Process for producing lithium hydroxide

Abstract

The invention relates to a method for producing high-purity lithium hydroxide from lithium-containing waste liquid of waste lithium secondary batteries.

Description

Technical Field

[0001] The invention relates to a method for producing high-purity lithium hydroxide from lithium-containing waste liquid of waste lithium secondary batteries. Background Art

[0002] With the development of technology and the increase in demand for various energy storage devices from ultra-small to medium-sized (e.g., mobile devices, laptops, radio equipment, electric vehicles, and electric motorcycles), the demand for secondary batteries as energy sources has increased dramatically. Among such secondary batteries, lithium secondary batteries with high energy density and working potential, long cycle life, and low self-discharge rate have been commercialized and widely used.

[0003] As the production and use of lithium secondary batteries continue to increase, the amount of waste will increase, and the technical demand for the reprocessing and recycling of waste lithium secondary batteries to process waste is emerging. In addition, due to fierce price competition and increasing demand for secondary batteries, secondary batteries and material-related industries are in urgent need of efforts such as low-priced raw materials, low-priced processes and improved yields. Therefore, attempts to recycle waste batteries after use and unqualified products, electrodes, etc. generated in the manufacturing process are increasing, and as the demand for lithium is also rapidly increasing, it is necessary to develop a method for recovering high-purity lithium hydroxide (the essential material of lithium secondary batteries) with high yield.

[0004] In order to produce lithium hydroxide from lithium waste liquid, it is essential to remove sulfate ions. In this regard, Korean Patent Application Publication No. 10-2016-0002578 discloses a method for producing lithium hydroxide from lithium sulfate using barium hydroxide. However, it is not disclosed that lithium hydroxide is recovered from lithium waste liquid, and the use of barium hydroxide to remove sulfate ions has a long reaction time and the barium remaining in the solution causes the purity and yield of the obtained lithium hydroxide to decrease. At the same time, the solubility of calcium hydroxide used for sulfate ion precipitation in the art is low in water, and there is a problem of being difficult to form a precipitate with sulfate ions, unless it is treated separately to improve solubility.

[0005] [Related technical literature]

[0006] [Patent Document]

[0007] (Patent Document 1) Korean Patent Application Publication No. 10-2016-0002578 Summary of the invention

[0008] The present invention is made to improve the technical problems in the above-mentioned field, and is directed to providing a method for producing high-purity lithium hydroxide with high yield from lithium-containing waste liquid without using a separate additive.

[0009] However, the problems that the present application seeks to solve are not limited to the above problems, and those skilled in the art will clearly understand other problems not mentioned herein through the following description.

[0010] In view of the above, one embodiment of the present invention provides a method for producing lithium hydroxide, the method comprising obtaining lithium sulfate from lithium-containing waste liquid; obtaining lithium hydroxide by reacting lithium sulfate with calcium hydroxide, wherein the lithium sulfate obtained from the lithium-containing waste liquid has a pH of 6 or less.

[0011] Beneficial effects

[0012] The method for producing lithium hydroxide according to the present invention can produce high-purity lithium hydroxide from lithium-containing waste liquid with high yield without using a separate additive (such as a phosphorus-containing material, a pH regulator or glycerol). In addition, since there is no separate process for removing the additive, the method for producing lithium hydroxide can be simplified.

[0013] In addition, by using the lithium-containing waste liquid of the present invention, a lithium sulfate aqueous solution having a pH adjusted to 6 or less can be obtained without a separate additive for adjusting the pH by evaporating and concentrating the lithium-containing waste liquid (from which valuable metals such as manganese, cobalt and nickel are separated and recovered) and then cooling and crystallizing. In addition, the lithium sulfate aqueous solution reacts with calcium hydroxide to obtain a lithium hydroxide aqueous solution, from which a lithium hydroxide powder can be obtained by a low-temperature process using an alcohol precipitant (such as isopropyl alcohol). BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The solubility of calcium hydroxide according to temperature is shown. DETAILED DESCRIPTION

[0015] As a method for obtaining high-purity lithium hydroxide from waste lithium secondary batteries with high yield, the present invention relates to a method for producing lithium hydroxide, which comprises obtaining lithium sulfate from lithium-containing waste liquid of waste lithium secondary batteries, and obtaining lithium hydroxide by reacting lithium sulfate with calcium hydroxide.

