Method for selectively leaching and regenerating positive electrode material from waste lithium ion battery

Abstract

The invention relates to a method for selectively leaching and regenerating a positive electrode material from a waste lithium ion battery, and belongs to the technical field of lithium ion batteries. The method comprises the following steps: discharging, disassembling, crushing, calcining and screening the waste lithium ion battery, adding an obtained positive active material into an oxalic acid solution, and stirring and reacting at 60-80 DEG C under the irradiation of an ultraviolet lamp to obtain a leaching solution rich in metal elements and leaching residue iron phosphate; adding sodium carbonate into the leachate for reaction to obtain lithium carbonate; and ball-milling and mixing iron phosphate, lithium carbonate and a carbon source, drying and calcining to obtain the regenerated lithium iron phosphate positive electrode material. The oxalic acid system is catalyzed by ultraviolet light to generate hydroxyl free radicals with strong oxidizing property, so that the leaching efficiency of lithium is remarkably improved, and the dissolution of iron is inhibited, thereby realizing the efficient separation of lithium and iron. The leaching residue is high-purity iron phosphate, lithium in the leaching solution is recycled in the form of lithium carbonate, and the leaching residue and the lithium carbonate can be directly used for regenerating the lithium iron phosphate positive electrode material as precursors, so that the technological process is greatly simplified, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to a method for selectively leaching and regenerating cathode materials from spent lithium-ion batteries, belonging to the field of lithium-ion battery technology. Background Technology

[0002] With the widespread use of lithium-ion batteries, a large number of waste lithium-ion batteries will be generated. On the one hand, waste lithium-ion batteries contain heavy metals such as nickel and cobalt, which, if not properly recycled, will pollute water sources and soil and harm human health. On the other hand, the ever-increasing demand for lithium-ion batteries has led to rising prices of raw materials such as lithium and cobalt. The lithium and cobalt elements contained in the cathode materials of lithium-ion batteries mostly come from salt lake brine and ores, which are costly to extract. If the cathode materials of waste lithium-ion batteries are considered as sources of lithium, cobalt, manganese, and nickel, and if they can be safely, efficiently, and without damage recycled, the resource shortage can be greatly alleviated.

[0003] There are currently three main processes for recycling waste lithium-ion battery cathode materials: pyrometallurgy, hydrometallurgy, and direct recycling. Direct recycling is currently only being carried out on a laboratory scale. In large-scale industrial production, many companies both domestically and internationally use pyrometallurgical and hydrometallurgical processes to recycle cathode materials. Compared to pyrometallurgical recycling technology, hydrometallurgical recycling technology has advantages such as high metal selectivity, high recycling efficiency, and high product added value. However, for acid leaching, simply using inorganic acids is insufficient to effectively break through the physicochemical structure of the waste battery surface, making it difficult to achieve ideal leaching results. Oxidizing agents are needed to assist acid leaching, and the required concentration of the leaching agent is relatively high. Existing leaching processes still have room for improvement in terms of low material consumption, low cost, and high-efficiency leaching.

[0004] In conclusion, developing a green leaching agent and recycling process to achieve low-cost and efficient recycling of spent lithium iron phosphate batteries is of great significance. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for selectively leaching and regenerating cathode materials from spent lithium-ion batteries, specifically involving an integrated method of ultraviolet-assisted oxalic acid leaching-precipitation-regeneration. This method utilizes ultraviolet light to catalyze the oxalic acid system to generate highly oxidizing hydroxyl radicals, significantly improving lithium leaching efficiency and inhibiting iron dissolution, thereby achieving efficient separation of lithium and iron. The leaching residue is high-purity iron phosphate, and the lithium in the leachate is recovered as lithium carbonate. Both can be used directly as precursors for regenerating lithium iron phosphate cathode materials without the need for external lithium and iron sources, greatly simplifying the process and reducing production costs.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] A method for selectively leaching and regenerating cathode material from spent lithium-ion batteries, wherein the cathode material of the spent lithium-ion batteries is lithium iron phosphate, and the method includes the following steps:

[0008] (1) Discharge and disassemble waste lithium-ion batteries to obtain positive electrode sheets; crush, calcine and screen the positive electrode sheets to obtain positive electrode active materials;

[0009] (2) The positive electrode active material is added to the oxalic acid solution, and under ultraviolet light irradiation, the mixture is stirred at 60-80°C. After the reaction is completed, the mixture is filtered and separated to obtain a leachate rich in metal elements and a leachate residue of ferric phosphate.

