Hard carbon material and preparation method therefor and use thereof, and battery

Abstract

Disclosed in the present invention are a hard carbon material and a preparation method therefor and the use thereof, and a battery. The preparation method for the hard carbon material comprises: mixing a solution containing PVC and an aromatic compound under heating conditions until a solvent is completely evaporated to dryness, so as to obtain an xerogel, wherein the mass ratio of the aromatic compound to the PVC is 2-25%; grinding, washing and drying the xerogel, so as to obtain a dehalogenated-PVC precursor; and carbonizing the dehalogenated-PVC precursor, so as to obtain the hard carbon material, wherein the carbonization is performed at a temperature of 700-1200°C for 1-4 h. The hard carbon material prepared in the present invention has relatively high atom economy and high electron conductivity, and has good electrochemical performance when being used for the preparation of a battery.

Description

Hard carbon material, preparation method, application and battery thereof

[0001] The present application claims priority to the patent applications with the application numbers 2024105413907, 2024105413945 and 2024118529189, the application dates of which are April 30, 2024, April 30, 2024 and December 16, 2024, respectively, and the application titles of which are “A hard carbon material, preparation method, application and battery thereof”, “A PVC derived hard carbon material, preparation method, application and battery thereof” and “A hard carbon material, preparation method, application and secondary battery thereof”, respectively. TECHNICAL FIELD

[0002] The present application specifically relates to a hard carbon material, preparation method, application and battery thereof. BACKGROUND

[0003] PVC (polyvinyl chloride) is a plastic material widely used in various fields, with good chemical stability, corrosion resistance, flame resistance and good processing performance. However, the production, use and disposal of PVC will cause environmental and health problems. The landfill disposal of PVC materials will exist in the environment for a long time due to its non-degradable characteristics, causing soil and groundwater pollution. PVC is not degradable under natural conditions and is difficult to recycle, and its waste will produce dioxins and other chlorine-containing organic matter and highly corrosive HCl during incineration due to high chlorine content, so it is one of the plastics that cause the most harm to the environment.

[0004] As the most typical chlorinated plastic, PVC is a thermoplastic plastic polymerized by free radicals from vinyl chloride monomers, with a theoretical chlorine content of up to 56.8% of its total mass. PVC combustion and pyrolysis will produce carcinogenic organic matter such as dioxins and furans, accompanied by HCl release. In China, the main management methods of PVC waste plastics are landfill, incineration and recycling. The proportions of PVC waste in landfill sites, incineration, mechanical and chemical recycling are 36.0%, 9.3%, 25.5% and 0.8%, respectively. However, landfill sites have limited space and are a serious waste of resources. Landfill disposal of PVC waste will release harmful additives, polluting the soil and groundwater. Incineration of PVC waste will release carbon dioxide and HCl, and may produce polychlorinated dioxins and furans. At the same time, the incineration residues contain heavy metals and are considered hazardous waste.

[0005] The traditional PVC recycling strategies such as mechanical recycling, reprocessing and reuse have low economic added value, and the material properties deteriorate during the recycling process, which is difficult to sustain in terms of cost. The current PVC waste treatment technology cannot achieve the slowing down of PVC plastic production, the improvement of PVC waste treatment rate and the turning of PVC consumption mode. In order to overcome the shortcomings of traditional recycling strategies, it is urgent to develop high-value green resource utilization technology of PVC and other halogen-containing polymers by tapping the intrinsic value of plastic waste. In addition to traditional plastic recycling, one of the best ways to slow down the pollution of PVC waste is to upgrade and reuse, which can increase its value and be used for new purposes. Upgrading and reusing is the process of converting waste resources or by-products into new materials with higher value, and chemical upgrading and reusing is a more potential alternative to traditional pyrolysis and recycling, because it can convert plastic waste into materials and chemicals with high value and multifunctionality, with higher selectivity and less energy required. In order to achieve environmental and economic advantages related to waste plastic recycling, it is necessary to develop effective upgrading and reusing technologies to reduce the content of Cl while realizing the upgrading of high-value and multifunctional chemicals to treat PVC waste plastics.

[0006] The growing concerns about energy and environmental problems caused by the burning and shortage of fossil fuel resources worldwide have stimulated interest in exploring efficient and renewable energy sources. Therefore, various advanced electrochemical energy storage and conversion devices have been developed to achieve sustainable development. Although the working principles of energy storage and conversion systems are different, seeking suitable electrode materials with ideal components and structures is the key prerequisite for developing high-performance devices. Among the developed electrode materials, carbon-based materials have attracted much attention due to their high electrical conductivity, good chemical stability and structural stability. Although carbon-based electrode materials have broad prospects, traditional carbon materials are prepared from fossil fuels as synthetic raw materials, which are harmful to the environment and expensive. Therefore, efforts are being made to develop suitable precursors that are rich in resources and have limited environmental impact. From the perspective of sustainable development, using plastic waste as a precursor for carbon synthesis is a good way to turn waste into treasure.

[0007] One of the most promising practical applications of upgrading and reusing PVC waste is to prepare high-value carbon-based electrode materials for energy storage, such as hard carbon. Hard carbon is a carbon material with high graphitization degree, high electrical conductivity and high stability, which is widely used in lithium-ion batteries, supercapacitors, fuel cells and other fields. With the rapid development of new energy fields and electronic information industries, the demand for high-performance hard carbon materials is increasing. The current hard carbon precursors include biomass, coal, sugars and other raw materials, which have high cost. Therefore, if waste polymers can be fully utilized as carbon sources, the raw material cost of hard carbon production will be greatly reduced.

[0008] As the negative material of alkali metal ion battery, the hard carbon is composed of vortex layer structure of twisted and folded carbon layers with large interlayer spacing. Due to its unique turbulent layer structure, hard carbon has the advantages of high theoretical capacity, strong rate capability and excellent cycle performance. However, it should be noted that the solid-state diffusion kinetics of lithium ions in the highly disordered structure of hard carbon is slow, which may lead to low conductivity and insufficient ion diffusion capacity, thereby limiting the actual capacity and rate performance, and showing low first-cycle coulombic efficiency. The inherent inert electrochemical surface interface and disordered structure of hard carbon may cause slow diffusion of lithium ions and electrons, resulting in low rate capacity and poor long cycle stability. Therefore, in order to effectively improve the rate performance and long cycle stability, it is of great significance to design a suitable hard carbon interface structure to improve the ion transport capacity and provide an efficient diffusion network.

[0009] Thermoplastic polyvinyl chloride is usually converted into disordered hard carbon composed of curled, twisted and folded carbon layers in an inert atmosphere, and the structure is very disordered, resulting in various defects and pores inside. The solid-state diffusion kinetics of lithium ions in the highly disordered structure of hard carbon is slow, which may lead to low conductivity and insufficient ion diffusion capacity, thereby limiting the actual capacity and rate performance, and showing low first-cycle coulombic efficiency. As the negative material of battery, it also has the following problems: (i) the carbon atom economy during the carbonization of polyvinyl chloride is low (about ~ 33at. %), which should be improved to obtain more carbon-based solid products instead of gaseous and liquid by-products; (ii) the electrical conductivity, interlayer spacing and porous structure of polyvinyl chloride derived carbon should be reasonably designed and controlled to reduce the charge transfer barrier and improve the initial coulombic efficiency; (iii) the polyvinyl chloride derived carbon should be functionally designed to improve its value, aiming to realize the upgrading of PVC to realize the way of "reducing production-recycling-upgrading" to maximize the recycling benefit of halogen-containing plastics. SUMMARY

[0010] The technical problem solved by the present application is to overcome the defects of low atomic economy, poor electronic conductivity and poor electrochemical performance of thermoplastic polyvinyl chloride in the preparation of hard carbon material in the prior art, and to provide a hard carbon material, a preparation method, an application and a battery. The hard carbon material prepared by the present application has high atomic economy and high electronic conductivity, and has excellent electrochemical performance when preparing a battery.

[0011] The PVC-derived carbon negative electrode needs to further improve its comprehensive performance, the key is to construct energy storage active sites, control pore structure and improve conductivity. The application uses PVC as raw material, through a simple and easy solvent wetting method combined with self-driven chemical vapor deposition, PVC waste is upgraded to high-conductivity PVC-based hard carbon material with slit / microporous filling structure. Through high-temperature elimination reaction of H in aromatic compounds and Cl in PVC, aromatic compounds are grafted onto the PVC polymer carbon chain, thereby increasing the content of sp 2 -C. In addition, the benzene ring structure adsorbed on the derived carbon slit pore wall is limited to deposit a few layers of graphene nanodomains at high temperature, providing additional energy storage sites through pore filling mechanism. Moreover, due to the high thermal stability of benzene ring, under the action of van der Waals force between the carbon plane π orbital on the pore wall and the electron density inside the benzene ring, the benzene ring tends to be adsorbed on the slit pore wall inside the PVC-derived carbon. Under the catalysis of the pore wall, the adsorbed species are cracked into a large number of flat few-layer graphene nanodomains, which are deposited and grown until the benzene ring molecules cannot enter the pores. More importantly, during the pyrolysis of PVC, the nanometer graphene carbon layer crystal domains obtained by rearrangement and growth block the gas transmission channel, limiting the diffusion of benzene vapor and the overflow of HCl during the pyrolysis of PVC, thereby forming a large number of closed slit pores and micropores in the PVC-derived carbon, which can provide additional storage sites for ions through pore filling mechanism. The structural design idea of embedding a few layers of graphene nanodomains in the open pores of the carbon material significantly improves the storage capacity of adsorbed and intercalated lithium.

[0012] The application solves the above technical problems through the following technical solutions:

[0013] The application provides a preparation method of hard carbon material, which comprises the following steps:

[0014] (1) mixing a solution containing PVC and aromatic compounds under heating conditions until the solvent is completely evaporated to obtain a dry gel; the mass ratio of the aromatic compound to the PVC is 2%-25%;

[0015] (2) grinding, washing and drying the dry gel to obtain a PVC dehalogenation precursor;

[0016] (3) carbonizing the PVC dehalogenation precursor to obtain the hard carbon material; the carbonization temperature is 700-1200 DEG C, and the carbonization time is 1-4h.

[0017] In step (1), the viscosity number K value of the PVC can be 50-80, preferably 55-70.

