Method for preparing hard carbon from biomass and plastic and application of hard carbon as negative electrode of sodium-ion battery

Abstract

The invention discloses a method for preparing hard carbon from biomass and plastic and application of the hard carbon as a negative electrode of a sodium-ion battery, the biomass is air-dried and crushed into powder, and then the powder and the plastic are subjected to a hydrothermal reaction to obtain a solid-liquid mixed hydrothermal product; and carrying out suction filtration and drying, carbonizing in a tubular atmosphere furnace, and grinding the obtained carbonized product to obtain the block-shaped sodium ion battery negative electrode material with good electrochemical performance. The method has the advantages that the two wastes are reasonably utilized, the problem of instability of a biomass structure is solved to a certain extent, the synthesized negative electrode material structure ensures rapid transmission of sodium ions, the capacity of the material is increased, and the electrochemical performance of the material can be remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a method for co-hydrothermally preparing a negative electrode material for sodium-ion batteries from biomass and plastics. Background Art

[0002] Since the commercialization of lithium-ion batteries, lithium batteries have been widely used in various fields such as energy storage systems and 3C products. However, the limited and uneven distribution of lithium resources in the earth's crust has hindered the further development of lithium batteries in fixed power grid energy storage systems. Sodium-ion batteries have been expected to be alternatives to lithium-ion batteries due to the abundant sodium resources, high safety, and similar working mechanisms. At present, the lack of high-performance negative electrode materials has greatly hindered the improvement of the energy density of sodium-ion batteries. Compared with many discovered negative electrode materials, hard carbon has medium specific capacity, low working potential, low cost, and long cycle life, with the best comprehensive performance, standing out among many materials and being the most promising negative electrode material for sodium-ion batteries.

[0003] Biomass, with its environmentally friendly and sustainable characteristics, has been widely used as a hard carbon precursor in the research of sodium battery negative electrodes. However, in the process of commercialization of sodium-ion batteries, due to factors such as different planting environments, species, and climates, the unevenness of biomass makes it difficult to supply stably and in batches. At the same time, plastics play an important role in our society. However, the service life of most plastics is low, and a large part of plastics become urban waste after use. In existing treatment methods, plastic waste faces problems such as being difficult to degrade in landfills and releasing toxic gases during incineration, causing irreversible environmental burdens. For example, polyvinyl chloride contains a high chlorine content and will produce dioxins during combustion, which is harmful to the human body. Co-hydrothermal carbonization is an effective method to solve the problems of these materials and utilize them. During the hydrothermal process, the emission gases can be better controlled, and the working temperature is relatively low. The raw materials are heated together with water in a closed reactor (autoclave) at a temperature of 180 to 280 °C and a self-pressure of 2 - 15 MPa, and the obtained hydrothermal carbon has the characteristics of hard carbon and can be used as a negative electrode material for sodium-ion batteries. As a chemical product, plastics have a more stable structure than biomass, and the uniform structure formed after co-hydrothermal treatment of the two raw materials can also solve the instability problem of biomass. Summary of the Invention

[0004] Object of the Invention: The technical problem to be solved by the present invention is to provide a method for co-hydrothermally preparing a negative electrode material for sodium-ion batteries from biomass and plastics, which can be used as a negative electrode for sodium-ion batteries to improve the performance of sodium-ion batteries in view of the deficiencies of the prior art.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for co-hydrothermal preparation of a negative electrode material for a sodium-ion battery from biomass and plastics, comprising the following steps:

[0007] (1) Add the dried and powdered biomass and plastic particles into a weakly acidic solution and mix evenly;

[0008] (2) Transfer the mixture in step (1) to a reaction kettle for hydrothermal reaction. Filter the product obtained from the hydrothermal reaction. Wash the solid product three times with water and dry it;

[0009] (3) Calcinate the dried solid obtained in step (2) in a tubular atmosphere furnace, and the product is obtained after grinding.

