Method for preparing ferric phosphate from waste lithium iron phosphate positive electrodes

Abstract

The present invention relates to a method for preparing ferric phosphate from waste lithium iron phosphate positive electrodes, and more specifically, to a method for preparing ferric phosphate from waste lithium iron phosphate positive electrodes, the method comprising the steps of: (a) adding a basic solution to a dissolution solution containing Fe and P to precipitate impurities; (b) removing impurities from the dissolution solution; and (c) adding an acidic solution to the dissolution solution removed of the impurities and adjusting the pH to 0.8 to 1.4 to prepare a storage solution containing Fe and P. The present invention has the effect of providing a method for preparing ferric phosphate from waste lithium iron phosphate positive electrodes, wherein precipitates do not form in a storage solution containing Fe and P and prepared by adding an acidic solution to a dissolution solution removed of impurities derived from waste lithium iron phosphate positive electrode materials and adjusting the pH within a predetermined range, even when the storage solution is stored at room temperature for a long period of time, and thus the storage solution is easy to store and transport, and high-purity FePO4 is prepared.

Description

Method for producing ferric phosphate from waste lithium iron phosphate anode

[0001] [Cross-reference with application(s)]

[0002] The present application claims the benefit of priority based on Korean Patent Application No. 10-2025-0008197 filed on January 20, 2025 and Korean Patent Application No. 10-2026-0007727 re-filed on January 15, 2026 based thereon, and all contents disclosed in the documents of said Korean patent applications are incorporated as part of this specification.

[0003] The present invention relates to a method for producing ferric phosphate (FePO4), a precursor of lithium iron phosphate, from a spent lithium iron phosphate anode. More specifically, the invention relates to a method for producing ferric phosphate from a spent lithium iron phosphate anode in which a storage solution prepared by adding a basic solution to a dissolved solution containing Fe and P obtained from a spent lithium iron phosphate anode material to remove impurities, then adding an acidic solution and adjusting the pH to a predetermined range, does not form a precipitate when stored at room temperature for a long time, thereby facilitating storage and transportation.

[0004] The demand for lithium-ion batteries has continuously increased since the 1990s alongside the portable electronic device market, and has recently surged globally due to the rapid expansion of the electric vehicle market. This could lead to instability in the supply and demand of lithium resources in the near future, and the continuously accumulating end-of-life waste batteries could also cause significant environmental problems. To address these issues, the recycling of used lithium-ion batteries is a critical technical challenge.

[0005] A lithium-ion battery is largely composed of a positive electrode in which a positive active material is coated on a metal foil such as aluminum, a negative electrode in which a negative active material is coated on a metal foil such as copper, a separator that prevents the positive and negative electrodes from mixing with each other, and an electrolyte that enables the movement of lithium ions between the positive and negative electrodes.

[0006] The cathode accounts for more than 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 active materials for the cathode. As the cathode contains valuable metals, methods to recover these valuable metals from spent lithium-ion battery cathodes are receiving significant attention.

[0007] Lithium iron phosphate (LiFePO4) possesses a highly stable hexahedral crystalline structure. To break down this stable structure and recover valuable metals, high concentrations of strong acids or bases are used on spent cathodes to dissolve the valuable metals, after which they are recovered as Li and FePO4. The recovered FePO4 is then dissolved again in a strong acid to create a solution of dissolved Fe and P, which is used to synthesize FePO4. However, this solution contains impurities derived from the spent cathode material, which leads to a decrease in the battery performance of the lithium iron phosphate produced from it. Furthermore, if FePO4 is synthesized after storing the solution, precipitates form in the solution, resulting in a decrease in the yield and purity of the manufactured FePO4.

[0008] Therefore, there is a need for a method to produce FePO4 from waste lithium iron phosphate cathodes that facilitates the removal of impurities derived from waste cathode materials from a solution in which Fe and P are dissolved, and prevents the formation of precipitates when the solution is stored for a long time.

[0009] [Prior Art Literature]

[0010] [Patent Literature]

[0011] Korean Patent Publication No. 2013-0113748

[0012] In order to solve the problems of the prior art described above, the present invention aims to provide a method for manufacturing FePO4 from a waste lithium iron phosphate cathode in which impurities derived from the waste cathode material are easily removed and no precipitate is formed when the dissolved solution containing Fe and P from which impurities have been removed is stored for a long time.

[0013]

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

[0015] To achieve the above objective, the present invention provides a method for producing FePO4 from a spent lithium iron phosphate cathode, characterized by comprising: I) a step of precipitating impurities by adding a basic solution to a solution containing Fe and P; (b) a step of removing impurities from the solution; and (c) a step of 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.

[0016] II) In the above I), the basic solution in step (a) may be an aqueous ammonia solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or an aqueous calcium hydroxide solution.

[0017] III) In the above I) or II), the solution containing Fe and P in step (a) may have a pH of 0.1 to 0.5.

[0018] IV) In the above I) to III), the solution in which the addition of the basic solution is completed in step (a) may have a pH of 1.7 to 2.5.

[0019] V) In the above I) to IV), step (a) may be carried out while stirring at room temperature.

[0020] VI) In the above I) to V), the basic solution in step (a) may have a basic component concentration of 0.8 to 1.3 molar (mol / L).

[0021] VII) In the above I) to VI), the basic solution may be continuously added in step (a).

[0022] VIII) In the above I) to VII), the solution of step (a) can be prepared by including: (i) a step of crushing a waste lithium iron phosphate cathode to obtain cathode material powder; (ii) a step of adding the obtained cathode material powder to an acidic solution with a concentration of 0.5 to 0.7 molar concentration (mol / L) to form a leaching solution in which lithium is dissolved and a leaching residue, and separating them; and (iii) a step of adding the separated leaching residue to an acidic solution with a concentration of 0.8 to 1.3 molar concentration (mol / L) to obtain a solution in which Fe and P are dissolved.

[0023] IX) In the above I) to VIII), the removal of impurities in step (b) may utilize vacuum filtration.

[0024] X) In the above I) to IX), the acidic solution in step (c) may be an aqueous sulfuric acid solution, an aqueous hydrochloric acid solution, or an aqueous nitric acid solution.

[0025] XI) In the above I) to X), the storage solution containing Fe and P in step (c) may have a precipitate of 0.03 g / L or less after being left at room temperature for 24 hours.

[0026] XII) In the above I) to XI), the method for producing FePO4 from the waste lithium iron phosphate cathode material may further include (d) the step of synthesizing FePO4 in a storage solution containing Fe and P.

[0027] In addition, XIII) The present invention provides a method for producing lithium iron phosphate comprising the step of producing FePO4 according to I) to XII); and the step of synthesizing lithium iron phosphate by reacting the produced FePO4 with a lithium precursor.

[0028] According to the present invention, there is an effect of providing a method for producing ferric phosphate from a waste lithium iron phosphate cathode, which allows for the easy removal of impurities derived from waste cathode material from a solution containing Fe and P, and by adding an acidic solution to the solution from which impurities have been removed and adjusting the pH to within a predetermined range, the storage solution containing Fe and P prepared does not form a precipitate even when stored at room temperature for a long time, making it easy to store and transport, and enabling the production of high-purity FePO4.

[0029] The following drawings attached to this specification illustrate embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention in conjunction with the detailed description provided below; therefore, the present invention should not be interpreted as being limited to the matters described in these drawings.

[0030]

[0031] FIG. 1 is a process diagram for a method of manufacturing FePO4 from a waste lithium iron phosphate cathode as one embodiment according to the present invention.

