A hard carbon material, preparation method thereof, application thereof and secondary battery

Abstract

The present invention discloses a hard carbon material and its preparation method, application and secondary battery. The preparation method comprises: mixing a halogen-containing polymer powder and a thermoplastic resin, heating and smelting the mixture, and cooling the mixture to obtain a mixture; then mixing the mixture with a reducing metal, heating and dehalogenating the mixture at 100-400°C under inert gas protection for 2-12 hours to obtain a dehalogenated sample; washing, drying and carbonizing the dehalogenated sample to obtain a hard carbon material; the thermoplastic resin is polypropylene and / or polyethylene; when the reducing metal is an alkali metal, the molar ratio of the halogen atoms in the halogen-containing polymer powder to the reducing metal is 1:(1-3); when the reducing metal is an alkaline earth metal, the molar ratio of the halogen atoms in the halogen-containing polymer powder to the reducing metal is 1:(0.5-1.5). The preparation method can achieve pollution-free treatment of halogen-containing polymer waste while achieving high value-added utilization, with the advantages of high efficiency, environmental protection, greenness and energy saving.

Description

Technical Field

[0001] The present invention particularly relates to a hard carbon material, a preparation method thereof, an application thereof and a secondary battery. Background Art

[0002] PVC (polyvinyl chloride) is a widely used plastic material in various fields, characterized by excellent chemical stability, corrosion resistance, flame retardancy, and good processing properties. However, the production, use, and disposal of PVC can create environmental and health issues. Due to its resistance to degradation, PVC is typically disposed of in landfills, where it remains in the environment for long periods, causing soil and groundwater contamination. PVC is non-biodegradable and difficult to recycle under natural conditions. Its high chlorine content also produces dioxins, other chlorine-containing organic compounds, and highly corrosive HCl during incineration, making it one of the most environmentally hazardous plastics.

[0003] Traditional PVC recycling strategies, such as mechanical recycling, processing, and reuse, have low economic added value. Material performance deteriorates during the recycling process, making them unsustainable in terms of cost. To overcome the shortcomings of traditional recycling strategies and tap into the intrinsic value of plastic waste, there is an urgent need to develop high-value-added, green resource utilization technologies for halogen-containing polymers like PVC.

[0004] Hard carbon, a carbon material with a high degree of graphitization, high conductivity, and high stability, is widely used in lithium-ion batteries, supercapacitors, fuel cells, and other fields. With the rapid development of new energy and the electronic information industry, the demand for high-performance hard carbon materials is increasing. Current hard carbon precursors, such as biomass, coal, and sugars, are relatively expensive. Therefore, fully utilizing waste polymers as a carbon source could significantly reduce the raw material cost of hard carbon production. Summary of the Invention

[0005] The technical problem addressed by the present invention is to overcome the shortcomings of prior art, such as the inadequate utilization of existing halogen-containing waste polymer materials and the high cost of hard carbon raw materials, by providing a hard carbon material, its preparation method, applications, and secondary batteries. The preparation method of the present invention achieves pollution-free treatment of halogen-containing polymer waste while realizing high-value-added utilization, offering advantages such as high efficiency, environmental friendliness, greenness, and energy conservation. The prepared hard carbon material exhibits excellent specific capacity and rate performance when used in batteries.

[0006] In the process of preparing hard carbon materials, the present invention uses halogen-containing polymers as raw materials, first heats and melts the halogen-containing polymers and thermoplastic resins (polypropylene, polyethylene) to obtain a mixture, and the thermoplastic resin can coat the halogen-containing polymer to prevent the halogen-containing polymer from having a larger pore size after HCl overflows during the subsequent dehalogenation process; the halogen-containing polymer and the reducing metal (alkali metal, alkaline earth metal) in the mixture first undergo a dehalogenation reaction to form a carbon-containing precursor and a salt, thereby removing the halogen in the halogen-containing polymer, and then carbonizing the carbon-containing precursor to obtain a hard carbon material with excellent electrochemical properties. During the dehalogenation reaction, the reducing metal catalyzes the dehalogenation reaction of the halogen-containing polymer more completely and fixes the highly polluting halogen atoms. The reducing metal and the generated salt will penetrate into the partially carbonized polymer as a template or pore-forming agent, thereby being applied to the high-performance negative electrode of sodium / lithium ion batteries to achieve higher specific capacity and rate performance. This preparation method can achieve pollution-free treatment of halogen-containing polymer waste while achieving high value-added utilization, with the advantages of high efficiency, environmental protection, greenness, and energy saving.

