A method for preparing iron phosphate from waste lithium iron phosphate cathodes

Abstract

The present invention relates to a method of preparing iron phosphate from a waste lithium iron phosphate cathode. More specifically, the present invention relates to a method of preparing iron phosphate from a waste lithium iron phosphate cathode, the method comprising the steps of: (a) precipitating impurities by adding an alkaline solution to a dissolving solution containing Fe and P; (b) removing the impurities from the dissolving solution; and (c) preparing a stock solution containing Fe and P by adding an acidic solution to the dissolving solution from which the impurities have been removed and adjusting the pH to 0.8 to 1.4. The present invention has the effect of providing a method of preparing iron phosphate from a waste lithium iron phosphate cathode, in which, when a stock solution containing Fe and P is prepared by adding an acidic solution to a dissolving solution from which impurities from a waste lithium iron phosphate cathode material have been removed and adjusting the pH within a predetermined range, the stock solution does not produce a precipitate even during long-term storage at room temperature, so that the stock solution is easy to store and transport, and high-purity FePO4 can be prepared.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2025-0008197, filed on January 20, 2025, with the Korean Intellectual Property Office, and Korean Patent Application No. 10-2026-0007727, refiled on January 15, 2026, based on the priority of the aforementioned patent, the disclosures of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a method for preparing iron phosphate (FePO4) from spent lithium iron phosphate cathode material, wherein iron phosphate (FePO4) is a precursor of lithium iron phosphate. More specifically, this invention relates to a method for preparing iron phosphate from spent lithium iron phosphate cathode material, wherein a storage solution is prepared by adding an alkaline solution to a solution containing Fe and P obtained from the spent lithium iron phosphate cathode material to remove impurities, adding an acidic solution, and adjusting the pH to a predetermined range. Even during long-term storage at room temperature, the storage solution does not produce precipitation, making it easy to store and transport. Background Technology

[0004] Since the 1990s, the demand for lithium-ion batteries has been increasing with the development of the portable electronic device market, and has surged globally due to the rapid expansion of the electric vehicle market in recent years. This could lead to instability in the supply of lithium resources in the near future, and the continuous accumulation of expired batteries could also cause serious environmental problems. To address these issues, the recycling of spent lithium-ion batteries is a crucial technological challenge.

[0005] A lithium-ion battery typically consists of a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode has a positive active material coated on a metal foil such as aluminum, and the negative electrode has a negative active material coated on a metal foil such as copper. The separator prevents the positive and negative electrodes from contacting each other, and the electrolyte allows lithium ions to migrate between the positive and negative electrodes.

[0006] The cathode accounts for over 60% of the cost of a lithium-ion battery, and lithium composite oxides such as lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (LiNiMnCoO2), lithium manganese oxide (LiMnO2), or lithium iron phosphate (LiFePO4) are used as the active materials in this cathode. Therefore, since the cathode contains valuable metals, methods for recovering these valuable metals from the cathodes of spent lithium-ion batteries are attracting considerable attention.

[0007] Lithium iron phosphate (LiFePO4) possesses a highly stable hexahedral crystal structure. To disrupt this stable structure and recover valuable metals, a high concentration of strong acid or base is used on the spent cathode material to dissolve the valuable metals, and then Li and FePO4 are recovered separately. The recovered FePO4 is then dissolved again in a strong acid to synthesize FePO4 from the solution containing dissolved Fe and P. However, the solution contains impurities from the spent cathode material, which leads to a decrease in the performance of lithium iron phosphate batteries manufactured from it. Furthermore, when FePO4 is synthesized after storing the solution, a precipitate forms in the solution, resulting in a decrease in the yield and purity of the prepared FePO4.

[0008] Therefore, there is a need for a method to prepare FePO4 from waste lithium iron phosphate cathodes, which can easily remove impurities from the waste cathode material from the solution containing Fe and P, and will not form precipitation during long-term storage of the solution.

[0009] [Related Technical Documents]

[0010] [Patent Literature]

[0011] KR 2013-0113748 A Summary of the Invention

[0012] [Technical Issues]

[0013] Therefore, the present invention was made in view of the above-mentioned problems, and one object of the present invention is to provide a method for preparing FePO4 from waste lithium iron phosphate cathode, wherein impurities from the waste cathode material are easily removed, and no precipitation is formed during long-term storage of the Fe and P containing the solution from which impurities have been removed.

[0014] The above and other objectives can be achieved by the invention described below.

[0015] [Technical Solution]

[0016] I) According to one aspect of the present invention, a method for preparing FePO4 from waste lithium iron phosphate cathode is provided, comprising: (a) precipitating impurities by adding an alkaline solution to a solution containing Fe and P; (b) removing impurities from the solution; and (c) preparing a storage solution containing Fe and P by adding an acidic solution to the solution from which impurities have been removed and adjusting the pH to 0.8 to 1.4.

[0017] II) According to I), in step (a), the alkaline solution can be an aqueous solution of ammonia, an aqueous solution of sodium hydroxide, an aqueous solution of potassium hydroxide, or an aqueous solution of calcium hydroxide.

[0018] III) According to I) or II), the pH of the solution containing Fe and P in step (a) can be from 0.1 to 0.5.

[0019] IV) According to I) to III), in step (a), after the addition of the alkaline solution is completed, the pH of the solution can be 1.7 to 2.5.

[0020] V) According to I) to IV), step (a) can be carried out with stirring at room temperature.

[0021] VI) According to I) to V), in step (a), the alkaline solution may contain an alkaline component with a molar concentration (mol / L) of 0.8 to 1.3.

[0022] VII) According to I) to VI), in step (a), an alkaline solution may be added continuously.

[0023] VIII) According to I) to VII), the solution of step (a) can be prepared by a process comprising the following steps: (i) obtaining cathode material powder by pulverizing waste lithium iron phosphate cathode; (ii) adding the obtained cathode material powder to an acidic solution with a molar concentration (mol / L) of 0.5 to 0.7 to form a leaching solution and leaching residue containing dissolved lithium, and separating the leaching solution and leaching residue; and (iii) adding the separated leaching residue to an acidic solution with a molar concentration (mol / L) of 0.8 to 1.3 to obtain a solution containing dissolved Fe and P.

[0024] IX) According to I) to VIII), in step (b), impurities can be removed by depressurization filtration.

[0025] X) According to I) to IX), in step (c), the acidic solution can be an aqueous solution of sulfuric acid, an aqueous solution of hydrochloric acid, or an aqueous solution of nitric acid.

[0026] XI) According to I) to X), in step (c), the storage solution containing Fe and P can form a precipitate of less than 0.03 g / L after being left at room temperature for 24 hours.

[0027] XII) According to I) to XI), the method for preparing FePO4 from waste lithium iron phosphate cathode material may further include: (d) synthesizing FePO4 from a storage solution containing Fe and P.

[0028] XIII) According to another aspect of the invention, a method for preparing lithium iron phosphate is provided, the method comprising preparing FePO4 according to I) to XII); and synthesizing lithium iron phosphate by reacting the prepared FePO4 with a lithium precursor.

