Method for recovering transition metals from lithium secondary batteries

Abstract

The method for recovering transition metals from a lithium secondary battery of the present invention includes the steps of preparing a positive electrode active material from the positive electrode of a lithium secondary battery, treating the positive electrode active material with a first acidic solution containing a reducing agent in an amount less than the amount equivalent to the reaction equivalent of the positive electrode active material to produce a first leachate, and treating the remaining positive electrode active material, excluding the fraction contained in the first leachate, with a second acidic solution containing a reducing agent to produce a second leachate, thereby improving the manganese extraction rate and cobalt purity.

Description

Technical Field

[0001] The present invention relates to a method for recovering transition metals of a lithium secondary battery, and more particularly, to a method for recovering transition metals from the positive electrode of a lithium secondary battery.

Background Art

[0002] A secondary battery is a battery that can be repeatedly charged and discharged, and has been widely applied to portable electronic communication devices such as camcorders, mobile phones, and notebook personal computers as the information communication and display industries have developed. Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and the like. Among them, lithium secondary batteries have been actively developed and applied because of their high operating voltage and energy density per unit weight, and their advantages in charging speed and weight reduction.

[0003] A lithium secondary battery can include an electrode assembly including a positive electrode, a negative electrode, and a separator, and an electrolyte that impregnates the electrode assembly. The lithium secondary battery can further include, for example, a pouch-shaped exterior material that houses the electrode assembly and the electrolyte.

[0004] As the positive electrode active material of the lithium secondary battery, a lithium metal oxide can be used. The lithium metal oxide can further contain transition metals such as nickel, cobalt, and manganese.

[0005] The lithium metal oxide as the positive electrode active material can be produced by reacting a lithium precursor with a nickel-cobalt-manganese (NCM) precursor containing nickel, cobalt, and manganese.

[0006] The use of the aforementioned high-cost valuable metals in the positive electrode active material results in significant costs for manufacturing the positive electrode material. Furthermore, in recent years, with growing concern for environmental protection, research into recycling methods for positive electrode active materials is progressing. For the recycling of the positive electrode active material, it is necessary to regenerate the transition metal precursor from the positive electrode with high efficiency and high purity. [Overview of the project] [Problems that the invention aims to solve]

[0007] The object of this invention is to provide a method for recovering transition metals from lithium secondary batteries with high efficiency and high purity. [Means for solving the problem]

[0008] A method for recovering transition metals from a lithium secondary battery according to an embodiment of the present invention includes the steps of: preparing a positive electrode active material from the positive electrode of a lithium secondary battery; treating the positive electrode active material with a first acidic solution containing an amount of reducing agent less than the amount equivalent to the reaction equivalent of the positive electrode active material to produce a first leachate; and treating the remaining positive electrode active material, after removing the fraction contained in the first leachate from the positive electrode active material, with a second acidic solution containing a reducing agent to produce a second leachate.

[0009] In some embodiments, the positive electrode active material may include a lithium transition metal oxide containing nickel, cobalt, and manganese.

[0010] In some embodiments, the amount of the reducing agent used in the step of generating the first leachate may be 0.2 to 0.4 times the amount equivalent to the reaction equivalent of the lithium transition metal oxide.

[0011] In some embodiments, the reaction equivalent of the reducing agent with respect to the lithium transition metal oxide may be 0.5 moles per mole of the lithium transition metal oxide.

[0012] In some embodiments, the reducing agent may be hydrogen peroxide.

[0013] In some embodiments, the amount of the reducing agent used in the step of generating the second leachate may be 0.8 to 1.2 times the amount equivalent to the reaction equivalent of the residual positive electrode active material.

[0014] In some embodiments, the cobalt and nickel content in the total weight of the transition metals contained in the first leaching solution may be 75 to 100% by weight, and the manganese content in the total weight of the transition metals contained in the second leaching solution may be 30 to 75% by weight.

[0015] In some embodiments, the step may further include sequentially extracting cobalt and nickel from the first leachate.

[0016] In some embodiments, the step may further include sequentially extracting manganese, cobalt, and nickel from the second leachate.

[0017] In some embodiments, the weight ratio of the residual positive electrode active material to the weight of the positive electrode active material may be 25 to 50% by weight.

