Recycling of Lithium Iron Phosphate (LFP) Batteries

Abstract

The invention described herein provides a method and system for recycling lithium iron phosphate batteries, the method and system comprising: 4 ) adding an oxidant to the battery recycle stream to form a leach solution, filtering the leach solution to remove residues and obtain a lithium-rich solution, adjusting the pH of the lithium-rich solution to filter out impurities and obtain a purified Li solution, and adding a precipitating agent to the purified Li solution, thereby precipitating lithium compounds.

Description

[Technical field]

[0001] Technical Field [Related Applications] This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 63 / 228,331, filed August 2, 2021, entitled “Lithium Iron Phosphate (LFP) battery recycling” by inventors Eric Gratz and Kee-Chan Kim, the entire contents of which are incorporated by reference herein. [Background technology]

[0002] background As the growing number of electric vehicles (EVs) nears the end of their useful life, battery material recycling is receiving increased attention. EVs, and the many consumer electronics and devices that more generally rely on rechargeable batteries rather than internal combustion engines, contribute to a recycling stream of exhausted (used) batteries. The current state of battery material recycling is inadequate for the number of used batteries expected from EVs. Additionally, there is a shortage of materials such as lithium that are essential for EV batteries. Summary of the Invention [Problem to be solved by the invention]

[0003] overview Therefore, new methods for cost-effective and economically viable recycling and upcycling of EV batteries are needed for safe disposal, waste management, recovery of critical materials, and sustainable use of resources. [Means for solving the problem]

[0004] One aspect of the invention described herein provides a method for recycling lithium iron phosphate batteries, the method comprising adding an oxidizing agent to a lithium iron phosphate (LiFePO4) battery recycle stream to form a leach solution, filtering the leach solution to remove residues and obtain a lithium-rich solution, adjusting the pH of the lithium-rich solution to filter out impurities and obtain a purified Li solution, and adding a precipitating agent to the purified Li solution, thereby precipitating lithium compounds.

[0005] An embodiment of this method further comprises turning off the lithium iron phosphate battery recycle stream prior to adding the oxidizer to obtain a granular battery powder. An embodiment of this method further comprises heating the leach solution prior to filtering. In an embodiment of this method, the leach solution is heated to a temperature in the range of 20° C. to 100° C. In an embodiment of this method, the residue comprises at least one of graphite and FePO4.

[0006] In one embodiment of this method, adjusting the pH of the lithium-rich solution further comprises adding a basic solution. In one embodiment of this method, the lithium-rich solution is adjusted to achieve a pH in the range of 5 to 13.

[0007] One embodiment of the method further includes achieving a concentration of the oxidizer relative to LiFePO4 between 0.3 and 3.0 M. One embodiment of the method further includes achieving a concentration of the oxidizer relative to LiFePO4 between 0.5 and 2.2 M.

[0008] One embodiment of this method further comprises adding an acid solution prior to adding the oxidizing agent. In one embodiment of this method, the acid solution is selected from an inorganic acid or an organic acid. In one embodiment of this method, the inorganic acid is at least one selected from sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. In another embodiment of this method, the organic acid is at least one selected from acetic acid, formic acid, propionic acid, butyric acid, oxalic acid, malonic acid, succinic acid, and adipic acid.

[0009] In one embodiment of this method, the precipitant is at least one selected from sodium carbonate, sodium phosphate, phosphoric acid, oxalic acid, and sodium oxalate. In one embodiment of this method, the lithium compound is at least one selected from lithium carbonate (Li2CO3), lithium phosphate (Li3PO4), and lithium oxalate (Li2C2O4).

[0010] One embodiment of this method further comprises maintaining the pH of the leach solution in the range of 1 to 6 or 2 to 6. In one embodiment of this method, the oxidizing agent or oxidant is peroxide (O2 2- ), persulfate (S2O8 2- ), sulfate (SO4 2- ), hypochlorite (ClO - ), chlorite (ClO2 - ), chlorate (ClO3 - ), perchlorate (ClO4 - ), nitrates (NO3 - ), nitrous oxide (NO), nitrogen dioxide (NO), and a halogen. In one embodiment of this method, the oxidant is at least one selected from hydrogen peroxide, sodium persulfate, and ammonium persulfate.