[0032] The inventors confirmed that by separating waste lithium iron phosphate cathode powder into a leaching solution containing lithium and a leaching residue containing Fe and P using an acidic solution, obtaining a dissolved solution containing Fe and P by leaching the leaching residue with an acidic solution, adding a basic solution to precipitate and remove impurities, and then adding an acidic solution to the dissolved solution from which impurities have been removed and adjusting the pH to a predetermined range, a storage solution containing Fe and P is prepared in which no precipitate is formed even when stored at room temperature for a long time, making storage and transportation easy, and high-purity FePO4 is produced. Based on this, they devoted themselves to further research and completed the present invention.

[0033]

[0034] The method for recovering lithium described herein will be explained in detail below.

[0035] However, terms and words used in this specification and claims cannot be interpreted as being limited to their ordinary or dictionary meanings, and must be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor may appropriately define the concept of the terms to best describe his application. Accordingly, it should be understood that the embodiments described in this specification and the configurations illustrated in the drawings are merely one embodiment of the invention and do not represent all of the technical spirit of the invention, and that there may be various equivalents and modifications that can replace them, and that they may be arranged, replaced, combined, separated, or designed into various other configurations.

[0036] All technical and scientific terms used in this description have the same meaning as commonly understood by those skilled in the art to which the present invention belongs, unless otherwise defined.

[0037]

[0038] Method for producing ferric phosphate from waste lithium iron phosphate anode

[0039] The method for producing ferric phosphate (FePO4) from a spent lithium iron phosphate cathode according to the present invention is characterized by comprising: (a) a step of precipitating impurities by adding a basic solution to a solution containing Fe and P; (b) a step of removing impurities from the solution; and (c) a step of 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. In this case, impurities derived from the spent lithium iron phosphate cathode material are easily removed from the solution, and the storage solution containing Fe and P has the effect of providing high yield and high purity FePO4 by suppressing the formation of precipitates even when stored at room temperature for a long time.

[0040]

[0041] The method for manufacturing FePO4 from waste lithium iron phosphate cathodes is described in detail below, divided into steps.

[0042]

[0043] (a) A step of adding a basic solution to a dissolved solution containing Fe and P to precipitate impurities.

[0044] The method for producing ferric phosphate from a spent lithium iron phosphate cathode of the present invention may include the step of (a) adding a basic solution to a dissolved solution containing Fe and P to precipitate impurities, and in this case, there is an advantage that the purity of the produced FePO4 is greatly improved.

[0045]

[0046] The solution containing Fe and P in step (a) above may, for example, have a pH of 0.1 to 0.5, preferably 0.2 to 0.4, and has the advantage of facilitating the leaching of Fe and P within this range.

[0047] In the present description, the solution containing Fe and P may be a compound or ion containing Fe and a compound or ion containing P, preferably an ion containing Fe and an ion containing P, and specifically, the ion containing Fe is Fe 2+ , Fe 3+ , or a mixture thereof, and ions containing P are PO4 3- , PO3 3- , and HPO3 2- It may be one or more types selected from the group consisting of

[0048]

[0049] In this description, pH measurement can be performed using measurement methods commonly used in the technical field to which this invention belongs, and unless otherwise specified, it can be measured using a general pH measuring device at room temperature, specifically using a METTLER TOLEDO SevenDirect SD30.

[0050] In this description, room temperature may be one point within the range of 20 ± 5 ℃.

[0051]

[0052] The solution containing Fe and P in step (a) above may, for example, contain 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, and in this case, there is an advantage of producing high yield and high purity FePO4.

[0053] The solution containing Fe and P in step (a) above may, for example, 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, and in this case, there is an advantage of producing high yield and high purity FePO4.

[0054] The solution containing Fe and P in step (a) above may, for example, contain lithium 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, and even more preferably 100 to 250 ppm, and in this case, there is an advantage of producing high-purity FePO4.

[0055] In this specification, ppm is based on weight unless otherwise defined.

[0056]

[0057] In this description, Fe, P, and Li can be measured by ICP analysis of the leachate. Specifically, 0.2 g of the leachate is taken, placed in a conical tube, and its exact weight is measured. Then, 0.1 ml of nitric acid with a concentration of 70 wt% is added to it, followed by the addition of 500 µl of an internal standard (scandium) with a concentration of 1000 g / kg, and the solution is diluted with ultrapure water to a volume of 50 ml for measurement by ICP analysis.

[0058]

[0059] In step (a) above, the basic solution may be, for example, an aqueous ammonia solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or an aqueous calcium hydroxide solution, and preferably an aqueous ammonia solution. In this case, there is an advantage that impurities derived from waste lithium iron phosphate cathode material, such as aluminum and titanium, are easily precipitated in the solution containing Fe and P.

[0060]

[0061] After the addition of the above basic solution is completed, the solution containing Fe and P may have a pH of, for example, 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, impurities derived from waste lithium iron phosphate cathode material, such as aluminum and titanium, which are leached together with Fe and P in the solution, are precipitated and have the advantage of being easily removed in a subsequent process.

[0062]

[0063] Step (a) above can be performed by adding a basic solution to the solution, for example, while stirring, and in this case, there is an advantage that impurities in the solution are precipitated within a short time.

[0064] The above stirring speed may be, for example, 300 to 700 rpm, preferably 350 to 600 rpm, more preferably 400 to 550 rpm, and within this range, there is an advantage that impurities in the solution are precipitated within a short time.

[0065]

[0066] In step (a) above, the basic solution may, for example, have a basic component concentration of 0.8 to 1.3 molar (mol / L), preferably 0.9 to 1.2 molar, more preferably 0.9 to 1.1 molar, and within this range, there is an advantage that the pH of the solution containing Fe and P is easy to control.

[0067]

[0068] In step (a) above, the basic solution can be continuously introduced, for example, and in this case, there is an advantage that impurities derived from the waste lithium iron phosphate cathode material, such as aluminum and titanium, are precipitated and easily removed.

[0069] In this description, the term "continuous feeding" means that it is not "batch feeding," and refers to feeding in a drop-by-drop, little-by-little, step-by-step, or continuous flow manner for at least 10 minutes, preferably at least 30 minutes, within the leaching time range.

[0070]

[0071] The solution of step (a) above can be prepared by, for example, (i) crushing a waste lithium iron phosphate cathode to obtain cathode material powder; (ii) introducing the obtained cathode material powder into an acidic solution with a concentration of 0.5 to 0.7 molar (mol / L) to form a leaching solution in which lithium is dissolved and a leaching residue, and separating them; and (iii) introducing the separated leaching residue into an acidic solution with a concentration of 0.8 to 1.3 molar (mol / L) to obtain a solution in which Fe and P are dissolved; and in this case, there is an advantage of synthesizing FePO4 in a high yield.

[0072]

[0073] In this description, the positive electrode refers to a positive electrode active material layer comprising a positive electrode active material, a binder, and a conductive material coated on a current collector.

[0074] In this description, the term "anode material" means that it includes an anode active material or is an anode active material.

[0075]

[0076] The above-mentioned spent lithium iron phosphate cathode may include, for example, a cathode active material having an olivine structure, and in this case, it has the advantages of excellent high-temperature stability and lifespan characteristics and low cost.

[0077] In this description, the olivine structure is a type of cathode active material structure with a hexahedron-shaped lattice structure in a 3D form. Since PO (phosphorus-oxygen) is strongly bonded, it can maintain its structure even if all lithium ions are removed, resulting in minimal performance degradation due to charging and discharging and excellent thermal stability. Additionally, it is economical because it uses inexpensive iron instead of expensive cobalt metal, but it has a lower energy density compared to other cathode materials, and has low electrical conductivity and lithium ion diffusion.

