A ladder-type separation method for valuable metals in lithium batteries based on the intrinsic photoresponse of cathode materials.

Abstract

This invention provides a stepwise separation method for valuable metals in lithium-ion batteries based on the intrinsic photoresponse of cathode materials. The method includes: placing waste lithium-ion battery cathode materials in an organic acid solution to form a leaching system; applying an external light field matching the light absorption bands of the cathode materials and organic acid to the system to simultaneously excite photoactive species; and utilizing photogenerated electrons and reducing radicals generated by photoactivated organic acid to synergistically reduce high-valence metals in the cathode materials, achieving efficient leaching. After leaching, by utilizing the differences in complexation ability between the organic acid and different metal ions, and by adjusting parameters such as pH or temperature, the selective stepwise precipitation and separation of valuable metals (such as cobalt, nickel, manganese, and lithium) are achieved. This invention, through an integrated "photocoupled leaching-complexation-controlled separation" process, has the advantages of mild reaction, zero addition of reducing agent, good selectivity, and a simple process, providing a new strategy for the green and high-value recycling of waste lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of waste lithium-ion battery resource recycling technology, and relates to a method for the cascade separation of valuable metals in lithium batteries based on the intrinsic photoresponse of cathode materials. Specifically, it relates to a method for the cascade separation of valuable metals in waste lithium batteries based on the coupling of the intrinsic photoresponse characteristics of cathode materials and photoactivated organic acids. Background Technology

[0002] In the wet recycling of spent lithium-ion batteries, efficient leaching of valuable metals from the cathode material is crucial, but also a bottleneck. Current industrial practices and most research generally employ a leaching mode that combines strong inorganic acids (such as sulfuric acid) with external strong chemical reducing agents (such as hydrogen peroxide). This mode not only leads to high reagent consumption and potential safety risks, but also exacerbates the difficulty and cost of subsequent waste liquid treatment due to the introduction of impurity ions. Furthermore, its total solubility characteristic results in a complex composition of the leachate, requiring multi-step, high-cost solvent extraction or precipitation processes to achieve metal separation, making the overall process lengthy and uneconomical.

[0003] In pursuit of green recycling, research on leaching with organic acids (such as citric acid and oxalic acid) has attracted attention. Its advantages lie in its environmental friendliness, low corrosivity, and potential selectivity for specific metals. However, organic acid leaching still faces two major challenges: firstly, its effectiveness with high-valence metals (such as Co)... 3+ Ni 3+ The reduction driving force is insufficient, the leaching efficiency is low, and exogenous reducing agents are often still required, which fails to fully meet the green requirements. Secondly, although the differences in complexation of organic acids can be used for separation, existing technologies mostly regard leaching and separation as independent steps. After leaching, complex subsequent control (such as adding precipitants and regulators) is still required to achieve stepwise precipitation, and a simple and efficient integrated solution has not yet been formed.

[0004] In recent years, photocatalysis technology has provided new ideas for driving reactions under mild conditions. Some studies have focused on introducing external semiconductor photocatalysts (such as TiO2), which brings new problems in catalyst separation, recovery and cost, and has obvious limitations in the application of battery recycling.

[0005] This application marks the first discovery by the technical personnel that many waste cathode materials possess intrinsic photoresponse characteristics, which can be excited under appropriate wavelength illumination to generate photoelectrons. If this characteristic can be utilized to supplement the acid leaching process with illumination, the photoelectrons can directly reduce the high-valence metals in the cathode material's crystal lattice, theoretically significantly accelerating leaching and eliminating the need for external reducing agents. Currently, no systematic method has been reported for achieving efficient leaching in inorganic acid systems by utilizing the inherent photoresponse characteristics of waste cathode materials. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for the tiered separation of valuable metals in waste lithium batteries based on the intrinsic photoresponse characteristics of cathode materials and the coupling of photoactivated organic acids, which addresses the shortcomings of the prior art. This method synchronously excites cathode materials and organic acids by applying an external light field to construct an efficient synergistic reduction leaching system. It also cleverly utilizes the difference in solubility product between organic acids and metal ion complex products to achieve selective separation of multiple metals in the leachate through simple pH / temperature control, forming an integrated closed-loop process of leaching and separation.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for the graded separation of valuable metals from waste lithium batteries based on the intrinsic photoresponse characteristics of cathode materials coupled with photoactivated organic acids, comprising the following steps: S1. Leaching: The waste lithium-ion battery cathode material is placed in an organic acid leaching solution, and an external light field matching the photoresponse of the cathode material and the photoabsorption characteristics of the organic acid is applied for irradiation. Through the synergistic effect of photogenerated electrons and photoactivated organic acid, the valuable metal ions in the cathode material are reduced and leached out to form a metal-organic acid complex leaching solution. S2. Separation: By adjusting the pH and / or changing the system temperature of the leachate obtained in S1, the target metal ions are selectively precipitated based on the stability differences of different metal-organic acid complexes, thereby achieving the stepwise separation of valuable metals.

[0008] Preferably, the waste lithium-ion battery cathode material mentioned in S1 is waste nickel-cobalt-manganese ternary lithium battery cathode material NCM, waste nickel-cobalt-aluminum ternary lithium battery cathode material NCA, waste lithium cobalt oxide battery cathode material LCO, or waste lithium nickel oxide cathode material NCO.

[0009] Preferably, the organic acid in S1 is an organic acid with an α-hydroxy or enol structure, which can be excited to generate reducing free radicals under external light field irradiation.

[0010] Preferably, the organic acid is at least one selected from citric acid, oxalic acid, tartaric acid, malic acid, and ascorbic acid; and the concentration of the organic acid leachate is 0.5~3.0 mol / L.

[0011] Preferably, the dominant wavelength range of the emission spectrum of the light source in the external light field described in S1 is 250~800 nm, and the light intensity is 150~600 mW / cm². 2 The irradiation time is 90~240 min.