[0018] In the present application, when the aromatic compound contains halogen, in addition to the high-temperature elimination reaction between H in the aromatic compound and Cl in the PVC, a high-temperature elimination reaction between Cl in the aromatic compound and H in the PVC also occurs.

[0019] In step (1), the aromatic compound generally refers to a compound containing at least one benzene ring according to the convention in the art, preferably an aromatic hydrocarbon and / or an aromatic hydrocarbon derivative.

[0020] The aromatic hydrocarbon generally refers to a hydrocarbon containing a benzene ring, including monocyclic aromatic hydrocarbon and / or polycyclic aromatic hydrocarbon. The monocyclic aromatic hydrocarbon generally refers to a hydrocarbon containing only one benzene ring, such as benzene or toluene. The polycyclic aromatic hydrocarbon generally refers to a hydrocarbon containing at least two or more benzene rings, including non-fused ring aromatic hydrocarbon (such as biphenyl) and / or fused ring aromatic hydrocarbon (such as naphthalene).

[0021] The aromatic hydrocarbon derivative preferably refers to aromatic acid and / or halogenated aromatic hydrocarbon. The aromatic acid is, for example, benzoic acid. The halogen in the halogenated aromatic hydrocarbon can be one or more of F, Cl, Br and I, preferably Cl. The number of halogen atoms in the halogenated aromatic hydrocarbon is at least 1. The halogenated aromatic hydrocarbon can be side chain halogenated aromatic hydrocarbon and / or aromatic ring halogenated aromatic hydrocarbon. The side chain halogenated aromatic hydrocarbon refers to halogen connected to the carbon atom in the side chain of the aromatic ring, and the aromatic ring halogenated aromatic hydrocarbon refers to halogen connected to the carbon atom in the aromatic ring. The aromatic ring halogenated aromatic hydrocarbon can be, for example, chlorobenzene or 1,2-dichlorobenzene.

[0022] In step (1), the mass ratio of the aromatic compound to the PVC is, for example, 5%, 9%, 12% or 18%, preferably 7%-15%.

[0023] In step (1), the solvent in the solution can be a solvent capable of dissolving PVC according to the convention in the art, for example, NMP.

[0024] In step (1), the ratio of the mass of the PVC to the volume of the solvent in the solution can be 1:(20-40) g / mL, for example, 1:30 g / mL.

[0025] In step (1), the method for preparing the solution containing PVC and aromatic compound preferably comprises the following process: stirring and mixing the PVC and solvent at room temperature until the PVC is completely dissolved, and then adding the aromatic compound.

[0026] In step (1), the mixing method can be conventional in the art, for example, stirring.

[0027] In step (1), the mixing temperature is preferably 140-180°C, for example, 150°C.

[0028] In step (1), the mixing process preferably comprises: stirring the solution containing PVC and aromatic compounds at 60-90℃ for 1-3h to obtain a sol, and then stirring the sol at 140-180℃ until the solvent is completely evaporated to obtain a xerogel.

[0029] In step (2), the washing operation and conditions can be conventional in the art, for example, using ethanol and water for washing.

[0030] In step (2), the drying operation and conditions can be conventional in the art.

[0031] In step (3), the PVC dehalogenation precursor is preferably ground into powder before carbonization.

[0032] In step (3), the carbonization is generally carried out in a protective atmosphere that does not react with the reaction system, for example, nitrogen or inert gas. The inert gas is, for example, argon.

[0033] The flow rate of the protective atmosphere can be 100-500sccm, preferably 200-400sccm, for example, 300sccm.

[0034] In step (3), the carbonization is generally carried out in a tube furnace.

[0035] In step (3), the carbonization temperature is preferably 700-900℃, for example, 800℃. The carbonization time is preferably 1-3h, for example, 2h. The heating rate to the carbonization temperature can be 2-10℃ / min, for example, 5℃ / min. After the carbonization is completed, it also includes the process of natural cooling to room temperature.

[0036] The application also provides a hard carbon material prepared by the preparation method as described above.

[0037] In the application, the internal part of the hard carbon material preferably has a few-layer graphene-like carbon layer structure. The few-layer graphene-like carbon layer generally refers to a material composed of 2-10 layers of graphene nanosheets. The few-layer graphene-like carbon layer structure is preferably distributed on the slit pore wall inside the hard carbon material.

[0038] In the application, the graphite layer spacing of the hard carbon material can be 0.340-0.385nm. The graphite layer spacing generally refers to the layer spacing d002 calculated according to the XRD test results by Bragg's law. 002 .

[0039] In the application, the pore size distribution range of the hard carbon material can be 0.1-6nm, preferably 2-4nm.

[0040] In the present invention, the specific surface area of the hard carbon material can be 1-5 m 2 / g, for example 1.15 m 2 / g, 1.2 m 2 / g or 1.25 m 2 / g, preferably 1.2-1.3 m 2 / g.

[0041] In the present invention, the I D / I G of the hard carbon material is preferably 0.948-1.05, for example 0.951 or 1.024, more preferably 1.0-1.03. The I D / I G refers to the intensity ratio of the D peak and the G peak.

[0042] In the present invention, the electrical conductivity of the hard carbon material can be 1.14-5 S m -1 , for example 1.158, 1.198, 1.206 or 1.721, preferably 1.18-1.22 S m -1 .

[0043] In the present invention, the reversible specific capacity of the hard carbon material at a current density of 50 mA g -1 is preferably 355-600 mAh g -1 , for example 362.5 mAh g -1 , 436.5 mAh g -1 , 552.6 mAh g -1 or 553.8 mAh g -1 .

[0044] In the present invention, the first cycle coulombic efficiency of the hard carbon material at a current density of 50 mA g -1 is preferably 70%-85%.

[0045] In the present invention, the reversible specific capacity of the hard carbon material at a current density of 0.5 A g -1 is preferably 440-540 mAh g -1 , more preferably 510-540 mAh g -1 .

[0046] In the present invention, the capacity retention rate of the hard carbon material at a current density of 0.5 A g -1 after 300 cycles is preferably 99% or more.

[0047] In the present invention, the reversible specific capacity of the hard carbon material at a current density of 1.5 A g -1 is preferably 120-210 mAh g -1More preferably 190-210 mAh g -1 .

[0048] In the present application, the hard carbon material has a capacity retention rate of preferably 99% or more after 1800 cycles at a current density of 1.5 A g -1

[0049] The present application also provides a use of the hard carbon material as described above in a battery.

[0050] The present application also provides a battery comprising the hard carbon material as described above.

[0051] In the present application, the battery is preferably a lithium ion battery or a sodium ion battery.

[0052] On the basis of common general knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining each preferred example of the present application.

[0053] The reagents and raw materials used in the present application are commercially available.

[0054] The positive progress effect of the present application is that:

[0055] (1) The hard carbon material prepared by the present application has high atom economy and high electronic conductivity, and has excellent electrochemical performance when used in the preparation of a battery;

[0056] (2) The preparation method of the present application is simple, low in cost, and conducive to industrialized production;

[0057] (3) The carbon atom economy of the PVC-derived carbon prepared by the present application is increased from 33% to more than 70%;

[0058] (4) The present application regulates the structure of the polyvinyl chloride-derived hard carbon by introducing aromatic compounds, promotes the growth of the internal few-layer graphene nanocrystalline domain of the polyvinyl chloride-derived hard carbon, improves its electronic conductivity, and at the same time, improves the specific capacity of the polyvinyl chloride-derived hard carbon negative electrode and improves the first-cycle coulombic efficiency to a certain extent.

[0059] The technical problem solved by the second aspect of the present application is to overcome the defects of poor rate performance and long cycle stability of the PVC-based hard carbon material in the prior art, and to provide a polyvinyl chloride-derived hard carbon material, a preparation method thereof, an application thereof, and a battery. The hard carbon material prepared by the present application has a larger specific surface area, a larger interlayer spacing, and a more developed ion / electron conduction network, and has excellent electrochemical performance when applied in a battery, especially has better rate performance and long cycle stability.

[0060] ​The application effectively realizes the regulation of internal defects of hard carbon by first heating and melting PVC powder and thermoplastic resin, and then pre-dehalogenation at low temperature and carbonization assisted by inorganic salt, so that the hard carbon material with larger specific surface area, larger interlayer spacing, more developed ion / electron conduction network and excellent electrochemical performance is prepared. The low-temperature pre-halogenation realizes the partial dehalogenation of PVC, and the active carbon chains of the partially dehalogenated PVC polymer and the active carbon chains of the thermoplastic resin are aggregated, thereby promoting the formation of subsequent high-conductivity carbon. In the subsequent high-temperature carbon layer rearrangement process assisted by inorganic halide salt, the HCl gas flow generated by the continuous dechlorination of the pre-dehalogenated PVC precursor impacts the internal structure, forming an internal dense disordered turbulent layer structure and closed pores; the presence of inorganic halide salt melt salt induces the rearrangement of the surface carbon layer, forming an ordered graphene carbon layer. The inorganic halide salt crystal acts as a graphene growth template and a sealing agent, guiding carbon atoms to gather at the grain boundaries and hindering the escape of HCl. The carbon atoms serve as nucleation centers for the growth of vertically oriented graphene layers.

[0061] The application solves the above technical problems by the following technical solutions:

[0062] The application provides a preparation method of a PVC-derived hard carbon material, which comprises the following steps:

[0063] (1) heating and melting PVC powder and thermoplastic resin to obtain material A, and then performing pre-dehalogenation on the material A under the protection of inert gas to obtain a pre-dehalogenated sample; wherein the thermoplastic resin is polypropylene and / or polyethylene, the mass ratio of the thermoplastic resin to the PVC powder is 5%-50%, the pre-dehalogenation temperature is 250-500 ℃, and the pre-dehalogenation time is 1-5 h;

[0064] (2) covering inorganic halide salt on the pre-dehalogenated sample in a reaction tube, vacuumizing and sealing the reaction tube, and then performing carbonization, washing and drying to obtain the PVC-derived hard carbon material; the mass ratio of the inorganic halide salt to the pre-dehalogenated sample is (1.2-4.5):1, the carbonization temperature is not lower than the melting point of the inorganic halide salt, and the carbonization time is 5-20 h.

[0065] In step (1), the PVC powder can have a viscosity number K value of 50-80, preferably 55-70.

[0066] In step (1), the polypropylene can have a melt index of 10-40 g / 10 min, for example, 35 g / 10 min.

