Method for preparing ferric phosphate

Abstract

The present invention relates to a method for preparing ferric phosphate (FePO4) and, more specifically, to a method for preparing ferric phosphate (FePO4), the method comprising the steps of: (a) adding an aqueous ammonia solution to a solution containing Fe and P to precipitate impurities and remove the impurities; (b) adding an aqueous hydrogen peroxide solution to a solution containing Fe and P from which impurities are removed to manufacture a hydrogen peroxide mixture; (c) heating the hydrogen peroxide mixture to synthesize FePO4; (d) separating the synthesized FePO4; (e) washing the separated FePO4 with an acidic washing solution having a pH of 1.3 to 1.6; and (f) heat-treating the washed FePO4 at 600 to 800 ℃ for 3 to 17 hours. According to the present invention, there is the effect of providing a method for preparing ferric phosphate (FePO4), which suppresses the generation of sulfides derived from sulfuric acid and basic solutions as in the prior art in a process of synthesizing FePO4 from waste lithium iron phosphate cathode materials, and removes the sulfides generated from the synthesized FePO4 to increase purity.

Description

Method for manufacturing ferric phosphate

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

[0002] The present application claims the benefit of priority based on Korean Patent Application No. 10-2025-0008198 filed on January 20, 2025 and Korean Patent Application No. 10-2026-0007728 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 cathode. More specifically, the invention relates to a method for producing FePO4 by introducing an aqueous ammonia solution into a solution in which spent lithium iron phosphate is dissolved in sulfuric acid to synthesize FePO4, and by subjecting the synthesized FePO4 to oxidative heat treatment, thereby suppressing the formation of sulfides originating from sulfuric acid and basic solutions during the synthesis process and easily removing sulfides introduced into FePO4.

[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) has a very stable hexahedral crystal structure, and in order to break down this stable structure and recover valuable metals, a high concentration of strong acid or strong base is used on the spent anode to dissolve the valuable metals, after which Li and FePO4 are recovered separately.

[0008] Specifically, in the process of synthesizing FePO4 by adding a basic solution to a solution containing Fe and P obtained by adding lithium iron phosphate to sulfuric acid, there is a problem in that the type and content of sulfide impurities vary depending on the type of basic solution, requiring different methods for their removal. If sulfur (S) remains in the lithium iron phosphate, which is the cathode active material, it acts as an impurity and degrades battery performance.

[0009] Therefore, there is a need for a method to produce FePO4 from spent lithium iron phosphate cathodes that suppresses the formation of sulfides originating from sulfuric acid and basic solutions during the synthesis process of FePO4, and also removes sulfides introduced from the synthesized FePO4.

[0010] [Prior Art Literature]

[0011] [Patent Literature]

[0012] Korean Patent Registration No. 10-1271669

[0013] In order to solve the problems of the conventional technology described above, the present invention aims to provide a method for manufacturing ferric phosphate, etc., in which a basic solution is added to a solution in which waste lithium iron phosphate is dissolved in sulfuric acid to synthesize FePO4, thereby suppressing the formation of sulfides derived from sulfuric acid and basic solutions as in the conventional method, and also enabling easy removal of sulfides introduced into the synthesized FePO4.

[0014]

[0015] The above and other objectives of the present invention can all be achieved by the present invention described below.

[0016] To achieve the above objective, the present invention provides a method for manufacturing FePO4 comprising: I) a step of adding an aqueous ammonia solution to a solution containing Fe and P to precipitate and remove impurities; (b) a step of adding an aqueous hydrogen peroxide solution to the solution containing Fe and P from which impurities have been removed to prepare a hydrogen peroxide mixture; (c) a step of synthesizing FePO4 by heating the hydrogen peroxide mixture; (d) a step of separating the synthesized FePO4; (e) a step of washing the separated FePO4 with an acidic washing solution having a pH of 1.3 to 1.6; and (f) a step of heat-treating the washed FePO4 at 600 to 800 ℃ for 3 to 17 hours.

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

[0018] III) In the above I) or II), after the addition of the aqueous ammonia solution in step (a) is completed, the solution may have a pH of 1.0 to 1.4.

[0019] IV) In the above I) to III), the solution of step (a) may be a solution in which waste lithium iron phosphate is dissolved in sulfuric acid.

[0020] V) In the above I) to IV), the solution of step (a) can be prepared by including: (i) a step of crushing a waste lithium iron phosphate cathode to obtain waste cathode material powder; (ii) a step of adding the obtained waste cathode material powder to sulfuric acid 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 sulfuric acid with a concentration of 0.8 to 1.3 molar concentration (mol / L) to obtain a solution containing Fe and P.

[0021] VI) In the above I) to V), the ammonia aqueous solution can be continuously added in step (a) while stirring the solution.

[0022] VII) In the above I) to VI), the aqueous ammonia solution in step (a) may have a concentration of 0.8 to 1.3 molar (mol / L).

[0023] VIII) In the above I) to VII), in step (b), an amount of aqueous hydrogen peroxide solution can be added such that it is 1 to 5 volume% of the solution based on hydrogen peroxide.

[0024] IX) In the above I) to VIII), the hydrogen peroxide mixture in step (c) may be heated to 28 to 60 ℃.

[0025] X) In the above I) to IX), the step of heating the hydrogen peroxide mixture in step (c) and then adding an aqueous ammonia solution to adjust the pH to 1.0 to 1.8 may be further included.

[0026] XI) In the above I) to X), in step (e), the solid-liquid ratio of the separated FePO4 and the acidic washing solution having a pH of 1.3 to 1.6 may be 15 to 25 mL / g.

[0027] XII) In the above I) to XI), the washing in step (e) may include adding an acidic washing solution to the separated FePO4 and stirring for 5 to 20 minutes.

[0028] XIII) In the above I) to XII), the washing in step (e) may include vacuum filtration.

[0029] XIV) In the above I) to XV), the FePO4 washed in step (e) can be dried and then introduced into step (f).

[0030] XV) In the above I) to XIV), the heat treatment in step (f) may be carried out under an air or oxygen atmosphere.

[0031] XVI) In the above I) to XV), after heat treatment in step (f), FePO4 may contain sulfur (S) at a level of 1100 ppm or less.

