A hard carbon material, a preparation method thereof, and a sodium-ion battery

Abstract

The present invention belongs to the technical field of batteries, and discloses a hard carbon material, a preparation method thereof, and a sodium ion battery. The method comprises the following steps: 1) mixing a zinc salt activator with plastic, carrying out hydrothermal reaction, and separating to obtain a hydrothermal product; 2) performing high-temperature pyrolysis on the hydrothermal product, and removing zinc ions to obtain the hard carbon material. The hard carbon material prepared by the method of the present invention has the advantages of large specific surface area, and also solves the problem of single pore size distribution. Assembling a battery with the hard carbon material can effectively improve the rate performance and cycling performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and relates to a hard carbon material, a preparation method thereof, and a sodium ion battery. Background Art

[0002] In recent years, the new energy vehicle industry has developed rapidly. As one of the most important components of new energy vehicles, power batteries have also developed rapidly in recent years. At the same time, there has been an increase in the raw materials of lithium ion batteries, especially the price of lithium salts. Sodium ion batteries are considered to be one of the most likely alternatives to lithium ion batteries. They have abundant raw materials, low prices, and similar electrochemical principles to lithium ion batteries, both being "rocking chair batteries". Therefore, sodium ion batteries have broad development prospects.

[0003] Since the ionic radius of sodium ion (Na + ) is larger than that of lithium ion (Li + ) (0.102 nm vs. 0.076 nm), traditional graphite materials cannot meet the sodium storage requirements. The emergence of hard carbon materials well compensates for the defect that sodium ions cannot be embedded in the graphite layer spacing, and is considered to be one of the most likely commercial negative electrode materials for sodium ion batteries. Hard carbon refers to non-graphitizable carbon, which is a kind of pyrolytic carbon obtained by pyrolyzing high molecular polymers, petrochemical products, biomass, etc. Due to the presence of a large number of heteroatoms (O, N, P, S, etc.) in the precursors for synthesizing hard carbon, this hinders the formation of crystalline regions during the heat treatment process, resulting in difficulty in graphitization even at high temperatures above 2500 °C. Hard carbon has a larger layer spacing than graphite, and more micropores, and correspondingly has more active sites for sodium ion insertion and extraction. Therefore, compared with graphite, hard carbon materials have a larger specific capacity. Moreover, hard carbon has better compatibility with PC electrolyte and is more suitable for working at low temperatures. In addition, hard carbon also has advantages such as good high-rate charge and discharge performance and long cycle life.

[0004] At present, most hard carbon materials are usually obtained by pyrolyzing glucose and high molecular polymers. For example, CN111384394A discloses a preparation method of a glucose-based hard carbon anode material, which includes the following steps: using glucose and water for batching to form a semi-finished product; heating the semi-finished product using a titanium reaction kettle; centrifuging the semi-finished product using a centrifuge to obtain hard carbon; drying and pulverizing the dehydrated hard carbon to form a finished product. CN114044508A discloses a hard carbon microsphere, its preparation method and application. The hard carbon microsphere is obtained by co-carbonization of at least two hard carbon precursors, and the hard carbon precursors are two or more of water-soluble phenolic resin, glucose, sucrose, starch, and lignin. CN113800496A discloses a hard carbon material, its preparation method and application. The preparation method includes the following steps: (1) mixing a carbon source and a templating agent to form a solid reactant, and the carbon source is at least one of high molecular polymers, petrochemical products, and biomass materials; (2) performing pre-carbonization treatment on the solid reactant in an inert gas atmosphere; (3) crushing the treated material into powder, removing the water-soluble templating agent for pore formation, and then obtaining a precursor material through drying; (4) performing heat treatment on the precursor material in an inert gas atmosphere to obtain a hard carbon material.

[0005] However, by using glucose and high molecular polymers as carbon sources, not only does it increase the price of hard carbon materials and limit the large-scale use of sodium-ion batteries. Moreover, it is worth noting that due to the relatively small specific surface area and single pore size distribution of most hard carbon materials, most of them are micropores, which makes their rate performance and cycle stability performance under high current density not ideal. Therefore, preparing high-performance and low-cost anode materials is of great significance to the entire energy storage field. Summary of the Invention

[0006] The object of the present invention is to provide a hard carbon material, its preparation method and a sodium-ion battery. The hard carbon material prepared by the method of the present invention has the advantage of a large specific surface area, and also solves the problem of single pore size distribution. Using this hard carbon material to assemble a battery can effectively improve the rate performance and cycle performance.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides a preparation method of a hard carbon material, and the method includes the following steps:

[0009] (1) After mixing a zinc salt activator and plastic, perform hydrothermal reaction and separate to obtain a hydrothermal product;

[0010] (2) After performing high-temperature pyrolysis on the hydrothermal product, remove zinc ions to obtain a hard carbon material.

