A method for selectively recovering lithium from spent lithium-ion battery cathode material

Abstract

The present application belongs to the technical field of waste metal recycling, and relates to a method for selectively recovering lithium from a positive electrode material of a waste lithium ion battery. Lithium in the positive electrode material of the waste lithium ion battery is selectively recovered through wet leaching. Active substances such as hydroxyl radicals and sulfate radicals generated in a liquid phase by a specific oxidizing agent are used to oxidize the positive electrode material, so that the microstructure of the positive electrode material collapses. The pH of the leaching system is adjusted to below 3.4. In addition to lithium, other metals remain in the solid phase, so that efficient and selective leaching of lithium is achieved. The lithium leaching efficiency can be as high as 98.3%. The lithium-rich filtrate obtained by leaching is subjected to chemical precipitation to prepare lithium carbonate. The overall lithium recovery rate can be as high as 97%, and the product purity is higher than 99.5%, meeting the GB / T11075-201X1 standard. The recovery method of the present application does not require the addition of acid and alkali additives, which can avoid secondary pollution to the environment. The method has low cost, simple process flow, and is easy to realize industrial application.

Description

Technical Field

[0001] This invention belongs to the field of waste metal recycling technology, and more specifically, relates to a method for selectively recovering metallic lithium from waste lithium-ion battery cathode materials. Background Technology

[0002] Lithium-ion batteries, with their excellent electrochemical performance, are widely used in consumer electronics, electric vehicles, and energy storage. With the nation's emphasis on synergistic efficiency in pollution reduction and carbon reduction, the new energy industry continues its vigorous development. Therefore, the production of lithium-ion batteries is showing a year-on-year increasing trend, and it is predicted that by 2030, the installed capacity of lithium-ion batteries will reach 10.5 TWh. However, the lifespan of lithium-ion batteries is only 3-10 years, and we are currently facing a wave of lithium-ion battery obsolescence. It is estimated that by 2030, the capacity of spent lithium-ion batteries will reach 314 GWh. Spent lithium-ion batteries not only contain a large number of metal elements, but also toxic electrolytes and heavy metals. Improper disposal will lead to resource waste and ecological pollution. Therefore, recycling metal resources from the cathode materials of spent lithium-ion batteries can not only make up for the current shortage of metal resources, but also reduce environmental pollution.

[0003] Common recycling technologies for spent lithium-ion batteries mainly rely on pyrometallurgy, based on high-temperature pyrolysis, and hydrometallurgy, based on low-temperature liquid-phase chemical reactions. Pyrometallurgical recycling of spent lithium-ion batteries involves adding slag-forming agents at temperatures above 800℃, recovering cobalt, nickel, copper, and other metals in the form of metallic alloys. However, this process suffers from significant problems such as high energy consumption, severe air pollution, low product purity, and failure to recover lithium resources. Hydrometallurgy, on the other hand, utilizes acids, alkalis, and microorganisms to leach metals from spent lithium-ion batteries, primarily involving three steps: metal leaching, metal ion separation, and end-product preparation. It has been reported that inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as citric acid, acetic acid, and maleic acid, can achieve high metal leaching efficiency when used as leaching agents. However, the separation of metal ions after leaching requires extraction and chemical precipitation. Since lithium metal is always separated in the final step, significant losses occur, resulting in a low overall recovery rate.

[0004] There are already some reports on the selective recovery of lithium from spent lithium-ion battery cathode materials. CN114293029A discloses a method for selectively extracting lithium from spent lithium-ion batteries, which involves mixing and reacting the active material of the lithium-ion battery cathode with oxalic acid dihydrate, leaching the product in water, and obtaining lithium carbonate through precipitation. The disadvantage of the above method is that the solid-solid reaction requires a high temperature and consumes a lot of energy. CN114956132A discloses a method for selectively extracting lithium from spent lithium-ion batteries, which involves ball milling the spent lithium-ion battery ternary cathode material with a ball milling agent, followed by ultrasonic water leaching, and then regenerating battery-grade lithium carbonate through chemical precipitation and drying crystallization. The disadvantage of the above method is that the ball milling speed is high, the energy consumption is high, and the loss of balls and cathode material is large, which is not conducive to large-scale application.

