A method for preparing a carbon-based catalyst by recycling a conductive agent from waste lithium iron phosphate batteries and its application

Abstract

The present application relates to the technical field of recycling waste batteries, and specifically discloses a method for preparing a carbon-based catalyst by recycling a conductive agent from waste lithium iron phosphate batteries. The method comprises the following steps: S1: removing the positive electrode of a lithium-ion battery that has been disassembled by discharge, and separating the lithium iron phosphate positive electrode material from the aluminum foil; S2: grinding the lithium iron phosphate positive electrode material after drying to obtain lithium iron phosphate positive electrode material powder; S3: acid leaching; S4: filtering and separating the mixed solution after heating and stirring, and treating the filtrate obtained after filtration to recover lithium; S5: washing, drying, and grinding the filter residue after filtration to obtain filter residue powder; S6: weighing 100-300mg of the filter residue powder, placing it in a high-temperature crucible, and then calcining it at 900℃ in a nitrogen atmosphere for 3-5h to obtain an Fe-N-P co-doped carbon catalyst. The invention provides a new idea for the recycling of waste lithium iron phosphate lithium-ion batteries, with a high lithium recovery rate and high-value reuse of the recovered conductive agent.

Description

Technical Field

[0001] The present application relates to the technical field of recycling of waste batteries, and more specifically, to a method for recycling a conductive agent from waste lithium iron phosphate batteries and preparing a carbon-based catalyst therefor. Background Art

[0002] The impending wave of power battery retirements has garnered global attention. Early lithium-ion batteries used in electric and hybrid vehicles can be simply divided into two categories based on their cathode materials: nickel-cobalt-manganese oxide (NCM) and lithium iron phosphate (LFP). Nickel, cobalt, and lithium are all high-value, rare resources. Currently, methods for recycling cathode materials include pyrometallurgy, hydrometallurgy, and biometallurgy. Hydrometallurgy combined with separation technology offers the advantages of low reaction temperature, low energy consumption, and high recovery rates. However, as a high-value auxiliary material, conductive agents in cathode materials have yet to be rationally utilized and are currently primarily discarded as solid waste or plastic fillers.

[0003] Conductive agents are distributed in the gaps between the positive electrode active materials, forming a conductive network and improving the conductivity of the positive electrode material. Commonly used conductive agents include traditional conductive agents such as carbon black and conductive graphite, as well as newer conductive agents such as carbon nanotubes and graphene. The conductive agent is typically prepared into a slurry, mixed with the positive electrode material and a binder, and then coated onto an aluminum foil substrate. Lithium-ion battery conductive agents have higher oil absorption and lower metallic impurity content than standard carbon black. New conductive agents such as carbon nanotubes and graphene utilize line-point and surface-point contact with the positive electrode material, superior to the point-to-point contact of traditional conductive carbon black. This results in lower impedance and requires less addition. However, the downside is higher price. In recent years, new composite conductive slurries combining conductive carbon black with carbon nanotubes or graphene have gained attention, effectively reducing costs and enhancing electron conduction. It is expected that with the rapid increase in the number of retired power batteries and the use of new conductive agents, the recyclable value of conductive agents will continue to increase.

[0004] Due to repeated charging and discharging, the recycled conductive agent is contaminated with impurities such as metal ions, compounds, and electrolyte decomposition products. Repurification presents technical and cost challenges, making it difficult to reuse in lithium-ion battery manufacturing. Therefore, the key to recycling and repurifying waste conductive agents is finding suitable applications. Currently, over 90% of the nearly 10,000 fuel cell vehicles in China use imported precious metal catalysts such as Pt / C and RuO2, accounting for 36% of the total fuel cell cost. Therefore, recovering conductive agents from waste lithium iron phosphate cathode materials to prepare carbon-based catalysts has important economic and scientific value. Summary of the Invention

[0005] The present disclosure provides a method for preparing a carbon-based catalyst by recycling a conductive agent from waste lithium iron phosphate batteries, so as to recycle the lithium iron phosphate positive electrode material of lithium-ion batteries. After recovering the lithium, the conductive carbon black and iron phosphate are separated, and heat treatment is performed to obtain an oxygen reduction catalyst with excellent performance, which can be used in fuel cells, metal-air batteries and water electrolysis.

