A method and system for recycling retired lithium-ion batteries by electrochemical indirect oxidation coupled with two-stage extraction

Abstract

The present application belongs to the technical field of retired power battery solid waste resourceization and new energy material closed loop recycling, and discloses a kind of electrochemical indirect oxidation coupled double-section extraction's retired lithium ion battery regeneration method and system, with retired battery positive black powder as raw material, using single-chamber electrolytic cell electro-oxidation bromine indirect oxidation black powder lattice realizes selective delithiation, cathode synchronous production alkali precipitation dissolves metal ions;Leaching liquor is enriched lithium by one-stage extraction-back extraction, and the raffinate returns to the electrolytic cell to realize the closed loop of bromine medium;Rich lithium back extraction liquid is prepared into lithium carbonate by precipitation, and lithium sink mother liquor enters two-stage extraction-back extraction, to realize the full recovery of lithium;Finally, delithiated solid phase and self-produced lithium carbonate are regenerated as positive electrode material by high-temperature solid-phase calcination.The present application uses single-chamber membraneless electrolytic cell, and there is no chlorine in the whole process, which realizes the full closed loop of electrolyte and lithium sink mother liquor, with the advantages of less reagent consumption, high product purity, wide application range, etc.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization of retired power batteries and closed-loop recycling of new energy materials, and relates to a method and system for regenerating retired lithium-ion batteries by electrochemical indirect oxidation coupled with two-stage extraction. Background Technology

[0002] With the large-scale expansion of the new energy vehicle industry, the installed capacity of lithium-ion power batteries continues to rise, and the resource recycling of waste lithium batteries has become a key link in supporting the sustainable development of the new energy industry and ensuring the security of lithium resource supply.

[0003] Among current recycling methods for spent lithium-ion battery cathode materials, electrochemical oxidation has attracted attention due to its ability to selectively oxidize and remove lithium under ambient pressure and near-ambient temperature conditions. However, existing electrochemical recycling technologies still face the following engineering challenges that urgently need to be addressed: Firstly, most existing electrochemical delithiation devices employ a dual-chamber membrane electrolyzer structure. This structure separates the anode and cathode regions using a diaphragm to prevent the mixing of anode and cathode products. For example, Chinese patent CN106823816A discloses an electrochemical method for recovering lithium from the cathode material of spent lithium batteries. This method divides the electrolyzer into an anode and cathode chamber using a monovalent cation-selective permeable membrane, allowing lithium ions to pass through the membrane and accumulate in the cathode chamber. However, the presence of the membrane introduces inherent engineering bottlenecks: the diaphragm is susceptible to wear and scratches from suspended black powder particles in the electrolyte; simultaneously, inorganic salt scaling and organic contamination easily occur on the membrane surface, leading to decreased membrane flux, increased membrane resistance, and consequently, increased cell voltage and energy consumption. The membrane module requires regular cleaning or replacement, resulting in high maintenance costs. Furthermore, the membrane structure limits mass transfer efficiency within the electrolyzer, leading to uneven black powder suspension and large local concentration gradients, which affect the uniformity and efficiency of the delithiation reaction. These membrane-related engineering problems have become key obstacles restricting the large-scale application of this technology.

[0004] Secondly, although chlorine (Cl) has been publicly used in existing technologies... -While chlorine-based electrochemical systems utilize chlorine (Cl2) as the oxidizing medium, they suffer from serious drawbacks in cathode material recycling. Chinese patent CN118563107A discloses a method for leaching valuable metals from spent lithium-ion battery cathode materials using active chlorine generated by the electrolysis of an alkali metal chloride aqueous solution. However, the chlorine gas generated by the anodic oxidation of chloride ions in this system has limited solubility in water, escaping in large quantities as a gaseous form. This not only results in low oxidation efficiency but also causes serious equipment corrosion and operational safety issues. Furthermore, the chlorine tail gas requires complex alkaline absorption or condensation recovery devices, significantly increasing equipment investment. More critically, chloride ions are strictly controlled impurities in lithium-ion battery cathode materials; even small amounts can form chloride impurities in subsequent recycled materials, severely affecting their electrochemical performance, necessitating a deep dechlorination process. Moreover, this process does not utilize simultaneous cathode alkali production for in-situ precipitation separation and does not establish a complete closed-loop circulation system, essentially remaining a semi-open-circuit oxidation leaching system.

[0005] Thirdly, for the extraction and recovery of lithium from lithium-containing solutions, existing technologies mainly employ chemical precipitation and solvent extraction. Chemical precipitation involves adding precipitants such as sodium carbonate to the lithium-containing solution, causing lithium to precipitate as lithium carbonate. This method is simple to operate and relatively low in cost, and has been maturely applied in conventional brine lithium extraction and battery recycling lithium precipitation processes. However, existing precipitation methods generally face the following problems in practical applications: On the one hand, the lithium precipitation process requires concentrating the solution to a high lithium concentration to improve the precipitation yield. For lithium-containing solutions with low lithium concentrations (such as dilute lithium alkaline filtrate after electrochemical delithiation), direct precipitation is inefficient and consumes a large amount of reagents. On the other hand, a considerable proportion of dissolved lithium remains in the lithium precipitation mother liquor. In conventional processes, this portion of lithium is difficult to recover effectively, and direct discharge not only wastes lithium resources but also generates high-salt wastewater. Solvent extraction is currently an effective means of separating and purifying lithium, but existing extraction systems generally require operation under high acidity or specific salting-out conditions, or the addition of co-extractants containing metal ions. For example, tributyl phosphate (TBP) extraction systems require high-concentration chloride salting-out conditions to extract lithium. Chinese patent CN111187911A discloses a method for selectively extracting lithium from spent ternary batteries using an extraction system composed of ionic liquid and TBP. However, this method introduces a large amount of chloride ions into subsequent processes, leading to significant equipment corrosion and dechlorination issues in the product. Some carboxylic acid extractants require the addition of Fe-containing compounds during the extraction process. 3+The use of metal ion-based co-extraction agents introduces foreign metal impurities into the system at the source, and these impurities are extremely difficult to remove in subsequent lithium carbonate products and recycled cathode materials. Furthermore, existing extraction systems are mostly designed for acidic or neutral lithium-containing solutions, while the lithium-containing filtrate obtained from electrochemical oxidation delithiation is alkaline. Directly using the aforementioned extraction systems requires pre-adjusting the pH with acid, increasing reagent consumption and process complexity. The lithium yield bottleneck and mother liquor treatment difficulties of the precipitation method, as well as the harsh operating conditions and impurity introduction issues of the extraction system, make it difficult to achieve a clean and efficient end-to-end integration with the electrochemical oxidation delithiation process.

[0006] In summary, existing electrochemical indirect oxidation recovery technologies still face core technical challenges, including membrane electrolysis engineering bottlenecks, inherent defects in chlorine-based media, and a lack of clean lithium extraction systems compatible with alkaline lithium-containing filtrates. These challenges hinder the realization of a closed-loop regeneration process. Therefore, there is an urgent need to develop a new electrochemical recovery method that eliminates the need for membrane separation, avoids the risks associated with chlorine-based systems, and can be cleanly integrated with alkaline lithium extraction systems. Summary of the Invention

[0007] The purpose of this invention is to address the problems existing in current retired lithium-ion battery recycling processes by proposing an electrochemical indirect oxidation coupled with two-stage extraction method and system for regenerating retired lithium-ion batteries. This is achieved by constructing a combined system of "single-chamber membrane-free electrolysis for bromine oxidation and lithium removal - two-stage extraction for closed-loop lithium extraction," leveraging the unique electrochemical advantages of bromide ions and the engineering advantages of a membrane-free single-chamber electrolyzer. β - The advantages of diketone extractants in alkaline lithium extraction, the dual closed-loop circulation of raffinate and lithium precipitation mother liquor, and other synergistic innovations enable precise and selective separation of lithium and closed-loop circulation of bromide electrolyte throughout the process. This fundamentally solves the core pain points of traditional processes, such as high pollution, high reagent loss, and difficulty in controlling product impurities, and enables low-cost, large-scale regeneration of retired batteries.

