Process for the preparation of feppo4 from spent lithium iron phosphate cathodes

Abstract

The present invention relates to a method of preparing FePO4 from a waste lithium iron phosphate cathode. More specifically, the present invention relates to a method of preparing FePO4 from a waste lithium iron phosphate cathode, which comprises the steps of: (a) preparing a hydrogen peroxide mixture by adding an aqueous hydrogen peroxide solution to a solution containing Fe and P components; (b) heating the hydrogen peroxide mixture; (c) synthesizing FePO4 by adding an aqueous ammonia solution to the heated hydrogen peroxide mixture; (d) isolating the synthesized FePO4; and (e) washing the isolated FePO4 with an acidic washing solution having a pH of 1.3 to 1.6. According to the present invention, the effect of the present invention is to provide a method of preparing FePO4 from a waste lithium iron phosphate cathode, which is characterized by easy removal of impurities from the waste lithium iron phosphate cathode material and inhibition of generation of a new by-product.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2024-0180051, filed with the Korean Intellectual Property Office on December 6, 2024, the disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates to a method for preparing FePO4 as a precursor of lithium iron phosphate from waste lithium iron phosphate cathode material, and more specifically, to a method for preparing FePO4 from waste lithium iron phosphate cathode material, characterized by easily removing impurities from the waste lithium iron phosphate cathode material and suppressing the generation of new byproducts. 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) has a very stable hexahedral crystal structure. To disrupt this stable structure and recover the valuable metal, a high concentration of strong acid or strong base is used on the spent cathode to dissolve the valuable metal, and then Li and FePO4 are recovered separately.

[0008] However, the FePO4 obtained during the recycling process contains excessive impurities from waste cathode materials and byproducts generated during the recycling process, which leads to the degradation of the performance of lithium iron phosphate batteries prepared from it.

[0009] Therefore, there is a need for a method to prepare FePO4 from waste lithium iron phosphate cathodes, in which impurities from the waste cathode materials can be easily removed and the generation of new byproducts can be suppressed.

[0010] [Existing technical documents]

[0011] [Patent Document] KR 2014-0126943 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, characterized in that impurities from waste cathode material are easily removed and the generation of new by-products is suppressed.

[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 is provided, comprising: (a) adding an aqueous hydrogen peroxide solution to a solution containing Fe and P components to prepare a hydrogen peroxide mixture; (b) heating the hydrogen peroxide mixture; (c) adding an aqueous ammonia solution to the heated hydrogen peroxide mixture to synthesize FePO4; (d) separating the synthesized FePO4; and (e) washing the separated FePO4 with an acidic washing solution of pH 1.3 to 1.6.

[0017] II) According to I), the solution of step (a) may have a pH of 0.1 to 0.5.

[0018] III) According to I) or II), in step (a), the amount of hydrogen peroxide aqueous solution added may be from 0.45% to 1.2% of the solution, based on hydrogen peroxide.

[0019] IV) According to I) to III), for the solution in step (a), an aqueous ammonia solution can be added to the solution containing the Fe and P components to precipitate impurities and remove them.

[0020] V) According to I) to IV), after the addition of the ammonia solution is completed, the solution containing the Fe and P components can have a pH of 1.0 to 1.4.

[0021] VI) According to I) to V), the solution of step (a) can be prepared by a process comprising the following steps: (i) crushing and sieving waste lithium iron phosphate cathode to obtain waste cathode material powder; (ii) adding the obtained waste cathode material powder to an acidic solution with a molar concentration of 0.5 mol / L to 0.7 mol / L to form a leachate and a leachate residue containing dissolved lithium, and separating the leachate and the leachate residue; and (iii) adding the separated leachate residue 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 components.

[0022] VII) According to I) to VI), in step (b), the hydrogen peroxide mixture may be heated to 28°C to 60°C.

[0023] VIII) According to I) to VII), in step (c), after the addition of the ammonia solution is completed, the heated hydrogen peroxide mixture may have a pH of 1 to 2.

[0024] IX) According to I) to VIII), in step (c), after the addition of the ammonia solution is completed, stirring can be carried out for another 30 to 60 minutes.

[0025] X) According to I) to IX), in step (c), an ammonia solution can be added continuously.

[0026] XI) According to I) to X), based on the following equation 1, the weight change rate of FePO4 washed in step (e) relative to FePO4 separated in step (d) may be less than ±0.3%.

[0027] [Equation 1]

[0028] Weight change rate (%) = [(AB) / A)] × 100, Where A is the weight of FePO4 separated in step (d), and B is the weight of FePO4 after washing in step (e).

[0029] XII) According to I) to XI), in step (e), the solid / liquid ratio of the separated FePO4 and the acidic washing solution with pH 1.3 to 1.6 can be from 15 mL / g to 25 mL / g.

[0030] XIII) According to I) to XII), in step (e), washing may include adding an acidic washing solution and stirring for 5 to 20 minutes.

[0031] XIV) According to I) to XIII), in step (e), washing may include depressurized filtration.

[0032] According to I) to XIV), the method for preparing FePO4 from waste lithium iron phosphate cathode may further include (f) drying and washing the FePO4.

[0033] XVI) According to another aspect of the present invention, a method for preparing FePO4 from waste lithium iron phosphate cathode is provided, comprising: (i) pulverizing and sieving the waste lithium iron phosphate cathode to obtain waste cathode material powder; (ii) adding the obtained waste cathode material powder to a molar concentration of 0.5 mol / L to 0.7 mol / L. (iii) In an acidic solution with a molar concentration of 0.8 mol / L to 1.3 mol / L, a leaching solution containing dissolved lithium and a leaching residue are formed, and the leaching solution and the leaching residue are separated; (iv) 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 components; (v) An aqueous ammonia solution is added to the solution containing Fe and P components to precipitate and remove impurities, thereby obtaining a solution with impurities removed; (v) An aqueous hydrogen peroxide solution is added to the solution with impurities removed to prepare a hydrogen peroxide mixture; (vi) The hydrogen peroxide mixture is heated; (vii) An aqueous ammonia solution is added to the heated hydrogen peroxide mixture to synthesize FePO4; (viii) The synthesized FePO4 is separated; (ix) The separated FePO4 is washed with an acidic washing solution with a pH of 1.3 to 1.6; and (x) The washed FePO4 is dried.

