A lithium ion battery positive electrode black powder closed-loop regeneration method based on acid-base self-circulation

Abstract

The present application belongs to the technical field of waste lithium ion battery recycling, and discloses a lithium ion battery positive electrode black powder closed-loop regeneration method based on acid-base self-circulation. The retired battery is pretreated to obtain positive electrode black powder, which is extracted by sulfuric acid-hydrogen peroxide, and selective precipitation / iron removal is carried out by lithium hydroxide. After solid-liquid separation, lithium sulfate-containing filtrate is obtained, which is concentrated and then introduced into a bipolar membrane electrodialysis system to in-situ co-produce sulfuric acid and lithium hydroxide, realizing self-circulation and reuse within the acid-base reagent process. Lithium hydroxide in the alkali chamber is carbonated to prepare lithium carbonate, and the lithium precipitation mother liquor is acidified and converted to realize closed-loop reuse. Finally, nickel-cobalt-manganese hydroxide or iron phosphate solid phase is mixed with self-made lithium carbonate, high-temperature calcination is carried out, and the positive electrode material is regenerated. The present application solves the problems of large acid and alkali consumption and large amount of waste liquid in traditional wet recovery, realizes multi-dimensional closed-loop circulation of acid, alkali and lithium precipitation mother liquor, and has simple process and low energy consumption, which is suitable for ternary and lithium iron phosphate battery systems.

Description

Technical Field

[0001] This invention belongs to the field of waste lithium-ion battery recycling technology, specifically relating to a closed-loop regeneration method for lithium-ion battery cathode black powder based on acid-base self-circulation. Background Technology

[0002] With the rapid development of the new energy vehicle industry, lithium-ion batteries (including ternary lithium batteries and lithium iron phosphate batteries) have become the mainstream category of on-board power batteries due to their advantages such as high energy density, excellent cycle performance, and wide applicability. Generally, the lifespan of lithium-ion batteries is 5 to 8 years. As early new energy vehicle power batteries gradually enter their retirement period, a wave of retired lithium-ion batteries is underway. Retired lithium-ion batteries are rich in valuable metals such as lithium, nickel, and cobalt, possessing extremely high resource recycling value. Improper disposal can lead to heavy metal pollution and resource waste. Therefore, developing efficient and green recycling technologies for retired lithium-ion batteries is of great significance for promoting the sustainable development of the new energy industry.

[0003] Currently, the recycling technologies for cathode materials from retired lithium-ion batteries are mainly divided into two categories: pyrometallurgy and hydrometallurgy. Pyrometallurgy suffers from high energy consumption, significant lithium volatilization loss, and low overall lithium recovery rate, limiting its industrial application. Hydrometallurgy, due to its mild reaction conditions and good metal purification effect, has become the mainstream approach in the industry. Existing hydrometallurgical recycling routes can be divided into extraction and separation for lithium extraction, membrane separation coupled with bipolar membrane for lithium extraction, etc. However, the relevant representative patent solutions still have multiple common pain points in the industry, making it difficult to achieve the goal of in-situ regeneration of cathode materials with full composition, low energy consumption, no impurity introduction, and a completely closed-loop material process.

[0004] For example, Chinese patent CN117163976A discloses a recovery process for preparing lithium hydroxide monohydrate using a combination of full membrane coupling and bipolar membranes. This process relies on a series of membrane stages (ultrafiltration, nanofiltration, reverse osmosis, and electrodialysis) to separate lithium from nickel, cobalt, and manganese, followed by bipolar membrane electrolysis to produce lithium hydroxide. While this process achieves the reuse of byproduct acid (only the byproduct sulfuric acid is refluxed to the acid leaching section), it still has the following problems: 1) Loss of transition metal resources, making closed-loop regeneration of cathode materials impossible: This process relies on nanofiltration to retain divalent metals such as nickel, cobalt, and manganese. However, the retained concentrate lacks accompanying precipitation, precursor preparation, and cathode roasting processes. High-value metals like nickel, cobalt, and manganese cannot be recycled; only lithium salts are extracted separately. The recycled products have low added value and cannot be directly reintroduced into the power battery industry chain. Furthermore, this process is unsuitable for lithium iron phosphate systems. After complete dissolution in strong acid, iron and phosphorus simultaneously enter the membrane concentrate and are lost, leaving no raw materials needed for regenerating lithium iron phosphate.

[0005] 2) Poor industrial stability and high operation and maintenance costs of multi-stage membrane series: To achieve the separation of lithium from polyvalent metals, five purification units, namely ultrafiltration, nanofiltration, reverse osmosis, and electrodialysis, need to be connected in series. The acid leaching solution contains carbon powder, binder colloids, and heavy metal particles, which can easily cause irreversible blockage of the nanofiltration and reverse osmosis membrane pores. This significantly increases the equipment footprint and power consumption. Membrane retention generates a large amount of high-salt hazardous wastewater containing heavy metals, requiring a large investment in the supporting wastewater treatment system, making continuous and stable industrial production difficult.

[0006] 3) Continuous contamination of the membrane system by impurities leads to cumulative lithium loss: Without a pre-treatment selective precipitation process, iron, nickel, cobalt, and manganese flow through the entire membrane system. Multivalent ions form a concentration polarization layer on the membrane surface, significantly reducing lithium-ion permeation efficiency. Example data shows that lithium loss in the membrane separation stage alone reaches approximately 4.8%. Back-end resin regeneration generates a large amount of saline wastewater, and trace amounts of heavy metals cannot be completely removed, making it difficult for the purity of lithium hydroxide products to meet high-end battery-grade standards.

[0007] Chinese patent CN113151680A, based on the use of bipolar membrane for acid and alkali production, introduces precursor preparation and mixed sintering regeneration of the positive electrode steps. However, its technical solution has a series of interconnected and substantial defects in terms of industrialization logic: 1) The process flow is lengthy and fragmented, lacking a multi-dimensional material closed loop, resulting in poor overall economic efficiency: The leaching, impurity removal, bipolar film, precursor synthesis, lithium salt crystallization, and cathode sintering processes are independent of each other. A multi-cycle coupling system involving acid, alkali, lithium, and CO2 is not established between these processes. Byproducts / waste liquid are generated with each single material pass-through, resulting in cumbersome process steps, low material utilization, and an excessively long resource recycling chain. Related mother liquor recovery processes are lacking (e.g., the regeneration process after resin adsorption saturation requires additional consumption of large amounts of acid and generates high-concentration heavy metal regeneration waste liquid), and the waste liquid discharge problem is not fundamentally solved, failing to meet the requirements of truly closed-loop clean production.

[0008] 2) Transition metal ions invade the bipolar membrane electrodialysis system throughout the entire process, posing an extremely high risk of membrane fouling and system collapse: This scheme directly introduces a solution containing large amounts of transition metal ions such as nickel, cobalt, and manganese into the bipolar membrane electrodialysis device. These high-valence metal ions and lithium ions engage in intense competitive migration under the electric field, severely reducing lithium migration efficiency and current efficiency. In particular, with the increasing OH content in the alkali chamber... - The formation of these substances and the increase in pH make it easy for transition metal ions to deposit hydroxides and phosphates on the membrane surface and inside the membrane stack, causing irreversible blockage and contamination of the bipolar membrane and cation exchange membrane. This leads to a sharp increase in operating and maintenance costs, and the long-term stability of the system cannot be guaranteed. The salt chamber of bipolar membrane devices typically requires the content of high-valence cations to be less than 1 mg / L. Therefore, there are very few cases in the industry where high-valence cations are directly introduced into bipolar membrane electrolysis devices.

[0009] 3) The bipolar membrane electrodialysis system lacks a lithium concentration step before processing, resulting in a heavy equipment burden and high operating costs: In this scheme, the impurity removal solution directly enters the bipolar membrane electrodialysis system without any pre-concentration of lithium ions. The processing of a large amount of solution means a sharp increase in the scale of the membrane stack. At the same time, most of the energy consumption of the electric field is consumed in the electrolysis of water rather than the effective enrichment of lithium, resulting in extremely high energy consumption per unit of lithium hydroxide product. This approach not only significantly increases equipment investment and floor space but also further exacerbates the heat load of subsequent lithium hydroxide evaporation and crystallization, creating a cycle of "cumulative amplification" of energy consumption. In fact, because this process does not separate transition metals such as nickel, cobalt, and manganese in advance, the bipolar membrane device cannot tolerate the salt solution (transition metal ion concentration above 1 g / L), let alone the salt solution containing even higher concentrations of high-valence cations after concentration. Therefore, it is impossible to add a concentration step to the existing process.

[0010] 4) Lithium hydroxide preparation relies on energy-intensive evaporation and crystallization, making it difficult to achieve the required product purity: This method directly evaporates and crystallizes the low-concentration lithium hydroxide solution output from the bipolar membrane alkaline chamber, essentially drying it out. Otherwise, due to the lack of a closed-loop lithium salt cycle, the lithium salt cannot be fully recovered. Because of the low lithium ion concentration in the system, a large amount of water is vaporized and removed, resulting in high energy consumption and unacceptable industrialization costs. More importantly, a small portion of the dissolved nickel, cobalt, and manganese ions may also pass through the cation exchange membrane into the alkaline chamber during bipolar membrane electrodialysis. Because of the drying operation, all impurity ions in the bipolar membrane alkaline chamber enter the lithium hydroxide, leading to an impurity content in the final lithium hydroxide solid far exceeding battery-grade standards. Sintering this low-purity lithium hydroxide with the precursor will inevitably introduce impurity phases into the regenerated cathode material, reducing the material's crystal structure and electrochemical performance.