[0011] One aspect of the invention described herein provides a method for recycling lithium iron phosphate batteries, the method including adding at least one of an oxidizer and an acid to a powdered lithium iron phosphate (LiFePO4) battery recycle stream to form a leach solution, maintaining a temperature of the leach solution between 20°C and 100°C, filtering the leach solution to remove graphite and FePO4 to obtain a lithium-rich solution, adjusting a pH of the lithium-rich solution to 11-13 to filter impurities and obtain a purified Li solution, and adding a precipitating agent to the purified Li solution, thereby precipitating lithium compounds.

[0012] One embodiment of this method further comprises, after filtration, obtaining purified graphite by at least one process selected from acid leaching and froth flotation.

[0013] One aspect of the invention described herein provides a method for recycling lithium iron phosphate batteries, the method including adding an acid to a powdered lithium iron phosphate (LiFePO4) battery recycle stream to form a leach solution, maintaining the temperature of the leach solution between 20°C and 100°C, filtering the leach solution to remove graphite and FePO4 to obtain a lithium-rich solution, adjusting the pH of the lithium-rich solution to 11-13 to filter impurities and obtain a purified Li solution, and adding a precipitating agent to the purified Li solution, thereby precipitating lithium compounds. [Brief description of the drawings]

[0014] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] FIG. 1 is a schematic diagram of a method for recycling lithium iron phosphate batteries that includes adding an oxidizing agent to a LiFePO4 battery recycle stream to form a leach solution and heating to oxidize the iron phosphate, thereby leaching lithium into the solution. The leach solution is then filtered to remove solid FePO4 and graphite to obtain a lithium-rich solution. Remaining impurities in the lithium-rich solution are precipitated and filtered to obtain a pure lithium solution. The lithium in the solution is precipitated using a precipitating agent. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Detailed Description of the Invention Embodiments of the invention described herein provide a recycling process for end-of-life lithium iron phosphate batteries that focuses on the recovery of lithium compounds from the cathode material of these batteries. In contrast to nickel-manganese-cobalt (NMC) based batteries, lithium iron phosphate (LFP) batteries do not rely on the relatively scarce nickel and cobalt. While NMC batteries may have slightly higher charge densities, LFP batteries are made from relatively inexpensive materials, of which lithium is the most highly sought after. Current methods for recycling lithium iron phosphate are not economically advantageous. Thus, a recycling stream towards lithium recovery is important, and enhanced graphite recovery would improve the overall efficiency of this method.

[0016] The method of recycling lithium iron phosphate batteries described herein involves adding an oxidizer to granular powder from the lithium iron phosphate (LiFePO4) battery recycle stream to form a leach solution, and maintaining the leach solution at 20°C to 100°C to leach lithium. Many oxidizers can be used, and these can be supplemented with organic or inorganic acids, as described further below. Oxidizers include peroxides (O2 2- ), persulfate (S2O8 2- ), sulfate (SO4 2- ), hypochlorite (ClO - ), chlorite (ClO2 - ), chlorate (ClO3 - ), perchlorate (ClO4 - ), nitrates (NO3 - ), nitrous oxide (NO), nitrogen dioxide (NO), halogens (Cl, Br, I), and the like. The oxidizer can be combined with an inorganic acid (such as sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid) or an organic acid (including mono- or di-carboxylic acids). Other suitable acids and oxidizers can be introduced.

[0017] FIG. 1 shows a recycling process 100 that begins with collecting a recycle stream 110 of spent batteries 105, such as from retired EVs or retired batteries from EVs, that are processed into a granular powder form 110. An oxidizer 112 and optional acid 114 are combined with the granular material from the recycle stream in a leach solution 120. The oxidizer 112 can achieve a concentration (molar ratio) of 0.3-3.0M oxidizer relative to the concentration of LiFePO4, and preferably achieves a concentration of 0.5-2.2M oxidizer relative to the concentration of LiFePO4. The optional acid 114 can be an organic or inorganic acid that is added prior to heating to leach lithium into the solution, so the acid is generally selected based on the removal of iron from the leach solution.

