Method for preparing porous carbon material through molten salt pyrolysis of waste PET, porous carbon material and application of porous carbon material

Abstract

The invention discloses a method for preparing a porous carbon material through molten salt pyrolysis of waste PET, the porous carbon material and application of the porous carbon material, a ZnCl2-NaCl-KCl ternary low-melting-point molten salt system is constructed, PET waste is induced in the environment to generate MOF intermediates in situ at a medium temperature, and the MOF intermediates are prepared into the porous carbon material. High-efficiency conversion from high-impurity and high-thermal-stability plastic waste to a highly-graphitized carbon material with an ordered structure is successfully realized, and a series of bottleneck problems of high pyrolysis temperature, poor carbon material performance, uncontrollable structure and the like in the prior art are solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of waste plastic resource utilization and lithium ion battery negative electrode material preparation, and particularly relates to a method for preparing porous carbon material by pyrolyzing waste PET in molten salt, the porous carbon material and application thereof. BACKGROUND

[0002] As a widely used polyester material, the annual output of polyethylene terephthalate (PET) has exceeded 25 million tons, accounting for about 6.2% of the total global plastic output. However, due to the problems of difficult efficient sorting, high cleaning cost and low additional value of PET waste, its recycling rate has always hovered around 20%, and most of it is still disposed of by landfill or incineration, not only wasting resources, but also causing serious carbon emissions and diffusion of persistent organic pollutants. With the promotion of the "double carbon" strategy and resource closed-loop system, how to efficiently convert a large amount of low-value PET waste into high-value-added materials has become a key direction that needs to be broken through in the field of green manufacturing and energy materials.

[0003] At present, the resource utilization of PET mainly includes physical regeneration and chemical depolymerization. The former is suitable for clean single plastic stream, but the mechanical properties of the product are declining, and it is trapped in the "downgrade utilization" dilemma; the latter such as alcoholysis, hydrolysis and other technologies can recover monomers, but the reaction conditions are harsh, the by-products are complex, and the energy consumption is high, which is difficult to adapt to large-scale promotion.

[0004] In recent years, pyrolysis has been widely used in recycling polyhydrocarbon plastics (such as PE, PP), but for PET, an oxygen-containing polyester, due to its low thermal conductivity (only about 0.15 W·m -1 ·K -1 ), high glass transition temperature, conventional pyrolysis needs to be treated at more than 600℃ for a long time, and the product is mostly disordered hard carbon with poor pore structure and conductivity, which seriously restricts its application performance as a battery carbon material. In addition, direct pyrolysis lacks a structure regulation mechanism, resulting in loose carbon material structure, unstable active sites, and lithium storage capacity generally below 400 mAh / g, far from meeting the comprehensive requirements of new energy vehicles and energy storage systems for high specific capacity, fast charging performance and long service life.

[0005] That is, the existing resource utilization technology for polyethylene terephthalate (PET) waste generally has the following defects and limitations:

[0006] 1. High pyrolysis energy consumption and carbon material structure degradation. The existing PET pyrolysis mostly uses conventional inert atmosphere high-temperature treatment, the temperature usually needs to exceed 600℃, and lacks a structure guiding mechanism, the product carbon material is mostly non-uniform hard carbon, which has problems such as low graphitization degree, poor porosity, unstable defects, etc., resulting in its electrical conductivity and lithium storage performance far lower than that of commercial graphite materials, poor cycle life and poor rate performance.

[0007] 2. Low thermal conduction efficiency and incomplete depolymerization. PET itself has low thermal conductivity, and uneven temperature conduction during pyrolysis process is easy to cause uneven distribution of carbonization reaction area, large difference in internal and external structure, and often contains coking residues in pyrolysis products, low carbon yield, poor repeatability, and difficult to industrialization.