[0018] In some embodiments, the first acidic solution and the second acidic solution may contain sulfuric acid. [Effects of the Invention]

[0019] In the method for recovering transition metals of a lithium secondary battery according to the foregoing exemplary embodiment, a relatively small amount of reducing agent is introduced to prepare a first leachate which is a cobalt and nickel-rich solution. After the preparation of the first leachate, a relatively large amount of reducing agent is introduced into the remaining residual positive electrode active material to prepare a second leachate which is a manganese-rich solution. In this case, the first leachate can be immediately introduced into the cobalt and nickel extraction step to recover cobalt with high purity, and the second leachate can be introduced into the manganese extraction step to achieve a high manganese extraction rate. Thereby, the recovery efficiency of the transition metals of the lithium secondary battery can be improved.

[0020] In some embodiments, the weight ratio of the residual positive electrode active material to the weight of the positive electrode active material can be relatively decreased. Thereby, the amount of the second leachate which is the raw material for the manganese extraction step is relatively decreased, and the manganese extraction rate and the manganese extraction efficiency can be improved.

Brief Description of the Drawings

[0021] [Figure 1] FIG. 1 is a schematic flowchart for explaining a method for recovering transition metals of a lithium secondary battery according to an exemplary embodiment. [Figure 2] FIG. 2 is a schematic graph showing the leaching rate of each transition metal according to the ratio of the reducing agent introduced.

Modes for Carrying Out the Invention

[0022] Embodiments of the present invention provide a method for recovering transition metals of a lithium secondary battery including two-stage transition metal leaching.

[0023] Hereinafter, embodiments of the present invention will be described more specifically with reference to the drawings. However, these embodiments are merely illustrative of the present invention and do not limit the present invention.

[0024] Unless otherwise defined, all terms used herein, including technical or scientific terms, shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined as in a commonly used dictionary shall be interpreted to have a meaning that coincides with the meaning in the context of the relevant art and shall not be interpreted in an idealized or overly formal sense unless clearly defined in this application.

[0025] FIG. 1 is a schematic flowchart for explaining a method for recovering transition metals of a lithium secondary battery according to an exemplary embodiment.

[0026] Referring to FIG. 1, a positive electrode active material can be prepared from the positive electrode of the lithium secondary battery (for example, step S10).

[0027] The lithium secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. The positive electrode and the negative electrode may each include a positive electrode active material layer and a negative electrode active material layer coated on a positive electrode current collector and a negative electrode current collector, respectively.

[0028] For example, the positive electrode active material included in the positive electrode active material layer may include an oxide containing lithium and a transition metal.

[0029] In some embodiments, the positive electrode active material may include a compound having a composition represented by the following Chemical Formula 1.

[0030] [Chemical Formula 1] Li x Ni 1-y M y O 2+z

[0031] In chemical formula 1, x is 0.9 ≤ x ≤ 1.2, y is 0 ≤ y ≤ 0.7, z is -0.1 ≤ z ≤ 0.1, and M may be one or more elements selected from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, or Zr.

[0032] In some embodiments, the positive electrode active material may be an NCM-based lithium oxide containing nickel, cobalt, and manganese.

[0033] The positive electrode can be separated from the lithium secondary battery and recovered. The positive electrode may be, for example, a used lithium secondary battery or a positive electrode that was damaged or defective during the manufacturing process.

[0034] For example, the positive electrode includes a positive electrode current collector (e.g., aluminum (Al)) and a positive electrode active material layer, and the positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material.

[0035] The conductive material may include, for example, carbon-based materials such as graphite, carbon black, graphene, and carbon nanotubes. The binder may include, for example, resin materials such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, and polymethyl methacrylate.

[0036] In exemplary embodiments, the recovered positive electrode can be crushed to collect the positive electrode active material. This allows the positive electrode active material to be collected in powder form. The positive electrode active material may include, as described above, a lithium transition metal oxide powder, for example, an NCM-based lithium oxide powder (e.g., Li(NCM)O2).

[0037] In exemplary embodiments, the positive electrode active material may include positive electrode active material particles, such as the NCM-based lithium oxide. For example, the positive electrode active material may be substantially composed of the positive electrode active material particles.

[0038] In some embodiments, the positive electrode active material can be heat-treated before being introduced into the reduction leaching process described later. For example, the heat treatment can remove at least partially impurities such as the conductive material and binder contained in the positive electrode active material layer. This allows a high-purity positive electrode active material (e.g., lithium transition metal oxide particles) to be introduced into the reduction leaching process.

