Method for selectively recovering metal elements in waste batteries by using functionalized deep eutectic solvent

Abstract

The application provides a method for selectively recovering metal elements in waste batteries by using a functional deep eutectic solvent, which comprises the following steps: mixing choline chloride, phosphoric acid and a choline hydroxide solution to obtain a deep eutectic solvent DES; pretreating a positive electrode of a waste lithium iron phosphate (LFP) battery and a waste lithium cobalt oxide (LCO) battery; and immersing the positive electrode in the deep eutectic solvent DES to make Li + enriched into the leaching solution, Fe is converted into FePO4 and left in the residue, and then cobalt is recovered by "ethanol-induced precipitation", lithium is recovered by "pH-controlled precipitation", and the DES is regenerated. 2+ This method realizes the closed loop of lithium iron phosphate and lithium cobalt oxide battery recycling in a green and economic way through the strategies of segmented targeted leaching and selective coordination precipitation, combined with solvent regeneration.

Description

Technical Field

[0001] This invention belongs to the field of waste lithium-ion battery recycling technology, and relates to a type of deep eutectic solvent selective leaching and closed-loop regeneration technology, specifically a method for selectively recovering metal elements from waste batteries using functionalized deep eutectic solvents. Background Technology

[0002] After the differentiation of the power and energy storage markets, lithium iron phosphate (LFP) batteries have accounted for more than 60% of electric vehicle installations due to their cost and safety advantages, while lithium cobalt oxide (LCO) remains the mainstream in high-end consumer electronics. The two types of waste batteries are emerging in parallel. The current recycling route faces three common problems: (1) poor selectivity: traditional acid leaching has no difference in destroying the Fe-P bond of LFP and the Co-O bond of LCO, resulting in co-dissolution of cobalt and iron, which requires cumbersome extraction and separation in the future; (2) economic imbalance: LFP does not contain precious metals and relies on scale to reduce costs, while LCO requires high-purity cobalt recycling, which cannot be achieved by a single process; (3) product degradation: Fe, Co and Li coexist in the mixed leachate, and the co-precipitation purity is <95%, which cannot be used directly as a battery-grade precursor and must be purified twice. Although DES has been studied in a single system, it is difficult to study the Co in the mixed solution. 2+ Fe 2+ Li + Due to the lack of selective coordination, one-step separation cannot be achieved.

[0003] Therefore, a synergistic recovery method integrating segmented targeted leaching, selective coordination precipitation, and solvent self-circulation is needed to enable both types of battery materials to be reused in a closed loop while meeting the requirements of green and low-cost operation. This invention fills this gap by combining co-selective DES leaching, iron fixation, and sequential Co / Li precipitation. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for selectively recovering metal elements from waste batteries using a functionalized deep eutectic solvent, which addresses the shortcomings of the prior art. This method achieves a closed loop for the recovery of lithium iron phosphate (LFP) and lithium cobalt oxide (LCO) in a green and economical manner through a stepwise, targeted selective leaching and coordination-precipitation strategy combined with solvent regeneration.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for selectively recovering metal elements from waste batteries using a functionalized deep eutectic solvent, comprising the following steps: Construction of S1 and DES systems Weigh out solutions of choline chloride, phosphoric acid, and choline hydroxide and add them to a reaction vessel. Stir until a colorless, transparent, viscous, and homogeneous liquid is obtained, which is the deep eutectic solvent DES. S2, Lithium-ion battery pretreatment After discharging the waste lithium iron phosphate battery modules and lithium cobalt oxide battery modules, the shells are broken and the positive electrode sheets are sorted out. The positive electrode sheets are placed in a constant temperature heat treatment at 227~277℃ for 30 minutes, and then the active powder is obtained by slight vibration or scraping. After being sieved through a 100-mesh sieve, the positive electrode black powder is obtained. S3 and DES selectively extract Li, Co, and Fe. The deep eutectic solvent obtained from S1 and the cathode black powder obtained from S2 were added to a reactor and reacted under constant temperature and stirring. Li + With Co 2 + The Fe is enriched in the leachate and converted into FePO4, which remains in the residue. S4, Serialization Precipitation and DES Regeneration Cobalt salt and lithium salt are recovered sequentially from the leachate obtained from S3, and closed-loop regeneration of DES is achieved. S401, Cobalt recovery: The leachate obtained from S3 was cooled to 5~15℃ and stirred at 200rpm. An ethanol-water mixed solvent was added dropwise. After aging for 1h, it was vacuum filtered. The precipitate was washed with ethanol-water and dried at 80℃ to obtain CoHPO4·3H2O solid. The filtrate was used for further lithium recovery. S402, Lithium Recovery: Add NaOH solution to the filtrate obtained from S401 to adjust the pH to 7.5~9.0, age at 5~15℃ for 1 hour, filter, wash with deionized water, and dry at 105℃ to obtain white battery-grade Li3PO4. The filtrate is used to regenerate DES. Regeneration of S403 and DES: The filtrate obtained from S402 is first vacuum distilled to recover the ethanol-water mixture, and the remaining liquid is supplemented with phosphoric acid to adjust the acidity, thus obtaining regenerated DES.

