Electrodialysis apparatus and method for producing lithium hydroxide

Abstract

The present invention relates to a bipolar electrodialysis device for producing lithium hydroxide, which has a structure in which a positive electrode cell containing a positive electrode, a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, a second bipolar membrane, and a negative electrode cell containing a negative electrode are arranged in this order, and the thickness of the anion-selective dialysis membrane is 70 to 170 μm.

Description

[Technical Field]

[0001] The present invention relates to an electrodialysis apparatus and a method for producing lithium hydroxide, and more specifically to an electrodialysis apparatus using a bipolar membrane and a method for producing lithium hydroxide using the same. [Background technology]

[0002] The global electric vehicle market is predicted to grow from 2.3 million units in 2019 to 21.9 million units in 2030. Battery performance is also continuously improving with higher capacity and longer lifespan. It is predicted that the share of high-nickel batteries, which have high energy density as positive electrode active materials for secondary batteries, will rise to 76% by 2030. Therefore, demand for lithium hydroxide, the lithium raw material for high-nickel positive electrode active materials, is also expected to increase.

[0003] Lithium, the raw material for lithium secondary batteries, has traditionally been extracted from salt lakes in the form of lithium carbonate, which is then reacted with lime to obtain a lithium hydroxide solution and crystallized to produce it. However, the lime process produces limestone as a by-product, and recycling the limestone generates a large amount of carbon dioxide when the kiln is operating, making it an environmentally unfriendly process.

[0004] To solve this problem, research is being conducted into a process for producing lithium hydroxide using electrodialysis with bipolar membranes. Electrodialysis using bipolar membranes is an environmentally friendly process that uses an electric current to separate specific ions and produce acid and alkaline solutions without producing by-products. However, if an inappropriate combination of ion exchange membranes is used in the electrodialysis device, the amount of lithium hydroxide produced is low compared to the electrical energy used, resulting in a significant decrease in energy efficiency. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a bipolar electrodialysis apparatus and a method for producing lithium hydroxide that are excellent in current efficiency for producing lithium hydroxide. [Means for solving the problem]

[0006] One embodiment of the present invention provides a bipolar electrodialysis device for producing lithium hydroxide, which has a structure in which a positive electrode cell including a positive electrode, a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, a second bipolar membrane, and a negative electrode cell including a negative electrode are sequentially arranged, and the anion-selective dialysis membrane has a thickness of 70 to 170 μm.

[0007] The first bipolar membrane and the second bipolar membrane may have a thickness of 140 to 255 μm.

[0008] The cation-selective dialysis membrane may have a thickness of 70 to 170 μm.

[0009] When the bipolar electrodialysis device is driven, the applied voltage may be 2.5 V or less.

[0010] The current efficiency of the bipolar electrodialysis device for producing lithium hydroxide may be 50% or more.

[0011] Another embodiment of the present invention provides a method for producing lithium hydroxide, comprising the steps of: preparing a lithium ion-containing aqueous solution; preparing a bipolar electrodialysis device in which a positive electrode cell including a positive electrode, a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, a second bipolar membrane, and a negative electrode cell including a negative electrode are sequentially arranged, the anion-selective dialysis membrane having a thickness of 70 to 170 μm; and obtaining a lithium hydroxide aqueous solution from the lithium ion-containing aqueous solution using the bipolar electrodialysis device, wherein the obtaining of the lithium hydroxide aqueous solution includes the steps of introducing the lithium ion-containing aqueous solution between the cation-selective dialysis membrane and the anion-selective dialysis membrane, and introducing pure water between the first bipolar membrane and the anion-selective dialysis membrane and between the second bipolar membrane and the cation-selective dialysis membrane; and applying a voltage to the bipolar electrodialysis device to form the lithium hydroxide aqueous solution.

[0012] In the step of preparing the lithium ion-containing aqueous solution, the lithium ion-containing aqueous solution may be a lithium sulfate aqueous solution or a lithium chloride aqueous solution.

[0013] In the step of preparing the bipolar electrodialysis device, the first bipolar membrane and the second bipolar membrane may have a thickness of 140 to 255 μm.

[0014] In the step of preparing the bipolar electrodialysis device, the cation selective dialysis membrane may have a thickness of 70 to 170 μm.

[0015] The step of obtaining the lithium hydroxide aqueous solution may include forming an acidic aqueous solution between the first bipolar membrane and the anion-selective dialysis membrane, forming a lithium hydroxide aqueous solution between the cation-selective dialysis membrane and the second bipolar membrane, and forming a desalted solution between the anion-selective dialysis membrane and the cation-selective dialysis membrane.