[0018] Following the leaching reaction, with or without an external heat source, the leach solution is filtered at 130 to separate the graphite and FePO4 135 (e.g., in the form of a filter cake) from the lithium-rich solution 132. This solution contains significant amounts of lithium contained in the recycle stream, attempting to balance the leaching of useful lithium without dissolving excess iron in the leach solution.

[0019] A strong base 134 is added to the lithium-rich solution to increase the pH to between 5 and 13, preferably in the range of pH 11 to 13, to filter out the impurities and form a purified Li solution 140. The remaining impurities are precipitated and filtered out at 136, and a precipitant 138 is added to the purified Li solution to precipitate a charging material containing lithium compounds suitable for use in recycled batteries.

[0020] The recovered lithium compounds are produced based on the precipitant added to the pure Li solution. For example, by adding sodium carbonate to the purified Li solution, lithium is recovered as lithium carbonate (Li2CO3) 142. Furthermore, by adding sodium phosphate or phosphoric acid to the purified Li solution, lithium can be recovered as lithium phosphate (Li3PO4) 144. Another alternative is to add oxalic acid or sodium oxalate to the purified Li solution to recover Li as lithium oxalate 146 (Li2C2O4). Other suitable fill material compounds can be precipitated based on the materials added to combine with the solution 140.

[0021] Graphite can be recovered from the graphite and FePO4 filter cake 135 by dissolving the FePO4 in a strong acid and washing it as shown at 150, or by removing the FePO4 138 by froth flotation to selectively separate the graphite 152 from the FePO4 precipitate 154.

[0022] Lithium recovery in industrial processes, including battery recycling, is achieved by precipitation from solution. Therefore, a high concentration of lithium relative to other elements is desirable to obtain high efficiency and purity. In the methods described herein, lithium is selectively leached from lithium iron phosphate batteries, and the resulting process can recover lithium with high efficiency using high purity industrial or battery grade lithium product.

[0023] More specifically, in the embodiments described herein, lithium ions are leached from a mixture of cathode and anode powders of spent LiFePO4 batteries by an oxidizing agent with or without an acid. The oxidizing agent is added at a concentration of 0.3-3 molar ratio with respect to LiFePO4. The preferred concentration is 0.5-2.2 molar ratio. The acid is selected from inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid, or organic acids. The organic acid is preferably of the formula RCOOH(R:H, or alkyl(C n H 2n+1, n: 1 to 6)) or a monocarboxylic acid having the formula HO2C-(CH2) n It is a dicarboxylic acid having -CO2H (n: 0 to 8). An example of a monocarboxylic acid is acetic acid, formic acid, propionic acid, or butyric acid. An example of a dicarboxylic acid is oxalic acid, malonic acid, succinic acid, or adipic acid.

[0024] The acid concentration in the leach solution is between 0M and 5M. In embodiments using inorganic acids, the preferred concentration is a molar ratio of acid to lithium ions between 0.5 and 1. In embodiments using organic acids, the preferred concentration is a molar ratio of acid to lithium ions between 3 and 5. In some embodiments, a base such as NaOH can be added to adjust the pH of the leach solution to a pH between 2 and 6. The ratio of the amount of solid LiFeSO4 to the amount of acid solution is between 100g and 1000g per liter, preferably between 200g and 500g per liter. The leach temperature is maintained between 20°C and 100°C depending on the oxidant or acid selected.

[0025] After completion of the leaching process, the treated mixture is filtered and the residue is washed with deionized water. The residue is a black solid containing graphite and FePO4. The impurities in the filtrate are removed by adjusting the pH to 5-13, preferably 11-13. The pH is adjusted by adding a strong base such as sodium hydroxide solution or potassium hydroxide solution at a concentration of 0-5M. The precipitate from the impurities is removed by filtration to obtain a filtrate rich in lithium ions.

[0026] The lithium ion-rich filtrate can be concentrated by evaporating water from the filtrate. Lithium is recovered as lithium carbonate (Li2CO3) by adding sodium carbonate, as lithium phosphate (Li3PO4) by adding sodium phosphate or phosphoric acid, or as lithium oxalate (Li2C2O4) by adding oxalic acid or sodium oxalate to the concentrated solution. Lithium hydroxide or lithium carbonate can be obtained from lithium oxalate by thermal conversion by heating, for example at 350°C to 500°C.