[0005] Furthermore, CN108390120 A discloses a method for selectively recovering lithium from waste lithium-ion battery cathode materials. This method involves adding an oxidant to the waste lithium-ion battery cathode material, converting lithium into water-soluble lithium salts using additives, and then leaching it in an acidic solution with a pH of 3-6 (such as carbon dioxide, hydrochloric acid, sulfuric acid, or nitric acid). The solution is then filtered to obtain a lithium-rich filtrate and leaching residue. High-purity lithium carbonate is prepared from the filtrate. This method requires oxidation, leaching, filtration, and precipitation to obtain lithium carbonate, resulting in a long process flow, a large number of reagents required, and a large consumption of additives (the mass ratio of additives to cathode materials reaches 50%). CN107978814A discloses a method for selectively separating lithium from waste lithium-ion battery cathode materials. This method involves reacting the waste lithium-ion battery cathode sheet with a separation liquid, an oxidizing additive, or an oxidizing gas, followed by filtration to obtain a lithium-rich filtrate. The process is short, but it still requires the addition of an acidic separation solution with a pH of around 3 (such as inorganic acids: sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid; organic acids: formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, etc.) or an alkaline separation solution with a pH of around 10 (such as sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, ammonia, sodium carbonate, etc.).

[0006] In addition, the literature [Front.Chem.Sci.Eng.2021,15(5):1243–1256] reported that selective leaching of metallic lithium in lithium nickel cobalt manganese oxide was carried out using 1.03 mol / L sulfuric acid, 200℃, solid-liquid ratio of 200 g / L, rotation speed of 500 rpm, and hydrothermal reaction for 4 hours, with a leaching efficiency of 95%. This method uses a large amount of acid, and the reaction temperature is too high, the energy consumption is high, and there is still room for further improvement in leaching efficiency. The literature [ACS Sustainable Chem. Eng. 2020, 8, 5165-5174] reports that when the molar ratio of sodium persulfate to lithium nickel cobalt manganese oxide is 0.33, the solid-liquid ratio is 400 g / L, sulfuric acid is added to adjust the pH of the leaching system to 1.95, the rotation speed is 300 rpm, and the reaction is carried out at 85°C for 240 min, 95% of lithium can be leached. Although the reaction temperature is moderate, this method still cannot avoid the use of a large amount of external acid, and there is still room for further improvement in leaching efficiency.

[0007] In summary, since the addition of acid and alkali reagents in existing lithium recovery processes can easily cause secondary pollution, it is worthwhile to focus on and study the development of a green process and technology that is characterized by mild temperature, no added acid or alkali, low energy consumption, low reagent consumption, and high lithium metal recovery rate. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a method for selectively recovering metallic lithium from waste lithium-ion battery cathode materials. The method uses only an oxidant as a leaching agent. Under the action of free radical active substances released from the leaching agent / oxidant, the waste lithium-ion battery cathode material is transformed from its original agglomerated layered structure and olivine structure into dispersed nanoparticles (amorphous oxides). This lowers the system pH, increases the system redox potential, and breaks the lithium-oxygen bonds, making it easier for lithium to be extracted and leached into the liquid phase. The resulting lithium-rich filtrate is obtained through filtration. Carbonate is added to the filtrate for chemical precipitation to prepare lithium carbonate. This shortens the recovery process, reduces the use of chemical reagents, and solves the problems of long processing times, harsh reaction conditions, and low overall lithium recovery rates in existing wet recycling technologies.

[0009] To achieve the above objectives, the present invention provides a method for selectively recovering lithium from waste lithium-ion battery cathode materials, comprising the following steps:

[0010] (1) The waste lithium-ion battery cathode material is mixed with deionized water to form a mixture, and a leaching agent is added to the mixture to form a leaching system. The leaching agent includes only an oxidant. The oxidant dissolves and dissociates into active substances in the mixture. The active substances increase the redox potential of the leaching system to at least 1.7V, so that the pH of the leaching system is <3.4.

[0011] (2) The leaching system obtained in step (1) is subjected to a leaching reaction. During the leaching process, the leaching system is mechanically stirred. Non-lithium metals in the leaching system exist in the original solid phase in an oxidized state and are not leached out. Metallic lithium is leached into the liquid phase to form a lithium-rich leaching solution.

[0012] (3) The lithium-rich leachate obtained in step (2) is filtered to obtain lithium-rich filtrate; a precipitant is added to the lithium-rich filtrate to obtain lithium carbonate precipitate for lithium recovery.

[0013] Preferably, the cathode material of the waste lithium-ion battery is one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium iron phosphate.

[0014] Preferably, in step (1), the solid / liquid ratio of the waste lithium-ion battery cathode material to deionized water is 20-400 g / L, and more preferably 20-200 g / L.