[0067] In step (1), the polyethylene can have a melt index of 10-40 g / 10 min, for example, 25 g / 10 min.

[0068] In step (1), the mass ratio of the thermoplastic resin to the PVC powder is preferably 5%-20%, for example, 10%.

[0069] In step (1), the heating melting is generally performed in a heating furnace. The heating furnace can be conventional in the art, for example, a tube furnace. The heating melting is generally performed under an inert atmosphere, for example, argon.

[0070] In step (1), the temperature of the heating melting can be 100-140°C, for example, 120°C.

[0071] In step (1), the time of the heating melting can be 1-4h, for example, 2h.

[0072] In step (1), the type of the inert gas can be conventional in the art, for example, argon.

[0073] In step (1), the flow rate of the inert gas can be 100-500sccm, preferably 200-400sccm, for example, 300sccm.

[0074] In step (1), the pre-dehalogenation reaction is generally performed in a tube furnace.

[0075] In step (1), the temperature of the pre-dehalogenation reaction is preferably 300-400°C, for example, 360°C.

[0076] In step (1), the time of the pre-dehalogenation reaction is preferably 1-3h, for example, 2h.

[0077] In step (1), the rate of the temperature rise to the temperature of the pre-dehalogenation reaction is preferably 2-10°C / min, for example, 5°C / min.

[0078] In step (1), after the pre-dehalogenation reaction, a natural cooling process to room temperature is generally included.

[0079] In step (1), after the pre-dehalogenation reaction, the pre-dehalogenated sample is preferably subjected to washing and drying.

[0080] The solvent used in the washing can be conventional in the art, for example, water and / or anhydrous ethanol. When the solvent used in the washing is a mixed solution of water and anhydrous ethanol, the volume ratio of water to anhydrous ethanol is preferably (1-5):1, for example, 3:1.

[0081] In step (2), the reaction tube can be conventional in the art, for example, a quartz glass test tube.

[0082] In step (2), after the vacuumization, the vacuum degree of the reaction tube is preferably 10 -2 mbar or less.

[0083] In step (2), the inorganic halide salt preferably has a melting point of not less than 700°C.

[0084] In step (2), the cation of the inorganic halide salt preferably comprises one or more of an alkali metal, an alkaline earth metal and a transition metal, more preferably an alkali metal.

[0085] In step (2), the cation of the inorganic halide salt preferably comprises one or more of an alkali metal, an alkaline earth metal and a transition metal, more preferably an alkali metal.

[0086] In step (2), the cation of the inorganic halide salt preferably comprises one or more of an alkali metal, an alkaline earth metal and a transition metal, more preferably an alkali metal.

[0087] In step (2), the cation of the inorganic halide salt preferably comprises one or more of an alkali metal, an alkaline earth metal and a transition metal, more preferably an alkali metal.

[0088] In step (2), the anion of the inorganic halide salt preferably comprises one or more of a Cl ion, a Br ion and an I ion, more preferably a Cl ion or a Br ion.

[0089] In step (2), the inorganic halide salt is preferably one or more of NaCl, KCl and NaBr.

[0090] In step (2), the mass ratio of the inorganic halide salt to the pre-dehalogenated sample is preferably (1.5-3.5):1, for example 2:1, 2.5:1 or 3.5:1.

[0091] In step (2), the temperature of the carbonization is preferably 10°C above the melting point of the inorganic halide salt and 200°C or lower.

[0092] In step (2), the time of the carbonization is preferably 5-15h, for example 10h.

[0093] When the inorganic salt is NaCl, the temperature of the carbonization is preferably 810-1000°C, for example 820°C, 850°C, 900°C or 950°C.

[0094] When the inorganic salt is NaBr, the temperature of the carbonization is preferably 780-900°C, for example 800°C.

[0095] When the inorganic salt is KCl, the temperature of the carbonization is preferably 800-1000°C, for example 820°C.

[0096] In step (2), the rate of temperature increase to the temperature of the carbonization is preferably 2-10°C / min, for example 5°C / min.

[0097] In step (2), the solvent used for the washing can be conventional in the art, such as water and / or anhydrous ethanol. When the solvent used for the washing is a mixed solution of water and anhydrous ethanol, the volume ratio of water to anhydrous ethanol is preferably 1:(1-5), such as 1:3.

[0098] In step (2), the dried product is preferably further ground.

[0099] The present application also provides a polyvinyl chloride derived hard carbon material prepared by the preparation method as described above.

[0100] In the present application, the polyvinyl chloride derived hard carbon material is preferably coated with a continuous few-layer graphene-like carbon layer on the outside. The few-layer graphene-like carbon layer generally refers to a material composed of 2-10 layers of graphene nanosheets. The number of layers of the few-layer graphene-like carbon layer is preferably less than 5.

[0101] In the present application, the interlayer spacing of the graphene layer of the polyvinyl chloride derived hard carbon material can be 0.352-0.40 nm, preferably 0.352-0.38 nm, such as 0.354 nm, 0.358 nm or 0.361 nm. The interlayer spacing of the graphene layer generally refers to the interlayer spacing d002 calculated according to the XRD test results by Bragg's law. 002 .

[0102] In the present application, the pore size distribution range of the polyvinyl chloride derived hard carbon material can be 7.5-15 nm, preferably 8-12 nm, such as 8.2 nm, 9 nm or 10.5 nm.

[0103] In the present application, the specific surface area of the polyvinyl chloride derived hard carbon material can be 4.8-15 m 2 / g, preferably 5-10 m 2 / g, such as 5.8 m 2 / g, 6.5 m 2 / g or 7.5 m 2 / g.

[0104] In the present application, the I D / I G of the polyvinyl chloride derived hard carbon material is preferably 0.94-1.05, such as 0.948, 0.965 or 0.991, more preferably 0.955-0.98. The I D / I G refers to the intensity ratio of the D peak and the G peak.

[0105] The present application also provides a use of the polyvinyl chloride derived hard carbon material as described above in a battery.

[0106] The present application also provides a battery comprising the polyvinyl chloride derived hard carbon material as described above.

[0107] In the present application, the battery is preferably a lithium ion battery or a potassium ion battery.

[0108] On the basis of common general knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining preferred examples of the present application.

[0109] The reagents and raw materials used in the present application are commercially available.

[0110] The positive progress effect of the present application is that:

[0111] (1) The hard carbon material prepared by the present application has a larger specific surface area, a larger interlayer spacing and a more developed ion / electron conduction network, and exhibits excellent rate performance and long cycle stability as a negative electrode material for lithium ion batteries and potassium ion batteries, especially better rate performance and long cycle stability;

[0112] (2) The carbon yield of the hard carbon material prepared by the present application is as high as 26%-33%;

[0113] (2) The preparation method of the present application is simple, low in cost and conducive to industrialized production;

[0114] (3) The present application provides a new solution for upgrading and utilizing waste halogenated plastics, promotes the extension of electrode material design for lithium ion batteries and potassium ion batteries to waste plastic resources, improves resource utilization efficiency and realizes sustainable development.

[0115] The technical problem solved by the third aspect of the present application is also to overcome the defects of the prior art that the existing halogen-containing waste polymer materials are not fully utilized and the cost of hard carbon raw materials is high, and to provide a hard carbon material, a preparation method thereof, applications and a secondary battery. The preparation method of the present application realizes pollution-free treatment of halogen-containing polymer waste materials while realizing high-value utilization, has the advantages of high efficiency, environmental protection, greenness and energy saving, and the prepared hard carbon material has excellent specific capacity and rate performance when applied to batteries.

[0116] The application is to prepare hard carbon material, using halogen-containing polymer as raw material, first melting halogen-containing polymer and thermoplastic resin (polypropylene, polyethylene) to obtain mixture, thermoplastic resin can coat halogen-containing polymer to avoid HCl overflow after halogen-containing polymer in subsequent dehalogenation process, halogen-containing polymer and reducing metal (alkali metal, alkaline earth metal) in mixture first carry out dehalogenation reaction to form carbon-containing precursor and salt, thereby removing halogen in halogen-containing polymer, and then carbonizing carbon-containing precursor to obtain hard carbon material with excellent electrochemical performance. In dehalogenation reaction process, reducing metal catalyzes halogen-containing polymer dehalogenation reaction more completely and fixes high-pollution halogen atom, and reducing metal and generated salt can penetrate into part of carbonized polymer as template agent or pore-forming agent, thereby being applied to sodium / lithium ion battery high-performance negative electrode to realize higher specific capacity and rate performance. The preparation method can realize pollution-free treatment of halogen-containing polymer waste, realize high-value utilization, and has advantages of high efficiency, environmental protection, green, energy saving and the like.

[0117] The application solves the above technical problems through the following technical scheme:

[0118] The application provides a preparation method of hard carbon material, which comprises the following steps:

[0119] After mixing halogen-containing polymer powder and thermoplastic resin, melting and heating, and cooling, mixture is obtained, then mixing the mixture with reducing metal, heating and dehalogenating in inert gas protection at 100-400℃ for 2-12h to obtain dehalogenated sample, and then washing, drying and carbonizing the dehalogenated sample to obtain hard carbon material;

[0120] 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%;

[0121] When the reducing metal is alkali metal element, the molar ratio of halogen atom in the halogen-containing polymer powder to the reducing metal is 1:(1-3);

[0122] When the reducing metal is alkaline earth metal element, the molar ratio of halogen atom in the halogen-containing polymer powder to the reducing metal is 1:(0.5-1.5).

[0123] In the application, the halogen-containing polymer powder is preferably polyvinyl chloride (PVC) and / or polyvinylidene chloride (PVDC). The particle size of the halogen-containing polymer powder can be 0.1-1μm. The halogen-containing polymer powder can also be the powder obtained by cleaning and mechanically crushing waste halogen-containing polymer product.

[0124] The viscosity number K value of the polyvinyl chloride can be 50-80, for example, 62-60.

[0125] In the present application, the polypropylene can have a melt index of 10 to 40 g / 10 min, for example 35 g / 10 min.

[0126] In the present application, the polyethylene can have a melt index of 10 to 40 g / 10 min, for example 25 g / 10 min.

[0127] In the present application, the mass ratio of the thermoplastic resin to the halogen-containing polymer powder is preferably 2% to 8%, for example 5%.

