Method for mildly, rapidly and selectively recycling lithium iron phosphate battery positive electrode material by wet process

Abstract

The invention discloses a method for mild and rapid wet-process selective recovery of a lithium iron phosphate battery positive electrode material, which comprises the following steps: adding a waste lithium iron phosphate positive electrode material into a leaching agent, namely a H2O2 and NH4HSO4 composite solution, carrying out wet-process leaching, and efficiently and selectively leaching Li in the waste lithium iron phosphate positive electrode material within 0.5-1 min, the highest leaching rate of Li reaches 99.9% and is recovered in a filtrate form, the lowest leaching rate of Fe reaches 0.01%, Fe exists in FePO4 and is recovered in a solid form in filter residues, the Li-containing filtrate reacts with sodium carbonate to obtain recovered lithium carbonate, and the Fe-containing filter residues and the recovered lithium carbonate are uniformly mixed and then subjected to high-temperature heat treatment with glucose to obtain the regenerated lithium iron phosphate battery positive electrode material. The technological process is short and simple, and the situation that the recovery rate is reduced and resources are wasted due to tedious steps is avoided.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling and reuse technology of waste lithium-ion battery electrode materials, specifically involving a mild and rapid wet selective recycling method for lithium iron phosphate battery cathode materials. Background Technology

[0002] Lithium iron phosphate (LFP) batteries are widely used in energy storage and electric vehicles due to their advantages such as good cycle life, high safety, and low production cost. With the continuous growth in demand for sustainable and green energy, the use of LFP batteries has increased dramatically. During use, lithium ions repeatedly insert and extract between the positive and negative electrode materials. With each charge-discharge cycle, the structure of the positive electrode material is damaged, leading to a decrease in battery capacity and eventual battery failure. Heavy metals and other harmful substances in waste batteries are difficult to degrade in the natural environment, accumulating over time. If not properly treated, they not only threaten the environment but also endanger human health. Furthermore, these discarded lithium-ion batteries contain abundant metal resources. Efficiently recycling valuable elements from waste LFP batteries can not only achieve resource utilization but is also crucial for environmental protection and sustainable development. Currently, my country's main technologies for recycling waste LFP batteries include direct recycling, pyrometallurgical processes, and hydrometallurgical processes. The consistency of lithium iron phosphate cathode materials repaired through direct regeneration processes often fails to meet the standards for new power electrode materials. Pyrometallurgical techniques are generally energy-intensive and have low recycling efficiency, making them difficult to apply in actual production. Hydrometallurgical techniques, however, have become the mainstream process for recycling lithium iron phosphate electrodes due to their advantages such as strong raw material applicability, diverse and flexible product solutions, and good comprehensive resource recycling.

[0003] Because the olivine structure of LiFePO4 is relatively stable, wet recovery processes typically require large amounts of strong acid. Prolonged leaching with strong acid is necessary to break down the electrode material's structure and recover valuable elements. Therefore, in research, wet recovery processes often use acid solutions as the transfer medium to transfer valuable metals such as Li and Fe from the electrode material in ionic form to the leaching solution for 1-2 hours, followed by purification. Then, through ion exchange, chemical precipitation, and solvent extraction, the metal ions are extracted from the solution as metal salts or oxides. This method is cumbersome and complex, with Li and Fe leaching simultaneously. Subsequent separation with appropriate reagents is required, resulting in raw material loss at each purification and conversion step, leading to increased costs and reduced recovery efficiency. Furthermore, the slow leaching rate results in long equipment downtime, accelerated corrosion, shortened equipment lifespan, and the potential introduction of new impurities. Some methods also generate toxic or acidic gases during recovery, polluting the environment and limiting the large-scale industrial application of this technology. Therefore, designing a fast, mild, simple, low-cost, and high-recyclability recycling process for waste lithium-ion battery electrode materials is a key research issue.