[0015] Preferably, the oxidant includes at least one of peroxymonosulfonate, persulfate, peroxyhydrosulfate, Fenton reagent, and Fenton-like reagent.

[0016] Preferably, the active substance in step (1) is a free radical, which includes one or more of hydroxyl radicals, sulfate radicals, superoxide radicals, and hydrogen superoxide radicals.

[0017] Preferably, the amount of peroxymonosulfonate, persulfate, or peroxymonosulfate added is 0.00434 g / mL to 6.15 g / mL, and more preferably 0.0136 g / mL to 1.5375 g / mL;

[0018] Preferably, the Fenton reagent is composed of hydrogen peroxide containing 30% hydrogen peroxide and ferrous sulfate, wherein the amount of hydrogen peroxide added is 0.01 mL / mL to 0.5 mL / mL, more preferably 0.1 mL / mL to 0.3 mL / mL, and the amount of ferrous sulfate added is 0.05 g / mL to 2.17 g / mL, more preferably 0.5 g / mL to 2.17 g / mL;

[0019] Preferably, the Fenton-like reagent is composed of hydrogen peroxide containing 30% hydrogen peroxide and ferric oxide, wherein the amount of hydrogen peroxide added is 0.05 mL / mL to 0.3 mL / mL, more preferably 0.1 mL / mL to 0.2 mL / mL, and the amount of ferric oxide added is 0.06 g / mL to 2.28 g / mL, more preferably 0.6 g / mL to 2.28 g / mL.

[0020] Preferably, the leaching reaction temperature in step (2) is 40-90℃, more preferably 50-80℃; the reaction time is 20-300min, more preferably 30-220min; and the stirring speed is 100rpm-800rpm, more preferably 200rpm-600rpm.

[0021] Preferably, the precipitant in step (3) is one or more combinations of carbonates or bicarbonates, wherein the carbonate or bicarbonate is preferably anhydrous sodium carbonate, anhydrous potassium carbonate, sodium bicarbonate or potassium bicarbonate, and the precipitation time in step (3) is 20-80 min, preferably 30-60 min.

[0022] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0023] (1) In view of the shortcomings of existing waste lithium-ion battery cathode material recycling technology, such as high energy consumption, secondary pollution, large amount of reagents and low comprehensive recovery rate of lithium metal, this invention proposes a process that uses only oxidant as leaching agent to selectively leach lithium under room temperature water leaching conditions and recover lithium in the form of lithium carbonate. This invention utilizes the active substances dissociated by the oxidant during hydrolysis to increase the redox potential of the system and reduce the pH value of the system, promote the collapse of the cathode material structure, so that metals other than lithium are oxidized to an oxidized state and exist stably in the original solid phase, while lithium metal is selectively leached into the liquid phase. After the lithium in the liquid phase is precipitated, high selectivity and short-range recovery of lithium metal can be achieved, avoiding the use of large amounts of strong acid and alkali to cause equipment corrosion, wastewater and other environmental pollution. The leaching rate of lithium metal can reach up to 98.3%.

[0024] (2) The water bath conditions used in the leaching reaction of the present invention are simple, the leaching reaction conditions are mild and the energy consumption is low. The waste lithium-ion battery cathode material used in the present invention can be various waste lithium-ion battery cathode materials, which has strong applicability and good promotion and application value. Attached Figure Description

[0025] Figure 1 This is a schematic flowchart of a green method for selectively recovering lithium from waste lithium-ion battery cathode materials, provided by the present invention.

[0026] Figure 2 This is the E-pH phase diagram of each metal in the cathode material of the waste lithium-ion battery used in this invention in an aqueous system.

[0027] Figure 3 This is a graph showing the pH trend of the selective leaching system for the cathode material of spent lithium-ion batteries used in this invention.

[0028] Figure 4The images shown are XRD patterns and SEM images of the waste lithium-ion battery cathode material before and after selective leaching in Example 2.

[0029] Figure 5 The XRD pattern and SEM image of the lithium carbonate precipitate prepared in Example 2.

[0030] Figure 6 The results of methanol and tert-butanol quenching experiments are shown in Comparative Example 1 during the selective leaching and lithium recovery process of waste lithium-ion batteries. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Figure 1 This is a flowchart illustrating a method for selectively recovering lithium from waste lithium-ion battery cathode materials provided by the present invention. Specifically, the method includes the following steps:

[0034] (1) The waste lithium-ion battery cathode material is mixed with deionized water to form a mixture, and a leaching agent is added to the mixture to form a leaching system. The leaching agent includes only an oxidant. The oxidant dissolves and dissociates into active substances in the mixture. The active substances increase the redox potential of the leaching system to at least 1.7V, so that the pH of the leaching system is <3.4.

