A method for preparing an iron-doped graphene catalyst by using waste lithium iron phosphate batteries

Abstract

The application belongs to the field of waste lithium ion battery recycling, and discloses a method for preparing an iron-doped graphene catalyst by using waste lithium iron phosphate batteries, which comprises the following steps: discharging, disassembling and separating the waste lithium iron phosphate batteries to obtain lithium iron phosphate powder and graphite; obtaining a lithium and iron-containing precursor solution by acid leaching and oxidizing the lithium iron phosphate powder; adjusting the pH to obtain an iron hydroxide precipitate; co-heating and reducing the iron hydroxide precipitate with the graphite to obtain elemental iron; preparing graphite oxide from the graphite by using the Hummers method; reducing the graphite oxide at high temperature to obtain graphene; and realizing iron doping by high-temperature solid-phase synthesis; realizing good industrial catalysis by the nanoscale complex effect of iron and graphene; and successfully realizing application in Li-CO2 batteries, with excellent catalytic effect, and the remaining lithium precursor solution in the reaction can be further used to extract lithium. According to the treatment method, the process is simple, the operation is simple, a high-value chemical catalyst can be obtained, and the economic benefit is high.

Description

Technical Field

[0001] This invention relates to a method for preparing iron-doped graphene catalysts using waste lithium iron phosphate batteries, belonging to the field of resource recycling of waste lithium batteries. Background Technology

[0002] Since its successful development and commercialization in 1991, lithium-ion batteries have seen continuous market expansion and have rapidly gained dominance in the secondary energy storage market, finding widespread application in electric vehicles, electronic devices, and energy storage equipment. Lithium iron phosphate batteries, due to their low cost and high safety, have a promising future in the new energy vehicle sector, and their market share continues to rise.

[0003] Lithium iron phosphate (LFP) batteries have limited cycle stability; their capacity significantly decreases and they become unusable after 3-8 years of operation. With the explosive growth in LFP battery usage and the limitations of their lifespan, a wave of LFP battery retirements is underway. Although discarded LFP batteries do not contain heavy metal pollutants such as lead and mercury, they still pose certain environmental hazards. Therefore, developing efficient recycling strategies for discarded LFP batteries is imperative.

[0004] Although progress has been made in waste battery recycling processes, represented by pyrometallurgy and hydrometallurgy, pyrometallurgical processes suffer from drawbacks such as generating large amounts of fluorine-containing waste gas, consuming significant amounts of energy, and having low yields. Hydrometallurgical technology involves lengthy processes of staged extraction, refining, and separation of mixed metal solutions, leading to increased costs and the generation of large amounts of saline wastewater. With increasing demands for air and water quality from society and daily life, as well as cost control considerations, these two processes are gradually becoming insufficient to meet the requirements of industry. Therefore, to overcome the shortcomings of these technologies, developing a new "green" approach that consumes less energy, generates less fluorine-containing waste gas, and produces less saline wastewater has become both necessary and urgent. Summary of the Invention

[0005] This invention addresses the issue of economical and green recycling of lithium iron phosphate batteries by providing a method for preparing iron-doped graphene catalysts from spent lithium iron phosphate batteries. The process is simple and easy to implement, with high recycling efficiency. The generated iron-doped graphene catalyst has been successfully applied in Li-CO2 batteries, exhibiting excellent catalytic performance.

[0006] To achieve the objectives of this invention, the following technical solution is adopted:

[0007] A method for preparing iron-doped graphene catalysts using spent lithium iron phosphate batteries includes:

[0008] S1: Pre-treat waste lithium iron phosphate batteries to obtain lithium iron phosphate powder and graphite;

[0009] S2: The lithium iron phosphate powder obtained in step S1 is mixed with dilute sulfuric acid and hydrogen peroxide and heated to obtain a lithium- and iron-containing precursor solution.

[0010] S3: Add ammonia to the lithium- and iron-containing precursor solution obtained in S2 to adjust the pH value to obtain ferric hydroxide precipitate;

[0011] S4: Calcining the ferric hydroxide precipitate obtained in S3 and a portion of the graphite obtained in S1 in a tube furnace;

[0012] S5: Prepare graphite oxide from a portion of the graphite obtained in S1 using the Hummers oxidation method;

[0013] S6: The elemental iron obtained in S4 and the graphene oxide obtained in S5 are calcined in a tube furnace to obtain an iron-doped graphene catalyst.

[0014] Furthermore, step S1 specifically involves pre-treating the waste lithium iron phosphate batteries by discharging, dismantling, and separating them to obtain lithium iron phosphate powder and graphite.