[0010] (3) Add sodium carbonate to the leachate and react. After the reaction is complete, filter and dry to obtain lithium carbonate.

[0011] (4) The iron phosphate, lithium carbonate and carbon source are ball-milled and mixed, dried and calcined to obtain the regenerated lithium iron phosphate cathode material.

[0012] Preferably, in step (1), the calcination temperature is 550±20℃ and the calcination time is 3~5h.

[0013] Preferably, in step (2), the concentration of the oxalic acid solution is 0.75 to 1.25 mol / L, and the solid-liquid ratio of the positive electrode active material to the oxalic acid solution is 40 to 60 g / L.

[0014] Preferably, in step (2), the power of the ultraviolet lamp is 6 to 10W and the irradiation time is 1 to 2 hours.

[0015] Preferably, in step (3), the drying temperature is 80-100℃ and the drying time is 12-24h.

[0016] Preferably, in step (4), the carbon source is glucose, the molar ratio of iron phosphate and lithium carbonate is 1:1.05 to 1.1, and the amount of glucose added is 5% to 6% of the total mass of iron phosphate and lithium carbonate.

[0017] Preferably, in step (4), the ball milling medium is ethanol, the ball milling speed is 400-600 rpm, and the ball milling time is 10-12 h.

[0018] Preferably, in step (4), during calcination, the temperature is first raised to 450±20℃ and held for 4 to 5 hours, and then raised to 750±20℃ and held for 12 hours.

[0019] Preferably, in step (4), the heating rate during calcination is 3 to 5 °C / min.

[0020] A regenerated lithium iron phosphate cathode material was prepared by the above method.

[0021] Beneficial effects

[0022] (1) The present invention constructs an ultraviolet light-oxalic acid synergistic leaching system, which achieves efficient and selective leaching of lithium without the need for external oxidants through a unique photochemical and electrochemical coupling reaction.

[0023] (2) This invention achieves highly efficient selective leaching of the target metal (lithium) and directional precipitation separation of the non-target metal (iron) under mild conditions. As Fe(II) is oxidized and fixed, the crystal lattice structure of LiFePO4 is disrupted, releasing lithium ions into the solution. Due to the high solubility of both lithium oxalate and phosphate, lithium ions are almost completely retained in the leachate, thus achieving selective and efficient lithium leaching. The iron content in the leachate is extremely low, and the leaching residue is pure iron phosphate, avoiding complex subsequent separation processes.

[0024] (3) The present invention uses the recycled products directly as precursors for the regeneration of cathode materials, realizing closed-loop recycling, with high material regeneration efficiency and excellent electrochemical performance. Attached Figure Description

[0025] Figure 1 This is a flowchart of the method described in this invention.

[0026] Figure 2 The image shows the XRD pattern of the leaching residue from Example 1.

[0027] Figure 3 The image shows the XRD pattern of the leaching residue in Comparative Example 1.

[0028] Figure 4 The image shows the XRD pattern of the regenerated lithium iron phosphate cathode material in Example 1.

[0029] Figure 5 The cycling performance of the regenerated lithium iron phosphate cathode material in Example 1 is shown.

[0030] Figure 6 The first three charge-discharge curves of the regenerated lithium iron phosphate cathode material in Example 1 are shown. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to specific embodiments.

[0032] like Figure 1 As shown, a method for selectively leaching and regenerating cathode materials from spent lithium-ion batteries, wherein the cathode material of the spent lithium-ion batteries is lithium iron phosphate, and the method includes the following steps:

[0033] (1) Discharge and disassemble waste lithium-ion batteries to obtain positive electrode sheets; crush, calcine and screen the positive electrode sheets to obtain positive electrode active materials;

[0034] (2) The positive electrode active material is added to the oxalic acid solution, and under ultraviolet light irradiation, the mixture is stirred at 60-80°C. After the reaction is completed, the mixture is filtered and separated to obtain a leachate rich in metal elements and a leachate residue of ferric phosphate.