[0016] In the step of obtaining the lithium hydroxide aqueous solution, the applied voltage may be 2.5V or less.

[0017] In the step of obtaining the lithium hydroxide aqueous solution, the difference between the maximum and minimum pH values ​​of the solution located in the space between the anion-selective dialysis membrane and the cation-selective dialysis membrane may be adjusted to 2 or less.

[0018] In the step of obtaining the lithium hydroxide aqueous solution, the lithium concentration of the obtained lithium hydroxide aqueous solution may be 10 g / L or more.

[0019] In the step of obtaining the lithium hydroxide aqueous solution, the desalted solution can be reused as the lithium ion-containing aqueous solution to be introduced between the cation selective dialysis membrane and the anion selective dialysis membrane.

[0020] After obtaining the lithium hydroxide aqueous solution, the method may further include concentrating and crystallizing the obtained lithium hydroxide aqueous solution; and drying the crystallized lithium hydroxide to obtain powdered lithium hydroxide.

[0021] After obtaining the lithium hydroxide aqueous solution, the method may further include concentrating lithium in the obtained lithium hydroxide aqueous solution by electrodialysis of the obtained lithium hydroxide aqueous solution.

[0022] The filtrate remaining after the electrodialysis can be concentrated by reverse osmosis and reused for electrodialysis.

[0023] The current efficiency of lithium hydroxide production can be greater than 50%. [Effects of the Invention]

[0024] The bipolar membrane electrodialysis apparatus and method for producing lithium hydroxide according to the present invention can improve the current efficiency for producing lithium hydroxide by appropriately controlling the physical properties of the bipolar membrane, cation-selective dialysis membrane, and anion-selective dialysis membrane used in the electrodialysis apparatus, as well as other process conditions, and can also ensure economic viability by providing a high lithium concentration in the resulting lithium hydroxide aqueous solution. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic diagram of a bipolar electrodialysis device according to one embodiment of the present invention. [Figure 2] 1 is a graph showing salt conductivity as a function of concentration time during operation of the bipolar electrodialysis device according to Example 1. [Figure 3] 1 is a graph showing salt conductivity as a function of concentration time when the bipolar electrodialysis device according to Comparative Example 1 is operated. [Figure 4] 1 is a graph showing salt conductivity as a function of concentration time when the bipolar electrodialysis device is operated according to Comparative Example 2. [Figure 5] 10 is a graph showing salt conductivity and salt pH depending on concentration time when the bipolar electrodialysis device is operated according to Comparative Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0026] Terms such as "first," "second," and "third" are used to describe various portions, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one portion, component, region, layer, or section from another portion, component, region, layer, or section. Therefore, a first portion, component, region, layer, or section described below can be referred to as a second portion, component, region, layer, or section without departing from the scope of the present invention.

[0027] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used in the specification, the term "comprising" refers to the inclusion of certain features, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0028] When a part is referred to as being "on" or "above" another part, it means that it is directly on top of the other part, or that there may be other parts between them. In contrast, when a part is referred to as being "directly on" another part, there are no other parts between them.

[0029] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are to be interpreted in addition to those having meanings consistent with the relevant technical literature and the presently disclosed content, and are not to be interpreted in an ideal or very formal sense unless otherwise defined.

[0030] Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0031] In this specification, the term "combination thereof" used in a Markush expression means a mixture or combination of one or more elements selected from the group of elements described in the Markush expression, and means including any one or more elements selected from the group of elements.

[0032] Although the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily practice the present invention.

[0033] 1. Bipolar electrodialysis equipment One embodiment of the present invention provides a bipolar electrodialysis device for producing lithium hydroxide, which has a structure in which a cathode cell including a cathode, a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, a second bipolar membrane, and an anode cell including a cathode are sequentially arranged, and the anion-selective dialysis membrane has a thickness of 70 to 170 μm.

[0034] FIG. 1 is a schematic diagram of a bipolar electrodialysis device according to one embodiment of the present invention. Referring to FIG. 1, a bipolar electrodialysis device according to one embodiment of the present invention has a structure in which a cathode cell including a cathode, a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, a second bipolar membrane, and an anode cell including a cathode are sequentially arranged.

[0035] Cation-selective dialysis membranes contain anionic groups inside and selectively allow only cations to pass through, while anion-selective dialysis membranes contain cation groups inside and selectively allow only anions to pass through. Bipolar membranes contain a water-splitting catalyst, which hydrolyzes water in an electric field to generate hydrogen ions and hydroxide ions.

