Method for recovering lithium precursor from spent lithium secondary battery cathode material

Abstract

The present application provides a method for recycling lithium precursor, the method comprises the following steps: a) mixing waste lithium secondary battery positive electrode material with urea to prepare a first mixture; b) calcining the first mixture to prepare a second mixture; and c) performing water washing treatment on the second mixture to obtain lithium hydroxide.

Description

Technical Field

[0001] This invention relates to a method for recovering lithium precursors from waste lithium secondary battery cathode materials. Background Technology

[0002] As the lithium-ion battery market expands into various fields such as batteries for information technology (IT) equipment, electric vehicles, and energy storage devices (ESS), the demand for lithium-ion batteries is increasing daily. With this increased demand, the volume of waste lithium-ion batteries is also increasing daily.

[0003] Cathode materials account for over 60% of the cost of lithium-ion batteries. Lithium cobalt oxide (LiCoO2) is commonly used as such an electrode due to its excellent reversibility, low self-discharge rate, high capacity, high energy density, and ease of synthesis. Furthermore, to reduce the amount of expensive cobalt used, composite oxides such as lithium nickel cobalt manganese oxide (Li(Ni,Co,Mn)O2) and lithium manganese oxide (LiMnO2), as well as lithium iron phosphate (LiFePO4), are used. Since the cathode materials described above contain approximately 5-7% lithium, methods for recovering lithium compounds from spent lithium-ion battery cathode materials are of great interest.

[0004] Existing technologies for recovering lithium from waste lithium-ion battery cathode materials typically employ two methods: first, extracting the waste cathode material with strong acids such as hydrochloric acid, sulfuric acid, and nitric acid, followed by neutralization with alkali to precipitate and recover cobalt and nickel as hydroxides; second, dissolving the cathode material in the presence of hydrogen peroxide with sulfuric acid or nitric acid, followed by neutralization precipitation to separate and recover the metals. However, these extraction processes require the use of strong acids, which evaporate into the atmosphere, causing severe environmental pollution, particularly due to serious equipment corrosion caused by the acids.

[0005] To address the aforementioned issues, a method has been proposed to recover lithium, cobalt, nickel, and other minerals by simply mixing waste cathode materials and carbon powder and then performing heat treatment in an oxidizing or reducing atmosphere. However, due to the cost associated with high-temperature heat treatment above 600°C and the reduced leaching efficiency compared to recovery methods using strong acids, the lithium recovery rate remains low. Summary of the Invention Technical problems to be solved

[0006] The purpose of this invention is to provide a method for recovering lithium hydroxide from waste lithium secondary battery cathode materials at low temperatures with a high yield. Technical solution

[0007] The present invention provides a method for recovering lithium precursors, the method comprising the following steps: a) mixing waste lithium secondary battery cathode material with urea to prepare a first mixture; b) calcining the first mixture to prepare a second mixture containing lithium hydroxide; and c) washing the second mixture with water to separate the lithium precursors.

[0008] According to one embodiment, the calcination temperature can be 450-600℃.

[0009] According to one implementation, step b) can be performed in an inert gas atmosphere.

[0010] According to one implementation scheme, the water washing can be carried out at 20-90°C.

[0011] According to one embodiment, the water washing treatment can form an aqueous solution of lithium hydroxide.

[0012] According to one embodiment, step c) may further include the step of crystallizing lithium hydroxide.

[0013] According to one embodiment, 5-50 parts by weight of the urea can be mixed with 100 parts by weight of the cathode material.

[0014] According to one embodiment, the cathode material can be represented by the following chemical formula 1.

[0015] [Chemical Formula 1]

[0016] Li x Ni a Co b M (1-a-b) O y

[0017] (In chemical formula 1, M is selected from Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, and B, 0 <x≤1.1,2≤y≤2.02,0.5≤a≤1,0≤b≤0.5)。

[0018] According to one implementation scheme, the recovery rate of lithium hydroxide from the waste lithium secondary battery cathode material can be over 50%. Beneficial effects

[0019] The method for recovering lithium precursors from waste lithium secondary battery cathode materials according to the present invention uses urea as a reducing agent, thus having the advantage of recovering lithium hydroxide in high yield even at low temperatures below 600°C.

[0020] Furthermore, lithium hydroxide can be effectively recovered without the need for strong acids such as sulfuric acid. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating a method for recovering lithium precursors according to an embodiment of the present invention. Detailed Implementation

[0022] The advantages, features, and methods of implementing the present invention will become clearer with reference to the accompanying drawings and detailed description of the embodiments. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different ways. These embodiments are provided merely to make the disclosure of the invention complete and to fully illustrate the scope of the invention to those skilled in the art, and the invention is defined only by the scope of the claims. Hereinafter, specific embodiments of the invention will be described in detail with reference to the accompanying drawings. Unrelated to the drawings, the same reference numerals denote the same constituent elements, and "and / or" includes all combinations of each item mentioned and more than one item.

