Method for synthesizing lithium iron manganese phosphate positive electrode material from waste lithium manganate battery positive electrode material

Abstract

The invention belongs to the field of resource recycling, and particularly relates to a method for preparing a lithium iron manganese phosphate positive electrode material from a waste lithium manganate battery positive electrode material. The waste lithium manganate battery is discharged, roasted, disassembled and ground to obtain the lithium manganate positive electrode material. The method comprises the following steps: adding dilute phosphoric acid and ascorbic acid into a lithium manganate positive electrode material to carry out synergistic acid leaching reaction, carrying out suction filtration to obtain filtrate containing manganese, lithium and phosphorus, adjusting the pH of the filtrate to form manganese-containing precipitate and lithium-containing filtrate, adjusting the pH of the lithium-containing filtrate, and carrying out evaporation concentration to obtain lithium-containing precipitate. And carrying out solid-phase grinding on the manganese precipitate, the lithium precipitate, carbon, iron and phosphorus, and carrying out high-temperature roasting to obtain the lithium ferric manganese phosphate positive electrode material. The method has the advantages of low cost, simple process, high recovery rate and the like, and solves the problem of recycling of the waste lithium manganate battery.

Description

Technical Field

[0001] The present invention belongs to the field of resource recycling, and more specifically, relates to a method for preparing lithium iron phosphate manganese cathode material from the cathode material of waste lithium manganese oxide batteries. Background Art

[0002] As an efficient and clean energy storage material, since the commercialization of the first Sony LiCoO2-based lithium-ion battery in 1992, lithium-ion batteries have been widely used in many fields such as new energy vehicles, portable electronic devices, and large-scale energy storage systems. However, the common service life of lithium-ion batteries is 3 - 10 years. Early-produced transition metal oxide lithium-ion batteries such as lithium cobalt oxide (LCO) and lithium manganese oxide (LMO) have faced a wave of retirements and the retirement volume is increasing year by year. The recycling and reuse of lithium-ion batteries is an inevitable choice. Since the cathode material of waste LMO batteries contains abundant lithium and manganese, and their contents are much higher than those of natural minerals, there are currently various technologies for recycling and regenerating the cathode material of waste LMO batteries. The recycling and regeneration of waste lithium-ion batteries are divided into two methods. One method is indirect regeneration, where the cathode material is re-synthesized from the leaching solution. The other method is direct regeneration, where the electrochemical performance is restored by supplementing lithium in the crystal lattice and restoring the microstructure that has changed during repeated charge and discharge processes. For example, the Chinese patent of CN118782948 discloses a direct regeneration method for the lithium iron phosphate cathode sheet of waste lithium-ion batteries. It is specifically recorded that the sheet-shaped cathode active material is collected from the waste lithium iron phosphate cathode sheet, and the cathode active material is immersed in a lithium supplement solution for lithium supplement regeneration. The regenerated sheet-shaped lithium iron phosphate can be directly attached to the aluminum current collector for reuse.

[0003] However, the theoretical capacity of the LMO cathode material with a spinel structure is relatively small, at 148 mAh / g. At the same time, due to the easy occurrence of manganese dissolution problems and Jahn-Teller distortion during the charge and discharge process of LMO, it leads to problems such as the destruction of the LMO material structure and poor cycling performance. Direct regeneration of the LMO cathode material does not have good economic feasibility. In order to pursue cathode materials with higher performance, it is meaningful to indirectly regenerate waste LMO cathode materials into lithium-ion battery cathode materials with more excellent performance. Currently, the olivine-structured lithium iron phosphate (LFP) cathode material has received wide attention due to its good electrochemical performance, thermal stability, and relatively high theoretical capacity (170 mAh / g). However, the relatively low working voltage (3.45 V vs Li / Li+) and theoretical energy density (578 W h kg-1) of LFP still cannot meet market demands. Research has found that since both Mn and Fe occupy the 4c site, Mn and Fe can be mutually doped to form a uniform iron-manganese solid solution. By doping Mn into LFP, a lithium manganese iron phosphate (LMFP) cathode material with a high theoretical energy density (700 W h kg-1) can be prepared. Therefore, it is feasible to recycle waste LMO cathode materials and then synthesize LMFP cathode materials by additionally supplementing part of the iron. For example, the Chinese patent CN118561254A discloses a method for recycling lithium salts from waste lithium-ion batteries and preparing lithium iron phosphate cathode materials. Specifically, it is recorded that oxalic acid or persulfate is used as the leaching agent, and under hydrothermal action, a leaching solution containing lithium metal ions and a precipitate of organic acid root complexes containing manganese and iron are obtained. The leaching solution is evaporated and crystallized to obtain lithium salts, and by regulating the element ratios of lithium, manganese, iron, and phosphorus, lithium manganese iron phosphate cathode materials are sintered under an inert atmosphere.