[0036] Although not shown in Figure 1, an acidic solution chamber (tank) may be further disposed outside the positive electrode cell, and a basic solution chamber (tank) may be further disposed outside the negative electrode cell. A solution located between the first bipolar membrane and the anion-selective dialysis membrane may circulate through the acidic solution chamber (tank), and a solution located between the cation-selective dialysis membrane and the second bipolar membrane may circulate through the basic solution chamber (tank).

[0037] The operating principle of a bipolar electrodialysis device according to one embodiment of the present invention will now be described.

[0038] First, a lithium ion-containing aqueous solution is introduced between the anion-selective dialysis membrane and the cation-selective dialysis membrane, and pure water is introduced between the first bipolar membrane and the anion-selective dialysis membrane, and between the cation-selective dialysis membrane and the second bipolar membrane.

[0039] At this time, when a voltage is applied to the bipolar electrodialysis device to which the lithium ion-containing aqueous solution and pure water have been introduced, and a current flows, an acidic solution is formed between the first bipolar membrane and the anion-selective dialysis membrane, a lithium hydroxide aqueous solution is formed between the cation-selective dialysis membrane and the second bipolar membrane, and a desalted solution, which is a residual liquid of the introduced lithium-containing aqueous solution in which the lithium salt has not yet reacted, is formed between the anion-selective dialysis membrane and the cation-selective dialysis membrane.

[0040] The formation of the acidic aqueous solution and the lithium hydroxide aqueous solution as described above can be more specifically explained as follows.

[0041] First, the process of forming the acidic aqueous solution will be described. Pure water introduced between the first bipolar membrane and the anion-selective dialysis membrane is hydrolyzed on the surface of the first bipolar membrane to decompose into hydrogen ions and hydroxide ions. The decomposed hydroxide ions move to the positive electrode cell, and the decomposed hydrogen ions move between the first bipolar membrane and the anion-selective dialysis membrane. Meanwhile, anions from the lithium-ion-containing aqueous solution introduced between the anion-selective dialysis membrane and the cation-selective dialysis membrane pass through the anion-selective dialysis membrane and move between the first bipolar membrane and the anion-selective dialysis membrane. The hydrogen ions and anions are then concentrated between the first bipolar membrane and the anion-selective dialysis membrane to form the acidic aqueous solution.

[0042] Next, we will explain the process by which a lithium hydroxide aqueous solution is formed. Pure water introduced between the cation-selective dialysis membrane and the second bipolar membrane is hydrolyzed on the surface of the second bipolar membrane and decomposed into hydrogen ions and hydroxide ions. The decomposed hydrogen ions move to the anode cell, and the decomposed hydroxide ions move between the cation-selective dialysis membrane and the second bipolar membrane. Meanwhile, lithium ions from the lithium ion-containing aqueous solution introduced between the anion-selective dialysis membrane and the cation-selective dialysis membrane pass through the cation-selective dialysis membrane and move between the cation-selective dialysis membrane and the second bipolar membrane. The hydroxide ions and lithium ions are then concentrated between the cation-selective dialysis membrane and the second bipolar membrane to form a lithium hydroxide aqueous solution.

[0043] As described above, to increase the current efficiency when producing a lithium hydroxide solution and an acidic solution from a lithium ion-containing aqueous solution, the rate at which pure water is hydrolyzed on the bipolar membrane surface and the rate at which lithium ions and anions contained in the lithium-containing aqueous solution are separated must be appropriately controlled. If these rates are not appropriately controlled, for example, if the rate at which pure water is hydrolyzed is faster than the rate at which lithium ions and anions contained in the lithium-containing aqueous solution are separated, the hydrolyzed hydrogen ions and hydroxide ions do not encounter their counterions. This results in a phenomenon known as back diffusion, in which hydrogen ions hydrolyzed at the first bipolar membrane permeate the anion-selective dialysis membrane and hydroxide ions hydrolyzed at the second bipolar membrane permeate the cation-selective dialysis membrane. As a result, the electrical energy input to the bipolar electrodialysis device is not fully utilized in the production of lithium hydroxide, resulting in a decrease in current efficiency.

[0044] Therefore, in order to increase the current efficiency of lithium hydroxide production, it is important to maintain an appropriate balance between the hydrolysis rate and the separation rate of lithium ions and anions from the lithium ion-containing aqueous solution by appropriately controlling the physical properties of the anion-selective dialysis membrane, bipolar membrane, and cation-selective dialysis membrane. The inventors of the present invention have conducted repeated research on this matter and have completed the present invention.