[0034] [Beneficial Effects]

[0035] According to the present invention, the present invention has the effect of providing a method for preparing FePO4 from waste lithium iron phosphate cathode, characterized by easy removal of impurities and suppression of the generation of by-products. Attached Figure Description

[0036] The accompanying drawings illustrate embodiments of the invention and, together with the detailed embodiments 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.

[0037] Figure 1 This is a process flow diagram of a method for preparing FePO4 from waste lithium iron phosphate cathode as an embodiment of the present invention.

[0038] Figure 2 This is a graph showing the removal rate of impurities in solutions containing Fe and P components in Examples 1 and 3 to 6 (pH 1.0 to 1.4).

[0039] Figure 3 It is a graph showing the content of F, P, Al and Ti components remaining after removing impurities from solutions containing Fe and P components in Examples 1 and 3 to 6 (pH 1.0 to 1.4).

[0040] Figure 4 This is a graph showing the content of remaining Al and Ti components in the final FePO4 prepared in Examples 1 and 3 to 6 (pH 1.0 to 1.4).

[0041] Figure 5 This is a graph showing the Al content in the final FePO4 prepared in Examples 1 and 7 to 15 (pH of the hydrogen peroxide mixture was 1.0 to 1.4).

[0042] Figure 6 This is a graph showing the Ti content in the final FePO4 prepared in Examples 1 and 7 to 15 (pH of the hydrogen peroxide mixture was 1.0 to 1.4). Detailed Implementation

[0043] The inventors have demonstrated that when waste lithium iron phosphate cathode material powder is separated into a leachate containing lithium components and a leachate residue containing Fe and P components using an acidic solution, and then an aqueous hydrogen peroxide solution is added to a solution containing Fe and P components obtained by leaching the Fe and P components from the leachate residue containing Fe and P components with an acidic solution, followed by heating and adding an aqueous ammonia solution to synthesize crude FePO4, and then washing the synthesized crude FePO4 with an acidic washing solution with a pH of 1.3 to 1.6 to remove impurities, the generation of byproducts is suppressed, and FePO4 with high yield and high purity is prepared. Based on these results, the inventors conducted further research to complete this invention.

[0044] The method for recovering lithium according to the present invention is described in detail below.

[0045] 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 meanings and concepts that correspond to 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, replaced, combined, separated, or designed in various other configurations.

[0046] 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.

[0047] Method for preparing FePO4 from waste lithium iron phosphate cathode material

[0048] The method for preparing FePO4 from waste lithium iron phosphate cathode of the present invention includes: step (a) adding an aqueous hydrogen peroxide solution to a solution containing Fe and P components to prepare a hydrogen peroxide mixture; step (b) heating the hydrogen peroxide mixture; step (c) adding an aqueous ammonia solution to the heated hydrogen peroxide mixture to synthesize FePO4; step (d) separating the synthesized FePO4; and step (e) washing the separated FePO4 with an acidic washing solution with a pH of 1.3 to 1.6. In this process, impurities can be easily removed, and the formation of new byproducts can be suppressed, thereby providing FePO4 with high yield and high purity.

[0049] The following section describes in detail each step of the method for preparing FePO4 from waste lithium iron phosphate cathode.

[0050] (a) A hydrogen peroxide mixture is prepared by adding an aqueous hydrogen peroxide solution to a solution containing Fe and P components.

[0051] The method of preparing FePO4 from waste lithium iron phosphate cathode of the present invention may include step (a), preparing a hydrogen peroxide mixture by adding an aqueous hydrogen peroxide solution to a solution containing Fe and P components. In this case, FePO4 can be readily synthesized.

[0052] For example, the solution containing Fe and P components in step (a) can have a pH of 0.1 to 0.5, preferably 0.2 to 0.4. Within this range, the Fe and P components can be readily leached.

[0053] For example, the solution containing Fe and P components in step (a) may contain an amount of Fe component 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, even more preferably 27,000 to 32,000 ppm, and even more preferably 27,000 to 30,000 ppm. In this case, FePO4 with high yield and high purity can be prepared.

[0054] For example, the solution containing Fe and P components in step (a) may contain P components in an amount 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, even more preferably 15,000 to 20,000 ppm, and even more preferably 15,000 to 17,000 ppm. In this case, FePO4 with high yield and high purity can be prepared.

[0055] For example, the solution containing Fe and P components in step (a) may contain a lithium component in an amount of 500 ppm or less, preferably 400 ppm or less, more preferably 300 ppm or less, even more preferably 250 ppm or less, even more preferably 10 to 250 ppm, and even more preferably 100 to 250 ppm. In this case, high-purity FePO4 can be prepared.

[0056] In this disclosure, unless otherwise specified, ppm is expressed by weight.

[0057] For example, in step (a), the amount of hydrogen peroxide aqueous solution added can be from 0.45 vol% to 1.2 vol% of the solution, preferably from 0.5 vol% to 1.1 vol%, and more preferably from 0.6 vol% to 1 vol%. Within this range, FePO4 can be readily synthesized.

[0058] For example, the concentration of the aqueous hydrogen peroxide solution can be from 25% to 40% by weight, preferably from 27% to 35% by weight, and more preferably from 29% to 33% by weight. Within this range, the generation of byproducts can be suppressed, and FePO4 can be readily synthesized.

[0059] For example, the hydrogen peroxide mixture can have a pH of 0.1 to 0.7, preferably 0.2 to 0.6, and more preferably 0.3 to 0.5. Within this range, the Fe component can be maintained as Fe. 3+ This inhibits the production of byproducts while promoting the synthesis of FePO4.

[0060] For example, for the solution in step (a), an aqueous ammonia solution can be added to the solution containing Fe and P components to precipitate impurities and remove them. In this case, the purity of the prepared FePO4 can be significantly improved.