[0029] [Beneficial Effects]

[0030] According to the present invention, the present invention has the advantage of providing a method for preparing iron phosphate from waste lithium iron phosphate cathode, which can easily remove impurities from waste cathode materials from a solution containing Fe and P, and wherein the storage solution containing Fe and P prepared by adding an acidic solution to the solution in which impurities have been removed and adjusting the pH to a predetermined range does not produce precipitation even during long-term storage at room temperature, making the storage solution easy to store and transport, and enabling the production of high-purity FePO4. Attached Figure Description

[0031] The accompanying drawings illustrate embodiments of the invention and, together with the detailed description provided below, serve to provide a further understanding of the technical spirit of the invention. Therefore, the invention should not be construed as limited to what is described in these drawings.

[0032] Figure 1 This is a process flow diagram of a method for preparing FePO4 from waste lithium iron phosphate cathode as one embodiment of the present invention. Detailed Implementation

[0033] The inventors have demonstrated that after separating waste lithium iron phosphate cathode material powder into a lithium-containing leachate and a leaching residue containing Fe and P using an acidic solution, a Fe- and P-containing solution is obtained by leaching the residue with an acidic solution. When a storage solution containing Fe and P is prepared by adding an alkaline solution to the solution to precipitate and remove impurities, and then adding an acidic solution to the impurity-removed solution to adjust the pH to a predetermined range, no precipitation occurs in the storage solution even during long-term storage at room temperature. This facilitates storage and transportation of the storage solution and produces high-purity FePO4. Based on these findings, the inventors conducted further research and completed this invention.

[0034] The method for preparing ferric phosphate according to the present invention is described in detail below.

[0035] The terms and words used in this specification and the appended claims should not be construed as limited to their ordinary or dictionary meanings, but rather as having meanings and concepts consistent with the technical spirit of the invention in order to best describe the invention. Furthermore, since the configurations shown in the examples and drawings of this specification are merely embodiments of the invention and do not represent the full technical spirit of the invention, it should be understood that many equivalents and variations exist that can replace the above configurations, and the invention can be arranged, substituted, combined, separated, or designed in various other configurations.

[0036] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0037] Methods for preparing iron phosphate from waste lithium iron phosphate cathodes

[0038] The method for preparing iron phosphate (FePO4) from waste lithium iron phosphate cathode of the present invention includes: step (a) precipitating impurities by adding an alkaline solution to a solution containing Fe and P; step (b) removing impurities from the solution; and step (c) preparing a storage solution containing Fe and P by adding an acidic solution to the solution after impurities have been removed and adjusting the pH to 0.8 to 1.4. In this case, impurities from the waste lithium iron phosphate cathode material can be easily removed from the solution. Furthermore, the storage solution containing Fe and P can provide high yield and high purity FePO4 because precipitation formation is suppressed even during long-term storage at room temperature.

[0039] The following section details the steps involved in preparing FePO4 from waste lithium iron phosphate cathodes.

[0040] (a) Precipitating impurities by adding an alkaline solution to a solution containing Fe and P.

[0041] The method for preparing iron phosphate from waste lithium iron phosphate cathode of the present invention may include step (a): precipitating impurities by adding an alkaline solution to a solution containing Fe and P. In this case, the purity of the prepared FePO4 can be significantly improved.

[0042] The pH of the Fe and P-containing solution in step (a) can be, for example, 0.1 to 0.5, preferably 0.2 to 0.4. Within this range, it is advantageous to promote the leaching of Fe and P.

[0043] In this disclosure, the solution containing Fe and P may include a compound or ion containing Fe and a compound or ion containing P, and preferably may include ions containing Fe and ions containing P. Specifically, the ions containing Fe may be Fe... 2+ Fe 3+ Or mixtures thereof, wherein the P-containing ions may be selected from PO4. 3- PO3 3- and HPO3 2- At least one of the groups.

[0044] In this disclosure, pH measurements can be performed using measurement methods commonly used in the art to which this invention pertains, and unless otherwise stated, measurements can be performed using a general pH measuring device at room temperature, specifically using a METTLER TOLEDOSevenDirect SD30.

[0045] In this disclosure, room temperature can be a point in the range of 20 ± 5°C.

[0046] For example, the Fe and P-containing solution in step (a) may include Fe at a concentration of 23,000 ppm or more, preferably 25,000 ppm or more, more preferably 26,000 ppm or more, even more preferably 27,000 ppm or more, and even more preferably 27,000 to 30,000 ppm. In this case, there is an advantage in preparing FePO4 with high yield and high purity.

[0047] For example, the Fe and P-containing solution in step (a) may contain P at a concentration of 10,000 ppm or more, preferably 12,000 ppm or more, more preferably 14,000 ppm or more, even more preferably 15,000 ppm or more, and even more preferably 15,000 to 17,000 ppm. In this case, there is an advantage in preparing FePO4 with high yield and high purity.

[0048] For example, the Fe and P-containing solution in step (a) may include lithium at a concentration of 500 ppm or less, preferably 400 ppm or less, more preferably 300 ppm or less, even more preferably 250 ppm or less, and even more preferably 100 to 250 ppm. In this case, there is an advantage in preparing high-purity FePO4.

[0049] In this disclosure, unless otherwise defined, ppm is by weight.

[0050] In this disclosure, Fe, P, and Li can be measured by ICP analysis of the leachate. Specifically, Fe, P, and Li can be measured as follows: Take an aliquot of 0.2 g of leachate, place the aliquot in a conical tube and measure its precise weight, add 0.1 ml of 70% by weight nitric acid, add 500 μl of 1000 g / kg internal standard (internal STD) (scandium), and dilute the mixture with ultrapure water to a final volume of 50 ml for ICP analysis.

[0051] For example, in step (a), the alkaline solution can be an aqueous solution of ammonia, sodium hydroxide, potassium hydroxide, or calcium hydroxide, preferably an aqueous solution of ammonia. In this case, impurities from the waste lithium iron phosphate cathode material, such as aluminum and titanium, can be easily precipitated from the solution containing Fe and P.

[0052] For example, after the addition of the alkaline solution is complete, the pH of the solution containing Fe and P can be 1.7 to 2.5, preferably 1.7 to 2.3, more preferably 1.7 to 2.1, and even more preferably 1.7 to 1.9. Within this range, it is advantageous that impurities from the waste lithium iron phosphate cathode material, such as aluminum and titanium, which are leached into the solution along with Fe and P, are precipitated and can therefore be easily removed in subsequent processes.

[0053] For example, in step (a), an alkaline solution can be added to the solution while stirring. In this case, there is the advantage that impurities in the solution can precipitate out in a short time.

[0054] For example, the stirring speed can be 300 to 700 rpm, preferably 350 to 600 rpm, and more preferably 400 to 550 rpm. Within this range, there is the advantage that impurities in the solution can precipitate out in a short time.

[0055] For example, in step (a), the alkaline solution may contain an alkaline component with a molar concentration (mol / L) of 0.8 to 1.3, preferably 0.9 to 1.2, and more preferably 0.9 to 1.1. Within this range, there is an advantage that the pH of the solution containing Fe and P can be easily adjusted.

[0056] For example, in step (a), an alkaline solution can be added continuously. In this case, the advantage is that impurities from the spent lithium iron phosphate cathode material, such as aluminum and titanium, can be precipitated and easily removed.

[0057] In this disclosure, "continuous addition" means that the substance is not "added in batches", and for example, it means that it is added dropwise, little by little, gradually or continuously for more than 10 minutes, preferably more than 30 minutes, within the leaching time range.