[0035] (2) The leaching system obtained in step (1) is subjected to a leaching reaction. During the leaching process, the leaching system is mechanically stirred. Non-lithium metals in the leaching system exist in the original solid phase in an oxidized state and are not leached out. Metallic lithium is leached into the liquid phase to form a lithium-rich leaching solution.

[0036] (3) The lithium-rich leachate obtained in step (2) is filtered to obtain lithium-rich filtrate; a precipitant is added to the lithium-rich filtrate to obtain lithium carbonate precipitate for lithium recovery.

[0037] In some embodiments, the waste lithium-ion battery cathode material can be various waste lithium-ion battery cathode materials, including one or more mixtures of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium iron phosphate.

[0038] In some embodiments, the solid / liquid ratio of the waste lithium-ion battery cathode material to deionized water is 20-400 g / L, more preferably 20-200 g / L.

[0039] In some embodiments, the oxidant is one or more of peroxymonosulfonate, persulfate, peroxyhydrosulfate, Fenton reagent, and Fenton-like reagents.

[0040] In some embodiments, the active substance is one or more of hydroxyl radicals, sulfate radicals, superoxide radicals, and hydrogen superoxide radicals.

[0041] In some embodiments, the amount of peroxymonosulfonate, persulfate, and peroxymonosulfate added is 0.00434 g / mL to 6.15 g / mL, more preferably 0.0136 g / mL to 1.5375 g / mL.

[0042] In some embodiments, the Fenton reagent is composed of hydrogen peroxide containing 30% hydrogen peroxide and ferrous sulfate, wherein the amount of hydrogen peroxide added is 0.01 mL / mL to 0.5 mL / mL, more preferably 0.1 mL / mL to 0.3 mL / mL; and the amount of ferrous sulfate added is 0.05 g / mL to 2.17 g / mL, more preferably 0.5 g / mL to 2.17 g / mL.

[0043] In some embodiments, the Fenton-like reagent is composed of hydrogen peroxide containing 30% hydrogen peroxide and ferric oxide, wherein the amount of hydrogen peroxide added is 0.05 mL / mL to 0.3 mL / mL, more preferably 0.1 mL / mL to 0.2 mL / mL; and the amount of ferric oxide added is 0.06 g / mL to 2.28 g / mL, more preferably 0.6 g / mL to 2.28 g / mL.

[0044] In some embodiments, the leaching reaction temperature in step (2) is 40-90°C, more preferably 50-80°C; the reaction time is 20-300 min, more preferably 30-220 min; and the stirring speed is 100 rpm-800 rpm, more preferably 200 rpm-600 rpm.

[0045] In some embodiments, the precipitant in step (3) is one or more combinations of carbonates or bicarbonates such as anhydrous sodium carbonate, anhydrous potassium carbonate, sodium bicarbonate, and potassium bicarbonate; the precipitation time is 20-80 min, more preferably 30-60 min, and this precipitation process can be carried out according to the principles of the art. + The E-pH phase diagram of LiHCO3 and Li2CO3 (e.g., in an aqueous solution at 25°C) is used to adjust the E and / or pH values ​​to achieve the desired Li content in lithium-rich solutions. + The transformation to Li2CO3.

[0046] In some embodiments, the mechanism for achieving selective lithium leaching is as follows: through Figure 2 The E-pH phase diagrams of lithium, cobalt, nickel, and manganese metals in aqueous solutions for lithium-ion battery cathode materials show that, at the same temperature, lithium metal has a larger dominant region in the ionic state than nickel, cobalt, and manganese metals. + Ni + Co 2+ Mn 2+ The four metal ions have corresponding redox potentials and pH ranges of -0.8V-1.7V (pH < 12), -0.2V-2.0V (pH < 3), -0.25V-1.5V (pH < 4.2), and -1.2V-1.2V (pH < 6), respectively. Therefore, by increasing the redox potential of the leaching system and adjusting the pH, the metals other than lithium in the cathode material can exist stably in the solid phase in their oxidized state, while lithium exists in the liquid phase in ionic form, thus achieving selective leaching of lithium metal. Taking sodium persulfate oxidant as an example, active substances such as hydroxyl radicals and sulfate radicals are generated during the leaching process, which can increase the redox potential of the leaching system to above 2.6V.