[0004] The recycling of the cathode materials of waste lithium manganese oxide batteries mainly includes pyrometallurgical recycling and hydrometallurgical recycling. Pyrometallurgical recycling recovers valuable metals in the cathode material in the form of alloys through high-temperature reduction roasting. However, the pyrometallurgical recycling process has high energy consumption, generates a large amount of harmful gases (such as NOx, SOx, etc.), and the recovery rate of Li during the recycling process is relatively low. Compared with pyrometallurgical recycling, hydrometallurgical recycling has the advantages of low energy consumption, high metal recovery rate, safety, and environmental protection, and is a recycling method with great development potential. For example, the Chinese patent CN119120936A discloses a synergistic leaching agent and method for recycling and regenerating the cathode materials of waste lithium-ion batteries. Specifically, it is recorded that an inorganic acid and a thiourea compound synergistic leaching agent are used to recover valuable elements in the cathode materials of waste lithium-ion batteries.

[0005] However, inorganic acids such as H2SO4, HCl, HNO3, etc. are often used for the cathode material of waste lithium manganese oxide batteries. During the recycling process, a large amount of waste liquid is generated and difficult to treat, and harmful gases such as SO2, Cl2, NOx, etc. will be generated during the subsequent roasting process of cathode material synthesis. Considering the recycling of waste LMO batteries in the context of green economy, H3PO4 is used as the leaching agent, and precipitates containing phosphorus, lithium, and manganese are obtained by adjusting the pH of the solution, making full use of the phosphorus element in H3PO4, reducing the generation of waste liquid and waste gas, and at the same time reducing the addition of phosphorus during the subsequent synthesis of cathode materials. In addition, since manganese in the lithium manganese oxide cathode material exists in the forms of +3 and +4 valence, reducing agents (such as glucose, H2O2, citric acid, etc.) usually need to be added to reduce the valence of manganese and improve the leaching effect. As a natural organic compound, ascorbic acid has vinylogous carboxylic acid and certain reducing ability. Adding an appropriate amount of ascorbic acid during the leaching process can promote the leaching reaction and is beneficial to the extraction of valuable metals in the cathode material. For example, the Chinese patent CN114277252A discloses a method for synergistic leaching of waste lithium-ion batteries with acetic acid / ascorbic acid. It is specifically recorded that a synergistic leaching system of acetic acid and ascorbic acid is used for the one-time recovery of key metals from waste lithium-ion batteries.

[0006] In summary, the method adopted in the present invention is as follows: synergistically leach the waste lithium manganese oxide cathode material with phosphoric acid and ascorbic acid, and realize the precipitation recovery of lithium and manganese elements in the cathode material by adjusting the pH of the leaching solution. Introduce iron element into the precipitate, and prepare lithium iron phosphate cathode material through solid-phase grinding and high-temperature roasting. Summary of the Invention

[0007] Aiming at the problem of recycling and treatment of retired lithium manganese oxide batteries, the purpose of the present invention is to provide a method for preparing lithium iron phosphate cathode material from the cathode material of waste lithium manganese oxide batteries.

[0008] To achieve the above purpose, the present invention provides a method for preparing lithium iron phosphate cathode material from the cathode material of waste lithium manganese oxide batteries, including the following steps:

[0009] (1) Leaching of lithium manganese oxide

[0010] The waste lithium manganese oxide battery is discharged, roasted, disassembled, and ground to obtain the lithium manganese oxide cathode material; the lithium manganese oxide cathode material is subjected to a synergistic acid leaching reaction at 25 - 80 °C for 60 min under the conditions of a solid-liquid ratio of 30 - 50 mL / g and dilute phosphoric acid with a concentration of 0.3 - 1 mol / L and a ratio of ascorbic acid to lithium manganese oxide cathode material of 0.3 - 1 g / g, and a filtrate containing manganese, lithium, and phosphorus is obtained through suction filtration.

