A method for closed-loop regeneration of retired lithium battery positive pole black powder by bromine medium electro-oxidation-bipolar membrane coupling without external strong acid and oxidant

Abstract

The present application belongs to the technical field of retired power battery solid waste resource utilization and lithium resource recycling and regeneration, and discloses a closed-loop regeneration method for retired lithium battery positive black powder coupled with bromine medium electro-oxidation and bipolar membrane, without external strong acid and oxidant. The method uses lithium bromide aqueous solution as electrolyte, generates bromine element by anodic electro-oxidation of bromide ions in the electrolytic cell, selectively oxidizes and removes lithium ions in the positive black powder, and synchronously produces alkali at the cathode to precipitate and dissolve impurity metal ions. The lithium-containing filtrate is concentrated and then enters the bipolar membrane electrodialysis device to co-produce lithium hydroxide and hydrogen bromide. The lithium hydroxide solution is precipitated by carbon dioxide to prepare lithium carbonate, and the lithium precipitation mother liquor is regenerated into lithium bromide circulation liquid by self-produced hydrogen bromide acidification. The lithium-removed solid phase is high-temperature calcined with self-produced lithium carbonate to regenerate the positive electrode material. The present application is suitable for two types of positive electrode materials, namely ternary and lithium iron phosphate, and has the advantages of closed-loop circulation of materials, less reagent consumption, high selectivity, near-zero discharge of waste liquid, high product purity and the like.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and lithium resource recycling technology of retired power batteries, specifically involving a closed-loop regeneration method for the positive electrode black powder of retired lithium batteries using bromine-medium electro-oxidation-bipolar film coupling without the need for external strong acids and oxidants. Background Technology

[0002] With the large-scale expansion of the new energy vehicle and energy storage power station industries, the installed capacity of lithium iron phosphate and nickel-cobalt-manganese ternary lithium-ion power batteries continues to climb, and the amount of retired waste lithium-ion batteries is also increasing dramatically. How to achieve efficient, clean, and closed-loop recycling of waste lithium batteries is a major issue of common concern to both academia and industry.

[0003] Currently, the main recycling technologies for cathode materials from spent lithium-ion batteries can be categorized as follows: (I) Strong Acid Full-Component Leaching Method. This is currently the most widely used process route in industrial applications. This method uses strong acids such as concentrated sulfuric acid and hydrochloric acid as leaching agents, combined with oxidizing / reducing agents, to dissolve all metals such as lithium, nickel, cobalt, and manganese in the cathode black powder into the liquid phase. Then, the metal elements are separated and recovered stepwise through solvent extraction, chemical precipitation, and pH fractionation. Chinese patents CN121450930A and CN110512080A belong to this category. Although this type of process is technically mature, it has inherent defects: the strong acid system lacks selectivity, and all metal elements in the black powder dissolve simultaneously, resulting in extremely cumbersome subsequent separation processes; the consumption of chemical reagents such as acids and alkalis is large, leading to high operating costs; the process generates a large amount of high-salt waste liquid, putting great pressure on environmental treatment, and is essentially a high-consumption, high-emission linear production mode.

[0004] (II) Selective Lithium Removal by Strong Chemical Oxidation. To overcome the drawback of the complete dissolution of components by strong acids, some technical routes have shifted to using external chemical oxidants (such as persulfate, ozone, etc.) to achieve selective lithium removal. Chinese patents CN106910959A and CN107546436A disclose methods for selectively oxidizing and extracting lithium from waste lithium iron phosphate cathode materials using strong oxidants such as persulfate, allowing lithium ions to enter the solution while most of the iron and phosphorus remain in the slag phase. This type of scheme simplifies the separation process to some extent, but its fundamental drawback is that: it requires continuous consumption of exogenous chemical oxidants, resulting in high reagent costs; and the by-salt impurities generated after the decomposition of the oxidant are easily retained in the solid phase or solution, causing lattice doping in the material during subsequent regeneration, which seriously affects the electrochemical performance of the regenerated material.

[0005] (III) Direct Electrochemical Oxidation Method. Electrochemical methods were once highly anticipated to reduce the consumption of chemical reagents. Chinese patents CN108417923A and CN117810588A, among others, disclosed technical solutions for direct electrochemical delithiation by using positive electrode black powder as the working electrode. However, this type of method requires the black powder to be mixed with conductive agents and binders and coated onto the current collector beforehand to form the electrode, which is a complicated process; the electrode is prone to cracking and powder shedding during electrolysis, resulting in incomplete delithiation; the single batch processing capacity is limited by the electrode area, making large-scale scaling difficult and unable to meet the needs of industrial production.

[0006] (iv) Electrochemical-assisted oxidation method. In recent years, some studies have explored the use of electrochemically generated active substances to assist in oxidation leaching. Chinese patent CN118563107A discloses a method for leaching valuable metals from waste lithium battery cathode materials by electrolyzing active chlorine in a chloride solution. However, this technology only uses active chlorine as an auxiliary oxidation method, does not utilize simultaneous alkali production at the cathode to achieve in-situ precipitation and separation, and does not construct a complete closed-loop circulation system; essentially, it is still a semi-open-circuit system. In addition, chlorine-based media cause severe corrosion to equipment, and the lithium battery industry has a low tolerance for chloride ion impurities, requiring deep dechlorination of the products.

[0007] In recent years, bipolar membrane electrodialysis technology has shown broad application prospects in lithium extraction from salt lakes, wastewater treatment, and lithium battery recycling. This technology can directly convert salt solutions into corresponding acids and bases under the influence of an electric field, without the need for external chemical reagents, and has significant advantages such as cleanliness, high efficiency, and closed-loop operation. Chinese patent CN113151680A discloses a method for treating waste lithium battery acid leaching solution with bipolar membrane electrodialysis after impurity removal to obtain lithium hydroxide solution and acid solution. However, this type of technology still relies on the upstream acid leaching process and does not achieve the recycling of the oxidation medium within the system.

[0008] In summary, existing waste lithium battery recycling technologies still suffer from the following core challenges: (1) high consumption of chemical reagents and high operating costs; (2) poor selectivity and lengthy separation processes; (3) large amounts of waste liquid are generated during the process, resulting in a heavy environmental burden; and (4) lack of closed-loop connection between various unit operations, leading to low resource utilization. Therefore, there is an urgent need to develop a green recycling method for waste lithium batteries that is highly selective, consumes less reagents, can achieve a closed-loop cycle throughout the entire process, and is suitable for large-scale production. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a closed-loop regeneration method for retired lithium battery cathode black powder using bromine-medium electro-oxidation and bipolar film coupling without the need for external strong acids and oxidants. Lithium bromide is used as the circulating medium, and the process involves selective delithiation via electro-oxidation, in-situ alkali production for impurity removal, and simultaneous co-production of hydrogen bromide and lithium hydroxide via bipolar film. The lithium precipitation mother liquor is regenerated by acidification with self-produced hydrogen bromide. The entire process involves internal circulation of bromine and lithium, with no introduction of external anionic impurities and near-zero waste discharge. Battery-grade lithium carbonate is directly produced, and the delithiation solid phase directly regenerates the cathode material, achieving a closed-loop recycling of materials throughout the entire process. This fundamentally solves the core problems of traditional processes, such as high reagent consumption, high waste discharge, and lengthy separation processes.

