Preparation method of hard carbon material based on waste paper

Abstract

The invention discloses a preparation method of a hard carbon material based on waste paper, which comprises the following steps: S1, crushing the waste paper, and cleaning obtained chippings with deionized water to remove a floating layer and oil stain; s2, soaking the cleaned material with a manganese chloride solution, and washing and drying the soaked material; s3, the dried material is subjected to pre-carbonization treatment, and the pre-carbonized material is smashed and screened; s4, carrying out acid pickling on the material obtained in the S3, and after acid pickling, drying, crushing and screening again; and S5, performing high-temperature carbonization on the screened material again to finally obtain the hard carbon material. The precursor of the final product is the waste paper, the basic unit of the material is the papermaking fiber, the material obtained by carbonizing the fiber has good morphology control, and the sodium ion battery made of the obtained hard carbon material has high gram volume and good multiplying power and cycle performance. High-value utilization of wastes is realized, and high economic value is created while the environment is protected.

Description

Technical Field

[0001] The invention relates to a method for preparing a hard carbon material based on waste paper. Background Art

[0002] Commonly used carbon-based materials mainly include graphite carbon and non-graphite carbon. Among them, non-graphite hard carbon is a more commonly used negative electrode material for sodium-ion batteries. Graphite has been widely used in lithium-ion batteries and is the earliest studied and best commercialized negative electrode material. However, compared with Na + Compared with the ionic radius, the interlayer spacing of graphite is too small. Researchers obtained expanded graphite by oxidizing graphite, which can be used as the negative electrode material of sodium ion batteries. Non-graphite mainly includes two categories: hard carbon and soft carbon. There is no obvious surface diffraction peak. Both are amorphous structures, composed of graphite crystallites and amorphous regions. Hard carbon, also known as difficult-to-graphitize carbon, has attracted widespread attention due to its large interlayer spacing and irregular structure, which is suitable for sodium ion deintercalation. It is pyrolytic carbon of high molecular polymers. It is difficult to graphitize even at a high temperature of 3000°C, and is suitable for use as a negative electrode material for sodium ion batteries. Soft carbon is not directly used as a negative electrode material, but is a raw material for making artificial graphite, or as a coating material to change to natural graphite, alloys and other negative electrode materials.

[0003] So far, the raw materials for synthesizing carbon-based negative electrode materials cannot be completely renewable. With the continuous advancement of the commercialization of sodium-ion batteries, the production of carbon-based negative electrode materials will inevitably consume a large amount of carbon precursors. Exploring low-cost and renewable carbon precursors to prepare carbon-based negative electrode materials for sodium-ion batteries with high reversible capacity and long cycle performance has gradually become a research hotspot in the field of sodium-ion batteries. In the past few years, the synthesis of carbon-based materials with excellent properties such as large specific surface area, controllable porosity and high conductivity using plant fibers as raw materials as negative electrode materials for sodium-ion batteries has attracted the attention of more and more researchers. Based on this, the present invention provides a method for preparing a hard carbon material based on waste paper, which can make high-value utilization of waste, protect the environment and create high economic value. Summary of the invention

[0004] The present invention provides a method for preparing a hard carbon material based on waste paper in order to solve the problems existing in the above-mentioned prior art.

[0005] The technical solutions adopted in the present invention are: A method for preparing a hard carbon material based on waste paper comprises the following steps: S1, crushing the waste paper for the first time, and washing the obtained scraps with deionized water to remove the floating layer and oil stains; S2, soaking the cleaned material in a manganese chloride solution, and washing and drying the soaked material; S3, pre-carbonizing the dried material, crushing and screening the pre-carbonized material; S4, pickling the material obtained in S3, drying it again and crushing it again after pickling; S5. Carbonizing the screened material again at high temperature to finally obtain the hard carbon material.

[0006] Furthermore, in the waste paper raw materials selected in S1, plant fibers must account for more than 70% of the total mass of the paper, and the length and width of the waste paper after initial crushing must be less than 5 cm.

[0007] Furthermore, in S2, when soaking in manganese chloride solution, the solution treatment concentration is less than 0.04 mol / L, and the soaking time is 2-24 hours.

[0008] Furthermore, in S2, the drying is complete drying in an environment of 60°C-140°C.

[0009] Furthermore, in S3, during the pre-carbonization treatment, the waste paper precursor is carbonized in an inert gas atmosphere, the carbonization atmosphere is high-purity argon or high-purity nitrogen, the heating rate is less than 10°C / minute, the low-temperature carbonization endpoint temperature is 350°C-600°C, and it is kept warm for more than 2 hours.

[0010] Furthermore, in S3, after screening, the particle size D99 is less than 15 microns, and D50 is less than 12 microns.