[0006] Preferably, the phosphoric acid in S1 is an 85% aqueous solution of phosphoric acid, the choline hydroxide solution has a mass concentration of 50%, and the molar ratio of choline chloride, phosphoric acid, and choline hydroxide is 1:2:(0.05~0.3).

[0007] Preferably, the stirring temperature in S1 is 75~85℃, the stirring speed is 200~400rpm, and the stirring time is 30~90min.

[0008] Preferably, the solid-liquid ratio of the deep eutectic solvent to the cathode black powder in S3 is 50~200g / L.

[0009] Preferably, the stirring speed in S3 is 350~500 rpm, the temperature is 90~110°C, and the time is 1.5~3h.

[0010] Preferably, in S401, the volume ratio of ethanol to water in the ethanol-water mixed solvent is 1:1, and the amount of the ethanol-water mixed solvent used is equal to the volume of the leachate.

[0011] Preferably, the concentration of the NaOH solution in S402 is 1.5~2.5 mol / L, and the dropping rate is 0.3~0.8 mL / min.

[0012] Preferably, the vacuum distillation temperature in S403 is 60~80℃ and the vacuum degree is 0.08~0.1MPa.

[0013] The method for selectively recovering metal elements from waste batteries using the functionalized deep eutectic solvent of the present invention achieves a final cobalt recovery rate of >90% and a purity of >95%; a lithium recovery rate of >99% and a purity of >98%; and iron remains in the residue in the form of FePO4 with an iron content of >95%.

[0014] This invention has significant technical advantages compared to existing technologies: This invention provides a method for selectively recovering metal elements from spent batteries using a functionalized deep eutectic solvent. The deep eutectic solvent (DES) is composed of choline chloride (ChCl), hydroxyl-functionalized choline salt (choline hydroxide), and phosphoric acid (H3PO4). The choline hydroxide component provides additional hydrogen bond donors and coordination sites ("peripheral functionalization" of the solvent) to enhance the complexity of metal ions. Co in LiCoO2 is reduced in situ using the solvent's own chloride ions at 90–110 °C and ambient pressure. 3+ →Co 2+ Simultaneously, lithium ions are leached out, and iron in LiFePO4 is converted into FePO4 residue for pre-separation. The leachate requires no external chemical reagents; the dielectric constant is adjusted using an ethanol-water solution at low temperature to induce cobalt phosphate self-precipitation. The pH is then adjusted to 7.5-9.0 to precipitate lithium phosphate. Finally, the DES is regenerated by vacuum distillation and recycled (efficiency decay <5% after 5 cycles). This forms a complete process for efficient and selective separation of lithium, cobalt, and iron, along with closed-loop solvent regeneration, under mild conditions. Compared with existing pyrometallurgical and hydrometallurgical processes, this invention has the following advantages: (1) Mild reaction conditions: The reaction temperature is 90~110°C, and the reaction is carried out at atmospheric pressure; (2) The reaction steps are simple: by combining Co 3+ A combination of selectivity achieved through reduction, Fe fixation (FePO4), and sequential phosphate precipitation; (3) High recovery rate and product quality: After mild leaching with phosphoric choline-based deep eutectic solvent (PCh-DES), selective precipitation of cobalt is achieved by low-temperature modulation of ethanol-water. Cobalt and lithium can be selectively separated without the addition of external reducing agent. The recovery rate of cobalt is >90% and the purity is >95%, while the recovery rate of lithium is >99% and the purity is >98%. (4) Solvent regeneration: It can be reused multiple times, with green closed-loop recycling and low performance loss; (5) By avoiding strong mineral acids and external oxidants, wastewater generation is reduced and the environmental burden is lessened.