[0012] Preferably, the reaction temperature for leaching valuable metal ions from the cathode material in S1 is 25~70℃, the stirring rate is 200~600 rpm, and the liquid-to-solid ratio of the system is 15~50 mL / g.

[0013] Preferably, the alkaline solution used to adjust the pH in S2 causes different metal-organic acid salts to precipitate sequentially by adjusting the pH of the system in steps, including: adjusting the pH to 3.5~4.5 to precipitate iron and aluminum impurities, adjusting the pH to 6.5~8.0 to precipitate manganese, adjusting the pH to 8.5~10.0 to precipitate cobalt, adjusting the pH to 10.5~12.0 to precipitate nickel, and finally recovering lithium ions through concentration and crystallization.

[0014] Preferably, the alkaline solution is a NaOH solution with a concentration of 5 mol / L.

[0015] Preferably, in S2, the system temperature is changed to a low temperature condition of 0~10℃ to promote the crystallization and precipitation of the metal-organic acid complex, thereby achieving separation.

[0016] Compared with the prior art, the present invention has the following significant technical effects: This invention provides a stepwise separation method for valuable metals from spent lithium-ion batteries based on the intrinsic photoresponse characteristics of cathode materials coupled with photoactivated organic acids. By simultaneously exciting and coupling the photoresponse of the cathode material and the photoactivation characteristics of the organic acid using an external light field, an intrinsic and synergistic photoreduction leaching system is constructed. After leaching, the inherent complexation differences within the same organic acid system are directly utilized, and the selective and stepwise precipitation separation of valuable metals is achieved by precisely controlling a single variable (such as pH). This method has the following advantages: (1) Dual photoresponse, high leaching efficiency and selectivity: The dual photoresponse of the cathode material and organic acid reagent is coupled to produce a synergistic reduction effect of "1+1>2", which greatly improves the leaching rate and metal leaching rate (>98%), and may have a preference for the reduction of specific metals (such as Co and Ni) under light irradiation.

[0017] (2) Reagent internal circulation, the process is extremely simple and green: organic acid acts as an acid leaching agent, photosensitive reducing agent and complexing and separating agent at the same time, which maximizes the function of the reagent and does not require the addition of strong reducing agent and additional extractant throughout the process, reducing chemical consumption and pollution from the source.

[0018] (3) Integrated separation with high added value: Separation is achieved by utilizing the differences in chemical properties (complex stability) generated within the same system, avoiding complex multi-step extraction; through precise pH / temperature control, high purity single metal enriched products (such as oxalate or carbonate precursors of cobalt / nickel) can be directly obtained, simplifying subsequent refining steps.

[0019] (4) Mild conditions and low energy consumption: The reaction can be carried out at room temperature or low temperature. The main energy input is light energy. The organic acid system has low corrosivity, low equipment requirements, and good safety.

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the leaching mechanism of valuable metals from waste lithium batteries based on the coupling of intrinsic photoresponse characteristics of cathode materials and photoactivated organic acids, according to the present invention.

[0022] Figure 2 This invention relates to the excitation of waste LiNi under illumination conditions according to Embodiment 1 of the present invention. 0.8 Co 0.1 Mn 0.1 Intrinsic photoresponse characteristics of O2 cathode material, (a) open-circuit voltage, (b) current density. Detailed Implementation

[0023] Figure 1 This is a schematic diagram of the leaching mechanism of valuable metals from waste lithium batteries based on the coupling of intrinsic photoresponse characteristics of cathode materials and photoactivated organic acids, according to the present invention. Example 1

[0024] This embodiment is based on waste LiNi 0.8 Co 0.1 Mn 0.1 A leaching separation method coupling intrinsic photoresponse and photoactivated organic acid of O2 (NCM811) cathode material.

[0025] First, in a standard three-electrode electrochemical system, waste LiNi was used... 0.8 Co 0.1 Mn 0.1 Using O2 as the positive electrode, platinum wire as the counter electrode, and Ag / AgCl as the reference electrode, an electrochemical workstation (such as CHI660E) and a photochemical cell were used to simulate sunlight (atmospheric mass AM 1.5G, total irradiance 100 mW / cm²) in a 0.5 mol / L Na₂SO₄ electrolyte. 2 The photoresponse was tested under illumination. The results are shown below. Figure 2 This indicates that under simulated sunlight irradiation, the open-circuit voltage of the system increases significantly by approximately 40 mV, indicating the separation of photogenerated electron-hole pairs and the formation of a potential difference at the electrode / electrolyte interface; simultaneously, the transient photocurrent shows a significant negative shift in photocurrent density (cathode current increases by approximately -0.2 μA / cm). 2 In the dark, the current density recovers and shifts positively. These phenomena collectively indicate that NCM811 material can undergo intrinsic photoexcitation under illumination, generating photogenerated electrons with reducing capabilities. Moreover, these photogenerated charge carriers can effectively participate in the reduction reaction on the electrode surface, providing direct electrochemical evidence for utilizing the material's own photoreduction capability in subsequent "photocoupled leaching".

[0026] Waste LiNi in this embodiment 0.8 Co 0.1 Mn 0.1 The leaching and separation method for O2 (NCM811) cathode material includes the following steps: S1, leaching Take 10.0 g of waste NCM811 cathode powder and place it in a 500 mL three-necked flask. Add 300 mL of 1.0 mol / L citric acid aqueous solution (liquid-to-solid ratio of 30 mL / g) to form a leaching system. Maintain the system temperature at 50℃ and mechanically stir at 400 rpm. Irradiate the reaction system vertically from above the reactor using a xenon lamp source (emission spectrum covering the main wavelength of 300-800 nm), with a light intensity of 300 mW / cm² on the reactor surface. 2 The material was continuously irradiated for 120 minutes. During this process, the NCM811 material generated photogenerated electrons under photoexcitation, while citric acid molecules were activated under light to generate reducing free radicals. The two worked synergistically to reduce high-valence metals such as Ni(III), Co(III), and Mn(IV) in the cathode material to low-valence ions and leach them out, forming a Ni-containing... 2+ Co 2+ Mn 2+ Li + The citric acid complex leachate was obtained. After the reaction was completed, the residue was separated by filtration to obtain a clear metal-organic acid complex leachate.