[0045] The thickness of the anion-selective dialysis membrane of the bipolar electrodialysis device according to one embodiment of the present invention may be 70 to 170 μm, more specifically 75 to 150 μm or 80 to 120 μm.

[0046] In this specification, the thickness of the dialysis membrane means the thickness measured using a digital micrometer after drying at 100° C. under atmospheric pressure for 6 hours.

[0047] If the thickness of the anion-selective dialysis membrane is too thin, the back diffusion of hydrogen ions hydrolyzed in the first bipolar membrane increases, which may result in a decrease in current efficiency for producing lithium hydroxide.If the thickness of the anion-selective dialysis membrane is too thick, the membrane resistance increases excessively, which may result in a decrease in current efficiency for producing lithium hydroxide.

[0048] The thickness of the first bipolar membrane and the second bipolar membrane may be 140 to 255 μm, more specifically, 180 to 255 μm.

[0049] In this specification, the thickness of the bipolar membrane refers to the thickness measured using a digital micrometer measuring device after drying at 100° C. under atmospheric pressure for 6 hours.

[0050] If the thickness of the first and second bipolar membranes is too thin, the production of H+ and OH-, which have fast ion migration speeds, will be excessive, causing a lot of back diffusion to the salt compartment, which can lead to a decrease in the current efficiency of lithium hydroxide production.If the thickness of the first and second bipolar membranes is too thick, the hydrolysis voltage will be too high, which can lead to a decrease in the current efficiency of lithium hydroxide production.

[0051] The thickness of the cation-selective dialysis membrane may be 70 to 170 μm, more specifically 75 to 150 μm or 80 to 120 μm.

[0052] In this specification, the thickness of the dialysis membrane means the thickness measured using a digital micrometer after drying at 100° C. under atmospheric pressure for 6 hours.

[0053] If the thickness of the cation-selective dialysis membrane is too thin, the pH of the solution between the anion-selective dialysis membrane and the cation-selective dialysis membrane increases rapidly, causing impurity precipitation and reducing the current efficiency for lithium hydroxide production.If the thickness of the cation-selective dialysis membrane is too thick, the membrane resistance increases, causing poor current flow.

[0054] Meanwhile, the applied voltage during operation of the bipolar electrodialysis device may be 2.5 V or less, more specifically, 2.4 V or less. If the applied voltage is too high, membrane degradation may occur due to overheating during operation, resulting in poor current efficiency for lithium hydroxide production.

[0055] By appropriately adjusting the physical properties of the anion-selective dialysis membrane, bipolar membrane, and cation-selective dialysis membrane and the applied voltage, the current efficiency of the bipolar electrodialysis device according to the present invention for producing lithium hydroxide can be as high as 50% or more.

[0056] 2. Lithium hydroxide manufacturing method Another embodiment of the present invention provides a method for producing lithium hydroxide, comprising the steps of: preparing a lithium ion-containing aqueous solution; preparing a bipolar electrodialysis device in which a positive electrode cell including a positive electrode, a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, a second bipolar membrane, and a negative electrode cell including a negative electrode are sequentially arranged, the anion-selective dialysis membrane having a thickness of 70 to 170 μm; and obtaining a lithium hydroxide aqueous solution from the lithium ion-containing aqueous solution using the bipolar electrodialysis device, wherein the obtaining of the lithium hydroxide aqueous solution comprises the steps of introducing the lithium ion-containing aqueous solution between the cation-selective dialysis membrane and the anion-selective dialysis membrane, and introducing pure water between the first bipolar membrane and the anion-selective dialysis membrane and between the second bipolar membrane and the cation-selective dialysis membrane; and applying a voltage to the bipolar electrodialysis device to form the lithium hydroxide aqueous solution.

[0057] Hereinafter, a method for preparing lithium hydroxide according to another embodiment of the present invention will be described in detail step by step. First, an aqueous solution containing lithium ions is prepared. In the step of preparing the lithium ion-containing aqueous solution, the lithium ion-containing aqueous solution may be a lithium sulfate aqueous solution or a lithium chloride aqueous solution.

[0058] The process for obtaining the lithium sulfate aqueous solution or the lithium chloride aqueous solution is not particularly limited.

[0059] The lithium concentration in the lithium sulfate aqueous solution or the lithium chloride aqueous solution may be 5 g / L to 14 g / L. When the lithium concentration satisfies this range, the yield efficiency of lithium hydroxide may be excellent.