[0061] For example, after the addition of the ammonia solution is complete, the solution containing the Fe and P components can have a pH of 1.0 to 1.4, preferably 1.1 to 1.4, and more preferably 1.2 to 1.4. Within this range, impurities can precipitate and can be easily removed.

[0062] In this disclosure, pH measurements can be performed using measurement methods commonly used in the technical field 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.

[0063] In this disclosure, room temperature can be a point in the range of 20 ± 5°C.

[0064] For example, the ammonia solution can have a molar concentration of 0.8 mol / L to 1.3 mol / L, preferably 0.9 mol / L to 1.2 mol / L, and more preferably 0.9 mol / L to 1.1 mol / L. Within this range, impurities such as aluminum and titanium can be readily precipitated from the solution containing Fe and P components.

[0065] For example, an aqueous ammonia solution can be continuously added to a solution containing Fe and P components. In this case, impurities can be sufficiently precipitated and removed.

[0066] 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.

[0067] For example, an aqueous ammonia solution can be added with stirring. In this case, the advantage is that it shortens the sedimentation time of impurities.

[0068] For example, reduced pressure filtration can be used to separate a solution containing added ammonia from impurities. In this case, there is the advantage that the solution and impurities can be easily separated separately using a simple method.

[0069] For example, since the separated impurities may include Fe and P components in addition to Al and Ti components, the Fe and P components can be recovered by leaching the separated impurities again in an acidic solution.

[0070] For example, the solution in step (a) can be prepared by a process comprising the following steps: (i) pulverizing and sieving waste lithium iron phosphate cathode to obtain waste cathode material powder; (ii) adding the obtained waste cathode material powder to an acidic solution with a molar concentration of 0.5 mol / L to 0.7 mol / L to form a leachate and leaching residue containing dissolved lithium, and separating the leachate and leaching residue; and (iii) adding the separated leaching residue 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 components. In this case, FePO4 can be synthesized in high yield.

[0071] 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.

[0072] In this disclosure, waste cathode material powder refers to a material in powder form obtained by crushing and sieving waste cathodes, and most of the current collectors are removed from the waste cathodes, but may include a small number of fine current collector particles with a size of a few micrometers.

[0073] In this disclosure, positive electrode material refers to a material that includes positive electrode active material or is a positive electrode active material.

[0074] 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.

[0075] 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.

[0076] The structure of olivine can be determined by X-ray diffraction (XRD) analysis.

[0077] For example, positive electrode active materials with an olivine structure can include lithium iron phosphate. In this case, it has the advantages of excellent high-temperature stability, long lifespan, and low cost.

[0078] For example, lithium iron phosphate 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.

[0079] [Chemical Formula 1]

[0080] (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).

[0081] Lithium iron phosphate may preferably include LiFePO4 with an olivine structure. In this case, it has the advantages of excellent high-temperature stability, long lifespan, and low cost.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] For example, in step (ii), the acid concentration of the acidic solution can be from 0.5 to 0.7 mol / L, preferably from 0.55 to 0.65 mol / L. Within this range, the advantage is that lithium is readily leached, and the Fe and P components are retained as leaching residues.

[0090] For example, in step (ii), the solid / liquid ratio of the positive electrode powder and 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.

[0091] In this disclosure, the solid / liquid ratio refers to the volume of liquid relative to the weight of solid, i.e., the volume (mL) of acidic solution relative to the content (g) of positive electrode powder.

[0092] 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.

[0093] For example, in step (iii), 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, there is the advantage that the Fe and P components are easily leached.

[0094] The acidic solution is preferably an acidic aqueous solution. In this case, there is an advantage that the Fe and P components are easily leached out.

[0095] For example, in step (iii), the acid concentration of the acidic solution can be from 0.8 to 1.3 mol / L, preferably from 0.9 to 1.2 mol / L, and more preferably from 0.9 to 1.1 mol / L. Within this range, there is an economic advantage because the Fe and P components are fully leached, thereby increasing the yield of FePO4.

[0096] (b) Heating the hydrogen peroxide mixture

[0097] The method of the present invention for preparing FePO4 from waste lithium iron phosphate cathode may include step (b), heating a mixture of hydrogen peroxide. In this case, FePO4 can be readily synthesized.

[0098] For example, in step (b), the hydrogen peroxide mixture can be heated to 28°C to 60°C, preferably 28°C to 55°C, more preferably 30°C to 50°C, and even more preferably 30°C to 42°C. Within this range, FePO4 can be readily synthesized.

[0099] (c) To synthesize FePO4 by adding an aqueous ammonia solution to a heated hydrogen peroxide mixture.

[0100] The method of the present invention for preparing FePO4 from waste lithium iron phosphate cathode may include step (c), synthesizing FePO4 by adding an aqueous ammonia solution to a heated hydrogen peroxide mixture. In this case, FePO4 can be synthesized in high yield.

[0101] For example, in step (c), after the addition of the ammonia solution is complete, the hydrogen peroxide mixture can have a pH of 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.

[0102] For example, in step (c), an aqueous ammonia solution can be added to the hydrogen peroxide mixture while stirring. In this case, FePO4 can be easily synthesized.

[0103] 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.

[0104] For example, in step (c), an aqueous ammonia solution can be added continuously. In this case, FePO4 can be synthesized stably without side reactions.

[0105] In step (c), it is preferable to maintain the heating temperature while adding the aqueous ammonia solution. In this case, FePO4 can be synthesized stably without side reactions.

[0106] For example, in step (c), after the addition of the ammonia solution is complete, further stirring can be performed for 30 to 60 minutes, preferably 35 to 55 minutes, more preferably 40 to 50 minutes. Under these conditions, FePO4 can be synthesized stably without side reactions.

[0107] In step (c), after the addition of the ammonia solution is complete, further stirring can preferably be performed at a heated temperature. In this case, FePO4 can be synthesized stably without side reactions.