[0006] In a first aspect, the present disclosure provides a method for preparing a carbon-based catalyst by using a recycled conductive agent from waste lithium iron phosphate batteries, the method comprising the following steps:

[0007] S1: Take out the positive electrode of the lithium-ion battery after discharge and disassembly, and separate the lithium iron phosphate positive electrode material from the aluminum foil;

[0008] S2: drying and grinding the lithium iron phosphate cathode material to obtain lithium iron phosphate cathode material powder;

[0009] S3: Acid leaching: Weigh lithium iron phosphate cathode material powder and add it to sulfuric acid and hydrogen peroxide solution to obtain a mixed solution, heat the mixed solution in a water bath to 60° C.-80° C., and continue stirring for 120-240 minutes;

[0010] S4: filtering and separating the heated and stirred mixed solution, and treating the filtrate obtained after filtration to recover lithium;

[0011] S5: washing, drying, and grinding the filtered residue to obtain a filter residue powder;

[0012] S6: Weigh 100-300 mg of the filter residue powder, put it into a high-temperature crucible, and then calcine it at 600°C-900°C in a nitrogen atmosphere for 3-5 hours. After turning off the power and cooling to room temperature, take it out to obtain an Fe-NP co-doped carbon catalyst.

[0013] Lithium iron phosphate cathode materials for lithium-ion batteries are recovered through acid leaching, where lithium dissolves in the leachate as sulfate, while the iron phosphate and conductive agent remain in the leachate residue. After solid-liquid separation, the leachate is used for lithium recovery. The leachate residue is cleaned, dried, and then heat-treated in a nitrogen atmosphere. Conductive carbon materials generally have a large specific surface area, a rich pore structure, high corrosion resistance, good thermal and mechanical stability, and excellent conductivity. Active sites are formed through heteroatom doping (such as N, P, and B), topological defects, and metal-nitrogen-carbon (MNC) co-doping. Furthermore, Fe sites with dual N and P coordination facilitate the adsorption / desorption of oxygen intermediates, resulting in higher oxygen reduction reaction (ORR) catalytic activity than single N doping. Furthermore, they are low-cost and have the potential to replace precious metal catalysts such as Pt, Ru, and Ir. This leads to the production of low-cost Fe-NC-based ORR catalysts, which can be used in fuel cells, metal-air batteries, water electrolysis, and super(pseudo)capacitors. This represents an effective approach for the high-value utilization of recycled conductive agents.

[0014] In some possible embodiments, the acid leaching of the lithium iron phosphate positive electrode material powder comprises the following steps:

[0015] A: Weigh 5-10g of lithium iron phosphate cathode material powder and add it to 100-300mL of 1-3molL -1 sulfuric acid, dissolving the powder in the sulfuric acid solution to obtain an initial acid leaching solution;

[0016] B: Slowly add 6-15 mL of hydrogen peroxide solution to the initial acid leaching solution to obtain a mixed solution;

[0017] C: Heat the mixed solution in a water bath to 60-80°C while continuously stirring the mixed solution for 120-240 minutes.

[0018] In some possible implementations, the content of the hydrogen peroxide solution is 10%-30%.

[0019] In some possible embodiments, the filtrate treatment method includes acid-base neutralization or carbonate precipitation treatment.

[0020] In some possible embodiments, the oil absorption value of the conductive carbon black is greater than or equal to 250 mL g -1 .

[0021] In some possible implementations, the main component of the lithium iron phosphate positive electrode material of the waste lithium-ion battery is lithium iron phosphate, and the main components of the filter residue after leaching are iron phosphate (FePO4) and carbon black.

[0022] In some possible embodiments, the catalyst comprises Fe2P and Fe2P2O7, and after calcination, CN, CP, Fe-N, pyridinic N, pyrrolic N and graphitic N groups are formed on the surface of the carbon black.

[0023] In a second aspect, the present disclosure provides an application of recycling a conductive agent from waste lithium iron phosphate batteries to prepare a carbon-based catalyst, wherein the carbon-based catalyst prepared by recycling a conductive agent from waste lithium iron phosphate batteries is used in a battery, wherein the working electrode of the battery is a catalyst-modified glassy carbon electrode, the counter electrode is a platinum wire, the reference electrode is a Hg / HgO electrode, and the electrolyte is a 0.1M KOH solution.

[0024] The Fe-NP co-doped carbon catalyst obtained by heat treatment has a simple preparation method, low cost, excellent oxygen reduction catalytic activity and stability, and can be used to replace precious metal catalysts in fuel cells, metal-air batteries and water electrolysis.