[0078] The above olivine structure can be confirmed through X-ray diffraction analysis (XRD).

[0079]

[0080] The positive active material having the above olivine structure may be, for example, a compound represented by the following chemical formula 1, and in this case, it has the advantages of excellent high-temperature stability and lifespan characteristics and low cost.

[0081] [Chemical Formula 1]

[0082]

[0083] (In the above chemical formula 1, M comprises 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 comprises one or more elements selected from the group consisting of F, S, and N, and a, b, and c are each -0.5≤a≤0.5, 0≤b≤0.5, and 0≤c≤0.1.)

[0084]

[0085] The positive electrode active material having the above olivine structure may preferably include lithium iron phosphate (LiFePO4), in which case it has excellent high-temperature stability and lifespan characteristics and has the advantage of being inexpensive.

[0086]

[0087] The positive electrode of the above-mentioned waste lithium-ion battery may be, for example, a discarded lithium-ion battery positive electrode, a defective product generated during the positive electrode coating process, or a positive electrode scrap discarded after cutting the electrode plate; preferably, it may be a discarded lithium-ion battery positive electrode, and in this case, there are eco-friendly and economic advantages in recycling resources by recovering FePO4, etc., along with expensive lithium.

[0088]

[0089] In step (i) above, grinding can be performed using, for example, dry grinding equipment, specifically using a hand mill, pin mill, disc mill, cutting mill, hammer mill, or blender. In this case, the current collector is finely cut into pieces, and the waste anode material is separated from the current collector pieces, which has the advantage of facilitating subsequent processes.

[0090]

[0091] The above-mentioned crushed waste anode can be obtained as waste anode material powder, for example, through sieving. In this case, the current collector remains on the top of the mesh while the waste anode material passes through the mesh, thereby separating them and further obtaining a powder of uniform size.

[0092] The above sieving can be performed, for example, with 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 size of the waste cathode material powder is homogenized, which has the advantage of facilitating leaching in the subsequent leaching step.

[0093] In this description, the sieve is not particularly limited as long as it follows the definition of the present invention and uses a method or device defined in the art to which the present invention belongs.

[0094] In this description, waste anode material powder refers to a waste anode obtained in powder form by crushing or sieving after crushing, and most of the current collectors are removed from the waste anode, and a small amount of current collectors with a particle size of about a few micrometers may be included.

[0095]

[0096] In step (ii) above, the acidic solution may be a solution containing one or more selected from the group consisting of, for example, 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 which case lithium is easily leached and Fe and P remain as leaching residues, which has the advantage.

[0097]

[0098] The above acidic solution may preferably be an acidic aqueous solution, in which case there is an advantage that lithium is easily and selectively leached out while Fe and P remain as leaching residues.

[0099]

[0100] In step (ii) above, the acidic solution may more preferably be sulfuric acid, and may be sulfuric acid with an acid concentration more preferably 0.5 to 0.7 molar concentration (mol / L), particularly preferably 0.55 to 0.65 molar concentration, and within this range, lithium is easily leached and Fe and P remain as leaching residues, which has the advantage.

[0101] In step (ii) above, the solid-liquid ratio of the anode powder and the acidic solution may be, for example, 7 to 15 mL / g, preferably 8 to 13 mL / g, more preferably 9 to 12 mL / g, and within this range, lithium is easily and selectively leached out, while Fe and P remain as leaching residues, which has the advantage.

[0102] In this description, the solid-to-liquid ratio refers to the volume of liquid relative to the weight of the solid, that is, the volume of acidic solution (mL) relative to the anode powder content (g).

[0103]

[0104] In this description, leaching refers to the selective dissolution of metal elements or compounds contained in a solid material using a solvent such as an inorganic acid, organic acid, or alkali.

[0105]

[0106] In the above step (ii), separation can preferably be carried out using vacuum filtration. In this case, the leachate and leachate residue are easily separated with only a simple process, process costs are reduced, and there are environmentally friendly advantages.

[0107]

[0108] In step (iii) above, the acidic solution may be a solution containing one or more selected from the group consisting of, for example, 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 which case there is an advantage that Fe and P are easily leached from the leaching residue obtained in step (ii).

[0109] The above acidic solution may preferably be an acidic aqueous solution, in which case there is an advantage that Fe and P are easily leached out.

[0110]

[0111] In step (iii) above, the acidic solution may more preferably be sulfuric acid, and the acid concentration may more preferably be 0.8 to 1.3 molar concentration (mol / L), particularly preferably 0.9 to 1.2 molar concentration, and particularly more preferably 0.9 to 1.1 molar concentration, and within this range, Fe and P are sufficiently leached, which has the economic advantage of increasing the yield of FePO4.

[0112] The reason the molar concentrations of the acidic solution in step (ii) and the acidic solution in step (iii) are different is that the molar concentration of the acidic solution in step (ii) is in a range that facilitates the leaching of lithium from the cathode material powder, and the molar concentration of the acidic solution in step (iii) is in a range that facilitates the leaching of Fe and P from the separated leaching residue; since the targets for leaching are different in steps (ii) and (iii), the molar concentrations of the acidic solutions are different.

[0113]

[0114] (b) Step of removing impurities from the solution

[0115] The method for producing ferric phosphate from a waste lithium iron phosphate cathode of the present invention may include (b) a step of removing impurities from a solution, in which case there is an advantage of improving the yield and purity of FePO4.

[0116]

[0117] The above-mentioned solution from which impurities have been removed may, for example, have a pH of 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 a basic solution is added to the solution and impurities are removed, the pH may be the same as or similar to the pH of the solution into which the basic solution was added.

[0118]

[0119] The separation of the dissolved solution and impurities into which the above basic solution has been introduced can be achieved, for example, by using reduced-pressure filtration, and in this case, there is an advantage that the dissolved solution and impurities can be easily separated with only a simple process.

[0120] The above vacuum filtration may preferably be vacuum vacuum filtration, specifically vacuum vacuum filtration using a filtration flask, and in this case, there is an advantage that FePO4 is easily separated.

[0121] In the present invention, vacuum reduced pressure filtration is not particularly limited to conventional vacuum reduced pressure filtration in the technical field to which the present invention belongs, and may include, for example, filtration in a partial vacuum state or a low pressure state.

[0122]

[0123] The above separated impurities may include, for example, Fe and P in addition to Al and Ti, and in this case, Fe and P can be recovered by leaching the separated impurities again into an acidic solution.

[0124]

[0125] (c) a step of preparing a storage solution containing Fe and P by adding an acidic solution to a dissolved solution from which impurities have been removed and adjusting the pH to 0.8 to 1.4.

[0126] The method for producing ferric phosphate from a spent lithium iron phosphate cathode according to the present invention may include the step of (c) introducing an acidic solution into a dissolved solution from which impurities have been removed and adjusting the pH to 0.8 to 1.4 to produce a storage solution containing Fe and P. In this case, since no precipitate is formed even when the storage solution is stored for a long time, there is an advantage that high-purity FePO4 can be produced even when transported or synthesized after long-term storage. In addition, by adjusting the pH to 0.8 to 1.4, the pH of the storage solution can be raised with a small amount of basic solution in the subsequent step of synthesizing FePO4, which provides process and economic advantages.

[0127] Meanwhile, even if the pH of the storage solution is lowered to less than 0.8, no precipitate is formed, but in this case, an excess amount of basic solution must be added to raise the pH in the subsequent process, the FePO4 synthesis step, which is disadvantageous in terms of process and economy.