[0023] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) may be used in the sense commonly understood by one of ordinary skill in the art to which this invention pertains. Throughout the specification, when a part is described as "comprising" or "including" a constituent element, this means, unless otherwise specifically stated to the contrary, that other constituent elements may also be included, rather than excluding other constituent elements. Furthermore, unless specifically mentioned herein, the singular form also includes the plural form.

[0024] When a layer, film, region, plate, or other part is described in this specification as being "above" or "on" other parts, this includes not only the case where it is "directly" located "on" other parts, but also the case where other parts are present in between.

[0025] As used in this specification, the term "precursor" refers to a compound containing a specific metal in order to provide a specific metal contained in an electrode active material.

[0026] Previously, batteries for IT devices such as laptops and smartphones dominated the lithium-ion battery market. However, in recent years, with the rapid growth of the electric vehicle market, there is a trend towards high-capacity lithium-ion batteries dominating the market. To cater to this rapid growth trend in the high-capacity lithium-ion battery market, nickel and easily synthesized lithium hydroxide are being used as the main raw materials to increase the capacity of lithium-ion batteries. Specifically, nickel has the characteristic that it cannot synthesize well with lithium at high temperatures. Therefore, by synthesizing lithium hydroxide, which has a lower melting point than lithium carbonate, with nickel, it is easy to synthesize a "high-nickel" cathode material with increased nickel content. Thus, there is a trend towards using lithium hydroxide as the main raw material for high-capacity lithium-ion batteries.

[0027] To cater to the trend in the high-capacity lithium secondary battery market, this invention provides a method for recovering lithium precursors containing lithium hydroxide from waste lithium secondary battery cathode materials. Specifically, the recovery method includes the following steps: a) mixing waste lithium secondary battery cathode materials with urea to prepare a first mixture; b) calcining the first mixture to prepare a second mixture containing lithium hydroxide; and c) washing the second mixture with water to separate the lithium precursor, thereby having the advantage of being able to recover lithium hydroxide at low temperatures and in high yields.

[0028] Step a) is the step of mixing the waste lithium secondary battery cathode material with urea as a solid reducing agent. Before step a), a further step of obtaining the cathode material from the waste lithium secondary battery may be included.

[0029] The waste lithium secondary battery includes a positive electrode, a negative electrode, and a separator between the positive and negative electrodes. The positive and negative electrodes may each include a positive electrode active material layer or a negative electrode active material layer coated on a positive electrode current collector or a negative electrode current collector, respectively. The waste lithium secondary battery may include lithium secondary batteries that cannot be reused (charged and discharged), such as lithium secondary batteries whose charge and discharge performance has significantly decreased due to prolonged use, or lithium secondary batteries damaged by physical impact or chemical reactions.

[0030] Lithium or lithium derivatives can be recovered by separating the positive electrode from the waste lithium secondary battery and recycling the waste positive electrode. The waste positive electrode includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer may contain positive electrode active material, conductive material, and binder. Specifically, the conductive material may contain carbon-based materials such as graphite, carbon black, graphene, and carbon nanotubes, and the binder may contain PVDF-co-HFP, polyvinylidene fluoride (PVDF), polyacrylonitrile, or polymethyl methacrylate.

[0031] The recovered waste positive electrode can be heat-treated in an oxidizing atmosphere at 100-500°C, preferably 350-450°C. Therefore, the conductive materials and binders contained in the positive electrode active material layer can be substantially completely removed; non-limitingly, more than 95% by weight can be removed.

[0032] The waste positive electrode that has undergone the aforementioned heat treatment can be separated into positive electrode current collectors and made into powder by pulverization. Specifically, after pulverizing the waste positive electrode, the positive electrode material can be obtained using a 5-100 μm mesh screening. The pulverization can be performed using a ball mill, but is not limited to it.

[0033] Through the above process, a positive electrode material can be obtained that substantially removes the positive current collector component and removes more than 90% by weight of the carbon-based components derived from the conductive material and the binder.

[0034] The cathode material can be represented by the following chemical formula 1.