[0058] For example, the solution in step (a) can be prepared by a process comprising the following steps: (i) obtaining cathode material powder by pulverizing waste lithium iron phosphate cathode; (ii) adding the obtained cathode material powder to an acidic solution with a molar concentration (mol / L) of 0.5 to 0.7 to form a leaching solution and leaching residue containing dissolved lithium, and separating the leaching solution and leaching residue; and (iii) adding the separated leaching residue to an acidic solution with a molar concentration (mol / L) of 0.8 to 1.3 to obtain a solution containing dissolved Fe and P. In this case, FePO4 can be obtained in high yield.

[0059] In this disclosure, the positive electrode refers to a current collector coated with a positive electrode active material layer, the positive electrode active material layer comprising a positive electrode active material, a binder, and a conductive material.

[0060] In this disclosure, positive electrode material refers to a material containing positive electrode active material, or a positive electrode active material.

[0061] For example, spent lithium iron phosphate cathodes may include cathode active materials with an olivine structure. In this case, they offer advantages such as excellent high-temperature stability, long lifespan, and low cost.

[0062] In this disclosure, the olivine structure is a cathode active material structure having a 3D cubic lattice structure in which PO (phosphorus-oxygen) bonds are strongly bonded. Because this structure can be maintained even when all lithium ions are removed, performance degradation due to charge-discharge is minimal, and thermal stability is excellent. Furthermore, the olivine structure is economical because it uses inexpensive iron instead of expensive cobalt metal; however, compared to other cathode materials, the olivine structure exhibits lower energy density, lower conductivity, and lower lithium-ion diffusion rate.

[0063] The structure of olivine can be determined by X-ray diffraction (XRD) analysis.

[0064] For example, a positive electrode active material with an olivine structure can be a compound represented by the following chemical formula 1. In this case, it has the advantages of excellent high-temperature stability, long lifespan, and low cost.

[0065] [Chemical Formula 1]

[0066] (In chemical formula 1, M includes one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y; X includes one or more elements selected from the group consisting of F, S and N; and a, b and c satisfy -0.5≤a≤0.5, 0≤b≤0.5 and 0≤c≤0.1, respectively).

[0067] Positive electrode active materials with an olivine structure are preferably lithium iron phosphate (LiFePO4). In this case, they have the advantages of excellent high-temperature stability, long lifespan, and low cost.

[0068] For example, the positive electrode of a waste lithium-ion battery can be a discarded lithium-ion battery positive electrode, a defective product generated during the positive electrode coating process, or positive electrode waste discarded after cutting the electrode plate, and preferably a discarded lithium-ion battery positive electrode. In this case, reusing resources by recycling FePO4 and expensive lithium has eco-friendly and economic advantages.

[0069] For example, in step (i), dry pulverizing equipment can be used for pulverization; specifically, a hand mill, pin mill, disc mill, cutting mill, hammer mill, or mixer can be used. In this case, the current collector is finely shredded into fragments, and the waste cathode material is separated from the current collector fragments, which provides the advantage of easy subsequent processing.

[0070] For example, pulverized waste cathode material can be obtained as waste cathode material powder by sieving. In this case, the current collector remains on the upper part of the screen, and the waste cathode material passes through the screen and is separated, which further provides the advantage of obtaining the waste cathode material as powder of uniform size.

[0071] For example, sieving can be performed using a sieve of 120 to 250 mesh, preferably 140 to 240 mesh, more preferably 170 to 230 mesh, and even more preferably 180 to 210 mesh. In this case, the advantage is that it makes the waste cathode material powder uniform in size, making the waste cathode material powder easier to leach in the subsequent leaching step.

[0072] In this disclosure, there are no particular limitations on screening when using the methods or apparatus defined in the technical field to which this invention pertains, as long as the definitions of this invention are followed.

[0073] In this disclosure, waste cathode material powder refers to material obtained in powder form by crushing, or crushing and sieving waste cathodes, wherein most of the current collector is removed from the waste cathode, and may include a small amount of current collectors with fine particle sizes of a few micrometers.

[0074] For example, in step (ii), the acidic solution may be a solution containing one or more of the group consisting of sulfuric acid, hydrochloric acid, hypochlorous acid, nitric acid, carbonic acid, acetic acid, and oxalic acid, and preferably a solution containing hydrochloric acid or sulfuric acid. In this case, the advantage is that lithium is easily leached, and the Fe and P components are retained as leaching residues.

[0075] The acidic solution is preferably an acidic aqueous solution. In this case, there is an advantage that lithium is easily and selectively leached, and the Fe and P components are retained as leaching residues.

[0076] In step (ii), the acidic solution may more preferably be sulfuric acid, and the acid concentration of the sulfuric acid may more preferably be a molar concentration of 0.5 to 0.7 mol / L, preferably a molar concentration of 0.55 to 0.65 mol / L. Within this range, there is an advantage that lithium is readily leached, and the Fe and P components are retained as leaching residues.

[0077] For example, in step (ii), the solid-liquid ratio of the positive electrode powder to the acidic solution can be 7 to 15 mL / g, preferably 8 to 13 mL / g, and more preferably 9 to 12 mL / g. Within this range, there is an advantage that lithium is readily and selectively leached, and the Fe and P components are retained as leaching residues.

[0078] In this disclosure, the solid-liquid ratio refers to the ratio of liquid volume to solid weight, that is, the ratio of acidic solution volume (mL) to positive electrode powder content (g).

[0079] In this disclosure, leaching refers to the selective dissolution of metallic elements or compounds contained in a solid material using solvents such as inorganic acids, organic acids, or bases.

[0080] In step (ii), vacuum filtration may be preferred for separation. In this case, the leachate and leachate residue can be easily separated by a simple method, thus providing advantages such as reduced treatment costs and eco-friendliness.

[0081] For example, in step (iii), the acidic solution may be a solution comprising one or more of the group consisting of sulfuric acid, hydrochloric acid, hypochlorous acid, nitric acid, carbonic acid, acetic acid, and oxalic acid, and may preferably be a solution comprising hydrochloric acid or sulfuric acid. In this case, there is the advantage that Fe and P can be readily leached from the leaching residue obtained in step (ii).

[0082] The acidic solution is preferably an acidic aqueous solution. In this case, there is an advantage that Fe and P can be easily leached out.

[0083] In step (iii), the acidic solution is more preferably sulfuric acid, and the acid concentration is more preferably a molar concentration (mol / L) of 0.8 to 1.3, particularly preferably a molar concentration (mol / L) of 0.9 to 1.2, and even more preferably a molar concentration (mol / L) of 0.9 to 1.1. Within this range, Fe and P can be sufficiently leached, thus providing an economic advantage for increasing the yield of FePO4.

[0084] The difference in molar concentration between the acidic solution in step (ii) and the acidic solution in step (iii) is because the molar concentration range in step (ii) promotes the leaching of lithium from the cathode material powder, while the molar concentration range in step (iii) promotes the leaching of Fe and P from the separated leaching residue. Since the substances leached in steps (ii) and (iii) are different, the molar concentration of the acidic solution is also different.

[0085] (b) Remove impurities from the solution

[0086] The method for preparing iron phosphate from waste lithium iron phosphate cathode of the present invention may include step (b), removing impurities from the solution. In this case, the yield and purity of FePO4 can be improved.