[0015] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 This is a flowchart of a method for selectively recovering metal elements from waste batteries using a functionalized deep eutectic solvent, according to the present invention. Figure 2 This is a molecular structure diagram of the deep eutectic solvent (DES) of the present invention; Figure 3 The following are the mass loss situations of different sample pretreatments according to the present invention: a: sample H1, b: sample H2, c: sample H3, d: combination of samples H1, H2 and H3; Figure 4 The effects of different leaching temperatures and leaching times on the extraction efficiency of Li and Co are shown in the present invention: a: 30℃, b: 40℃, c: 50℃, d: 60℃, e: 70℃, f: 80℃, g: 90℃. Figure 5 This is a comparison of SEM images of waste lithium battery powder and XRD patterns of recycled metal products. a: XRD pattern of cobalt product, b: XRD pattern of lithium product, c: SEM pattern of lithium battery powder before leaching, d: SEM pattern of lithium battery powder after leaching. Figure 6 This invention relates to the effect of adding different concentrations of H3PO4 on the regenerated DES cycle performance, a: 1 mol / L, b: 2 mol / L, c: 4 mol / L. Detailed Implementation

[0017] This invention provides a method for selectively recovering metal elements from spent batteries using a functionalized deep eutectic solvent, see below. Figure 1 The method includes the following steps: Construction of S1 and DES systems Weigh out choline chloride (ChCl), 85% phosphoric acid aqueous solution and 50% choline hydroxide solution and put them into a reaction vessel. The molar ratio of choline chloride, phosphoric acid and choline hydroxide is 1:2:(0.05~0.3). Stir continuously for 30~90 min at 75~85℃ and 200~400 rpm. The system gradually changes from turbid to colorless, transparent, viscous and homogeneous liquid, which is the deep eutectic solvent (DES).

[0018] Figure 2The diagram shows the molecular structure of a deep eutectic solvent (DES) composed of choline chloride (ChCl), hydroxyl-functionalized choline salt (choline hydroxide), and phosphoric acid (H3PO4). This solvent forms an internal network of choline dihydrophosphate-hydrogen phosphate hydrogen bonds, while the hydroxyl functional groups provide new coordination sites on the "solvent periphery," significantly enhancing the binding of Co. 3+ / Li + Its complexing and electron transfer capabilities lay the foundation for subsequent in-situ reduction and selective leaching.

[0019] S2, Lithium-ion battery pretreatment After collecting waste lithium iron phosphate (LFP) and lithium cobalt oxide (LCO) battery modules, they are safely discharged (constant current to 0 V), and then the casings are broken open using an automated shearing device. The positive electrode sheet, negative electrode copper foil, separator, and electrolyte are then manually separated. The positive electrode sheet is placed in an oven for heat treatment, allowing the electrolyte to fully evaporate while the polyvinylidene fluoride (PVDF) binder undergoes only thermal decomposition (not carbonization), losing its adhesive strength. Subsequently, the active powder is detached from the aluminum foil substrate by slight vibration or scraping. After crushing and sieving through a 100-mesh sieve, positive electrode black powder with a particle size <100 μm is obtained.

