Method for converting waste battery diaphragm into high-value carbon material and application

Abstract

The invention belongs to the technical field of comprehensive utilization of solid wastes, and particularly relates to a method for converting a waste battery diaphragm into a high-value carbon material and application. The method for converting the waste battery diaphragm into the high-value carbon material comprises the following steps: (1) mixing the waste battery diaphragm with urea, and pyrolyzing to obtain pyrolytic carbon; (2) modifying the pyrolytic carbon with alkali liquor to obtain a high-value carbon material; wherein in the step (1), the pyrolysis is stage heating pyrolysis, and stage heating comprises the following steps: firstly, heating to 200-300 DEG C, and keeping the temperature; the temperature is increased to 350-400 DEG C, and heat preservation is carried out; and the temperature is raised to 500-800 DEG C, and heat preservation is performed. According to the preparation method, urea can react with the battery diaphragm in the carbonization process to form a nitrogen-doped carbon material, and an N and O-doped carbon material is formed through subsequent treatment, so that not only is the pore structure of the carbon material improved, but also the surface active sites of the carbon material can be increased; therefore, the adsorption capacity of the adsorbent on industrial pollutants (such as methylene blue and / or microplastics) is remarkably enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of comprehensive utilization of solid waste, and particularly relates to a method and use for converting waste battery separators into high-value carbon materials. Background Art

[0002] With the rapid development of the global new energy vehicle and energy storage industries, the production of battery products such as lithium batteries has shown explosive growth, and the resulting battery waste has become a dual challenge of environmental pollution and resource waste. At present, battery recycling technologies mainly focus on the recycling and regeneration of electrode active materials (such as metals like cobalt and lithium) and electrolytes. However, the plastic separators (mainly polyethylene and polypropylene), which account for about 15%-25% of the battery mass, have long faced the dilemmas of "difficult to recycle, expensive to treat, and low resource utilization rate" due to their chemical stability and non-degradable characteristics. According to statistics, the global annual output of waste battery separators exceeds one million tons. If traditional disposal methods such as landfilling or incineration are used, it is extremely easy to cause environmental risks such as microplastic pollution and toxic gas release. Therefore, the development of high-value utilization technologies for separator waste has become a bottleneck that the industry urgently needs to break through.

[0003] The current research on the recycling of waste battery separators is still in the laboratory exploration stage. The mainstream technical routes include mechanical crushing and mixing with electrode materials for regeneration, co-pyrolysis with electrolytes to prepare composite carbon materials, etc. However, the above methods have significant defects: the mixing treatment process is prone to introducing metal impurities, resulting in the deterioration of the performance of the regenerated materials; the co-pyrolysis technology is limited by the difficulty of controlling electrolyte residues and is difficult to achieve continuous production. In addition, existing research mostly focuses on the preparation of low-value-added carbon-based fuels or fillers, and their economic and environmental benefits are limited.

[0004] It is worth noting that the separator material itself has excellent characteristics of a high carbon-hydrogen ratio (C / H>6) and low ash content (<0.5%), and theoretically can be used as an ideal precursor for preparing high specific surface area functional carbon materials. However, the existing technology has not yet broken through the key process of its directional conversion into adsorption carbon materials. Summary of the Invention

[0005] The present invention has developed a method for converting waste battery separators into high-value carbon materials. This method can convert waste battery separators into high-value carbon materials, and the converted high-value carbon materials have excellent adsorption rates for pollutants (such as methylene blue and / or microplastics) in water.

[0006] To achieve the above object, the present invention can adopt the following technical solutions:

[0007] On the one hand, the present invention provides a method for converting waste battery separators into high-value carbon materials, including: (1) mixing waste battery separators and urea, and pyrolyzing to obtain pyrolytic carbon; (2) modifying the pyrolytic carbon with an alkaline solution to obtain high-value carbon materials; wherein, in step (1), the pyrolysis is stage-wise temperature-rising pyrolysis, and the stage-wise temperature-rising includes: first heating to 200°C to 300°C and holding the temperature; then heating to 350°C to 400°C and holding the temperature; then heating to 500°C to 800°C and holding the temperature.

[0008] Preferably, in the above method, the stage-wise temperature-rising includes one or more of the following conditions:

[0009] (i) The heating rate of the stage-wise temperature-rising is 2°C / min to 6°C / min;

[0010] (ii) The holding time at 200°C to 300°C is 0.5 h to 1.5 h;

[0011] (iii) The holding time at 350°C to 400°C is 0.1 h to 1 h;

[0012] (iv) The holding time at 500°C to 800°C is 1 h to 2 h.

