How to recover lithium

Abstract

The present invention relates to a method for recovering lithium, and more specifically, the method includes the steps of: (i) heat-treating a waste cathode in which a cathode active material layer containing an olivine structure, a binder, and carbon is applied to a current collector; or a cathode active material layer powder obtained by crushing the same; at 220 to 280°C to recover a cathode material having an olivine structure as a powder; (ii) dissolving the recovered cathode material powder having an olivine structure in an aqueous acetic acid solution to produce a cathode material solution; and (iii) adding an aqueous solution of hydrogen peroxide (H2O2) to the cathode material solution. The present invention relates to a lithium recovery method, comprising the steps of (i) introducing a solution into a cathode material to obtain a leachate and a leach residue in which lithium has dissolved, (ii) separating the leachate from the leach residue, and (v) concentrating the leachate, wherein in the step (ii), the aqueous acetic acid solution contains 0.8 to 1.2 moles of acetic acid per mole of positive electrode active material in the cathode material powder, and (iii), the aqueous hydrogen peroxide solution contains 0.4 to 0.6 moles of hydrogen peroxide per mole of positive electrode active material in the cathode material powder. The present invention relates to an environmentally friendly lithium recovery method, which allows for a high lithium recovery rate by easily obtaining a positive electrode material powder from used cathodes having an olivine structure, and furthermore, by storing FePO4 as the leach residue and reusing it as a raw material for lithium iron phosphate, significantly improving productivity and economic efficiency, and does not require wastewater treatment.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority from Korean Patent Application Nos. 10-2023-0143673 and 10-2023-0143674, filed October 25, 2023, and Korean Patent Application No. 10-2024-0144577, which was refiled on October 22, 2024, based on these applications, and all contents disclosed in the documents of these Korean patent applications 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 that involves low-temperature heat treatment of used positive electrodes having a positive electrode active material layer containing an olivine structure, a binder, and carbon applied to a current collector, or a powder of the positive electrode active material layer obtained by crushing the same, to recover a powder of the positive electrode material having an olivine structure, dissolving the recovered powder of the positive electrode material in a weakly acidic aqueous solution of acetic acid, and then adding an aqueous hydrogen peroxide solution to selectively leach lithium, thereby easily obtaining powder of the positive electrode material from the used positive electrodes and achieving a high lithium recovery rate. Furthermore, the leaching residue, FePO4, is stored and reused as a raw material for lithium iron phosphate, thereby significantly improving productivity and economy 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] Lithium-ion batteries are 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] In particular, lithium iron phosphate (LiFePO4) has a very stable hexahedral crystal structure, but in order to break down this stable structure and recover valuable metals, a wet process is used in which highly concentrated strong acids or strong bases 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 the cost of treating it, thereby increasing production costs.

[0007] Therefore, there is a need to develop a lithium recovery method that can recover lithium from the positive electrode material of used lithium-ion batteries, which has a hard crystalline structure, with a high yield, reduce production costs, and is environmentally friendly. [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 problems of the prior art as described above, the present invention provides a lithium recovery method that involves low-temperature heat treatment of waste positive electrodes or a positive electrode active material layer powder obtained by crushing the waste positive electrodes to recover a positive electrode material powder having an olivine structure, dissolving the recovered positive electrode material powder in a weakly acidic aqueous acetic acid solution, and then adding an aqueous hydrogen peroxide solution to selectively leach lithium, thereby easily obtaining a powder of positive electrode material from the waste positive electrodes and achieving a high lithium recovery rate. Furthermore, by storing FePO4 as the leaching residue and reusing it as a raw material for lithium iron phosphate, productivity and economy are greatly improved, and 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 object, I) the present invention provides a method for producing a cathode material having an olivine structure in the form of a powder by heat-treating a used cathode, in which a cathode active material layer containing an olivine structure, a binder, and carbon is applied to a current collector, or a powder of the cathode active material layer obtained by crushing the used cathode, at 220 to 280°C; (ii) dissolving the recovered cathode material powder having the olivine structure in an aqueous acetic acid solution to produce a cathode material solution; and (iii) adding an aqueous hydrogen peroxide (H2O2) solution to the cathode material solution. (iv) a step of separating the leachate from the leachate residue; and (v) a step of concentrating the leachate, wherein in step (ii), the aqueous acetic acid solution contains 0.8 to 1.2 mol of acetic acid per 1 mol of positive electrode active material in the positive electrode material powder, and in step (iii), the aqueous hydrogen peroxide solution contains 0.4 to 0.6 mol of hydrogen peroxide per 1 mol of positive electrode active material in the positive electrode material powder.

[0012] II) In the above I), the positive electrode material having an olivine structure may contain lithium iron phosphate.

[0013] III) In the above I) or II), the positive electrode material having an olivine structure may be a compound represented by the following chemical formula 1.

[0014] (chemical formula 1) Li 1+a Fe 1-b M b (PO 4-c )X c

[0015] 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 −0.5≦a≦0.5, 0≦b≦0.5, and 0≦c≦0.1, respectively.

[0016] IV) In the above I) to III), the crushing in step (i) may be carried out using a hand mill, pin mill, disk mill, cutting mill, hammer mill, mixer or blender.

[0017] V) In the above I) to IV), the heat treatment in the step (i) may be carried out for 30 minutes to 6 hours.

[0018] VI) In the above I) to V), the heat treatment in the step (i) may be carried out in an air or oxygen atmosphere.

[0019] VII) In the above I) to VI), in the step (ii), the pH of the aqueous acetic acid solution may be 2 to 3.5.

[0020] VIII) In the above I) to VII), in the step (iii), the aqueous hydrogen peroxide solution may be added in portions.

[0021] IX) In the above I) to VIII), after the addition of the aqueous hydrogen peroxide solution in the step (iii) is completed, the pH of the positive electrode material solution may be 3 to 5.5.

[0022] X) In the above I) to IX), the steps (ii) and (iii) may be carried out at a temperature of 35 to 70°C.

[0023] XI) In the above I) to X), in the step (iv), the separation of the leaching solution and the leaching residue may be performed by vacuum filtration.

[0024] XII) In any of I) to XI), the lithium recovery method may have a lithium recovery rate calculated by the following mathematical formula 1 of 83 mass % or more.

[0025] [Formula 1] Lithium recovery rate (mass%) = [Lithium content in the leachate (g) / Lithium content in the cathode material powder recovered after heat treatment (g)] × 100 XIII) In the above I) to XII), the leaching residue in step (iv) may contain FePO4.

[0026] XIV) In the above I) to XIII), in the step (v), the leaching solution may be concentrated by evaporation under reduced pressure.

[0027] XV) In the above I) to XIV), the method for recovering lithium may include a step of concentrating the leaching residue obtained in the step (iv) to obtain FePO4.