[0039] The temperature of the heat treatment may be, for example, about 100 to 500°C, preferably about 350 to 450°C. Within this range, the impurities can be substantially removed, and the decomposition and damage of the positive electrode active material can be prevented.

[0040] In an exemplary embodiment, a first leachate can be generated by treating the prepared positive electrode active material with a first acidic solution containing a reduced amount less than the reaction equivalent of the positive electrode active material (e.g., step S20).

[0041] For example, by adding a reducing agent in an amount less than the reaction equivalent of the positive electrode active material, a relatively small amount of manganese can be leached into the first leachate. This increases the cobalt purity in the cobalt extraction step of the first leachate, and increases the manganese extraction rate of the second leachate, as described later.

[0042] For example, as used herein, the expression "a reduced amount less than the reaction equivalent of the positive electrode active material" may mean a number of moles of reducing agent less than the number of moles equivalent to the reaction equivalent of the positive electrode active material, or a weight of reducing agent less than the number of moles equivalent to the reaction equivalent of the positive electrode active material.

[0043] For example, the "amount equivalent to the reaction equivalent of the positive electrode active material" may mean the amount of reducing agent necessary to substantially reduce the positive electrode active material.

[0044] For example, the reducing agent may include at least one of hydrogen peroxide (H2O2), SO2, Na2S, NaHS, Na2S2O5, NaHSO3, Na2S2O3, KHSO3, K2SO3, FeSO4, H2S, glucose, sucrose, and ascorbic acid. Preferably, the reducing agent may be hydrogen peroxide. Using this type of reducing agent, for example, the reduction of lithium transition metal oxides contained in the positive electrode active material can be easily achieved.

[0045] The first acidic solution may be an acidic solvent, and for example, it may include at least one of sulfuric acid (H2SO4), hydrochloric acid (HCl), nitric acid (HNO3), oxalic acid, and citric acid. Preferably, the first acidic solution may include sulfuric acid. When an acidic solution of this type is used as an acidic solvent, for example, the lithium transition metal oxide can be easily leached as a lithium precursor and a transition metal precursor.

[0046] For example, if the reducing agent is hydrogen peroxide and the first acidic solution is sulfuric acid, the aforementioned leaching can be carried out by a reaction represented by, for example, the reaction shown in reaction formula 1 below.

[0047] [Reaction Equation 1] 2Li(NCM)O2+H2O2+3H2SO4→Li2SO4+2(NCM)SO4+4H2O+O2

[0048] Therefore, the reaction equivalent of the reducing agent to the lithium transition metal oxide may be 0.5 moles per mole of lithium transition metal oxide.

[0049] Figure 2 is a schematic graph showing the leaching rates of each transition metal based on the ratio of reducing agent added. Specifically, Figure 2 is a schematic graph showing the leaching rates of transition metals based on the ratio of hydrogen peroxide added to the reaction equivalent of the positive electrode active material.

[0050] As shown in Figure 2, in the range where the ratio of hydrogen peroxide added to the reaction equivalent of the positive electrode active material is low (for example, 0.4 or less), it is possible to achieve both a very low manganese leaching rate and a high nickel and cobalt leaching rate.

[0051] In some embodiments, the amount of reducing agent used in the step of generating the first leachate may be 0.2 to 0.4 times the amount equivalent to the reaction equivalent of the lithium transition metal oxide. In this case, as shown in Figure 2, the leaching rate of manganese is very low and the leaching rates of nickel and cobalt are high, so the nickel and cobalt content in the first leachate can be increased and the manganese content can be significantly decreased. As a result, as will be described later, the first leachate can be immediately introduced into the cobalt extraction step without going through the manganese extraction step.

[0052] As shown in Figure 1, a second leach can be produced by treating the remaining positive electrode active material, after removing the fractions contained in the first leach, with a second acidic solution containing a reducing agent (for example, step S30).

[0053] For example, the term "residual positive electrode active material" may refer to the material remaining after separating the first leachate from the positive electrode active material. For example, the residual positive electrode active material may be composed of substantially the same elements as the aforementioned positive electrode active material, or it may have a different composition from the positive electrode active material. For example, the residual positive electrode active material may have a higher manganese content and lower cobalt and nickel content than the positive electrode active material.