[0010] Specifically, in step (1), the biomass is selected from any one or a combination of two or more of pomelo peel, watermelon peel, corn stalk, rice husk, sugarcane bagasse, cellulose, and lignin. It is dried at 65 °C for 24 hours and then crushed. The sieve size is 60 mesh. The plastic particles are selected from any one or a combination of two or more of polyvinyl chloride (PVC), polypropylene (PP), and polyethylene terephthalate (PET). The particle size is 100 mesh. Magnetic stirring is used for mixing, and the mixing and stirring time is 2 h;

[0011] Specifically, in step (2), the hydrothermal reaction conditions are as follows: After heating to 220 °C at a heating rate of 10 °C / min, keep the temperature for 6 h, and then naturally cool to room temperature. The mass ratio of biomass to plastic is 7:3 to 5:5. The weak acid is citric acid, acetic acid, or oxalic acid (60 mL, pH = 3 - 5). The inner lining of the reaction kettle is polytetrafluoroethylene, and the filling ratio of the reaction kettle is 60 - 70%;

[0012] Specifically, in step (2), 150 - 200 mL of distilled water is used, the washing time is 30 - 60 min, and the solid product is dried overnight in an oven at 65 °C.

[0013] Specifically, in step (3), the calcination is carried out under nitrogen protection. Heat to 600 - 100 °C at a heating rate of 5 - 10 °C / min and keep the temperature for 2 h, and then cool to room temperature at a cooling rate of 5 - 10 °C / min. The grinding time is 0.5 - 3 h, and the particle size of the sieved powder is less than 80 mesh.

[0014] Furthermore, the carbonized product obtained by co-hydrothermal treatment of biomass and plastics prepared by the above preparation method is also within the protection scope of the present invention.

[0015] Furthermore, the present invention also claims the application of the carbonized product obtained by co-hydrothermal treatment of biomass and plastics as a negative electrode material for a sodium-ion battery.

[0016] Furthermore, the present invention also claims protection for a sodium-ion battery, the negative electrode of which is prepared from the above-mentioned co-hydrothermal carbonization product of biomass and plastic.

[0017] Beneficial effects:

[0018] (1) The present invention uses biomass raw materials rich in resources and plastic, a chemical industrial raw material, for co-hydrothermal treatment, making rational use of the two kinds of waste.

[0019] (2) By mixing the two raw materials through the hydrothermal process, on the one hand, the harmful substances that may be generated in plastic treatment are removed, and on the other hand, the unstable characteristics of biomass raw materials are solved, synthesizing a sodium-ion battery negative electrode material with good performance.

[0020] (3) As a sodium-ion battery negative electrode material, the product of the present invention has a relatively high reversible specific capacity, good cycle stability, and excellent electrochemical performance. Description of the drawings

[0021] The following further specific descriptions of the present invention will be made in conjunction with the drawings and specific embodiments, and the above and / or other advantages of the present invention will become clearer.

[0022] Figure 1 (50μm) Scanning electron microscope of the sodium-ion battery negative electrode material prepared in Example 1.

[0023] Figure 2 (10nm) Transmission electron microscope of the sodium-ion battery negative electrode material prepared in Example 1.

[0024] Figure 3 X-ray diffraction patterns of Example 1 (Co-55-800), Comparative Example 1 (RPP-800), and Comparative Example 2 (HC-PP-800).

[0025] Figure 4 Nitrogen desorption curves of Example 1 (Co-55-800), Example 2 (Co-55-600), Example 3 (Co-55-1000).

[0026] Figure 5 Pore size distribution diagrams of Example 1 (Co-55-800), Example 2 (Co-55-600), Example 3 (Co-55-1000).

[0027] Figure 6 Charge-discharge curves of Example 1 (Co-55-800), Comparative Example 1 (RPP-800), and Comparative Example 2 (HC-PP-800) at a current density of 0.05 A / g, the second time.

[0028] Figure 7Cycling performance of the sodium-ion battery prepared in Example 1 at a charge / discharge current of 0.05 A / g for 100 cycles.

[0029] Figure 8 Impedance spectrum of the sodium-ion battery prepared in Example 1 at a frequency range from 100,000 to 0.01 Hz after 20 charge / discharge cycles at 0.05 A / g. Detailed implementation manners

[0030] The present invention can be better understood according to the following examples.