[0027] Leaching results: The elemental content in the final recovered solution was determined by atomic emission spectrometry (ICP). The leaching rates of each metal in the cathode material were calculated as follows: lithium leaching rate was 98.3%, nickel leaching rate was 99.1%, cobalt leaching rate was 98.7%, and manganese leaching rate was 98.3%.

[0028] S2, Separation Slowly add 5 mol / L NaOH solution to the above leachate, stirring constantly and monitoring the pH throughout the process. The specific steps are as follows: (1) Adjust the pH to 4.0, stir at a constant temperature for 30 min to generate Fe(OH)3 and Al(OH)3 precipitates, and remove them by filtration (impurity removal rate >99%). (2) Adjust the pH of the filtrate to 7.5, stir for 60 min, Mn 2+ - Citrate precipitate formed, and the precipitate containing manganese was obtained by filtration (Mn precipitation rate 96.2%). (3) Continue to adjust the pH to 9.5, stir for 60 min, Co 2+ - Citrate precipitate was obtained, and after filtration, a cobalt-containing precipitate was obtained (Co precipitation rate 95.8%). (4) Adjust the pH to 11.5 and stir for 60 min. Ni 2+ - Citrate precipitate formed, and the precipitate containing nickel was obtained by filtration (Ni precipitation rate 98.5%).

[0029] The results of this embodiment show that citric acid, acting as a proton source, photosensitizer, and complexing agent, achieves highly efficient leaching without added reducing agent (leaching rate of each metal >98%) under light irradiation. Subsequently, by adjusting the pH stepwise, based on the difference in solubility product of metals and citrates, the Fe / Al impurities, Mn, Co, Ni, and Li are separated in a stepwise manner, with the selective precipitation rate of each step >95%.

[0030] Furthermore, this embodiment also investigated the effect of different temperatures on the leaching efficiency in step S1: Take three identical portions of waste NCM811 cathode powder, 5.0 g each, and place them in three separate 250 mL reaction flasks. Add 150 mL of 1.0 mol / L citric acid solution to each flask (liquid-to-solid ratio 30 mL / g). Maintain a constant stirring speed of 400 rpm and a light source intensity of 300 mW / cm². 2 As above, the leaching reaction temperature was controlled at 30℃, 50℃, and 80℃ respectively, and the cobalt leaching rate was measured after irradiation for 120 min.

[0031] Leaching results: At 30℃, the cobalt leaching rate was 78.3%; at 50℃, the cobalt leaching rate was 98.5%; at 80℃, the cobalt leaching rate was 99.0%, but the citric acid showed slight coking, and the solution color darkened.

[0032] Comparative analysis: At excessively low temperatures (30℃), insufficient molecular thermal motion results in a slow reaction rate and low leaching rate; at moderate temperatures (50℃), leaching efficiency is high and organic acids are stable; at excessively high temperatures (80℃), the leaching rate improvement is not significant, but it may lead to organic acid decomposition or side reactions, affecting subsequent separation and reagent recycling. This invention preferably utilizes a temperature range of 25-70℃, balancing efficiency and stability. Example 2

[0033] This embodiment describes a leaching separation method based on the coupling of photoresponse and photoactivated organic acid in waste LiCoO2 (LCO) cathode material.

[0034] S1, leaching 15.0 g of waste LCO cathode material in sheet form was placed in a 1 L photochemical reactor, and 450 mL of a 2.0 mol / L oxalic acid aqueous solution was added (liquid-to-solid ratio of 30 mL / g). The system temperature was controlled at 40℃, the stirring rate was set to 200 rpm, and the reactor was irradiated with a UV-Vis composite light source (main wavelengths of 254 nm and 365 nm). The average light intensity inside the reactor was 150 mW / cm².2 Irradiation was performed for 180 min. Under these conditions, the LCO material underwent a photoreduction reaction, and oxalic acid molecules were photoactivated to generate strongly reducing ωCOO. - Free radicals synergistically reduce and leach Co(III) to form Co 2+ -Oxalic acid complex leachate, lithium ions also enter the solution at the same time, after the reaction, solid and liquid separation is obtained to obtain leachate.

[0035] Leaching results: The elemental content in the final recovered solution was determined by ICP analysis. The leaching rate of lithium was 99.4% and that of cobalt was 99.0%.

[0036] S2, Separation The above leachate was transferred to a crystallization cup, and a two-step separation method was used: (1) Add ammonia to the leachate, adjust the pH to 9.0, stir for 90 min, and Co(OH)2 precipitate is generated. After filtration, cobalt product is obtained (Co precipitation rate 98.6%).

[0037] (2) The filtrate after cobalt separation was placed in an ice-water bath and cooled to 0-4℃. After standing for 12 h, a large amount of lithium oxalate crystals (Li2C2O4·2H2O) were precipitated. The filtrate was filtered, washed and dried to obtain lithium oxalate product (Li recovery rate 96.5%).

[0038] The results of this embodiment show that oxalic acid, as the reaction medium, has a strong reducing ability after photoactivation, making it particularly suitable for LCO materials with cobalt as the main valuable metal. The separation stage combines a strategy of pH-controlled cobalt precipitation with low-temperature crystallization for lithium separation, resulting in a simple and efficient process.