[0128] In the present application, the heating melting is generally performed in a heating furnace. The heating furnace can be conventional in the art, for example a tube furnace. The heating melting is generally performed under an inert gas atmosphere, for example argon.

[0129] In the present application, the temperature of the heating melting can be 100 to 140°C, for example 120°C.

[0130] In the present application, the time of the heating melting can be 1 to 4 h, for example 2 h.

[0131] In the present application, the alkali metal element is preferably Na and / or K.

[0132] In the present application, the alkaline earth metal element is preferably one or more of Mg, Ca and Ba.

[0133] In the present application, when the reducing metal is an alkali metal element, the mole ratio of the halogen atom in the halogen-containing polymer powder to the reducing metal is preferably 1:(1-2), for example 1:1.1, 1:1.2 or 1:1.3.

[0134] In the present application, when the reducing metal is an alkaline earth metal element, the mole ratio of the halogen atom in the halogen-containing polymer powder to the reducing metal is preferably 1:(0.5-1), for example 1:0.55.

[0135] In the present application, the temperature of the heating dehalogenation is preferably 200 to 400°C, for example 250°C.

[0136] In the present application, the time of the heating dehalogenation is preferably 2 to 6 h, for example 3 h.

[0137] In the present application, the heating dehalogenation is generally performed in a tube furnace.

[0138] In the present application, the inert gas can be conventional in the art, for example nitrogen or argon.

[0139] In the present application, the operation and condition of the washing can be conventional in the art, for example, washing with a mixed solution of deionized water and anhydrous ethanol; the volume ratio of the deionized water to the anhydrous ethanol in the mixed solution can be 3:1.

[0140] In the present application, the operation and condition of the drying can be conventional in the art.

[0141] In the present application, the carbonization is generally carried out in an inert gas atmosphere, for example, nitrogen or argon, according to the convention in the art.

[0142] In the present application, the temperature of the carbonization is preferably 600-1000℃, for example, 800℃, 850℃ or 900℃.

[0143] In the present application, the time of the carbonization can be 0.5-10h, preferably 3-6h, for example, 4h.

[0144] The present application also provides a hard carbon material prepared by the preparation method as described above.

[0145] In the present application, the specific surface area of the hard carbon material is preferably 6-10m 2 g -1 .

[0146] In the present application, the hard carbon material preferably has a sodium storage specific capacity >250mAh / g at a high rate of 20C.

[0147] In the present application, the hard carbon material preferably has a lithium storage specific capacity >300mAh / g at a high rate of 20C.

[0148] The present application also provides a use of the hard carbon material as described above in a secondary battery.

[0149] The present application also provides a secondary battery comprising the hard carbon material as described above.

[0150] In the present application, the secondary battery is preferably a lithium ion battery or a sodium ion battery.

[0151] On the basis of common knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, i.e., to obtain each preferred example of the present application.

[0152] The reagents and raw materials used in the present application are commercially available.

[0153] The positive progress effect of the present application is that:

[0154] The preparation method of the application does not rely on organic solvent to dissolve the high molecular material, can realize more efficient dechlorination reaction through a simple solid phase method, promotes graphitization while avoiding chlorine emission, in addition, the template and pore forming effect of the metal and salt helps to improve the specific surface area of the material, and 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 DRAWINGS

[0155] Fig. 1 is a high-resolution transmission electron microscope (HRTEM) image of the hard carbon material prepared in Example 1a;

[0156] Fig. 2 is a high-resolution transmission electron microscope (HRTEM) image of the hard carbon material prepared in Comparative Example 1a;

[0157] Fig. 3(a) is an HRTEM image of the hard carbon material prepared in Example 1b; Fig. 3(b) is an FFT image of the hard carbon material prepared in Example 1b;

[0158] Fig. 4 is a scanning electron microscope (SEM) image of the hard carbon material prepared in Example 1c. DETAILED DESCRIPTION

[0159] The application will be further described in the following examples, but the application is not limited to the scope of the examples. The experimental methods in the following examples without specific conditions are selected according to conventional methods and conditions, or according to the instructions of the commercial products.

[0160] The raw materials used in the following Examples 1a-8a and Comparative Example 1a are shown in Table 1:

[0161] Table 1

[0162] The raw materials used in Examples 1a-8a and Comparative Example 1a are all obtained from conventional commercial sources and are used without further treatment.

[0163] Example 1a

[0164] (1) 1 g of PVC was dissolved in 30 mL of N-methyl pyrrolidone (NMP), and stirred at room temperature for 10 minutes; after the PVC was completely dissolved in the NMP, 0.09 g of chlorobenzene was added, and stirring was continued under heating at 70°C; in this process, as the solvent continuously evaporated, the solution gradually became viscous and formed a colloidal system; after stirring for 2 hours, the sol-gel process was completed, and the obtained transparent sol was placed on a magnetic heating stirring table at 150°C for continuous stirring until the solvent was completely evaporated, obtaining a dark gray dry gel; the obtained dry gel was ground into powder, washed with ethanol and water, and dried in an oven for 12 hours, obtaining a benzene ring assisted PVC dehalogenation precursor;

[0165] (2) Subsequently, the benzene ring-assisted PVC dehalogenation precursor was ground into powder and carbonized in a tube furnace, heated to 800℃ at an argon atmosphere of 300 sccm, and the heating rate was 5℃ / min -1 , and the carbonization was maintained for 120 minutes; after the completion of the carbonization reaction, it was naturally cooled to room temperature to obtain a hard carbon material.

[0166] Example 2a

[0167] Compared with Example 1a, except that the amount of chlorobenzene was adjusted to 0.05g, the rest of the operation and conditions were the same as Example 1a.

[0168] Example 3a

[0169] Compared with Example 1a, except that the amount of chlorobenzene was adjusted to 0.12g, the rest of the operation and conditions were the same as Example 1a.

[0170] Example 4a

[0171] Compared with Example 1a, except that the amount of chlorobenzene was adjusted to 0.18g, the rest of the operation and conditions were the same as Example 1a.

[0172] Example 5a

[0173] Compared with Example 1a, except that chlorobenzene was replaced by toluene, the rest of the operation and conditions were the same as Example 1a.

[0174] Example 6a

[0175] Compared with Example 1a, except that chlorobenzene was replaced by 1,2-dichlorobenzene, the rest of the operation and conditions were the same as Example 1a.

[0176] Example 7a

[0177] Compared with Example 1a, except that chlorobenzene was replaced by naphthalene, the rest of the operation and conditions were the same as Example 1a.

[0178] Example 8a

[0179] Compared with Example 1a, except that chlorobenzene was replaced by benzoic acid, the rest of the operation and conditions were the same as Example 1a.

[0180] Comparative Example 1a

[0181] Compared with Example 1a, except that no chlorobenzene was added, the rest of the operation and conditions were the same as Example 1a.

[0182] Effect Example

[0183] (1) Morphology characterization

[0184] Figure 1 is a high-resolution transmission electron microscopy (HRTEM) image of the hard carbon material prepared in Example 1a; and Figure 2 is a high-resolution transmission electron microscopy (HRTEM) image of the hard carbon material prepared in Comparative Example 1a. As can be seen from Figures 1 and 2, the hard carbon material prepared in Comparative Example 1a is in the form of micrometer-sized block particles, no porous structure is observed, and no obvious particle agglomeration is observed on the surface of the block, and the internal structure is a typical hard carbon structure of highly disordered turbine structure and short-range ordered curved carbon layer structure randomly wound. In contrast, as can be clearly seen from Figure 1, the hard carbon material prepared in Example 1a has a porous structure and a more loose surface, and local carbon lattice edges are gradually formed, and the number of few-layer graphene nanocrystalline domains and micropores is significantly increased, which indicates that the adsorption and deposition of benzene rings mainly occur on the pore walls, and a large number of graphene nanocrystalline domains are generated inside the hard carbon material, which helps lithium ions to easily enter the internal phase of the material, thereby improving the lithium ion storage capacity.

[0185] Table 2: Intercalation distance calculated from FFT diffraction of HRTEM images

[0186] At the same time, the intercalation distance of the hard carbon material is reduced from 0.433 nm in Comparative Example 1a to 0.401 nm in Example 1a and 0.380 nm in Example 4a. Although the intercalation distance is reduced as the graphene-like nanocrystalline domains grow, the intercalation distance of the hard carbon material is still greater than the average intercalation distance of graphite (0.335 nm), which is conducive to ion intercalation and transfer. The presence and continuous growth of these ordered nanocrystalline domains not only fill the pores, but also cause more carbon layers to fold, bend, and crosslink to form a rich pore structure. The stacking of the crosslinked and twisted carbon layers introduces microporous structures and more slit pores, which not only provide more intercalation sites for pores and increase the platform capacity, but also provide a way for lithium ions to enter the internal phase of the electrode material, thereby shortening the diffusion distance of lithium ions in the bulk phase.

[0187] (2) XRD characterization

[0188] According to the test results of XRD, the hard carbon material prepared in Example 1a shows two similar broad diffraction peaks near 2θ ≈ 23° and 44°, which correspond to the Bragg reflection of the (001) and (100) crystal planes of graphite, respectively. These two broad peaks indicate that the carbon layer structure in the hard carbon material has low crystallinity, which is a characteristic peak of disordered carbon. As the amount of chlorobenzene additive increases, the (002) peak moves to a higher diffraction angle, indicating that the average interlayer distance between the graphite layers is reduced, and the interlayer distance d 002 from 0.394 nm (Comparative Example 1a) to 0.363 nm (Example 1a) and 0.358 nm (Example 4a), which is consistent with the observation of HRTEM.

[0189] (3) Raman, nitrogen adsorption-desorption characterization test, FT-IR spectrum test

[0190] The hard carbon materials prepared in the examples and Comparative Example 1a were subjected to Raman, nitrogen adsorption-desorption characterization test and FT-IR spectrum test according to the conventional operation in the art.

