A hard carbon material, its preparation method, application and battery

Abstract

The present invention discloses a hard carbon material, a preparation method, an application thereof, and a battery. The preparation method includes: mixing a solution containing PVC and an aromatic compound 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%; grinding, washing, and drying the dry gel to obtain a PVC dehalogenation precursor; carbonizing the PVC dehalogenation precursor to obtain the hard carbon material; the temperature of the carbonization is 700 - 1200 °C, and the time of the carbonization is 1 - 4 h. The hard carbon material prepared by the present invention has high atomic economy and high electron conductivity, and has excellent electrochemical performance when preparing a battery.

Description

Technical Field

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

[0002] As the most typical chlorinated plastic, PVC is a thermoplastic polymerized from vinyl chloride monomers by free radical polymerization, and its theoretical chlorine content is as high as 56.8% of its total mass. When PVC burns and pyrolyzes, carcinogenic organic compounds such as dioxins and furans are generated, along with the release of HCl. In China, the management methods of waste PVC plastics mainly include landfill, incineration, and recycling. The proportions of PVC waste in landfills, incinerators, mechanical and chemical recycling are 36.0%, 9.3%, 25.5%, and 0.8% respectively. However, landfill space is limited and resources are severely wasted. Landfilling PVC waste causes harmful additives to be released, polluting soil and groundwater. Incinerating PVC waste releases carbon dioxide and HCl, and may produce polychlorinated dioxins and furans. At the same time, the incineration residue may contain heavy metals and is considered hazardous waste.

[0003] Currently, the technologies for treating PVC waste cannot achieve the reduction of PVC plastic production, the improvement of PVC waste treatment rate, and the reversal of PVC consumption patterns. In addition to traditional plastic recycling, one of the best ways to mitigate PVC waste pollution is to upgrade and recycle it to increase its value and use it for new purposes. Upgrading and recycling is the process of converting waste resources or by-products into new materials with higher value. Chemical upgrading and recycling is a more promising alternative than traditional pyrolysis and recycling because it converts plastic waste into materials and chemicals with high value and versatility, with stronger selectivity and less energy required. To achieve the environmental and economic advantages related to the recycling of waste plastics, effective upgrading and recycling technologies must be developed to convert and upgrade high-value, versatile chemicals while reducing the Cl content to treat polyvinyl chloride waste plastics.

[0004] Concerns about energy and environmental problems caused by the combustion and shortage of fossil fuel resources are increasing worldwide, which has stimulated the interest in exploring efficient and renewable energy sources. Therefore, various advanced Advanced Electrochemical Energy Storage and Conversion devices to achieve sustainable development. Among the developed electrode materials, Carbon-based materials have attracted much attention due to their advantages such as high electrical conductivity, good chemical stability, and stable structure. Although carbon-based electrode materials have broad prospects, traditional carbon materials are all 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 with rich resources and 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.

[0005] Thermoplastic polyvinyl chloride is usually converted into disordered hard carbon composed of curled, twisted, and folded carbon layers in an inert atmosphere. The structure is very disordered, resulting in various internal defects and pores. 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 ability, thus limiting the actual capacity and rate performance and showing a low initial Coulomb efficiency. As the negative electrode material of the battery, it also has the following problems: (i) The carbon atom economy in the carbonization process of polyvinyl chloride is relatively low (about ~33 at.%), which should be improved to obtain more carbon-based solid products instead of gaseous and liquid by-products; (ii) The conductivity, layer 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 Coulomb efficiency; (iii) The polyvinyl chloride-derived carbon should be functionally designed to improve its value, aiming to realize the "reduce mass production - recycle - upgrade utilization" approach for PVC upgrade utilization to maximize the circular benefits of halogen-containing plastics. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the defects of low atomic economy, poor electron conductivity, and poor electrochemical performance in the prior art when preparing hard carbon materials from thermoplastic polyvinyl chloride, and to provide a hard carbon material, its preparation method, application, and battery. The hard carbon material prepared by the present invention has high atomic economy and high electron conductivity, and has excellent electrochemical performance when preparing a battery.