[0011] Furthermore, in S4, high concentration hydrochloric acid with a concentration of 3 mol / L-12 mol / L is used for pickling to remove ash from the material, and the cleaning time is 2-24 hours.

[0012] Furthermore, in S4, the acid-washed hard carbon is dried at a temperature of 60° C. to 140° C., and then ground again after drying.

[0013] Furthermore, in S5, when high-temperature carbonization is performed again, the carbonization atmosphere is argon or nitrogen, and the temperature rise curve is divided into two sections.

[0014] Furthermore, the heating curve is divided into two sections: The intermediate temperature is any temperature between 700℃ and 900℃. Under the protection of inert gas, the material is heated from room temperature to the intermediate temperature at a heating rate of 5℃ / min-20℃ / min. When the temperature reaches the intermediate temperature, the heating rate slows down to 0.5℃ / min-5℃ / min. When the temperature reaches the high-temperature carbonization temperature, carbonization is carried out at a constant temperature. The high-temperature carbonization temperature is 1200° C.-1400° C., and the carbonization time is 1 h-6 h, and the preparation of the hard carbon material is finally completed.

[0015] The present invention has the following beneficial effects: The present invention first pre-carbonizes and then high-temperature carbonizes. The two carbonization treatments can better improve the performance of hard carbon. Pre-carbonization can fully decompose waste paper, and high-temperature carbonization can convert carbon materials into hard carbon structural materials required by sodium ion batteries. In addition, the second high-temperature carbonization is divided into two stages of heating. The first stage is under the protection of inert gas, from room temperature to 700℃-900℃, and then slowly rises to 1200℃-1400℃ for constant temperature carbonization; the first stage of rapid heating improves carbonization efficiency and reduces energy consumption, while the second stage of slow heating process is to reduce defects in carbon materials and improve the performance of the final hard carbon material.

[0016] The precursor for preparing hard carbon in the present invention is waste paper, and the basic unit of the material is papermaking fiber. The material obtained after microscopic carbonization has good morphology control, and the sodium ion battery made of the hard carbon material obtained has high gram capacity, good rate and cycle performance. It realizes the high-value utilization of waste, protects the environment and creates high economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A flow chart was prepared for the present invention.

[0018] Figure 2 This is a scanning electron micrograph of the hard carbon negative electrode material.

[0019] Figure 3 Performance of sodium ion button cells with hard carbon anode materials DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with the accompanying drawings. Example 1

[0021] like Figure 1 The present invention provides a method for preparing a hard carbon material based on waste paper, comprising the following steps: S1. Crush the waste paper into small pieces of 2cm x 1cm, and wash the obtained scraps with deionized water to remove the floating layer and oil stains.

[0022] S2. Soak the cleaned material in a manganese chloride solution with a solution treatment concentration of less than 0.1 mol / L for 2-24 hours, wash the soaked material, and then completely dry it in an environment of 60°C-140°C.

[0023] S3. Pre-carbonize the dried material. During the pre-carbonization treatment, the waste paper is carbonized in an inert gas atmosphere. The carbonization atmosphere is high-purity argon or high-purity nitrogen. The heating rate is less than 10°C / minute. The low-temperature carbonization temperature is 350°C-600°C, and the temperature is kept for more than 2 hours. The pre-carbonized material is crushed and sieved by a blade crusher, ball mill, or air flow mill. After screening, the particle size D99 is less than 15 microns, and D50 is less than 12 microns.

[0024] S4, pickling the material obtained in S3 with high concentration hydrochloric acid of 3mol / L-12mol / L to remove ash in the material, and the cleaning time is 2-24 hours. After pickling, drying is performed again, and the drying temperature is 60℃-140℃, and then crushing is performed in a ball mill, and the rotation speed of the ball mill is 200 rpm-800 rpm, and the ball milling time is 2h-4h.

[0025] S5, carbonizing the dried and crushed material again at high temperature to finally obtain the hard carbon material. During the second high temperature carbonization, the carbonization atmosphere is argon or nitrogen, and the temperature rise curve is divided into two sections, specifically: The intermediate temperature is any temperature between 700°C and 900°C. Under the protection of inert gas, the material is heated from room temperature to the intermediate temperature at a heating rate of 5°C / min-20°C / min. When the temperature reaches the intermediate temperature, the heating rate is slowed down to 0.5°C / min-5°C / min. When the temperature reaches the high-temperature carbonization temperature, constant temperature carbonization is performed. The high-temperature carbonization temperature is 1200°C-1400°C, and the carbonization time is 1h-6h, and the preparation of the hard carbon material is finally completed. Example 2

[0026] After the hard carbon material is prepared, it is dispersed in deionized water with conductive carbon black, hydroxymethyl cellulose and styrene butadiene rubber, and stirred at a speed of 2000 for 2 hours to form a negative electrode active material slurry. Among them, the weight ratio of hard carbon: conductive carbon black: hydroxymethyl cellulose: styrene butadiene rubber is 92%: 3%: 2%: 3%. The slurry is coated on copper foil, then dried at 100°C for 10 minutes, and rolled to obtain a negative electrode sheet.