[0016] The method for producing lithium hydroxide according to the present invention is capable of producing high-purity lithium hydroxide at a high yield from lithium-containing waste liquid without using a separate additive (such as a phosphorus-containing material, a pH adjuster or glycerol), and since there is no separate process for removing the additive, the method for producing lithium hydroxide can be simplified.

[0017] In addition, by using the lithium-containing waste liquid of the present invention, a lithium sulfate aqueous solution having a pH adjusted to 6 or less can be obtained without a separate additive for adjusting the pH by evaporating and concentrating the lithium-containing waste liquid (from which valuable metals such as manganese, cobalt and nickel are separated and recovered) and then cooling and crystallizing. In addition, the lithium sulfate aqueous solution reacts with calcium hydroxide to obtain a lithium hydroxide aqueous solution, from which a lithium hydroxide powder can be obtained by a low-temperature process using an alcohol precipitant (such as isopropyl alcohol).

[0018] Hereinafter, the method for producing lithium hydroxide according to the present invention will be described in detail. However, the present invention is not limited thereto.

[0019] <Method for producing lithium hydroxide>

[0020] The method for producing lithium hydroxide of the present invention comprises obtaining lithium sulfate from lithium-containing waste liquid; and obtaining lithium hydroxide by reacting lithium sulfate with calcium hydroxide, wherein the lithium sulfate obtained from the lithium-containing waste liquid has a pH of 6 or lower.

[0021] In addition, the method for producing lithium hydroxide of the present invention may also include obtaining lithium-containing waste liquid from waste lithium secondary batteries, pretreating the lithium-containing waste liquid, and preparing lithium hydroxide powder.

[0022] (1) Obtaining lithium sulfate from lithium-containing waste liquid

[0023] The method for producing lithium hydroxide of the present invention comprises obtaining lithium sulfate from lithium-containing waste liquid.

[0024] The method may also include recovering one or more metal salts selected from manganese, nickel and cobalt from the lithium-containing waste liquid before obtaining lithium sulfate. Here, the lithium-containing waste liquid may refer to valuable metals separated and recovered from waste lithium secondary batteries, such as manganese, cobalt and nickel.

[0025] As an example, in the present invention, the metal salt can be recovered by solvent extraction or precipitation, and in solvent extraction, a phosphoric acid-based material (e.g., di-(2-ethylhexyl)phosphoric acid, di-(2-ethylhexyl)phosphonic acid or bis-(2,4,4-trimethylpentyl)phosphonic acid) or a carboxyl-based material (e.g., neodecanoic acid) can be used, and in precipitation, an oxime-based material (e.g., dimethylglyoxime, diethylglyoxime, dipropylglyoxime or ethylmethylglyoxime) can be used, however, these materials are not limited thereto.

[0026] In the process of obtaining lithium sulfate from lithium-containing waste liquid, alkaline materials and sulfuric acid are used to recover metal salts, etc., and the pH value of lithium sulfate obtained by the above process without special treatment can be 6 or lower. Artificially lowering the pH leads to a decrease in purity and yield, and artificially raising the pH leads to an increase in the Na content, thereby causing impurity problems and purity / yield reduction. For example, at least one or more selected from the group consisting of NaOH, KOH, Ca(OH)2 and NH4OH can be used as an alkaline material, and using NaOH is most preferred.

[0027] In one embodiment, when sodium hydroxide is used as an alkaline material to separate and recover metal salts in a process of obtaining lithium sulfate from lithium-containing waste liquid, sulfuric acid solution and sodium hydroxide may react to generate sodium sulfate, which is an impurity.

[0028] Obtaining lithium sulfate from lithium-containing waste liquid may also include removing sodium sulfate (Na2SO4) by evaporating and concentrating the lithium-containing waste liquid and then cooling and crystallizing the recovered metal salt. The concentration is preferably concentrated to 70%, but is not limited thereto.