[0032] Additionally, XVII) The present invention comprises the steps of: (a) adding an aqueous ammonia solution to a solution containing Fe and P to precipitate and remove impurities; (b) adding an aqueous hydrogen peroxide solution to the solution containing Fe and P from which impurities have been removed to prepare a hydrogen peroxide mixture; (c) heating the hydrogen peroxide mixture to synthesize FePO4; (d) separating the synthesized FePO4; (e) washing the separated FePO4 with an acidic washing solution having a pH of 1.3 to 1.6; (f) heat-treating the washed FePO4 at 600 to 800 °C for 3 to 17 hours; (g) adding a lithium precursor to the heat-treated FePO4 and calcining it to produce lithium iron phosphate; (h) mixing a solution containing a carbon source with the produced lithium iron phosphate to produce a lithium iron phosphate solution; (i) spray-drying the produced lithium iron phosphate solution; and (j) a step of reducing and heat-treating the dried lithium iron phosphate; or (a) a step of adding an aqueous ammonia solution to a solution containing Fe and P to precipitate and remove impurities; (b) a step of adding an aqueous hydrogen peroxide solution to the solution containing Fe and P from which impurities have been removed to prepare a hydrogen peroxide mixture; (c) a step of synthesizing FePO4 by heating the hydrogen peroxide mixture; (d) a step of separating the synthesized FePO4; (e) a step of washing the separated FePO4 with an acidic washing solution having a pH of 1.3 to 1.6; (f') a step of adding a lithium precursor to the washed FePO4 and heat-treating it at 600 to 800 °C for 3 to 17 hours to produce lithium iron phosphate; (g') a step of mixing a solution containing a carbon source with the produced lithium iron phosphate to produce a lithium iron phosphate solution; (h') a step of spray-drying the produced lithium iron phosphate solution; and (i') a step of reducing the dried lithium iron phosphate; a method for manufacturing lithium iron phosphate is provided.

[0033] According to the present invention, there is an effect of providing a method for manufacturing FePO4 from a waste lithium iron phosphate cathode, wherein a basic solution is added to a solution in which waste lithium iron phosphate is dissolved in sulfuric acid to synthesize FePO4, and an aqueous ammonia solution is added to suppress the formation of sulfides derived from sulfuric acid and basic solutions as in the conventional method, and furthermore, by easily removing sulfides introduced into the synthesized FePO4 through oxidative heat treatment, the sulfur (S) component in FePO4 is lowered and purity is increased.

[0034] 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.

[0035]

[0036] 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.

[0037]

[0038] 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 sulfuric acid, leaching the leaching residue in sulfuric acid, and adding an aqueous ammonia solution as a basic solution to the dissolved solution containing Fe and P to synthesize FePO4, and then subjecting the synthesized FePO4 to oxidative heat treatment, the formation of sulfides originating from sulfuric acid and basic solutions as in the conventional method is suppressed, and sulfides introduced into the synthesized FePO4 are easily removed. Based on this, they devoted themselves to further research and completed the present invention.

[0039]

[0040] The method for recovering lithium described herein will be explained in detail below.

[0041] 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.

[0042] 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.

[0043]

[0044] Method for manufacturing ferric phosphate (FePO4)

[0045] The method for producing ferric phosphate (FePO4) according to the present invention comprises: (a) a step of adding an aqueous ammonia solution to a solution containing Fe and P to precipitate impurities and remove them; (b) a step of adding an aqueous hydrogen peroxide solution to the solution containing Fe and P from which impurities have been removed to produce a hydrogen peroxide mixture; (c) a step of synthesizing FePO4 by heating the hydrogen peroxide mixture; (d) a step of separating the synthesized FePO4; (e) a step of washing the separated FePO4 with an acidic washing solution having a pH of 1.3 to 1.6; and (f) a step of heat-treating the washed FePO4 at 600 to 800 ℃ for 3 to 17 hours. In this case, the formation of sulfides derived from sulfuric acid and basic solutions during the FePO4 synthesis process is suppressed, and sulfides introduced into the synthesized FePO4 are easily removed, thereby providing the effect of providing high-purity FePO4.

[0046]

[0047] The method for manufacturing ferric phosphate (FePO4) is described in detail below, divided into steps.

[0048]

[0049] (a) A step of adding an aqueous ammonia solution to a dissolved solution containing Fe and P to precipitate impurities and remove them.

[0050] The method for producing ferric phosphate (FePO4) according to the present invention may include the step of (a) adding an aqueous ammonia solution to a dissolved solution containing Fe and P to precipitate and remove impurities, and in this case, the purity of the produced FePO4 is significantly improved and the formation of sulfides derived from sulfuric acid and basic solutions as in the past is reduced, which has the advantage of being significantly improved and reduced.

[0051] If a basic solution such as sodium hydroxide is used in addition to the aqueous ammonia solution in step (a) above, the formation of sulfides increases, and the sulfides introduced into the synthesized FePO4 are not cleanly removed in the subsequent heat treatment step and remain in the synthesized FePO4, causing a decrease in purity and battery performance.

[0052] In addition, when an aqueous ammonia solution according to the present invention is used as a basic solution, (NH4)2SO4 is produced as a sulfide, and when a conventional aqueous sodium hydroxide solution is used as a basic solution, Na2SO4 is produced as a sulfide. Since the melting point of (NH4)2SO4 is 235 to 280 ℃, which is lower than the melting point of Na2SO4 at 884 ℃, it is removed more easily and cleanly through a subsequent heat treatment process.

[0053]

[0054] 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.

[0055] 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

[0056]

[0057] 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.

[0058] In this description, room temperature may be one point within the range of 20 ± 5 ℃.

[0059]

[0060] 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.

[0061] 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.

[0062] 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.

[0063] In this specification, ppm is based on weight unless otherwise defined.

[0064] 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.

[0065]

[0066] After the addition of the above-mentioned ammonia aqueous solution is completed, the solution containing Fe and P may have a pH of, for example, 1.0 to 1.4, preferably 1.1 to 1.4, and more preferably 1.1 to 1.3. 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.

[0067]

[0068] Step (a) above can be performed by adding an aqueous ammonia solution to the solution, for example, while stirring, and in this case, there is an advantage of shortening the impurity precipitation time.

[0069] 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.

[0070]

[0071] In step (a) above, the aqueous ammonia solution may have a concentration of, for example, 0.8 to 1.3 molar (mol / L), preferably 0.9 to 1.2 molar, and 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.