[0035] [Chemical Formula 1]

[0036] Li x Ni a Co b M (1-a-b) O y

[0037] (In chemical formula 1, M is selected from Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, and B, 0 <x≤1.1,2≤y≤2.02,0.5≤a≤1,0≤b≤0.5)。

[0038] In step a), 5-50 parts by weight, preferably 7-30 parts by weight, and more preferably 10-25 parts by weight of urea can be mixed with 100 parts by weight of the cathode material to prepare a first mixture. This mixing can be dry mixing, rather than mixing by adding a liquid substance such as a solvent, and the mixing can be carried out in a fluidized bed reactor. Specifically, the mixing process can be carried out at 15-90°C, preferably 25-50°C, for 1-3 hours. By calcining and washing the first mixture prepared under the above conditions, the cathode material is fully reduced, thereby improving the conversion rate of lithium hydroxide, and thus lithium hydroxide can be recovered in high yield after step c).

[0039] Step b) involves calcining the first mixture prepared in step a) to prepare the second mixture. This can be carried out at 450-600°C, preferably 470-600°C, more preferably 500-550°C, for 1-4 hours, and more preferably 2-3 hours. The calcination process can be conducted in an inert gas atmosphere; as a non-limiting example, the inert gas may include argon or nitrogen. Specifically, the reactor atmosphere can be replaced by purging with the aforementioned inert gas. When step c) is performed after the calcination process under the above conditions, lithium hydroxide can be recovered with a recovery rate of 50% or higher. The recovery rate refers to the recovery rate of lithium hydroxide from the cathode material of waste lithium-ion batteries. Specifically, it can be calculated by analyzing the total lithium content in the cathode material before recovery and using it as a 100% baseline, and then analyzing the lithium content in the recovered lithium hydroxide to calculate the lithium hydroxide recovery rate.

[0040] The second mixture prepared in step b) may contain lithium hydroxide (LiOH) and a mixture containing a transition metal. The mixture containing the transition metal may contain a transition metal and an oxide containing the transition metal, such as nickel, cobalt, or manganese. The transition metal in the mixture may be formed by the separation of the transition metal component during the calcination process of the lithium composite oxide used as the cathode material, which is then converted into lithium hydroxide.

[0041] Step c) involves water washing the second mixture prepared in step b), which can be performed at 20-90°C, preferably at 20-60°C. Specifically, distilled water, pure water, or soft water can be used as the washing solution. The second mixture and the washing solution can be mixed at a solid-liquid ratio of 10-500 g / L. The water washing process can be repeated 1-3 times, with each washing cycle lasting from 30 minutes to 2 hours. Under these conditions, an aqueous solution containing lithium hydroxide can be separated from the second mixture. The transition metal mixture in the second mixture can precipitate in the aqueous solution, thus allowing for the acquisition of a high-purity lithium precursor containing lithium hydroxide through filtration.

[0042] Alternatively, the mixture containing transition metals separated by precipitation can be treated with an acid solution to form precursors in the form of each transition metal salt. As a non-limiting example, by using sulfuric acid as the acid solution, NiSO4, MnSO4, and CoSO4, which are transition metal precursors, can be recovered separately.

[0043] Step c) may further include the step of crystallizing lithium hydroxide in the separated aqueous solution. Specifically, crystalline lithium hydroxide can be obtained by concentrating the aqueous solution. The concentration method can be selected and used without restriction as long as it is a concentration method that can obtain crystalline form in the aqueous phase, such as vacuum concentration, freeze concentration, evaporation concentration, heating concentration, precipitation concentration, reverse osmosis concentration, etc.

[0044] Figure 1 This is a flowchart illustrating the recovery of lithium precursors from waste lithium secondary batteries according to one embodiment of the present invention. Figure 1 As shown, lithium hydroxide can be obtained from waste lithium secondary battery cathode materials through the following steps: a step of preparing waste lithium secondary battery cathode materials (S10); a step of mixing the cathode material with urea reducing agent (S20); a step of calcining the mixed cathode material and urea (S30); a step of washing the calcined product with water (S40); and a step of crystallizing the washed product (S50). Through the above process, lithium hydroxide can be recovered at a recovery rate of 50% or more, preferably 70-90%.

[0045] The present invention will now be described in detail through embodiments, but these embodiments are only used to illustrate the present invention in more detail, and the scope of the present invention is not limited to the following embodiments.

[0046] Example

[0047] Example 1

[0048] Step 1: Prepare positive electrode materials from waste lithium secondary batteries

[0049] Waste cathode material separated from waste lithium secondary batteries is heat-treated at 400°C for 3 hours, then pulverized by milling, and finally sieved through a sieve with an 80μm aperture to obtain powdered cathode material. At this point, the cathode contains LiNi, the cathode active material, in a weight ratio of 92:5:3. 0.8 Co 0.1 Mn 0.1 The positive electrode active material layer consists of O2, conductive material acetylene black (Denka black), and binder PVDF.

