protective gas introduced during the heating process is one or more of nitrogen, argon, and helium, and the flow rate is 4-400mL / min, to obtain a fully cured melamine-modified resin precursor; Step 3, high temperature carbonization: the fully cured melamine modified resin precursor obtained in step 2 is subjected to two-stage heat treatment in a nitrogen atmosphere, the first stage is maintained at a constant temperature of 500°C for 10 hours, and the second stage is maintained at a constant temperature of 1400°C for 2 hours. After the second stage of heat treatment, a loose porous sponge-like melamine modified acrylic resin hard carbon material can be obtained; The nitrogen ventilation flow rate during high-temperature carbonization is 6-350 mL / min, and the heating rate during the two-stage heat treatment is 0.5-10° C. / min.

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