[0004] Considering that simultaneous leaching of Li and Fe indiscriminately would require subsequent separation and purification of the two metals, increasing the complexity of the recovery process, a suitable leaching process could be chosen to separate Li and Fe during leaching, significantly reducing recovery steps and optimizing the process. Therefore, this invention designs a method for selectively recovering Li and Fe, effectively reducing process steps and increasing recovery rate. Since Li and Fe are the most valuable metal elements in LiFePO4, increasing their leaching rate improves the economic efficiency of the recovery process. Separating and recovering Li and Fe is more economically efficient and has significant industrial production value. Existing research has developed some selective separation technologies; however, due to the relatively stable structure of LiFePO4, the leaching agents used in these studies cannot meet the requirements of achieving selective leaching in a short time with high efficiency, mild conditions, and simple processes. For example, the technique of separating Li and Fe using HCl as the extractant and NaClO as the oxidant achieves a Li leaching rate of 95% and a Fe leaching rate of less than 0.1% in a short time; however, this process may generate Cl2, polluting the environment. Using Fe2(SO4)3 as an oxidant, LiFePO4 was converted to FePO4, achieving a lithium extraction rate of 97.1%. However, excess Fe needs to be removed from the solution before preparing the Li product, which may lead to Li loss. Furthermore, current wet leaching processes generally have long leaching times, often requiring 1 hour or more to reach a stable leaching rate. For example, using a composite solution of NaH2PO4 and H2O2 for wet leaching, 2g of waste LFP material requires continuous leaching for 40 minutes to reach the maximum Li leaching rate, indicating that the leaching rate still needs further improvement.

[0005] Patent document CN202411691103.7 discloses a method for preparing battery-grade iron phosphate and lithium carbonate from waste lithium iron phosphate batteries. The method involves slurrying waste lithium iron phosphate cathode material, adding concentrated sulfuric acid for leaching, then adding sodium sulfite to control the reaction potential, and filtering after the reaction to obtain a leachate. Iron is then added to the leachate to remove copper, and after filtering, copper-removed solution and copper slag are obtained. Sodium dihydrogen phosphate is then added to the copper-removed solution to remove aluminum, and after filtering, aluminum slag and a purified solution are obtained. The pH of the purified solution is adjusted, and hydrogen peroxide is added, reacting to obtain iron phosphate dihydrate precipitate and iron phosphate mother liquor. The iron phosphate dihydrate is treated to obtain battery-grade anhydrous iron phosphate. The pH of the iron phosphate mother liquor is adjusted, and after filtering, purified residue and a lithium sulfate solution are obtained. Sodium carbonate is added to the lithium sulfate solution, and after heating and reacting, the slurry is filtered to obtain wet lithium carbonate, which is then processed to obtain battery-grade lithium carbonate. However, this patent document uses a conventional strong acid solution for wet leaching of valuable elements and does not contain any technical concept related to efficient and selective wet leaching of lithium.

[0006] Patent document CN202311854719.7 discloses a method for producing lithium phosphate from waste lithium iron phosphate batteries. The method involves processing the waste lithium iron phosphate batteries to obtain lithium iron phosphate battery powder; preparing the lithium iron phosphate battery powder into a slurry and adding concentrated sulfuric acid to obtain a leachate; adding an oxidant to the leachate and filtering to obtain a lithium sulfate solution; adding calcium hydroxide to the lithium sulfate solution to remove copper, aluminum, and iron elements, and filtering after sufficient reaction to obtain a primary filtrate; adjusting the pH of the primary filtrate with ammonia water, and then adding ammonium carbonate or ammonium bicarbonate to remove calcium, magnesium, nickel, and manganese impurities, and filtering to obtain a lithium-rich solution; concentrating the lithium-rich solution to obtain a concentrated solution; adjusting the pH of the concentrated solution with ammonia water, and adding a saturated ammonium phosphate solution, diammonium hydrogen phosphate solution, or ammonium dihydrogen phosphate solution; washing the product and drying to obtain high-purity lithium phosphate. However, this patent document uses a conventional strong acid solution for wet leaching of valuable elements and does not contain any related technical concept for efficient and selective wet leaching of lithium. Summary of the Invention

[0007] The technical problem solved by this invention is to provide a mild and rapid wet selective recovery method for lithium iron phosphate battery cathode materials. This method proposes the synergistic effect of NH4HSO4 and H2O2 to selectively recover Li and Fe from the cathode materials of lithium iron phosphate batteries. This process uses acidic salts and low-concentration oxidants, offering significant advantages in its green and mild nature. It can also efficiently and selectively extract Li from LiFePO4 within a very short time of 0.5-1 min, achieving a Li leaching rate of up to 99.9% recovered in liquid form, while the Fe leaching rate is less than 0.01%. Fe exists in FePO4 and is recovered in solid form in the filter residue. The process is short and simple to operate.