[0011] The method of the present invention uses plastic as the carbon source and zinc salt as the activator. Through hydrothermal reaction, the zinc salt is evenly distributed in the carbon source, and the closed condition of hydrothermal synthesis is conducive to the toxic reaction system that is harmful to human health, minimizing environmental pollution as much as possible. The zinc salt activator serves the purpose of creating pores during high-temperature pyrolysis, which can increase the specific surface area of the hard carbon material, endowing it with more active sites. At the same time, the zinc salt activator is mild and will not completely etch the carbon source. The prepared hard carbon material has micropores and mesopores distributed on its surface. The micropores can provide more active sites for sodium storage, and the mesopores are beneficial to improving its rate performance, making its electrochemical performance more excellent when used as the negative electrode material of a sodium-ion battery.

[0012] The following are the preferred technical solutions of the present invention, but they do not limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0013] Preferably, the zinc salt activator in step (1) includes at least one of zinc sulfate, zinc acetate, and zinc chloride, and preferably at least two of zinc sulfate, zinc acetate, and zinc chloride. Different types of activators can generate pores with different pore sizes during pyrolysis, solving the problem of single pore size distribution and meeting different sodium storage requirements.

[0014] Preferably, the zinc salt activator in step (1) is a mixture of zinc chloride and zinc acetate, and the mass ratio of zinc chloride to zinc acetate is (1 - 3):1, such as 1:1, 1.2:1, 1.5:1.2, 2:1, 2.5:1, or 3:1, etc.

[0015] Preferably, the mass ratio of the plastic to the zinc salt activator is 1:(10 - 30), such as 1:10, 1:12, 1:14, 1:15, 1:18, 1:20, 1:22, 1:25, 1:27, or 1:30, etc.

[0016] Preferably, the plastic is waste plastic.

[0017] The main components of waste plastic are polyethylene (PE), polyvinyl chloride (PV), polypropylene (PP), polystyrene resin (PS), etc. Its raw materials are also high molecular polymers. Waste plastic is difficult to degrade. Using it as the raw material to prepare hard carbon material realizes the recycling of waste. At the same time, compared with using expensive raw materials such as glucose and high molecular polymers to prepare hard carbon, the preparation cost can be significantly reduced.

[0018] Using waste plastic as the carbon source has practical value and provides a solution for recycled plastic products such as plastic bags.

[0019] In the present invention, the waste plastics may be recycled waste plastic products, such as plastic wrap or other transparent plastic bags.

[0020] Preferably, the plastic is broken into pieces before use. The smaller the size, the better. For example, the transparent plastic bag can be cut into pieces with a size of less than or equal to 6 mm, such as 6 mm, 5.8 mm, 5.5 mm, 5.3 mm, 5.2 mm, 5 mm, 4.5 mm, 4 mm, 3.5 mm, 3 mm, 2.5 mm, 2 mm, 1.5 mm or 1 mm.

[0021] Preferably, the temperature of the hydrothermal reaction is 160°C to 220°C, for example, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C or 220°C.

[0022] Preferably, the hydrothermal reaction time is 8 h to 15 h, for example, 8 h, 9 h, 10 h, 10.5 h, 11 h, 12 h, 13 h, 14 h or 15 h.

[0023] Preferably, the method further comprises grinding the hydrothermal product before the high-temperature pyrolysis.

[0024] Preferably, the temperature of the high temperature pyrolysis is 1200°C to 1600°C, for example, 1200°C, 1250°C, 1350°C, 1400°C, 1500°C, 1550°C or 1600°C.

[0025] Preferably, the heating rate of the high temperature pyrolysis is 2°C / min-10°C / min, for example, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 8°C / min or 10°C / min.

[0026] Preferably, the holding time of the high temperature pyrolysis is 1 h to 8 h, for example, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h or 8 h.

[0027] Preferably, the zinc ions are removed by acid washing.

[0028] Preferably, the acid comprises at least one of sulfuric acid, nitric acid or hydrochloric acid.