[0013] More preferably, in the above method, the stage-wise temperature-rising includes: first heating to 240°C and holding the temperature for 1 h; then heating to 380°C and holding the temperature for 0.5 h; then heating to 600°C to 800°C and holding the temperature for 1 h to 2 h.

[0014] Preferably, in the above method, the mass ratio of the waste battery separator to urea is 1:(0.1 to 8).

[0015] More preferably, in the above method, the mass ratio of the waste battery separator to urea is 1:(0.5 to 6).

[0016] Preferably, in the above method, the alkaline solution is selected from one or more of potassium hydroxide, sodium hydroxide, or cesium hydroxide.

[0017] More preferably, in the above method, the concentration of the alkaline solution is 0.1 M to 5 M.

[0018] Preferably, in the above method, the waste battery separator is one or more combinations of single-layer PP, single-layer PE, double-sided PP / PE, or three-layer PP / PE / PP.

[0019] On the other hand, the present invention provides a high-value carbon material prepared by the method in the present invention.

[0020] On still another aspect, the present invention provides a use of the high-value carbon material in the present invention in adsorbing methylene blue and / or microplastics in water bodies.

[0021] The beneficial effects of the present invention include:

[0022] (1) In the method for converting waste battery separators into high-value carbon materials provided by the present invention, urea, as an inexpensive and environmentally friendly nitrogen source, can react with the battery separators during the carbonization process to form nitrogen-doped carbon materials, and through subsequent treatment, N, O-doped carbon materials are formed. This doping not only helps to improve the pore structure of the carbon materials, but also increases their surface active sites, thereby significantly enhancing their adsorption capacity for industrial pollutants (such as methylene blue and / or microplastics).

[0023] (2) The method for converting waste battery separators into high-value carbon materials provided by the present invention is simple and feasible, without the need for a catalyst, and can achieve the clean disposal of waste battery separators without additional cost. Moreover, it minimizes the use of chemicals, has high effect stability, little environmental pollution, and broad development prospects. Detailed Embodiments

[0024] The examples given are for better illustration of the present invention, but the content of the present invention is not limited only to the examples given. Therefore, those skilled in the art who make non-essential improvements and adjustments to the implementation solutions based on the above invention content still fall within the protection scope of the present invention.

[0025] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. Unless having significantly different meanings in the context, the singular form of expressions includes the plural form of expressions. As used herein, it should be understood that terms such as "including", "having", "containing" are intended to indicate the presence of features, numbers, operations, components, parts, elements, materials or combinations. The terms of the present invention are disclosed in the specification, and are not intended to exclude the possibility of the existence or addition of one or more other features, numbers, operations, components, parts, elements, materials or their combinations. As used herein, depending on the circumstances, " / " can be interpreted as "and" or "or".

[0026] An embodiment of the present invention provides a method for converting waste battery separators into high-value carbon materials, including: (1) mixing waste battery separators and urea, and pyrolyzing to obtain pyrolytic carbon; (2) modifying the pyrolytic carbon with an alkaline solution to obtain high-value carbon materials; wherein, in step (1), the pyrolysis is stagewise temperature-rising pyrolysis, and the stagewise temperature-rising includes: first heating to 200°C to 300°C and holding the temperature; then heating to 350°C to 400°C and holding the temperature; then heating to 500°C to 800°C and holding the temperature.

[0027] It should be noted that through the pyrolysis process of urea-assisted and gradient temperature-rising and holding, after mixing waste battery separators and urea, high-temperature pyrolytic carbonization is carried out, and then modification with an alkaline solution can obtain carbon materials with high N and O contents (high-value carbon materials), realizing the resource utilization of battery separator waste.

[0028] In some specific examples, in the above method, the stepwise heating includes one or more of the following conditions:

[0029] (i) The heating rate of the stepwise heating is 2°C / min to 6°C / min. For example, it can be 3°C / min, 4°C / min, 5°C / min, etc.;

[0030] (ii) The holding time at the stage of 200°C to 300°C is 0.5 h to 1.5 h. For example, the temperature can be 230°C, 250°C, 280°C, etc., and the time can be 0.8 h, 1 h, 1.2 h, etc.;

[0031] (iii) The holding time at the stage of 350°C to 400°C is 0.1 h to 1 h. For example, the temperature can be 360°C, 370°C, 380°C, 390°C, etc., and the time can be 0.3 h, 0.5 h, 0.8 h, etc.;

[0032] (iv) The holding time at the stage of 500°C to 800°C is 1 h to 2 h. For example, the temperature can be 550°C, 600°C, 650°C, 700°C, 750°C, etc., and the time can be 1.3 h, 1.5 h, 1.8 h, etc.