[0191] Table 3 Structural parameters of hard carbon materials

[0192] According to the Raman test of the hard carbon materials prepared in Example 1a, Example 4a and Comparative Example 1a, all showed a wide band in the wave band near 1600 cm -1 and 1350 cm -1 , which corresponded to G band (graphite band: related to E 2 vibration mode of sp 2g carbon ring) and D band (disordered band: A 2 vibration mode of sp 1g carbon ring), respectively. The ID / IG ratio of Comparative Example 1a, Example 1a and Example 4a was 1.032, 1.024 and 0.951, respectively, which indicated that the defect content in the sample of Example 4a was significantly less than that of Comparative Example 1a and Example 1a, and the different benzene ring addition amount had obvious regulation effect on the disorder degree of the hard carbon material. In addition, a weak 2D peak appeared near 2700 cm -1 in Example 4a, which represented short-range or medium-range ordered stacking of few-layer carbon layers. The appearance of 2D peak indicated that sufficient aromatic precursor was added in the preparation process, which decomposed to produce sp 2 intermediate containing benzene ring at high temperature, which was adsorbed on the pore wall and could act as the crystal nucleus of graphitized carbon atoms, which was beneficial to the growth of graphene-like nano domains.

[0193] It was found by nitrogen adsorption-desorption characterization of hard carbon material that the specific surface area, average pore volume and average pore size decreased with the increase of the amount of benzene ring added. With the increase of the amount of chlorobenzene added, the pore size significantly decreased, and the pore distribution obviously shifted to micropore, which indicated that the internal abundant pores of the original comparative example 1a were filled by the deposited few-layer graphene nanodomains. The significant decrease in pore size distribution was caused by the adsorption of benzene ring molecules on the internal slit pore wall through the van der Waals force between the electron cloud density and the π orbital of the carbon plane. The adsorption of benzene ring molecules on the pore wall and the continuous deposition of graphene carbon layer blocked the pores, reducing the pore size. At the same time, the few-layer graphene nanodomains formed on the slit pore wall prevented the evaporation of gas during the pyrolysis process, thereby forming closed pores inside the carbon material. The pore size distribution range of example 4a was significantly smaller than that of example 1a, and the pore size of example 4a was reduced to below 0.96 nm (the Stokes radius of Li + + + +

[0194] According to the infrared test results, there are obvious chlorinated hydrocarbon characteristic peaks in PVC: C-Cl stretching vibration peaks between 600-640 cm -1 , H-CCl deformation vibration peaks near 1180-1350 cm -1 , deformation vibration peaks of -CH2 near 1433 cm -1 , and stretching vibration peaks of C-H in H-C-H and Cl-C- near ~ 2906 cm -1 and 2967 cm -1 . After high-temperature carbonization, all the chlorinated hydrocarbon characteristic peaks disappeared, and a C=C bending vibration peak appeared near ~ 1670 cm -1 , which indicated that the chlorine in the molecular chain of comparative example 1a had been completely removed, and conjugated carbon-carbon double bonds existed. With the introduction of benzene structure, a shear vibration peak of R-C=CH- near ~ 1350 cm -1 was observed in example 1a, which indicated that after the introduction of benzene ring, the electronic rearrangement caused by the interaction between the π orbital of the PVC-derived carbon layer and the electronic structure of the benzene structure was more conducive to the preservation of sp 2 -C structure during carbonization, and the addition of aromatic additives was conducive to the formation of more few-layer ordered graphene layers in the hard carbon derived from polyvinyl chloride.

[0195] (4) Conductivity test

[0196] ​​​​The electrical conductivity of the hard carbon materials prepared in Examples la-4a and Comparative Example la was measured by pressing the materials into a sheet at room temperature, 25°C. A certain amount of PVP was added as a binder when the sheet was pressed, and the resistance of the pressed sheet was then measured by an ohmmeter, and the conductivity is shown in Table 4.

[0197] R = p(L / πr 2 ); σ = 1 / p, where the resistance R (BPC sheet resistance of the pressed sheet, unit: Ω) was measured by an ohmmeter; L (thickness of the pressed sheet, unit: m) was measured using a vernier caliper; r (radius of the carbon sheet, unit: m) was fixed at 3 x 10 -3 m.

[0198] Table 4

[0199] (5) Electrochemical performance test

[0200] The electrochemical performance of the PVC-derived high-conductivity carbon series samples was studied by preparing them into coin cells. 400 mg of the hard carbon materials prepared in Examples la-8a and Comparative Example la were weighed as active electrode materials, respectively, 50 mg of conductive carbon black Super P, and 50 mg of PVDF (mass ratio of 8:1:1) were ground and mixed uniformly, then added to NMP solvent and placed on a homogenizer to disperse uniformly to obtain PVC-based high-conductivity carbon slurry. The slurry was coated on a copper foil and dried in a vacuum oven at 85°C overnight. Subsequently, the obtained electrode copper foil was cut into a circular sheet with a diameter of 12 mm to prepare a battery electrode piece, and the average mass loading was approximately 2 mg cm -2 .

[0201] The electrochemical test of the samples was carried out by assembling CR-2016 type coin cells in an argon-filled glove box. The electrolyte used was LB046, with a specific formula of 1 mol L -1 LiClO4in a mixed solution of ethylene carbonate EC / DEC (1:1 v / v), with 5 wt% FEC additive, using a single layer of polypropylene PP as the battery separator, and using a lithium metal sheet as the negative electrode. The charge and discharge test was carried out by a LAND CT2001A battery tester in a potential range of 0.001-3.0 V.

[0202] The hard carbon materials were prepared into electrodes, and their lithium storage performance was tested in half-cells, and Table 5 shows the first cycle charge and discharge data of the hard carbon material negative electrode at a current density of 50 mA g -1 .

[0203] Table 5

[0204] Table 6

[0205] From the data of Table 5 and Table 6, it can be seen that the examples 1a-8a show higher reversible specific capacity and better first cycle coulombic efficiency than the comparative example 1a, the higher reversible specific capacity can be attributed to the additional few-layer graphene-like nanodomains in their structure, and the better first cycle efficiency can be attributed to their lower specific surface area and the reduced defects which reduce side reactions with electrolyte. From the above physical and structural characterizations, it can be seen that after introducing benzene ring structure, the microstructure of the hard carbon material is restructured, and more few-layer ordered graphene-like carbon layer structures are grown. These ordered graphene microcrystalline carbon domains provide a network for transporting electrons, while the pores formed by the interlaced curved carbon layers and the ordered carbon layers also provide additional sites for lithium ion intercalation / deintercalation and lithium ion storage, thereby achieving an increase in capacity.

[0206] The raw material information used in the following examples 1b-6b and comparative examples 1b-6b is shown in Table 7:

[0207] Table 7

[0208] Example 1b

[0209] (1) Pre-dehalogenation:

[0210] 1g of PVC and 0.1g of polypropylene were heated and melted in a heating furnace (under an argon atmosphere), the heating temperature was 120°C, and the heating time was 2h, and after cooling, substance A was obtained;

[0211] Substance A was placed in a quartz crucible and placed in a tube furnace for pre-dehalogenation, heated to 360°C under a flow of 300sccm argon, and kept at 360°C for 120 minutes, the heating rate was 5°C / min -1 ; after natural cooling to room temperature, the obtained block was ground into powder, washed with a mixture of deionized water and anhydrous ethanol in a volume ratio of 3:1, and dried to obtain the prepared pre-dehalogenation sample;

[0212] (2) Carbonization: an appropriate amount of pre-dehalogenation sample powder was weighed into a quartz glass test tube, and NaCl solid was directly covered on the pre-dehalogenation sample powder, and under vacuum conditions (vacuum conditions below 10 -2 mbar), the upper end of the quartz tube was sealed by melting with a hydrogen-oxygen flame, and the mass ratio of NaCl to pre-dehalogenation sample was 2:1; then, the quartz tube was placed in a muffle furnace and carbonized at 820°C for 10h, the heating rate was 5°C / min. After the carbonization reaction was completed, it was cooled to room temperature and taken out, the quartz glass tube was broken, and the obtained material was washed with a mixture of water and ethanol (volume ratio of 1:3) to remove the NaCl flux, dried, and then ground into powder and collected to obtain the PVC-derived hard carbon material.

[0213] Example 2b

[0214] The remaining operations and conditions are the same as those of Example 1b, except that the mass ratio of NaCl and pre-dehalogenated sample in step (2) is adjusted to 3:1.

[0215] Example 3b

[0216] The remaining operations and conditions are the same as those of Example 1b, except that the temperature of carbonization in step (2) is adjusted to 900℃.

[0217] Example 4b

[0218] The remaining operations and conditions are the same as those of Example 1b, except that NaCl in step (2) is replaced by sodium bromide, and the temperature of carbonization is adjusted to 800℃.

[0219] Example 5b

[0220] The remaining operations and conditions are the same as those of Example 1b, except that NaCl in step (2) is replaced by potassium chloride.

[0221] Example 6b

[0222] The remaining operations and conditions are the same as those of Example 1b, except that polypropylene in step (1) is replaced by polyethylene.

[0223] Comparative Example 1b

[0224] Commercial hard carbon BHC-550 (purchased from Chengdu Baishige Technology Co., Ltd.).

[0225] Comparative Example 2b

[0226] The remaining operations and conditions are the same as those of Example 1b, except that no NaCl is added in step (2).

[0227] Comparative Example 3b (directly carbonizing PVC)

[0228] An appropriate amount of PVC powder is weighed into a quartz tube, which is sealed after being vacuumed, and then placed in a muffle furnace for carbonization at 820℃ for 10h, with a heating rate of 5℃ / min. After the carbonization reaction is completed, the temperature is lowered to room temperature, and then the quartz glass tube is broken to obtain the material. The obtained material is washed clean with a mixture of deionized water and anhydrous ethanol in a volume ratio of 3:1, and then dried. The obtained material is ground into powder and collected to obtain the hard carbon material.

[0229] Comparative Example 4b

[0230] The rest of the operations and conditions are the same as those in Example 1b, except that the mass ratio of NaCl to pre-dehalogenated sample in step (2) is adjusted to 5:1.

[0231] Comparative Example 5b

[0232] The rest of the operations and conditions are the same as those in Example 1b, except that the temperature of carbonization in step (2) is adjusted to 700°C.

[0233] Comparative Example 6b

[0234] The rest of the operations and conditions are the same as those in Example 1b, except that polypropylene is not added.

[0235] Effect Example

[0236] (1) Morphology characterization

[0237] The prepared polyvinyl chloride derived hard carbon material and the pre-dehalogenated sample were subjected to morphology characterization. According to the SEM observation results, the pre-dehalogenated sample was loose and random agglomerated particles with a fluffy surface and no special morphology, and after NaCl assisted high temperature carbonization, hard carbon block particles with clear edges were formed. Through HRTEN and FFT images (Figure 3), it was further observed that the prepared hard carbon material had an external continuous few-layer (n<5) graphene carbon layer and an internal disordered turbulent structure composite hard carbon structure.

