A method for preparing hard carbon from biomass and plastics and its application as a negative electrode in sodium-ion batteries.

Abstract

This invention discloses a method for preparing hard carbon from biomass and plastics and its application as a negative electrode in sodium-ion batteries. The biomass is air-dried, crushed into powder, and then reacted with plastics via a hydrothermal reaction to obtain a solid-liquid mixture. This mixture is then filtered, dried, and carbonized in a tubular atmosphere furnace. The resulting carbonized product is ground to obtain a blocky sodium-ion battery negative electrode material with excellent electrochemical performance. The advantages of this method are that it rationally utilizes two types of waste materials, partially addresses the structural instability of biomass, and ensures rapid sodium ion transport in the synthesized negative electrode material, increasing its capacity and significantly improving its electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a method for preparing sodium-ion battery anode materials using a co-hydrothermal method combining biomass and plastics. Background Technology

[0002] Since the commercialization of lithium-ion batteries, they have been widely used in energy storage systems, 3C products, and other fields. However, the limited and uneven distribution of lithium resources in the Earth's crust hinders the further development of lithium batteries in stationary grid energy storage systems. Sodium-ion batteries, due to their abundant sodium resources, high safety, and similar working mechanism, were once expected to be a substitute for lithium-ion batteries. However, the current lack of high-performance anode materials has greatly hampered the improvement of the energy density of sodium-ion batteries. Compared with many discovered anode materials, hard carbon has the best overall performance, with moderate specific capacity, low operating potential, low cost, and long cycle life, making it the most promising anode material for sodium-ion batteries.

[0003] Biomass, due to its environmentally friendly and sustainable characteristics, is widely used as a hard carbon precursor in sodium-ion battery anode research. However, in the commercialization of sodium-ion batteries, the uneven distribution of biomass caused by different planting environments, species, and climates makes stable, large-scale supply difficult. Meanwhile, plastics play a significant role in our society. However, most plastics have a short lifespan, with a large portion becoming municipal waste after use. Current treatment methods for plastic waste face problems such as difficulty in landfill degradation and the release of toxic gases during incineration, causing irreversible environmental burdens. For example, polyvinyl chloride (PVC), due to its high chlorine content, produces dioxins during combustion, posing a health hazard. Co-hydrothermal carbonization is an effective method to address these problems and utilize these materials. The hydrothermal process allows for better control of emissions and operates at relatively low temperatures. The raw materials are heated together with water in a closed reactor (autoclave) at 180-280°C and self-pressure (2-15 MPa), resulting in hydrothermal carbon with hard carbon characteristics, which can be used as a sodium-ion battery anode material. As a chemical product, plastics have a more stable structure than biomass. The homogeneous structure formed by hydrothermal treatment of the two raw materials can also solve the instability problem of biomass. Summary of the Invention

[0004] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for preparing sodium-ion battery anode materials by co-hydrothermal synthesis of biomass and plastics, thereby improving the performance of sodium-ion batteries.

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

[0006] A method for preparing sodium-ion battery anode materials via hydrothermal co-processing of biomass and plastics includes the following steps:

[0007] (1) Add the dried and ground biomass and plastic granules to a weakly acidic solution and mix them evenly.

[0008] (2) The mixture in step (1) is transferred to the reactor for hydrothermal reaction. The product obtained by hydrothermal reaction is filtered, the solid product is washed with water three times and dried.

[0009] (3) The dried solid obtained in step (2) is calcined in a tubular atmosphere furnace, and the product is then ground to obtain the final product.

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

[0011] Specifically, in step (2), the hydrothermal reaction conditions are as follows: the temperature is raised to 220°C at a heating rate of 10°C / min, then kept at that temperature for 6 hours, and then naturally cooled to room temperature. The mass ratio of biomass to plastic is 7:3 to 5:5. The weak acid is citric acid, acetic acid, and oxalic acid in 60 mL (pH = 3 to 5). The lining of the reactor is polytetrafluoroethylene, and the filling ratio of the reactor is 60 to 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), calcination is carried out under nitrogen protection, with the temperature raised to 600-100℃ at a rate of 5-10℃ / min and held for 2 hours, and then cooled to room temperature at a rate of 5-10℃ / min. The grinding time is 0.5-3 hours, and the powder particle size after sieving is less than 80 mesh.

[0014] Furthermore, the biomass and plastic carbonization products obtained by the above preparation method after hydrothermal co-processing are also within the scope of protection of this invention.