[0020] To explore the heat treatment temperature of the positive electrode, three samples were pretreated according to the conditions in Table 1: H1: direct disassembly; H2: disassembly after heat treatment at 600℃ for 15 min; H3: disassembly after heat treatment at 600℃ for 35 min. Thermogravimetric analysis (TGA) results ( Figure 3 The results showed that due to the decomposition of the binder and additives, H1 (without high-temperature treatment) exhibited significant mass loss; H2 (600°C, 15 min) showed a marked reduction in mass loss; and H3 (600°C / 35 min) showed minimal mass loss, indicating that PVDF and organic components had almost completely decomposed. Therefore, 200°C was determined to be the critical temperature for electrolyte evaporation, and 400–600°C was identified as the deep decomposition range for the organic binder. To achieve the dual technical objectives of complete electrolyte removal and binder failure without carbonization, this invention selected 227–277°C as the heat treatment temperature and maintained it at this temperature for 30 min. This temperature range is higher than the electrolyte evaporation point, ensuring complete electrolyte evaporation; simultaneously, it is significantly lower than the 400°C threshold for deep decomposition of the organic binder, causing only thermal decomposition and loss of adhesion of the polyvinylidene fluoride (PVDF) binder, thus avoiding secondary pollution of the active powder caused by binder carbonization.

[0021] Table 1 Different processing conditions S3 and DES selectively extract Li, Co, and Fe. The DES obtained in S1 and the cathode black powder obtained in S2 were added to a reactor at a solid-liquid ratio of 50-200 g / L. The stirring speed was set to 350-500 rpm, and the temperature was kept constant at 90-110°C for 1.5-3 hours. After the reaction was completed, the slurry was rapidly cooled to room temperature by circulating cooling water through the jacket. Vacuum filtration was then performed. The residue was washed twice with deionized water and dried at 105°C to obtain a solid rich in FePO4, which can be directly used to regenerate LiFePO4 cathodes. The filtrate is enriched with Li + With Co 2+ The leachate is then further processed into a serialized precipitation step.

[0022] In this invention, when using DES to recover Li, Co, and Fe, DES simultaneously plays a triple role as an "acid attacking agent + coordinating complexing agent + in-situ reducing agent," and the reaction principle is as follows: First, for the LiCoO2 component, phosphoric acid provides protons (H... + This causes LiCoO2 to dissolve, releasing Li + and Co 3+ Chloride ions donate electrons at the liquid-solid interface, converting Co into carbon dioxide. 3+ Reduced to more soluble Co 2+ At the same time, it is oxidized to Cl2: LiCoO2 + 4H + +2Cl - →Li + +Co 2+ +2H₂O + Cl₂↑ The generated Cl2 is captured by an alkaline scrubber, ensuring zero gas emissions and eliminating the need for external reducing agents such as hydrogen sulfide.

[0023] Secondly, for the LiFePO4 component, proton exchange first releases Li + Fe 2+ via Cl2 / Cl - The redox couple is reoxidized to Fe 3+ In high concentrations of PO4 3- An extremely insoluble FePO4 precipitate immediately forms in the environment and is trapped in the solid phase. LiFePO4 + 1 / 2Cl2 → Li + +FePO4↓+Cl - Therefore, iron remains in the residue as FePO4, with an iron content >95% as determined by ICP-OES. It can be directly used for the resynthesis of LiFePO4 without additional iron removal steps; while Li + and Co 2+ They then converge into the liquid phase, achieving process separation of iron / lithium / cobalt and preventing iron-cobalt co-solution.

[0024] Figure 4 The effects of different leaching temperatures and leaching times on the extraction efficiency of Li and Co were investigated, with a: 30℃, b: 40℃, c: 50℃, d: 60℃, e: 70℃, f: 80℃, and g: 90℃. The results showed that at 90℃, the extraction efficiency of Co (98.8%) and Li (99.9%) was very high, with a leaching time of 240 min.

[0025] S4, Serialization Precipitation and DES Regeneration High-purity cobalt salt and lithium salt are recovered sequentially from the leachate obtained from S3, and closed-loop regeneration of DES is achieved.

[0026] S401, "Ethanol-induced precipitation" of cobalt: The leachate obtained from S3 is transferred to a low-temperature reactor, cooled to 5-15°C, and stirred at 200 rpm. An ethanol-water mixed solvent (v / v = 1:1) of equal volume to the leachate is added dropwise using a computer-controlled peristaltic pump. The addition of ethanol lowers the dielectric constant of the system, disrupts the original hydrogen-bonded solvation sheath of DES, leading to supersaturation of the Co-Cl / PO4 complex and selective precipitation. Simultaneously, ethanol's weak reducing properties ensure a small amount of residual Co is preserved. 3+ Completely restored to Co 2+ After aging for 1 hour, the mixture was vacuum filtered. The precipitate was washed with an ethanol-water mixed solvent (v / v=1:1) and dried at 80℃ to obtain solid CoHPO4·3H2O. The cobalt recovery rate was >90%, and the purity was >95% as determined by ICP-OES. It can be directly calcined to produce CoO or used for the synthesis of ternary precursors. The filtrate was used for further lithium recovery.