[0008] 3. Lack of atomic structure control, unable to construct functional porous framework. In the traditional pyrolysis process, there is lack of structure guiding control means, which cannot guide the formation of ordered pore or molecular sieve-like framework structure, resulting in low specific surface area of the obtained carbon material, uncontrollable defect distribution, limited ion migration channel, and unable to effectively improve the lithium ion intercalation and deintercalation efficiency and cycle stability.

[0009] 4. Extremely high process temperature, high energy consumption and cost. Commercial synthetic graphite materials often require long time high temperature graphitization treatment above 2800℃, which has extremely high energy consumption and harsh equipment requirements, and is not conducive to large-scale green manufacturing. The existing technology for preparing graphite materials from waste plastics has not effectively reduced the carbonization temperature, and still cannot get rid of the high energy consumption limit. SUMMARY

[0010] This section is intended to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, the abstract and the title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0011] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0012] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art, and to provide a method for preparing porous carbon material by molten salt pyrolysis of waste PET.

[0013] To solve the above technical problems, the present application provides the following technical scheme: including,

[0014] The pretreated waste PET bottles are used as the original carbon source, and ZnCl2, NaCl and KCl are vacuum dried to obtain a uniform dry molten salt system;

[0015] The original carbon source is mixed with the molten salt system, and a intermediate is obtained by constant temperature reaction in an inert atmosphere;

[0016] The intermediate is subjected to high temperature carbonization reaction under argon protection, and the obtained carbon material is vacuum dried to obtain the porous carbon material.

[0017] As a preferred scheme of the method for preparing the porous carbon material by pyrolyzing the waste PET in the molten salt, the PET content of the waste PET bottle is greater than or equal to 70 wt%, and the impurity content is less than or equal to 5 wt%, and the impurities include PVC, PE and PP.

[0018] As a preferred scheme of the method for preparing the porous carbon material by pyrolyzing the waste PET in the molten salt, the mass ratio of ZnCl2, NaCl and KCl in the molten salt system is 5-7:1-3:1-3.

[0019] As a preferred scheme of the method for preparing the porous carbon material by pyrolyzing the waste PET in the molten salt, the temperature for vacuum drying of ZnCl2, NaCl and KCl is 100-140 DEG C.

[0020] As a preferred scheme of the method for preparing the porous carbon material by pyrolyzing the waste PET in the molten salt, the mixing mass ratio of the original carbon source and the molten salt system is 1:3-5.

[0021] As a preferred scheme of the method for preparing the porous carbon material by pyrolyzing the waste PET in the molten salt, the reaction temperature of the constant temperature reaction is 250-350 DEG C, and the reaction time is 4-12 h.

[0022] As a preferred scheme of the method for preparing the porous carbon material by pyrolyzing the waste PET in the molten salt, the heating rate of the high-temperature carbonization reaction is 2-10 DEG C / min, preferably 5 DEG C / min, the reaction temperature is 700-900 DEG C, and the time is 0.5-3 h, preferably 2 h.

[0023] As a preferred scheme of the method for preparing the porous carbon material by pyrolyzing the waste PET in the molten salt, the temperature for vacuum drying of the carbon material is 65-75 DEG C, and the time is 10-14 h.

[0024] The purpose of the present application is to overcome the deficiencies in the prior art, and provide a porous carbon material prepared by pyrolyzing waste PET in a molten salt and its application as a negative electrode material for lithium ion batteries.

[0025] The present application has the following advantages:

[0026] 1. Improve the thermal efficiency and carbon yield of the PET pyrolysis process, by constructing a ZnCl2-NaCl-KCl molten salt system with high thermal conductivity and low melting point, significantly improving the uniformity and reaction rate of pyrolysis, promoting uniform polymer cracking, and improving the yield and structural consistency of the carbon material.

[0027] 2. Construct a MOF-like intermediate structure induced by medium temperature, use Zn 2+The coordination reaction with TPA generates MOF-5-like structure skeleton at 300℃, providing a structure template for subsequent carbonization, and realizing in-situ construction of porous conductive network and nanometer layered skeleton.

