A method for recycling valuable elements from waste lithium-ion battery cathode materials

Abstract

This invention belongs to the field of electronic waste recycling and resource recovery technology, and relates to a method for recycling valuable elements from the positive electrode material of spent lithium-ion batteries. The invention uses graphite from the negative electrode obtained from dismantling spent batteries as a reducing agent, which is mixed with positive electrode material powder and then subjected to controlled carbothermic reduction in a non-oxidizing atmosphere. This process directionally converts high-valence transition metals in the positive electrode into low-valence oxides, and lithium into water-soluble lithium salts. Subsequently, lithium is preferentially leached with pure water under low-temperature, closed conditions, yielding a lithium solution and filter residue rich in nickel, cobalt, and manganese. The filter residue is then gently leached with an aqueous deep eutectic solvent to recover nickel, cobalt, and manganese. Finally, a nickel-cobalt-manganese oxalate precursor is prepared by oxalic acid precipitation, and the deep eutectic solvent is regenerated and recycled by atmospheric distillation. This invention achieves preferential lithium recovery and gentle leaching of transition metals through precise phase control, with no added reducing agents, no harmful gas emissions, and a closed-loop solvent cycle throughout the process, combining resource recovery efficiency with environmental and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of electronic waste recycling and resource utilization technology, specifically relating to a method for recycling valuable elements from waste lithium-ion battery cathode materials. Background Technology

[0002] In recent years, the rapid growth of the electric vehicle market has led to a continuous increase in the installed capacity of lithium-ion batteries, resulting in a corresponding increase in the number of retired batteries. It is estimated that by 2050, the total amount of retired lithium-ion batteries globally may reach 381 million tons. This includes spent lithium-ion battery cathode materials (such as LiCoO2, LiNiO2, LiMn2O4, LiNi...). x Co y Mn 1-x-y O2 contains valuable metals such as lithium, nickel, cobalt, and manganese, and its efficient recycling is of great significance for resource recycling and environmental protection.

[0003] Currently, the recovery of valuable metals from spent lithium-ion batteries mainly relies on three technical approaches: pyrometallurgy, hydrometallurgy, and direct regeneration. The common principle of these methods is to disrupt the crystal structure of the material by lowering the high valence state of transition metals. Pyrometallurgy offers a compact process, high processing efficiency, and strong adaptability to fluctuations in raw material composition; however, most lithium ends up in the slag and is not recovered (ACS Sustainable Chemistry & Engineering, 2018, 6, 1504-1521). Hydrometallurgy can achieve higher metal recovery rates, but its core leaching step typically relies on the combined use of high-concentration inorganic acids and reducing agents (such as H₂O₂). Lithium and transition metals enter the solution simultaneously, resulting in lithium dispersion and loss during subsequent separation, and also generating harmful gases and acidic wastewater. Direct regeneration aims to restore the electrochemical performance of the cathode material, but it has strict requirements for raw material uniformity and is difficult to apply to spent battery materials with complex compositions (Joule, 2024, 8, 1364-1379).

[0004] Carbothermal reduction technology has attracted attention as an improved solution. This technology mixes the cathode material with a carbonaceous reducing agent and calcines it in a non-oxidizing atmosphere, converting the cathode material into water-leached Li₂CO₃, Li₂O, and transition metals or low-valence oxides, thus avoiding the consumption of external reducing agents during acid leaching. However, existing carbothermal reduction processes generally use high calcination temperatures (>700℃), causing Ni and Co to be reduced to their metallic state (Angewandte Chemie International Edition, 2023, 135, e202300074). During subsequent acid leaching, metallic Ni and Co react with acid to generate flammable and explosive H₂ gas (Journal of Cleaner Production, 2022, 386, 135831); simultaneously, Li₂CO₃ may volatilize or decompose at high temperatures. Furthermore, carbothermal reduction products often involve co-leaching all metals in a single step with inorganic acids or deep eutectic solvents, resulting in lithium and transition metals entering the solution simultaneously, with lithium being dispersed and lost during subsequent separation.