[0033] In some specific examples, in the above method, the stepwise heating includes: first heating to 240°C and holding for 1 h; then heating to 380°C and holding for 0.5 h; then heating to 600°C to 800°C and holding for 1 h to 2 h.

[0034] In some specific examples, in the above method, the mass ratio of the waste battery separator to urea is 1:(0.1 - 8), such as 1:(0.5 - 6), 1:(1 - 5), or 1:(2 - 4), etc.

[0035] In some specific examples, in the above method, the alkaline solution is selected from one or more of potassium hydroxide, sodium hydroxide, or cesium hydroxide.

[0036] In some specific examples, in the above method, the concentration of the alkaline solution is 0.1 M to 5 M, such as 1 M, 2 M, 3 M, 4 M, etc.

[0037] In some specific examples, in the above method, the waste battery separator is one or more combinations of single - layer PP, single - layer PE, double - sided PP / PE, or three - layer PP / PE / PP.

[0038] The embodiment of the present invention also provides a high - value carbon material prepared by the method in the present invention.

[0039] The embodiment of the present invention also provides a use of the high - value carbon material in the present invention in adsorbing methylene blue and / or micro - plastics in water bodies.

[0040] It should be noted that due to the relatively high N and O element contents in the high-value carbon material of the present invention, the lyophilicity of the carbon material in an aqueous solution is increased. This is because the C=N and C=O functional groups may interact with dye molecules through hydrogen bonding and π-π stacking, etc., while the C-N and C-O-N functional groups may form interactive effects through hydrogen bonding, making it easier for the industrial dye methylene blue and microplastics to adsorb onto the carbon material.

[0041] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with specific examples, but the content of the present invention is not limited to the following examples only.

[0042] In the following examples, the crushed waste diaphragm is sourced from Changzhou Houde Renewable Resources Technology Co., Ltd.

[0043] I. Preparation of high-value carbon material from waste diaphragm

[0044] Example 1

[0045] (1) The crushed waste diaphragm and urea are fully mixed at a mass ratio of 1:0.5. After mixing, it is heated to 240 °C at a heating rate of 10 °C / min and kept at 240 °C for 1 h; after the heat preservation ends, it is heated to 380 °C at a heating rate of 10 °C / min and kept at 380 °C for 0.5 h; after the heat preservation ends, it is heated to 600 °C at a heating rate of 10 °C / min and pyrolyzed at 600 °C for 2 h; nitrogen is introduced simultaneously during all heating processes; after pyrolysis, it is cooled to room temperature under a nitrogen atmosphere to obtain pyrolytic carbon;

[0046] (2) 0.5 g of pyrolytic carbon is added to 20 ml of potassium hydroxide solution (1 M) and stirred for 1 h to make it evenly mixed. After standing for 24 h, it is washed with deionized water until the supernatant is neutral and filtered to obtain a precipitate; then the precipitate is placed in an oven at 80 °C and dried for 6 h to obtain a high-value carbon material. The N content of the high-value carbon material is 20.12%, and the O content is 3.32%, denoted as 0.5-N-O-600.

[0047] Example 2

[0048] (1) The crushed waste diaphragm and urea are fully mixed at a mass ratio of 1:1. After mixing, it is heated to 240 °C at a heating rate of 10 °C / min and kept at 240 °C for 1 h; after the heat preservation ends, it is heated to 380 °C at a heating rate of 5 °C / min and kept at 380 °C for 0.5 h; after the heat preservation ends, it is heated to 600 °C at a heating rate of 5 °C / min and pyrolyzed at 600 °C for 2 h; nitrogen is introduced simultaneously during all heating processes; after pyrolysis, it is cooled to room temperature under a nitrogen atmosphere to obtain pyrolytic carbon;

[0049] (2) Add 0.5 g of pyrolytic carbon to 20 ml of potassium hydroxide solution (1 M), stir for 0.5 h to make it evenly mixed, let it stand for 24 h, wash it with deionized water until the supernatant is neutral and filter to obtain a precipitate; then place the precipitate in an oven at 100 °C and dry it for 6 h to obtain a high-value carbon material. The N content of the high-value carbon material is 22.36%, and the O content is 3.76%, denoted as 1-N-O-600.