[0025] In some possible embodiments, the glassy carbon working electrode is modified with a pre-prepared slurry, and the working electrode of the cell is a catalyst-modified glassy carbon electrode, comprising the following processing steps:

[0026] Weigh 4-6 mg of catalyst powder and add it to a glass bottle. Then add 800-1000 μL of deionized water, 200-400 μL of alcohol, and 100-200 μL of 5% Nafion solution. Ultrasonicate in an ice-water bath for 30-60 minutes to prepare a working electrode modification slurry. Use a pipette to draw 5-8 μL of the modified slurry, drop it on a glassy carbon electrode, and dry it naturally to prepare a battery working electrode.

[0027] In some possible embodiments, the carbon-based catalyst is used in a zinc-air battery. The preparation method of the zinc-air battery comprises the following steps: weighing 25 mg of the Fe-NP co-doped catalyst and the reference carbon black powder, ultrasonically dispersing them in 10 mL of ethanol, and spraying them evenly on the surface of 5 cm×5 cm carbon paper using a spray gun to prepare a catalyst with a catalyst loading of 1 mg cm -2 The positive electrode is dried and then used; the zinc negative electrode sheet needs to be sanded before use. The assembly of the zinc-air battery starts from the negative electrode, and from left to right it is the negative electrode plate-zinc sheet-frame (for charging electrolyte)-positive electrode-positive electrode plate, fixed package, and 6molL is filled into the frame in the middle of the battery. -1 KOH and 0.2 molL -1 The Zn(Ac)2 electrolyte was prepared after standing for 2 hours.

[0028] In summary, this application has the following beneficial effects:

[0029] 1. Since the lithium iron phosphate cathode material of waste lithium-ion batteries is recycled in this application, the lithium iron phosphate cathode material is treated with sulfuric acid and hydrogen peroxide for acid leaching, and the leachate and filter residue are separated. After filtration and separation, the filtrate can be treated to recover lithium. The filter residue includes iron phosphate and conductive carbon black. After washing, drying, grinding, and then high-temperature heat treatment, the filter residue powder is calcined at 900°C in a nitrogen atmosphere for 3h. The nitrogen doping itself can also catalyze the ORR. In addition, nitrogen is an inert gas with stable chemical properties. After forming a stable Fe-N center in an inert atmosphere, more nitrogen-containing micropores will be generated during the nitrogen heat treatment process, which significantly improves the activity. The catalyst obtained by heat treatment at 900°C has a large specific surface area and micropore specific surface area, showing the best activity. Continuing to increase the temperature, the specific surface area decreases, and the activity decreases, thereby obtaining an Fe-NP co-doped carbon catalyst;

[0030] 2. The Fe-NP co-doped carbon catalyst obtained by heat treatment is preferably prepared in this application because the preparation method is simple, the cost is low, and the catalyst has excellent oxygen reduction catalytic activity and stability. It can be used to replace precious metal catalysts in fuel cells, metal-air batteries and water electrolysis. Conductive carbon materials generally have a large specific surface area, rich pore structure, high corrosion resistance, good thermal and mechanical stability, and excellent conductivity. Active sites are formed by heteroatom (such as N, P, B, etc.) doping, topological defects, and metal-nitrogen-carbon (MNC) co-doping. In addition, the Fe sites with N and P dual coordination are conducive to the adsorption / desorption process of oxygen intermediates, and higher oxygen reduction reaction catalytic activity can be obtained than single N doping. It is also low in cost and is expected to replace precious metal catalysts such as Pt, Ru, and Ir for use in fuel cells, metal-air batteries, and water electrolysis.

[0031] 3. The method of the present application provides a new approach to the recycling of waste lithium iron phosphate lithium-ion batteries, with a high lithium recovery rate and high-value reuse of the recovered conductive agent.

[0032] It should be understood that the foregoing general description and the following detailed description are merely exemplary and explanatory and are not intended to limit the scope of protection of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the preparation process of the catalyst of the present application;

[0034] Figure 2 This is a SEM image of the leached residue after lithium extraction in this application;

[0035] Figure 3 is a SEM image of the catalyst after heat treatment in this application;

[0036] Figure 4 This is the XRD analysis of the lithium iron phosphate cathode material of this application;

[0037] Figure 5 This is the XRD analysis of the leached residue of the lithium iron phosphate cathode material of the present application;

[0038] Figure 6 This is the XRD analysis of the catalyst obtained by heat treatment of the leaching residue of this application;

[0039] Figure 7 This is the XPS fitting diagram of the C peak of the C-FP catalyst of the present application;

[0040] Figure 8 This is the XPS fitting diagram of the N peak of the C-FP catalyst of the present application;

