Method for recycling and utilizing waste lithium iron phosphate positive electrode materials

Abstract

The present invention belongs to the field of electrode material recycling, and specifically relates to a method for recycling waste lithium iron phosphate positive electrode materials. The waste lithium iron phosphate positive electrode materials are subjected to quenching pretreatment to obtain a pretreated material; wherein the temperature of the quenching medium used in the quenching stage is below 50°C; a mixture containing the pretreated material and a carbon material is roasted in an oxygen-containing atmosphere; then subjected to water leaching to obtain a lithium extract and lithium iron phosphate slag; the roasting temperature is between 100 and 300°C; and in the mixture, the weight ratio of LiFePO4 / C is 1:1 to 5. The present invention also includes the use of the iron phosphate slag obtained by the preparation method in zinc-air batteries. The process of the present invention can achieve synergy, help to effectively destroy the lattice structure of waste lithium iron phosphate, so that lithium can be effectively leached under mild conditions. Not only that, the process also helps to adjust the iron phosphate grains and microstructure, which can unexpectedly show excellent performance in the catalysis of zinc-air batteries.

Description

Technical Field

[0001] The present invention belongs to the field of battery waste recycling, and in particular relates to the field of recycling waste lithium iron phosphate battery materials. Background Art

[0002] Due to the limited lifespan of lithium-ion batteries, the widespread use of portable electronic devices and new energy vehicles in recent years has generated a large amount of waste lithium-ion batteries. It is estimated that by 2023, more than 11 million tons of lithium-ion batteries will be discarded worldwide. Waste lithium-ion batteries contain hazardous organic chemicals that harm the environment and human health. Furthermore, waste lithium-ion batteries contain a large amount of valuable metals, at concentrations higher than those found in natural ores. Therefore, to protect the environment and conserve resources, efficient and sustainable recycling of waste lithium-ion batteries is a top priority.

[0003] Lithium iron phosphate (LFP), one of the earliest large-scale commercialized cathode materials for electric vehicles, is in urgent need of recycling as early electric vehicles and buses are gradually retired. For a period of time, the disposal problem of LFP batteries seemed to be solved because retired power batteries could be used for stationary power storage. However, because the safety risks of reusing batteries still require further technological breakthroughs, cascade utilization projects have been temporarily suspended, making recycling the best option for disposing of retired LFP electric vehicle batteries. The main processes for recycling LFP are hydrometallurgical and pyrometallurgical. Hydrometallurgical processes produce a large amount of wastewater, which puts great pressure on subsequent environmental protection. Traditional pyrometallurgical processes require expensive oxidants and a large amount of energy. Summary of the Invention

[0004] In response to the problems faced by the existing recycling of waste lithium iron phosphate positive electrodes, the first purpose of the present invention is to provide a method for recycling waste lithium iron phosphate positive electrode materials, aiming to improve the low-temperature recovery rate of lithium and improve the recovery of fine-grained, highly surface-active and catalytically active iron phosphate.

[0005] The second purpose of the present invention is to provide the ferric phosphate obtained by the recovery method and its application.

[0006] The lattice lithium in the lithium iron phosphate material of waste lithium iron phosphate mostly requires high temperature roasting to be effectively destroyed and usually requires high water immersion temperature to obtain good extraction effect. To solve this problem, the present invention provides a gentle and efficient recovery method, specifically:

[0007] A method for recycling waste lithium iron phosphate positive electrode materials, comprising the following steps:

[0008] Step (1): Preprocessing

[0009] The waste lithium iron phosphate cathode material is subjected to a rapid cooling treatment to obtain a pretreated material; wherein the temperature of the rapid cooling medium used in the rapid cooling stage is below -50°C;

[0010] Step (2): Calcination-Water Soaking

[0011] The mixture containing the pretreated material and the carbon material is subjected to a roasting treatment in an oxygen-containing atmosphere; and then subjected to a water leaching treatment to obtain a lithium extract and lithium iron phosphate slag;

[0012] The calcination temperature is between 100 and 300° C.; in the mixture, the weight ratio of LiFePO4 to C is 1:1 to 5.

[0013] The present invention innovatively subjects waste lithium iron phosphate positive electrode materials to a quenching treatment in advance, and then roasts them with a carbon material in an oxygen-containing atmosphere. Furthermore, the temperature of the quenching medium, the weight ratio of LiFePO4 / C, and the roasting temperature are jointly controlled. This can achieve synergy and help effectively destroy the lattice structure of the waste lithium iron phosphate, allowing lithium to be effectively leached under mild conditions. Furthermore, the process also helps to adjust the iron phosphate grains and microstructure, which can unexpectedly demonstrate excellent performance in the catalysis of zinc-air batteries.

