Method for recovering lithium

Abstract

The present invention relates to a method for recovering lithium and, more specifically, to a method for recovering lithium, the method comprising the steps of: (i) heat-treating waste positive electrodes having a positive electrode active material layer applied on a current collector, the positive electrode active material layer containing a positive electrode material having an olivine structure, a binder, and carbon, or a positive electrode active material layer powder obtained by crushing the waste positive electrodes, at 220-280°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 prepare a positive electrode material solution; (iii) adding an aqueous hydrogen peroxide (H2O2) solution to the positive electrode material solution to obtain a lithium-dissolved leachate and leach residue; (iv) separating the leachate and the leach residue; and (v) concentrating the leachate, wherein the aqueous acetic acid solution in step (ii) contains 0.8-1.2 moles of acetic acid per 1 mole of positive electrode active material in the positive electrode material powder, and the aqueous hydrogen peroxide solution in step (iii) contains 0.4-0.6 moles of hydrogen peroxide per 1 mole of positive electrode active material in the positive electrode material powder. According to the present invention, a positive electrode material powder is easily obtained from waste positive electrodes having an olivine structure, and thus the recovery rate of lithium is high. In addition, FePO4 is preserved as leach residue and reused as a raw material for lithium iron phosphate, and thus productivity and economic feasibility are significantly improved. Moreover, this method for recovering lithium is an eco-friendly lithium recovery method that does not require wastewater treatment.

Description

Lithium recovery method

[0001] 〔Cross-citation with the applicant(s)〕

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0143673, filed October 25, 2023, and Korean Patent Application No. 10-2023-0143674, filed October 25, 2023, and Korean Patent Application No. 10-2024-0144577, filed October 22, 2024, which are refiled based on the Korean Patent Application No. 10-2024-0144577, filed October 22, 2024, and all disclosures in the documents of the Korean Patent Applications are incorporated herein by reference.

[0003] The present invention relates to a method for recovering lithium, and more particularly, to a method for recovering lithium, which comprises: performing low-temperature heat treatment on a waste positive electrode having a positive electrode active material layer comprising a positive electrode material having an olivine structure, a binder, and carbon, or a positive electrode active material layer powder obtained by crushing the same; recovering 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 positive electrode material powder from the waste positive electrode, having a high lithium recovery rate, and further, preserving FePO4 as a leaching residue and reusing it as a raw material for lithium iron phosphate, thereby greatly improving productivity and economic efficiency, and is environmentally friendly and does not require wastewater treatment.

[0004] Demand for lithium-ion batteries has steadily increased since the 1990s alongside the growth of the portable electronic device market, and has recently surged further worldwide due to the rapid expansion of the electric vehicle market. This could lead to instability in the lithium resource supply and demand in the near future, and the continuous accumulation of waste batteries that have reached the end of their useful life could also pose significant environmental problems. To address these issues, recycling used lithium-ion batteries is a critical technological challenge.

[0005] Lithium-ion batteries are largely composed of a cathode in which a positive active material layer is coated on a metal foil such as aluminum, a negative electrode in which a negative 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.

[0006] The cathode accounts for more than 60% of the cost of a lithium-ion battery. Lithium cobalt oxide (LiCoO2) is used as the cathode because it has excellent reversibility, low self-discharge rate, high capacity, high energy density, and is easy to synthesize. In addition, lithium composite oxides such as lithium nickel cobalt manganese oxide (LiNiMnCoO2), lithium manganese oxide (LiMnO2), or lithium iron phosphate (LiFePO4) that also contain nickel and manganese are used to reduce the amount of expensive cobalt used. Since the above cathode materials contain about 5-7% lithium, a method for recovering lithium from waste lithium-ion battery cathode materials is receiving a lot of attention.

[0007] In particular, lithium iron phosphate (LiFePO4) possesses a highly stable hexahedral crystal structure. To recover valuable metals by disrupting this stable structure, a wet process is used, using highly concentrated strong acids or bases to obtain Li, Fe, and P as their respective compounds. This process generates a large amount of toxic wastewater, which poses environmental problems and increases production costs due to the costs of treating it.

[0008] Therefore, there is a need to develop a method for recovering lithium with a high yield from cathode materials with a solid crystal structure of waste lithium-ion batteries, while reducing production costs and being environmentally friendly.

[0009]

[0010] [Prior Art Literature]

[0011] [Patent Document]

[0012] Korean Patent Publication No. 2007-0112278

[0013] In order to solve the problems of the prior art as described above, the present invention provides a method for recovering lithium, which comprises: performing low-temperature heat treatment on a spent positive electrode or a positive electrode active material layer powder obtained by crushing the same to recover 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 selectively leaching lithium by adding an aqueous hydrogen peroxide solution, thereby easily obtaining positive electrode material in powder form from a spent positive electrode, having a high lithium recovery rate, and further preserving FePO4 as a leaching residue to reuse it as a raw material for lithium iron phosphate, thereby greatly improving productivity and economic efficiency; and providing an environmentally friendly method for recovering lithium by not using a strong acid or a strong base; and reducing process costs by not requiring neutralization and wastewater treatment.

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

[0015] In order to achieve the above object, I) the present invention comprises the steps of: (i) heat-treating a spent positive electrode having an olivine structure, a positive electrode active material layer including a positive electrode material, a binder, and carbon, coated on a current collector; or a positive electrode active material layer powder obtained by crushing the same; at 220 to 280°C to recover a 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 prepare a positive electrode material solution; (iii) adding a hydrogen peroxide (H2O2) aqueous solution to the positive electrode material solution to obtain a leachate and a leachate residue in which lithium is dissolved; (iv) separating the leachate and the leachate residue; And (v) a step of concentrating the leachate; and in step (ii), the acetic acid aqueous solution contains 0.8 to 1.2 moles of acetic acid per mole of positive electrode active material in the positive electrode powder, and in step (iii), the hydrogen peroxide aqueous solution contains 0.4 to 0.6 moles of hydrogen peroxide per mole of positive electrode active material in the positive electrode powder.

[0016] II) In the above I), the cathode material having the olivine structure may include lithium iron phosphate.

[0017] III) In the above I) or II), the cathode material having the olivine structure may be a compound represented by the following chemical formula 1.

[0018] [Chemical Formula 1]

[0019]

[0020] (In the above chemical formula 1, M includes at least one element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X includes at least one element 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.)

[0021] IV) In the above I) to III), the crushing in step (i) can be performed using a hand mill, pin mill, disc mill, cutting mill, hammer mill, mixer or blender.

[0022] V) In the above I) to IV), the heat treatment of step (i) can be performed for 30 minutes to 6 hours.

[0023] VI) In the above I) to V), the heat treatment of step (i) can be performed in an air or oxygen atmosphere.

[0024] VII) In the above I) to VI), the acetic acid aqueous solution in step (ii) may have a pH of 2 to 3.5.

[0025] VIII) In the above I) to VII), the hydrogen peroxide aqueous solution can be injected in divided portions in step (iii).

[0026] IX) In the above I) to VIII), after the addition of the hydrogen peroxide aqueous solution in step (iii) is completed, the positive electrode solution may have a pH of 3 to 5.5.

[0027] X) In the above I) to IX), steps (ii) and (iii) can be performed at 35 to 70°C.

[0028] XI) In the above I) to X), separation of the leachate and leach residue in the above step (iv) can be performed using reduced pressure filtration.

[0029] XII) In the above I) to XI), the lithium recovery method may have a lithium recovery rate of 83 wt% or more calculated by the following mathematical formula 1.

[0030] [Mathematical Formula 1]

[0031] Lithium recovery rate (wt%) = [Lithium content in the leachate (g) / Lithium content in the cathode powder recovered after heat treatment (g)] * 100

[0032] XIII) In the above I) to XII), the leaching residue of step (iv) may contain FePO4.

[0033] XIV) In the above I) to XIII), the concentration of the extract in the step (v) can utilize reduced pressure evaporation.

[0034] XV) In the above I) to XIV), the method for recovering lithium may include a step of concentrating the leaching residue obtained in the above step (iv) to obtain FePO4.

[0035] XVI) In the above I) to XV), the method for recovering lithium may include a step (iv-1) of adding lithium to the obtained FePO4 and calcining to produce LiFePO4, and a step (iv-2) of adding carbon to the produced LiFePO4 and calcining.

