Application of lithium iron phosphate reclaimed material and method for preparing oil by catalyzing waste plastics

Abstract

The invention relates to the technical field of waste resource utilization, in particular to application of a lithium iron phosphate recycled material and a method for preparing oil by catalyzing waste plastics. The method comprises the steps that firstly, electrolyte and a binding agent left on a waste positive plate are removed through segmented pyrolysis, and the lithium iron phosphate recycled material is obtained; and doping transition metal components to prepare a catalyst for catalyzing the waste plastics to prepare high-value oil products. According to the waste lithium iron phosphate battery, the lithium iron phosphate positive electrode waste is recycled and converted into the catalyst, the cost advantage is better achieved, high-value oil products are prepared by introducing transition metal elements, cooperating with iron elements in the battery waste and catalyzing waste plastics, and the value of waste utilization is maximized.

Description

Technical Field

[0001] The invention relates to the technical field of waste resource utilization, and in particular to uses of lithium iron phosphate recycled materials and a method for catalyzing waste plastics to produce oil. Background Art

[0002] Due to the increasing annual production and sales of new energy vehicles, there is an urgent need to safely and efficiently handle the rapidly growing retired lithium batteries. With the popularization of electric vehicles, the amount of scrapped lithium batteries is increasing, and the demand and ownership of lithium batteries will increase day by day in recent years. At the same time, the number of scrapped lithium iron phosphate batteries is also rising year by year. Lithium iron phosphate batteries are an ideal power lithium battery material due to their wide source of raw materials, outstanding safety performance, good cycle performance, good thermal stability, low cost, and no environmental pollution. However, if not properly handled, it will still cause serious environmental problems. At present, the main method for lithium battery treatment is recycling, using wet or pyrometallurgical recovery, but the recycling process is complicated, wet recycling will produce a large amount of waste liquid and consume solvents, and pyrometallurgical recovery consumes huge energy.

[0003] The resource recovery of waste lithium iron phosphate cathode materials is mainly based on wet processes, which leach out the metal ions in the waste materials and then separate them through step-by-step precipitation to convert them into industrial raw materials such as iron phosphate, iron hydroxide, lithium carbonate, and lithium phosphate with higher purity. After the waste lithium iron phosphate cathode materials are recycled, their electrochemical properties can be further improved through modification, so that their performance is close to or reaches the level of new batteries, so that they can be used again in battery manufacturing. The recycling and reuse of waste lithium iron phosphate cathode materials not only helps to protect the environment, but also brings significant economic benefits. Therefore, how to recycle and reuse the waste lithium iron phosphate cathode materials is a hot issue.

[0004] Plastics (such as polyethylene, polypropylene, polyvinyl chloride and other polymer materials) have the advantages of low price and simple processing process, and are widely used in various production and life fields. The output of plastic products has been in a state of growth, and the amount of waste plastics has also been rising. However, since many plastic products are difficult to decompose under natural conditions, they also cause serious white pollution after being discarded. At present, the more convenient and simple operation in the waste plastic treatment method is direct landfill and incineration, but the incineration treatment method will seriously pollute the air and soil environment, and the landfill treatment will waste precious land resources. The technology of re-oiling waste plastics can better alleviate the pollution problem of the environment in the waste plastic treatment process, and the re-oiling of waste plastics can obtain organic hydrocarbon liquids with high application value and economic value. However, the catalysts used in the re-oiling of waste plastics are mostly precious metal catalysts, such as Ru-based, Pt-based catalysts, etc., which are costly. How to use the discarded lithium iron phosphate positive electrode material and waste plastics for organic resource utilization is a technical problem to be solved by the present invention. Summary of the invention

[0005] In order to solve the above technical problems, the use of lithium iron phosphate recycling materials and the method of catalyzing waste plastics to produce oil are provided. The present invention does not require the complicated and energy-intensive recycling process of waste lithium iron phosphate. Relatively pure waste lithium iron phosphate positive electrode materials can be obtained by pyrolysis, and the waste plastics can be used as catalysts to catalyze the conversion of high-value oil products.