[0108] (d) Separation and synthesis of FePO4

[0109] The method of the present invention for preparing FePO4 from waste lithium iron phosphate cathode may include step (d), separating the synthesized FePO4. In this case, impurities can be easily removed in a washing step as a subsequent process, and energy can be saved.

[0110] For example, separation can be achieved using vacuum filtration. In this case, the synthesized FePO4 can be easily removed.

[0111] Vacuum filtration is preferred, and specifically, vacuum filtration using a filter flask. In this case, FePO4 can be easily separated.

[0112] In this invention, vacuum pressure reduction filtration is not particularly limited, as long as it is a common type of vacuum pressure reduction filtration in the technical field to which this invention pertains. For example, vacuum pressure reduction filtration may include filtration under partial vacuum or low pressure conditions.

[0113] (e) Wash the separated FePO4 with an acidic washing solution with a pH of 1.3 to 1.6.

[0114] The method of the present invention for preparing FePO4 from waste lithium iron phosphate cathode may include step (e), washing the separated FePO4 with an acidic washing solution of pH 1.3 to 1.6. In this case, impurities can be easily removed and the purity of the synthesized FePO4 can be improved because no byproducts due to the re-leaching of FePO4 are generated.

[0115] For example, an acidic washing solution having 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 acidic washing solution can be readily prepared, and impurities can be easily removed.

[0116] The acidic washing solution preferably has a pH of 1.3 to 1.5, more preferably 1.3 to 1.4. Within this range, 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 generated.

[0117] For example, in step (e), the solid / liquid ratio of FePO4 and the acidic washing solution with a pH of 1.3 to 1.6 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 byproducts can be avoided.

[0118] For example, in step (e), washing can be performed by adding an acidic washing solution 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 can be generated.

[0119] For example, in step (e), washing may include vacuum filtration. In this case, FePO4 and the acidic washing solution can be easily separated.

[0120] Based on Equation 1 below, the weight change rate of FePO4 washed in step (e) relative to FePO4 separated in step (d) can be, for example, less than ±0.3%, preferably less than ±0.1%, more preferably less than ±0.05%, and even more preferably less than ±0.02%. Within this range, FePO4 can be prepared with high purity and high yield because impurities have been removed and no byproducts are generated.

[0121] Furthermore, the purity and yield of the prepared FePO4 can be controlled by adjusting the conditions of the washing step (e) within the range of weight change rate.

[0122] [Equation 1]

[0123] Weight change rate (%) = [(AB) / A)] × 100

[0124] (A is the weight of FePO4 separated in step (d), and B is the weight of FePO4 after washing in step (e))

[0125] (f) FePO4 after drying and washing

[0126] The method for preparing FePO4 from waste lithium iron phosphate cathodes may further include step (f), drying the washed FePO4. In this case, there is an effect of stable transportation and storage of the washed FePO4.

[0127] 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, until the weight no longer changes, for example, for 1 hour to 24 hours. Within this range, there is an effective effect in removing the moisture contained in the washed FePO4.

[0128] In this invention, there are no particular limitations on vacuum drying, as long as the vacuum drying is the kind commonly used in the technical field to which this invention pertains. For example, vacuum drying may include drying under partial vacuum or low pressure conditions.

[0129] Down Figure 1 This is a flowchart of a method for preparing FePO4 from waste lithium iron phosphate cathode according to one embodiment of the present invention.

[0130] Reference Figure 1 First, prepare the waste lithium iron phosphate cathode (step S10).

[0131] Waste lithium iron phosphate cathodes are preferably discarded lithium-ion battery cathodes, defective products generated during the cathode coating process, or cathode waste discarded after cutting the electrode plates, and more preferably discarded lithium-ion battery cathodes.

[0132] The positive electrode has a structure in which the positive electrode active material and the conductive material are bonded to the aluminum foil by an adhesive.

[0133] The positive electrode may include a positive electrode active material with an olivine structure, preferably lithium iron phosphate with an olivine structure, and more preferably LiFePO4 with an olivine structure. In this case, it has the advantages of excellent high-temperature stability, long lifespan, and low cost.

[0134] Next, the waste lithium iron phosphate cathode is crushed and sieved to obtain waste cathode material powder (step S20).

[0135] The pulverization can be carried out using dry pulverization equipment, specifically, a hand grinder, pin mill, disc mill, cutting mill, hammer mill, or mixer (as a specific example, a mixer). In this case, the current collector is finely shredded into fragments, and the waste positive electrode material is separated from the current collector fragments. In this case, the current collector and the positive electrode material can be easily separated.

[0136] For example, the current collector can be separated from the crushed waste cathode by sieving, and waste cathode material powder of uniform size can be obtained.

[0137] 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 waste cathode material powder of uniform size can be obtained.

[0138] Next, the waste cathode material powder is added to an acidic solution with a molar concentration of 0.5 mol / L to 0.7 mol / L to form a leachate containing dissolved lithium and a leachate residue, which are then separated (step S30).

[0139] For example, the acidic solution may be a solution containing at least one selected from the group consisting of sulfuric acid, hydrochloric acid, hypochlorous acid, nitric acid, carbonic acid, acetic acid, and oxalic acid, and specifically, it may be an aqueous solution of sulfuric acid. In this case, the advantage is that lithium is readily and selectively leached, and the Fe and P components are retained as leaching residues.

[0140] 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.

[0141] The acid concentration of the acidic solution can be from 0.55 to 0.65 mol / L, with 0.6 mol / L as a specific example. In this case, lithium is readily and selectively leached, while the Fe and P components are retained as leaching residues.

[0142] In step S30, the solid / liquid ratio of the waste cathode material powder and the acidic solution can preferably be 7 to 15 mL / g, with 10 mL / g as a specific example. In this case, the advantage is that lithium is fully leached, while the Fe and P components are not leached and remain as leaching residues.

[0143] Next, 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 components (step S40).

[0144] 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, an aqueous solution of sulfuric acid. In this case, the Fe and P components can be leached.

[0145] The acidic solution is preferably an acidic aqueous solution. In this case, the Fe and P components can be leached out.