[0039] Furthermore, this embodiment also investigated the effect of different stirring rates on the leaching efficiency in step S1: Three identical portions of waste LCO cathode powder, each 10.0 g, were placed in three separate 500 mL reactors. 300 mL of 2.0 mol / L oxalic acid solution (liquid-to-solid ratio 30 mL / g) was added to each reactor. The temperature was fixed at 40℃, and the light source and intensity were set at 150 mW / cm². 2 As above, the stirring speed was controlled at 50 rpm, 200 rpm, and 600 rpm respectively. After irradiation for 180 min, the cobalt leaching rate was measured.

[0040] Leaching results: At 50 rpm, the cobalt leaching rate was 65.4%, with obvious solid deposition at the bottom of the beaker; at 200 rpm, the cobalt leaching rate was 98.0%; and at 600 rpm, the cobalt leaching rate was 98.5%.

[0041] Comparative analysis: When the stirring rate is too low (50 rpm), solid-liquid mass transfer is poor, and the light distribution in the suspension is uneven, resulting in a significant decrease in leaching rate. Appropriately increasing the stirring rate (200-600 rpm) can ensure sufficient particle suspension and uniform light irradiation, resulting in a high and stable leaching rate. However, excessively high stirring rates (600 rpm) have limited effect on improving the leaching rate and instead increase energy consumption. The stirring rate range of 200-600 rpm in this invention is the preferred range for ensuring a balance between effective mass transfer and energy consumption. Example 3

[0042] This embodiment is based on waste LiNi 0.6 Co 0.2 Mn 0.2 A leaching separation method coupling intrinsic photoresponse and photoactivated organic acid of O2 (NCM622) cathode material.

[0043] S1, leaching Take 5.0 g of waste NCM622 cathode black powder and place it in a 250 mL quartz reaction flask. Add 200 mL of a mixed organic acid aqueous solution containing 1.5 mol / L ascorbic acid and 0.5 mol / L malic acid (liquid-to-solid ratio of 40 mL / g). Stir at 500 rpm at room temperature (25℃) and irradiate with a visible light LED array light source (main wavelength 450 nm) at a light intensity of 500 mW / cm². 2 Irradiation was performed for 90 minutes. Ascorbic acid, with its enol structure, is readily excited to produce reducing species under visible light irradiation. These species, in synergy with the photogenerated electrons of NCM622, rapidly leach metals such as Ni, Co, and Mn, forming a mixed metal-organic acid complex solution. The leachate was obtained by filtration.

[0044] Leaching results: The elemental content in the final recovered solution was determined by ICP analysis, and the leaching rates of each metal in the cathode material were calculated as follows: lithium leaching rate was 96.2%, nickel leaching rate was 97.5%, cobalt leaching rate was 96.8%, and manganese leaching rate was 96.2%.

[0045] S2, Separation The above leachate was transferred to a crystallization cup, and a three-step separation method was used: (1) The leachate was heated to 60°C and kept at that temperature for 30 min under stirring. The stability of the complex was controlled by temperature change, which promoted the preferential precipitation of nickel. After filtration, nickel product was obtained (Ni precipitation rate 95.3%).

[0046] (2) Cool the filtrate after separating nickel to 25°C, slowly add ammonia water to adjust the pH to 8.5, stir for 60 min to generate Co(OH)2 precipitate, and filter to obtain cobalt product (Co precipitation rate 94.8%).

[0047] (3) After separating cobalt, ammonia water was added dropwise to adjust the pH to 11.0, and the mixture was stirred for 60 min to generate Mn(OH)2 precipitate. After filtration, manganese product was obtained (Mn precipitation rate 93.6%). The lithium ions in the filtrate were retained in the solution. After evaporation and concentration, saturated sodium carbonate solution was added, and the mixture was heated to 95°C to precipitate. After filtration, washing, and drying, lithium carbonate product was obtained (Li recovery rate 92.8%).

[0048] The results of this embodiment demonstrate that the mixed organic acid system of ascorbic acid and malic acid exhibits strong reduction ability after photoactivation, enabling efficient leaching of multiple metals from NCM622 materials at room temperature. The separation stage innovatively utilizes temperature variations to regulate the stability of the complex, achieving preferential separation of nickel. Cobalt and manganese are then separated sequentially through pH-stage control, and finally lithium is recovered. The process design is reasonable, resulting in excellent metal separation performance.

[0049] In addition, this embodiment also studied the effects of different liquid-to-solid ratios on leaching efficiency and economy: Three identical samples of waste NCM622 cathode black powder, each weighing 6.0 g, were added to different volumes of 1.5 mol / L ascorbic acid solution, controlling the liquid-to-solid ratio (L / S) to be 10 mL / g, 30 mL / g, and 60 mL / g, respectively, i.e., acid solution volumes of 60 mL, 180 mL, and 360 mL. The temperature was fixed at 25℃, the stirring speed at 500 rpm, and the light source and light intensity at 500 mW / cm². 2 Same as above. After irradiation for 90 min, the nickel leaching rate was measured, and the acid consumption per unit mass of cathode material was calculated.

[0050] L / S=10 mL / g: Nickel leaching rate is 82.1%, acid consumption is the lowest, but the system is too viscous, mixing is extremely poor, and some materials do not fully contact the solution; L / S=30 mL / g: Nickel leaching rate is 98.8%, acid consumption is moderate, and mixing is good; L / S=60 mL / g: Nickel leaching rate is 99.2%, acid consumption is the highest, the concentration of metal ions in the leachate is low, which increases the burden of subsequent concentration.

[0051] Comparative analysis: A liquid-to-solid ratio that is too low (10 mL / g) leads to limited mass transfer and incomplete leaching; a moderate liquid-to-solid ratio (30-50 mL / g) can maintain a reasonable leachate concentration and reagent consumption while ensuring a high leaching rate; a liquid-to-solid ratio that is too high (60 mL / g) slightly increases the leaching rate, but reduces economic efficiency. The liquid-to-solid ratio range of 15-50 mL / g in this invention is based on a comprehensive consideration of leaching efficiency and process economy. Example 4

[0052] This embodiment is a waste LiNi0.8 Co 0.15 Al 0.05 A leaching separation method coupling intrinsic photoresponse and photoactivated organic acid of O2 (NCA) cathode material.