[0006] In order to achieve the above objectives, the present invention is implemented by the following technical solutions:

[0007] The use of lithium iron phosphate recycled materials includes the following steps:

[0008] S1, removing residual electrolyte and binder between positive electrode waste and current collector by segmented pyrolysis of positive electrode sheets disassembled from waste lithium-ion batteries, and collecting positive electrode waste separated from the positive electrode sheets as lithium iron phosphate recovery material;

[0009] S2. The lithium iron phosphate recovered material is doped with transition metal elements and used as a catalyst in a waste plastic oil production process.

[0010] Furthermore, the process of the segmented pyrolysis is: heating the temperature to 200-300°C at a heating rate of 1-10°C / min and keeping it for 20-60min to remove the residual electrolyte, and then heating the temperature to 500-600°C at a heating rate of 1-10°C / min in an inert gas atmosphere and keeping it for 0.5-2h to remove the binder (mainly PVDF binder), so as to separate the positive electrode waste and the current collector.

[0011] Preferably, the process of staged pyrolysis is: heating to 250°C at a heating rate of 5°C / min and keeping warm for 40 minutes to remove residual electrolyte, and then heating to 550°C at a heating rate of 5°C / min and keeping warm for 1 hour in an inert gas atmosphere.

[0012] Furthermore, the transition metal element is selected from one or more of nickel, iron, chromium, chromium, cobalt, copper, zinc, titanium and vanadium.

[0013] Furthermore, the catalyst is recycled lithium iron phosphate doped with nickel.

[0014] Furthermore, the preparation process of the catalyst includes the following steps: impregnating the lithium iron phosphate recycled material with a nickel salt aqueous solution, then drying it, placing it in a tubular furnace and calcining it under a reducing atmosphere to obtain a lithium iron phosphate recycled material doped with nickel catalyst, wherein the nickel element accounts for 5-20wt% of the overall catalyst.

[0015] Preferably, the nickel salt in the nickel salt aqueous solution is selected from one of nickel sulfate, nickel chloride, nickel acetate and nickel nitrate.

[0016] Preferably, the reducing atmosphere is a mixed gas of nitrogen and hydrogen, wherein the volume proportion of the hydrogen in the mixed gas is 3-10%; the calcination treatment is performed by heating the temperature to 400-600° C. at a heating rate of 1-10° C. / min and keeping the temperature for 2-4 hours.

[0017] Another aspect of the present invention provides a method for catalyzing waste plastics to produce oil, comprising the following steps:

[0018] The lithium iron phosphate recycled material obtained in the above-mentioned use of lithium iron phosphate recycled material is doped with transition metal elements as a catalyst, placed in an intermittent hydrothermal reactor with waste plastics and solvent, mixed evenly and then sealed, and filled with inert gas for multiple times at room temperature to exclude the air in the reactor, and the temperature is increased to perform cracking reaction. After the reaction is completed, it is cooled, the reaction mixture in the reactor is taken out and extracted at room temperature, and then the solid-liquid is separated, and the liquid part is rotary evaporated to recover the extractant and the solvent, and the oil product is obtained after rotary evaporation.

[0019] Furthermore, the waste plastic is selected from polyolefin waste, such as polyethylene, polypropylene, etc.; the solvent is selected from one or more of methanol, ethanol, and isopropanol, and the solvent is used to provide the reducing gas hydrogen required in the cracking reaction; the usage ratio of the waste plastic, the catalyst, and the solvent is 5g:5-15g:0.2-0.5L.

[0020] Furthermore, the cleavage reaction is carried out at a temperature of 250-400°C for at least 10 hours; preferably, the cleavage reaction is carried out at a temperature of 280-380°C for 12-24 hours; the extractant used in the room temperature extraction is dichloromethane; and the rotary evaporation temperature is in the range of 40-45°C.