[0007] The comprehensive performance of the PVC-derived carbon negative electrode urgently needs to be further improved. The key lies in the construction of energy storage active sites, pore structure regulation, and improvement of conductivity. The present invention uses PVC as a raw material and combines a simple and feasible solvent wet treatment with self-driven chemical vapor deposition to upgrade polyvinyl chloride waste into a high-conductivity polyvinyl chloride-based hard carbon material with a slit / micropore filling structure. Through the aromatic the high-temperature elimination reaction of H in the group compound and Cl in PVC aromatizes the compound and grafts it onto PVC polymer carbon chain, thereby increasing the sp 2The content of -C. In addition, the benzene ring structure that is easily adsorbed on the wall of the slit pores of the derived carbon is deposited at a lower temperature limit in the high temperature to form few-layer graphene-like nanodomains, providing additional energy storage sites through the pore filling mechanism. Moreover, due to the high thermal stability of the benzene ring, under the van der Waals force between the π orbitals of the carbon plane on the pore wall and the electron density inside the benzene ring, the benzene ring tends to be adsorbed on the wall of the slit pores inside the PVC-derived carbon. Under the catalytic action of the pore wall, the adsorbed species are cracked into a large number of flat few-layer graphene nanodomains, which deposit and grow until the benzene ring molecules can no longer enter the pores. More importantly, during the pyrolysis of PVC, the nanographene carbon layer crystallites obtained by rearrangement growth block the gas transmission channels, restricting 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. These slit pores and micropores can provide additional storage sites for ions through the pore filling mechanism. The structural design concept of embedding few-layer graphene-like nanodomains in the open pores of carbon materials proposed in this patent significantly improves the storage capacity of adsorption and intercalation lithium.

[0008] The present invention solves the above technical problems through the following technical solutions:

[0009] The present invention provides a method for preparing a hard carbon material, which includes the following steps:

[0010] (1) Mix a solution containing PVC and an aromatic compound 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%;

[0011] (2) Grind, wash, and dry the dry gel to obtain a PVC dehalogenation precursor;

[0012] (3) Carbonize the PVC dehalogenation precursor to obtain the hard carbon material; the temperature of the carbonization is 700-1200 °C, and the time of the carbonization is 1-4 h.

[0013] In step (1), the K value of the viscosity number of the PVC can be 50-80, preferably 55-70.

[0014] In the present invention, when the aromatic compound contains halogen, in addition to the high-temperature elimination reaction of H in the aromatic compound and Cl in the PVC, there will also be a high-temperature elimination reaction of Cl in the aromatic compound and H in the PVC.

[0015] In step (1), according to the routine in the art, the aromatic compound generally refers to a compound containing at least 1 benzene ring, preferably an aromatic hydrocarbon and / or an aromatic hydrocarbon derivative.

[0016] wherein the aromatic hydrocarbon generally refers to a hydrocarbon containing a benzene ring, including monocyclic aromatic hydrocarbons and / or polyAromatic hydrocarbons. The monocyclic aromatic hydrocarbons generally refer to hydrocarbons containing only one benzene ring, such as benzene or toluene. The polycyclic aromatic hydrocarbons generally refer to hydrocarbons having at least two or more benzene rings, including non-condensed polycyclic aromatic hydrocarbons (such as biphenyl) and / or condensed polycyclic aromatic hydrocarbons (such as naphthalene).

[0017] Among them, the aromatic hydrocarbon derivatives are preferably aromatic acids and / or halogenated aromatic hydrocarbons. 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 a side-chain halogenated aromatic hydrocarbon and / or an aromatic ring halogenated aromatic hydrocarbon. The side-chain halogenated aromatic hydrocarbon refers to a halogen connected to a carbon atom of the aromatic ring side chain, and the aromatic ring halogenated aromatic hydrocarbon refers to a halogen connected to a carbon atom of the aromatic ring. The aromatic ring halogenated aromatic hydrocarbon can be, for example, chlorobenzene or 1,2-dichlorobenzene.