[0072]

[0073] In step (a) above, the aqueous ammonia 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.

[0074] 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.

[0075]

[0076] The solution in step (a) above may be, for example, a solution in which waste lithium iron phosphate is dissolved in sulfuric acid, and in this case, Fe and P are easily leached out, which has the advantage of producing high-purity and high-yield FePO4.

[0077]

[0078] The solution of step (a) above can be prepared by, for example, (i) crushing waste lithium iron phosphate cathode material to obtain cathode material powder; (ii) adding the obtained cathode material powder to sulfuric acid 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) adding the separated leaching residue to sulfuric acid 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 with a high yield.

[0079]

[0080] 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.

[0081] In this description, the term "anode material" means that it includes an anode active material or is an anode active material.

[0082]

[0083] 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.

[0084] 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.

[0085] The above olivine structure can be confirmed through X-ray diffraction analysis (XRD).

[0086]

[0087] 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.

[0088] [Chemical Formula 1]

[0089]

[0090] (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.)

[0091]

[0092] 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.

[0093]

[0094] 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.

[0095]

[0096] 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.

[0097]

[0098] 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.

[0099] 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.

[0100] 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.

[0101]

[0102] In this description, waste anode material powder refers to a waste anode obtained in powder form by crushing or crushing and sieving, 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.

[0103]

[0104] In step (ii) above, the sulfuric acid may be, for example, at a concentration of 0.5 to 0.7 molar (mol / L), preferably 0.55 to 0.65 molar, and within this range, lithium is easily leached and Fe and P remain as leaching residues, which has the advantage.

[0105] In step (ii) above, the solid-liquid ratio of the anode powder and sulfuric acid 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.

[0106] 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 sulfuric acid (mL) relative to the anode powder content (g).

[0107]

[0108] 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.

[0109]

[0110] In the above step (ii), separation can preferably be achieved using vacuum filtration. In this case, the leachate and leachate residue are easily separated through a simple process, reducing process costs and offering environmentally friendly advantages.

[0111]

[0112] In step (iii) above, the concentration of sulfuric acid may be, for example, 0.8 to 1.3 molar concentration (mol / L), preferably 0.9 to 1.2 molar concentration, more preferably 0.9 to 1.1 molar concentration, and there is an economic advantage in that Fe and P are sufficiently leached from the leaching residue separated within this range, thereby increasing the yield of FePO4.

[0113] The reason the molar concentrations of the sulfuric acid in step (ii) and the sulfuric acid in step (iii) are different is that the molar concentration of the sulfuric acid in step (ii) is a range that allows lithium to be easily leached from the cathode material powder, and the molar concentration of the sulfuric acid in step (iii) is a range that allows Fe and P to be easily leached from the separated leaching residue; since the leaching targets are different in steps (ii) and (iii), the molar concentrations of the sulfuric acid are different.

[0114]

[0115] The separation of the dissolved solution and impurities into which the above-mentioned ammonia aqueous solution has been introduced can be achieved, for example, by using reduced-pressure filtration, and in this case, there is an advantage in that the dissolved solution and impurities can be easily separated with only a simple process.

[0116] 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.

[0117] 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.

[0118]

[0119] The above-mentioned solution from which impurities have been removed may, for example, have a pH of 1.0 to 1.4, preferably 1.1 to 1.4, and more preferably 1.1 to 1.3. In this case, since impurities are removed by adding an aqueous ammonia solution to the solution, the pH may be the same as or similar to the pH of the solution into which the aqueous ammonia solution has been added.

[0120]

[0121] The above-mentioned 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 back into an acidic solution.

[0122]

[0123] (b) a step of preparing a hydrogen peroxide mixture by adding an aqueous hydrogen peroxide solution to a dissolved solution containing Fe and P from which impurities have been removed.

[0124] The method for producing ferric phosphate (FePO4) according to the present invention may include the step of (b) introducing an aqueous hydrogen peroxide solution into a dissolved solution containing Fe and P from which impurities have been removed to produce a hydrogen peroxide mixture, and in this case, there is an advantage that the synthesis of FePO4 is easy.

[0125]

[0126] For example, the above-mentioned aqueous hydrogen peroxide solution can be added in an amount of 1 to 5 volume% of the solution based on hydrogen peroxide, preferably in an amount of 1 to 4 volume% of the solution, more preferably in an amount of 1 to 3 volume% of the solution, and even more preferably in an amount of 1.5 to 2.5 volume% of the solution, and there is an advantage that the synthesis of FePO4 is easy within this range.

[0127]

[0128] 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.

[0129]

[0130] 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.

[0131]

[0132] In step (b) above, the temperature rise resulting from the addition of an aqueous hydrogen peroxide solution to the solution containing Fe and P is minimal; for example, the mixture 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 mixture must be raised.

[0133]

[0134] (c) Step of synthesizing FePO4 by heating the hydrogen peroxide mixture

[0135] The method for producing ferric phosphate (FePO4) according to the present invention may include (c) a step of synthesizing FePO4 by heating a hydrogen peroxide mixture, and in this case, there is an advantage that FePO4 synthesis is easy.

[0136]

[0137] In step (c) 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.

[0138]

[0139] In step (c) above, the method may further include a step of heating the hydrogen peroxide mixture and, for example, adding an aqueous ammonia solution to adjust the pH to 1.0 to 1.8. In this case, the pH is maintained constant during the synthesis process, thereby allowing FePO4 to be synthesized in high yield, suppressing the formation of sulfides, and also having the advantage that any sulfides introduced into the synthesized FePO4 are cleanly removed by heat treatment.

[0140] If a basic aqueous solution, such as a sodium hydroxide solution, is added in addition to the ammonia aqueous solution to the heated hydrogen peroxide mixture, the generation of sulfides increases during the synthesis process. Furthermore, the sulfides introduced into the synthesized FePO4 have a higher melting point than the sulfides produced by adding the ammonia aqueous solution, so they are not cleanly removed during the subsequent heat treatment process and remain in large quantities in the lithium iron phosphate, which is the positive electrode active material, thereby degrading the performance of the battery.

[0141]

[0142] The above ammonia aqueous solution may have, for example, a concentration of 0.8 to 1.3 molar (mol / L), preferably 0.9 to 1.2 molar, and more preferably 0.9 to 1.1 molar, and has the effect of facilitating pH adjustment.