[0021] Beneficial technical effects:

[0022] The present invention utilizes the cathode material of discarded lithium iron phosphate batteries as a catalyst, thereby avoiding the cumbersome and complicated recycling process of discarded lithium iron phosphate cathode materials, which not only consumes high energy and a large amount of solvents, but also pollutes the environment. Converting the cathode material into a catalyst has a greater cost advantage.

[0023] The present invention uses the iron element contained in the lithium iron phosphate recycled material obtained from the discarded lithium ion battery, dopes the lithium iron phosphate recycled material with non-precious metal nickel, and introduces the nickel element to cooperate with the iron element in the waste material. The two act as efficient catalytic Ni-Fe components to catalyze the production of oil from waste plastics, thereby obtaining high-value oil products, maximizing the value of waste utilization, and making the best use of waste. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Unless otherwise specifically stated, the numerical value set forth in these embodiments does not limit the scope of the present invention. The technology and method known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology and method should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values.

[0026] The experimental methods in the following examples without specifying specific conditions are usually measured in accordance with national standards; if there is no corresponding national standard, the method is carried out in accordance with the general standard requirements or general methods.

[0027] Example 1

[0028] The use of lithium iron phosphate recycled materials includes the following steps:

[0029] S1. Dismantle the waste lithium-ion battery to obtain the positive electrode sheet, take 20g of the positive electrode sheet, put it into a crucible, put it into a tubular furnace for pyrolysis, introduce inert gas argon, heat it to 250℃ at a heating rate of 5℃ / min and keep it warm for 40min, then heat it to 550℃ at a heating rate of 5℃ / min and keep it warm for 1h in an inert gas argon atmosphere. After the pyrolysis is completed, it is observed that the positive electrode waste and the current collector on the positive electrode sheet are not completely separated. The separated positive electrode waste is collected, and the obtained positive electrode waste is a relatively pure lithium iron phosphate recovery material (purity>98wt%, wherein the iron content is>34wt%);

[0030] S2. Doping the recycled lithium iron phosphate with nickel and using it as a catalyst in the process of making oil from waste plastics;

[0031] The preparation process of the catalyst comprises the following steps: 1 g of nickel sulfate is dissolved in 20 mL of deionized water to prepare a nickel sulfate aqueous solution, which is then impregnated onto 4 g of the powder of the lithium iron phosphate recovery material obtained in S1, dried overnight in an oven at 80° C., then placed in a tube furnace, heated to 500° C. at a heating rate of 5° C. / min, and introduced with 5% H 2 -95%N 2(volume ratio) reducing protective gas, calcined at 500°C for 3h, taken out after cooling, and obtained lithium iron phosphate recycled material doped nickel catalyst (nickel element accounts for 8.67wt%), this catalyst is recorded as M1.

[0032] Example 2

[0033] The use of lithium iron phosphate recycled materials includes the following steps:

[0034] S1, same as S1 in Example 1;

[0035] S2. Doping the recycled lithium iron phosphate with nickel and using it as a catalyst in the process of making oil from waste plastics;

[0036] The preparation process of the catalyst comprises the following steps: 1 g of nickel chloride is dissolved in 20 mL of deionized water to prepare a nickel chloride aqueous solution, which is then impregnated onto 4 g of the powder of the lithium iron phosphate recovery material obtained in S1, dried overnight in an oven at 80° C., then placed in a tube furnace, heated to 500° C. at a heating rate of 5° C. / min, and introduced with 5% H 2 -95%N 2 (volume ratio) reducing protective gas, calcined at 500°C for 3h, taken out after cooling, and obtained lithium iron phosphate recycled material doped with nickel catalyst (nickel element accounts for 10.18wt%), this catalyst is recorded as M2.