[0018] In step (1), the mass ratio of the aromatic compound to the PVC is, for example, 5%, 9%, 12%, or 18%, preferably 7%-15%.

[0019] In step (1), the solvent in the solution can be a solvent that can conventionally dissolve PVC in the art, such as NMP.

[0020] 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.

[0021] In step (1), the method for preparing the solution containing PVC and the aromatic compound preferably includes the following process: mixing the PVC and the solvent by stirring at room temperature until the PVC is completely dissolved, and then adding the aromatic compound.

[0022] In step (1), the mixing method can be conventional in the art, such as stirring.

[0023] In step (1), the mixing temperature is preferably 140 - 180°C, for example, 150°C.

[0024] In step (1), the mixing process preferably includes: first stirring the solution containing PVC and the aromatic compound at 60 - 90°C for 1 - 3 h to obtain a sol, and then stirring the sol at 140 - 180°C until the solvent is completely evaporated to obtain a xerogel.

[0025] In step (2), the washing operation and conditions can be conventional in the art, such as washing with ethanol and water.

[0026] In step (2), the drying operation and conditions can be conventional in the art.

[0027] In step (3), it is preferably to grind the PVC dehalogenation precursor into powder before carbonization End.

[0028] In step (3), the carbonization is generally carried out under a protective atmosphere that does not react with the reaction system, such as nitrogen or inert gas. The inert gas is, for example, argon.

[0029] Among them, the flow rate of the protective atmosphere introduced can be 100 - 500 sccm, preferably 200 - 400 sccm, such as 300 sccm.

[0030] In step (3), the carbonization is generally carried out in a tubular furnace.

[0031] In step (3), the temperature of the carbonization is preferably 700 - 900 °C, such as 800 °C. The time of the carbonization is preferably 1 - 3 h, such as 2 h. The rate of heating to the temperature of the carbonization can be 2 - 10 °C / min, such as 5 °C / min. After the carbonization is completed, it also includes cooling, and the process of naturally cooling to room temperature.

[0032] The present invention also provides a hard carbon material prepared by the preparation method as described above.

[0033] In the present invention, the interior 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 walls inside the hard carbon material.

[0034] In the present invention, the graphite layer spacing of the hard carbon material can be 0.340 - 0.385 nm. The graphite layer spacing generally refers to the layer spacing d calculated according to the XRD test results through Bragg's law 002 .

[0035] In the present invention, the pore size distribution range of the hard carbon material can be 0.1 - 6 nm, preferably 2 - 4 nm.

[0036] In the present invention, the specific surface area of the hard carbon material can be 1 - 5 m 2 / g, such as 1.15 m 2 / g, 1.2 m 2 / g or 1.25 m 2 / g, preferably 1.2 - 1.3 m 2 / g.

[0037] In the present invention, the I D / I G is preferably 0.948 - 1.05, such as 0.951 or 1.024, more preferably 1.0 - 1.03. The I D / IG Refers to the intensity ratio of the D peak and the G peak.

[0038] In the present invention, the conductivity of the hard carbon material can be 1.14 - 5 S m -1 , such as 1.158, 1.198, 1.206 or 1.721, preferably 1.18 - 1.22 S m -1 .

[0039] 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 , such as 362.5 mAh g -1 , 436.5 mAh g -1 , 552.6 mAh g -1 or 553.8 mAh g -1 .

[0040] In the present invention, the first-cycle Coulomb efficiency of the hard carbon material at a current density of 50 mA g -1 is relatively Preferably 70% - 85%.

[0041] 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 .

[0042] In the present invention, the capacity retention rate of the hard carbon material after 300 cycles at a current density of 0.5 A g -1 is preferably above 99%.

[0043] 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 -1 , more preferably 190 - 210 mAh g -1 .