[0041] Figure 9 Comparison of the voltammetric curves of conductive carbon black (SUPERP) and the C-FP catalyst of the present application in oxygen-saturated 0.1M KOH;

[0042] Figure 10 Comparison of linear scan curves of conductive carbon black (SUPERP) and the C-FP catalyst of the present application in oxygen-saturated 0.1M KOH;

[0043] Figure 11 This is the Koutecky-Levic plot of the rotating disk electrode of the C-FP catalyst of the present application in oxygen-saturated 0.1M KOH;

[0044] Figure 12 The H2O2% yield and electron transfer number of the C-FP catalyst of the present application obtained by rotating ring disk electrode analysis in oxygen-saturated 0.1M KOH;

[0045] Figure 13 This is the current-time IT curve of the C-FP catalyst of the present application in oxygen-saturated 0.1M KOH;

[0046] Figure 14 The open circuit voltage test of conductive carbon black (SUPERP) and the C-FP catalyst of the present application in zinc-air batteries;

[0047] Figure 15 Conductive carbon black (SUPERP) and the C-FP catalyst of the present application were used in the charge-discharge cycle test of zinc-air batteries;

[0048] Figure 16 Conductive carbon black (SUPERP) and the C-FP catalyst of this application were used in the full discharge capacity test of zinc-air batteries;

[0049] Figure 17 The polarization and power density curves of the conductive carbon black (SUPERP) and the C-FP catalyst of the present application in zinc-air batteries;

[0050] Figure 18 This is the RDE scanning curve of SUPER P catalyst at different scanning rates;

[0051] Figure 19 is the RDE scanning curve of C-FP catalyst at different scan rates;

[0052] Figure 20 This is the Koutecky-Levic plot of the rotating disk electrode of SUPER P catalyst in oxygen-saturated 0.1MKOH;

[0053] Figure 21 is the Koutecky-Levic plot of the rotating disk electrode of C-FP catalyst in oxygen-saturated 0.1MKOH;

[0054] Figure 22The H2O2% yield and electron transfer number of SUPER P catalyst were obtained by rotating ring disk electrode analysis in oxygen-saturated 0.1M KOH.

[0055] Figure 23 The H2O2% yield and electron transfer number of C-FP catalyst were obtained by rotating ring disk electrode analysis in oxygen-saturated 0.1M KOH. DETAILED DESCRIPTION

[0056] The present application is further described in detail below with reference to the examples. It is particularly noted that if no specific conditions are specified in the following examples, the reactions are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following examples can be obtained from common commercial sources.

[0057] The high-temperature crucible for heat treatment of the filter residue powder is placed in a tube furnace for continuous heating; the old lithium iron phosphate battery is first discharged to below 2.0V.

[0058] Preparation examples of raw materials and / or intermediates

[0059] Preparation Example 1

[0060] The acid leaching treatment of lithium iron phosphate cathode material powder includes the following steps:

[0061] A: Weigh 5g of lithium iron phosphate cathode material powder and add it to 100mL of 1molL -1 In sulfuric acid, the powder is dissolved in the sulfuric acid solution to obtain an initial acid leaching solution;

[0062] B: Slowly add 6 mL of 30% hydrogen peroxide solution to the initial acid leaching solution to obtain a mixed solution;

[0063] C: Heat the mixed solution to 60°C in a water bath while continuously stirring the mixed solution for 120 minutes.

[0064] Preparation Example 2

[0065] The acid leaching treatment of lithium iron phosphate cathode material powder includes the following steps:

[0066] A: Weigh 8g of lithium iron phosphate cathode material powder and add it to 200mL of 2molL -1 In sulfuric acid, the powder is dissolved in the sulfuric acid solution to obtain an initial acid leaching solution;

[0067] B: Slowly add 12 mL of 30% hydrogen peroxide solution to the initial acid leaching solution to obtain a mixed solution;

[0068] C: Heat the mixed solution to 60°C in a water bath while continuously stirring the mixed solution for 180 minutes.

[0069] Preparation Example 3

[0070] The acid leaching treatment of lithium iron phosphate cathode material powder includes the following steps:

[0071] A: Weigh 10g of lithium iron phosphate cathode material powder and add it to 300mL of 3molL -1 sulfuric acid, dissolving the powder in the sulfuric acid solution to obtain an initial acid leaching solution;

[0072] B: Slowly add 15 mL of 30% hydrogen peroxide solution to the initial acid leaching solution to obtain a mixed solution;

[0073] C: Heat the mixed solution to 60°C in a water bath while continuously stirring the mixed solution for 240 minutes.

