A method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode material

Abstract

The invention provides a method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode materials. The method first adds recycled waste lithium iron phosphate positive electrode sheets into an electrolytic anode chamber, then adds an oxidant solution, uses a cation membrane to isolate the electrolytic anode chamber from the electrolytic cathode chamber, adds a LiOH solution into the electrolytic cathode chamber, connects the electrolytic anode chamber and the electrolytic cathode chamber to an external power supply through electrodes, and conducts electrolysis by powering on until the reaction is finished, then separates the solid and liquid in the electrolytic anode chamber, and collects filtrate, filter residue and current collector sheets respectively; concentrates and dries the solution in the electrolytic cathode chamber to obtain regenerated LiOH, or introduces carbon dioxide to separate the solid and liquid to obtain Li2CO3 precipitation; the method of the invention can realize cyclic leaching of waste lithium iron phosphate positive electrode materials, and the leaching effect is good, and can realize the regeneration and cyclic utilization of lithium iron.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling lithium iron phosphate positive electrode materials, and more specifically, to a method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode materials. Background Art

[0002] Lithium-ion batteries (LIBs) have the advantages of high discharge voltage, long cycle life and no memory effect, and are widely used in mobile electronic devices, electric vehicles, electrochemical energy storage and other fields. The rapid development of electric vehicles has led to the explosive growth of power batteries, and lithium iron phosphate (LFP / LiFePO4) positive electrode materials have the advantages of good thermal stability, high safety and low cost. It is one of the most important lithium battery materials and occupies a large market share. However, the average service life of power lithium-ion batteries is 5-8 years. Since lithium iron phosphate is the most mainstream power battery supporting system in the early stage of the industry, the scrapping period of lithium iron phosphate batteries will come first, and there will be an explosive wave of lithium iron phosphate battery retirement in the next few years.

[0003] Retired lithium iron phosphate contains rich metal resources, including lithium, copper, aluminum, iron and other valuable metals. The content of copper and aluminum is 18.7%, with a potential value of about 18.87; the content of lithium is about 1%, which is also of high value. Among them, my country's lithium reserves account for about 22.9% of the world's total. The cost of lithium resource development and utilization is high, and the external dependence on lithium raw material supply is high. The relative shortage of low-cost lithium will inevitably affect the sustainable development of my country's portable electronic devices, new energy vehicles and other industries. Recycling lithium resources from waste batteries can reduce the waste of resources, better alleviate the pressure of importing lithium resources, avoid environmental pollution caused by waste batteries, and greatly promote the sustainable development of the battery industry.

[0004] The recycling process of used batteries is generally pretreatment, separation, recycling, impurity removal and reuse. In the existing recycling of used lithium iron phosphate batteries, the battery shell, positive and negative electrode materials and diaphragm are first separated and recycled separately through discharge and disassembly. At present, the main methods for recycling and reusing used lithium iron phosphate are precipitation method, high-temperature solid phase repair, high-temperature solid phase regeneration technology, biological leaching technology and mechanical activation treatment. The precipitation method, which is widely used today, requires the use of inorganic strong acid and hydrogen peroxide to leach the used lithium iron phosphate, and then the Fe and Li are separated by a chemical precipitation process. It consumes a lot of chemical reagents and may produce a large amount of waste gas, which may cause secondary pollution to the environment. Summary of the invention

[0005] Based on the above-mentioned technical problems existing in the prior art, the present application provides a method for the cyclic leaching and regeneration of waste lithium iron phosphate positive electrodes. The method uses an oxidant as a targeted redox reaction between the redox medium and the material, utilizes an external power supply to drive the cyclic regeneration of the medium, and guides the continuous oxidation cyclic leaching of lithium iron phosphate. Effective leaching of lithium iron phosphate can be achieved through a lower concentration of oxidant, which not only saves costs but is also environmentally friendly.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] A method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode, characterized in that it comprises the following steps:

[0008] S1. Add the recycled waste lithium iron phosphate positive electrode sheet into the electrolytic anode chamber, and then add the oxidant solution;

[0009] S2, using a cationic membrane to isolate the electrolytic anode chamber and the electrolytic cathode chamber;

[0010] S3, adding LiOH solution into the electrolytic cathode chamber;

[0011] S4, the electrolysis anode chamber and the electrolysis cathode chamber are connected to an external power supply through electrodes, and power is supplied to perform electrolysis until the reaction is completed, and then the solid and liquid in the electrolysis anode chamber are separated, and the filtrate, the filter residue and the current collector sheet are collected respectively; the solution in the electrolysis cathode chamber is concentrated and dried to obtain regenerated LiOH, or carbon dioxide is introduced to obtain Li2CO3 precipitation by solid-liquid separation;

[0012] Wherein, the oxidant is any one of Na2S2O8, (NH4)2S2O8, K2S2O8, Li2S2O8, NaClO, and KClO.