[0007] The present invention solves the above technical problems through the following technical solutions:

[0008] The present invention provides a method for preparing a hard carbon material, which comprises the following steps:

[0009] A halogen-containing polymer powder and a thermoplastic resin are mixed, heated and melted, and cooled to obtain a mixture; the mixture is then mixed with a reducing metal, and heated at 100-400° C. for dehalogenation for 2-12 hours in an inert gas atmosphere to obtain a dehalogenated sample; the dehalogenated sample is washed, dried, and carbonized to obtain a hard carbon material;

[0010] Wherein, the thermoplastic resin is polypropylene and / or polyethylene, and the mass ratio of the thermoplastic resin to the halogen-containing polymer powder is 2%-10%;

[0011] When the reducing metal is an alkali metal, the molar ratio of the halogen atoms in the halogen-containing polymer powder to the reducing metal is 1:(1-3);

[0012] When the reducing metal is an alkaline earth metal, the molar ratio of the halogen atoms in the halogen-containing polymer powder to the reducing metal is 1:(0.5-1.5).

[0013] In the present invention, the halogen-containing polymer powder is preferably polyvinyl chloride (PVC) and / or polyvinylidene chloride (PVDC). The particle size of the halogen-containing polymer powder may be 0.1-1 μm. The halogen-containing polymer powder may also be a powder obtained by washing and mechanically crushing waste halogen-containing polymer products.

[0014] The viscosity K value of the polyvinyl chloride may be 50-80, such as 62-60.

[0015] In the present invention, the melt index of the polypropylene may be 10-40 g / 10 min, for example, 35 g / 10 min.

[0016] In the present invention, the melt index of the polyethylene may be 10-40 g / 10 min, for example, 25 g / 10 min.

[0017] In the present invention, the mass ratio of the thermoplastic resin to the halogen-containing polymer powder is preferably 2%-8%, for example, 5%.

[0018] In the present invention, the heating and melting is generally carried out in a heating furnace. The heating furnace can be conventional in the art, such as a tubular furnace. The heating and melting is generally carried out under an inert atmosphere (such as argon).

[0019] In the present invention, the heating and melting temperature may be 100-140°C, for example 120°C.

[0020] In the present invention, the heating and melting time may be 1-4 hours, for example 2 hours.

[0021] In the present invention, the alkali metal element is preferably Na and / or K.

[0022] In the present invention, the alkaline earth metal element is preferably one or more of Mg, Ca and Ba.

[0023] In the present invention, when the reducing metal is an alkali metal, the molar ratio of the halogen atoms in the halogen-containing polymer powder to the reducing metal is preferably 1:(1-2), such as 1:1.1, 1:1.2 or 1:1.3.

[0024] In the present invention, when the primary metal is an alkaline earth metal, the molar ratio of the halogen atoms in the halogen-containing polymer powder to the reducing metal is preferably 1:(0.5-1), for example, 1:0.55.

[0025] In the present invention, the temperature of the heating dehalogenation is preferably 200-400°C, for example 250°C.

[0026] In the present invention, the heating dehalogenation time is preferably 2-6 hours, for example 3 hours.

[0027] In the present invention, the heating dehalogenation is generally carried out in a tube furnace.

[0028] In the present invention, the inert gas may be conventional in the art, such as nitrogen or argon.

[0029] In the present invention, the washing operation and conditions can be conventional in the art, for example, washing is performed using a mixed solution of deionized water and anhydrous ethanol; in the mixed solution, the volume ratio of the deionized water to the anhydrous ethanol can be 3:1.

[0030] In the present invention, the drying operation and conditions may be conventional in the art.

[0031] In the present invention, according to the conventional art, the carbonization is generally performed in an inert gas atmosphere, such as nitrogen or argon.