[0087] For example, the pH of the solution after impurities have been removed can be 1.7 to 2.5, preferably 1.7 to 2.3, more preferably 1.7 to 2.1, and even more preferably 1.7 to 1.9. In this case, since the alkaline solution is added to the solution and the impurities are removed, the pH can be at the same or similar level as the pH of the solution to which the alkaline solution has been added.

[0088] For example, vacuum filtration can be used to separate the solution and impurities from the solution containing an alkaline solution. The advantage in this case is that the solution and impurities can be easily separated using a simple method.

[0089] Vacuum filtration is preferred, and specifically, vacuum filtration using a filter flask. In this case, FePO4 can be easily separated.

[0090] In this invention, vacuum depressurization filtration is a common vacuum depressurization filtration technique in the technical field to which this invention pertains. Vacuum depressurization filtration is not particularly limited, and for example, depressurization filtration may include filtration under partial vacuum or low pressure conditions.

[0091] For example, in addition to Al and Ti, the separated impurities may also include Fe and P. In this case, Fe and P can be recovered by leaching the separated impurities again in an acidic solution.

[0092] (c) A stock solution containing Fe and P is prepared by adding an acidic solution to a solution from which impurities have been removed and adjusting the pH to 0.8 to 1.4.

[0093] The method for preparing iron phosphate from waste lithium iron phosphate cathode of the present invention may include step (c), preparing a storage solution containing Fe and P by adding an acidic solution to a solution from which impurities have been removed and adjusting the pH to 0.8 to 1.4. In this case, no precipitation will form even during long-term storage of the storage solution, providing the advantage that high-purity FePO4 can be prepared even after transportation or long-term storage. Furthermore, by adjusting the pH to 0.8 to 1.4, the pH of the storage solution can be increased with a small amount of alkaline solution in subsequent steps of FePO4 synthesis, providing both technological and economic advantages.

[0094] On the other hand, although no precipitation occurs even when the pH of the storage solution drops to less than 0.8, this is disadvantageous in terms of method and economy because an excess of alkaline solution must be added to increase the pH in the subsequent FePO4 synthesis step.

[0095] For example, the precipitate may include iron phosphate synthesized from Fe and P in a non-stoichiometric ratio in a storage solution.

[0096] For example, in step (c), the acidic solution can be an aqueous solution of sulfuric acid, hydrochloric acid, or nitric acid, preferably an aqueous solution of hydrochloric acid. In this case, there is the advantage that the pH of the solution can be easily adjusted.

[0097] For example, in step (c), the acidic solution may include an amount of acid component of 25 to 40% by weight, preferably 25 to 37% by weight, more preferably 27 to 35% by weight, and even more preferably 29 to 32% by weight. In this case, there is the advantage that the pH of the solution can be easily adjusted.

[0098] For example, in step (c), the pH of the storage solution can be from 0.8 to 1.4, preferably from 0.8 to 1.3, more preferably from 0.9 to 1.2, and even more preferably from 0.9 to 1.1. Within this range, no precipitation will form even after prolonged storage at room temperature, thus facilitating storage and transportation, improving the yield and purity of FePO4, and reducing the amount of alkaline solution input used to raise the pH in subsequent steps of FePO4 synthesis.

[0099] For example, in step (c), the storage solution containing Fe and P may have a precipitate formed after being left at room temperature for 24 hours with a concentration of less than 0.03 g / L, preferably less than 0.02 g / L, more preferably less than 0.01 g / L, even more preferably less than 0.001 g / L, and even more preferably from 0.0001 to 0.001 g / L. Within this range, no precipitate will form even after long-term storage, thus facilitating storage and transportation, and improving the yield and purity of FePO4.

[0100] In this disclosure, the weight of the resulting precipitate can be measured by filtering the storage solution to separate the precipitate and drying the separated precipitate.

[0101] (d) Synthesis of FePO4 from a storage solution containing Fe and P

[0102] The method for preparing iron phosphate from waste lithium iron phosphate cathode of the present invention may further include step (d), synthesizing FePO4 from a storage solution containing Fe and P. In this case, no precipitation is formed even after long-term storage at room temperature during transportation and storage, thus offering the advantage of being able to synthesize FePO4 in high yield and with high purity.

[0103] For example, the step of synthesizing FePO4 from a storage solution containing Fe and P may include the following steps: (di) preparing a hydrogen peroxide mixture by adding an aqueous hydrogen peroxide solution to the storage solution containing Fe and P; (d-ii) heating the hydrogen peroxide mixture; (d-iii) synthesizing FePO4 by adding an aqueous ammonia solution to the heated hydrogen peroxide mixture; (d-iv) separating the synthesized FePO4; and (dv) washing the separated FePO4 with an acidic washing solution with a pH of 1.3 to 1.6. In this case, impurities from spent lithium iron phosphate cathode materials are easily removed, and the generation of new byproducts is suppressed.

[0104] For example, in step (di), the aqueous hydrogen peroxide solution can be added in an amount such that the hydrogen peroxide is 0.45 to 1.2 vol% relative to the volume of the storage solution, preferably 0.5 to 1 vol%, more preferably 0.6 to 1 vol%. Within this range, FePO4 can be readily synthesized.

[0105] For example, the concentration of the aqueous hydrogen peroxide solution can be 25 to 40% by weight, preferably 27 to 35% by weight, more preferably 29 to 33% by weight. Within this range, no byproducts are generated, and FePO4 can be readily synthesized.

[0106] For example, the pH of the hydrogen peroxide mixture can be from 0.1 to 0.7, preferably from 0.2 to 0.6, and more preferably from 0.3 to 0.5. Within this range, FePO4 can be readily synthesized while maintaining Fe as Fe 3+ To suppress the production of byproducts.

[0107] For example, in step (di), the temperature rise caused by adding the aqueous hydrogen peroxide solution to the storage solution containing Fe and P is negligible, and the temperature of the mixture prepared after adding the aqueous hydrogen peroxide solution is less than 28°C, or below 27°C, or below 26°C; specifically, it could be above 20°C, or room temperature. Therefore, to promote the synthesis of FePO4, it is necessary to increase the temperature of the hydrogen peroxide mixture.

[0108] For example, in step (d-ii), the hydrogen peroxide mixture can be heated to 28 to 60°C, preferably 28 to 55°C, more preferably 30 to 50°C, and even more preferably 30 to 42°C. Within this range, FePO4 can be readily synthesized.

[0109] For example, in step (d-iii), after the addition of the ammonia solution is complete, the pH can be 1 to 2, preferably 1.1 to 1.7, and more preferably 1.2 to 1.5. Within this range, FePO4 can be synthesized in high yield.

[0110] For example, in step (d-iii), an aqueous ammonia solution can be added to the hydrogen peroxide mixture while stirring. In this case, FePO4 can be easily synthesized.

[0111] For example, the stirring speed can be 300 to 700 rpm, preferably 350 to 600 rpm, and more preferably 400 to 550 rpm. Within this range, FePO4 can be easily synthesized.

[0112] For example, in step (d-iii), aqueous ammonia solution can be added continuously. In this case, FePO4 can be synthesized stably without side reactions.