[0008] The technical solution of this invention is: This invention provides a method for regenerating retired lithium-ion batteries using electrochemical indirect oxidation coupled with two-stage extraction, comprising the following steps: S1. Raw material pretreatment: The retired lithium-ion batteries are subjected to deep discharge, mechanical disassembly, crushing and multi-stage sorting to remove impurities such as shell, separator and copper and aluminum foil to obtain pure positive electrode black powder. S2. Electrochemical indirect oxidation delithiation: An aqueous solution of lithium bromide is fed into a single-chamber electrolytic cell, and the cathode black powder is suspended in the aqueous solution of lithium bromide; bromide ions are electro-oxidized at the anode to generate elemental bromine, and the elemental bromine oxidizes the lattice of the cathode black powder to achieve selective delithiation of lithium ions. After reduction, the elemental bromine regenerates bromide ions; hydroxide ions are generated simultaneously at the cathode, so that the dissolved metal ions precipitate into the solid phase in the form of hydroxides. S3. Solid-liquid separation: After electrolysis, the solid-liquid mixture in the electrolytic cell is filtered to obtain a delithiated filter cake and an alkaline lithium-containing filtrate; the delithiated filter cake is dried to obtain a positive electrode black powder precursor. S4. First-stage extraction and back-extraction: The alkaline lithium-containing filtrate is subjected to first-stage extraction using an extractant to separate a first-stage raffinate and a first-stage lithium-loaded organic phase; the first-stage lithium-loaded organic phase is subjected to back-extraction using sulfuric acid solution to separate a first-stage lithium-rich back-extraction solution and a first-stage delithiated organic phase. S5. Lithium carbonate preparation: Sodium carbonate solution is added to the lithium-rich back-extraction solution obtained in step S4 to induce a carbonation precipitation reaction. After filtration, crude lithium carbonate and lithium precipitation mother liquor are obtained. The crude lithium carbonate is washed and dried to obtain battery-grade lithium carbonate. S6. Two-stage extraction and back-extraction: The lithium precipitation mother liquor is subjected to two-stage extraction using an extractant to separate the two-stage raffinate and the two-stage extracted lithium-loaded organic phase; the two-stage extracted lithium-loaded organic phase is back-extracted using sulfuric acid solution to separate the two-stage back-extracted lithium-rich solution and the two-stage back-extracted delithiated organic phase. S7. Closed-loop regeneration of cathode material: The cathode black powder precursor obtained in step S3 and the battery-grade lithium carbonate obtained in step S5 are precisely proportioned according to the target cathode material stoichiometric ratio. After matching the carbon source and / or phosphorus source, the mixture is calcined at high temperature in a solid state, cooled, crushed, and sieved to obtain the regenerated cathode material.

[0009] Furthermore, in step S1, the retired lithium-ion battery is a lithium iron phosphate battery or a nickel-cobalt-manganese ternary lithium-ion battery.

[0010] Further, in step S2, the single-chamber electrolytic cell is a corrosion-resistant, diaphragm-free electrolytic cell, the anode is a shape-stabilized bromine-electrode electrode, and the cathode is one of a titanium electrode, a stainless steel electrode, a nickel electrode, or a graphite electrode; the mass fraction of the lithium bromide aqueous solution is 0.5%~5%; the solid-liquid ratio of the positive electrode black powder to the lithium bromide aqueous solution is 10~100 g / L; electrolysis is carried out in constant current or constant voltage mode, with a cell voltage of 1.5~3.0 V, preferably 1.8~2.5 V; electrolysis is carried out with stirring at room temperature for 1~6 h; the bromide ions in the system only serve as an intermediate oxidation medium, and there is no continuous loss during circulation.

[0011] Furthermore, in steps S4 and S6, the extractant is alkaline and stable, exhibits high selectivity for lithium extraction, does not co-extract bromide ions, and does not contain any metal co-extraction components throughout the process. The extractant comprises a main extractant and a co-extractant, wherein the main extractant is... β -Diketone compounds, the β- The diketone compound is selected from one of 2-thiophenecarboxyltrifluoroacetone (HTTA), benzoyltrifluoroacetone (HBTA), and dibenzoylmethane (DBM); the co-extractant is a neutral phosphorus co-extractant, preferably one of trioctylphosphine oxide (TOPO), tributyl phosphate (TBP), and mixed trialkylphosphine oxide (Cyanex 923); the concentration of the sulfuric acid solution is 0.1~1.0 mol / L.

[0012] Further, in steps S4 and S6, the extraction operation conditions are: the extraction ratio (volume ratio of organic phase to aqueous phase) is (1:4) to (2:1), and the extraction method is 2 to 6 stages of countercurrent extraction; the back extraction operation conditions are: the back extraction ratio (volume ratio of organic phase to aqueous phase) is (1:1) to (5:1), and the back extraction method is 2 to 5 stages of countercurrent back extraction.

[0013] Further, in step S5, the mass fraction of the sodium carbonate solution is 10%~30%, preferably 20%~25%; the amount of sodium carbonate added is 1.05~1.20 times the theoretical amount required for complete lithium precipitation; the reaction temperature is 70~95℃, and the reaction time is 0.5~1.5 h.

[0014] Furthermore, in step S4, the first raffinate is a bromine-containing aqueous solution, which is completely recycled back to step S2 as an electrolyte for reuse, thereby achieving a closed-loop circulation of bromide ions; the first stripped lithium-free organic phase is returned to the first extraction cycle for reuse.

[0015] Furthermore, in step S6, the organic phase of the second-stage back-extraction delithiation is returned to the second-stage extraction cycle for reuse; the lithium-rich liquid of the second-stage back-extraction is entirely incorporated into the lithium-rich liquid of the first-stage back-extraction obtained in step S4, and together they are sent to step S5 for lithium precipitation again to achieve full extraction of lithium resources.

[0016] Further, in step S7, when the raw material is lithium iron phosphate black powder, additional carbon and phosphorus sources are required. Lithium carbonate and delithiation filter cake are mixed at a Li:Fe molar ratio of 1.00~1.05:1, the amount of carbon source added is 5%~20% of the molar amount of iron, and the amount of phosphorus source added is Fe:P molar ratio of 1:1. The calcination temperature is 600~800℃, the time is 2~8 h, and the calcination atmosphere is nitrogen or argon. When the raw material is nickel cobalt manganese ternary black powder, additional carbon source is required. Lithium carbonate and delithiation filter cake are mixed at a Li:(Ni+Co+Mn) molar ratio of 1.02~1.08:1, and the amount of carbon source added is 3%~15% of the total molar amount of transition metals (Ni+Co+Mn). The mixture is first reduced and calcined at 500~650℃ for 1~4 h in an inert atmosphere of nitrogen or argon, and then switched to an air or pure oxygen atmosphere and calcined at 800~950℃ for 3~10 h.

[0017] Further, in step S7, the carbon source is selected from one or more of glucose, sucrose, starch, citric acid, and acetylene black; the phosphorus source is selected from at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and triammonium phosphate.