[0031] Example 1

[0032] Cut pomelo peel (PP) into pieces of about 2 * 3 cm, and then dry them in an oven at 65 °C for 24 hours. After that, use an electric grinder to crush these samples and sieve them to a mesh size of 60 mesh. Take 4 g of pomelo peel and 4 g of polyvinyl chloride, add 60 mL of citric acid solution with a pH of 3.61, stir magnetically for 30 min, then transfer it to a 100 mL autoclave with a polytetrafluoroethylene liner, and carry out a hydrothermal reaction in the autoclave at a temperature of 220 °C for 6 h. After the reaction, naturally cool it to room temperature. Filter and separate the obtained mixed slurry to obtain a solid product, wash it three times with water and then dry it. Further carbonize the dried sample in a tubular atmosphere furnace, use nitrogen as the protective gas, heat it to 800 °C at a rate of 5 °C / min and hold for 2 h, and then cool it to room temperature at a rate of 10 °C / min. Take out the sample and grind it to obtain the negative electrode material (Co-55-800) of the sodium-ion battery.

[0033] Example 2

[0034] Cut pomelo peel (PP) into pieces of about 2 * 3 cm, and then dry them in an oven at 65 °C for 24 hours. After that, use an electric grinder to crush these samples and sieve them to a mesh size of 60 mesh. Take 4 g of polyvinyl chloride and 4 g of pomelo peel, add 60 mL of citric acid solution with a pH of 3.61, stir magnetically for 30 min, then transfer it to a 100 mL autoclave with a polytetrafluoroethylene liner, and carry out a hydrothermal reaction in the autoclave at a temperature of 220 °C for 6 h. After the reaction, naturally cool it to room temperature. Filter and separate the obtained mixed slurry to obtain a solid product, wash it three times with water and then dry it. Further carbonize the dried sample in a tubular atmosphere furnace, use nitrogen as the protective gas, heat it to 600 °C at a rate of 5 °C / min and hold for 2 h, and then cool it to room temperature at a rate of 10 °C / min. Take out the sample and grind it to obtain the negative electrode material (Co-55-600) of the sodium-ion battery.

[0035] Example 3

[0036] Cut the pomelo peel (PP) into pieces about 2*3 cm, and then dry them in an oven at 65 °C for 24 hours. After that, use an electric grinder to crush these samples and sieve them to a mesh size of 60 mesh. Take 4 g each of polyvinyl chloride and pomelo peel, add 60 mL of citric acid solution with a pH of 3.61, stir magnetically for 30 min, then transfer it to a 100 mL autoclave lined with polytetrafluoroethylene, and carry out a hydrothermal reaction in the autoclave at a temperature of 220 °C for 6 h. After the reaction, cool it naturally to room temperature. Filter and separate the obtained mixed slurry to obtain a solid product, wash it three times with water and then dry it. Further carbonize the dried sample in a tube-type atmosphere furnace, use nitrogen as the protective gas, heat it to 1000 °C at a rate of 5 °C / min and hold for 2 h, and then cool it to room temperature at a rate of 10 °C / min. Take out the sample, grind it, and then obtain the anode material (Co-55-1000) for sodium-ion batteries.

[0037] Example 4

[0038] Cut the orange peel (PP) into pieces about 2*3 cm, and then dry them in an oven at 65 °C for 24 hours. After that, use an electric grinder to crush these samples and sieve them to a mesh size of 60 mesh. Take 5.6 g of orange peel and 2.4 g of polyvinyl chloride, add 60 mL of citric acid solution with a pH of 3.61, stir magnetically for 30 min, then transfer it to a 100 mL autoclave lined with polytetrafluoroethylene, and carry out a hydrothermal reaction in the autoclave at a temperature of 220 °C for 6 h. After the reaction, cool it naturally to room temperature. Filter and separate the obtained mixed slurry to obtain a solid product, wash it three times with water and then dry it. Further carbonize the dried sample in a tube-type atmosphere furnace, use nitrogen as the protective gas, heat it to 800 °C at a rate of 5 °C / min and hold for 2 h, and then cool it to room temperature at a rate of 10 °C / min. Take out the sample, grind it, and then obtain the anode material (Co-73-800) for sodium-ion batteries.