[0050] Example 3

[0051] (1) Thoroughly mix the crushed waste diaphragm and urea at a mass ratio of 1:2. After mixing, heat it to 240 °C at a heating rate of 10 °C / min and keep it at 240 °C for 1 h; after the heat preservation ends, heat it to 380 °C at a heating rate of 3 °C / min and keep it at 380 °C for 0.5 h; after the heat preservation ends, heat it to 600 °C at a heating rate of 3 °C / min and pyrolyze it at 600 °C for 1 h; nitrogen is passed through during all heating processes; after pyrolysis, cool it to room temperature under a nitrogen atmosphere to obtain pyrolytic carbon;

[0052] (2) Add 0.5 g of pyrolytic carbon to 20 ml of potassium hydroxide solution (1 M), stir for 1 h to make it evenly mixed, let it stand for 24 h, wash it with deionized water until the supernatant is neutral and filter to obtain a precipitate; then place the precipitate in an oven at 80 °C and dry it for 6 h to obtain a high-value carbon material. The N content of the high-value carbon material is 24.18%, and the O content is 4.35%, denoted as 2-N-O-600.

[0053] Example 4

[0054] (1) Thoroughly mix the crushed waste diaphragm and urea at a mass ratio of 1:4. After mixing, heat it to 240 °C at a heating rate of 5 °C / min and keep it at 240 °C for 1 h; after the heat preservation ends, heat it to 380 °C at a heating rate of 5 °C / min and keep it at 380 °C for 0.5 h; after the heat preservation ends, heat it to 600 °C at a heating rate of 5 °C / min and pyrolyze it at 600 °C for 1 h; nitrogen is passed through during all heating processes; after pyrolysis, cool it to room temperature under a nitrogen atmosphere to obtain pyrolytic carbon;

[0055] (2) Add 0.5 g of pyrolytic carbon to 20 ml of potassium hydroxide solution (1 M), stir for 1 h to make it evenly mixed, let it stand for 24 h, wash it with deionized water until the supernatant is neutral and filter to obtain a precipitate; then place the precipitate in an oven at 80 °C and dry it for 6 h to obtain a high-value carbon material. The N content of the high-value carbon material is 39.52%, and the O content is 4.39%, denoted as 4-N-O-600.

[0056] Example 5

[0057] (1) The crushed waste diaphragm and urea are fully mixed at a mass ratio of 1:6. After mixing, the temperature is raised to 240 °C at a heating rate of 5 °C / min, and held at 240 °C for 1 h. After the heat preservation is completed, the temperature is raised to 380 °C at a heating rate of 5 °C / min, and held at 380 °C for 0.5 h. After the heat preservation is completed, the temperature is raised to 600 °C at a heating rate of 5 °C / min, and pyrolyzed at 600 °C for 2 h. Nitrogen is passed through during all heating processes. After pyrolysis, it is cooled to room temperature under a nitrogen atmosphere to obtain pyrolytic carbon;

[0058] (2) 0.5 g of pyrolytic carbon is added to 20 ml of potassium hydroxide solution (1 M) and stirred for 1 h to make it evenly mixed. After standing for 24 h, it is washed with deionized water until the supernatant is neutral and filtered to obtain a precipitate. Then the precipitate is placed in an oven at 80 °C and dried for 6 h to obtain a high-value carbon material. The N content of the high-value carbon material is 40.01%, and the O content is 4.56%, denoted as 6-N-O-600.

[0059] Example 6

[0060] (1) The crushed waste diaphragm and urea are fully mixed at a mass ratio of 1:4. After mixing, the temperature is raised to 240 °C at a heating rate of 5 °C / min, and held at 240 °C for 1 h. After the heat preservation is completed, the temperature is raised to 380 °C at a heating rate of 5 °C / min, and held at 380 °C for 0.5 h. After the heat preservation is completed, the temperature is raised to 700 °C at a heating rate of 5 °C / min, and pyrolyzed at 700 °C for 2 h. Nitrogen is passed through during all heating processes. After pyrolysis, it is cooled to room temperature under a nitrogen atmosphere to obtain pyrolytic carbon;

[0061] (2) 0.5 g of pyrolytic carbon is added to 20 ml of potassium hydroxide solution (1 M) and stirred for 0.5 h to make it evenly mixed. After standing for 24 h, it is washed with deionized water until the supernatant is neutral and filtered to obtain a precipitate. Then the precipitate is placed in an oven at 100 °C and dried for 6 h to obtain a high-value carbon material. The N content of the high-value carbon material is 36.14%, and the O content is 4.03%, denoted as 4-N-O-700.