[0010] The technical solution of this invention is: S1. Raw material pretreatment: The retired lithium battery is deep discharged, disassembled, crushed and sorted in multiple stages to remove impurities such as shell, separator and copper and aluminum foil to obtain pure positive electrode black powder. S2, Electro-oxidation Delithiation: An aqueous solution of lithium bromide is fed into a single-chamber electrolytic cell, and the cathode black powder is suspended in the aqueous solution of lithium bromide; the anode electro-oxidizes bromide ions to generate elemental bromine, and the elemental bromine oxidizes the lattice of the cathode black powder to selectively remove lithium; the cathode is simultaneously reduced to generate hydroxide ions and hydrogen. S3. Precipitation and solid-liquid separation: When the system is first started up, a small amount of external lithium hydroxide solution is used as the initial alkaline solution and the hydroxide ions generated in step S2 are used to adjust the pH of the system so that the metal ions dissolved from the positive electrode black powder enter the solid phase in the form of precipitation; after precipitation, the solid-liquid mixture in the electrolytic cell is discharged and the solid and liquid are separated to obtain the delithiated filter cake and lithium-containing filtrate. S4. Bipolar membrane electrodialysis for acid and alkali production: After the lithium-containing filtrate is concentrated, it is sent to the bipolar membrane electrodialysis device. Under the action of the electric field, bromide ions migrate into the acid chamber and are enriched to generate hydrogen bromide solution, while lithium ions migrate into the alkali chamber and are enriched to generate lithium hydroxide solution. Part of the generated lithium hydroxide solution is returned to step S3 for pH control of the system during the stable operation phase. S5. Acid-base separation and lithium carbonate preparation: Carbon dioxide is passed through the remaining lithium hydroxide solution in the alkali chamber to carry out a carbonation reaction, and solid-liquid separation is performed to obtain lithium carbonate and lithium precipitation mother liquor; Part of the hydrogen bromide solution obtained in the acid chamber is recycled to the electrolytic cell in step S2 for reuse, and the rest is used for acidification conversion in step S6. S6, Acidification and Conversion of Lithium Precipitate Mother Liquor: The lithium precipitate mother liquor is mixed and reacted with hydrogen bromide solution to obtain a regenerated lithium bromide aqueous solution and carbon dioxide; the carbon dioxide is recycled for the carbonation process, and the regenerated lithium bromide aqueous solution is refluxed into step S2 for reuse. S7. Cathode material regeneration: The cathode black powder precursor obtained after drying the lithium-free filter cake in step S3 is mixed with the lithium carbonate dried product in step S5 according to the required metering ratio for cathode material. After matching with carbon source and / or phosphorus source, the mixture is ball-milled at high temperature, dried and calcined to obtain regenerated cathode material.

[0011] Furthermore, in step S1, the retired lithium battery is a lithium iron phosphate battery or a nickel-cobalt-manganese ternary lithium-ion battery.

[0012] Furthermore, in step S2, the electrolytic cell is a corrosion-resistant single-chamber membrane-free electrolytic cell, the anode is a shape-stable bromine-degrading electrode, and the cathode is one of a titanium electrode, a stainless steel electrode, a nickel electrode, or a graphite electrode.

[0013] Further, in step S2, the mass fraction of the lithium bromide aqueous solution is 1%~10%, preferably 2%~5%; hydrogen bromide may be added to the electrolyte, with an initial concentration of 0.1~1 mol / L; the positive electrode black powder is added at a solid-liquid ratio of 20~150 g / L, preferably 50~100 g / L; electrolysis is carried out in constant current or constant voltage mode, with a cell voltage of 1.5~3.0 V, preferably 1.8~2.5 V; electrolysis is carried out at room temperature with stirring, and the electrolysis time is 1~6 h.

[0014] Furthermore, in step S3, the solution pH is controlled to 11-13, and the precipitation reaction time is 0.5-3 h.

[0015] Further, in step S4, the concentration treatment is selected from either evaporation concentration or membrane concentration, and the lithium ion concentration after concentration is ≥10 g / L; the bipolar membrane electrodialysis device is a three-chamber bipolar membrane electrodialysis device, equipped with a monovalent selective cation exchange membrane and a monovalent selective anion exchange membrane; the current density is 20~50 mA / cm². 2 Preferably 25~40 mA / cm 2 The low-lithium, dilute lithium bromide tail liquid discharged from the salt chamber is partially recycled as the initial liquid for the acid and / or alkali chambers.

[0016] Furthermore, in step S5, the temperature of the carbonation precipitation reaction is 70~95℃, the excess carbon dioxide coefficient is 1.05~1.2, and the reaction is maintained at this temperature for 0.5~1.5 h; Furthermore, in step S6, the amount of hydrogen bromide added in the acidification conversion section is 1.05 to 1.20 times the theoretical amount required for the complete reaction of the total alkali content of carbonate and hydroxide ions in the mother liquor, and the reaction temperature is 50 to 80°C; the escaped carbon dioxide gas is collected under negative pressure and then recirculated into step S5 after pressurization for carbonation precipitation reaction.

[0017] Further, in step S7, when the cathode black powder is lithium iron phosphate black powder, additional carbon and phosphorus sources are required. The molar ratio of Li to Fe is 1.02~1.05:1, the amount of carbon source added is 5%~15% of the molar amount of Fe, and the phosphorus source is added according to the Fe:P molar ratio of 1:1. The mixture is calcined at 600~800℃ for 3~8 h under a nitrogen or argon atmosphere. When the cathode black powder is nickel-cobalt-manganese ternary black powder, additional carbon source is required. The molar ratio of Li to (Ni+Co+Mn) is 1.02~1.08:1, and the amount of carbon source added is 5%~15% of the total molar amount of (Ni+Co+Mn). The mixture is first-stage reduction calcined at 500~650℃ for 1~4 h under a nitrogen or argon inert atmosphere, and then switched to an air or pure oxygen atmosphere for calcination at 800~950℃ for 4~10 h. h; the carbon source is selected from at least one of glucose, sucrose, starch, citric acid, and acetylene black; the phosphorus source is selected from at least one of phosphoric acid, lithium phosphate, lithium dihydrogen phosphate, or ammonium dihydrogen phosphate.