[0037] Example 3

[0038] The use of lithium iron phosphate recycled materials includes the following steps:

[0039] S1, same as S1 in Example 1;

[0040] S2. Doping the recycled lithium iron phosphate with nickel and using it as a catalyst in the process of making oil from waste plastics;

[0041] The preparation process of the catalyst comprises the following steps: 1 g of nickel acetate is dissolved in 20 mL of deionized water to prepare a nickel acetate aqueous solution, which is then impregnated onto 4 g of the lithium iron phosphate recovered material powder obtained in S1, dried overnight in an oven at 80° C., then placed in a tube furnace, heated to 500° C. at a heating rate of 5° C. / min, and introduced with 5% H 2 -95%N 2 (volume ratio) reducing protective gas, calcined at 500°C for 3h, taken out after cooling, and obtained lithium iron phosphate recycled material doped with nickel catalyst (nickel element accounts for 5.57wt%), this catalyst is recorded as M3.

[0042] Example 4

[0043] The use of lithium iron phosphate recycled materials includes the following steps:

[0044] S1, same as S1 in Example 1;

[0045] S2. Doping the recycled lithium iron phosphate with nickel and using it as a catalyst in the process of making oil from waste plastics;

[0046] The preparation process of the catalyst comprises the following steps: 1 g of nickel nitrate is dissolved in 20 mL of deionized water to prepare a nickel nitrate aqueous solution, which is then impregnated onto 4 g of the powder of the lithium iron phosphate recovery material obtained in S1, dried overnight in an oven at 80° C., then placed in a tube furnace, heated to 500° C. at a heating rate of 5° C. / min, and introduced with 5% H 2 -95%N 2 (volume ratio) reducing protective gas, calcined at 500°C for 3h, taken out after cooling, and obtained lithium iron phosphate recycled material doped nickel catalyst (nickel element accounts for 7.44wt%), this catalyst is recorded as M4.

[0047] Example 5

[0048] The method for catalyzing waste plastics to produce oil comprises the following steps:

[0049] Take 2.5 mL of methanol as solvent, place 50 mg of waste plastic HDPE and 60 mg of lithium iron phosphate recycled material doped with nickel catalyst M1 in an intermittent hydrothermal reactor, mix them evenly and seal them, and fill in inert gas Ar three times at room temperature to exclude the air in the reactor, heat it to 290 ° C and carry out cracking reaction for 12 hours; after the reaction, cool the reactor in ice water, take out the reaction mixture in the reactor and add 5 mL of extractant dichloromethane to extract at room temperature for 40 minutes, and then perform solid-liquid separation. The extractant and the solvent were recovered from the obtained liquid portion by rotary evaporation at 42°C, and the remainder was the oil obtained by the reaction. The types of products were detected by GCMS, and the total yield of the obtainable oil was 20.47% (C5-C22, straight-chain alkanes), of which the gasoline yield was 4.47% (C5-C12), the aviation fuel yield was 11.83% (C8-C16), the diesel yield was 17.56% (C10-C22), and the lubricating oil yield was 3.85% (C22-C25).

[0050] Example 6

[0051] The method for catalyzing waste plastics to produce oil comprises the following steps:

[0052] Take 2.5 mL of ethanol as a solvent, place 50 mg of waste plastic HDPE and 80 mg of lithium iron phosphate recycled material doped with nickel catalyst M2 in an intermittent hydrothermal reactor, mix them evenly and seal them, and fill them with inert gas Ar three times at room temperature to exclude the air in the reactor, heat it to 320 ° C and carry out cracking reaction for 18 hours; after the reaction, cool the reactor in ice water, take out the reaction mixture in the reactor and add 5 mL of extractant dichloromethane to extract at room temperature for 40 minutes, and then perform solid-liquid separation. The extractant and the solvent were recovered from the obtained liquid portion by rotary evaporation at 42°C, and the remainder was the oil obtained by the reaction. The types of products were detected by GCMS, and the total yield of the obtainable oil was 34.20% (C5-C22, straight-chain alkanes), of which the gasoline yield was 6.46% (C5-C12), the aviation fuel yield was 15.28% (C8-C16), the diesel yield was 24.69% (C10-C22), and the lubricating oil yield was 4.94% (C22-C25).

