How to recover lithium

Abstract

The present invention relates to a method for recovering lithium, and more specifically, to a method for recovering lithium, comprising the steps of: (a) dissolving a cathode material powder having an olivine structure, obtained from the cathodes of waste lithium-ion batteries, in an aqueous acetic acid solution to produce a solution; (b) adding an aqueous hydrogen peroxide (H2O2) solution to the solution to obtain a leachate in which lithium has been dissolved and a leachate residue; (c) separating the leachate from the leachate residue; and (d) concentrating the leachate, wherein the step (b) is carried out at 45 to 65°C; the step (a) uses 0.8 to 1.2 mols of acetic acid per mol of the cathode active material in the cathode material powder; and the step (b) uses 0.4 to 0.6 mols of hydrogen peroxide per mol of the cathode active material in the cathode material powder. According to the present invention, a cathode material having an olivine structure is selectively leached using an oxidizing agent within a predetermined temperature range in a weakly acidic aqueous acetic acid solution, thereby recovering lithium with a high yield. Furthermore, FePO4 is stored as the leaching residue and reused as a raw material for lithium iron phosphate. This provides an effect of providing a lithium recovery method that significantly improves productivity and economy, and is environmentally friendly because it does not require wastewater treatment.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0114299 filed on August 30, 2023, and Korean Patent Application No. 10-2024-0106755, refiled on August 9, 2024 based thereon, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for recovering lithium, and more specifically, to an environmentally friendly lithium recovery method in which a positive electrode material having an olivine structure is dissolved in a weakly acidic aqueous solution of acetic acid, and then an aqueous solution of hydrogen peroxide is added to selectively leach lithium within a predetermined temperature range, thereby recovering lithium with a high yield, and further storing FePO4 as the leaching residue and reusing it as a raw material for lithium iron phosphate, thereby significantly improving productivity and economic efficiency and eliminating the need for wastewater treatment. [Background technology]

[0003] Demand for lithium-ion batteries has been steadily increasing since the 1990s, along with the portable electronics market, and has further increased worldwide with the recent rapid expansion of the electric vehicle market. This could lead to an unstable supply and demand of lithium resources in the near future, and the continuous accumulation of end-of-life batteries could also pose a major environmental problem. To solve these problems, recycling used lithium-ion batteries is a very important technological challenge.

[0004] A lithium-ion battery is broadly composed of a positive electrode in which a positive electrode active material layer is coated on a metal foil such as aluminum, a negative electrode in which a negative electrode active material layer is coated on a metal foil such as copper, a separator that prevents the positive and negative electrodes from mixing, and an electrolyte that allows lithium ions to move between the positive and negative electrodes.

[0005] The positive electrode accounts for over 60% of the cost of a lithium-ion battery. This positive electrode is made of lithium cobalt oxide (LiCoO2), which has excellent reversibility, a low self-discharge rate, high capacity, and high energy density, and is easy to synthesize. To reduce the amount of expensive cobalt used, lithium composite oxides containing Ni and Mn, such as lithium nickel cobalt manganese oxide (LiNiMnCoO2) or lithium manganese oxide (LiMnO2), or lithium iron phosphate (LiFePO4) are used. Because these positive electrode materials contain approximately 5-7% lithium, methods for recovering lithium from the positive electrode materials of used lithium-ion batteries are attracting considerable attention.

[0006] However, lithium iron phosphate (LiFePO4) has a very stable hexahedral crystal structure, so in order to break down this stable structure and recover valuable metals, a wet process is used in which high concentrations of strong acid or strong base are used to extract Li, Fe, and P as their respective compounds. This process generates a large amount of toxic wastewater, which causes environmental problems and increases production costs due to the high cost of treating it.

[0007] Therefore, there is a need to develop an environmentally friendly method for recovering lithium from cathode materials with a highly stable crystalline structure obtained from the cathodes of used lithium-ion batteries, with a high yield, while reducing production costs. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Korean Patent Publication No. 10-2007-0112278 Summary of the Invention [Problem to be solved by the invention]

[0009] In order to solve the above-mentioned problems of the prior art, the present invention provides a method for recovering lithium from cathode material of used lithium-ion batteries. The method comprises dissolving a powder of cathode material having an olivine structure obtained from the cathodes of used lithium-ion batteries in an aqueous acetic acid solution to prepare a solution, and then adding an aqueous hydrogen peroxide (H2O2) solution to the prepared solution at 45-65°C to obtain lithium at a high recovery rate. The leaching residue is preserved as FePO4 and reused as a raw material for lithium iron phosphate, thereby significantly improving economic efficiency. The method is environmentally friendly because it does not use a strong acid or strong base, and does not require neutralization or wastewater treatment, thereby reducing process costs.

[0010] The above and other objects of the present invention can all be achieved by the present invention described below. [Means for solving the problem]

[0011] In order to achieve the above-mentioned object, I) the present invention provides a method for recovering lithium, comprising the steps of: (a) dissolving a powder of positive electrode material having an olivine structure obtained from the positive electrodes of waste lithium-ion batteries in an aqueous acetic acid solution to produce a solution; (b) adding an aqueous hydrogen peroxide (H2O2) solution to the solution to obtain a leachate in which lithium has been dissolved and a leachate residue; (c) separating the leachate from the leachate residue; and (d) concentrating the leachate.

[0012] Furthermore, II) the present invention provides a method for recovering lithium, comprising the steps of: (a) dissolving a cathode material powder having an olivine structure obtained from the cathodes of waste lithium-ion batteries in an aqueous acetic acid solution to produce a solution; (b) adding an aqueous hydrogen peroxide (H2O2) solution to the solution to obtain a leachate and a leach residue in which lithium has been dissolved; (c) separating the leachate and the leach residue; and (d) concentrating the leachate, wherein the step (b) is carried out at a temperature of 45 to 65°C; the step (a) uses 0.8 to 1.2 mols of acetic acid per mol of the cathode active material in the cathode material powder; and the step (b) uses 0.4 to 0.6 mols of hydrogen peroxide per mol of the cathode active material in the cathode material powder.

[0013] III) In the above I) or II), the positive electrode material having an olivine structure can preferably contain lithium iron phosphate.

[0014] IV) In the above I) to III), the positive electrode material having an olivine structure may preferably be a compound represented by the following chemical formula 1.

[0015] [Chemical formula 1] Li 1+a Fe 1-b M b (PO 4-c )X c (In the above Chemical Formula 1, M includes one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; X includes one or more elements selected from the group consisting of F, S, and N; and a, b, and c are −0.5≦a≦0.5, 0≦b≦0.5, and 0≦c≦0.1, respectively.)