[0044] In the present invention, the capacity retention rate of the hard carbon material after 1800 cycles at a current density of 1.5 A g -1 is preferably above 99%.

[0045] The present invention also provides an application of the hard carbon material as described above in a battery.

[0046] The present invention also provides a battery, which includes the hard carbon material as described above.

[0047] In the present invention, the battery is preferably a lithium-ion battery or a sodium-ion battery.

[0048] On the basis of conforming to the common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present invention.

[0049] The reagents and raw materials used in the present invention are all commercially available.

[0050] The positive and progressive effects of the present invention are as follows:

[0051] (1) The hard carbon material prepared by the present invention has high atomic economy and high electron conductivity, and has excellent electrochemical performance when preparing batteries;

[0052] (2) The preparation method of the present invention is simple, low in cost, and conducive to industrial production;

[0053] (3) The atomic economy of the PVC-derived carbon prepared by the present invention is increased from 33% to more than 70%;

[0054] (4) The present invention regulates the structure of polyvinyl chloride-based derived hard carbon by introducing aromatic compounds, promotes the growth of few-layer graphene-like nanocrystalline domains inside the polyvinyl chloride-derived hard carbon, improves its electron conductivity, and at the same time realizes the improvement of the specific capacity of the polyvinyl chloride-derived hard carbon negative electrode, and to a certain extent improves the first-cycle Coulomb efficiency. Description of the Drawings

[0055] Figure 1 It is a high-resolution transmission electron microscope image of the hard carbon material prepared in Example 1;

[0056] Figure 2 It is a high-resolution transmission electron microscope image of the hard carbon material prepared in Comparative Example 1. Detailed Description of the Invention

[0057] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. The experimental methods without specific conditions in the following examples are carried out according to conventional methods and conditions, or selected according to the product instructions.

[0058] The raw material information used in the following examples and comparative examples is shown in Table 1:

[0059] Table 1

[0060]

[0061] The raw materials used in the examples and comparative examples are all obtained through conventional commercial channels and have not been further processed before use.

[0062] Example 1

[0063] (1) Dissolve 1 g of PVC in 30 mL of N-methylpyrrolidone (NMP) and stir at room temperature for 10 minutes. After the PVC is completely dissolved in NMP, add 0.09 g of chlorobenzene and continue stirring under heating at 70 °C. During this process, as the solvent evaporates continuously, the solution gradually becomes viscous and forms a colloidal system. After stirring for 2 hours, the sol-gel process is completed. Place the obtained transparent sol on a magnetic heating stirrer at 150 °C and stir continuously until the solvent is completely evaporated to obtain a dark gray xerogel. Grind the obtained xerogel into powder, wash it with ethanol and water, and dry it in an oven for 12 hours to obtain a benzene ring-assisted PVC dehalogenation precursor.

[0064] (2) Subsequently, grind the benzene ring-assisted PVC dehalogenation precursor into powder and perform carbonization in a tube furnace. Under an argon atmosphere of 300 sccm, heat it to 800 °C at a heating rate of 5 °C / min -1 , and keep carbonizing for 120 minutes. After the carbonization reaction is completed, cool it naturally to room temperature to obtain a hard carbon material.

[0065] Example 2

[0066] Compared with Example 1, except that the dosage of chlorobenzene is adjusted to 0.05 g, the rest of the operations and conditions are the same as those in Example 1.

[0067] Example 3

[0068] Compared with Example 1, except that the dosage of chlorobenzene is adjusted to 0.12 g, the rest of the operations and conditions are the same as those in Example 1.

[0069] Example 4

[0070] Compared with Example 1, except that the dosage of chlorobenzene is adjusted to 0.18 g, the rest of the operations and conditions are the same as those in Example 1.

[0071] Example 5

[0072] Compared with Example 1, except that chlorobenzene is replaced by toluene, the rest of the operations and conditions are the same as those in Example 1.

[0073] Example 6

[0074] Compared with Example 1, except that chlorobenzene is replaced by 1,2-dichlorobenzene, the rest of the operations and conditions are the same as those in Example 1.