[0029] Cooling crystallization utilizes the solubility difference between sodium sulfate and lithium sulfate, and can be carried out without utilizing additional material processing. Cooling crystallization for removing sodium sulfate can be carried out in a temperature range of 0°C to 10°C, preferably in a temperature range of 2°C to 5°C. When the temperature is higher than 10°C, the solubility of Na2SO4 increases, making it difficult to separate Na2SO4, so it is preferred to reduce the solubility of Na2SO4 at a temperature of 10°C or lower and then remove Na2SO4 through a precipitation filter.

[0030] (2) Lithium hydroxide is obtained by reacting lithium sulfate and calcium hydroxide

[0031] The method for producing lithium hydroxide of the present invention comprises obtaining lithium hydroxide by reacting lithium sulfate and calcium hydroxide.

[0032] In the present invention, preferably lithium sulfate and calcium hydroxide are added in the same molar number and reacted at room temperature. When the temperature is increased in order to increase the reactivity, the solubility of calcium hydroxide decreases, and a large amount of unreacted material exists due to undissolved calcium hydroxide, thereby reducing the final yield.

[0033] In the present invention, the reactivity of calcium hydroxide with lithium is better than that of barium hydroxide, resulting in a short reaction time, no unreacted calcium substance remaining, and a high yield of the produced lithium hydroxide.

[0034] The pH of the lithium sulfate obtained from the lithium-containing waste liquid can be 6 or lower, preferably 4.5 to 6, and most preferably 5 to 6. Since no additional step is required for adjusting the pH in this step, there is an advantage of simplifying the process of the method for producing lithium hydroxide of the present invention. The solubility of calcium hydroxide in water is low, however, when the lithium sulfate aqueous solution meets the pH of 6 or lower, excellent solubility and reactivity can be obtained without adding additional solvents (such as glycerol). When the pH of lithium sulfate is greater than 6, the calcium hydroxide added to react with lithium sulfate is insoluble, and the reactivity with sulfate ions is rapidly reduced, thereby reducing the yield and purity of lithium hydroxide. In addition, artificially reducing the pH causes a decrease in purity and yield, and artificially increasing the pH causes an increase in the Na content, thereby causing impurity problems and a decrease in purity / yield.

[0035] In the present invention, there is no separate additive for dissolving calcium hydroxide in water, so an additional process for removing the additive is not required, which simplifies the process. For example, when glycerol is added to dissolve calcium hydroxide in water, spray drying at a high temperature of 290° C. or higher is required to remove the glycerol, and since it is difficult to completely remove the glycerol even by spray drying, the purity of lithium hydroxide is reduced.

[0036] like Figure 1 As shown, as the temperature increases, the reactivity with lithium sulfate increases and the solubility of calcium hydroxide in water decreases. Therefore, the reaction of lithium sulfate and calcium hydroxide is preferably carried out at room temperature, most preferably at about 20°C.

[0037] The obtaining of lithium hydroxide may also include reacting lithium sulfate with calcium hydroxide to generate a lithium hydroxide aqueous solution and calcium sulfate, and removing the calcium sulfate through a filtering process.

[0038] The obtaining of lithium hydroxide may also include obtaining lithium hydroxide powder by precipitating lithium hydroxide using a precipitant. Specifically, a precipitant may be added to a lithium hydroxide aqueous solution for precipitation, and the resultant may be dried to obtain lithium hydroxide powder.

[0039] Furthermore, precipitation and drying may be performed at a temperature range of 10° C. to 30° C., preferably at a temperature range of 15° C. to 25° C., and most preferably at room temperature of about 20° C. A temperature higher than 30° C. is not preferred because the solubility of calcium sulfate increases, making it difficult to separate calcium sulfate, and a temperature lower than 10° C. is not preferred because materials other than calcium sulfate (e.g., metal salts) are precipitated together.

[0040] Examples of the precipitating agent may include alcohols such as isopropanol, butanol, and pentanol.

[0041] (3) Pretreatment for preparing lithium-containing waste liquid

[0042] In the method for producing lithium hydroxide of the present invention, the lithium-containing waste liquid can be obtained from waste lithium secondary batteries, and in order to obtain the lithium-containing waste liquid, the process of immediately crushing the waste lithium secondary batteries and then heat treating the result can also be included.