[0005] Deep eutectic solvents are considered potential green leaching media due to their low volatility, designability, and metal coordination ability. In recent years, studies have attempted to use deep eutectic solvents for the extraction of metals from spent lithium-ion battery cathode materials. Patent CN121951229A discloses a ternary deep eutectic solvent composed of choline chloride, oxalic acid, and ascorbic acid, which can selectively leach lithium at 60-120℃ for 6-15 minutes under high water content (35-60%) conditions, but transition metals (Ni, Co, Mn) remain in the residue without further recovery. Patent CN121913558A discloses a deep eutectic solvent formulated with betaine hydrochloride as a hydrogen bond acceptor and L-tartaric acid as a hydrogen bond donor. Utilizing the difference in solubility of different metal tartrates, it achieves in-situ separation of lithium and transition metals at 95-200℃. However, this process requires high leaching temperatures and two precipitation processes—hot filtration and cooling—to separately recover the transition metals and lithium. Deep eutectic solvent processes generally suffer from leaching temperatures exceeding 90°C and solid-liquid ratios below 20 g / g, limiting processing efficiency. Furthermore, most deep eutectic solvents directly leach the original cathode material, failing to synergize with steps such as carbothermal reduction pretreatment and lithium preferential extraction, resulting in a lengthy overall process or incomplete separation of lithium from transition metals.

[0006] In summary, existing technologies for recycling cathode materials from waste lithium-ion batteries suffer from problems such as high energy consumption, low lithium recovery rate, harsh leaching conditions, and high risk of secondary pollution. Summary of the Invention

[0007] The purpose of this invention is to overcome the defects of the prior art and provide a method for recycling valuable elements from waste lithium-ion battery cathode materials.

[0008] Existing recycling technologies for spent lithium-ion battery cathode materials generally suffer from high energy consumption, low lithium recovery rates, stringent leaching conditions, and significant risks of secondary pollution. The core reason for this is that traditional recycling processes require the introduction of external reducing agents and rely on high-temperature roasting. To address this, this invention fully utilizes the carbon source within the spent batteries themselves as an intrinsic reducing agent, enabling selective and preferential separation of lithium elements under low-temperature roasting conditions. This not only significantly reduces recycling energy consumption but also effectively avoids secondary pollution problems introduced by added chemical reagents. Based on an integrated recycling approach involving in-situ reduction of negative electrode graphite, precise phase control, and gentle leaching with a water-containing deep eutectic solvent, this invention constructs a simple, high-recovery, green, low-carbon, and solvent-recyclable method for recovering valuable elements from spent lithium-ion battery cathode materials, systematically overcoming the aforementioned shortcomings.

[0009] The objective of this invention can be achieved through the following technical solutions: A method for recycling valuable elements from spent lithium-ion battery cathode materials includes the following steps: S1. Pretreatment: The waste lithium-ion batteries are pretreated to obtain positive electrode material powder and negative electrode graphite powder respectively. S2. Controllable carbothermal reduction: The positive electrode material powder and the negative electrode graphite powder are mixed and carbothermal reduction reaction is carried out under a non-oxidizing atmosphere to obtain thermal reaction products. S3. Low-Temperature Water Immersion Lithium Extraction: The thermal reaction product is mixed with ultrapure water and leached under low-temperature, closed conditions to selectively dissolve the lithium-containing components. After solid-liquid separation, a lithium-containing solution and a filter residue rich in valuable metals such as nickel, cobalt, and manganese are obtained. Based on the high solubility of lithium salts at low temperatures, selective lithium extraction is achieved. The resulting lithium-containing solution is concentrated by evaporation and crystallization to recover Li2CO3. The recovered Li2CO3 can be purified and used directly as a lithium source for lithium-ion battery cathodes, or it can be converted into lithium hydroxide or further processed to prepare electrolyte lithium salts. The low-purity crude product can also be used in industrial fields such as glass, ceramics, and aluminum electrolysis, realizing the graded closed-loop utilization of lithium resources.

[0010] S4. Mild leaching: The valuable metal filter residue is mixed with a deep eutectic solvent and leached at 40~60°C to dissolve the nickel, cobalt and manganese in the filter residue in the deep eutectic solvent. The nickel-cobalt-manganese leaching solution is obtained by solid-liquid separation. S5. Solvent Regeneration: An aqueous oxalic acid solution is added to the nickel-cobalt-manganese leaching solution to precipitate a nickel-cobalt-manganese oxalate precursor. The filtered filtrate is recovered by distillation to regenerate the deep eutectic solvent, achieving its recycling. The obtained nickel-cobalt-manganese oxalate precipitate is washed, dried, and calcined at high temperature to obtain a nickel-cobalt-manganese ternary cathode material, which can be directly used in the preparation of lithium-ion battery electrodes, realizing closed-loop regeneration of nickel-cobalt-manganese resources.