[0027] S402, Lithium's "pH-controlled precipitation": Transfer the filtrate obtained from S401 to an automatic titration vessel, and add 1.5~2.5 mol / L NaOH solution dropwise at a rate of 0.3~0.8 mL / min to precisely raise the pH from 0 to 7.5~9.0; as the acidity decreases, PO4... 3- Concentration increases, with Li + The product, Li3PO4, has extremely low solubility. After aging at 5-15°C for 1 hour, followed by filtration, washing with deionized water, and drying at 105°C, white battery-grade Li3PO4 is obtained with a lithium recovery rate >99% and a purity >98%. This Li3PO4 can be subsequently carbonated to prepare Li2CO3 or co-fired with FePO4 to regenerate LiFePO4. The filtrate is used to regenerate DES.

[0028] Regeneration of S403 and DES: The filtrate obtained from S402 is first distilled at 60~80℃ and 0.08~0.1MPa vacuum to recover the ethanol-water mixture (condensed and reused). The remaining liquid is supplemented with a trace amount of phosphoric acid to adjust the acidity, thus obtaining regenerated DES, which can be recycled more than 5 times with a metal leaching efficiency decrease of <5%, thereby completing the entire green, closed-loop, selective recovery process of lithium, cobalt and iron.

[0029] Figure 5 This image compares the SEM images of waste lithium battery powder with the XRD patterns of the recycled metal products. a: XRD pattern of cobalt product; b: XRD pattern of lithium product; c: SEM image of lithium battery powder before leaching; d: SEM image of lithium battery powder after leaching. As shown in the figure, by comparing the XRD patterns of the recovered Co and Li products with those of the standard CoHPO4·3H2O and Li3PO4, it can be seen that the diffraction angles and crystal planes of the recovered products and the standard materials are basically consistent, proving that Co and Li were successfully converted into CoHPO4·3H2O and Li3PO4. The SEM comparison images before and after metal recycling show that the particles were large and agglomerated before recycling; after recycling, the particles became smaller and more dispersed, proving that metal leaching caused the particles to break up.

[0030] By adding different concentrations of phosphoric acid to adjust the acidity, regenerated DES was obtained, and multiple cycles of recycling were performed to test the metal leaching efficiency. Figure 6 This study investigates the effect of adding different concentrations of H3PO4 on the cycle performance of regenerated DES: a: 1 mol / L, b: 2 mol / L, c: 4 mol / L. As shown in the figure, under conditions of 90°C and a reaction time of 2 hours, with 1 mol / L H3PO4, the initial leaching efficiency (~80-85%) drops sharply to ~40-50% after six cycles due to insufficient acid strength. 4 mol / L H3PO4 reaches the peak initial efficiency (~98% Co, ~95% Li), but rapidly degrades to ~60-70%, possibly due to the high acidity disrupting solvent stability. 2 mol / L H3PO4 maintains balanced performance, retaining ~85-90% efficiency over six cycles because optimal viscosity and ion availability ensure stable leaching without solvent degradation. Therefore, 2 mol / L H3PO4 is an ideal choice for sustainable reuse, providing sustained efficiency for closed-loop battery recycling. Example 1

[0031] This embodiment describes a method for selectively recovering metal elements from spent batteries using a functionalized deep eutectic solvent, comprising the following steps: Construction of S1 and DES systems Weigh 6.98 g of choline chloride (ChCl), 11.52 g of 85% phosphoric acid aqueous solution, and 2.66 g of 50% choline hydroxide solution and add them to the reaction vessel (the molar ratio of choline chloride, phosphoric acid, and choline hydroxide is 1:2:0.2). Stir continuously for 60 min at 80℃ and 300 rpm. The system gradually changes from turbid to a colorless, transparent, viscous, and homogeneous liquid, which is the deep eutectic solvent DES.