[0028] XVI) In the above I) to XV), the method for recovering lithium may include: (iv-1) adding lithium to the obtained FePO4 and calcining the mixture to produce LiFePO4; and (iv-2) adding carbon to the produced LiFePO4 and calcining the mixture. [Effects of the Invention]

[0029] According to the present invention, used positive electrodes, which have a positive electrode material having an olivine structure, which is a very stable structure, coated on a current collector and which are coated with a positive electrode active material layer containing a binder and carbon, or a powder of the positive electrode active material layer obtained by crushing such used positive electrodes, are subjected to low-temperature heat treatment to recover a positive electrode material powder having an olivine structure. The recovered positive electrode material powder is then dissolved in a weakly acidic aqueous solution of acetic acid, and an aqueous solution of hydrogen peroxide is then added to selectively leach lithium, thereby easily recovering the positive electrode material as a powder from the used positive electrodes and recovering lithium with a high yield. Furthermore, the leaching residue, FePO4, is stored and reused as a raw material for lithium iron phosphate, thereby significantly improving productivity and economic efficiency.

[0030] Furthermore, since no strong acid or strong base is used in the leaching, there is an effect that the amount of wastewater generated is small, the process cost is reduced, and it is environmentally friendly.

[0031] 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 details shown in these drawings. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a flowchart illustrating a method for recovering lithium from waste positive electrodes according to one embodiment of the present invention. [Figure 2] 1 is a flowchart illustrating a method for recovering lithium from waste positive electrodes according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0033] The inventors were researching a method for recovering lithium from used positive electrodes containing a positive electrode material with a very stable olivine structure. They discovered that the used positive electrodes, or a powder of the positive electrode active material layer obtained by crushing the used positive electrodes, can be subjected to low-temperature heat treatment to thermally decompose the carbon and binder in the positive electrode active material layer, thereby recovering a powder of the positive electrode material with an olivine structure. The recovered positive electrode material powder is then dissolved in a weakly acidic aqueous solution of acetic acid, and then an aqueous hydrogen peroxide solution is added to selectively leach lithium. This finding confirmed that powdered positive electrode material can be easily obtained from the used positive electrodes, lithium can be recovered with a high yield, and FePO4 is preserved in the leaching residue, which can be reused as a raw material for lithium iron phosphate, greatly improving economic efficiency. Furthermore, because no strong acid or strong base is used, lithium can be recovered in an environmentally friendly manner. Based on this, further research was conducted, leading to the completion of the present invention.

[0034] The lithium recovery method of the present invention will be described in detail below.

[0035] 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 consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concepts 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 examples 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.

[0036] 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.

[0037] How to recover lithium The lithium recovery method of the present invention includes the steps of: (i) heat-treating a waste positive electrode, in which a positive electrode active material layer containing a positive electrode material having an olivine structure, a binder, and carbon is applied to a current collector; or a powder of the positive electrode active material layer obtained by crushing the waste positive electrode, at 220 to 280°C to recover the positive electrode material having an olivine structure as a powder; (ii) dissolving the recovered positive electrode material powder having an olivine structure in an aqueous acetic acid solution to produce a positive electrode material solution; and (iii) adding an aqueous solution of hydrogen peroxide (H2O2) to the positive electrode material solution. (iv) separating the leachate from the leachate residue; and (v) concentrating the leachate, wherein in step (ii), the aqueous acetic acid solution contains 0.8 to 1.2 moles of acetic acid per mole of the positive electrode active material in the powdered positive electrode material, and in step (iii), the aqueous hydrogen peroxide solution contains 0.4 to 0.6 moles of hydrogen peroxide per mole of the positive electrode active material in the powdered positive electrode material. This method offers the advantages of easily obtaining positive electrode powder from used positive electrodes, achieving a high lithium recovery rate, saving the leachate residue (FePO4) and reusing it as a raw material for lithium iron phosphate, significantly improving economic efficiency, and reducing the environmental impact by not using a strong acid or strong base, thereby eliminating the need for neutralization and wastewater treatment.

[0038] The lithium recovery method will be described in detail below, divided into stages.

[0039] (i) A step of heat-treating a waste positive electrode in which a positive electrode active material layer containing a positive electrode material having an olivine structure, a binder, and carbon is applied onto a current collector, or a positive electrode active material layer powder obtained by crushing the waste positive electrode, at 220 to 280°C, and recovering the positive electrode material having an olivine structure as a powder. The method for recovering lithium of the present invention includes the step of (i) heat-treating a waste positive electrode, in which a positive electrode active material layer containing a positive electrode material having an olivine structure, a binder, and carbon is applied onto a current collector, or a powder of the positive electrode active material layer obtained by crushing the waste positive electrode, at 220 to 280°C to recover the positive electrode material having an olivine structure as a powder. In this case, the positive electrode active material layer and the current collector can be easily separated, which has the advantage of allowing lithium to be recovered in a high yield in the subsequent leaching step.

[0040] In this application, the term "olivine structure" refers to a type of cathode material structure in which the lattice structure is a three-dimensional (3D) hexahedron with strong bonds between phosphorus and oxygen atoms. Because the structure can be maintained even if all lithium ions are removed, there is little performance degradation during charging and discharging, and the thermal stability is excellent. Furthermore, since inexpensive iron can be used instead of expensive cobalt metal, it is economical, but its energy density, electrical conductivity, and lithium ion diffusivity are lower than those of other cathode materials.

[0041] The olivine structure can be confirmed through X-ray diffraction analysis (XRD).

[0042] 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.

[0043] The lithium iron phosphate may be, for example, a compound represented by the following Chemical Formula 1, which has advantages of being inexpensive and having excellent high-temperature stability and lifespan characteristics.

[0044] (chemical formula 1) Li 1+a Fe 1-b M b (PO 4-c )X c

[0045] 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 −0.5≦a≦0.5, 0≦b≦0.5, and 0≦c≦0.1, respectively.

[0046] 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.

[0047] The discarded positive electrodes may preferably be positive electrodes separated from used and discarded lithium secondary batteries, defective positive electrode sheets or positive electrode scraps generated in the manufacturing process of lithium secondary batteries, or more preferably positive electrode scraps remaining after punching a positive electrode plate from a positive electrode sheet. In this case, there is an economic advantage in that resources can be reused by recovering FePO4 and the like together with expensive lithium.

[0048] The crushing in step (i) can be performed using, for example, a hand mill, a pin mill, a disc mill, a cutting mill, a hammer mill, a mixer, or a blender. Preferably, a mixer can be used. In this case, the waste positive electrodes are finely chopped into small pieces, and the current collector and the positive electrode active material layer are separated, thereby easily obtaining the positive electrode active material layer as a powder. In addition, in a subsequent heat treatment process, the binder and carbon are sufficiently pyrolyzed, thereby increasing the recovery rate of lithium.

[0049] In step (i), the waste positive electrodes may be crushed to a size of, for example, 10 mm × 10 mm or less, preferably 7 mm × 7 mm or less, more preferably 5 mm × 5 mm or less, even more preferably 3 mm × 3 mm or less, and even more preferably 0.1 to 3 mm × 0.1 to 3 mm or less. In this case, the waste positive electrodes are finely chopped into small pieces, and the current collector and the positive electrode active material layer are separated, which has the advantage of making it easy to obtain the positive electrode active material layer as a powder.

[0050] In this application, "10 mm x 10 mm or less" is meant to include (10 mm or less) x 10 mm, (10 mm) x (10 mm or less), and (10 mm or less) x (10 mm or less).

