Method for preparing ferrocobalt composite diaphragm based on waste lithium iron phosphate positive electrode material and application

Abstract

The invention belongs to the technical field of battery material recovery and reutilization, and particularly relates to a method for preparing a ferrocobalt composite diaphragm based on a waste lithium iron phosphate positive electrode material and application of the ferrocobalt composite diaphragm based on the waste lithium iron phosphate positive electrode material. Then preparing a solution A and a solution B by utilizing 2-methylimidazole, a Co (NO3) 2.6 H2O solution and a dopamine hydrochloride solution respectively, and then fusing the solution A with the solution B and FePO4 to prepare ZIF-67 (at) PDA / Fe; and then carrying out heat treatment on the ZIF-67 (at) PDA / Fe in a nitrogen environment to obtain the ferrocobalt hollow composite diaphragm. According to the invention, resource recycling is realized, a high-quality diaphragm material is provided for a high-performance lithium-sulfur battery, and the development of a clean energy technology is promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery material recovery and reuse, and specifically relates to a method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode materials and application thereof. Background Art

[0002] As the global demand for renewable energy and clean energy continues to increase, the new energy vehicle market is experiencing rapid growth. The widespread popularity of electric vehicles and portable electronic devices has led to a sharp increase in the demand for lithium-ion batteries. The resulting problem of waste battery disposal has also become increasingly prominent. Waste lithium-ion batteries contain a large amount of valuable metals such as lithium and iron. If they are directly discarded, it will not only cause a waste of resources, but also cause serious pollution to the environment. Therefore, it is urgent to develop efficient and environmentally friendly waste battery material recycling and reuse technologies.

[0003] In recent years, the recycling technology of waste lithium-ion batteries has attracted widespread attention and has developed rapidly. In 2010, pyrometallurgical technology was widely used in the field of recycling waste lithium-ion batteries, but this technology has high energy consumption and is prone to secondary pollution. Since 2015, inorganic acid leaching, in particular, has gradually become the mainstream. However, strong acids are corrosive and have safety hazards during transportation, storage, and use. After 2020, organic acid leaching has gradually been favored by researchers due to its lower corrosiveness and higher safety, becoming a more environmentally friendly recycling method. At the same time, lithium-sulfur batteries are considered to be a strong candidate for the next generation of energy storage systems due to their high theoretical energy density (about 2600Wh / kg) and low cost. However, lithium-sulfur batteries face many challenges in practical applications, and the polysulfide shuttle effect is one of them. This effect causes the battery capacity to decay rapidly, and the cycle performance also decreases. In order to inhibit the polysulfide shuttle effect, efficient diaphragm materials are urgently needed to improve the cycle performance and stability of the battery.

[0004] In 2013, some international research teams began to focus on the effects of transition metal oxides (including cobalt-iron-based materials) on the performance of lithium-sulfur batteries. For example, a research team from the Ulsan National Institute of Science and Technology (UNIST) in South Korea published research results on the use of transition metal oxides as catalysts to improve the performance of lithium-sulfur batteries. In 2014, researchers from the Institute of Physics, Chinese Academy of Sciences, reported a diaphragm modified with cobalt-iron alloy nanoparticles, which can effectively inhibit the shuttle effect of polysulfides and significantly improve the cycle stability and rate performance of lithium-sulfur batteries. This allows cobalt-iron-based materials to be used in lithium-sulfur battery diaphragms for the first time, and also lays the groundwork for the subsequent use of recycled materials from waste batteries to prepare such diaphragms. In 2015, as the research continued to deepen, scientists began to explore how to further optimize the performance of lithium-sulfur batteries by designing different forms of cobalt-iron-based materials, such as hollow structures and core-shell structures. In the same year, a research team from the University of Texas at Austin published a paper introducing a new type of hollow cobalt-iron nanospheres, which showed excellent electrochemical performance in lithium-sulfur batteries, highlighting the great potential of hollow cobalt-iron structural materials and prompting researchers to think about more economical and environmentally friendly sources of preparation, and recycled materials from waste batteries came into view. In 2016, a research team from the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, developed a three-dimensional porous carbon fiber diaphragm modified with cobalt-iron alloy nanoparticles. The diaphragm has good mechanical strength, can effectively promote lithium ion transmission, and inhibit the dissolution of polysulfides, further consolidating the research enthusiasm of cobalt-iron-based materials in the field of lithium-sulfur battery diaphragms, and making the urgency of obtaining raw materials from waste batteries more prominent.

[0005] Cobalt-iron hollow composite materials have great potential in the modification of lithium-sulfur battery separators due to their unique structure and excellent physical and chemical properties. Such materials usually have a high specific surface area, good conductivity and catalytic activity, and can efficiently adsorb polysulfides and promote their conversion, thereby improving the overall performance of the battery. However, traditional synthesis methods often require complex process flows and expensive precursors, which greatly limits their large-scale application. This urgently requires finding new sources of materials and synthesis processes. Recycling materials from waste lithium iron phosphate batteries is undoubtedly a very promising direction.