[0043] The pretreatment process may also include discharging the waste lithium secondary battery before comminution. When the discharge is complete, the subsequent valuable metal recovery process may also be smoothly carried out in the atmosphere rather than in an inert atmosphere. The discharge may be carried out in a discharge solution. Distilled water may be used as a discharge solution. The degree of completion of the discharge may be determined by the decrease in voltage over time. Most of the electrolyte in the waste lithium secondary battery is removed during the discharge process.

[0044] The pulverization can be performed by grinding. The grinding can be mechanical grinding, and in particular, the grinding can be one or more selected from the group consisting of roller milling, ball milling, jet milling, planetary milling and disc milling.

[0045] The pulverized material may have a particle size of 1 μm to 15 μm, may preferably have a particle size of 1 μm to 7 μm, and may more preferably have a particle size of 2 μm to 5 μm.

[0046] The pretreatment process may also include classification after pulverization. The pulverized material is separated into a mostly fine electrode composite powder and other components (positive electrode, negative electrode, separator) by a classification process, preferably by classification using a sieve, and the electrode composite powder is recovered from the pulverized material.

[0047] The pretreatment process may also include gravity separation after classification. The crushed material is preferably separated by gravity using a washing tank equipped with a water level, the separator in the crushed material is removed, and the electrode composite material, the separator and the current collector, etc. can be separated.

[0048] The pretreatment process may further include magnetic separation after gravity separation. When the waste lithium secondary battery also contains stainless steel (SUS), the stainless steel (SUS) is selectively removed from the pulverized material by magnetic separation.

[0049] During the pretreatment, heat treatment may be performed after magnetic separation. Heat treatment is to remove impurities other than the positive electrode active material contained in the waste lithium secondary battery, such as positive electrode binder, positive electrode conductor, negative electrode active material, negative electrode binder, negative electrode conductor and pouch, and may be performed at a temperature range of 600°C to less than 1000°C, preferably at a temperature range of 700°C to 900°C, and more preferably at a temperature range of 800°C to 900°C. When the heat treatment temperature is higher than 1000°C, lithium in the positive electrode active material may even be removed.

[0050] In addition, after the heat treatment, the pretreatment process may include a process of further removing remaining impurities such as a carbon material (negative electrode active material) and copper by mixing sulfuric acid with the pretreatment material.

[0051] The waste lithium secondary battery includes a positive electrode, a negative electrode, a separator and an electrolyte, and may also include a soft pack. In particular, the waste lithium secondary battery includes a separator disposed between the negative electrode and the positive electrode, and an electrolyte solution including an electrolyte supplied to the separator. More particularly, the above-mentioned waste lithium secondary battery may be manufactured, for example, by stacking the negative electrode, the separator and the positive electrode in sequence, and then winding or folding the result to place it in a cylindrical or prismatic battery case or a soft pack, and then injecting an organic electrolyte into the battery case or the soft pack.

[0052] The positive electrode of the waste lithium secondary battery may include lithium metal or lithium transition metal oxide, and may be prepared using methods known in the art. For example, the positive electrode may be prepared by mixing a solvent and, as needed, a binder, a conductor, and a dispersant into a positive electrode active material and stirring the result to prepare a slurry, then applying (coating) the slurry on a positive electrode current collector, compressing, and then drying the result.

[0053] Examples of the positive electrode active material may include a material selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(Ni x Co y Mn z )O2 (here, 0<x<1, 0<y<1, 0<z<1, and x+y+z=1), LiNi 1-a Co a O2 (here, 0≤a<1), LiCo 1-b Mn b O2 (here, 0≤b<1), LiNi 1-c Mn c O2 (here, 0≤c<1), LiMn 2-d Ni d O4 (here, 0<d<2), LiMn 2-e Co e One or more of the group consisting of O4 (here, 0<e<2), LiCoPO4, LiFePO4 and combinations thereof, but not limited thereto.

[0054] As the solvent of the positive electrode, N-methyl-2-pyrrolidone (NMP), acetone, water or a mixture thereof can be used, and as the conductor of the positive electrode, a conductive auxiliary material such as polyacrylic acid, acetylene black, furnace black, graphite, carbon fiber or fullerene can be used.