[0016] V) In the above I) to IV), the positive electrode material powder may preferably be obtained by crushing the positive electrodes of used lithium ion batteries and separating the positive electrode material powder from the current collector.

[0017] VI) In the above I) to V), in step (a), the mass ratio of the positive electrode material powder to the acetic acid aqueous solution may preferably be 1:6 to 1:10.

[0018] VII) In the above I) to VI), in step (a), acetic acid can be preferably used in an amount of 0.8 to 1.2 moles per mole of the positive electrode active material in the positive electrode material powder.

[0019] VIII) In the above I) to VII), in step (b), the aqueous hydrogen peroxide solution can be preferably used in an amount of 0.4 to 0.6 mol per 1 mol of the positive electrode active material in the positive electrode material powder.

[0020] IX) In the above I) to VIII), in the step (a), the aqueous acetic acid solution may have a concentration of 0.5 to 1 molar (mol / L).

[0021] X) In the above I) to IX), in the step (b), the aqueous hydrogen peroxide solution may have a concentration of 25 to 40% by mass.

[0022] XI) In the above I) to X), the lithium recovery method may have a lithium recovery rate of 90 mass % or more as calculated by the following Equation 1:

[0023] [Formula 1] Lithium recovery rate (mass%) = [Lithium content in leachate (g) / Lithium content in cathode powder (g)] × 100

[0024] XII) In the above I) to XI), the step (b) can be preferably carried out at a pH of 3.5 to 5.5.

[0025] XIII) In the above I) to XII), the step (b) can be preferably carried out under stirring.

[0026] XIV) In the above I) to XIII), in the step (c), the separation of the leaching solution and the leaching residue can preferably be performed by vacuum filtration.

[0027] XV) In the above I) to XIV), the leaching residue may preferably contain FePO4.

[0028] XVI) In the above I) to XV), in the step (d), the leachate can be concentrated preferably by evaporation under reduced pressure.

[0029] XVII) In the above I) to XVI), the lithium recovery method can preferably include a step of vacuum drying the leaching residue obtained in the step (c) to obtain a compound containing FePO4.

[0030] XVIII) In the above I) to XVII), the obtained compound containing FePO4 can be preferably produced as lithium iron phosphate by adding lithium and firing, and then adding carbon and firing. [Effects of the Invention]

[0031] According to the present invention, a cathode material having an olivine structure, which is a very stable structure, is dissolved in a weakly acidic aqueous solution of acetic acid, and then an aqueous solution of hydrogen peroxide is added to selectively leach lithium within a predetermined temperature range, thereby recovering lithium with a high yield, and storing FePO4 as the leaching residue and reusing it as a raw material for lithium iron phosphate, thereby significantly improving productivity and economic efficiency.

[0032] Furthermore, since no strong acid or strong base is used for leaching, no wastewater is generated, which reduces process costs and is environmentally friendly.

[0033] The following drawings attached to this specification illustrate embodiments of the present invention and, together with the detailed description below, serve to further understand the technical concept of the present invention. Therefore, the present invention should not be interpreted as being limited to the matters depicted in these drawings. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is an example of the present invention, showing the results of measuring the leaching residue obtained from Example 1 by X-ray diffraction analysis (XRD). [Figure 2] 1 shows the results of measuring the leaching residue obtained from Comparative Example 1 by X-ray diffraction analysis (XRD). [Figure 3] 1 shows the results of measuring the leaching residue obtained from Comparative Example 2 by X-ray diffraction analysis (XRD). [Figure 4] 1 is a process diagram of a method for recovering lithium from a cathode material of a used lithium ion battery according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] The inventors were researching a method for recovering lithium from cathode materials for lithium-ion batteries that have a very stable olivine structure. They found that when a solution of a cathode material with an olivine structure dissolved in a weakly acidic aqueous acetic acid solution was dissolved, a hydrogen peroxide solution of a predetermined concentration was added to the solution, and leaching was carried out at 45 to 65°C, a high lithium recovery rate was achieved, and FePO4 was preserved in the leaching residue. This could be reused as a raw material for lithium iron phosphate, greatly improving economic efficiency. They also found that lithium could be recovered in an environmentally friendly manner, as no strong acid or strong base was used. Based on this, they continued their research and completed the present invention.

[0036] The lithium recovery method of the present invention will be described in detail below.

[0037] However, the terms and words used in this specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts that correspond to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of terms in order to best describe his or her invention. Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely one embodiment of the present invention and do not represent the entire technical idea of ​​the present invention, and that various equivalents and modifications may be available to replace them, and that they may be arranged, substituted, combined, separated, or designed in various other configurations.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0039] How to recover lithium The present invention provides a method for recovering lithium, comprising the steps of: (a) dissolving a powder of cathode material having an olivine structure obtained from the cathodes of used lithium-ion batteries in an aqueous acetic acid solution to produce a solution; (b) adding an aqueous hydrogen peroxide (H2O2) solution to the solution to obtain a leachate containing dissolved lithium and a leach residue; (c) separating the leachate from the leach residue; and (d) concentrating the leachate. This method offers the advantages of a high lithium recovery rate, significant economical improvement by preserving the leach residue (FePO4) and reusing it as a raw material for lithium iron phosphate, and environmental friendliness due to the absence of strong acids or bases, and reduced process costs due to the elimination of the need for neutralization and wastewater treatment.

[0040] The present invention also provides a method for recovering lithium, which comprises the steps of: (a) dissolving a cathode material powder having an olivine structure obtained from the cathode of a waste lithium-ion battery in an aqueous acetic acid solution to produce a solution; (b) adding an aqueous hydrogen peroxide (H2O2) solution to the solution to obtain a leachate and a leach residue in which lithium has been dissolved; (c) separating the leachate and the leach residue; and (d) concentrating the leachate, wherein the step (b) is carried out at a temperature of 45 to 65°C; the step (a) uses 0.8 to 1.2 mols of acetic acid per mol of the cathode active material in the cathode material powder; and the step (b) uses 0.4 to 0.6 mols of hydrogen peroxide per mol of the cathode active material in the cathode material powder. In this case, the lithium recovery rate is high, and the leaching residue is preserved as FePO4 and reused as a raw material for lithium iron phosphate, which significantly improves economic efficiency. In addition, since no strong acid or strong base is used, it is environmentally friendly and does not require neutralization or wastewater treatment, which has the advantage of reducing process costs.

[0041] The lithium recovery method will be described in detail below, divided into stages.