[0011] 5) Precursor synthesis relies on exogenous sodium / ammonium salts, continuously introducing foreign impurities into the system and compromising the quality of regenerated materials: This scheme requires the continuous purchase and addition of large amounts of externally sourced alkali solutions (ammonia, sodium carbonate, sodium hydroxide, etc.) and auxiliaries during the preparation of the solution output from the salt chamber and the synthesis of the precursor. The addition of these exogenous reagents introduces a large amount of sodium into the system. + NH4 + Foreign impurity ions. In the coprecipitation reaction, Na... + These substances readily become trapped within or on the surface of the precursor crystal lattice through peritectic or adsorption processes, making them difficult to remove completely with conventional water washing. Ultimately, they enter the high-temperature sintering process along with the precursor, causing irreversible damage to the layered or olivine structure of the recycled cathode material. Furthermore, the continued reliance on externally sourced chemicals means that this process remains dependent on large quantities of external reagents and generates substantial amounts of high-salt wastewater containing sodium or ammonium, increasing the cost of downstream environmental treatment.

[0012] 6) The lithium iron phosphate system employs total leaching, resulting in high acid and alkali consumption and a significantly increased bipolar membrane processing load: This method uses sulfuric acid / phosphoric acid for the complete dissolution and leaching of waste lithium iron phosphate battery materials, rather than selective lithium extraction. This approach allows iron and phosphorus to simultaneously enter the liquid phase, leading to a sharp increase in acid consumption during the leaching stage (theoretically three times higher than selective leaching). Furthermore, a large amount of alkaline solution is required subsequently to reprecipitate and separate the iron from the solution. More importantly, the large volume of leachate and the introduction of a large amount of sulfate ions required for total leaching multiply the volume of the feed solution entering the bipolar membrane system and the processing load, further increasing equipment scale and power consumption, thus reducing economic efficiency when processing retired lithium iron phosphate batteries.

[0013] In summary, although the scheme disclosed in CN113151680A involves the reuse of bipolar membrane acid production, as well as the precursor preparation and mixed sintering regeneration process, the various units are isolated from each other, resulting in a chain of technical defects such as uncontrolled energy consumption, difficulty in achieving product standards, easy collapse of the membrane system, continuous accumulation of impurities, and a large variety and volume of waste liquid. It is impossible to build a stable, economical, and clean closed-loop regeneration industrial system. Therefore, there is an urgent need to develop an integrated retired lithium battery recycling and regeneration process that features deep coupling throughout the entire process, multi-dimensional material closed-loop, low energy consumption, no external impurities, and direct in-situ regeneration of ternary / lithium iron phosphate cathode materials. Summary of the Invention

[0014] To address the shortcomings of existing wet recycling processes for waste lithium batteries, such as severe membrane contamination, introduction of sodium / ammonium impurities into the system, high consumption of acid and alkali reagents, low lithium recovery efficiency, single-material recycling, inability to simultaneously adapt to ternary and lithium iron phosphate waste, and poor electrochemical performance of regenerated cathodes, this invention provides a closed-loop regeneration method for lithium-ion battery cathode black powder based on acid-alkali self-circulation. This method achieves a six-fold synergistic closed loop, eliminates the introduction of external metal impurities throughout the process, and features low energy consumption, low reagent consumption, and one-step regeneration of ternary / lithium iron phosphate cathode materials that meet power battery standards.

[0015] The technical solution of this invention is: This invention provides a closed-loop regeneration method for lithium-ion battery cathode black powder based on acid-base self-circulation, comprising sequential, coupled, and inseparable complete process steps: S1. Battery pretreatment: Discharge, disassemble, crush, and sort retired lithium-ion batteries to obtain positive electrode black powder; the retired lithium-ion batteries are selected from ternary lithium batteries or lithium iron phosphate batteries. S2. Differentiated metal component leaching: The cathode black powder is leached using a sulfuric acid-hydrogen peroxide composite leaching system; the cathode black powder of the ternary power battery is leached with all metals to obtain the first solid phase and the first filtrate containing lithium, nickel, cobalt and manganese; the cathode black powder of the lithium iron phosphate system is leached with lithium selective leaching, the iron element is generated in situ to form the iron phosphate solid phase and remains, and only lithium enters the liquid phase to form the leaching slurry; S3. Selective solid-liquid separation of self-produced lithium hydroxide: The first filtrate or leaching slurry obtained in step S2 is subjected to selective precipitation by adjusting the pH with lithium hydroxide solution. After solid-liquid separation, a second filtrate containing only lithium sulfate and a second solid phase of transition metal without lithium are obtained. No external precipitating agents containing sodium / ammonium, such as sodium hydroxide, sodium carbonate, or ammonia, are added throughout this process. S4. Pre-concentration coupled bipolar membrane acid-base co-production cycle: First, the second filtrate produced in step S3 is concentrated to make the lithium ion concentration in the system ≥1.5 mol / L, and then sent to the three-compartment bipolar membrane electrodialysis system to co-produce sulfuric acid and lithium hydroxide solution in situ. S5, Carbonation precipitation of lithium: The lithium hydroxide solution produced in step S4 is reacted with carbon dioxide to undergo a carbonation reaction. After solid-liquid separation, 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. Acidification and conversion of lithium precipitation mother liquor: The lithium precipitation mother liquor is acidified by the sulfuric acid solution produced in step S4. The lithium in the mother liquor is converted back into lithium sulfate conversion solution and all of it is returned to the second filtrate of step S3. S7. In-situ regenerated cathode material: The transition metal second solid phase obtained in step S3 is mixed with the battery-grade lithium carbonate obtained in step S5, and a carbon source is added and optionally a phosphorus source is added before high-temperature calcination to prepare the finished cathode material.

[0016] It is important to note that steps S1 to S7 constitute an inseparable overall technical solution of this invention, with strict stoichiometric correspondences and material conservation constraints between each step. For example, the sulfuric acid consumed in step S2 (leaching) and step S6 (acidification), as well as the lithium hydroxide consumed in step S3 (precipitation) and step S5 (carbonation), are precisely replenished by the sulfuric acid and lithium hydroxide produced from the bipolar membrane electrodialysis decomposition of lithium sulfate in step S4; the CO2 consumed in step S5 (carbonation) is precisely regenerated in situ by the mother liquor acidification in step S6 and the roasting in step S7; the second solid phase obtained in step S3 and the lithium carbonate obtained in step S5 close the cathode material recycling chain through the high-temperature solid-phase reaction in step S7. The entire process does not introduce exogenous metal ion impurities such as sodium and ammonium. Each process synergistically constructs a six-fold integrated material closed loop: acid cycle, alkali cycle, lithium salt cycle, transition metal precursor cycle, carbon dioxide cycle, and cathode regeneration. These material cycles are interdependent and indispensable; the absence or substitution of any single process will lead to the collapse of the overall closed-loop system.

[0017] Preferably, the process parameters for step S2 extraction are as follows: solid-liquid ratio 20~150 g / L, sulfuric acid concentration 1~4 mol / L, hydrogen peroxide addition 0.3~1.2 mol / L, extraction temperature 50~80℃, and reaction time 1~4 h.

[0018] Preferably, the precipitation control conditions in step S3 are as follows: for the ternary system, an inert atmosphere is used, the reaction temperature is room temperature to 60°C, the pH is 10.5 to 12.0, and the reaction time is 1 to 4 h; for the lithium iron phosphate system, the pH is adjusted to ensure complete precipitation of trace iron, the reaction temperature is room temperature to 60°C, and the reaction time is 0.5 to 2 h; for the lithium iron phosphate system, a second solid phase can be obtained by solid-liquid separation before adding lithium hydroxide.

[0019] Preferably, the concentration method in step S4 is evaporation concentration or membrane concentration, and the concentrated Li ≥ 1.5 mol / L; the bipolar membrane current density is 25~100 mA / cm². 2 The salt chamber is only circulated with pre-concentrated high-purity lithium sulfate. The high-valence metal solid phases of nickel, cobalt, manganese and iron have been completely separated in step S3, and no high-valence metals enter the membrane stack to cause fouling on the membrane surface.

[0020] Preferably, in step S4, the acid chamber of the three-compartment bipolar membrane electrodialysis system is equipped with a dual reflux sulfuric acid branch, one of which returns to the extraction section in step S2 for recycling, and the other is supplied to the subsequent mother liquor acidification section; the alkali chamber is equipped with a dual reflux lithium hydroxide branch, one of which returns to step S3 as a selective precipitant, and the other is supplied to the carbonation lithium precipitation section.

[0021] Preferably, the carbonation process parameters in step S5 are as follows: reaction temperature 60~90℃, excess carbon dioxide (CO2) coefficient 1.05~1.2, reaction time 0.5~1.5 h, and solid sodium impurities in the obtained crude lithium carbonate ≤0.01%; Preferably, the amount of sulfuric acid added in step S5 is 1.0 to 1.1 times the theoretical amount of total alkali in the neutralization mother liquor. The carbon dioxide collected in the closed process during acidification in step S6 and the carbon dioxide collected under negative pressure during the roasting process in step S7 are combined and pressurized before being recycled to the carbonation process in step S5.

[0022] Preferably, the calcination control parameters for step S7 are as follows: ternary materials are calcined at 750~950℃ for 3~10 h in an oxygen or air atmosphere; lithium iron phosphate materials are calcined at 600~800℃ for 3~10 h in an inert atmosphere, with 0%~10% excess lithium added.

[0023] Preferably, the carbon source is selected from one or more of glucose, sucrose, starch, citric acid, and acetylene black.

[0024] Preferably, the phosphorus source is selected from phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and triammonium phosphate, and is replenished at a Fe:P molar ratio of 1:1 during use.