[0055] The binder of the positive electrode plays the role of completely attaching the particles of the positive electrode active material and also completely attaching the positive electrode active material to the positive electrode current collector, and examples of the binder may include polyacrylic acid, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, etc.

[0056] The positive electrode current collector has a thickness of about 3 μm to about 500 μm, and is not particularly limited as long as it has high conductivity and does not cause chemical changes to the corresponding battery. For example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, aluminum or stainless steel surface-treated with a material selected from the group consisting of carbon, nickel, titanium, silver, and a combination thereof can be used. The current collector can increase the bonding strength with the positive electrode active material by forming a small unevenness on the surface, and various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, or a non-woven fabric can be used.

[0057] The negative electrode of the waste lithium secondary battery can be prepared using methods known in the art. For example, the negative electrode can be prepared by mixing a solvent and, as needed, a binder, a conductor, and a dispersant into a negative electrode active material and stirring the result to prepare a slurry, then applying (coating) the slurry on a negative electrode current collector, compressing, and then drying the result.

[0058] The negative electrode active material may generally be a carbon material capable of intercalating and deintercalating lithium ions, lithium metal, silicon, tin, etc. The negative electrode active material may preferably be a carbon material, and as the carbon material, may include low crystalline carbon, high crystalline carbon, etc. Representative examples of low crystalline carbon may include soft carbon and hard carbon, and representative examples of high crystalline carbon may include natural graphite, primary graphite, pyrolytic carbon, carbon fibers based on mesophase pitch, mesophase carbon microbeads, mesophase pitch, and high temperature calcined carbon, such as coke derived from petroleum or coal tar pitch.

[0059] As the solvent of the negative electrode, N-methyl-2-pyrrolidone (NMP), acetone, water or a mixture thereof can be used, and as the conductor of the negative electrode, a conductive auxiliary material such as polyacrylic acid, acetylene black, furnace black, graphite, carbon fiber or fullerene can be used.

[0060] The binder of the negative electrode plays the role of completely attaching the particles of the negative electrode active material and also completely attaching the negative electrode active material to the current collector, and examples of the binder may include polyacrylic acid, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, etc.

[0061] Typically, the negative electrode current collector is manufactured to have a thickness of about 3 μm to about 500 μm. This negative electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes to the corresponding battery. For example, it may include copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium or silver, or aluminum-cadmium alloy. In addition, like the positive electrode current collector, the negative electrode current collector can also enhance the bonding strength with the negative electrode active material by forming fine unevenness on the surface, and various forms such as films, sheets, foils, nets, porous bodies, foams or non-woven fabrics can be used.

[0062] There is no limitation on the type of separator of the waste lithium secondary battery, for example, a porous substrate made of a polyolefin-based polymer (the polyolefin-based polymer is selected from the group consisting of ethylene homopolymer, propylene homopolymer, ethylene-butene copolymer, ethylene-hexene copolymer and ethylene-methacrylate copolymer); a porous substrate made of a polymer (the polymer is selected from the group consisting of polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfite and polyethylene naphthalene); a porous substrate made of a mixture of inorganic particles and a binder polymer, etc. In particular, in order to facilitate the transfer of lithium ions of the lithium ion supply core portion to the external electrode, it is preferred to use a separator made of a non-woven fabric corresponding to a porous substrate made of a polymer selected from the group consisting of polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfite, polyethylene naphthalene and a combination thereof.

[0063] The separator has a pore size of about 0.01 μm to about 10 μm, and generally has a thickness of about 5 μm to about 300 μm.

[0064] As the electrolyte of the waste lithium secondary battery, as examples, it can be used: a gel polymer electrolyte using PEO, PVdF, PVdF-HFP, PMMA, PAN or PVAC; a solid electrolyte using PEO, PPO (polypropylene oxide), PEI (polyethylene imine), PES (polyethylene sulfide) or PVAc (polyvinyl acetate), etc. In addition, as the electrolyte, it can also be used: a non-aqueous electrolyte liquid using ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl formate (MF), γ-butyrolactone (γ-BL), cyclopentane, methyl acetate (MA) or methyl propionate (MP). In addition, the electrolyte may also include a lithium salt, and examples of such lithium salts may include LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lower aliphatic carboxylic acid lithium or lithium tetraphenylborate, etc.