[0018] Another aspect of the present invention provides a system for realizing the above-mentioned closed-loop regeneration method of bromine-medium electro-oxidation-bipolar membrane coupled retired lithium battery cathode black powder, comprising: a single-chamber electrolytic cell, a precipitation and impurity removal and solid-liquid separation unit, a concentration unit, a bipolar membrane electrodialysis unit, a lithium carbonate preparation unit, a lithium precipitation mother liquor acidification and conversion unit, a cathode material regeneration unit, and a built-in parameter configuration module. The single-chamber electrolytic cell is equipped with a positive electrode black powder inlet, a lithium bromide aqueous solution inlet, a hydrogen bromide solution inlet, a hydrogen outlet, and a solid-liquid mixture outlet; The precipitation and solid-liquid separation unit includes a precipitation reactor and a first solid-liquid separation device. The precipitation reactor is provided with a lithium hydroxide solution reflux port, a solid-liquid mixture inlet, and a slurry outlet. The solid-liquid mixture inlet is connected to the solid-liquid mixture outlet of the single-chamber electrolytic cell through a pipeline. The slurry outlet is connected to the inlet of the first solid-liquid separation device. The first solid-liquid separation device is provided with a solid phase outlet and a liquid phase outlet. The inlet of the concentration unit is connected to the liquid phase outlet of the first solid-liquid separation device; The bipolar membrane electrodialysis unit is a three-chamber bipolar membrane electrodialysis device, including an acid chamber, a salt chamber, and an alkali chamber. The inlet of the salt chamber is connected to the concentrate outlet of the concentration unit. A monovalent selective cation exchange membrane is installed between the acid chamber and the alkali chamber, and a monovalent selective anion exchange membrane is installed between the alkali chamber and the salt chamber. The outlet of the acid chamber is connected to the hydrogen bromide solution inlet of the electrolyzer through a first reflux pipeline. The outlet of the alkali chamber is connected to the lithium hydroxide solution reflux outlet of the precipitation reactor through a second reflux pipeline. The lithium carbonate preparation unit includes a carbonation reactor, a second solid-liquid separation device, and a lithium carbonate drying device. The carbonation reactor is equipped with a carbon dioxide inlet, an alkali inlet, and an outlet. The alkali inlet is connected to the outlet of the alkali chamber of the bipolar membrane electrodialysis unit. The outlet of the carbonation reactor is connected to the inlet of the second solid-liquid separation device, and the solid phase outlet of the second solid-liquid separation device is connected to the lithium carbonate drying device. The lithium precipitation mother liquor acidification conversion unit includes an acidification reactor. The inlet of the acidification reactor is connected to the liquid phase outlet of the second solid-liquid separation device. The acidification reactor is provided with a hydrogen bromide solution inlet and a lithium bromide aqueous solution outlet. The hydrogen bromide solution inlet is connected to the outlet of the acid chamber, and the lithium bromide aqueous solution outlet is connected to the lithium bromide aqueous solution inlet of the single-chamber electrolyzer. The cathode material regeneration unit includes a ball mill, a drying device, and a high-temperature calcining furnace. The ball mill is equipped with a lithium carbonate inlet, a cathode black powder precursor inlet, a carbon source inlet, and a phosphorus source inlet for lithium iron phosphate regeneration. The outlet of the drying device is connected to the cathode black powder precursor inlet of the ball mill via a pipeline. The outlet of the lithium carbonate drying device is connected to the lithium carbonate inlet of the ball mill via a pipeline. The outlet of the ball mill is connected to the inlet of the high-temperature calcining furnace. The built-in parameter configuration module includes an electrolytic cell current / voltage control unit, a precipitation reaction pH control unit, a lithium carbonate precipitation temperature and carbon dioxide dosage control unit, a roasting atmosphere and temperature parameter configuration unit, and automatic interlocking actuators for all equipment.

[0019] The advantages and positive effects of this invention are: (1) Extremely low reagent consumption and reduced operating costs: This invention uses lithium bromide as the electrolyte medium. Bromine ions are oxidized to elemental bromine at the anode, and after the elemental bromine oxidizes the black powder, it is reduced back to bromide ions, realizing a catalytic cycle of "oxidation-reduction-regeneration". Theoretically, there is no net consumption of bromide ions, and only a very small amount needs to be replenished. Compared with the traditional strong acid leaching process, which requires a large amount of acid and oxidizing / reducing agents to be continuously consumed, the reagent consumption of this invention is greatly reduced.

[0020] (2) Integrated selective delithiation and simultaneous impurity removal, simplifying the process: This invention relies on an electrolytic cell to construct an in-situ coupled system of bromine oxidation delithiation at the anode and alkaline precipitation at the cathode for impurity removal. The bromine generated at the anode selectively oxidizes lithium in the black powder lattice, causing lithium to enter the solution in ionic form, while nickel, cobalt, manganese, iron, and other metal ions precipitate in situ as hydroxides in the alkaline environment generated at the cathode. After electrolysis, only one solid-liquid separation step is needed to effectively separate lithium from impurity metals, eliminating the need for external alkali solution to adjust pH, multi-stage extraction, or stepwise precipitation, significantly shortening the process flow.

[0021] (3) Bipolar membrane technology enables clean conversion of salts into acids and alkalis: This invention uses bipolar membrane electrodialysis technology to treat lithium-containing filtrate, directly converting lithium bromide into hydrogen bromide and lithium hydroxide. The entire process requires no external chemical reagents and does not generate secondary pollution. Unlike traditional lithium precipitation processes that require the addition of precipitants such as sodium carbonate, this invention directly introduces carbon dioxide after the bipolar membrane produces alkali to obtain high-purity lithium carbonate, reducing the introduction and emission of sodium salts from the source.

[0022] (4) High product purity, which can be directly used for battery regeneration: The lithium hydroxide obtained by this invention can be carbonated to obtain battery-grade lithium carbonate products; the resulting hydrogen bromide solution can be returned to the electrolytic cell for recycling, and can also be used as an acid source for the acidification and conversion of lithium precipitation mother liquor. The delithiation filter cake can be used as a precursor for the regeneration of cathode materials. After being mixed with self-produced lithium carbonate in a certain proportion and calcined at high temperature, the cathode materials can be directly regenerated, realizing a complete closed loop of "waste battery cathode → lithium salt → new battery cathode".

[0023] (5) Wide range of applications and easy to scale up: This invention can be adapted to both lithium iron phosphate and nickel-cobalt-manganese ternary systems of cathode black powder, and has wide applicability; the entire process is free from the introduction of sulfate and chloride ions, and low-impurity lithium hydroxide is obtained by bipolar membrane separation, and battery-grade lithium carbonate is directly produced after carbonization; the single-chamber electrolysis, solid-liquid separation, concentration, bipolar membrane electrodialysis, and carbonation precipitation are all mature unit operations in the chemical industry, without special harsh working conditions, controllable equipment investment, easy to realize continuous and large-scale industrial production, and suitable for the construction of a 10,000-ton-level retired battery recycling production line. Attached Figure Description

[0024] Figure 1 This is a flowchart of the closed-loop regeneration method for the positive electrode black powder of retired lithium batteries using bromine dielectric electro-oxidation-bipolar film coupling in Example 1.

[0025] Figure 2 The flowchart shows the traditional sulfuric acid / hydrogen peroxide whole-component leaching-fractional extraction process in Comparative Example 1. Detailed Implementation

[0026] 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.