[0011] (2) Recovery of valuable elements

[0012] The filtrate containing manganese, lithium, and phosphorus obtained by suction filtration is adjusted to a pH of 5.5 - 8.0 by adding alkaline reagents (sodium hydroxide, lithium hydroxide, ammonia water) to obtain a manganese precipitate (Mn3(PO4)2·3H2O) and a filtrate containing lithium. The pH of the filtrate containing lithium is adjusted to 9.0 - 12.0, and after evaporation and concentration (105 - 120 °C, 1 - 3 h), a lithium precipitate (Li3PO4) is obtained. Mn3(PO4)2·3H2O and Li3PO4 are washed and dried.

[0013] (3) Synthesis of lithium iron phosphate manganese

[0014] Mn3(PO4)2·3H2O, Li3PO4, iron (ferrous sulfate, iron phosphate, ferrous phosphate), phosphorus (ammonium dihydrogen phosphate), and carbon (glucose) are subjected to solid-phase grinding. The molar ratio of lithium, manganese, iron, and phosphorus elements is 1.05:x:1 - x:1 (the value of x is 1 - 9), and the mass of carbon is 15% of the mass of the lithium iron phosphate manganese cathode material. The mixed materials are calcined at 650 - 750 °C for 6 - 10 h in an argon atmosphere to obtain the lithium iron phosphate manganese cathode material.

[0015] The advantage of the present invention is that valuable elements (Mn, Li) in the lithium manganese oxide cathode material are leached by phosphoric acid and ascorbic acid, manganese and lithium are recovered by adjusting the pH, and they are used as the main raw materials to prepare the lithium iron phosphate manganese cathode material. The entire recycling process makes full use of the three elements of manganese, lithium, and phosphorus in the raw materials, and has the characteristics of being green, economical, and simple to operate. Detailed implementation manners

[0016] The present invention will be described in detail below with reference to the embodiments, but the protection scope of the present invention is not limited to the following embodiments. Brief description of the drawings

[0017] Figure 1 XRD patterns of the samples obtained in each embodiment

[0018] Example 1

[0019] (1) After discharging, calcining, disassembling, and grinding, a lithium manganese oxide cathode material is obtained. The lithium manganese oxide cathode material and ascorbic acid are added to a dilute phosphoric acid solution. The liquid-solid ratio of the lithium manganese oxide cathode material to the dilute phosphoric acid is controlled at 30 mL / g, the phosphoric acid concentration is 0.3 mol / L, and the ratio of ascorbic acid to the lithium manganese oxide cathode material is 0.3 g / g. Leaching is carried out at 25 °C for 60 min to obtain a mixed slurry.

[0020] (2) Filter the mixed slurry obtained in step 1, and obtain a filtrate after separating the filter residue; adjust the pH of the filtrate to 5.5 with sodium hydroxide, and obtain a lithium-containing filtrate and a manganese-containing filter residue after filtration; adjust the pH of the lithium-containing filtrate to 9.0 with sodium hydroxide, evaporate and concentrate at 105 °C for 1 h, and obtain a lithium-containing filter residue after filtration.

[0021] (3) Mix 15% of the mass of the lithium iron manganese phosphate cathode material, the manganese filter residue, the lithium filter residue, ferrous sulfate heptahydrate and iron phosphate evenly, and control Li:Mn:Fe:P = 1.05:0.55:0.45:1; calcine at 650 °C for 10 h under an argon atmosphere to obtain the lithium iron manganese phosphate cathode material.

[0022] Example 2

[0023] (1) After discharging, calcining, disassembling and grinding, obtain a lithium manganese oxide cathode material. Add the lithium manganese oxide cathode material and ascorbic acid to a dilute phosphoric acid solution, control the liquid-solid ratio of the lithium manganese oxide cathode material to the dilute phosphoric acid to be 50 mL / g, the phosphoric acid concentration to be 0.5 mol / L, and the ratio of ascorbic acid to the lithium manganese oxide cathode material to be 0.7 g / g, and leach at 60 °C for 60 min to obtain a mixed slurry.

[0024] (2) Filter the mixed slurry obtained in step 1, and obtain a filtrate after separating the filter residue; adjust the pH of the filtrate to 8.0 with sodium hydroxide, and obtain a lithium-containing filtrate and a manganese-containing filter residue after filtration; adjust the pH of the lithium-containing filtrate to 12.0 with sodium hydroxide, evaporate and concentrate at 105 °C for 3 h, and obtain a lithium-containing filter residue after filtration.

[0025] (3) Mix 15% of the mass of the lithium iron manganese phosphate cathode material, the manganese filter residue, the lithium filter residue, and ferrous phosphate evenly, and control Li:Mn:Fe:P = 1.05:0.55:0.45:1; calcine at 700 °C for 9 h under an argon atmosphere to obtain the lithium iron manganese phosphate cathode material.

