Method for recovering lithium from waste batteries

Abstract

The present application relates to a kind of recovery method of lithium in waste battery, belong to lithium battery technical field.The present application includes the following steps: waste lithium battery is discharged, embrittlement, broken and sorted to obtain positive pole powder;In 330~370 ℃ containing catalyst water vapor atmosphere, catalyst pyrolysis is removed binder;After pyrolysis, powder and ammonium persulfate-glucose mixed activation aid ball milling;After ball milling, material is added in choline chloride-lactic acid eutectic solvent and leaching, pass in CO2, solid-liquid separation obtains lithium-rich liquid and iron-phosphorus slag.The catalyst in the present application includes nickel ferrite core, titanium dioxide shell layer coated on the surface of core and phosphotungstic acid loaded on the surface of shell layer, can be magnetically selected recovery and low-temperature high-efficiency pyrolysis, reduce fluorine emission.The recovery method of the present application has the advantages such as high lithium recovery rate, good selectivity, green low carbon, etc.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology and relates to a method for recycling lithium from waste batteries. Background Technology

[0002] Waste lithium iron phosphate batteries contain a large amount of valuable elements such as lithium, iron, and phosphorus. Recycling them is beneficial for resource recycling.

[0003] Currently, the mainstream recycling methods for spent lithium iron phosphate batteries fall into two main categories: pyrometallurgy and hydrometallurgy. Pyrometallurgy primarily involves high-temperature roasting to convert valuable metal elements into alloys or oxides, followed by subsequent separation and recovery. This method offers high throughput and wide applicability, but suffers from high energy consumption, easy loss of lithium due to high-temperature volatilization, and difficulties in treating fluorine-containing waste gas. Hydrometallurgy, on the other hand, uses acid or alkaline solutions to leach valuable elements from the cathode material, followed by extraction and precipitation steps for separation and recovery. Hydrometallurgy typically employs strong inorganic acids combined with reducing agents to simultaneously leach lithium, iron, and phosphorus into the solution, then adjusts the pH to precipitate iron phosphate, and recovers lithium from the iron-precipitated liquid. This process has the following drawbacks: high acid and alkali consumption, generating large amounts of high-salt wastewater, resulting in significant environmental pressure; lithium is easily lost during iron precipitation, leading to a low overall lithium recovery rate; and the process is lengthy, resulting in high equipment investment and operating costs.

[0004] CN118651832A discloses a method for recovering battery-grade iron phosphate and lithium salts from lithium iron phosphate waste and its applications. The method involves dissolving the waste in a phosphoric acid solution, adding acid and an oxidant, diluting with water to a pH of 1.0-1.5, and then crystallizing at high temperature to obtain hydrated iron phosphate and a lithium-containing filtrate. The lithium-containing filtrate, after evaporation to remove water, can be recycled for dissolving lithium iron phosphate waste. This method uses a phosphoric acid solution as the leaching solvent, eliminating the need for subsequent alkali leaching and allowing for cyclic leaching, achieving efficient recovery of all elements (Li, Fe, and P). However, this method requires multiple cycles of enrichment followed by concentration and crystallization, resulting in a long lithium recovery cycle. Furthermore, this method does not address the treatment of fluorides in the battery and cannot effectively handle cathode materials with residual fluorine-containing binders.

[0005] CN121198729A discloses a method and system for recycling and processing waste lithium batteries. It employs a process route of discharge, low-temperature embrittlement, multi-stage sorting, catalytic cracking, and mixed acid leaching to achieve comprehensive recovery of valuable metals. However, the catalytic cracking step of this method uses γ-Al₂O₃-supported MnO₂ / CeO₂ and physically mixed ZSM-5 molecular sieve as a catalyst. This catalyst is easily deactivated in a fluorine-containing atmosphere, has a short lifespan, and is difficult to recover, increasing operating costs. Summary of the Invention

[0006] The purpose of this invention is to provide a method for recycling lithium from waste batteries, which has the characteristics of high recycling efficiency.