[0143] The addition of an aqueous ammonia solution to the above hydrogen peroxide mixture can be carried out, for example, while stirring, and in this case, there is an advantage that FePO4 is easily synthesized.

[0144] 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.

[0145] For example, the ammonia aqueous solution can be added to the above hydrogen peroxide mixture in a continuous manner, and in this case, there is an advantage that FePO4 is synthesized stably without side reactions.

[0146] After the addition of the above ammonia aqueous solution is completed, the hydrogen peroxide mixture may have a pH of, for example, 1.0 to 2.0, preferably 1.1 to 1.6, more preferably 1.2 to 1.5, and there is an advantage that FePO4 is synthesized in high yield within this range.

[0147] After the addition of the above ammonia aqueous solution is completed, stirring can be performed for, for example, 30 to 60 minutes, preferably 35 to 55 minutes, and more preferably 40 to 50 minutes, and in this case, there is an advantage that FePO4 is synthesized stably without side reactions.

[0148]

[0149] (d) Step of separating the synthesized FePO4

[0150] The method for producing ferric phosphate (FePO4) according to the present invention may include (d) a step of separating the synthesized FePO4, in which case there is an advantage of easily removing impurities and saving energy in the subsequent washing step.

[0151] The above separation can be performed using, for example, vacuum filtration, and in this case, there is an advantage that the synthesized FePO4 is easily separated.

[0152] The above vacuum filtration is not particularly limited to vacuum filtration commonly used in the technical field to which the present invention belongs, and preferably may be vacuum vacuum filtration, specifically vacuum vacuum filtration using a filtration flask, in which case there is an advantage that FePO4 is easily separated.

[0153]

[0154] (e) washing the separated FePO4 with an acidic washing solution having a pH of 1.3 to 1.6

[0155] The method for producing ferric phosphate (FePO4) according to the present invention may include (e) a step of washing the separated FePO4 with an acidic washing solution having a pH of 1.3 to 1.6, and in this case, impurities are easily removed and no by-products are generated by the re-leaching of FePO4, so there is an advantage that the purity of the synthesized FePO4 is increased.

[0156]

[0157] 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.

[0158]

[0159] 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.

[0160]

[0161] In step (e) above, the solid-liquid ratio of FePO4 to the acidic washing solution having a pH of 1.3 to 1.6 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 by-products are not generated.

[0162]

[0163] In step (e) above, washing may include 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.

[0164]

[0165] In step (e) above, the washing is not particularly limited to washing methods commonly used in the technical field to which the present invention belongs, but may include vacuum filtration of the mixture of separated FePO4 and acidic washing solution, in which case there is an advantage of easily separating FePO4 and the acidic washing solution.

[0166]

[0167] The FePO4 washed in step (e) above can be introduced into step (f) after drying, for example, and in this case, there is an advantage of improved heat treatment efficiency.

[0168] The above drying may preferably be vacuum drying, and as a specific example, it may be carried out under vacuum at 70 to 200°C, more preferably at 75 to 130°C, and even more preferably at 75 to 100°C for 1 to 24 hours until there is no further change in weight, and within this range, it has the effect of efficiently removing moisture contained in the washed FePO4.

[0169]

[0170] 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.

[0171]

[0172] (f) a step of heat-treating the washed FePO4 at 600 to 800 ℃ for 3 to 17 hours

[0173] The method for producing ferric phosphate (FePO4) according to the present invention may include (f) a step of heat-treating washed FePO4 at 600 to 800 ℃ for 3 to 17 hours, in which case sulfides introduced into the synthesized FePO4 are removed, thereby improving the yield and purity of FePO4. Below the above temperature range, productivity is reduced because heat treatment must be performed for a long time to remove sulfides, and above the above temperature range, the synthesized FePO4 is sintered, and an additional process of crushing and grinding it to form powder must be carried out, which reduces economic efficiency and productivity.

[0174]

[0175] The above heat treatment temperature may preferably be 650 to 750 ℃, more preferably 670 to 720 ℃, and within this range, there is an advantage that sulfides introduced into the synthesized FePO4 are easily removed.

[0176] The above heat treatment time may preferably be 4 to 16 hours, more preferably 5 to 15 hours, even more preferably 7 to 15 hours, even more preferably 10 to 15 hours, and particularly preferably 13 to 15 hours. Within this range, sulfides introduced into FePO4 are removed, which has the advantage of improving the yield and purity of FePO4. If the heat treatment time is shorter than the above time, sulfides are not removed, and if the heat treatment time is exceeded, the yield and purity of FePO4 are not improved, and energy consumption increases.

[0177]

[0178] In this description, the heat treatment time refers to the time spent processing at the corresponding heat treatment temperature, and the time taken to reach the corresponding heat treatment temperature is not calculated.

[0179] The above heat treatment may have a temperature rise rate of, for example, 1 to 20 ℃ / min, preferably 2 to 15 ℃ / min, more preferably 3 to 10 ℃ / min, and even more preferably 3 to 7 ℃ / min, and has the advantage of being able to be implemented within this range without putting strain on the heat treatment equipment.

[0180]

[0181] The above heat treatment can be carried out, for example, in an air or oxygen atmosphere, preferably under an air atmosphere, and in this case, there is an advantage that sulfides introduced into FePO4 are removed, thereby improving the yield and purity of FePO4.

[0182] The above oxygen atmosphere may, for example, have an oxygen purity of 59% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and even more preferably 90 to 99%, and in this case, there is an advantage that the sulfides introduced into FePO4 are removed, thereby improving the yield and purity of FePO4.

[0183] The purity % of the above oxygen may be volume % or mol %.

[0184] The purity of the oxygen described herein is not particularly limited when measured by a measurement method commonly used in the technical field to which the present invention belongs.

[0185]

[0186] After heat treatment in step (f) above, FePO4 may contain sulfur (S) of, for example, 1100 ppm or less, preferably 700 ppm or less, more preferably 500 ppm or less, even more preferably 300 ppm, even more preferably 200 ppm or less, and particularly preferably 1 to 200 ppm, and within this range, there is an advantage that the yield and purity of FePO4 are improved.

[0187] In this specification, ppm is based on weight unless otherwise defined.