[0018] Another aspect of the present invention provides a system for realizing the above-mentioned electrochemical indirect oxidation coupled dual-stage extraction method for regenerating retired lithium-ion batteries, comprising: a single-chamber electrolytic cell, a first filtration unit, a first-stage extraction unit, a first-stage back-extraction unit, a lithium precipitation reactor, a second filtration unit, a second-stage extraction unit, a second-stage back-extraction unit, a mixing and calcination unit, and a system built-in parameter configuration module. The single-chamber electrolytic cell is a diaphragm-free electrolytic cell, which is equipped with an anode and a cathode. The electrolytic cell is equipped with a lithium bromide aqueous solution inlet, a positive electrode black powder inlet, a stirring device, and a solid-liquid mixture outlet. The inlet of the first filtration unit is connected to the solid-liquid mixture outlet of the single-chamber electrolytic cell via a pipeline. The first filtration unit is provided with a solid phase outlet and a liquid phase outlet; the solid phase outlet is connected to a drying device. The aqueous phase inlet of the first extraction unit is connected to the liquid phase outlet of the first filtration unit through a pipeline. The first extraction unit is equipped with an extractant inlet, a raffinate outlet, and a lithium-loaded organic phase outlet. The raffinate outlet is connected to the lithium bromide aqueous solution inlet of the single-chamber electrolyzer through a first reflux pipeline, forming a closed-loop circulation circuit containing bromine raffinate. The organic phase inlet of the first-stage back-extraction unit is connected to the lithium-loaded organic phase outlet of the first-stage extraction unit. The first-stage back-extraction unit is equipped with a back-extraction acid inlet, a regenerated organic phase outlet, and a first-stage back-extraction lithium-rich liquid outlet. The regenerated organic phase outlet is connected to the extractant inlet of the first-stage extraction unit through a pipeline. The lithium-rich liquid inlet of the lithium precipitation reactor is connected to the lithium-rich liquid outlet of a section of the back-extraction unit through a pipeline. The lithium precipitation reactor is equipped with a sodium carbonate solution inlet, a heating device and a lithium carbonate slurry outlet. The inlet of the second filtration unit is connected to the lithium carbonate slurry outlet of the lithium precipitation reactor. The second filtration unit is provided with a solid phase outlet and a liquid phase outlet. The solid phase outlet is connected in sequence to a lithium carbonate washing device and a lithium carbonate drying device, and outputs battery-grade lithium carbonate. The liquid phase outlet outputs lithium precipitation mother liquor. The aqueous phase inlet of the second-stage extraction unit is connected to the liquid phase outlet of the second filtration unit through a pipeline; the second-stage extraction unit is equipped with an extractant inlet, a raffinate outlet, and a lithium-loaded organic phase outlet; the first-stage extraction unit and the second-stage extraction unit share an extractant storage tank and an interconnected circulation pipeline, and the extractant can be bidirectionally interconnected and reused; the second-stage raffinate is equipped with an independent collection and disposal pipeline. The organic phase inlet of the two-stage back-extraction unit is connected to the lithium-loaded organic phase outlet of the two-stage extraction unit. The two-stage back-extraction unit is equipped with a back-extraction acid inlet, a regenerated organic phase outlet, and a two-stage back-extraction lithium-rich liquid outlet. The two-stage back-extraction lithium-rich liquid outlet is connected to the first-stage back-extraction lithium-rich liquid outlet of the first-stage back-extraction unit through a pipeline, and after merging, they are connected to the lithium-rich liquid inlet of the lithium precipitation reactor. The regenerated organic phase outlet is connected to the extractant inlet of the two-stage extraction unit through a pipeline. The mixing and calcining unit includes a drying device, a ball milling device, and a high-temperature calcining furnace. The ball milling device is equipped with a lithium carbonate inlet, a cathode black powder precursor inlet, a carbon source inlet, and an optional phosphorus source inlet. The outlet of the drying device is connected to the cathode black powder precursor inlet of the ball milling device via a pipeline. The outlet of the lithium carbonate drying device is connected to the lithium carbonate inlet of the ball milling device via a pipeline. The outlet of the ball milling device is connected to the inlet of the high-temperature calcining furnace. The system's built-in parameter configuration module includes an electrolytic cell current / voltage control unit, an extraction ratio control unit, a lithium precipitation reaction temperature and sodium carbonate dosage control unit, and all equipment is equipped with automatic interlocking actuators.

[0019] The overall innovative concept and analysis of multiple core collaborative innovations of this invention are as follows: The first core innovation is a single-chamber, membrane-free electrochemical bromine production system based on lithium bromide, which avoids the bottlenecks of dual-chamber membrane electrolysis and the inherent defects of chlorine-based media. This invention employs a single-chamber, membrane-free electrolyzer. Compared to membrane-separated dual-chamber electrolyzers, the single-chamber electrolyzer structure is greatly simplified, eliminating problems such as membrane fouling, membrane degradation, and increased cell voltage due to membrane resistance, significantly reducing equipment investment and maintenance costs. Furthermore, this invention uses lithium bromide as the single circulating medium, greatly suppressing the oxygen evolution side reaction; the bromine oxidation product is liquid at room temperature, making it less prone to volatilization and escape; after oxidizing black powder, elemental bromine is reduced to bromide ions, theoretically resulting in no net consumption and requiring only a very small amount of replenishment; the lithium battery industry has a much higher tolerance for bromine impurities than chlorine, eliminating the need for deep depurification of the product.

[0020] The second core innovation is the in-situ coupling of the anode and cathode in a single-chamber electrolysis process, achieving selective lithium removal and impurity precipitation separation in one step. This invention utilizes a single-chamber membrane-free electrolyzer to construct an in-situ acid-base coupling system. Because the anode and cathode are located in the same cavity within the single-chamber electrolyzer, the bromine generated at the anode and the hydroxide ions generated at the cathode undergo instantaneous coupling during electrolysis—other metal ions dissolved during the bromine oxidation delithiation process are instantly precipitated and retained in the solid phase by the alkaline solution at the cathode, eliminating the need for external alkaline solution to adjust the pH. After electrolysis, only one solid-liquid separation step is required to obtain a delithiated filter cake (containing metal hydroxide precipitate) and an alkaline lithium-containing filtrate, significantly shortening the process flow. Simultaneously, the black powder is directly suspended in the electrolyte within the single-chamber electrolyzer, eliminating the need for electrode fabrication, binders, and conductive agents. This allows for large batch processing capacities, making it suitable for continuous industrial production.

[0021] The third core innovation is the coupling of a two-stage lithium extraction process: a closed-loop extraction stage using electrolyte and a deep extraction stage using lithium precipitation mother liquor. This significantly improves the overall lithium recovery rate. This invention utilizes a screened and adopted... β The synergistic extraction system, composed of diketone chelating extractants and neutral phosphorus co-extractants, exhibits high selectivity for lithium ions under alkaline conditions and is completely free of metal ion co-extraction components, thus preventing the introduction of foreign metal impurities at the source. Furthermore, a two-stage extraction and recovery chain is established: ① First-stage extraction of the alkaline filtrate from electrolysis, with the bromine-containing extraction residue directly returned to the electrolyzer, achieving a fully closed-loop oxidation medium; ② Second-stage extraction of the lithium-precipitated mother liquor using the same extraction system for deep lithium extraction. The organic components of the two extraction stages are mutually reused, requiring only the addition of one aqueous phase pipeline to achieve full lithium recovery, resulting in low industrial modification and equipment investment costs.

[0022] The fourth core innovation: Integrated regeneration of lithium removal filter cake and self-produced lithium carbonate with precise lithium matching and high-temperature roasting. The lithium removal filter cake is directly used as the precursor substrate for cathode regeneration. It is precisely controlled in molar ratio with self-produced battery-grade lithium carbonate to compensate for high-temperature lithium volatilization. A trace amount of carbon source is added and uniformly dispersed. After high-temperature solid-phase roasting, it is directly regenerated to obtain a brand-new cathode material, suitable for both lithium iron phosphate and ternary cathode material systems. The entire process involves internal material recycling, with all lithium and other materials being converted into battery-grade cathode raw materials, fully realizing the entire process of "waste battery dismantling - electrochemical selective lithium removal - dual-stage extraction closed-loop lithium extraction - cathode regeneration".