[0042] (a) dissolving a cathode material powder in an aqueous acetic acid solution to prepare a solution; The method for recovering lithium of the present invention includes the step of (a) producing a solution by dissolving a powder of a positive electrode material having an olivine structure obtained from the positive electrodes of used lithium-ion batteries in an aqueous acetic acid solution. In this case, lithium can be recovered at a high yield without using a strong acid or strong base, and no wastewater treatment is required, which is advantageous in being environmentally friendly.

[0043] In this description, the term "olivine structure" refers to a type of cathode material structure, which has a 3D hexahedral lattice structure in which phosphorus and oxygen atoms are strongly bonded. Since the structure can be maintained even if all lithium ions are removed, it has little performance degradation during charge and discharge and excellent thermal stability. In addition, it is economical because inexpensive iron can be used instead of expensive cobalt metal, but its energy density, electrical conductivity, and lithium ion diffusivity are lower than other cathode materials.

[0044] The olivine structure can be confirmed through X-ray diffraction analysis (XRD).

[0045] The cathode material in this description means that it includes or is an active cathode material.

[0046] The positive electrode material having the olivine structure may include, for example, lithium iron phosphate, which has the advantages of being inexpensive and having excellent high-temperature stability and lifespan characteristics.

[0047] The positive electrode material having an olivine structure may be, for example, a compound represented by the following chemical formula 1, which has the advantages of being inexpensive and having excellent high-temperature stability and lifespan characteristics.

[0048] [Chemical formula 1] Li 1+a Fe 1-b M b (PO 4-c )X c (In the above Chemical Formula 1, M includes one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; X includes one or more elements selected from the group consisting of F, S, and N; and a, b, and c are −0.5≦a≦0.5, 0≦b≦0.5, and 0≦c≦0.1, respectively.)

[0049] The lithium iron phosphate may preferably include LiFePO4 having an olivine structure, which has the advantages of being inexpensive, excellent in high-temperature stability and life characteristics.

[0050] As an example, the cathode material powder may be obtained by crushing the cathodes of used lithium-ion batteries and separating the cathode material powder from the current collector. In this case, there is an economic advantage in that resources can be reused by recovering FePO4 and the like together with expensive lithium.

[0051] The positive electrode of the waste lithium ion battery may be, for example, a positive electrode of a discarded lithium ion battery, a defective product generated during the process of coating a positive electrode, or a scrap positive electrode discarded after cutting an electrode plate. Preferably, the positive electrode of a discarded lithium ion battery may be used. In this case, there is an economic advantage in that resources can be reused by recovering FePO4 and the like together with expensive lithium.

[0052] For example, the crushing may be performed by cutting or shredding the positive electrodes of the discarded lithium ion batteries, and preferably may be performed using dry crushing equipment, specifically, a hand mill, a pin mill, a disc mill, a cutting mill, or a hammer mill.

[0053] The crushed positive electrode can be pulverized, for example, with a mixer, hand mill, pin mill, disc mill, cutting mill, or hammer mill, and preferably with a mixer. In this case, there is an advantage that the current collector pieces are chopped into small pieces and the positive electrode material is peeled off and separated from the current collector pieces.

[0054] The pulverized cathode material can be obtained as a powder by, for example, sieving, which has the effect of making leaching easier.

[0055] The acetic acid aqueous solution may be, for example, an acetic acid aqueous solution having a molar concentration (mol / L) of 0.5 to 1, preferably an acetic acid aqueous solution having a molar concentration of 0.6 to 0.9, more preferably an acetic acid aqueous solution having a molar concentration of 0.7 to 0.9, and even more preferably an acetic acid aqueous solution having a molar concentration of 0.75 to 0.85. Within this range, lithium can be recovered in high yield without using a strong acid or a strong base, and no wastewater treatment is required, which is advantageous in terms of being environmentally friendly.

[0056] In step (a), the mass ratio of the positive electrode material powder to the acetic acid aqueous solution may be, for example, 1:6 to 1:10, preferably 1:6.5 to 1:9.5, more preferably 1:7 to 1:9, even more preferably 1:7.5 to 1:8.5, and even more preferably 1:7.5 to 1:8, and within this range, there is an advantage that the positive electrode material powder is easily dissolved in the acetic acid aqueous solution.

[0057] The acetic acid aqueous solution may have a pH of, for example, 2.0 to 3.5, preferably 2.5 to 3.5, and more preferably 2.5 to 3.0. Within this range, the positive electrode material is easily dissolved, which is advantageous in that the recovery rate of lithium increases.

[0058] In this description, pH can be measured by a measurement method commonly used in the technical field to which the present invention pertains, and unless otherwise specified, pH can be measured at room temperature using a general pH measuring device, specifically, a Thermo Scientific Orion Star A Series.

[0059] In this description, normal temperature may be a point within the range of 20±5°C.

[0060] In the step (a), for example, acetic acid is used in an amount of 0.8 to 1.2 moles per mole of the positive electrode active material in the positive electrode material powder, preferably 0.85 to 1.15 moles, more preferably 0.9 to 1.1 moles, and even more preferably 0.95 to 1.05 moles, and within this range, there is an advantage that the reaction between the positive electrode material powder and acetic acid proceeds smoothly.

[0061] In this description, 1 mol of the positive electrode active material is based on the positive electrode active material in the positive electrode material powder containing the positive electrode active material having an olivine structure.

[0062] The step (a) may be carried out at, for example, room temperature to 70°C, preferably 45 to 70°C, more preferably 50 to 70°C, even more preferably 52 to 65°C, still more preferably 55 to 65°C, and particularly preferably 57 to 62°C, and within this range, there is an advantage that the positive electrode material is easily dissolved in the aqueous acetic acid solution.

[0063] For example, the step (a) may be carried out under stirring, which has the advantage of shortening the dissolution time.

[0064] The stirring speed may be, for example, 300 to 700 rpm, preferably 350 to 650 rpm, more preferably 400 to 600 rpm, and even more preferably 450 to 550 rpm. Within this range, there are advantages in that the positive electrode material is easily dissolved in the acetic acid aqueous solution and the stirring time is shortened.

[0065] (b) Obtaining the leachate and leach residue The method for recovering lithium of the present invention may include the step of (b) adding an aqueous solution of hydrogen peroxide (H2O2) to the dissolving solution to obtain a leachate in which lithium has been dissolved and a leach residue. In this case, lithium is selectively leached into the leachate, thereby achieving a high lithium recovery rate, and the leach residue can be preserved as FePO4 and reused as a raw material for lithium iron phosphate, resulting in significant improvements in productivity and economy.