[0128] The above precipitate may, for example, include iron phosphate synthesized in a storage solution in which the stoichiometric ratio of Fe and P is not matched.

[0129]

[0130] In step (c) above, the acidic solution may be, for example, an aqueous sulfuric acid solution, an aqueous hydrochloric acid solution, or an aqueous nitric acid solution, and preferably an aqueous hydrochloric acid solution, in which case there is an advantage of easy pH adjustment of the solution.

[0131]

[0132] In step (c) above, the acidic solution may contain, for example, 25 to 40 weight% of an acid component, preferably 25 to 37 weight%, more preferably 27 to 35 weight%, and even more preferably 29 to 32 weight%, and in this case, there is an advantage that the pH of the solution can be easily adjusted.

[0133]

[0134] In step (c) above, the storage solution may have a pH of, for example, 0.8 to 1.4, preferably 0.8 to 1.3, more preferably 0.9 to 1.2, and even more preferably 0.9 to 1.1. Within this range, no precipitate is formed even when stored at room temperature for a long time, making storage and transportation easy, and improving the yield and purity of FePO4. There is also the advantage of reducing the amount of basic solution required to raise the pH in the subsequent process of synthesizing FePO4.

[0135]

[0136] In step (c) above, the storage solution containing Fe and P may have a precipitate formed after being left at room temperature for 24 hours, for example, 0.03 g / L or less, preferably 0.02 g / L or less, more preferably 0.01 g / L or less, even more preferably 0.001 g / L or less, and even more preferably 0.0001 to 0.001 g / L. Since no precipitate is formed even when stored for a long time within this range, there is an advantage of easy storage and transportation and improved yield and purity of FePO4.

[0137] The precipitate generated in the present invention can be separated by filtering the storage solution, and the separated precipitate can be measured by dry weight.

[0138]

[0139] (d) A step of synthesizing FePO4 in a storage solution containing Fe and P

[0140] The method for producing ferric phosphate from a waste lithium iron phosphate cathode of the present invention may further include (d) a step of synthesizing FePO4 in a storage solution containing Fe and P, in which case there is an advantage of synthesizing FePO4 with high yield and high purity, as no precipitate is formed even after long-term storage at room temperature due to transportation and storage.

[0141]

[0142] The step of synthesizing FePO4 in the above-mentioned storage solution containing Fe and P may include, for example, (di) a step of preparing a hydrogen peroxide mixture by adding an aqueous hydrogen peroxide solution to the storage solution containing Fe and P; (d-ii) a step of heating the hydrogen peroxide mixture; (d-iii) a step of synthesizing FePO4 by adding an aqueous ammonia solution to the heated hydrogen peroxide mixture; (d-iv) a step of separating the synthesized FePO4; and (dv) a step of washing the separated FePO4 with an acidic washing solution having a pH of 1.3 to 1.6; in this case, impurities derived from the waste lithium iron phosphate cathode material are easily removed, and the generation of new by-products is suppressed.

[0143]

[0144] In the above (di) step, an aqueous hydrogen peroxide solution can be added in an amount that is, for example, 0.45 to 1.2 volume% of the solution based on hydrogen peroxide, preferably 0.5 to 1 volume% of the solution, and more preferably 0.6 to 1 volume% of the solution, and there is an advantage that the synthesis of FePO4 is easy within this range.

[0145] The above-mentioned aqueous hydrogen peroxide solution may, for example, have a concentration of 25 to 40 weight%, preferably 27 to 35 weight%, more preferably 29 to 33 weight%, and within this range, there is an advantage that the synthesis of FePO4 is easy without the generation of by-products.

[0146]

[0147] The above hydrogen peroxide mixture may, for example, have a pH of 0.1 to 0.7, preferably 0.2 to 0.6, and more preferably 0.3 to 0.5, and within this range Fe is Fe 3+ It has the effect of facilitating the synthesis of FePO4 while suppressing the generation of by-products by maintaining it.

[0148]

[0149] In step (di) above, the temperature rise resulting from the addition of an aqueous hydrogen peroxide solution to the storage solution containing Fe and P is minimal; for example, the mixed solution prepared after the addition of the aqueous hydrogen peroxide solution is less than 28°C, 27°C or lower, or 26°C or lower, and as a specific example, it may be 20°C or higher or room temperature. Therefore, in order for FePO4 synthesis to proceed easily, the temperature of the hydrogen peroxide mixed solution must be raised.

[0150] In step (d-ii) above, the heating can be performed by heating the hydrogen peroxide mixture to, for example, 28 to 60 ℃, preferably 28 to 55 ℃, more preferably 30 to 50 ℃, and even more preferably 30 to 42 ℃, and there is an advantage that FePO4 synthesis is easily carried out within this range.

[0151]

[0152] After the addition of the aqueous ammonia solution is completed in step (d-iii) above, the pH may be, for example, pH 1 to 2, preferably pH 1.1 to 1.7, more preferably pH 1.2 to 1.5, and there is an advantage that FePO4 is synthesized in high yield within this range.

[0153]

[0154] In step (d-iii) above, the addition of an aqueous ammonia solution to the hydrogen peroxide mixture can be carried out, for example, while stirring, and in this case, there is an advantage that FePO4 is easily synthesized.

[0155] The above stirring speed may be, for example, 300 to 700 rpm, preferably 350 to 600 rpm, more preferably 400 to 550 rpm, and there is an advantage that FePO4 is easily synthesized within this range.

[0156] In step (d-iii) above, the aqueous ammonia solution can be continuously fed, for example, and in this case, there is an advantage that FePO4 is synthesized stably without side reactions.

[0157] After the addition of the aqueous ammonia solution is completed in step (d-iii) above, stirring can be performed for, for example, 30 to 60 minutes, preferably 35 to 55 minutes, more preferably 40 to 50 minutes, and in this case, there is an advantage that FePO4 is synthesized stably without side reactions.

[0158] In step (d-iii) above, an aqueous ammonia solution is added, and after the addition is completed, additional stirring can preferably be performed at a heated temperature. In this case, there is an advantage that the synthesis of FePO4 is carried out stably without side reactions.

[0159]

[0160] The step (d-iv) of separating the synthesized FePO4 above may utilize vacuum filtration, for example, and in this case, there is an advantage that the synthesized FePO4 is easily separated.

[0161] The above vacuum filtration may preferably be vacuum vacuum filtration, specifically vacuum vacuum filtration using a filtration flask, and in this case, there is an advantage that FePO4 is easily separated.

[0162]

[0163] The FePO4 separated in step (dv) above is washed with an acidic washing solution having a pH of 1.3 to 1.6, for example. In this case, impurities are easily removed and no by-products are generated by the re-leaching of FePO4, which has the advantage of increasing the purity of the synthesized FePO4.

[0164] The above acidic washing solution with a pH of 1.3 to 1.6 can be prepared, for example, by adding sulfuric acid, hydrochloric acid, or a mixture thereof to distilled water, and preferably by adding hydrochloric acid. In this case, there is an advantage that the acidic washing solution is easy to prepare and impurities can be easily removed.

[0165]

[0166] The above acidic washing solution may preferably have a pH of 1.3 to 1.5, more preferably 1.3 to 1.4, and within this range, impurities are easily removed and no by-products are generated by the re-leaching of FePO4, which has the advantage of increasing the purity of the synthesized FePO4.

[0167] In the above (dv) step, the solid-liquid ratio of the separated FePO4 and the acidic washing solution may be, for example, 15 to 25 mL / g, preferably 17 to 23 mL / g, more preferably 19 to 22 mL / g, and within this range, there is an advantage that impurities are reduced and no by-products are generated.