[0007] The objective of this invention can be achieved through the following technical solutions: A method for recycling lithium from waste batteries, the method comprising the following steps: S1: Discharge the waste lithium iron phosphate batteries to a voltage below 1.5V, then perform embrittlement treatment for 10~20 min, and crush and sort the embrittled batteries to obtain positive electrode powder; S2: The cathode powder is catalytically cracked in a water vapor atmosphere containing a catalyst. The amount of catalyst added is 5% of the mass of the cathode powder, the temperature is 330~370℃, the treatment time is 20~40min, and the fluorine-containing gas generated by cracking is absorbed by NaOH solution. S3: Mix the pyrolyzed positive electrode powder with the activating agent and ball mill it for 1-2 hours. The ball milling ratio is (10-30):1. S4: Add the ball-milled material to the leaching agent and stir and leach at 40~60℃ for 1~2 h. Separate the leached material into solid and liquid to obtain lithium-rich leachate and iron-phosphorus-rich leachate residue.

[0008] As a preferred embodiment of the present invention, the embrittlement treatment temperature in S1 is -30~-50℃.

[0009] As a preferred embodiment of the present invention, the catalyst in S2 includes a nickel ferrite core, a titanium dioxide shell coating the surface of the core, and phosphotungstic acid supported on the surface of the shell.

[0010] As a preferred embodiment of the present invention, the method for preparing the catalyst in S2, Includes the following steps: S01. Add titanate to nickel ferrite dispersion and react, then separate the solid and liquid phases and collect the solid phase; S02. After thermal decomposition of the solid phase, it is added to a phosphotungstic acid solution for reaction, and the solid phase is collected and heat-treated. In step S01, the reaction pH is 3-4, the reaction temperature is 25-35℃, and the reaction time is 2-4 hours. In step S02, the thermal decomposition temperature is 450~500℃, the time is 1~2h, and the heating rate is 3~5℃ / min; In step S02, the reaction temperature is 25-35℃, the time is 8-12 hours, and the mass concentration of phosphotungstic acid in the aqueous solution is 5-15 wt%. In step S02, the heat treatment temperature is 180~200℃ and the time is 1~2h.

[0011] As a preferred embodiment of the present invention, the mass ratio of nickel ferrite to tetrabutyl titanate is 1:(2~5).

[0012] As a preferred embodiment of the present invention, the volume ratio of water to tetrabutyl titanate is (0.5~2):1.

[0013] As a preferred embodiment of the present invention, the activating agent in S3 is a mixture of ammonium persulfate and glucose, wherein the mass ratio of ammonium persulfate to glucose is (1~3):1.

[0014] As a preferred embodiment of the present invention, the ball milling speed in S3 is 300~800 rpm.

[0015] As a preferred embodiment of the present invention, the leaching agent in S4 is a eutectic solvent, which is composed of choline chloride and lactic acid in a molar ratio of 1:2, and water of 5-10 wt% of the total mass of the eutectic solvent is added during preparation.

[0016] As a preferred embodiment of the present invention, carbon dioxide gas is introduced during the leaching process in step S4.

[0017] The activating agent is a mixture of ammonium persulfate and glucose in a mass ratio of (1~3):1. On the one hand, the ammonium persulfate decomposes under the mechanical force of ball milling to produce highly active SO4. - • Free radicals, with their strong oxidizing properties, can attack the weak Li-O bonds in lithium iron phosphate cathode powder, causing lithium ions to be extracted from the crystal lattice. Iron ions are located at octahedral coordination sites, tightly wrapped by oxygen atoms, resulting in a high migration energy barrier. During ball milling, they react with the abundant phosphate groups in LFP to form an iron phosphate (FePO4) passivation layer, physically blocking subsequent leaching. On the other hand, glucose, as a reducing agent, can capture excess free radicals generated by the decomposition of ammonium persulfate, preventing excessive oxidation from damaging the surface passivation layer. When the mass ratio of ammonium persulfate to glucose is controlled within the range of (1~3):1, the oxidation and reduction capabilities reach the optimal balance. Compared with ammonium persulfate alone, this mixed additive can increase the lattice distortion rate of lithium, significantly improve the leaching rate of lithium in subsequent leaching, and at the same time reduce the co-solubility of iron and significantly shorten the ball milling time, achieving efficient and low-energy-consumption preferential lithium extraction.

[0018] The catalyst of this invention (no prior art has been found for the catalytic decomposition of PVDF; please provide prior art for reference) uses nickel ferrite as a magnetic core, which can be efficiently recovered and recycled after the catalytic cracking reaction via magnetic separation, significantly reducing the cost of the catalyst; it uses titanium dioxide as a shell, utilizing its excellent resistance to fluorine corrosion to avoid the problem of easy fluorination and deactivation of traditional supports such as alumina in fluorine-containing atmospheres. At the same time, the titanium dioxide shell can capture some HF in situ during the reaction to generate Ti. The surface species reduce the release of gaseous HF by 30-40%, thus alleviating the subsequent alkali absorption load; the supported phosphotungstic acid possesses extremely strong Brønsted acidity, enabling efficient catalysis of C in PVDF at low temperatures. The protonation breaking of the F bond significantly reduces the catalytic cracking temperature compared to existing technologies, avoiding lithium volatilization loss and lattice damage at high temperatures.