[0032] In the present invention, the carbonization temperature is preferably 600-1000°C, such as 800°C, 850°C or 900°C.

[0033] In the present invention, the carbonization time may be 0.5 to 10 hours, preferably 3 to 6 hours, for example 4 hours.

[0034] The present invention also provides a hard carbon material prepared by the above-mentioned preparation method.

[0035] In the present invention, the specific surface area of ​​the hard carbon material is preferably 6-10m 2 g -1 .

[0036] In the present invention, the hard carbon material preferably has a sodium storage capacity greater than 250 mAh / g at a high rate of 20C.

[0037] In the present invention, the hard carbon material preferably has a lithium storage capacity greater than 300 mAh / g at a high rate of 20C.

[0038] The present invention also provides a use of the hard carbon material as described above in a secondary battery.

[0039] The present invention also provides a secondary battery comprising the hard carbon material as described above.

[0040] In the present invention, the secondary battery is preferably a lithium ion battery or a sodium ion battery.

[0041] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0042] The reagents and raw materials used in the present invention are commercially available.

[0043] The positive progress effect of the present invention is:

[0044] The preparation method of the present invention does not rely on organic solvents to dissolve polymer materials. It can directly achieve a more efficient dechlorination reaction through a simple solid-phase method, promoting graphitization while avoiding chlorine emissions. In addition, the template and pore-forming effects of metals and salts help to increase the specific surface area of ​​the material. The prepared hard carbon material has better electrochemical performance as a lithium / sodium ion battery, especially better specific capacity and 20C rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a scanning electron microscope image of the hard carbon material prepared in Example 1. DETAILED DESCRIPTION

[0046] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0047] The raw material information used in the following examples and comparative examples is shown in Table 1:

[0048] Table 1

[0049]

[0050] Example 1

[0051] (1) 1 g of PVC and 0.05 g of polyethylene were mixed and heated in a tube furnace (under argon atmosphere) at 120°C for 2 h. After cooling, substance A was obtained.

[0052] (2) Substance A and metallic sodium were mixed evenly in a crucible according to the molar ratio of chlorine atoms to metallic sodium in the raw material PVC of 1:1.3, and then placed in a tube furnace. In a high-purity argon atmosphere, the mixture was heated to 250°C at a heating rate of 3°C / min, maintained for 3 hours, and then cooled to room temperature to obtain a dehalogenated sample;

[0053] (3) The dehalogenated sample was washed three times with a mixture of deionized water and anhydrous ethanol in a volume ratio of 3:1, and dried to obtain a hard carbon precursor. The hard carbon precursor was then carbonized in a high-purity argon gas using a tubular furnace at a temperature of 5°C / min to 800°C and maintained for 4 hours, and then cooled to obtain a hard carbon negative electrode material.

[0054] Example 2

[0055] Compared with Example 1, except that the polyvinyl chloride powder was replaced by PVDC powder (Dow SARAN 516, extrusion type), the other parameters and conditions were the same as those in Example 1.

[0056] Example 3

[0057] Compared with Example 1, except that metallic sodium is replaced by metallic potassium, the other parameters and conditions are the same as those in Example 1.

[0058] Example 4

[0059] Compared with Example 1, except that metallic sodium was replaced by metallic potassium and the molar ratio of chlorine atoms to metallic potassium in PVC was adjusted to 1:1.1, other parameters and conditions were the same as those in Example 1.

[0060] Example 5

[0061] Compared with Example 1, except that metallic sodium was replaced by metallic magnesium and the molar ratio of chlorine atoms to metallic magnesium in PVC was adjusted to 1:0.55, other parameters and conditions were the same as those in Example 1.

[0062] Example 6

[0063] Compared with Example 1, except that metallic sodium was replaced by metallic calcium and the molar ratio of chlorine atoms to metallic calcium in PVC was adjusted to 1:0.55, other parameters and conditions were the same as those in Example 1.

[0064] Example 7

[0065] Compared with Example 1, except that the carbonization temperature in step (3) is adjusted to 900° C., the other parameters and conditions are the same as those in Example 1.