[0146] The acid concentration of the acidic solution can preferably be from 0.9 to 1.2 mol / L, with 1.0 mol / L as a specific example. In this case, there is an economic advantage because the Fe and P components are fully leached, thereby increasing the yield of FePO4.

[0147] Solutions containing Fe and P components preferably have a pH of 0.1 to 0.5, and as a specific example, a pH of 0.2 to 0.4. Within this range, the advantage is that the Fe and P components are present in a leached state.

[0148] Next, an aqueous ammonia solution is added to the solution containing Fe and P components (step S50).

[0149] In step S50, adding an aqueous ammonia solution to a solution containing Fe and P components to precipitate and remove impurities can significantly improve the purity of the prepared FePO4.

[0150] For example, a solution containing Fe and P components can contain more than 23,000 ppm of Fe, specifically more than 27,000 ppm. In this case, FePO4 can be prepared in high yield and with high purity.

[0151] For example, a solution containing Fe and P components can contain more than 10,000 ppm, specifically more than 15,000 ppm of P component. In this case, FePO4 with high yield and high purity can be prepared.

[0152] For example, a solution containing Fe and P components may include a lithium component in amounts of less than 500 ppm, specifically less than 250 ppm. In this case, high-purity FePO4 can be prepared.

[0153] The molar concentration of the ammonia solution can preferably be from 0.8 to 1.3 mol / L, with 1.0 mol / L as a specific example. In this case, impurities such as aluminum and titanium precipitate and are easily removed.

[0154] After the ammonia solution is added, the solution preferably has a pH of 1.0 to 1.4, with 1.2 being a specific example. In this case, impurities such as aluminum and titanium precipitate and are easily removed.

[0155] Ammonia solution can be continuously added to the solution. In this case, impurities such as aluminum and titanium precipitate and are easily removed.

[0156] For example, an aqueous ammonia solution can be added with stirring. In this case, there is the advantage that impurities precipitate out in a short time.

[0157] The step of separating impurities from a solution containing added ammonia is preferably performed using vacuum filtration. In this case, the solution and impurities can be easily separated separately by a simple method.

[0158] Next, an aqueous hydrogen peroxide solution is added to a solution containing Fe and P components from which impurities have been separated to prepare a hydrogen peroxide mixture (step S60).

[0159] In step S60, the amount of hydrogen peroxide aqueous solution added is preferably 0.45% to 1.2% of the solution, based on hydrogen peroxide. As a specific example, the amount added is 0.6% to 1.0% of the solution. Under these conditions, FePO4 can be easily synthesized.

[0160] The concentration of the hydrogen peroxide aqueous solution is preferably from 25% to 40% by weight, with 30% by weight being a specific example. In this case, the Fe component can be maintained as Fe. 3+ This inhibits the production of byproducts while promoting the synthesis of FePO4.

[0161] Next, the hydrogen peroxide mixture is heated (step S70).

[0162] The hydrogen peroxide mixture can be heated to a preferred temperature of 28°C to 60°C, and in a specific example, to 30°C. Under these conditions, FePO4 can be readily synthesized.

[0163] Next, an aqueous ammonia solution is added to the heated hydrogen peroxide mixture to synthesize FePO4 (step S80).

[0164] After the process of adding the ammonia solution to the heated hydrogen peroxide mixture is completed, the pH can preferably be 1 to 2, and as a specific example, the pH is 1.2. Under these conditions, FePO4 can be synthesized in high yield.

[0165] In step S80, it is preferable to add the ammonia solution while stirring, more preferably while stirring at 300 to 700 rpm. As a specific example, the ammonia solution is added while stirring at 500 rpm. In this case, FePO4 can be synthesized in high yield.

[0166] In step S80, it is preferable to add the aqueous ammonia solution continuously. In this case, FePO4 can be synthesized stably without side reactions.

[0167] While adding the ammonia solution, it is preferable to maintain the heating temperature. Under these conditions, FePO4 can be synthesized stably without side reactions.

[0168] In step S80, after the addition of the ammonia solution, it is preferable to perform an additional stirring for 30 to 60 minutes, specifically 40 minutes. Under these conditions, FePO4 can be synthesized stably without side reactions.

[0169] In step S80, 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.

[0170] Next, the synthesized FePO4 is separated (step S90).

[0171] In step S80, by separating the synthesized FePO4, impurities can be easily removed in the washing step, which is a subsequent process, and energy can be saved.

[0172] The separation can preferably be carried out using reduced pressure filtration, more preferably vacuum reduced pressure filtration, and specifically using vacuum reduced pressure filtration in a filter flask. In this case, FePO4 can be easily removed.

[0173] Next, the separated FePO4 is washed with an acidic washing solution with a pH of 1.3 to 1.6 (step S100).

[0174] Impurities such as Fe can be easily removed through the washing process. x PO x (It is a non-stoichiometric FePO4), and can improve the purity of synthesized FePO4 because it does not produce byproducts.

[0175] 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.

[0176] As a specific example, the acidic washing solution can have a pH of 1.3 to 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 generated.

[0177] In step S100, the solid / liquid ratio of FePO4 and the acidic washing solution is preferably 15 to 25 mL / g, with 20 mL / g as a specific example. In this case, the formation of byproducts can be suppressed, and impurities, such as Fe, can be easily removed. x PO x (It is a non-stoichiometric FePO4). Furthermore, since no byproducts are produced, the purity of the synthesized FePO4 can be improved.

[0178] In step S100, 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.

[0179] In step S100, washing may preferably include vacuum filtration. In this case, FePO4 and the acidic washing solution can be easily separated.

[0180] Based on Equation 1 below, the weight change rate of FePO4 synthesized in step S80 relative to the FePO4 washed in step S100 can be less than ±0.3%, and specifically less than ±0.02%. Within this range, impurities can be reduced and no by-products are generated, resulting in excellent battery performance.

[0181] [Equation 1]

[0182] Weight change rate (%) = [(AB) / A)] × 100

[0183] (A is the weight of the synthesized FePO4 obtained in step S80, and B is the weight of the washed FePO4 obtained in step S100.)