[0066] In this description, leaching refers to dissolving soluble materials to remove the solution and separate the soluble and insoluble components.

[0067] The step (b) may be carried out at, for example, 45 to 65°C, preferably 50 to 65°C, more preferably 52 to 65°C, even more preferably 55 to 65°C, and even more preferably 57 to 62°C. Within this temperature range, there are advantages in that the lithium recovery rate is greatly increased and the leaching of Fe and P components is greatly reduced.

[0068] If the step (a) is carried out at a lower temperature than the step (b), the aqueous hydrogen peroxide solution can be added after the temperature is raised to the temperature of the step (b), which has the advantage of increasing the lithium recovery rate.

[0069] In step (b), the aqueous hydrogen peroxide solution acts as an oxidizing agent, making it easier to leach lithium from the cathode material.

[0070] The hydrogen peroxide (H2O2) aqueous solution may have a hydrogen peroxide concentration of, for example, 25 to 40 mass %, preferably 27 to 35 mass %, and more preferably 27 to 32 mass %. Within this range, lithium is selectively leached, thereby increasing the lithium recovery rate. Furthermore, FePO4 can be stored as a leaching residue and reused as a raw material for lithium iron phosphate, which offers the advantages of significantly improving productivity and economic efficiency.

[0071] In step (b), for example, the aqueous hydrogen peroxide solution may be used in an amount of 0.4 to 0.6 mol per mol of the positive electrode active material in the positive electrode material powder, preferably 0.4 to 0.55 mol, more preferably 0.45 to 0.55 mol, and even more preferably 0.47 to 0.52 mol. Within this range, lithium is selectively leached, thereby increasing the lithium recovery rate, and FePO4 is stored as a leaching residue and reused as a raw material for lithium iron phosphate, resulting in significant improvements in productivity and economy.

[0072] In the step (b), the mass ratio of the positive electrode material powder to the aqueous hydrogen peroxide solution may be, for example, 1:0.3 to 1:0.8, preferably 1:0.3 to 1:0.7, and more preferably 1:0.4 to 1:0.6. Within this range, the pH of the solution is maintained at 3.5 to 5.5, and lithium is selectively leached, resulting in an increased recovery rate.

[0073] The step (b) may be carried out at a pH of, for example, 3.5 to 5.5, preferably 4.0 to 5.5, and more preferably 4.0 to 5.0. By not using a strong acid or strong base within this range, no wastewater treatment is required, which has the advantages of being environmentally friendly and reducing process costs.

[0074] For example, the step (b) may be carried out under stirring, which has the advantage of shortening the leaching time.

[0075] The stirring speed may be, for example, 300 to 700 rpm, preferably 350 to 650 rpm, more preferably 400 to 600 rpm, and even more preferably 450 to 550 rpm, and within this range, there is an advantage that lithium can be easily leached from the solution.

[0076] The stirring time may be, for example, 0.5 hours or more, preferably 0.5 to 2 hours, more preferably 0.5 to 1.5 hours, even more preferably 0.7 to 1.3 hours, and still more preferably 0.9 to 1.2 hours. Within this range, lithium is sufficiently leached from the solution, which is advantageous in that lithium is recovered in a high yield.

[0077] In the present description, the stirring method or stirring device is not particularly limited as long as it is a stirring method or stirring device commonly used in the technical field to which the present invention pertains.

[0078] In step (b), the aqueous hydrogen peroxide solution may be added continuously or all at once, for example, and is preferably added continuously. Specifically, it may be added continuously while stirring, which has the advantage that the pH of the solution does not change and lithium is selectively and sufficiently leached. In the case of the all at once addition, for example, the aqueous hydrogen peroxide solution may be added all at once at the same time as stirring begins or just before stirring, which has the advantage that lithium is selectively leached.

[0079] In this description, "continuous addition" means not "added all at once," and refers to addition drop by drop, little by little, step by step, or in a continuous flow for 10 minutes or more, preferably 30 minutes or more, within the range of the infusion time.

[0080] An example of the reaction mechanism occurring in the dissolution and leaching steps is shown in Chemical Formula 2 below.

[0081] [Chemical formula 2] LiFePO4+CH3COOH+0.5H2O2→FePO4+Li + +CH3COO - +H2O

[0082] In the formula 2, the dissolved state of LiFePO4 changes depending on the pH of the solution in which it is dissolved. + , Fe 2+ , PO4 3- At pH 6 or higher, it exists in the form of Li3PO4, Fe 3+ At pH 2-6, Li + In the present invention, the pH of the acetic acid solution in which the positive electrode material is dissolved is controlled to 2.0 to 3.5, and an aqueous hydrogen peroxide solution is added as an oxidizing agent to dissolve the Fe 2+ Fe 3+ By oxidizing the solution to a pH of 3.5 to 5.5, lithium ions can be more easily leached. Furthermore, by continuously adding an aqueous hydrogen peroxide solution and maintaining the pH of the solution within the range of 3.5 to 5.5, and by carrying out the leaching at 45 to 65°C, lithium leaching can be carried out more stably and sufficiently, allowing lithium to be obtained at a high recovery rate.

[0083] (c) separating the leachate and the leach residue. The method for recovering lithium of the present invention may include (c) a step of separating the leachate from the leach residue. In this case, lithium is recovered from the leachate with a high yield, and FePO4 is preserved from the leach residue and reused as a raw material for lithium iron phosphate, thereby offering the advantages of excellent productivity and economy.

[0084] In step (c), the separation of the leachate and the leach residue can be achieved, for example, by vacuum filtration. In this case, the leachate and the leach residue can be easily separated using only a simple process, which has the advantages of reducing process costs and being environmentally friendly.

[0085] The reduced pressure filtration may preferably be vacuum reduced pressure filtration, specifically vacuum reduced pressure filtration using a filter flask, which has the advantage that the leachate and the leach residue can be easily separated.

[0086] In this description, vacuum reduced pressure filtration is not particularly limited as long as it is a common vacuum reduced pressure filtration in the technical field to which the present invention pertains, and may include, for example, filtration under a partial vacuum or low pressure.

[0087] The leaching residue may contain, for example, FePO4, which can be reused as a raw material for lithium iron phosphate, thereby increasing economic benefits and reusing resources.

[0088] (d) concentrating the leachate The method for recovering lithium of the present invention may include the step (d) of concentrating the leachate, which has the advantage of making it easier to recover lithium.