[0025] Another aspect of the present invention provides a system for realizing the closed-loop regeneration method of lithium-ion battery cathode black powder based on acid-base self-circulation, comprising a pretreatment unit, an extraction and solid-liquid separation unit, a precipitation and solid-liquid separation unit, a concentration unit, a bipolar membrane electrodialysis unit, a lithium carbonate precipitation unit, a lithium precipitation mother liquor acidification and conversion unit, and a cathode material preparation unit. The pretreatment unit is equipped with a positive electrode black powder outlet; The extraction and solid-liquid separation unit is equipped with a positive electrode black powder inlet, a hydrogen peroxide inlet, a sulfuric acid solution inlet, an outlet, and a solid phase outlet. The positive electrode black powder inlet is connected to the positive electrode black powder outlet of the pretreatment unit. The precipitation and solid-liquid separation unit is equipped with a feed inlet, an alkali recycling inlet, a mother liquor recycling inlet, a liquid phase outlet, and a solid phase outlet. The feed inlet is connected to the discharge outlet of the extraction and solid-liquid separation unit. The feed inlet of the concentration unit is connected to the liquid phase outlet of the precipitation and solid-liquid separation unit; The feed inlet of the bipolar membrane electrodialysis unit is connected to the discharge outlet of the concentration unit; its acid chamber outlet is divided into two paths, one path is connected to the sulfuric acid solution inlet of the extraction and solid-liquid separation unit, and the other path is connected to the sulfuric acid solution inlet of the lithium precipitation mother liquor acidification and conversion unit; its alkali chamber outlet is divided into two paths, one path is connected to the alkali solution recycling inlet of the precipitation and solid-liquid separation unit, and the other path is connected to the lithium hydroxide solution inlet of the carbonation lithium precipitation unit. The lithium carbonate precipitation unit is equipped with a carbon dioxide inlet, a lithium hydroxide solution inlet, a lithium carbonate solid phase outlet, and a lithium precipitation mother liquor outlet. The lithium hydroxide solution inlet is connected to the alkali chamber outlet of the bipolar membrane electrodialysis unit. The lithium precipitation mother liquor acidification conversion unit is equipped with a lithium precipitation mother liquor inlet, a sulfuric acid solution inlet, and a lithium sulfate conversion liquid outlet. The lithium precipitation mother liquor inlet is connected to the lithium precipitation mother liquor outlet of the carbonation lithium precipitation unit, and the lithium sulfate conversion liquid outlet is connected to the mother liquor recycling inlet of the precipitation and solid-liquid separation unit. The feed inlet of the cathode material preparation unit is connected to the lithium carbonate solid phase outlet of the lithium carbonate precipitation unit and the solid phase outlet of the precipitation and solid-liquid separation unit, respectively.

[0026] The core reaction principle of this invention is as follows: The entire process of this invention revolves around two main lines: "leaching → separation → enrichment → recovery" of lithium ions and "consumption → regeneration → recycling" of acid / alkali media. The specific reaction path is broken down by process as follows: 1. Principle of the synergistic leaching reaction of sulfuric acid and hydrogen peroxide Ternary cathode materials (represented by LiMO2, where M = Ni, Co, Mn) undergo redox leaching in a sulfuric acid and hydrogen peroxide system. The hydrogen peroxide removes the high-valence M... 3+ / M4+ Restore to M 2+ Simultaneously, it promotes lattice disruption, allowing lithium, nickel, cobalt, and manganese to enter the liquid phase entirely in the form of sulfates. The reaction stoichiometry can be simplified as follows: Under acidic oxidation conditions, lithium iron phosphate cathode materials exhibit selective lithium-ion release while iron remains in the FePO4 solid phase, achieving lithium-iron separation. The reaction formula is as follows: The first filtrate produced in the above leaching process (a ternary system containing Li) + Ni 2+ Co 2+ Mn 2+ ) or leachable slurry (lithium iron phosphate system containing Li) + (and FePO4 solid phase) provide reactants for subsequent separation processes.

[0027] 2. Principle of Lithium Hydroxide-Based Precipitation / Iron Removal Reaction In the ternary system, the pH of the filtrate was adjusted to 10.5-12.0 using self-produced lithium hydroxide, Ni 2+ Co 2+ Mn 2+ With OH - Simultaneous co-precipitation according to stoichiometric ratios generates nickel, cobalt, and manganese hydroxide precursors, while lithium ions remain in the liquid phase. In lithium iron phosphate systems, lithium hydroxide is added to the leaching slurry or lithium-containing filtrate to reduce the trace amounts of Fe that may dissolve during the leaching process. 3+ The lithium ions are removed by precipitation as ferric hydroxide, while the FePO4 main solid phase remains intact, and the lithium ions are completely retained in the lithium sulfate filtrate. The core chemical advantage of this process is that the precipitant is lithium hydroxide, and no sodium ions are introduced into the system. This avoids the cumbersome operation of subsequent deep sodium removal and ensures the high purity of the lithium sulfate filtrate entering the bipolar membrane system, which is conducive to the long-term stable operation of the membrane system.

[0028] 3. Principle of in-situ acid-base co-production reaction in bipolar membrane electrodialysis The concentrated lithium sulfate filtrate enters a three-compartment bipolar membrane electrodialysis system. Under the drive of a DC electric field, water molecules in the bipolar membrane interface layer dissociate to generate H+. + and OH - Meanwhile, the Li in the intermediate salt chamber + Driven by the electric field, they migrate towards the cathode side and react with OH generated by the cathode bipolar film. - Lithium hydroxide is formed and enters the alkali chamber; SO42- Migrating towards the anode side, and reacting with H generated by the anode bipolar film. + The resulting product is sulfuric acid, which enters the acid chamber. The overall net reaction can be represented as: Li₂SO₄ + 2H₂O (electric field driven) → H₂SO₄ (acid chamber) + 2LiOH (base chamber) This process enables direct acid-base dissociation of the salt solution. The sulfuric acid produced in the acid chamber is allocated for black powder leaching and mother liquor acidification, while the lithium hydroxide produced in the alkali chamber is allocated for precipitation / iron removal and lithium carbonate precipitation, forming an integrated acid-base self-circulation network.

[0029] 4. Principle of Lithium Carbonation Precipitation and Mother Liquor Acidification Conversion Reaction The high-concentration lithium hydroxide solution produced in the alkali chamber is passed through CO2 gas to undergo a carbonation reaction, during which lithium ions precipitate out as solid lithium carbonate. The reaction formula is as follows: Compared to traditional precipitation methods using sodium carbonate as a precipitant, lithium carbonate precipitation not only avoids the use of exogenous sodium carbonate reagents, but also avoids the impact of sodium impurities on the product and the generation of related sodium-containing waste liquid. Furthermore, the mother liquor after lithium carbonate precipitation contains a small amount of Li. + CO3 2- and OH - Directly discarding dilute alkaline solutions would result in the loss of lithium resources. This invention introduces an acidification conversion process: using sulfuric acid produced by a bipolar membrane to precisely acidify the lithium precipitation mother liquor, removing CO3 from the mother liquor. 2- It is converted into CO2 gas and escapes, while Li + It is converted back into soluble Li₂SO₄, and the reaction formula is as follows: The lithium sulfate in the conversion solution is returned and mixed with the second filtrate, so that the residual lithium in the mother liquor is 100% recovered. The high-purity CO2 released by acidification is collected and pressurized under negative pressure and then reused in the carbonation lithium precipitation process, forming a gas-liquid closed-loop cycle of "lithium precipitation → mother liquor acidification → CO2 reuse → lithium precipitation again", which greatly reduces carbon source consumption and greenhouse gas emissions.

[0030] 5. Reaction principle of high-temperature solid-phase calcination regenerated cathode material In the ternary system, the transition metal second solid phase (nickel, cobalt, and manganese hydroxide precursor) obtained in step S3 is mixed with self-produced battery-grade lithium carbonate at the target stoichiometric ratio and calcined at high temperature in an oxygen or air atmosphere. The hydroxide first decomposes into oxides, which then undergo a solid-phase reaction with the lithium salt to regenerate an electrochemically active layered ternary cathode material. The overall reaction is as follows: During the calcination process, lithium ions are embedded between the transition metal oxide layers, restoring the complete layered rock salt structure. This is accompanied by grain growth and morphology regulation, ultimately yielding a regenerated ternary cathode material with excellent electrochemical performance.

[0031] In the lithium iron phosphate system, the transition metal second solid phase (iron phosphate solid phase and possibly iron hydroxide mixed solid phase) obtained in step S3 is dried and then mixed with self-produced lithium carbonate, carbon source, and phosphate supplemented if necessary, according to the target stoichiometric ratio, and calcined at high temperature under an inert atmosphere. When pure FePO4 is used as the iron source, the carbon source will partially absorb the Fe. 3+ Reduced to Fe 2+ Simultaneously, lithium ions are intercalated to form olivine-type LiFePO4: (In the actual reaction, the carbon source is pyrolyzed into amorphous carbon, which simultaneously acts as a reducing agent and a precursor for conductive agents.) When the raw material route contains Fe(OH)3, phosphate needs to be added to compensate for the phosphorus deficiency, and Fe is removed through carbothermic reduction. 3 + Reduced to Fe 2+ The overall reaction can be expressed as: 2Fe(OH)3+ 2H3PO4→ 2FePO4+ 6H2O (The subsequent calcination reaction of FePO4 follows the same path as described above) or LiFePO4 can be directly generated from Fe(OH)3, phosphate, lithium carbonate, and a carbon source via a one-step high-temperature solid-state reaction, with the carbon source simultaneously undergoing Fe... 3+ →Fe 2+ The reduction task is achieved through the pyrolysis of the carbon source during calcination to form a uniformly coated carbon layer, simultaneously completing crystal phase reconstruction, particle size control, and conductive network construction, ultimately yielding a regenerated lithium iron phosphate cathode material with good rate performance and cycle stability.

[0032] 6. Full-process reaction network coupling relationship The five core reactions described above are interconnected, with a high degree of matching between material and energy flows: the sulfuric acid consumed in leaching and the lithium hydroxide consumed in precipitation are precisely replenished by the decomposition of lithium sulfate via bipolar membrane electrodialysis; the CO2 consumed in carbonation is precisely generated in situ through mother liquor acidification and high-temperature calcination; the converted lithium sulfate returns to the bipolar membrane system; and finally, the cathode material cycle chain is closed by a high-temperature solid-phase reaction between the precursor solid phase and the self-produced lithium carbonate. The overall reaction is: Ternary lithium battery: 2H₂O₂ → 2H₂O + O₂ Lithium iron phosphate battery: H2O2 + C (for high-temperature calcination and reduction) → H2O + CO The entire process constitutes a near-zero-emission chemical plant that primarily consumes H2O2 and electricity on a macroscopic scale, fundamentally ensuring the closed-loop characteristics and green, low-carbon attributes of this invention.