[0188]

[0189] In the above (f) heat treatment step, a lithium precursor can be introduced, for example, into the washed FePO4 for heat treatment. In this case, the sulfides introduced into the manufactured FePO4 are removed, and lithium is intercalated into FePO4 to synthesize lithium iron phosphate, which has the advantage of reducing process costs.

[0190] 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.

[0191] In this description, intercalation refers to a reaction in which lithium ions are inserted into a crystal structure.

[0192]

[0193] Method for manufacturing lithium iron phosphate (LFP)

[0194] The method for manufacturing lithium iron phosphate (LFP) according to the present invention comprises: (a) a step of adding an aqueous ammonia solution to a dissolved solution containing Fe and P to precipitate impurities and remove them; (b) a step of adding an aqueous hydrogen peroxide solution to the dissolved solution containing Fe and P from which impurities have been removed to prepare a hydrogen peroxide mixture; (c) a step of synthesizing FePO4 by heating the hydrogen peroxide mixture; (d) a step of separating the synthesized FePO4; (e) a step of washing the separated FePO4 with an acidic washing solution having a pH of 1.3 to 1.6; (f) a step of heat-treating the washed FePO4 at 600 to 800 ℃ for 3 to 17 hours; (g) a step of manufacturing lithium iron phosphate by adding a lithium precursor to the heat-treated FePO4 and calcining it; and (h) a step of manufacturing a lithium iron phosphate solution by mixing a solution containing a carbon source with the manufactured lithium iron phosphate. Lithium iron phosphate can be manufactured by including the steps of (i) spray-drying the prepared lithium iron phosphate solution; and (j) reducing the dried lithium iron phosphate. In this case, the lithium iron phosphate can be easily manufactured, thereby recycling resources and providing excellent economic advantages.

[0195]

[0196] In another example, the method for manufacturing lithium iron phosphate (LFP) according to the present invention comprises: (a) a step of adding an aqueous ammonia solution to a solution containing Fe and P to precipitate impurities and remove them; (b) a step of adding an aqueous hydrogen peroxide solution to the solution containing Fe and P from which impurities have been removed to prepare a hydrogen peroxide mixture; (c) a step of synthesizing FePO4 by heating the hydrogen peroxide mixture; (d) a step of separating the synthesized FePO4; (e) a step of washing the separated FePO4 with an acidic washing solution having a pH of 1.3 to 1.6; (f') a step of adding a lithium precursor to the washed FePO4 and calcining at 600 to 800 °C for 3 to 17 hours to produce lithium iron phosphate; (g') a step of mixing a solution containing a carbon source with the prepared lithium iron phosphate to produce a lithium iron phosphate solution; and (h') a step of spray-drying the prepared lithium iron phosphate solution. Lithium iron phosphate can be manufactured by including the step of (i') reducing heat treatment of the dried lithium iron phosphate; in this case, by easily manufacturing lithium iron phosphate, resources can be recycled and there is an excellent economic advantage.

[0197]

[0198] 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.

[0199]

[0200] In the above steps (g) and (f'), calcination can be carried out, for example, at 600 to 800 ℃, preferably at 650 to 750 ℃, and within this range, lithium is easily intercalated in FePO4 to synthesize lithium iron phosphate, which has the advantage of excellent high-temperature stability and lifespan characteristics when applied to a secondary battery.

[0201] In the above steps (g) and (f'), 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.

[0202] In steps (g) and (f') above, calcination 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.

[0203]

[0204] In the above steps (h) and (g'), 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.

[0205] 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.

[0206] 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.

[0207] 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.

[0208]

[0209] In steps (h) and (g') above, the mixing of the prepared lithium iron phosphate and the solution containing the carbon source can be performed, for example, by milling (hereinafter referred to as 'first 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 subsequent steps.

[0210] The above first 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 within a narrow range.

[0211]

[0212] In steps (i) and (h') 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.

[0213] 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.

[0214]

[0215] In steps (j) and (i') above, 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.

[0216] The above 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.

[0217] The above 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.

[0218]

[0219] The lithium iron phosphate recovered after reduction heat treatment in steps (j) and (i') above may further include, for example, a milling step (hereinafter referred to as 'secondary milling'). In this case, aggregation, particle breakage, and the generation of fine particles in the finally obtained regenerated lithium iron phosphate can be 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.

[0220]

[0221] The above secondary 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 recycled lithium iron phosphate can be precisely controlled within a narrow range, and there is also the advantage of improving the purity of the recycled lithium iron phosphate by preventing the ingress of foreign substances that may occur during the milling process.

[0222]

[0223] Figure 1 below is a flowchart of a method for producing ferric phosphate (FePO4) from a waste lithium iron phosphate anode according to one embodiment of the present invention.

[0224]

[0225] Referring to FIG. 1, first, a spent lithium iron phosphate cathode is prepared (step S10).

[0226] 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.

[0227] 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.

[0228] The above-mentioned anode may include an anode active material having an olivine structure, preferably lithium iron phosphate having an olivine structure, and more preferably LiFePO4 having an olivine structure, in which case there are advantages such as excellent high-temperature stability and lifespan characteristics and low cost.

[0229]

[0230] Next, the waste lithium iron phosphate anode is crushed to obtain waste anode material powder (step S20).

[0231] 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.

[0232]

[0233] 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.

[0234] 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 can be separated and waste cathode material powder of uniform size can be obtained.

[0235]

[0236] Next, waste cathode material powder is added to sulfuric acid at 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 (step S30).

[0237] The above sulfuric acid may preferably have a molar concentration of 0.55 to 0.65 molar (mol / L), and as a specific example, may have a molar concentration of 0.6 molar. In this case, there is an advantage that lithium is easily and selectively leached out while Fe and P remain as leaching residues.

[0238] In step S30, the solid-liquid ratio of waste cathode material powder to sulfuric acid 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.

[0239]

[0240] Next, the lithium-dissolved leaching solution and the leaching residue are separated (step S40).

[0241] 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.

[0242]

[0243] Next, the separated leaching residue is added to sulfuric acid at a concentration of 0.8 to 1.3 molar (mol / L) to obtain a dissolved solution containing Fe and P (step S50).

[0244] The above sulfuric acid may preferably have a concentration of 0.9 to 1.2 molar, and as a specific example, 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 economic advantages.