[0168]

[0169] In the above (dv) step, washing can be performed by adding an acidic washing solution to the separated FePO4 and stirring for, for example, 5 to 20 minutes, preferably 5 to 15 minutes, more preferably 10 to 15 minutes, and in this case, there is an advantage that impurities are reduced and by-products are not generated.

[0170]

[0171] In the above (dv) step, washing may include, for example, vacuum filtration, in which case there is an advantage of easily separating FePO4 and the acidic washing solution.

[0172]

[0173] The above (dv) step may further include a step of drying the washed FePO4, in which case the washed FePO4 has the effect of being stably transported and stored.

[0174]

[0175] The above drying can preferably be vacuum drying, and as a specific example, it can be carried out under vacuum at 70 to 200°C, more preferably at 80 to 130°C, until there is no further change in weight, and as an example, for 1 to 24 hours, and within this range, it has the effect of efficiently removing moisture contained in the washed FePO4.

[0176]

[0177] In the present invention, vacuum drying is not particularly limited to vacuum drying methods and / or conditions commonly practiced in the technical field to which the present invention belongs, and may include, for example, drying in a partial vacuum state or a low-pressure state.

[0178]

[0179] Since the manufactured FePO4 is produced using a storage solution containing Fe and P according to the present invention, which does not generate precipitates even after long-term storage, it has the advantage of not being significantly limited by time during manufacturing and having no changes in recovery rate, purity, or physical properties over time.

[0180]

[0181] Method for manufacturing lithium iron phosphate (LFP)

[0182] The method for manufacturing lithium iron phosphate (LFP) according to the present invention may include (e) a step of synthesizing lithium iron phosphate by reacting the FePO4 produced in step (d) with a lithium precursor, and in this case, by easily manufacturing lithium iron phosphate, there is an effect of recycling resources and providing excellent economic advantages.

[0183]

[0184] The above step (e) may be prepared by including, for example, (e-1) a step of preparing lithium iron phosphate by adding a lithium precursor to prepared FePO4 and calcining it; (e-2) a step of preparing a lithium iron phosphate solution by mixing a solution containing a carbon source with the calcined lithium iron phosphate; (e-3) a step of spray-drying the prepared lithium iron phosphate solution; and (e-4) a step of reducing the dried lithium iron phosphate; in this case, the particle size and particle size distribution of the prepared lithium iron phosphate are evenly controlled, the crystal structure has an olivine structure, and there is an advantage of being able to provide good battery characteristics when applied to a secondary battery.

[0185] The above lithium precursor may include, for example, one or more of LiOH, Li2CO3, LiNO3, and Li2O, and in this case, there is an advantage in that lithium iron phosphate having an olivine structure is synthesized.

[0186] In the above step (e-1), calcination can be carried out, for example, at 600 to 800 ℃, preferably at 650 to 750 ℃, and within this range, lithium is easily intercalated into FePO4 to synthesize lithium iron phosphate, which has the advantage of excellent high-temperature stability and lifespan characteristics when applied to a secondary battery.

[0187] In this description, intercalation refers to the reaction in which lithium ions are inserted into a crystal structure.

[0188] In the above step (e-1), calcination can be carried out for, for example, 8 to 12 hours, preferably 9 to 11 hours, more preferably 9.5 to 10.5 hours, and within this range, lithium is intercalated in FePO4 to synthesize lithium iron phosphate, and the generation of impurities is reduced, so that when applied to a secondary battery, the charge / discharge characteristics are excellent.

[0189] In the above step (e-1), the firing can be carried out, for example, under an inert atmosphere, and preferably under a nitrogen atmosphere, in which case there is an advantage that oxidation is prevented.

[0190] In the above step (e-2), the carbon source may be one or more selected from the group consisting of, for example, glucose, sucrose, fructose, galactose, lactose, maltose, polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenolic resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene difluoride, polyacrylonitrile, polyvinyl chloride, and asphalt. In this case, there are advantages such as easy and economical coating, and excellent improvement of battery characteristics.

[0191] The above solvent is not particularly limited as long as it is a solvent commonly used in coating agents in the technical field to which the present invention belongs, and preferably may be an aqueous solvent, more preferably may be water, and even more preferably may be deionized water.

[0192] In this description, the aqueous solvent is not particularly limited to any aqueous solvent commonly used in the technical field to which the present invention belongs, and for example, it is a water-based solvent, and for specific examples, water or water mixed with other components may be used.

[0193] The above carbon source may be, for example, 1 to 20 parts by weight, preferably 5 to 18 parts by weight, and more preferably 7 to 15 parts by weight based on 100 parts by weight of lithium iron phosphate, and within this range, a carbon coating layer is uniformly formed on the surface of the lithium iron phosphate, thereby improving the electrical conductivity of the lithium iron phosphate and improving the capacity characteristics and battery characteristics of the secondary battery containing it.

[0194]

[0195] In the above step (e-2), the mixing of the solution containing the calcined lithium iron phosphate and the carbon source can be performed, for example, by milling, preferably using a ball mill, a high energy ball mill, a vibrating mill, or a roll mill, and more preferably using a ball mill. In this case, the lithium iron phosphate and the solution containing the carbon source are mixed uniformly, which has the advantage of uniformly forming a carbon coating layer on the lithium iron phosphate in a subsequent step.

[0196] In the above step (e-2), milling can be performed for, for example, 2 to 20 hours, preferably 5 to 18 hours, more preferably 10 to 16 hours, and even more preferably 12 to 16 hours, and within this range, there is an advantage of suppressing the generation of fine particles and smoothly controlling the particle size distribution of lithium iron phosphate to a narrow range.

[0197]

[0198] In step (e-3) above, by spray-drying the prepared lithium iron phosphate solution, a carbon source is evenly coated onto the lithium iron phosphate, which has the advantage of uniformly forming a carbon coating layer on the surface of the lithium iron phosphate in the subsequent reduction heat treatment step.

[0199] The above spray drying method may be used without particular limitation if it is a spray drying method and / or equipment commonly used in the technical field to which the present invention belongs. Examples include, but are not limited to, an ultrasonic spray drying device, an air nozzle spray drying device, an ultrasonic nozzle spray drying device, a filter expansion droplet generator, or an electrostatic spray drying device.

[0200]

[0201] In the above (e-4) step, the reduction heat treatment can be carried out, for example, at 500 to 700 ℃, preferably at 550 to 650 ℃, and within this range, carbon is coated on the surface of the lithium iron phosphate, which has the advantage of improving electrical conductivity.

[0202] In the above (e-4) step, the reduction heat treatment can be carried out for, for example, 3 to 6 hours, preferably 4 to 5 hours, more preferably 3.5 to 4.5 hours, and within this range, there is an advantage of improving the electrical conductivity of lithium iron phosphate.

[0203] In the above (e-4) step, the reduction heat treatment can be carried out, for example, under an inert atmosphere, and preferably under a nitrogen atmosphere, in which case there is an advantage that oxidation of the carbon source is prevented.

[0204]

[0205] The lithium iron phosphate recovered after reduction heat treatment in the above step (e-4) may further include, for example, a milling step (e-5). In this case, aggregation, particle breakage, and the generation of fine particles in the finally obtained regenerated lithium iron phosphate are prevented, and the particle size distribution can be controlled within a narrow range. Additionally, there is an advantage in that battery performance degradation caused by fine particles is prevented, and the thermal stability and lifespan characteristics of the battery are further improved. Furthermore, there is an advantage in that when the regenerated lithium iron phosphate is ultimately applied to the cathode of a secondary battery, it can provide good battery characteristics equivalent to or better than those of a fresh cathode active material.