[0036] According to the present invention, a waste positive electrode having a positive electrode active material layer comprising a positive electrode material, a binder, and carbon having an olivine structure, which is a very stable structure, applied on a current collector, or a positive electrode active material layer powder obtained by crushing the same, is subjected to low-temperature heat treatment to recover a positive electrode powder having an olivine structure, and the recovered positive electrode powder is dissolved in a weakly acidic aqueous acetic acid solution and then an aqueous hydrogen peroxide solution is added to selectively leach lithium, thereby easily obtaining a positive electrode material in the form of a powder from the waste positive electrode and recovering lithium at a high yield, and further, FePO4 is preserved as a leaching residue and reused as a raw material for lithium iron phosphate, thereby greatly improving productivity and economic efficiency.

[0037] In addition, since strong acids or bases are not used in leaching, less wastewater is generated, which reduces process costs and has an environmentally friendly effect.

[0038] The following drawings attached to this specification illustrate embodiments of the present invention and, together with the detailed description given below, serve to further understand the technical idea of ​​the present invention, and therefore, the present invention should not be construed as being limited to the matters described in these drawings.

[0039] Figure 1 is a process diagram for a method for recovering lithium from a waste cathode according to one embodiment of the present invention.

[0040] Figure 2 is a process diagram for a method for recovering lithium from a waste cathode according to another embodiment of the present invention.

[0041]

[0042] The present inventors, while studying a method for recovering lithium from a spent positive electrode including a positive electrode material having a very stable olivine structure, have discovered that when a spent positive electrode or a positive electrode active material layer powder obtained by crushing the same is subjected to low-temperature heat treatment to thermally decompose carbon and binder in the positive electrode active material layer, thereby recovering a positive electrode material having an olivine structure as a powder, and 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, the positive electrode material is easily obtained as a powder from the spent positive electrode, lithium is recovered at a high yield, and FePO4 is preserved in the leachate residue, which is reused as a raw material for lithium iron phosphate, thereby greatly improving economic efficiency and recovering lithium in an environmentally friendly manner without using a strong acid or strong base, and based on this, they have devoted themselves to further research and completed the present invention.

[0043]

[0044] The method for recovering lithium described herein is described in detail below.

[0045] However, the terms or words used in this specification and claims cannot be interpreted as limited to their usual or dictionary meanings, and should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own application in the best way. Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are only one embodiment of the present invention and do not represent all of the technical idea of ​​the present invention, and it should be understood that there may be various equivalents and modified examples that can replace them, and that they can be arranged, replaced, combined, separated, or designed in various other configurations.

[0046] All technical and scientific terms used in this document, unless otherwise defined, have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains.

[0047]

[0048] Lithium recovery method

[0049] The method for recovering lithium of the present invention comprises the steps of: (i) heat-treating a spent positive electrode having an olivine structure, a positive electrode active material layer including a binder and carbon, or a positive electrode active material layer powder obtained by crushing the positive electrode, at 220 to 280°C to recover a positive electrode material having an olivine structure as a powder; (ii) dissolving the recovered positive electrode powder having an olivine structure in an aqueous acetic acid solution to prepare a positive electrode solution; (iii) adding an aqueous hydrogen peroxide (H2O2) solution to the positive electrode solution to obtain a leachate and a leachate residue in which lithium is dissolved; (iv) separating the leachate and the leachate residue; And (v) a step of concentrating the leachate; wherein in step (ii), the acetic acid aqueous solution contains 0.8 to 1.2 moles of acetic acid per mole of positive electrode active material in the positive electrode powder, and in step (iii), the hydrogen peroxide aqueous solution contains 0.4 to 0.6 moles of hydrogen peroxide per mole of positive electrode active material in the positive electrode powder. In this case, the recovery rate of lithium is high by easily obtaining positive electrode powder from the spent positive electrode, and the leachate residue is reused as a raw material for lithium iron phosphate by preserving FePO4, thereby greatly improving economic efficiency, and it is environmentally friendly because it does not use a strong acid or a strong base, and there is an advantage in that the process cost is reduced because neutralization and wastewater treatment are not required.

[0050]

[0051] Below, the lithium recovery method is explained in detail step by step.

[0052]

[0053] (i) A step of heat-treating a spent positive electrode having an olivine structure, a positive electrode active material layer including a binder and carbon, or a positive electrode active material layer powder obtained by crushing the positive electrode having an olivine structure, at 220 to 280°C to recover a positive electrode having an olivine structure as a powder.

[0054] The method for recovering lithium of the present invention comprises the steps of: (i) heat-treating a spent positive electrode having an olivine structure, a positive electrode active material layer including a binder and carbon, or a positive electrode active material layer powder obtained by crushing the positive electrode, at 220 to 280°C to recover a positive electrode material having an olivine structure as a powder; In this case, the positive electrode active material layer and the current collector are easily separated, so that the positive electrode active material layer can be obtained as a powder, and there is an advantage of recovering lithium at a high yield in a subsequent process, which is a subsequent process, a leaching process.

[0055]

[0056] The olivine structure used in this paper is a type of cathode material structure, a hexahedral lattice structure with a 3D shape, where phosphorus and oxygen atoms are strongly bonded. Because this structure can be maintained even after all lithium ions have been lost, it exhibits minimal performance degradation due to charge and discharge and excellent thermal stability. Furthermore, it is economical because inexpensive iron can be used instead of expensive cobalt metal, but its energy density, electrical conductivity, and lithium ion diffusion are lower than those of other cathode materials.

[0057] The above olivine structure can be confirmed through X-ray diffraction analysis (XRD).

[0058]

[0059] The cathode material having the above olivine structure may include, for example, lithium iron phosphate, in which case it has the advantages of excellent high-temperature stability and lifespan characteristics and low cost.

[0060] The above lithium iron phosphate may be, for example, a compound represented by the following chemical formula 1, in which case it has the advantages of excellent high-temperature stability and lifespan characteristics and low cost.

[0061] [Chemical Formula 1]

[0062]

[0063] (In the above chemical formula 1, M includes at least one element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X includes at least one element 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.)

[0064]

[0065] The above lithium iron phosphate may preferably include LiFePO4 having an olivine structure, in which case it has the advantages of excellent high-temperature stability and lifespan characteristics and low cost.

[0066]

[0067] The above-mentioned waste cathode may preferably be a cathode separated from a lithium secondary battery discarded after use, a defective cathode sheet or cathode scrap generated in a lithium secondary battery manufacturing process, or more preferably, a cathode scrap remaining after punching out a cathode plate from a cathode sheet. In this case, there is an economic advantage of recycling resources by recovering FePO4, etc. together with expensive lithium.

[0068]

[0069] The crushing in the above step (i) can be performed using, for example, a hand mill, pin mill, disk mill, cutting mill, hammer mill, mixer or blender, and preferably, a mixer. In this case, the waste positive electrode is chopped into small pieces, so that the current collector and the positive electrode active material layer are separated, so that the positive electrode active material layer can be easily obtained as a powder, and in the subsequent heat treatment process, the binder and carbon are sufficiently thermally decomposed, thereby increasing the recovery rate of lithium.

[0070] In the above step (i), the waste positive electrode can be crushed into pieces having a size of, for example, 10 mm x 10 mm or less, preferably 7 mm x 7 mm or less, more preferably 5 mm x 5 mm or less, even more preferably 3 mm x 3 mm or less, and even more preferably 0.1 to 3 mm x 0.1 to 3 mm or less, and in this case, the waste positive electrode is chopped into pieces so that the current collector and the positive electrode active material layer are separated, thereby providing an advantage of easily obtaining the positive electrode active material layer in powder form.

[0071] In this description, '10 mm * 10 mm or less' means including (10 mm or less) * 10 mm, (10 mm) * (10 mm or less), and (10 mm or less) * (10 mm or less).

[0072]

[0073] The above-mentioned crushed waste cathode may preferably include a step of sieving to separate the current collector and the cathode active material layer and obtain the cathode active material layer in powder form, and in this case, there is an advantage in that the binder and carbon are sufficiently removed in the subsequent heat treatment step.

[0074] The above sieve may be sieved with a sieve of, for example, 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 during the crushing process are separated, the size of the pulverized positive electrode active material layer is uniform, and the binder and carbon are sufficiently thermally decomposed in the subsequent heat treatment step, thereby providing an advantage of easily obtaining the positive electrode material as a powder.

[0075]

[0076] The heat treatment in step (i) may be, 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, and within this range, carbon and binder are thermally decomposed, thereby recovering a cathode material having an olivine structure from the current collector as a powder, thereby having the advantage of recovering lithium at a high yield in the subsequent leaching step.

[0077]

[0078] The heat treatment in step (i) above can be performed 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, and within this range, carbon and binder are thermally decomposed, thereby recovering a cathode material having an olivine structure from the current collector as a powder, thereby having the advantage of recovering lithium at a high yield in the subsequent leaching step.