[0028] 3. The preparation of graphitized high-performance carbon materials at ≤800℃ conditions effectively retains the hierarchical pore structure derived from MOFs and improves the graphitization degree of carbon materials, avoiding traditional high-temperature graphitization processes, reducing energy consumption and carbon footprint.

[0029] 4. Significantly improving the electrochemical performance of carbon materials in lithium-ion batteries, including high specific capacity (600-900 mAh / g), long life (more than 1000 cycles), high rate response (stable cycling at multiple current densities) and low impedance characteristics, meeting the comprehensive requirements of high-performance energy storage applications. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

[0031] Figure 1 Flow chart for preparing porous carbon materials from waste PET by molten salt pyrolysis according to the present application.

[0032] Figure 2 SEM image of the intermediate P-300-M prepared in Example 1 of the present application.

[0033] Figure 3 XRD pattern of the carbon materials prepared in Example 1-Example 3 and Comparative Example 1 of the present application.

[0034] Figure 4 Raman pattern of the carbon materials prepared in Example 1-Example 3 and Comparative Example 1 of the present application.

[0035] Figure 5 Electrochemical performance test result graph of the carbon material prepared in Example 1 of the present application.

[0036] Figure 6 Light-emitting effect graph of the full cell assembled by the carbon material prepared in Example 1 of the present application after series-parallel connection driving LED light strip. DETAILED DESCRIPTION

[0037] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below.

[0038] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details set forth in this description. In other instances, well-known methods have not been described in detail in order not to unnecessarily obscure aspects of the present application.

[0039] It is also noted that, as used herein, "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation of the application. The appearances of the phrase "in one embodiment" or "in an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.

[0040] The raw materials used in the present application are commercially available unless otherwise specified. The waste PET bottles are solid materials with PET (polyethylene terephthalate) as the main component, such as food-grade or beverage bottle recyclates, with a PET content of ≥70 wt%, allowing the presence of common processing aids or colorants, and a total impurity content (such as PVC, PE, PP) of ≤5 wt%. After washing, drying, removing bottle caps and labels, the PET bottle bodies are cut into 2-5 mm wide long strip solids as the original carbon source.

[0041] Example 1

[0042] Reference Figure 1 The present embodiment provides a method for preparing a porous carbon material by pyrolyzing waste PET in a molten salt. Specifically,

[0043] 1) The waste PET bottles are washed, dried, and then cut into 2-5 mm wide long strip solids as the original carbon source;

[0044] 2) Three inorganic salts, ZnCl2, NaCl, and KCl, are weighed according to a mass ratio of 6:2:2, mixed, and then vacuum dried at 120°C for 5h to remove adsorbed water, obtaining a uniform dry molten salt system;

[0045] 3) The original carbon source PET raw material is mixed with the dry molten salt system in a mass ratio of 1:4 in a porcelain boat, and placed in a sealed muffle furnace with inert atmosphere protection, and reacted at 300°C for 10 hours under constant temperature conditions, obtaining an intermediate, denoted as P-300-M. Figure 2 The SEM image of P-300-M shows that the surface has a flaky layered structure, containing organic residues, Zn-O coordination bonds, and typical MOF-5 derived morphology.

[0046] The pyrolysis temperature in this step is significantly lower than the conventional plastic pyrolysis temperature, but with the help of the high thermal conductivity, excellent fluidity, and ion coordination ability of the molten salt system, Zn 2+The terephthalic acid (TPA) monomer released in the PET pyrolysis process can be coordinated at low temperature to form a MOF-5 (metal organic framework) type intermediate with a crystal structure in situ, and a Zn4O(CO2-TPA)6 type topological structure is constructed, which provides a micro-skeletal template for subsequent directional carbonization. In this process, the molten salt not only acts as a heat carrier and solvent, but also physically limits the migration and aggregation of the skeletal structure, prevents the structure from collapsing, and promotes the formation of uniform pores.