[0032] S2, Lithium-ion battery pretreatment After discharging the collected waste lithium iron phosphate battery modules and lithium cobalt oxide battery modules, the positive electrode sheets were broken and sorted out. The positive electrode sheets were placed in a constant temperature heat treatment at 250℃ for 30 minutes, and then slightly vibrated to obtain active powder. After being sieved through a 100-mesh sieve, positive electrode black powder with a particle size of <100μm was obtained. The positive electrode black powder contained 4.1wt% Li, 9.6wt% Co, and 8.0wt% Fe.

[0033] S3 and DES selectively extract Li, Co, and Fe. The DES obtained in S1 and the cathode black powder obtained in S2 were added to a reactor at a solid-liquid ratio of 100 g / L. The stirring speed was set to 400 rpm and the temperature was kept constant at 100°C for 2 hours. + With Co 2+ The Fe is enriched in the leachate and converted into FePO4, which remains in the residue.

[0034] S4, Serialization Precipitation and DES Regeneration Cobalt salt and lithium salt are recovered sequentially from the leachate obtained from S3, and closed-loop regeneration of DES is achieved. S401, Cobalt Recovery: The leachate obtained in S3 was transferred to a low-temperature reactor, cooled to 10°C, and stirred at 200 rpm. An equal volume of ethanol-water mixed solvent (v / v = 1:1) was added dropwise using a peristaltic pump. After aging for 1 hour, the mixture was vacuum filtered. The precipitate was washed with the ethanol-water mixed solvent (v / v = 1:1) and dried at 80°C to obtain solid CoHPO4·3H2O. The cobalt recovery rate was 98.8%, and the purity was 96.2% as determined by ICP-OES. The filtrate was used for further lithium recovery.

[0035] S402, Lithium Recovery: The filtrate obtained in S401 was transferred to an automatic titration vessel, and 2 mol / L NaOH solution was added dropwise at a rate of 0.5 mL / min to precisely raise the pH from 0 to 8.0. The solution was aged at 10℃ for 1 hour, filtered, washed with deionized water, and dried at 105℃ to obtain white battery-grade Li3PO4 with a lithium recovery rate of 99.9% and a purity of 99.1%. The filtrate was used to regenerate DES.

[0036] Regeneration of S403 and DES: The filtrate obtained from S402 is first distilled at 70℃ and 0.09MPa vacuum, and the ethanol-water mixture is recovered by condensation. The remaining liquid is then adjusted with 1mol / L phosphoric acid to obtain regenerated DES. Example 2

[0037] This embodiment describes a method for selectively recovering metal elements from spent batteries using a functionalized deep eutectic solvent, comprising the following steps: Construction of S1 and DES systems 6.98 g of choline chloride (ChCl), 11.52 g of 85% phosphoric acid aqueous solution, and 1.33 g of 50% choline hydroxide solution were weighed and added to a reaction vessel (the molar ratio of choline chloride, phosphoric acid, and choline hydroxide was 1:2:0.05). The mixture was stirred continuously at 75°C and 200 rpm for 90 min. The system gradually changed from turbid to a colorless, transparent, viscous, and homogeneous liquid, yielding the deep eutectic solvent DES.

[0038] S2, Lithium-ion battery pretreatment After discharging the collected waste lithium iron phosphate battery modules and lithium cobalt oxide battery modules, the casings were broken and the positive electrode sheets were sorted out. The positive electrode sheets were then subjected to constant temperature heat treatment at 227℃ for 30 minutes, followed by scraping to obtain active powder, which was then sieved through a 100-mesh sieve to obtain the particle size. The cathode black powder contains 3.9 wt% Li, 15.3 wt% Co, and 0.4 wt% Fe.

[0039] S3 and DES selectively extract Li, Co, and Fe. The DES obtained in S1 and the cathode black powder obtained in S2 were added to a reactor at a solid-liquid ratio of 50 g / L. The stirring speed was set to 350 rpm and the temperature was kept constant at 110°C for 1.5 h. + With Co 2+ The Fe is enriched in the leachate and converted into FePO4, which remains in the residue.