[0245] 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.

[0246]

[0247] Next, an aqueous ammonia solution is added to the dissolved solution containing Fe and P (step S60).

[0248] Step S60 has the advantage of significantly improving the purity of FePO4 produced by adding an aqueous ammonia solution to a dissolved solution containing Fe and P to precipitate and remove impurities, and suppressing the formation of sulfides derived from sulfuric acid and basic solutions as in the past.

[0249] If a basic solution such as sodium hydroxide is used in step S60, the formation of sulfides increases, and furthermore, the generated sulfides are not cleanly removed in the subsequent heat treatment step and remain in the synthesized FePO4, causing a decrease in purity and performance.

[0250] 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.

[0251] 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.

[0252] 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.

[0253]

[0254] The above ammonia aqueous solution may, for example, have a 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.

[0255] After the addition of the above-mentioned ammonia aqueous solution is completed, the solution may preferably have a pH of 1.0 to 1.4, and as a specific example, a pH of 1.2. In this case, there is an advantage that impurities such as aluminum and titanium are precipitated and easily removed.

[0256] The above ammonia aqueous solution can be continuously added to the solution, and in this case, there is an advantage that impurities such as aluminum and titanium precipitate and are easily removed.

[0257] The above ammonia aqueous solution can be introduced, for example, under stirring, and in this case, there is an advantage that impurities precipitate within a short period of time.

[0258]

[0259] Next, impurities are removed from the solution into which the ammonia aqueous solution has been added (step S70).

[0260] The removal of the dissolved solution and impurities to which the above-mentioned ammonia aqueous 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.

[0261]

[0262] Next, an aqueous hydrogen peroxide solution is added to a dissolved solution containing Fe and P from which impurities have been removed to prepare a hydrogen peroxide mixture (step S80).

[0263] In step S80, the aqueous hydrogen peroxide solution can preferably be added in an amount of 1 to 5 volume% of the solution based on hydrogen peroxide, and as a specific example, in an amount of 2 volume% of the solution, and in this case, there is an advantage that the synthesis of FePO4 is easy.

[0264] 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.

[0265]

[0266] Next, the hydrogen peroxide mixture is heated (step S90).

[0267] 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.

[0268]

[0269] Next, FePO4 is synthesized by adding an aqueous ammonia solution to a heated hydrogen peroxide mixture (step S100).

[0270] After the ammonia aqueous solution is added to the heated hydrogen peroxide mixture, the pH can preferably be 1 to 1.8, and as a specific example, 1.2. In this case, the pH is maintained at a constant level during synthesis, which has the advantage of stably synthesizing FePO4 in a high yield.

[0271] In step S100, 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.

[0272] In step S100, 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.

[0273] 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.

[0274] After the addition of the aqueous ammonia solution in step S100 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.

[0275] In step S100, 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.

[0276]

[0277] Next, the synthesized FePO4 is separated (step S110).

[0278] Separating the FePO4 synthesized in step S100 has the advantage of facilitating the removal of impurities in the subsequent washing step and saving energy.

[0279] 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.

[0280]

[0281] Next, the separated FePO4 is washed with an acidic washing solution having a pH of 1.3 to 1.6 (step S120).

[0282] Through the above washing step, iron phosphate with an incorrect stoichiometric ratio, i.e., Fe x PO yThere 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.

[0283] 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 a mixture thereof 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.

[0284] 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.

[0285]

[0286] In step S120, 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.

[0287]

[0288] In step S120, 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.

[0289] Washing in step S120 may preferably include vacuum filtration, in which case there is an advantage of easily separating FePO4 and the acidic washing solution.

[0290] Step S120 may further include a step of drying the washed FePO4, in which case it has the effect of efficiently removing moisture contained in the washed FePO4.

[0291] 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.

[0292]

[0293] Next, the washed FePO4 is heat-treated (step S130).

[0294] The above heat treatment has the effect of easily removing sulfides introduced into FePO4.

[0295] The above heat treatment can preferably be carried out at 600 to 800 ℃, and as a specific example, at 700 ℃. In this case, there is an advantage that the sulfides introduced into FePO4 are removed, thereby improving the yield and purity of FePO4.

[0296]

[0297] The above heat treatment can preferably be carried out for 3 to 17 hours, and as a specific example, for 5 to 15 hours, and within this range, sulfides introduced into FePO4 are removed, which has the advantage of improving the yield and purity of FePO4.

[0298] The above heat treatment can be carried out, for example, under an air or oxygen atmosphere, and specifically under an air atmosphere. In this case, there is an advantage in that sulfides introduced into FePO4 are removed, thereby improving the yield and purity of FePO4.

[0299] The above oxygen atmosphere may, for example, have an oxygen purity of 59% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and even more preferably 90 to 99%, and in this case, there is an advantage that the sulfides introduced into FePO4 are removed, thereby improving the yield and purity of FePO4.

[0300] The above heat treatment is preferably performed at a temperature rise rate of 1 to 20 ℃ / min, more preferably at a temperature rise rate of 3 to 10 ℃ / min, and as a specific example, 3 ℃ / min. Within this range, it can be implemented without putting strain on the heat treatment equipment and has the advantage of not causing thermal shock to the synthesized FePO4.

[0301] The above heat treatment is performed using various types of furnaces, for example, a box-type furnace, and considering productivity, a rotary kiln capable of continuous processing is used.

[0302] After the above heat treatment, it can be slowly cooled or rapidly cooled in the atmosphere.

[0303]

[0304] After heat treatment in step S130, the FePO4 may contain sulfur (S) of, for example, 1100 ppm or less, preferably 700 ppm or less, more preferably 500 ppm or less, even more preferably 300 ppm, even more preferably 200 ppm or less, and particularly preferably 1 to 200 ppm, and within this range, there is an advantage that the yield and purity of FePO4 are improved.

[0305]

[0306] 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.

[0307]

[0308] [Example]

[0309] Example 1

[0310] 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 analysis (XRD) of the obtained spent anode material powder confirmed that it contained lithium iron phosphate powder with an olivine structure.

[0311] 100 g of the waste cathode material powder prepared above 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.

[0312] 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.

[0313] 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 1.2, thereby precipitating impurities such as aluminum and titanium.