[0074] Preparation Example 4

[0075] A method for preparing a carbon-based catalyst by recycling a conductive agent from waste lithium iron phosphate batteries comprises the following steps:

[0076] S1: Take out the positive electrode of the lithium-ion battery after discharge and disassembly, and separate the lithium iron phosphate positive electrode material from the aluminum foil;

[0077] S2: drying and grinding the lithium iron phosphate cathode material to obtain lithium iron phosphate cathode material powder;

[0078] S3: acid leaching: the mixed solution obtained after acid leaching treatment in Preparation Example 2;

[0079] S4: filtering and separating the heated and stirred mixed solution, and treating the filtrate obtained after filtration to recover lithium;

[0080] S5: washing, drying, and grinding the filtered residue to obtain a filter residue powder;

[0081] S6: Weigh 100 mg of filter residue powder, put it into a high-temperature crucible, and then calcine it at 900° C. for 3 h in a nitrogen atmosphere. Turn off the power and cool it to room temperature before taking it out to obtain an Fe-NP co-doped carbon catalyst.

[0082] Preparation Example 5

[0083] A method for preparing a carbon-based catalyst by recycling a conductive agent from waste lithium iron phosphate batteries comprises the following steps:

[0084] S1: Take out the positive electrode of the lithium-ion battery after discharge and disassembly, and separate the lithium iron phosphate positive electrode material from the aluminum foil;

[0085] S2: drying and grinding the lithium iron phosphate cathode material to obtain lithium iron phosphate cathode material powder;

[0086] S3: acid leaching: the mixed solution obtained after acid leaching treatment in Preparation Example 2;

[0087] S4: filtering and separating the heated and stirred mixed solution, and treating the filtrate obtained after filtration to recover lithium;

[0088] S5: washing, drying, and grinding the filtered residue to obtain a filter residue powder;

[0089] S6: Weigh 200 mg of the filter residue powder, put it into a high-temperature crucible, and then calcine it at 900° C. for 4 h in a nitrogen atmosphere. After turning off the power and cooling it to room temperature, take it out to obtain an Fe-NP co-doped carbon catalyst.

[0090] Preparation Example 6

[0091] A method for preparing a carbon-based catalyst by recycling a conductive agent from waste lithium iron phosphate batteries comprises the following steps:

[0092] S1: Take out the positive electrode of the lithium-ion battery after discharge and disassembly, and separate the lithium iron phosphate positive electrode material from the aluminum foil;

[0093] S2: drying and grinding the lithium iron phosphate cathode material to obtain lithium iron phosphate cathode material powder;

[0094] S3: acid leaching: the mixed solution obtained after acid leaching treatment in Preparation Example 2;

[0095] S4: filtering and separating the heated and stirred mixed solution, and treating the filtrate obtained after filtration to recover lithium;

[0096] S5: washing, drying, and grinding the filtered residue to obtain a filter residue powder;

[0097] S6: Weigh 300 mg of the filter residue powder, put it into a high-temperature crucible, and then calcine it at 900° C. for 5 h in a nitrogen atmosphere. After turning off the power and cooling it to room temperature, take it out to obtain an Fe-NP co-doped carbon catalyst.

[0098] Comparative Preparation Example 1

[0099] An Fe-NP co-doped carbon catalyst was obtained according to the method of Preparation Example 5, except that the filter residue powder was calcined at 700° C. for 4 h in a nitrogen atmosphere.

[0100] Comparative Preparation Example 2

[0101] An Fe-NP co-doped carbon catalyst was obtained according to the method of Preparation Example 5, except that the filter residue powder was calcined at 900° C. in an ammonia atmosphere for 4 h.

[0102] Example

[0103] Example 1

[0104] A lithium-ion battery with a carbon-based catalyst, wherein the working electrode is the catalyst-modified glassy carbon electrode obtained in Preparation Example 5, the counter electrode is a platinum wire, the reference electrode is a Hg / HgO electrode, and the electrolyte is a 0.1M KOH solution;

[0105] The glassy carbon working electrode was modified using a pre-prepared slurry, including the following processing steps: 4 mg of the catalyst powder obtained in Preparation Example 5 was weighed and added to a glass bottle, followed by the addition of 800 μL of deionized water, 200 μL of alcohol, and 100 μL of 5% Nafion solution, and ultrasonicated in an ice-water bath for 30 minutes to prepare a working electrode modification slurry; 5 μL of the modified slurry was taken with a pipette, dropped onto the glassy carbon electrode, and naturally dried to prepare a battery working electrode.

