Method for recycling lithium-rich layered oxide cathode material from waste lithium battery

Abstract

The application discloses a method for recycling waste ternary positive electrode materials by green and environment-friendly eutectic solvent hydrometallurgy and regenerating high specific capacity lithium-rich materials. The method uses a eutectic solvent synthesized by citric acid and ethylene glycol as a leaching agent, and carries out hydrometallurgical leaching reaction on the pretreated ternary positive electrode active material at 90-100 DEG C. By adding lithium acetate, manganese acetate, cobalt acetate and other acetates, the molar ratio of lithium ions, manganese ions, nickel ions and cobalt ions in the leaching solution is 1.2:0.13:0.13:0.54. Then, a sol-gel method is used to prepare a gel-like substance, which is dried and calcined twice to prepare the regenerated lithium-rich layered oxide positive electrode material. The method does not use strong acid, has no excess wastewater discharge, and has the characteristics of green environmental protection and high recovery rate.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for recycling lithium-rich layered oxide cathode material from waste lithium batteries, belonging to the technical field of lithium ion batteries. BACKGROUND

[0002] Waste lithium ion batteries contain heavy metal elements such as nickel and cobalt, which are carcinogenic and mutagenic chemicals, and toxic organic electrolytes. Using the traditional landfill method to treat waste batteries may have adverse effects on human health and the environment. However, at the same time, the valuable metal elements such as nickel, cobalt, manganese and lithium in waste batteries are very important resources, so they are also called metal mines.

[0003] At present, the recycling of waste batteries mainly focuses on valuable metals such as nickel, cobalt, manganese and lithium. Researchers have developed three major categories of recycling processes, including pyrometallurgy, hydrometallurgy and direct recycling. Pyrometallurgical recycling process requires high temperature environment to reduce transition metal oxides, which consumes a lot of energy; direct regeneration is limited to laboratory scale and is difficult to apply in practice. Compared with the above two methods, hydrometallurgical process is widely used in industrial production due to its high efficiency and low cost.

[0004] The traditional hydrometallurgical process consumes a large amount of sulfuric acid and emits a large amount of greenhouse gases. Deep eutectic solvents (DES) are a general term for biodegradable green solvents. In 2003, Abbott et al. proposed that DES can have leaching effect on metal oxides under certain conditions. Therefore, the use of deep eutectic solvents for battery recycling can reduce the use of strong acid and make the hydrometallurgical process green and environmentally friendly.

[0005] For the hydrometallurgical process, the subsequent selective separation of valuable metals such as nickel, cobalt, manganese and lithium is relatively complex. Researchers have begun to explore methods for directly synthesizing new materials from leaching solutions, but the performance of these cathode materials often fails to meet expectations. Lithium-rich layered oxides have higher specific capacity than ordinary layered NCM cathodes, so lithium-rich layered oxide cathode materials will have the potential to replace ordinary ternary NCM layered cathode materials in the future. However, the research on recycling lithium-rich layered oxide cathode materials from waste battery leaching solution is not perfect. SUMMARY

[0006] Therefore, the purpose of the present application is to provide a method for recycling lithium-rich layered oxide cathode material from waste lithium batteries.

[0007] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows.

[0008] A method for recycling lithium-rich layered oxide cathode material from waste lithium batteries, the method comprising the following steps:

[0009] (1) disassembling waste lithium batteries, recovering positive active material; wherein the positive active material is a nickel-cobalt-manganese ternary positive material;

[0010] (2) hydrometallurgical leaching of the positive active material in a eutectic solvent to obtain a leaching solution containing metal ions; wherein the eutectic solvent is a mixed solvent of ethylene glycol and citric acid, the molar ratio of ethylene glycol to citric acid is 6:1~12:1, the solid-liquid ratio of positive active material to eutectic solvent is 5g / L~30g / L, the leaching reaction temperature is 85℃~120℃, and the leaching reaction time is 4h~8h;

[0011] (3) adjusting the molar ratio of lithium ions, manganese ions, nickel ions and cobalt ions in the leaching solution to the required proportion of lithium-rich layered oxide positive material by using metal acetate, and adjusting the solution pH to 7~7.5 with ammonia water to obtain a gel-like substance;

[0012] (4) drying the gel-like substance and first heat treating at 450℃~500℃ for 5h~6h, then heating to 850℃~950℃ and heat treating for 10h~12h to regenerate a lithium-rich layered oxide positive material, with the chemical formula xLi2MnO3·(1-x)LiTMO2, 0

[0013] Preferably, in step (1), the waste lithium batteries are discharged and safely disassembled, the positive electrode is separated and collected, then the positive electrode is treated with sodium hydroxide to remove the aluminum current collector, and finally the organic binder and conductive agent are removed by sintering in an oxygen atmosphere to recover the positive active material.