[0206]

[0207] In the above step (e-5), the milling may be, for example, a jet mill, and in this case, while preventing damage to the crystal structure of lithium iron phosphate, the particle size and particle distribution of the finally obtained regenerated lithium iron phosphate can be precisely controlled within a narrow range, and there is also an advantage that the purity of the regenerated lithium iron phosphate is improved by preventing the ingress of foreign substances that may occur during the milling process.

[0208]

[0209] Figure 1 below is a flowchart of a method for manufacturing FePO4 from a waste lithium iron phosphate cathode as one embodiment according to the present invention.

[0210]

[0211] Referring to FIG. 1, first, a spent lithium iron phosphate cathode is prepared (step S10).

[0212] The above waste lithium iron phosphate anode may preferably be a discarded lithium-ion battery anode, a defective product generated during the anode coating process, or an anode scrap discarded after cutting the electrode plate, and preferably, a discarded lithium-ion battery anode may be prepared.

[0213] The above-mentioned anode has a structure in which an anode active material and a conductive material are bonded to an aluminum foil by a binder.

[0214] The above-mentioned anode may include an anode active material having an olivine structure, and preferably may be lithium iron phosphate (LiFePO4) having an olivine structure, in which case it has excellent high-temperature stability and lifespan characteristics and has the advantage of being inexpensive.

[0215]

[0216] Next, the waste lithium iron phosphate anode is crushed to obtain waste anode material powder (step S20).

[0217] The above grinding can be performed using dry grinding equipment, specifically using a hand mill, pin mill, disc mill, cutting mill, hammer mill, or blender. As a specific example, grinding is performed using a blender, and in this case, the current collector is cut into small pieces and the anode material separates from the current collector, thus providing the advantage of easily separating the current collector and the anode material.

[0218]

[0219] The above-mentioned crushed waste anode can be separated from the current collector, for example, through a sieve, and obtained as waste anode material powder of uniform size.

[0220] The above sieving can preferably be performed using a sieve with a mesh size of 120 to 250, specifically a sieve with a mesh size of 200, in which case the current collector is removed and waste cathode material powder of uniform size can be obtained.

[0221]

[0222] Next, waste cathode material powder is introduced into an acidic solution with a concentration of 0.5 to 0.7 molar (mol / L) to form a leaching solution in which lithium is dissolved and a leaching residue, and these are separated (step S30).

[0223] The above acidic solution may be a solution containing one or more selected from the group consisting of, for example, sulfuric acid, hydrochloric acid, hypochlorous acid, nitric acid, carbonic acid, acetic acid, and oxalic acid, and specifically may be an aqueous sulfuric acid solution, in which case lithium is easily and selectively leached and Fe and P remain as leaching residues, which has the advantage.

[0224] The above acidic solution may preferably be an acidic aqueous solution, in which case there is an advantage that lithium is easily and selectively leached out while Fe and P remain as leaching residues.

[0225]

[0226] The acidic solution may preferably have an acid concentration of 0.55 to 0.65 molar concentration (mol / L), and as a specific example, may be 0.6 molar concentration. In this case, there is an advantage that lithium is easily and selectively leached out while Fe and P remain as leaching residues.

[0227] 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, and as a specific example, 10 mL / g. In this case, lithium is sufficiently leached, but Fe and P are not leached and remain as leaching residue, which has the advantage.

[0228]

[0229] Next, the lithium-dissolved leaching solution and the leaching residue are separated (step S40).

[0230] The above separation can preferably be performed using vacuum filtration, in which case the leachate and leachate residue are easily separated with only a simple process, reducing process costs and offering the advantages of being environmentally friendly.

[0231]

[0232] Next, the separated leaching residue is added to an acidic solution with a concentration of 0.8 to 1.3 molar (mol / L) to obtain a dissolved solution containing Fe and P (step S50).

[0233] The above acidic solution may be a solution containing one or more selected from the group consisting of, for example, sulfuric acid, hydrochloric acid, hypochlorous acid, nitric acid, carbonic acid, acetic acid, and oxalic acid, and specifically may be an aqueous sulfuric acid solution, in which case there is an advantage of leaching Fe and P.

[0234] The above acidic solution may preferably be an acidic aqueous solution, in which case there is an advantage that Fe and P are easily leached out.

[0235]

[0236] The acidic solution above may preferably have an acid concentration of 0.9 to 1.2 molar, and as a specific example, may have a concentration of 1.0 molar. In this case, Fe and P are sufficiently leached from the leaching residue obtained in step S40, so the yield of FePO4 is increased, which has an economic advantage.

[0237]

[0238] The above-mentioned solution containing Fe and P may preferably have a pH of 0.1 to 0.5, and as a specific example, may have a pH of 0.2 to 0.4, and there is an advantage that Fe and P exist in a leached state within this range.

[0239]

[0240] Next, a basic solution is added to the solution containing Fe and P (step S60).

[0241] Step S60 has the advantage of significantly improving the purity of the FePO4 produced by adding a basic solution to a dissolved solution containing Fe and P to precipitate and remove impurities.

[0242] The above-mentioned solution containing Fe and P may contain Fe at a concentration of 23,000 ppm or more, for example, 27,000 ppm, and in this case, there is an advantage in producing high yield and high purity FePO4.

[0243] The above-mentioned solution containing Fe and P may contain P at a concentration of 10,000 ppm or more, for example, 15,000 ppm, and in this case, there is an advantage in producing high yield and high purity FePO4.

[0244] The above-mentioned solution containing Fe and P may contain lithium at a concentration of 500 ppm or less, for example, and 250 ppm as a specific example, and in this case, there is an advantage in producing high-purity FePO4.

[0245]

[0246] The above basic solution may be, for example, an aqueous ammonia solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or an aqueous calcium hydroxide solution, and specifically, an aqueous ammonia solution. In this case, there is an advantage that impurities derived from waste lithium iron phosphate cathode material, such as aluminum and titanium, are precipitated and easily removed.

[0247]

[0248] The above basic solution may, for example, have a basic component concentration of 0.8 to 1.3 molar (mol / L), preferably 0.9 to 1.2 molar, more preferably 0.9 to 1.1 molar, and as a specific example, may have a concentration of 1 molar. In this case, pH adjustment is easy, and there is an advantage that impurities derived from waste lithium iron phosphate cathode material, such as aluminum and titanium, are precipitated and easily removed.

[0249] After the addition of the above basic solution is completed, the solution may preferably have a pH of 1.7 to 2.5, and as a specific example, a pH of 1.8. In this case, there is an advantage that impurities derived from the waste lithium iron phosphate cathode material, such as aluminum and titanium, are precipitated and easily removed.

[0250] The above basic solution can be continuously added to the solution, and in this case, there is an advantage that impurities derived from waste lithium iron phosphate cathode material, such as aluminum and titanium, are precipitated and easily removed.

[0251] The above basic solution can be added, for example, under stirring, and in this case, there is an advantage that impurities precipitate within a short time.

[0252]

[0253] Next, impurities are removed from the solution into which the basic solution has been added (step S70).

[0254] The removal of the dissolved solution and impurities into which the above basic solution has been introduced can preferably be performed using reduced-pressure filtration, and in this case, there is an advantage that the dissolved solution and impurities can be easily separated with only a simple process.

[0255]

[0256] Next, an acidic solution is added to the solution from which impurities have been removed and adjusted to a pH of 0.8 to 1.4 to prepare a storage solution containing Fe and P (step S80).