[0008] To achieve efficient and selective recovery of the precious metal Li from spent lithium iron phosphate (SLFP) batteries, this invention proposes a process flow of "battery pretreatment - efficient wet leaching - regeneration". First, the retired SLFP batteries are discharged to prevent leakage hazards during disassembly. After discharge, the battery casing is cut, the core is removed and disassembled, and the positive electrode sheet coated with LiFePO4 is collected and dried to remove residual electrolyte and active material. After drying, the spent SLFP positive electrode material is scraped from the electrode sheet. Then, a wet leaching process is performed. The spent SLFP positive electrode material is leached in a composite solution of H2O2 and NH4HSO4 at a specific temperature and time. During the leaching process, the final leaching rate can be controlled by adjusting the ratio of reactants to leaching agent, the solid-liquid ratio, the hydrogen peroxide concentration, the leaching temperature, and the leaching time. Under optimized conditions—a molar ratio of waste lithium iron phosphate powder to NH4HSO4 of 1:0.8, a solid-liquid ratio of 50 g / L, a H2O2 mass fraction of 0.5%, and a leaching temperature of 40°C—a 99.9% Li leaching rate was achieved in just 1 minute, while only 0.01% Fe was leached. The waste lithium iron phosphate cathode material was essentially converted to FePO4, achieving highly efficient and selective separation and recovery of Li and Fe. After the leaching process, solid-liquid separation was performed. The liquid contained a large amount of Li, which was enriched and precipitated to obtain lithium carbonate, which was then used in the subsequent calcination of iron phosphate to synthesize lithium iron phosphate, achieving lithium recovery. The solid was dried to obtain a lithium iron phosphate battery cathode material precursor, which was then added with lithium carbonate obtained from the solution and ball-milled with glucose and alcohol to ensure uniform mixing and reduced particle size, allowing for a more complete calcination reaction. After ball milling, the mixture was placed in an inert atmosphere for high-temperature calcination to synthesize regenerated lithium iron phosphate cathode material (RLFP). To further verify the feasibility of this closed-loop process, the electrochemical performance of RLFP was evaluated by assembling recycled lithium iron phosphate cathode materials into half-cells. Within the potential range of 2.5–4.2 V, RLFP exhibits a charge-discharge platform equivalent to SLFP, with good rate capability and cycle stability, meeting the requirements for commercial applications of lithium-ion batteries. This demonstrates the feasibility and superiority of the closed-loop recycling process.

[0009] The relevant reactions during the leaching process are as follows:

[0010] 2LiFePO4+2NH4HSO4+3H2O2=2FePO4↓+2Li2SO4+(NH4)2SO4+2H2O

[0011] To achieve selective lithium extraction, the acid salt NH4HSO4 was used in synergistic leaching with H2O2. The oxidation reaction weakened the Li-O bonds in LFP, promoting the release of lithium from the octahedral FeO6 layer. Simultaneously, NH4HSO4, as an acid salt, also provided H2O2 to the system. +As a stabilizer for H2O2, it prevents its decomposition, fully utilizes its oxidizing effect, and reduces the amount of H2O2 used. During the leaching process, hydrogen peroxide can... 2+ Oxidized to Fe 3+ The lithium precipitates as FePO4, which is poorly soluble in water, while lithium dissolves in the solution as ions. Solid-liquid separation can effectively separate Li and Fe. This simple process achieves efficient, rapid, and selective lithium extraction within 1 minute. Furthermore, this recovery process extracts lithium without damaging the basic framework structure of lithium-ion polymers (LFPs), providing a foundation for the regeneration of LiFePO4 cathode materials through high-temperature calcination of the recovered FePO4. In addition, the waste brine after lithium precipitation can be recycled, avoiding increased wastewater treatment costs and cumbersome processing steps.

[0012] To achieve the above-mentioned objectives, the technical solution of this invention is implemented through the following method: A mild and rapid wet selective recycling method for lithium iron phosphate battery cathode materials, characterized in that the specific process is as follows: waste lithium iron phosphate cathode materials are added to a leaching agent, namely a composite solution of H2O2 and NH4HSO4, for wet leaching. Li in the waste lithium iron phosphate cathode materials is selectively leached efficiently within 0.5-1 min, with the leaching rate of Li reaching up to 99.9% and being recovered in the form of filtrate. The leaching rate of Fe is as low as 0.01%, with Fe existing in FePO4 and being recovered in solid form in the filter residue. The Li-containing filtrate is reacted with sodium carbonate to obtain recovered lithium carbonate. The Fe-containing filter residue and the recovered lithium carbonate are uniformly mixed and then heat-treated with glucose at high temperature to obtain regenerated lithium iron phosphate battery cathode materials.