[0106] Example 2

[0107] A lithium-ion battery with a carbon-based catalyst, wherein the working electrode is the catalyst-modified glassy carbon electrode obtained in Preparation Example 5, the counter electrode is a platinum wire, the reference electrode is a Hg / HgO electrode, and the electrolyte is a 0.1M KOH solution;

[0108] The glassy carbon working electrode was modified using a pre-prepared slurry, including the following processing steps: 5 mg of the catalyst powder obtained in Preparation Example 5 was weighed and added to a glass bottle, followed by the addition of 900 μL of deionized water, 300 μL of alcohol, and 150 μL of 5% Nafion solution, and ultrasonicated in an ice-water bath for 40 minutes to prepare a working electrode modification slurry; 7 μL of the modified slurry was taken with a pipette, dropped onto the glassy carbon electrode, and naturally dried to prepare a battery working electrode.

[0109] Example 3

[0110] A lithium-ion battery with a carbon-based catalyst, wherein the working electrode is the catalyst-modified glassy carbon electrode obtained in Preparation Example 5, the counter electrode is a platinum wire, the reference electrode is a Hg / HgO electrode, and the electrolyte is a 0.1M KOH solution;

[0111] The glassy carbon working electrode was modified using a pre-prepared slurry, including the following processing steps: 6 mg of the catalyst powder obtained in Preparation Example 5 was weighed and added to a glass bottle, followed by the addition of 1000 μL of deionized water, 400 μL of alcohol, and 200 μL of 5% Nafion solution, and ultrasonicated in an ice-water bath for 60 minutes to prepare a working electrode modification slurry; 8 μL of the modified slurry was taken with a pipette, dropped onto the glassy carbon electrode, and naturally dried to prepare a battery working electrode.

[0112] Example 4

[0113] A zinc-air battery with an Fe-NP co-doped catalyst and conductive carbon black as the positive electrode, the preparation method comprising the following steps: weighing 25 mg of the Fe-NP co-doped catalyst obtained in Preparation Example 5 and a reference carbon black powder, ultrasonically dispersing them in 10 mL of ethanol, and spraying them evenly on the surface of a 5 cm × 5 cm carbon paper using a spray gun to prepare a catalyst with a catalyst loading of 1 mg cm -2 The positive electrode is dried and then used; the zinc negative electrode sheet needs to be sanded before use. The assembly of the zinc-air battery starts from the negative electrode, and from left to right it is the negative electrode plate-zinc sheet-frame (for charging electrolyte)-positive electrode-positive electrode plate, fixed package, and 6molL is filled into the frame in the middle of the battery. -1 KOH and 0.2 molL -1 The Zn(Ac)2 electrolyte was prepared after standing for 2 hours.

[0114] Comparative Example

[0115] Comparative Example 1

[0116] A lithium-ion battery using a carbon-based catalyst was prepared according to the method of Example 2, except that the glassy carbon working electrode was not modified with the pre-prepared slurry.

[0117] Comparative Example 2

[0118] A lithium-ion battery containing a carbon-based catalyst was prepared according to the method of Example 2, except that when the glassy carbon working electrode was modified with the pre-prepared slurry, the catalyst used was Fe-NC catalyst.

[0119] Comparative Example 3

[0120] A lithium-ion battery containing a carbon-based catalyst was prepared according to the method of Example 2, except that when the glassy carbon working electrode was modified with the pre-prepared slurry, a PANI-Fe-C catalyst was used as the catalyst.

[0121] Comparative Example 4

[0122] A zinc-air battery was prepared according to the method of Example 4, except that no reference carbon black powder was added.

[0123] Scanning electron microscopy was used to characterize the material morphology changes before (filter residue) and after (catalyst) calcination, and X-ray diffraction analysis was used to characterize the composition of the lithium iron phosphate positive electrode material of spent lithium-ion batteries, the filter residue after leaching, and the catalyst after heat treatment.

[0124] X-ray diffraction (XRD) analysis showed that the main component of the cathode material of waste lithium-ion batteries is lithium iron phosphate. Figure 4 , while the components of the leaching residue are mainly iron phosphate (FePO4) and carbon black Figure 5, the lithium leaching rate reached 99.3%. After the leached slag was calcined in N2 atmosphere, XRD analysis showed that FePO4 disappeared and Fe2P and Fe2P2O7 were generated. Figure 6 .