[0051] The crushed waste positive electrodes may be sieved to separate the current collector and the positive electrode active material layer, thereby obtaining the positive electrode active material layer as a powder. In this case, it is advantageous that the binder and carbon can be sufficiently removed in a subsequent heat treatment step.

[0052] The sieving may be performed, for example, using a sieve of 120 to 250 mesh, preferably 140 to 240 mesh, more preferably 170 to 230 mesh, and even more preferably 180 to 210 mesh. In this case, the current collector pieces separated in the crushing process are separated, the size of the crushed positive electrode active material layer is made uniform, and the binder and carbon are sufficiently pyrolyzed in the subsequent heat treatment step, thereby easily obtaining the positive electrode material as a powder.

[0053] The heat treatment in step (i) can be carried out at, for example, 220 to 280°C, preferably 230 to 280°C, more preferably 240 to 280°C, and even more preferably 240 to 270°C. Within this temperature range, the carbon and binder are thermally decomposed, thereby advantageously recovering a powder of a cathode material having an olivine structure from the current collector, and recovering lithium in a high yield in the subsequent leaching step.

[0054] The heat treatment in step (i) can be carried out for, for example, 30 minutes to 6 hours, preferably 1 hour to 5.5 hours, more preferably 1 hour to 5 hours, even more preferably 1 hour to 4 hours, and even more preferably 1 hour to 3 hours. Within this range, the carbon and binder are thermally decomposed, thereby advantageously recovering a powder of a cathode material having an olivine structure from the current collector, and recovering lithium in a high yield in the subsequent leaching step.

[0055] In the present application, the heat treatment time refers to the time required for treatment at the heat treatment temperature, and does not include the time required to reach the heat treatment temperature.

[0056] The heat treatment in step (i) can be carried out, for example, in an air or oxygen atmosphere, preferably in air. In this case, the carbon and the binder are thermally decomposed, which has the effect of easily obtaining a powder of a cathode material having an olivine structure from the current collector.

[0057] For example, the purity of the oxygen may be 59% or more, preferably 80% or more, more preferably 90% or more, and even more preferably 90 to 99%. Within this range, there is an advantage that the binder and carbon are removed without remaining.

[0058] The oxygen purity % may be volume % or mol %.

[0059] The purity of oxygen in the present application is not particularly limited, as long as it is measured by a measurement method commonly used in the technical field to which the present invention pertains.

[0060] The cathode material in this application means that it contains a cathode active material or is a cathode active material.

[0061] (ii) dissolving the recovered cathode material powder having an olivine structure in an acetic acid aqueous solution to produce a cathode material solution; The lithium recovery method of the present invention includes (ii) a step of dissolving the recovered cathode material powder having an olivine structure in an aqueous acetic acid solution to produce a cathode material solution. In this case, lithium can be recovered at a high yield without using a strong acid or a strong base, and there is an advantage that wastewater treatment is not required, which is environmentally friendly.

[0062] In the step (ii), the acetic acid aqueous solution may contain, for example, 0.8 to 1.2 moles of acetic acid 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.

[0063] In the present application, 1 mol of the positive electrode active material is based on the positive electrode active material having an olivine structure in the positive electrode material powder.

[0064] In the present application, the mole number of the positive electrode active material in the positive electrode powder can be measured by a measurement method commonly used in the technical field to which the present invention pertains, for example, by ICP (inductively coupled plasma) analysis. Specifically, it can be calculated from the contents of Li, Fe, and P measured by ICP analysis.

[0065] The pH of the acetic acid aqueous solution may be, 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.

[0066] In the present application, pH may be measured by a measurement method commonly used in the technical field to which the present invention pertains, and unless otherwise specified, pH may be measured at room temperature using a general pH measuring device, specifically, a Thermo Scientific Orion Star A series.

[0067] In this application, normal temperature may be a point within the range of 20±5°C.

[0068] The aqueous acetic acid solution may preferably be an aqueous acetic acid solution having a molar concentration (mol / L) of 0.6 to 0.9, more preferably an aqueous acetic acid solution having a molar concentration of 0.7 to 0.9, and even more preferably an aqueous acetic acid 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 there are advantages in that no wastewater treatment is required, making it environmentally friendly.

[0069] In step (ii) above, 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.

[0070] The step (ii) may be carried out at, for example, 35 to 70°C, preferably 40 to 65°C, more preferably 45 to 60°C, even more preferably 45 to 55°C, and even more preferably 47 to 52°C, and within this range, there is an advantage that the positive electrode material can be easily dissolved in an aqueous acetic acid solution.

[0071] For example, the step (ii) may be carried out under stirring, which has the advantage of shortening the dissolution time.

[0072] 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 is an advantage that the positive electrode material is sufficiently dissolved in the acetic acid aqueous solution and the dissolution time is shortened.

[0073] The stirring time may be, for example, 10 to 60 minutes, preferably 20 to 50 minutes, and more preferably 25 to 40 minutes. Within this range, the cathode material is sufficiently dissolved in the acetic acid aqueous solution, and the dissolution time is advantageously shortened.

[0074] (iii) Obtaining the leachate and leach residue The lithium recovery method of the present invention can include the step of (iii) adding an aqueous solution of hydrogen peroxide (H2O2) to the cathode material solution to obtain a leachate in which lithium has 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.

[0075] As used herein, leaching refers to dissolving soluble materials to remove the solution and separate the soluble and insoluble components.

[0076] In the step (iii), the aqueous hydrogen peroxide solution acts as an oxidizing agent, making it easier to leach lithium from the cathode material.

[0077] In the step (iii), 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 the leaching residue, FePO4, can be stored and reused as a raw material for lithium iron phosphate, resulting in significant improvements in productivity and economy.

[0078] In the step (iii), the aqueous hydrogen peroxide solution can be preferably added in portions, more preferably three or more equal amounts, more preferably three to seven portions, and even more preferably four to six portions. In this case, the pH of the cathode material solution is gradually changed, and lithium is selectively and sufficiently leached.

[0079] After the addition of the aqueous hydrogen peroxide solution in step (iii) is completed, the pH of the cathode material solution may be, for example, pH 3 to 5.5, preferably pH 3.5 to 5.5, and more preferably pH 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.

[0080] The step (iii) may be carried out at, for example, 35 to 70°C, preferably 40 to 65°C, more preferably 45 to 60°C, even more preferably 45 to 55°C, and even more preferably 47 to 52°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.

[0081] In step (iii), the mass ratio of the cathode material powder to the hydrogen peroxide aqueous solution may be, for example, 1:0.2 to 1:0.6, preferably 1:0.3 to 1:0.5, and more preferably 1:0.3 to 1:0.4. Within this range, the pH of the cathode material solution is maintained at 3.5 to 5.5 after the addition of the hydrogen peroxide aqueous solution is completed, which has the advantages of selectively leaching lithium, increasing the recovery rate, and eliminating the need for wastewater treatment, which is environmentally friendly and reduces process costs.

[0082] For example, the step (iii) may be carried out under stirring, which has the advantage of shortening the leaching time.

[0083] 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 is easily leached from the positive electrode material solution.