[0089] In step (d), the leachate can be concentrated by, for example, evaporation under reduced pressure. Specifically, the leachate can be evaporated under reduced pressure immediately without a separate cooling step. In this case, there is an advantage that high-purity lithium can be obtained at a high recovery rate.

[0090] The evaporation under reduced pressure may be carried out at, for example, 70 to 90°C and 5 to 20 mbar, preferably 75 to 85°C and 7 to 12 mbar. In this case, there is an advantage that lithium can be recovered stably in a high yield within a short period of time.

[0091] The leachate can be concentrated to recover lithium, and the lithium can be recovered, for example, as lithium acetate. In this case, the lithium recovery rate can be, for example, 90% by mass or more, preferably 95% by mass or more, and within this range, there is an advantage that economic efficiency is maximized.

[0092] The recovery rate of lithium from the leachate can be measured by a measurement method commonly used in the art. For example, the recovery rate of lithium from the leachate can be measured by inductively coupled plasma (ICP) analysis. Specifically, 0.2 g of the leachate is taken and placed in a conical tube. The exact mass is measured, and 0.1 ml of 70% nitric acid is added to the leachate. 500 μl of 1000 mg / kg internal STD(Sc) is added. The solution is then diluted to 50 ml with ultrapure water and measured by ICP. If necessary, the solution can be further diluted with ultrapure water to ensure that the sample concentration falls within the standard material calibration curve. The lithium content in the cathode material powder can be measured by ICP analysis using the above method, and the lithium recovery rate can be calculated using Equation 1 below.

[0093] [Formula 1] Lithium recovery rate (mass%) = [Lithium content in leachate (g) / Lithium content in cathode powder (g)] × 100

[0094] Furthermore, the lithium recovery method of the present invention may, for example, include a step of vacuum drying the leaching residue obtained in step (c) to obtain a compound containing FePO4. In this case, the compound can be easily produced as a raw material for lithium iron phosphate, which has the effect of reusing resources and being economically advantageous.

[0095] The vacuum drying can be carried out, for example, at 120 to 150°C, preferably 125 to 140°C, and more preferably 125 to 135°C, and within this range, there is an advantage that a compound containing FePO4 can be obtained within a short period of time.

[0096] In the present description, the vacuum drying is not particularly limited as long as it is a vacuum drying method and / or conditions that are commonly used in the technical field to which the present invention pertains.

[0097] The obtained FePO4 can be manufactured into lithium iron phosphate by, for example, adding lithium and firing (hereinafter referred to as a "first firing step"), and then adding carbon and firing (hereinafter referred to as a "second firing step"). Since the FePO4 can be easily manufactured as a raw material for lithium iron phosphate, it has the effect of recycling resources and being economically advantageous.

[0098] The firing (first firing step) after adding the lithium may be carried out at, for example, 600 to 800°C, preferably 650 to 750°C, and within this range, lithium is effectively introduced into the FePO4.

[0099] The calcination (first calcination step) after adding the lithium can be carried out for, for example, 8 to 12 hours, preferably 9 to 11 hours, and more preferably 9.5 to 10.5 hours. Within this range, lithium is effectively introduced into the FePO4.

[0100] The firing (first firing step) after adding lithium may be carried out, for example, in an inert atmosphere, preferably in a nitrogen atmosphere, which has the advantage of preventing oxidation.

[0101] The firing (secondary firing step) after adding the carbon may be carried out at, for example, 500 to 700°C, preferably 550 to 650°C. Within this range, the carbon coats the surface of LiFePO4, which has the advantage of improving electrical conductivity.

[0102] The calcination after adding the carbon (secondary calcination step) can be carried out for, for example, 3 to 6 hours, preferably 4 to 5 hours, and more preferably 3.5 to 4.5 hours. Within this range, there is an advantage in improving the electrical conductivity of LiFePO4.

[0103] The firing after adding the carbon (second firing step) may be performed, for example, in an inert atmosphere, preferably in a nitrogen atmosphere, which has the advantage of preventing oxidation.

[0104] FIG. 4 below is a flowchart of a method for recovering lithium from the cathode material of used lithium ion batteries, which is one embodiment of the present invention.

[0105] Referring to FIG. 4, first, a positive electrode of a used lithium ion battery is prepared (step S10).

[0106] The positive electrode of the waste lithium ion battery may be preferably a positive electrode of a discarded lithium ion battery, a defective product generated during a positive electrode coating process, or a positive electrode scrap discarded after cutting an electrode plate, and preferably, a positive electrode of a discarded lithium ion battery may be prepared.

[0107] The positive electrode has a structure in which a positive electrode active material layer and a positive electrode material including a conductive material are bound on an aluminum foil by a binder.

[0108] Next, the prepared positive electrodes of the waste lithium ion batteries are crushed and pulverized into pieces of an appropriate size (step S20).

[0109] Here, crushing includes cutting or shredding the positive electrode into pieces of a size that is easy to handle. For example, the crushed positive electrode may be 1 cm x 1 cm in size. The crushing may be performed using various dry crushing equipment such as a hand mill, pin mill, disc mill, cutting mill, or hammer mill, or a high-speed cutter may be used to increase productivity.

[0110] The crushing step may be performed or the size of the pieces may be determined in consideration of the handling of the cathode and the properties required for equipment used in subsequent processes. For example, when equipment capable of continuous processing is used, the cathode should be crushed into smaller pieces since good flowability is required.

[0111] The crushed positive electrode is then pulverized using a mixer, a hand mill, a pin mill, a disc mill, a cutting mill, or a hammer mill. As a specific example, when the crushed positive electrode is pulverized using a mixer, the current collector pieces are chopped into small pieces, and the positive electrode material is peeled off and separated from the current collector pieces.

[0112] Next, the pulverized positive electrode material is sieved to obtain a positive electrode material powder having an olivine structure (step S30).

[0113] The sieving is advantageous in that it allows obtaining powder with a uniform size and separating the current collector pieces.

[0114] Next, the obtained positive electrode material powder is dissolved in an aqueous acetic acid solution to produce a solution (step S40).

[0115] In this case, the concentration of the acetic acid aqueous solution may preferably be 0.5 to 1 molar (mol / L), and specifically, may be 0.8 molar. Within this range, the cathode material powder is easily dissolved, and since no strong acid or strong base is used, there are advantages in that no wastewater treatment is required, which is environmentally friendly and reduces process costs.

[0116] The positive electrode material having an olivine structure may preferably be lithium iron phosphate having an olivine structure, and more preferably may be LiFePO4 having an olivine structure, which has the advantages of being excellent in high-temperature stability and life characteristics, and inexpensive.