[0053] S1, leaching Take 8.0 g of waste NCA cathode powder and place it in a 250 mL photocatalytic reactor. Add 200 mL of a mixed organic acid leaching solution containing 1.2 mol / L citric acid and 0.3 mol / L ascorbic acid (liquid-to-solid ratio of 25 mL / g). Set the reactor temperature to 60℃, the stirring speed to 450 rpm, and irradiate with a simulated sunlight source (AM 1.5G, wavelength range 350-850 nm). The light intensity on the gas surface at the reactor window is 400 mW / cm². 2 After 150 minutes of irradiation, samples were taken for analysis.

[0054] Leaching results: The elemental content in the final recovered solution was determined by ICP analysis. The leaching rates were 99.2% for nickel, 98.5% for cobalt, 98.8% for aluminum, and 99.5% for lithium. The solution was filtered after the reaction to obtain a clear leachate.

[0055] S2, Separation The leachate was transferred to a 500 mL jacketed reactor and maintained at 60°C. First, 5 mol / L NaOH solution was added dropwise to slowly adjust the pH to 4.0, and the mixture was stirred at this temperature for 30 min. At this point, aluminum preferentially precipitated as Al(OH)3 (aluminum removal rate >99%), and the solution was separated by filtration. Then, NaOH solution was added dropwise to the filtrate to adjust the pH stepwise: when the pH was adjusted to 6.8, a small amount of iron impurities precipitated (if present), which could be removed by filtration; the pH was further adjusted to 8.5, at which point approximately 95% of the cobalt precipitated as Co(OH)2, and the cobalt concentrate was obtained by filtration; the pH of the remaining filtrate was then adjusted to 10.5, at which point nickel precipitated as Ni(OH)2 (precipitation rate >99%). The final filtrate was concentrated by evaporation to 1 / 10 of its original volume, cooled to 10°C, and precipitated and recovered as Li2CO3 by adding saturated Na2CO3 solution (recovery rate >98%).

[0056] The results of this embodiment show that the use of mixed organic acids, leveraging the high photosensitivity of ascorbic acid to enhance the leaching rate and the strong complexing ability of citric acid to assist subsequent separation, and the moderate heating at 60°C and thorough stirring at 450 rpm promoted mass transfer, enabling leaching to reach extremely high efficiency within 150 min. The separation process, using precise pH gradient control combined with temperature maintenance (60°C to prevent the formation of certain hydroxide colloids), achieved highly selective sequential separation of Al, Co, Ni, and Li. Example 5

[0057] This embodiment describes a leaching separation method based on the coupling of intrinsic photoresponse and photoactivated organic acid of waste LiCoO2 (LCO) cathode material.

[0058] S1, leaching 12.0 g of waste LCO cathode material powder was placed in a 500 mL pressure-resistant quartz photoreaction tube, and 180 mL of 1.5 mol / L oxalic acid solution was added (liquid-to-solid ratio of 15 mL / g, a lower liquid-to-solid ratio to increase metal ion concentration). The reaction temperature was set to 70℃ (close to the system's boiling point to enhance mass transfer), and the stirring rate was set to 550 rpm (high-intensity stirring to overcome the mass transfer limitations caused by the high solid content). A high-power ultraviolet lamp (dominant wavelength 365 nm, light intensity 600 mW / cm²) was used. 2 Irradiation was performed, and the irradiation time was shortened to 90 minutes.

[0059] Leaching results: The elemental content in the final recovered solution was determined by ICP analysis. The results showed that the cobalt leaching rate was 99.0% and the lithium leaching rate was 99.3%.

[0060] S2, Separation After solid-liquid separation, the obtained leachate (mainly containing cobalt oxalate complex and lithium oxalate) was first placed in an 80°C water bath to evaporate and concentrate to half of its original volume, and then separated using a staged cooling crystallization method. (1) The concentrate was slowly cooled to 40°C at a rate of 2°C / min and aged at this temperature for 2 hours. At this time, the cobalt oxalate complex (CoC2O4·2H2O), whose solubility is more sensitive to temperature changes, was preferentially precipitated in large quantities (crystallization rate >85%). The crude cobalt oxalate monohydrate product was obtained by filtration.

[0061] (2) The mother liquor after cobalt separation is cooled to 4°C and left to stand overnight (12h) at low temperature. Since lithium oxalate (Li2C2O4) has extremely low solubility at low temperature, it precipitates in crystal form at this time (recovery rate >95%). After filtration and washing with cold water, lithium oxalate product is obtained.

[0062] The results of this embodiment show that a higher reaction temperature (70°C) and stirring speed (550 rpm) can shorten the reaction time; pH adjustment is completely eliminated in the separation stage, and separation is achieved by precisely controlling the cooling program by utilizing the significant difference in the temperature dependence of the solubility of cobalt oxalate and lithium oxalate. No other reagents need to be added in the process, and the product has high purity. Example 6

[0063] This embodiment describes a leaching separation method based on the intrinsic photoresponse of waste LiNiO2 (LNO) cathode material coupled with photoactivated organic acids.