[0075] Example 7

[0076] Compared with Example 1, except that chlorobenzene is replaced by naphthalene, the rest of the operations and conditions are the same as those in Example 1.

[0077] Example 8

[0078] Compared with Example 1, except that chlorobenzene was replaced with benzoic acid, the remaining operations and conditions were the same as those in Example 1.

[0079] Comparative Example 1

[0080] Compared with Example 1, except that chlorobenzene was not added, the remaining operations and conditions were the same as those in Example 1.

[0081] Effect Example

[0082] (1) Morphology Characterization

[0083] Figure 1 It is the high-resolution transmission electron microscopy (HRTEM) image of the hard carbon material prepared in Example 1; Figure 2 It is the high-resolution transmission electron microscopy (HRTEM) image of the hard carbon material prepared in Comparative Example 1. According to Figure 1 and Figure 2 it can be seen that the hard carbon material prepared in Comparative Example 1, due to the absence of the benzene ring structure introduction, shows micron-sized blocky particles, no porous structure is observed, there is no obvious particle aggregation on the surface of the block, and the interior shows a typical hard carbon structure with a highly disordered turbostratic structure randomly intertwined with a short-range ordered curved carbon layer structure; while for the hard carbon material prepared in Example 1, from Figure 1 it can be clearly observed that there is a pore structure and a more porous surface, local carbon lattice edges are gradually formed, the number of few-layer graphene nanocrystalline domains and micropores increases significantly, which indicates that the adsorption and deposition of the benzene ring 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 interior of the material body and achieve an increase in the lithium ion storage capacity.

[0084] Table 2 Interlayer spacing calculated from FFT diffraction of HRTEM images

[0085] sample Interlayer spacing (nm) Example 1 0.401 Example 4 0.380 Comparative Example 1 0.433

[0086] Meanwhile, the interlayer spacing of the hard carbon material decreases from 0.433 nm in Comparative Example 1 to 0.401 nm in Example 1 and 0.380 nm in Example 4. Although the interlayer spacing decreases with the growth of the graphene nanocrystalline domains, the interlayer spacing of the hard carbon material is still greater than the average interlayer spacing of graphite (0.335 nm), which is beneficial for ion insertion and transfer. The existence 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 crosslinked and kinked carbon layer stacking introduces micropore structures and more slit pores. Micropores not only provide more pore embedding sites and increase the plateau capacity, but also can provide a way for lithium ions to enter the interior of the electrode material and shorten the diffusion distance of lithium ions in the bulk phase.

[0087] (2) XRD Characterization

[0088] According to the XRD test results, the hard carbon material prepared in Example 1 shows two similar broad diffraction peaks near 2θ≈23° and 44°, corresponding to the Bragg reflections of the (001) and (100) crystal planes of graphite, respectively. These two broad peaks indicate that the crystallinity of the carbon layer structure in the hard carbon material is low, which are characteristic peaks of disordered carbon. With the increase of chlorobenzene additive, the (002) peak shifts to a higher diffraction angle, indicating that the average interlayer spacing between graphite layers decreases. The interlayer spacing d is calculated by Bragg's law 002 decreases from 0.394 nm (Comparative Example 1) to 0.363 nm (Example 1) and 0.358 nm (Example 4), which is consistent with the observation by HRTEM.

[0089] (3) Raman, nitrogen adsorption-desorption characterization test, FT-IR spectroscopy test

[0090] The hard carbon materials prepared in the examples and Comparative Example 1 are subjected to Raman, nitrogen adsorption-desorption characterization test and FT-IR spectroscopy test according to the conventional operations in the art.