[0014] The waste lithium iron phosphate positive electrode material of the present invention is obtained by disassembling and stripping waste lithium iron phosphate batteries. The stripping method can be known in the industry. For example, waste lithium-ion batteries can be discharged, disassembled, and stripped (e.g., stripped using the organic solvent NMP) to obtain waste positive electrode powder. In the present invention, considering the simplicity of the process, the waste lithium iron phosphate positive electrode material may also contain at least one of a conductive agent, a binder, and an electrolyte.

[0015] In the present invention, there is no special requirement for the content of waste lithium iron phosphate positive electrode material. Considering the economic efficiency of the process, the content of the active material is preferably above 50 wt.%, more preferably above 80 wt.%, and further preferably 80-95 wt.%.

[0016] In the present invention, a cooling medium is innovatively used to rapidly cool the waste lithium iron phosphate positive electrode material. Combined with the temperature control of the cooling medium, it can unexpectedly cooperate with the subsequent roasting process to improve the low-temperature leaching effect of lithium. Not only that, it also improves the catalytic ability of the recovered iron phosphate.

[0017] In the present invention, the waste lithium iron phosphate positive electrode material and the quenching medium can be mixed in any order as required.

[0018] In the present invention, the quenching medium is liquid nitrogen or dry ice, preferably liquid nitrogen;

[0019] In the present invention, theoretically, the more cooling medium, the better, but for cost considerations, the cooling medium is preferably sufficient to immerse the waste lithium iron phosphate positive electrode material. For example, for cost considerations, when the cooling medium is a liquid medium, its liquid-to-solid ratio is, for example, 5 to 20 mL / g solid. When the medium is solid, the weight ratio between it and the positive electrode material can be 1 to 2:1 to 2.

[0020] In the present invention, there is no particular requirement for the time of the rapid cooling treatment, as long as the cooling medium is completely volatilized. For example, the time can be between 1 and 30 minutes.

[0021] In the present invention, after the rapid cooling treatment, the cooling medium is volatilized in the form of natural volatilization.

[0022] In the present invention, the mixture of the pretreated material and the carbon material is calcined in an oxygen-containing atmosphere, and the calcination temperature and the combined control of LiFePO4 / C are further coordinated to improve the mild leaching rate of lithium and the physical and chemical characteristics of the iron phosphate, such as the grain size and surface activity, thereby improving its catalytic effect.

[0023] In the present invention, the carbon material is a waste negative electrode material, preferably, it is a material obtained by stripping the negative electrode sheet of the waste lithium iron phosphate battery.

[0024] In the present invention, the weight ratio of LiFePO4 / C can be 1:2-4.

[0025] In the present invention, in step (2), the oxygen-containing atmosphere is at least one of oxygen, oxygen-protective gas mixture, and air;

[0026] Preferably, the volume content of oxygen in the oxygen-containing atmosphere is not less than 5% by volume, preferably 10 to 35% by volume, and may further be air;

[0027] Preferably, the oxygen-containing atmosphere also contains no more than 20% by volume, preferably 5-15% by volume, of water vapor. Studies have found that adding a certain proportion of water vapor to the calcination system helps improve the gentle leaching of lithium and also improves the subsequent physicochemical structure of the iron phosphate, thereby enhancing its catalytic performance.

[0028] In the present invention, the mixture can be directly heated to the desired temperature for calcination. As a preferred solution, the mixture can be pre-heated and then subsequently calcined. The temperature of the heat treatment stage is 30-100°C, preferably 50-60°C. The heat treatment holding time is 1-10 hours.

[0029] Preferably, the roasting is fluidized roasting;

[0030] Preferably, the calcination temperature is 200-250°C.

[0031] Preferably, the calcination time is 2 to 5 hours.

[0032] In the present invention, after calcination, the molten metal may be cooled in the furnace and then subsequently subjected to water leaching. In a preferred embodiment of the present invention, the molten metal may be cooled by air cooling after calcination. This is more conducive to gentle leaching of lithium and the catalytic activity of iron phosphate.

[0033] In the present invention, the gas used for air cooling is carbon dioxide.

[0034] In the present invention, the calcined material is subjected to water immersion treatment.