[0066] Example 8

[0067] Compared with Example 1, except that polyethylene is replaced by polypropylene, the other parameters and conditions are the same as those of Example 1.

[0068] Comparative Example 1

[0069] Compared with Example 1, except that metallic sodium is not added in step (1), the other parameters and conditions are the same as those in Example 1.

[0070] Effect embodiment

[0071] (1) SEM and specific surface area test

[0072] Figure 1 This is a scanning electron microscope image of the hard carbon material prepared in Example 1.

[0073] The specific surface area of ​​the prepared hard carbon material was tested using Anton Paar's specific surface area and pore size analyzer NOVATouch. The test results are shown in Table 1.

[0074] (2) Electrochemical performance test

[0075] Preparation of negative electrode sheets: The hard carbon materials prepared in Examples 1 to 8 and Comparative Example 1 were subjected to half-cell tests. The test method was as follows: the hard carbon material, superconductive carbon black (Super P), and PVDF were configured in a mass ratio of 8:1:1, uniformly mixed using a homogenizer, and then coated on a copper foil current collector and dried in a vacuum oven at 90°C overnight. Subsequently, the obtained electrode sheets were cut into discs with a diameter of 12 mm for battery electrode sheets for standby use, with an average mass loading of ≈2 mg cm -2 .

[0076] The button cell batteries were assembled in an argon-filled glove box. The lithium-ion batteries used a lithium metal sheet as the counter electrode and a polypropylene monolayer as the separator. The electrolyte consisted of a 1M LiClO₄ solution in ethylene carbonate / diethyl carbonate (EC / DEC, 1:1 volume ratio) supplemented with 10 wt.% fluoroethylene carbonate (FEC), where wt.% refers to the mass percentage of FEC in the electrolyte. Charge and discharge tests were conducted on a LAND CT2001A battery tester over a potential range of 0.001–3.0 V.

[0077] The sodium-ion battery uses a sodium metal sheet as the counter electrode, a single layer of glass fiber as the separator, and a nickel foam disc. The electrolyte is a 1M NaPF6 solution in diethylene glycol dimethyl ether. After assembly, the battery was aged for 8 hours. Constant current charge / discharge tests were performed on a LAND CT2001A battery test system over a voltage range of 0.001 to 3.0 V vs. Li / Li. + .

[0078] The test results are shown in Table 2:

[0079] Table 2

[0080]

[0081] According to the above experimental results, the hard carbon negative electrode material prepared by the present invention has excellent electrochemical properties, especially specific capacity and rate performance.

[0082] In Comparative Example 1, due to the lack of metal catalysis during the preparation process, the dehalogenation reaction is less efficient at the same temperature, which is not conducive to the formation of highly conductive carbon. In addition, due to the lack of the template effect of metal and salt, the prepared hard carbon material has a small specific surface area and a low specific capacity.

[0083] Although specific embodiments of the present invention have been described above, those skilled in the art will appreciate that these are merely illustrative and that the scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, and such changes and modifications are intended to fall within the scope of the present invention.

Claims

1. A method for preparing a hard carbon material, characterized in that: It includes the following steps: A halogen-containing polymer powder and a thermoplastic resin are mixed, heated and melted, and cooled to obtain a mixture; the mixture is then mixed with a reducing metal, and heated at 100-400° C. for dehalogenation for 2-12 hours in an inert gas atmosphere to obtain a dehalogenated sample; the dehalogenated sample is washed, dried, and carbonized to obtain a hard carbon material; Wherein, the thermoplastic resin is polypropylene and / or polyethylene, and the mass ratio of the thermoplastic resin to the halogen-containing polymer powder is 2%-10%; When the reducing metal is an alkali metal, the molar ratio of the halogen atoms in the halogen-containing polymer powder to the reducing metal is 1:(1-3); When the reducing metal is an alkaline earth metal, the molar ratio of the halogen atoms in the halogen-containing polymer powder to the reducing metal is 1:(0.5-1.5).

2. The method for preparing a hard carbon material according to claim 1, wherein: The halogen-containing polymer powder is polyvinyl chloride and / or polyvinylidene chloride.