[0033] The core inventive concept of this invention: This invention differs from existing processes that involve independent and isolated steps and single-stage material reuse. It innovatively constructs an integrated and inseparable coupled process chain, which includes differentiated extraction, selective phase separation of self-produced lithium hydroxide, lithium liquid pre-concentration, bipolar membrane acid-alkali dual-branch co-production, carbonation refining and lithium precipitation, mother liquor acidification and lithium recovery, and roasting CO2 recycling. The entire process relies on three core media—lithium sulfate, lithium hydroxide, and carbon dioxide—to form a six-fold closed-loop system with interdependence and material conservation (acid cycle, alkali cycle, lithium salt cycle, transition metal precursor cycle, carbon dioxide cycle, and cathode regeneration cycle). The absence or removal of any step will disrupt the overall material balance and prevent the achievement of all beneficial technical effects.

[0034] The core innovation logic is explained in layers: (1) Differentiated leaching design: Ternary lithium is fully dissolved and all transition metals are dissolved simultaneously, while lithium iron phosphate is selectively extracted and iron phosphate solid phase is precipitated in situ. This reduces the acid consumption of the lithium iron phosphate process and the volume of subsequent membrane treatment liquid from the source, and achieves compatibility of two types of waste with one process.

[0035] (2) Pre-production of lithium hydroxide selective precipitation: without purchasing sodium and ammonium precipitating agents, the transition metals are pre-separated by using the self-produced alkali of the bipolar membrane at the back end. High-priced metals do not enter the bipolar membrane stack at all, which completely solves the industry pain points of membrane fouling and short lifespan, and at the same time, the introduction of sodium impurities is completely eliminated.

[0036] (3) Pre-concentrated coupled bipolar membrane acid-base dual-path distribution: After precipitation, the lithium sulfate solution is first concentrated to above 1.5 mol / L before electrolysis, which greatly reduces the energy consumption of electrolysis; acid and base are set up with two independent recycling branches respectively. Sulfuric acid is supplied for extraction + mother liquor acidification, and lithium hydroxide is supplied for precipitation + carbonation. All acid and base are internally consumed, and the consumption of externally purchased reagents is greatly reduced.

[0037] (4) Carbonation refining + mother liquor acidification of lithium closed loop: high-purity lithium hydroxide is prepared by reacting bipolar membrane high-purity lithium hydroxide with CO2, avoiding the high energy consumption and trace metal impurities caused by evaporation crystallization of lithium hydroxide and purification; the mother liquor of lithium precipitation is acidified to regenerate lithium sulfate and reflux to the front end, the mother liquor lithium is 100% recovered, and there is no loss of lithium resources.

[0038] (5) Closed-loop CO2 circulation throughout the process: All CO2 consumed by carbonation comes from the self-generated recovery of roasting and acidification conversion processes, eliminating the need to continuously purchase carbon dioxide from external sources, thus reducing production costs and carbon emissions.

[0039] (6) The transition metal solid phase is directly used as a precursor, and combined with the self-produced lithium carbonate high-temperature in-situ regenerated cathode, the entire industrial chain of "waste powder → metal separation → lithium refining → cathode finished product" is fully opened up, eliminating the need to sell intermediate salts externally, and the added value of resource utilization is greatly improved.

[0040] Advantages and beneficial effects of the present invention: (1) No sodium, ammonium or other impurities are introduced throughout the process. The sodium impurities in the regenerated ternary cathode and lithium iron phosphate cathode are stable at ≤0.01%, which meets the national standard impurity limit for power batteries and solves the defect of capacity decay caused by sodium salts intercalating into the lattice in the existing process.

[0041] (2) Transition metals are separated in the solid phase before the membrane, and high-valence metals do not enter the bipolar membrane at all, eliminating hydroxide scaling on the membrane surface. The membrane stack can operate continuously and stably for a long time, which greatly reduces the cost of membrane replacement and equipment maintenance.

[0042] (3) The pre-concentration process, combined with the bipolar membrane dual-branch acid-base cycle, significantly reduces electrolysis energy consumption and reduces the procurement cost of chemical reagents.

[0043] (4) The six materials are integrated into a closed loop, with acid, alkali, lithium, transition metal, CO2 and positive electrode precursor all circulating internally. Waste liquid and waste gas are nearly zero-emission, green and low-carbon, and there is no continuous production of high-salt hazardous waste.

[0044] (5) Carbonation refining replaces simple evaporation crystallization of lithium salt, which greatly reduces energy consumption, completely removes trace amounts of transition metal impurities, and the purity of lithium carbonate reaches battery grade standards, without the need for additional deep impurity removal processes.

[0045] (6) The lithium mother liquor is acidified and refluxed, and the comprehensive lithium recovery rate is close to 100%, which prevents the loss of lithium resources in the mother liquor and greatly improves the utilization rate of metal resources.

[0046] (7) CO2 is fully closed-loop, and the carbon dioxide produced by roasting and acidification is supplied to the carbonation process. There is no need to purchase industrial carbon dioxide from outside, which reduces carbon emissions and raw material costs.

[0047] (8) Differentiated leaching scheme: a single process is compatible with both ternary and lithium iron phosphate retired cathode powders. The acid consumption of selective leaching of lithium iron phosphate is reduced by more than 50% compared with the full dissolution process. The equipment is highly versatile and adaptable to different recycling companies' raw material sources.

[0048] (9) Direct in-situ regeneration of finished power battery cathodes eliminates the need to separate lithium salts and precursor intermediates for external sales, thus fully connecting the entire industrial chain from waste batteries to new cathodes and increasing the added value of resource utilization.

[0049] (10) The reaction conditions of each process are mild, mainly at room temperature and medium and low temperature. The equipment is mature and easy to scale up industrially, and has strong adaptability to continuous automated production. Attached Figure Description

[0050] Figure 1 This is a flowchart of the closed-loop regeneration process of the cathode black powder of the retired NCM523 ternary battery in Example 1.

[0051] Figure 2 The image shows the XRD pattern of the regenerated NCM523 ternary battery cathode material in Example 1.

[0052] Figure 3 This is a flowchart of the closed-loop regeneration process of the cathode black powder from retired lithium iron phosphate batteries in Example 4.

[0053] Figure 4 The image shows the XRD pattern of the regenerated lithium iron phosphate cathode material in Example 4.

[0054] Figure 5 This is a flowchart of the closed-loop regeneration process of the cathode black powder from retired lithium iron phosphate batteries in Example 5. Detailed Implementation

[0055] 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.

[0056] Example 1: Closed-loop regeneration of cathode materials from retired NCM523 ternary batteries A closed-loop regeneration method for lithium-ion battery cathode black powder based on acid-base self-circulation, using retired NCM523 ternary batteries, is described below. Figure 1 The specific steps are as follows: S1. Battery pretreatment: Take retired commercial NCM523 power batteries, deep discharge them with sodium chloride solution, mechanically disassemble, crush, and air classify them to remove impurities such as the outer shell, separator, copper and aluminum foil, and obtain pure positive electrode black powder.

[0057] S2. Leaching of all metal components: Leaching was carried out using a sulfuric acid-hydrogen peroxide system. Process parameters: solid-liquid ratio 80 g / L, sulfuric acid concentration 2.5 mol / L, hydrogen peroxide addition 0.7 mol / L, leaching temperature 65℃, and constant temperature stirring reaction for 2.5 h. After the reaction was completed, the mixture was filtered to obtain a small amount of the first solid phase and the first filtrate rich in nickel, cobalt, manganese and lithium.

[0058] S3, Nickel-Cobalt-Manganese Coprecipitation: During the initial startup of the system, an external lithium hydroxide solution was used as the initial precipitant. After the system stabilized, the lithium hydroxide solution produced in step S4 was used as the precipitant. The precipitant was added to the first filtrate and reacted under nitrogen inert protection. The reaction temperature was 40°C, the pH of the system was kept stable at 11.2, and the reaction was carried out with constant temperature stirring for 2 hours. After solid-liquid separation, a second solid phase containing nickel, cobalt, and manganese hydroxides and a second filtrate containing lithium sulfate were obtained.

[0059] S4. Pre-concentration coupled bipolar membrane acid-base co-production cycle: After evaporating and concentrating the second filtrate containing lithium sulfate to a lithium concentration of 2.8 mol / L, it is introduced into a three-compartment bipolar membrane electrodialysis system to co-produce sulfuric acid solution and lithium hydroxide solution in situ, with an operating current density of 60 mA / cm². 2 The acid chamber produces sulfuric acid solution, of which a portion is used for the acidification and conversion of the lithium precipitation mother liquor, and the rest is recycled to the leaching process in step S2; the alkali chamber produces lithium hydroxide solution, of which 55% is recycled to step S3 as a selective precipitant during the stable operation phase of the system, and the remainder is used for subsequent carbonation precipitation of lithium.

[0060] S5, Lithium Carbonation Precipitation: The remaining lithium hydroxide solution in the alkaline chamber is reacted with carbon dioxide to generate lithium carbonate precipitate. The carbonation reaction temperature is 75℃, the excess carbon dioxide coefficient is 1.1, and the reaction is carried out under constant temperature bubbling for 1.0 h. Solid-liquid separation yields crude lithium carbonate and clarified lithium precipitation mother liquor. The crude lithium carbonate is washed and dried to obtain battery-grade lithium carbonate.

[0061] S6. Acidification and closed-loop recovery of lithium mother liquor: The sulfuric acid solution produced in the acid chamber of step S4 is used for acidification. The amount of sulfuric acid added is 1.05 times the theoretical amount of acid required for the complete reaction of the total alkali of carbonate and hydroxide ions in the system. During the acidification and conversion process, the carbon dioxide that escapes is collected under negative pressure in a closed loop. All the lithium sulfate conversion liquid obtained from acidification is recycled and mixed into the second filtrate to achieve lithium lossless closed-loop recovery.