[0035] (3) Add sodium carbonate to the leachate and react. After the reaction is complete, filter and dry to obtain lithium carbonate.

[0036] (4) The iron phosphate, lithium carbonate and carbon source are ball-milled and mixed, dried and calcined to obtain the regenerated lithium iron phosphate cathode material.

[0037] Example 1

[0038] Waste lithium-ion batteries (with lithium iron phosphate as the positive electrode material) were immersed in a sodium chloride solution for discharge treatment. The positive electrode sheet was disassembled, immersed in a sodium hydroxide solution, filtered and dried, and then calcined in a muffle furnace at 550°C for 4 hours to obtain the positive electrode active material.

[0039] The positive electrode active material was added to a 1M oxalic acid solution at a solid-liquid ratio of 50 g / L. The mixture was stirred under ultraviolet light (8W) and reacted at 70°C for 1.5 h. The leachate rich in metal elements and the leaching residue ferric phosphate were obtained by filtration. The leaching rate was calculated to be 99.2%.

[0040] Sodium carbonate was added to the leachate to obtain lithium carbonate precursor. The leaching residue (ferric phosphate) and lithium carbonate precursor were washed sequentially with deionized water and ethanol, and then dried in a vacuum drying oven at 80°C for 12 hours. Ferric phosphate and lithium carbonate were mixed at a ratio of 1:1.05, and glucose (5 wt% of the total mass of ferric phosphate and lithium carbonate) was added. The mixture was then ball-milled in a planetary ball mill for 12 hours (ethanol as the milling medium, 500 rpm). The mixture was heated to 450°C at a rate of 5°C / min and held at that temperature for 4 hours, then heated to 750°C at a rate of 5°C / min and held at that temperature for 12 hours to obtain the regenerated cathode material.

[0041] Figure 2 The XRD pattern of the leaching residue of the example shows that the sample has obvious characteristic peaks of FePO4 and good crystallinity, and does not contain LiFePO4 phase.

[0042] Figure 4 The XRD pattern of the regenerated cathode material in this example shows that the peaks of the sample and LiFePO4 are in good correspondence, proving that the regenerated cathode material is the LiFePO4 phase.

[0043] Figure 5 To demonstrate the cycling performance of the recycled lithium iron phosphate cathode material in this embodiment, the battery retained a capacity of 97.2 mAh·g after 100 cycles at 1C. -1 .

[0044] Figure 6 The figures show the charge-discharge curves of the regenerated lithium iron phosphate cathode material in the first three cycles of the example. At a current density of 0.1C, the battery achieved a discharge specific capacity of 167.4 mAh / g in the first cycle.

[0045] Example 2

[0046] Waste lithium-ion batteries (with lithium iron phosphate as the positive electrode material) were immersed in a sodium chloride solution for discharge treatment. The positive electrode sheet was disassembled, immersed in a sodium hydroxide solution, filtered and dried, and then calcined in a muffle furnace at 550°C for 4 hours to obtain the positive electrode active material.

[0047] The positive electrode active material was added to a 0.75M oxalic acid solution at a solid-liquid ratio of 40 g / L. The mixture was stirred under ultraviolet light (8W) and reacted at 60°C for 1 h. The solution was filtered to obtain a metal-rich leachate and ferric phosphate leaching residue. The leaching rate was calculated to be 84.3%.

[0048] Sodium carbonate was added to the leachate to obtain lithium carbonate precursor. The leaching residue (ferric phosphate) and lithium carbonate precursor were washed sequentially with deionized water and ethanol, and then dried in a vacuum drying oven at 80°C for 12 hours. Ferric phosphate and lithium carbonate were mixed at a ratio of 1:1.05, and glucose (5 wt% of the total mass of ferric phosphate and lithium carbonate) was added. The mixture was then ball-milled in a planetary ball mill for 12 hours (ethanol as the milling medium, 500 rpm). The mixture was heated to 450°C at a rate of 5°C / min and held at that temperature for 4 hours, then heated to 750°C at a rate of 5°C / min and held at that temperature for 12 hours to obtain the regenerated cathode material.