[0079] In this description, the heat treatment time refers to the time spent at the heat treatment temperature and does not include the time taken to reach the heat treatment temperature.

[0080]

[0081] The heat treatment of step (i) above can be performed, for example, in an air or oxygen atmosphere, and preferably can be performed in air. In this case, the carbon and binder are thermally decomposed, thereby having the effect of easily obtaining a positive electrode material having an olivine structure as a powder from the current collector.

[0082] The oxygen may have a purity of, for example, 59% or more, preferably 80% or more, more preferably 90% or more, and even more preferably 90 to 99%, and within this range, there is an advantage in that the binder and carbon are removed without residue.

[0083] The purity % of the above oxygen can be volume % or mol %.

[0084] The purity of the oxygen of this invention is not particularly limited when measured using a measurement method commonly used in the technical field to which the present invention belongs.

[0085]

[0086] The cathode material of this description means a cathode active material or a cathode active material.

[0087]

[0088] (ii) A step of preparing a cathode material solution by dissolving the cathode material powder having the recovered olivine structure in an acetic acid aqueous solution.

[0089] The method for recovering lithium of the present invention includes (ii) a step of preparing a cathode material solution by dissolving the recovered cathode material powder having an olivine structure in an aqueous acetic acid solution, and in this case, lithium is recovered at a high yield without using a strong acid or strong base, and wastewater treatment is not required, so there is an environmentally friendly advantage.

[0090]

[0091] In the above step (ii), the acetic acid aqueous solution contains, for example, 0.8 to 1.2 moles of acetic acid per mole of positive electrode active material in the positive electrode 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 in that the reaction between the positive electrode powder and acetic acid is smooth.

[0092] In this description, 1 mole of positive electrode active material is based on the positive electrode active material having an olivine structure in the positive electrode material powder.

[0093] In this description, the mole number of 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, and for example, can be measured through ICP analysis. Specifically, it can be calculated from the Li, Fe, and P contents measured through ICP analysis.

[0094]

[0095] The above acetic acid aqueous solution may have, for example, a pH of 2.0 to 3.5, preferably a pH of 2.5 to 3.5, and more preferably a pH of 2.5 to 3.0, and within this range, the positive electrode material is easily dissolved, which has the advantage of increasing the recovery rate of lithium.

[0096] In this description, pH measurement can be measured by a measurement method commonly used in the technical field to which the present invention belongs, and unless otherwise described, can be measured using a general pH measuring device at room temperature, and specifically, can be measured using a Thermo Scientific Orion Star A Series.

[0097] In this description, room temperature may be a point within the range of 20 ± 5 ℃.

[0098]

[0099] The above acetic acid aqueous solution may preferably be an acetic acid aqueous solution having a molar concentration (mol / L) 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, and within this range, lithium can be recovered at a high yield without using a strong acid or strong base, and wastewater treatment is not required, so there is an environmentally friendly advantage.

[0100]

[0101] In the above step (ii), the weight ratio of the positive electrode powder and 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 in that the positive electrode powder is easily dissolved in the acetic acid aqueous solution.

[0102]

[0103] The above step (ii) can be carried out, for example, at a temperature of 35 to 70°C, preferably at a temperature of 40 to 65°C, more preferably at a temperature of 45 to 60°C, even more preferably at a temperature of 45 to 55°C, and even more preferably at a temperature of 47 to 52°C, and within this range, there is an advantage in that the cathode material is easily dissolved in an aqueous acetic acid solution.

[0104] The above step (ii) can be carried out, for example, under stirring, in which case there is an advantage of shortening the dissolution time.

[0105] The above 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 in that the positive electrode material is sufficiently dissolved in the acetic acid aqueous solution and the dissolution time is shortened.

[0106] The above stirring time may be, for example, 10 to 60 minutes, preferably 20 to 50 minutes, and more preferably 25 to 40 minutes, and within this range, there is an advantage in that the positive electrode material is sufficiently dissolved in the acetic acid aqueous solution and the dissolution time is shortened.

[0107]

[0108] (iii) Step of obtaining the leachate and leach residue

[0109] The method for recovering lithium of the present invention may include (iii) a step of adding a hydrogen peroxide (H2O2) aqueous solution to the cathode material solution to obtain a leachate and a leachate residue in which lithium is dissolved. In this case, lithium is selectively leached into the leachate, so that the recovery rate of lithium is high, and the leachate residue preserves FePO4 and is reused as a raw material for lithium iron phosphate, thereby greatly improving productivity and economic efficiency.

[0110] In this description, leaching refers to dissolving soluble substances to remove the solution and separating the soluble and insoluble components.

[0111]

[0112] In the above step (iii), the hydrogen peroxide aqueous solution acts as an oxidizing agent and facilitates the leaching of lithium from the positive electrode material.

[0113]

[0114] In the above step (iii), the hydrogen peroxide aqueous 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 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 preserved as a leaching residue and reused as a raw material for lithium iron phosphate, thereby greatly improving productivity and economic efficiency.

[0115]

[0116] In the above step (iii), the hydrogen peroxide aqueous solution can be preferably injected in divided portions, more preferably in the same amount three or more times, more preferably three to seven times, and even more preferably four to six times. In this case, there is an advantage that the pH of the positive electrode solution gradually changes and lithium is selectively and sufficiently leached.

[0117]

[0118] After the addition of the hydrogen peroxide aqueous solution in the above step (iii), the positive electrode solution may have, for example, a pH of 3 to 5.5, preferably a pH of 3.5 to 5.5, and more preferably a pH of 4.0 to 5.0. Within this range, no strong acid or strong base is used, so wastewater treatment is not required, which has the advantage of being environmentally friendly and reducing process costs.

[0119]

[0120] The above step (iii) may be carried out, for example, at a temperature of 35 to 70°C, preferably at a temperature of 40 to 65°C, more preferably at a temperature of 45 to 60°C, even more preferably at a temperature of 45 to 55°C, and even more preferably at a temperature of 47 to 52°C, and within this range, there is an advantage in that the recovery rate of lithium is greatly increased and the leaching of Fe and P components is greatly reduced.

[0121]

[0122] In the above step (iii), the weight ratio of the positive electrode powder and the hydrogen peroxide aqueous solution may be, for example, 1:0.2 to 1:0.6, preferably 1:0.3 to 1:0.5, more preferably 1:0.3 to 1:0.4, and within this range, after the addition of the hydrogen peroxide aqueous solution, the pH of the positive electrode solution is maintained at 3.5 to 5.5, so that lithium is selectively leached, the recovery rate is increased, and wastewater treatment is not required, so there is an advantage of being environmentally friendly and reducing process costs.

[0123]

[0124] The above step (iii) can be carried out, for example, under stirring, in which case there is an advantage of shortening the leaching time.

[0125] The above 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 in that lithium is easily leached from the cathode material solution.

[0126] The above 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 even more preferably 1.2 to 1.7 hours, and within this range, lithium is sufficiently leached from the cathode material solution, so that lithium is recovered at a high yield.

[0127]

[0128] The reaction mechanism occurring in the above dissolution step and leaching step is as follows, for example, in chemical formula 2.

[0129] [Chemical Formula 2]

[0130] LiFePO4+ CH3COOH + 0.5H2O2---> FePO4+ Li + + CH3COO - + H2O

[0131]

[0132] In the above chemical formula 2, the dissolved state of LiFePO4 varies depending on the pH of the solution in which it is dissolved. At pH 2 or lower, Li + , Fe 2+ PO4 3- It exists in the form of Li3PO4, Fe at pH 6 or higher. 3+ It exists in the form of Li at pH 2 to 6. + And exists in the form of FePO4. In the present invention, the pH of the acetic acid aqueous solution that dissolves the cathode material is controlled to 2 to 3.5, and an aqueous hydrogen peroxide solution is added thereto as an oxidizing agent to form Fe 2+ to Fe 3+ By oxidizing it, lithium ions can be more easily leached. Furthermore, a hydrogen peroxide aqueous solution is preferably continuously added so that the pH of the cathode material solution is within the range of 3 to 5.5, and leaching is performed at 35 to 70°C so that lithium leaching proceeds more stably and sufficiently, thereby obtaining lithium with a high recovery rate.

[0133]

[0134] (iv) Step of separating the leachate and leach residue

[0135] The method for recovering lithium of the present invention may include (iv) a step of separating the leachate and the leach residue, in which case lithium is recovered from the leachate at a high yield and FePO4 is preserved from the leach residue and reused as a raw material for lithium iron phosphate, thereby having the advantages of excellent productivity and economic feasibility.