[0027] In the glove box, CR2032 button cells are assembled in the order of negative electrode shell, shrapnel, steel sheet, sodium sheet, glass fiber diaphragm, negative electrode sheet, and positive electrode shell. 40 µL of electrolyte is dripped on both sides of the diaphragm. The electrolyte is sodium hexafluorophosphate electrolyte (1 mol NaPF6 is dissolved in a mixed solvent of EC / PC / EMC=35:5:60 (mass ratio)). The assembled battery is charged and discharged between 0V-2V. When assembling the battery, in order to ensure that the electrolyte does not decompose and the metal sodium sheet is not oxidized, the entire assembly process is carried out in a glove box environment filled with high-purity argon. When the water content and oxygen content in the glove box are not higher than 0.01ppm, the sodium ion button cell is assembled.

[0028] Figure 2 This is a scanning electron micrograph of the hard carbon negative electrode material. It can be seen that the particle size of the crushed hard carbon material is about 10um, and some carbon particles retain the fiber rod-like characteristics, which is beneficial to improving the cycling performance and rate performance of sodium ion batteries. Figure 3 The performance of the sodium ion button battery with hard carbon negative electrode material shows that the first discharge capacity is 327 mAh / g, the first charge capacity is 283 mAh / g, and the first round coulombic efficiency is 86.5%.

[0029] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be regarded as within the protection scope of the present invention.

Claims

1. A method for preparing a hard carbon material based on waste paper, characterized in that: The following steps are involved: S1, crushing the waste paper for the first time, and washing the obtained scraps with deionized water to remove the floating layer and oil stains; S2, soaking the cleaned material in a manganese chloride solution, and washing and drying the soaked material; S3, pre-carbonizing the dried material, crushing and screening the pre-carbonized material; S4, pickling the material obtained in S3, drying it again and crushing it again after pickling; S5. Carbonizing the screened material again at high temperature to finally obtain the hard carbon material.

2. The method for preparing a hard carbon material based on waste paper according to claim 1, characterized in that: In the waste paper raw materials selected in S1, plant fibers must account for more than 70% of the total mass of the paper, and the length and width of the waste paper after initial crushing must be less than 5 cm.

3. The method for preparing a hard carbon material based on waste paper according to claim 1, characterized in that: In S2, when soaking in manganese chloride solution, the solution treatment concentration is less than 0.04 mol / L, and the soaking time is 2-24 hours.

4. The method for preparing a hard carbon material based on waste paper according to claim 1, characterized in that: In S2, the drying is performed completely in an environment of 60°C-140°C.

5. The method for preparing a hard carbon material based on waste paper according to claim 1, characterized in that: In S3, during the pre-carbonization treatment, the waste paper is carbonized in an inert gas atmosphere, the carbonization atmosphere is high-purity argon or high-purity nitrogen, the heating rate is less than 10°C / minute, the low-temperature carbonization endpoint temperature is 350°C-600°C, and it is kept warm for more than 2 hours.

6. The method for preparing a hard carbon material based on waste paper according to claim 1, characterized in that: In S3, the particle size D99 after screening is less than 15 microns, and D50 is less than 12 microns.

7. The method for preparing a hard carbon material based on waste paper according to claim 1, characterized in that: In S4, high concentration hydrochloric acid with a concentration of 3 mol / L to 12 mol / L is used for pickling to remove ash from the material, and the cleaning time is 2 to 24 hours.

8. The method for preparing a hard carbon material based on waste paper according to claim 1, characterized in that: In S4, the acid-washed hard carbon is dried at a temperature of 60°C to 140°C, and then ground again after drying.

9. The method for preparing a hard carbon material based on waste paper according to claim 1, characterized in that: In S5, when high-temperature carbonization is performed again, the carbonization atmosphere is argon or nitrogen, and the temperature rise curve is divided into two sections.

10. The method for preparing a hard carbon material based on waste paper according to claim 8, characterized in that: The heating curve is divided into two sections: The intermediate temperature is any temperature between 700℃ and 900℃. Under the protection of inert gas, the material is heated from room temperature to the intermediate temperature at a heating rate of 5℃ / min-20℃ / min. When the temperature reaches the intermediate temperature, the heating rate slows down to 0.5℃ / min-5℃ / min. When the temperature reaches the high-temperature carbonization temperature, carbonization is carried out at a constant temperature. The high-temperature carbonization temperature is 1200° C.-1400° C., and the carbonization time is 1 h-6 h, and the preparation of the hard carbon material is finally completed.

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