[0184] Next, the washed FePO4 is dried (step S110).

[0185] Step S110 may further include the step of drying the washed FePO4. In this case, there is an effect of stable transportation and storage of the washed FePO4.

[0186] 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.

[0187] 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.

[0188] Example 1: [Weight change rate based on pH of acidic washing solution]

[0189] Example 1

[0190] Waste lithium iron phosphate cathode material was pulverized using a mixer to separate the current collector. The waste lithium iron phosphate cathode material from the separated current collector was sieved through a 200-mesh sieve to obtain waste cathode material powder with an olivine structure. The results of X-ray diffraction (XRD) analysis of the obtained waste cathode material powder confirmed that the powder has an olivine structure.

[0191] At room temperature, 100 g of the prepared waste cathode material powder was added to 1000 mL of a 0.6 mol / L sulfuric acid aqueous solution and leached to form a leachate containing dissolved lithium and a leaching residue. The leachate and leaching residue were separated by vacuum filtration to obtain the leaching residue. The components of Li, Fe, P, and S in the obtained leaching residue were measured by ICP analysis, and the results are shown in Table 1 below.

[0192] The leaching residue was leached in a 1 mol / L sulfuric acid aqueous solution at a solid / liquid ratio of 10 mL / g for 20 hours at room temperature to obtain a solution containing Fe and P components. ICP analysis confirmed that the solution had a pH of 0.1 to 0.5 and contained 27,000 ppm Fe and 15,000 ppm P components.

[0193] Take 50 mL of a solution containing Fe and P components, and continuously add 1 mol / L ammonia solution at a rate of 1 mL / min while stirring at room temperature to bring the pH of the solution to 1.2, thereby precipitating impurities such as aluminum and titanium.

[0194] The solution containing impurities such as aluminum and titanium is separated by vacuum filtration to remove the impurities.

[0195] Hydrogen peroxide was added at a concentration of 30% by weight to 50 mL of a solution from which impurities had been removed, and the temperature was raised to 30°C to prepare the hydrogen peroxide mixture. The process was carried out with stirring at 500 rpm.

[0196] A 1 mol / L ammonia solution was continuously added to a heated hydrogen peroxide mixture at a rate of 0.1 mL / min to maintain the pH of the mixture at 1.2, thereby synthesizing FePO4. The mixture was then stirred at 500 rpm.

[0197] The synthesized FePO4 and mixtures were separated using vacuum filtration.

[0198] The separated FePO4 was mixed with an acidic solution (washing solution) prepared with distilled water and hydrochloric acid at pH 1.3, and washed by stirring at 500 rpm for 10 minutes.

[0199] After washing, FePO4 and the washing solution were separated by vacuum filtration to obtain washed FePO4.

[0200] The FePO4 after washing was vacuum dried at 80°C to obtain the final FePO4.

[0201] Example 2

[0202] The same method as in Example 1 was performed, except that the FePO4 separated after synthesis was washed by mixing the separated FePO4 with an acidic solution (washing solution) with pH 1.5 prepared with distilled water and hydrochloric acid.

[0203] Comparative Example 1

[0204] The same method as in Example 1 was performed, except that the FePO4 separated after synthesis was washed by mixing the separated FePO4 with an acidic solution (washing solution) with pH 1.0 prepared with distilled water and hydrochloric acid.

[0205] Comparative Example 2

[0206] The same method as in Example 1 was performed, except that the FePO4 separated after synthesis was washed by mixing the separated FePO4 with an acidic solution (washing solution) with pH 1.2 prepared with distilled water and hydrochloric acid.

[0207] Comparative Example 3

[0208] The same method as in Example 1 was performed, except that the FePO4 separated after synthesis was washed by mixing it with an acidic solution (washing solution) with pH 1.7 prepared with distilled water and hydrochloric acid.

[0209] Comparative Example 4

[0210] The same method as in Example 1 was performed, except that the FePO4 separated after synthesis was washed by mixing the separated FePO4 with an acidic solution (washing solution) with pH 2.0 prepared with distilled water and hydrochloric acid.

[0211] Comparative Example 5

[0212] The same method as in Example 1 was performed, except that the FePO4 separated after synthesis was washed by mixing the separated FePO4 with an acidic solution (washing solution) with pH 6.0 prepared with distilled water and hydrochloric acid.

[0213] [Experimental Example I: [Composition of Leaching Residue]] ICP Analysis: 0.2 g of leaching residue was collected and placed in a conical tube, and its precise weight was measured. Next, 0.1 mL of 70% nitric acid was added, followed by 500 μL of 1000 g / kg internal standard (Sc). The mixture was then diluted with ultrapure water to a volume of 50 mL and measured by ICP. The results are shown in Table 1 below.

[0214] [Table 1]

[0215] As shown in Table 1, the leaching residue separated after leaching the waste cathode material powder obtained by crushing and sieving waste lithium iron phosphate cathodes in a 0.6 mol / L sulfuric acid aqueous solution mainly consists of Fe and P components. Among the elements present in small amounts, lithium components were confirmed to be present in relatively small amounts, while aluminum and titanium components were present in relatively large amounts.

[0216] [Experimental Example II: [Weight Change Rate of FePO4 Based on pH of Acidic Washing Solution] Weight change rate (%): The weight change rate of FePO4 after washing is calculated based on the weight of the synthesized FePO4 according to Equation 1 below.

[0217] [Equation 1]

[0218] Weight change rate (%) = [(AB) / A)] × 100

[0219] (A is the weight of synthesized FePO4, and B is the weight of washed FePO4)

[0220] [Table 2]

[0221] As shown in Table 2, in Examples 1 and 2 where the pH of the acidic washing solution was 1.3 to 1.6, the weight change rate was less than ±0.3%, indicating almost no change and suggesting the absence of byproducts. However, it was confirmed that in Comparative Examples 1 to 5, where the pH was outside this range, the absolute values ​​of the weight change rate were larger. Furthermore, when the pH of the acidic washing solution was less than the range of the present invention, the washed FePO4 was released, resulting in a negative (-) weight change rate. When the pH of the acidic washing solution exceeded the range of the present invention, byproducts were generated in the washed FePO4, resulting in a positive (+) weight change rate.