[0035] In the present invention, based on the treatment process, effective water immersion can be achieved under mild conditions and low liquid-to-solid ratio conditions. For example, the liquid-to-solid ratio during the water immersion stage is 10-30 mL / g;

[0036] Preferably, the temperature during the immersion stage does not exceed 45°C, preferably 15-35°C.

[0037] The present invention also provides ferric phosphate slag obtained by the recovery method.

[0038] The present invention benefits from the combination of the processes, and can endow the ferrophosphate slag with special physical and chemical properties. More importantly, the material obtained by the processes has unexpected catalytic advantages in catalysis.

[0039] The present invention also provides an application of the iron phosphate slag obtained by the recovery method, which is used as a catalyst for high-activity zinc-air catalysis.

[0040] Beneficial effects

[0041] The present invention innovatively pre-quenches waste lithium iron phosphate positive electrode materials and then roasts them with carbon materials in an oxygen-containing atmosphere. Furthermore, the quenching medium, the weight ratio of LiFePO4 / C, and the roasting temperature are jointly controlled. This achieves synergy and helps to effectively destroy the lattice structure of the waste lithium iron phosphate, allowing lithium to be effectively leached under mild conditions. Furthermore, the process also helps to adjust the iron phosphate grains and microstructure, which can unexpectedly demonstrate excellent performance in the catalysis of zinc-air batteries.

[0042] The present invention also found that, based on the innovative process, further combining the roasting mechanism, atmosphere and air cooling processes can help further synergize and improve the mild leaching rate of lithium, and also help improve the catalytic performance of the co-produced iron phosphate. DETAILED DESCRIPTION

[0043] The present invention will be further described in detail below with reference to specific examples, but the present invention is not limited to the following examples.

[0044] In the present invention, there is no special requirement for the content of lithium iron phosphate active material in the waste iron phosphate positive electrode material. Considering the economic efficiency of the process, its content is preferably above 50wt.%. In the following cases, unless otherwise stated, its active content is 85-90wt.%.

[0045] In the following cases, unless otherwise specified, the temperature during the treatment stage refers to room temperature, for example, 20-25°C.

[0046] Example 1:

[0047] ① Stripping: Place the waste power lithium iron phosphate battery in 2 mol / L salt water for 30 hours of discharge treatment, dry the discharged battery at 85 ° C, disassemble and separate the positive and negative electrodes, soak the positive electrode sheet in N-methylpyrrolidone, separate the current collector in the electrode sheet, filter, wash and dry to obtain waste positive electrode powder; similarly, soak the negative electrode sheet in N-methylpyrrolidone, separate the current collector in the electrode sheet, filter, wash and dry to obtain waste negative electrode powder;

[0048] ② Pretreatment: Place the spent cathode powder in liquid nitrogen (10-15 mL / g solid) for rapid cooling, and wait for the nitrogen to volatilize to obtain the pretreated material;

[0049] ③ Calcination: The pretreated waste positive electrode powder and waste negative electrode powder (the weight ratio of LiFePO4 / C is 1:3) are evenly mixed and placed in a tubular furnace and calcined in air. The calcination temperature T is 200°C and kept warm for 3 hours. The mixture is cooled with the furnace to obtain calcined sand.

[0050] ④ Lithium extraction by water leaching: Grind the larger particles in the calcined sand into fine powder, take 10g of the calcined sand fine powder and place it in a 200mL beaker. Add 100mL of deionized water at a liquid-solid ratio of 10:1mL / g, and place the beaker in a water bath at a constant temperature of 30℃. Then, perform liquid-solid separation to obtain water leaching liquid and water leaching residue (ferric phosphate residue). The water leaching residue is washed and dried to obtain the recovered iron phosphate for use.

[0051] The recovery rate of lithium ions in waste lithium iron phosphate positive electrodes is 99.5%.

[0052] The recovered iron phosphate catalyst was slurried with a binder and coated on a titanium mesh (the catalyst loading on the Ti mesh was 1 mg cm-2). After curing and drying, the positive electrode was obtained. The positive electrode was then assembled with a Zn plate negative electrode and 6 mol KOH as the electrolyte to form a zinc-air battery. -2 It exhibits a high specific capacity of 710.3 mAh / g at a constant current density.

[0053] Example 2

[0054] Compared with Example 1, the only difference is that in step ②, dry ice is used instead of liquid nitrogen, wherein the weight ratio of dry ice to positive electrode material is 1:1, and conventional stirring equipment is used for stirring during the process. Other operations and parameters are the same as in Example 1.