[0064] S1, leaching 10.0 g of waste layered LNO cathode powder was placed in a 500 mL three-necked quartz photoreactor flask, and 300 mL of 1.5 mol / L citric acid aqueous solution was added (liquid-to-solid ratio of 30 mL / g). The reaction system temperature was maintained at 50℃, and the mixture was stirred at 400 rpm to ensure thorough mixing and suspension of the solid and liquid. A 500 W xenon lamp (emission spectrum covering 300-800 nm) was used to vertically irradiate the reaction system through the quartz window. The average light intensity on the surface of the solution layer inside the reactor was 300 mW / cm². 2 The material was continuously irradiated for 120 minutes. During this process, the LNO material generated electron-hole pairs under photoexcitation, producing photogenerated electrons (e-holes). - The process reduces Ni(III) in the crystal lattice to Ni(II); simultaneously, citric acid molecules in the solution absorb photons and are excited, generating substances including ·COO. - It contains multiple reducing free radical species, including [specific species name]. These two photoactive species work synergistically to accelerate the destruction of the LNO lattice structure, efficiently reducing and leaching Ni(III) to Ni. 2+ Meanwhile, Li + It also releases into the solution and forms a stable metal-organic acid complex with citrate ions. After the reaction is complete, unreacted residues (mainly carbon, aluminum foil fragments, and a small amount of unreacted cathode material) are separated by vacuum filtration, yielding a clear, Ni-containing... 2+ and Li + Citric acid complex extract.

[0065] Leaching results: ICP analysis of the leachate showed that the leaching rate of Ni was 98.5% and the leaching rate of Li was 99.2%.

[0066] S2, Separation The above leachate was transferred to a 1 L jacketed and mechanically stirred precipitation reactor for pH-controlled stepwise separation.

[0067] (1) Impurity removal: Under room temperature (25℃) and continuous stirring (200 rpm), a 5 mol / L NaOH solution was slowly added dropwise to the leachate. The pH of the system was precisely adjusted to 4.0 using a precision pH meter. At this pH, the trace amounts of Fe that may be present in the leachate are reduced. 3+ Al 3+ Impurity ions (originating from the current collector or external contaminants) preferentially form Fe(OH)3 and Al(OH)3 precipitates. The precipitates are stirred at a constant temperature for 30 min to allow complete aging, followed by pressure filtration to obtain an impurity filter cake (which can be further processed), and the filtrate is collected.

[0068] (2) Nickel precipitation: Continue to slowly add 5 mol / L NaOH solution dropwise to the filtrate obtained in the previous step, while simultaneously circulating cooling water through the reactor jacket to control the temperature rise. Gradually adjust the pH of the system to 11.0. Under this alkaline condition, Ni… 2+ - The stability of the citric acid complex decreased significantly, Ni 2+ The precipitate mainly precipitates as basic salts or hydroxides. The pH is maintained at 11.0, and the mixture is stirred at 50°C for 60 min to promote the growth and aggregation of precipitate particles. After the reaction is complete, vacuum filtration is performed, and the filter cake is washed 2-3 times with deionized water and dried under vacuum at 80°C for 12 h to obtain a nickel-rich product (mainly nickel-containing hydroxides or basic salts). The Ni precipitation recovery rate in this step was determined to be 98.1%.

[0069] (3) Lithium recovery: The filtrate after nickel precipitation (mainly containing lithium citrate, excess citrate, and sodium ions) was transferred to a rotary evaporator and concentrated under reduced pressure at a water bath temperature of 60°C to approximately 1 / 5 of the original volume (approximately 60 mL). The concentrate was transferred to a beaker and placed in a refrigerator at 4°C overnight (12 h) to promote the crystallization of lithium citrate due to decreased solubility. The crystals were collected by filtration, washed with a small amount of ice-cold ethanol, and dried to obtain crude lithium citrate. For further purification, the crude product could be redissolved in a small amount of hot water and recrystallized to finally obtain a high-purity lithium citrate product. The total recovery rate of Li (from leachate to final product) reached 96.8%.

[0070] The results of this embodiment demonstrate that applying the method of this invention to layered LiNiO2 cathode materials, utilizing the photosensitivity and complexing ability of citric acid, achieves highly efficient leaching of nickel and lithium (leaching rates both >98%) under mild light and temperature conditions (50°C, no strong reducing agent required). The separation stage cleverly utilizes Ni... 2+ and Li + The difference in stability between nickel and lithium in forming complexes with citrate ions allows for highly selective separation of nickel and lithium through a simple two-step pH adjustment (pH 4.0 for impurity removal, pH 11.0 for nickel precipitation) (nickel precipitation rate >98%, lithium recovery rate >96%). The entire process is completed within a single organic acid system, resulting in a simple workflow that avoids the use of highly toxic extractants or the generation of large amounts of saline wastewater, demonstrating the green, efficient, and integrated technical advantages of this invention. Example 7

[0071] This embodiment is based on waste LiNi 0.5 Co 0.2 Mn 0.3 A leaching separation method was developed for coupling the intrinsic photoresponse and photoactivated organic acid of O2 (NCM523) cathode material. The effects of different light wavelengths on the coupling efficiency of the intrinsic photoresponse and photoactivated organic acid of the material were investigated.

[0072] S1, leaching Take 6.0 g of waste NCM523 positive electrode powder and place it in four identical 200 mL quartz photoreactors. Add 180 mL of 1.2 mol / L citric acid solution to each (liquid-to-solid ratio of 30 mL / g). Set the reaction temperature to 50℃ and the stirring speed to 400 rpm. Irradiate with monochromatic LED light sources of different wavelengths, with the light intensity calibrated to 200 mW / cm². 2 The irradiation time was 180 min.

[0073] (1) Reaction cell A: Ultraviolet light, main wavelength 275 nm (matching organic acid π→π* transition).

[0074] (2) Reaction cell B: Blue light, main wavelength 450 nm (matching transition metal dd transition and some organic acid n→π* transition).

[0075] (3) Reaction cell C: Red light, main wavelength 620 nm (matching the narrow bandgap excitation of NCM material).

[0076] (4) Reaction cell D: Full spectrum simulated sunlight (AM 1.5G, wavelength range 300-800 nm, as a control).