[0053] Example 7

[0054] The method for catalyzing waste plastics to produce oil comprises the following steps:

[0055] Take 2.5mL of isopropanol as solvent, place 50mg of waste plastic HDPE and 100mg of lithium iron phosphate recycled material doped with nickel catalyst M3 in an intermittent hydrothermal reactor, mix them evenly and seal them, and fill in inert gas Ar three times at room temperature to exclude air in the reactor, heat to 350℃ and carry out cracking reaction for 24h; after the reaction, cool the reactor in ice water, take out the reaction mixture in the reactor and add 5mL of extractant dichloromethane to extract at room temperature for 40min, and then carry out solid-liquid separation. The extractant and the solvent were recovered from the obtained liquid portion by rotary evaporation at 42°C, and the remainder was the oil obtained by the reaction. The types of products were detected by GCMS, and the total yield of the obtainable oil was 40.40% (C5-C22, straight-chain alkanes), of which the gasoline yield was 12.34% (C5-C12), the aviation fuel yield was 23.67% (C8-C16), the diesel yield was 27.07% (C10-C22), and the lubricating oil yield was 2.73% (C22-C25).

[0056] Example 8

[0057] The method for catalyzing waste plastics to produce oil comprises the following steps:

[0058] Take 2.5 mL of methanol as solvent, place 50 mg of waste plastic HDPE and 120 mg of lithium iron phosphate recycled material doped with nickel catalyst M3 in an intermittent hydrothermal reactor, mix them evenly and seal them, and fill in inert gas Ar three times at room temperature to exclude air in the reactor, heat it to 380 ° C and carry out cracking reaction for 24 hours; after the reaction, cool the reactor in ice water, take out the reaction mixture in the reactor and add 5 mL of extractant dichloromethane to extract at room temperature for 40 minutes, and then perform solid-liquid separation The obtained liquid portion was subjected to rotary evaporation at 42°C to recover the extractant and the solvent, and the remainder was the oil product obtained by the reaction. The product types were detected by GCMS, and the total yield of the obtainable oil was 19.78% (C5-C22, straight-chain alkanes), of which the gasoline yield was 4.22% (C5-C12), the aviation fuel yield was 9.81% (C8-C16), the diesel yield was 14.59% (C10-C22), and the lubricating oil yield was 3.08% (C22-C25).

[0059] Example 9

[0060] The method for catalyzing waste plastics to produce oil comprises the following steps:

[0061] Take 2.5mL of methanol as solvent, place 50mg of waste plastic HDPE and 100mg of lithium iron phosphate recycled material doped with nickel catalyst M4 in an intermittent hydrothermal reactor, mix them evenly and seal them, and fill in inert gas Ar three times at room temperature to exclude the air in the reactor, heat it to 290℃ and carry out cracking reaction for 18h; after the reaction, cool the reactor in ice water, take out the reaction mixture in the reactor and add 5mL of extractant dichloromethane to extract at room temperature for 40min, and then carry out solid-liquid separation The obtained liquid portion was subjected to rotary evaporation at 42°C to recover the extractant and the solvent, and the remainder was the oil product obtained by the reaction. The product types were detected by GCMS, and the total yield of the obtainable oil was 10.50% (C5-C22, straight-chain alkanes), of which the gasoline yield was 2.50% (C5-C12), the aviation fuel yield was 4.26% (C8-C16), the diesel yield was 7.78% (C10-C22), and the lubricating oil yield was 2.11% (C22-C25).