[0029] As a further preferred technical solution of the preparation method of the present invention, the preparation method comprises the following steps:

[0030] (1) crushing the recycled waste plastic products to obtain plastic scraps with a size of less than or equal to 6 mm;

[0031] (2) Dissolve zinc chloride powder in water, mix it with shredded plastic, then pour it into a polytetrafluoroethylene (PTFE) liner. After that, place the PTFE liner in a reaction kettle and carry out hydrothermal treatment at 160 °C to 220 °C for 8 h to 15 h.

[0032] (3) Collect the hydrothermal product, grind it evenly, place it in a porcelain boat, and heat it in a tube furnace at a heating rate of 2 °C / min to 10 °C to 1200 °C to 1600 °C, and keep it at this temperature for 1 h to 8 h.

[0033] (4) After cooling to room temperature, take out the sample, wash it 3 times with hydrochloric acid to remove zinc ions, then wash it 3 times with water, and then put it in an oven to dry to obtain the hard carbon material.

[0034] In one embodiment, the hydrochloric acid used in step (4) is diluted hydrochloric acid with a concentration of 0.5 mol / L to 1.5 mol / L, such as 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.3 mol / L or 1.5 mol / L, etc.

[0035] Second invention, the present invention provides a hard carbon material prepared by the preparation method as described in the first aspect.

[0036] In the third aspect, the present invention provides a sodium-ion battery, and the sodium-ion battery includes the hard carbon material as described in the second aspect.

[0037] The numerical ranges described in the present invention not only include the above-listed point values, but also include any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the range.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The method of the present invention uses plastic as a carbon source, and the zinc salt activator plays a role in creating pores during high-temperature pyrolysis, which can increase the specific surface area of the hard carbon material, making it have more active sites. At the same time, the zinc salt activator is mild and will not completely etch the carbon source. The prepared hard carbon material has micropores and mesopores on its surface. The micropores can provide more sodium storage active sites, and the mesopores are beneficial to improving its rate performance. When used as the negative electrode material of a sodium-ion battery, its electrochemical performance is more excellent.

[0040] (2) The hard carbon material with micropores-mesopores is obtained by adding an appropriate proportion of activator and an appropriate hydrothermal temperature. The hard carbon material obtained by this method can provide a capacity retention rate of more than 86.0% after 200 cycles at a current density of 0.5 A / g when used in a sodium-ion battery, and the rate performance (3 A / g -1 ​-1 / 1A g -1 ) can reach more than 87.5%. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0042] Example 1

[0043] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0044] (1) The recycled waste plastic wrap is crushed to a size of 5 mm to obtain crushed plastic.

[0045] (2) Take 20 g of zinc chloride powder and dissolve it in 50 ml of water, mix it with 1 g of crushed plastic, and then pour it into 100 ml of polytetrafluoroethylene liner. Then, place the polytetrafluoroethylene liner in a reactor and hydroheat it at 200°C for 12 h.

[0046] (3) The hydrothermal products were collected, ground, placed in a porcelain boat, and heated to 1300 °C in a tube furnace at a heating rate of 5 °C / min and kept at this temperature for 3 h.

[0047] (4) After cooling to room temperature, take out the sample, wash it three times with diluted hydrochloric acid to remove zinc ions, then wash it three times with water, and then put it in an oven to dry for 12 hours. The dried sample is a hard carbon material.

[0048] Example 2

[0049] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0050] (1) The recycled waste plastic wrap is crushed to a size of 3 mm to obtain crushed plastic.

[0051] (2) Take 25 g of zinc acetate powder and dissolve it in 60 ml of water, mix it with 1 g of crushed plastic, and then pour it into 100 ml of polytetrafluoroethylene liner. Then, place the polytetrafluoroethylene liner in a reactor and hydroheat it at 180°C for 15 h.

[0052] (3) The hydrothermal products were collected, ground, placed in a porcelain boat, and heated to 1500 °C in a tube furnace at a heating rate of 8 °C / min and kept at this temperature for 1 h.

[0053] (4) After cooling to room temperature, take out the sample, wash it with diluted hydrochloric acid four times to remove zinc ions, then wash it with water three times, and then put it in an oven to dry for 8 hours. The dried sample is a hard carbon material.

[0054] Example 3

[0055] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0056] (1) The recycled waste plastic wrap is crushed to a size of 1 mm to obtain crushed plastic.