[0117] The mass ratio of the positive electrode material powder to the acetic acid aqueous solution may be, for example, 1:6 to 1:10, and specifically, 1:7.8. Within this range, there is an advantage that the positive electrode material powder is easily dissolved in the acetic acid aqueous solution.

[0118] The pH of the acetic acid aqueous solution may be, for example, 2.0 to 3.5, specifically 2.5 to 3.0. Within this range, no wastewater treatment is required, which is advantageous in that it is environmentally friendly and reduces process costs.

[0119] The acetic acid is used in an amount of, for example, 0.8 to 1.2 moles per mole of the positive electrode active material in the positive electrode material powder, and specifically, 1 mole. Within this range, there is an advantage that the reaction between the positive electrode material powder and the acetic acid proceeds smoothly.

[0120] The step (S40) of preparing the solution may be performed at room temperature to 70°C, for example, and specifically at 60°C. This temperature range has the advantage that the cathode material powder can be easily dissolved.

[0121] Next, an aqueous solution of hydrogen peroxide (H2O2) is added to the dissolution solution, and a leachate in which lithium has been dissolved and a leach residue are obtained (step S50).

[0122] The leaching step (S50) may be carried out at a temperature of, for example, 45 to 65°C, and specifically, at 60°C. Within this temperature range, lithium is selectively leached at a high concentration, thereby increasing the lithium recovery rate. Furthermore, FePO4 can be stored as a leaching residue and reused as a raw material for lithium iron phosphate, which has the advantage of significantly improving productivity and economic efficiency.

[0123] The hydrogen peroxide solution, for example, acts as an oxidizing agent and selectively leaches lithium from the solution.

[0124] The concentration of the hydrogen peroxide (H2O2) aqueous solution may be, for example, 25 to 40 mass %, and specifically 30 mass %. Within this range, lithium is selectively leached at a high concentration, thereby increasing the lithium recovery rate. Furthermore, FePO4 can be stored as a leaching residue and reused as a raw material for lithium iron phosphate, which has the advantage of significantly improving productivity and economic efficiency.

[0125] The concentration of hydrogen peroxide in the solution may be, for example, 1 to 3.5% by volume, and specifically 1.8% by volume. Within this range, lithium is selectively leached at a high concentration, thereby increasing the lithium recovery rate. Furthermore, FePO4 can be stored as a leaching residue and reused as a raw material for lithium iron phosphate, which has the advantage of significantly improving productivity and economic efficiency.

[0126] The aqueous hydrogen peroxide solution may be used in an amount of, for example, 0.4 to 0.6 mol per mol of the positive electrode active material in the positive electrode material powder, and specifically, 0.5 mol. Within this range, lithium is selectively leached, thereby increasing the lithium recovery rate, and the leaching residue, FePO4, is stored and reused as a raw material for lithium iron phosphate, resulting in significant improvements in productivity and economy.

[0127] In the leaching step (S50), the mass ratio of the cathode material powder to the hydrogen peroxide aqueous solution may be, for example, 1:0.3 to 1:0.8, specifically 1:0.6. Within this range, there is an advantage that lithium can be selectively and sufficiently leached.

[0128] The leaching may be carried out at a pH of, for example, 3.5 to 5.5, and specifically, at a pH of 4 to 5. Within this range, lithium is selectively and sufficiently leached, impurities are reduced, and economic efficiency is significantly improved. In addition, since no strong acid or strong base is used, no wastewater treatment is required, which is advantageous in that it is environmentally friendly and reduces process costs.

[0129] The leaching may be carried out, for example, under stirring, specifically at 500 rpm, and within this range, lithium is advantageously easily leached from the solution.

[0130] The leaching can be preferably carried out by stirring while continuously adding an aqueous hydrogen peroxide solution. In this case, the pH of the solution does not change, which has the advantage that lithium can be leached sufficiently stably and the recovery rate is high.

[0131] The stirring time may be, for example, 0.5 hours or more, and specifically, 1 hour. Within this range, lithium is sufficiently leached from the solution, which is advantageous in that lithium is recovered in a high yield.

[0132] Next, the leachate and the leach residue are separated (step S60).

[0133] The separation of the leachate and leach residue can preferably be performed by vacuum filtration, which has the advantages of allowing the leachate and leach residue to be easily separated using only a simple process, reducing process costs, and being environmentally friendly.

[0134] Through the separation, a leachate in which lithium is dissolved (step S70) and a leach residue (step S90) are obtained.

[0135] The recovery rate of lithium in the leaching solution can be calculated by the following Equation 1, and may be, for example, 90% by mass or more, specifically 95% by mass or more. Within this range, there is an advantage that a high recovery rate maximizes economic efficiency.

[0136] [Formula 1] Lithium recovery rate (mass%) = [Lithium content in leachate (g) / Lithium content in cathode powder (g)] × 100

[0137] Next, the leachate in which lithium has been dissolved is concentrated (step S80).

[0138] The concentration of the leachate may be, for example, by evaporation under reduced pressure. Specifically, the leachate in which Li has been dissolved may be immediately concentrated by evaporation under reduced pressure without a separate cooling process. In this case, there is an advantage that high-purity lithium can be obtained at a high recovery rate.

[0139] The vacuum evaporation may be carried out, for example, at 70 to 90°C and 5 to 20 mbar, and specifically, at 80°C and 10 mbar. In this case, there is an advantage that high-purity lithium can be stably recovered in a high yield within a short period of time.

[0140] The leachate is concentrated to obtain lithium, which may then be recovered as lithium acetate.

[0141] As an optional step, the separated leaching residue is vacuum dried to obtain compounds containing FePO4 (step S100).

[0142] The leaching residue preferably contains FePO4, and in this case, there is an effect that economic benefits are increased by reusing it as a raw material for lithium iron phosphate.

[0143] The vacuum drying can be carried out at, for example, 120 to 150°C, specifically 130°C, and within this range, there is an advantage that a compound containing FePO4 can be obtained within a short time.

[0144] The FePO4 can be prepared into lithium iron phosphate by first adding lithium to the FePO4 and firing the mixture (first firing step), and then adding carbon and firing the mixture (second firing step). This method has the advantage of recycling resources and increasing economic benefits.

[0145] For example, the primary firing step may involve adding lithium to a compound containing FePO4 and firing at 600 to 800°C for 8 to 12 hours in an inert atmosphere. Within this temperature range, lithium is sufficiently introduced into the FePO4 phase, resulting in the conversion to LiFePO4.