[0125] X-ray electron spectroscopy (XPS) analysis showed that CN, CP, Fe-N, pyridinic N, pyrrolic N and graphitic N groups were formed on the surface of carbon black after calcination. Figure 7 and Figure 8 This indicates that the carbon black recovered after heat treatment reacts with FePO₄ to form an Fe-NP co-doped catalyst (C-FP). The graphitic N can increase the ORR limiting current density, the pyridinic N is beneficial for increasing the onset potential, and the Fe atoms easily coordinate with the pyridinic N to form an Fe-N structure, which works synergistically with the CN to enhance oxygen reduction catalysis.

[0126] Cyclic voltammetry (CV), time-current (it), rotating disk electrode (RDE, LSV), and rotating ring disk electrode (RRDE, LSV) analyses were performed using a CHI760 electrochemical workstation. The electrolyte was a 0.1M KOH solution bubbled with oxygen for 30 min.

[0127] When testing the cyclic voltammetry curve, set the voltage window to -0.6V~0.2V and the scan rate to 20mVs -1 The test results show that both the catalyst (C-FP) and the conductive carbon black (SUPERP) have oxygen reduction peaks in the CV cycle, but the oxygen reduction peak current density and voltage of the catalyst (C-FP) are greater than those of the conductive carbon black (SUPERP), indicating that the oxygen reduction performance of the catalyst (C-FP) is better. Figure 9 .

[0128] When testing the rotating disk electrode and rotating ring disk electrode, set the voltage window to -0.6V-0.2V and the scan rate to 5mVs -1 The potential of the ring electrode is set to 0.9 V. The test results show that the onset potential of the catalyst (C-FP) is 0.845 V, which is higher than the onset potential of the conductive carbon black (SUPERP) of 0.81 V, and the current density of the catalyst (C-FP) is also greater than that of the conductive carbon black (SUPERP) reference. Figure 10 The analysis of rotating disk electrode and rotating ring disk electrode also showed that the electron transfer number of the catalyst (C-FP) during ORR was between 3.5 and 3.8. Figure 11 and Figure 12 It can be seen that the ORR on the catalyst (C-FP) is a process close to four electron transfers, that is, the oxygen molecules are mainly reduced to water.

[0129] The voltage was set to 0.3V during the current-time curve test and the test time was 80,000s (22.2h). In the long-term IT curve test, it was found that the catalyst had high stability and the current only decayed to 73.5% of the initial value. Figure 13 .

[0130] The test results show that the open circuit voltage of the zinc-air battery using C-FP catalyst as the positive electrode is 1.44V. Figure 14 The charge and discharge voltage difference is 1.04V, and it can be stably cycled for more than 100h. Figure 15 When the battery is fully discharged, the specific density is calculated based on the mass of the consumed zinc foil to be 581 mAh g Zn -1 Reference Figure 16 , the power density reached 80mWcm -2 Reference Figure 17 In comparison, the open circuit voltage of the zinc-air battery using conductive carbon black as the positive electrode is 1.37V. Figure 14 The charge and discharge voltage difference is 1.19V, which means it can only be cycled stably for 18 hours. Figure 15 When the battery is fully discharged, the specific density is calculated based on the mass of the consumed zinc foil to be 453 mAhg Zn -1 Reference Figure 16 , the power density reached 11mWcm -2 Reference Figure 17 It can be seen that the C-FP catalyst prepared by recycling the conductive agent is superior to conductive carbon black in strengthening rechargeable zinc-air batteries.

[0131] SUPER P( Figure 18 ) and C-FP( Figure 19 ) catalysts were analyzed by RDE, and then the electron transfer numbers in the ORR process were calculated by the Koutecky-Levich (KL) equation to be 1.9 ( Figure 20 ) and 3.7( Figure 21 ). RRDE analysis shows that in the range of -0.8 to -0.4 V, the SUPERP catalyst ( Figure 22 ) is a process close to 2 electron transfer, and the yield of H2O2 is higher than 80%. Figure 23 ) is a process close to 4 electron transfer, and the yield of H2O2 is less than 40%, that is, O2 is mainly reduced to H2O.

[0132] ICP testing showed that the iron content in the solid remained almost unchanged before and after acid leaching, and the lithium leaching rate was 99.37% (Tables 1 and 2).

[0133] Table 1 ICP of waste lithium iron phosphate cathode

[0134]

[0135] Table 2 ICP of filter residue after acid leaching

[0136]

[0137] The above description is merely an exemplary embodiment of the present disclosure, but the scope of protection of the present disclosure is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present disclosure should be included in the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure should be based on the scope of protection of the claims.