[0060] Next, a bipolar electrodialysis device is prepared.

[0061] In this case, the bipolar electrodialysis device includes a cathode cell including a cathode, a first bipolar membrane, an anion selective dialysis membrane, a cation selective dialysis membrane, a second bipolar membrane, and an anode cell including a cathode, which are arranged in sequence.

[0062] In particular, the thickness of the anion-selective dialysis membrane is 70 to 170 μm, more specifically, 75 to 150 μm or 80 to 120 μm. The advantages of adjusting the thickness of the anion-selective dialysis membrane have been described above, and will not be discussed further.

[0063] The thickness of the first bipolar membrane and the second bipolar membrane may be 140 to 255 μm, more specifically, 180 to 255 μm. The advantages of adjusting the thickness of the first bipolar membrane and the second bipolar membrane have been described above, and will not be described here.

[0064] The thickness of the cation-selective dialysis membrane may be 70 to 170 μm, more specifically 75 to 150 μm or 80 to 120 μm. The advantages of adjusting the thickness of the cation-selective dialysis membrane have been described above and will not be discussed further.

[0065] Next, an aqueous solution of lithium hydroxide is obtained from the aqueous solution containing lithium ions using the bipolar electrodialysis device.

[0066] More specifically, the step of obtaining the lithium hydroxide aqueous solution includes the steps of: injecting the lithium ion-containing aqueous solution between the cation-selective dialysis membrane and the anion-selective dialysis membrane; injecting pure water between the first bipolar membrane and the anion-selective dialysis membrane and between the second bipolar membrane and the cation-selective dialysis membrane; and applying a voltage to the bipolar electrodialysis device to form the lithium hydroxide aqueous solution.

[0067] In this case, the step of obtaining the lithium hydroxide aqueous solution may include forming an acidic aqueous solution between the first bipolar membrane and the anion selective dialysis membrane, forming a lithium hydroxide aqueous solution between the cation selective dialysis membrane and the second bipolar membrane, and forming a desalted solution between the anion selective dialysis membrane and the cation selective dialysis membrane. The principles of these processes are as described above and therefore will not be repeated.

[0068] In particular, the applied voltage may be equal to or less than 2.5 V, more specifically, equal to or less than 2.4 V. The advantages of adjusting the applied voltage have been described above, and will not be described further.

[0069] The difference between the maximum and minimum pH values ​​of the solution located in the space between the anion-selective dialysis membrane and the cation-selective dialysis membrane is adjusted to 2 or less, more specifically, 1.5 or less. The range of pH fluctuation of the solution located in the space between the anion-selective dialysis membrane and the cation-selective dialysis membrane can be used as a measure of the degree of back diffusion, as described above. Therefore, by adjusting the difference between the maximum and minimum pH values ​​within this range, the occurrence of back diffusion is minimized, and lithium hydroxide production current efficiency can be excellent.

[0070] Meanwhile, the desalted solution can be reused as the input solution between the cation-selective dialysis membrane and the anion-selective dialysis membrane, thereby improving the economy during operation of the process and reducing lithium loss.

[0071] Optionally, after obtaining the lithium hydroxide aqueous solution, the method may further include concentrating and crystallizing the obtained lithium hydroxide aqueous solution, and drying the crystallized lithium hydroxide to obtain powdered lithium hydroxide, thereby recovering the lithium hydroxide in powder form.

[0072] If necessary, the method may further include, after the step of obtaining the lithium hydroxide aqueous solution, a step of concentrating lithium in the obtained lithium hydroxide aqueous solution by electrodialysis of the obtained lithium hydroxide aqueous solution.

[0073] At this time, the filtrate remaining after the electrodialysis can be concentrated by reverse osmosis and reused for electrodialysis.

[0074] The method for producing lithium hydroxide according to another embodiment of the present invention may have a lithium hydroxide production current efficiency of 50% or more.

[0075] The lithium concentration of the obtained lithium hydroxide aqueous solution may be 10 g / L or more, more specifically, 15 or 20 g / L or more. Generally, the lower the target lithium concentration of the obtained lithium hydroxide aqueous solution, the higher the current efficiency for lithium hydroxide production. However, if the lithium concentration of the obtained lithium hydroxide aqueous solution is reduced too much in order to increase the current efficiency for lithium hydroxide production, a problem arises in that the amount of water required for drying to crystallize lithium hydroxide in a subsequent step increases.