[0113] For example, in step (d-iii), after the addition of the ammonia solution is complete, stirring can be performed for an additional 30 to 60 minutes, preferably 35 to 55 minutes, and more preferably 40 to 50 minutes. Under these conditions, FePO4 can be synthesized stably without side reactions.

[0114] In step (d-ii), after the addition of the ammonia solution is complete, further stirring can be carried out at a heated temperature. Under these conditions, the synthesis of FePO4 can be achieved stably without side reactions.

[0115] For example, the step (d-iv) of separating the synthesized FePO4 can be performed using vacuum filtration. In this case, the synthesized FePO4 can be easily separated.

[0116] Vacuum filtration is preferred over vacuum filtration, and more specifically, it can be vacuum filtration using a filter flask. In this case, FePO4 can be easily separated.

[0117] For example, in step (dv), the separated FePO4 is washed with an acidic washing solution with a pH of 1.3 to 1.6. In this case, the purity of the synthesized FePO4 can be improved because impurities are easily removed, and no byproducts due to the re-leaching of FePO4 are generated.

[0118] As a specific example, an acidic washing solution with a pH of 1.3 to 1.6 can be a mixture of distilled water and hydrochloric acid, sulfuric acid, or a mixture thereof; as a specific example, it can be a mixture of distilled water and hydrochloric acid. In this case, the acidic washing solution can be easily prepared, and impurities can be easily removed.

[0119] The pH of the acidic washing solution is preferably 1.3 to 1.5, more preferably 1.3 to 1.4. Within this range, the purity of the synthesized FePO4 can be improved because impurities are easily removed without generating byproducts due to the re-leaching of FePO4.

[0120] For example, in step (dv), the solid-liquid ratio of the separated FePO4 to the acidic washing solution can be 15 to 25 mL / g, preferably 17 to 23 mL / g, and more preferably 19 to 22 mL / g. Within this range, impurities can be reduced and no byproducts are generated.

[0121] For example, in step (dv), washing can be performed by adding an acidic washing solution to the separated FePO4 and stirring for 5 to 20 minutes, preferably 5 to 15 minutes, more preferably 10 to 15 minutes. In this case, impurities can be reduced and no byproducts are generated.

[0122] For example, in step (dv), washing may include vacuum filtration. In this case, FePO4 and the acidic washing solution can be easily separated.

[0123] The process may further include a step of drying the FePO4 washed in step (dv). In this case, there is an effect of stable transportation and storage of the washed FePO4.

[0124] Drying can preferably be vacuum drying, and as a specific example, it can be carried out under vacuum at 70°C to 200°C, more preferably 80°C to 130°C, for 1 hour to 24 hours until there is no further weight change. Within this range, there is an effective effect in removing the moisture contained in the washed FePO4.

[0125] In this invention, when vacuum drying is a vacuum drying method and / or condition that is commonly performed in the technical field to which this invention pertains, vacuum drying is not particularly limited and may include drying under partial vacuum or low pressure conditions.

[0126] Since FePO4 is prepared using the storage solution containing Fe and P of the present invention, it does not precipitate even after long-term storage. Therefore, there is no significant time limitation in the manufacturing process, and the advantage is that the recovery rate, purity and physical properties do not change over time.

[0127] Methods for preparing lithium iron phosphate (LFP)

[0128] The method for preparing lithium iron phosphate (LFP) according to the present invention may include step (e), synthesizing lithium iron phosphate by reacting the FePO4 prepared in step (d) with a lithium precursor. In this case, lithium iron phosphate is readily prepared, resources can be recovered, and it offers excellent economic advantages.

[0129] For example, to prepare lithium iron phosphate, step (e) may include the following steps: (e-1) preparing lithium iron phosphate by adding a lithium precursor to the prepared FePO4 and calcining it; (e-2) preparing a lithium iron phosphate solution by mixing the calcined lithium iron phosphate with a solution containing a carbon source; (e-3) spray drying the prepared lithium iron phosphate solution; and (e-4) subjecting the dried lithium iron phosphate to a reduction heat treatment. In this case, the particle size and particle size distribution of the prepared lithium iron phosphate can be uniformly controlled, the crystal structure has an olivine structure, and it has the advantage of providing excellent battery characteristics when applied to secondary batteries.

[0130] For example, lithium precursors may include one or more of LiOH, Li₂CO₃, LiNO₃, and Li₂O. In this case, lithium iron phosphate with an olivine structure can be synthesized.

[0131] For example, in step (e-1), calcination can be carried out at 600 to 800°C, preferably 650 to 750°C. Within this range, lithium can be readily intercalated into FePO4 to synthesize lithium iron phosphate, thus providing the advantages of excellent high-temperature stability and lifespan characteristics when applied to secondary batteries.

[0132] In this disclosure, intercalation refers to the reaction in which lithium ions are inserted into the crystal structure.

[0133] For example, in step (e-1), calcination can be carried out for 8 to 12 hours, preferably 9 to 11 hours, and more preferably 9.5 to 10.5 hours. Within this range, lithium is intercalated into FePO4 to synthesize lithium iron phosphate, and the generation of impurities is reduced, thereby providing excellent charge and discharge characteristics when applied to secondary batteries.

[0134] For example, in step (e-1), calcination can be carried out under an inert atmosphere, preferably a nitrogen atmosphere. In this case, oxidation can be prevented.

[0135] For example, in step (e-2), the carbon source may include one or more selected from the group consisting of glucose, sucrose, fructose, galactose, lactose, maltose, polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenolic resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride, and bitumen. In this case, there are advantages such as easy coating, economic advantages, and excellent improvement in battery characteristics.

[0136] When the solvent is a solvent commonly used in coating agents in the technical field to which this invention pertains, the solvent is not particularly limited, but the solvent is preferably an aqueous solvent, more preferably water, and even more preferably deionized water.

[0137] In this disclosure, the aqueous solvent is not particularly limited when it is an aqueous solvent commonly used in the technical field to which this invention pertains, and for example, the aqueous solvent is a water-based solvent, and specifically, water or a mixture of water and other components can be used.

[0138] For example, based on 100 parts by weight of lithium iron phosphate, the amount of carbon source used can be 1 to 20 parts by weight, preferably 5 to 18 parts by weight, and more preferably 7 to 15 parts by weight. Within this range, a carbon coating can be uniformly formed on the surface of the lithium iron phosphate to improve conductivity, thereby providing the advantage of improved capacity characteristics and battery characteristics of the secondary battery including it.

[0139] For example, in step (e-2), the solution containing calcined lithium iron phosphate and a carbon source can be mixed by grinding, preferably using a ball mill, high-energy ball mill, vibratory mill, or roller mill, more preferably a ball mill. In this case, by ensuring uniform mixing of the solution containing lithium iron phosphate and the carbon source, a uniform carbon coating can be formed on the lithium iron phosphate in subsequent steps.

[0140] For example, in step (e-2), the grinding can be carried out for 2 to 20 hours, preferably 5 to 18 hours, more preferably 10 to 16 hours, and even more preferably 12 to 16 hours. Within this range, the generation of fine powder can be suppressed, and the particle size distribution of lithium iron phosphate can be stably controlled within a narrow range.

[0141] In step (e-3), the carbon source is uniformly applied to the lithium iron phosphate by spray drying the prepared lithium iron phosphate solution, which provides the advantage of uniformly forming a carbon coating on the surface of the lithium iron phosphate in the subsequent reduction heat treatment step.