[0011] Further, the pretreatment in step S1 includes: discharging and disassembling the waste lithium-ion battery to obtain positive electrode sheets and negative electrode sheets respectively; crushing, grinding and sieving the positive electrode sheets to obtain positive electrode material powder; and heat-treating the negative electrode sheets under an inert atmosphere to remove glue, crush and sieve to obtain negative electrode graphite powder.

[0012] Furthermore, the heat treatment temperature is 450~550℃.

[0013] Further, in step S2, the mass ratio of the positive electrode material powder to the negative electrode graphite powder is 1:0.07~1:0.10; the temperature of the carbothermic reduction reaction is 550~700℃, and the reduction reaction time is 2.5~3.5 hours; the non-oxidizing atmosphere is argon or nitrogen atmosphere.

[0014] Preferably, the mass ratio of the positive electrode material powder to the negative electrode graphite powder is 1:0.075; the carbothermic reduction reaction time is 3 hours; and the non-oxidizing atmosphere is a nitrogen atmosphere.

[0015] In step S2, by adjusting the amount of graphite and the temperature of the carbothermic reduction reaction, the partial pressure of oxygen and carbon monoxide in the system are controlled, so that the high-valence transition metals (Ni, Co, Mn) in the cathode material are selectively reduced to low-valence oxides NiO, CoO, and MnO, and lithium is simultaneously converted into water-soluble Li2O and Li2CO3.

[0016] Furthermore, the temperature of the low-temperature water immersion in step S3 is 5~15℃, preferably 5℃, the liquid-to-solid ratio is 20~50mL / g, preferably 20 mL / g, the water immersion time is 50~120 min, preferably 60 min, and CO2 is isolated during immersion.

[0017] Furthermore, in step S4, the deep eutectic solvent comprises a hydrogen bond acceptor, a hydrogen bond donor, and a diluent.

[0018] Furthermore, the hydrogen bond acceptor is choline chloride; the hydrogen bond donor is citric acid or lactic acid, preferably citric acid; and the diluent is water. The molar ratio of hydrogen bond acceptor, hydrogen bond donor, and diluent in the deep eutectic solvent is 1:1:2 to 1:1:6, preferably 1:1:4.

[0019] The deep eutectic solvent is an aqueous deep eutectic system, with water added as a diluent to reduce solvent viscosity, improve mass transfer, and not damage the hydrogen bond coordination structure.

[0020] Furthermore, in step S4, the leaching temperature is 40~60℃, the leaching time is 5~12 hours, preferably 8 hours, and the solid-liquid ratio is 1:5~1:10 g / g, preferably 1:8 g / g.

[0021] Further, in step S5, the ratio of the oxalic acid to the total molar amounts of nickel, cobalt, and manganese in the nickel-cobalt-manganese leaching solution is (1.5~2.5):1, preferably 2:1.

[0022] Further, in step S5, the distillation is a stepwise atmospheric distillation. First, the distillation is carried out at 80~100℃ for 2~4 hours with stirring to remove most of the water introduced during the oxalic acid precipitation process. Then, the distillation is carried out at 140~160℃ for 2~4 hours with stirring to remove the residual oxalic acid and the remaining water.

[0023] Preferably, the stepwise atmospheric distillation is performed by first stirring at 90°C for 3 hours, and then stirring at 150°C for 3 hours.

[0024] It should be noted that the coexistence of lithium (Li), nickel (Ni), cobalt (Co), and manganese (Mn) is only a preferred application scenario of this invention and is not a limiting condition for the scope of protection. Any material containing lithium as a valuable metal and also containing one or more of nickel, cobalt, and manganese falls within the protection scope of the method of this invention and is not subject to the constraint of the simultaneous existence of the four metals.

[0025] Compared with the prior art, the present invention has the following beneficial effects: First, this invention directly uses negative electrode graphite powder obtained from the dismantling of waste batteries as the sole carbon source for carbothermic reduction, without the need for externally purchased reducing agents, thus realizing the resource utilization of battery negative electrode solid waste and "treating waste with waste".

[0026] Secondly, this invention employs low-temperature pure water leaching for lithium extraction after carbothermic reduction. Precise phase control converts lithium into water-soluble lithium salts while retaining transition metals as water-insoluble low-valence oxides, thus achieving solid-liquid separation of lithium from nickel, cobalt, and manganese. Existing technologies generally use acid or deep eutectic solvents for one-time co-leaching of all metals, resulting in lithium and transition metals entering the solution simultaneously, leading to low lithium recovery rates. This invention avoids lithium dispersion loss through a stepwise recovery strategy of "lithium first, then transition metals." Experiments show that under conditions of 5°C, a liquid-to-solid ratio of 20 mL / g, and CO2 isolation, a single leaching rate of lithium reaches 96.5% after 60 min.