[0047] 4) The intermediate P-300-M is transferred to a tube furnace, heated to 800°C at a heating rate of 5°C / min under argon protection, and kept at this temperature for 2 hours to realize carbonization, and the obtained carbon material is dried in a vacuum drying box at a temperature of 70°C for 12h, and the finally obtained carbon material is named as P-800-M.

[0048] Example 2

[0049] The difference between this example and Example 1 is that the carbonization temperature in step 4) is adjusted to 700°C, and the rest of the process steps are referred to Example 1, and the carbon material of this example is obtained, which is named as P-700-M.

[0050] Example 3

[0051] The difference between this example and Example 1 is that the carbonization temperature in step 4) is adjusted to 900°C, and the rest of the process steps are referred to Example 1, and the carbon material of this example is obtained, which is named as P-900-M.

[0052] Comparative Example 1

[0053] The difference between this example and Example 1 is that no molten salt is added, and the PET is directly subjected to carbonization pyrolysis treatment at 800°C, and the carbon material of this example is obtained, which is named as P-800-D.

[0054] The carbon materials of Example 1-Example 3 and Comparative Example 1 are characterized, and the results are shown in Figure 3 、 Figure 4 , Figure 3 is the XRD pattern of the carbon material, Figure 4 is the Raman pattern of the carbon material, it can be seen that the carbon material prepared in the examples of the present application has obvious structural characteristics superior to conventional pyrolytic carbon (Comparative Example 1), the interlayer spacing is reduced to 0.435 nm, the XRD analysis shows that the (002) diffraction peak approaches the standard graphite 26.5°, the D / G peak intensity ratio in the Raman spectrum is significantly reduced, indicating that it has a high degree of carbon atom order and good conductivity. At the same time, the carbon material retains the microporous and mesoporous network derived from the MOF structure, which is beneficial to the rapid migration and effective storage of lithium ions in the electrode.

[0055] Electrochemical performance testing verified the results as follows: Figure 5 As shown, this material exhibits an initial specific capacity of up to 900 mAh / g at a current density of 0.1 A / g. Figure 5 A), after stable cycling, it still maintains above 600mAh / g ( Figure 5 B), after 1000 cycles at a rate of 0.5A / g, its capacity retention rate reached 99.72% ( Figure 5 C), far exceeding commercial graphite (approximately 372 mAh / g) and conventional hard carbon control samples.

[0056] Applications as a negative electrode material for lithium-ion batteries

[0057] Negative electrode preparation: The prepared porous carbon material, Super P conductive agent and PVDF binder are mixed in a mass ratio of 8:1:1, and an appropriate amount of NMP solvent is added to form a uniform slurry. The slurry is coated on a copper foil current collector, dried under vacuum at 80°C for 12 hours, rolled into shape, and punched for later use.

[0058] Positive electrode preparation: Commercially available LiFePO4 positive electrode material was selected and mixed with Super P and PVDF at a mass ratio of 9:0.5:0.5 to prepare a slurry. The slurry was coated on an aluminum foil current collector, dried under vacuum at 80°C for 12 hours, and then rolled and stamped.

[0059] Battery assembly: The negative and positive electrodes prepared above are used as the positive and negative electrodes, respectively, with a polypropylene membrane (Celgard 2400) as the separator and a 1 mol·L⁻¹ electrolyte. -1 LiPF6 / EC:DEC:DMC (1:1:1, volume ratio) were assembled into button or pouch cells in an argon-protected glove box.

[0060] The assembled full battery exhibited stable charge-discharge curves when tested at a 0.1C rate, with an initial discharge specific capacity of approximately 150 mAh·g. -1 (Measured by the positive electrode).

[0061] like Figure 6 As shown, after being connected in series and parallel, the battery can drive an LED light strip containing 60 LED beads to light up stably, which intuitively proves the feasibility of the carbon material prepared by this invention in lithium-ion batteries.