[0142] When spray drying is a commonly used spray drying method and / or device in the technical field to which this invention pertains, spray drying can be used without particular limitation, and can be used, for example, ultrasonic spray drying device, air nozzle spray drying device, ultrasonic nozzle spray drying device, filter expansion droplet generator or electrostatic spray drying device, but is not limited thereto.

[0143] For example, in step (e-4), the reduction heat treatment can be carried out at 500 to 700°C, preferably 550 to 650°C. Within this range, there is an advantage in improving conductivity when carbon is coated on the surface of lithium iron phosphate.

[0144] For example, in step (e-4), the reduction heat treatment can be carried out for 3 to 6 hours, preferably 4 to 5 hours, and more preferably 3.5 to 4.5 hours. Within this range, there is an advantage in improving the conductivity of lithium iron phosphate.

[0145] For example, in step (e-4), the reduction heat treatment can be carried out under an inert atmosphere, preferably under a nitrogen atmosphere. In this case, there is an advantage in preventing the oxidation of the carbon source.

[0146] For example, a further step (e-5) can be included, whereby the lithium iron phosphate recovered after the reduction heat treatment in step (e-4) is ground. In this case, agglomeration, particle breakage, and the generation of fine powder in the final obtained recycled lithium iron phosphate are prevented. The particle size distribution can be controlled within a narrow range, preventing battery performance degradation due to fine powder, and further improving the battery's thermal stability and lifespan characteristics. Furthermore, there is an advantage that when the recycled lithium iron phosphate is ultimately used as the cathode in a secondary battery, it can provide battery characteristics comparable to or better than those of newly prepared cathode active materials.

[0147] For example, in step (e-5), the grinding can be jet grinding. In this case, the particle size and particle size distribution of the final recycled lithium iron phosphate can be precisely controlled within a narrow range, while preventing damage to the crystal structure of lithium iron phosphate. Furthermore, by preventing the introduction of foreign matter that may occur during the grinding process, the purity of the recycled lithium iron phosphate can be improved.

[0148] Down Figure 1 This is a flowchart of a method for preparing FePO4 from waste lithium iron phosphate cathode as one embodiment of the present invention.

[0149] Reference Figure 1 First, prepare the waste lithium iron phosphate cathode (step S10).

[0150] Waste lithium iron phosphate cathodes are preferably discarded lithium-ion battery cathodes, defective products generated during cathode coating, or cathode waste discarded after cutting electrode plates, and more preferably discarded lithium-ion battery cathodes.

[0151] The positive electrode has a structure in which positive active material and conductive material are bonded to aluminum foil by an adhesive.

[0152] The positive electrode can include a positive electrode active material with an olivine structure, preferably lithium iron phosphate (LiFePO4) with an olivine structure. In this case, it has the advantages of excellent high-temperature stability, long lifespan and low cost.

[0153] Next, waste cathode material powder is obtained by crushing the waste lithium iron phosphate cathode (step S20).

[0154] The grinding can be carried out using dry grinding equipment, particularly hand grinders, pin mills, disc mills, cutting mills, hammer mills, or mixers (a mixer being a specific example). In this case, the current collector is finely shredded into fragments, and the positive electrode material is separated from the current collector. In this configuration, the current collector and the positive electrode material can be easily separated.

[0155] For example, the current collector can be separated from the crushed waste cathode by sieving, and waste cathode material powder with uniform size can be obtained.

[0156] The sieving is preferably performed using a 120 to 250 mesh sieve; as a specific example, a 200 mesh sieve is used. In this case, the current collector is separated, and uniformly sized waste cathode material powder can be obtained.

[0157] Next, the waste cathode material powder is added to an acidic solution with a molar concentration (mol / L) of 0.5 to 0.7 to form a leaching solution and leaching residue containing dissolved lithium, and the leaching solution and leaching residue are separated (step S30).

[0158] For example, the acidic solution can be a solution containing one or more of the group consisting of sulfuric acid, hydrochloric acid, hypochlorous acid, nitric acid, carbonic acid, acetic acid, and oxalic acid, and specifically, it can be an aqueous solution of sulfuric acid. In this case, the advantage is that lithium is readily and selectively leached, while Fe and P are retained as leaching residues.

[0159] The acidic solution is preferably an acidic aqueous solution. In this case, there is an advantage that lithium is easily and selectively leached, while Fe and P are retained as leaching residues.

[0160] In acidic solutions, the acid concentration is preferably between 0.55 and 0.65 molar concentrations (mol / L), with 0.6 molar concentrations (mol / L) being a specific example. In this case, the advantage is that lithium is readily and selectively leached, while Fe and P remain as leaching residues.

[0161] In step S30, the solid-liquid ratio of the waste cathode material powder to the acidic solution is preferably 7 to 15 mL / g, with 10 mL / g being a specific example. The advantage of this is that lithium is fully leached, but Fe and P are not leached and remain as leaching residues.

[0162] Next, the leaching solution containing dissolved lithium and the leaching residue are separated (step S40).

[0163] Separation can preferably be carried out using vacuum filtration. In this case, the leachate and leachate residue can be easily separated by a simple process, which reduces process costs and provides eco-friendly advantages.

[0164] Next, the separated leaching residue is added to an acidic solution with a molar concentration (mol / L) of 0.8 to 1.3 to obtain a solution containing Fe and P (step S50).

[0165] For example, the acidic solution can be a solution containing one or more of the following: sulfuric acid, hydrochloric acid, hypochlorous acid, nitric acid, carbonic acid, acetic acid, and oxalic acid, and specifically, the acidic solution can be an aqueous solution of sulfuric acid. In this case, there is an advantage in leaching Fe and P.

[0166] The acidic solution is preferably an acidic aqueous solution. In this case, Fe and P can be easily leached out.

[0167] In the acidic solution, the acid concentration is preferably a molar concentration of 0.9 to 1.2, and as a specific example, a molar concentration of 1.0. In this case, Fe and P are fully leached from the leaching residue obtained in step S40, which increases the yield of FePO4 and provides economic advantages.

[0168] The pH of the solution containing Fe and P is preferably from 0.1 to 0.5, and as a specific example, the pH is from 0.2 to 0.4. Within this range, there is an advantage that Fe and P exist in a leached state.

[0169] Next, an alkaline solution is added to the solution containing Fe and P (step S60).

[0170] Step S60 significantly improves the purity of the prepared FePO4 by adding an alkaline solution to the solution containing Fe and P to precipitate and remove impurities.

[0171] For example, a solution containing Fe and P can contain more than 23,000 ppm of Fe, with 27,000 ppm being a specific example. In this case, there is an advantage in preparing FePO4 with high yield and high purity.

[0172] For example, a solution containing Fe and P can contain more than 10,000 ppm of P, with 15,000 ppm being a specific example. In this case, there is an advantage in preparing FePO4 with high yield and high purity.

[0173] For example, a solution containing Fe and P can contain less than 500 ppm of lithium; as a specific example, it may contain 250 ppm of lithium. In this case, there is an advantage in preparing high-purity FePO4.

[0174] For example, the alkaline solution can be an aqueous solution of ammonia, sodium hydroxide, potassium hydroxide, or calcium hydroxide; as a specific example, it can be an aqueous solution of ammonia. In this case, the advantage is that impurities from spent lithium iron phosphate cathode materials, such as aluminum and titanium, will precipitate and be easily removed.