[0136]

[0137] In the above step (e), separation of the leachate and leach residue can be achieved by using, for example, reduced pressure filtration. In this case, the leachate and leach residue can be easily separated with a simple process, reducing process costs and providing the advantage of being environmentally friendly.

[0138] The above-mentioned pressure-reducing filtration may preferably be vacuum pressure-reducing filtration, and specifically, may be vacuum pressure-reducing filtration using a filtration flask, in which case there is an advantage that the leaching liquid and the leaching residue are easily separated.

[0139] In the present invention, vacuum decompression filtration is not particularly limited as long as it is a conventional vacuum decompression filtration in the technical field to which the present invention belongs, and may include, for example, filtration in a partial vacuum state or a low pressure state.

[0140]

[0141] The above leaching residue may contain, for example, FePO4, in which case it can be reused as a raw material for lithium iron phosphate, thereby increasing economic benefits and providing the advantage of recycling resources.

[0142]

[0143] (v) Step of concentrating the extract

[0144] The method for recovering lithium of the present invention may include (v) a step of concentrating the leachate, in which case there is an advantage of easily recovering lithium.

[0145]

[0146] In the above step (v), the concentration of the leachate can be achieved by, for example, using reduced pressure evaporation. As a specific example, the leachate can be directly evaporated under reduced pressure without a separate cooling process. In this case, there is an advantage of obtaining high-purity lithium with a high recovery rate.

[0147]

[0148] The above-mentioned reduced pressure evaporation can be carried out, for example, at 70 to 90°C and 5 to 20 mbar, and preferably at 75 to 85°C and 7 to 12 mbar, in which case there is an advantage of stably recovering lithium at a high yield within a short period of time.

[0149]

[0150] The above-mentioned leachate is concentrated to obtain lithium, and at this time, lithium can be recovered as, for example, lithium acetate, and in this case, there is an advantage of obtaining high-purity lithium with a high recovery rate.

[0151]

[0152] The above lithium recovery method may have a lithium recovery rate calculated by the following mathematical formula 1 of, for example, 83 wt% or more, preferably 87 wt% or more, more preferably 90 wt% or more, even more preferably 93 wt% or more, still more preferably 95 wt% or more, and particularly preferably 96 to 100 wt%, and within this range, lithium is sufficiently selectively leached and the leaching of iron (Fe) and phosphorus (P) components is greatly reduced, so that there is an advantage of excellent economic efficiency.

[0153] [Mathematical Formula 1]

[0154] Lithium recovery rate (wt%) = [Lithium content in the leachate (g) / Lithium content in the cathode powder recovered after heat treatment (g)] * 100

[0155]

[0156] In the above mathematical expression 1, the lithium content contained in the leachate can be measured by a measuring method commonly used in the technical field to which the present invention pertains, and for example, it can be measured through ICP analysis of the leachate. Specifically, 0.2 g of the leachate is collected, placed in a conical tube, the exact weight is measured, 0.1 ml of 70% concentration nitric acid is added thereto, 500 ㎕ of 1000 mg / kg internal STD (Sc) is added, and diluted to 50 ml with ultrapure water, and measured by ICP. If necessary, further dilution with ultrapure water can be performed so that the sample concentration falls within the standard material calibration curve. In addition, the lithium content contained in the positive electrode active material layer powder recovered after heat treatment in the above mathematical expression 1 can be measured by ICP.

[0157]

[0158] In addition, the method for recovering lithium of the present invention may include, for example, a step of vacuum drying the leaching residue obtained in step (iv) to obtain a compound containing FePO4, in which case the raw material for lithium iron phosphate is easily manufactured, thereby recycling resources and providing excellent economic benefits.

[0159] The above vacuum drying can be performed, for example, at a temperature of 120 to 150°C, preferably 125 to 140°C, and more preferably 125 to 135°C, and has the advantage of obtaining a compound containing FePO4 within a short period of time within this range.

[0160] In this description, vacuum drying is not particularly limited as long as it is vacuum drying commonly performed in the technical field to which the present invention belongs.

[0161]

[0162] The step of obtaining the compound containing FePO4 may preferably include a step (iv-1) of adding lithium to the obtained FePO4 and calcining to produce LiFePO4, and a step (iv-2) of adding carbon to the produced LiFePO4 and calcining. In this case, the lithium iron phosphate cathode material is easily manufactured, thereby recycling resources and providing excellent economic benefits.

[0163]

[0164] In the above step (iv-1), the calcination can be performed at, for example, 600 to 800°C, preferably 650 to 750°C, and within this range, there is an effect of sufficient introduction of lithium into FePO4.

[0165] In the above step (iv-1), the calcination can be performed for, for example, 8 to 12 hours, preferably 9 to 11 hours, and more preferably 9.5 to 10.5 hours, and within this range, there is an effect of sufficient introduction of lithium into FePO4.

[0166] In the above step (iv-1), the calcination can be carried out, for example, under an inert atmosphere, preferably under a nitrogen atmosphere, in which case there is an advantage in that oxidation is prevented.

[0167] In the above step (iv-2), the calcination can be performed at, for example, 500 to 700°C, preferably 550 to 650°C, and within this range, carbon is coated on the surface of LiFePO4, which has the advantage of improving electrical conductivity.

[0168] In the above step (iv-2), the calcination can be performed for, for example, 3 to 6 hours, preferably 4 to 5 hours, and more preferably 3.5 to 4.5 hours, and within this range, carbon has the advantage of improving the electrical conductivity of LiFePO4.

[0169] In the above step (iv-2), the calcination can be carried out, for example, under an inert atmosphere, preferably under a nitrogen atmosphere, in which case there is an advantage in that oxidation is prevented.

[0170] In the present description, unless otherwise defined, the heat treatment may be carried out at a temperature increase rate of 1 to 20°C / min, preferably 3 to 10°C / min, until the heat treatment temperature is reached.

[0171]

[0172] The following drawing 1 is a flow chart of a method for recovering lithium according to one embodiment of the present invention.

[0173] Referring to Fig. 1, first, a positive electrode is prepared (step S10).

[0174] The above-mentioned waste cathode may preferably be a discarded lithium ion battery cathode, a defective product generated during the cathode coating process, or a cathode scrap discarded after cutting the electrode plate, and preferably, a discarded lithium ion battery cathode can be prepared.

[0175] The above positive electrode has a structure in which a positive electrode active material layer containing a positive electrode material and carbon is bonded to an aluminum foil by a binder.

[0176] The above cathode material is a cathode material having an olivine structure, preferably lithium iron phosphate having an olivine structure, and more preferably LiFePO4 having an olivine structure, in which case it has the advantages of excellent high-temperature stability and lifespan characteristics and low cost.

[0177]

[0178] Next, the prepared positive electrode is crushed into an appropriate size (step S20).

[0179] Here, shredding includes cutting or shredding the positive electrode into a size that is easy to handle. As a specific example, the shredded waste positive electrode may have a size of 5 mm * 5 mm. The shredding may be performed using various dry crushing equipment such as a mixer, a blender, a hand mill, a pin mill, a disk mill, a cutting mill, and a hammer mill, and as a specific example, the crushing is performed using a mixer, and in this case, the waste positive electrode is finely chopped to easily separate the current collector and the positive electrode active material layer, and is uniformly heat-treated in the subsequent heat treatment step, so that the binder and carbon in the positive electrode active material layer are easily removed, thereby increasing the lithium recovery rate.

[0180]

[0181] Next, the shredded waste cathode is separated from the current collector and cathode active material layer through a sieve (step S30).

[0182] The waste cathode crushed in the above step S20 can be sieved through a sieve of 120 to 250 mesh, and as a specific example, sieved through a sieve of 200 mesh to separate the current collector and obtain the cathode active material layer in powder form.

[0183]

[0184] Next, the obtained positive electrode active material layer powder is subjected to low-temperature heat treatment to recover a positive electrode material having an olivine structure as powder (step S40). Here, the heat treatment is performed to thermally decompose the carbon and binder within the positive electrode active material layer.

[0185] Through the heat treatment as described above, the carbon and binder inside the anode are thermally decomposed and removed, and the anode material is easily sorted into powder form.

[0186] The above heat treatment can be performed, for example, in an air or oxygen atmosphere, and as a specific example, can be performed in air. In this case, the binder and carbon are not carbonized but react with oxygen and fly away as gases such as CO and CO2, so both the binder and carbon are removed and the cathode material is recovered.

[0187] The above heat treatment is preferably performed at 220 to 280°C, and as a specific example, at 250°C. Below 220°C, it is difficult to remove the binder, and above 280°C, the binder is easily removed, but the lithium recovery rate decreases.