[0047] Figure 3 The graph shows the pH trend of the selective leaching system for cathode materials from spent lithium-ion batteries. Figure 3 As can be seen, after adding the oxidant, the pH dropped to 3.2 after 5 minutes of leaching, and stabilized below 2 after 120 minutes of leaching. Under the action of active substances such as free radicals, the cathode material of waste lithium-ion batteries transformed from the original aggregated layered structure and olivine structure into dispersed nanoparticles, i.e., amorphous oxides. In addition, with the hydrolysis of persulfate, the pH of the system decreased significantly, the hydrogen ion concentration in the liquid phase increased significantly, and the redox potential of the system increased, making it easier for lithium to be extracted and leached into the liquid phase, achieving efficient and selective leaching of lithium.

[0048] In addition, in some embodiments, the lithium-ion leaching efficiency of the leaching system is measured by inductively coupled plasma mass spectrometry, using the formula... Calculate. Where X MThe leaching efficiency of metal i, %; C i The mass concentration of metal i is g / mL; V is the filtrate volume, mL; m i Let be the mass of metal i in the cathode powder of waste lithium-ion batteries, in g.

[0049] The following are specific examples:

[0050] Example 1

[0051] This embodiment provides a method for selectively recovering lithium from spent lithium-ion battery cathode materials using an oxidant under conditions without added acid bath. Figure 1 A flowchart for selectively recovering lithium from spent lithium-ion battery cathode materials using an oxidant, as provided in this embodiment, includes the following steps:

[0052] (1) Take 2g of waste lithium-ion battery cathode material. The waste lithium-ion battery cathode material is a mixture of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and lithium nickel cobalt manganese oxide, which contains 0.1404g of lithium. Mix it with deionized water in a three-necked flask at a solid-liquid ratio of 200g / L. Add 0.369g / mL potassium peroxymonosulfonate and leach it for 110min at 50℃ in a water bath with a stirring speed of 300rpm.

[0053] Under the influence of transition metals cobalt, nickel, and manganese, potassium peroxide monosulfonate is activated and dissociates into sulfate radicals. The redox potential of the sulfate radicals is higher than that of potassium peroxide monosulfonate itself, thus exerting a strong oxidizing effect on the transition metals in the cathode material. At the same time, during the dissociation process of potassium peroxide monosulfonate, the pH of the system drops to 2, and the redox potential is 2.3V, which is more conducive to the selective leaching of lithium metal.

[0054] (2) The leachate was filtered to obtain a lithium-rich filtrate. The leaching efficiency was 98.3% as measured by inductively coupled plasma mass spectrometry. The three metals, nickel, cobalt and manganese, were basically not leached.

[0055] (3) Add anhydrous sodium carbonate with a lithium ion molar ratio of 0.65:1 to that in the lithium-rich filtrate, react for 30 min, and obtain 0.7271 g of lithium carbonate. The lithium recovery rate is calculated to be 97.3%, and the purity is higher than 99.5%.

[0056] Example 2

[0057] (1) 2g of waste lithium-ion battery cathode material, which is a mixture of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and lithium nickel cobalt manganese oxide, containing 0.1404g of lithium, is mixed with deionized water in a three-necked flask at a solid-liquid ratio of 100g / L. 0.119g / mL of sodium persulfate is added, and the mixture is leached in a water bath at 80℃ for 220min with a stirring speed of 400rpm.

[0058] Sodium persulfate can dissociate into sulfate radicals and hydroxyl radicals successively under transition metal and thermal conditions. The redox potentials of these radicals are higher than those of sodium persulfate itself, thus exerting a strong oxidizing effect on the transition metals in the cathode material. During the sodium persulfate leaching process, the pH of the leaching system decreases sharply with prolonged leaching time, then stabilizes at 1.3, while the redox potential rises to 2.6V. This further facilitates the efficient and selective leaching of lithium metal. Figure 4 The images show the XRD and SEM images of the cathode material of the waste lithium-ion battery before and after leaching in this embodiment. It can be seen that after oxidative leaching, the cathode material has been dispersed from the original agglomerated spherical particles into nanoparticles with transition metal oxides as the main component. This proves that oxidation causes the cathode material structure to collapse. The lower pH of the leaching system promotes the easier extraction and insertion of lithium from the layered structure. At the same time, the pH of the system drops to 2.4 and the redox potential is 1.8V during the dissociation of potassium peroxymonosulfonate.