[0062] Example 7

[0063] (1) The crushed waste diaphragm and urea are fully mixed at a mass ratio of 1:4. After mixing, the temperature is raised to 240 °C at a heating rate of 5 °C / min, and held at 240 °C for 1 h. After the heat preservation is completed, the temperature is raised to 380 °C at a heating rate of 5 °C / min, and held at 380 °C for 0.5 h. After the heat preservation is completed, the temperature is raised to 800 °C at a heating rate of 5 °C / min, and pyrolyzed at 800 °C for 2 h. Nitrogen is passed through during all heating processes. After pyrolysis, it is cooled to room temperature under a nitrogen atmosphere to obtain pyrolytic carbon;

[0064] (2) Add 0.5 g of pyrolytic carbon into 20 ml of potassium hydroxide solution (1 M) and stir for 0.5 h to mix evenly. After standing for 24 h, wash with deionized water until the supernatant is neutral and filter to obtain the precipitate; then place the precipitate in an oven at 110°C and dry for 6 h to obtain a high-value carbon material. The high-value carbon material has an N content of 33.28% and an O content of 3.56%, which is recorded as 4-NO-800.

[0065] Example 8

[0066] (1) The crushed waste diaphragm and urea were fully mixed in a mass ratio of 1:4, and after mixing, the temperature was increased to 240°C at a heating rate of 5°C / min, and kept at 240°C for 1 hour; after the insulation, the temperature was increased to 380°C at a heating rate of 3°C / min, and kept at 380°C for 0.5 hour; after the insulation, the temperature was increased to 600°C at a heating rate of 3°C / min, and pyrolyzed at 600°C for 1 hour; argon was passed through all the heating processes; after the pyrolysis was completed, it was cooled to room temperature in an argon atmosphere to obtain pyrolytic carbon;

[0067] (2) Add 0.5 g of pyrolytic carbon into 20 ml of potassium hydroxide solution (1 M) and stir for 0.5 h to mix evenly. After standing for 24 h, wash with deionized water until the supernatant is neutral and filter to obtain the precipitate; then place the precipitate in an oven at 100 ° C and dry for 6 h to obtain a high-value carbon material. The N content of the high-value carbon material is 38.56%, and the O content is 4.23%, which is recorded as 4R-NO-600.

[0068] Comparative Example 1

[0069] (1) The crushed waste diaphragm and urea were fully mixed at a mass ratio of 1:0.5, and after mixing, the temperature was increased to 600°C at a heating rate of 10°C / min, and pyrolyzed at 600°C for 2h; nitrogen was simultaneously passed through the entire heating process; after the pyrolysis was completed, the pyrolysis carbon was cooled to room temperature under a nitrogen atmosphere to obtain;

[0070] (2) Add 0.5 g of pyrolytic carbon into 20 ml of potassium hydroxide solution (1 M) and stir for 1 h to mix evenly. After standing for 24 h, wash with deionized water until the supernatant is neutral and filter to obtain the precipitate; then place the precipitate in an oven at 80°C and dry for 6 h to obtain a high-value carbon material. The high-value carbon material has an N content of 5.03% and an O content of 2.21%, and is recorded as D-0.5-NO-600.

[0071] Comparative Example 2

[0072] (1) The crushed waste diaphragm and urea were fully mixed in a mass ratio of 1:1, and after mixing, the temperature was increased to 600°C at a heating rate of 10°C / min, and pyrolyzed at 600°C for 2h; nitrogen was simultaneously passed through the entire heating process; after the pyrolysis was completed, the pyrolysis carbon was obtained after cooling to room temperature in a nitrogen atmosphere;

[0073] (2) Add 0.5 g of pyrolytic carbon to 20 ml of potassium hydroxide solution (1 M), stir for 0.5 h to make it evenly mixed, let it stand for 24 h, wash it with deionized water until the supernatant is neutral and filter to obtain a precipitate; then place the precipitate in an oven at 100 °C and dry for 6 h to obtain a high-value carbon material. The N content of the high-value carbon material is 5.32%, and the O content is 2.86%. It is denoted as D-1-N-O-600.