[0006] For example, a high-stability non-precious metal oxygen reduction catalyst and a membrane electrode preparation method thereof disclosed in a Chinese patent application with application number CN 202411104463.2. The method mainly involves synthesizing a zeolite imidazole metal organic framework compound (ZIF-67) using cobalt nitrate hexahydrate and dimethylimidazole as raw materials, adding an inorganic salt of cerium or an organic compound of cerium during the synthesis of ZIF-67, and obtaining a catalyst precursor encapsulating the pre-transition metal cerium. Then, a non-precious metal oxygen reduction catalyst (Ce-Co / N / C) containing cerium is obtained by high-temperature cracking under an inert atmosphere. The catalyst has excellent oxygen reduction catalytic performance. When applied to the cathode catalyst layer of a proton exchange membrane fuel cell, it has outstanding performance in a single cell and exhibits excellent stability. However, although the direct addition of a cerium source during the synthesis of ZIF-67 can directly integrate cerium ions into the framework, this method is difficult to accurately control the ratio and spatial distribution between cerium, cobalt, and other elements that may exist. Due to the large size of cerium ions, changes in the crystal structure of ZIF-67 may occur, thereby affecting the morphology and performance of the final product. Moreover, the behavior of cerium during high-temperature cracking is difficult to predict, which may cause cerium to exist in an undesirable phase, such as cerium oxide particles, thereby reducing the catalytic efficiency. The method of using ZIF-67 to coat PDA and doping Fe elements in this patent can more accurately control the distribution of Fe and Co elements. ZIF-67 (cobalt-based zeolite imidazole framework material) provides uniformly dispersed active sites as a template, and the presence of the PDA layer can form a nitrogen-rich carbon layer during pyrolysis, which not only helps to improve conductivity and stability, but also enhances the anchoring effect on metal atoms and prevents their agglomeration. In addition, the introduction of Fe can optimize the catalytic activity by adjusting the local electronic structure. .

[0007] Another example is a recycling process for waste lithium iron phosphate positive electrode materials disclosed in a Chinese patent application with application number CN 202410970414.0, which mainly includes grading, high-temperature dimethylacetamide steam infiltration, multiple deionization rinses, separation of aluminum foil and active substances, mixed grinding, and high-temperature calcination, and finally obtains lithium iron phosphate repair materials. The patent adopts a recycling process to obtain key elements such as cobalt and iron from waste lithium iron phosphate positive electrode materials by using high-temperature dimethylacetamide steam infiltration, and then prepares cobalt-iron hollow composite diaphragm materials for lithium-sulfur batteries, but its preparation process is complicated, and the prepared cobalt-iron material does not have a stable face and hollow structure, which greatly reduces its catalytic sites and material surface area. This patent introduces ZIF-67 / PDA substrate in the process of recycling waste lithium iron phosphate positive electrode materials, which not only ensures the utilization of cobalt and iron elements, but also makes the material have a stable face and hollow structure.

[0008] Therefore, it is necessary to study a simple, efficient and environmentally friendly method for recycling waste iron phosphate lithium-ion battery positive electrode materials, and successfully apply the recycled materials to the preparation of cobalt-iron hollow composite diaphragm materials for lithium-sulfur batteries. This is of great positive significance for solving the problem of handling waste battery materials and promoting the development of high-performance lithium-sulfur batteries. Summary of the invention

[0009] The purpose of the present invention is to provide a method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode material in view of the problems of complex process flow and expensive precursors of the above-mentioned traditional synthetic cobalt-iron hollow composite diaphragm material for lithium-sulfur batteries.

[0010] To achieve the above object, the present invention adopts the following technical solution:

[0011] A method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode material comprises the following steps:

[0012] Step 1: Classify the waste lithium iron phosphate battery materials to obtain lithium iron phosphate positive electrode sheets;

[0013] Step 2: Mix the lithium iron phosphate positive electrode sheet, a citric acid solution with a concentration of 1.0 to 1.5 mol / L, and an ascorbic acid solution with a concentration of 0.1 to 0.3 mol / L in a ratio of 1:1 and add the mixture to a container, and sequentially perform leaching reaction, filtration, and washing to separate the solid product FePO4;

[0014] Step 3, fully dissolving 2-methylimidazole and Co(NO3)2·6H2O in a methanol solution, stirring for 2-6 hours to obtain a solution A; adding dopamine hydrochloride to the methanol solution, and placing it in an ultrasonic instrument for ultrasonic stirring to obtain a solution B;

[0015] Step 4, quickly add solution B to solution A at a ratio of 1:1, and stir evenly for 12 to 24 hours to fully mix to obtain solution C; dissolve the FePO4 obtained in step 2 in deionized water to obtain solution D;

[0016] Step 5, slowly pouring solution D into the stirring solution C, the solution ratio is 1:1, and stirring is continued for 24-48 hours after mixing evenly to obtain a mixed solution E; then repeatedly centrifuging and washing with ethanol and deionized water, and drying in an oven to obtain ZIF-67@PDA / Fe;

[0017] Step 6: heat-treating the ZIF-67@PDA / Fe obtained in step 5, specifically:

[0018] The ZIF-67@PDA / Fe was placed in a tube furnace, heated to 900°C in a nitrogen environment and maintained for 2 to 4 hours, and then cooled to room temperature to obtain a cobalt-iron hollow composite material (CoFeNC@NC);

[0019] Step 7, the cobalt iron hollow composite material (CoFeNC@NC), conductive carbon black Super P, and polyvinylidene fluoride (PVDF) are uniformly ground in a mass ratio of 8:1:1, and then NMP is added with a volume ratio of 1:1 to the grinding material for uniform grinding to obtain a mixed slurry, the mixed slurry is coated on the PP diaphragm, and dried at a temperature of 50 to 70°C to obtain a cobalt iron hollow composite diaphragm.

[0020] Furthermore, a lithium-sulfur battery is assembled using the cobalt-iron hollow composite diaphragm prepared by the above method.

[0021] Furthermore, in step 2, the leaching reaction temperature is 80°C and the reaction time is 50-70°C.