[0027] Example 1: Closed-loop recycling of retired NCM523 ternary cathode black powder A closed-loop regeneration method for cathode black powder from retired lithium batteries using bromine-dielectric electro-oxidation-bipolar film coupling without the need for exogenous strong acids and oxidants. The retired lithium batteries are ternary NCM523 batteries. The regeneration process flow is as follows: Figure 1 The specific steps are as follows: S1. Raw material pretreatment: Take retired commercial NCM523 power batteries, and after deep discharge with sodium chloride solution, mechanically disassemble, crush, wind sort and screen them to remove impurities such as shell, separator, copper and aluminum foil to obtain pure positive electrode black powder.

[0028] S2, Electro-oxidation Delithiation: A 3% (w / w) lithium bromide aqueous solution was prepared as the electrolyte, and hydrogen bromide was added to an initial concentration of 0.3 mol / L to maintain an acidic environment. The NCM523 cathode black powder obtained in step S1 was added to a single-chamber diaphragm-free electrolytic cell at a solid-liquid ratio of 60 g / L and uniformly suspended and stirred. The anode of the electrolytic cell was a titanium-based ruthenium-iridium stabilizing bromine electrode, and the cathode was a stainless steel electrode. A constant voltage mode was adopted, with a cell voltage of 2.0 V and electrolysis at room temperature with stirring for 2.5 h. The anode electro-oxidized bromide ions to generate elemental bromine, and the elemental bromine oxidized the black powder lattice, causing lithium to selectively escape into the solution. The elemental bromine itself was reduced to bromide ions for regeneration, and the cathode simultaneously reduced to generate hydroxide ions and hydrogen gas.

[0029] S3. Precipitation and Solid-Liquid Separation: During the initial system startup, an external lithium hydroxide solution is used as the initial alkali solution, and the pH is adjusted to 11 using hydroxide ions generated in step S2. After the system stabilizes, the pH is adjusted using hydroxide ions generated at the cathode in conjunction with the lithium hydroxide solution in the bipolar membrane electrodialysis alkali chamber of step S4. This causes the nickel, cobalt, and manganese dissolved from the cathode black powder to precipitate into the solid phase as hydroxides. Solid-liquid separation yields a delithiated filter cake (containing nickel, cobalt, and manganese hydroxide precipitates) and a lithium-containing filtrate.

[0030] S4. Bipolar Membrane Electrodialysis for Acid and Alkali Production: The lithium-containing filtrate obtained in step S3 is concentrated to a lithium concentration of 15 g / L using electrodialysis. The concentrate is then transferred to a three-chamber bipolar membrane electrodialysis device equipped with an Astom CSE sulfonic acid cation exchange membrane and an ACS quaternary ammonium anion exchange membrane. Constant current mode is used with a current density of 30 mA / cm². 2 The system operates at room temperature. Under the influence of an electric field, lithium ions in the salt chamber migrate through the cation exchange membrane into the alkali chamber, where they combine with hydroxide ions generated by the hydrolysis of the bipolar membrane to form a lithium hydroxide solution. Bromine ions migrate through the anion exchange membrane into the acid chamber, where they combine with hydrogen ions generated by the hydrolysis of the bipolar membrane to form a hydrogen bromide solution. A portion of the lithium hydroxide solution enriched in the alkali chamber is refluxed to step S3 for pH adjustment during the system's stable operation.

[0031] S5. Acid-base separation and lithium carbonate preparation: The remaining lithium hydroxide solution from the alkali chamber in step S4 is loaded into a carbonation reactor, heated to 85°C, and carbon dioxide gas (excess carbon dioxide coefficient 1.10) is introduced. The mixture is kept at this temperature and stirred for 1.0 h to generate lithium carbonate precipitate and lithium precipitation mother liquor. The lithium carbonate precipitate is vacuum filtered, washed three times with pure water at 80°C, and dried at 105°C for 4 h to obtain battery-grade lithium carbonate product. The purity of lithium carbonate is 99.8% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) combined with acid-base titration. A portion of the hydrogen bromide solution obtained from the acid chamber in step S4 is transferred to the acidification section of the lithium precipitation mother liquor in step S6, while the remainder is returned to the electrolytic cell in step S2 for acidification conversion.

[0032] S6. Acidification and Conversion of Lithium Precipitation Mother Liquor: The lithium precipitation mother liquor (mainly containing residual lithium ions and carbonate ions) after carbonation precipitation in step S5 is transferred to the acidification reactor and heated to 65°C. Hydrogen bromide solution diverted from step S5 is slowly added at 1.10 times the theoretical amount required for complete reaction of carbonate and hydroxide ions in the lithium precipitation mother liquor, and the reaction is stirred for 1.0 h. During the reaction, a negative pressure closed system is used to collect the escaping carbon dioxide gas, which is then pressurized and circulated back into the carbonation precipitation reactor in step S5. After the reaction, a regenerated lithium bromide aqueous solution is obtained, which is entirely recycled back to the electrolytic cell in step S2 for reuse.

[0033] S7. Cathode Material Regeneration: The lithium-depleted filter cake from step S3 is dried at 80°C for 6 hours. The obtained cathode black powder precursor and the battery-grade lithium carbonate obtained in step S5 are precisely proportioned according to a Li:(Ni+Co+Mn) molar ratio of 1.05:1, and an additional carbon source (glucose) is added at 5% of the total molar amount of transition metals (Ni+Co+Mn). The mixture is ball-milled for 4 hours and placed in a tube furnace. The first stage of reduction roasting is carried out at 600°C for 2 hours under a nitrogen inert atmosphere to reduce the high-valence transition metal ions. Then, the atmosphere is switched to air and the temperature is raised to 850°C for the second stage of oxidation roasting for 7 hours. The mixture is then cooled to room temperature with the furnace and crushed through a 200-mesh sieve to obtain the regenerated NCM523 cathode material.

[0034] The main phase purity of the recycled NCM523 cathode material was tested to be 93.8%. After assembling coin cells, the first charge-discharge test at a 0.1 C rate showed an initial discharge capacity of 156.2 mAh / g.

[0035] Example 2: Closed-loop regeneration of cathode black powder from retired ternary NCM811 batteries The process flow is the same as in Example 1. The specific steps are as follows: S1. Raw material pretreatment: The only difference from step S1 in Example 1 is that the retired lithium battery is a commercial NCM811 high-nickel ternary power battery.

[0036] S2, Electro-oxidative delithiation: The only difference from step S2 in Example 1 is that the mass fraction of lithium bromide aqueous solution is 4%, the initial concentration of hydrogen bromide is 0.5 mol / L, the positive electrode black powder is added at a solid-liquid ratio of 80 g / L, the cathode is a titanium electrode, the cell voltage is 2.3 V, and the electrolysis is carried out at room temperature with stirring for 3.0 h.

[0037] S3, Precipitation and solid-liquid separation: The only difference from step S3 in Example 1 is that the pH of the solution is adjusted to 11.5.