[0188] The above heat treatment is preferably performed at a temperature increase rate of 1 to 20°C / min, more preferably 3 to 10°C / min, and a specific example is 5°C / min. Within this range, the heat treatment can be performed without causing a strain on the heat treatment equipment, and has the advantage of not causing thermal shock to the anode scrap.

[0189] The above heat treatment can be performed for a period of time sufficient to allow the binder and carbon to be sufficiently thermally decomposed, for example, preferably 30 minutes or more, more preferably 30 minutes to 6 hours, and a specific example is 1 hour to 5 hours. Within this range, the binder and carbon are sufficiently thermally decomposed, and the thermal decomposition efficiency is excellent.

[0190] The above heat treatment is performed using various types of furnaces, for example, a box-type furnace, and considering productivity, a rotary kiln capable of continuous treatment.

[0191] After the above heat treatment, it can be cooled slowly or rapidly in the air.

[0192]

[0193] Next, the cathode material powder having the recovered olivine structure is dissolved in an acetic acid aqueous solution to prepare a cathode material solution (step S50).

[0194] The above acetic acid aqueous solution is used in an amount of, for example, 0.8 to 1.2 moles of acetic acid per mole of positive electrode active material in the positive electrode powder, and as a specific example, can be used in an amount of 1 mole, and within this range, there is an advantage in that the reaction between the positive electrode powder and acetic acid is smooth.

[0195] The above acetic acid aqueous solution may have a pH of, for example, 2.0 to 3.5, and as a specific example, a pH of 2.5 to 3.0. Within this range, wastewater treatment is not required, so it has the advantage of being environmentally friendly and reducing process costs.

[0196]

[0197] The concentration of the above acetic acid aqueous solution may preferably be 0.6 to 0.9 molar concentration, and as a specific example, may be 0.8 molar concentration. Within this range, the cathode material powder is easily dissolved, and since a strong acid or strong base is not used, wastewater treatment is not required, and there are advantages of being environmentally friendly and reducing process costs.

[0198]

[0199] The weight ratio of the above cathode material powder and the acetic acid aqueous solution may be, for example, 1:6 to 1:10, and as a specific example, may be 1:8, and within this range, there is an advantage in that the cathode material powder is easily dissolved in the acetic acid aqueous solution.

[0200]

[0201] The step (S50) of preparing the above cathode material solution can be performed at, for example, 35 to 70°C, and as a specific example, can be performed at 50°C, and has the advantage that the cathode material powder is easily dissolved within this range.

[0202] The step (S50) of preparing the above positive electrode material solution can be performed under stirring, for example, and as a specific example, can be performed under a stirring speed of 500 rpm. In this case, there is an advantage in that the positive electrode material powder is easily dissolved in the acetic acid aqueous solution, thereby shortening the dissolution time.

[0203] The above stirring time may be, for example, 10 to 60 minutes, and as a specific example, 30 minutes, and within this range, the cathode material powder is easily dissolved in the acetic acid aqueous solution, so that the dissolution time is advantageously shortened.

[0204]

[0205] Next, a hydrogen peroxide (H2O2) aqueous solution is added to the cathode material solution to obtain a lithium-dissolved leachate and leachate residue (step S60).

[0206] The above-mentioned hydrogen peroxide aqueous solution acts as an oxidizing agent, for example, and selectively leaches lithium from the cathode material solution.

[0207] The above-mentioned hydrogen peroxide aqueous solution can be used in an amount of, for example, 0.4 to 0.6 moles of hydrogen peroxide per mole of positive electrode active material in the positive electrode powder, and as a specific example, can be used in an amount of 0.5 moles. Within this range, lithium is selectively leached, thereby increasing the lithium recovery rate, and FePO4 is preserved as a leaching residue and reused as a raw material for lithium iron phosphate, thereby greatly improving productivity and economic efficiency.

[0208]

[0209] The above leaching step (S60) can be carried out, for example, at 35 to 70°C, and as a specific example, can be carried out at 50°C, and within this range, lithium is selectively leached at a high concentration, thereby increasing the lithium recovery rate and preserving FePO4 as a leaching residue to be reused as a raw material for lithium iron phosphate, thereby greatly improving productivity and economy.

[0210]

[0211] In the above leaching step (S60), the weight ratio of the cathode material powder and the hydrogen peroxide aqueous solution may be, for example, 1:0.2 to 1:0.6, and specifically, 1:0.3, and there is an advantage in that lithium is selectively and sufficiently leached within this range.

[0212]

[0213] In the above leaching step (S60), the hydrogen peroxide aqueous solution can preferably be injected in divided portions, and as a specific example, it is injected in four divided portions in equal amounts, and in this case, there is an advantage that the pH of the cathode material solution gradually changes and lithium is selectively and sufficiently leached.

[0214]

[0215] After the addition of the hydrogen peroxide aqueous solution in the above leaching step (S60), the positive electrode solution has a pH of 3 to 5.5, and a specific example thereof may be 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, wastewater treatment is not required, so there is an advantage of being environmentally friendly and reducing process costs.

[0216]

[0217] The above leaching can be carried out under stirring, for example, and as a specific example, can be carried out under stirring at 500 rpm, and there is an advantage that lithium is easily leached from the cathode material solution within this range.

[0218] The above stirring time may be, for example, 0.5 hours or more, and as a specific example, stirring may be performed for 1.5 hours, and within this range, lithium is sufficiently leached from the cathode material solution, which has the advantage of recovering lithium at a high yield.

[0219]

[0220] Next, the leachate and leach residue are separated (step S70).

[0221] The separation of the above-mentioned leachate and leach residue can preferably be accomplished by using reduced pressure filtration, in which case the leachate and leach residue can be easily separated with a simple process, reducing process costs and providing the advantage of being environmentally friendly.

[0222] Through the above separation, a leachate (step S80) containing dissolved lithium compounds and a leach residue (step S100) are obtained.

[0223]

[0224] Next, the lithium-dissolved leachate is concentrated (step S90).

[0225] The concentration of the above-mentioned leachate can be achieved by, for example, reduced pressure evaporation. As a specific example, the leachate containing dissolved Li can be concentrated directly by reduced pressure evaporation without a separate cooling process. In this case, there is an advantage in that high-purity lithium is obtained with a high recovery rate.

[0226]

[0227] The above-mentioned reduced pressure evaporation can be carried out, for example, at 70 to 90°C and 5 to 20 mbar, and as a specific example, can be carried out at 80°C and 10 mbar, in which case there is an advantage of stably recovering high-purity lithium at a high yield within a short period of time.

[0228] The above-mentioned leachate is concentrated to obtain lithium.

[0229]

[0230] As an optional step, the separated leaching residue is vacuum dried to obtain a compound containing FePO4 (step S110).

[0231] The above leaching residue may preferably contain FePO4, and in this case, there is an effect of increasing economic benefits by reusing it as a raw material for lithium iron phosphate.

[0232] The above vacuum drying can be performed at, for example, 120 to 150°C, specifically 130°C, and has the advantage of stably obtaining a compound containing FePO4 within this range in a short period of time.

[0233]

[0234] The above step S110 may specifically include i) a step of adding lithium to the obtained FePO4 and calcining to produce LiFePO4, and ii) a step of adding carbon to the produced LiFePO4 and calcining, in which case, a lithium iron phosphate cathode material is easily produced, thereby recycling resources and providing excellent economic benefits.

[0235]

[0236] In the above step i), the calcination can be performed at 600 to 800°C for 8 to 12 hours under an inert atmosphere, and within this range, lithium is sufficiently introduced into the FePO4 phase, thereby having the effect of being converted into LiFePO4.

[0237] As a specific example, lithium can be added to a compound containing FePO4 and calcined at 700°C for 10 hours under a nitrogen atmosphere, and within this range, lithium is sufficiently introduced into the FePO4 phase, resulting in conversion into LiFePO4 with excellent performance.

[0238]

[0239] In the above step ii), the calcination can be performed, for example, at 500 to 700°C for 3 to 6 hours under an inert atmosphere, and there is an advantage of improving the electrical conductivity of LiFePO4 within this range.

[0240] As a specific example, carbon can be added to calcined LiFePO4 and calcined at 600°C for 4 hours under a nitrogen atmosphere, which has the advantage of improving the electrical conductivity of LiFePO4 within this range.

[0241]

[0242] Unless otherwise specified in this description, the firing atmosphere may be air, the pressure may be atmospheric pressure, and the temperature may be room temperature.

[0243] In this description, room temperature may be a point within the range of 20 ± 5 ℃.

[0244]

[0245] In addition, the following Figure 2 is a flow chart of a method for recovering lithium according to another embodiment of the present invention.