[0022] Furthermore, the step 3 is to dissolve 2-methylimidazole and Co(NO3)2·6H2O in 60 mL of deionized water at a molar ratio of 5:1-20:1 to obtain solution A; add 20-40 mg of dopamine hydrochloride to 20 mL of methanol solution and ultrasonically stir for 5 to 10 minutes to obtain solution B.

[0023] Furthermore, in step 5, the mixed solution E is repeatedly centrifuged and washed 3 to 6 times with ethanol and deionized water, and dried in an oven at 60° C. for 12 to 24 hours to obtain ZIF-67@PDA / Fe;

[0024] Furthermore, the heat treatment conditions of step 6 are as follows: ZIF-67@PDA / Fe is heated to 900°C in a nitrogen environment at a heating rate of 2-5°C / min and maintained for 2-4 hours.

[0025] The present invention provides a method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode materials. In the recovery stage: a mixed solution of citric acid and ascorbic acid is used for leaching treatment, lithium elements are efficiently extracted from waste lithium iron phosphate battery positive electrode materials, and lithium iron phosphate (LiFePO4) is efficiently converted into iron phosphate (FePO4). The corrosive problems and many safety hazards caused by traditional inorganic strong acid methods are avoided, and the safety and environmental protection of the operation process are significantly improved. The recovery process not only has a high recovery rate and simple operation, but also reduces the requirements for equipment and environmental pollution. It is suitable for large-scale production applications. It is particularly critical that no other metal salts are introduced during the recovery process, which reduces the material cost and makes the final product more competitive in the market in terms of purity and cost control.

[0026] In the stage of re-utilization of recycled FePO4: through the synthesis of ZIF-67@PDA / Fe intermediates, the precise and controllable synthesis of materials was achieved. Not only did the process flow simplify, but also the utilization rate of the material and its performance were improved. The prepared cobalt-iron hollow composite diaphragm material exhibited extremely excellent electrochemical properties, which were specifically reflected in the high first discharge capacity (not less than 1260mAh / g), excellent rate performance (under 2C current charge and discharge conditions, the discharge capacity can still reach 930mAh / g) and good cycle performance (the capacity retention rate reached more than 88% after 100 charge and discharge cycles at a current density of 0.5C). The battery was tested at rates of 0.5C, 1C, 2C, 3C, 2C, and 1C, and 10 cycles were performed at each rate. Finally, a capacity recovery rate of up to 90% was achieved at 1C.

[0027] The entire preparation process only includes conventional steps such as leaching, separation, synthesis and heat treatment. It is simple to operate, easy to control, suitable for large-scale industrial production, and helps to reduce production costs and improve production efficiency. The prepared cobalt-iron hollow composite diaphragm material not only solves the problem of processing waste lithium iron phosphate battery positive electrode materials, but also provides high-quality diaphragm materials for the preparation of high-performance lithium-sulfur batteries, realizes the effective recycling of resources, reduces environmental pollution, and improves the sustainability of battery materials.

[0028] In summary, the method of the present invention realizes resource recycling, provides high-quality diaphragm materials for high-performance lithium-sulfur batteries, and promotes the development of clean energy technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Flow chart for preparing cobalt-iron hollow composite materials for recycling.

[0030] Figure 2 This is a schematic diagram of the structure of the cobalt-iron hollow composite material recovered and prepared in Example 1.

[0031] Figure 3 This is the rate performance diagram of the lithium-sulfur battery recovered and prepared in Example 1.

[0032] Figure 4 This is the cycle performance diagram of the lithium-sulfur battery recycled and prepared in Example 1. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0034] Example 1

[0035] like Figure 1 As shown, the present embodiment provides a method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode material, comprising the following steps:

[0036] 1) Classifying waste lithium iron phosphate battery materials to obtain lithium iron phosphate positive electrode sheets;

[0037] 2) Prepare 1.0 mol / L citric acid solution and 0.1 mol / L ascorbic acid solution respectively, the ratio of citric acid solution to ascorbic acid solution is 1:1, mix well and add into a three-necked flask.

[0038] 3) placing the three-necked flask containing the mixture of the citric acid solution and the ascorbic acid solution in a water bath at 80° C. for leaching reaction for 60 minutes; after the reaction is completed, filtering and washing to separate the solid product FePO4.

[0039] 4) Weigh 5 mmol of 2-methylimidazole and 1 mmol of Co(NO3)2·6H2O, dissolve them in 60 mL of methanol, and stir them for 2 hours to obtain solution A. Weigh 20 mg of dopamine hydrochloride and add them to 20 mL of methanol solution, stir them for 5 minutes under ultrasonic stirring to obtain solution B.

[0040] 5) Solution B was quickly added to solution A at a ratio of 1:1, and stirred evenly for 12 hours to obtain solution C. The FePO4 obtained in step 3) was dissolved in 75 mL of deionized water to obtain solution D.

[0041] 6) Solution D was slowly poured into the stirring solution C, and after mixing evenly, stirring was continued for 24 hours. Then, the solution was repeatedly centrifuged and washed four times with ethanol and deionized water, and dried in an oven at 60° C. for 12 hours to obtain ZIF-67@PDA / Fe.

[0042] 7) The ZIF-67@PDA / Fe obtained in step 6) was placed in a tubular furnace, heated to 900°C at a heating rate of 2°C / min in a nitrogen environment and maintained for 2 hours. It was then cooled to room temperature to obtain a cobalt-iron hollow composite material (CoFeNC@NC).