[0084] The stirring time may be, for example, 0.5 hours or more, preferably 0.5 to 3 hours, more preferably 1 to 2.5 hours, even more preferably 1 to 2 hours, and still more preferably 1.2 to 1.7 hours. Within this range, lithium is sufficiently leached from the positive electrode material solution, which is advantageous in that lithium is recovered in a high yield.

[0085] An example of the reaction mechanism occurring in the dissolution and leaching steps is shown in Chemical Formula 2 below.

[0086] (Chemical formula 2) LiFePO4+CH3COOH+0.5H2O2→FePO4+Li + +CH3COO - +H2O 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 to 5.5, lithium ions can be more easily leached. Furthermore, by continuously adding an aqueous hydrogen peroxide solution to the solution, and by carrying out the leaching at a temperature of 35 to 70°C, lithium can be leached more stably and sufficiently, thereby obtaining lithium at a high recovery rate.

[0087] (iv) Separating the leachate from the leach residue The method for recovering lithium of the present invention may include (iv) 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.

[0088] In step (iv), 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.

[0089] 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 leaching solution and the leaching residue can be easily separated.

[0090] In the present application, 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.

[0091] 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.

[0092] (v) concentrating the leachate The method for recovering lithium of the present invention may include (v) a step of concentrating the leachate, which has the advantage of making it easier to recover lithium.

[0093] In step (v), 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.

[0094] The evaporation under reduced pressure may be carried out, for example, at 70 to 90°C under 5 to 20 mbar, and preferably at 75 to 85°C under 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.

[0095] The leachate is concentrated to obtain lithium, which may be recovered as lithium acetate, for example. This method has the advantage of obtaining high-purity lithium at a high recovery rate.

[0096] The lithium recovery method may have a lithium recovery rate calculated by the following mathematical formula 1 of, for example, 83% by mass or more, preferably 87% by mass or more, more preferably 90% by mass or more, even more preferably 93% by mass or more, even more preferably 95% by mass or more, and particularly preferably 96 to 100% by mass. Within this range, lithium is sufficiently and selectively leached, and the leaching of iron (Fe) and phosphorus (P) components is significantly reduced, resulting in excellent economic efficiency.

[0097] [Formula 1] Lithium recovery rate (mass%) = [Lithium content in the leachate (g) / Lithium content in the cathode material powder recovered after heat treatment (g)] × 100 In Equation 1, the lithium content of the leachate can be measured by a measurement method commonly used in the art. For example, the lithium content of the leachate can be measured using 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 an internal standard (Sc) at 1000 mg / kg is added, and the mixture is diluted to 50 mL with ultrapure water and measured using ICP. If necessary, the mixture can be further diluted with ultrapure water to ensure that the sample concentration falls within the standard calibration curve. In addition, in Equation 1, the lithium content of the positive electrode active material layer powder recovered after heat treatment can be measured using ICP.

[0098] Furthermore, the lithium recovery method of the present invention may, for example, include a step of vacuum drying the leaching residue obtained in step (iv) to obtain a compound containing FePO4. In this case, by easily producing the raw material for lithium iron phosphate, resources can be reused, which is economically advantageous.

[0099] 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.

[0100] In the present application, the vacuum drying is not particularly limited as long as it is vacuum drying that is commonly performed in the technical field to which the present invention pertains.

[0101] The step of obtaining the compound containing FePO4 preferably includes the steps of (iv-1) adding lithium to the obtained FePO4 and calcining the mixture to produce LiFePO4, and (iv-2) adding carbon to the produced LiFePO4 and calcining the mixture. In this case, the lithium iron phosphate cathode material can be easily produced, which has the effect of recycling resources and being economically advantageous.

[0102] In the step (iv-1), the firing 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 sufficiently.

[0103] In the step (iv-1), the calcination 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.

[0104] In the step (iv-1), the calcination may be carried out, for example, in an inert atmosphere, preferably in a nitrogen atmosphere, which has the advantage of preventing oxidation.

[0105] In the step (iv-2), the firing may be carried out, for example, at 500 to 700°C, preferably 550 to 650°C. Within this range, carbon is coated on the surface of LiFePO4, which has the advantage of improving electrical conductivity.

[0106] In the step (iv-2), the calcination 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, carbon has the advantage of improving the electrical conductivity of LiFePO4.

[0107] In the step (iv-2), the calcination may be carried out, for example, in an inert atmosphere, preferably in a nitrogen atmosphere, which has the advantage of preventing oxidation.

[0108] In the present application, unless otherwise defined, the heat treatment may be performed at a temperature increase rate of 1 to 20°C / min, preferably 3 to 10°C / min, until the heat treatment temperature is reached.

[0109] FIG. 1 below is a flowchart of a lithium recovery method according to one embodiment of the present invention.

[0110] Referring to FIG. 1, first, a discarded positive electrode is prepared (step S10).

[0111] The discarded positive electrodes may be preferably discarded positive electrodes of lithium ion batteries, defective products generated during a positive electrode coating process, or scrap positive electrodes discarded after cutting an electrode plate, and preferably, discarded positive electrodes of lithium ion batteries may be prepared.

[0112] The positive electrode has a structure in which a positive electrode active material layer containing a positive electrode material and carbon is bound on an aluminum foil by a binder.

[0113] The cathode material is a cathode material having an olivine structure, and may be preferably lithium iron phosphate having an olivine structure, or more preferably LiFePO4 having an olivine structure, which has the advantages of being excellent in high-temperature stability and life characteristics, and inexpensive.

[0114] Next, the prepared waste positive electrodes are crushed into pieces of an appropriate size (step S20).

[0115] Here, the crushing includes cutting or shredding the cathode into pieces of easily handleable size. For example, the crushed waste cathodes may be 5 mm x 5 mm in size. The crushing may be performed using various dry crushing equipment such as a mixer, blender, hand mill, pin mill, disc mill, cutting mill, or hammer mill. For example, crushing using a mixer is preferred. In this case, the waste cathodes are finely chopped and easily separated into a current collector and a cathode active material layer. The resulting material is then uniformly heat-treated in a subsequent heat treatment step, which allows the binder and carbon in the cathode active material layer to be easily removed, thereby increasing the lithium recovery rate.

[0116] Next, the crushed waste positive electrodes are separated into a current collector and a positive electrode active material layer through a sieve (step S30).

[0117] The waste positive electrodes crushed in step S20 can be sieved using a 120 to 250 mesh sieve. As a specific example, the current collector is separated by sieving using a 200 mesh sieve, and the positive electrode active material layer is obtained as a powder.

[0118] Next, the obtained positive electrode active material layer powder is subjected to low-temperature heat treatment, and a positive electrode material having an olivine structure is recovered as a powder (step S40). Here, the heat treatment is performed to thermally decompose the carbon and binder in the positive electrode active material layer.

[0119] Through the heat treatment, carbon and binder in the positive electrode are thermally decomposed and removed, and the positive electrode material can be easily separated in powder form.

[0120] The heat treatment can be carried out, for example, in an air or oxygen atmosphere, specifically in air. In this case, the binder and carbon react with oxygen without carbonization and are blown away as gases such as CO and CO, so that the binder and carbon are completely removed and the cathode material is recovered.