[0054] In exemplary embodiments, the amount of reducing agent used in the step of generating the second leachate can be 0.8 to 1.2 times the amount equivalent to the reaction equivalent of the residual positive electrode active material, preferably 0.9 to 1.1 times.

[0055] For example, in the step of generating the second leachate, an amount equivalent to the reaction equivalent of the residual positive electrode active material can be added. In this case, the term "reaction equivalent" can include not only the exact equivalent required for the reaction, but also a value that takes into account process errors.

[0056] For example, the type of reducing agent and the type of second acidic solution added in the step of generating the second leachate may be substantially the same as the type of reducing agent and the type of first acidic solution added in the step of generating the first leachate.

[0057] In this case, as shown in Figure 2, a high manganese leaching rate can increase the manganese content in the second leachate. For example, since a large amount of cobalt and nickel were separated into the first leachate, the second leachate may have a high manganese content and a low cobalt and nickel content. This ensures a high manganese extraction rate and manganese extraction efficiency in the manganese extraction step.

[0058] As mentioned above, the first leachate may have a higher content of nickel and cobalt than manganese, and the second leachate may have a higher content of manganese than nickel and cobalt.

[0059] In some embodiments, the cobalt and nickel content in the first leachate may be 75-100% by weight of the total weight of the transition metals, and the manganese content in the second leachate may be 30-75% by weight of the total weight of the transition metals. The metals may include manganese, cobalt, nickel and / or lithium.

[0060] In this case, the first leachate may be a cobalt and nickel-rich (Co / Ni rich) solution, and the second leachate may be a manganese-rich (Mn rich) solution. As described later, the first leachate can be immediately added to the cobalt and nickel extraction step to extract high-purity cobalt, and the second leachate can be added to the manganese extraction step to increase the manganese extraction rate and extraction efficiency.

[0061] In some embodiments, the reducing agent can be introduced in a manner that differs depending on the ratio of transition metal content in the positive electrode active material. For example, the NCM content ratio of the positive electrode active material may be selected from Ni:Co:Mn = 40:30:30, 60:20:20, or 80:10:10.

[0062] For example, the amount of reducing agent added can be increased as the Ni content increases. This allows the amount of reducing agent added to be flexibly changed according to the transition metal composition ratio of the positive electrode active material, enabling the transition metal to be leached under optimal leaching conditions.

[0063] In some embodiments, the weight ratio of residual positive electrode active material to the weight of positive electrode active material may be 25 to 50% by weight. In this case, the weight of the solution (e.g., second leachate) introduced into the manganese extraction step can be reduced. This increases the manganese extraction efficiency and improves the purity of the extracted manganese.

[0064] In some embodiments, transition metals can be recovered from the first and second leachates described above (for example, step S40).

[0065] For example, the positive electrode active material can be treated with an acidic solution containing an amount of reducing agent equivalent to the reaction equivalent of the positive electrode active material to prepare a single leachate, which can then be immediately added to the manganese extraction step. However, in this case, the manganese and cobalt content in the single leachate is high, and cobalt or nickel may be extracted along with the manganese. As a result, the manganese extraction rate and cobalt purity may decrease.

[0066] According to some embodiments, the step may further include sequentially extracting cobalt and nickel from the first leachate.

[0067] The first leachate can be added to, for example, a cobalt extraction step (e.g., step S43), and after cobalt extraction, it can be added to a nickel extraction step (e.g., step S45). This allows for the extraction of high-purity cobalt and nickel from the first leachate, which is a cobalt and nickel-rich solution. For example, the aforementioned cobalt extraction and nickel extraction can be performed consecutively.

[0068] According to some embodiments, the step may further include sequentially extracting manganese, cobalt, and nickel from the second leachate.

[0069] The second leachate can be added, for example, to the manganese extraction step (e.g., step S41), and then sequentially to the cobalt extraction step (e.g., step S43) and the nickel extraction step (e.g., step S45). This allows for the recovery of manganese from the second leachate, which is a manganese-rich solution, with a high manganese extraction rate. For example, the manganese extraction, cobalt extraction, and nickel extraction described above can be performed in succession.

[0070] In some embodiments, the transition metal recovery step described above may not include a step of extracting manganese from the first leachate. The manganese content of the first leachate may be very low or substantially absent, and the first leachate can be immediately introduced into the cobalt extraction step to extract high-purity cobalt while increasing process efficiency.