[0074] Comparative Example 3

[0075] (1) Thoroughly mix the crushed waste separator and urea at a mass ratio of 1:2. After mixing, heat it to 600 °C at a heating rate of 10 °C / min and pyrolyze at 600 °C for 1 h; nitrogen is passed through during all heating processes; after pyrolysis, cool it to room temperature under a nitrogen atmosphere to obtain pyrolytic carbon;

[0076] (2) Add 0.5 g of pyrolytic carbon to 20 ml of potassium hydroxide solution (1 M), stir for 1 h to make it evenly mixed, let it stand for 24 h, wash it with deionized water until the supernatant is neutral and filter to obtain a precipitate; then place the precipitate in an oven at 80 °C and dry for 6 h to obtain a high-value carbon material. The N content of the high-value carbon material is 5.87%, and the O content is 2.89%. It is denoted as D-2-N-O-600.

[0077] Comparative Example 4

[0078] (1) Thoroughly mix the crushed waste separator and urea at a mass ratio of 1:4. After mixing, heat it to 600 °C at a heating rate of 5 °C / min and pyrolyze at 600 °C for 1 h; nitrogen is passed through during all heating processes; after pyrolysis, cool it to room temperature under a nitrogen atmosphere to obtain pyrolytic carbon;

[0079] (2) Add 0.5 g of pyrolytic carbon to 20 ml of potassium hydroxide solution (1 M), stir for 1 h to make it evenly mixed, let it stand for 24 h, wash it with deionized water until the supernatant is neutral and filter to obtain a precipitate; then place the precipitate in an oven at 80 °C and dry for 6 h to obtain a high-value carbon material. The N content of the high-value carbon material is 9.43%, and the O content is 3.14%. It is denoted as D-4-N-O-600.

[0080] Comparative Example 5

[0081] (1) Thoroughly mix the crushed waste separator and urea at a mass ratio of 1:6. After mixing, heat it to 600 °C at a heating rate of 5 °C / min and pyrolyze at 600 °C for 2 h; nitrogen is passed through during all heating processes; after pyrolysis, cool it to room temperature under a nitrogen atmosphere to obtain pyrolytic carbon;

[0082] (2) Add 0.5 g of pyrolytic carbon to 20 ml of potassium hydroxide solution (1 M), stir for 1 h to mix evenly, let it stand for 24 h, wash with deionized water until the supernatant is neutral, and filter to obtain a precipitate; then place the precipitate in an oven at 80 °C and dry for 6 h to obtain a high-value carbon material. The N content of the high-value carbon material is 9.61%, and the O content is 3.21%, denoted as D-6-N-O-600.

[0083] Comparative Example 6

[0084] (1) Thoroughly mix the crushed waste separator and urea at a mass ratio of 1:4. After mixing, heat it to 700 °C at a heating rate of 5 °C / min and pyrolyze at 700 °C for 2 h; nitrogen is passed through during all heating processes; after pyrolysis, cool it to room temperature under a nitrogen atmosphere to obtain pyrolytic carbon.

[0085] (2) Add 0.5 g of pyrolytic carbon to 20 ml of potassium hydroxide solution (1 M), stir for 0.5 h to mix evenly, let it stand for 24 h, wash with deionized water until the supernatant is neutral, and filter to obtain a precipitate; then place the precipitate in an oven at 100 °C and dry for 6 h to obtain a high-value carbon material. The N content of the high-value carbon material is 8.40%, and the O content is 2.98%, denoted as D-4-N-O-700.

[0086] Comparative Example 7

[0087] (1) Thoroughly mix the crushed waste separator and urea at a mass ratio of 1:4. After mixing, heat it to 800 °C at a heating rate of 5 °C / min and pyrolyze at 800 °C for 2 h; nitrogen is passed through during all heating processes; after pyrolysis, cool it to room temperature under a nitrogen atmosphere to obtain pyrolytic carbon.

[0088] (2) Add 0.5 g of pyrolytic carbon to 20 ml of potassium hydroxide solution (1 M), stir for 0.5 h to mix evenly, let it stand for 24 h, wash with deionized water until the supernatant is neutral, and filter to obtain a precipitate; then place the precipitate in an oven at 110 °C and dry for 6 h to obtain a high-value carbon material. The N content of the high-value carbon material is 7.73%, and the O content is 2.93%, denoted as D-4-N-O-800.