[0043] 8) The obtained cobalt iron hollow composite material (CoFeNC@NC), Super P and PVDF were uniformly ground at a mass ratio of 8:1:1, and then NMP was added at a volume ratio of 1:1 to the grinding material for uniform grinding. The mixed slurry was quickly coated on the PP diaphragm, and the coated cobalt iron hollow composite modified diaphragm was placed in a 60°C oven and left to stand for 24 hours to obtain a cobalt iron hollow composite diaphragm.

[0044] 9) Assembling a lithium-sulfur battery using the cobalt-iron hollow composite diaphragm obtained in step 8). The assembled lithium-sulfur battery has excellent performance.

[0045] Example 2

[0046] A method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode material comprises the following steps:

[0047] 1) Classifying waste lithium iron phosphate battery materials to obtain lithium iron phosphate positive electrode sheets;

[0048] 2) Prepare citric acid and ascorbic acid solutions with concentrations of 1.5 mol / L and 0.1 mol / L respectively, mix them and add them into a three-necked flask.

[0049] 3) placing the three-necked flask containing the mixture of the citric acid solution and the ascorbic acid solution in a water bath at 80° C. for leaching reaction for 60 minutes; after the reaction is completed, filtering and washing to separate the solid product FePO4.

[0050] 4) Weigh 5 mmol of 2-methylimidazole and 1 mmol of Co(NO3)2·6H2O, dissolve them in 60 mL of methanol, and stir them for 2 hours to obtain solution A. Weigh 20 mg of dopamine hydrochloride and add them to 20 mL of methanol solution, stir them for 5 minutes under ultrasonic stirring to obtain solution B.

[0051] 5) Solution B was quickly added to Solution A and stirred evenly for 12 hours to obtain Solution C. The FePO4 obtained in step 3) was dissolved in 75 mL of deionized water to obtain Solution D.

[0052] 6) Solution D was slowly poured into the stirring solution C at a ratio of 1:1. After mixing evenly, stirring was continued for 24 hours. Then, the mixture was repeatedly centrifuged and washed four times with ethanol and deionized water, and dried in an oven at 60°C for 12 hours to obtain ZIF-67@PDA / Fe.

[0053] 7) The ZIF-67@PDA / Fe obtained in step 6) was placed in a tubular furnace, heated to 900°C at a heating rate of 2°C / min in a nitrogen environment and maintained for 2 hours. It was then cooled to room temperature to obtain a cobalt-iron hollow composite material (CoFeNC@NC).

[0054] 8) The obtained cobalt iron hollow composite material (CoFeNC@NC), Super P and PVDF were uniformly ground at a mass ratio of 8:1:1, and then NMP was added at a volume ratio of 1:1 to the grinding material for uniform grinding. The mixed slurry was quickly coated on the PP diaphragm, and the coated cobalt iron hollow composite modified diaphragm was placed in a 60°C oven and left to stand for 24 hours to obtain a cobalt iron hollow composite diaphragm.

[0055] 9) Assembling a lithium-sulfur battery using the cobalt-iron hollow composite diaphragm obtained in step 8). The assembled lithium-sulfur battery has excellent performance.

[0056] Example 3

[0057] A method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode material comprises the following steps:

[0058] 1) Classifying waste lithium iron phosphate battery materials to obtain lithium iron phosphate positive electrode sheets;

[0059] 2) Prepare citric acid and ascorbic acid solutions with concentrations of 1.5 mol / L and 0.3 mol / L respectively, mix them and add them into a three-necked flask.

[0060] 3) placing the three-necked flask in a water bath at 80° C. for leaching reaction for 60 minutes; after the reaction is completed, filtering and washing to separate the solid product FePO4.

[0061] 4) Weigh 5 mmol of 2-methylimidazole and 1 mmol of Co(NO3)2·6H2O, dissolve them in 60 mL of methanol, and stir them for 2 hours to prepare solution A. Weigh 20 mg of dopamine hydrochloride and add them to 20 mL of methanol solution, stir them for minutes under ultrasonic stirring to prepare solution B.

[0062] 5) Solution B was quickly added to Solution A and stirred evenly for 12 hours to obtain Solution C. The FePO4 obtained in step 3) was dissolved in 75 mL of deionized water to obtain Solution D.

[0063] 6) Solution D was slowly poured into the stirring solution C, and after mixing evenly, stirring was continued for 24 hours. Then, the solution was repeatedly centrifuged and washed four times with ethanol and deionized water, and dried in an oven at 60° C. for 12 hours to obtain ZIF-67@PDA / Fe.

[0064] 7) The ZIF-67@PDA / Fe obtained in step 6) was placed in a tubular furnace, heated to 900°C at a heating rate of 2°C / min in a nitrogen environment and maintained for 2 hours. It was then cooled to room temperature to obtain a cobalt-iron hollow composite material (CoFeNC@NC).

[0065] 8) The obtained cobalt iron hollow composite material (CoFeNC@NC), Super P and PVDF were uniformly ground at a mass ratio of 8:1:1, and then NMP was added at a volume ratio of 1:1 to the grinding material for uniform grinding. The mixed slurry was quickly coated on the PP diaphragm, and the coated cobalt iron hollow composite modified diaphragm was placed in a 60°C oven and left to stand for 24 hours to obtain a cobalt iron hollow composite diaphragm.

[0066] 9) Assembling a lithium-sulfur battery using the cobalt-iron hollow composite diaphragm obtained in step 8). The assembled lithium-sulfur battery has excellent performance.

[0067] Example 4

[0068] A method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode material comprises the following steps:

[0069] 1) Classifying waste lithium iron phosphate battery materials to obtain lithium iron phosphate positive electrode sheets;

[0070] 2) Prepare citric acid and ascorbic acid solutions with concentrations of 1.5 mol / L and 0.3 mol / L respectively, mix them and add them into a three-necked flask.