[0057] (2) Take 10 g of zinc sulfate powder and dissolve it in 50 ml of water, mix it with 1 g of crushed plastic, and then pour it into 100 ml of polytetrafluoroethylene liner. Then, place the polytetrafluoroethylene liner in a reactor and hydroheat it at 210°C for 8 h.

[0058] (3) The hydrothermal products were collected, ground, placed in a porcelain boat, and heated to 1200 °C in a tube furnace at a heating rate of 3 °C / min and kept at this temperature for 8 h.

[0059] (4) After cooling to room temperature, take out the sample, wash it three times with diluted hydrochloric acid to remove zinc ions, then wash it three times with water, and then put it in an oven to dry for 10 hours. The dried sample is a hard carbon material.

[0060] Example 4

[0061] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0062] (1) The recycled waste plastic wrap is crushed to a size of 3 mm to obtain crushed plastic.

[0063] (2) Take 15 g of zinc chloride powder and dissolve it in 50 ml of water, mix it with 1 g of crushed plastic, and then pour it into 100 ml of polytetrafluoroethylene liner. Then, place the polytetrafluoroethylene liner in a reactor and hydroheat it at 190°C for 9 hours.

[0064] (3) The hydrothermal products were collected, ground, placed in a porcelain boat, and heated to 1400°C in a tube furnace at a heating rate of 5°C / min and kept at this temperature for 3.5 h.

[0065] (4) After cooling to room temperature, take out the sample, wash it three times with diluted hydrochloric acid to remove zinc ions, then wash it three times with water, and then put it in an oven to dry for 8 hours. The dried sample is a hard carbon material.

[0066] Example 5

[0067] The difference from Example 1 is that the zinc chloride powder is replaced by a mixture of 10 g of zinc chloride powder and 10 g of zinc acetate powder.

[0068] Example 6

[0069] The difference from Example 1 is that the consumption of zinc chloride powder is 8g.

[0070] Example 7

[0071] The difference from Example 1 is that the amount of zinc chloride powder used is 33 g.

[0072] Example 8

[0073] The difference from Example 1 is that the temperature of the hydrothermal reaction is 140 °C.

[0074] Example 9

[0075] The difference from Example 1 is that the temperature of the hydrothermal reaction is 230 °C.

[0076] Comparative Example 1

[0077] The difference from Example 1 is that step (2) is as follows: Take 20 g of zinc chloride and mix it with 1 g of shredded plastic to obtain a mixture.

[0078] This mixture is used to replace the hydrothermal product in step (3) of Example 1.

[0079] Comparative Example 2

[0080] The difference from Example 1 is that no zinc chloride powder is added.

[0081] Test:

[0082] I. Pore size distribution test:

[0083] According to its reversible physical adsorption behavior on the surface of the sample under certain conditions, the specific surface area is tested by the method of nitrogen adsorption. Take at least 100 mg of the hard carbon material powder of Examples 1-9 and Comparative Examples 1-3 for BET (Brunauer-Emmett-Teller) test to obtain the pore size distribution and specific surface area of the sample.

[0084] II. Electrode sheet preparation: Use the hard carbon materials obtained in Examples 1-9 and Comparative Examples 1-3 above as active materials, and grind and mix them with the binder sodium alginate and the conductive agent acetylene black according to a mass ratio of 8:1:1, add NMP as a solvent to prepare a uniform battery slurry, and obtain electrode sheets with a diameter of 12 mm through operations such as coating, drying, and slicing.

[0085] III. Battery assembly: Use a metal sodium block as the counter electrode, the electrolyte is 1 mol / L NaPF6 solution, and the solvent is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1. Assemble a CR2025 type button sodium ion battery in a glove box.

[0086] IV. Battery test: The rate performance and cycle performance of the sodium ion battery are tested on a Neware battery test system (CT-3008-5V / 10 mA).

[0087] Cyclic performance test: Constant current charge and discharge cycling was carried out at a current density of 0.5 A g -1 in the voltage range of 0.005 - 2.0 V, with a 5-minute rest, for 200 cycles, and the capacity retention rate after 200 cycles was recorded.

[0088] Rate performance test: 0.1 A g -1 , 0.2 A g -1 , 0.5 A g -1 , 1 A g -1 , 2 A g -1 and 3 A g -1 were selected for testing. Each rate was tested for 10 cycles. The rate performance was the ratio of the capacity after 10 cycles at 3 A g -1 rate to the capacity after 10 cycles at 1 A g -1 rate.