[0175] For example, as a specific instance, the alkaline solution may contain an alkaline component with a molar concentration (mol / L) of 0.8 to 1.3, preferably 0.9 to 1.2, and more preferably 0.9 to 1.1. In this case, pH adjustment is easy, and impurities from spent lithium iron phosphate cathode materials, such as aluminum and titanium, will precipitate and be easily removed.

[0176] After the alkaline solution is added, the pH of the solution can preferably be between 1.7 and 2.5, with 1.8 as a specific example. In this case, the advantage is that impurities from the waste lithium iron phosphate cathode material, such as aluminum and titanium, will precipitate and be easily removed.

[0177] Alkaline solutions can be continuously added to the solvent. An advantage of this is that impurities from spent lithium iron phosphate cathode materials, such as aluminum and titanium, will precipitate and be easily removed.

[0178] For example, an alkaline solution can be added with stirring. In this case, there is the advantage that impurities precipitate within a short time.

[0179] Next, impurities are removed from the solution in which an alkaline solution has been added (step S70).

[0180] Vacuum filtration is a preferred method for removing impurities from the solution. In this case, there is the advantage of easily separating the solution and impurities using a simple method.

[0181] Next, an acidic solution is added to the solution from which impurities have been removed, and the pH is adjusted to 0.8 to 1.4 to prepare a storage solution containing Fe and P (step S80).

[0182] For example, the acidic solution could be an aqueous solution of sulfuric acid, hydrochloric acid, or nitric acid; as a specific example, it could be an aqueous solution of hydrochloric acid. In this case, there is the advantage of being able to easily adjust the pH of the stored solution.

[0183] For example, an acidic solution may contain 25 to 40% by weight of acid, and as a specific example, 30% by weight of acid. In this case, there is the advantage of being able to easily adjust the pH of the solution.

[0184] The pH of the storage solution is preferably between 0.8 and 1.4, and as a specific example, the pH is 1. In this case, no precipitation will form even after long-term storage at room temperature, which facilitates storage and transportation, improves the yield and purity of FePO4, and provides process and economic advantages by reducing the amount of alkaline solution required to increase the pH in subsequent FePO4 synthesis steps.

[0185] For example, after the storage solution is left at room temperature for 24 hours, it may have a precipitate of less than 0.03 g / L, preferably less than 0.02 g / L, more preferably less than 0.01 g / L, even more preferably less than 0.001 g / L, and even more preferably from 0.0001 to 0.001 g / L. Within this range, no precipitate forms even during long-term storage, thereby facilitating storage and transportation while improving the yield and purity of FePO4.

[0186] Next, an aqueous hydrogen peroxide solution is added to a storage solution containing Fe and P to prepare a hydrogen peroxide mixture (step S90).

[0187] In step S90, the amount of hydrogen peroxide aqueous solution added is preferably 0.45 to 1.2% by volume of the storage solution, and as a specific example, the amount added is 0.6 to 1.0% by volume. Under these conditions, FePO4 can be easily synthesized.

[0188] The concentration of the hydrogen peroxide aqueous solution is preferably 25 to 40% by weight, with 30% by weight being a specific example. Under these conditions, FePO4 can be readily synthesized while retaining Fe as Fe2+. 3+ To suppress the production of byproducts.

[0189] Next, the hydrogen peroxide mixture is heated (step S100).

[0190] The hydrogen peroxide mixture can be heated to a preferred temperature of 28 to 60°C, and in a specific example, to 30°C. Under these conditions, FePO4 can be readily synthesized.

[0191] Next, FePO4 is synthesized by adding an aqueous ammonia solution to a heated hydrogen peroxide mixture (step S110).

[0192] After adding the aqueous ammonia solution to the heated hydrogen peroxide mixture, the pH can preferably be 1 to 2, with 1.2 being a specific example. Under these conditions, FePO4 can be synthesized in high yield.

[0193] In step S110, an aqueous ammonia solution can preferably be added while stirring, more preferably while stirring at 300 to 700 rpm, and specifically, at 500 rpm. In this case, FePO4 can be synthesized in high yield.

[0194] In step S110, it is preferable to add the aqueous ammonia solution continuously. In this case, FePO4 can be synthesized stably without side reactions.

[0195] While adding the ammonia solution, it is preferable to maintain the heating temperature. Under these conditions, FePO4 can be synthesized stably without side reactions.

[0196] In step S110, after the addition of the ammonia solution, further stirring can preferably be carried out for 30 to 60 minutes, specifically 40 minutes. Under these conditions, FePO4 can be synthesized stably without side reactions.

[0197] In step S110, after the addition of the ammonia solution, further stirring can be carried out at a heated temperature. Under these conditions, the synthesis of FePO4 can be achieved stably without side reactions.

[0198] Next, the synthesized FePO4 is separated (step S120).

[0199] In step S120, by separating the synthesized FePO4, impurities can be easily removed in the washing step as a subsequent process, and energy can be saved.

[0200] Separation can preferably be carried out using reduced pressure filtration, more preferably using vacuum reduced pressure filtration, especially using a filter flask for vacuum reduced pressure filtration. In this case, FePO4 can be easily removed.

[0201] Next, the separated FePO4 was washed with an acidic washing solution with a pH of 1.3 to 1.6 and dried (step S130).

[0202] During the washing step, substances such as non-stoichiometric iron phosphate (Fe) can be easily removed. x PO y (where x is not 1, y is not 4, and x:y is not 1:4) and other impurities, while not producing by-products, thus having the advantage of increased purity of the synthesized FePO4.

[0203] For example, an acidic washing solution with a pH of 1.3 to 1.6 can be prepared by mixing distilled water with sulfuric acid, hydrochloric acid, or a mixture thereof, and preferably by mixing with hydrochloric acid. In this case, the preparation of the acidic washing solution is easy, and impurities can be easily removed.

[0204] As a specific example, the pH of the acidic washing solution can be between 1.3 and 1.5. Under these conditions, impurities can be easily removed, and the purity of the synthesized FePO4 can be improved because no byproducts resulting from the re-leaching of FePO4 are produced.

[0205] In step S130, the solid-liquid ratio of FePO4 to the acidic washing solution is preferably 15 to 25 mL / g, with 20 mL / g being a specific example. In this case, the formation of byproducts is suppressed, and non-stoichiometric iron phosphate (Fe2PO4) can be easily removed. x PO y It removes impurities and does not produce byproducts, thus having the advantage of improving the purity of the synthesized FePO4.

[0206] In step S130, washing can be performed by adding an acidic washing solution and preferably stirring for 5 to 20 minutes (for example, stirring for 10 minutes). In this case, impurities can be reduced and no byproducts can be generated.

[0207] In step S130, washing may preferably include vacuum filtration. In this case, FePO4 and the acidic washing solution can be easily separated.

[0208] Drying can preferably be performed under vacuum at 70°C to 200°C until the weight no longer changes, and as a specific example, it can be performed at 80°C to 130°C for 1 to 24 hours. Within this range, there is an effective removal of moisture contained in the washed FePO4.

[0209] The invention will now be described in more detail with reference to the following preferred embodiments. However, these embodiments are provided for illustrative purposes only and should not be construed as limiting the scope and spirit of the invention. Furthermore, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention, and such changes and modifications are also within the scope of the appended claims.