[0027] Third, this invention targets the filter residue after lithium removal, employing a specific composition and ratio of aqueous deep eutectic solvent to selectively leach nickel, cobalt, and manganese under mild conditions (40-60℃, 1:5-1:10 g / g). Compared to existing deep eutectic solvents that directly leach the original cathode material (requiring >90℃ and a solid-liquid ratio ≤1:20 g / g), this invention reduces the leaching temperature by 30-50℃, increases the solid-liquid ratio by 2-4 times, and significantly improves processing efficiency. Under optimized conditions (50℃, solid-liquid ratio 1:8 g / g, 8 h), the leaching efficiencies for nickel, cobalt, and manganese reach 96.7%, 98.4%, and 100.0%, respectively. This solvent system can be recycled through an oxalic acid precipitation-stepwise distillation process. After three cycles, the leaching efficiencies for nickel, cobalt, and manganese remain at 88.6%, 87.6%, and 91.5%, respectively, effectively reducing reagent consumption and secondary pollution.

[0028] Fourth, this invention produces no harmful gases (such as CO and fluoride gases) or highly acidic / alkaline wastewater throughout the entire process, making it a green and low-carbon recycling process. Techno-economic analysis and life cycle assessment based on the EverBatt 2023 model show that the unit profit of this invention is RMB 63.5 / kg, higher than hydrometallurgy (RMB 58.6 / kg), direct recycling (RMB 48.7 / kg), and pyrometallurgy (RMB 33.1 / kg). The revenue from the recycled products reaches RMB 115.9 / kg (estimated at the current exchange rate of 1 USD ≈ RMB 6.8157); greenhouse gas emissions are 844 g·kg. -1 The energy consumption is 20.8 MJ·kg -1 .

[0029] The aforementioned distinguishing features are not a simple combination of existing technologies, but a systematic innovation centered around the overall technical concept of "precise phase control - stepwise selective separation - gentle leaching with green solvent - solvent recycling". Each step is synergistic and indispensable, achieving unexpected technical results. Attached Figure Description

[0030] Figure 1 This is a phase stability region diagram of the main compounds in the Ni-Li-CO system at 650℃ in Example 1 of the present invention, showing the changes in oxygen partial pressure (log[P(O2) / atm]) and carbon monoxide partial pressure (log[P(CO) / atm]). Figure 2 This is a phase stability region diagram of the main compounds in the Co-Li-CO system at 650℃ in Example 1 of the present invention, showing the changes in oxygen partial pressure (log[P(O2) / atm]) and carbon monoxide partial pressure (log[P(CO) / atm]). Figure 3This is a phase stability region diagram of the main compounds in the Mn-Li-CO system at 650℃ in Example 1 of the present invention, showing the changes in oxygen partial pressure (log[P(O2) / atm]) and carbon monoxide partial pressure (log[P(CO) / atm]). Figure 4 The XPS fine spectra of the waste NCM cathode material and the product after carbothermal reduction (650℃, 3h, graphite addition 7.5wt%) in Example 1 of this invention are shown, where (a) Ni 2p; (b) Co 2p; (c) Mn 2p. Figure 5 This is a curve showing the effect of different water immersion temperatures, water immersion times, and liquid-to-solid ratios on the lithium leaching efficiency in the carbothermic reduction products in Example 1 of the present invention. (a) Leaching temperature (20 mL·g) -1 (a) 60 min); (b) leaching time (20 mL·g -1 (c) Liquid-to-solid ratio (15 ℃, 60 min); Figure 6 The curves showing the leaching efficiency of valuable metals (Ni, Co, Mn) in the water-leached filter residue by the deep eutectic solvent (ChCl:CA:H2O=1:1:4, 50℃) in Example 1 of the present invention are as follows: Figure 7 This is the result of linear fitting of the leaching process of Ni and Co in deep eutectic solvent based on the solid product layer diffusion control model in Example 1 of the present invention. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0032] Unless otherwise specified, all raw materials used in this invention are commercially available products.