[0059] (2) The leachate was filtered to obtain lithium-rich filtrate and filter residue. The lithium concentration in the leachate was measured by inductively coupled plasma mass spectrometry, and the leaching efficiency was calculated to be 98.02%. The three metals, nickel, cobalt and manganese, were basically not leached.

[0060] (3) Sodium bicarbonate with a lithium ion molar ratio of 0.60:1 to that in the lithium-rich filtrate was added, and the reaction was carried out for 40 min to obtain 0.7249 g of lithium carbonate with a recovery rate of 97.0% and a purity of over 99.5%.

[0061] The oxidative leaching process exhibits excellent lithium selectivity, and the lithium carbonate prepared by chemical precipitation has high purity. Its XRD and SEM spectra are shown below. Figure 5 As shown.

[0062] Example 3

[0063] (1) Take 2g of waste lithium-ion battery positive electrode material. The waste lithium-ion battery positive electrode material is a mixture of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and lithium nickel cobalt manganese oxide, of which lithium is 0.1404g. Mix it with deionized water in a three-necked flask at a solid-liquid ratio of 400g / L. Add 0.464g / mL potassium persulfate. The leaching reaction is carried out at 90℃ in a water bath for 240min with a stirring speed of 500rpm. During the dissociation of potassium persulfate, the pH of the system drops to 2.5 and the redox potential is 2.0V.

[0064] (2) The leachate was filtered to obtain lithium-rich filtrate and filter residue. The lithium concentration in the leachate was measured by inductively coupled plasma mass spectrometry, and the leaching efficiency was calculated to be 98.2%. The three metals, nickel, cobalt and manganese, were basically not leached.

[0065] (3) Add potassium carbonate with a lithium ion molar ratio of 0.55:1 to the lithium ion in the lithium-rich filtrate, react for 50 min, and obtain 0.7264 g of lithium carbonate with a recovery rate of 97.2% and a purity of over 99.5%.

[0066] Example 4

[0067] (1) Take 2g of waste lithium-ion battery cathode material, which is lithium iron phosphate containing 0.088g of lithium. Mix it with deionized water in a three-necked flask at a solid-liquid ratio of 20g / L. Add Fenton's reagent (0.15mL / mL of 30% hydrogen peroxide and 0.05g / mL of ferrous sulfate). In a water bath at 40℃, leach for 300min with a stirring speed of 300rpm. During the dissociation of Fenton's reagent, the pH of the system drops to 3.2 and the redox potential is 1.7V.

[0068] (2) The leachate was filtered to obtain lithium-rich filtrate and filter residue. The lithium concentration in the leachate was measured by inductively coupled plasma mass spectrometry, and the leaching efficiency was calculated to be 98.1%, with no iron leached.

[0069] (3) Add potassium carbonate with a lithium ion molar ratio of 0.5:1 to the lithium ion in the lithium-rich filtrate, react for 60 min, and obtain 0.4548 g of lithium carbonate with a recovery rate of 97.1% and a purity of over 99.5%.

[0070] Example 5

[0071] (1) Take 2g of waste lithium-ion battery cathode material, which is lithium iron phosphate containing 0.088g of lithium. Mix it with deionized water in a three-necked flask at a solid-liquid ratio of 40g / L. Add Fenton-like reagent (0.2mL / mL of 30% hydrogen peroxide and 0.228g / mL of ferric oxide). In a water bath at 50℃, leach for 300min with a stirring speed of 600rpm. During the dissociation of Fenton-like reagent, the pH of the system drops to 3.4 and the redox potential is 1.7V.

[0072] (2) The leachate was filtered to obtain lithium-rich filtrate and filter residue. The lithium concentration in the leachate was measured by inductively coupled plasma mass spectrometry, and the leaching efficiency was calculated to be 97.6%, with no iron leached.

[0073] (3) Add potassium carbonate with a lithium ion molar ratio of 0.8:1 to that in the lithium-rich filtrate, react for 80 min, and obtain 0.4528 g of lithium carbonate with a recovery rate of 96.6% and a purity of over 99.5%.

[0074] To facilitate comparison of the necessity of the method described in this invention, the advantages of this invention will be explained below in conjunction with comparative examples.

[0075] Comparative Example 1

[0076] (1) Dissolve 2g of waste lithium-ion battery cathode material in deionized water at a solid-liquid ratio of 100g / L, and leach it in a water bath at 80℃ for 220min.