[0210] [Example]

[0211] Example 1

[0212] Waste lithium iron phosphate cathode material was pulverized using a mixer to separate the current collector. The separated current collector material was then sieved through a 200-mesh sieve to obtain a powder with an olivine structure. X-ray diffraction (XRD) analysis of the obtained waste cathode material powder confirmed that the powder contained lithium iron phosphate powder with an olivine structure.

[0213] At room temperature, 100 g of the prepared waste cathode material powder was added to 1000 ml of sulfuric acid aqueous solution with a molar concentration of 0.6 (mol / L) and leached to form a leaching solution containing dissolved lithium and a leaching residue. The leaching solution and the leaching residue were separated by vacuum filtration to obtain the leaching residue.

[0214] The resulting leaching residue was leached in a 1 molar concentration sulfuric acid aqueous solution at room temperature for 20 hours at a solid-liquid ratio of 10 mL / g to obtain a solution containing Fe and P. ICP analysis confirmed that the solution contained 27,000 ppm Fe, 15,000 ppm P, and 250 ppm Li. At this point, the pH of the solution was 0.3.

[0215] Take 50 ml of a solution containing Fe and P, and continuously add 1 molar concentration of ammonia solution at a rate of 1 ml / min while stirring at room temperature to adjust the pH of the solution to 1.8, thereby precipitating impurities such as aluminum and titanium.

[0216] Impurities such as aluminum and titanium are removed by separating the dissolved solution through vacuum filtration.

[0217] A 30% by weight aqueous solution of hydrochloric acid was added to 50 ml of purified solution to adjust the pH to 1, thereby preparing a storage solution containing Fe and P.

[0218] pH measurements were performed at room temperature using a METTLER TOLEDO SevenDirect SD30.

[0219] For ICP analysis, 0.2 g of the solution was sampled into a conical tube and weighed precisely. Then, 0.1 ml of 70% by weight nitric acid was added, followed by 500 μl of 1000 mg / kg internal standard (scandium). The mixture was diluted to 50 ml with ultrapure water, and the contents of Fe, P, and Li were measured by ICP analysis.

[0220] Example 2

[0221] The method was carried out in the same manner as in Example 1, except that a storage solution containing Fe and P was prepared by adding a 30% by weight aqueous solution of hydrochloric acid to 50 ml of a solution that had been purified of impurities to adjust the pH to 1.1.

[0222] Example 3

[0223] The method was carried out in the same manner as in Example 1, except that a storage solution containing Fe and P was prepared by adding a 30% by weight aqueous solution of hydrochloric acid to 50 ml of a solution that had been purified of impurities to adjust the pH to 1.3.

[0224] Example 4

[0225] The method was carried out in the same manner as in Example 1, except that a storage solution containing Fe and P was prepared by adding a 30% by weight aqueous solution of hydrochloric acid to 50 ml of a solution that had been purified of impurities to adjust the pH to 1.4.

[0226] Example 5

[0227] The method was carried out in the same manner as in Example 1, except that a storage solution containing Fe and P was prepared by adding a 30% by weight aqueous hydrochloric acid solution to 50 ml of a solution that had been purified of impurities to adjust the pH to 0.8.

[0228] Comparative Example 1

[0229] The method was carried out in the same manner as in Example 1, except that a storage solution containing Fe and P was prepared by adding a 30% by weight aqueous solution of hydrochloric acid to 50 ml of a solution that had been purified of impurities to adjust the pH to 1.5.

[0230] Comparative Example 2

[0231] The method was carried out in the same manner as in Example 1, except that a storage solution containing Fe and P was prepared by adding a 30% by weight aqueous solution of hydrochloric acid to 50 ml of a solution from which impurities had been removed to adjust the pH to 1.6.

[0232] [Experimental Example I: [Measurement of Precipitate in Storage Solution]

[0233] The storage solutions prepared in Examples 1 to 5 and Comparative Examples 1 and 2 were left at room temperature for 24 hours. The storage solutions were then filtered to separate the precipitate, and the separated precipitate was dried and weighed. The results are shown in Table 1 below.

[0234] [Table 1]

[0235] As shown in Table 1, the storage solutions of the present invention (Examples 1 to 5) were confirmed to produce almost no precipitation, with a precipitate weight of less than 0.02 g / L after standing at room temperature for 24 hours. In particular, no precipitation was formed in Examples 1 to 3 and 5 at pH values ​​of 0.8 to 1.3. The solubility of substances varies with pH. Within the pH range of the present invention, Fe and P remain dissolved without forming precipitates. Conversely, in Comparative Examples 1 and 2, where the pH values ​​exceed the range of the present invention, Fe and P deviate from their dissolved state, resulting in the formation of substantial precipitates.

Claims

1. A method for preparing iron phosphate from waste lithium iron phosphate cathode, comprising: (a) Impurities are precipitated by adding an alkaline solution to a solution containing Fe and P; (b) Remove impurities from the solution; and (c) A storage solution containing Fe and P is prepared by adding an acidic solution to a solution from which impurities have been removed and adjusting the pH to 0.8 to 1.

4.

2. The method according to claim 1, wherein, In step (a), the alkaline solution is an aqueous solution of ammonia, sodium hydroxide, potassium hydroxide, or calcium hydroxide.

3. The method according to claim 1, wherein, The pH of the Fe and P-containing solution in step (a) is 0.1 to 0.

5.

4. The method according to claim 1, wherein, In step (a), after the addition of the alkaline solution is completed, the pH of the solution is 1.7 to 2.

5.

5. The method according to claim 1, wherein, Step (a) is carried out with stirring at room temperature.

6. The method according to claim 1, wherein, In step (a), the alkaline solution contains an alkaline component with a molar concentration of 0.8 mol / L to 1.3 mol / L.

7. The method according to claim 1, wherein, In step (a), the alkaline solution is added continuously.

8. The method according to claim 1, wherein, The solution in step (a) is prepared by a process comprising the following steps: (i) obtaining cathode material powder by pulverizing waste lithium iron phosphate cathode; (ii) adding the obtained cathode material powder to an acidic solution with a molar concentration of 0.5 mol / L to 0.7 mol / L to form a leaching solution and a leaching residue containing dissolved lithium, and separating the leaching solution and the leaching residue. (iii) The separated leaching residue is added to an acidic solution with a molar concentration of 0.8 mol / L to 1.3 mol / L to obtain a solution containing Fe and P.

9. The method according to claim 1, wherein, In step (b), impurities are removed using reduced pressure filtration.

10. The method according to claim 1, wherein, In step (c), the acidic solution is an aqueous solution of sulfuric acid, hydrochloric acid, or nitric acid.

11. The method according to claim 1, wherein, In step (c), the storage solution containing Fe and P forms a precipitate of less than 0.03 g / L after being left at room temperature for 24 hours.

12. The method according to claim 1, wherein, The method for preparing FePO4 from waste lithium iron phosphate cathode material further includes: (d) synthesizing FePO4 from the storage solution containing Fe and P.

13. A method for preparing lithium iron phosphate, comprising: Ferric phosphate is prepared using the method for preparing ferric phosphate as described in any one of claims 1 to 12; and Lithium iron phosphate is synthesized by reacting the prepared iron phosphate with a lithium precursor.

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