[0257] The above acidic solution may be, for example, an aqueous sulfuric acid solution, an aqueous hydrochloric acid solution, or an aqueous nitric acid solution, and specifically, an aqueous hydrochloric acid solution, in which case there is an advantage in that the pH of the storage solution can be easily adjusted.

[0258] The above acidic solution may, for example, contain 25 to 40 weight percent of an acid component, and specifically, 30 weight percent, and in this case, there is an advantage that the pH of the solution can be easily adjusted.

[0259]

[0260] The above storage solution may preferably have a pH of 0.8 to 1.4, and as a specific example, may have a pH of 1. In this case, no precipitate is formed even when stored at room temperature for a long time, making storage and transportation easy, and the yield and purity of FePO4 are improved. Additionally, the amount of basic solution required to raise the pH in the subsequent step of synthesizing FePO4 is reduced, providing process and economic advantages.

[0261] The above storage solution may have a precipitate formed after being left at room temperature for 24 hours, for example, of 0.03 g / L or less, preferably 0.02 g / L or less, more preferably 0.01 g / L or less, even more preferably 0.001 g / L or less, and even more preferably 0.0001 to 0.001 g / L. Since no precipitate is formed even when stored for a long time within this range, there is an advantage of easy storage and transportation and improved yield and purity of FePO4.

[0262]

[0263] Next, an aqueous hydrogen peroxide solution is added to a storage solution containing Fe and P to prepare a hydrogen peroxide mixture (step S90).

[0264] In step S90, the aqueous hydrogen peroxide solution can preferably be added in an amount of 0.45 to 1.2 volume% of the storage solution based on hydrogen peroxide, and as a specific example, can be added in an amount of 0.6 to 1.0 volume% of the storage solution, and in this case, there is an advantage that the synthesis of FePO4 is easy.

[0265] The above aqueous hydrogen peroxide solution may preferably have a concentration of 25 to 40 weight%, and as a specific example, 30 weight%, in this case Fe is Fe 3+ It has the effect of facilitating the synthesis of FePO4 while suppressing the generation of by-products by maintaining it.

[0266]

[0267] Next, the hydrogen peroxide mixture is heated (step S100).

[0268] The above hydrogen peroxide mixture can preferably be heated to 28 to 60°C, and as a specific example, to 30°C, in which case there is an advantage that FePO4 synthesis is easy.

[0269]

[0270] Next, FePO4 is synthesized by adding an aqueous ammonia solution to a heated hydrogen peroxide mixture (step S110).

[0271] After adding an aqueous ammonia solution to the heated hydrogen peroxide mixture, the pH can preferably be 1 to 2, and as a specific example, 1.2, and in this case, there is an advantage that FePO4 is synthesized in a high yield.

[0272] In step S110, the aqueous ammonia solution can preferably be introduced while stirring, and more preferably while stirring at 300 to 700 rpm, and as a specific example, while stirring at 500 rpm, in this case there is an advantage that FePO4 is synthesized in a high yield.

[0273] In step S110, the aqueous ammonia solution can preferably be continuously fed, and in this case, there is an advantage that FePO4 is synthesized stably without side reactions.

[0274] Preferably, the temperature can be maintained while the above-mentioned aqueous ammonia solution is introduced, and in this case, there is an advantage that FePO4 is synthesized stably without side reactions.

[0275] After the addition of the aqueous ammonia solution in step S110 is completed, stirring can be further performed for preferably 30 to 60 minutes, specifically for 40 minutes, and in this case, there is an advantage that FePO4 is synthesized stably without side reactions.

[0276] In step S110, an aqueous ammonia solution is added, and after the addition is completed, additional stirring can preferably be performed at a heated temperature. In this case, there is an advantage that the synthesis of FePO4 is carried out stably without side reactions.

[0277]

[0278] Next, the synthesized FePO4 is separated (step S120).

[0279] Separating the FePO4 synthesized in step S120 has the advantage of facilitating the removal of impurities in the subsequent washing step and saving energy.

[0280] The above separation can preferably be achieved using reduced pressure filtration, more preferably vacuum reduced pressure filtration, specifically vacuum reduced pressure filtration using a filtration flask, in which case there is an advantage that FePO4 is easily separated.

[0281]

[0282] Next, the separated FePO4 is washed and dried with an acidic washing solution having a pH of 1.3 to 1.6 (step S130).

[0283] Through the above washing step, iron phosphate with an incorrect stoichiometric ratio, i.e., Fe x PO y There is an advantage in that the purity of the synthesized FePO4 is increased as impurities such as (where x is not 1, y is not 4, and x:y is not 1:4) are easily removed and no by-products are generated.

[0284] The above acidic washing solution with a pH of 1.3 to 1.6 may, as a specific example, be a mixture of hydrochloric acid, sulfuric acid, or both of these with distilled water, and as a specific example, hydrochloric acid may be mixed, in which case there is an advantage that the acidic washing solution is easy to prepare and impurities are easily removed.

[0285] The above acidic washing solution may have a specific pH of 1.3 to 1.5, and in this case, impurities are easily removed and no by-products are generated by the re-leaching of FePO4, which has the advantage of increasing the purity of the synthesized FePO4.

[0286]

[0287] In step S130, the solid-liquid ratio of FePO4 to the acidic washing solution may preferably be 15 to 25 mL / g, and as a specific example, 20 mL / g; in this case, the formation of byproducts is suppressed, and iron phosphate with an unsatisfactory stoichiometric ratio, i.e., Fe x PO y There is an advantage in that impurities such as [such as] are easily removed and no by-products are generated, thereby increasing the purity of the synthesized FePO4.

[0288]

[0289] In step S130, washing can be performed by introducing an acidic washing solution and preferably for 5 to 20 minutes, specifically for 10 minutes, under stirring, and in this case, there is the advantage that impurities are reduced and by-products are not generated.

[0290] In step S130, washing may preferably include vacuum filtration, which has the advantage of easily separating FePO4 from the acidic washing solution.

[0291]

[0292] The above drying can preferably be vacuum drying, and more preferably, can be carried out under vacuum at 70 to 200°C until there is no further change in weight, and as a specific example, can be carried out at 80 to 130°C for 1 to 24 hours, and within this range, it has the effect of efficiently removing moisture contained in the washed FePO4.

[0293]

[0294] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the following embodiments are merely illustrative of the invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the invention, and that such variations and modifications fall within the scope of the appended claims.

[0295]

[0296] [Example]

[0297] Example 1

[0298] The spent lithium iron phosphate anode was crushed with a blender to separate the current collector. The spent lithium iron phosphate anode material from which the current collector had been separated was sieved through a 200-mesh sieve to obtain spent anode material powder having an olivine structure. X-ray diffraction (XRD) analysis of the obtained spent anode material powder confirmed that it contained lithium iron phosphate powder with an olivine structure.

[0299] 100 g of the above-prepared waste cathode material powder was added to 1000 ml of an aqueous sulfuric acid solution with a concentration of 0.6 molar (mol / L) at room temperature and leached to form a leaching solution containing dissolved lithium and a leaching residue, and the leaching residue was obtained by separating them by vacuum filtration.

[0300] The leaching residue obtained above was leached in a 1 molar aqueous sulfuric acid solution at room temperature for 20 hours at a solid-to-liquid ratio of 10 mL / g to obtain a solution containing Fe and P. The solution contained 27,000 ppm of Fe, 15,000 ppm of P, and 250 ppm of Li, which was confirmed by ICP analysis. At this time, the pH of the solution was 0.3.