[0023] The advantages and positive effects of this invention are: (1) The use of a single-chamber membrane-free electrolytic cell eliminates problems such as membrane material cost, membrane fouling, and increased cell voltage caused by membrane internal resistance. Equipment investment and operation and maintenance costs are greatly reduced, making it easier to scale up and conduct continuous production.

[0024] (2) Bromine ions are electro-oxidized to elemental bromine at the anode, and the elemental bromine is reduced to bromide ions after oxidizing black powder, thus realizing the catalytic cycle of "oxidation-reduction-regeneration". Theoretically, only a very small amount of supplementation is needed, and the consumption of reagents is extremely low.

[0025] (3) The entire process uses a single bromine cycle medium, abandoning the chlorine-based scheme, so there is no risk related to chloride ions. Furthermore, no metal ion-containing co-extraction agents are added to the extraction system throughout the process, thus eliminating the introduction of foreign metal impurities from the source and saving the deep impurity removal process.

[0026] (4) Relying on the in-situ coupling of the anode and cathode of single-chamber electrolysis, the oxidation delithiation and precipitation impurity removal are carried out simultaneously. After electrolysis, only one solid-liquid separation is required to achieve lithium entering the liquid phase and impurity metals remaining in the solid phase, without the need to add alkali solution to adjust pH.

[0027] (5) The first stage of extraction recovers most of the lithium in the lithium-containing filtrate of the electrolysis, and the second stage of extraction recovers the residual dissolved lithium in the lithium precipitation mother liquor. The two-stage extraction closed-loop lithium extraction results in a high overall lithium recovery rate.

[0028] (6) This invention does not require screening of high-quality raw materials or black powder sheeting. It can be adapted to both lithium iron phosphate and nickel-cobalt-manganese ternary systems for retired cathode black powder, and has a wide range of applications.

[0029] (7) The single-chamber electrolysis, solid-liquid separation, solvent extraction, and lithium carbonate precipitation involved in this invention are all mature unit operations in the chemical industry, without special harsh working conditions, low investment, and can be continuously produced on a large scale. Attached Figure Description

[0030] Figure 1 This is a flowchart of the regeneration method for retired ternary NCM523 batteries in Example 1.

[0031] Figure 2 This is a photograph of the delithiation filter cake obtained in step S3 of Example 1.

[0032] Figure 3 The image shows the XRD pattern of the delithiation filter cake obtained in step S3 of Example 1.

[0033] Figure 4 This is a photograph of the battery-grade lithium carbonate obtained in step S5 of Example 1.

[0034] Figure 5 The image shows the XRD pattern of battery-grade lithium carbonate obtained in step S5 of Example 1.

[0035] Figure 6 This is a photograph of the regenerated NCM523 cathode material obtained by high-temperature calcination in Example 1.

[0036] Figure 7 The image shows the XRD pattern of the regenerated NCM523 cathode material obtained by high-temperature calcination in Example 1.

[0037] Figure 8 The image shows the XRD pattern of the delithiation filter cake obtained in step S3 of Example 3.

[0038] Figure 9 The image shows the XRD pattern of battery-grade lithium carbonate obtained by filtration in step S5 of Example 3.

[0039] Figure 10 The image shows the XRD pattern of the regenerated lithium iron phosphate cathode material obtained by high-temperature calcination in Example 3. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0041] Example 1: Closed-loop regeneration of cathode black powder from retired ternary NCM523 batteries A method for regenerating retired ternary NCM523 batteries using electrochemical indirect oxidation coupled with two-stage extraction is described below. Figure 1 The specific steps are as follows: S1. Raw material pretreatment: Take retired commercial NCM523 ternary power batteries, deep discharge them with sodium chloride solution, mechanically disassemble, crush, and air classify them to remove impurities such as shell, separator, copper and aluminum foil, and obtain pure NCM523 positive electrode black powder.

[0042] S2. Electrochemical Indirect Oxidative Lithium Removal: A 3% (w / w) lithium bromide aqueous solution was prepared and fed into a diaphragm-free single-chamber electrolytic cell. The NCM523 cathode black powder obtained in S1 was added to the electrolytic cell at a solid-liquid ratio of 50 g / L and uniformly suspended. The anode was a titanium-based ruthenium-iridium stabilizing bromine electrode, and the cathode was a stainless steel electrode. A constant voltage mode was used, with a cell voltage of 2.0 V and electrolysis at room temperature with stirring for 2 h. At the anode, bromide ions were electrolyzed to generate elemental bromine. The elemental bromine oxidized the black powder lattice, achieving selective lithium removal, while the elemental bromine was reduced to bromide ions for regeneration. Simultaneously, hydroxide ions were generated at the cathode, causing the dissolved nickel, cobalt, and manganese to precipitate into the solid phase as hydroxides.

[0043] S3. Solid-liquid separation: The solid-liquid mixture in the electrolytic cell is discharged as a whole and filtered to obtain a delithiation filter cake and an alkaline lithium-containing filtrate (pH≈10.5); the delithiation filter cake is dried at 80℃ to obtain the positive electrode black powder precursor.

[0044] S4. First-stage extraction and back-extraction: The alkaline lithium-containing filtrate obtained from S3 is subjected to first-stage extraction using an extractant (the extractant includes a main extractant and a co-extractant; the main extractant is 2-thiophenecarboxylic acid trifluoroacetone, and the co-extractant is trioctylphosphine oxide; the molar ratio of the main extractant to the co-extractant is 1:2; the diluent is sulfonated kerosene). The volume ratio of the organic phase to the aqueous phase is 1:1, and a four-stage countercurrent extraction is used to separate the first-stage raffinate and the first-stage lithium-loaded organic phase. The first-stage raffinate is a bromine-containing aqueous solution, which is entirely recycled back to the S2 single-chamber electrolyzer for reuse, achieving a closed-loop circulation of bromide ions. The first-stage lithium-loaded organic phase is back-extracted using a 0.5 mol / L sulfuric acid solution, with a volume ratio of the organic phase to the aqueous phase of 3:1. A three-stage countercurrent back-extraction is used to separate the first-stage back-extracted lithium-rich solution and the first-stage back-extracted delithiated organic phase. The first-stage back-extracted delithiated organic phase is returned to the first-stage extraction cycle for further extraction.

[0045] S5. Lithium carbonate preparation: A 25% (w / w) sodium carbonate solution (1.10 times the theoretical amount required for complete lithium precipitation) was added to the lithium-rich solution obtained in step S4. The mixture was stirred at 85°C for 1.0 h. After filtration, crude lithium carbonate and lithium precipitation mother liquor were obtained. The crude lithium carbonate was washed three times with pure water at 80°C and dried at 105°C to obtain battery-grade lithium carbonate. The purity of the battery-grade lithium carbonate was 99.8% as determined by inductively coupled plasma atomic emission spectrometry.

[0046] S6. Second-stage extraction and back-extraction: The lithium precipitation mother liquor obtained in step S5 is subjected to second-stage extraction using the same extractant as in step S4, under the same extraction conditions as in step S4, to separate the second-stage raffinate and the second-stage lithium-loaded organic phase. The second-stage lithium-loaded organic phase is back-extracted using 0.5 mol / L sulfuric acid solution, under the same back-extraction conditions as in step S4, to separate the second-stage back-extracted lithium-rich solution and the second-stage back-extracted delithiated organic phase; the entire second-stage back-extracted lithium-rich solution is incorporated into the first-stage back-extracted lithium-rich solution obtained in step S4, and both are sent to step S5 for lithium precipitation again; the second-stage back-extracted delithiated organic phase is returned to the second-stage extraction cycle for extraction.