[0146] For example, the primary firing step may involve adding lithium to a compound containing FePO4 and firing at 700°C for 10 hours in a nitrogen atmosphere. Within this range, lithium is sufficiently introduced into the FePO4 phase, resulting in the conversion to LiFePO4.

[0147] Thereafter, the secondary firing step can be performed, for example, at 500 to 700°C for 3 to 6 hours in an inert atmosphere, and within this range, there is an advantage in that the electrical conductivity of LiFePO4 is improved.

[0148] For example, the secondary firing step can be performed by adding carbon to the fired LiFePO4 and firing it at 600°C for 4 hours in a nitrogen atmosphere. Within this range, there is an advantage in improving the electrical conductivity of LiFePO4.

[0149] In this description, unless otherwise specified, the reaction or calcination atmosphere may be air, the pressure may be atmospheric pressure, and the temperature may be room temperature, but are not particularly limited.

[0150] In this description, normal temperature may be a point within the range of 20±5°C.

[0151] Preferred examples are presented below to aid in understanding the present invention. However, the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical idea of ​​the present invention. Naturally, such changes and modifications also fall within the scope of the appended claims.

[0152] [Example] Example 1 The cathodes of used lithium-ion batteries were crushed and then pulverized in a mixer to separate the current collectors. The cathode material from which the current collectors were separated was sieved to obtain cathode material powder (LiFePO4) with an olivine structure. X-ray diffraction analysis (XRD) of the obtained cathode material powder confirmed that it was a powder with an olivine structure.

[0153] 12 g of the obtained cathode material powder (LiFePO4) having an olivine structure was dissolved in 94 ml of an aqueous acetic acid solution with a 0.8 molar concentration (mol / L) at 60°C under stirring to prepare a solution. The pH of the aqueous acetic acid solution was 2.5 to 3.0, and the amount of acetic acid was 1 mole per mole of the cathode active material in the cathode material powder. The stirring was carried out at 500 rpm.

[0154] To the prepared solution, 6 ml of a 30 wt% H2O2 aqueous solution was added at 60°C under continuous stirring for 1 hour to obtain a leachate containing dissolved Li and a leach residue. The stirring was performed at 500 rpm. 0.5 moles of hydrogen peroxide was used per mole of the positive electrode active material in the positive electrode powder.

[0155] The leachate containing dissolved Li was separated from the leach residue by vacuum filtration, and the leachate containing dissolved Li was immediately concentrated by vacuum evaporation without a separate cooling process, and Li was recovered as lithium acetate. The recovery rate of the leachate containing dissolved Li was measured.

[0156] The leaching residue was evaporated under reduced pressure to obtain FePO4.

[0157] Comparative Example 1 16.75 g of LiFePO4 powder with an olivine structure obtained from waste lithium-ion batteries and 13.27 g of Na2SO8 as an oxidant were added to 100 ml of distilled water and leached at 25°C for 1 hour to obtain a leachate and leach residue. The mixture was stirred at 500 rpm during the leaching process.

[0158] The leachate in which Li was dissolved and the leach residue were separated by filtration under reduced pressure, and the leachate in which Li was dissolved was evaporated under reduced pressure to obtain Li as lithium sulfate.

[0159] Comparative Example 2 10 g of LiFePO4 powder with an olivine structure obtained from waste lithium-ion batteries was added to 100 ml of 30 mass% H2O2 aqueous solution as an oxidant and 400 ml of distilled water, and leaching was carried out at 25°C for 1 hour to obtain a leachate and leach residue. The mixture was stirred at 500 rpm during leaching. 15.5 moles of hydrogen peroxide were used per mole of positive electrode active material in the positive electrode powder.

[0160] The leachate in which Li was dissolved and the leach residue were separated by vacuum filtration, and the leachate in which Li was dissolved was not subjected to a concentration step because the leachate had very low lithium leaching.

[0161] Comparative Example 3 The same procedure as in Example 1 was carried out, except that the dissolution and leaching were carried out at 25°C.

[0162] Comparative Example 4 The same procedure as in Example 1 was carried out, except that the dissolution and leaching were carried out at 80°C.

[0163] Comparative Example 5 The same procedure as in Example 1 was carried out except that 12 g of powdered LiFePO4 having an olivine structure obtained from waste lithium-ion batteries was dissolved in a mixed solution of 94 ml of 0.8 molar acetic acid aqueous solution and 6 ml of 30 mass % HO aqueous solution, and the solution was leached for 1 hour while stirring at 500 rpm. At this time, the pH of the mixed solution of acetic acid aqueous solution and hydrogen peroxide aqueous solution was 7.

[0164] Comparative Example 6 The same procedure as in Example 1 was carried out, except that 1.5 ml of a 30 wt % H2O2 aqueous solution at 60°C was continuously added to the prepared solution with stirring for 1 hour to obtain a leachate in which Li was dissolved and a leach residue. At this time, 0.2 mol of hydrogen peroxide was used based on 1 mol of the positive active material in the positive electrode powder.

[0165] Comparative Example 7 The same procedure as in Example 1 was carried out, except that 8 ml of a 30 wt % H2O2 aqueous solution at 60°C was continuously added to the prepared solution with stirring for 1 hour to obtain a leachate in which Li was dissolved and a leach residue. At this time, 0.8 mol of hydrogen peroxide was used based on 1 mol of the positive electrode active material in the positive electrode powder.

[0166] Comparative Example 8 The same procedure as in Example 1 was carried out, except that 12 g of the obtained cathode material powder (LiFePO4) having an olivine structure was dissolved in 94 ml of an aqueous acetic acid solution with a concentration of 0.49 molar under stirring at 60° C. to prepare a solution. At this time, the amount of acetic acid was 0.6 mol based on 1 mol of the cathode active material in the cathode material powder.

[0167] Comparative Example 9 The same procedure as in Example 1 was carried out, except that 12 g of the obtained cathode material powder (LiFePO4) having an olivine structure was dissolved in 94 ml of an aqueous acetic acid solution with a concentration of 1.13 molar at 60° C. under stirring to prepare a solution. At this time, the amount of acetic acid was 1.4 moles based on 1 mole of the cathode active material in the cathode material powder.

[0168] Comparative Example 10 The same procedure as in Example 1 was carried out, except that the prepared solution was leached at 70°C.

[0169] [Test Example I: Li recovery rate depending on the amount of acetic acid and hydrogen peroxide added] The leachates in Example 1, Comparative Examples 1, 2, and 6 to 9 in which Li was dissolved were measured by ICP analysis, and the results are shown in Table 1 below.