[0015] Furthermore, this invention also claims protection for the application of the above-mentioned biomass and plastic co-hydrothermal carbonization product as a sodium-ion battery anode material.

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

[0017] Beneficial effects:

[0018] (1) This invention utilizes abundant biomass raw materials and chemical raw material plastics for hydrothermal treatment, making rational use of the two types of waste.

[0019] (2) The present invention mixes two raw materials through a hydrothermal process, which removes harmful substances that may be generated during plastic processing and solves the problem of unstable biomass raw materials, thus synthesizing a high-performance sodium-ion battery anode material.

[0020] (3) The product of this invention, as a negative electrode material for sodium-ion batteries, has a high reversible specific capacity, good cycle stability, and excellent electrochemical performance. Attached Figure Description

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0022] Figure 1 A scanning electron microscope (50 μm) showing the sodium-ion battery anode material prepared in Example 1.

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

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

[0025] Figure 4 The nitrogen desorption curves are for Examples 1 (Co-55-800), 2 (Co-55-600), and 3 (Co-55-1000).

[0026] Figure 5 The pore size distribution diagrams are for Examples 1 (Co-55-800), 2 (Co-55-600), and 3 (Co-55-1000).

[0027] Figure 6 The second 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 are shown.

[0028] Figure 7The sodium-ion battery prepared in Example 1 is shown in a graph after 100 charge-discharge cycles at 0.05 A / g.

[0029] Figure 8 The impedance spectrum of the sodium-ion battery prepared in Example 1 after 20 charge-discharge cycles at 0.05 A / g, at frequencies from 100,000 to 0.01 Hz. Detailed Implementation

[0030] The present invention can be better understood from the following embodiments.

[0031] Example 1

[0032] Grapefruit peel (PP) was cut into pieces approximately 2*3 cm and dried in an oven at 65℃ for 24 hours. Afterward, the samples were pulverized using an electric grinder and sieved to a 60-mesh sieve. 4 g each of grapefruit peel and polyvinyl chloride (PVC) were added to 60 mL of citric acid solution (pH 3.61), and the mixture was magnetically stirred for 30 min before being transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). A hydrothermal reaction was carried out in the reactor at 220℃ for 6 h, followed by natural cooling to room temperature. The resulting slurry was filtered and separated to obtain a solid product, which was washed three times with water and then dried. The dried sample was further carbonized in a tubular atmosphere furnace under nitrogen as a protective gas, heated to 800℃ at 5℃ / min and held for 2 h, then cooled to room temperature at 10℃ / min. The sample was then removed, ground, and the sodium-ion battery anode material (Co-55-800) was obtained.

[0033] Example 2

[0034] Grapefruit peel (PP) was cut into pieces approximately 2*3 cm and dried in an oven at 65℃ for 24 hours. Afterward, the samples were pulverized using an electric grinder and sieved to a 60-mesh sieve. 4 g each of polyvinyl chloride (PVC) and grapefruit peel were added to 60 mL of citric acid solution (pH 3.61), and the mixture was magnetically stirred for 30 min before being transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). A hydrothermal reaction was carried out in the reactor at 220℃ for 6 h, followed by natural cooling to room temperature. The resulting slurry was filtered and separated to obtain a solid product, which was washed three times with water and then dried. The dried sample was further carbonized in a tubular atmosphere furnace under nitrogen protection, heated to 600℃ at 5℃ / min and held for 2 h, then cooled to room temperature at 10℃ / min. The sample was then removed, ground, and the sodium-ion battery anode material (Co-55-600) was obtained.

[0035] Example 3

[0036] Grapefruit peel (PP) was cut into pieces approximately 2*3 cm and dried in an oven at 65℃ for 24 hours. Afterward, the samples were pulverized using an electric grinder and sieved to a 60-mesh sieve. 4 g each of polyvinyl chloride (PVC) and grapefruit peel were added to 60 mL of citric acid solution (pH 3.61), and the mixture was magnetically stirred for 30 min before being transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). A hydrothermal reaction was carried out in the reactor at 220℃ for 6 h, followed by natural cooling to room temperature. The resulting slurry was filtered and separated to obtain a solid product, which was washed three times with water and then dried. The dried sample was further carbonized in a tubular atmosphere furnace under nitrogen as a protective gas, heated to 1000℃ at a rate of 5℃ / min and held for 2 h, then cooled to room temperature at a rate of 10℃ / min. The sample was then removed, ground, and the sodium-ion battery anode material (Co-55-1000) was obtained.