[0071] In some embodiments, the extractants used in the manganese extraction, cobalt extraction, and nickel extraction steps may include at least one of phosphate-based extractants, phosphate-based extractants, phosphine oxide-based extractants, and carboxylic acid-based extractants.

[0072] For example, the extractant may include at least one of the following: di-2-ethylhexyl phosphoric acid (D2EHPA), bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272), 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (PC88A), tributyl phosphate, trioctyl phosphine oxide, and alkyl monocarboxylic acid.

[0073] According to some embodiments, the aforementioned extractant can be diluted with an organic solvent diluent. For example, the organic solvent may include at least one of kerosene, hexane, benzene, and toluene. For example, the molar ratio of the extractant in the diluent may be 0.4 to 0.7.

[0074] For example, the diluted extractant can be saponified by reacting it with a basic compound (e.g., NaOH). In this case, the H groups of the acidic extractant are replaced with Na groups, which prevents a decrease in the pH of the extraction solution during transition metal extraction.

[0075] For example, transition metals can be extracted by mixing the saponified extractant with the solution to be extracted (e.g., the first or second leachate) such that the organic phase / aqueous phase ratio is 1 to 5. For instance, the organic phase / aqueous phase ratio can be increased as the transition metal content of the solution to be extracted increases. This allows for the adoption of an optimal organic phase / aqueous phase ratio based on the transition metal content, thereby achieving an excellent transition metal extraction rate.

[0076] In some embodiments, D2EHPA can be used as an extractant in the manganese extraction process, and Cyanex 272 can be used as an extractant in the cobalt extraction process. In addition, D2EHPA or PC88A can be used as an extractant in the nickel extraction process.

[0077] For example, the step of recovering the transition metals mentioned above can be carried out by a continuous multi-stage extraction process. In this case, by going through multiple extraction stages, the proportion of the target metal in the organic phase increases, and ultimately the recovery rate of the transition metals can be improved.

[0078] The following are specific examples to aid in understanding the present invention, but these examples are merely illustrative and do not limit the scope of the appended claims. It will be obvious to those skilled in the art that various changes and modifications can be made to these examples within the scope of the present invention and the technical concept, and it is also obvious that these variations and modifications fall within the scope of the appended claims.

[0079] Example 1 One kilogram of positive electrode material separated from a waste lithium secondary battery was heat-treated at 450°C for one hour. The heat-treated positive electrode material was cut into small units and pulverized by milling to obtain a sample of Li-Ni-Co-Mn oxide positive electrode active material (Step S10).

[0080] 0.1 kg of the positive electrode active material sample and 0.4 times the amount of hydrogen peroxide equivalent to the reaction equivalent of the positive electrode active material were prepared to make a 35% hydrogen peroxide solution, which was then added to 0.6 kg of 3 M sulfuric acid solvent and reacted for 6 hours under conditions of 80°C and 1 atm. After the reaction, the remaining residual positive electrode active material and the solution were separated to produce the first leachate and residual positive electrode active material (step S20).

[0081] The residual positive electrode active material and 1.0 times the amount of hydrogen peroxide equivalent to the reaction equivalent of the residual positive electrode active material were prepared as a 35% hydrogen peroxide solution and added to a 3M sulfuric acid solvent, and the mixture was reacted for 6 hours. After the reaction, the resulting solution was separated to produce a second leachate (step S30).

[0082] The first leachate produced was introduced into a cobalt extraction process to recover cobalt, and then immediately introduced into a nickel extraction process to recover nickel. The second leachate was introduced into a manganese extraction process to recover manganese, and then immediately introduced into a cobalt extraction process and a nickel extraction process to recover cobalt and nickel (step S40).

[0083] In the manganese extraction process, a 50% saponified 1M D2EHPA solution was used as the extractant. Specifically, a 1M D2EHPA solution was prepared by diluting D2EHPA with kerosene. NaOH was added to the diluted 1M D2EHPA solution in a number of moles equivalent to 50% of the number of moles of D2EHPA to carry out the saponification process, thereby obtaining the 50% saponified 1M D2EHPA solution. The obtained 50% saponified 1M D2EHPA (organic phase) and the second leachate (aqueous phase) were mixed so that the organic phase / aqueous phase ratio was 4.5, and manganese was extracted.