[0047] S7. Closed-loop regeneration of cathode material: The cathode black powder precursor obtained in S3 and the battery-grade lithium carbonate obtained in S5 are precisely mixed at a molar ratio of Li / (Ni+Co+Mn) of 1.05:1. Glucose, a carbon source, is added in an amount of 10% of the total molar amount of transition metals (Ni+Co+Mn). The mixture is reduced and calcined at 600℃ for 2 h under a nitrogen atmosphere, and then oxidized and calcined at 850℃ for 8 h under an air atmosphere. After cooling, crushing and sieving, the regenerated NCM523 cathode material is obtained.

[0048] The physical image and XRD pattern of the delithiation filter cake obtained in step S3 are shown below. Figure 2 and Figure 3 , Figure 3 The PDF standard card number for NCM523 is 70-4314; the physical image and XRD pattern of the battery-grade lithium carbonate obtained in step S5 are shown below. Figure 4 and Figure 5 Physical images and XRD patterns of the regenerated NCM523 cathode material obtained by high-temperature calcination are shown below. Figure 6 and Figure 7 Testing revealed that the main phase purity of the recycled NCM523 cathode material was 93.5%. After assembling into coin cells, the first charge-discharge test at a 0.1 C rate showed an initial discharge capacity of 155.9 mAh / g.

[0049] Example 2: Closed-loop regeneration of cathode black powder from retired ternary NCM811 batteries The process flow is the same as in Example 1. The specific steps are as follows: S1. Raw material pretreatment: The only difference from step S1 in Example 1 is that the retired battery is a commercial NCM811 high-nickel ternary power battery.

[0050] S2, Electrochemical indirect oxidation delithiation: The only difference from step S2 in Example 1 is that the mass fraction of the lithium bromide aqueous solution is 4%, and NCM811 cathode black powder is added at a solid-liquid ratio of 80 g / L; the cathode is a titanium electrode, the cell voltage is 2.3 V, and the electrolysis is carried out at room temperature with stirring for 3 hours.

[0051] S3, Solid-liquid separation: Same as step S3 in Example 1.

[0052] S4. First-stage extraction and back-extraction: The only difference from step S4 in Example 1 is that the main extractant is benzoyltrifluoroacetone, the co-extractant is tributyl phosphate, and the molar ratio is 1:3.

[0053] S5. Preparation of lithium carbonate: The only difference from step S5 in Example 1 is that the amount of sodium carbonate added is 1.15 times the theoretical amount, the reaction temperature is 90℃, and the reaction time is 1.5 h; the purity of battery-grade lithium carbonate is 99.9% as detected by inductively coupled plasma atomic emission spectrometry.

[0054] S6, Second-stage extraction and back-extraction: Same as step S4.

[0055] S7. Closed-loop regeneration of cathode material: The only difference from step S7 in Example 1 is that the materials are precisely proportioned according to the Li / (Ni+Co+Mn) molar ratio of 1.08:1, and the amount of glucose added as carbon source is 6% of the total molar amount of transition metals; the material is reduced and calcined at 650°C under a nitrogen atmosphere for 3 h, and then oxidized and calcined at 920°C under a pure oxygen atmosphere for 6 h to obtain the regenerated NCM811 cathode material.

[0056] The purity of the main phase of the regenerated NCM811 cathode material was 93.3% after testing. The initial discharge capacity was 180.5 mAh / g after testing with a coin cell, using the same method as in Example 1.

[0057] Example 3: Closed-loop regeneration of cathode black powder from retired lithium iron phosphate batteries The process flow is the same as in Example 1. The specific steps are as follows: S1. Raw material pretreatment: The only difference from step S1 in Example 1 is that the retired battery is a lithium iron phosphate battery.

[0058] S2, Electrochemical Indirect Oxidative Delithiation: The only difference from step S2 in Example 1 is that the lithium bromide aqueous solution has a mass fraction of 2.5%, and lithium iron phosphate black powder is added at a solid-liquid ratio of 60 g / L; the cell voltage is 1.8 V, and electrolysis is carried out at room temperature with stirring for 2 h. Hydroxide ions are generated at the cathode, causing the dissolved iron ions to precipitate into the solid phase in the form of ferric hydroxide.

[0059] S3, Solid-liquid separation: Same as step S3 in Example 1.

[0060] S4, First-stage extraction and back-extraction: The only difference from step S4 in Example 1 is that the main extractant is dibenzoylmethane; back-extraction is performed using a 0.3 mol / L sulfuric acid solution.

[0061] S5. Preparation of lithium carbonate: The only difference from step S5 in Example 1 is that the mass fraction of sodium carbonate solution is 20% (the amount added is 1.08 times the theoretical amount), and the reaction is carried out at a constant temperature of 80°C with stirring for 1.0 h; the purity of battery-grade lithium carbonate is 99.9% as detected by inductively coupled plasma atomic emission spectrometry.

[0062] S6, Second-stage extraction and back-extraction: Same as step S4.

[0063] S7. Closed-loop regeneration of cathode material: The cathode black powder precursor obtained in S3 and the battery-grade lithium carbonate obtained in S5 are mixed at a Li:Fe molar ratio of 1.03:1. Carbon source (sucrose) and phosphorus source (ammonium dihydrogen phosphate) are added. The amount of carbon source added is 5% of the molar amount of iron element, and the amount of phosphorus source added is made up according to the iron-phosphorus molar ratio of 1:1 in the target lithium iron phosphate chemical formula. Under nitrogen atmosphere, it is calcined at 700℃ for 6 hours. After cooling, crushing and sieving, the regenerated lithium iron phosphate cathode material is obtained.

[0064] The XRD pattern of the delithiation filter cake obtained from step S3 is shown below. Figure 8 As shown, the XRD pattern of battery-grade lithium carbonate obtained in step S5 is as follows. Figure 9 As shown, the XRD pattern of the regenerated lithium iron phosphate cathode material obtained by high-temperature calcination is as follows. Figure 10 As shown, the purity of the main phase of the regenerated lithium iron phosphate cathode material was 95.3% after testing; the initial discharge capacity was 156.8 mAh / g after testing with a coin cell, using the same method as in Example 1.

[0065] Example 4: Closed-loop regeneration of cathode black powder from retired lithium iron phosphate batteries (under different process conditions) The process flow is the same as in Example 1. The specific steps are as follows: S1. Raw material pretreatment: Same as step S1 in Example 3.

[0066] S2, Electrochemical indirect oxidation delithiation: The only difference from step S2 in Example 1 is that the lithium bromide aqueous solution has a mass fraction of 3.5%, black powder is added at a solid-liquid ratio of 100 g / L, the cathode is a titanium electrode, the cell voltage is 2.2 V, and electrolysis is carried out at room temperature with stirring for 5 h.

[0067] S3, Solid-liquid separation: Same as step S3 in Example 1.

[0068] S4, First-stage extraction and back-extraction: The only difference from step S4 in Example 1 is that the co-extractant is a mixed trialkylphosphine oxide (Cyanex 923), the molar ratio of the main extractant to the co-extractant is 1:3; the volume ratio of the organic phase to the aqueous phase during extraction is 2:1, and 5-stage countercurrent extraction is performed; 0.4 mol / L sulfuric acid is used for back-extraction, and the volume ratio of the organic phase to the aqueous phase during back-extraction is 4:1, and 4-stage countercurrent back-extraction is performed.

[0069] S5. Lithium carbonate preparation: The only difference from step S5 in Example 1 is that the amount of sodium carbonate added is 1.12 times the theoretical amount, the reaction temperature is 90℃, and the reaction time is 1.5 h. Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis showed that the purity of battery-grade lithium carbonate was 99.7%.

[0070] S6, Second-stage extraction and back-extraction: Same as step S4.