[0089] Comparative Example 8

[0090] (1) Thoroughly mix the crushed waste separator and urea at a mass ratio of 1:4. After mixing, heat it to 600 °C at a heating rate of 5 °C / min and pyrolyze at 600 °C for 1 h; argon is passed through during all heating processes; after pyrolysis, cool it to room temperature under a nitrogen atmosphere to obtain pyrolytic carbon.

[0091] (2) Add 0.5 g of pyrolytic carbon to 20 ml of potassium hydroxide solution (1 M), stir for 0.5 h to make it evenly mixed, let it stand for 24 h, wash it with deionized water until the supernatant is neutral and filter to obtain a precipitate; then place the precipitate in an oven at 100 °C and dry for 6 h to obtain a high-value carbon material. The N content of the high-value carbon material is 8.57%, and the O content is 2.96%, denoted as D-4R-N-O-600.

[0092] II. Characterization of high-value carbon materials

[0093] The high-value carbon materials prepared in Examples 1 to 8 and Comparative Examples 1 to 8 were subjected to BET tests to obtain the specific surface area (S BET ), the pore volume was tested by N2 adsorption-desorption experiments, and the elemental content of the carbon materials was verified by X-ray photoelectron spectroscopy analysis. The results are shown in Table 1.

[0094] Table 1 BET specific surface area, pore volume and elemental content of carbon materials

[0095]

[0096] From the data results of Examples 1-8 and Comparative Examples 1-8, it can be seen that when heat preservation operations are carried out at 240 °C and 380 °C, more N elements can be introduced into the carbon materials, thereby increasing the defects of the carbon materials, and thus introducing more O elements. At the same time, due to the introduction of N and O elements, the defects of the carbon materials increase, resulting in a decrease in the specific surface area and volume response of the carbon materials. As the pyrolysis temperature increases and the pyrolysis time extends, the lattice structure in the carbon materials gradually tends to be ordered. This is because high temperature promotes the removal of non-carbon elements (such as oxygen and nitrogen), thereby reducing the content of heteroatoms. In this process, carbon atoms recombine and form a more stable graphitized structure or quasi-graphite structure, resulting in an increase in the order of the lattice.

[0097] III. Application of high-value carbon materials

[0098] (I) Methylene blue adsorption test in water

[0099] Prepare a methylene blue solution with a concentration of 100 mg / L. Place 5 mg of the high-value carbon materials 0.5-N-O-600, 0.5-N-O-600, 2-N-O-600, 4-N-O-600, 6-N-O-600, 4-N-O-700, 4-N-O-800, and 4R-N-O-600 prepared in Examples 1 to 8 into 20 ml of the methylene blue solution respectively. Conduct an adsorption test under normal temperature and pressure and in a water bath (25 °C) with a shaking speed of 160 r / min on a shaking table for 6 hours. Measure the removal rate of methylene blue in the water (Prepare an aqueous solution of methylene blue with a concentration of 100 mg / L using deionized water, and then dilute it with deionized water to standard solutions with concentrations of 1 mg / L, 2 mg / L, 4 mg / L, 8 mg / L, and 10 mg / L respectively. Measure the standard curve of the standard solutions with a UV spectrophotometer at a wavelength of 664 nm, and obtain the removal rate by measuring the absorbance of the solution after adsorption). The results are shown in Table 2 below.

[0100] Table 2 Removal rates of methylene blue in water by different high-value carbon materials

[0101] Example Carbon material Removal rate of methylene blue (%) Example 1 0.5-N-O-600 78.5 Example 2 0.5-N-O-600 73.6 Example 3 2-N-O-600 71.2 Example 4 4-N-O-600 91.2 Example 5 6-N-O-600 91.8 Example 6 4-N-O-700 88.3 Example 7 4-N-O-800 85.6 Example 8 4R-N-O-600 82.1 Comparative Example 1 D-0.5-N-O-600 56.7 Comparative Example 2 D-1-N-O-600 65.3 Comparative Example 3 D-2-N-O-600 62.2 Comparative Example 4 D-4-N-O-600 78.3 Comparative Example 5 D-6-N-O-600 78.8 Comparative Example 6 D-4-N-O-700 78.6 Comparative Example 7 D-4-N-O-800 76.3 Comparative Example 8 D-4R-N-O-600 76.6