[0238] (2) XRD characterization

[0239] According to the XRD test results, the hard carbon materials prepared in Example 1b, Example 3b and Comparative Example 5b all have two broad characteristic peaks near 25° and 42°, corresponding to the (002) and (100) crystal face diffraction in typical disordered amorphous carbon structure, which confirms that the hard carbon material is a typical disordered hard carbon. With the increase of carbonization temperature, the (002) crystal face near 25° is further broadened, and the peak position moves to the left, and the peak intensity gradually weakens, indicating that the structure disorder degree increases, and the interlayer spacing of the in-plane curved carbon layer increases. According to Bragg's law, the interlayer spacing d 002 from 0.351 nm in Comparative Example 5b to 0.354 nm in Example 1b, and then to 0.361 nm in Example 3b, while the interlayer spacing of Comparative Example 1b is only 0.347 nm. The increase of the interlayer spacing also proves that during the NaCl assisted high temperature carbonization process, the generated HCl cannot be discharged in time, and the HCl gas enclosed in the NaCl molten salt continuously impacts the internal structure of the hard carbon material during the carbonization process, promoting the generation of more dense disordered structure inside, providing driving force for the expansion of the interlayer spacing.

[0240] In addition, according to the XRD test results of Examples 1b-2b and Comparative Example 4b, with the increase of the amount of NaCl added, the hard carbon material showed an increasingly strong (002) characteristic peak near 25°, and the peak width narrowed, but the peak position did not shift. According to the test results in Table 8, for Examples 1b-2b and Comparative Example 4b, with the increase of NaCl added, the I D / I G value first decreased and then increased, and Comparative Example 4b showed the largest I D / I G value, which also proved from the side that with the increase of the NaCl sealing agent, the sealing effect was better, making it more difficult for the HCl gas generated during the pyrolysis process of the pre-dehalogenated sample to escape, and the damage to the internal structure was stronger, so the degree of disorder of the internal disordered turbulent structure of Comparative Example 4b was higher.

[0241] (3) Raman, nitrogen adsorption-desorption characterization test, FT-IR spectrum test

[0242] The hard carbon materials prepared in the examples and comparative examples and the pre-dehalogenated sample prepared in Example 1b were subjected to Raman, nitrogen adsorption-desorption characterization test and FT-IR spectrum test according to the conventional operation in the art.

[0243] According to the Raman test results, the ID / IG peak intensity ratio of the pre-dehalogenated sample prepared in Example 1b, Comparative Example 1b, Comparative Example 5b, Example 1b, and Example 3b was 1.067, 1.048, 0.910, 0.965 and 0.991, respectively. The lower the ratio of the intensity of the D peak and the G peak (ID / IG), the lower the degree of defects in the material. This shows that with the introduction of NaCl flux, the degree of defects is significantly lower than that of commercial hard carbon BHC550; in addition, with the increase of carbonization temperature, the damage of the HCl gas flow generated during the carbonization process of the pre-dehalogenated sample to the structure is greater, so the degree of defects of the hard carbon material at the corresponding temperature is higher, and the internal structure is more disordered, which is consistent with the XRD results.

[0244] Table 8 Structure parameters of materials

[0245] In addition, the HCl gas flow generated during the carbonization process of the pre-dehalogenated sample also has a greater pore-forming effect on the internal structure of the hard carbon material. According to the test results in Table 8, with the increase of the carbonization temperature, the specific surface area and pore size of the hard carbon material increase. These results show that under vacuum conditions, the faster the gas generated by the dechlorination reaction escapes as the temperature increases, the more intense the impact of the gas on the internal structure, so that the hard carbon material has more microstructure, and thus the degree of disorder increases and the pore structure develops, which is beneficial for the subsequent use of the hard carbon material as an energy storage material, providing more active sites for ion storage and increasing the specific capacity of the material.

[0246] From the FT-IR spectra of the PVC sample, it can be seen that there are C-Cl stretching vibration peaks between 600-640 cm -1 , H-CCl deformation vibration peaks between 1180-1350 cm -1 , and Cl-C- deformation vibration peaks between 2906-2967 cm -1 , and a series of chlorinated hydrocarbon characteristic peaks. After pre-dehalogenation, the C-Cl peaks near 600-640 cm -1 and the Cl-C- peaks near 2906-2967 cm -1 are significantly weakened. At the same time, the H-CCl deformation vibration peaks between 1180-1350 cm -1 are transformed into -CH2 deformation vibration peaks. At the same time, the appearance of new C=C bending vibration peaks near ~1670 cm -1 is observed, which indicates that after low-temperature pre-dehalogenation reaction, chlorine has been partially removed, and C=C-containing sp 2 intermediates exist in the molecular chain of the pre-dehalogenated sample. After subsequent high-temperature carbonization, all the chlorinated hydrocarbon characteristic peaks and C=C peaks in the hard carbon material obtained in Example 1b disappear, indicating the completion of the dehalogenation reaction. At the same time, due to the growth and rearrangement of the carbon layer, it is difficult for the C=C olefin intermediates to remain under the impact of HCl gas flow, forming a disordered turbulent layer structure. In addition, from the Raman test results of PVC, pre-dehalogenated sample and hard carbon material, it is found that after pre-dehalogenation, the pre-dehalogenated sample has produced part of sp 2 hybrid carbon intermediates compared with PVC, the D peak and G peak appear. By calculating the intensity ratio of the D peak to the G peak of the pre-dehalogenated sample precursor is 1.067, which is higher than that of the hard carbon material 0.965. Thus, through the subsequent carbonization process, through the removal of Cl and the rearrangement of the carbon layer, the defects in the hard carbon are significantly reduced. The removal of chlorine-related characteristic peaks in the hard carbon material and the optimization of the surface carbon defect level further confirm the formation of the unique structure of the outer graphene carbon layer and the inner turbulent layer disordered carbon.

[0247] (4) The carbon yield of the few-layer graphene-coated PVC-derived hard carbon material prepared by the two-step method is as high as 26%-33%, which is much higher than the carbon yield of other reported PVC-derived carbons. Therefore, from the environmental and economic perspectives, the conversion of PVC waste plastics into high-value carbon-based materials by the two-step pyrolysis method not only promotes resource recycling, but also provides a possibility for sustainable law.

[0248] (5) Electrochemical performance test of lithium ion battery

[0249] The prepared samples were subjected to electrochemical measurements by assembling CR-2016 button cells. The working electrode tab was prepared by coating the mixed slurry on a copper foil current collector, which was then dried in a vacuum oven at 85°C overnight, and then cut into a circular tab with a diameter of 1 cm x 1 cm. The slurry was composed of active material (prepared hard carbon material), super conductive carbon black (Super P) and binder PVDF dispersed in NMP at a weight ratio of 8:1:1. The button cell was prepared in an argon-filled glove box, using lithium metal sheet as the negative electrode, polypropylene (PP) single layer as the battery separator, and KB046 electrolyte was 1 mol L -1 LiClO4was dissolved in a mixed solution of EC / DEC (volume ratio 1:1) with the addition of 5wt% fluoroethylene carbonate (FEC) additive. The charge / discharge test was carried out on a LAND CT2001A battery test system at a temperature of 20°C. The voltage range for rate performance and long-term cycle performance was 0.001 to 2.5V vs. Li / Li + (1C = 250mAh g -1 ).

[0250] Table 9 First cycle charge-discharge data of hard carbon material obtained at 0.5C constant current

[0251] According to the results in Table 9, comparing Example 1b-2b and Comparative Example 4b, it can be seen that when the mass ratio of NaCl and pre-dehalogenated sample is not in the range of (1.2-4.5):1, the specific capacity and first cycle coulombic efficiency of the prepared hard carbon material are lower; comparing Example 1b, Example 3b and Comparative Example 5b, it can be seen that when the carbonization temperature is lower than the melting point of the salt, the initial reversible specific capacity and first cycle coulombic efficiency of the prepared hard carbon material are both lower.

[0252] The rate test procedure was set to 0.5C, 1C, 2C, 5C, 10C, 20C, 30C, 40C, 50C and 60C (1C = 250mAh g -1 After the complete rate test, the current was returned to 0.5C again. The reversible capacity of the hard carbon material negative electrode prepared in Example 1b at 0.5C, 1C, 2C, 5C, 10C, 20C, 30C, 40C, 50C and 60C currents were 396.0, 362.7, 335.3, 297.1, 267.8, 229.9, 208.5, 191.5, 176.3 and 163.4 mAh g -1 When the current was suddenly restored to 0.5C, the reversible capacity of the hard carbon material prepared in Example 1b quickly recovered to 392.1 mAh g -1, which is much higher than 60%. This indicates that the hard carbon material prepared in Example 1b still has excellent rate performance from the industrial level evaluation. In contrast, the reversible capacities of Comparative Example 1b, Comparative Example 2b, Comparative Example 3b, Comparative Example 5b and Example 3b at 60C are 30.7, 31.0, 31.1, 33.8 and 34.5 mAh g -1 .

[0253] The first cycle charge-discharge behavior of Comparative Example 1b, Comparative Examples 2b-3b can be found: using the same precursor carbon source, the introduction of NaCl molten salt as graphene template and sealing agent is indispensable for the formation of the unique structure of hard carbon material. Although PVC-derived pyrolytic carbon is removed by high-temperature treatment to reduce the degree of carbon material defects, high-conductivity carbon is prepared, so Examples 1b, Comparative Examples 2b-3b have a first cycle coulombic efficiency significantly better than that of Comparative Example 1b commercial hard carbon BHC550. But due to the lack of NaCl-assisted surface carbon layer rearrangement process, the solid-state diffusion process in the interior of Comparative Examples 2b-3b materials is limited, so they show limited rate capacity.