[0076] According to the method for producing lithium hydroxide according to another embodiment of the present invention, not only is the lithium concentration of the resulting lithium hydroxide aqueous solution sufficiently high at 10 g / L or more, but there is also the advantage that the current efficiency for producing lithium hydroxide can also be increased by controlling the electrodialysis process conditions as described above.

[0077] Hereinafter, the present invention will be described in more detail with reference to examples, but the following examples are merely preferred examples of the present invention and are not intended to limit the scope of the present invention. [Example]

[0078] Example 1 (1) Preparation of bipolar electrodialysis device A bipolar electrodialysis device was prepared using a 250 μm thick first bipolar membrane, a 100 μm thick anion-selective dialysis membrane, a 100 μm thick cation-selective dialysis membrane, and a 250 μm thick second bipolar membrane (BPU).

[0079] (2) Bipolar electrodialysis device drive First, a lithium sulfate aqueous solution and pure water were prepared. At this time, the lithium concentration in the lithium sulfate aqueous solution was 10.5 g / L. Thereafter, an aqueous lithium sulfate solution was introduced between the cation-selective dialysis membrane and the anion-selective dialysis membrane of the prepared bipolar electrodialysis device, and pure water was introduced between the first bipolar membrane and the anion-selective dialysis membrane and between the second bipolar membrane and the cation-selective dialysis membrane of the prepared bipolar electrodialysis device. Thereafter, a voltage of 2.3 V was applied to the bipolar electrodialysis device to drive the bipolar electrodialysis device, thereby obtaining an aqueous solution of lithium hydroxide.

[0080] Comparative Example 1: Anion-selective dialysis membrane thickness 60 μm A bipolar electrodialysis device was prepared and operated in the same manner as in Example 1, except that the thickness of the anion-selective dialysis membrane was 60 μm.

[0081] Comparative Example 2: Anion-selective dialysis membrane thickness 180 μm A bipolar electrodialysis device was prepared and operated in the same manner as in Example 1, except that the thickness of the anion-selective dialysis membrane was 180 μm.

[0082] Comparative Example 3: Thickness of the first bipolar membrane and the second bipolar membrane: 130 μm A bipolar electrodialysis device was prepared and operated in the same manner as in Example 1, except that the thickness of the first bipolar membrane and the second bipolar membrane was 130 μm.

[0083] Comparative Example 4: Thickness of the first bipolar membrane and the second bipolar membrane: 260 μm A bipolar electrodialysis device was prepared and operated in the same manner as in Example 1, except that the thickness of the first bipolar membrane and the second bipolar membrane was 260 μm.

[0084] Comparative Example 5: Cation-selective dialysis membrane thickness 60 μm A bipolar electrodialysis device was prepared and operated in the same manner as in Example 1, except that the thickness of the cation-selective dialysis membrane was 60 μm.

[0085] Comparative Example 6: Cation-selective dialysis membrane thickness 180 μm A bipolar electrodialysis device was prepared and operated in the same manner as in Example 1, except that the thickness of the anion-selective dialysis membrane was 180 μm.

[0086] Comparative Example 7: Applied voltage 3.0V The bipolar electrodialysis device was prepared and operated in the same manner as in Example 1, except that a voltage of 3.0 V was applied when the bipolar electrodialysis device was operated.

[0087] Table 1 below summarizes the physical properties and applied voltages of the bipolar electrodialysis devices of Example 1 and Comparative Examples 1 to 7.

[0088] [Table 1]

[0089] Experimental Example 1: Salt Conductivity or pH Evaluation The salt conductivity or salt pH was measured as a function of the concentration time during operation of the bipolar electrodialysis devices according to Example 1, Comparative Examples 1 and 2, and Comparative Example 5, and the results are shown in Figures 2 to 5. Here, the salt conductivity or salt pH refers to the conductivity or pH of the solution located in the interstitial space between the anion-selective dialysis membrane and the cation-selective dialysis membrane.

[0090] Referring to FIG. 2, it was confirmed that the bipolar electrodialysis device according to Example 1 was able to reduce the salt conductivity to a good level and perform good ion separation by appropriately adjusting the thickness of the anion-selective dialysis membrane, the thickness of the first and second bipolar membranes, the thickness of the cation-selective dialysis membrane, and the applied voltage. As a result, it was predicted that the current efficiency for producing lithium hydroxide would be very good.

[0091] 3, it was confirmed that the bipolar electrodialysis device according to Comparative Example 1 had an excessively thin anion-selective dialysis membrane, which caused back diffusion of hydrogen ions through the anion-selective dialysis membrane into the space between the anion-selective dialysis membrane and the cation-selective dialysis membrane, resulting in a steady increase in salt conductivity rather than a decrease in it, which was expected to result in a decrease in the current efficiency for lithium hydroxide production.