[0027] In certain configurations, graphite can also be recovered. Graphite is recycled from the black solids by leaching of FePO4 or by froth flotation. For leaching, the black solids are added to a dilute (2-9M) or concentrated mineral acid, e.g., sulfuric acid, hydrochloric acid or nitric acid, preferably a 4-6M acid solution. The mixture is heated and stirred at 25°C to 80°C. The purified graphite is collected by filtration and rinsed with 1-5M mineral acid. The purified graphite is then washed with deionized water until the filtrate has a neutral pH. In the froth flotation process, the graphite is floated and the iron phosphate is precipitated or sedimented.

[0028] Several methods are described herein for selectively leaching lithium ions from spent LFP powders, including acid-only leaching, oxidant-only leaching, and acid and oxidant leaching using a variety of acids, including inorganic and organic acids.

[0029] Strong inorganic acids dissolve LFP and lithium ions are leached out along with iron and phosphate ions. Co-precipitation of lithium ions and iron hydroxide precipitates reduces lithium recovery efficiency and requires removal of iron impurities. In dilute acid solutions, lithium ions do not leach from LFP solids without the aid of an oxidant. However, lithium ions in LFP are selectively leached in dilute acid solutions ([H2SO4] / [LFP]: approx. 0.6) using hydrogen peroxide as the oxidant. In the dilute acid solution system, hydrogen peroxide oxidizes the ferrous ions in LFP and liberates Li ions from LFP. Additional acid helps dissolve the lithium ions liberated from LFP into solution, thus balancing the charge. Among inorganic acids, sulfuric acid is the preferred choice. However, high concentrations of sulfate ions hinder the recovery of Li2CO3, as sodium sulfate in the lithium recovery solution is often co-precipitated due to the moderate solubility of Na2SO4. Therefore, dilute sulfuric acid solution is preferred for selective Li leaching and Li2CO3 recovery.

[0030] Sodium persulfate (Na2S2O8) is a strong oxidant and can quantitatively and completely leach lithium from LFP by oxidatively liberating Li ions from LiFePO4 in aqueous solution without the use of acid. However, a by-product of the reaction is sulfate ions, which results in a reduced recovery of Li2CO3. In some embodiments, ammonium persulfate (NH4)2S2O8 is used to reduce interference.

[0031] Environmentally friendly organic acids are alternative acids to selectively leach lithium ions from LFP instead of strong inorganic acids. Since organic acids such as formic acid and acetic acid are weak acids in aqueous solution and have carboxyl functional groups to chelate metal ions, these acids have been observed to selectively leach lithium ions from LFP via oxidative liberation of lithium ions from LiFe(II)PO4 to Fe(III)PO4. Hydrogen peroxide has been observed to be a good oxidant for these reactions. Acetate is a stronger chelating agent than formate. Therefore, the required molar ratio of acetate to LFP is smaller compared to that of formate to LFP, which results in lower cost.

[0032] The invention described herein is the most practical method. However, it is recognized that deviations and modifications are possible within the scope of the invention and that those skilled in the art will make such modifications. With respect to the above description, it is recognized that the optimal dimensional relationships of the parts of the invention will be apparent to those skilled in the art, including variations in size, material, shape, form, function, process, and method of operation, assembly, and use, and all equivalent relationships to those shown in the drawings and described in the specification are intended to be encompassed by the present invention.

[0033] The foregoing is therefore considered as merely illustrative of the principles of the invention. Moreover, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and therefore, all suitable modifications and equivalents may be utilized which are within the scope of the invention and the claims. The contents of all references cited in this application, including issued patents and published patent applications, are hereby incorporated by reference.

[0034] The present invention has been fully described above and is further illustrated by the following examples and claims.

[0035] Example 1: Sulfuric acid with hydrogen peroxide Selective lithium ion leaching from LFP was investigated in sulfuric acid solutions of various concentrations with and without hydrogen peroxide (sulfuric acid to LFP molar ratio [H2SO4] / [LFP] from 0.6 to 4.9, H2O2 to LFP molar ratio [H2O2] / [LFP]: 2.2 or 0, LFP (g): water (mL): 1:5, temperature: ambient temperature, uncontrolled from 30 to 50 °C, reaction / stirring time: 3 to 4 h after completion of hydrogen peroxide addition).