[0038] S4. Bipolar membrane electrodialysis for acid and alkali production: The only difference from step S4 in Example 1 is that an alkali-resistant disc-tube reverse osmosis system is used to concentrate the lithium to a concentration of 18 g / L; the bipolar membrane electrodialysis current density is 35 mA / cm². 2 .

[0039] S5, Acid-Base Separation and Lithium Carbonate Preparation: The only difference from step S5 in Example 1 is that carbon dioxide (excess carbon dioxide coefficient 1.15) is introduced and precipitated at 90°C, followed by stirring and maintaining the temperature for 1.5 h. The lithium carbonate purity was found to be 99.7% after testing (using the same method as in Example 1).

[0040] S6, Acidification and Conversion of Lithium Precipitated Mother Liquor: The only difference from step S6 in Example 1 is that the lithium precipitated mother liquor is heated to 70°C, and hydrogen bromide solution is added dropwise at 1.15 times the theoretical amount required for complete reaction of the total alkalinity of carbonate and hydroxide ions in the lithium precipitated mother liquor. The reaction is stirred for 1.2 h.

[0041] S7. Cathode material regeneration: The only difference from step S7 in Example 1 is that the molar ratio of Li:(Ni+Co+Mn) is 1.08:1; sucrose is used as the carbon source, and the amount added is 8% of the total molar amount of transition metals (Ni+Co+Mn); the first stage of reduction roasting is carried out at 650°C under a nitrogen atmosphere for 3 h, and then the atmosphere is switched to pure oxygen and the temperature is raised to 920°C for the second stage of oxidation roasting for 6 h.

[0042] The purity of the main phase of the regenerated NCM811 cathode material was tested to be 93.5%. In a coin cell test, using the same method as in Example 1, the initial discharge capacity was 181.1 mAh / g.

[0043] Example 3: Closed-loop regeneration of cathode black powder from retired lithium iron phosphate batteries The process flow is the same as in Example 1. The specific steps are as follows: S1. Raw material pretreatment: The only difference from step S1 in Example 1 is that the retired lithium battery is a commercial lithium iron phosphate battery.

[0044] S2, Electro-oxidative Lithium Removal: The only difference from step S2 in Example 1 is that the lithium bromide aqueous solution has a mass fraction of 2.5%, and the initial concentration of hydrogen bromide is 0.2 mol / L; lithium iron phosphate black powder is added to a single-chamber diaphragm-free electrolytic cell at a solid-liquid ratio of 60 g / L and uniformly suspended; the cell voltage is 1.8 V, and electrolysis is carried out at room temperature with stirring for 2.0 h; alkali is produced at the cathode, causing the dissolved iron ions to precipitate into the solid phase in the form of ferric hydroxide. It should be noted that the main lithium iron phosphate delithiation process follows a topological chemical mechanism, and the lattice iron dissolution rate is extremely low under standard conditions; however, under the industrial operation boundaries allowed by this invention (such as long-term leaching or high acidity), the surface layer of iron iron phosphate will undergo simultaneous dissolution of trace amounts of iron and phosphate due to proton erosion. This loss of phosphate will directly affect the stoichiometry of the recycled material, so it needs to be compensated for in subsequent processes.

[0045] S3. Precipitation and solid-liquid separation: The only difference from step S3 in Example 1 is that the pH of the solution is adjusted to 12. X-ray diffraction phase analysis shows that the lithium-free filter cake still retains the iron phosphate olivine crystal phase; at the same time, the electrolyte test revealed trace amounts of co-dissolution of iron and phosphorus, indicating that there is a non-negligible trace loss of phosphate.

[0046] S4, Bipolar membrane electrodialysis for acid and alkali production: The only difference from step S4 in Example 1 is that lithium is concentrated to 20 g / L; the bipolar membrane electrodialysis current density is 25 mA / cm². 2 .

[0047] S5, Acid-Base Separation and Lithium Carbonate Preparation: The only difference from step S5 in Example 1 is that carbon dioxide (excess coefficient 1.08) is introduced and the mixture is precipitated at 80°C, with stirring and maintaining the temperature for 1.5 h. The lithium carbonate purity was found to be 99.9% after testing (using the same method as in Example 1).

[0048] S6, Acidification and Conversion of Lithium Precipitated Mother Liquor: The only difference from step S6 in Example 1 is that the lithium precipitated mother liquor is heated to 60°C, and hydrogen bromide solution is added dropwise at 1.08 times the theoretical amount required for complete reaction of the total alkalinity of carbonate and hydroxide ions in the lithium precipitated mother liquor, and the reaction is stirred for 0.8 h.

[0049] S7. Cathode Material Regeneration: Considering the trace co-dissolution loss of iron and phosphorus in S3, an additional phosphorus source is added during the formulation to ensure that the regenerated lithium iron phosphate has an accurate Li:Fe:P stoichiometric ratio. The cathode black powder precursor and battery-grade lithium carbonate are formulated at a molar ratio of Li:Fe = 1.03:1. At the same time, ammonium dihydrogen phosphate is added to the formulation as a compensating phosphorus source, with the amount of phosphorus being 1.02 times the molar amount of iron. 5% glucose is added as a carbon source. The mixture is ball-milled for 3 h, calcined at 700℃ for 6 h under a nitrogen atmosphere, cooled, crushed, and sieved to obtain the regenerated lithium iron phosphate cathode material.

[0050] The purity of the main phase of the regenerated lithium iron phosphate cathode material was tested to be 95.5%. In a coin cell test, using the same method as in Example 1, the initial discharge capacity was 155.3 mAh / g.

[0051] Example 4 A system for implementing the closed-loop regeneration method of bromine-medium electro-oxidation-bipolar membrane coupled retired lithium battery cathode black powder in Examples 1-3, the system includes: a single-chamber electrolytic cell, a precipitation and impurity removal and solid-liquid separation unit, a concentration unit, a bipolar membrane electrodialysis unit, a lithium carbonate preparation unit, a lithium precipitation mother liquor acidification and conversion unit, a cathode material regeneration unit, and a built-in parameter configuration module.

[0052] The single-chamber electrolytic cell is a corrosion-resistant, membrane-free single-chamber electrolytic cell, equipped with a positive electrode black powder inlet, a lithium bromide aqueous solution inlet, a hydrogen bromide solution inlet, a hydrogen outlet, and a solid-liquid mixture outlet. The anode is a shape-stabilized bromine-degrading electrode, and the cathode is one of a titanium electrode, stainless steel electrode, nickel electrode, or graphite electrode. A stirring device is installed in the cell to suspend the positive electrode black powder in the lithium bromide electrolyte. Hydrogen produced as a byproduct at the cathode is discharged through the hydrogen outlet and then diluted and vented.