[0092] 4, it was confirmed that the bipolar electrodialysis device according to Comparative Example 2 had an excessively thick anion-selective dialysis membrane, which increased the membrane resistance, causing a rapid drop in current and a decrease in salt conductivity, but the rate of decrease was very slow, which predicted a decrease in the current efficiency for lithium hydroxide production.

[0093] 5, it was confirmed that the thickness of the cation-selective dialysis membrane in the bipolar electrodialysis device according to Comparative Example 5 was too thin, causing the pH of the salt to increase rapidly in the latter half of the operation time, resulting in the deposition of impurities. This was expected to result in a decrease in the current efficiency for lithium hydroxide production.

[0094] Experimental example 2: Evaluation of the difference between the maximum and minimum salt pH values When the bipolar electrodialysis device was operated using Example 1 and Comparative Examples 1 to 7, the difference between the maximum and minimum pH values ​​of the solution located in the space between the anion-selective dialysis membrane and the cation-selective dialysis membrane was evaluated, and the results are shown in Table 2 below.

[0095] [Table 2]

[0096] Referring to Table 2, it was confirmed that the bipolar electrodialysis device according to Example 1 had little change in pH value during operation, with a small difference between the maximum and minimum values ​​of 1.0, whereas the bipolar electrodialysis devices according to Comparative Examples 1, 3, and 5 had large change in pH value during operation, with a difference between the maximum and minimum values ​​of greater than 2. Furthermore, it was confirmed that the difference between the maximum and minimum values ​​was satisfactory in Comparative Example 7, but that overheating during operation caused degradation of the polymer membrane. On the other hand, it was confirmed that the bipolar electrodialysis devices according to Comparative Examples 2, 4, and 6 did not operate.

[0097] Experimental Example 3: Evaluation of current efficiency for lithium hydroxide production The lithium hydroxide production current efficiency of the bipolar electrodialysis devices operated in Example 1 and Comparative Examples 1 to 7 was measured, and the results are shown in Table 3. More specifically, the lithium hydroxide production current efficiency was calculated by the following method.

[0098] [Formula 1] Lithium hydroxide production current efficiency = [Li production amount (mol) × Faraday constant (C / mol)] / [current density (A / m 2 ) x membrane area (m 2 ) × time (S)]

[0099] [Table 3]

[0100] Referring to Table 3, it was confirmed that the current efficiency of lithium hydroxide production of the bipolar electrodialysis device according to Example 1 was excellent at over 50%, while the current efficiency of lithium hydroxide production of the bipolar electrodialysis devices according to Comparative Examples 1, 3, 5, and 7 was inferior at less than 50%. On the other hand, it was confirmed that the bipolar electrodialysis devices according to Comparative Examples 2, 4, and 6 did not work.

[0101] Experimental Example 4: Evaluation of the lithium concentration of the obtained lithium hydroxide aqueous solution The lithium concentrations of the lithium hydroxide aqueous solutions obtained in Example 1 and Comparative Examples 1 to 7 were measured, and the results are shown in Table 4 below.

[0102] [Table 4]

[0103] Referring to Table 4, it was confirmed that the lithium concentration of the lithium hydroxide aqueous solution obtained in Example 1 was 20 g / L, which was sufficiently high.

[0104] Therefore, it was confirmed that the method for producing lithium hydroxide according to the present invention not only improves the current efficiency of lithium hydroxide production to 50% or more, but also increases the lithium concentration of the obtained lithium hydroxide aqueous solution.

[0105] It was confirmed that the lithium concentration of the lithium hydroxide aqueous solution obtained in Example 1 was high at 10 g / L or more, while the lithium concentrations of the lithium hydroxide aqueous solutions obtained in Comparative Examples 1 to 7 were low at 10 g / L or less.

[0106] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this and can be embodied in various modifications within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is to be understood that these modifications also fall within the scope of the present invention.

[0107] Therefore, the true scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. 1. A bipolar electrodialysis apparatus for the production of lithium hydroxide, comprising: The battery has a structure in which a positive electrode cell including a positive electrode, a first bipolar membrane, an anion selective dialysis membrane, a cation selective dialysis membrane, a second bipolar membrane, and a negative electrode cell including a negative electrode are sequentially arranged, A bipolar electrodialysis device, wherein the thickness of the anion selective dialysis membrane is 70 to 170 μm.