[0013] In the technical solution of the present invention, the reaction principle is as follows Figure 1 As shown (taking sodium persulfate as the oxidant), specifically: in the electrolytic anode chamber, the oxidant oxidizes the lithium iron phosphate positive electrode material to generate iron phosphate precipitation and leaches lithium ions at the same time, and the oxidant undergoes a reduction reaction. The oxidant after the reduction reaction loses electrons under the action of electrolysis and recovers the strong oxidation effect, and continues to oxidize the lithium iron phosphate, thereby realizing the cyclic leaching of the lithium iron phosphate by the oxidant; the reactions occurring in the electrolytic anode chamber are as follows:

[0014] 2LiFePO4+S2O8 2- →2FePO4+2Li + +2SO4 2- ;

[0015] 2SO4 2- -2e→S2O8 2- ;

[0016] The lithium ions leached from the electrolytic anode chamber enter the electrolytic cathode chamber through the cation membrane, and the lithium ions in the electrolytic cathode chamber are continuously enriched; while the electrons in the electrolytic anode chamber are transferred to the cathode chamber through the circuit, and the water in the electrolytic cathode chamber obtains electrons to generate hydroxide, thereby achieving the charge balance of the solution in the electrolytic cathode chamber and obtaining a lithium-rich solution; the reactions occurring in the electrolytic cathode chamber are as follows:

[0017] O2+2H2O+4e - →4OH - (with oxygen);

[0018] 2H2O+2e - →H2+2OH - (without oxygen);

[0019] As the reaction proceeds, lithium iron phosphate particles continue to fall off from the current collector, achieving the separation of the positive electrode active material and the current collector.

[0020] In some embodiments, the concentration of the oxidant solution is 0-0.5 mol / L; the oxidant concentration is >0.

[0021] In some embodiments, the solid-to-liquid ratio in the electrolysis anode chamber is 5 to 100 g / L.

[0022] In some embodiments, the concentration of LiOH in the electrolysis cathode chamber is 0 to 0.2 mol / L.

[0023] In some embodiments, the external power supply voltage is 0-2V, and the current density is 0-30mA / cm 2 ;Power supply voltage>0, current density>0.

[0024] In some embodiments, the electrolysis temperature is 10-60°C.

[0025] In some embodiments, the electrode is an inert electrode, including but not limited to platinum, gold, graphite, etc.

[0026] In some embodiments, the cationic membrane is a DuPont 117 proton membrane.

[0027] In some embodiments, the method further comprises the following steps:

[0028] S5. Mix the filter residue in step S4 and the regenerated LiOH or Li2CO3 precipitate, add the corresponding lithium source to make the molar amount of Li excess by 5-10%, then add the carbon source, mix well, and calcine in an inert atmosphere at 600-1000° C. to obtain a regenerated lithium iron phosphate positive electrode active material.

[0029] In some embodiments, the carbon source is at least one of sucrose, glucose, and citric acid.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention uses an oxidant as a targeted redox reaction between a redox medium and a material, utilizes an external power source to drive the cyclic regeneration of the medium, and guides the continuous oxidation leaching of lithium iron phosphate. A relatively small amount of oxidant can be used to achieve the oxidation of waste lithium iron phosphate, while promoting the leaching of lithium ions, and the oxidant can be recycled and reused.

[0032] The present invention reduces the process of stripping the active material and the current collector during the lithium iron phosphate leaching and recovery process, and directly separates the solid and liquid to obtain a lithium-rich solution, a current collector and iron phosphate precipitation after the reaction is completed, and the process flow is simple.

[0033] The method provided by the invention can continuously extract lithium, the Faraday efficiency of electric energy utilization is maintained above 97%, the lithium leaching rate is higher than 95%, and the contents of aluminum and iron in the lithium-rich solution are lower than 0.02%, with high purity.

[0034] In addition, the recovered iron phosphate and lithium can be directly used for the regeneration of lithium iron phosphate, thus realizing the recycling of iron and lithium.

[0035] In addition, the process flow of the present invention is simple, the redox medium can be recycled, there is no need for step-by-step operation, the oxidant has strong selectivity, low impurity content, no need for further removal, and strong industrial adaptability; and the entire process does not require the introduction of acid and alkali, and no stirring is required to disperse the iron-lithium particles in the solution. The contact area between the oxidant and the material is large, the oxidation reaction speed is fast, the amount of oxidant used is small, the cost is low, and there is no outflow of wastewater and waste gas, which is clean and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the principle diagram of cyclic leaching of waste lithium iron phosphate positive electrode of this application;

[0037] Figure 2 This is the process flow chart of this application;

[0038] Figure 3 These are the SEM, XRD and Mapping images of the iron phosphate after oxidation leaching of the waste lithium iron phosphate positive electrode sheet of Example 1 of the present application. DETAILED DESCRIPTION