[0014] Preferably, in step (2), the molar ratio of ethylene glycol to citric acid is 8:1~10:1.

[0015] Preferably, in step (2), the solid-liquid ratio of positive active material to eutectic solvent is 10g / L~20g / L.

[0016] Preferably, in step (2), the leaching reaction temperature is 90℃~100℃, and the leaching reaction time is 5h~6h.

[0017] Preferably, in step (3), the molar ratio of lithium ions, manganese ions, nickel ions and cobalt ions in the leaching solution is adjusted to 1.2:0.13:0.13:0.54 by using metal acetate.

[0018] Preferably, in step (4), the heating rate is 2℃ / min~5℃ / min.

[0019] Preferably, in the chemical formula of the lithium-rich layered oxide positive material, x=0.5.

[0020] Beneficial effects

[0021] (1) The present application provides a process for recovering ternary positive electrode material by hydrometallurgy using a eutectic solvent, and regenerating high specific energy lithium-rich layered positive electrode material, wherein the composition of the eutectic solvent is ethylene glycol and citric acid, and by controlling the molar ratio of ethylene glycol and citric acid, the solid-liquid ratio of leaching reaction, and the reaction temperature and time, the leaching rate of metal ions can be effectively improved, which is beneficial to the subsequent sol-gel preparation of lithium-rich layered positive electrode material; at the same time, the present application omits the selective separation step in the traditional hydrometallurgical process, greatly simplifying the process; the recycling and regeneration method is simple, efficient, pollution-free, and the product has high added value.

[0022] (2) The present application provides a eutectic solvent with excess ethylene glycol, which is beneficial to reduce the viscosity and improve the mass transfer efficiency; wherein a large number of hydroxyl groups are oxidized to aldehyde groups during the recycling process, thereby providing a reducing leaching environment, which is beneficial to the reduction of transition metal elements from high valence state which is not easy to dissolve to divalent which is easy to dissolve. The eutectic solvent is a liquid with a large number of intermolecular hydrogen bonds; wherein ethylene glycol acts as a hydrogen bond donor, and citric acid acts as a hydrogen bond acceptor, a large number of hydrogen bonds are formed between the hydroxyl groups of ethylene glycol and the carboxyl groups of citric acid. During the leaching process, the hydrogen ions provided by citric acid will destroy the transition metal ion-oxygen bond. At the same time, the hydroxyl group is oxidized to aldehyde group to reduce the high valence state of the transition metal ion. If the amount of ethylene glycol is too small, it cannot provide enough reducing environment. If the content of citric acid is too small, it cannot provide enough hydrogen ions.

[0023] (3) The process proposed by the present application can directly regenerate high specific energy positive electrode material from the battery positive electrode material leaching solution, thereby avoiding the cumbersome and complex metal element separation process.

[0024] (4) The eutectic solvent proposed by the present application can not only dissolve valuable metal elements as a leaching agent during the recycling process, but also act as a metal ion chelating agent in the process of sol-gel synthesis of regenerated positive electrode material.

[0025] (5) The regenerated battery positive electrode material has high specific capacity and cycle stability, greatly improving the performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is the scanning electron microscope graph of the regenerated lithium-rich layered oxide positive electrode material in Example 1.

[0027] Figure 2 It is the XRD spectrum of the regenerated lithium-rich layered oxide positive electrode material in Example 1.

[0028] Figure 3 It is the cycle stability of lithium-rich layered oxide positive electrode material in the examples and comparative examples. DETAILED DESCRIPTION

[0029] The application will be further described in detail below with reference to specific examples.