[0077] (2) The leachate was filtered and the concentration of metals in the leachate was tested. The leaching efficiency of lithium in the leachate was only 5.7%, the recovery rate of lithium was 5.6%, and the three metals of nickel, cobalt and manganese were basically not leached.

[0078] This comparative example illustrates that water alone cannot effectively leach lithium from waste lithium-ion battery cathode materials, with a leaching system pH of 10.3. However, when using an oxidant for leaching, active substances such as hydroxyl radicals and sulfate radicals can be released. This plays a major role in the oxidation of transition metals in waste lithium-ion battery cathode materials. The transition metals remain in the solid phase as metal oxides, and the pH of the system can be adjusted, thereby achieving efficient and selective leaching of lithium metal.

[0079] Comparative Example 2

[0080] (1) Dissolve 2g of waste lithium-ion battery cathode material in deionized water at a solid-liquid ratio of 100g / L, add 0.119g / mL of sodium persulfate, add 0.2ml of methanol and 0.45ml of tert-butanol respectively, and leach at 80℃ for 220min.

[0081] (2) The leachate was filtered, and the concentration of metals in the leachate was tested. After methanol quenching, the leaching efficiencies of lithium, nickel, cobalt, and manganese in the leachate were 62.0%, 32.1%, 28.8%, and 19.8%, respectively. After tert-butanol quenching, the leaching efficiencies of lithium, nickel, cobalt, and manganese in the leachate were 47.6%, 19.3%, 16.5%, and 8.4%, respectively. The recovery rates of lithium in the methanol and tert-butanol quenching experiments were 61.4% and 47.1%, respectively.

[0082] Figure 6The results of methanol and tert-butanol quenching experiments during the oxidative leaching of spent lithium-ion batteries show that sulfate and hydroxyl radicals are present during the selective leaching of lithium using sodium persulfate. After quenching, the redox potential of the leaching system drops to 0.5V, and the pH of the leaching system is 1.5. Nickel, cobalt, and manganese are all leached to varying degrees. This comparative example shows that when 0.2 ml of methanol and 0.45 ml of tert-butanol are added to the leaching system, methanol can simultaneously quench both sulfate and hydroxyl radicals, while tert-butanol can quench hydroxyl radicals. With increasing leaching time, the leaching efficiency of lithium, nickel, cobalt, and manganese all show an increasing trend, while the leaching efficiency of Li is lower than that without quenching agents. Therefore, in the initial stage of sodium persulfate oxidative leaching, sulfate radicals play a dominant role in inhibiting the leaching of nickel, cobalt, and manganese. After 80 minutes of leaching, sulfate and hydroxyl radicals jointly inhibit the leaching of nickel, cobalt, and manganese. Comparative studies have demonstrated that free radicals are the main active substances in the sodium persulfate leaching system and play an oxidizing role on transition metals, causing the cathode material structure to collapse. Cobalt and manganese exist in the solid phase in an oxidized state and do not leach out, thereby promoting the selective leaching of lithium.

[0083] Comparative Example 3

[0084] (1) Dissolve 2g of waste lithium-ion battery cathode material in deionized water at a solid-liquid ratio of 500g / L, add 0.119g / mL of sodium persulfate, and leach at 80℃ for 220min.

[0085] (2) The leachate was filtered and the concentration of metals in the leachate was tested. The leaching efficiency of lithium in the leachate was 62.8%, the recovery rate was 62.2%, and other metals were not leached.

[0086] This comparison illustrates that the solid-liquid ratio also affects leaching efficiency to some extent. Under the premise of constant other reaction conditions, appropriately reducing the solid-liquid ratio will increase the contact between the spent lithium-ion battery cathode material and the liquid phase, thus improving leaching mass transfer efficiency to a certain extent. However, the solid-liquid ratio should not be too low, as this will result in some oxidant not dissolving completely, reducing its oxidation efficiency.

[0087] Comparative Example 4

[0088] (1) Dissolve 2g of waste lithium-ion battery cathode material in deionized water at a solid-liquid ratio of 100g / L, add 0.119g / mL of sodium persulfate, and leach for 220min in a water bath at 20℃.

[0089] (2) The leachate was filtered and the concentration of metals in the leachate was tested. The leaching efficiency of lithium in the leachate was 51.6%, the recovery rate of lithium was 51.1%, and other metals were not leached.