[0040] S4, Serialization Precipitation and DES Regeneration Cobalt salt and lithium salt are recovered sequentially from the leachate obtained from S3, and closed-loop regeneration of DES is achieved. S401, Cobalt Recovery: The leachate obtained in S3 was transferred to a low-temperature reactor, cooled to 5°C, and stirred at 200 rpm. An equal volume of ethanol-water mixed solvent (v / v = 1:1) was added dropwise using a peristaltic pump. After aging for 1 hour, the mixture was vacuum filtered. The precipitate was washed with the ethanol-water mixed solvent (v / v = 1:1) and dried at 80°C to obtain solid CoHPO4·3H2O. The cobalt recovery rate was 96%, and the purity was 95.8% as determined by ICP-OES. The filtrate was used for further lithium recovery.

[0041] S402, Lithium Recovery: The filtrate obtained in S401 was transferred to an automatic titration vessel, and 1.5 mol / L NaOH solution was added dropwise at a rate of 0.3 mL / min to precisely raise the pH from 0 to 7.5. The solution was aged at 5°C for 1 hour, filtered, washed with deionized water, and dried at 105°C to obtain white battery-grade Li3PO4 with a lithium recovery rate of 99.2% and a purity of 99.0%. The filtrate was used to regenerate DES.

[0042] Regeneration of S403 and DES: The filtrate obtained from S402 is first distilled at 60℃ and 0.08MPa vacuum, and the ethanol-water mixture is recovered by condensation. The remaining liquid is then supplemented with 2mol / L phosphoric acid to adjust the acidity, thus obtaining regenerated DES. Example 3

[0043] This embodiment describes a method for selectively recovering metal elements from spent batteries using a functionalized deep eutectic solvent, comprising the following steps: Construction of S1 and DES systems Weigh 6.98 g of choline chloride (ChCl), 11.52 g of 85% phosphoric acid aqueous solution, and 3.99 g of 50% choline hydroxide solution and add them to the reaction vessel (the molar ratio of choline chloride, phosphoric acid, and choline hydroxide is 1:2:0.3). Stir continuously for 30 min at 85℃ and 400 rpm. The system gradually changes from turbid to a colorless, transparent, viscous, and homogeneous liquid, which is the deep eutectic solvent DES.

[0044] S2, Lithium-ion battery pretreatment After discharging the collected waste lithium iron phosphate battery modules and lithium cobalt oxide battery modules, the casings are broken open and the positive electrode sheets are sorted out; the positive electrode sheets are then subjected to constant temperature heat treatment at 277℃. The active powder was then obtained by scraping and sifting through a 100-mesh sieve, resulting in cathode black powder with a particle size of <100μm. The cathode black powder contained 3.5wt% Li, 2.9wt% Co, and 10.2wt% Fe.

[0045] S3 and DES selectively extract Li, Co, and Fe. The DES obtained in S1 and the cathode black powder obtained in S2 were added to a reactor at a solid-liquid ratio of 200 g / L. The stirring speed was set to 500 rpm and the temperature was kept constant at 90°C for 3 hours. + With Co 2+ The Fe is enriched in the leachate and converted into FePO4, which remains in the residue. S4, Serialization Precipitation and DES Regeneration Cobalt salt and lithium salt are recovered sequentially from the leachate obtained from S3, and closed-loop regeneration of DES is achieved. S401, Cobalt Recovery: The leachate obtained in S3 was transferred to a low-temperature reactor, cooled to 15°C, and stirred at 200 rpm. An equal volume of ethanol-water mixed solvent (v / v = 1:1) was added dropwise using a peristaltic pump. After aging for 1 hour, the mixture was vacuum filtered. The precipitate was washed with the ethanol-water mixed solvent (v / v = 1:1) and dried at 80°C to obtain solid CoHPO4·3H2O. The cobalt recovery rate was 95%, and the purity was 96.5% as determined by ICP-OES. The filtrate was used for further lithium recovery.

[0046] S402, Lithium Recovery: The filtrate obtained in S401 was transferred to an automatic titration vessel, and 2.5 mol / L NaOH solution was added dropwise at a rate of 0.8 mL / min to precisely raise the pH from 0 to 9.0. After aging at 15℃ for 1 h, followed by filtration, washing with deionized water, and drying at 105℃, white battery-grade Li3PO4 was obtained with a lithium recovery rate of 99.6% and a purity of 99.0%. The filtrate was used to regenerate DES.