[0030] In the following examples or comparative examples:

[0031] Assembled button cell: First, polyvinylidene fluoride (PVDF) dispersed in anhydrous N-methyl pyrrolidone (NMP) was mixed with regenerated lithium-rich layered positive electrode material and conductive carbon black to fully disperse; then evenly coated on aluminum foil, dried at 120°C and cut into small round pieces as button cell positive electrode, wherein the mass ratio of positive electrode material: conductive carbon black: conductive carbon black: PVDF is 80: 10: 10; finally, 2032 button cell was assembled in an argon glove box with water and oxygen less than 0.01 ppm. Its electrochemical performance at 0.1C current was tested.

[0032] Example 1:

[0033] The waste lithium battery was safely discharged to below 0.2V, then disassembled and the positive electrode sheet was separated. Excess sodium hydroxide was added to dissolve the positive electrode current collector, and the positive electrode active material NCM ternary positive electrode material was collected. A eutectic solvent (DES) was prepared with a molar ratio of ethylene glycol: citric acid = 9:1. The positive electrode active material was added to the DES at a solid-liquid ratio of 15g / L, heated at 95°C for 5.5h, until the active material was completely dissolved, and the leaching rate was calculated to be 99.2%. The element concentration in the solution was measured by ICP-MS, and transition metal acetate and lithium acetate were added to adjust the ratio of lithium, nickel, cobalt and manganese to 1.2:0.13:0.13:0.54.

[0034] The pH value of the solution was adjusted to 7-7.5 by adding ammonia water, and after heating and evaporation to a gel state, it was transferred to a 120°C oven for drying for 24h. After taking out, it was heated to 500°C in a muffle furnace at a heating rate of 5°C / min for 6h, and then heated to 900°C at a heating rate of 5°C / min for 12h, and then annealed with the furnace. The obtained product is a lithium-rich layered positive electrode material.

[0035] The scanning electron microscope results of the material are shown in Figure 2 The microparticles have a particle size of less than 0.5 microns. The XRD pattern of the material shows that the crystal structure has R-3m space group α- NaFeO2 structure characteristics, while the peak at 20-25° indicates that it has a superlattice belonging to the layered Li2MnO3 phase of C2 / m space group.

[0036] The discharge capacity of the assembled battery in the first week is 275.6mAh / g, and the discharge capacity retention rate after 80 cycles is 64.4%.

[0037] Example 2:

[0038] The battery was disassembled after safe discharge to below 0.2V and the positive electrode sheet was separated. Excess sodium hydroxide was added to dissolve the positive electrode current collector, and the positive electrode active material was collected. The eutectic solvent was configured with a molar ratio of ethylene glycol: citric acid = 8: 1. The positive electrode active material was added to the DES at a solid-liquid ratio of 10 g / L, heated at 90°C for 5h, until the active material was completely dissolved, and the leaching rate was calculated to be 99.1%. The element concentration in the solution was measured by ICP-MS, and transition metal acetate and lithium acetate were added to adjust the lithium nickel cobalt manganese ratio to 1.2:0.13:0.13:0.54.

[0039] The pH value of the solution was adjusted to between 7-7.5 by adding ammonia water, and after heating and evaporation to a gel state, it was transferred to a 120°C oven for drying for 24h. After taking out, it was heated to 500°C at a heating rate of 5°C / min in a muffle furnace for sintering for 6h, and then heated to 950°C at a heating rate of 5°C / min for 12h, and then annealed with the furnace slowly cooling. The obtained product is a lithium-rich layered positive electrode material.

[0040] The assembled battery has a first week discharge capacity of 267mAh / g, and the discharge capacity retention rate after 80 cycles is 74.3%.

[0041] Example 3:

[0042] The battery was disassembled after safe discharge to below 0.2V and the positive electrode sheet was separated. Excess sodium hydroxide was added to dissolve the positive electrode current collector, and the positive electrode active material was collected. The eutectic solvent was configured with a molar ratio of ethylene glycol: citric acid = 10: 1. The positive electrode active material was added to the DES at a solid-liquid ratio of 20 g / L, heated at 100°C for 6h, until the active material was completely dissolved, and the leaching rate was calculated to be 99.1%. The element concentration in the solution was measured by ICP-MS, and transition metal acetate and lithium acetate were added to adjust the molar ratio of lithium nickel cobalt manganese to 1.2:0.13:0.13:0.54.