[0013] A mild and rapid wet selective recycling method for lithium iron phosphate battery cathode materials comprises the following steps: using retired lithium iron phosphate batteries as raw materials, the retired lithium iron phosphate batteries are first soaked in a saturated NaCl solution for 30-60 hours. Then, the battery casing is cut with an electric saw, the core is removed, and the cathode sheet is separated from the core. The cathode sheet is cut into appropriately sized pieces and placed in a tube furnace for vacuum pyrolysis at 400-500℃ for 3-15 hours to remove active materials and electrolyte, yielding waste lithium iron phosphate cathode materials. Subsequently, the obtained waste lithium iron phosphate cathode materials are subjected to wet recycling: 50g of waste lithium iron phosphate cathode materials and 0.25-2 times the theoretical molar amount of NH4HSO4 are weighed. 4. Add high-purity water and H2O2 at a solid-liquid ratio of 50-200 g / L and a hydrogen peroxide mass fraction of 0.01%-0.1%. Stir continuously in a constant-temperature water bath at 20-70℃ for 0.5-2 minutes. During this leaching process, NH4HSO4 and H2O2 leach synergistically. NH4HSO4, as an acid salt, provides an acidic environment to maintain the stability and effectiveness of hydrogen peroxide. Simultaneously, the oxidation weakens the Li-O bonds in LFP, promoting the release of lithium from the octahedral FeO6 layer. After leaching, separate the solid-liquid mixture, rinse the residue multiple times, adjust the pH of the lithium-containing filtrate to 9-11, heat to 50-70℃, and add a saturated sodium carbonate solution dropwise to allow the lithium to leach. + After complete precipitation, continue stirring for 30-60 minutes and allow to stand before filtering and drying to obtain recovered lithium carbonate. After drying the leaching residue, ball mill it with the recovered lithium carbonate at a molar ratio of 1:1.05, and add 10wt%-20wt% glucose and 1-1.5g / mL alcohol solution. The ball-to-material ratio is 10:1. After ball milling, dry the residue and calcine it at 600-800℃ for 8-12 hours under a nitrogen atmosphere to obtain regenerated lithium iron phosphate battery cathode material.

[0014] The overall process flow and steps are as follows: battery pretreatment - wet leaching - purification, regeneration and synthesis - battery reassembly.

[0015] Step S1: Immerse the retired lithium iron phosphate battery in a saturated NaCl solution for 48 hours to release the residual charge of the waste LiFePO4 battery. Then, cut the battery casing with an electric saw, remove the core, separate the positive electrode sheet from the core, cut it into appropriately sized electrode sheets, and place it in a tube furnace for vacuum pyrolysis at 450°C for 4 hours to remove the active material and electrolyte. Subsequently, scrape the powder from the positive electrode sheet to obtain the waste lithium iron phosphate positive electrode material.

[0016] Step S2: Perform wet high-efficiency leaching on the pretreated waste lithium iron phosphate cathode material: Add 50g of waste lithium iron phosphate cathode material to a leaching solution containing 0.85 times the theoretical molar amount of cathode material of NH4HSO4 and 0.5% H2O2 at a solid-liquid ratio of 50g / L. The leaching temperature is 40℃ and the leaching time is 1min.

[0017] Step S3, Purification, Regeneration, and Synthesis: The leached solid-liquid mixture is poured into a funnel for solid-liquid separation. The residue can be rinsed multiple times to ensure the washing solution is neutral and free of impurity ion adsorption. A saturated sodium carbonate solution is slowly added dropwise to the lithium-containing filtrate, allowing the Li... + After complete precipitation, continue stirring for 45 minutes and let stand for 2 hours to allow small crystals to aggregate into large crystals. Filter and dry to obtain recovered lithium carbonate. Dry the leaching iron-containing filter residue and mix it with recovered lithium carbonate at a molar ratio of 1:1.05. Add 15wt% glucose and 1.2g / mL alcohol solution, with a ball-to-material ratio of 10:1. Ball mill at 300rpm for 270 minutes. Finally, calcine at 700℃ for 10 hours under an inert atmosphere to obtain regenerated LiFePO4, i.e., RLFP.

[0018] Step S4, Battery Reassembly: RLFP, acetylene black, PVDF, and an appropriate amount of N-methylpyrrolidone (NMP) were slurried at a mass ratio of 8:1:1. The mixture was uniformly coated onto aluminum foil and dried to prepare an RLFP positive electrode. The RLFP positive electrode was then assembled into a CR2025 half-cell. The electrochemical performance of the CR2025 half-cell assembled with the RLFP positive electrode was recorded using a battery testing system within a voltage window of 2.5–4.2 V.