[0071] S7. Closed-loop regeneration of cathode material: The only difference from step S7 in Example 3 is that the Li:Fe molar ratio is 1.05:1, and the carbon source (glucose) and phosphorus source (phosphoric acid) are matched. The amount of carbon source added is 10% of the molar amount of iron element, and the amount of phosphorus source added is made up according to the iron-phosphorus molar ratio of 1:1 in the target lithium iron phosphate chemical formula. The material is calcined at 750°C for 5 h under a nitrogen atmosphere.

[0072] The purity of the main phase of the recycled lithium iron phosphate cathode material was 95.0% as tested. The initial discharge capacity was 154.5 mAh / g when tested with a coin cell using the same method as in Example 1.

[0073] Example 5 A system for regenerating retired lithium-ion batteries using electrochemical indirect oxidation coupled with two-stage extraction as described in Examples 1-4 includes a single-chamber electrolyzer, a first filtration unit, a first-stage extraction unit, a first-stage back-extraction unit, a lithium precipitation reactor, a second filtration unit, a second-stage extraction unit, a second-stage back-extraction unit, a mixing and calcination unit, and a system-built-in parameter configuration module. Each unit is equipped with an interlocking automatic control mechanism, thus establishing a complete universal closed-loop regeneration production line for retired lithium iron phosphate / ternary batteries. The structural and pipeline coupling relationships of each unit are as follows: The single-chamber electrolytic cell is a corrosion-resistant, diaphragm-free electrolytic cell. It contains an anode and a cathode. The anode uses a titanium-based ruthenium-iridium stabilizing bromine electrode, and the cathode uses a stainless steel electrode (which can be switched to a titanium, nickel, or graphite electrode depending on the raw material type). The electrolytic cell is equipped with a lithium bromide aqueous solution inlet, a positive electrode black powder inlet, a stirring device, and a solid-liquid mixture outlet. The electrolytic cell is equipped with a current / voltage control unit, with a cell voltage control range of 1.5~3.0 V, preferably 1.8~2.5 V.

[0074] The inlet of the first filtration unit is connected to the solid-liquid mixture outlet of the single-chamber electrolyzer via a pipeline, and is equipped with a solid phase outlet and a liquid phase outlet; the solid phase outlet is connected to a drying device; the liquid phase outlet is connected to the aqueous phase inlet of a first-stage extraction unit.

[0075] The first-stage extraction unit is equipped with an extractant inlet, a raffinate outlet, and a lithium-loaded organic phase outlet. The raffinate outlet is connected to the lithium bromide aqueous solution inlet of the single-chamber electrolyzer via a first reflux pipeline, forming a closed-loop circulation circuit containing lithium bromide raffinate. The first-stage extraction unit is equipped with an automatic extraction ratio control module, with a ratio range (volume ratio of organic phase to aqueous phase) of 1:4 to 2:1 and 2 to 6 extraction stages.

[0076] The organic phase inlet of the first-stage back-extraction unit is connected to the lithium-loaded organic phase outlet of the first-stage extraction unit. The first-stage back-extraction unit is equipped with a back-extraction acid inlet (the back-extraction acid is a sulfuric acid solution with a concentration of 0.1~1.0 mol / L), a regenerated organic phase outlet, and a first-stage back-extraction lithium-rich solution outlet. The regenerated organic phase outlet is connected to the extractant inlet of the first-stage extraction unit through a pipeline to realize the recycling of the organic phase.

[0077] The lithium-rich liquid inlet of the lithium precipitation reactor is connected to the lithium-rich liquid outlet of a section of the back-extraction unit through a pipeline. The lithium precipitation reactor is equipped with a sodium carbonate solution inlet, a heating device (temperature control 70~95℃) and a lithium carbonate slurry outlet.

[0078] The inlet of the second filtration unit is connected to the lithium carbonate slurry outlet of the lithium precipitation reactor. The second filtration unit is equipped with a solid phase outlet and a liquid phase outlet. The solid phase outlet is connected in sequence to the lithium carbonate washing equipment and the lithium carbonate drying equipment, and outputs battery-grade lithium carbonate to the feed end of the ball mill.

[0079] The aqueous phase inlet of the second-stage extraction unit is directly connected to the liquid phase outlet of the second filtration unit through a pipeline. The second-stage extraction unit is equipped with an extractant inlet, a raffinate outlet, and a lithium-loaded organic phase outlet. The first-stage extraction unit and the second-stage extraction unit share an extractant storage tank and interconnected circulation pipeline, and the extractant can be bidirectionally interconnected and reused.

[0080] The organic phase inlet of the two-stage back-extraction unit is connected to the lithium-loaded organic phase outlet of the two-stage extraction unit. It is equipped with a back-extraction acid inlet, a regenerated organic phase outlet, and a two-stage back-extraction lithium-rich liquid outlet. The two-stage back-extraction lithium-rich liquid outlet is connected to the first-stage back-extraction lithium-rich liquid outlet of the first-stage back-extraction unit through a pipeline. After merging, they are connected to the lithium-rich liquid inlet of the lithium precipitation reactor. The regenerated organic phase outlet is connected to the extractant inlet of the two-stage extraction unit through a pipeline to realize the recycling of the organic phase.

[0081] The mixing and calcination unit includes a drying device, a closed ball milling device, and a high-temperature calcination furnace with controllable atmosphere. The closed ball milling device is equipped with a lithium carbonate inlet, a cathode black powder precursor inlet, a carbon source inlet, and an optional phosphorus source inlet. The outlet of the drying device is connected to the cathode black powder precursor inlet of the closed ball milling device via a pipeline, and the outlet of the lithium carbonate drying device is connected to the lithium carbonate inlet of the closed ball milling device via a pipeline. After ball milling and mixing, the mixture is sent to the high-temperature calcination furnace with controllable atmosphere. The calcination furnace switches the atmosphere according to the type of raw material, and the calcined product is cooled, crushed, and screened to obtain the finished recycled cathode material.

[0082] The system has a built-in parameter configuration module, including an electrolytic cell current / voltage control unit, an extraction ratio control unit, a lithium precipitation reaction temperature control unit, and a sodium carbonate dosage control unit. It is equipped with a fully automatic interlocking actuator: when the extraction ratio deviates from the set value, the organic / aqueous phase feed flow rate is automatically adjusted; when the lithium precipitation reaction temperature exceeds the range of 70~95℃, the heating device is adjusted in conjunction with the system; when the sodium carbonate dosage deviates from the theoretical dosage by 1.05~1.20 times, the metering pump is adjusted in conjunction with the system; the roasting unit automatically matches the corresponding roasting temperature, holding time, and protective atmosphere according to the type of black powder raw material, realizing fully automated continuous closed-loop operation.

[0083] Comparative Example 1: Single-stage extraction only (two-stage extraction process omitted) This comparative example aims to verify the necessity of the two-stage extraction process of the present invention for improving the overall lithium recovery rate.

[0084] The only difference between this comparative example and Example 1 (retired ternary NCM523 battery) is that step S6 (two-stage extraction and back-extraction process) is omitted. That is, the lithium precipitation mother liquor obtained after lithium precipitation filtration in step S5 is no longer subjected to two-stage extraction and is directly discharged as wastewater. The remaining steps (S1~S5, S7) and process parameters are exactly the same as in Example 1.