[0062] S7. Closed-loop preparation of ternary cathode material: The second solid phase containing nickel, cobalt, and manganese hydroxide from step S3 is dried at 110°C for 2 h, and the materials are prepared according to the stoichiometric ratio of NCM523, with an excess of 3% battery-grade lithium carbonate; calcination is carried out in an oxygen atmosphere at a calcination temperature of 880°C for 7 h; after cooling, crushing, and sieving, regenerated NCM523 cathode material is obtained; the carbon dioxide generated during the calcination process is collected, mixed with the carbon dioxide from step S6, pressurized, and then fed back to the carbonation reaction step for recycling.

[0063] X-ray diffraction (XRD) analysis showed that the XRD pattern of the regenerated NCM523 ternary cathode material was consistent with the standard card. Figure 2 Inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis showed that the Ni:Co:Mn molar ratio was 0.500:0.198:0.302, consistent with the target composition. After assembling coin cells, the first charge-discharge cycle at a 0.1 C rate was tested, and the initial discharge specific capacity was 158.6 mAh / g.

[0064] Example 2: Regeneration of cathode material from retired NCM811 high-nickel ternary batteries The closed-loop regeneration process for the cathode material of retired NCM811 ternary batteries is the same as in Example 1. The specific steps are as follows: S1. Battery pretreatment: The only difference from step S1 in Example 1 is that the retired battery is an NCM811 high-nickel battery.

[0065] S2, All-metal component leaching: The only difference from step S2 in Example 1 is that the solid-liquid ratio is 60 g / L, the sulfuric acid concentration is 3.0 mol / L, the hydrogen peroxide addition is 1.0 mol / L, the leaching temperature is 70℃, and the reaction time is 3.0 h.

[0066] S3, Nickel-Cobalt-Manganese Coprecipitation: The only difference from step S3 in Example 1 is that the reaction temperature is 35°C, the pH of the system is controlled at 11.5, and the reaction time is 2.5 h, to ensure efficient coprecipitation of nickel, cobalt, and manganese and complete separation of lithium.

[0067] S4, Pre-concentration coupled bipolar membrane acid-base co-production cycle: The only difference from step S4 in Example 1 is that reverse osmosis is used to concentrate to 2.5 mol / L lithium ions; the bipolar membrane current density is 70 mA / cm². 2 .

[0068] S5, Lithium Carbonation: The only difference from step S5 in Example 1 is that the carbonation reaction temperature is 80°C, the excess carbon dioxide coefficient is 1.15, and the reaction time is 1.2 h.

[0069] S6, Acidification and Conversion of Lithium Precipitated Mother Liquor: The only difference from step S6 in Example 1 is that the excess sulfuric acid addition coefficient is 1.06.

[0070] S7. In-situ regenerated cathode material: The only difference from step S7 in Example 1 is that battery-grade lithium carbonate is added in excess by 5%, the calcination temperature is 910°C, and the holding time is 8 hours.

[0071] ICP-OES analysis showed that the Ni:Co:Mn molar ratio was 0.798:0.101:0.101, consistent with the target composition. Coin cell testing, using the same method as in Example 1, showed that the initial discharge specific capacity of the regenerated NCM811 material was 180.5 mAh / g.

[0072] Example 3: Regeneration of cathode material from retired NCM333 low-nickel, low-cobalt ternary batteries The closed-loop regeneration process for the cathode material of retired NCM333 ternary batteries is the same as in Example 1. The specific steps are as follows: S1. Battery pretreatment: The only difference from step S1 in Example 1 is that the retired battery is an NCM333 battery.

[0073] S2, All-metal component leaching: The only difference from step S2 in Example 1 is that the solid-liquid ratio is 100 g / L, the sulfuric acid concentration is 2.0 mol / L, the hydrogen peroxide addition is 0.5 mol / L, the leaching temperature is 60℃, and the reaction time is 2.0 h.

[0074] S3, Nickel-Cobalt-Manganese Coprecipitation: The only difference from step S3 in Example 1 is that the reaction temperature is room temperature, the pH of the system is controlled at 10.8, and the reaction time is 1.5 h.

[0075] S4, Pre-concentration coupled bipolar membrane acid-base co-production cycle: The only difference from step S4 in Example 1 is that the concentration is increased to 3.0 mol / L lithium ions; the operating current density is 50 mA / cm². 2 .

[0076] S5, Lithium Carbonation: The only difference from step S5 in Example 1 is that the carbonation reaction temperature is 70°C and the reaction time is 0.8 h.

[0077] S6, Acidification and Conversion of Lithium Precipitated Mother Liquor: The only difference from step S6 in Example 1 is that the amount of sulfuric acid added is 1.08 times the theoretical amount of acid needed for the complete reaction of the total alkali content of carbonate and hydroxide ions in the system.

[0078] S7. In-situ regenerated cathode material: The only difference from step S7 in Example 1 is that the material is prepared according to the NCM333 metering ratio, with an excess of 2% lithium source, a calcination temperature of 830℃, and a holding time of 6 h.

[0079] ICP-OES analysis showed that the Ni:Co:Mn molar ratio was 0.332:0.334:0.334, consistent with the target composition. Coin cell testing, using the same method as in Example 1, showed that the initial discharge specific capacity of the regenerated NCM333 material was 147.2 mAh / g.

[0080] Example 4: Regeneration of cathode material from retired lithium iron phosphate batteries (two solid-liquid separations, iron phosphate solid phase) See the closed-loop regeneration process for cathode materials of retired lithium iron phosphate batteries. Figure 3 The specific steps are as follows: S1. Battery pretreatment: The only difference from step S1 in Example 1 is that the retired battery is a lithium iron phosphate battery.

[0081] S2. Selective Lithium Leaching: Selective leaching is carried out using a sulfuric acid-hydrogen peroxide system. Hydrogen peroxide is used to oxidize ferrous iron to ferric iron to form ferric phosphate precipitate, resulting in an leaching slurry. Process parameters: solid-liquid ratio 100 g / L, sulfuric acid concentration 1.5 mol / L, hydrogen peroxide addition 0.3 mol / L, leaching temperature 55℃, and constant temperature stirring reaction for 3.0 h.

[0082] S3. Two solid-liquid separations: First, the leachate obtained in step S2 is separated into a solid phase of iron phosphate and a lithium-containing filtrate. Then, lithium hydroxide solution is added to the lithium-containing filtrate to adjust the pH value to 6.5. The mixture is reacted at room temperature for 0.5 h to precipitate the trace iron as iron hydroxide. The second solid-liquid separation yields a second filtrate containing lithium sulfate, and a solid phase containing iron hydroxide is also obtained (this solid phase is collected separately; in this embodiment, the roasting process only uses the aforementioned separated iron phosphate solid phase).

[0083] S4. Pre-concentration coupled bipolar membrane acid-base co-production cycle: After evaporating and concentrating the second filtrate to a lithium ion concentration of 2.0 mol / L, it is introduced into a three-compartment bipolar membrane electrodialysis system with an operating current density of 45 mA / cm². 2 The acid chamber produces sulfuric acid solution, a portion of which is used for the acidification and conversion of the lithium precipitation mother liquor, while the rest is recycled to the leaching process in step S2. The alkali chamber produces lithium hydroxide solution, a portion of which is recycled to step S3 as a precipitant, and the remainder is used for subsequent carbonation precipitation of lithium.

[0084] S5, Carbonation Lithium Precipitation: The lithium hydroxide solution produced in the alkaline chamber is reacted with carbon dioxide to undergo a carbonation reaction at a reaction temperature of 75℃, with an excess carbon dioxide coefficient of 1.1, and the reaction is carried out under constant temperature bubbling for 1.0 h; solid-liquid separation yields crude lithium carbonate, which is then washed and dried to obtain battery-grade lithium carbonate, while lithium precipitation mother liquor is also obtained.

[0085] S6. Acidification and closed-loop recovery of lithium mother liquor: The sulfuric acid solution produced in the acid chamber of step S4 is used for acidification. The amount of sulfuric acid added is 1.05 times the theoretical amount of acid required for the complete reaction of the total alkali in the system. During the acidification and conversion process, carbon dioxide is collected under negative pressure in a closed loop. All the lithium sulfate conversion liquid obtained from acidification is recycled and mixed into the second filtrate to achieve lithium lossless closed-loop recovery.

[0086] S7. Closed-loop preparation of lithium iron phosphate cathode material: The iron phosphate solid phase obtained in step S3 is dried at 110℃ for 4 h, and mixed with the battery-grade lithium carbonate and carbon source (glucose) obtained in step S5. The molar ratio of iron phosphate to lithium carbonate is calculated according to the stoichiometric ratio of the target lithium iron phosphate chemical formula, with an excess of 3% lithium carbonate and 10% of the molar amount of iron added. The mixture is calcined under a nitrogen atmosphere at 750℃ for 8 h. After cooling, crushing, and sieving, regenerated lithium iron phosphate cathode material is obtained. The carbon dioxide generated during the calcination process is collected, mixed with the carbon dioxide in step S6, pressurized, and then recycled back to the carbonation reaction step for reuse.

[0087] XRD analysis showed that the XRD pattern of the regenerated lithium iron phosphate cathode material was consistent with the standard card. Figure 4 ICP-OES analysis showed that the Fe:P molar ratio was 0.995:1.000, consistent with the target composition. Coin cell testing, conducted using the same method as in Example 1, yielded an initial discharge specific capacity of 156.6 mAh / g.

[0088] Example 5: Regeneration of cathode material from retired lithium iron phosphate batteries (single solid-liquid separation, mixed solid phase of iron phosphate and iron hydroxide) See the closed-loop regeneration process for cathode materials of retired lithium iron phosphate batteries. Figure 5 The specific steps are as follows: S1. Battery pretreatment: Same as step S1 in Example 4.