[0019] The advantages and beneficial effects of this invention are as follows: This invention recycles waste lithium iron phosphate cathode materials, fully realizing resource recycling and reuse, and reducing environmental damage. High leaching rates can be achieved in a short time, with fast leaching speed and short processing time, effectively reducing energy consumption in industrial applications. The mild process flow, without strong acids or alkalis and with low concentrations of oxidants, reduces corrosion and wear during equipment use, has practical significance for industrial applications, and is environmentally friendly. Furthermore, the innovative use of a composite solution of ammonium bisulfate and hydrogen peroxide not only allows lithium ions to be extracted from the lithium iron phosphate structure, but also... 3- It can also react with Fe produced by oxidation 3+A precipitate is formed, and then a simple filtration step achieves complete selective recovery of Li and Fe, with a selectivity of up to 99.9%. The process flow of this invention is short and simple, avoiding the reduced recovery rate and resource waste caused by cumbersome steps. Under optimized conditions, a 99.9% Li leaching rate can be achieved in just 1 minute, while only 0.01% Fe is leached. Waste lithium iron phosphate cathode material is essentially converted into FePO4, achieving highly efficient and selective separation and recovery of Li and Fe. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the present invention.

[0021] Figure 2 The XRD patterns of the waste LFP cathode before and after leaching are shown.

[0022] Figure 3 The image shows the electrochemical performance of the CR2025 half-cell assembled from the RLFP cathode in Example 1. Detailed Implementation

[0023] The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.

[0024] Example 1

[0025] A mild and rapid wet selective recovery method for lithium iron phosphate cathode materials, the specific steps of which are as follows: [Following the steps outlined] Figure 1 The process flow shown involves first immersing retired lithium iron phosphate batteries in a saturated NaCl solution for 48 hours. Then, the battery casing is cut with an electric saw, the core is removed, and the positive electrode sheet is separated from the core. These sheets are then cut into appropriately sized pieces and placed in a high-temperature pyrolysis gasification furnace at 450°C for 12 hours to remove active materials and electrolyte, yielding waste lithium iron phosphate positive electrode material. 50g of the waste lithium iron phosphate positive electrode material and 0.85 times the theoretical molar amount of NH4HSO4 are weighed and added to high-purity water and H2O2 at a solid-liquid ratio of 50g / L and a hydrogen peroxide mass fraction of 0.5%. The mixture is stirred continuously for 1 minute in a constant-temperature water bath at 40°C. After leaching, the solid-liquid mixture is poured into a funnel for solid-liquid separation, and the residue is rinsed multiple times. The pH of the filtrate is adjusted to 10, heated to 60°C, and a saturated sodium carbonate solution is slowly added dropwise to allow Li... +After complete precipitation, the mixture was added dropwise and stirred for 45 minutes, then allowed to stand for 2 hours before filtration and drying to obtain recovered lithium carbonate. The leaching residue was dried and then ball-milled with recovered lithium carbonate (iron phosphate: lithium carbonate = 1:1.05, molar ratio). 15 wt% glucose and 1.2 g / mL alcohol solution were added, with a ball-to-material ratio of 10:1. The mixture was ball-milled at 300 rpm for 270 minutes. After ball milling, the liquid was dried, placed in a crucible, and calcined in a tube furnace at 700 °C for 10 hours under a nitrogen atmosphere to obtain recovered LiFePO4, i.e., RLFP. Then, RLFP, acetylene black, PVDF, and an appropriate amount of N-methylpyrrolidone (NMP) were slurried at a mass ratio of 8:1:1. The mixture was uniformly coated on aluminum foil and dried at 80 °C for 10 hours to prepare RLFP positive electrode sheets. Finally, the RLFP positive electrode sheets were assembled into CR2025 half-cells. Within a voltage window of 2.5–4.2 V, the electrochemical performance of CR2025 half-cells assembled with RLFP cathodes was recorded using a battery testing system. Figure 3 As shown, under the above optimized conditions, a 99.9% Li leaching rate can be achieved in just 1 minute, while only 0.01% Fe is leached. The waste lithium iron phosphate cathode material is basically converted into FePO4, achieving efficient and selective separation and recovery of Li and Fe.

[0026] Example 2

[0027] Same as Example 1, except that the stirring was carried out in a constant temperature water bath at 20°C, and all other conditions were the same; under these conditions, 89.44% of Li was leached out in 1 minute, while only 0.01% of Fe was leached out.

[0028] Example 3

[0029] Same as Example 1, except that the stirring was carried out in a constant temperature water bath at 30°C, and all other conditions were the same; under these conditions, 89.58% of Li was leached out in 1 minute, while only 0.01% of Fe was leached out.