[0084] Furthermore, in the cobalt extraction process, 40% saponified 0.8M Cyanex 272 was used as the extractant. The 40% saponified 0.8M Cyanex 272 (organic phase) and the second leachate (aqueous phase) were mixed so that the organic phase / aqueous phase ratio was 2.0, and cobalt was extracted.

[0085] Furthermore, in the nickel extraction process, 60% saponified 1M PC88A was used as the extractant. The 60% saponified 1M PC88A (organic phase) and the second leachate (aqueous phase) were mixed so that the organic phase / aqueous phase ratio was 3.5, and nickel was extracted.

[0086] Example 2 The transition metal was recovered in the same manner as in Example 1, except that in the first leachate generation step, 0.28 times the amount of reducing agent corresponding to the reaction equivalent of the positive electrode active material was added, and the 50% saponified 1M D2EHPA (organic phase) and the second leachate (aqueous phase) were mixed so that the organic phase / aqueous phase ratio was 3.7.

[0087] Example 3 The transition metal was recovered in the same manner as in Example 1, except that in the first leachate generation step, 0.5 times the amount of reducing agent, equivalent to the reaction equivalent of the positive electrode active material, was added.

[0088] Example 4 The transition metal was recovered in the same manner as in Example 1, except that in the first leachate generation step, a reducing agent equivalent to 0.1 times the reaction equivalent of the positive electrode active material was added.

[0089] Comparative Example The transition metals were recovered in the same manner as in Example 1, except that a sample of the positive electrode active material and 1.0 times the amount of reducing agent equivalent to the reaction equivalent of the positive electrode active material were added to a sulfuric acid solvent to obtain a leachate, no further leaching process was performed on the remaining positive electrode active material, and the obtained leachate was successively added to the manganese extraction process, cobalt extraction process, and nickel extraction process to recover manganese, cobalt, and nickel.

[0090] The equivalent ratio of hydrogen peroxide, the percentage of residual positive electrode active material, and the composition in the first leachate preparation step for the above examples and comparative examples are shown in Table 1 below. However, in the case of comparative examples, the figures are shown based on a single leachate.

[0091] [Table 1]

[0092] As shown in Table 1, in Examples 1 to 3, the amount of hydrogen peroxide added to the first leachate generation step is 0.5 times or less the amount equivalent to the reaction equivalent of the positive electrode active material. Therefore, the number of moles of hydrogen peroxide added in the first leachate preparation step is 50% or less of the total number of moles added. Here, the remaining hydrogen peroxide is added to the second leachate generation step, so the number of moles of hydrogen peroxide added in the first leachate generation step is less than or equal to the number of moles of hydrogen peroxide added in the second leachate generation step.

[0093] In this case, only a small amount of manganese leached into the first leachate, while most of the manganese leached into the second leachate.

[0094] However, in Example 3, where the amount of hydrogen peroxide introduced in the first leachate generation step exceeded 0.4 times the amount equivalent to the reaction equivalent of the positive electrode active material, a relatively larger amount of manganese leached into the first leachate compared to Examples 1 and 2.

[0095] Furthermore, in Example 4, where the amount of hydrogen peroxide introduced in the first leachate generation step was less than 0.2 times the amount equivalent to the reaction equivalent of the positive electrode active material, a relatively larger amount of cobalt and nickel leached into the second leachate compared to Examples 1 and 2.

[0096] Experimental example (1) Measurement of the extraction rate of each transition metal from the second leachate. The weights of manganese, cobalt, nickel, and lithium in the second leachate, as well as the weights of manganese, cobalt, nickel, and lithium extracted from the second leachate, were measured. The weight of extracted manganese relative to the weight of the transition metal in the positive electrode active material was then calculated as a weight percentage for each metal. However, in the comparative example, the extraction rate of each transition metal was measured from a single leachate.

[0097] (2) Purity of cobalt extracted from the first leachate In the aforementioned examples and comparative examples, the weight ratio of cobalt in the transition metal extracted into the organic phase was measured by ICP-OES, and the purity of the cobalt was calculated. The measurement results are shown in Table 2 below.

[0098] [Table 2]

[0099] As shown in Table 2, in the example where a smaller amount of reducing agent than the reaction equivalent of the positive electrode active material was added in the first leachate generation step, a relatively higher manganese extraction rate and higher cobalt purity were secured compared to the comparative example where a single leachate was prepared by adding an amount of reducing agent equivalent to the reaction equivalent from the beginning.