[0047] Regeneration of S403 and DES: The filtrate obtained from S402 is first distilled at 80℃ and 0.1MPa vacuum, and the ethanol-water mixture is recovered by condensation. The remaining liquid is then supplemented with 4mol / L phosphoric acid to adjust the acidity, thus obtaining regenerated DES.

[0048] 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 selectively recovering metal elements from spent batteries using a functionalized deep eutectic solvent, characterized in that, Includes the following steps: Construction of S1 and DES systems Weigh out solutions of choline chloride, phosphoric acid, and choline hydroxide and add them to a reaction vessel. Stir until a colorless, transparent, viscous, and homogeneous liquid is obtained, which is the deep eutectic solvent DES. S2, Lithium-ion battery pretreatment After discharging the waste lithium iron phosphate battery modules and lithium cobalt oxide battery modules, the shells are broken and the positive electrode sheets are sorted out. The positive electrode sheets are placed in a constant temperature heat treatment at 227~277℃ for 30 minutes, and then the active powder is obtained by slight vibration or scraping. After being sieved through a 100-mesh sieve, the positive electrode black powder is obtained. S3 and DES selectively extract Li, Co, and Fe. The deep eutectic solvent obtained from S1 and the cathode black powder obtained from S2 were added to a reactor and reacted under constant temperature and stirring. Li + With Co 2+ The Fe is enriched in the leachate and converted into FePO4, which remains in the residue. S4, Serialization Precipitation and DES Regeneration Cobalt salt and lithium salt are recovered sequentially from the leachate obtained from S3, and closed-loop regeneration of DES is achieved. S401, Cobalt recovery: The leachate obtained from S3 was cooled to 5~15℃ and stirred at 200rpm. An ethanol-water mixed solvent was added dropwise. After aging for 1h, it was vacuum filtered. The precipitate was washed with ethanol-water and dried at 80℃ to obtain CoHPO4·3H2O solid. The filtrate was used for further lithium recovery. S402, Lithium Recovery: Add NaOH solution to the filtrate obtained from S401 to adjust the pH to 7.5~9.0, age at 5~15℃ for 1 hour, filter, wash with deionized water, and dry at 105℃ to obtain white battery-grade Li3PO4. The filtrate is used to regenerate DES. Regeneration of S403 and DES: The filtrate obtained from S402 is first vacuum distilled to recover the ethanol-water mixture, and the remaining liquid is supplemented with phosphoric acid to adjust the acidity, thus obtaining regenerated DES.

2. The method according to claim 1, characterized in that, The phosphoric acid in S1 is an 85% aqueous solution of phosphoric acid, the choline hydroxide solution has a mass concentration of 50%, and the molar ratio of choline chloride, phosphoric acid and choline hydroxide is 1:2:(0.05~0.3).

3. The method according to claim 1, characterized in that, The stirring temperature described in S1 is 75~85℃, the stirring speed is 200~400rpm, and the stirring time is 30~90min.

4. The method according to claim 1, characterized in that, The solid-liquid ratio of the deep eutectic solvent to the cathode black powder in S3 is 50~200g / L.

5. The method according to claim 1, characterized in that, The stirring speed described in S3 is 350~500 rpm, the temperature is 90~110°C, and the time is 1.5~3h.

6. The method according to claim 1, characterized in that, In S401, the volume ratio of ethanol to water in the ethanol-water mixed solvent is 1:1, and the amount of the ethanol-water mixed solvent used is equal to the volume of the leachate.

7. The method according to claim 1, characterized in that, The concentration of the NaOH solution in S402 is 1.5~2.5 mol / L, and the dropping rate is 0.3~0.8 mL / min.

8. The method according to claim 1, characterized in that, The vacuum distillation temperature described in S403 is 60~80℃, and the vacuum degree is 0.08~0.1MPa.

9. The method according to claim 1, characterized in that, Cobalt recovery rate >90%, purity >95%; lithium recovery rate >99%, purity >98%; iron remains in the residue as FePO4, with an iron content >95%.

Images