[0089] The test results are shown in Table 1.

[0090] Table 1

[0091]

[0092]

[0093] From the comparison between Example 1 and Example 5, it can be seen that the active material prepared by mixing zinc chloride and zinc acetate powders has a larger specific surface area, can provide more sodium storage sites, and moreover, the active material contains both micropores and mesopores, which is more conducive to improving the rate performance of the active material.

[0094] From the comparison between Example 1 and Examples 6 - 7, it can be seen that in Example 6, the amount of activator used is too small, resulting in a smaller specific surface area, which is not conducive to sodium ion storage; in Example 7, the amount of activator is too large. Although the specific surface area increases, it leads to the collapse of the structure of the active material, resulting in a decrease in the rate performance of the material.

[0095] From the comparison between Example 1 and Examples 8 - 9, it can be seen that too high or too low hydrothermal reaction temperature both lead to uneven mixing during the premixing process of the material, resulting in poor rate performance and cyclic performance of the finally obtained material.

[0096] From the comparison between Example 1 and Comparative Example 1, it can be seen that the hydrothermal process can pre-mix the activator and waste plastics evenly, which is more conducive to the subsequent high-temperature carbonization process. In Comparative Example 1, direct mixing results in a smaller specific surface area of the obtained active substance, which is not conducive to sodium ion storage.

[0097] From the comparison between Example 1 and Comparative Example 2, it can be seen that under the condition of not adding any activator, the specific surface area of the obtained material is very small, and it is basically difficult to provide sites for sodium ion insertion / extraction.

[0098] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing a hard carbon material, characterized in that, The method comprises the following steps: (1) After mixing a zinc salt activator with plastics, performing hydrothermal reaction and separating to obtain a hydrothermal product; (2) After performing high-temperature pyrolysis on the hydrothermal product, removing zinc ions to obtain a hard carbon material; The zinc salt activator comprises at least two of zinc sulfate, zinc acetate and zinc chloride; The mass ratio of the plastics to the zinc salt activator is 1:(12-30); The temperature of the hydrothermal reaction is 160°C - 220°C; The plastics are waste plastics, and the waste plastics are food wrap.

2. The preparation method according to claim 1, wherein In step (1), the zinc salt activator is a mixture of zinc chloride and zinc acetate, and the mass ratio of zinc chloride to zinc acetate is (1-3):

1.

3. The preparation method according to claim 1, wherein, The plastics are subjected to crushing treatment before use.

4. The preparation method according to claim 1, characterized in that, The time of the hydrothermal reaction is 8h - 15h.

5. The preparation method according to claim 1, characterized in that, The method further comprises performing grinding treatment on the hydrothermal product before high-temperature pyrolysis.

6. The preparation method according to claim 1, characterized in that, The temperature of the high-temperature pyrolysis is 1200°C - 1600°C.

7. The preparation method according to claim 1, characterized in that, The heating rate of the high-temperature pyrolysis is 2°C / min - 10°C / min.

8. The preparation method according to claim 1, characterized in that, The heat preservation time of the high-temperature pyrolysis is 1h - 8h.

9. The preparation method according to claim 1, characterized in that The zinc ions are removed by pickling.

10. The preparation method according to claim 9, wherein, The acid comprises at least one of sulfuric acid, nitric acid or hydrochloric acid.

11. According to the preparation method described in claim 1, characterized in that, The method comprises the following steps: (1) Crushing the recycled waste plastic products to obtain crushed plastics with a size less than or equal to 6 mm; (2) Dissolving zinc chloride powder in water, mixing it with the crushed plastics, then pouring it into a polytetrafluoroethylene inner liner, and then placing the polytetrafluoroethylene inner liner in a reaction kettle for hydrothermal reaction at 160°C - 220°C for 8h - 15h; (3) Collecting the hydrothermal product, grinding it evenly, placing it in a porcelain boat, and heating it to 1200°C - 1600°C in a tubular furnace at a heating rate of 2°C / min - 10°C and keeping it warm for 1h - 8h; (4) After cooling to room temperature, taking out the sample, washing it 3 times with hydrochloric acid to remove zinc ions, then washing it 3 times with water, and then putting it into an oven to dry to obtain a hard carbon material.

12. A hard carbon material prepared by the preparation method according to any one of claims 1-11.

13. A sodium-ion battery, characterized in that, The sodium ion battery comprises the hard carbon material according to claim 12.

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