[0026] Example 3

[0027] (1) After discharging, calcining, disassembling and grinding, obtain a lithium manganese oxide cathode material. Add the lithium manganese oxide cathode material and ascorbic acid to a dilute phosphoric acid solution, control the liquid-solid ratio of the lithium manganese oxide cathode material to the dilute phosphoric acid to be 50 mL / g, the phosphoric acid concentration to be 1 mol / L, and the ratio of ascorbic acid to the lithium manganese oxide cathode material to be 1 g / g, and leach at 80 °C for 60 min to obtain a mixed slurry;

[0028] (2) Filter the mixed slurry obtained in step 1, and obtain a filtrate after separating the filter residue; adjust the pH of the filtrate to 8.0 with sodium hydroxide, and obtain a lithium-containing filtrate and a manganese-containing filter residue after filtration; adjust the pH of the lithium-containing filtrate to 12.0 with sodium hydroxide, evaporate and concentrate at 120 °C for 3 h, and obtain a lithium-containing filter residue after filtration;

[0029] (3) Mix 15% by mass of the lithium iron manganese phosphate cathode material with glucose, manganese filter residue, lithium filter residue, and ferrous sulfate heptahydrate evenly, and control Li:Mn:Fe:P = 1.05:0.55:0.45:1; calcine at 750 °C for 7 h in an argon atmosphere to obtain the lithium iron manganese phosphate cathode material.

Claims

1. A method for synthesizing lithium iron phosphate cathode material from the cathode material of waste lithium manganese oxide batteries, characterized in that, It includes the following steps: (1) Discharge, roast, and disassemble the waste lithium manganese oxide battery to obtain the lithium manganese oxide cathode material. Then, carry out a synergistic acid leaching reaction for 60 min at a certain temperature with the lithium manganese oxide cathode material according to a solid-liquid ratio of 30-50 mL / g, dilute phosphoric acid with a certain concentration, and ascorbic acid in a certain proportion. Filter to obtain a filtrate containing manganese, lithium, and phosphorus; (2) Add an alkaline reagent to the filtrate obtained in step (1) to adjust the pH, and obtain a manganese precipitate and a filtrate containing lithium; (3) Adjust the pH of the filtrate containing lithium obtained in step (2), and obtain a lithium precipitate through evaporation and concentration; (4) Wash and dry the manganese precipitate and the lithium precipitate obtained in step (2) and step (3); (5) Carry out solid-phase grinding on the manganese precipitate, the lithium precipitate obtained in step (4), an iron source, a phosphorus source, and a carbon source according to a certain proportion, and carry out high-temperature roasting in an argon atmosphere to obtain a lithium iron manganese phosphate cathode material.

2. The method according to claim 1, wherein The concentration of the dilute phosphoric acid described in step (1) is 0.3-1 mol / L; the ratio of the ascorbic acid to the lithium manganese oxide cathode material described in step (1) is 0.3-1 g / g; the certain temperature described in step (1) is 25-80 °C.

3. The method according to claim 1, wherein The alkaline reagent described in step (2) is one or more of sodium hydroxide, lithium hydroxide, and ammonia water.

4. The method according to claim 1, characterized in that The pH adjustment described in step (2) is 5.5-8.

0.

5. The method according to claim 1, characterized in that The pH adjustment described in step (3) is 9.0-12.

0.

6. The method according to claim 1, wherein The temperature of the evaporation and concentration described in step (3) is 105-120 °C; the time of the evaporation and concentration described in step (3) is 1-3 h.

7. The method according to claim 1, wherein The carbon source described in step (5) is glucose; the iron source described in step (5) is one or more of ferrous sulfate, iron phosphate, and ferrous phosphate; the phosphorus source described in step (5) is ammonium dihydrogen phosphate.

8. The method according to claim 1, characterized in that The molar ratio of lithium, manganese, iron, and phosphorus elements in the manganese precipitate, the lithium precipitate, and iron and phosphorus in step (5) is 1.05: x: 1 - x: 1 (the value of x is 0.1-0.9), and the mass of carbon in step (5) is 15% of the mass of the lithium iron manganese phosphate cathode material.

9. The method according to claim 1, characterized in that The high-temperature roasting temperature described in step (5) is 650-750 °C; the high-temperature roasting time described in step (5) is 7-10 h.

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