[0049] XRD analysis showed that the peaks of the example sample and LiFePO4 corresponded perfectly, proving that the regenerated cathode material was the LiFePO4 phase.

[0050] Example 3

[0051] Waste lithium-ion batteries (with lithium iron phosphate as the positive electrode material) were immersed in a sodium chloride solution for discharge treatment. The positive electrode sheet was disassembled, immersed in a sodium hydroxide solution, filtered and dried, and then calcined in a muffle furnace at 550°C for 4 hours to obtain the positive electrode active material.

[0052] The positive electrode active material was added to a 1.25M oxalic acid solution at a solid-liquid ratio of 60 g / L. The mixture was stirred under ultraviolet light (power 8W) and reacted at 80℃ for 2 h. The leachate rich in metal elements and the leaching residue ferric phosphate were obtained by filtration. The leaching rate was calculated to be 87.6%.

[0053] Sodium carbonate was added to the leachate to obtain lithium carbonate precursor. The leaching residue (ferric phosphate) and lithium carbonate precursor were washed sequentially with deionized water and ethanol, and then dried in a vacuum drying oven at 80°C for 12 hours. Ferric phosphate and lithium carbonate were mixed at a ratio of 1:1.05, and glucose (5 wt% of the total mass of ferric phosphate and lithium carbonate) was added. The mixture was then ball-milled in a planetary ball mill for 12 hours (ethanol as the milling medium, 500 rpm). The mixture was heated to 450°C at a rate of 5°C / min and held at that temperature for 4 hours, then heated to 750°C at a rate of 5°C / min and held at that temperature for 12 hours to obtain the regenerated cathode material.

[0054] XRD analysis showed that the peaks of the example sample and LiFePO4 corresponded perfectly, proving that the regenerated cathode material was the LiFePO4 phase.

[0055] Comparative Example 1:

[0056] Waste lithium-ion batteries (with lithium iron phosphate as the positive electrode material) were immersed in a sodium chloride solution for discharge treatment. The positive electrode sheet was disassembled, immersed in a sodium hydroxide solution, filtered and dried, and then calcined in a muffle furnace at 550°C for 4 hours to obtain the positive electrode active material.

[0057] The positive electrode active material was added to a 1M oxalic acid solution at a solid-liquid ratio of 50 g / L. The mixture was stirred under normal light irradiation and reacted at 70°C for 1.5 h. The solution was filtered to obtain a metal-rich leachate and ferric phosphate leaching residue. The lithium leaching rate was calculated to be 62.3%.

[0058] Sodium carbonate was added to the leachate to obtain lithium carbonate precursor. The leaching residue (ferric phosphate) and lithium carbonate precursor were washed sequentially with deionized water and ethanol, and then dried in a vacuum drying oven at 80°C for 12 hours. Ferric phosphate and lithium carbonate were mixed at a ratio of 1:1.05, and glucose (5 wt% of the total mass of ferric phosphate and lithium carbonate) was added. The mixture was then ball-milled in a planetary ball mill for 12 hours. The mixture was heated to 450°C at a rate of 5°C / min and held at that temperature for 4 hours, and then heated to 750°C at a rate of 5°C / min and held at that temperature for 12 hours to obtain the regenerated cathode material.

[0059] Appendix Figure 3 The XRD pattern of the comparative leaching residue shows that the peaks of the comparative sample correspond perfectly with those of LiFePO4 and FePO4, proving that the comparative sample is composed of LiFePO4 and FePO4 phases.

[0060] This invention utilizes ultraviolet light energy to generate highly oxidizing hydroxyl radicals in situ within the reaction system. These radicals provide the necessary oxidizing environment for the oxidation of Fe(II) in LiFePO4 to Fe(III). This is a green, low-cost "on-demand production" model for oxidants, fundamentally avoiding the problems of adding, transporting, storing, and leaving residues of chemical oxidants.