[0254] Table 10 Long cycle stability of Example 1b and Comparative Example 1b

[0255] According to the results in Table 10, the hard carbon material prepared in Example 1b shows the highest capacity retention rate regardless of the different current densities. Benefiting from its unique structure, the hard carbon material electrode has the best electrochemical performance: the few-layer graphene carbon layer promotes the rapid transport of ions / electrons, significantly improving the reaction kinetics; the disordered turbulent structure is conducive to the preservation of the structure of the hard carbon material electrode during electrochemical cycling, reducing the fragmentation of the electrode. Under the action of NaCl-assisted graphitization, the electrical conductivity of the hard carbon material is improved, accompanied by the development of the pore structure, which is beneficial to the repeated insertion / extraction of lithium ions. Therefore, from the environmental and economic points of view, the preparation of few-layer graphene-coated PVC-derived hard carbon by NaCl-assisted stepwise pyrolysis realizes the development of high-value, functional carbon-based materials, and provides a new idea for the upgrading utilization of PVC waste plastics.

[0256] (6) Electrochemical performance test of potassium ion battery

[0257] The prepared samples were subjected to electrochemical measurements by assembling CR-2016 button cells. The working electrode tabs were prepared by coating the mixed slurry on copper foil current collectors, which were then dried in a vacuum oven at 85 °C overnight, and then cut into 1 cm x 1 cm circular tabs. The slurry was composed of active material (prepared hard carbon material), super conductive carbon black (Super P), and binder PVDF dispersed in NMP at a weight ratio of 8:1:1. The button cells were prepared in an argon-filled glovebox, using potassium metal sheet as the negative electrode, polypropylene (PP) single layer as the cell separator, and LB046 electrolyte was 1 mol L -1 KPF6 was dissolved in a mixed solution of EC / DEC (volume ratio 1:1) with 5 wt% fluoroethylene carbonate (FEC) additive. Charge / discharge tests were performed on a LAND CT2001A battery test system at 20 °C. The voltage range for rate capability and long-term cycling capability was 0.001 to 2.5 V vs. K / K + (1 C = 250 mAh g -1 ).

[0258] The prepared hard carbon material of Example 1b was studied for potassium ion storage performance by assembling K / K + half-cells. It exhibited a capacity of 312.2 / 478.6 mAh g -1 in the first cycle of charge / discharge at 0.5 C with an initial efficiency of 65.2%, while the commercial BHC550 of Comparative Example 1b exhibited a capacity of 265.8 / 373.2 mAh g -1 with an initial efficiency of 71.2%. The reversible capacity of Example 1b at 0.5 C, 1 C, 2 C, 5 C, and 10 C was 333.4, 294.1, 256.4, 205.3, and 168.2 mAh g -1 , respectively. Even at a high current density of 20 C, the specific capacity of Example 1b could still maintain at 128.7 mAh g -1 , keeping 76.3% of the reversible capacity at 10 C current density. The specific capacity of BHC550 and graphite electrode of Comparative Example 1b at 20 C was 67.2 mA h g -1 . When the current density was suddenly reset back to 0.5 C, the specific capacity of Example 1b and BHC550 of Comparative Example 1b recovered to 297.4 and 203.3 mAh g -1 , respectively. The superior high-rate performance of potassium ion of Example 1b could be attributed to the few-layer graphene layers in the hard carbon material that facilitated the storage and transport of potassium ions during the intercalation / deintercalation process. The hard carbon material maintained 234.5 mAh g -1The high reversible capacity of the ordered graphene-coated PVC-derived hard carbon prepared by NaCl-assisted method can be maintained at 74.27% after 300 cycles. The capacity retention rate of Example 1b is 68% after 800 cycles at 5C, and the average capacity attenuation rate per cycle is 0.04%. Therefore, the ordered graphene-coated PVC-derived hard carbon prepared by NaCl-assisted method can have high capacity, high rate performance and good cycle stability when used as a negative electrode of a potassium ion battery.

[0259] The raw material information used in the following Examples 1c-8c and Comparative Example 1c is shown in Table 11:

[0260] Table 11

[0261] Example 1c

[0262] (1) 1 g of PVC and 0.05 g of polyethylene were mixed and then subjected to heating and melting in a tube furnace (under an argon atmosphere) at a heating temperature of 120°C for 2 h. After cooling, substance A was obtained.

[0263] (2) Substance A and metallic sodium were mixed uniformly at a molar ratio of chlorine atoms in the raw material PVC to metallic sodium of 1:1.3 and then placed in a crucible, which was then added to a tube furnace. The mixture was heated to 250°C at a heating rate of 3°C / min under a high-purity argon atmosphere, maintained for 3 h, and then cooled to room temperature to obtain a dehalogenated sample.

[0264] (3) The dehalogenated sample was washed three times with a mixture of deionized water and anhydrous ethanol at a volume ratio of 3:1, and then dried to obtain a hard carbon precursor. The hard carbon precursor was then carbonized in a tube furnace under a high-purity argon atmosphere at a temperature of 800°C for 4 h, and then cooled to obtain a hard carbon negative electrode material.

[0265] Example 2c

[0266] Compared with Example 1c, except that the PVC powder was replaced by PVDC powder (Dow SARAN 516, extruded type), the other parameters and conditions were the same as those of Example 1c.

[0267] Example 3c

[0268] Compared with Example 1c, except that the metallic sodium was replaced by metallic potassium, the other parameters and conditions were the same as those of Example 1c.

[0269] Example 4c

[0270] Compared with Example 1c, except that the metallic sodium was replaced by metallic potassium and the molar ratio of chlorine atoms in PVC to metallic potassium was adjusted to 1:1.1, the other parameters and conditions were the same as those of Example 1c.

[0271] Example 5c

[0272] Compared with Example 1c, the rest of the parameters and conditions are the same as Example 1c, except that the metal sodium is replaced by metal magnesium, and the molar ratio of chlorine atoms in PVC to metal magnesium is adjusted to 1:0.55.

[0273] Example 6c

[0274] Compared with Example 1c, the rest of the parameters and conditions are the same as Example 1c, except that the metal sodium is replaced by metal calcium, and the molar ratio of chlorine atoms in PVC to metal calcium is adjusted to 1:0.55.

[0275] Example 7c

[0276] Compared with Example 1c, the rest of the parameters and conditions are the same as Example 1c, except that the carbonization temperature in step (3) is adjusted to 900°C.

[0277] Example 8c

[0278] Compared with Example 1c, the rest of the parameters and conditions are the same as Example 1c, except that the polyethylene is replaced by polypropylene.

[0279] Comparative Example 1c

[0280] Compared with Example 1c, the rest of the parameters and conditions are the same as Example 1c, except that no metal sodium is added in step (1).

[0281] Effect Example

[0282] (1) SEM and specific surface area test

[0283] Figure 4 is a scanning electron microscope image of the hard carbon material prepared in Example 1c.

[0284] The specific surface area of the prepared hard carbon material was tested by using an Anton Paar specific surface area and pore size analyzer NOVATouch, and the test results are shown in Table 12.

[0285] (2) Electrochemical performance test

[0286] Negative electrode sheet preparation: the hard carbon materials prepared in Examples 1c to 8c and Comparative Example 1c were respectively subjected to half-cell tests, and the test method was as follows: the hard carbon material, super conductive 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 90°C vacuum oven overnight. Subsequently, the obtained electrode sheet was cut into a circular sheet-shaped battery electrode sheet with a diameter of 12 mm for standby use, and the average mass load ≈2mg cm -2 .

[0287] The assembly of the button cell was carried out in an argon-filled glove box, and the lithium ion battery used lithium metal sheet as the counter electrode and polypropylene single layer as the battery separator; 1M LiClO4 mixed solution of ethylene carbonate / diethyl carbonate (EC / DEC, volume ratio 1:1), electrolyte added with 10wt.% fluorocarbon ethylene (FEC) additive, wt.% refers to the mass percentage of FEC in the electrolyte. The charge and discharge test was carried out on a LAND CT2001A battery tester in the potential range of 0.001-3.0V.

[0288] The sodium ion battery used sodium metal sheet as the counter electrode, glass fiber single layer as the battery separator, and additional foam nickel round sheet, and the electrolyte was 1M NaPF6 diethylene glycol dimethyl ether solution. After assembly, it was aged for 8h. The constant current charge / discharge test was carried out on a LAND CT2001A battery test system, and the voltage range was 0.001 to 3.0V vs. Li / Li + .

[0289] The test results are shown in Table 12:

[0290] Table 12

[0291] According to the above experimental results, the hard carbon negative electrode material prepared by the application has excellent electrochemical performance, especially the specific capacity and rate performance.

[0292] Comparative Example 1c, due to the lack of metal catalysis during preparation, the dehalogenation reaction is less efficient at the same temperature, which is not conducive to the formation of high-conductivity carbon, and in addition, the lack of metal and salt template, the specific surface area of the prepared hard carbon material is small, and the specific capacity is low.

[0293] Although the specific embodiments of the application are described above, those skilled in the art should understand that this is only an example, and the protection scope of the application is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the application, and these changes and modifications all fall within the protection scope of the application.

Claims

1. A method for producing a hard carbon material, characterized by, It comprises the following steps: (1) mixing a solution containing PVC and aromatic compounds under heating conditions until the solvent is completely evaporated to obtain a dry gel; The mass ratio of the aromatic compound to the PVC is 2%-25%; (2) obtaining a PVC dehalogenation precursor by grinding, washing and drying the dry gel; (3) carbonizing the PVC dehalogenation precursor to obtain the hard carbon material; the carbonization temperature is 700-1200℃, and the carbonization time is 1-4h.

2. The method for producing a hard carbon material according to claim 1, wherein The PVC has a viscosity number K value of 50-80; And / or, the aromatic compound is a compound containing at least one benzene ring, preferably an aromatic hydrocarbon and / or an aromatic hydrocarbon derivative.

3. The method for producing a hard carbon material according to claim 2, wherein The aromatic hydrocarbon is a monocyclic aromatic hydrocarbon and / or a polycyclic aromatic hydrocarbon; Preferably, the monocyclic aromatic hydrocarbon is benzene or toluene; Preferably, the polycyclic aromatic hydrocarbon is a non-fused ring aromatic hydrocarbon and / or a fused ring aromatic hydrocarbon, such as biphenyl or naphthalene; And / or, the aromatic hydrocarbon derivative is an aromatic acid and / or a halogenated aromatic hydrocarbon; Preferably, the aromatic acid is benzoic acid; Preferably, the halogen in the halogenated aromatic hydrocarbon is one or more of F, Cl, Br and I; Preferably, the number of halogen atoms in the halogenated aromatic hydrocarbon is at least 1; Preferably, the halogenated aromatic hydrocarbon is a side chain halogenated aromatic hydrocarbon and / or an aromatic ring halogenated aromatic hydrocarbon, such as chlorobenzene or 1,2-dichlorobenzene.