[0015] Furthermore, in step S2, the volume ratio of dilute sulfuric acid to hydrogen peroxide is 1:2 to 2:1; the concentration of dilute sulfuric acid is 1 mol / L.

[0016] Furthermore, in step S2, the heating temperature is 40-80 degrees Celsius, preferably 60 degrees Celsius, and the heating time is 0.5-2 hours, preferably 1 hour.

[0017] Furthermore, in step S3, ammonia is added to adjust the pH value to 3-4.5, preferably 3.7.

[0018] Furthermore, in step S4, the mass ratio of ferric hydroxide to graphite is 4:1 to 1:1, preferably 2:1.

[0019] Furthermore, in step S4, in order to ensure that the ferric hydroxide precipitate and graphite are mixed evenly, they can be mixed and ground before calcination.

[0020] Furthermore, in step S4, the calcination temperature is 800-1000 degrees Celsius, preferably 850 degrees Celsius, the calcination time is 2-5 hours, preferably 4 hours, and the environment is an argon atmosphere.

[0021] Furthermore, in step S6, the mass ratio of elemental iron to graphite oxide is 1:3-1:10, preferably 1:10; the calcination temperature is 450-550 degrees Celsius, preferably 500 degrees Celsius; the calcination time is 4-6 hours, preferably 5 hours; and the environment is an argon atmosphere.

[0022] The iron-doped graphene catalyst obtained by this method can be used as the catalytic cathode in Li-CO2 batteries.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The method of the present invention for treating waste lithium iron phosphate batteries is simple and easy to operate.

[0025] (2) The method of the present invention can process waste lithium iron phosphate batteries to obtain high-value-added chemical catalysts, resulting in high economic benefits.

[0026] (3) The method of the present invention treats waste lithium iron phosphate batteries. The mother liquor after precipitation can be used for further lithium extraction, which can realize the comprehensive utilization of waste lithium iron phosphate batteries and effectively recover various metals in lithium iron phosphate batteries.

[0027] (4) The catalyst prepared by the method of the present invention can be successfully applied in Li-CO2 batteries and has excellent catalytic effect. Attached Figure Description

[0028] Figure 1 The flowchart illustrates a method for recycling spent lithium iron phosphate batteries and preparing iron-doped graphene catalysts according to the present invention.

[0029] Figure 2 This is a photograph of the iron-doped graphene catalyst prepared in Example 1 used to assemble a Li-CO2 battery.

[0030] Figure 3 The image shows the XRD pattern of the iron-doped graphene catalyst prepared in Example 1.

[0031] Figure 4 The data are obtained from discharge tests of the iron-catalyzed graphene catalysts obtained in each embodiment at 25±5℃, 100 mA / g current density, and 20 μA current.

[0032] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention. Detailed Implementation

[0033] The following will provide further illustrative examples of the present application through embodiments and accompanying drawings. However, the examples described below are merely simplified illustrations of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

[0034] Example 1

[0035] This embodiment discloses a method for recycling spent lithium iron phosphate batteries and preparing iron-doped graphene catalysts; its flowchart is shown below. Figure 1 As shown:

[0036] S1. Place the waste lithium iron phosphate batteries in a 5% saline solution and allow them to fully discharge for 24 hours. After discharge, disassemble the batteries to obtain the battery core. Then separate the positive and negative electrodes and the separator. After separation, soak the cores in NMP solution to remove the electrolyte, thereby obtaining lithium iron phosphate positive and negative electrode materials. Calcine the positive electrode material in a muffle furnace at 200°C for 2 hours to obtain waste lithium iron phosphate powder; sonicate the negative electrode in NMP for 2 hours to obtain copper foil (recyclable) and graphite.

[0037] S2. Weigh 1.5738 g of lithium iron phosphate powder obtained in step S1 into a 150 mL flask, add 40 mL of 1 mol / L sulfuric acid and 20 mL of hydrogen peroxide, and then heat in an oil bath to 60 °C. After 1 h, stop heating, filter, and obtain a lithium and iron precursor solution.

[0038] S3. Add the precursor solution obtained in step S2 to a beaker, and slowly add ammonia water dropwise in a fume hood to adjust the pH to 3.7. Filter, wash, and dry to obtain 0.9972 g of ferric hydroxide precipitate.

[0039] S4. Weigh 0.4947 g of the graphite and ferric hydroxide precipitate obtained in S1, grind them, and place them in a tube furnace. Under an argon atmosphere, heat the furnace to 850°C at a rate of 5°C / min, and then cool it to room temperature at a rate of 10°C / min after 4 h to obtain 0.6238 g of solid powder.

[0040] S5. Weigh the graphite obtained in S1 and use the Hummers oxidation method to obtain graphite oxide.