[0085] In Comparative Example 1, step S4, a single-stage extraction and recovery yielded a lithium-rich back-extraction solution. After lithium precipitation via carbonation in step S5, the residual dissolved lithium concentration in the mother liquor was approximately 1.8 g / L (based on elemental lithium). This residual lithium was discharged with the mother liquor and could not be recovered. Calculations showed that in Example 1, starting from the original lithium-containing alkaline filtrate (total lithium content 100%), the primary lithium recovery rate after single-stage extraction and precipitation was approximately 82.3%, while the discharge of the mother liquor resulted in a lithium resource loss of approximately 17.7%. In contrast, Example 1 of this invention utilizes a two-stage extraction process for deep recovery of the lithium-precipitated mother liquor, allowing for the recapture and reuse of over 90% of the residual lithium, achieving a comprehensive lithium recovery rate of over 98.5% for the entire process. The results demonstrate that single-stage extraction alone cannot solve the problem of lithium dissolution loss in the lithium-precipitated mother liquor. This invention employs a two-stage extraction process for independent closed-loop recovery of the lithium-precipitated mother liquor, significantly improving the comprehensive utilization rate of lithium resources.

[0086] Comparative Example 2: A conventional carboxylic acid extraction system (containing Fe) was used. 3+ (Co-extractant) as a substitute for the present invention β -Diketone extraction system This comparative example aims to verify the methods used in this invention. β - The advantage of combining diketones with neutral phosphorus co-extractants in avoiding the introduction of foreign metal impurities in alkaline lithium-containing filtrate systems.

[0087] The only difference between this comparative example and Example 3 (retired lithium iron phosphate battery) is that the extractant in steps S4 and S6 is replaced with a conventional carboxylic acid extraction system, specifically using cycloalkanoic acid and Fe. 3+ Co-extractant (cycloalkanoic acid concentration 0.8 mol / L, Fe) 3+ The added amount (0.2 times the molar amount of lithium) was dissolved in sulfonated kerosene as the extraction organic phase. Other process parameters, such as the extraction phase, number of stages, and back-extraction acid concentration, remained consistent with Example 3. However, since conventional carboxylic acid extraction systems require acidic conditions for effective lithium extraction, and the lithium-containing filtrate obtained from the electrochemical delithiation of this invention is strongly alkaline (pH≈10.5), Comparative Example 2 required an additional pretreatment step of "sulfuric acid acidification to adjust pH to 4.5" before the extraction operation.

[0088] Comparative Example 2: After acidification pretreatment, lithium extraction was achieved in the extraction process, but a large amount of Fe was detected in the lithium-rich solution after back-extraction. 3+ (Content approximately 85 mg / L) and residual sulfate. The lithium carbonate product prepared by precipitation with sodium carbonate from this lithium-rich back-extraction solution contained an iron impurity content as high as 0.032%, far exceeding the industry standard for battery-grade lithium carbonate (typically requiring Fe ≤ 0.001%). After high-temperature solid-phase regeneration of this lithium carbonate with the delithiation filter cake, regenerated lithium iron phosphate cathode material was obtained. When coin cells were assembled using this material and tested at 0.1C charge / discharge, the initial discharge capacity was only 122.3 mAh / g, far lower than the regenerated material obtained in Example 3, and the capacity retention rate after 50 cycles was only 82%, indicating significant deterioration in electrochemical performance. Simultaneously, due to the introduction of a large amount of sulfate during acidification pretreatment, severe salt accumulation occurred in the lithium precipitation mother liquor, making direct return to the system for recycling impossible. The results indicate that conventional extraction systems containing metal co-extractants cannot achieve a clean connection with the alkaline lithium-containing filtrate of this invention, introducing fatal metal impurities from the source and severely damaging the electrochemical performance of the regenerated cathode material. This invention, however, uses a metal-free co-extractant... β - The diketone extraction system can directly and selectively extract lithium under alkaline conditions without acidification pretreatment, and does not introduce foreign metal impurities throughout the process, ensuring the high purity of lithium carbonate and the final recycled materials.

[0089] The embodiments of the present invention have been shown and described above. Those skilled in the art can make improvements or modifications based on the above description. For example, if the pretreated black powder contains aluminum as the anode current collector, it is dissolved in dilute acid or dilute alkali solution, and then washed and filtered to obtain aluminum-free black powder; before oxidative leaching of lithium, polyvinylidene fluoride (PVDF) in the black powder is recovered by dissolving and leaching with N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF), or it is removed directly by pyrolysis; the electro-oxidation to produce bromine and the bromine oxidation leaching of lithium are carried out separately (i.e., the bromine-containing solution obtained by electro-oxidation is exported from the electrolytic cell to oxidize the black powder) to protect the electrodes; a porous membrane is set between the anode chamber and the cathode chamber to reduce the consumption of bromine produced at the cathode; sulfuric acid is used to remove carbonate ions from the mother liquor of lithium precipitation, or a portion of the acidic back-extraction solution obtained from one stage of back-extraction is diverted for acidification of the mother liquor of lithium precipitation to remove carbonate ions; an appropriate amount of lithium hydroxide is added to the alkaline filtrate obtained after solid-liquid separation after electrolysis to eliminate the influence of unreacted bromine ions on the extraction organic phase, and at the same time to supplement lithium bromide. All equivalent substitutions and process fine-tunings based on the coupled closed-loop regeneration approach of "single-chamber membrane-free electrochemical bromine oxidation delithiation - two-stage metal-free alkaline extraction - solid-phase roasting regeneration" fall within the protection scope of this invention.

Claims

1. A method for regenerating retired lithium-ion batteries using electrochemical indirect oxidation coupled with two-stage extraction, characterized in that, Includes the following steps: S1. Raw material pretreatment: The retired lithium-ion batteries are deep discharged, disassembled, crushed and sorted to remove impurities and obtain pure positive electrode black powder. S2. Electrochemical indirect oxidation delithiation: An aqueous solution of lithium bromide is fed into a single-chamber electrolytic cell, and the cathode black powder is suspended in the aqueous solution of lithium bromide; the anode electro-oxidizes bromide ions to generate elemental bromine, and the elemental bromine oxidizes the lattice of the cathode black powder to achieve selective delithiation of lithium ions; hydroxide ions are generated simultaneously at the cathode, so that the dissolved metal ions precipitate into the solid phase in the form of hydroxides. S3. Solid-liquid separation: After electrolysis, the solid-liquid mixture is filtered to obtain a delithiated filter cake and an alkaline lithium-containing filtrate; the delithiated filter cake is dried to obtain a positive electrode black powder precursor; S4. First-stage extraction and back-extraction: The alkaline lithium-containing filtrate is subjected to first-stage extraction using an extractant to separate a first-stage raffinate and a first-stage lithium-loaded organic phase; the first-stage lithium-loaded organic phase is subjected to back-extraction using sulfuric acid solution to separate a first-stage lithium-rich back-extraction solution and a first-stage delithiated organic phase. S5. Lithium carbonate preparation: Add sodium carbonate solution to the lithium-rich back-extraction solution obtained in step S4, and after precipitation reaction, filter to obtain crude lithium carbonate and lithium precipitation mother liquor; the crude lithium carbonate is washed and dried to obtain battery-grade lithium carbonate. S6. Two-stage extraction and back-extraction: The lithium precipitation mother liquor is subjected to two-stage extraction using an extractant to separate the two-stage raffinate and the two-stage extracted lithium-loaded organic phase; the two-stage extracted lithium-loaded organic phase is back-extracted using sulfuric acid solution to separate the two-stage back-extracted lithium-rich solution and the two-stage back-extracted delithiated organic phase. S7. Closed-loop regeneration of cathode material: The cathode black powder precursor obtained in step S3 and the battery-grade lithium carbonate obtained in step S5 are mixed according to the stoichiometric ratio of the target cathode material, and after matching carbon source and / or phosphorus source, they are calcined at high temperature in a solid state, cooled, crushed and sieved to obtain the regenerated cathode material.

2. The method according to claim 1, characterized in that, In step S1, the retired lithium-ion battery is a lithium iron phosphate battery or a nickel-cobalt-manganese ternary lithium-ion battery.