[0121] The heat treatment is preferably carried out at 220 to 280°C, specifically at 250°C. If the temperature is lower than 220°C, it is difficult to remove the binder, and if the temperature exceeds 280°C, the binder is easily removed, but the lithium recovery rate decreases.

[0122] The heat treatment is preferably carried out at a temperature increase rate of 1 to 20°C / min, more preferably 3 to 10°C / min, and specifically 5°C / min. Within this range, there are advantages in that the load on the heat treatment equipment is reduced and thermal shock or the like does not occur to the cathode scrap.

[0123] The heat treatment may be carried out for a period of time sufficient to pyrolyze the binder and carbon, preferably 30 minutes or more, more preferably 30 minutes to 6 hours, and specifically 1 hour to 5 hours. Within this range, the binder and carbon are pyrolyzed sufficiently, and excellent pyrolysis efficiency is achieved.

[0124] The heat treatment may be carried out using various types of furnaces, for example, a box-type furnace, or, in consideration of productivity, a rotary kiln capable of continuous treatment.

[0125] After the heat treatment, the material can be cooled slowly or rapidly in the air.

[0126] Next, the recovered cathode material powder having an olivine structure is dissolved in an aqueous acetic acid solution to produce a cathode material solution (step S50).

[0127] The acetic acid aqueous solution is used in an amount that provides 0.8 to 1.2 moles of acetic acid per mole of the positive electrode active material in the positive electrode material powder, for example, and may be used in an amount that provides 1 mole, and within this range, there is an advantage that the reaction between the positive electrode material powder and acetic acid proceeds smoothly.

[0128] The pH of the acetic acid aqueous solution may be, for example, 2.0 to 3.5, and specifically, 2.5 to 3.0. Within this range, there are advantages in that no wastewater treatment is required, making it environmentally friendly and reducing process costs.

[0129] The concentration of the acetic acid aqueous solution may be preferably 0.6 to 0.9 molar, 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.

[0130] 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.

[0131] The step (S50) of preparing the cathode material solution may be carried out at, for example, 35 to 70°C, and specifically, at 50°C, which has the advantage that the cathode material powder can be easily dissolved within this range.

[0132] The step (S50) of preparing the cathode material solution may be performed, for example, with stirring, specifically, with a stirring speed of 500 rpm. In this case, there is an advantage that the cathode material powder is easily dissolved in the acetic acid aqueous solution, and the dissolution time is shortened.

[0133] The stirring time may be, for example, 10 to 60 minutes, and specifically 30 minutes. Within this range, the positive electrode material powder is easily dissolved in the acetic acid aqueous solution, and the dissolution time is advantageously shortened.

[0134] Next, an aqueous solution of hydrogen peroxide (H2O2) is added to the positive electrode material solution, and a leachate in which lithium has dissolved and a leach residue are obtained (step S60).

[0135] The hydrogen peroxide solution, for example, acts as an oxidizing agent and selectively leaches lithium from the cathode material solution.

[0136] The aqueous hydrogen peroxide solution may be used in an amount that provides 0.4 to 0.6 moles of hydrogen peroxide per mole of the positive electrode active material in the positive electrode material powder, for example, and specifically 0.5 moles. Within this range, lithium is selectively leached, increasing the lithium recovery rate, and the leaching residue, FePO4, can be stored and reused as a raw material for lithium iron phosphate, resulting in significant improvements in productivity and economy.

[0137] The leaching step (S60) may be carried out at a temperature of, for example, 35 to 70°C, and specifically, at 50°C. Within this temperature range, lithium is selectively leached at a high concentration, thereby increasing the lithium recovery rate. Furthermore, FePO4 is 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.

[0138] In the leaching step (S60), the mass ratio of the positive electrode material powder to the hydrogen peroxide aqueous solution may be, for example, 1:0.2 to 1:0.6, specifically 1:0.3, and within this range, there is an advantage that lithium can be selectively and sufficiently leached.

[0139] In the leaching step (S60), the hydrogen peroxide solution can be added in divided amounts, for example, four equal amounts can be added in divided amounts. In this case, the pH of the cathode material solution can be gradually changed, which is advantageous in that lithium can be selectively and sufficiently leached.

[0140] After the addition of the hydrogen peroxide solution in the leaching step (S60) is completed, the cathode material solution has a pH of 3 to 5.5, and specifically, may have a pH of 4 to 5. Within this range, lithium is selectively and sufficiently leached, impurities are reduced, and economic efficiency is greatly 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.

[0141] 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 positive electrode material solution.

[0142] The stirring time may be, for example, 0.5 hours or more, and specifically, 1.5 hours. Within this range, lithium is sufficiently leached from the cathode material solution, which is advantageous in that lithium is recovered in a high yield.

[0143] Next, the leachate and the leach residue are separated (step S70).

[0144] The separation of the leachate and leach residue can preferably be performed using 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.

[0145] Through the separation, a leachate (step S80) in which the lithium compound is dissolved and a leach residue (step S100) are obtained.

[0146] Next, the leachate in which lithium has been dissolved is concentrated (step S90).

[0147] The concentration of the leachate can be, for example, by evaporation under reduced pressure. Specifically, the leachate in which Li has been dissolved can be immediately concentrated by evaporation under reduced pressure without a separate cooling step. In this case, there is an advantage that high-purity lithium can be obtained at a high recovery rate.

[0148] The vacuum evaporation can be carried out, for example, at 70 to 90°C under 5 to 20 mbar, and specifically, at 80°C under 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.

[0149] The leachate is concentrated to obtain lithium.

[0150] As an optional step, the separated leaching residue is vacuum dried to obtain compounds containing FePO4 (step S110).

[0151] 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.

[0152] 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 stably within a short period of time.

[0153] Specifically, step S110 may include: i) adding lithium to the obtained FePO4 and calcining the mixture to produce LiFePO4; and ii) adding carbon to the produced LiFePO4 and calcining the mixture. In this case, the lithium iron phosphate cathode material can be easily produced, which has the effect of reusing resources and being economically advantageous.

[0154] In step i), the calcination can be performed at 600 to 800°C for 8 to 12 hours in an inert atmosphere. Within this range, lithium is sufficiently introduced into the FePO4 phase and converted into LiFePO4.

[0155] As a specific example, lithium can be added to a compound containing FePO4 and fired at 700°C for 10 hours in a nitrogen atmosphere. Within this range, lithium is sufficiently incorporated into the FePO4 phase, resulting in the conversion to LiFePO4, which has excellent performance.

[0156] In the step ii), the calcination can be carried out, for example, at 500 to 700°C for 3 to 6 hours in an inert atmosphere. Within this range, there is an advantage that the electrical conductivity of LiFePO4 is improved.

[0157] As a specific example, carbon can be added to calcined LiFePO4 and calcined at 600°C for 4 hours in a nitrogen atmosphere, and within this range, there is an advantage in improving the electrical conductivity of LiFePO4.

[0158] In the present application, unless otherwise specified, the firing atmosphere may be air, the pressure may be atmospheric pressure, and the temperature may be room temperature.

[0159] In this application, normal temperature may be a point within the range of 20±5°C.

[0160] FIG. 2 below is a flowchart of a lithium recovery method according to another embodiment of the present invention.

[0161] Referring to FIG. 2, first, discarded positive electrodes are prepared (step S10).