[0019] A eutectic solvent (choline chloride: lactic acid = 1:2) is used as the leaching agent. First, the DES formed by choline chloride and lactic acid in a molar ratio of 1:2 has suitable viscosity and conductivity, which can effectively wet and penetrate the ball-milled particles, allowing the activated lithium species to dissolve rapidly. Second, the acidic environment provided by lactic acid can selectively dissolve the active intermediates of lithium, while having extremely low corrosiveness to the iron phosphate passivation layer, enabling efficient lithium leaching. Third, this eutectic solvent uses biologically derived choline chloride and lactic acid as raw materials, which is biodegradable, non-toxic, and harmless, and has a low vapor pressure, avoiding the environmental pollution problems of traditional volatile organic solvents. In addition, the eutectic solvent can be recycled, and its leaching activity remains basically unchanged after simple evaporation and dehydration, significantly reducing reagent consumption and wastewater discharge.

[0020] The introduction of CO2 gas during the leaching process has the following effects: the continuous introduction of CO2 bubbles plays a role in mechanical stirring and enhancing mass transfer, breaks the diffusion boundary layer at the solid-liquid interface, and allows the leaching agent to fully contact the particle surface, thus shortening the leaching time; the weak acidity of CO2 can inhibit the excessive ionization of lactic acid in the eutectic solvent, prevent the pH from dropping and causing the passivation layer to be destroyed, and CO2 can be easily removed after the reaction is completed.

[0021] The beneficial effects of this invention are: In the mechanochemical activation stage, this invention employs an activation aid composed of ammonium persulfate and glucose in a mass ratio of (1-3):1. The ammonium persulfate decomposes to generate highly reactive free radicals that attack the Li-O bonds, while glucose captures excess free radicals, enabling efficient lithium ion migration to form a highly reactive intermediate. Compared to a single aid, this significantly increases the lithium leaching rate, reduces the iron co-solubility, and shortens the ball milling time. Secondly, the catalytic cracking step utilizes a core-shell catalyst of nickel ferrite and titanium dioxide supported on phosphotungstic acid. Its strong acidity allows for efficient cleavage of the CF bonds in PVDF at low temperatures of 330-370℃, preventing lithium loss through high-temperature volatilization. The titanium dioxide shell resists fluorine corrosion and captures some HF in situ, reducing gaseous fluorine emissions by 30-40%. The nickel ferrite core endows the catalyst with magnetic separation and recovery capabilities, allowing for recycling and significantly reducing costs. Furthermore, the selective leaching stage uses a eutectic solvent with a choline chloride to lactic acid molar ratio of 1:2. This eutectic solvent has suitable viscosity, is biodegradable, and has an extremely low vapor pressure. It has a high selective dissolution capacity for activated lithium species and a very low corrosion effect on the passivation layer. At the same time, the introduction of CO2 bubbles enhances mass transfer and shortens the leaching time. Detailed Implementation

[0022] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0023] It should be noted that, unless otherwise specified, the present invention does not specifically limit the source of the raw materials used in the following embodiments. Commercially available products or products prepared by conventional preparation methods that are well known to those skilled in the art can be used. Experimental methods that do not specify specific conditions are all conventional methods and conventional conditions well known in the art.