[0089] S2, Selective Lithium Leaching: The only difference from step S2 in Example 4 is that the solid-liquid ratio is 120 g / L, the sulfuric acid concentration is 1.8 mol / L, the hydrogen peroxide addition is 0.35 mol / L, the leaching temperature is 60℃, and the reaction is carried out under constant temperature stirring for 2.5 h.

[0090] S3. Single solid-liquid separation: Lithium hydroxide solution is directly added to the leachate obtained in step S2 to adjust the pH value to 6.5. The reaction is carried out at room temperature for 0.5 h, so that the trace iron dissolved is precipitated as ferric hydroxide. The solid-liquid separation is carried out in one step to obtain a mixed solid phase containing ferric phosphate and ferric hydroxide, as well as a second filtrate containing lithium sulfate.

[0091] S4, Bipolar Membrane In-situ Acid-Base Co-production Cycle: The only difference from step S4 in Example 4 is that lithium ions are concentrated to 1.8 mol / L, and the operating current density is 50 mA / cm². 2 .

[0092] S5, Lithium Carbonation Precipitation: The only difference from step S5 in Example 4 is that the reaction temperature is 80°C, the excess carbon dioxide coefficient is 1.15, and the constant temperature bubbling reaction is 1.2 h.

[0093] S6, Acidification and Closed-Loop Recovery of Lithium Precipitated Mother Liquor: The only difference from step S6 in Example 4 is that the amount of sulfuric acid added is 1.06 times the theoretical amount of total alkali in the system.

[0094] S7. Closed-loop preparation of lithium iron phosphate cathode material: The mixed solid phase containing iron phosphate and iron hydroxide obtained in step S3 is dried at 110℃ for 4 h, and mixed with battery-grade lithium carbonate, carbon source, and phosphate obtained in step S5; the molar ratio of the mixed solid phase to lithium carbonate is calculated according to the stoichiometric ratio of the target lithium iron phosphate chemical formula, with lithium carbonate in 5% excess; the amount of carbon source (sucrose) added is 10% of the molar amount of iron in the iron source; due to the use of the mixed solid phase route containing iron hydroxide, the amount of phosphate (ammonium dihydrogen phosphate) added is made up according to the iron-phosphorus molar ratio of 1:1 in the target lithium iron phosphate chemical formula. Calcination is carried out under a nitrogen atmosphere at 700℃ for 6 h; after cooling, pulverizing, and sieving, regenerated lithium iron phosphate cathode material is obtained.

[0095] ICP-OES analysis showed that the Fe:P molar ratio was 0.993:1.000, consistent with the target composition. Button cell testing, conducted using the same method as in Example 1, yielded an initial discharge specific capacity of 155.8 mAh / g.

[0096] Example 6 A system for implementing the methods described in Examples 1-5 includes a pretreatment unit, an extraction and solid-liquid separation unit, a precipitation and solid-liquid separation unit, a concentration unit, a bipolar membrane electrodialysis unit, a carbonation lithium precipitation unit, a lithium precipitation mother liquor acidification and conversion unit, and a positive electrode material preparation unit.

[0097] The pretreatment unit is used to discharge, disassemble, crush, and sort retired lithium batteries to obtain positive electrode black powder, and is equipped with a positive electrode black powder outlet.

[0098] The extraction and solid-liquid separation unit is used to perform sulfuric acid-hydrogen peroxide co-extraction on the cathode black powder and separate it to obtain the first filtrate and the first solid phase (for processing cathode black powder of ternary power batteries), or the extraction slurry (for processing cathode black powder of lithium iron phosphate power batteries). It is equipped with a cathode black powder inlet, a hydrogen peroxide inlet, a sulfuric acid solution inlet, an outlet, and a solid phase outlet; the cathode black powder inlet is connected to the cathode black powder outlet of the pretreatment unit.

[0099] The precipitation and solid-liquid separation unit is used to add lithium hydroxide to the first filtrate for precipitation treatment, and to separate the second filtrate and the second solid phase. It is equipped with a feed inlet, an alkali recycling inlet, a mother liquor recycling inlet, a liquid phase outlet and a solid phase outlet; the feed inlet is connected to the discharge outlet of the extraction and solid-liquid separation unit.

[0100] The concentration unit is used to concentrate the second filtrate, and its inlet is connected to the liquid phase outlet of the sedimentation and solid-liquid separation unit.

[0101] The bipolar membrane electrodialysis unit is used to electrolyze the concentrated second filtrate to obtain sulfuric acid solution in the acid chamber and lithium hydroxide solution in the alkali chamber. The feed inlet is connected to the discharge outlet of the concentration unit. The acid chamber outlet is divided into two paths: one path is connected to the sulfuric acid solution inlet of the leaching and solid-liquid separation unit, and the other path is connected to the sulfuric acid solution inlet of the lithium precipitation mother liquor acidification and conversion unit. The alkali chamber outlet is divided into two paths: one path is connected to the alkali solution recycling inlet of the precipitation and solid-liquid separation unit, and the other path is connected to the lithium hydroxide solution inlet of the carbonation lithium precipitation unit.

[0102] The lithium carbonate precipitation unit is used to react lithium hydroxide solution with carbon dioxide to separate crude lithium carbonate and lithium precipitation mother liquor. It is equipped with a carbon dioxide inlet, a lithium hydroxide solution inlet, a lithium carbonate solid phase outlet, and a lithium precipitation mother liquor outlet. The lithium hydroxide solution inlet is connected to the alkali chamber outlet of the bipolar membrane electrodialysis unit.

[0103] The lithium precipitation mother liquor acidification and conversion unit is used to acidify lithium precipitation mother liquor with sulfuric acid solution to obtain a conversion liquid containing lithium sulfate. It is equipped with a lithium precipitation mother liquor inlet, a sulfuric acid solution inlet, and a lithium sulfate conversion liquid outlet. The lithium precipitation mother liquor inlet is connected to the lithium precipitation mother liquor outlet of the carbonation lithium precipitation unit. The lithium sulfate conversion liquid outlet is connected to the mother liquor recycling inlet of the precipitation and solid-liquid separation unit.

[0104] The cathode material preparation unit is used to prepare recycled cathode materials using a second solid phase and battery-grade lithium carbonate. The feed inlet is connected to the lithium carbonate solid phase outlet of the lithium carbonate precipitation unit and the solid phase outlet of the precipitation and solid-liquid separation unit, respectively.

[0105] Comparative Example 1: The all-membrane separation process was used to verify its metal loss and membrane blockage defects. This comparative example replicates the multi-stage membrane separation lithium extraction process in CN117163976A. Using the NCM523 ternary battery from Example 1 as raw material, the black powder is leached with hydrochloric acid and hydrogen peroxide, followed by a four-stage series separation of lithium via ultrafiltration / nanofiltration / reverse osmosis / electrodialysis. The concentrated solution containing nickel, cobalt, and manganese heavy metals is directly treated as hazardous waste. The lithium-rich solution is fed into a bipolar membrane to produce lithium hydroxide. There is no selective co-precipitation, and no precursor or cathode regeneration process. The specific operating steps are as follows: (1) Battery pretreatment: Take retired NCM523 power batteries, deep discharge them with sodium chloride solution, mechanically disassemble, crush them, and sieve them with a 20-mesh vibrating screen to remove aluminum foil, copper foil, separator and shell impurities, and obtain pure NCM523 positive electrode black powder.

[0106] (2) Hydrochloric acid-hydrogen peroxide acid leaching: Add the positive electrode black powder to a 6 mol / L hydrochloric acid solution at a solid-liquid ratio of 30 g / L, slowly add 30% hydrogen peroxide at a volume ratio of 5%, and stir at 80℃ for 6 h. After the reaction is completed, filter to obtain acidified leaching solution and insoluble carbon residue.

[0107] (3) Multi-stage membrane separation and enrichment: ① Ultrafiltration pretreatment: The acidified leachate is diluted 4 times with deionized water and then passed through an ultrafiltration membrane to remove oil and suspended particles; ② Nanofiltration separation: The ultrafiltration permeate enters the nanofiltration membrane system, and the membrane pressure is controlled at 3.0 MPa, the temperature at 25℃, and the feed water flow rate at 3.0 L / min. The concentration-to-dilution ratio is adjusted to 5:5, so that multivalent ions such as nickel, cobalt, and manganese are retained on the concentrate side, and lithium ions enter the desalination side to obtain a primary lithium-rich solution; ③ Reverse osmosis concentration: The primary lithium-rich solution obtained by nanofiltration is passed into the reverse osmosis device, and the pressure is controlled at 3.5 MPa to obtain a reverse osmosis lithium-rich solution; ④ Electrodialysis deep concentration: The lithium-rich solution obtained by reverse osmosis is further concentrated by electrodialysis. The concentration is stopped when the conductivity of the feed solution drops to 5 mS / cm; ⑤ Resin deep purification: The lithium-rich solution obtained by electrodialysis is concentrated at 8 BV / h The solution is fed into a self-made nickel-cobalt-manganese ion-imprinted resin column to obtain a refined lithium-rich solution. After the resin is saturated, it is regenerated with 6% hydrochloric acid, and the regenerated solution is returned to the acid leaching section.

[0108] (4) Bipolar membrane electrodialysis for lithium hydroxide production: The above-mentioned refined lithium-rich solution is directly fed into the salt chamber of the three-compartment bipolar membrane electrodialysis system. The initial conductive solution in the acid chamber is 0.05% dilute sulfuric acid solution, and the initial conductive solution in the alkali chamber is 0.05% lithium hydroxide solution. The operating current density is 100 A / m 2 The alkaline chamber yields a lithium hydroxide enrichment solution, which is then concentrated by evaporation, crystallization, and drying to obtain lithium hydroxide monohydrate.