[0043] The pH value of the solution was adjusted to between 7-7.5 by adding ammonia water, and after heating and evaporation to a gel state, it was transferred to a 120°C oven for drying for 24h. After taking out, it was heated to 500°C at a heating rate of 5°C / min in a muffle furnace for sintering for 6h, and then heated to 850°C at a heating rate of 5°C / min for 12h, and then annealed with the furnace slowly cooling. The obtained product is a lithium-rich layered positive electrode material.

[0044] The assembled battery has a first week discharge capacity of 273.1mAh / g, and the discharge capacity retention rate after 80 cycles is 59.5%.

[0045] Comparative Example 1:

[0046] The battery was disassembled after safe discharge to below 0.2V and the positive electrode sheet was separated. Excess sodium hydroxide was added to dissolve the positive electrode current collector, and the positive electrode active material was collected. A eutectic solvent was prepared with a molar ratio of ethylene glycol: citric acid = 9:1. The positive electrode active material was added to the DES at a solid-liquid ratio of 20g / L, heated at 90°C for 5h until the active material was completely dissolved, and the leaching rate was calculated to be 99.1%. The element concentration in the solution was measured by ICP-MS, and transition metal acetate and lithium acetate were added to adjust the molar ratio of lithium nickel cobalt manganese to 1.2:0.13:0.13:0.54.

[0047] The pH value of the solution was adjusted to between 7-7.5 by adding ammonia water, and after heating and evaporation to a gel state, it was transferred to a 120°C oven for drying for 24h. After taking out, it was heated to 500°C at a heating rate of 5°C / min in a muffle furnace for sintering for 6h, and then heated to 800°C at a heating rate of 5°C / min for 12h, and then annealed with the furnace slowly cooling. The obtained product was a lithium-rich layered positive electrode material.

[0048] The assembled battery had a first week discharge capacity of 266.9mAh / g, and the discharge capacity retention rate after 80 cycles was 51.5%.

[0049] Comparative Example 2:

[0050] The battery was disassembled after safe discharge to below 0.2V and the positive electrode sheet was separated. Excess sodium hydroxide was added to dissolve the positive electrode current collector, and the positive electrode active material was collected. A eutectic solvent was prepared with a molar ratio of ethylene glycol: citric acid = 9:1. The positive electrode active material was added to the DES at a solid-liquid ratio of 20g / L, heated at 90°C for 5h until the active material was completely dissolved, and the leaching rate was calculated to be 99.1%. The element concentration in the solution was measured by ICP-MS, and transition metal acetate and lithium acetate were added to adjust the molar ratio of lithium nickel cobalt manganese to 1.2:0.13:0.13:0.54.

[0051] The pH value of the solution was adjusted to between 7-7.5 by adding ammonia water, and after heating and evaporation to a gel state, it was transferred to a 120°C oven for drying for 24h. After taking out, it was heated to 500°C at a heating rate of 5°C / min in a muffle furnace for sintering for 6h, and then heated to 1000°C at a heating rate of 5°C / min for 12h, and then annealed with the furnace slowly cooling. The obtained product was a lithium-rich layered positive electrode material.

[0052] The assembled battery had a first week discharge capacity of 280.3mAh / g, and the discharge capacity retention rate after 80 cycles was 49.66%.

[0053] Comparative Example 3:

[0054] The battery was disassembled and the positive electrode sheet was separated after safe discharge to below 0.2V. Excess sodium hydroxide was added to dissolve the positive electrode current collector, and the positive electrode active material was collected. The eutectic solvent was configured with a molar ratio of ethylene glycol: citric acid = 9:1. The positive electrode active material was added to the DES at a solid-liquid ratio of 50g / L, heated at 90°C for 5h, and the leaching rate was calculated to be 65.9%.

[0055] Comparative Example 4:

[0056] The battery was disassembled and the positive electrode sheet was separated after safe discharge to below 0.2V. Excess sodium hydroxide was added to dissolve the positive electrode current collector, and the positive electrode active material was collected. The eutectic solvent was configured with a molar ratio of ethylene glycol: citric acid = 9:1. The positive electrode active material was added to the DES at a solid-liquid ratio of 20g / L, heated at 60°C for 5h, and the leaching rate was calculated to be 55.9%.