[0162] The discarded positive electrodes may be preferably discarded positive electrodes of lithium ion batteries, defective products generated during a positive electrode coating process, or scrap positive electrodes discarded after cutting an electrode plate, and preferably, discarded positive electrodes of lithium ion batteries may be prepared.

[0163] The positive electrode has a structure in which a positive electrode active material layer containing a positive electrode material and carbon is bound on an aluminum foil by a binder.

[0164] The cathode material is a cathode material having an olivine structure, and may be preferably lithium iron phosphate having an olivine structure, or more preferably LiFePO4 having an olivine structure, which has the advantages of being excellent in high-temperature stability and life characteristics, and inexpensive.

[0165] Next, the waste positive electrodes are heat-treated to obtain positive electrode material powder having an olivine structure (step S20). Here, the heat treatment is performed to thermally decompose the carbon and binder in the positive electrodes.

[0166] Through the heat treatment, carbon and binder in the positive electrode are thermally decomposed and removed, and since the binder is removed, the positive electrode material is separated from the current collector, and the separated positive electrode material can be easily sorted in powder form.

[0167] The heat treatment can be carried out, for example, in an air or oxygen atmosphere, specifically in air. In this case, the binder and carbon react with oxygen without being carbonized and are blown away as gases such as CO and CO. Thus, the binder and carbon are completely removed and the positive electrode material is separated from the current collector.

[0168] The heat treatment is preferably carried out at 220 to 280°C, specifically at 230 to 270°C. If the temperature is lower than 220°C, it is difficult to remove the binder, and the current collector cannot be separated. If the temperature exceeds 280°C, the lithium recovery rate decreases.

[0169] The heat treatment is preferably carried out at a temperature increase rate of 1 to 20°C / min, more preferably 3 to 10°C / min, and specifically 5°C / min. Within this range, there are advantages in that the load on the heat treatment equipment is reduced and thermal shock or the like does not occur to the cathode scrap.

[0170] The heat treatment may be carried out for a period of time sufficient to pyrolyze the binder and carbon, preferably 30 minutes or more, more preferably 30 minutes to 6 hours, and specifically 1 hour to 5 hours. Within this range, the binder and carbon are pyrolyzed sufficiently, and excellent pyrolysis efficiency is achieved.

[0171] The heat treatment may be carried out using various types of furnaces, for example, a box-type furnace, or, in consideration of productivity, a rotary kiln capable of continuous treatment.

[0172] After the heat treatment, the material can be cooled slowly or rapidly in the air.

[0173] Next, the recovered cathode material powder having an olivine structure is sieved to make the particle size uniform (step S30).

[0174] The cathode material powder recovered after the heat treatment in step S20 can be preferably sieved, more preferably sieved through a 120 to 250 mesh sieve. Specifically, sieving through a 200 mesh sieve to obtain a uniform size has the advantage of facilitating the subsequent leaching step.

[0175] Next, the recovered cathode material powder having an olivine structure is dissolved in an aqueous acetic acid solution to produce a cathode material solution (step S40).

[0176] The acetic acid aqueous solution is used in an amount that provides 0.8 to 1.2 moles of acetic acid per mole of the positive electrode active material in the positive electrode material powder, for example, and may be used in an amount that provides 1 mole, and within this range, there is an advantage that the reaction between the positive electrode material powder and acetic acid proceeds smoothly.

[0177] The pH of the acetic acid aqueous solution may be, for example, 2.0 to 3.5, and specifically, 2.5 to 3.0. Within this range, there are advantages in that no wastewater treatment is required, making it environmentally friendly and reducing process costs.

[0178] The concentration of the acetic acid aqueous solution may be preferably 0.6 to 0.9 molar, 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.

[0179] 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 1:8. Within this range, there is an advantage that the positive electrode material powder is easily dissolved in the acetic acid aqueous solution.

[0180] The step (S40) of preparing the cathode material solution may be performed at, for example, 35 to 70°C, and specifically, at 50°C, which has the advantage that the cathode material powder can be easily dissolved within this temperature range.

[0181] The step (S40) of preparing the cathode material solution may be performed, for example, with stirring, specifically, with a stirring speed of 500 rpm. In this case, there is an advantage that the cathode material powder is easily dissolved in the acetic acid aqueous solution, and the dissolution time is shortened.

[0182] Next, an aqueous solution of hydrogen peroxide (H2O2) is added to the positive electrode material solution, and a leachate in which lithium has dissolved and a leach residue are obtained (step S50).

[0183] The hydrogen peroxide solution, for example, acts as an oxidizing agent and selectively leaches lithium from the cathode material solution.

[0184] The aqueous hydrogen peroxide solution may be used in an amount that provides 0.4 to 0.6 moles of hydrogen peroxide per mole of the positive electrode active material in the positive electrode material powder, for example, and specifically 0.5 moles. Within this range, lithium is selectively leached, increasing the lithium recovery rate, and the leaching residue, FePO4, can be stored and reused as a raw material for lithium iron phosphate, resulting in significant improvements in productivity and economy.

[0185] The leaching step (step S50) may be carried out at a temperature of, for example, 35 to 70°C, and specifically, at 50°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.

[0186] In the leaching step (step S50), the mass ratio of the positive electrode material powder to the hydrogen peroxide aqueous solution may be, for example, 1:0.2 to 1:0.6, and specifically may be 1:0.3. Within this range, there is an advantage that lithium can be selectively and sufficiently leached.

[0187] In the leaching step (step S50), the hydrogen peroxide solution can be preferably added in divided amounts, for example, by adding four equal amounts in divided amounts. In this case, the pH of the cathode material solution is gradually changed, which has the advantage of allowing lithium to be selectively and sufficiently leached.

[0188] After the addition of the hydrogen peroxide solution in the leaching step (step S50) is completed, the pH of the cathode material solution is 3 to 5.5, and specifically, may be 4 to 5. Within this range, lithium is selectively and sufficiently leached, impurities are reduced, and economic efficiency is greatly 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.

[0189] 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 positive electrode material solution.

[0190] The stirring time may be, for example, 0.5 hours or more, and specifically, 1.5 hours. Within this range, lithium is sufficiently leached from the cathode material solution, which is advantageous in that lithium is recovered in a high yield.

[0191] Next, the leachate and the leach residue are separated (step S60).

[0192] The separation of the leachate and leach residue can preferably be performed using 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.

[0193] Through the separation, a leachate (step S70) in which the lithium compound is dissolved and a leach residue (step S90) are obtained.

[0194] Next, the leachate in which lithium has been dissolved is concentrated (step S80).

[0195] The concentration of the leachate can be, for example, by evaporation under reduced pressure. Specifically, the leachate in which Li has been dissolved can be immediately concentrated by evaporation under reduced pressure without a separate cooling step. In this case, there is an advantage that high-purity lithium can be obtained at a high recovery rate.

[0196] The vacuum evaporation can be carried out, for example, at 70 to 90°C under 5 to 20 mbar, and specifically, at 80°C under 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.

[0197] The leachate is concentrated to obtain lithium, which may then be recovered as lithium acetate.

[0198] As an optional step, the separated leaching residue is vacuum dried to obtain compounds containing FePO4 (step S100).