[0071] 3) placing the three-necked flask in a water bath at 80° C. for leaching reaction, with a solid-liquid ratio of 1:20 and a reaction time of 60 minutes; after the reaction is completed, the solid product FePO4 is separated by filtration and washing.

[0072] 4) Weigh 5 mmol of 2-methylimidazole and 1 mmol of Co(NO3)2·6H2O, dissolve them in 60 mL of methanol, and stir them for 2 hours to obtain solution A. Weigh 20 mg of dopamine hydrochloride and add them to 20 mL of methanol solution, stir them for 5 minutes under ultrasonic stirring to obtain solution B.

[0073] 5) Solution B was quickly added to Solution A and stirred evenly for 12 hours to obtain Solution C. The FePO4 obtained in step 3) was dissolved in 75 mL of deionized water to obtain Solution D.

[0074] 6) Solution D was slowly poured into the stirring solution C, and after mixing evenly, stirring was continued for 24 hours. Then, the solution was repeatedly centrifuged and washed four times with ethanol and deionized water, and dried in an oven at 60° C. for 12 hours to obtain ZIF-67@PDA / Fe.

[0075] 7) The ZIF-67@PDA / Fe obtained in step 6) was placed in a tubular furnace, heated to 900°C at a heating rate of 2°C / min in a nitrogen environment and maintained for 2 hours. It was then cooled to room temperature to obtain a cobalt-iron hollow composite material (CoFeNC@NC).

[0076] 8) The obtained cobalt iron hollow composite material (CoFeNC@NC), Super P and PVDF were uniformly ground at a mass ratio of 8:1:1, and then NMP was added at a volume ratio of 1:1 to the grinding material for uniform grinding. The mixed slurry was quickly coated on the PP diaphragm, and the coated cobalt iron hollow composite modified diaphragm was placed in a 60°C oven and left to stand for 24 hours to obtain a cobalt iron hollow composite diaphragm.

[0077] 9) Assembling a lithium-sulfur battery using the cobalt-iron hollow composite diaphragm obtained in step 8). The assembled lithium-sulfur battery has excellent performance.

[0078] Example 5

[0079] A method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode material comprises the following steps:

[0080] 1) Classifying waste lithium iron phosphate battery materials to obtain lithium iron phosphate positive electrode sheets;

[0081] 2) Prepare citric acid and ascorbic acid solutions with concentrations of 1.5 mol / L and 0.3 mol / L respectively, mix them and add them into a three-necked flask.

[0082] 3) placing the three-necked flask in a water bath at 80° C. for leaching reaction, with a solid-liquid ratio of 1:20 and a reaction time of 60 minutes; after the reaction is completed, the solid product FePO4 is separated by filtration and washing.

[0083] 4) Weigh 10 mmol of 2-methylimidazole and 1 mmol of Co(NO3)2·6H2O, dissolve them in 60 mL of methanol, and stir them for 2 hours to obtain solution A. Weigh 20 mg of dopamine hydrochloride and add them to 20 mL of methanol solution, stir them for 5 minutes under ultrasonication to obtain solution B.

[0084] 5) Solution B was quickly added to Solution A and stirred evenly for 12 hours to obtain Solution C. The FePO4 obtained in step 3) was dissolved in 75 mL of deionized water to obtain Solution D.

[0085] 6) Solution D was slowly poured into the stirring solution C, and after mixing evenly, stirring was continued for 24 hours. Then, the solution was repeatedly centrifuged and washed four times with ethanol and deionized water, and dried in an oven at 60° C. for 12 hours to obtain ZIF-67@PDA / Fe.

[0086] 7) The ZIF-67@PDA / Fe obtained in step 6) was placed in a tubular furnace, heated to 900°C at a heating rate of 2°C / min in a nitrogen environment and maintained for 2 hours. It was then cooled to room temperature to obtain a cobalt-iron hollow composite material (CoFeNC@NC).

[0087] 8) The obtained cobalt iron hollow composite material (CoFeNC@NC), Super P and PVDF were uniformly ground at a mass ratio of 8:1:1, and then NMP with a grinding material volume ratio of 1:1 was added for uniform grinding. The mixed slurry was quickly coated on the PP diaphragm, and the coated cobalt iron hollow composite modified diaphragm was placed in a 60°C oven and left to stand for 24 hours to obtain a cobalt iron hollow composite diaphragm.

[0088] 9) Assembling a lithium-sulfur battery using the cobalt-iron hollow composite diaphragm obtained in step 8). The assembled lithium-sulfur battery has excellent performance.

[0089] Example 6

[0090] A method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode material comprises the following steps:

[0091] 1) Classifying waste lithium iron phosphate battery materials to obtain lithium iron phosphate positive electrode sheets;

[0092] 2) Mix a 1.5 mol / L citric acid solution and a 0.3 mol / L ascorbic acid solution and add them into a three-necked flask.

[0093] 3) The three-necked flask was placed in a water bath at 80° C. for reaction, with a solid-liquid ratio of 1:20 and a reaction time of 60 minutes. After the reaction was completed, the solid product FePO4 was separated by filtration and washing.

[0094] 4) Weigh 20 mmol of 2-methylimidazole and 1 mmol of Co(NO3)2·6H2O, dissolve in 60 mL of methanol, stir thoroughly for 2 hours, and mark as solution A. Weigh 20 mg of dopamine hydrochloride and add to 20 mL of methanol solution, ultrasonicate for 5 minutes, and mark as solution B.