[0091] Table 3 Structural parameters of hard carbon materials

[0092]

[0093] According to the Raman test on the hard carbon materials prepared in Example 1, Example 4 and Comparative Example 1, broad bands in the vicinity of 1600 cm -1 and 1350 cm -1 are all shown. These two peaks correspond to the G band (graphite band: related to the E 2 vibration mode of sp 2g carbon rings) and the D band (disorder band: A 2 vibration mode of sp 1g carbon rings), respectively. The ID / IG ratios of Comparative Example 1, Example 1 and Example 4 are 1.032, 1.024 and 0.951, respectively. This indicates that the defect content in the Example 4 sample is significantly less than that in Comparative Example 1 and Example 1, and different benzene ring addition amounts have an obvious regulatory effect on the degree of disorder of the hard carbon material. In addition, a weak 2D peak appears near 2700 cm -1 in Example 4, which represents short-range or medium-range ordered stacked few-layer carbon layers. The appearance of the 2D peak indicates that a sufficient amount of aromatic precursor is added during the preparation process, and the sp 2 intermediate containing benzene rings is decomposed at high temperature and adsorbed on the pore walls, which can serve as the crystal nuclei for the graphitization of carbon atoms and is beneficial to the growth of graphene-like nanostructures.

[0094] It was found through the nitrogen adsorption and desorption characterization of the hard carbon materials that the specific surface area, average pore volume, and average pore diameter decreased with the increase in the benzene ring addition amount. With the increase in the chlorobenzene addition amount, the pore size decreased significantly, and the pore distribution shifted significantly towards micropores, indicating that the abundant pores inside the original Comparative Example 1 were filled with a few layers of graphene-like nanodomains deposited. The significant decrease in the pore size distribution was caused by the adsorption of benzene ring molecules on the inner slit pore walls through the van der Waals force between their electron cloud density and the π orbitals of the carbon plane. The adsorption of benzene ring molecules on the pore walls and the continuous deposition of graphene carbon layers blocked the pores and reduced the pore size. At the same time, the few-layer graphene-like nanodomains formed on the slit pore walls prevented the evaporation of gas during the pyrolysis process, thus forming closed pores inside the carbon material. The pore size distribution range of Example 4 was significantly smaller than that of Example 1. Due to excessive filling of nanodomains, the pore size of Example 4 decreased to less than 0.96 nm (the Stokes radius of Li + in carbonate-based electrolyte is about 0.48 nm), which hindered the solvated Li + from embedding into the micropores, resulting in a reduction in Li + intercalation and hindering the effective transport of dissolved Li + ions.

[0095] According to the infrared test results, obvious characteristic peaks of chlorinated hydrocarbons exist in PVC: the C-Cl stretching vibration peak between 600 and 640 cm -1 , the H-CCl deformation vibration peak near 1180 - 1350 cm -1 , the deformation vibration peak of -CH2 near 1433 cm -1 , and the stretching vibration peaks of H-C-H and C-H in Cl-C- near ~2906 cm -1 and 2967 cm -1 . After high-temperature carbonization, all the characteristic peaks of chlorinated hydrocarbons disappeared, and a bending vibration peak of C=C appeared near ~1670 cm -1 , indicating that all the chlorine in the molecular chain of Comparative Example 1 had been removed and there were conjugated carbon-carbon double bonds. With the introduction of the benzene structure, a shear vibration peak of R-C=CH- was observed near ~1350 cm -1 in Example 1. This shows that the electron rearrangement caused by the interaction between the π orbitals in the PVC-derived carbon layer and the electronic structure of the benzene structure is more conducive to retaining the sp 2 -C structure during the carbonization process, and the addition of aromatic additives is beneficial to generating more few-layer ordered graphene-like layers in the polyvinyl chloride-derived hard carbon.

[0096] (4) Conductivity test

[0097] At room temperature of 25 °C, the conductivity of the hard carbon materials prepared in Examples 1-4 and Comparative Example 1 was measured by pressing them into tablets. A certain amount of PVP was added as a binder when pressing into sheet-like samples, and then the resistance of the pressed tablet samples was measured by an ohmmeter. The conductivity is shown in Table 4.