[0055] Testing was performed according to the method of Example 1, and the results showed that the recovery rate of lithium ions in the waste lithium iron phosphate positive electrode was 99.1%. Under the highly active catalysis of iron phosphate slag, the zinc-air battery exhibited a high specific capacity of 705.6 mAh / g.

[0056] Example 3

[0057] Compared with Example 1, the only difference is that the process of step ③ is changed. The experimental groups are:

[0058] Group A: Before calcination, the mixture was kept at 60°C for 2 h and then calcined;

[0059] Group B: 5-15v% water vapor was added to the atmosphere during the calcination stage.

[0060] Group C: After the calcination treatment, the carbon dioxide was used for air cooling instead of the furnace cooling.

[0061] Group D: After the calcination treatment, nitrogen gas was used for air cooling, replacing the furnace cooling.

[0062] Group E: During the roasting stage, the solid material is in fluidization;

[0063] Group F: The calcination temperature is 300°C and the calcination time is 2h.

[0064] In step ④ of each group, the temperature of the water immersion stage was controlled at 20° C., and other operations and parameters were the same as those in Example 1.

[0065] Tested according to the method of Example 1, the results were:

[0066] Group A: The lithium ion recovery rate was 99.4%. Under the highly active catalysis of iron phosphate slag, the zinc-air battery showed a high specific capacity of 715.7 mAh / g.

[0067] Group B: The recovery rate of lithium ions was 99.3%. Under the highly active catalysis of iron phosphate slag, the zinc-air battery showed a high specific capacity of 717.6 mAh / g.

[0068] Group C: The lithium ion recovery rate was 99.2%. Under the highly active catalysis of iron phosphate slag, the zinc-air battery showed a high specific capacity of 718.7 mAh / g.

[0069] Group D: The lithium ion recovery rate was 99.1%. Under the highly active catalysis of iron phosphate slag, the zinc-air battery showed a high specific capacity of 711.6 mAh / g.

[0070] Group E: The lithium ion recovery rate was 99.7%. Under the highly active catalysis of iron phosphate slag, the zinc-air battery showed a high specific capacity of 720.4 mAh / g.

[0071] Group F: The lithium ion recovery rate was 99.5%. Under the highly active catalysis of iron phosphate slag, the zinc-air battery showed a high specific capacity of 712.7 mAh / g.

[0072] The present invention unexpectedly discovered that calcination after pre-heat treatment, calcination in a water vapor atmosphere, air cooling with carbon dioxide, and fluidized bed calcination can unexpectedly improve the leaching effect, allowing similar lithium leaching effects to be achieved at lower temperatures. Furthermore, the electrochemical performance of the co-produced iron phosphate in zinc-air batteries can also be unexpectedly improved.

[0073] Example 4

[0074] Compared with Example 3, the only difference is that the process of step ③ is changed, and the only difference is that:

[0075] In an air atmosphere containing 5-15v% water vapor, the mixture is pre-heated at 50°C for 2h, then heated to 250°C and calcined for 2.5h, and then carbon dioxide is introduced for air cooling. Other operations and procedures are the same as those in Example 3.

[0076] The test was conducted according to the method of Example 3, and the results showed that the recovery rate of lithium ions was 99.3%. Under the highly active catalysis of iron phosphate slag, the zinc-air battery showed a high specific capacity of 738.7 mAh / g.

[0077] Comparative Example 1

[0078] Compared with Example 1, the only difference is that the processing of step ② is not performed. Other operations and parameters are the same as those in Example 1.

[0079] The test results were as follows: the recovery rate of lithium ions was 75.1%. Under the catalysis of the highly active iron phosphate slag, the zinc-air battery showed a specific capacity of 642.5 mAh / g.

[0080] Comparative Example 2

[0081] The only difference from Example 1 is that in step ②, the waste positive electrode powder is placed in a glass container and then immersed in cooling oil at -18°C (indirect contact with the cooling medium) for 2 hours. Other operations and parameters are the same as in Example 1.

[0082] The test results were as follows: the recovery rate of lithium ions was 81.5%. Under the catalysis of the highly active iron phosphate slag, the zinc-air battery showed a specific capacity of 672.8.7 mAh / g.

[0083] Comparative Example 3

[0084] Compared with Example 1, the only difference is that in ③, the weight ratio of LiFePO4 / C is not controlled within the required range, specifically: the weight ratio of LiFePO4 / C is 1:0.5;

[0085] The test results were as follows: the recovery rate of lithium ions was 73.7%. Under the high activity catalysis of iron phosphate slag, the zinc-air battery showed a specific capacity of 641.5 mAh / g.