[0095] 5) Solution B was quickly added to Solution A and stirred evenly for 12 hours, which was labeled as Solution C. The FePO4 obtained in step 3) was dissolved in 75 mL of deionized water, which was labeled as Solution D.

[0096] 6) Solution D was slowly poured into the stirring solution C, and the mixture was stirred for 24 hours after being evenly mixed. Then, the mixture was centrifuged and washed four times with ethanol and deionized water, and dried in an oven at 60°C for 12 hours to obtain ZIF-67@PDA / Fe.

[0097] 7) The dried ZIF-67@PDA / Fe product was placed in a tube furnace, heated to 900°C at a heating rate of 2°C / min in a nitrogen environment and maintained for 2 hours. It was then cooled to room temperature to obtain the final product, a cobalt-iron hollow composite material (CoFeNC@NC).

[0098] 8) The obtained cobalt-iron hollow composite material (CoFeNC@NC), Super P and PVDF were uniformly ground at a mass ratio of 8:1:1, and then an appropriate amount of NMP was added for uniform grinding. The mixed slurry was quickly coated on the PP diaphragm, and the coated cobalt-iron hollow composite modified diaphragm was placed in a 60°C oven and allowed to stand for 24 hours to obtain a cobalt-iron hollow composite diaphragm.

[0099] 9) Assembling a lithium-sulfur battery using the cobalt-iron hollow composite diaphragm obtained in step 8). The assembled lithium-sulfur battery has excellent performance.

[0100] Example 7

[0101] A method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode material comprises the following steps:

[0102] 1) Classifying waste lithium iron phosphate battery materials to obtain lithium iron phosphate positive electrode sheets;

[0103] 2) Mix a 1.5 mol / L citric acid solution and a 0.3 mol / L ascorbic acid solution and add them into a three-necked flask.

[0104] 3) The three-necked flask was placed in a water bath at 80° C. for leaching reaction, with a solid-liquid ratio of 1:20 and a reaction time of 60 minutes. After the reaction was completed, the solid product FePO4 was separated by filtration and washing.

[0105] 4) Weigh 10 mmol of 2-methylimidazole and 1 mmol of Co(NO3)2·6H2O, dissolve in 60 mL of methanol, stir thoroughly for 2 hours, and mark as solution A. Weigh 30 mg of dopamine hydrochloride and add to 20 mL of methanol solution, ultrasonicate for 5 minutes, and mark as solution B.

[0106] 5) Solution B was quickly added to Solution A and stirred evenly for 12 hours, which was labeled as Solution C. The FePO4 obtained in step 3) was dissolved in 75 mL of deionized water, which was labeled as Solution D.

[0107] 6) Solution D was slowly poured into the stirring solution C, and the mixture was stirred for 24 hours after being evenly mixed. Then, the mixture was centrifuged and washed four times with ethanol and deionized water, and dried in an oven at 60°C for 12 hours to obtain ZIF-67@PDA / Fe.

[0108] 7) The ZIF-67@PDA / Fe obtained in step 6) is placed in a tubular furnace and heated to 900°C at a heating rate of 2°C / min in a nitrogen environment and maintained for 2 hours. After cooling to room temperature, a cobalt-iron hollow composite material (CoFeNC@NC) is obtained.

[0109] 8) The cobalt-iron hollow composite material (CoFeNC@NC), Super P and PVDF were uniformly ground at a mass ratio of 8:1:1, and then NMP with a grinding material volume ratio of 1:1 was added for uniform grinding. The mixed slurry was quickly coated on the PP diaphragm, and the coated cobalt-iron hollow composite modified diaphragm was placed in a 60°C oven and allowed to stand for 24 hours to obtain a cobalt-iron hollow composite diaphragm.

[0110] 9) Assembling a lithium-sulfur battery using the cobalt-iron hollow composite diaphragm obtained in step 8). The assembled lithium-sulfur battery has excellent performance.

[0111] Example 8

[0112] A method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode material comprises the following steps:

[0113] 1) Classifying waste lithium iron phosphate battery materials to obtain lithium iron phosphate positive electrode sheets;

[0114] 2) Mix 1.5 mol / L citric acid and 0.3 mol / L ascorbic acid and add them into a three-necked flask.

[0115] 3) The reaction was carried out in a water bath at 80° C., with a solid-liquid ratio of 1:20 and a reaction time of 60 minutes. After the reaction was completed, the solid product FePO4 was separated by filtration and washing.

[0116] 4) Weigh 10 mmol of 2-methylimidazole and 1 mmol of Co(NO3)2·6H2O, dissolve in 60 mL of methanol, stir thoroughly for 2 hours, and mark as solution A. Weigh 40 mg of dopamine hydrochloride and add to 20 mL of methanol solution, perform ultrasonic operation for 5 minutes, and mark as solution B.

[0117] 5) Solution B was quickly added to Solution A and stirred evenly for 12 hours, which was labeled as Solution C. The FePO4 obtained in step 3) was dissolved in 75 mL of deionized water, which was labeled as Solution D.

[0118] 6) Solution D was slowly poured into the stirring solution C, and the mixture was stirred for 24 hours after being evenly mixed. Then, the mixture was centrifuged and washed repeatedly with ethanol and deionized water for 4 times, and dried in an oven at 60°C for 12 hours to obtain ZIF-67@PDA / Fe.

[0119] 7) The ZIF-67@PDA / Fe product obtained in step 6) was placed in a tubular furnace, heated to 900°C at a heating rate of 2°C / min in a nitrogen environment and maintained for 2 hours. After cooling to room temperature, a cobalt-iron hollow composite material (CoFeNC@NC) was obtained.