[0062] Example 3

[0063] 1) After washing and drying the waste PET bottles, cut them into strips 2-5 mm wide as the original carbon source;

[0064] 2) ZnCl2, NaCl and KCl were weighed with a mass ratio of 6.5:1.5:2, respectively, and mixed, and then vacuum dried at 120°C for 5h to remove adsorbed water, to obtain a uniform dry molten salt system;

[0065] 3) The original carbon source PET raw material and the dry molten salt system were mixed in a mass ratio of 1:5 in a porcelain boat, and placed in a sealed muffle furnace with inert atmosphere protection, and reacted at 280°C for 12 hours, to obtain an intermediate, denoted as P-280-M.

[0066] 4) The intermediate P-280-M was transferred to a tube furnace, heated to 780°C at a heating rate of 4°C / min under argon protection, and kept at this temperature for 2 hours to realize carbonization, and the obtained carbon material was dried in a vacuum drying oven at a temperature of 75°C for 10h, and the final obtained carbon material was named as P-780-M.

[0067] Example 4

[0068] 1) The waste PET bottle was washed and dried, and then cut into a long strip solid with a width of 2-5mm as the original carbon source;

[0069] 2) ZnCl2, NaCl and KCl were weighed with a mass ratio of 5.5:2.5:2, respectively, and mixed, and then vacuum dried at 120°C for 5h to remove adsorbed water, to obtain a uniform dry molten salt system;

[0070] 3) The original carbon source PET raw material and the dry molten salt system were mixed in a mass ratio of 1:3 in a porcelain boat, and placed in a sealed muffle furnace with inert atmosphere protection, and reacted at 320°C for 8 hours, to obtain an intermediate, denoted as P-320-M.

[0071] 4) The intermediate P-320-M was transferred to a tube furnace, heated to 820°C at a heating rate of 6°C / min under argon protection, and kept at this temperature for 1.5 hours to realize carbonization, and the obtained carbon material was dried in a vacuum drying oven at a temperature of 65°C for 14h, and the final obtained carbon material was named as P-820-M.

[0072] The carbon materials prepared in Examples 2-3 were tested for electrochemical performance under the same conditions as Example 1, and compared with Example 1, and the results are shown in Table 1.

[0073] Table 1

[0074] Initial specific capacity / mAh.g -1 ]] Capacity retention after 1000 cycles / % Example 1 900 99.72 Example 3 610 99 Example 4 590 98.8

[0075] As can be seen from Table 1, the related performance of the carbon materials obtained in Examples 3 and 4 is slightly lower than that of Example 1, but is still significantly better than that of commercial graphite.

[0076] Comparative Example 2

[0077] The difference between this comparative example and Example 1 is that the molten salt system in step 2) is adjusted to be NaCl and KCl with a mass ratio of 1:1, and the remaining steps are all referred to Example 1.

[0078] The result is that no MOF-5-like intermediate is generated, the SEM shows disordered particles, and the specific capacity of the prepared carbon material is only 250 mAh·g -1 , and the cycle performance is poor.

[0079] Comparative Example 3

[0080] The difference between this comparative example and Example 1 is that the molten salt system in step 2) is adjusted to be ZnCl2 and NaCl with a mass ratio of 6:2, and the mixing ratio of the raw carbon source PET raw material to the molten salt system in step 3) is 7:3, and the remaining steps are all referred to Example 1.

[0081] The result is that the MOF-5-like intermediate obtained has no obvious lamellar structure, the pore size distribution is uneven, and the specific capacity of the carbon material prepared subsequently is 380 mAh·g -1 , and the rate performance is reduced

[0082] Comparative Example 4

[0083] The difference between this comparative example and Example 1 is that the molten salt system in step 2) is adjusted to be NaNO3:KNO3 with a mass ratio of 1:1, and the remaining steps are all referred to Example 1.

[0084] The carbon source treated under the molten salt conditions in this comparative example cannot form a MOF-5-like intermediate in the low-temperature reaction, the specific surface area of the product is low, the specific capacity is only 300 mAh·g -1 , and the cycle life is only maintained at 80%.