[0301] 50 ml of the above-mentioned solution containing Fe and P was taken, and while stirring at room temperature, an aqueous ammonia solution with a concentration of 1 molar was continuously added at a rate of 1 ml / min to make the pH of the solution 1.8, thereby precipitating impurities such as aluminum and titanium.

[0302] The above-mentioned dissolved solution containing precipitated impurities such as aluminum and titanium was separated by vacuum filtration to remove the impurities.

[0303] A storage solution containing Fe and P was prepared by adding an aqueous hydrochloric acid solution with a concentration of 30 wt% to 50 ml of the above-mentioned solution from which impurities had been removed, adjusting the pH to 1.

[0304] The above pH was measured at room temperature using a METTLER TOLEDO SevenDirect SD30.

[0305] For the above ICP analysis, 0.2 g of the solution was taken, placed in a conical tube, and its exact weight was measured. Then, 0.1 ml of nitric acid with a concentration of 70 wt% was added to it, followed by the addition of 500 µl of 1000 mg / kg internal standard (scandium), and the solution was diluted with ultrapure water to a volume of 50 ml to measure the content of Fe, P, Li, etc. through ICP analysis.

[0306]

[0307] Example 2

[0308] In the above Example 1, the procedure was carried out in the same manner as Example 1, except that a hydrochloric acid aqueous solution with a concentration of 30 wt% was added to 50 ml of the solution from which impurities had been removed to adjust the pH to 1.1 to prepare a storage solution containing Fe and P.

[0309]

[0310] Example 3

[0311] In the above Example 1, the procedure was carried out in the same manner as Example 1, except that a hydrochloric acid aqueous solution with a concentration of 30 wt% was added to 50 ml of the solution from which impurities had been removed to adjust the pH to 1.3 to prepare a storage solution containing Fe and P.

[0312]

[0313] Example 4

[0314] In the above Example 1, the procedure was carried out in the same manner as Example 1, except that a hydrochloric acid aqueous solution with a concentration of 30 wt% was added to 50 ml of the solution from which impurities had been removed to adjust the pH to 1.4 to prepare a storage solution containing Fe and P.

[0315]

[0316] Example 5

[0317] In the above Example 1, the procedure was carried out in the same manner as Example 1, except that a hydrochloric acid aqueous solution with a concentration of 30 wt% was added to 50 ml of the solution from which impurities had been removed to adjust the pH to 0.8 to prepare a storage solution containing Fe and P.

[0318]

[0319] Comparative Example 1

[0320] In the above Example 1, the procedure was carried out in the same manner as Example 1, except that a hydrochloric acid aqueous solution with a concentration of 30 wt% was added to 50 ml of the solution from which impurities had been removed to adjust the pH to 1.5 to prepare a storage solution containing Fe and P.

[0321]

[0322] Comparative Example 2

[0323] In the above Example 1, the procedure was carried out in the same manner as Example 1, except that a hydrochloric acid aqueous solution with a concentration of 30 wt% was added to 50 ml of the solution from which impurities had been removed to adjust the pH to 1.6 to prepare a storage solution containing Fe and P.

[0324]

[0325] [Test Example I: Measurement of Precipitate Formation in Storage Solution]

[0326] The storage solutions prepared in Examples 1 to 5 and Comparative Examples 1 and 2 were left at room temperature for 24 hours, after which the storage solutions were filtered to separate the precipitates, and the separated precipitates were dried and weighed, as shown in Table 1 below.

[0327]

[0328] Classification Storage Solution pH Precipitate Weight (g / L) Example 11.00 Example 21.10 Example 31.30 Example 41.40.02 Example 50.80 Comparative Example 11.54 Comparative Example 21.66

[0329] As shown in Table 1 above, it was confirmed that the storage solution according to the present invention (Examples 1 to 5) had a precipitate weight of 0.02 g / L or less after being left at room temperature for 24 hours, indicating that almost no precipitate was formed. In particular, no precipitate was formed in Examples 1 to 3 and 5, which had a pH of 0.8 to 1.3. This is because the solubility of each substance varies depending on the pH, and within the above pH range, Fe and P remain in a dissolved state, so no precipitate is formed. On the other hand, in Comparative Examples 1 and 2, where the pH exceeded the range of the present invention, it was found that Fe and P were removed from a dissolved state and a large amount of precipitate was formed.

Claims

1. (a) A step of adding a basic solution to a dissolved solution containing Fe and P to precipitate impurities; (b) a step of removing impurities from the solution; and (c) a step of preparing a storage solution containing Fe and P by adding an acidic solution to a dissolved solution from which impurities have been removed and adjusting the pH to 0.8 to 1.4; characterized by comprising Method for producing ferric phosphate from waste lithium iron phosphate anode.

2. In Paragraph 1, The basic solution in step (a) above is characterized as being an aqueous ammonia solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or an aqueous calcium hydroxide solution. Method for producing ferric phosphate from waste lithium iron phosphate anode.

3. In Paragraph 1, The solution containing Fe and P in step (a) above is characterized by having a pH of 0.1 to 0.

5. Method for producing ferric phosphate from waste lithium iron phosphate anode.

4. In Paragraph 1, The solution in which the addition of the basic solution is completed in step (a) above is characterized by having a pH of 1.7 to 2.

5. Method for producing ferric phosphate from waste lithium iron phosphate anode.

5. In Paragraph 1, The above step (a) is characterized by being carried out while stirring at room temperature. Method for producing ferric phosphate from waste lithium iron phosphate anode.

6. In Paragraph 1, In step (a) above, the basic solution is characterized by having a basic component at a concentration of 0.8 to 1.3 molar (mol / L). Method for producing ferric phosphate from waste lithium iron phosphate anode.

7. In Paragraph 1, The basic solution is characterized by being continuously added in step (a) above. Method for producing ferric phosphate from waste lithium iron phosphate anode.

8. In Paragraph 1, The solution of step (a) above is characterized by comprising: (i) a step of crushing a spent lithium iron phosphate cathode to obtain cathode material powder; (ii) a step of adding the obtained cathode material powder to an acidic solution with a concentration of 0.5 to 0.7 molar (mol / L) to form a leaching solution in which lithium is dissolved and a leaching residue, and separating them; and (iii) a step of adding the separated leaching residue to an acidic solution with a concentration of 0.8 to 1.3 molar (mol / L) to obtain a solution in which Fe and P are dissolved. Method for producing ferric phosphate from waste lithium iron phosphate anode.

9. In Paragraph 1, The removal of impurities in step (b) above is characterized by using vacuum filtration. Method for producing ferric phosphate from waste lithium iron phosphate anode.

10. In Paragraph 1, The acidic solution in step (c) above is characterized as being an aqueous sulfuric acid solution, an aqueous hydrochloric acid solution, or an aqueous nitric acid solution. Method for producing ferric phosphate from waste lithium iron phosphate anode.

11. In Paragraph 1, The storage solution containing Fe and P in step (c) above is characterized by having a precipitate of 0.03 g / L or less after being left at room temperature for 24 hours. Method for producing ferric phosphate from waste lithium iron phosphate anode.

12. In Paragraph 1, The above method for producing FePO4 from waste lithium iron phosphate cathode material is characterized by further including (d) a step of synthesizing FePO4 in a storage solution containing Fe and P. Method for producing ferric phosphate from waste lithium iron phosphate anode.

13. A method comprising the steps of: manufacturing ferric phosphate according to any one of claims 1 to 12; and synthesizing lithium iron phosphate by reacting the manufactured ferric phosphate with a lithium precursor. Method for manufacturing lithium iron phosphate.

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