[0033] This invention uses graphite from the dismantled waste batteries as a reducing agent, which is mixed with positive electrode material powder and then subjected to controlled carbothermic reduction in a non-oxidizing atmosphere. This process directionally converts high-valence transition metals in the positive electrode into low-valence oxides and lithium into water-soluble lithium salts. Subsequently, lithium is preferentially leached with pure water under low-temperature, closed-loop conditions, yielding a lithium solution and a filter residue rich in valuable metals such as nickel, cobalt, and manganese. The filter residue is then gently leached with a hydrous deep eutectic solvent to efficiently recover nickel, cobalt, and manganese. Finally, a nickel-cobalt-manganese oxalate precursor is prepared by oxalic acid precipitation, and the deep eutectic solvent is regenerated and recycled using stepwise atmospheric distillation. This invention achieves preferential lithium recovery and gentle leaching of transition metals through precise phase control. The entire process requires no external reducing agent, produces no harmful gas emissions, and allows for closed-loop solvent recycling, resulting in significant resource utilization efficiency, economic benefits, and environmental benefits.

[0034] It should be noted that the following embodiments only use citric acid as a representative hydrogen bond donor for verification. However, other hydrogen bond donors such as lactic acid, based on the same leaching mechanism, can also achieve the mild and efficient leaching effect of the present invention, and they are technical solutions that can be directly and equivalently replaced by citric acid by those skilled in the art.

[0035] Example 1 A method for recycling valuable elements from spent lithium-ion battery cathode materials, the specific steps of which are as follows: S1. LiNi was obtained from the dismantling of ternary lithium battery packs from discarded new energy vehicles. x Co y Mn 1-x-y O2 (NCM) positive and negative electrode sheets. The positive electrode sheet was crushed, ground, and passed through a 150-mesh sieve to obtain positive electrode material powder. Inductively coupled plasma optical emission spectrometry (ICP-OES) analysis revealed the following mass percentage contents of each metal element in the positive electrode material powder: Li 7.70 wt%, Ni 19.83 wt%, Co 19.89 wt%, Mn 15.71 wt%.

[0036] The negative electrode sheet was heat-treated at 500℃ for 30 minutes and then sieved through a 150-mesh screen to obtain negative electrode graphite powder. The carbon content was determined to be 99.47 wt% by a carbon-sulfur analyzer.

[0037] S2. The positive electrode material powder obtained in step S1 and the negative electrode graphite powder are mixed evenly at a mass ratio of 1:0.075, placed in a tube furnace, heated to 650°C at a heating rate of 8°C / min under the protection of high-purity argon, and kept at the temperature for 3 hours. After the reaction is completed, it is cooled to room temperature under the argon flow to obtain the carbothermic reaction product.

[0038] The core of this step lies in utilizing thermodynamic phase diagrams ( Figures 1-3 It can precisely guide the carbothermic reduction conditions to achieve selective control of the product phase. Figures 1-3 The stability regions of each condensed phase in the Ni-OC, Co-OC, and Mn-OC systems at equilibrium with Li2O / Li2CO3 at 650℃ are shown, respectively, as a function of oxygen partial pressure (log[P(O2) / atm]) and carbon monoxide partial pressure (log[P(CO) / atm]). Figure 1Taking the Ni-Li-CO system as an example, when the oxygen partial pressure and carbon monoxide partial pressure are low, nickel exists as metallic Ni(s); while when the oxygen partial pressure increases, it exists as NiO(s). Different regions in the diagram correspond to different stable phases (such as metals, low-valence oxides, high-valence oxides, carbonates, etc.), used to determine the stability window of low-valence oxides to guide the determination of optimal reduction conditions (graphite dosage, atmosphere) and avoid the formation of elemental metals. The desired product of this invention is a low-valence oxide (NiO, CoO, MnO) rather than an elemental metal, because elemental metals significantly increase the difficulty of subsequent deep eutectic solvent leaching and pose safety risks. Therefore, the reaction conditions must be controlled within the corresponding "low-valence oxide stability region" in the phase diagram.