[0246] Referring to Fig. 2, first, a positive electrode is prepared (step S10).

[0247] The above-mentioned waste cathode may preferably be a discarded lithium ion battery cathode, a defective product generated during the cathode coating process, or a cathode scrap discarded after cutting the electrode plate, and preferably, a discarded lithium ion battery cathode can be prepared.

[0248] The above positive electrode has a structure in which a positive electrode active material layer containing a positive electrode material and carbon is bonded to an aluminum foil by a binder.

[0249] The above cathode material is a cathode material having an olivine structure, preferably lithium iron phosphate having an olivine structure, and more preferably LiFePO4 having an olivine structure. In this case, there are advantages of excellent high-temperature stability and lifespan characteristics and low cost.

[0250]

[0251] Next, the waste cathode is heat-treated to obtain cathode powder having an olivine structure (step S20). Here, the heat treatment is performed to thermally decompose carbon and binder within the cathode.

[0252] Through the heat treatment as described above, the carbon and binder inside 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 is easily sorted into powder form.

[0253] The above heat treatment can be performed, for example, in an air or oxygen atmosphere, and as a specific example, can be performed in air. In this case, the binder and carbon are not carbonized but react with oxygen and fly away as gases such as CO and CO2, so that both the binder and carbon are removed and the cathode material is separated from the current collector.

[0254] The above heat treatment is preferably performed at 220 to 280°C, and specifically, at 230 to 270°C. Below 220°C, it is difficult to remove the binder, making it impossible to separate the current collector, and above 280°C, the lithium recovery rate decreases.

[0255] The above heat treatment is preferably performed at a temperature increase rate of 1 to 20°C / min, more preferably 3 to 10°C / min, and a specific example is 5°C / min. Within this range, the heat treatment can be performed without causing a strain on the heat treatment equipment, and has the advantage of not causing thermal shock to the anode scrap.

[0256] The above heat treatment can be performed for a period of time sufficient to allow the binder and carbon to be sufficiently thermally decomposed, for example, preferably 30 minutes or more, more preferably 30 minutes to 6 hours, and a specific example is 1 hour to 5 hours. Within this range, the binder and carbon are sufficiently thermally decomposed, and the thermal decomposition efficiency is excellent.

[0257] The above heat treatment is performed using various types of furnaces, for example, a box-type furnace, and considering productivity, a rotary kiln capable of continuous treatment.

[0258] After the above heat treatment, it can be cooled slowly or rapidly in the air.

[0259]

[0260] Next, the cathode material powder having the recovered olivine structure is sieved to ensure uniform particle size (step S30).

[0261] The cathode material powder recovered after heat treatment in the above step S20 can be preferably sieved, more preferably sieved through a sieve of 120 to 250 mesh, and as a specific example, sieved through a sieve of 200 mesh to have a uniform size, thereby having the advantage of facilitating the subsequent leaching step.

[0262]

[0263] Next, the cathode material powder having the recovered olivine structure is dissolved in an acetic acid aqueous solution to prepare a cathode material solution (step S40).

[0264] The above acetic acid aqueous solution is used in an amount of, for example, 0.8 to 1.2 moles of acetic acid per mole of positive electrode active material in the positive electrode powder, and as a specific example, can be used in an amount of 1 mole, and within this range, there is an advantage in that the reaction between the positive electrode powder and acetic acid is smooth.

[0265] The above acetic acid aqueous solution may have a pH of, for example, 2.0 to 3.5, and as a specific example, a pH of 2.5 to 3.0. Within this range, wastewater treatment is not required, so it has the advantage of being environmentally friendly and reducing process costs.

[0266]

[0267] The concentration of the above acetic acid aqueous solution may preferably be 0.6 to 0.9 molar concentration, and as a specific example, may be 0.8 molar concentration. Within this range, the cathode material powder is easily dissolved, and since a strong acid or strong base is not used, wastewater treatment is not required, and there are advantages of being environmentally friendly and reducing process costs.

[0268]

[0269] The weight ratio of the above cathode material powder and the acetic acid aqueous solution may be, for example, 1:6 to 1:10, and as a specific example, may be 1:8, and within this range, there is an advantage in that the cathode material powder is easily dissolved in the acetic acid aqueous solution.

[0270]

[0271] The step (S40) of preparing the above cathode material solution can be performed at, for example, 35 to 70°C, and as a specific example, can be performed at 50°C, and has the advantage that the cathode material powder is easily dissolved within this range.

[0272] The step (S40) of preparing the above cathode material solution can be performed under stirring, for example, and as a specific example, can be performed under a stirring speed of 500 rpm. In this case, there is an advantage in that the cathode material powder is easily dissolved in the acetic acid aqueous solution, thereby shortening the dissolution time.

[0273]

[0274] Next, a hydrogen peroxide (H2O2) aqueous solution is added to the cathode material solution to obtain a lithium-dissolved leachate and leachate residue (step S50).

[0275] The above-mentioned hydrogen peroxide aqueous solution acts as an oxidizing agent, for example, and selectively leaches lithium from the cathode material solution.

[0276] The above-mentioned hydrogen peroxide aqueous solution can be used in an amount of, for example, 0.4 to 0.6 moles of hydrogen peroxide per mole of positive electrode active material in the positive electrode powder, and as a specific example, can be used in an amount of 0.5 moles. Within this range, lithium is selectively leached, thereby increasing the lithium recovery rate, and FePO4 is preserved as a leaching residue and reused as a raw material for lithium iron phosphate, thereby greatly improving productivity and economic efficiency.

[0277]

[0278] The above leaching step (step S50) can be carried out, for example, at 35 to 70°C, and as a specific example, can be carried out at 50°C, and within this range, lithium is selectively leached at a high concentration, thereby increasing the lithium recovery rate and preserving FePO4 as a leaching residue to be reused as a raw material for lithium iron phosphate, thereby greatly improving productivity and economy.

[0279]

[0280] In the above leaching step (step S50), the weight ratio of the cathode material powder and the hydrogen peroxide aqueous solution may be, for example, 1:0.2 to 1:0.6, and specifically, 1:0.3, and there is an advantage in that lithium is selectively and sufficiently leached within this range.

[0281] In the above leaching step (step S50), the hydrogen peroxide aqueous solution can preferably be injected in divided portions, and as a specific example, it is injected in four divided portions in equal amounts, in which case the pH of the cathode material solution gradually changes and there is an advantage that lithium is selectively and sufficiently leached.

[0282]

[0283] After the addition of the hydrogen peroxide aqueous solution in the above leaching step (step S50), the positive electrode solution has a pH of 3 to 5.5, and a specific example thereof may be 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, wastewater treatment is not required, so there is an advantage of being environmentally friendly and reducing process costs.

[0284]

[0285] The above leaching can be carried out under stirring, for example, and as a specific example, can be carried out under stirring at 500 rpm, and there is an advantage that lithium is easily leached from the cathode material solution within this range.

[0286] The above stirring time may be, for example, 0.5 hours or more, and as a specific example, stirring may be performed for 1.5 hours, and within this range, lithium is sufficiently leached from the cathode material solution, which has the advantage of recovering lithium at a high yield.

[0287]

[0288] Next, the leachate and leach residue are separated (step S60).

[0289] The separation of the above-mentioned leachate and leach residue can preferably be accomplished by using reduced pressure filtration, in which case the leachate and leach residue can be easily separated with a simple process, reducing process costs and providing the advantage of being environmentally friendly.

[0290] Through the above separation, a leachate (step S70) containing dissolved lithium compounds and a leach residue (step S90) are obtained.

[0291]

[0292] Next, the lithium-dissolved leachate is concentrated (step S80).

[0293] The concentration of the above-mentioned leachate can be achieved by, for example, reduced pressure evaporation. As a specific example, the leachate containing dissolved Li can be concentrated directly by reduced pressure evaporation without a separate cooling process. In this case, there is an advantage in that high-purity lithium is obtained with a high recovery rate.

[0294]

[0295] The above-mentioned reduced pressure evaporation can be carried out, for example, at 70 to 90°C and 5 to 20 mbar, and as a specific example, can be carried out at 80°C and 10 mbar, in which case there is an advantage of stably recovering high-purity lithium at a high yield within a short period of time.

[0296] The above-mentioned leachate is concentrated to obtain lithium, and at this time, the lithium can be recovered as lithium acetate.

[0297]

[0298] As an optional step, the separated leaching residue is vacuum dried to obtain a compound containing FePO4 (step S100).

[0299] The above leaching residue may preferably contain FePO4, and in this case, there is an effect of increasing economic benefits by reusing it as a raw material for lithium iron phosphate.