[0039] Example 5

[0040] Cut the orange peel (PP) into pieces about 2*3 cm, and then dry them in an oven at 65 °C for 24 hours. After that, use an electric grinder to crush these samples and sieve them to a mesh size of 60 mesh. Take 4.8 g of orange peel and 3.2 g of polyvinyl chloride, add 60 mL of citric acid solution with a pH of 3.61, stir magnetically for 30 min, then transfer it to a 100 mL autoclave lined with polytetrafluoroethylene, and carry out a hydrothermal reaction in the autoclave at a temperature of 220 °C for 6 h. After the reaction, cool it naturally to room temperature. Filter and separate the obtained mixed slurry to obtain a solid product, wash it three times with water and then dry it. Further carbonize the dried sample in a tube-type atmosphere furnace, use nitrogen as the protective gas, heat it to 800 °C at a rate of 5 °C / min and hold for 2 h, and then cool it to room temperature at a rate of 10 °C / min. Take out the sample, grind it, and then obtain the anode material (Co-64-800) for sodium-ion batteries.

[0041] Comparative Example 1

[0042] 8g of grapefruit peel powder was further carbonized in a tubular atmosphere furnace, with nitrogen as the protective gas, and the temperature was raised to 800℃ at 5℃ / min for 2h, and then cooled to room temperature at 10℃ / min. The sample was taken out and ground to obtain the negative electrode material for sodium ion battery (RPP-800).

[0043] Comparative Example 2

[0044] The grapefruit peel (PP) was cut into pieces of about 2*3cm and then dried in an oven at 65°C for 24 hours. After that, the samples were crushed using an electric pulverizer and sieved to a mesh size of 60 mesh. Take 8g of grapefruit peel, add 60mL of citric acid solution with a pH of 3.61, stir magnetically for 30min, and move to a 100mL polytetrafluoroethylene-lined autoclave, carry out a hydrothermal reaction in the reactor, react at a temperature of 220°C for 6h, and naturally cool to room temperature after the reaction. The obtained mixed slurry was filtered and separated to obtain a solid product, which was washed three times with water and dried. The dried sample was further carbonized in a tubular atmosphere furnace, with nitrogen as the protective gas, and the temperature was raised to 800°C at 5°C / min for 2h, and then cooled to room temperature at 10°C / min. After taking out the sample and grinding it, the sodium ion battery negative electrode material (HC-PP-800) was obtained.

[0045] The sodium ion battery negative electrode materials prepared in Examples 1, 2, 3, 4, 5 and Comparative Examples 1 and 2 were mixed with conductive agent acetylene black and polyvinylidene fluoride at a mass ratio of 8:1:1, and the mixture was prepared into a slurry with N-methylpyrrolidone, and applied to a copper foil. The prepared slurry coating was placed in a vacuum drying oven and dried at 60°C for 12 hours. A circular pole piece with a diameter of 12 mm was pressed out with a tablet press to obtain an experimental battery negative electrode, with a sodium sheet as the counter electrode, a glass fiber disc as the diaphragm, an organic solution of sodium perchlorate as the electrolyte, and a spring and a gasket were added to assemble a 2032 model button battery in a glove box.

[0046] Figure 1 This is a scanning electron microscope image of the sodium ion battery negative electrode material prepared in Example 1. It can be seen that the material is in blocky particles with a smooth surface and no obvious holes. Figure 2 The transmission electron microscope can clearly show the hard carbon structure after hydrothermal carbonization, which has both pseudo-graphite layers and microporous structures. The abundant circular micropores are wrapped by carbon layers, forming a microstructure of inner micropores and outer pseudo-graphite carbon layers. The existence of these two structures provides more active sites for the storage of sodium ions. Sodium ions are stored in the structure by different mechanisms, increasing the capacity of the battery. Figure 3From the comparison of X-ray diffraction patterns (XRD), it can be clearly seen that the hard carbon obtained by co-hydrothermal carbonization of the two raw materials has a higher crystallinity and a higher degree of carbonization than the hard carbon obtained by hydrothermal carbonization of pomelo peel alone and the hard carbon obtained by direct carbonization of pomelo peel without hydrothermal treatment. Figure 4 Figure 111 shows the desorption curves of Example 1, Comparative Example 1, and Comparative Example 2. After calculation and comparison, the specific surface area of Example 1 is 2.64 m 2 / g, which is significantly smaller than that of Comparative Example 1 (372.71 m 2 / g) and Comparative Example 2 (217.52 m 2 / g). After co-hydrothermal treatment, the surface of the bulk sample becomes significantly smoother, and many small pores are filled or transformed into slightly larger closed pores, which can store sodium better. Figure 5 Figure 112 shows the pore size distributions of Example 1, Example 2, and Example 3. It can be seen that the samples after co-hydrothermal treatment have similar pore size distributions, and Example 1 has more pores around 10 nm. Figure 6 Figure 113 shows that when the samples of Example 1, Comparative Example 1, and Comparative Example 2 are used as electrode materials, the second-cycle discharge capacities of the sodium-ion batteries at a current density of 0.05 A / g are 219.32 mAh / g, 98.00 mAh / g, and 200.59 mAh / g, respectively. Figure 7 Among them, when the electrode material is charged and discharged 100 times at a current density of 0.05 A / g, a mass specific capacity of 211.3 mAh / g is still retained. Figure 8 Figure 115 shows the AC impedance of Example 1, and it can be observed that the electron diffusion performance in the material is good.