[0037] Example 4

[0038] Orange peel (PP) was cut into pieces approximately 2*3 cm and dried in an oven at 65°C for 24 hours. Afterward, the samples were pulverized using an electric grinder and sieved to a 60-mesh sieve. 5.6 g of orange peel and 2.4 g of polyvinyl chloride (PVC) were added to 60 mL of citric acid solution (pH 3.61), and the mixture was magnetically stirred for 30 min. The mixture was then transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE) and subjected to a hydrothermal reaction at 220°C for 6 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting slurry was filtered and separated to obtain a solid product, which was washed three times with water and then dried. The dried sample was further carbonized in a tubular atmosphere furnace under nitrogen as a protective gas, heated to 800°C at a rate of 5°C / min and held for 2 h, then cooled to room temperature at a rate of 10°C / min. The sample was then removed, ground, and the sodium-ion battery anode material (Co-73-800) was obtained.

[0039] Example 5

[0040] Orange peel (PP) was cut into pieces approximately 2*3 cm and dried in an oven at 65℃ for 24 hours. Afterward, the samples were pulverized using an electric grinder and sieved to a 60-mesh sieve. 4.8 g of orange peel and 3.2 g of polyvinyl chloride (PVC) were added to 60 mL of citric acid solution (pH 3.61), and the mixture was magnetically stirred for 30 min. The mixture was then transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE) and subjected to a hydrothermal reaction at 220℃ for 6 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting slurry was filtered and separated to obtain a solid product, which was washed three times with water and then dried. The dried sample was further carbonized in a tubular atmosphere furnace under nitrogen as a protective gas, heated to 800℃ at a rate of 5℃ / min and held for 2 h, then cooled to room temperature at a rate of 10℃ / min. The sample was then removed, ground, and the sodium-ion battery anode material (Co-64-800) was obtained.

[0041] Comparative Example 1

[0042] Take 8g of grapefruit peel powder and further carbonize it in a tube furnace with nitrogen as the protective gas. The temperature is increased to 800℃ at 5℃ / min and held for 2 hours, then cooled to room temperature at 10℃ / min. After grinding the sample, sodium-ion battery anode material (RPP-800) is obtained.

[0043] Comparative Example 2

[0044] Grapefruit peel (PP) was cut into pieces approximately 2*3 cm and dried in an oven at 65℃ for 24 hours. Afterward, the samples were pulverized using an electric grinder and sieved to a 60-mesh sieve. 8 g of grapefruit peel was added to 60 mL of citric acid solution (pH 3.61), and after magnetic stirring for 30 min, transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). A hydrothermal reaction was carried out in the reactor at 220℃ for 6 h, followed by natural cooling to room temperature. The resulting slurry was filtered and separated to obtain a solid product, which was washed three times with water and then dried. The dried sample was further carbonized in a tubular atmosphere furnace under nitrogen as a protective gas, heated to 800℃ at a rate of 5℃ / min and held for 2 h, then cooled to room temperature at a rate of 10℃ / min. The sample was then removed, ground, and the sodium-ion battery anode material (HC-PP-800) was obtained.

[0045] The sodium-ion battery anode materials prepared in Examples 1, 2, 3, 4, and 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. The mixture was then prepared into a slurry using N-methylpyrrolidone and coated onto copper foil. The resulting slurry coating was placed in a vacuum drying oven and dried at 60°C for 12 hours. A circular electrode sheet with a diameter of 12 mm was pressed out using a tablet press to obtain the experimental battery anode. A sodium sheet was used as the counter electrode, a glass fiber disc as the separator, and an organic solution of sodium perchlorate as the electrolyte. Spring contacts and gaskets were added, and the cells were assembled into a 2032 model button cell in a glove box.