[0039] To achieve this goal, a suitable reduction temperature must first be selected. In this embodiment, 650℃ is chosen because Li₂CO₃ does not undergo significant decomposition at this temperature (it decomposes easily above 800℃), and the reduction kinetics of transition metal oxides are moderate. Secondly, by adjusting the mixing ratio of the positive electrode material to the negative electrode graphite (1:0.075 in this embodiment), the oxygen consumption capacity of the reduction reaction can be quantitatively controlled. Graphite, as a reducing agent, mainly undergoes the reactions: C + O₂ → CO₂ and C + CO₂ → 2CO, thereby controlling the partial pressure of oxygen and carbon monoxide in the system. According to the phase diagram, when the amount of graphite is too small (below 1:0.07), the oxygen partial pressure is insufficiently reduced, and the system may still fall into the high-valence oxide region; when the amount of graphite is too large (above 1:0.10), the carbon monoxide partial pressure is too high, and the system may enter the metallic elemental region. The preferred 1:0.075 ratio in this embodiment, as tested experimentally, ensures that the effective oxygen partial pressure and carbon monoxide partial pressure in the reaction system are in a high proportion within the range of... Figures 1-3 The system utilizes a "window region" where NiO, CoO, and MnO coexist. Simultaneously, high-purity argon is used as a protective atmosphere to further eliminate interference from external oxygen. Figure 4 XPS analysis results confirmed that after reduction at 650℃, Ni, Co, and Mn mainly exist in the form of divalent oxides, consistent with thermodynamic predictions, indicating that the phase control strategy of this invention is successful.

[0040] S3. The carbothermic reaction product obtained in S2 is mixed with ultrapure water at a liquid-to-solid ratio of 20 mL / g, and leached with stirring at 5°C for 60 min. CO2 must be isolated during the leaching process to prevent Li2CO3 from redepositing and reducing the lithium leaching rate. After the reaction, the mixture is vacuum filtered to obtain a lithium-containing solution and a filter residue rich in valuable metals such as nickel, cobalt, and manganese. Figure 5The results of water leaching experiments were presented for NCM reduction products with a graphite addition of 0.75 wt% (i.e., NCM:graphite = 1:0.0075), after calcination at 650 °C for 3 h. Under the optimal conditions of a liquid-to-solid ratio of 20 mL / g, a leaching time of 60 min, and a temperature of 5 °C, the lithium leaching efficiency reached 96.5%. After water leaching, the mixture was vacuum filtered. The filter residue was washed three times with ultrapure water and dried at 60 °C for 24 h to obtain a solid residue rich in nickel, cobalt, and manganese, which was used for subsequent processing. To recover lithium, the leachate was evaporated and concentrated to approximately 20% of its original volume in a 100 °C water bath. The resulting white precipitate was collected by filtration, washed with boiling water, and dried to finally obtain Li₂CO₃ powder.

[0041] S4. Mix choline chloride (ChCl), citric acid (CA), and ultrapure water in a molar ratio of 1:1:4 and stir at a constant temperature of 60°C until a homogeneous and transparent liquid is formed, which is denoted as ChCl-CA-H2O (1:1:4).

[0042] S5. The filter residue rich in valuable metals such as nickel, cobalt, and manganese obtained in S3 is mixed with the ChCl-CA-H2O (1:1:4) prepared in S4 at a solid-liquid ratio of 1:8 g / g, and leached at 50℃ for 8 hours. After the reaction is completed, the mixture is filtered and separated to obtain a leachate containing Ni, Co, and Mn and a small amount of solid residue. Figure 6 The results showed that after leaching at 50°C for 8 hours, the leaching efficiencies of Ni, Co, and Mn reached 96.7%, 98.4%, and 100.0%, respectively. Figure 7 The kinetic fitting results show that the leaching process of Ni and Co is controlled by diffusion of the solid product layer, which is consistent with the coordination leaching mechanism of the deep eutectic solvent used.

[0043] S6. Collect the filtrate after leaching. Add an oxalic acid aqueous solution (0.7M concentration, oxalic acid to total molar ratio of Ni, Co, and Mn in the filtrate: 2:1) to the filtrate and react with stirring at 75°C to precipitate the nickel-cobalt-manganese oxalate precursor. After filtration, stir the filtrate at 90°C for 3 hours, then at 150°C for 3 hours, and perform stepwise distillation to remove water and excess oxalic acid, obtaining regenerated deep eutectic solvent. Use the regenerated deep eutectic solvent for leaching a new batch of filter residues rich in valuable metals such as nickel, cobalt, and manganese. Under the same conditions, the leaching efficiencies for Ni, Co, and Mn are 96.1%, 98.9%, and 99.9% (first cycle), respectively. After three cycles, the leaching efficiencies remain at 88.6% for Ni, 87.6% for Co, and 91.5% for Mn. Further recovery is possible by adding a small amount of citric acid.