[0030] Example 4

[0031] Same as Example 1, except that the stirring was carried out in a constant temperature water bath at 50°C, and all other conditions were the same; under these conditions, a 99.9% leaching rate of Li was achieved in 1 minute, while only 0.01% of Fe was leached.

[0032] Example 5

[0033] Same as Example 1, except that the stirring was carried out in a constant temperature water bath at 60°C, and all other conditions were the same; under these conditions, a 99.9% leaching rate of Li was achieved in 1 minute, while only 0.01% of Fe was leached.

[0034] Example 6

[0035] Same as Example 1, except that the stirring was carried out in a constant temperature water bath at 70°C, and all other conditions were the same; under these conditions, a 99.9% leaching rate of Li was achieved in 1 minute, while only 0.01% of Fe was leached.

[0036] Example 7

[0037] Same as Example 1, except that: stirring was continued for 0.5 min, and everything else was the same; under these conditions, a leaching rate of 91.93% for Li was achieved in 2 min, while only 0.01% for Fe was leached.

[0038] Example 8

[0039] Same as Example 1, except that: stirring was continued for 2 minutes, and everything else was the same; under these conditions, 99.9% of Li was leached out in 2 minutes, while only 0.01% of Fe was leached out.

[0040] Example 9

[0041] Same as Example 1, except that: stirring was continued for 3 minutes, otherwise the same. Under these conditions, a 99.9% leaching rate of Li was achieved in 3 minutes, while only 0.01% of Fe was leached.

[0042] Example 10

[0043] Same as Example 1, except that stirring was continued for 5 minutes, otherwise the process was the same. Under these conditions, a 99.9% leaching rate of Li was achieved in 5 minutes, while only 0.01% of Fe was leached.

[0044] Example 11

[0045] Same as Example 1, except that: stirring was continued for 10 minutes, otherwise the process was the same. Under these conditions, a 99.9% leaching rate of Li was achieved in 10 minutes, while only 0.01% of Fe was leached.

[0046] Example 12

[0047] Same as Example 1, except that: stirring was continued for 15 minutes, otherwise the process was the same. Under these conditions, a 99.9% leaching rate of Li was achieved in 15 minutes, while only 0.01% of Fe was leached.

[0048] Example 13

[0049] Same as Example 1, except that: stirring was continued for 20 minutes, otherwise the process was the same. Under these conditions, a 99.9% leaching rate of Li was achieved in 20 minutes, while only 0.01% of Fe was leached.

[0050] Example 14

[0051] Same as Example 1, except that: stirring was continued for 30 minutes, otherwise the process was the same. Under these conditions, a 99.9% leaching rate of Li was achieved in 30 minutes, while only 0.01% of Fe was leached.

[0052] Example 15

[0053] Same as Example 1, except that: stirring was continued for 60 minutes, all other aspects were the same. Under these conditions, a 99.9% leaching rate of Li was achieved in 60 minutes, while only 0.01% of Fe was leached.

[0054] Example 16

[0055] Same as Example 1, except that NH4HSO4 was not added during the leaching process; all other conditions were the same. Under these conditions, a leaching rate of 15.50% for Li was achieved in 90 minutes, while only 1.06% for Fe was leached.

[0056] Example 17

[0057] Same as Example 1, except that 0.5 times the theoretical molar amount of the cathode material NH4HSO4 was added, otherwise the same. Under these conditions, a leaching rate of 90.88% for Li was achieved in 90 minutes, while only 0.01% for Fe was leached.

[0058] Example 18

[0059] Same as Example 1, except that 0.75 times the theoretical molar amount of the cathode material NH4HSO4 was added; all other conditions were the same. Under these conditions, a 97.60% Li leaching rate was achieved in 90 minutes, while only 0.03% Fe was leached.

[0060] Example 19

[0061] Same as Example 1, except that 0.95 times the theoretical molar amount of the cathode material NH4HSO4 was added, otherwise the same. Under these conditions, a 99.9% Li leaching rate was achieved in 90 minutes, while only 0.01% Fe was leached.

[0062] Example 20

[0063] Same as Example 1, except that 1.15 times the theoretical molar amount of the cathode material NH4HSO4 was added; all other conditions were the same. Under these conditions, a 99.9% Li leaching rate was achieved in 90 minutes, while only 1.33% Fe was leached.

[0064] Example 21

[0065] Same as Example 1, except that 1.25 times the theoretical molar amount of the cathode material NH4HSO4 was added, otherwise the same. Under these conditions, a 99.9% leaching rate of Li was achieved in 90 minutes, while only 1.98% of Fe was leached.