[0109] Experimental results: Nanofiltration retains nickel, cobalt, and manganese concentrate containing a large amount of valuable transition metals. Without a supporting precipitation and regeneration process, the total recovery rate of nickel, cobalt, and manganese is less than 5%, and only lithium hydroxide can be produced. It is impossible to prepare cathode materials in a closed loop, resulting in extremely low resource value-added. Carbon powder and colloids in the acid leaching solution continuously clog the nanofiltration membrane. After 48 hours of continuous operation, the flux decreases by 38%, requiring shutdown for acid washing and regeneration. The lithium loss in the membrane separation section is 4.8%, and the overall lithium recovery rate measured in this comparative example after stacking multiple membranes is only about 90.1%. There is no internal circulation of self-produced lithium hydroxide, and only the by-product sulfuric acid is reused, which significantly increases the cost of reagent procurement.

[0110] Comparative Example 1 shows that the whole membrane separation process only extracts lithium salts separately, abandoning high-value metals such as nickel, cobalt, and manganese, and cannot achieve closed-loop regeneration of the positive electrode. The multi-stage membrane system has poor industrial stability, which is fundamentally different from the core innovation of this invention, namely "transition metal pre-separation, six-fold material coupling closed loop, and dual-system compatibility".

[0111] Comparative Example 2: A bipolar membrane electrodialysis coupled cathode material regeneration process without multiple material closed loops, verifying all its cascading defects. This comparative example replicates the waste lithium battery recycling route in CN113151680A. Using the NCM523 ternary battery from Example 1 as raw material, the black powder is extracted with sulfuric acid and hydrogen peroxide → iron powder and resin are used for impurity removal → the raw solution is directly fed into a three-chamber bipolar membrane (without pre-lithium concentration) → sodium carbonate / ammonia is added to the salt chamber solution to synthesize the precursor, and the dilute lithium hydroxide solution in the alkali chamber is directly evaporated and crystallized. There is no selective pre-precipitation, no carbonation purification, no acidification and reuse of lithium precipitation mother liquor, and no CO2 closed-loop collection. The specific operation steps are as follows: (1) Battery pretreatment: Same as step S1 in Example 2, to obtain positive electrode black powder.

[0112] (2) Sulfuric acid-hydrogen peroxide all-metal leaching: The positive electrode black powder and 1 mol / L sulfuric acid were mixed at a mass ratio of 1:1, and 30% hydrogen peroxide with a mass of 0.5 times that of the black powder was added. The mixture was reacted at 20℃ for 60 min, and the leaching residue was separated by filtration to obtain the leaching stock solution containing lithium, nickel, cobalt and manganese.

[0113] (3) Chemical impurity removal + resin adsorption stage: Add iron powder with an excess coefficient of 20% to the leachate, stir and react, adjust the pH to 4.0 with lithium carbonate, react at 35℃ for 60 min, and filter to remove iron slag. Pass the filtrate through an aminophosphoric acid chelating resin column at 30℃ and a flow rate of 3 BV / h to obtain the impurity removal solution.

[0114] (4) Direct bipolar membrane electrodialysis (without pre-concentration): The above-mentioned impurity-removed solution is directly pumped into the salt chamber of the three-chamber bipolar membrane electrodialysis device. The conductive solution in the acid chamber is 0.05% sulfuric acid, and the conductive solution in the alkali chamber is 0.05% lithium hydroxide. A constant current of 4.0 A is applied. The alkali chamber outputs lithium hydroxide solution, the acid chamber outputs dilute sulfuric acid, and the salt chamber outputs a mixed metal salt solution after lithium removal (containing a large amount of Ni). 2+ Co 2+ Mn 2+ and a small amount of Li + ).

[0115] (5) Precursor synthesis (addition of sodium salt): The salt chamber output solution is adjusted to a Ni:Co:Mn molar ratio of 8:1:1, and then simultaneously added to the reactor with 5% sodium hydroxide solution and 10% ammonia solution (the mass ratio of salt solution to ammonia solution after adjustment is 10:1). The reaction is carried out at 50℃ and pH=11.5 for 80 h. After filtration, washing, and drying, the ternary precursor is obtained. This process requires continuous external purchase of sodium hydroxide and ammonia solution to introduce Na. + and NH4 + .

[0116] (6) Evaporation and crystallization of lithium hydroxide: The dilute lithium hydroxide solution output from the alkali chamber is directly evaporated and crystallized (dried to dryness) to obtain solid lithium hydroxide (because it is not concentrated, the energy consumption is extremely high and there are trace amounts of transition metal impurities).

[0117] (7) Sintering of cathode material: The above-mentioned lithium hydroxide solid (with an excess coefficient of 5%) is mixed with the precursor and ball-milled for 3 h, and then calcined at 700°C for 10 h in an oxygen atmosphere to obtain the regenerated cathode material.

[0118] Experimental results: The lithium concentration of the leaching solution was approximately 0.42 mol / L. Directly introducing the solution into the bipolar membrane without concentration required a membrane stack area 3.7 times that of the concentrated process described in this invention, and increased the power consumption per unit mass of lithium hydroxide by 210%. A large amount of Ni... 2+ Co 2+ Mn 2+ The membrane surface was enriched with deposits, and after 48 hours of operation, the membrane stack pressure difference increased by 45%. A large amount of metal hydroxide scale was detected on the membrane surface, and the current efficiency dropped from the initial 73% to 48%, posing a risk of system shutdown.

[0119] In the preparation of the ternary precursor, purchased sodium carbonate was added. According to our comparative analysis, the sodium content of the precursor after water washing was 0.092%, and the sodium content of the regenerated cathode material after calcination reached 0.058%, far exceeding the sodium impurity limit for battery-grade cathode materials (typically required to be ≤0.03%). After calcination with evaporated lithium hydroxide, the regenerated ternary cathode exhibited a first charge-discharge capacity of only 140.3 mAh / g at 0.1 C.

[0120] The direct evaporation and crystallization of low-concentration lithium hydroxide in the alkali chamber consumes 12.6 times the steam energy of the "carbonation precipitation of lithium" route of this invention (mainly due to alkali preheating). Trace amounts of cobalt and iron impurities remain in the crude lithium hydroxide, failing to meet battery-grade lithium salt standards. Because only the bipolar membrane byproduct sulfuric acid is refluxed into the leaching section, there is no internal separation and impurity removal of lithium hydroxide, and the overall acid and alkali consumption is 65% higher than that of this invention. High-salt alkaline waste liquid is continuously produced, making near-zero emissions impossible. For lithium iron phosphate systems, if full leaching is used in this route, acid consumption will increase by more than three times compared to the selective lithium extraction of this invention. All iron and phosphorus enter the liquid phase, causing a doubling of the bipolar membrane load and reducing economic efficiency.

[0121] Comparative Example 2 shows that the bipolar membrane electrodialysis coupled cathode material regeneration process without multiple material closed loops suffers from multiple cascading defects, including membrane fouling, high energy consumption, cathode degradation due to exogenous impurities, and high acid and alkali consumption, making it impossible to achieve low-cost, high-quality in-situ cathode regeneration. Even if only a single parameter is adjusted (such as increasing concentration), the inherent shortcomings of the bipolar membrane system, such as membrane blockage, exogenous sodium impurities in the precursor, and acid consumption due to complete dissolution of lithium iron phosphate, cannot be completely eliminated.

[0122] Comparative Example 3: Multi-stage lithium extraction-precursor preparation-cathode sintering and regeneration process combination, defects in the combined process. This comparative example combines the multi-stage membrane lithium extraction unit in CN117163976A with the precursor preparation and sintering process in CN113151680A: First, lithium is separated using ultrafiltration-nanofiltration (concentrated water is collected, salt is added, and sodium salt is added to synthesize the precursor). Then, LiOH is produced using a bipolar membrane in the lithium-rich solution and directly evaporated for crystallization. The remaining processes involve no pre-selective precipitation, no concentration, no carbonic acid refining, no mother liquor acidification, and no CO2 recycling. The specific operating steps are as follows: (1) Battery pretreatment: Same as Comparative Example 1, step (1).

[0123] (2) Hydrochloric acid-hydrogen peroxide acid leaching: Same as step (2) of Comparative Example 1.

[0124] (3) Multi-stage membrane separation of lithium and collection of transition metal concentrate: Ultrafiltration and nanofiltration are performed in the same way as in Comparative Example 1, step (3). Nanofiltration concentrate is collected separately and used as the metal source for subsequent precursor synthesis. Nanofiltration desalinated water is further concentrated by reverse osmosis, electrodialysis, and resin purification to obtain a refined lithium-rich solution. The specific parameters are the same as in Comparative Example 1, step (3).

[0125] (4) Precursor synthesis (using nanofiltration concentrate with added sodium salt): The nanofiltration concentrate collected in step (3) was adjusted to a Ni:Co:Mn molar ratio of 5:2:3, and then 5% sodium hydroxide solution and 10% ammonia solution were added. The mixture was reacted at 50℃ and pH=11.5 for 80 h. After filtration, washing, and drying, the ternary precursor was obtained. This process also introduces a large amount of Na. + and NH4 + .

[0126] (5) Bipolar membrane electrodialysis to produce lithium hydroxide: Same as step (4) of Comparative Example 1 (6) Sintering of cathode material: The lithium hydroxide solid (excess coefficient 5%) obtained in step (5) is mixed with the ternary precursor obtained in step (4) and ball-milled, and then calcined at 700°C for 10 h in an oxygen atmosphere to obtain the regenerated cathode material.

[0127] Experimental Results: Nanofiltration concentrate is enriched with nickel, cobalt, and manganese. Precursor preparation still requires the addition of purchased sodium carbonate, leading to a continuous introduction of sodium impurities and unresolved issues with the deterioration of the electrochemical performance of the regenerated cathode. Multi-stage membrane clogging and lithium loss (4.7%) persist. Separate treatment of transition metal concentrate requires an additional filtration and preparation unit, doubling the overall process length and increasing equipment investment by 70%. Even with the combined technology, the lack of internal diversion and impurity removal of lithium hydroxide and closed-loop CO2 recovery from roasting results in only a slight reduction in acid and alkali consumption and wastewater discharge, failing to achieve near-zero emissions. Direct sintering of low-purity lithium hydroxide produced by bipolar membranes cannot eliminate impurities in the material.