[0050] Step 2: Steps for recovering lithium precursors from waste lithium secondary battery cathode materials

[0051] 10g of the cathode material obtained in step 1 and 2g of urea were dry-mixed and then calcined at 450°C for 2 hours under a nitrogen atmosphere to obtain a primary precursor mixture. The primary precursor mixture was then recovered, and 19 times the weight of distilled water relative to the recovered mixture was added. The concentration of lithium dissolved in the distilled water was analyzed to measure the content of each lithium compound obtained, which is recorded in Table 1 below.

[0052] Evaluation Example: Evaluation of the yield of lithium hydroxide from waste lithium secondary batteries

[0053] (Examples 2 to 7)

[0054] Except that in step 2 of Example 1, the calcination temperature is set to the temperature recorded in Table 1 below instead of 450°C, the same method as in Example 1 is used.

[0055] (Comparative Examples 1 to 2)

[0056] Except that solid carbon (carbon black, Denka) was used instead of urea in step 2 of Example 1, and the calcination temperature was set to the temperature described in Table 1 below, the same method as in Example 1 was used.

[0057] Lithium hydroxide gravimetric X-ray diffraction (XRD) analysis

[0058] The products obtained by Examples 1 to 7 and Comparative Examples 1 to 2 were subjected to XRD analysis. Based on the XRD results, the content of the substances was obtained by crystal structure analysis according to the Rietveld method and recorded in Table 1 below.

[0059] [Table 1]

[0060] In Table 1, lithium conversion rate refers to the ratio of lithium content in the aqueous phase obtained during the washing process to the total lithium content in the cathode material before the reaction. The contents (wt%) of lithium carbonate, lithium hydroxide, and lithium oxide are relative to the total weight of the primary precursor mixture obtained in step 2. The recovery rate of lithium hydroxide refers to the lithium content in the recovered lithium hydroxide relative to the total lithium content in the cathode material before recovery.

[0061] As shown in Table 1, Examples 1 to 6, which used urea as a reducing agent, showed higher lithium hydroxide recovery rates compared to Comparative Examples 1 to 2, which used solid carbon reducing agents. Specifically, it was confirmed that under calcination conditions at temperatures above 450°C, specifically 450-600°C, the lithium hydroxide content tended to increase with increasing calcination temperature, and all showed high lithium hydroxide recovery rates of 50% or more. Furthermore, when the calcination temperature was below 450°C (Example 7), the lithium hydroxide content decreased; therefore, the preferred calcination temperature is 450-600°C.

[0062] In Comparative Example 1, where solid carbon was used as the reducing agent, the calcination process was carried out under the same conditions as in Example 1, but the content of lithium hydroxide and lithium carbonate in the recovered product was 0. That is, it can be seen that when solid carbon is used as the reducing agent, no lithium hydroxide is produced at a temperature of 450°C, and the lithium conversion rate is 6%, which is also very low.

[0063] In Comparative Example 2, where solid carbon was used as a reducing agent and the calcination temperature was 840°C, it was confirmed that lithium oxide was obtained as a primary precursor. Through additional processes, lithium hydroxide could be obtained with a final recovery rate of 49%, but this required a temperature much higher than that of the embodiments according to the present invention.

Claims

1. A method for recovering lithium precursors, comprising the following steps: a) Mix waste lithium secondary battery cathode material with urea to prepare a first mixture; b) Calcining the first mixture in an inert gas atmosphere to prepare a second mixture containing lithium hydroxide; and c) The second mixture is washed with water to separate the lithium precursor. The calcination temperature is 450-600℃.

2. The method for recovering lithium precursors according to claim 1, wherein, The water washing process is carried out at 20-90℃.

3. The method for recovering lithium precursors according to claim 1, wherein, The water washing process forms an aqueous solution of lithium hydroxide.

4. The method for recovering lithium precursors according to claim 1, wherein, Step c) further includes the step of crystallizing lithium hydroxide.

5. The method for recovering lithium precursors according to claim 1, wherein, 5-50 parts by weight of urea are mixed with 100 parts by weight of the cathode material.

6. The method for recovering lithium precursors according to claim 1, wherein, The cathode material is represented by the following chemical formula 1: [Chemical Formula 1] Li x Ni a Co b M (1-a-b) O y In chemical formula 1, M is selected from Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, and B, 0 <x≤1.1,2≤y≤2.02,0.5≤a≤1,0≤b≤0.5。 7. The method for recovering lithium precursors according to claim 1, wherein, Based on the total lithium content in the waste lithium secondary battery cathode material, the lithium hydroxide recovery rate of the method is over 50%.

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