[0053] The precipitation and solid-liquid separation unit includes a precipitation reactor and a first solid-liquid separation device. The precipitation reactor has a lithium hydroxide solution reflux port, a solid-liquid mixture inlet, and a slurry outlet. The solid-liquid mixture inlet is connected via pipeline to the solid-liquid mixture outlet of the single-chamber electrolyzer to receive the solid-liquid mixture containing delithiated black powder and impurity metal ions after electrolysis. The lithium hydroxide solution reflux port is connected via pipeline to the outlet of the alkali chamber of the bipolar membrane electrodialysis unit to receive the lithium hydroxide solution generated in the alkali chamber to adjust the system pH. The precipitation reactor is equipped with a pH sensor and a stirrer. The slurry outlet is connected to the inlet of the first solid-liquid separation device, which has a solid phase outlet and a liquid phase outlet. The solid phase outlet is used to output the delithiated filter cake, and the liquid phase outlet is used to output the lithium-containing filtrate.

[0054] The inlet of the concentration unit is connected to the liquid phase outlet of the first solid-liquid separation device to concentrate lithium in the filtrate to a concentration of not less than 10 g / L. The outlet of the concentrate is connected to the bipolar membrane electrodialysis unit. The bipolar membrane electrodialysis unit is a three-chamber bipolar membrane electrodialysis device, including an acid chamber, a salt chamber, and an alkali chamber. The inlet of the salt chamber is connected to the concentrate outlet of the concentration unit. A monovalent selective cation exchange membrane is installed between the acid chamber and the salt chamber, and a monovalent selective anion exchange membrane is installed between the salt chamber and the alkali chamber. The outlet of the acid chamber is connected to the hydrogen bromide solution inlet of the electrolyzer through a first reflux pipeline; the outlet of the alkali chamber is connected to the lithium hydroxide solution reflux outlet of the precipitation reactor through a second reflux pipeline. The salt chamber has a tail liquid outlet, and at least part of the discharged low-lithium dilute lithium bromide tail liquid is refluxed back as the initial liquid for the acid chamber and / or the alkali chamber.

[0055] The lithium carbonate preparation unit includes a carbonation reactor, a second solid-liquid separation unit, and a lithium carbonate drying device. The carbonation reactor has a carbon dioxide inlet, an alkali inlet, and an outlet. The alkali inlet is connected to the outlet of the alkali chamber of the bipolar membrane electrodialysis unit to receive lithium hydroxide solution; the carbon dioxide inlet is connected to a carbon dioxide gas source. The outlet of the carbonation reactor is connected to the inlet of the second solid-liquid separation unit, which has a solid phase outlet and a liquid phase outlet. The solid phase outlet is connected to the lithium carbonate drying device, and the outlet of the lithium carbonate drying device outputs battery-grade lithium carbonate.

[0056] The lithium precipitated mother liquor acidification and conversion unit includes an acidification reactor. The acidification reactor is equipped with a lithium precipitated mother liquor inlet, a hydrogen bromide solution inlet, a lithium bromide aqueous solution outlet, and a carbon dioxide exhaust port. The lithium precipitated mother liquor inlet is connected to the liquid phase outlet of the second solid-liquid separation unit to receive the lithium precipitated mother liquor; the hydrogen bromide solution inlet is connected to the outlet of the acid chamber to receive the hydrogen bromide solution generated in the acid chamber. The lithium bromide aqueous solution outlet is connected to the lithium bromide aqueous solution inlet of the single-chamber electrolyzer, returning the regenerated lithium bromide solution generated by the acidification reaction to the electrolyzer for reuse. The carbon dioxide exhaust port is connected to the carbon dioxide inlet of the carbonation reactor via a recovery pipeline equipped with a booster pump, recycling the carbon dioxide generated by the acidification reaction for the carbonation process.

[0057] The cathode material regeneration unit includes a drying unit, a ball mill, and a high-temperature calcining furnace. The ball mill has a lithium carbonate inlet, a cathode black powder precursor inlet, a carbon source inlet, and a phosphorus source inlet for lithium iron phosphate regeneration. The drying unit's inlet is connected to the solid phase outlet of the first solid-liquid separation unit, and its outlet is connected via a pipeline to the cathode black powder precursor inlet of the ball mill. The lithium carbonate drying unit's outlet is connected via a pipeline to the lithium carbonate inlet of the ball mill, and the ball mill's outlet is connected to the high-temperature calcining furnace inlet.

[0058] The built-in parameter configuration module is a DCS or PLC control system, which is connected to the signals of the above-mentioned process equipment. It includes: electrolytic cell current / voltage control unit, precipitation reaction pH control unit, lithium carbonate precipitation temperature and carbon dioxide dosage control unit, roasting atmosphere and temperature and time parameter configuration unit, and automatic interlocking actuators for all equipment. These are distributed at the key pipelines and interfaces of each process equipment, including emergency shut-off valves, pressure relief valves, temperature switches and liquid level switches. When any process parameter exceeds the safety threshold, an alarm, adjustment or emergency shutdown is automatically triggered.

[0059] Comparative Example 1: Traditional sulfuric acid / hydrogen peroxide whole-component leaching-fractional extraction process This comparative example aims to illustrate the advantages of the "bromine-medium electro-oxidation selective lithium removal-bipolar membrane electrodialysis closed-loop" process of this invention compared to the traditional sulfuric acid full-component leaching and recovery process. The raw materials and pretreatment are consistent with those in Example 1 (NCM523) to demonstrate the differences between the two technical routes under the same raw material conditions. The process flow is shown below. Figure 2 The specific steps are as follows: (1) Raw material pretreatment: Same as step S1 in Example 1.

[0060] (2) Leaching of all components with sulfuric acid and hydrogen peroxide: Prepare a 2 mol / L sulfuric acid leaching solution, and add the cathode black powder to a temperature-controlled reactor with stirring at a solid-liquid ratio of 50 g / L; add 30% hydrogen peroxide at a quantitative amount of 1.3 times the theoretical amount required for complete reduction of all high-valence metal ions in the black powder; heat the system to 85℃ and leach with constant temperature stirring for 2.5 h. After leaching, filter to remove carbonaceous insoluble residues to obtain a mixed metal sulfate leaching solution; slowly add sodium hydroxide to the leaching solution to adjust the pH to 3.3, keep warm and stir for 0.5 h, and filter again to remove hazardous waste residue to obtain a mixed metal sulfate solution after impurity removal.

[0061] (3) Extraction and separation of manganese: The metal mixture after impurity removal in step (2) is extracted. The ratio of the organic phase for extraction is: 20% volume fraction P204 (di-(2-ethylhexyl) phosphate) + 80% sulfonated kerosene, with a saponification rate of 25%. A two-stage countercurrent extraction process is adopted, with a phase O / A ratio of 2.5 for the first stage and 2.0 for the second stage. The pH of the aqueous phase is controlled to be 3.0. After extraction, the manganese-loaded organic phase is first washed with 0.5 mol / L dilute sulfuric acid (phase O / A = 10) to elute the co-extracted cobalt and nickel and return them to the aqueous phase. Then, manganese is back-extracted with 1 mol / L sulfuric acid (phase O / A = 4) to obtain a manganese sulfate solution. The organic phase is then regenerated and recycled.