[0300] The above vacuum drying can be performed at, for example, 120 to 150°C, specifically 130°C, and has the advantage of stably obtaining a compound containing FePO4 within this range in a short period of time.

[0301]

[0302] The above step S100 may specifically include i) a step of adding lithium to the obtained FePO4 and calcining to produce LiFePO4, and ii) a step of adding carbon to the produced LiFePO4 and calcining, in which case, a lithium iron phosphate cathode material is easily produced, thereby recycling resources and providing excellent economic benefits.

[0303]

[0304] In the above step i), the calcination can be performed at 600 to 800°C for 8 to 12 hours under an inert atmosphere, and within this range, lithium is sufficiently introduced into the FePO4 phase, thereby having the effect of being converted into LiFePO4.

[0305] As a specific example, lithium can be added to a compound containing FePO4 and calcined at 700°C for 10 hours under a nitrogen atmosphere, and within this range, lithium is sufficiently introduced into the FePO4 phase, resulting in conversion into LiFePO4 with excellent performance.

[0306]

[0307] In the above step ii), the calcination can be performed, for example, at 500 to 700°C for 3 to 6 hours under an inert atmosphere, and within this range, there is an advantage of improving the electrical conductivity of LiFePO4.

[0308] As a specific example, carbon can be added to calcined LiFePO4 and calcined at 600°C for 4 hours under a nitrogen atmosphere, which has the advantage of improving the electrical conductivity of LiFePO4 within this range.

[0309]

[0310] Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

[0311]

[0312] [Example]

[0313] Example 1

[0314] A waste cathode having a cathode active material layer comprising a cathode material, a binder, and carbon having an olivine structure applied on a current collector was crushed into a size of 5 mm x 5 mm using a mixer and then sieved through a 200 mesh sieve to separate the current collector, thereby obtaining a cathode active material layer in the form of a powder. The obtained cathode active material layer was heat-treated in air at 250°C for 5 hours to thermally decompose the carbon and binder in the cathode active material layer, thereby recovering a cathode material having an olivine structure as a powder (LiFePO4). The recovered cathode material powder was confirmed to be a powder having an olivine structure as a result of X-ray diffraction analysis (XRD).

[0315] 12 g of the recovered positive electrode powder (LiFePO4) having the olivine structure was added to 96 ml of a 0.8 molar concentration acetic acid aqueous solution and dissolved under stirring at 50°C to prepare a positive electrode solution. At this time, the pH of the 0.8 molar concentration acetic acid aqueous solution was 2.5 to 3.0, and the acetic acid aqueous solution contained 1 mol of acetic acid per 1 mol of the positive electrode active material in the positive electrode powder. Here, stirring was performed at 500 rpm for 30 minutes. The mole number of the positive electrode active material in the positive electrode powder was calculated from the Li, Fe, and P contents measured through ICP analysis.

[0316] The prepared cathode material solution was stirred at 50°C, and a 30 wt% H2O2 aqueous solution was added 1 ml at a time for 1.5 hours, 4 times in total, to obtain a lithium-dissolved leachate and leachate residue. The stirring was performed at 500 rpm. At this time, the hydrogen peroxide aqueous solution contained 0.5 mol of hydrogen peroxide per 1 mol of the cathode active material in the cathode material powder.

[0317] The above lithium-dissolved leachate and leachate residue were separated by vacuum filtration, and then the lithium-dissolved leachate was concentrated by vacuum evaporation without a separate cooling process to obtain lithium acetate.

[0318] The above leaching residue was evaporated under reduced pressure to obtain FePO4.

[0319]

[0320] Example 2

[0321] The same procedure as Example 1 was followed, except that the heat treatment was performed for 1 hour.

[0322]

[0323] Comparative Example 1

[0324] The same procedure as Example 1 was followed, except that the heat treatment step was not performed.

[0325]

[0326] Comparative Example 2

[0327] The same procedure as in Example 1 was followed, except that the heat treatment step was performed at 200°C for 1 hour.

[0328]

[0329] Comparative Example 3

[0330] The same procedure as in Example 1 was followed, except that the heat treatment step was performed at 200°C for 5 hours.

[0331]

[0332] Comparative Example 4

[0333] The same procedure as in Example 1 was followed, except that the heat treatment step was performed at 300°C for 1 hour.

[0334]

[0335] Comparative Example 5

[0336] The same procedure as in Example 1 was followed, except that the heat treatment step was performed at 300°C for 5 hours.

[0337]

[0338] [Test Example I: Lithium, Iron, and Phosphorus Recovery Rates and Residual Carbon Content]

[0339] In the above Examples 1 and 2 and Comparative Examples 1 to 5, the lithium (Li), iron (Fe) and phosphorus (P) contents were measured through ICP analysis of the leached solution in which Li was dissolved, and the lithium (Li), iron (Fe) and phosphorus (P) recovery rates were calculated using the following mathematical equations 1 to 3. The residual carbon (C) content was measured through CS analysis, and the results are shown in Table 1 below.

[0340]

[0341] [Mathematical Formula 1]

[0342] Lithium recovery rate (wt%) = [Lithium content in the leachate (g) / Lithium content in the cathode powder recovered after heat treatment (g)] * 100

[0343] [Equation 2]

[0344] Iron recovery rate (wt%) = [Iron content in the leachate (g) / Iron content in the cathode powder recovered after heat treatment (g)] * 100

[0345] [Equation 3]

[0346] Phosphorus recovery rate (wt%) = [Phosphorus content in the leachate (g) / Phosphorus content in the cathode powder recovered after heat treatment (g)] * 100

[0347]

[0348] In the above mathematical formulas 1 to 3, the lithium, iron, and phosphorus contents in the leachate were measured by collecting 0.2 g of the leachate, placing it in a conical tube, and measuring the exact weight. After adding 0.1 ml of 70% nitric acid, 500 μl of 1000 mg / kg internal STD (Sc) was added, and diluted to 50 ml with ultrapure water, and the lithium, iron, and phosphorus contents were measured through ICP analysis.

[0349] In addition, the lithium, iron, and phosphorus contents contained in the cathode material powder recovered after heat treatment in the above mathematical formulas 1 to 3 were each measured through ICP analysis.

[0350]

[0351] The above residual carbon content was measured through CS analysis of the carbon content contained in the cathode material powder recovered after heat treatment. Specifically, after measuring the blank for the calibration curve, the carbon standard was measured at least three times. After adding a combustion agent to a crucible containing 10 mg of the sample, it was placed on the lower electrode of the CS analyzer, and the sample was injected from the upper part to combust and the carbon component content was measured.

[0352]

[0353] Heat treatment conditions Residual carbon content (wt%) Lithium recovery rate (wt%) Iron recovery rate (wt%) Iron recovery rate (wt%) Example 1 250 ℃* 5 hours 2.949 7.7 0.4 1.2 Example 2 250 ℃* 1 hour 3.149 6.5 0.3 1.4 Comparative example 1 Not implemented 3.269 3.8 0.5 1.7 Comparative example 2 200 ℃* 1 hour 3.248 0.30.31.1 Comparative example 3 200 ℃* 5 hours 3.209 3.00.41.7 Comparative example 4 300 ℃* 1 hour 2.917 9.20.30.7 Comparative example 5 300 ℃* 5 hours 2.707 2.5 1.00.1

[0354] As shown in Table 1 above, it was confirmed that Examples 1 and 2 according to the present invention had a very high lithium recovery rate and low iron and phosphorus recovery rates compared to Comparative Examples 1 to 5.

[0355] In addition, Comparative Example 1, which was not heat-treated, and Comparative Examples 2 and 3, which were heat-treated at 200°C, had a high residual carbon content.

[0356] In addition, Comparative Examples 2 and 3, which were heat-treated at 200°C, had low lithium recovery rates, and Comparative Examples 4 and 5, which were heat-treated at 300°C, had significantly reduced Li recovery rates due to oxidation of Fe.

[0357]

[0358] [Additional Examples]

[0359] Additional Example 1

[0360] A spent positive electrode having a positive electrode active material layer including a positive electrode material having an olivine structure, a binder, and carbon applied on a current collector was heat-treated in air at 230°C for 1 hour to thermally decompose the carbon and binder in the positive electrode, thereby recovering a positive electrode material having an olivine structure from the current collector as a powder (LiFePO4). The recovered positive electrode material powder was confirmed to be an olivine structure powder by X-ray diffraction analysis (XRD).

[0361] The cathode material powder having the above-mentioned recovered olivine structure was sieved through a 200 mesh sieve.