[0065] In one embodiment of the present application, in addition to the separator, an organic solid electrolyte and / or an inorganic solid electrolyte may be used in the waste lithium secondary battery, but the use is not limited thereto. Here, when an organic solid electrolyte and / or an inorganic solid electrolyte is used, the solid electrolyte may also act as a separator in some cases, and the separator may not be used.

[0066] Examples of organic solid electrolytes may include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyvinyl alcohol or polyvinylidene fluoride, but are not limited thereto. Inorganic solid electrolytes may be selected from the group consisting of, for example, Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2 and combinations thereof, but are not limited thereto.

[0067] Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are used to more specifically describe the present invention, and the scope of the present invention is not limited to the following Examples.

[0068] <Example 1 to Example 3>

[0069] The positive electrode material separated from the waste lithium secondary battery is crushed into powder. The obtained powder is reacted with a sulfuric acid solution for 6 hours or more to obtain a leaching solution containing Li. Manganese, cobalt and nickel are separated and recovered from the leaching solution containing Li by solvent extraction and precipitation, and a lithium-containing waste liquid is obtained.

[0070] When necessary metals are recovered by solvent extraction, the optimal extraction conditions for Mn are obtained at a pH of about 4, the optimal extraction conditions for Co are determined at a pH of about 5, and the optimal extraction conditions for Ni are obtained at a pH < 6. Therefore, manganese, cobalt or nickel is extracted under the above pH conditions, and the pH of the obtained lithium-containing waste liquid is adjusted to pH 5.5, pH 4.5 and pH 4, respectively, by the sulfuric acid solution used when extracting the metal salt.

[0071] Subsequently, the obtained lithium-containing waste liquid was evaporated and concentrated to 70 w / v%, and then cooled and crystallized at 5° C. to precipitate Na2SO4, filtered and removed Na2SO4, to obtain a lithium sulfate aqueous solution (LiSO4·H2O). Here, Example 1 uses the obtained lithium sulfate aqueous solution with a pH of 5.5, Example 2 uses the obtained lithium sulfate aqueous solution with a pH of 4.5, and Example 3 uses the obtained lithium sulfate aqueous solution with a pH of 4.

[0072] Using the obtained lithium sulfate aqueous solution as a starting material, calcium hydroxide (Ca(OH)2) powder (4.0 g) was added as an additive to the lithium sulfate aqueous solution (1000 mL) and reacted at room temperature. Through the reaction, calcium sulfate (CaSO4·H2O) was precipitated to obtain a lithium hydroxide (LiOH) solution. The precipitated calcium sulfate was removed by filtration, and lithium hydroxide was precipitated by adding isopropanol at room temperature, and the result was dried to obtain lithium hydroxide powder.

[0073] <Comparative Example 1>

[0074] Lithium sulfate monohydrate and deionized water (softened water) were stirred to obtain a lithium sulfate aqueous solution. After adding barium hydroxide (13.8 g) as an additive to the lithium sulfate aqueous solution (1000 mL), the result was stirred to react and then filtered. Here, barium hydroxide was introduced in the same molar number as lithium sulfate. After filtering, the filtrate was spray-dried at 150° C. to 200° C. to obtain lithium hydroxide powder.

[0075] <Comparative Example 2>

[0076] Lithium sulfate monohydrate and deionized water (softened water) were stirred to obtain a lithium sulfate aqueous solution. Glycerol was added to the lithium sulfate aqueous solution (1000 mL) to increase the solubility of calcium hydroxide, and calcium hydroxide powder (4.0 g) was added thereto as an additive. The resultant was stirred and the resulting precipitate was separated. The filtrate from which the precipitate was removed was spray dried at a temperature of 290° C. or higher to remove the glycerol, to obtain lithium hydroxide powder.

[0077] In Comparative Examples 1 and 2, artificially lowering the pH resulted in decreased purity and yield, and raising the pH resulted in increased Na content, leading to impurity problems and decreased purity / yield.

[0078] <Comparative Example 3>

[0079] Lithium hydroxide powder was prepared under the same conditions as in Example 1, except that a lithium sulfate aqueous solution having a pH of 6.5 was used.