[0024] Example 1 S1: Preprocessing Waste lithium iron phosphate batteries were discharged to 0.5V, placed at -40℃ for 15 minutes to embrittle them, crushed, and then screened by a vibrating sieve (200 mesh) to obtain positive electrode powder. S2: Catalytic cracking Take 500g of positive electrode powder and place it in a rotary kiln. Then, introduce water vapor with a volume concentration of 20% and a space velocity of 2000 h⁻¹. -1 The carrier gas is used to add a catalyst, the amount of which is 5% of the mass of the positive electrode powder. The mixture is then pyrolyzed at 350℃ for 30 min. The pyrolysis tail gas is then passed into a 5wt% NaOH solution for absorption to obtain a NaF solution. The catalyst is prepared by the following method: Nickel ferrite nanoparticles were dispersed in anhydrous ethanol, and tetrabutyl titanate and water were added. The mass ratio of nickel ferrite to tetrabutyl titanate was 1:3.5, and the volume ratio of water to tetrabutyl titanate was 1.2:1. The pH was adjusted to 3.5, and the mixture was stirred at 25°C for 3 hours. The mixture was then centrifuged and dried, transferred to a muffle furnace, heated to 480°C at a rate of 4°C / min, and held at that temperature for 1.5 hours to obtain a solid phase. The obtained solid phase was added to a 10 wt% phosphotungstic acid aqueous solution at a solid-liquid ratio of 1:8 (g / mL), stirred for 10 hours, dried under vacuum at 85°C, and then heat-treated at 190°C for 1.5 hours to obtain the catalyst. S3: Mechanochemical activation Take 200g of pyrolysis cathode powder, add 20g of activation aid (ammonium persulfate: glucose = 2:1 mass ratio) (dry activation step), place it in a planetary ball mill, ball-to-material ratio 20:1, speed 600rpm, and ball mill for 1.5h; S4: Selective Leaching Take 190g of the ball-milled material and add 1000mL of eutectic solvent (choline chloride and lactic acid mixed in a molar ratio of 1:2, with a water content of 8 wt% of the total mass of choline chloride and lactic acid). Stir and leach at 50℃ while simultaneously introducing CO2 gas at a rate of 0.5L / min. After leaching for 1.5h, filter under pressure to obtain lithium-rich leachate and iron-phosphorus-rich leachate residue. S5: Lithium precipitate The lithium-rich leachate was evaporated and concentrated to 1 / 3 of its original volume, and saturated Na₂CO₃ solution was added until the Li₂O₃ concentration reached the desired level. + After complete precipitation, the mixture was reacted at 90°C for 1 hour, filtered, washed, and dried to obtain the Li2CO3 product.

[0025] Example 2 The mass ratio of ammonium persulfate to glucose was 1:1, and all other parameters were the same as in Example 1.

[0026] Example 3 The mass ratio of ammonium persulfate to glucose was 3:1, and all other parameters were the same as in Example 1.

[0027] Example 4 The catalyst in S2 is prepared by the following method: Nickel ferrite nanoparticles were dispersed in anhydrous ethanol, and tetrabutyl titanate and water were added. The mass ratio of nickel ferrite to tetrabutyl titanate was 1:2, and the volume ratio of water to tetrabutyl titanate was 0.5:1. The pH was adjusted to 3, and the mixture was stirred at 25°C for 2 hours. The mixture was then centrifuged and dried, transferred to a muffle furnace, heated to 450°C at a rate of 3°C / min, and held at that temperature for 1 hour to obtain a solid phase. The obtained solid phase was added to a 5 wt% phosphotungstic acid aqueous solution at a solid-liquid ratio of 1:8 (g / mL), stirred for 8 hours, dried under vacuum at 80°C, and then heat-treated at 180°C for 1 hour to obtain the catalyst. The rest of the process was the same as in Example 1.

[0028] Example 5 The catalyst in S2 is prepared by the following method: Nickel ferrite nanoparticles were dispersed in anhydrous ethanol, and tetrabutyl titanate and water were added. The mass ratio of nickel ferrite to tetrabutyl titanate was 1:5, and the volume ratio of water to tetrabutyl titanate was 2:1. The pH was adjusted to 4, and the mixture was stirred at 25°C for 4 hours. The mixture was then centrifuged and dried, transferred to a muffle furnace, heated to 500°C at a rate of 5°C / min, and held at that temperature for 2 hours to obtain a solid phase. The obtained solid phase was added to a 15wt% phosphotungstic acid aqueous solution at a solid-liquid ratio of 1:8 (g / mL), stirred for 12 hours, dried under vacuum at 90°C, and then heat-treated at 200°C for 2 hours to obtain the catalyst. The rest of the process was the same as in Example 1.

[0029] Comparative Example 1 The only activating agent used was ammonium persulfate; all other aspects were the same as in Example 1.

[0030] Comparative Example 2 The only activating agent used was glucose; all other aspects were the same as in Example 1.

[0031] Comparative Example 3 The S4 leaching agent was changed to a mixture of 2 mol / L H2SO4 and 0.5 mol / L H3PO4, the leaching temperature was 80℃, and the leaching time was 3 hours. All other aspects were the same as in Example 1.

[0032] Comparative Example 4 CO2 is not introduced during the S4 leaching process, and everything else is the same as in Example 1.