[0036] Selective leaching of lithium ions was achieved in dilute sulfuric acid solutions ([H2SO4] / [LFP]: 0.6-0.7) using hydrogen peroxide as oxidant ([H2O2] / [LFP]: 2.2). The selective leaching efficiency was 100% and the leaching of iron was less than 0.1%. When the recycle stream contained contamination with nickel, cobalt, and manganese, the recovery of lithium ions as lithium carbonate (after removal of impurity ions by precipitation at pH: 11-12) was affected because sodium sulfate co-precipitates with Li2CO3 in the lithium-enriched solution. When the recycle stream contained pure LFP material, impurity removal was performed at pH: 7-8 and improved recovery of Li2CO3 was observed (56% vs. 30%). The improvement in Li ions is due to the reduced loss of Li ions due to impurity removal, the lower impurity concentration, and the adjustment of a lower pH, which results in less sodium ion introduction. Hydrogen peroxide is required to selectively leach lithium ions in dilute sulfuric acid solutions. 2LiFePO4(s)+H2SO4(aq)+H2O2(aq)→2Li + (aq) + FePO4(s) + 2H2O(aq) + SO4 2- (aq)

[0037] However, as the concentration of sulfuric acid increases, LFP starts to dissolve in the acid solution. The higher the acid concentration, the more LFP dissolution is observed. Thus, with increasing Li ion concentration, the iron and phosphate ion concentrations in solution increase, leading to a loss of Li selectivity above a molar ratio of [H2SO4] / [LFP]:2.4, with leaching of 100% Li and 80-100% Fe in the absence of H2O2. The presence of iron and phosphate ions affects the recovery of lithium as lithium carbonate. When the pH of the solution is increased, some lithium ions precipitate as Li3PO4 along with the existing phosphate ions, and the ferric ions are removed as Fe(OH)3, causing a loss of Li in the recovery of Li2CO3.

[0038] Impurities (Cu, Al, Fe, Ni, Co, Mn, etc.) in the Li-rich solution were removed by precipitating the impurities as metal hydroxides at pH: 7-12. The pH of the solution was adjusted depending on the nature of the impurities present in the solution. When the impurities included Cu, Al, and Fe, the pH was adjusted to 7-8. When the impurities included Ni, Co, and Mn, the pH was adjusted to 11-13.

[0039] The excess sodium ions in the solution are reduced by increasing the concentration of Li2SO4 in the lithium-rich solution (approximately 1.5 times the volume at the solubility from the ICP analysis results) by reducing the volume of the solution so that all Li2SO4 dissolves in the solution. The large solubility difference between Na2SO4 and Li2SO4 is then used to crystallize Na2SO4 at low temperatures (0-5°C).

[0040] [Table 1]

[0041] The lithium ions in the leach solution are precipitated by adding sodium carbonate (1.25 times the stoichiometric amount). Sodium carbonate is added to the highly concentrated Li solution either as a solid or as a saturated solution. Adding sodium carbonate as a saturated solution was observed to improve the yield and purity of lithium. The results of several trials using different recycle streams, including lithium purity and yield, are shown in Table 1.

[0042] Example 2: Using sodium persulfate (Na2S2O8) as the oxidant The selective leaching of lithium ions from LFP is due to the presence of Fe in LFP. 2+ Fe in aqueous solution 3+ This was achieved by oxidation to 2LiFePO4(s)+Na2S2O8(s)→Li + (aq) + FePO4(s) + 2Na + (aq) + 2SO4 2- (aq)

[0043] Sodium persulfate reduces the amount of Fe in LFP in aqueous solution. 2+ In this example, no acid was required and water was used as the solvent. Sodium persulfate was slowly added to the LFP dispersion solution mixture. The reaction conditions were as follows: ratio of LFP (g) to water (mL): 1:2, molar ratio of Na2S2O8 to LFP, [Na2S2O8] / [LFP]: 1.00-1.37, temperature: ambient temperature, stirring time: 1-4 hours.