3. The method according to claim 1, characterized in that, In step S2, the single-chamber electrolytic cell is a corrosion-resistant, diaphragm-free electrolytic cell. The anode is a shape-stabilized bromine-electrolyte electrode, and the cathode is one of a titanium electrode, a stainless steel electrode, a nickel electrode, or a graphite electrode. The mass fraction of the lithium bromide aqueous solution is 0.5% to 5%. The solid-liquid ratio of the positive electrode black powder to the lithium bromide aqueous solution is 10 to 100 g / L. Electrolysis is carried out in constant current or constant voltage mode, with a cell voltage of 1.5 to 3.0 V. Electrolysis is carried out with stirring at room temperature for 1 to 6 hours.

4. The method according to claim 1, characterized in that, In steps S4 and S6, the extractant includes a main extractant and a co-extractant, wherein the main extractant is... β -Diketone compounds, the β - The diketone compound is selected from one of 2-thiophenecarboxyltrifluoroacetone, benzoyltrifluoroacetone, and dibenzoylmethane; the co-extractant is a neutral phosphorus co-extractant, which is selected from one of trioctylphosphine oxide, tributyl phosphate, and mixed trialkylphosphine oxide; the concentration of the sulfuric acid solution is 0.1~1.0 mol / L.

5. The method according to claim 1, characterized in that, In steps S4 and S6, the extraction operation conditions are: the volume ratio of organic phase to aqueous phase is (1:4) to (2:1), and the extraction method is 2 to 6 stages of countercurrent extraction; the back extraction operation conditions are: the volume ratio of organic phase to aqueous phase is (1:1) to (5:1), and the back extraction method is 2 to 5 stages of countercurrent back extraction.

6. The method according to claim 1, characterized in that, In step S5, the mass fraction of the sodium carbonate solution is 10%~30%; the amount of sodium carbonate added is 1.05~1.20 times the theoretical amount required for complete lithium precipitation; the reaction temperature is 70~95℃, and the reaction time is 0.5~1.5 h.

7. The method according to claim 1, characterized in that, In step S4, the first stage of raffinate is returned to step S2 as an electrolyte for recycling, and the first stage of delithiated organic phase is returned to the first stage of extraction for recycling. In step S6, the second stage of delithiated organic phase is returned to the second stage of extraction for recycling. All the lithium-rich liquid from the second stage of extraction is incorporated into the lithium-rich liquid from the first stage of extraction obtained in step S4, and together they are sent to step S5 for lithium precipitation again to achieve full extraction of lithium resources.

8. The method according to claim 1, characterized in that, In step S7, when the raw material is lithium iron phosphate black powder, additional carbon and phosphorus sources are required. Lithium carbonate and delithiation filter cake are mixed at a Li:Fe molar ratio of 1.00~1.05:1, the amount of carbon source added is 5%~20% of the molar amount of iron, and the amount of phosphorus source added is Fe:P molar ratio of 1:

1. The calcination temperature is 600~800℃, the time is 2~8 h, and the calcination atmosphere is nitrogen or argon. When the raw material is nickel cobalt manganese ternary black powder, additional carbon source is required. Lithium carbonate and delithiation filter cake are mixed at a Li:(Ni+Co+Mn) molar ratio of 1.02~1.08:1, and the amount of carbon source added is 3%~15% of the total molar amount of transition metals (Ni+Co+Mn). The mixture is first reduced and calcined at 500~650℃ for 1~4 h in an inert atmosphere of nitrogen or argon, and then switched to an air or pure oxygen atmosphere and calcined at 800~950℃ for 3~10 h.

9. The method according to claim 8, characterized in that, The carbon source is selected from one or more of glucose, sucrose, starch, citric acid, and acetylene black; the phosphorus source is selected from at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and triammonium phosphate.

10. A system for implementing the electrochemical indirect oxidation coupled with two-stage extraction method for regenerating retired lithium-ion batteries according to any one of claims 1 to 9, characterized in that, include: A single-chamber electrolytic cell, which is a diaphragm-free electrolytic cell, is equipped with an anode and a cathode. The electrolytic cell is equipped with a lithium bromide aqueous solution inlet, a positive electrode black powder inlet, a stirring device, and a solid-liquid mixture outlet. The first filtration unit has its inlet connected to the solid-liquid mixture outlet of the single-chamber electrolytic cell via a pipeline. The first filtration unit is provided with a solid phase outlet and a liquid phase outlet. The solid phase outlet is connected to a drying device. A first-stage extraction unit has its aqueous phase inlet connected to the liquid phase outlet of the first filtration unit via a pipeline. The first-stage extraction unit is equipped with an extractant inlet, a raffinate outlet, and a lithium-loaded organic phase outlet. The raffinate outlet is connected to the lithium bromide aqueous solution inlet of the single-chamber electrolyzer via a first reflux pipeline, forming a closed-loop circulation circuit containing bromine raffinate. A first-stage back-extraction unit has an organic phase inlet connected to a lithium-loaded organic phase outlet of a first-stage extraction unit. The first-stage back-extraction unit is equipped with a back-extraction acid inlet, a regenerated organic phase outlet, and a first-stage back-extraction lithium-rich liquid outlet. The regenerated organic phase outlet is connected to the extractant inlet of the first-stage extraction unit via a pipeline. The lithium precipitation reactor has a lithium-rich liquid inlet connected to a section of the lithium-rich liquid outlet of a section of the back-extraction unit via a pipeline. The lithium precipitation reactor is equipped with a sodium carbonate solution inlet, a heating device, and a lithium carbonate slurry outlet. The second filtration unit has its inlet connected to the lithium carbonate slurry outlet of the lithium precipitation reactor. The second filtration unit is equipped with a solid phase outlet and a liquid phase outlet. The solid phase outlet is connected in sequence to a lithium carbonate washing device and a lithium carbonate drying device, and outputs battery-grade lithium carbonate. The liquid phase outlet outputs lithium precipitation mother liquor. The two-stage extraction unit has its aqueous phase inlet connected to the liquid phase outlet of the second filtration unit via a pipeline; the two-stage extraction unit is equipped with an extractant inlet, a raffinate outlet, and a lithium-loaded organic phase outlet; the first-stage extraction unit and the second-stage extraction unit share an extractant storage tank and interconnected circulation pipeline, and the extractant can be bidirectionally interconnected and reused; the second-stage raffinate is equipped with an independent collection and disposal pipeline. The two-stage back-extraction unit has an organic phase inlet connected to the lithium-loaded organic phase outlet of the two-stage extraction unit. The two-stage back-extraction unit is equipped with a back-extraction acid inlet, a regenerated organic phase outlet, and a two-stage back-extraction lithium-rich liquid outlet. The two-stage back-extraction lithium-rich liquid outlet is connected to the first-stage back-extraction lithium-rich liquid outlet of the first-stage back-extraction unit through a pipeline, and the two outlets are then connected to the lithium-rich liquid inlet of the lithium precipitation reactor. The regenerated organic phase outlet is connected to the extractant inlet of the two-stage extraction unit through a pipeline. The mixing and calcining unit includes a drying device, a ball milling device, and a high-temperature calcining furnace. The ball milling device is equipped with a lithium carbonate inlet, a cathode black powder precursor inlet, a carbon source inlet, and an optional phosphorus source inlet. The outlet of the drying device is connected to the cathode black powder precursor inlet of the ball milling device via a pipeline. The outlet of the lithium carbonate drying device is connected to the lithium carbonate inlet of the ball milling device via a pipeline. The outlet of the ball milling device is connected to the inlet of the high-temperature calcining furnace. The system has a built-in parameter configuration module, including an electrolytic cell current / voltage control unit, an extraction ratio control unit, a lithium precipitation reaction temperature and sodium carbonate dosage control unit, and all equipment is equipped with automatic interlocking actuators.

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