[0199] 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.

[0200] 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 stably within a short period of time.

[0201] Specifically, step S100 may include: i) adding lithium to the obtained FePO4 and calcining the mixture to produce LiFePO4; and ii) adding carbon to the produced LiFePO4 and calcining the mixture. In this case, the lithium iron phosphate cathode material can be easily produced, which has the effect of reusing resources and being economically advantageous.

[0202] In step i), the calcination can be performed at 600 to 800°C for 8 to 12 hours in an inert atmosphere. Within this range, lithium is sufficiently introduced into the FePO4 phase and converted into LiFePO4.

[0203] As a specific example, lithium can be added to a compound containing FePO4 and fired at 700°C for 10 hours in a nitrogen atmosphere. Within this range, lithium is sufficiently incorporated into the FePO4 phase, resulting in the conversion to LiFePO4, which has excellent performance.

[0204] In the step ii), the calcination can be carried out, for example, at 500 to 700°C for 3 to 6 hours in an inert atmosphere, and within this range, there is an advantage that the electrical conductivity of LiFePO4 is improved.

[0205] As a specific example, carbon can be added to calcined LiFePO4 and calcined at 600°C for 4 hours in a nitrogen atmosphere, and within this range, there is an advantage in improving the electrical conductivity of LiFePO4.

[0206] 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.

[0207] [Example] Example 1 A used cathode, in which a cathode active material layer containing an olivine-structured cathode material, a binder, and carbon was coated on a current collector, was crushed to a size of 5 mm x 5 mm in a mixer and then sieved through a 200-mesh sieve to separate the current collector, obtaining the cathode active material layer as a powder. The obtained cathode active material layer was heat-treated in air at 250°C for 5 hours to pyrolyze the carbon and binder in the cathode active material layer, and the cathode material with an olivine structure was recovered as a powder (LiFePO4). X-ray diffraction analysis (XRD) of the recovered cathode material powder confirmed that it was a powder with an olivine structure.

[0208] 12 g of the recovered olivine-structured cathode powder (LiFePO4) was added to 96 mL of a 0.8 molar acetic acid aqueous solution and dissolved under stirring at 50°C to prepare a cathode solution. The pH of the 0.8 molar acetic acid aqueous solution was 2.5 to 3.0, and the acetic acid aqueous solution contained 1 mole of acetic acid per mole of the cathode active material in the cathode powder. The stirring was performed at 500 rpm for 30 minutes. The moles of the cathode active material in the cathode powder were calculated from the contents of Li, Fe, and P measured through ICP analysis.

[0209] A 30% by weight H2O2 aqueous solution was added to the prepared cathode material solution at 50°C with stirring for 5 hours, 1 mL at a time, four times, to obtain a leachate containing dissolved lithium and a leach residue. The stirring was performed at 500 rpm. The hydrogen peroxide aqueous solution contained 0.5 moles of hydrogen peroxide per mole of the cathode active material in the cathode material powder.

[0210] The leachate containing dissolved lithium was separated from the leach residue by vacuum filtration, and the leachate containing dissolved lithium was immediately concentrated by vacuum evaporation without a separate cooling process to obtain lithium acetate.

[0211] The leaching residue was evaporated under reduced pressure to obtain FePO4.

[0212] Example 2 The same procedure as in Example 1 was carried out, except that the heat treatment was carried out for 1 hour.

[0213] Comparative Example 1 The same procedure as in Example 1 was carried out, except that the heat treatment step was not carried out.

[0214] Comparative Example 2 The same procedure as in Example 1 was carried out, except that the heat treatment step was carried out at 200° C. for 1 hour.

[0215] Comparative Example 3 The same procedure as in Example 1 was carried out, except that the heat treatment step was carried out at 200° C. for 5 hours.

[0216] Comparative Example 4 The same procedure as in Example 1 was carried out, except that the heat treatment step was carried out at 300° C. for 1 hour.

[0217] Comparative Example 5 The same procedure as in Example 1 was carried out, except that the heat treatment step was carried out at 300° C. for 5 hours.

[0218] [Test Example I: Recovery rates of lithium, iron, and phosphorus, and residual carbon content] In Examples 1 and 2 and Comparative Examples 1 to 5, the contents of lithium (Li), iron (Fe), and phosphorus (P) were measured using ICP analysis for the leachate in which Li was dissolved, and the recovery rates of lithium (Li), iron (Fe), and phosphorus (P) were calculated using the following Equations 1 to 3. The content of residual carbon (C) was measured using CS analysis, and the results are shown in Table 1 below.

[0219] [Formula 1] Lithium recovery rate (mass%) = [Lithium content in the leachate (g) / Lithium content in the cathode material powder recovered after heat treatment (g)] × 100 [Formula 2] Iron recovery rate (mass%) = [iron content in leachate (g) / iron content in cathode material powder recovered after heat treatment (g)] × 100 [Formula 3] Phosphorus recovery rate (mass%) = [Phosphorus content in leachate (g) / Phosphorus content in cathode material powder recovered after heat treatment (g)] × 100 In Equations 1 to 3, the lithium, iron, and phosphorus contents of the leaching solution were measured by taking 0.2 g of the leaching solution, placing it in a conical tube, and measuring the exact mass. 0.1 mL of 70% nitric acid was added to the leachate, and then 500 μL of an internal standard (Sc) at 1000 mg / kg was added. The solution was then diluted to 50 mL with ultrapure water, and the lithium, iron, and phosphorus contents were measured by ICP analysis.

[0220] In addition, in the above Equations 1 to 3, the contents of lithium, iron, and phosphorus contained in the cathode material powder recovered after the heat treatment were measured by ICP analysis.

[0221] The residual carbon content was measured by CS analysis of the carbon content contained in the cathode material powder recovered after the heat treatment. Specifically, a calibration blank was measured, and then a carbon standard was measured three or more times. A combustion improver was added to a crucible containing 10 mg of sample, and the crucible was placed on the lower electrode of the CS analyzer. The sample was then injected into the upper part and combusted to measure the carbon content.

[0222] [Table 1]

[0223] As shown in Table 1 above, it was confirmed that, compared with Comparative Examples 1 to 5, Examples 1 and 2 according to the present invention had a very high recovery rate of lithium, and low recovery rates of iron and phosphorus.

[0224] Furthermore, Comparative Example 1, which was not subjected to heat treatment, and Comparative Examples 2 and 3, which were subjected to heat treatment at 200°C, had a high content of residual carbon.

[0225] Furthermore, Comparative Examples 2 and 3, which were heat-treated at 200°C, had a low lithium recovery rate, and Comparative Examples 4 and 5, which were heat-treated at 300°C, had a large decrease in Li recovery rate due to oxidation of Fe.

[0226] [Additional Examples] Additional Example 1 The cathode material powder was recovered from the collector as a powder (LiFePO4) with an olivine structure. X-ray diffraction analysis (XRD) of the recovered cathode material powder confirmed that it was an olivine structure.

[0227] The recovered positive electrode material powder having an olivine structure was sieved through a 200 mesh sieve.