[0314] The above-mentioned dissolved solution containing precipitated impurities such as aluminum and titanium was separated by vacuum filtration to remove the impurities.

[0315] A hydrogen peroxide aqueous solution (30 wt% concentration) was added to 50 ml of the above-mentioned solution from which impurities had been removed, in an amount equal to 2 volume% of the solution based on hydrogen peroxide, and the temperature was raised to 30 ℃ to prepare a hydrogen peroxide mixture. At this time, the process was carried out under stirring at 500 rpm.

[0316] FePO4 was synthesized by continuously adding a 1 molar aqueous ammonia solution to the heated hydrogen peroxide mixture at a rate of 0.1 ml / min to maintain the pH of the mixture at 1.2. At this time, the mixture was stirred at 500 rpm and the heated temperature was maintained.

[0317] The above-mentioned synthesized FePO4 and the mixture were separated using vacuum filtration.

[0318] The above-described separated FePO4 was mixed with an acidic solution (washing solution) with a pH of 1.3 prepared with distilled water and hydrochloric acid at a solid-to-liquid ratio of 20 mL / g and washed for 10 minutes by stirring at 500 rpm.

[0319] After the above washing, FePO4 and the washing solution were separated using vacuum filtration, and the washed FePO4 was obtained.

[0320] The washed FePO4 was vacuum dried at 80°C to obtain FePO4.

[0321] The above-mentioned dried FePO4 was heat-treated at 700 ℃ for 5 hours in an air atmosphere to obtain the final FePO4. At this time, the temperature increase rate was 3 ℃ / min.

[0322] The above pH was measured at room temperature using a METTLER TOLEDO SevenDirect SD30.

[0323]

[0324] Example 2

[0325] In the above Example 1, the above dry FePO4 was heat-treated at 700°C for 10 hours under an air atmosphere, except that the above Example 1 was carried out in the same manner as Example 1.

[0326]

[0327] Example 3

[0328] In the above Example 1, the above dry FePO4 was heat-treated at 700°C for 15 hours under an air atmosphere, except that the above Example 1 was carried out in the same manner as Example 1.

[0329]

[0330] Comparative Example 1

[0331] In the above Example 1, the above dried FePO4 was not heat-treated, except that the above Example 1 was carried out in the same manner as Example 1.

[0332]

[0333] Comparative Example 2

[0334] 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 analysis (XRD) of the obtained spent anode material powder confirmed that it contained lithium iron phosphate powder with an olivine structure.

[0335] 100 g of the waste cathode material powder prepared above 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.

[0336] 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.

[0337] 50 ml of the above-mentioned solution containing Fe and P was taken, and while stirring at room temperature, a 1 molar aqueous sodium hydroxide solution was continuously added at a rate of 1 ml / min to make the pH of the solution 1.2, thereby precipitating impurities such as aluminum and titanium.

[0338] The above-mentioned dissolved solution containing precipitated impurities such as aluminum and titanium was separated by vacuum filtration to remove the impurities.

[0339] A hydrogen peroxide aqueous solution (30 wt% concentration) was added to 50 ml of the above-mentioned solution from which impurities had been removed, in an amount equal to 2 volume% of the solution based on hydrogen peroxide, and the temperature was raised to 30 ℃ to prepare a hydrogen peroxide mixture. At this time, the process was carried out under stirring at 500 rpm.

[0340] FePO4 was synthesized by continuously adding a 1 molar aqueous sodium hydroxide solution to the heated hydrogen peroxide mixture at a rate of 0.1 ml / min to maintain the pH of the mixture at 1.2. At this time, stirring was performed at 500 rpm.

[0341] The above-mentioned synthesized FePO4 and the mixture were separated using vacuum filtration.

[0342] The above-described separated FePO4 was mixed with an acidic solution (washing solution) with a pH of 1.3 prepared with distilled water and hydrochloric acid at a solid-to-liquid ratio of 20 mL / g and washed for 10 minutes by stirring at 500 rpm.

[0343] After the above washing, FePO4 and the washing solution were separated using vacuum filtration, and the washed FePO4 was obtained.

[0344] The washed FePO4 was vacuum dried at 80°C to obtain FePO4.

[0345]

[0346] Comparative Example 3

[0347] In Comparative Example 2 above, the above dried FePO4 was heat-treated at 700°C for 5 hours under an air atmosphere, except that the procedure was carried out in the same manner as Comparative Example 2 above.

[0348]

[0349] Comparative Example 4

[0350] In Comparative Example 2 above, the above dried FePO4 was heat-treated at 700°C for 10 hours under an air atmosphere, except that the procedure was carried out in the same manner as Comparative Example 2 above.

[0351]

[0352] Comparative Example 5

[0353] In Comparative Example 2 above, the above dried FePO4 was heat-treated at 700°C for 15 hours under an air atmosphere, except that the procedure was carried out in the same manner as Comparative Example 2 above.

[0354]

[0355] [Test Example I: Measurement of Sulfur (S) Content in Final FePO4]

[0356] The sulfur (S) content of FePO4 prepared in Examples 1 to 3 and Comparative Examples 1 to 5 was measured by ICP analysis and is shown in Table 1 below.

[0357]

[0358] * ICP analysis: 40.1 g of FePO was aliquoted and placed in a conical tube, and the exact weight was measured. Then, 0.1 ml of nitric acid with a concentration of 70 wt% was added, followed by the addition of 500 µl of 1000 g / kg internal standard (scandium), and the solution was diluted with ultrapure water to a total volume of 50 ml for ICP analysis. The results are shown in Table 1 below.

[0359]

[0360] Classification Basic Solution Heat Treatment Temperature (°C) Heat Treatment Time (hr) Sulfur (S) Content (ppm) Example 1 Ammonia Aqueous Solution 700 510 45 Example 2 Ammonia Aqueous Solution 700 10 261 Example 3 Ammonia Aqueous Solution 700 151 92 Comparative Example 1 Ammonia Aqueous Solution --75 33 Comparative Example 2 Sodium Hydroxide Aqueous Solution --17 173 Comparative Example 3 Sodium Hydroxide Aqueous Solution 700 590 59 Comparative Example 4 Sodium Hydroxide Aqueous Solution 700 10 81 74 Comparative Example 5 Sodium Hydroxide Aqueous Solution 700 15 81 62

[0361] As shown in Table 1 above, it was confirmed that the sulfur content of FePO4 according to the present invention (Examples 1 to 3) was significantly reduced compared to Comparative Examples 1 to 5. Specifically, looking at Comparative Examples 1 and 2, Comparative Example 1, which used an aqueous ammonia solution as the basic solution, showed a significantly reduced sulfur content compared to Comparative Example 2, which used an aqueous sodium hydroxide solution. From this, it was found that the formation of sulfides is suppressed when an aqueous ammonia solution is used as the basic solution.