[0102] (II) Adsorption test of microplastics in water

[0103] Prepare a solution of polystyrene microplastics with a diameter of 1 - 6 μm and a concentration of 100 mg / L. Place 5 mg of the high-value carbon materials 0.5-N-O-600, 0.5-N-O-600, 2-N-O-600, 4-N-O-600, 6-N-O-600, 4-N-O-700, 4-N-O-800, and 4R-N-O-600 prepared in Examples 1 to 8 into 20 ml of the microplastic solution respectively. Conduct an adsorption test under normal temperature and pressure and in a water bath (25 °C) with a shaking speed of 160 r / min on a shaking table for 6 hours. Measure the removal rate of microplastics in the water (Centrifuge in a saturated salt solution (NaCl) to make the microplastics float on the surface, wash and dry them, and then weigh them. Calculate the removal rate based on the mass ratio before and after adsorption). The results are shown in Table 3 below.

[0104] Table 3 Removal rates of microplastics in water by different high-value carbon materials

[0105] Example Carbon material Removal rate of microplastics (%) Example 1 0.5-N-O-600 79.6 Example 2 0.5-N-O-600 75.2 Example 3 2-N-O-600 72.8 Example 4 4-N-O-600 93.4 Example 5 6-N-O-600 95.7 Example 6 4-N-O-700 92.1 Example 7 4-N-O-800 87.8 Example 8 4R-N-O-600 86.1 Comparative Example 1 D-0.5-N-O-600 69.3 Comparative Example 2 D-1-N-O-600 68.2 Comparative Example 3 D-2-N-O-600 66.2 Comparative Example 4 D-4-N-O-600 79.3 Comparative Example 5 D-6-N-O-600 78.2 Comparative Example 6 D-4-N-O-700 77.2 Comparative Example 7 D-4-N-O-800 74.1 Comparative Example 8 D-4R-N-O-600 76.5

[0106] As can be seen from Tables 2 and 3 above, due to the relatively high content of N and O elements in the N, O-doped high-value carbon materials, the lyophilicity of the carbon materials in aqueous solutions is increased. This is because the C=N and C=O functional groups may interact with dye molecules through hydrogen bonding and π-π stacking, while the C-N and C-O-N functional groups may form interactive effects through hydrogen bonding, making it easier for the industrial dye methylene blue and microplastics to adsorb onto the carbon materials.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A method for converting waste battery separators into high-value carbon materials, characterized in that, Comprising: (1) Mixing waste battery separator and urea, and pyrolyzing to obtain pyrolytic carbon; (2) Modifying the pyrolytic carbon with an alkali solution to obtain a high-value carbon material; Among them, in step (1), the pyrolysis is stepwise temperature-raising pyrolysis, and the stepwise temperature-raising includes: first raising the temperature to 200°C - 300°C and holding for heat preservation; then raising the temperature to 350°C - 400°C and holding for heat preservation; then raising the temperature to 500°C - 800°C and holding for heat preservation.

2. The method according to claim 1, wherein The stepwise temperature-raising includes one or more of the following conditions: (i) The heating rate of the stepwise temperature-raising is 2°C / min - 6°C / min; (ii) The heat preservation time in the 200°C - 300°C stage is 0.5h - 1.5h; (iii) The heat preservation time in the 350°C - 400°C stage is 0.1h - 1h; (iv) The heat preservation time in the 500°C - 800°C stage is 1h - 2h.

3. The method according to claim 2, wherein The stepwise temperature-raising includes: first raising the temperature to 240°C and holding for 1h; then raising the temperature to 380°C and holding for 0.5h; then raising the temperature to 600°C - 800°C and holding for 1h - 2h.

4. The method according to any one of claims 1 to 3, characterized in that, The mass ratio of the waste battery separator to urea is 1:(0.1 - 8).

5. The method according to claim 4, characterized in that, The mass ratio of the waste battery separator to urea is 1:(0.5 - 6).

6. The method according to claim 1, 2, 3 or 5, characterized in that The alkali solution is selected from one or more of potassium hydroxide, sodium hydroxide or cesium hydroxide.

7. The method according to claim 6, wherein The concentration of the alkali solution is 0.1M - 5M.

8. The method according to claim 1, 2, 3, 5 or 7, characterized in that The waste battery separator is one or more combinations of single-layer PP, single-layer PE, double-sided PP / PE or three-layer PP / PE / PP.

9. The high-value carbon material prepared by the method according to any one of claims 1 to 8.

10. Use of the high-value carbon material according to claim 9 in adsorbing methylene blue and / or microplastics in water bodies.

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