3. The method for preparing a hard carbon material according to claim 2, wherein: The viscosity number K value of the polyvinyl chloride is 50-80.

4. The method for preparing a hard carbon material according to claim 3, wherein: The viscosity number K value of the polyvinyl chloride is 60-62.

5. The method for preparing a hard carbon material according to claim 1, wherein: The particle size of the halogen-containing polymer powder is 0.1-1 μm.

6. The method for preparing a hard carbon material according to claim 1, wherein: The alkali metal element is Na and / or K.

7. The method for preparing a hard carbon material according to claim 1, wherein: The alkaline earth metal element is one or more of Mg, Ca and Ba.

8. The method for preparing a hard carbon material according to claim 1, wherein: When the reducing metal is an alkali metal element, the molar ratio of the halogen atoms in the halogen-containing polymer powder to the reducing metal is 1:(1-2).

9. The method for preparing a hard carbon material according to claim 8, wherein: When the reducing metal is an alkali metal, the molar ratio of the halogen atoms in the halogen-containing polymer powder to the reducing metal is 1:1.1, 1:1.2 or 1:1.

3.

10. The method for preparing a hard carbon material according to claim 1, wherein: When the primary metal is an alkaline earth metal, the molar ratio of the halogen atoms in the halogen-containing polymer powder to the reducing metal is 1:(0.5-1).

11. The method for preparing a hard carbon material according to claim 10, wherein: When the primary metal is an alkaline earth metal, the molar ratio of the halogen atoms in the halogen-containing polymer powder to the reducing metal is 1:0.

55.

12. The method for preparing a hard carbon material according to claim 1, wherein: The melt index of the polypropylene is 10-40 g / 10 min.

13. The method for preparing a hard carbon material according to claim 12, wherein: The melt index of the polypropylene is 35 g / 10 min.

14. The method for preparing a hard carbon material according to claim 1, wherein: The polyethylene has a melt index of 10-40 g / 10 min.

15. The method for preparing a hard carbon material according to claim 14, wherein: The polyethylene has a melt index of 25 g / 10 min.

16. The method for preparing a hard carbon material according to claim 1, wherein: The mass ratio of the thermoplastic resin to the halogen-containing polymer powder is 2%-8%.

17. The method for preparing a hard carbon material according to claim 16, wherein: The mass ratio of the thermoplastic resin to the halogen-containing polymer powder is 5%.

18. The method for preparing a hard carbon material according to claim 1, wherein: The heating and melting temperature is 100-140°C.

19. The method for preparing a hard carbon material according to claim 18, wherein: The heating and melting temperature is 120°C.

20. The method for preparing a hard carbon material according to claim 1, wherein: The heating and melting time is 1-4 hours.

21. The method for preparing a hard carbon material according to claim 20, wherein: The heating and melting time is 2 hours.

22. The method for preparing a hard carbon material according to claim 1, wherein: The temperature of the heating dehalogenation is 200-400°C.

23. The method for preparing a hard carbon material according to claim 22, wherein: The temperature of the heating dehalogenation is 250°C.

24. The method for preparing a hard carbon material according to claim 1, wherein: The heating dehalogenation time is 2-6 hours.

25. The method for preparing a hard carbon material according to claim 24, wherein: The heating dehalogenation time is 3 hours.

26. The method for preparing a hard carbon material according to claim 1, wherein: The carbonization temperature is 600-1000°C.

27. The method for preparing a hard carbon material according to claim 26, wherein: The carbonization temperature is 800°C, 850°C or 900°C.

28. The method for preparing a hard carbon material according to claim 1, wherein: The carbonization time is 0.5 to 10 hours.

29. The method for preparing a hard carbon material according to claim 28, wherein: The carbonization time is 3 to 6 hours.

30. The method for preparing a hard carbon material according to claim 29, wherein: The carbonization time is 4 hours.

31. A hard carbon material, characterized in that The hard carbon material is prepared according to the method for preparing the hard carbon material according to any one of claims 1 to 30.

32. Use of the hard carbon material according to claim 31 in a secondary battery.

33. A secondary battery, characterized in that: It includes the hard carbon material as claimed in claim 31.

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