[0044] Example 2 A method for recycling valuable elements from waste lithium-ion battery cathode materials is disclosed. The specific steps are basically the same as in Example 1, except that the carbothermic reduction temperature in step S2 is 550℃, and the holding time is 3.5 hours. Testing showed that the lithium leaching efficiency in this example was 91.2%; after leaching with a deep eutectic solvent, the leaching efficiencies for Ni, Co, and Mn were 95.1%, 96.8%, and 99.5%, respectively.

[0045] Example 3 A method for recycling valuable elements from waste lithium-ion battery cathode materials has the same specific steps as in Example 1, except that the carbothermal reduction temperature in step S2 is 700°C and the holding time is 2.5 hours.

[0046] XRD analysis showed that Ni, Co, and Mn in the thermal reaction products mainly existed as divalent oxides (NiO, CoO, MnO), and no obvious diffraction peaks of metallic Ni or Co were detected, indicating that selective reduction to the target low-valence oxides could still be achieved at this temperature. The lithium leaching efficiency was measured to be 92.8%. After leaching with a deep eutectic solvent, the leaching efficiencies of Ni, Co, and Mn were 94.6%, 95.3%, and 99.2%, respectively. These were slightly lower than the 96.7%, 98.4%, and 100.0% of Example 1 (650℃), but still remained at a high level, indicating that the reduction temperature of 700℃ was still within the effective range and could support the mild leaching and lithium-preferred recovery process of this invention.

[0047] Example 4 A method for recycling valuable elements from waste lithium-ion battery cathode materials is disclosed. The specific steps are essentially the same as in Example 1, except that in step S4, the deep eutectic solvent is prepared using choline chloride, lactic acid, and ultrapure water in a molar ratio of 1:1:4 (ChCl-LA-H2O, 1:1:4). Testing showed that the leaching efficiencies for Ni, Co, and Mn were 94.5%, 96.2%, and 98.8%, respectively, close to those of the citric acid system, indicating that lactic acid can also serve as an effective hydrogen bond donor.

[0048] Comparative Example 1 A method for recovering valuable elements from waste lithium-ion battery cathode materials is disclosed. The specific steps are essentially the same as in Example 1, except that the carbothermic reduction treatment in step S2 and the lithium extraction by water extraction in step S3 are omitted. Instead, the cathode material powder is directly leached under the same deep eutectic solvent conditions as in Example 1 (50°C, solid-liquid ratio 1:8, 8h). The leaching efficiencies for Ni, Co, and Mn were measured to be 72.3% for Ni, 75.1% for Co, and 78.6% for Mn. This indicates that the untreated NCM layered structure is stable and cannot be efficiently leached by the deep eutectic solvent under mild conditions.

[0049] Comparative Example 2 A method for recovering valuable elements from waste lithium-ion battery cathode materials employs essentially the same carbothermal reduction conditions as in Example 1, but at a reduction temperature of 800°C, yielding a product containing elemental Ni and Co. The product is then leached using a conventional hydrometallurgical method: a 1.5 mol / L sulfuric acid solution is used at 60°C, with H₂O₂ added as a reducing agent to promote acid leaching.

[0050] The specific steps are as follows: S1. LiNi was obtained from the dismantling of ternary lithium battery packs from discarded new energy vehicles. x Co y Mn 1-x-y O2 (NCM) positive and negative electrode sheets were prepared. The positive electrode sheet was crushed, ground, and passed through a 150-mesh sieve to obtain positive electrode material powder. Inductively coupled plasma optical emission spectrometry (ICP-OES) analysis revealed the following mass percentages of metal elements in the positive electrode material powder: Li 7.70 wt%, Ni 19.83 wt%, Co 19.89 wt%, and Mn 15.71 wt%. The negative electrode sheet was heat-treated at 500℃ for 30 minutes and then vibrated through a 150-mesh sieve to obtain negative electrode graphite powder. Carbon and sulfur analysis showed that the carbon content of this graphite powder was 99.47 wt%.

[0051] S2. The positive electrode material powder obtained in step S1 is mixed with the negative electrode graphite powder at a mass ratio of 1:0.075. The mixture is placed in a tube furnace and heated to 800°C at a heating rate of 8°C / min under the protection of high-purity argon. The mixture is kept at this temperature for 3 hours. After the reaction is completed, the mixture is cooled to room temperature under an argon flow to obtain a reduction product containing metals Li, Ni, Co, and Mn.