[0085] Comparative Example 5

[0086] The difference between this comparative example and Example 1 is that the ternary molten salt system in step 2) is adjusted to be ZnCl2, NaCl and KCl with a mass ratio of 7.5:1:1.5, and the remaining steps are all referred to Example 1.

[0087] The result is that the MOF-5-like intermediate obtained is not complete, the lamellar structure is broken, the BET specific surface area of the prepared carbon material is about 800 m 2 / g, the initial specific capacity at a current density of 0.1 A / g is 620 mAh·g -1， , and the specific capacity after 100 cycles is 430 mAh·g -1 , and the cycle retention rate is less than 75%.

[0088] Comparative Example 6

[0089] The difference between the present comparative example and example 1 is that the ternary molten salt system of step 2) is adjusted to ZnCl2, NaCl and KCl with a mass ratio of 4:3:3, and the rest of the process steps refer to example 1.

[0090] Zn 2+ The concentration is insufficient, and the MOF-5 type intermediate cannot be continuously generated during the low-temperature induction process. The product has loose pore structure, single average pore size, and the specific surface area of the prepared carbon material is about 700 m 2 / g, and the initial specific capacity at a current density of 0.1 A / g is 580 mAh·g -1， The specific capacity after 100 cycles is 400 mAh·g -1 , and the cycle retention rate is less than 70%.

[0091] Comparative example 7

[0092] The difference between the present comparative example and example 1 is that the KCl in the ternary molten salt system of step 2) is KF, and the rest of the process steps refer to example 1.

[0093] The results show that the fluorine ion in the molten salt system of the present comparative example triggers a side reaction during the medium-temperature induction stage, resulting in the failure of the MOF-5 type intermediate to be stably formed, and the BET specific surface area of the finished product porous carbon decreases to 750 m 2 / g, and the initial specific capacity at a current density of 0.1 A / g is 600 mAh·g -1， The specific capacity after 100 cycles is 420 mAh·g -1 , and the cycle retention rate is less than 78%.

[0094] In summary, the present application successfully realizes the efficient conversion of high-impurity, heat-stable plastic waste to structure-ordered, high-graphitized carbon material by constructing a ZnCl2-NaCl-KCl ternary low-melting point molten salt system and inducing the in-situ generation of MOF type intermediates from PET waste at medium temperature in this environment, overcoming a series of bottleneck problems such as high pyrolysis temperature, poor carbon material performance, and uncontrollable structure in the prior art.

[0095] Firstly, in terms of heat conduction efficiency, compared with the conventional inert atmosphere direct pyrolysis method, the present application significantly improves the heat uniformity and heat conduction rate during the pyrolysis reaction process by using the ZnCl2-dominated molten salt system. Since the thermal conductivity of PET itself is extremely low, traditional pyrolysis often leads to carbon skeleton aggregation, dense structure and limited porosity, resulting in small specific surface area of carbon material, poor electrical conductivity, and unstable yield. In the present application, the high heat capacity and ionic medium characteristics of the molten salt effectively improve the local heat energy utilization rate and prevent the structure from collapsing and particle aggregation during carbonization, thereby achieving uniform control of the microstructure and significant improvement of the product quality.

[0096] Secondly, in terms of carbon structure construction, the application introduces Zn 2+ The MOF-5 type metal organic framework intermediate is formed by coordination reaction with terephthalic acid (TPA) generated by PET pyrolysis at low temperature. After carbonization in a molten salt confined environment, the intermediate can effectively retain the layered structure and ordered channels, and obtain higher graphitization degree (XRD diffraction peak close to 26.5°, and Raman ID / IG value significantly reduced) than conventional pyrolytic carbon, the interlayer spacing is reduced to 0.435 nm, and the hierarchical pore distribution is maintained. The structural advantages significantly improve the lithium ion diffusion rate and electronic conduction capacity of the material, which directly translates into more excellent electrochemical performance.