[0362] 12 g of the cathode material powder (LiFePO4) having the above-described olivine structure was added to 96 ml of a 0.8 molar concentration acetic acid aqueous solution and dissolved under stirring at 50°C to prepare a cathode material solution. At this time, the pH of the 0.8 molar concentration acetic acid aqueous solution was 2.5 to 3.0, and the acetic acid aqueous solution contained 1 mol of acetic acid per 1 mol of the cathode active material in the cathode material powder. Here, stirring was performed at 500 rpm for 30 minutes.

[0363] The prepared cathode material solution was stirred at 50°C, and a 30 wt% H2O2 aqueous solution was added 1 ml at a time for 1.5 hours, 4 times in total, to obtain a lithium-dissolved leachate and leachate residue. The stirring was performed at 500 rpm. At this time, the hydrogen peroxide aqueous solution contained 0.5 mol of hydrogen peroxide per 1 mol of the cathode active material in the cathode material powder.

[0364] The above lithium-dissolved leachate and leachate residue were separated by vacuum filtration, and then the lithium-dissolved leachate was concentrated by vacuum evaporation without a separate cooling process to obtain lithium acetate.

[0365] The above leaching residue was evaporated under reduced pressure to obtain FePO4.

[0366]

[0367] Additional Example 2

[0368] The same procedure as in Additional Example 1 was followed, except that the heat treatment was performed for 5 hours.

[0369]

[0370] Additional Example 3

[0371] The same procedure as in Additional Example 1 was followed, except that the heat treatment was performed at 250°C for 1 hour.

[0372]

[0373] Additional Example 4

[0374] The same procedure as in Additional Example 1 was followed, except that the heat treatment was performed at 250°C for 5 hours.

[0375]

[0376] Additional Example 5

[0377] The same procedure as in Additional Example 1 was followed, except that the heat treatment was performed at 270°C for 1 hour.

[0378]

[0379] Additional Example 6

[0380] The same procedure as in Additional Example 1 was followed, except that the heat treatment was performed at 270°C for 5 hours.

[0381]

[0382] Additional Comparative Example 1

[0383] The same procedure as in Additional Example 1 was followed, except that the heat treatment was performed at 200°C for 1 hour.

[0384]

[0385] Additional Comparative Example 2

[0386] The same procedure as in Additional Example 1 was followed, except that the heat treatment was performed at 200°C for 5 hours.

[0387]

[0388] Additional Comparative Example 3

[0389] The same procedure as in Additional Example 1 was followed, except that the heat treatment was performed at 300°C for 1 hour.

[0390]

[0391] Additional Comparative Example 4

[0392] The same procedure as in Additional Example 1 was followed, except that the heat treatment was performed at 300°C for 5 hours.

[0393]

[0394] [Additional Test Example I: Lithium, Iron, and Phosphorus Recovery]

[0395] In the above additional examples 1 to 6 and additional comparative examples 1 to 4, the recovery rates of lithium (Li), iron (Fe), and phosphorus (P) were calculated using the above mathematical formulas 1 to 3 by measuring the Li dissolved in the leachate through ICP analysis, and the results are shown in Table 2 below.

[0396]

[0397] In the above mathematical formulas 1 to 3, the lithium, iron, and phosphorus contents in the leachate were measured by collecting 0.2 g of the leachate, placing it in a conical tube, and measuring the exact weight. After adding 0.1 ml of 70% nitric acid, 500 μl of 1000 mg / kg internal STD (Sc) was added, and diluted to 50 ml with ultrapure water, and the lithium, iron, and phosphorus contents were measured through ICP analysis.

[0398] In addition, the lithium, iron, and phosphorus contents contained in the cathode material powder recovered after heat treatment in the above mathematical formulas 1 to 3 were each measured through ICP analysis.

[0399]

[0400] Heat treatment conditionsLithium recovery rate (wt%)Iron recovery rate (wt%)Recovery rate (wt%)Additional example 1230 ℃* 1 hour 91.40.61.8Additional example 2230 ℃* 5 hours 87.90.51.7Additional example 3250 ℃* 1 hour 95.40.41.4Additional example 4250 ℃* 5 hours 96.50.41.1Additional example 5270 ℃* 1 hour 96.30.31.1Additional example 6270 ℃* 5 hours 88.80.41.1Additional comparative example 1200 ℃* 1 hour---Additional comparative example 2200 ℃* 5 hours---Additional comparative example 3300 ℃* 1 hour 78.20.40.8Additional comparative example 4300 ℃* 5 hours 66.50.50.1

[0401] As shown in Table 2 above, it was confirmed that additional examples 1 to 6 according to the present invention had a very high lithium recovery rate and low iron and phosphorus recovery rates compared to additional comparative examples 1 to 4.

[0402] In addition, in Comparative Examples 1 and 2 heat-treated at 200°C, the binder was not thermally decomposed, so the cathode material could not be recovered as powder from the current collector, and in Comparative Examples 3 and 4 heat-treated at 300°C, the Li recovery rate was reduced due to oxidation of Fe.

Claims

1. (i) A step of heat-treating a spent positive electrode having an olivine structure, a positive electrode active material layer including a binder and carbon, or a positive electrode active material layer powder obtained by crushing the positive electrode having an olivine structure, at 220 to 280°C to recover a positive electrode having an olivine structure in the form of powder; (ii) a step of preparing a cathode material solution by dissolving the cathode material powder having the recovered olivine structure in an aqueous acetic acid solution; (iii) a step of adding a hydrogen peroxide (H2O2) aqueous solution to the cathode material solution to obtain a lithium-dissolved leachate and leachate residue; (iv) a step of separating the above-mentioned leachate and leach residue; and (v) a step of concentrating the above-mentioned leaching solution; In the above step (ii), the acetic acid aqueous solution contains 0.8 to 1.2 moles of acetic acid per mole of positive electrode active material in the positive electrode powder, In the above step (iii), the hydrogen peroxide aqueous solution is characterized in that it contains 0.4 to 0.6 moles of hydrogen peroxide per mole of positive electrode active material in the positive electrode powder. Method for recovering lithium.

2. In paragraph 1, The cathode material having the above olivine structure is characterized in that it includes lithium iron phosphate. Method for recovering lithium.

3. In paragraph 1, The cathode material having the above olivine structure is characterized by being a compound represented by the following chemical formula 1. Method for recovering lithium. [Chemical Formula 1] (In the above chemical formula 1, M includes at least one element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X includes at least one element 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.) 4. In paragraph 1, The crushing of the above step (i) is characterized by using a hand-mill, pin-mill, disc-mill, cutting-mill, hammer-mill, mixer or blender. Method for recovering lithium.

5. In paragraph 1, The heat treatment of step (i) is characterized in that it is performed for 30 minutes to 6 hours. Method for recovering lithium.

6. In paragraph 1, The heat treatment of step (i) is characterized in that it is performed in an air or oxygen atmosphere. Method for recovering lithium.

7. In paragraph 1, In the above step (ii), the acetic acid aqueous solution is characterized in that it has a pH of 2.0 to 3.

5. Method for recovering lithium.

8. In paragraph 1, In the above step (iii), the hydrogen peroxide aqueous solution is characterized by being injected in portions. Method for recovering lithium.

9. In paragraph 1, In the above step (iii), after the addition of the hydrogen peroxide aqueous solution, the cathode material solution is characterized in that it has a pH of 3 to 5.

5. Method for recovering lithium.

10. In paragraph 1, The above steps (ii) and (iii) are characterized in that they are performed at a temperature of 35 to 70°C. Method for recovering lithium.

11. In paragraph 1, The separation of the leachate and leach residue in the above step (iv) is characterized by using reduced pressure filtration. Method for recovering lithium.

12. In paragraph 1, The above lithium recovery method is characterized in that the lithium recovery rate calculated by the following mathematical formula 1 is 83 wt% or more. Method for recovering lithium. [Mathematical Formula 1] Lithium recovery rate (wt%) = [Lithium content in the leachate (g) / Lithium content in the cathode powder recovered after heat treatment (g)] * 100 13. In paragraph 1, The leaching residue of the above step (iv) is characterized in that it contains FePO4. Method for recovering lithium.

14. In paragraph 1, The concentration of the extract in the above step (v) is characterized by using reduced pressure evaporation. Method for recovering lithium.

15. In paragraph 1, The above lithium recovery method is characterized in that it includes a step of concentrating the leaching residue obtained in the above step (iv) to obtain FePO4. Method for recovering lithium.

16. In paragraph 15, The above lithium recovery method is characterized by including a step (iv-1) of adding lithium to the obtained FePO4 and calcining to produce LiFePO4, and a step (iv-2) of adding carbon to the produced LiFePO4 and calcining. Method for recovering lithium.

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