[0222] [Example II: Removal of impurities based on the pH of the solution containing Fe and P after adding ammonia solution]

[0223] Example 3

[0224] The same method as in Example 1 was performed, except that 50 mL of a solution containing Fe and P components was taken out and an ammonia solution with a molar concentration of 1 mol / L was continuously added at a rate of 1 mL / min while stirring at room temperature to bring the pH of the solution to 1.0, thereby precipitating impurities such as aluminum and titanium.

[0225] Example 4

[0226] The same method as in Example 1 was performed, except that 50 mL of a solution containing Fe and P components was taken out and a 1 mol / L ammonia solution was continuously added at a rate of 1 mL / min while stirring at room temperature to bring the pH of the solution to 1.1, thereby precipitating impurities such as aluminum and titanium.

[0227] Example 5

[0228] The same method as in Example 1 was performed, except that 50 mL of a solution containing Fe and P components was taken out and an ammonia solution with a molar concentration of 1 mol / L was continuously added at a rate of 1 mL / min while stirring at room temperature to bring the pH of the solution to 1.3, thereby precipitating impurities such as aluminum and titanium.

[0229] Example 6

[0230] The same method as in Example 1 was performed, except that 50 mL of a solution containing Fe and P components was taken out and an ammonia solution with a molar concentration of 1 mol / L was continuously added at a rate of 1 mL / min while stirring at room temperature to bring the pH of the solution to 1.4, thereby precipitating impurities such as aluminum and titanium.

[0231] [Experimental Example III: Measurement of impurity removal rate, residual element content, and elemental content in the final FePO4]

[0232] In Examples 1 and 3 through 6, solutions from which impurities were removed in the same manner as described above were used, and the content of each element was measured by ICP analysis. The results are shown below. Figure 2 and 3 In addition, the Al and Ti contents of the final FePO4 prepared in Examples 1 and 3 to 6 were measured by ICP analysis, and the results are shown in... Figure 4 middle.

[0233] like Figure 2 As shown, impurities such as Al and Ti components were removed in solutions containing Fe and P components with added ammonia solution at pH ranges from 1.0 to 1.4 (Examples 1 and 3 to 6). In particular, it was confirmed that the removal rate of Al and Ti components was high at pH values ​​above 1.2.

[0234] In addition, such as Figure 3 As shown, solutions with removed impurities (Examples 1 and 3 to 6) within a pH range of 1.0 to 1.4 exhibited low levels of Al and Ti components. Specifically, at pH values ​​above 1.2 (Examples 1, 5, and 6), the levels of Al and Ti components were even lower. These results confirm that adjusting the pH of solutions containing Fe and P components to 1.2 to 1.4 by adding an aqueous ammonia solution effectively removes Al and Ti components. Figure 3 In the curve diagram, "solution" refers to the solution containing Fe and P components before the addition of the ammonia solution.

[0235] In addition, Figure 2 and 3 In this process, at pH values ​​of 1.2 to 1.4 (Examples 1, 5, and 6), not only the Al and Ti components but also the Fe and P components were precipitated and removed. These Fe and P components can be recovered and reused by leaching them again in an acidic solution.

[0236] also, Figure 4 The measurements of Al and Ti content in the final FePO4 are shown. (For example...) Figure 4 As shown, the synthesized FePO4 (Examples 1 and 3 to 6) obtained by removing impurities from a solution containing Fe and P components by adding an aqueous ammonia solution has low contents of Al and Ti components. In particular, it was confirmed that the contents of Al and Ti components were even lower at pH values ​​above 1.2 (Examples 1, 5 and 6).

[0237] [Example III: Al and Ti content in final FePO4 as a function of pH of heated hydrogen peroxide mixture]

[0238] Example 7

[0239] FePO4 was synthesized by continuously adding an aqueous ammonia solution with a molar concentration of 1 mol / L to a heated hydrogen peroxide mixture at a rate of 0.1 mL / min to maintain the pH of the hydrogen peroxide mixture at 1.0.

[0240] Example 8

[0241] FePO4 was synthesized by continuously adding an aqueous ammonia solution with a molar concentration of 1 mol / L to a heated hydrogen peroxide mixture at a rate of 0.1 mL / min to maintain the pH of the hydrogen peroxide mixture at 1.1.

[0242] Example 9

[0243] FePO4 was synthesized by continuously adding an aqueous ammonia solution with a molar concentration of 1 mol / L to a heated hydrogen peroxide mixture at a rate of 0.1 mL / min to maintain the pH of the hydrogen peroxide mixture at 1.3.

[0244] Example 10

[0245] FePO4 was synthesized by continuously adding an aqueous ammonia solution with a molar concentration of 1 mol / L to a heated hydrogen peroxide mixture at a rate of 0.1 mL / min to maintain the pH of the hydrogen peroxide mixture at 1.4.

[0246] Example 11

[0247] Waste lithium iron phosphate cathode material was pulverized using a mixer to separate the current collector. The waste lithium iron phosphate cathode material from the separated current collector was sieved through a 200-mesh sieve to obtain waste cathode material powder with an olivine structure. The results of X-ray diffraction (XRD) analysis of the obtained waste cathode material powder confirmed that the powder has an olivine structure.

[0248] At room temperature, 100 g of the prepared waste cathode material powder was added to 1000 mL of a 0.6 mol / L sulfuric acid aqueous solution and leached to form a leachate containing dissolved lithium and a leaching residue. The leachate and leaching residue were separated by vacuum filtration to obtain the leaching residue. The components of Li, Fe, P, and S in the obtained leaching residue were measured by ICP analysis, and the results were the same as those in Table 1.

[0249] The leaching residue was leached in a 1 mol / L sulfuric acid aqueous solution at a solid / liquid ratio of 10 mL / g for 20 hours at room temperature to obtain a solution containing Fe and P components. ICP analysis confirmed that the solution contained 27,000 ppm Fe and 15,000 ppm P components.