[0047] The present invention provides an idea and method for preparing a negative electrode material for a sodium-ion battery by co-hydrothermal treatment of biomass and plastics. There are many specific methods and ways to implement this technical solution. The above description is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. Each component not clearly defined in this embodiment can be implemented by existing technologies.

Claims

1. A method for co-hydrothermally preparing a negative electrode material for a sodium-ion battery from biomass and plastics, characterized in that, It includes the following steps: (1) Add the dried and powdered biomass and plastic particles into a weak acidic solution and mix them evenly; (2) Transfer the mixture in step (1) to a reaction kettle for hydrothermal reaction. Filter the product obtained from the hydrothermal reaction. Wash the solid product three times with water and dry it; (3) Calcinate the dried solid obtained in step (2) in a tubular atmosphere furnace. The product is obtained after grinding.

2. The method for preparing the anode material for sodium ion batteries by co-hydrothermal treatment of biomass and plastics according to claim 1, wherein In step (1), the biomass is selected from any one or a combination of two or more of pomelo peel, watermelon peel, corn stalk, rice husk, sugarcane bagasse, cellulose, and lignin. It is dried at 65 °C for 24 hours and then crushed. The sieve size is 60 mesh. The plastic particles are selected from any one or a combination of two or more of polyvinyl chloride (PVC), polypropylene (PP), and polyethylene terephthalate (PET). The particle size is 100 mesh. Magnetic stirring is used for mixing, and the mixing and stirring time is 2 h.

3. The method for preparing the anode material for sodium-ion batteries by co-hydrothermal treatment of biomass and plastics according to claim 1, wherein In step (2), the hydrothermal reaction conditions are specifically as follows: Heat up to 220 °C at a heating rate of 10 °C / min, keep the temperature for 6 h, and then cool naturally to room temperature. The mass ratio of biomass to plastic is 7:3 to 5:

5. The weak acidic solution is prepared with citric acid, acetic acid, and oxalic acid to be 60 mL (pH = 3 - 5). The inner lining of the reaction kettle is polytetrafluoroethylene, and the filling ratio of the reaction kettle is 60 - 70%.

4. The method for co-hydrothermally preparing the anode material for sodium ion batteries from biomass and plastics according to claim 1, wherein In step (2), 150 - 200 mL of distilled water is used, the washing time is 30 - 60 min, and the solid product is dried overnight in an oven at 65 °C.

5. The method for preparing the anode material for a sodium ion battery by co-hydrothermal treatment of biomass and plastics according to claim 1, characterized in that, In step (3), the calcination is carried out under nitrogen protection. Heat up to 600 - 1000 °C at a heating rate of 5 °C / min, keep the temperature for 2 h, and then cool to room temperature at a cooling rate of 5 - 10 °C / min. The grinding time is 0.5 - 3 h, and the particle size of the powder after sieving is less than 80 mesh.

6. The biomass and plastic co-hydrothermal carbon material prepared by the preparation method according to any one of claims 1 - 5.

7. The application of the biomass and plastic co-hydrothermally prepared carbon material according to claim 6 as the negative electrode of a sodium ion battery.

8. A sodium-ion battery, characterized in that, The negative electrode thereof is prepared by calcination after co-hydrothermal treatment of the biomass and plastic according to claim 6.

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