[0052] S3. The reduction product obtained in step S2 is leached at 60 °C with a 1.5 mol / L sulfuric acid solution, and 5 vol% H2O2 is added as a reducing agent. The leaching time is 3 h, and the liquid-to-solid ratio is 6 mL / g. Although the leaching efficiency of Ni, Co, and Mn can reach over 98%, this process consumes a large amount of strong acid, causing corrosion to the equipment and generating acidic wastewater and a large amount of hydrogen gas, resulting in poor environmental friendliness.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., 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 recycling valuable elements from waste lithium-ion battery cathode materials, characterized in that, Includes the following steps: S1. Pretreatment: The waste lithium-ion batteries are pretreated to obtain positive electrode material powder and negative electrode graphite powder respectively. S2. Controllable carbothermal reduction: The positive electrode material powder and the negative electrode graphite powder are mixed and carbothermal reduction reaction is carried out under a non-oxidizing atmosphere to obtain thermal reaction products. S3. Low-temperature water leaching for lithium extraction: The thermal reaction product is mixed with ultrapure water and leached under low-temperature and closed conditions. After solid-liquid separation, a lithium-containing solution and a filter residue rich in valuable metals such as nickel, cobalt, and manganese are obtained. S4. Mild leaching: The valuable metal filter residue is mixed with a deep eutectic solvent and leached at 40~60℃. After solid-liquid separation, a nickel-cobalt-manganese leaching solution is obtained. S5. Solvent regeneration: Add oxalic acid aqueous solution to the nickel-cobalt-manganese leaching solution to precipitate nickel-cobalt-manganese oxalate precursor; the filtered filtrate is recovered by distillation to regenerate the deep eutectic solvent.

2. The method for recycling valuable elements from waste lithium-ion battery cathode materials according to claim 1, characterized in that, The pretreatment in step S1 includes: discharging and disassembling the waste lithium-ion battery to obtain positive electrode sheets and negative electrode sheets respectively; crushing, grinding and sieving the positive electrode sheets to obtain positive electrode material powder; and heat-treating the negative electrode sheets in an inert atmosphere to remove glue, crush and sieve to obtain negative electrode graphite powder.

3. The method for recycling valuable elements from waste lithium-ion battery cathode materials according to claim 2, characterized in that, The heat treatment temperature is 450~550℃.

4. The method for recycling valuable elements from waste lithium-ion battery cathode materials according to claim 1, characterized in that, In step S2, the mass ratio of the positive electrode material powder to the negative electrode graphite powder is 1:0.07 to 1:0.10; the temperature of the carbothermic reduction reaction is 550 to 700°C, and the reduction reaction time is 2.5 to 3.5 hours; the non-oxidizing atmosphere is argon or nitrogen atmosphere.

5. The method for recycling valuable elements from waste lithium-ion battery cathode materials according to claim 1, characterized in that, The temperature of the low-temperature water immersion in step S3 is 5~15℃, the liquid-to-solid ratio is 20~50 mL / g, the immersion time is 50~120 min, and CO2 is isolated during immersion.

6. The method for recycling valuable elements from waste lithium-ion battery cathode materials according to claim 1, characterized in that, In step S4, the deep eutectic solvent comprises a hydrogen bond acceptor, a hydrogen bond donor, and a diluent.

7. The method for recycling valuable elements from waste lithium-ion battery cathode materials according to claim 6, characterized in that, The hydrogen bond acceptor is choline chloride; the hydrogen bond donor is citric acid or lactic acid; the diluent is water. The molar ratio of hydrogen bond acceptor, hydrogen bond donor, and diluent in the deep eutectic solvent is 1:1:2 to 1:1:

6.

8. The method for recycling valuable elements from waste lithium-ion battery cathode materials according to claim 1, characterized in that, In step S4, the leaching temperature is 40~60℃, the leaching time is 5~12 hours, and the solid-liquid ratio is 1:5~1:10g / g.

9. The method for recycling valuable elements from waste lithium-ion battery cathode materials according to claim 1, characterized in that, In step S5, the ratio of the oxalic acid to the total molar amounts of nickel, cobalt, and manganese in the nickel-cobalt-manganese leaching solution is (1.5~2.5):

1.

10. The method for recycling valuable elements from waste lithium-ion battery cathode materials according to claim 1, characterized in that, In step S5, the distillation is a stepwise atmospheric distillation, firstly by stirring and distilling at 80~100℃ for 2~4 hours, and then by stirring and distilling at 140~160℃ for 2~4 hours.

Images