[0041] S6. The graphene oxide obtained in S5 and the solid powder obtained in S4 were uniformly mixed at a mass ratio of 10:1 and placed in a tube furnace. Under an argon atmosphere, the temperature was increased to 500℃ at a rate of 5℃ / min, and then cooled to room temperature at a rate of 10℃ / min after 5 h. 6.5380 g of iron-doped graphene catalyst was obtained. The remaining lithium precursor solution from the reaction can be further used for lithium extraction.

[0042] Figure 2 To utilize the prepared iron-doped graphene as the catalytic cathode in Li-CO2 batteries, Figure 2 The bottle contains carbon dioxide, which catalyzes the reduction of carbon dioxide during battery operation. Then, it reacts with lithium at the negative electrode, causing lithium metal to discharge. The small light bulb in the picture is successfully lit, demonstrating the successful application of the catalyst in the Li-CO2 battery. Figure 3 The image shows the XRD pattern of the prepared iron-doped graphene catalyst. Figure 4 Line 3 in the figure represents the discharge test data of the catalyst at 25±5℃, 100 mA / g current density, and 20 μA current, with a discharge capacity of 8091 mAh / g.

[0043] Example 2

[0044] S1. Place the waste lithium iron phosphate batteries in a 5% saline solution and allow them to fully discharge for 24 hours. After discharge, disassemble the batteries to obtain the battery core. Then separate the positive and negative electrodes and the separator. After separation, soak the cores in NMP solution to remove the electrolyte, thereby obtaining lithium iron phosphate positive and negative electrode materials. Calcine the positive electrode material in a muffle furnace at 200°C for 2 hours to obtain waste lithium iron phosphate powder; sonicate the negative electrode in NMP for 2 hours to obtain copper foil (recyclable) and graphite.

[0045] S2. Weigh 1.5625 g of lithium iron phosphate powder obtained in step S1 into a 150 mL flask, add 40 mL of 1 mol / L sulfuric acid and 20 mL of hydrogen peroxide, and then heat in an oil bath to 60 °C. After 1 h, stop heating, filter, and obtain a lithium and iron precursor solution.

[0046] S3. Add the precursor solution obtained in step S2 to a beaker, and slowly add ammonia water dropwise in a fume hood to adjust the pH to 3.7. Filter, wash, and dry to obtain 0.9896 g of ferric hydroxide precipitate.

[0047] S4. Weigh 0.4903 g of the graphite and ferric hydroxide precipitate obtained in S1, grind them, and place them in a tube furnace. Under an argon atmosphere, heat the furnace to 850°C at a rate of 5°C / min, and then cool it to room temperature at a rate of 10°C / min after 4 h to obtain 0.6105 g of solid powder.

[0048] S5. Weigh the graphite obtained in S1 and use the Hummers oxidation method to obtain graphite oxide.

[0049] S6. The graphene oxide obtained in S5 and the solid powder obtained in S4 were uniformly mixed at a mass ratio of 3:1 and placed in a tube furnace. Under an argon atmosphere, the temperature was increased to 500℃ at a rate of 5℃ / min, and then cooled to room temperature at a rate of 10℃ / min after 5 h. 2.2135 g of iron-doped graphene catalyst was obtained. The remaining lithium precursor solution from the reaction can be further used for lithium extraction.

[0050] Figure 4 Line 1 in the figure represents the discharge test data of the catalyst at 25±5℃, 100 mA / g current density, and 20 μA current, with a discharge capacity of 6970 mAh / g.

[0051] Example 3

[0052] S1. Place the waste lithium iron phosphate batteries in a 5% saline solution and allow them to fully discharge for 24 hours. After discharge, disassemble the batteries to obtain the battery core. Then separate the positive and negative electrodes and the separator. After separation, soak the cores in NMP solution to remove the electrolyte, thereby obtaining lithium iron phosphate positive and negative electrode materials. Calcine the positive electrode material in a muffle furnace at 200°C for 2 hours to obtain waste lithium iron phosphate powder; sonicate the negative electrode in NMP for 2 hours to obtain copper foil (recyclable) and graphite.

[0053] S2. Weigh 1.5431 g of lithium iron phosphate powder obtained in step S1 into a 150 mL flask, add 40 mL of 1 mol / L sulfuric acid and 20 mL of hydrogen peroxide, and then heat in an oil bath to 60°C. After 1 h, stop heating, filter, and obtain a lithium and iron precursor solution.

[0054] S3. Add the precursor solution obtained in step S2 to a beaker, and slowly add ammonia water dropwise in a fume hood to adjust the pH to 3.7. Filter, wash, and dry to obtain 0.9614 g of ferric hydroxide precipitate.