4. The method for producing a hard carbon material according to claim 1, wherein The preparation method satisfies one or more of the following conditions: (1) The mass ratio of the aromatic compound to the PVC is 7%-15%; (2) The solvent in the solution is a solvent capable of dissolving PVC, such as NMP; (3) The ratio of the mass of the PVC to the volume of the solvent in the solution is 1:(20-40) g / mL.

5. The method for preparing hard carbon material as described in claim 1, characterized in that, The preparation method satisfies one or more of the following conditions: (1) In step (1), the preparation method of the solution containing PVC and aromatic compounds comprises the following process: stirring and mixing the PVC and the solvent at room temperature until the PVC is completely dissolved, and then adding the aromatic compound; (2) In step (1), the mixing temperature is 140-180℃; (3) In step (1), the mixing process comprises: first stirring and mixing the solution containing PVC and aromatic compounds at 60-90℃ for 1-3h to obtain a sol, and then stirring and mixing the sol at 140-180℃ until the solvent is completely evaporated to obtain a dry gel.

6. The method of producing a hard carbon material according to claim 1, wherein In step (3), the carbonization temperature is 700-900℃; And / or, the carbonization time is 1-3h.

7. A hard carbon material, characterized by, It is prepared according to the preparation method of the hard carbon material according to any one of claims 1-6.

8. The hard carbon material of claim 7, wherein, The hard carbon material satisfies one or more of the following conditions: (1) The hard carbon material has a few-layer graphene-like carbon layer structure inside; (2) The graphite interlayer spacing of the hard carbon material is 0.340-0.385nm; (3) The pore size distribution range of the hard carbon material is 0.1-6nm; (4) the specific surface area of the hard carbon material is 1-5 m 2 / g; (5) the I D / I G of the hard carbon material is 0.948-1.05; (6) the electrical conductivity of the hard carbon material is 1.14-5 S m -1 ; (7) the hard carbon material has a reversible specific capacity of 355-600 mAh g -1 at a current density of 50 mA g -1 -1 (8) the hard carbon material has a first cycle coulombic efficiency of 70-85% at a current density of 50 mA g -1 -1. (9) the hard carbon material has a reversible specific capacity of 440-540 mAh g - 1 at a current density of 0.5 A g -1 ; (10) the hard carbon material has a capacity retention rate of 99% or more after 300 cycles at a current density of 0.5 A g -1 -300 (11) the hard carbon material has a reversible specific capacity of 120-210 mAh g -1 when the current density is 1.5 A g -1 ; (12) the hard carbon material has a capacity retention rate of 99% or more after 1800 cycles at a current density of 1.5 A g -1 1.5 A g 9. Use of the hard carbon material according to claim 7 or 8 in a battery.

10. A battery, characterized by It comprises the hard carbon material according to claim 7 or 8.

11. A method of producing a polyvinyl chloride derived hard carbon material, characterized by, It comprises the following steps: (1) heating and melting PVC powder and a thermoplastic resin, cooling to obtain a substance A; and then pre-dehalogenating the substance A under inert gas protection to obtain a pre-dehalogenated sample; wherein the thermoplastic resin is polypropylene and / or polyethylene, the mass ratio of the thermoplastic resin to the PVC powder is 5%-50%, the pre-dehalogenation temperature is 250-500℃, and the pre-dehalogenation time is 1-5h; (2) covering inorganic halide salt on the pre-dehalogenated sample in a reaction tube, vacuumizing and sealing the reaction tube, and then carbonizing, washing and drying to obtain the PVC-derived hard carbon material; the mass ratio of the inorganic halide salt to the pre-dehalogenated sample is (1.2-4.5):1, the carbonization temperature is not lower than the melting point of the inorganic halide salt, and the carbonization time is 5-20h.

12. The method for preparing polyvinyl chloride-derived hard carbon material as described in claim 11, characterized in that, Step (1) satisfies one or more of the following conditions: (1) the heating and melting temperature is 100-140℃; (2) the heating and melting time is 1-4h; (3) the pre-dehalogenation temperature is 300-400℃; (4) the pre-dehalogenation time is 1-3h.

13. The method for preparing polyvinyl chloride-derived hard carbon material as described in claim 11, characterized in that, The preparation method satisfies one or more of the following conditions: (1) the PVC powder has a viscosity number K value of 50-80; (2) the polypropylene has a melt index of 10-40g / 10min; (3) the polyethylene has a melt index of 10-40g / 10min; (4) the mass ratio of the thermoplastic resin to the PVC powder is 5%-20%.

14. The method for preparing polyvinyl chloride-derived hard carbon material as described in claim 11, characterized in that, The inorganic halide salt satisfies one or more of the following conditions: (1) the melting point of the inorganic halide salt is not lower than 700℃; (2) the cation of the inorganic halide salt comprises one or more of alkali metal, alkaline earth metal and transition metal; wherein the alkali metal preferably comprises Na and / or K; the alkaline earth metal preferably comprises one or more of Mg, Ca, Sr and Ba; the transition metal preferably comprises one or more of Fe, Co, Ni, Cu and Zn; (3) the anion of the inorganic halide salt comprises one or more of Cl ion, Br ion and I ion, preferably Cl ion or Br ion; (4) the inorganic halide salt is one or more of NaCl, KCl and NaBr; (5) the mass ratio of the inorganic halide salt to the pre-dehalogenated sample is (1.5-3.5):

1.

15. The method for preparing polyvinyl chloride-derived hard carbon material as described in claim 11, characterized in that, In step (2), the carbonization temperature is preferably above 10℃ of the melting point of the inorganic halide salt and below 200℃; when the inorganic salt is NaCl, the carbonization temperature is preferably 810-1000℃; when the inorganic salt is NaBr, the carbonization temperature is preferably 780-900℃; when the inorganic salt is KCl, the carbonization temperature is preferably 800-1000℃; and / or, the carbonization time is 5-15h.

16. A polyvinyl chloride derived hard carbon material, characterized in that, The PVC-derived hard carbon material is prepared according to the preparation method of any one of claims 11-15.

17. The polyvinyl chloride derived hard carbon material of claim 16, wherein, The polyvinyl chloride derived hard carbon material has a continuous outer coating of few-layer graphene carbon layers.

18. The polyvinyl chloride derived hard carbon material of claim 16, wherein, The polyvinyl chloride derived hard carbon material satisfies one or more of the following conditions: (1) The polyvinyl chloride derived hard carbon material has a graphite interlayer spacing of 0.352-0.40 nm; (2) The polyvinyl chloride derived hard carbon material has a pore size distribution range of 7.5-15 nm; (3) the polyvinyl chloride derived hard carbon material has a specific surface area of 4.8-15 m 2 / g; (4) the polyvinyl chloride derived hard carbon material has an I D / I G of 0.94-1.

05.

19. Use of the polyvinyl chloride derived hard carbon material of any one of claims 16-18 in a battery.

20. A battery, characterized by It comprises the polyvinyl chloride derived hard carbon material of any one of claims 16-18.

21. A method of producing a hard carbon material, characterized by, It comprises the following steps: The halogen-containing high polymer powder and the thermoplastic resin are mixed and then heated and melted, and the mixture is obtained after cooling; then the mixture is mixed with a reducing metal, and heated to remove halogen at 100-400°C for 2-12h in an inert gas protection to obtain a halogen-removed sample; the halogen-removed sample is washed, dried, and carbonized to obtain a hard carbon material; The thermoplastic resin is polypropylene and / or polyethylene, and the mass ratio of the thermoplastic resin to the halogen-containing high polymer powder is 2%-10%; When the reducing metal is an alkali metal element, the molar ratio of halogen atoms in the halogen-containing high polymer powder to the reducing metal is 1:(1-3); When the reducing metal is an alkaline earth metal element, the molar ratio of halogen atoms in the halogen-containing high polymer powder to the reducing metal is 1:(0.5-1.5).

22. The method of claim 21, wherein the hard carbon material is prepared by the process comprising: The halogen-containing high polymer powder is polyvinyl chloride (PVC) and / or polyvinylidene chloride (PVDC); The viscosity number K value of the polyvinyl chloride is preferably 50-80, for example 62-60; And / or, the particle size of the halogen-containing high polymer powder is 0.1-1μm.

23. The method of producing a hard carbon material according to claim 21, wherein The alkali metal element is Na and / or K; And / or, the alkaline earth metal element is one or more of Mg, Ca, and Ba.

24. The method of producing a hard carbon material according to claim 21, wherein When the reducing metal is an alkali metal element, the molar ratio of halogen atoms in the halogen-containing high polymer powder to the reducing metal is 1:(1-2), for example 1:1.1, 1:1.2, or 1:1.3; And / or, when the reducing metal is an alkaline earth metal element, the molar ratio of halogen atoms in the halogen-containing high polymer powder to the reducing metal is 1:(0.5-1), for example 1:0.

55.

25. The method of producing a hard carbon material according to claim 21, wherein The melt index of the polypropylene is 10-40g / 10min, for example 35g / 10min; And / or, the melt index of the polyethylene is 10-40g / 10min, for example 25g / 10min; And / or, the mass ratio of the thermoplastic resin to the halogen-containing high polymer powder is 2%-8%, for example 5%.

26. The method of producing a hard carbon material according to claim 21, wherein The temperature of the heating and melting is 100-140°C, for example 120°C; And / or, the time of the heating and melting is 1-4h, for example 2h.

27. The method of producing a hard carbon material according to claim 21, wherein The temperature of the heating to remove halogen is 200-400°C, for example 250°C; And / or, the time of the heating to remove halogen is 2-6h, for example 3h; And / or, the temperature of the carbonization is 600-1000°C, for example 800°C, 850°C, or 900°C; and / or the carbonization time is 0.5-10 h, preferably 3-6 h, for example 4 h.

28. A hard carbon material, characterized by, which is produced according to the production method of the hard carbon material according to any one of claims 21-27.

29. Use of the hard carbon material according to claim 28 in a secondary battery.

30. A secondary battery characterized by comprising: which comprises the hard carbon material according to claim 28.

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