[0120] 8) The obtained cobalt-iron hollow composite material (CoFeNC@NC), Super P and PVDF were uniformly ground at a mass ratio of 8:1:1, and then an appropriate amount of NMP was added for uniform grinding. The mixed slurry was quickly coated on the PP diaphragm, and the coated cobalt-iron hollow composite modified diaphragm was placed in a 60°C oven and allowed to stand for 24 hours to obtain a cobalt-iron hollow composite diaphragm.

[0121] 9) Assembling a lithium-sulfur battery using the cobalt-iron hollow composite diaphragm obtained in step 8). The assembled lithium-sulfur battery has excellent performance.

[0122] Example 9

[0123] A method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode material comprises the following steps:

[0124] 1) Classifying waste lithium iron phosphate battery materials to obtain lithium iron phosphate positive electrode sheets;

[0125] 2) Mix a 1.5 mol / L citric acid solution and a 0.3 mol / L ascorbic acid solution and add them into a three-necked flask.

[0126] 3) The three-necked flask obtained in step 2) was placed in a water bath at 80° C. for reaction, with a solid-liquid ratio of 1:20 and a reaction time of 60 minutes. After the reaction was completed, the solid product FePO4 was separated by filtration and washing.

[0127] 4) Weigh 10 mmol of 2-methylimidazole and 1 mmol of Co(NO3)2·6H2O, dissolve in 60 mL of methanol, stir thoroughly for 2 hours, and mark as solution A. Weigh 40 mg of dopamine hydrochloride and add to 20 mL of methanol solution, perform ultrasonic operation for 5 minutes, and mark as solution B.

[0128] 4) Solution B was quickly added to Solution A, and stirred evenly for 12 hours, which was marked as Solution C. FePO4 recovered from the cathode material of waste lithium iron phosphate batteries was dissolved in 75 mL of deionized water, which was marked as Solution D.

[0129] 5) Solution D was slowly poured into the stirring solution C, and after mixing evenly, stirring was continued for 24 hours. Then, ethanol and deionized water were repeatedly centrifuged and washed 4 times, and dried in an oven at 60°C for 12 hours to obtain ZIF-67@PDA / Fe.

[0130] 6) The ZIF-67@PDA / Fe obtained in step 5) is placed in a tubular furnace, heated to 900°C at a heating rate of 5°C / min in a nitrogen environment and maintained for 2 hours. After cooling to room temperature, a cobalt-iron hollow composite material (CoFeNC@NC) is obtained.

[0131] 7) The obtained cobalt-iron hollow composite material (CoFeNC@NC), Super P and PVDF were uniformly ground at a mass ratio of 8:1:1, and then an appropriate amount of NMP was added for uniform grinding. The mixed slurry was quickly coated on the PP diaphragm, and the coated cobalt-iron hollow composite modified diaphragm was placed in a 60°C oven and allowed to stand for 24 hours to obtain a cobalt-iron hollow composite diaphragm.

[0132] 9) Assembling a lithium-sulfur battery using the cobalt-iron hollow composite diaphragm obtained in step 8). The assembled lithium-sulfur battery has excellent performance.

[0133] Example 10

[0134] A method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode material comprises the following steps:

[0135] 1) Classifying waste lithium iron phosphate battery materials to obtain lithium iron phosphate positive electrode sheets;

[0136] 2) A 1.5 mol / L citric acid solution and a 0.3 mol / L ascorbic acid solution were prepared into solutions respectively, mixed and added into a three-necked flask.

[0137] 3) The reaction was carried out in a water bath at 80° C., with a solid-liquid ratio of 1:20 and a reaction time of 60 minutes. After the reaction was completed, the solid product FePO4 was separated by filtration and washing.

[0138] 4) Weigh 10 mmol of 2-methylimidazole and 1 mmol of Co(NO3)2·6H2O, dissolve in 60 mL of methanol, stir thoroughly for 2 hours, and mark as solution A. Weigh 40 mg of dopamine hydrochloride and add to 20 mL of methanol solution, perform ultrasonic operation for 5 minutes, and mark as solution B.

[0139] 5) Rapidly add solution B to solution A, stir evenly for 12 hours, and mark it as solution C. Dissolve FePO4 recovered from the cathode material of waste lithium iron phosphate battery in 75 mL of deionized water, and mark it as solution D.

[0140] 6) Solution D was slowly poured into the stirring solution C, and the mixture was stirred for 24 hours after being evenly mixed. Then, the mixture was centrifuged and washed four times with ethanol and deionized water, and dried in an oven at 60°C for 12 hours to obtain ZIF-67@PDA / Fe.

[0141] 7) The ZIF-67@PDA / Fe product obtained in step 6) was placed in a tubular furnace, heated to 900°C at a heating rate of 5°C / min in a nitrogen environment and maintained for 3 hours, and then cooled to room temperature to obtain the final product, a cobalt-iron hollow composite material (CoFeNC@NC).

[0142] 8) The obtained cobalt-iron hollow composite material (CoFeNC@NC), Super P and PVDF were uniformly ground at a mass ratio of 8:1:1, and then an appropriate amount of NMP was added for uniform grinding. The mixed slurry was quickly coated on the PP diaphragm, and the coated cobalt-iron hollow composite modified diaphragm was placed in a 60°C oven and allowed to stand for 24 hours to obtain a cobalt-iron hollow composite diaphragm.

[0143] 9) Assembling a lithium-sulfur battery using the cobalt-iron hollow composite diaphragm obtained in step 8). The assembled lithium-sulfur battery has excellent performance.