[0044] The molar ratio of [Na2S2O8] / [LFP] was calculated and observed to be around 1.37 to achieve 100% Li leaching. When using mill shredded LFP spent battery material, a mixture of cathode and anode with some contamination of Ni, Mn and Co from NMC spent batteries, the Li leaching rate dropped to 75%. When sodium persulfate is contacted with water, it is converted into acid and hydrogen peroxide as shown in the following equation: Thus, the acidity of the solution increases and Fe is leached from the LFP. Na2S2O8(s)+2H2O(l)→2Na + (aq)+2H + aq) + 2SO4 2- (aq) + H2O2(aq)

[0045] The sodium sulfate from the sodium persulfate interferes with the ability to recover the Li leached from solution as Li2CO3. Thus, even if the leaching efficiency was 100%, the recovery of Li2CO3 was low (<50%) and the purity was less than 99%. The results of several tests, including lithium purity and yield, are shown in Table 2.

[0046] [Table 2]

[0047] Example 3: Formic Acid with Hydrogen Peroxide Formic acid (HCOOH) has a suitable pK a(3.75), it was used as an alternative acid for selective leaching of Li from LFP, making the leaching solution less acidic, which reduces the possibility of leaching of Fe. The reaction conditions were as follows: ratio of LFP (g) to water (mL): 1:2 (4 for commercial sample), molar ratio of formic acid to LFP, [HCOOH] / [LFP]: 3-6, [NaOH] / [HCOOH]: 0-0.5 (molar ratio), [H2O2] / [LFP]: 2.2-3.4 (molar ratio), stirring time: 2-12 h, temperature: 30-50 °C.

[0048] Lithium ions were selectively leached from the LFP material in a weak organic acid solution. The initial pH of the LFP-dispersed formic acid solution is 1 or higher depending on the amount of formic acid used. After the addition of hydrogen peroxide, the pH of the leaching solution increases by about 1 unit or more. Since the leaching solution is less acidic compared to strong inorganic acids (e.g., H2SO4, HCl, or HNO3), the dissolution of LiFeSO4 or FeSO4 was greatly suppressed. To completely leach Li from the LFP, a molar ratio of formic acid to LFP of 4.5-6 was used together with a molar ratio of hydrogen peroxide of 2.2. A ratio of 1:4 LFP (g) to HO (mL) was sufficient to complete the leaching. This ratio can be further optimized. LiFePO4(s)+1 / 2H2O2(l)+HCOOH(l)→Li + (aq) + FePO4(s) + HCOO - (aq) + H2O(l)

[0049] The hydrogen peroxide oxidizes the ferrous ions in the LFP to ferric ions. The Li ions in the LFP are liberated from the LFP solids, and the by-product FePO4 remains as a solid in the leaching process. The formic acid in the aqueous solution favors the oxidation reaction by hydrogen peroxide and provides a pH buffering effect during the leaching process. The results of several tests, including lithium purity and yield, are shown in Table 3.

[0050] [Table 3]

[0051] Example 4: Acetic acid with hydrogen peroxide Acetic acid (AcOH) is a weak organic acid with a carboxyl functional group (pK a :4.76) and is a good chelating ligand for metal ions. Acetic acid has a pK a It is evident from the values ​​that acetic acid is a weaker acid compared to formic acid. Thus, acetic acid / sodium acetate buffer solution could inhibit the leaching of iron during selective and oxidative lithium ion leaching from LFP. The reaction conditions were as follows: ratio of LFP (g) to water (mL): 1:2 (4 for commercial sample), molar ratio of AcOH to LFP, [AcOH] / [LFP]: 1-3, [NaOH] / [AcOH]: 0-0.5 (molar ratio), [H2O2] / [LFP]: 2.2-2.5 (molar ratio), stirring time: 3 h to overnight. Temperature: 30-50 C. Acetic acid / sodium acetate buffer solution was prepared for the leaching experiments by adding sodium hydroxide in a molar ratio of 1 / 3 to acetic acid.