[0362] In addition, it was found that the sulfur content of Examples 1 to 3, which used an aqueous ammonia solution as the basic solution at the same heat treatment time, was significantly reduced compared to Comparative Examples 3 to 5. From this, it was confirmed that using an aqueous ammonia solution as the basic solution in the FePO4 manufacturing step and heat-treating FePO4 suppresses the formation of sulfides derived from sulfuric acid and basic solutions as in the past, and that sulfides introduced into the synthesized FePO4 are easily removed. That is, when an aqueous ammonia solution is used as the basic solution according to the present invention, (NH4)2SO4 is formed as a sulfide, whereas when a conventional aqueous sodium hydroxide solution is used, Na2SO4 is formed as a sulfide; however, since (NH4)2SO4 has a lower melting point than Na2SO4, it was found that it is removed more easily and cleanly through heat treatment.

Claims

1. (a) A step of adding an aqueous ammonia solution to a dissolved solution containing Fe and P to precipitate impurities and remove them; (b) a step of preparing a hydrogen peroxide mixture by adding an aqueous hydrogen peroxide solution to a dissolved solution containing Fe and P from which impurities have been removed; (c) A step of synthesizing FePO4 by heating a hydrogen peroxide mixture; (d) a step of separating the synthesized FePO4; (e) washing the separated FePO4 with an acidic washing solution having a pH of 1.3 to 1.6; and (f) a step of heat-treating the washed FePO4 at 600 to 800 ℃ for 3 to 17 hours; characterized by comprising Method for manufacturing ferric phosphate.

2. In Paragraph 1, The solution of step (a) above is characterized by having a pH of 0.1 to 0.

5. Method for manufacturing ferric phosphate.

3. In Paragraph 1, The solution is characterized by having a pH of 1.0 to 1.4 after the addition of the aqueous ammonia solution is completed in step (a) above. Method for manufacturing ferric phosphate.

4. In Paragraph 1, The solution of step (a) above is characterized as being a solution in which waste lithium iron phosphate is dissolved in sulfuric acid. Method for manufacturing ferric phosphate.

5. 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 spent cathode material powder; (ii) a step of adding the obtained spent cathode material powder to sulfuric acid at 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 sulfuric acid at a concentration of 0.8 to 1.3 molar (mol / L) to obtain a solution containing Fe and P. Method for manufacturing ferric phosphate.

6. In Paragraph 1, In the above step (a), the ammonia aqueous solution is characterized by being continuously added while stirring the solution. Method for manufacturing ferric phosphate.

7. In Paragraph 1, The ammonia aqueous solution in step (a) above is characterized by having a concentration of 0.8 to 1.3 molar (mol / L). Method for manufacturing ferric phosphate.

8. In Paragraph 1, The above step (b) is characterized by adding an amount of aqueous hydrogen peroxide solution that is 1 to 5 volume percent of the solution based on hydrogen peroxide. Method for manufacturing ferric phosphate.

9. In Paragraph 1, Characterized by heating the hydrogen peroxide mixture to 28 to 60 ℃ in step (c) above. Method for manufacturing ferric phosphate.

10. In Paragraph 1, The method is further characterized by including the step of heating the hydrogen peroxide mixture in step (c) above and then adding an aqueous ammonia solution to adjust the pH to 1.0 to 1.

8. Method for manufacturing ferric phosphate.

11. In Paragraph 1, In step (e) above, the solid-liquid ratio of the separated FePO4 and the acidic washing solution having a pH of 1.3 to 1.6 is characterized as being 15 to 25 mL / g. Method for manufacturing ferric phosphate.

12. In Paragraph 1, The washing in step (e) above is characterized by including adding an acidic washing solution to the separated FePO4 and stirring for 5 to 20 minutes. Method for manufacturing ferric phosphate.

13. In Paragraph 1, The washing in step (e) above is characterized by including vacuum filtration. Method for manufacturing ferric phosphate.

14. In Paragraph 1, Characterized by drying the FePO4 washed in step (e) and then introducing it into step (f). Method for manufacturing ferric phosphate.

15. In Paragraph 1, The heat treatment in step (f) above is characterized by being carried out under an air or oxygen atmosphere. Method for manufacturing ferric phosphate.

16. In Paragraph 1, The FePO4 after heat treatment in step (f) above is characterized by containing 1100 ppm or less of sulfur (S). Method for manufacturing ferric phosphate.

17. (a) a step of adding an aqueous ammonia solution to a solution containing Fe and P to precipitate impurities and remove them; (b) a step of adding an aqueous hydrogen peroxide solution to the solution containing Fe and P from which impurities have been removed to prepare a hydrogen peroxide mixture; (c) a step of synthesizing FePO4 by heating the hydrogen peroxide mixture; (d) a step of separating the synthesized FePO4; (e) a step of washing the separated FePO4 with an acidic washing solution having a pH of 1.3 to 1.6; (f) a step of heat-treating the washed FePO4 at 600 to 800 °C for 3 to 17 hours; (g) a step of adding a lithium precursor to the heat-treated FePO4 and calcining it to produce lithium iron phosphate; (h) a step of mixing a solution containing a carbon source with the produced lithium iron phosphate to prepare a lithium iron phosphate solution; (i) a step of spray-drying the produced lithium iron phosphate solution; and (j) the dried A step of heat-treating lithium iron phosphate by reduction; or (f') a step of preparing lithium iron phosphate by adding a lithium precursor to washed FePO4 and heat-treating it at 600 to 800 ℃ for 3 to 17 hours; (g') a step of preparing a lithium iron phosphate solution by mixing the prepared lithium iron phosphate with a solution containing a carbon source; (h') a step of spray-drying the prepared lithium iron phosphate solution; and (i') a step of reducing the dried lithium iron phosphate; characterized by comprising Method for manufacturing lithium iron phosphate.

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