[0057] Comparative Example 5:

[0058] The battery was disassembled and the positive electrode sheet was separated after safe discharge to below 0.2V. Excess sodium hydroxide was added to dissolve the positive electrode current collector, and the positive electrode active material was collected. The eutectic solvent was configured with a molar ratio of ethylene glycol: citric acid = 3:1. The positive electrode active material was added to the DES at a solid-liquid ratio of 20g / L, heated at 90°C for 5h, and the leaching rate was calculated to be 45.8%.

[0059] Comparative Example 6:

[0060] The battery was disassembled and the positive electrode sheet was separated after safe discharge to below 0.2V. Excess sodium hydroxide was added to dissolve the positive electrode current collector, and the positive electrode active material was collected. The eutectic solvent was configured with a molar ratio of ethylene glycol: citric acid = 15:1. The positive electrode active material was added to the DES at a solid-liquid ratio of 20g / L, heated at 90°C for 5h, and the leaching rate was calculated to be 81.2%.

[0061] In summary, the invention includes but is not limited to the above examples, any equivalent replacement or partial improvement made within the spirit and principles of the invention will be considered within the protection scope of the invention.

Claims

1. A method for recycling lithium-rich layered oxide cathode material from waste lithium batteries, characterized in that: The method comprises the following steps: (1) disassembling waste lithium batteries to recover positive active materials; wherein the positive active material is a nickel-cobalt-manganese ternary positive material; (2) wet metallurgical leaching of the positive active material in a eutectic solvent to obtain a leaching solution containing metal ions; wherein the eutectic solvent is a mixed solvent of ethylene glycol and citric acid, the molar ratio of ethylene glycol to citric acid is 6:1~12:1, the solid-liquid ratio of positive active material to eutectic solvent is 5g / L~30g / L, the leaching reaction temperature is 85℃~120℃, and the leaching reaction time is 4h~8h; (3) adjusting the molar ratio of lithium ions, manganese ions, nickel ions and cobalt ions in the leaching solution to the required proportion of lithium-rich layered oxide positive material by using metal acetate, and adjusting the pH of the solution to 7~7.5 with ammonia water to obtain a gel-like substance; (4) drying the gel-like substance and first heating at 450℃~500℃ for 5h~6h, then heating to 850℃~950℃ for 10h~12h to regenerate a lithium-rich layered oxide positive material, the chemical formula of which is xLi2MnO3·(1-x)LiTMO2, 0 2. The method for recycling lithium-rich layered oxide cathode material from waste lithium batteries according to claim 1, characterized in that: In step (1), the waste lithium battery is discharged and safely disassembled, the positive electrode is separated and collected, then the positive electrode is treated with sodium hydroxide to remove the aluminum current collector, and finally the organic binder and conductive agent are removed by sintering in an oxygen atmosphere to recover the positive active material.

3. The method for recycling lithium-rich layered oxide cathode material from waste lithium batteries according to claim 1, characterized in that: In step (2), the molar ratio of ethylene glycol to citric acid is 8:1~10:

1.

4. The method for recycling lithium-rich layered oxide cathode material from waste lithium batteries according to claim 1, characterized in that: In step (2), the solid-liquid ratio of the positive active material to the eutectic solvent is 10g / L~20g / L.

5. The method for recycling lithium-rich layered oxide cathode material from waste lithium batteries according to claim 1, characterized in that: In step (2), the leaching reaction temperature is 90℃~100℃, and the leaching reaction time is 5h~6h.

6. The method for recycling lithium-rich layered oxide cathode material from waste lithium batteries according to claim 1, characterized in that: In step (3), the molar ratio of lithium ions, manganese ions, nickel ions and cobalt ions in the leaching solution is adjusted to 1.2:0.13:0.13:0.54 by using metal acetate.

7. The method for recycling lithium-rich layered oxide cathode material from waste lithium batteries according to claim 1, characterized in that: In step (4), the heating rate is 2℃ / min~5℃ / min.

8. The method for recycling lithium-rich layered oxide cathode material from waste lithium batteries according to claim 1, characterized in that: The chemical formula of the lithium-rich layered oxide positive material is x=0.5.

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