[0039] Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar modifications without violating the connotation of the present invention, so the present invention is not limited to the specific implementation disclosed below.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0041] Example 1

[0042] like Figure 2 As shown, a method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode comprises the following steps:

[0043] (1) Discharge the waste lithium-ion batteries completely, disassemble, peel, cut, dry the positive electrode sheets of a certain size, and keep them for later use;

[0044] (2) Weigh an appropriate amount of waste lithium iron phosphate positive electrode sheets and place them in the anode chamber of an H-type electrolytic cell, add 40 mL of a 0.2 mol / L sodium persulfate solution, and the liquid volume of the liquid phase leached to the solid-liquid ratio of the waste lithium iron phosphate positive electrode sheets is 50 g / L;

[0045] (3) using a cationic membrane to isolate the anode chamber from the cathode chamber;

[0046] (4) Add 40 mL of 0.1 mol / L LiOH solution into the cathode chamber;

[0047] (5) The anode chamber and cathode chamber are connected to an external power supply through platinum electrodes, and the power is turned on for electrolysis until the reaction is completed; during the electrolysis process, the control voltage is 1.2V and the current density is 5mA / cm 2 , the temperature in the anode chamber is 25°C;

[0048] (6) filtering and sorting the mixed slurry in the anode chamber by vacuum filtration, and repeatedly washing with distilled water to obtain aluminum foil and iron phosphate precipitate, respectively; placing the lithium iron phosphate precipitate in an oven, drying at 80° C. for 10 h, grinding, and storing; recovering the filtrate; concentrating and drying the lithium-rich solution in the cathode chamber to obtain lithium hydroxide;

[0049] (7) Mixing the lithium iron phosphate precipitate dried in step (6) with lithium hydroxide, adding lithium hydroxide until the molar excess of lithium is 5%, then adding citric acid as a carbon source, grinding and mixing evenly, placing in a tubular furnace, heating to 350° C. in an argon atmosphere and calcining for 1 hour, then heating to 650° C. and calcining for 10 hours, to obtain a regenerated lithium iron phosphate positive electrode active material.

[0050] In this embodiment, the Faraday efficiency of the electric energy utilization rate is maintained at 98.8%. The metal ion content in the sample is measured by inductively coupled plasma optical emission spectrometry (ICP-OES). The lithium leaching rate is 96.6%, and the iron content in the lithium-rich solution is 0.018%.

[0051] In this application, the SEM, XRD and Mapping images of the iron phosphate obtained after electrolytic leaching are as follows: Figure 3 shown.

[0052] Example 2

[0053] like Figure 2 As shown, a method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode comprises the following steps:

[0054] (1) Discharge the waste lithium-ion batteries completely, disassemble, peel, cut, dry the positive electrode sheets of a certain size, and keep them for later use;

[0055] (2) Weigh an appropriate amount of waste lithium iron phosphate positive electrode sheets and place them in the anode chamber of an H-type electrolytic cell, add 40 mL of 0.1 mol / L ammonium persulfate solution, and the liquid volume of the liquid phase leached to the solid-liquid ratio of the waste lithium iron phosphate positive electrode sheets is 100 g / L;

[0056] (3) using a cationic membrane to isolate the anode chamber from the cathode chamber;

[0057] (4) Add 40 mL of 0.2 mol / L LiOH solution into the cathode chamber;

[0058] (5) The anode chamber and cathode chamber are connected to an external power supply through platinum electrodes, and the power is turned on for electrolysis until the reaction is completed; during the electrolysis process, the control voltage is 1.5V and the current density is 10mA / cm 2 , the temperature in the anode chamber is 45°C;

[0059] (6) filtering and sorting the mixed slurry in the anode chamber by vacuum filtration, and repeatedly washing with distilled water to obtain aluminum foil and iron phosphate precipitate respectively, placing the lithium iron phosphate precipitate in an oven, drying at 80° C. for 10 h, grinding, and storing; recovering the filtrate; introducing carbon dioxide into the lithium-rich solution in the cathode chamber to obtain Li2CO3 precipitate, washing, drying, and lithium carbonate;

[0060] (7) Mixing the lithium iron phosphate precipitate dried in step (6) with lithium carbonate, adding lithium carbonate until the lithium molar amount is 10% in excess, and then adding glucose as a carbon source. After grinding and mixing, the mixture is placed in a tubular furnace, heated to 350° C. in an argon atmosphere and calcined for 1 hour, and then heated to 750° C. and calcined for 10 hours to obtain a regenerated lithium iron phosphate positive electrode active material.

[0061] In this embodiment, the Faraday efficiency of the electric energy utilization rate is maintained at 97%, and the metal ion content in the sample is measured by inductively coupled plasma optical emission spectrometry (ICP-OES). The lithium leaching rate is 95.1%, and the iron content in the lithium-rich solution is 0.02%.