[0086] Comparative Example 4

[0087] Compared with Example 1, the only difference is that in ③, the calcination temperature is 50°C;

[0088] The test results were as follows: the recovery rate of lithium ions was 62.8%. Under the high activity catalysis of iron phosphate slag, the zinc-air battery showed a high specific capacity of 614.7 mAh / g.

[0089] Comparative Example 5

[0090] Compared with Example 1, the only difference is that in ③, the calcination atmosphere is a nitrogen atmosphere.

[0091] The test results were as follows: the recovery rate of lithium ions was 51.9%. Under the high activity catalysis of iron phosphate slag, the zinc-air battery showed a high specific capacity of 651.7 mAh / g.

Claims

1. A method for recycling waste lithium iron phosphate positive electrode materials, characterized in that the steps include: Step (1): Preprocessing The waste lithium iron phosphate cathode material is subjected to a rapid cooling pretreatment to obtain a pretreated material; wherein the temperature of the rapid cooling medium used in the rapid cooling stage is below -50°C; Step (2): Calcination-Water Soaking The mixture containing the pretreated material and the carbon material is subjected to a roasting treatment in an oxygen-containing atmosphere; and then subjected to a water leaching treatment to obtain a lithium extract and iron phosphate slag; The calcination temperature is 100-300° C.; in the mixture, the weight ratio of LiFePO4 / C is 1:1-5.

2. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: The waste lithium iron phosphate positive electrode material is a positive electrode material obtained by stripping the positive electrode sheet of a waste lithium iron phosphate battery.

3. The method for recycling waste lithium iron phosphate cathode materials according to claim 2, characterized in that: The content of LiFePO4 in the waste lithium iron phosphate positive electrode material is not less than 50wt%.

4. The method for recycling waste lithium iron phosphate cathode materials according to claim 3, characterized in that: The content of LiFePO4 in the waste lithium iron phosphate positive electrode material is above 80wt%.

5. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: The quenching medium is liquid nitrogen or dry ice.

6. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: The carbon material is a waste negative electrode material, which is obtained by stripping the negative electrode sheet of the waste lithium iron phosphate battery.

7. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: In step (2), the oxygen-containing atmosphere is at least one of oxygen, oxygen-protective gas mixture, and air.

8. The method for recycling waste lithium iron phosphate cathode materials according to claim 7, characterized in that: In step (2), the volume content of oxygen in the oxygen-containing atmosphere is not less than 5v%.

9. The method for recycling waste lithium iron phosphate cathode materials according to claim 8, characterized in that: In step (2), the volume content of oxygen in the oxygen-containing atmosphere is 10-35v%.

10. The method for recycling waste lithium iron phosphate cathode materials according to claim 7, characterized in that: The oxygen-containing atmosphere is also added with water vapor in an amount not higher than 20v%.

11. The method for recycling waste lithium iron phosphate cathode materials according to claim 10, characterized in that: 5-15V% water vapor is also added to the oxygen-containing atmosphere.

12. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: In step (2), the mixed material is heat-treated in advance and then subsequently calcined.

13. The method for recycling waste lithium iron phosphate cathode materials according to claim 12, characterized in that: In step (2), the temperature of the heat treatment stage is 30-100°C.

14. The method for recycling waste lithium iron phosphate cathode materials according to claim 13, characterized in that: In step (2), the temperature of the heat treatment stage is 50-60°C.

15. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: In step (2), the holding time of the heat treatment is 1 to 10 h.

16. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: In step (2), the roasting is fluidized roasting.

17. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: In step (2), the calcination time is 2 to 5 hours.

18. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: In step (2), after roasting, the product is cooled in the furnace or air-cooled.

19. The method for recycling waste lithium iron phosphate cathode materials according to claim 18, characterized in that: In step (2), the gas used for air cooling is carbon dioxide.

20. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: The liquid-to-solid ratio in the water immersion stage is 10~30 / mL / g.

21. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: The temperature during the immersion phase does not exceed 45°C.

22. The method for recycling waste lithium iron phosphate cathode materials according to claim 21, characterized in that: The temperature during the immersion stage is 20~35℃.

23. Ferric phosphate slag obtained by the recovery method according to any one of claims 1 to 22.

24. Use of the iron phosphate slag obtained by the recovery method according to any one of claims 1 to 22, characterized in that: It is used as a catalyst in zinc-air batteries.