[0128] Comparative Example 3 shows that even when CN117163976A and CN113151680A technologies are used in combination, the core defects such as external impurities, high energy consumption, lithium loss, lengthy process, and lack of multi-dimensional material closed loop still exist, and the complete technical solution of this invention cannot be obtained.

[0129] Comparative Example 4: Removing the pre-concentration step to verify the necessity of concentration. The remaining steps of this comparative example are completely consistent with those of Example 1 of the present invention, except that step S4, the filtrate concentration process, is deleted, and the low-concentration lithium sulfate filtrate after precipitation is directly fed into the three-compartment bipolar membrane electrodialysis system.

[0130] Experimental results: With a raw lithium-ion concentration of 0.45 mol / L, to achieve the same lithium hydroxide production capacity without concentration, the effective area of ​​the membrane stack needs to be increased by 3.6 times, resulting in a 220% increase in equipment investment and circulating pump energy consumption. A large number of ineffective water molecules participate in electrolysis, reducing the current efficiency from 82% to 46%. Under the same operating time, the lithium hydroxide concentration in the alkaline chamber is only 0.8%. At this low lithium concentration, the lithium carbonate crystals are small, leading to increased filtration and washing losses and an additional 1.2% lithium loss.

[0131] Comparative Example 4 shows that bipolar membrane pre-concentration is an indispensable key process of this invention. CN113151680A completely lacks this design. Even if the concentration step is simply added, the original defects such as excessive sodium salt in the precursor and membrane blockage cannot be solved. The complete closed-loop system of this invention cannot be obtained by simply adjusting the parameters.

[0132] 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, N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF) are used to dissolve and separate polyvinylidene fluoride (PVDF) and carbon powder in the first solid phase to achieve resource recovery; before dissolving and leaching with sulfuric acid and hydrogen peroxide, the black powder is treated with dilute acid and / or dilute alkali to remove iron and aluminum; the second filtrate and / or concentrate is deeply purified to extend membrane life; the dilute lithium sulfate tail liquid discharged from the bipolar membrane salt chamber is collected and recycled for use as acid and / or alkali chamber liquid in subsequent bipolar membrane operations; when co-precipitating nickel, cobalt, and manganese, an appropriate amount of ammonia or ammonium salt is added to obtain hydroxides with high tap density. All equivalent substitutions and process fine-tunings based on the coupled closed-loop regeneration approach of "sulfuric acid / hydrogen peroxide extraction - selective precipitation of self-produced lithium hydroxide - in-situ acid-base co-production of bipolar membrane - lithium carbonate precipitation - mother liquor acidification and reuse - solid-phase roasting regeneration" fall within the protection scope of this invention.

Claims

1. A closed-loop regeneration method for lithium-ion battery cathode black powder based on acid-base self-circulation, characterized in that, This includes a complete process sequence in which material flows are coupled and inseparable: S1. Battery pretreatment: Discharge, disassemble, crush, and sort retired lithium-ion batteries to obtain positive electrode black powder; the retired lithium-ion batteries are selected from ternary lithium batteries or lithium iron phosphate batteries. S2. Differentiated metal component leaching: The cathode black powder is leached using a sulfuric acid-hydrogen peroxide composite leaching system; the cathode black powder of the ternary system is leached with all metal co-dissolution to obtain the first solid phase and the first filtrate; the cathode black powder of the lithium iron phosphate system is leached with lithium selective leaching, the iron element is generated in situ to form the iron phosphate solid phase and remains, and only lithium enters the liquid phase to form the leaching slurry. S3. Selective solid-liquid separation of self-produced lithium hydroxide: The first filtrate or leaching slurry obtained in step S2 is subjected to selective precipitation by adjusting the pH with lithium hydroxide solution. After solid-liquid separation, a second filtrate containing only lithium sulfate and a second solid phase of transition metal without lithium are obtained. S4. Pre-concentration coupled bipolar membrane acid-base co-production cycle: First, the second filtrate produced in step S3 is concentrated to make the lithium ion concentration in the system ≥1.5 mol / L, and then sent to the three-compartment bipolar membrane electrodialysis system to co-produce sulfuric acid solution and lithium hydroxide solution in situ. S5, Carbonation precipitation of lithium: The lithium hydroxide solution produced in step S4 is passed through carbon dioxide to carry out a carbonation reaction. After solid-liquid separation, crude lithium carbonate and lithium precipitation mother liquor are obtained. After washing and drying, the crude lithium carbonate is used to obtain battery-grade lithium carbonate. S6. Acidification and conversion of lithium precipitation mother liquor: The lithium precipitation mother liquor is acidified by the sulfuric acid solution produced in step S4. The lithium in the mother liquor is converted back into lithium sulfate conversion solution and all of it is returned to the second filtrate of step S3. S7. In-situ regenerated cathode material: The transition metal second solid phase obtained in step S3 is mixed with the battery-grade lithium carbonate obtained in step S5, and a carbon source is added and optionally a phosphorus source is added before high-temperature calcination to prepare the finished cathode material.

2. The method according to claim 1, characterized in that, The process parameters for step S2 extraction are as follows: solid-liquid ratio 20~150 g / L, sulfuric acid concentration 1~4 mol / L, hydrogen peroxide addition 0.3~1.2 mol / L, extraction temperature 50~80℃, and reaction time 1~4 h.

3. The method according to claim 1, characterized in that, Step S3 Precipitation control conditions: For the ternary system, an inert atmosphere is used for protection, the reaction temperature is room temperature to 60℃, the pH is 10.5~12.0, and the reaction time is 1~4 h; for the lithium iron phosphate system, the pH is adjusted to ensure complete precipitation of trace iron, the reaction temperature is room temperature to 60℃, and the reaction time is 0.5~2 h; for the lithium iron phosphate system, solid-liquid separation can be performed before adding lithium hydroxide to obtain a second solid phase.

4. The method according to claim 1, characterized in that, The concentration method in step S4 is either evaporation concentration or membrane concentration; the bipolar membrane system operates at a current density of 25~100 mA / cm². 2 .

5. The method according to claim 1, characterized in that, In step S4, the salt chamber of the three-compartment bipolar membrane electrodialysis system is only supplied with pre-concentrated high-purity lithium sulfate. The acid chamber is equipped with a dual reflux sulfuric acid branch, one of which returns to the leaching section in step S2 for recycling, and the other is supplied to the subsequent mother liquor acidification section. The alkali chamber is equipped with a dual reflux lithium hydroxide branch, one of which returns to step S3 as a selective precipitant, and the other is supplied to the carbonation lithium precipitation section.

6. The method according to claim 1, characterized in that, The carbonation process parameters for step S5 are as follows: reaction temperature 60~90℃, carbon dioxide excess coefficient 1.05~1.2, reaction time 0.5~1.5 h, and sodium impurity ≤0.01% in the obtained crude lithium carbonate.

7. The method according to claim 1, characterized in that, In step S6, the amount of sulfuric acid added is 1.0 to 1.1 times the theoretical amount of total alkali in the neutralization mother liquor. The carbon dioxide collected in the closed process of step S6 and the carbon dioxide collected under negative pressure in the roasting process of step S7 are combined and pressurized and then circulated to the carbonation process of step S5.

8. The method according to claim 1, characterized in that, The calcination control parameters for step S7 are as follows: ternary materials are calcined at 750~950℃ for 3~10 h in an oxygen or air atmosphere; lithium iron phosphate materials are calcined at 600~800℃ for 3~10 h in an inert atmosphere; lithium is added in excess at 0%~10%.

9. The method according to claim 1, 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 phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and triammonium phosphate, and is replenished at a Fe:P molar ratio of 1:1 when used.

10. A system for implementing the method according to any one of claims 1 to 9, characterized in that, include: The pretreatment unit is equipped with a positive electrode black powder outlet; The extraction and solid-liquid separation unit is provided with a positive electrode black powder inlet, a hydrogen peroxide inlet, a sulfuric acid solution inlet, an outlet, and a solid phase outlet. The positive electrode black powder inlet is connected to the positive electrode black powder outlet of the pretreatment unit. The precipitation and solid-liquid separation unit is provided with a feed inlet, an alkali recycling inlet, a mother liquor recycling inlet, a liquid phase outlet and a solid phase outlet, wherein the feed inlet is connected to the discharge outlet of the extraction and solid-liquid separation unit. The concentration unit has its inlet connected to the liquid phase outlet of the precipitation and solid-liquid separation unit; A bipolar membrane electrodialysis unit, the inlet of which is connected to the outlet of the concentration unit; Its acid chamber outlet is divided into two paths: one path is connected to the sulfuric acid solution inlet of the leaching and solid-liquid separation unit, and the other path is connected to the sulfuric acid solution inlet of the lithium precipitation mother liquor acidification and conversion unit; its alkali chamber outlet is divided into two paths: one path is connected to the alkali solution recycling inlet of the precipitation and solid-liquid separation unit, and the other path is connected to the lithium hydroxide solution inlet of the carbonation lithium precipitation unit. The lithium carbonate precipitation unit is equipped with a carbon dioxide inlet, a lithium hydroxide solution inlet, a lithium carbonate solid phase outlet, and a lithium precipitation mother liquor outlet. The lithium hydroxide solution inlet is connected to the alkali chamber outlet of the bipolar membrane electrodialysis unit. The lithium precipitation mother liquor acidification and conversion unit is provided with a lithium precipitation mother liquor inlet, a sulfuric acid solution inlet and a lithium sulfate conversion liquid outlet. The lithium precipitation mother liquor inlet is connected to the lithium precipitation mother liquor outlet of the carbonation lithium precipitation unit, and the lithium sulfate conversion liquid outlet is connected to the mother liquor recycling inlet of the precipitation and solid-liquid separation unit. The cathode material preparation unit has its feed inlet connected to the lithium carbonate solid phase outlet of the lithium carbonate precipitation unit and the solid phase outlet of the precipitation and solid-liquid separation unit, respectively.

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