[0090] This comparative example illustrates that, since the leaching of lithium metal is an exothermic reaction, the leaching efficiency of lithium metal at room temperature is much lower than that at 80°C. This indicates that temperature and transition metals play a combined role in the activation of the oxidant. Only the free radicals generated by the activation of the transition metal are less at higher temperatures, thus reducing the leaching efficiency of lithium metal.

[0091] Comparative Example 5

[0092] (1) 2g of waste lithium-ion battery cathode material was dissolved in leachate with pH values ​​of 2, 4, 6, 8 and 10 at a solid-liquid ratio of 200g / L. The oxidation-reduction potentials of the leachate after pH adjustment were 0.5V, 0.2V, 0.3V, 0.3V and 0.1V, respectively. The leachate reaction was carried out in a water bath at 80℃ for 120min with a stirring speed of 300rpm.

[0093] (2) The leachate was filtered and the concentration of metal in the leachate was tested. The leaching efficiencies of lithium in the leachate were 18.9%, 12.1%, 9.8%, 8.5%, and 6.6%, respectively. The lithium recovery rates were 18.7%, 12.0%, 9.7%, 8.4%, and 6.5%.

[0094] This comparative example demonstrates that adjusting the pH can selectively leach lithium metal, with an acidic pH promoting leaching. However, adjusting only the pH value results in a low redox potential in the leachate, leading to leaching efficiency and recovery rates of less than 20%. Comparing Examples 1-5, it is evident that the redox potential of the leachate must be increased beyond a certain threshold (1.7V) to significantly improve the efficient and selective leaching of lithium metal.

[0095] Table 1 compares the leaching process conditions and effects between the examples and the comparative examples.

[0096] Table 1 Comparison of leaching process conditions and effects between the examples and comparative examples

[0097]

[0098] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for selectively recovering lithium from waste lithium-ion battery cathode materials, characterized in that, The process includes the following steps: (1) mixing waste lithium-ion battery cathode material with deionized water to form a mixture, adding a leaching agent to the mixture to form a leaching system, wherein the leaching agent consists only of an oxidant, the oxidant dissolves and dissociates into an active substance in the mixture, and the active substance raises the redox potential of the leaching system to at least 1.7V, thereby making the pH of the leaching system < 3.4; the waste lithium-ion battery cathode material is one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide; the solid / liquid ratio of the waste lithium-ion battery cathode material to deionized water is 20-200 g / L; The oxidant includes at least one of peroxymonosulfonate, persulfate, peroxyhydrosulfate, Fenton's reagent, and Fenton-like reagent; the amount of peroxymonosulfonate, persulfate, or peroxyhydrosulfate added is 0.0136 g / mL to 1.5375 g / mL; The Fenton reagent is composed of hydrogen peroxide containing 30% hydrogen peroxide and ferrous sulfate, wherein the amount of hydrogen peroxide added is 0.1 mL / mL to 0.3 mL / mL; and the amount of ferrous sulfate added is 0.5 g / mL to 2.17 g / mL. The Fenton-like reagent is composed of hydrogen peroxide containing 30% hydrogen peroxide and ferric oxide, wherein the amount of hydrogen peroxide added is 0.1 mL / mL-0.2 mL / mL; and the amount of ferric oxide added is 0.6 g / mL-2.28 g / mL. (2) The leaching system obtained in step (1) is subjected to a leaching reaction. During the leaching process, the leaching system is stirred. Non-lithium metals in the leaching system exist in the original solid phase in an oxidized state and do not leach out. Metallic lithium is leached into the liquid phase to form a lithium-rich leaching solution. The leaching reaction temperature is 50-80℃. (3) The lithium-rich leachate in step (2) is filtered to obtain a lithium-rich filtrate; a precipitant is added to the lithium-rich filtrate to obtain lithium carbonate precipitate for lithium recovery.

2. The method according to claim 1, characterized in that, The active substance is a free radical, which includes one or more of hydroxyl radicals, sulfate radicals, superoxide radicals, and hydrogen superoxide radicals.

3. The method according to claim 1, characterized in that, The leaching reaction time in step (2) is 30-220 min; the stirring speed is 200 rpm-600 rpm.

4. The method according to claim 1, characterized in that, The precipitant in step (3) is one or more combinations of carbonate or bicarbonate, wherein the carbonate is anhydrous sodium carbonate or anhydrous potassium carbonate, and the bicarbonate is sodium bicarbonate or potassium bicarbonate. The precipitation time in step (3) is 20-80 min.

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