[0228] 12 g of the sieved cathode material powder (LiFePO4) having an olivine structure was added to 96 mL of a 0.8 molar acetic acid aqueous solution and dissolved under stirring at 50°C to produce a cathode material solution. At this time, the pH of the 0.8 molar acetic acid aqueous solution was 2.5 to 3.0, and the acetic acid aqueous solution contained 1 mole of acetic acid per mole of the cathode active material in the cathode material powder. Here, stirring was performed at 500 rpm for 30 minutes.

[0229] A 30% by weight H2O2 aqueous solution was added to the prepared cathode material solution at 50°C with stirring for 1.5 hours, 1 mL at a time, four times, to obtain a leachate containing dissolved lithium and a leach residue. The stirring was performed at 500 rpm. The hydrogen peroxide aqueous solution contained 0.5 moles of hydrogen peroxide per mole of the cathode active material in the cathode material powder.

[0230] The leachate containing dissolved lithium was separated from the leach residue by vacuum filtration, and the leachate containing dissolved lithium was immediately concentrated by vacuum evaporation without a separate cooling process to obtain lithium acetate.

[0231] The leaching residue was evaporated under reduced pressure to obtain FePO4.

[0232] Additional Example 2 Additional Example 1 was carried out in the same manner as Additional Example 1, except that the heat treatment was carried out for 5 hours.

[0233] Additional Example 3 Additional Example 1 was carried out in the same manner as Additional Example 1, except that the heat treatment was carried out at 250° C. for 1 hour.

[0234] Additional Example 4 Additional Example 1 was carried out in the same manner as Additional Example 1, except that the heat treatment was carried out at 250° C. for 5 hours.

[0235] Additional Example 5 Additional Example 1 was carried out in the same manner as Additional Example 1, except that the heat treatment was carried out at 270° C. for 1 hour.

[0236] Additional Example 6 Additional Example 1 was carried out in the same manner as Additional Example 1, except that the heat treatment was carried out at 270° C. for 5 hours.

[0237] Additional Comparative Example 1 Additional Example 1 was carried out in the same manner as Additional Example 1, except that the heat treatment was carried out at 200° C. for 1 hour.

[0238] Additional Comparative Example 2 Additional Example 1 was carried out in the same manner as Additional Example 1, except that the heat treatment was carried out at 200° C. for 5 hours.

[0239] Additional Comparative Example 3 Additional Example 1 was carried out in the same manner as Additional Example 1, except that the heat treatment was carried out at 300° C. for 1 hour.

[0240] Additional Comparative Example 4 Additional Example 1 was carried out in the same manner as Additional Example 1, except that the heat treatment was carried out at 300° C. for 5 hours.

[0241] [Additional Test Example I: Recovery Rates of Lithium, Iron, and Phosphorus] In the additional examples 1 to 6 and the additional comparative examples 1 to 4, the leachate in which Li was dissolved was measured by ICP analysis, and the recovery rates of lithium (Li), iron (Fe), and phosphorus (P) were calculated using Equations 1 to 3. The results are shown in Table 2 below.

[0242] In Equations 1 to 3, the lithium, iron, and phosphorus contents of the leaching solution were measured by taking 0.2 g of the leaching solution, placing it in a conical tube, and measuring the exact mass. 0.1 mL of 70% nitric acid was added to the leachate, and then 500 μL of an internal standard (Sc) at 1000 mg / kg was added. The solution was then diluted to 50 mL with ultrapure water, and the lithium, iron, and phosphorus contents were measured by ICP analysis.

[0243] In addition, in the above Equations 1 to 3, the contents of lithium, iron, and phosphorus contained in the cathode material powder recovered after the heat treatment were measured by ICP analysis.

[0244] [Table 2]

[0245] As shown in Table 2 above, it was confirmed that Additional Examples 1 to 6 according to the present invention had a very high recovery rate of lithium and low recovery rates of iron and phosphorus compared to Additional Comparative Examples 1 to 4.

[0246] In addition, in the additional Comparative Examples 1 and 2 in which the heat treatment was performed at 200°C, the binder was not thermally decomposed, and therefore the positive electrode material could not be recovered as a powder from the current collector. In the additional Comparative Examples 3 and 4 in which the heat treatment was performed at 300°C, the recovery rate of Li decreased due to the oxidation of Fe.

Claims

1. (i) heat-treating, at 220 to 280°C, a used positive electrode having a positive electrode active material layer containing a positive electrode material having an olivine structure, a binder, and carbon applied to a current collector, or a powder of the positive electrode active material layer obtained by crushing the used positive electrode, to recover a powder of the positive electrode material having an olivine structure; (ii) dissolving the recovered cathode material powder having an olivine structure in an acetic acid aqueous solution to produce a cathode material solution; (iii) adding hydrogen peroxide (H ２ O ２ ) aqueous solution to obtain a leachate containing dissolved lithium and a leach residue; (iv) separating the leachate and leach residue; (v) concentrating the leachate; In the step (ii), the acetic acid aqueous solution contains 0.8 to 1.2 moles of acetic acid per mole of the positive electrode active material in the positive electrode material powder; In the step (iii), the aqueous hydrogen peroxide solution contains 0.4 to 0.6 mol of hydrogen peroxide per 1 mol 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 crushing in step (i) is performed using a hand mill, a pin mill, a disc mill, a cutting mill, a hammer mill, a mixer, or a blender.

5. 2. The method for recovering lithium according to claim 1, wherein the heat treatment in step (i) is carried out for 30 minutes to 6 hours.

6. 2. The method for recovering lithium according to claim 1, wherein the heat treatment in step (i) is carried out in an air or oxygen atmosphere.

7. 2. The method for recovering lithium according to claim 1, wherein in step (ii), the pH of the acetic acid aqueous solution is 2.0 to 3.

5.

8. 2. The method for recovering lithium according to claim 1, wherein in step (iii), the aqueous hydrogen peroxide solution is added in portions.

9. 2. The method for recovering lithium according to claim 1, wherein after the addition of the aqueous hydrogen peroxide solution in step (iii) is completed, the pH of the cathode material solution is 3 to 5.

5.

10. 2. The method for recovering lithium according to claim 1, wherein the steps (ii) and (iii) are carried out at 35 to 70°C.

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

12. In the lithium recovery method, the lithium recovery rate calculated by the following formula 1 is 83 mass% or more, [Formula 1] Lithium recovery rate (mass%) = [lithium content (g) contained in leachate / lithium content (g) contained in the positive electrode material powder recovered after heat treatment] × 100 The method for recovering lithium according to claim 1, wherein

13. The leaching residue of step (iv) is FePO ４ 2. The method for recovering lithium according to claim 1, comprising:

14. 2. The method for recovering lithium according to claim 1, wherein in step (v), evaporation under reduced pressure is used to concentrate the leaching solution.

15. The lithium recovery method includes concentrating the leaching residue obtained in step (iv) to obtain FePO ４ 2. The method for recovering lithium according to claim 1, comprising the step of obtaining

16. The lithium recovery method is (iv-1) the obtained FePO ４ Lithium was added to the mixture and sintered to obtain LiFePO ４ and (iv-2) the step of preparing the LiFePO ４ 16. The method for recovering lithium according to claim 15, further comprising the step of adding carbon to the mixture and calcining the mixture.

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