[0080] Experimental Example 1: Comparison based on additives

[0081] In this experimental example, the purity and yield of lithium hydroxide according to the type of additive added for reaction with lithium sulfate, and the reactivity of lithium sulfate and the additive were evaluated. The results are shown in Table 1 below.

[0082] [Table 1]

[0083] additive purity(%) Yield (%) purity Yield Responsiveness Comparative Example 1 <![CDATA[Ba(OH)2]]> 94.9 64.1 △ △ △ Comparative Example 2 <![CDATA[Ca(OH)2]]> 97.4 90.6 △ ○ ○ Example 1 <![CDATA[Ca(OH)2]]> 99.9 95.1 ◎ ◎ ◎

[0084] Experimental Example 2: Comparison of pH based on lithium sulfate

[0085] In this experimental example, the purity and yield of lithium hydroxide according to the pH conditions of lithium sulfate and the reactivity of lithium sulfate and additives were evaluated. The results are shown in Table 2 below.

[0086] [Table 2]

[0087]

[0088] The evaluation criteria of purity, yield and reactivity in Tables 1 and 2 are as follows: Here, purity refers to the content excluding Ca as an impurity from the total content.

[0089] <Purity Evaluation Criteria>

[0090] ◎: When the purity of lithium hydroxide is 99.9% or higher

[0091] ○: When the purity of lithium hydroxide is 98.0% to 99.8%

[0092] △: When the purity of lithium hydroxide is less than 98.0%

[0093] <Evaluation Criteria for Yield>

[0094] ◎: When the yield of lithium hydroxide is greater than 95.0%

[0095] ○: When the yield of lithium hydroxide is 75.0% to 95.0%

[0096] △: When the yield of lithium hydroxide is less than 75%

[0097] <Evaluation Criteria for Reactivity>

[0098] ◎: The yield after 4 hours of reaction is greater than 95%

[0099] ○: The yield is 75% to 95% when the reaction time is 4 hours

[0100] △: The yield after 4 hours of reaction is less than 75%

[0101] Referring to Table 1 and Table 2, Comparative Example 1 using barium hydroxide as an additive has a problem of residual Ba in the solution due to the long reaction time, and Comparative Example 2 adding glycerol has a problem of residual Ca due to the CaSO4 produced after the reaction partially dissolved in the added glycerol, and it is determined that both Comparative Example 1 and Comparative Example 2 have the problem of reduced purity and yield of lithium hydroxide. At the same time, when the pH is 6.5 or higher, as in Comparative Example 3, Ca(OH)2 cannot be well dissolved, and it is determined that the reactivity of lithium sulfate and calcium hydroxide decreases rapidly, so the yield of lithium hydroxide decreases, and the unreacted substances also reduce the purity of lithium hydroxide.

[0102] On the other hand, when calcium hydroxide is used as an additive and the pH of the lithium sulfate aqueous solution is 6 or less, as in Examples 1 to 3 of the present invention, lithium sulfate and calcium hydroxide have excellent reactivity without an additive (such as glycerol), and therefore, a high yield is obtained due to no reduction in purity caused by residual metals or residual additives and no side reactions. In particular, when a lithium sulfate aqueous solution having a pH of 5.5 is used, purity and yield are the most excellent.

Claims

1. A method for producing lithium hydroxide, the method comprising: Obtaining a lithium-containing waste liquid by recovering one or more metal salts selected from manganese, nickel and cobalt from waste lithium secondary batteries; The lithium-containing waste liquid is concentrated by evaporation and then cooled and crystallized to remove sodium sulfate (Na2SO4) to obtain a lithium sulfate aqueous solution; Obtaining lithium hydroxide by reacting the lithium sulfate aqueous solution with calcium hydroxide; and Remove calcium sulfate precipitates, Wherein, the method does not include the step of adding barium hydroxide, wherein the lithium sulfate aqueous solution has a pH of 6 or less, and In the process of obtaining lithium hydroxide, no glycerol is added.

2. The method according to claim 1 further comprises obtaining lithium hydroxide powder by precipitating the obtained lithium hydroxide using a precipitant.

3. The method according to claim 2, wherein: The precipitating agent is an alcohol.

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