[0144] Figure 2To demonstrate the structure of the recycled cobalt-iron hollow composite material prepared in the embodiment, Figure 2 As shown in the figure, the cobalt-iron composite material generated by high temperature treatment in a nitrogen environment exhibits a series of clear and unique morphological features. The material not only inherits the original crystal dodecahedron structure of the ZIF-67 precursor, but also achieves uniform dispersion at the nanoscale. During the pyrolysis process, the presence of the PDA layer acts as a template for carbonization to prevent its agglomeration, thereby ensuring that the material has good dispersion and a highly conductive carbon matrix.

[0145] After high-temperature treatment in a nitrogen environment, the stability of the material during the transformation process is guaranteed, unnecessary oxidation reactions are avoided, and the uniform distribution of metal atoms is promoted. This synthetic route can form a core-shell structure or a mosaic structure, in which the core part is composed of cobalt iron oxide or alloy, and the shell is a nitrogen-containing carbon layer derived from PDA. In addition, due to the gas escape during the decomposition of PDA and the volume shrinkage associated with the decomposition of ZIF-67, a hollow pore structure is formed inside the material, which not only increases the specific surface area of ​​the material, but also optimizes the material transfer path, exposing more active sites, and has a positive effect on the catalytic performance.

[0146] Figure 3 To demonstrate the rate performance of the recycled lithium-sulfur battery given in Example 1, Figure 3 As shown, in the rate test, the prepared cobalt iron oxide diaphragm lithium-sulfur battery achieved high specific capacities of 1283, 1201, 1125, and 887 mAh / g at fast charging rates of 0.5C, 1C, 2C, and 3C, respectively, and also reached 1097 mAh / g when it was subsequently restored to 1C, i.e., a high recovery rate of 91%, all of which indicate that the prepared cobalt-iron composite diaphragm lithium-sulfur battery has excellent performance and stability.

[0147] Figure 4 The cycle performance diagram of the lithium-sulfur battery prepared by implementation 1 is shown. Figure 4 As shown in the figure, under the current charge and discharge conditions of 2C, the discharge capacity is still maintained above 930mAh / g after 100 cycles; under the current density of 0.5C, the initial discharge capacity is as high as 1268mAh / g. After 100 charge and discharge cycles, the capacity retention rate is more than 90%, and the charge and discharge efficiency of all test processes is above 98%.

Claims

1. A method for preparing a cobalt-iron composite diaphragm based on waste lithium iron phosphate positive electrode material, characterized in that: The following steps are involved: Step 1: Classify the waste lithium iron phosphate battery materials to obtain lithium iron phosphate positive electrode sheets; Step 2: Mix the lithium iron phosphate positive electrode sheet, a citric acid solution with a concentration of 1.0 to 1.5 mol / L, and an ascorbic acid solution with a concentration of 0.1 to 0.3 mol / L in a ratio of 1:1 and add the mixture to a container, and sequentially perform leaching reaction, filtration, and washing to separate the solid product FePO4; Step 3, fully dissolving 2-methylimidazole and Co(NO3)2·6H2O in a methanol solution, stirring for 2-6 hours to obtain a solution A; adding dopamine hydrochloride to the methanol solution, and placing it in an ultrasonic instrument for ultrasonic stirring to obtain a solution B; Step 4, quickly add solution B to solution A at a ratio of 1:1, and stir evenly for 12 to 24 hours to fully mix to obtain solution C; dissolve the FePO4 obtained in step 2 in deionized water to obtain solution D; Step 5, slowly pouring solution D into the stirring solution C, the solution ratio is 1:1, and stirring is continued for 24-48 hours after mixing evenly to obtain a mixed solution E; then repeatedly centrifuging and washing with ethanol and deionized water, and drying in an oven to obtain ZIF-67@PDA / Fe; Step 6: heat-treating the ZIF-67@PDA / Fe obtained in step 5, specifically: The ZIF-67@PDA / Fe was placed in a tube furnace, heated to 900°C in a nitrogen environment and maintained for 2 to 4 hours, and then cooled to room temperature to obtain a cobalt-iron hollow composite material (CoFeNC@NC); Step 7, the cobalt iron hollow composite material (CoFeNC@NC), conductive carbon black Super P, and polyvinylidene fluoride (PVDF) are uniformly ground in a mass ratio of 8:1:1, and then NMP is added with a volume ratio of 1:1 to the grinding material for uniform grinding to obtain a mixed slurry, the mixed slurry is coated on the PP diaphragm, and dried at a temperature of 50 to 70°C to obtain a cobalt iron hollow composite diaphragm.

2. The method according to claim 1, characterized in that: In step 2, the leaching reaction temperature is 80° C. and the reaction time is 50-70° C.

3. The method according to claim 1, characterized in that The step 3 is to dissolve 2-methylimidazole and Co(NO3)2·6H2O in 60 mL of deionized water at a molar ratio of 5:1-20:1 to obtain solution A; add 20-40 mg of dopamine hydrochloride to 20 mL of methanol solution, and ultrasonically stir for 5-10 minutes to obtain solution B.

4. The method according to claim 1, characterized in that In step 5, the mixed solution E is repeatedly centrifuged and washed 3 to 6 times with ethanol and deionized water, and dried in an oven at 60° C. for 12 to 24 hours to obtain ZIF-67@PDA / Fe; 5. The method according to claim 1, characterized in that The heat treatment conditions of step 6 are as follows: ZIF-67@PDA / Fe is heated to 900° C. at a heating rate of 2-5° C. / min in a nitrogen environment and maintained for 2-4 hours.

6. Use of the cobalt-iron hollow composite diaphragm prepared by the method according to claims 1 to 5 in lithium-sulfur batteries.

Images