[0062] (4) Cobalt extraction and separation: After manganese removal, the raffinate aqueous phase enters the cobalt-nickel separation section. The organic phase is 20% (v / v) P507 (2-ethylhexylphosphonic acid mono-2-ethylhexyl ester) + 80% sulfonated kerosene, with a saponification rate of 50%. The extraction ratio O / A = 3:1, and the pH of the aqueous phase is stably controlled at 4.2 to achieve selective cobalt extraction. The cobalt-loaded organic phase is back-extracted with 2 mol / L sulfuric acid, with a back-extraction ratio O / A = 2:3, to obtain a high-purity cobalt sulfate solution. The organic phase is regenerated and reused. The raffinate mainly contains nickel and lithium.

[0063] (5) Extraction and separation of nickel: The aqueous phase remaining from step (4) is sent to the nickel-lithium separation and extraction section. The organic phase is prepared as 20% P2O4 + 80% sulfonated kerosene by volume, with a saponification rate of 30%. A multi-stage countercurrent extraction mode is adopted, with a constant aqueous phase equilibrium pH of 5.2 and an extraction phase O / A ratio of 2.0. The nickel-loaded organic phase is back-extracted with 1 mol / L sulfuric acid, with a back-extraction phase O / A ratio of 4. After back-extraction, a high-purity nickel sulfate solution is obtained, and the organic phase is regenerated and recycled.

[0064] (6) Lithium precipitation with sodium carbonate: After concentrating the lithium sulfate solution, heat it to 80°C and add excess sodium carbonate (1.2 times the theoretical requirement) to precipitate lithium. Keep the mixture warm and stir for 1.5 h. After precipitation, vacuum filter the lithium carbonate filter cake and wash it with hot water several times to remove adsorbed sodium ions and sulfate ions. Dry it at 105°C to obtain the lithium carbonate product.

[0065] The above comparative example uses strong acid to dissolve nickel, cobalt, manganese and lithium indiscriminately. However, it has to rely on multi-stage extraction to separate them one by one. The whole process consumes a lot of sulfuric acid, hydrogen peroxide and organic extractants, introduces a lot of sodium ions and sulfate ions, and produces oily wastewater and high-salt waste liquid containing sodium sulfate. Moreover, the lithium carbonate product cannot meet the battery-grade standard due to sodium entrainment.

[0066] In contrast, this invention utilizes the selective oxidation capability of elemental bromine to remove lithium into the solution, while nickel, cobalt, and manganese remain in situ in the solid phase. A single solid-liquid separation step achieves complete separation of lithium from impurities. Bipolar membrane electrodialysis is then used to cleanly convert the lithium-containing filtrate into high-purity lithium hydroxide and hydrogen bromide. The lithium precipitation mother liquor is acidified with self-produced hydrogen bromide to regenerate the lithium bromide recycling solution. The entire process involves the recycling of lithium bromide, with no external precipitant consumption, no introduction of foreign impurities such as sodium ions and sulfate, no organic phase pollution, and near-zero wastewater discharge. Battery-grade lithium carbonate is directly produced. The lithium removal filter cake and self-produced lithium carbonate can be roasted to regenerate the cathode material. This invention has significant advantages in terms of process intensification, reagent consumption, product purity, environmental friendliness, and scalability that are incomparable to the comparison.

[0067] The embodiments of the present invention have been shown and described above. For those skilled in the art, improvements or modifications can be made based on the above description. For example, if the pretreated black powder contains aluminum as the anode current collector, it can be dissolved in a dilute acid or dilute alkali solution, washed, and filtered to obtain aluminum-free black powder; before oxidative lithium extraction, polyvinylidene fluoride (PVDF) in the black powder can be recovered by dissolving and leaching with N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF), or directly removed by pyrolysis; the electro-oxidation for bromine production and the bromine oxidation for lithium extraction are performed separately (i.e., the bromine-containing solution obtained from electro-oxidation is exported from the electrolytic cell to oxidize the black powder) to protect the electrodes; a porous membrane is installed between the anode and cathode chambers to reduce the consumption of bromine produced at the cathode; the lithium-containing filtrate after solid-liquid separation undergoes deep impurity removal to extend the membrane's lifespan. All equivalent substitutions and process fine-tuning based on the coupled closed-loop regeneration concept of "electrochemical selective oxidation removal - bipolar membrane acid and alkali production - carbonation lithium precipitation - solid-phase roasting regeneration" fall within the scope of protection of this invention.

Claims

1. A closed-loop regeneration method for the positive electrode black powder of decommissioned lithium batteries using bromine-dielectric electro-oxidation-bipolar film coupling without the need for exogenous strong acids and oxidants, characterized in that... Includes the following steps: S1. Raw material pretreatment: The retired lithium batteries are subjected to deep discharge, disassembly, crushing, multi-stage sorting and impurity removal to obtain pure positive electrode black powder; S2, Electro-oxidation Delithiation: An aqueous solution of lithium bromide is fed into a single-chamber electrolytic cell, and the cathode black powder is suspended in the aqueous solution of lithium bromide; the anode electro-oxidizes bromide ions to generate elemental bromine, and the elemental bromine oxidizes the lattice of the cathode black powder to selectively remove lithium, while hydroxide ions and hydrogen are generated simultaneously at the cathode. S3. Precipitation and solid-liquid separation: When the system is first started up, an external lithium hydroxide solution is used as the initial alkaline solution, and the hydroxide ions generated in step S2 are used to adjust the pH of the system so that the metal ions dissolved from the positive electrode black powder enter the solid phase in the form of precipitation. After precipitation, the solid-liquid mixture in the electrolytic cell is discharged and separated to obtain a delithiated filter cake and a lithium-containing filtrate. S4. Bipolar membrane electrodialysis for acid and alkali production: After the lithium-containing filtrate is concentrated, it is sent to the bipolar membrane electrodialysis device. Under the action of the electric field, bromide ions migrate into the acid chamber and are enriched to generate hydrogen bromide solution, while lithium ions migrate into the alkali chamber and are enriched to generate lithium hydroxide solution. Part of the generated lithium hydroxide solution is returned to step S3 for pH control of the system during the stable operation phase. S5. Acid-base separation and lithium carbonate preparation: Carbon dioxide is passed through the remaining lithium hydroxide solution in the alkali chamber to carry out a carbonation reaction, and solid-liquid separation is performed to obtain lithium carbonate and lithium precipitation mother liquor; Part of the hydrogen bromide solution obtained in the acid chamber is recycled to the electrolytic cell in step S2 for reuse, and the rest is used for acidification conversion in step S6. S6, Acidification and Conversion of Lithium Precipitate Mother Liquor: The lithium precipitate mother liquor is mixed and reacted with hydrogen bromide solution to obtain a regenerated lithium bromide aqueous solution and carbon dioxide; the carbon dioxide is recycled for the carbonation process, and the regenerated lithium bromide aqueous solution is reused in step S2. S7. Cathode material regeneration: The cathode black powder precursor obtained after drying the lithium removal filter cake in step S3 is mixed with the lithium carbonate drying product in step S5 according to the required metering ratio for cathode material. After matching the carbon source and / or phosphorus source, the mixture is ball-milled and calcined at high temperature to obtain the regenerated cathode material.