[0055] S4. Weigh 0.4820 g of the graphite and ferric hydroxide precipitate obtained in S1, grind them, and place them in a tube furnace. Under an argon atmosphere, heat the furnace to 850°C at a rate of 5°C / min, and then cool it to room temperature at a rate of 10°C / min after 4 h to obtain 0.5984 g of solid powder.

[0056] S5. Weigh the graphite obtained in S1 and use the Hummers oxidation method to obtain graphite oxide.

[0057] S6. The graphene oxide obtained in S5 and the solid powder obtained in S4 were uniformly mixed at a mass ratio of 10:1 and placed in a tube furnace. Under an argon atmosphere, the temperature was increased to 450℃ at a rate of 5℃ / min, and then cooled to room temperature at a rate of 10℃ / min after 5 h. 6.2824 g of iron-doped graphene catalyst was obtained. The remaining lithium precursor solution from the reaction can be further used for lithium extraction.

[0058] Figure 4 Line 2 in the figure represents the discharge test data of the catalyst at 25±5℃, 100 mA / g current density, and 20 μA current, with a discharge capacity of 7405 mAh / g.

[0059] The above description is only a partial embodiment of the present invention. For those skilled in the art, improvements can be made without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing iron-doped graphene catalysts using spent lithium iron phosphate batteries, characterized in that, Includes the following steps: S1: Pre-treat waste lithium iron phosphate batteries to obtain lithium iron phosphate powder and graphite; S2: The lithium iron phosphate powder obtained in step S1 is mixed with dilute sulfuric acid and hydrogen peroxide and heated to obtain a lithium- and iron-containing precursor solution. S3: Adjust the pH of the lithium- and iron-containing precursor solution obtained in S2 to obtain ferric hydroxide precipitate; S4: Calcining the ferric hydroxide precipitate obtained in S3 with a portion of the graphite obtained in S1; S5: Prepare graphite oxide from a portion of the graphite obtained in S1 using the Hummers oxidation method; S6: The elemental iron obtained in S4 and the graphene oxide obtained in S5 are calcined to obtain an iron-doped graphene catalyst.

2. The method as described in claim 1, characterized in that, Step S1 involves discharging, dismantling, and pre-treating the waste lithium iron phosphate batteries to obtain lithium iron phosphate powder and graphite.

3. The method as described in claim 1, characterized in that, In step S2, the volume ratio of dilute sulfuric acid to hydrogen peroxide is 1:2 to 2:1; the concentration of dilute sulfuric acid is 1 mol / L.

4. The method as described in claim 1, characterized in that, In step S2, the heating temperature is 40-80 degrees Celsius.

5. The method as described in claim 1, characterized in that, In step S2, the heating temperature is 60 degrees Celsius.

6. The method as described in claim 1, characterized in that, In step S2, the heating time is 0.5-2 h.

7. The method as described in claim 1, characterized in that, In step S2, the heating time is 1 hour.

8. The method as described in claim 1, characterized in that, In step S3, ammonia is added to adjust the pH value to 3-4.

5.

9. The method as described in claim 1, characterized in that, In step S3, ammonia is added to adjust the pH value to 3.

7.

10. The method as described in claim 1, characterized in that, In step S4, the mass ratio of ferric hydroxide to graphite is 4:1 to 1:

1.

11. The method as described in claim 1, characterized in that, In step S4, the mass ratio of ferric hydroxide to graphite is 2:

1.

12. The method as described in claim 1, characterized in that, In step S4, the calcination temperature is 800-1000 degrees Celsius.

13. The method as described in claim 1, characterized in that, In step S4, the calcination temperature is 850 degrees Celsius.

14. The method as described in claim 1, characterized in that, In step S4, the calcination time is 2-5 h.

15. The method as described in claim 1, characterized in that, In step S4, the calcination time is 4 hours.

16. The method as described in claim 1, characterized in that, In step S6, the mass ratio of elemental iron to graphite oxide is 1:3 to 1:

10.

17. The method as described in claim 1, characterized in that, In step S6, the mass ratio of elemental iron to graphite oxide is 1:

10.

18. The method as described in claim 1, characterized in that, In step S6, the calcination temperature is 450-550 degrees Celsius, and the environment is an argon atmosphere.

19. The method as described in claim 1, characterized in that, In step S6, the calcination temperature is 500 degrees Celsius.

20. The method as described in claim 1, characterized in that, In step S6, the calcination time is 4-6 hours.

21. The method as described in claim 1, characterized in that, In step S6, the calcination time is 5 h.

22. The use of the iron-doped graphene catalyst prepared by the method according to any one of claims 1-21 as the catalytic cathode of a Li-CO2 battery.

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