[0098] R = ρ(L / πr 2 ); σ = 1 / ρ, where the resistance R (the BPC sheet resistance of the pressed tablet, unit: Ω) Measured by an ohmmeter; L (Tablet thickness, unit: m), measured using a vernier caliper; r (carbon sheet radius, unit: m), is fixed at 3×10 -3 m.

[0099] Table 4

[0100]

[0101] (5) Electrochemical performance test

[0102] The electrochemical performance of the PVC-derived highly conductive carbon series samples was studied by preparing them into button cells. 400 mg of the hard carbon materials prepared in Examples 1-8 and Comparative Example 1 were weighed respectively and used as the active electrode materials, 50 mg of conductive carbon black SuperP, and 50 mg of PVDF (mass ratio 8:1:1) were ground and mixed evenly, then added to the NMP solvent and dispersed evenly on a homogenizer to obtain the polyvinyl chloride-based highly conductive carbon slurry. The slurry was coated on the copper foil and dried overnight in a vacuum oven at 85 °C. Subsequently, the obtained electrode copper foil was cut into circular sheet-like battery electrode sheets with a diameter of 12 mm for standby, and the average mass loading was approximately 2 mg cm -2 .

[0103] The electrochemical test of the samples was carried out by assembling CR-2016 type button cells in an argon-filled glove box. The electrolyte used was LB046, and the specific formula was a mixed solution of 1 mol L -1 LiClO4 in ethylene carbonate EC / DEC (1:1 v / v), with 5 wt% FEC additive. A single layer of polypropylene PP was used as the battery separator, and a lithium metal sheet was used as the negative electrode. The charge-discharge test was carried out by a LAND CT2001A battery tester in the potential range of 0.001 - 3.0 V.

[0104] The hard carbon materials were made into electrodes, and their lithium storage performance was tested in a half-cell. Table 5 shows the first-cycle charge-discharge data of the hard carbon material negative electrode at a current density of 50 mAg -1 .

[0105] Table 5

[0106]

[0107]

[0108] Table 6

[0109]

[0110] According to the data in Table 5 and Table 6, Examples 1-8 show higher reversible specific capacities and better first-cycle Coulombic efficiencies compared to Comparative Example 1. The higher reversible specific capacities may be attributed to the presence of additional few-layer graphene-like nanodomains in their structures, while the better first efficiency may be attributed to their lower specific surface areas and significantly reduced defects, which reduce side reactions with the electrolyte. From the above physical property and structural characterizations, it can be seen that after introducing the benzene ring structure, the microstructure of the hard carbon material undergoes carbon layer reconstruction, growing more few-layer ordered graphene-like carbon layer structures. These ordered graphene microcrystalline carbon domains provide an electron transport network while the pores formed by the interlaced bent carbon layers and the ordered carbon layers also provide additional sites for lithium-ion insertion / extraction and lithium-ion storage, synergistically achieving an increase in capacity.

[0111] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that this is only for illustration purposes. The protection scope of the present invention is defined by the appended claims. Without departing from the principles and essence of the present invention, those skilled in the art can make various changes or modifications to these embodiments, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing a hard carbon material, characterized in that: It includes the following steps: (1) mixing a solution containing PVC and an aromatic compound 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%; the aromatic compound is an aromatic hydrocarbon and / or an aromatic hydrocarbon derivative, and the aromatic hydrocarbon derivative is an aromatic acid and / or a halogenated aromatic hydrocarbon; (2) grinding, washing and drying the xerogel to obtain a PVC dehalogenated precursor; (3) Carbonizing the PVC dehalogenated precursor to obtain the hard carbon material; the carbonization temperature is 700-1200° C., and the carbonization time is 1-4 hours.

2. The method for preparing a hard carbon material according to claim 1, characterized in that: The viscosity K value of the PVC is 50-80.

3. The method for preparing a hard carbon material according to claim 1, characterized in that: The aromatic hydrocarbons are monocyclic aromatic hydrocarbons and / or polycyclic aromatic hydrocarbons.

4. The method for preparing a hard carbon material according to claim 3, characterized in that: The monocyclic aromatic hydrocarbon is benzene or toluene.