[0097] In terms of energy consumption control, the application performs MOF induction reaction at 250-350℃ and carbonization treatment at 700-900℃, which is significantly lower than the high-temperature sintering process of 2800℃ required by traditional graphite material preparation, reduces the energy consumption level by more than 90%, shortens the carbonization time, reduces the process steps, and improves the overall energy utilization efficiency and the green sustainability of the preparation process. The molten salt itself can be recycled and used, without secondary pollution, and has good environmental friendliness.

[0098] In terms of battery performance, the prepared carbon material shows significantly higher specific capacity and cycle stability than graphite in lithium ion battery half-cell tests. The initial capacity is as high as 900mAh / g, and the stable capacity is maintained at more than 600mAh / g; after 1000 cycles at a current density of 0.5A / g, the capacity retention rate is still as high as 99.72%, which is much better than traditional hard carbon materials. Its good rate performance and low resistance characteristics also ensure stable operation under high-power load conditions. In addition, the prepared carbon material also shows excellent cycle performance and LED lighting ability in actual full cells (matched with LiFePO4 positive electrode), which verifies its application feasibility and engineering conversion potential in actual energy storage systems.

[0099] The application not only realizes overall surpassing of the prior art in terms of structure control, performance improvement, energy consumption reduction and resource utilization rate, but also establishes a new path for recycling plastic solid waste with high engineering adaptability, green low carbon and economic efficiency, which has significant technical popularization value and environmental governance significance.

[0100] It should be noted that the above examples are only used to illustrate the technical solutions of the application and are not limiting. Although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the application, which should be covered in the scope of the claims of the application.

Claims

1. A method for preparing porous carbon materials by molten salt pyrolysis of waste PET, characterized in that: include, Waste PET bottles were pretreated and used as the original carbon source. ZnCl2, NaCl and KCl were vacuum dried to obtain a uniformly dried molten salt system. The original carbon source is mixed with a molten salt system and reacted at an inert atmosphere at a constant temperature to obtain an intermediate. The intermediate is subjected to a high-temperature carbonization reaction under argon protection, and the resulting carbon material is vacuum dried to obtain porous carbon material.

2. The method for preparing porous carbon materials by molten salt pyrolysis of waste PET as described in claim 1, characterized in that: The waste PET bottles have a PET content of ≥70wt% and an impurity content of ≤5wt%, including PVC, PE, and PP.

3. The method for preparing porous carbon materials by molten salt pyrolysis of waste PET as described in claim 1, characterized in that: The mass ratio of ZnCl2, NaCl and KCl in the molten salt system is 5-7:1-3:1-3.

4. The method for preparing porous carbon materials by molten salt pyrolysis of waste PET as described in claim 3, characterized in that: The vacuum drying temperature for ZnCl2, NaCl, and KCl is 100–140 °C.

5. The method for preparing porous carbon materials by molten salt pyrolysis of waste PET as described in claim 3, characterized in that: The mass ratio of the original carbon source to the molten salt system is 1:3 to 5.

6. The method for preparing porous carbon materials by molten salt pyrolysis of waste PET as described in claim 1, characterized in that: The isothermal reaction is carried out at a temperature of 250–350°C for 4–12 hours.

7. The method for preparing porous carbon materials by molten salt pyrolysis of waste PET as described in claim 1, characterized in that: The heating rate of the high-temperature carbonization reaction is 2-10℃ / min, the reaction temperature is 700-900℃, and the time is 0.5-3h.

8. The method for preparing porous carbon materials by molten salt pyrolysis of waste PET as described in claim 7, characterized in that: The carbon material is vacuum dried at a temperature of 65–75°C for 10–14 hours.

9. Porous carbon materials prepared by the method described in any one of claims 1 to 8.

10. The application of the porous carbon material as described in claim 9 as a negative electrode material for lithium-ion batteries.

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