[0062] Example 10

[0063] The method for catalyzing waste plastics to produce oil comprises the following steps:

[0064] Take 2.5 mL of ethanol as a solvent, place 50 mg of waste plastic HDPE and 100 mg of lithium iron phosphate recycled material doped with nickel catalyst M4 in an intermittent hydrothermal reactor, mix them evenly and seal them, and fill in inert gas Ar three times at room temperature to exclude the air in the reactor, heat it to 320 ° C and carry out cracking reaction for 18 hours; after the reaction, cool the reactor in ice water, take out the reaction mixture in the reactor and add 5 mL of extractant dichloromethane to extract at room temperature for 40 minutes, and then perform solid-liquid separation. The extractant and the solvent were recovered from the obtained liquid portion by rotary evaporation at 42°C, and the remainder was the oil obtained by the reaction. The types of products were detected by GCMS, and the total yield of the obtainable oil was 26.60% (C5-C22, straight-chain alkanes), of which the gasoline yield was 5.18% (C5-C12), the aviation fuel yield was 13.06% (C8-C16), the diesel yield was 19.30% (C10-C22), and the lubricating oil yield was 5.18% (C22-C25).

[0065] Embodiment 11

[0066] The method for catalyzing waste plastics to produce oil comprises the following steps:

[0067] Take 2.5mL of isopropanol as solvent, place 50mg of waste plastic HDPE and 100mg of lithium iron phosphate recycled material doped with nickel catalyst M4 in an intermittent hydrothermal reactor, mix them evenly and seal them, and fill in inert gas Ar three times at room temperature to exclude air in the reactor, heat to 350℃ and carry out cracking reaction for 18h; after the reaction, cool the reactor in ice water, take out the reaction mixture in the reactor and add 5mL of extractant dichloromethane to extract at room temperature for 40min, and then carry out solid-liquid separation. The extractant and the solvent were recovered from the obtained liquid portion by rotary evaporation at 42°C, and the remainder was the oil obtained by the reaction. The types of products were detected by GCMS, and the total yield of the obtainable oil was 35.40% (C5-C22, straight-chain alkanes), of which the gasoline yield was 12.68% (C5-C12), the aviation fuel yield was 24.67% (C8-C16), the diesel yield was 27.07% (C10-C22), and the lubricating oil yield was 2.73% (C22-C25).

[0068] Example 12

[0069] The method for catalyzing waste plastics to produce oil comprises the following steps:

[0070] Take 2.5 mL of methanol as solvent, place 50 mg of waste plastic HDPE and 100 mg of lithium iron phosphate recycled material doped with nickel catalyst M4 in an intermittent hydrothermal reactor, mix them evenly and seal them, and fill in inert gas Ar three times at room temperature to exclude the air in the reactor, heat it to 380 ° C for cracking reaction for 18 hours; after the reaction, cool the reactor in ice water, take out the reaction mixture in the reactor and add 5 mL of extractant dichloromethane to extract at room temperature for 40 minutes, and then perform solid-liquid separation. The extractant and the solvent were recovered from the obtained liquid portion by rotary evaporation at 42°C, and the remainder was the oil obtained by the reaction. The types of products were detected by GCMS, and the total yield of the obtainable oil was 28.50% (C5-C22, straight-chain alkanes), of which the gasoline yield was 9.26% (C5-C12), the aviation fuel yield was 17.79% (C8-C16), the diesel yield was 21.76% (C10-C22), and the lubricating oil yield was 2.67% (C22-C25).

[0071] Comparative Example

[0072] This case is a comparative case under the optimal conditions of Example 7, using undoped lithium iron phosphate recycled material as a catalyst to catalyze waste plastics to oil, specifically including the following steps:

[0073] Take 2.5 mL of isopropanol as a solvent, place 50 mg of waste plastic HDPE and 100 mg of lithium iron phosphate recovered material obtained in S1 in Example 1 in an intermittent hydrothermal reactor, mix them evenly and seal them, and fill them with inert gas Ar three times at room temperature to exclude the air in the reactor, heat it to 350 ° C and carry out cracking reaction for 24 hours; after the reaction, cool the reactor in ice water, take out the reaction mixture in the reactor and add 5 mL of extractant dichloromethane to extract at room temperature for 40 minutes, and then carry out solid-liquid The extractant and the solvent were recovered from the obtained liquid portion by rotary evaporation at 42°C, and the remainder was the oil obtained by the reaction. The types of products were detected by GCMS, and the total yield of the obtained oil was 4.23% (C5-C22, straight-chain alkanes), of which the gasoline yield was 0.44% (C5-C12), the aviation fuel yield was 1.47% (C8-C16), the diesel yield was 1.75% (C10-C22), and the lubricating oil yield was 0.57% (C22-C25).