5. The method for preparing a hard carbon material according to claim 3, characterized in that: The polycyclic aromatic hydrocarbons are non-condensed aromatic hydrocarbons and / or condensed aromatic hydrocarbons.

6. The method for preparing a hard carbon material according to claim 3, characterized in that: The polycyclic aromatic hydrocarbons are biphenyl or naphthalene.

7. The method for preparing a hard carbon material according to claim 1, characterized in that: The aromatic acid is benzoic acid.

8. The method for preparing a hard carbon material according to claim 1, characterized in that: The halogen in the halogenated aromatic hydrocarbon is one or more of F, Cl, Br and I.

9. The method for preparing a hard carbon material according to claim 1, characterized in that: The number of halogen atoms in the halogenated aromatic hydrocarbon is at least 1.

10. The method for preparing a hard carbon material according to claim 1, characterized in that: The halogenated aromatic hydrocarbon is a side chain halogenated aromatic hydrocarbon and / or an aromatic ring halogenated aromatic hydrocarbon.

11. The method for preparing a hard carbon material according to claim 10, characterized in that: The aromatic ring halogenated aromatic hydrocarbon is chlorobenzene or 1,2-dichlorobenzene.

12. The method for preparing a hard carbon material according to claim 1, characterized in that: The preparation method meets 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 that can dissolve PVC; (3) The ratio of the mass of the PVC to the volume of the solvent in the solution is 1: (20-40) g / mL.

13. The method for preparing a hard carbon material according to claim 1, characterized in that: The solvent in the solution is NMP.

14. The method for preparing a hard carbon material according to claim 1, characterized in that: The preparation method meets one or more of the following conditions: (1) In step (1), the method for preparing the solution containing PVC and an aromatic compound comprises the following process: stirring and mixing the PVC and a 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° C.; (3) In step (1), the mixing process includes: first stirring the solution containing PVC and aromatic compounds at 60-90° C. for 1-3 hours to obtain a sol, and then stirring the sol at 140-180° C. until the solvent is completely evaporated to obtain a dry gel.

15. The method for preparing a hard carbon material according to claim 1, characterized in that: In step (3), the carbonization temperature is 700-900°C; And / or, the carbonization time is 1-3h.

16. A hard carbon material, characterized in that: The hard carbon material is prepared according to the method for preparing the hard carbon material according to any one of claims 1 to 15.

17. The hard carbon material according to claim 16, characterized in that The hard carbon material satisfies one or more of the following conditions: (1) The interior of the hard carbon material has a few-layer graphene-like carbon layer structure; (2) The graphite interlayer spacing of the hard carbon material is 0.340-0.385 nm; (3) The pore size distribution range of the hard carbon material is 0.1-6 nm; (4) The specific surface area of ​​the hard carbon material is 1-5 m 2 / g; (5) I of the hard carbon material D / I G 0.948-1.05; (6) The electrical conductivity of the hard carbon material is 1.14-5Sm -1 ; (7) The hard carbon material is subjected to a current density of 50 mAg -1 The reversible specific capacity is 355-600 mAh g -1 ; (8) The hard carbon material is subjected to a current density of 50 mAg -1 The first-cycle Coulomb efficiency is 70%-85%; (9) The hard carbon material is subjected to a current density of 0.5 Ag. -1 The reversible specific capacity is 440-540 mAh g -1 ; (10) The hard carbon material is subjected to a current density of 0.5 Ag. -1 The capacity retention rate after 300 cycles is over 99%; (11) The hard carbon material is subjected to a current density of 1.5 Ag. -1 The reversible specific capacity is 120-210 mAh g -1 ; (12) The hard carbon material is subjected to a current density of 1.5 Ag. -1 The capacity retention rate after 1800 cycles is over 99%.

18. Use of the hard carbon material according to claim 16 or 17 in a battery.

19. A battery, characterized in that: It comprises the hard carbon material as claimed in claim 16 or 17.

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