[0250] Hydrogen peroxide was added to 50 mL of a solution at a concentration of 30% by weight (based on hydrogen peroxide), and the temperature was raised to 30°C to prepare a hydrogen peroxide mixture. The process was carried out with stirring at 500 rpm.

[0251] A 1 mol / L ammonia solution was continuously added to a heated hydrogen peroxide mixture at a rate of 0.1 mL / min to maintain the pH of the mixture at 1.0, thereby synthesizing FePO4. The mixture was then stirred at 500 rpm.

[0252] The synthesized FePO4 and mixtures were separated using vacuum filtration.

[0253] The separated FePO4 was mixed with an acidic solution (washing solution) prepared with distilled water and hydrochloric acid at pH 1.3, and washed by stirring at 500 rpm for 10 minutes.

[0254] After washing, FePO4 and the washing solution were separated by vacuum filtration to obtain washed FePO4.

[0255] The FePO4 after washing was vacuum dried at 80°C to obtain the final FePO4.

[0256] Example 12

[0257] FePO4 was synthesized by continuously adding an aqueous ammonia solution with a molar concentration of 1 mol / L to a heated hydrogen peroxide mixture at a rate of 0.1 mL / min to maintain the pH of the hydrogen peroxide mixture at 1.1.

[0258] Example 13

[0259] FePO4 was synthesized by continuously adding an aqueous ammonia solution with a molar concentration of 1 mol / L to a heated hydrogen peroxide mixture at a rate of 0.1 mL / min to maintain the pH of the hydrogen peroxide mixture at 1.2.

[0260] Example 14

[0261] FePO4 was synthesized by continuously adding an aqueous ammonia solution with a molar concentration of 1 mol / L to a heated hydrogen peroxide mixture at a rate of 0.1 mL / min to maintain the pH of the hydrogen peroxide mixture at 1.3.

[0262] Example 15

[0263] FePO4 was synthesized by continuously adding an aqueous ammonia solution with a molar concentration of 1 mol / L to a heated hydrogen peroxide mixture at a rate of 0.1 mL / min to maintain the pH of the hydrogen peroxide mixture at 1.4.

[0264] [Experimental Example IV: [Measurement of Impurity Content in Final FePO4]

[0265] The Al and Ti contents in the final FePO4 (Examples 1 and 7 to 10) prepared by using an impurity removal step with an ammonia solution and altering the pH of the hydrogen peroxide mixture were measured by ICP analysis, as well as the Al and Ti contents in the final FePO4 (Examples 11 to 15) prepared by altering the pH of the hydrogen peroxide mixture without an impurity removal step. The results are shown in... Figure 5 and 6 middle.

[0266] like Figure 5 As shown, in Examples 1 and 7 to 10, where an impurity removal step was performed using an ammonia solution, the Al content in the final FePO4 prepared was further reduced compared to Examples 11 to 15, where no impurity removal step was performed. Furthermore, it was confirmed that the inflow of Al increased with increasing pH of the hydrogen peroxide mixture.

[0267] In addition, such as Figure 6 As shown, in Examples 1 and 7 to 10, where the impurity removal step was performed using an ammonia solution, the Ti content decreased with increasing pH. Specifically, at pH values ​​above 1.2 (Examples 1, 9, and 10), the Ti content was significantly low. Furthermore, in Examples 11 to 15, where the impurity removal step was not performed, the Ti content was low at pH values ​​below 1.2, but increased at pH values ​​above 1.2.

Claims

1. A method for preparing FePO4 from waste lithium iron phosphate cathode, comprising: (a) A hydrogen peroxide mixture was prepared by adding an aqueous hydrogen peroxide solution to a solution containing Fe and P components; (b) Heating the hydrogen peroxide mixture; (c) To synthesize FePO4 by adding an aqueous ammonia solution to a heated hydrogen peroxide mixture; (d) Separation of synthesized FePO4; and (e) Wash the separated FePO4 with an acidic washing solution with a pH of 1.3 to 1.

6.

2. The method according to claim 1, wherein, The solution in step (a) has a pH of 0.1 to 0.

5.

3. The method according to claim 1, wherein, In step (a), the amount of the aqueous hydrogen peroxide solution added is from 0.45% to 1.2% of the solution containing Fe and P components, based on hydrogen peroxide.

4. The method according to claim 1, wherein, For the solution containing Fe and P components in step (a), an aqueous ammonia solution is added to the solution containing Fe and P components to precipitate impurities and remove the impurities.

5. The method according to claim 4, wherein, After the addition of the ammonia solution is completed, the solution containing Fe and P components has a pH of 1.0 to 1.

4.

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

7. The method according to claim 1, wherein, In step (b), the hydrogen peroxide mixture is heated to 28°C to 60°C.

8. The method according to claim 1, wherein, In step (c), after the addition of the ammonia solution is completed, the heated hydrogen peroxide mixture has a pH of 1 to 2.

9. The method according to claim 1, wherein, In step (c), after the addition of the ammonia solution is complete, the mixture is stirred for another 30 to 60 minutes.

10. The method according to claim 1, wherein, In step (c), the ammonia solution is added continuously.

11. The method according to claim 1, wherein, Based on Equation 1 below, the weight change rate of FePO4 obtained in step (e) relative to the FePO4 separated in step (d) is less than ±0.3%. [Equation 1] Weight change rate (%) = [(AB) / A)] × 100, Where A is the weight of FePO4 separated in step (d), and B is the weight of FePO4 after washing in step (e).

12. The method according to claim 1, wherein, In step (e), the solid / liquid ratio of the separated FePO4 and the acidic washing solution with a pH of 1.3 to 1.6 is 15 mL / g to 25 mL / g.

13. The method according to claim 1, wherein, In step (e), the washing includes adding the acidic washing solution and stirring for 5 to 20 minutes.

14. The method according to claim 1, wherein, In step (e), the washing includes depressurization filtration.

15. The method of claim 1, further comprising: (f) FePO4 after drying and washing.

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