Claims

1. A method for preparing a carbon-based catalyst by recycling a conductive agent from waste lithium iron phosphate batteries, characterized in that: The method comprises the following steps: S1: Take out the positive electrode of the lithium-ion battery after discharge and disassembly, and separate the lithium iron phosphate positive electrode material from the aluminum foil; S2: drying and grinding the lithium iron phosphate cathode material to obtain lithium iron phosphate cathode material powder; S3: Acid leaching: Weigh lithium iron phosphate cathode material powder and add it to sulfuric acid and hydrogen peroxide solution to obtain a mixed solution, heat the mixed solution in a water bath to 60° C.-80° C., and continue stirring for 120-240 minutes; S4: filtering and separating the heated and stirred mixed solution, and treating the filtrate obtained after filtration to recover lithium; S5: washing, drying, and grinding the filtered residue to obtain a residue powder; the main component of the lithium iron phosphate positive electrode material is lithium iron phosphate, and the main components of the residue after leaching are iron phosphate and carbon black; S6: Weigh 100-300 mg of the filter residue powder, place it in a high-temperature crucible, and then calcine it at 600°C-900°C in a nitrogen atmosphere for 3-5 hours. Turn off the power and cool it to room temperature before taking it out to obtain the Fe-NP co-doped carbon catalyst; The catalyst comprises Fe2P and Fe2P2O7, and after calcination, CN, CP, Fe-N, pyridinic N, pyrrolic N and graphitic N groups are formed on the surface of the carbon black.

2. The method for preparing a carbon-based catalyst according to claim 1, characterized in that: The acid leaching of the lithium iron phosphate positive electrode material powder comprises the following steps: A: Weigh 5-10g of lithium iron phosphate cathode material powder and add it to 100-300mL of 1-3molL -1 dissolving the powder in a sulfuric acid solution to obtain an initial acid leaching solution; B: Slowly add 6-15 mL of hydrogen peroxide solution to the initial acid leaching solution to obtain a mixed solution; C: Heat the mixed solution in a water bath to 60-80°C while continuously stirring the mixed solution for 120-240 minutes.

3. The method for preparing a carbon-based catalyst according to claim 2, characterized in that: The content of the hydrogen peroxide solution is 10%-30%.

4. The method for preparing a carbon-based catalyst according to claim 1, characterized in that: The treatment method of the filtrate includes acid-base neutralization or carbonate precipitation treatment.

5. The method for preparing a carbon-based catalyst according to claim 1, characterized in that: The oil absorption value of the carbon black is greater than or equal to 250mLg -1 .

6. An application of a carbon-based catalyst, characterized in that: The carbon-based catalyst prepared by the method for preparing a carbon-based catalyst according to any one of claims 1 to 5 is used in a battery, wherein the working electrode of the battery is a catalyst-modified glassy carbon electrode, the counter electrode is a platinum wire, the reference electrode is a Hg / HgO electrode, and the electrolyte is a 0.1M KOH solution.

7. The use of the carbon-based catalyst according to claim 6, characterized in that: The working electrode of the cell is a catalyst-modified glassy carbon electrode, which includes the following processing steps: Weigh 4-6 mg of catalyst powder and add it to a glass bottle. Then add 800-1000 μL of deionized water, 200-400 μL of alcohol, and 100-200 μL of 5% Nafion solution. Ultrasonicate in an ice-water bath for 30-60 minutes to prepare a working electrode modification slurry. Use a pipette to draw 5-8 μL of the modified slurry, drop it on a glassy carbon electrode, and dry it naturally to prepare a battery working electrode.

8. An application of a carbon-based catalyst, characterized in that: The carbon-based catalyst prepared by the method for preparing a carbon-based catalyst according to any one of claims 1 to 5 is used for a zinc-air battery, and the preparation method of the zinc-air battery comprises the following steps: weighing 25 mg of the Fe-NP co-doped carbon catalyst and the reference carbon black powder respectively, ultrasonically dispersing them in 10 mL of ethanol, and spraying them evenly on the surface of 5 cm × 5 cm carbon paper using a spray gun to prepare a catalyst with a catalyst loading of 1 mg cm -2 The positive electrode is dried and set aside for use; the zinc negative electrode sheet needs to be sanded before use. The assembly of the zinc-air battery starts from the negative electrode, and from left to right it is the negative electrode plate-zinc sheet-frame-positive electrode-positive electrode plate, fixed package, and 6molL is filled into the frame in the middle of the zinc-air battery. -1 KOH and 0.2 molL -1 The Zn(Ac)2 electrolyte was prepared after standing for 2 hours.

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