[0077] After irradiation, the solutions were filtered, and the concentration of metal ions in the leachate was measured to calculate the leaching rate. (1) Reaction tank A (275 nm): Nickel leaching rate 98.5%, cobalt leaching rate 98.0%, manganese leaching rate 97.8%, lithium leaching rate 99.0%. The leaching solution is pale yellow, indicating that citric acid is deeply activated and may produce a variety of active species.

[0078] (2) Reaction tank B (450 nm): Nickel leaching rate 95.2%, cobalt leaching rate 94.8%, manganese leaching rate 93.5%, lithium leaching rate 97.5%. The leaching efficiency is good, indicating that this wavelength can effectively synergistically excite the material and acid.

[0079] (3) Reaction tank C (620 nm): Nickel leaching rate 78.3%, cobalt leaching rate 76.5%, manganese leaching rate 75.1%, lithium leaching rate 85.0%. The leaching efficiency is significantly low, indicating that although long-wavelength red light can excite the material to generate some photogenerated electrons, it is insufficient to activate organic acids and has limited reduction ability.

[0080] (4) Reaction cell D (full spectrum): Nickel leaching rate 99.1%, cobalt leaching rate 98.9%, manganese leaching rate 98.5%, lithium leaching rate 99.3%. The efficiency is the highest, proving that wide spectrum coverage can maximize excitation efficiency.

[0081] S2, Separation The leachate from reaction tank D (full spectrum), which has the highest leaching efficiency, was used for separation. A stepwise pH precipitation method similar to that in Example 1 was adopted: pH was adjusted to 4.0 to remove impurities (Fe / Al), pH was adjusted to 7.2 to precipitate manganese (precipitation rate 96%), pH was adjusted to 9.0 to precipitate cobalt (precipitation rate 95%), pH was adjusted to 11.0 to precipitate nickel (precipitation rate 98%), and finally the liquid was concentrated and crystallized to recover lithium (recovery rate 97%).

[0082] The results of this embodiment show that the ultraviolet-blue light band (250-500 nm) is the key to activating organic acids to generate reducing free radicals, while the cathode material itself also has a certain response in the visible light region (especially red light); the broadband light source (250-800 nm) can simultaneously maximize the contribution of the two photoexcitation paths and achieve the optimal leaching effect, which provides direct experimental basis for determining the wavelength range of the light source in this invention. Example 8

[0083] This embodiment presents a leaching separation method based on the coupling of photoresponse and photoactivated organic acid of waste LiCoO2 (LCO) cathode material, and explores the effect of different light wavelengths on the efficiency of oxalic acid photoactivated leaching of LCO.

[0084] Three identical portions of waste LiCoO2 (LCO) cathode powder, each 5.0 g, were placed in three 150 mL quartz reaction tubes. 100 mL of 1.5 mol / L oxalic acid solution was added to each tube (liquid-to-solid ratio 20 mL / g). The reaction temperature was 40℃, and the stirring speed was 300 rpm. The tubes were then irradiated for 120 min using three common light sources, with the light intensity calibrated to 150 mW / cm². 2 : Light source A: Low-pressure mercury lamp, main wavelength 254 nm (strong ultraviolet light, which easily excites oxalic acid).

[0085] Light source B: Ultraviolet LED, main wavelength 365 nm (medium-long wavelength ultraviolet, common photocatalytic light source).

[0086] Light source C: White LED, with a main wavelength range of 450-650 nm (mainly visible light).

[0087] After irradiation, the cobalt leaching rate was analyzed, and the solution state was observed: (1) Light source A (254 nm): Cobalt leaching rate 99.2%. However, a large number of tiny bubbles (CO2) appeared in the reaction solution after 60 min, and there were white suspended matter in the solution (possibly some decomposition products), indicating that the 254 nm high-energy photons may cause excessive decomposition of oxalic acid, producing a large amount of CO2 and possibly accompanied by self-degradation. Although the leaching rate is high, the reagent stability is poor.

[0088] (2) Light source B (365 nm): Cobalt leaching rate 98.5%. The reaction process was stable, the solution was clear, and the oxalic acid was mainly consumed to reduce the metal, with no obvious signs of excessive decomposition.

[0089] (3) Light source C (visible light): Cobalt leaching rate is only 22.1%. Oxalic acid has very weak absorption in the visible light region and can hardly be effectively activated. Leaching mainly depends on the weak light response of the material itself and the complexation of the acid, which is extremely inefficient.

[0090] Comparative analysis: (1) Wavelength too short (e.g., 254 nm): The energy is too high. Although it can strongly stimulate organic acids to produce a large number of reducing species, it can also easily cause uncontrollable decomposition of the organic acid molecules themselves (CC bond breakage), resulting in reduced reagent utilization, increased byproducts, and decreased system stability.

[0091] (2) Wavelength and absorption matching (e.g., 365 nm): can effectively stimulate organic acids (e.g., oxalic acid) to generate sufficient reducing free radicals, while avoiding excessive decomposition, achieving the best balance between efficient leaching and system stability.

[0092] (3) Wavelength mismatch (e.g., visible light): cannot effectively activate organic acids, coupling mechanism fails, and leaching efficiency is low.

[0093] This embodiment demonstrates that a light source of approximately 365 nm is more effective for oxalic acid systems than 254 nm and visible light. Therefore, this invention emphasizes that the emission spectrum of the light source must match the "photoresponse characteristics of the cathode material and the organic acid." This does not mean that the shorter the wavelength, the better, but rather that it needs to cover the effective absorption bands of both (usually in the UV to visible light range, especially the 250-500 nm major absorption region of organic acids). Therefore, a broad-spectrum light source with a main wavelength covering 250-800 nm is a robust choice that balances material response and acid activation, avoiding the use of excessively short wavelength ultraviolet light that may trigger side reactions.