2. 2. The bipolar electrodialysis apparatus according to claim 1, wherein the first bipolar membrane and the second bipolar membrane have a thickness of 140 to 255 μm.

3. 2. The bipolar electrodialysis device according to claim 1, wherein the thickness of the cation-selective dialysis membrane is 70 to 170 μm.

4. 2. The bipolar electrodialysis device according to claim 1, wherein the applied voltage during operation of the bipolar electrodialysis device is 2.5 V or less.

5. 2. The bipolar electrodialysis apparatus according to claim 1, wherein the lithium hydroxide production current efficiency of the bipolar electrodialysis apparatus is 50% or more.

6. providing an aqueous solution containing lithium ions; preparing a bipolar electrodialysis device in which a positive electrode cell including a positive electrode, a first bipolar membrane, an anion selective dialysis membrane, a cation selective dialysis membrane, a second bipolar membrane, and a negative electrode cell including a negative electrode are sequentially arranged, and the thickness of the anion selective dialysis membrane is 70 to 170 μm; and A method for producing lithium hydroxide, comprising the step of obtaining an aqueous lithium hydroxide solution from the aqueous lithium ion-containing solution using the bipolar electrodialysis apparatus, The step of obtaining the lithium hydroxide aqueous solution introducing the lithium ion-containing aqueous solution between the cation-selective dialysis membrane and the anion-selective dialysis membrane, and introducing pure water between the first bipolar membrane and the anion-selective dialysis membrane and between the second bipolar membrane and the cation-selective dialysis membrane; and applying a voltage to the bipolar electrodialysis device to form an aqueous solution of lithium hydroxide.

7. preparing the lithium ion-containing aqueous solution; 7. The method for producing lithium hydroxide according to claim 6, wherein the lithium ion-containing aqueous solution is a lithium sulfate aqueous solution or a lithium chloride aqueous solution.

8. providing the bipolar electrodialysis device; 7. The method for producing lithium hydroxide according to claim 6, wherein the first bipolar membrane and the second bipolar membrane have a thickness of 140 to 255 μm.

9. providing the bipolar electrodialysis device; The method for producing lithium hydroxide according to claim 6, wherein the thickness of the cation-selective dialysis membrane is 70 to 170 μm.

10. The step of obtaining the lithium hydroxide aqueous solution comprises:

7. The method for producing lithium hydroxide according to claim 6, wherein an acidic aqueous solution is formed between the first bipolar membrane and the anion-selective dialysis membrane, a lithium hydroxide aqueous solution is formed between the cation-selective dialysis membrane and the second bipolar membrane, and a desalted solution is formed between the anion-selective dialysis membrane and the cation-selective dialysis membrane.

11. In the step of obtaining the lithium hydroxide aqueous solution, 7. The method for producing lithium hydroxide according to claim 6, wherein the applied voltage is 2.5 V or less.

12. In the step of obtaining the lithium hydroxide aqueous solution, 7. The method for producing lithium hydroxide according to claim 6, wherein the difference between the maximum and minimum pH values ​​of the solution located in the space between the anion-selective dialysis membrane and the cation-selective dialysis membrane is adjusted to 2 or less.

13. In the step of obtaining the lithium hydroxide aqueous solution, 7. The method for producing lithium hydroxide according to claim 6, wherein the lithium concentration of the obtained aqueous lithium hydroxide solution is 10 g / L or more.

14. In the step of obtaining the lithium hydroxide aqueous solution, 7. The method for producing lithium hydroxide according to claim 6, wherein the desalted solution is reused as an input solution to be input between the cation selective dialysis membrane and the anion selective dialysis membrane.

15. After obtaining the lithium hydroxide aqueous solution, concentrating and crystallizing the obtained lithium hydroxide aqueous solution; and 7. The method for producing lithium hydroxide according to claim 6, further comprising drying the crystallized lithium hydroxide to obtain lithium hydroxide in powder form.

16. After obtaining the lithium hydroxide aqueous solution, 7. The method for producing lithium hydroxide according to claim 6, further comprising the step of electrodialyzing the obtained lithium hydroxide aqueous solution to concentrate lithium in the obtained lithium hydroxide aqueous solution.

17. The method for producing lithium hydroxide according to claim 16, wherein the filtrate remaining after the electrodialysis is concentrated by reverse osmosis and reused for electrodialysis.

18. 7. The method for producing lithium hydroxide according to claim 6, wherein the current efficiency for producing lithium hydroxide is 50% or more.

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