[0066] Example 22

[0067] Same as Example 1, except that the solid-liquid ratio was 60 g / L, and all other conditions were the same. Under these conditions, a 90.02% leaching rate of Li was achieved in 90 minutes, while only 0.01% of Fe was leached.

[0068] Example 23

[0069] Same as Example 1, except that the solid-liquid ratio was 70 g / L, and all other conditions were the same. Under these conditions, a leaching rate of 93.17% for Li was achieved in 90 minutes, while only 1.67% for Fe was leached.

[0070] Example 24

[0071] Same as Example 1, except that the solid-liquid ratio is 90 g / L, and all other conditions are the same. Under these conditions, a 95.31% leaching rate of Li was achieved in 90 minutes, while only 0.01% of Fe was leached.

[0072] Example 25

[0073] Same as Example 1, except that the solid-liquid ratio was 100 g / L, and all other conditions were the same. Under these conditions, an 84.5% leaching rate of Li was achieved in 90 minutes, while only 5.73% of Fe was leached.

[0074] Example 26

[0075] Same as Example 1, except that the solid-liquid ratio was 150 g / L, and all other conditions were the same. Under these conditions, a 71.5% leaching rate of Li was achieved in 90 minutes, while only 6.62% of Fe was leached.

[0076] Example 27

[0077] Same as Example 1, except that the solid-liquid ratio was 200 g / L, and all other conditions were the same. Under these conditions, a leaching rate of 63.2% for Li was achieved in 90 minutes, while only 6.71% for Fe was leached.

[0078] Example 28

[0079] Same as Example 1, except that no H2O2 was added during the leaching process; all other aspects were the same. Under these conditions, a leaching rate of 62.7% for Li was achieved in 90 minutes, while only 0.01% for Fe was leached.

[0080] Example 29

[0081] Same as Example 1, except that the mass fraction of H2O2 is 0.2%, and all other parameters are the same. Under these conditions, an 81.2% leaching rate of Li was achieved in 90 minutes, while only 6.97% of Fe was leached.

[0082] Example 30

[0083] Same as Example 1, except that the mass fraction of H2O2 is 0.3%, and all other parameters are the same. Under these conditions, a 95.5% leaching rate of Li was achieved in 90 minutes, while only 2.85% of Fe was leached.

[0084] Example 31

[0085] Same as Example 1, except that the mass fraction of H2O2 is 1.0%, and all other parameters are the same. Under these conditions, a 99.9% leaching rate of Li was achieved in 90 minutes, while only 0.06% of Fe was leached.

[0086] Example 32

[0087] Same as Example 1, except that the mass fraction of H2O2 is 2.0%, and all other parameters are the same. Under these conditions, a 99.9% leaching rate of Li was achieved in 90 minutes, while only 0.01% of Fe was leached.

[0088] Example 33

[0089] Same as Example 1, except that the mass fraction of H2O2 is 4.0%, and all other parameters are the same. Under these conditions, a 99.9% leaching rate of Li was achieved in 90 minutes, while only 0.02% of Fe was leached.

[0090] Example 34

[0091] Same as Example 1, except that the mass fraction of H2O2 is 8.0%, and all other parameters are the same. Under these conditions, a 99.9% leaching rate of Li was achieved in 90 minutes, while only 0.06% of Fe was leached.

[0092] Example 35

[0093] Same as Example 1, except that the mass fraction of H2O2 is 10.0%, and all other parameters are the same. Under these conditions, a 99.9% leaching rate of Li was achieved in 90 minutes, while only 0.01% of Fe was leached.

[0094] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are only illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from the scope of the principles of the present invention, and all such changes and modifications fall within the protection scope of the present invention.

Claims

1. A method for mild and fast wet selective recovery of lithium iron phosphate battery cathode material, characterized by The specific process is: the waste lithium iron phosphate positive material is added into a leaching agent, i.e., a composite solution of H2O2 and NH4HSO4, for wet leaching, Li in the waste lithium iron phosphate positive material is selectively leached in a high efficiency within 0.5-1 min, the leaching rate of Li is up to 99.9% and is recovered in the form of filtrate, the leaching rate of Fe is as low as 0.01%, Fe is recovered in the form of solid in FePO4 in the filter residue, the Li-containing filtrate is reacted with sodium carbonate to obtain recovered lithium carbonate, and the Fe-containing filter residue and the recovered lithium carbonate are uniformly mixed and high-temperature heat treated with glucose to obtain regenerated lithium iron phosphate battery positive material.