[0061] Oxalic acid is not the sole leaching agent in this system; it also exhibits a synergistic effect with ultraviolet light. (1) Leaching agent (providing H+) + Oxalic acid, as a weak organic acid, can provide H+. + (2) Complexing agent: oxalate ion (C2O4) reacts with dissolved metal ions in an acid-dissolving reaction. 2- It has a strong complexing ability with Fe(III) and can form stable soluble complexes (such as [Fe(C2O4)3]). 3- This promotes the dissolution of the passivation layer on the surface of lithium iron phosphate particles and accelerates the further reaction of the inner layer material; on the other hand, it also stabilizes Fe(III) in the solution and prevents it from prematurely hydrolyzing and precipitating. (3) Reducing agent (for Fe(III)): It is worth noting that oxalic acid and its decomposition products have a certain reducing effect on Fe(III). However, under the reaction conditions controlled by this invention (specific concentration, temperature, and ultraviolet light), the kinetic advantage of the oxidation reaction (dominated by ·OH) is much greater than that of the reduction reaction, ensuring that Fe(II) can be continuously and effectively oxidized to Fe(III).

[0062] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A method for selectively leaching and regenerating cathode materials from spent lithium-ion batteries, characterized in that: The positive electrode material of the waste lithium-ion battery is lithium iron phosphate, and the method steps include: (1) Discharge and disassemble waste lithium-ion batteries to obtain positive electrode sheets; crush, calcine and screen the positive electrode sheets to obtain positive electrode active materials; (2) The positive electrode active material is added to the oxalic acid solution, and under ultraviolet light irradiation, the mixture is stirred at 60-80°C. After the reaction is completed, the mixture is filtered and separated to obtain a leachate rich in metal elements and a leachate residue of ferric phosphate. (3) Add sodium carbonate to the leachate and react. After the reaction is complete, filter and dry to obtain lithium carbonate. (4) The iron phosphate, lithium carbonate and carbon source are ball-milled and mixed, dried and calcined to obtain the regenerated lithium iron phosphate cathode material.

2. The method for selectively leaching and regenerating cathode materials from spent lithium-ion batteries as described in claim 1, characterized in that: In step (1), the calcination temperature is 550±20℃ and the calcination time is 3~5h.

3. The method for selectively leaching and regenerating cathode materials from spent lithium-ion batteries as described in claim 1, characterized in that: In step (2), the concentration of the oxalic acid solution is 0.75 to 1.25 mol / L, and the solid-liquid ratio of the positive electrode active material to the oxalic acid solution is 40 to 60 g / L.

4. The method for selectively leaching and regenerating cathode materials from spent lithium-ion batteries as described in claim 1, characterized in that: In step (2), the power of the ultraviolet lamp is 6-10W and the irradiation time is 1-2h.

5. The method for selectively leaching and regenerating cathode materials from spent lithium-ion batteries as described in claim 1, characterized in that: In step (3), the drying temperature is 80-100℃ and the drying time is 12-24h.

6. The method for selectively leaching and regenerating cathode materials from spent lithium-ion batteries as described in claim 1, characterized in that: In step (4), the carbon source is glucose, the molar ratio of iron phosphate and lithium carbonate is 1:1.05 to 1.1, and the amount of glucose added is 5% to 6% of the total mass of iron phosphate and lithium carbonate.

7. The method for selectively leaching and regenerating cathode materials from spent lithium-ion batteries as described in claim 1, characterized in that: In step (4), the ball milling medium is ethanol, the ball milling speed is 400-600 rpm, and the ball milling time is 10-12 h.

8. The method for selectively leaching and regenerating cathode materials from spent lithium-ion batteries as described in claim 1, characterized in that: In step (4), during calcination, the temperature is first raised to 450±20℃ and held for 4 to 5 hours, and then raised to 750±20℃ and held for 12 hours.

9. The method for selectively leaching and regenerating cathode materials from spent lithium-ion batteries as described in claim 1, characterized in that: In step (4), the heating rate during calcination is 3-5℃ / min.

10. A recycled lithium iron phosphate cathode material, characterized in that: It is prepared by the method described in any one of claims 1 to 9.

Images