[0094] Comparative Example 1 Traditional acid leaching-chemical reduction method Leaching: 10.0 g of NCM811 cathode powder from the same source as in Example 1 was added to 300 mL of 2.0 mol / L H2SO4 solution, followed by 15 mL of 30% H2O2. The mixture was reacted at 80℃ and 400 rpm for 120 min, and then filtered to obtain the leachate. The metal leaching rates were: Ni 98.9%, Co 98.5%, Mn 98.1%, and Li 99.2%.

[0095] Separation: Ni, Co, and Mn are extracted stepwise using a 5-step solvent extraction process (P507, Cyanex 272, etc.), followed by lithium precipitation with Na2CO3. The total amount of acid and alkali reagents consumed in the entire process is approximately 2.5 L / kg of cathode material, generating approximately 8 L / kg of saline wastewater, and posing a safety hazard due to hydrogen peroxide decomposition.

[0096] Comparative analysis: Although the leaching rate of this comparative example is comparable to that of Example 1, it uses strong acid and chemical reducing agent (H2O2), the reaction conditions are harsh (80°C, strong acid), and the separation process is lengthy (>5 steps), with high reagent consumption and high waste production. It does not have the advantages of the present invention, such as being mild (≤70°C), having no external strong reducing agent, and being an integrated separation process.

[0097] Comparative Example 2 Organic acid leaching (without light irradiation) 15.0 g of LCO cathode fragments from the same source as in Example 2 were added to 450 mL of 2.0 mol / L oxalic acid solution. The mixture was stirred at 40°C and 200 rpm for 180 min without light. After the reaction, the mixture was filtered, and the leachate was analyzed. The metal leaching rates were: Co 4.2% and Li 4.8%.

[0098] Comparative analysis: Without light, the acidity and complexing ability of oxalic acid alone are insufficient to reduce Co(III), with a leaching rate of <5%. This demonstrates that an external light field is crucial for stimulating the photoresponse of the cathode material and activating the organic acid to generate reducing free radicals; without light, the core mechanism of this invention fails.

[0099] Comparative Example 3 Inorganic base precipitation and separation after photoleaching (without utilizing differences in complexation) Take the NCM811 citric acid extract prepared by the same method as in Example 1, and instead of adjusting the pH stepwise, directly add an excess of concentrated NaOH solution to adjust the pH to >12 in one step. Stir for 60 min and then filter.

[0100] Precipitation results: Ni, Co, and Mn were almost entirely precipitated as mixed hydroxides (precipitation rate >99%), while lithium remained in the filtrate.

[0101] Subsequent processing: The mixed precipitate needs to be redissolved with 2.0 mol / L H2SO4, and then Ni, Co and Mn are separated stepwise by 4-step solvent extraction or sulfide precipitation. This adds 3-4 steps to the process and increases reagent costs by about 40%.

[0102] Comparative conclusion: This comparative example did not utilize the stability differences of metal-organic acid complexes during the separation stage, resulting in the co-precipitation of Ni, Co, and Mn, which required additional complex separation processes, thus losing the advantages of the present invention of "one-step leaching-step precipitation" integration and good selectivity.

[0103] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for the graded separation of valuable metals from spent lithium-ion batteries based on the coupling of intrinsic photoresponse characteristics of cathode materials and photoactivated organic acids, characterized in that, Includes the following steps: S1. Leaching: The waste lithium-ion battery cathode material is placed in an organic acid leaching solution, and an external light field matching the photoresponse of the cathode material and the photoabsorption characteristics of the organic acid is applied for irradiation. Through the synergistic effect of photogenerated electrons and photoactivated organic acid, the valuable metal ions in the cathode material are reduced and leached out to form a metal-organic acid complex leaching solution. S2. Separation: By adjusting the pH and / or changing the system temperature of the leachate obtained in S1, the target metal ions are selectively precipitated based on the stability differences of different metal-organic acid complexes, thereby achieving the stepwise separation of valuable metals.

2. The method according to claim 1, characterized in that, The waste lithium-ion battery cathode material mentioned in S1 is waste nickel-cobalt-manganese ternary lithium battery cathode material NCM, waste nickel-cobalt-aluminum ternary lithium battery cathode material NCA, waste lithium cobalt oxide battery cathode material LCO, or waste lithium nickel oxide cathode material NCO.

3. The method according to claim 1, characterized in that, The organic acid described in S1 is an organic acid with an α-hydroxy or enol structure, which can be excited to generate reducing free radicals under external light field irradiation.

4. The method according to claim 3, characterized in that, The organic acid is at least one of citric acid, oxalic acid, tartaric acid, malic acid, and ascorbic acid; the concentration of the organic acid leachate is 0.5~3.0 mol / L.

5. The method according to claim 1, characterized in that, The light source of the external light field described in S1 emits a dominant wavelength range of 250–800 nm and has a light intensity of 150–600 mW / cm². 2 The irradiation time is 90~240 min.

6. The method according to claim 1, characterized in that, The reaction temperature for leaching valuable metal ions from the cathode material described in S1 is 25~70℃, the stirring rate is 200~600 rpm, and the liquid-to-solid ratio of the system is 15~50 mL / g.

7. The method according to claim 1, characterized in that, The alkaline solution used to adjust the pH in S2 causes different metal-organic acid salts to precipitate sequentially by adjusting the pH of the system in steps, including: adjusting the pH to 3.5~4.5 to precipitate iron and aluminum impurities, adjusting the pH to 6.5~8.0 to precipitate manganese, adjusting the pH to 8.5~10.0 to precipitate cobalt, adjusting the pH to 10.5~12.0 to precipitate nickel, and finally recovering lithium ions through concentration and crystallization.

8. The method according to claim 7, characterized in that, The alkaline solution is a NaOH solution with a concentration of 5 mol / L.

9. The method according to claim 1, characterized in that, In S2, the system temperature is changed to a low temperature of 0~10℃ to promote the crystallization of metal-organic acid complexes and achieve separation.

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