[0100] However, in Example 3, where the amount of manganese in the first leachate generation step exceeded 0.4 times the amount equivalent to the reaction equivalent of the positive electrode active material, a relatively larger amount of manganese leached into the first leachate compared to Examples 1 and 2. As a result, a relatively larger amount of cobalt leached into the second leachate. Consequently, the purity of cobalt in the second leachate was relatively lower compared to Examples 1 and 2.

[0101] Furthermore, in Example 4, where the amount of cobalt and nickel leached out from the first leachate in the first leachate generation step was less than 0.2 times the amount equivalent to the reaction equivalent of the positive electrode active material, a relatively smaller amount of cobalt and nickel leached out compared to Examples 1 and 2. As a result, the cobalt and nickel content in the second leachate increased, and the manganese extraction rate decreased compared to Examples 1 and 2.

[0102] In a comparative example where the entire amount equivalent to the reaction equivalent of the positive electrode active material was immediately added to the positive electrode active material sample in the first leaching step, without going through a separate residual positive electrode active material leaching step, the manganese extraction rate and cobalt purity were significantly lower than in the examples.

Claims

1. The steps include preparing the positive electrode active material from the positive electrode of a lithium secondary battery, The steps include: treating the positive electrode active material with a first acidic solution containing a reducing agent in an amount less than the reaction equivalent of the positive electrode active material to produce a first leachate; The steps include: treating the remaining positive electrode active material, after removing the fraction contained in the first leachate from the positive electrode active material, with a second acidic solution containing a reducing agent to produce a second leachate; The process includes the step of recovering transition metals from the first leachate and the second leachate, The positive electrode active material includes a lithium transition metal oxide containing nickel, cobalt, and manganese. The amount corresponding to the reaction equivalent of the positive electrode active material means the amount corresponding to the reaction equivalent of the lithium transition metal oxide contained in the positive electrode active material. The amount equivalent to the reaction equivalent of the lithium transition metal oxide is determined based on the stoichiometric reaction ratio of the lithium transition metal oxide and the reducing agent. A method for recovering transition metals from lithium secondary batteries.

2. The method for recovering transition metals from a lithium secondary battery according to claim 1, wherein the amount of the reducing agent used in the step of generating the first leachate is 0.2 to 0.4 times the amount equivalent to the reaction equivalent of the lithium transition metal oxide.

3. The method for recovering transition metals from a lithium secondary battery according to claim 2, wherein the reaction equivalent of the reducing agent used in the step of generating the first leachate with respect to the lithium transition metal oxide is 0.5 moles per mole of the lithium transition metal oxide.

4. The method for recovering transition metals from a lithium secondary battery according to claim 3, wherein the reducing agent used in the step of generating the first leachate is hydrogen peroxide.

5. The amount of the reducing agent used in the step of generating the second leachate is 0.8 to 1.2 times the amount equivalent to the reaction equivalent of the residual positive electrode active material, and the amount equivalent to the reaction equivalent of the residual positive electrode active material means the amount equivalent to the reaction equivalent of the lithium transition metal oxide contained in the residual positive electrode active material. The method for recovering transition metals from a lithium secondary battery according to claim 1, wherein the amount equivalent to the reaction equivalent of the lithium transition metal oxide is determined based on the stoichiometric reaction ratio of the lithium transition metal oxide and the reducing agent.

6. The cobalt and nickel content in the total weight of the transition metals contained in the first leachate is 75 to 100% by weight. The method for recovering transition metals from a lithium secondary battery according to claim 1, wherein the manganese content in the total weight of the transition metals contained in the second leachate is 30 to 75% by weight.

7. The method for recovering transition metals from a lithium secondary battery according to claim 6, further comprising the step of sequentially extracting cobalt and nickel from the first leachate.

8. A method for recovering transition metals from a lithium secondary battery according to claim 6, further comprising the step of sequentially extracting manganese, cobalt, and nickel from the second leachate.

9. The method for recovering transition metals from a lithium secondary battery according to claim 1, wherein the weight ratio of the residual positive electrode active material to the weight of the positive electrode active material is 25 to 50% by weight.

10. The method for recovering transition metals from a lithium secondary battery according to claim 1, wherein the first acidic solution and the second acidic solution contain sulfuric acid.

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