[0170] *Li recovery rate (mass%): 0.2 g of the leaching solution was taken and placed in a conical tube, and the exact mass was measured. 0.1 ml of 70% nitric acid was added, followed by 500 μl of 1000 mg / kg internal STD (Sc), and the solution was diluted to 50 ml with ultrapure water. The lithium content was measured using ICP analysis, and the recovery rate was calculated using Equation 1 below. The lithium content in the cathode powder was also measured using ICP analysis using the same method as above, and the lithium recovery rate was calculated using Equation 1 below.

[0171] [Formula 1] Lithium recovery rate (mass%) = [Lithium content in leachate (g) / Lithium content in cathode powder (g)] × 100

[0172] [Table 1]

[0173] As shown in Table 1, Example 1 according to the present invention had a much higher Li recovery rate than Comparative Examples 1, 2, and 6 to 9, and the Fe and P recovery rates were at similar or equivalent levels. This confirms that lithium was selectively leached in Example 1.

[0174] [Test Example II: XRD Analysis] The results of XRD analysis of the leaching residues separated in Example 1 and Comparative Examples 1 and 2 are shown in the following Figures 1 to 3, respectively. *XRD analysis: 2 g of sample was placed in an XRD measurement holder and measured at an accelerating voltage of 40 kV and 30 mA, 2θ 10-80°, step size 0.02, and speed 2° / min.

[0175] As shown in Figure 1 below, the XRD results for the leaching residue of Example 1 according to the present invention confirmed that a FePO4 peak was observed, but no LiFePO4 peak was observed. This confirmed that FePO4 was preserved in the leaching residue of Example 1 according to the present invention. Furthermore, it was found that Example 1 had a clearer FePO4 peak intensity than Comparative Examples 1 and 2.

[0176] In addition, as shown in Figures 2 and 3 below, not only FePO4 peaks but also LiFePO4 peaks were observed in the XRD results of the leaching residues of Comparative Examples 1 and 2. This confirmed that the leaching residues of Comparative Examples 1 and 2 contained a large amount of Li.

[0177] [Test Example III: Recovery rates of Li, Fe, and P depending on leaching temperature] The recovery rates of Li, Fe, and P for the leachates of Example 1, Comparative Example 3, and Comparative Example 10 were measured by ICP analysis, and the results are shown in Table 2 below. Here, the recovery rates of Fe and P were measured by ICP analysis using the same method as that for measuring the recovery rate of Li.

[0178] [Table 2]

[0179] As shown in Table 2, Example 1 according to the present invention had a much higher Li recovery rate than Comparative Examples 3, 4, and 10, and the Fe and P recovery rates were similar or equivalent. This confirms that the leaching solution of Example 1 selectively leached only lithium.

[0180] [Test Example IV: Recovery rates of Li, Fe, and P depending on the order of adding hydrogen peroxide solution] The recovery rates of Li, Fe, and P in the leachates of Example 1 and Comparative Example 5 were measured by ICP analysis, and the results are shown in Table 3 below.

[0181] [Table 3]

[0182] As shown in Table 3, it was confirmed that Example 1 according to the present invention had a higher recovery rate of Li and lower recovery rates of Fe and P than Comparative Example 5. This shows that in Example 1, only lithium was selectively leached, and only trace amounts of Fe and P were leached, compared to Comparative Example 5.

Claims

1. (a) dissolving a powder of a cathode material having an olivine structure obtained from the cathode of a waste lithium ion battery in an acetic acid aqueous solution to prepare a solution; (b) adding hydrogen peroxide (H ２ O ２ ) aqueous solution to obtain a leachate containing dissolved lithium and a leach residue; (c) separating the leachate and the leach residue; (d) concentrating the leachate; The step (b) is carried out at 45 to 65°C; In the step (a), acetic acid is used in an amount of 0.8 to 1.2 moles per mole of the positive electrode active material in the positive electrode material powder; In the step (b), 0.4 to 0.6 moles of hydrogen peroxide are used per mole of the positive electrode active material in the positive electrode material powder.

2. The method for recovering lithium according to claim 1 , wherein the positive electrode material having an olivine structure contains lithium iron phosphate.

3. The cathode material having an olivine structure is a compound represented by the following chemical formula 1: [Chemical formula 1] Li １＋ａ Fe １－ｂ M ｂ (PO ４－ｃ )X ｃ 2. The method of claim 1, wherein, in Chemical Formula 1, M includes one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; X includes one or more elements selected from the group consisting of F, S, and N; and a, b, and c are in the ranges of −0.5≦a≦0.5, 0≦b≦0.5, and 0≦c≦0.1, respectively.

4. 2. The method for recovering lithium according to claim 1, wherein the positive electrode material powder is obtained by crushing the positive electrodes of used lithium ion batteries and separating the positive electrode material powder from the current collector.

5. 2. The method for recovering lithium according to claim 1, wherein in step (a), the mass ratio of the positive electrode material powder to the acetic acid aqueous solution is 1:6 to 1:

10.

6. 2. The method for recovering lithium according to claim 1, wherein in the step (a), the concentration of the aqueous acetic acid solution is 0.5 to 1 molar (mol / L).

7. 2. The method for recovering lithium according to claim 1, wherein in the step (b), the concentration of the aqueous hydrogen peroxide solution is 25 to 40 mass %.

8. The lithium recovery method has a lithium recovery rate of 90 mass% or more as calculated by the following Equation 1: [Formula 1] Lithium recovery rate (mass%) = [lithium content in leachate (g) / lithium content in positive electrode material powder (g)] × 100 The method for recovering lithium according to claim 1, wherein

9. 2. The method for recovering lithium according to claim 1, wherein the step (b) is carried out at a pH of 3.5 to 5.

5.

10. 2. The method for recovering lithium according to claim 1, wherein the step (b) is carried out with stirring.

11. 2. The method for recovering lithium according to claim 1, wherein in step (c), the separation of the leaching solution and the leaching residue is performed by vacuum filtration.

12. The leaching residue is FePO ４ 2. The method for recovering lithium according to claim 1, comprising:

13. 2. The method for recovering lithium according to claim 1, wherein in step (d), the leaching solution is concentrated by evaporation under reduced pressure.

14. The leaching residue obtained in step (c) is vacuum dried to obtain FePO ４ The method for recovering lithium according to claim 1, further comprising the step of obtaining

15. The obtained FePO ４ The method for recovering lithium according to claim 14, wherein the lithium iron phosphate is produced by adding lithium and firing the resulting solution, and then adding carbon and firing the resulting solution.

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