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

3. The method according to claim 1, characterized in that, In step S2, the electrolytic cell is a corrosion-resistant single-chamber membrane-free electrolytic cell, the anode is a shape-stable bromine-electrode electrode, and the cathode is selected from one of titanium electrode, stainless steel electrode, nickel electrode or graphite electrode.

4. The method according to claim 1, characterized in that, In step S2, the mass fraction of the lithium bromide aqueous solution is 1%~10%; the positive electrode black powder is added at a solid-liquid ratio of 20~150 g / L; the electrolysis adopts constant current or constant voltage mode, and the cell voltage is 1.5~3.0 V; Electrolysis is carried out at room temperature with stirring, and the electrolysis time is 1~6 h.

5. The method according to claim 1, characterized in that, In step S3, the solution pH is controlled to 11-13, and the precipitation reaction time is 0.5-3 h.

6. The method according to claim 1, characterized in that, In step S4, the concentration treatment is selected from either evaporation concentration or membrane concentration, and the lithium ion concentration after concentration is ≥10 g / L; the bipolar membrane electrodialysis device is a three-chamber bipolar membrane electrodialysis device, equipped with a monovalent selective cation exchange membrane and a monovalent selective anion exchange membrane; the current density is 20~50 mA / cm². 2 The low-lithium dilute lithium bromide tail liquid discharged from the salt chamber is partially recycled as the initial liquid for the acid and / or alkali chambers.

7. The method according to claim 1, characterized in that, In step S5, the temperature of the carbonation precipitation reaction is 70~95℃, the excess carbon dioxide coefficient is 1.05~1.2, and the reaction is kept at this temperature for 0.5~1.5 h.

8. The method according to claim 1, characterized in that, In step S6, the amount of hydrogen bromide added in the acidification conversion section is 1.05 to 1.20 times the theoretical amount required for the complete reaction of the total alkali content of carbonate and hydroxide ions in the mother liquor, and the reaction temperature is 50 to 80°C. The escaped carbon dioxide gas is collected under negative pressure and then recirculated into step S5 after pressurization for carbonation precipitation reaction.

9. The method according to claim 1, characterized in that, In step S7, when the cathode black powder is lithium iron phosphate black powder, additional carbon and phosphorus sources are required. The molar ratio of Li to Fe is 1.02~1.05:1, the amount of carbon source added is 5%~15% of the molar amount of Fe, and the phosphorus source is added according to the Fe:P molar ratio of 1:

1. The mixture is calcined at 600~800℃ for 3~8 h under a nitrogen or argon atmosphere. When the cathode black powder is nickel-cobalt-manganese ternary black powder, additional carbon source is required. The molar ratio of Li to (Ni+Co+Mn) is 1.02~1.08:1, and the amount of carbon source added is 5%~15% of the total molar amount of (Ni+Co+Mn). The mixture is first-stage reduction calcined at 500~650℃ for 1~4 h under a nitrogen or argon inert atmosphere, and then switched to an air or pure oxygen atmosphere for calcination at 800~950℃ for 4~10 h. h; the carbon source is selected from at least one of glucose, sucrose, starch, citric acid, and acetylene black; the phosphorus source is selected from at least one of phosphoric acid, lithium phosphate, lithium dihydrogen phosphate, or ammonium dihydrogen phosphate.

10. A system for implementing the closed-loop regeneration method of bromine-dielectric electro-oxidation-bipolar film coupled retired lithium battery cathode black powder according to any one of claims 1 to 9, characterized in that, include: A single-chamber electrolytic cell is provided with a positive electrode black powder inlet, a lithium bromide aqueous solution inlet, a hydrogen bromide solution inlet, a hydrogen outlet, and a solid-liquid mixture outlet; The precipitation and solid-liquid separation unit includes a precipitation reactor and a first solid-liquid separation device. The precipitation reactor is provided with a lithium hydroxide solution reflux port, a solid-liquid mixture inlet, and a slurry outlet. The solid-liquid mixture inlet is connected to the solid-liquid mixture outlet of a single-chamber electrolytic cell via a pipeline. The slurry outlet is connected to the inlet of the first solid-liquid separation device. The first solid-liquid separation device is provided with a solid phase outlet and a liquid phase outlet. The concentration unit has its inlet connected to the liquid phase outlet of the first solid-liquid separation device; The bipolar membrane electrodialysis unit is a three-chamber bipolar membrane electrodialysis device, comprising an acid chamber, a salt chamber, and an alkali chamber. The inlet of the salt chamber is connected to the concentrate outlet of the concentration unit. A monovalent selective cation exchange membrane is installed between the acid chamber and the alkali chamber, and a monovalent selective anion exchange membrane is installed between the alkali chamber and the salt chamber. The outlet of the acid chamber is connected to the hydrogen bromide solution inlet of the electrolyzer via a first reflux pipeline. The outlet of the alkali chamber is connected to the lithium hydroxide solution reflux outlet of the precipitation reactor via a second reflux pipeline. The lithium carbonate preparation unit includes a carbonation reactor, a second solid-liquid separation device, and a lithium carbonate drying device. The carbonation reactor is equipped with a carbon dioxide inlet, an alkali inlet, and an outlet. The alkali inlet is connected to the outlet of the alkali chamber of the bipolar membrane electrodialysis unit. The outlet of the carbonation reactor is connected to the inlet of the second solid-liquid separation device, and the solid phase outlet of the second solid-liquid separation device is connected to the lithium carbonate drying device. The lithium precipitation mother liquor acidification conversion unit includes an acidification reactor. The inlet of the acidification reactor is connected to the liquid phase outlet of the second solid-liquid separation device. The acidification reactor is provided with a hydrogen bromide solution inlet and a lithium bromide aqueous solution outlet. The hydrogen bromide solution inlet is connected to the outlet of the acid chamber, and the lithium bromide aqueous solution outlet is connected to the lithium bromide aqueous solution inlet of the single-chamber electrolyzer. The cathode material regeneration unit includes a ball mill, a drying device, and a high-temperature calcining furnace. The ball mill is equipped with a lithium carbonate inlet, a cathode black powder precursor inlet, a carbon source inlet, and a phosphorus source inlet for lithium iron phosphate regeneration. The outlet of the drying device is connected to the cathode black powder precursor inlet of the ball mill via a pipeline. The outlet of the lithium carbonate drying device is connected to the lithium carbonate inlet of the ball mill via a pipeline. The outlet of the ball mill is connected to the inlet of the high-temperature calcining furnace. The built-in parameter configuration module includes an electrolytic cell current / voltage control unit, a precipitation reaction pH control unit, a lithium carbonate precipitation temperature and carbon dioxide dosage control unit, a roasting atmosphere and temperature parameter configuration unit, and automatic interlocking actuators for all equipment.

Images