[0046] Figure 1 This is a scanning electron microscope image of the sodium-ion battery anode material prepared in Example 1. It can be seen that the material is in the form of blocky particles with a smooth surface and no obvious pores. Figure 2 Transmission electron microscopy clearly reveals the hard carbon structure after hydrothermal carbonization, which contains both a pseudo-graphite layer and a microporous structure. Numerous circular micropores are encapsulated by the carbon layer, forming a microstructure with internal micropores and an outer pseudo-graphite carbon layer. The presence of these two structures provides more active sites for sodium ion storage, allowing sodium ions to be stored within the structure through different mechanisms, thus increasing the battery capacity. Figure 3The X-ray diffraction (XRD) comparison clearly shows that the hard carbon obtained by hydrothermally carbonizing the two raw materials has a higher degree of crystallinity and carbonization than the hard carbon obtained by hydrothermally carbonizing grapefruit peel alone or by directly carbonizing grapefruit peel without hydrothermal treatment. Figure 4 The graphs show the desorption curves of Example 1, Comparative Examples 1 and 2. Calculations show that the specific surface area of ​​Example 1 is 2.64 m². 2 / g, significantly smaller than Comparative Example 1 (372.71m). 2 / g) and Comparative Example 2 (217.52m) 2 After hydrothermal treatment, the surface of the block sample becomes noticeably smoother, and many tiny pores are filled or transformed into slightly larger closed pores, which allows for better sodium storage. Figure 5 Using the pore size distributions of Examples 1, 2, and 3, it can be seen that the samples after co-hydrothermal treatment have similar pore size distributions, with Example 1 having more pores around 10 nm. Figure 6 When using the samples of Example 1, Comparative Example 1, and Comparative Example 2 as electrode materials, the second discharge capacities of the sodium-ion batteries at a current density of 0.05 A / g were 219.32 mAh / g, 98.00 mAh / g, and 200.59 mAh / g, respectively. Figure 7 In the experiment, the electrode material retained a specific capacity of 211.3 mAh / g after 100 charge-discharge cycles at a current density of 0.05 A / g. Figure 8 As shown in Example 1, the AC impedance indicates good electron diffusion performance in the material.

[0047] This invention provides a method and approach for preparing sodium-ion battery anode materials using a co-hydrothermal method combining biomass and plastics. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing sodium-ion battery anode materials via hydrothermal co-processing of biomass and plastics, characterized in that, Includes the following steps: (1) Add the dried and ground biomass and plastic granules to a weakly acidic solution and mix them evenly; (2) The mixture in step (1) is transferred to the reactor for hydrothermal reaction. The product obtained by hydrothermal reaction is filtered, the solid product is washed with water three times and dried. (3) The dried solid obtained in step (2) is calcined in a tube atmosphere furnace, and the product is then ground to obtain the final product. In step (1), the biomass is selected from any one or a combination of two or more of grapefruit peel, watermelon peel, corn stalk, rice husk, sugarcane bagasse, cellulose, and lignin; the plastic granules are selected from any one or a combination of two or more of polyvinyl chloride (PVC), polypropylene (PP), and polyethylene terephthalate (PET). In step (2), the hydrothermal reaction conditions are as follows: the temperature is raised to 220°C at a heating rate of 10°C / min, then kept at that temperature for 6 hours, and then naturally cooled to room temperature. The mass ratio of biomass to plastic is 7:3 to 5:

5. The weak acid solution is prepared by 60 mL of citric acid, acetic acid and oxalic acid, and the pH of the weak acid solution is 3 to 5. In step (3), calcination is carried out under nitrogen protection, with the temperature increased to 600-1000℃ at a heating rate of 5℃ / min and held for 2 hours, and then cooled to room temperature at a cooling rate of 5-10℃ / min.

2. The method for preparing sodium-ion battery anode materials by co-hydrothermal synthesis of biomass and plastics according to claim 1, characterized in that, In step (1), the biomass is dried at 65°C for 24 hours and then crushed, and the sieve size is 60 mesh; the plastic particles have a particle size of 100 mesh, and the mixing is done by magnetic stirring for 2 hours.

3. The method for preparing sodium-ion battery anode materials by co-hydrothermal synthesis of biomass and plastics according to claim 1, characterized in that, In step (2), the lining of the reactor is polytetrafluoroethylene, and the filling ratio of the reactor is 60-70%.

4. The method for preparing sodium-ion battery anode materials by co-hydrothermal synthesis of biomass and plastics according to claim 1, characterized in that, In step (2), the washing time is 30-60 minutes, and the solid product is dried overnight in an oven at 65°C.

5. The method for preparing sodium-ion battery anode materials by co-hydrothermal synthesis of biomass and plastics according to claim 1, characterized in that, In step (3), the grinding time is 0.5 to 3 hours, and the powder particle size after sieving is less than 80 mesh.

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

7. The application of the biomass and plastic hydrothermal carbon material as described in claim 6 as the negative electrode of a sodium-ion battery.

8. A sodium-ion battery, characterized in that, Its negative electrode is prepared by calcination of the biomass and plastic hydrothermal carbon material described in claim 6.

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