[0074] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. The use of lithium iron phosphate recovered material is characterized by: The steps include: S1. Pyrolyzing the positive electrode sheets disassembled from the waste lithium-ion batteries in sections, and collecting the positive electrode waste separated from the positive electrode sheets as lithium iron phosphate recovery materials; S2. The lithium iron phosphate recovered material is doped with transition metal elements and used as a catalyst in a waste plastic oil production process.

2. The use of lithium iron phosphate recovered material according to claim 1, characterized in that: The process of the segmented pyrolysis is: heating to 200-300°C at a heating rate of 1-10°C / min and keeping warm for 20-60min, then heating to 500-600°C at a heating rate of 1-10°C / min in an inert gas atmosphere and keeping warm for 0.5-2h, so as to separate the positive electrode waste and the current collector.

3. The use of lithium iron phosphate recovered material according to claim 2, characterized in that: The transition metal element is selected from one or more of nickel, iron, chromium, chromium, cobalt, copper, zinc, titanium and vanadium.

4. The use of the lithium iron phosphate recovered material according to any one of claims 1 to 3, characterized in that: The catalyst is lithium iron phosphate recycled material doped with nickel element.

5. The use of lithium iron phosphate recovered material according to claim 4, characterized in that: The preparation process of the catalyst comprises the following steps: impregnating the lithium iron phosphate recycled material with a nickel salt aqueous solution, then drying, placing in a tubular furnace and calcining in a reducing atmosphere to obtain a lithium iron phosphate recycled material doped with nickel catalyst, wherein the nickel element accounts for 5-20wt% of the overall catalyst.

6. The use of lithium iron phosphate recovered material according to claim 5, characterized in that: The nickel salt in the nickel salt aqueous solution is selected from one of nickel sulfate, nickel chloride, nickel acetate and nickel nitrate.

7. The use of lithium iron phosphate recovered material according to claim 5, characterized in that: The reducing atmosphere is a mixed gas of nitrogen and hydrogen, wherein the volume proportion of the hydrogen in the mixed gas is 3-10%; the calcination treatment is performed by heating the temperature to 400-600° C. at a heating rate of 1-10° C. / min and maintaining the temperature for 2-4 hours.

8. A method for catalyzing waste plastics to produce oil, characterized in that: The steps include: The lithium iron phosphate recycled material obtained in the use of the lithium iron phosphate recycled material according to any one of claims 1 to 7 is doped with transition metal elements as a catalyst, placed in an intermittent hydrothermal reactor with waste plastics and a solvent, mixed evenly, and then sealed, and filled with inert gas for multiple times at room temperature to exclude the air in the reactor, and the temperature is increased to perform a cracking reaction. After the reaction is completed, it is cooled, the reaction mixture in the reactor is taken out and extracted at room temperature, and then the solid-liquid is separated, and the liquid part is rotary evaporated to recover the extractant and the solvent, and the oil product is obtained after rotary evaporation.

9. The method for catalyzing waste plastics to produce oil according to claim 8, characterized in that: The waste plastic is selected from polyolefin waste, such as polyethylene, polypropylene, etc.; the solvent is selected from one or more of methanol, ethanol, and isopropanol, and the solvent is used to provide the reducing gas hydrogen required in the cracking reaction; the usage ratio of the waste plastic, the catalyst, and the solvent is 5g:5-15g:0.2-0.5L.

10. The method for catalyzing waste plastics to produce oil according to claim 8, characterized in that: The cracking reaction is carried out at a temperature of 250-400°C for at least 10 hours; the extractant used in the room temperature extraction is dichloromethane; and the rotary evaporation temperature is in the range of 40-45°C.