[0062] Example 3

[0063] like Figure 2 As shown, a method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode comprises the following steps:

[0064] (1) Discharge the waste lithium-ion batteries completely, disassemble, peel, cut, dry the positive electrode sheets of a certain size, and keep them for later use;

[0065] (2) Weigh an appropriate amount of waste lithium iron phosphate positive electrode sheets and place them in the anode chamber of an H-type electrolytic cell, add 40 mL of a 0.3 mol / L sodium hypochlorite solution, and the liquid volume of the liquid phase leached to the solid-liquid ratio of the waste lithium iron phosphate positive electrode sheets is 80 g / L;

[0066] (3) using a cationic membrane to isolate the anode chamber from the cathode chamber;

[0067] (4) Add 40 mL of 0.1 mol / L LiOH solution into the cathode chamber;

[0068] (5) The anode chamber and cathode chamber are connected to an external power supply through platinum electrodes, and the power is turned on for electrolysis until the reaction is completed; during the electrolysis process, the control voltage is 1.2V and the current density is 5mA / cm 2 , the temperature in the anode chamber is 35°C;

[0069] (6) filtering and sorting the mixed slurry in the anode chamber by vacuum filtration, and repeatedly washing with distilled water to obtain aluminum foil and iron phosphate precipitate, respectively; placing the lithium iron phosphate precipitate in an oven, drying at 80° C. for 10 h, grinding, and storing; recovering the filtrate; concentrating and drying the lithium-rich solution in the cathode chamber to obtain lithium hydroxide;

[0070] (7) Mixing the lithium iron phosphate precipitate dried in step (6) with lithium hydroxide, adding lithium hydroxide until the molar excess of lithium is 5%, then adding citric acid as a carbon source, grinding and mixing evenly, placing in a tubular furnace, heating to 350° C. in an argon atmosphere and calcining for 1 hour, then heating to 800° C. and calcining for 10 hours, to obtain a regenerated lithium iron phosphate positive electrode active material.

[0071] In this embodiment, the Faraday efficiency of the electric energy utilization rate is maintained at 97.2%. The metal ion content in the sample is measured by inductively coupled plasma optical emission spectrometry (ICP-OES). The lithium leaching rate is 95.5%, and the iron content in the lithium-rich solution is 0.02%.

[0072] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0073] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode, characterized in that: The following steps are involved: S1. Add the recycled waste lithium iron phosphate positive electrode sheet into the electrolytic anode chamber, and then add the oxidant solution; S2, using a cationic membrane to isolate the electrolytic anode chamber and the electrolytic cathode chamber; S3, adding LiOH solution into the electrolytic cathode chamber; S4, the electrolysis anode chamber and the electrolysis cathode chamber are connected to an external power supply through electrodes, and power is supplied to perform electrolysis until the reaction is completed, and then the solid and liquid in the electrolysis anode chamber are separated, and the filtrate, the filter residue and the current collector sheet are collected respectively; the solution in the electrolysis cathode chamber is concentrated and dried to obtain regenerated LiOH, or carbon dioxide is introduced to separate the solid and liquid to obtain Li2CO3 precipitation; Wherein, the oxidant is any one of Na2S2O8, (NH4)2S2O8, K2S2O8, Li2S2O8, NaClO, and KClO.

2. The method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode according to claim 1, characterized in that: The concentration of the oxidant solution is 0-0.5 mol / L.

3. The method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode according to claim 1, characterized in that: The solid-liquid ratio in the electrolysis anode chamber is 5 to 100 g / L.

4. The method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode according to claim 1, characterized in that: The concentration of LiOH in the electrolytic cathode chamber is 0-0.2 mol / L.

5. The method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode according to claim 1, characterized in that: The external power supply voltage is 0-2V, and the current density is 0-30mA / cm 2 .

6. The method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode according to claim 1, characterized in that: The electrolysis temperature is 10-60°C.

7. The method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode according to claim 1, characterized in that: The electrode is an inert electrode.

8. The method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode according to claim 1, characterized in that: The cationic membrane is DuPont 117 proton membrane.

9. The method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode according to any one of claims 1 to 8, characterized in that: The following steps are also included: S5. Mix the filter residue in step S4 and the regenerated LiOH or Li2CO3 precipitate, add the corresponding lithium source to make the molar amount of Li excess by 5-10%, then add the carbon source, mix well, and calcine in an inert atmosphere at 600-1000° C. to obtain a regenerated lithium iron phosphate positive electrode active material.

10. The method for cyclic leaching and regeneration of waste lithium iron phosphate positive electrode according to claim 9, characterized in that: The carbon source is at least one of sucrose, glucose and citric acid.

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