[0033] Comparative Example 5 The catalyst was prepared without the addition of an aqueous solution of phosphotungstic acid, and all other steps were the same as in Example 1.

[0034] Performance testing The lithium leaching rate of the examples and comparative examples was calculated as follows: lithium leaching rate (%) = (mass of lithium in the leachate) / (total mass of lithium in the raw cathode powder) × 100%; the purity (%) of Li2CO3 obtained from the examples and comparative examples was tested according to the YS / T 582-2013 standard, and the specific experimental results are summarized in the table below.

[0035]

[0036] Compared with Example 1, the lithium leaching rate of Comparative Example 1 decreased to 96.5%, and the purity decreased to 98.8%; the lithium leaching rate of Comparative Example 2 was only 72.3%, proving the necessity of the oxidation-reduction synergy of the activation aid; although the lithium leaching rate of Comparative Example 3 reached 97.8%, the co-dissolution of iron led to a significant decrease in the purity of Li2CO3 after subsequent separation, and the overall lithium recovery rate was significantly reduced; the lithium leaching rate of Comparative Example 4 decreased to 95.2% and the purity decreased to 98.5% without CO2; the catalyst in Comparative Example 5 did not contain the active component phosphotungstic acid, resulting in insufficient cracking activity and a decrease in lithium leaching rate.

[0037] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention are still within the scope of the present invention.

Claims

1. A method for recovering lithium from waste batteries, characterized in that, The recycling method Includes the following steps, S1: Discharge the waste lithium batteries to a voltage below 1.5V, then perform embrittlement treatment for 10~20 minutes, and crush and sort the embrittled batteries to obtain positive electrode powder; S2: Catalytic cracking of cathode powder is carried out in a water vapor atmosphere containing catalyst, with the amount of catalyst added being 5% of the mass of cathode powder, and the temperature being 330~370℃. S3: Mix the pyrolyzed cathode powder with the activating agent and then ball mill it; S4: Add the ball-milled material to the leaching agent and stir and leach at 40~60℃ for 1~2 h. Separate the leached material into solid and liquid to obtain lithium-rich leachate and iron-phosphorus-rich leachate residue.

2. The method for recovering lithium from waste batteries according to claim 1, characterized in that, The embrittlement treatment temperature in S1 is -30~-50℃.

3. The method for recovering lithium from waste batteries according to claim 1, characterized in that, The catalyst in S2 includes a nickel ferrite core, a titanium dioxide shell covering the surface of the core, and phosphotungstic acid supported on the surface of the shell.

4. The method for recovering lithium from waste batteries according to claim 3, characterized in that, The preparation method of the catalyst in S2 includes the following steps: S01. Add titanate to nickel ferrite dispersion and react, then separate the solid and liquid phases and collect the solid phase; S02. After thermal decomposition of the solid phase, it is added to a phosphotungstic acid solution for reaction, and the solid phase is collected and heat-treated. In step S01, the reaction pH is 3-4, the reaction temperature is 25-35℃, and the reaction time is 2-4 hours. In step S02, the thermal decomposition temperature is 450~500℃, the time is 1~2h, and the heating rate is 3~5℃ / min; In step S02, the reaction temperature is 25-35℃, the time is 8-12 hours, and the mass concentration of phosphotungstic acid in the aqueous solution is 5-15 wt%. In step S02, the heat treatment temperature is 180~200℃ and the time is 1~2h.

5. The method for recovering lithium from waste batteries according to claim 4, characterized in that, The mass ratio of nickel ferrite to tetrabutyl titanate is 1:(2~5).

6. The method for recovering lithium from waste batteries according to claim 4, characterized in that, The volume ratio of water to tetrabutyl titanate is (0.5~2):

1.

7. The method for recovering lithium from waste batteries according to claim 1, characterized in that, The activating agent in S3 is a mixture of ammonium persulfate and glucose, wherein the mass ratio of ammonium persulfate to glucose is (1~3):

1.

8. The method for recovering lithium from waste batteries according to claim 1, characterized in that, The ball milling speed in S3 is 300~800 rpm.

9. The method for recovering lithium from waste batteries according to claim 1, characterized in that, The leaching agent in S4 is a eutectic solvent, which is composed of choline chloride and lactic acid in a molar ratio of 1:2, and water is added at 5-10 wt% of the total mass of the eutectic solvent during preparation.

10. A method for recovering lithium from waste batteries according to claim 1, characterized in that, Carbon dioxide gas is introduced during the leaching process in S4.

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