2. The method for mild and fast wet selective recovery of lithium iron phosphate battery cathode material according to claim 1, characterized in that The specific treatment process of the waste lithium iron phosphate positive material is: the retired lithium iron phosphate battery is soaked in a saturated NaCl solution for 30-60 h, the battery shell is cut by an electric saw, the core is taken out, the positive plate is split from the core, the positive plate is cut into a proper size, is put into a tube furnace and is vacuum pyrolyzed at 400-500 DEG C for 3-15 h to remove active substances and electrolyte, and the waste lithium iron phosphate positive material is obtained.

3. The method for mild and fast wet selective recovery of lithium iron phosphate battery cathode material according to claim 2, characterized in that The specific leaching process of the waste lithium iron phosphate positive material is: 50 g of waste lithium iron phosphate positive material and 0.25-2 times of the theoretical molar amount of NH4HSO4 of the positive material are weighed, high-purity water and H2O2 are added according to a solid-liquid ratio of 50-200 g / L and a mass fraction of 0.01%-0.1%, and the mixture is continuously stirred in a 20-70 DEG C constant-temperature water bath for 0.5-2 min, in which process, NH4HSO4 and H2O2 are cooperatively leached, NH4HSO4 as an acid salt provides an acidic environment for the system to maintain the stability and effectiveness of H2O2, and the oxidation weakens the Li-O bond in LFP and promotes the release of lithium from the octahedral FeO6 layer.

4. The method for mild and fast wet selective recovery of lithium iron phosphate battery cathode material according to claim 3, characterized in that: After the end of leaching, the solid-liquid mixture is subjected to solid-liquid separation, the residue is washed multiple times, the pH of the lithium-containing filtrate is adjusted to 9-11, it is heated to 50-70°C and saturated sodium carbonate solution is added dropwise, so that Li + is precipitated completely, stirring is continued for 30-60 min and, after standing, the recovered lithium carbonate is filtered and dried; the leaching residue is dried and, after ball milling with the recovered lithium carbonate in a 1:1.05 molar ratio, 10wt%-20wt% glucose and 1-1.5g / mL alcohol solution are added, the ball-to-material ratio is 10:1, after ball milling the mixture is dried and calcined at 600-800°C for 8-12h under a nitrogen atmosphere to obtain the regenerated lithium iron phosphate battery cathode material.

5. The method for mild and fast wet selective recovery of lithium iron phosphate battery cathode material according to claim 1, characterized in that The specific steps are: soaking the retired lithium iron phosphate battery in saturated NaCl solution for 48 h, cutting the battery shell with an electric saw, taking out the core, separating the positive plate from the core, cutting the positive plate into appropriate size, putting it into a tube furnace and vacuum pyrolyzing at 450℃ for 12 h to remove active material and electrolyte, obtaining waste lithium iron phosphate positive material; then wet recovery is carried out on the obtained waste lithium iron phosphate positive material: taking 50 g of waste lithium iron phosphate positive material and 0.85 times of the theoretical molar amount of NH4HSO4, adding high-purity water and H2O2 according to the solid-liquid ratio of 50 g / L and the mass fraction of hydrogen peroxide of 0.5%, continuously stirring in a constant temperature water bath at 40℃ for 1 min, in which NH4HSO4 and H2O2 are cooperatively leached, NH4HSO4 as an acid salt provides an acidic environment for the system to maintain the stability and effectiveness of hydrogen peroxide, and the oxidation weakens the Li-O bond in LFP, promoting the release of lithium from the octahedral FeO6 layer; after the leaching is completed, the solid-liquid mixture is subjected to solid-liquid separation, the residue is washed several times, the pH of the lithium-containing filtrate is adjusted to 10, heated to 60℃ and dropped into saturated sodium carbonate solution, so that Li + is completely precipitated, continue to stir for 45 min and stand, then filter and dry to obtain recovered lithium carbonate; after the leaching residue is dried, it is ball milled with the recovered lithium carbonate at a molar ratio of 1:1.05, 15wt% glucose and 1.2g / mL alcohol solution are added, the ball material ratio is 10:1, after ball milling, drying and calcining at 700℃ for 10h under nitrogen atmosphere, the regenerated lithium iron phosphate battery positive material is obtained, under the above conditions, the leaching process can achieve 99.9% Li leaching rate in only 1 min, while Fe has only 0.01% leaching, the waste lithium iron phosphate positive material is basically converted into FePO4, achieving high efficient selective separation and recovery of Li and Fe.

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