[0052] Complete lithium leaching was observed even when the molar ratio of AcOH to LFP was 1:1. Since acetate is a good chelating ligand for metal ions, an equal amount of AcOH to LFP was sufficient to achieve leaching. Furthermore, iron leaching was completely inhibited in AcOH / AcONa buffer solutions (initial pH > 4). A 1:4 ratio of LFP (g) to HO (mL) was sufficient to complete leaching. LiFePO4(s)+1 / 2H2O2(l)+AcOH(l)→Li + (aq) + FePO4(s) + AcO - (aq) + H2O(l)

[0053] The initial pH of the acetic acid / acetate buffer solution was about 4. The initial pH completely prevented the dissolution of iron phosphate and achieved selective leaching of lithium ions from the LFP. Hydrogen peroxide was used as an oxidizing agent, which turns into hydroxide ions at the end of the oxidative leaching process and contributes to the increase in pH of the leaching solution. Acetic acid is a good ligand and a 1:1 molar ratio was required to complete the leaching process. Acetic acid has a cost advantage as it is cheaper than formic acid.

[0054] The results of several tests, including lithium purity and yield, are shown in Table 4.

[0055] [Table 4]

Claims

**Claim 1**:Crushing the recycling stream of a lithium iron phosphate battery to obtain a granular powder of the battery. After said crushing, adding an oxidizing agent to the granular powder from the recycling stream of the lithium iron phosphate (LiFePO4) battery to form a leaching solution. Filtering the leaching solution to remove a residue containing FePO4 and graphite to obtain a lithium-rich solution. Adjusting the pH of the lithium-rich solution to filter out impurities and obtain a purified Li solution. Adding a precipitating agent to the purified Li solution to thereby precipitate a lithium compound. A method for recycling a lithium iron phosphate battery, comprising the above steps. **Claim 2** The method according to claim 1, further comprising heating the leaching solution to a temperature in the range of 20°C to 100°C before filtering. **Claim 3** The method according to claim 1, wherein the residue contains at least one of graphite and FePO4. **Claim 4** The method according to claim 1, wherein adjusting the pH of the lithium-rich solution further comprises adding a basic solution. **Claim 5** The method according to claim 4, wherein the lithium-rich solution is adjusted to achieve a pH in the range of 5 to 13. **Claim 6** The method according to claim 1, further comprising achieving a concentration of the oxidizing agent in the range of 0.3 to 3.0 M relative to the concentration of LiFePO4. **Claim 7** The method according to claim 1, further comprising achieving a concentration of the oxidizing agent in the range of 0.5 to 2.2 M relative to the concentration of LiFePO4. **Claim 8** The method according to claim 1, wherein adding the oxidizing agent further comprises adding an acid solution. **Claim 9** The method according to claim 8, wherein the acid solution is selected from inorganic acids or organic acids. **Claim 10** The method according to claim 9, wherein the inorganic acid is at least one selected from sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. **Claim 11** The method according to claim 9, wherein the organic acid is at least one selected from acetic acid, formic acid, propionic acid, butyric acid, oxalic acid, malonic acid, succinic acid, and adipic acid. **Claim 12** The method according to claim 1, wherein the precipitating agent is at least one selected from sodium carbonate, sodium phosphate, phosphoric acid, oxalic acid, and sodium oxalate. **Claim 13** The method according to claim 1, wherein the lithium compound is at least one selected from lithium carbonate (Li₂CO₃), lithium phosphate (Li₃PO₄), and lithium oxalate (Li₂C₂O₄).

14. The method according to claim 1, further comprising maintaining the pH of the leaching solution in the range of 1 to 6.

15. The method according to claim 1, wherein the oxidizing agent is at least one selected from peroxide (O₂²⁻), persulfate (S₂O₈²⁻), sulfate (SO₄²⁻), hypochlorite (ClO⁻), chlorite (ClO₂⁻), chlorate (ClO₃⁻), perchlorate (ClO₄⁻), nitrate (NO₃⁻), nitrous oxide (N₂O), nitrogen dioxide (NO₂), and halogen.

16. The method according to claim 1, wherein the oxidizing agent is at least one selected from hydrogen peroxide, sodium persulfate, and ammonium persulfate.

17. In the addition of the oxidizing agent, an acid is added, and the oxidizing agent is added so that the molar ratio of the oxidizing agent to the concentration of the lithium iron phosphate (LiFePO₄) is 0.3 to 3.0 M. The method according to claim 1.

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