Lithium iodide non-aqueous solution, lithium iodide, non-aqueous solvate of lithium iodide, method for producing non-aqueous lithium iodide solution, method for producing lithium iodide, and method for producing non-aqueous solvate of lithium iodide

Abstract

Provided is a lithium iodide nonaqueous solution containing a nonaqueous solvent and lithium iodide. This lithium iodide nonaqueous solution is characterized in that the water content per lithium iodide unit (Y / X), determined by the water content Y (ppm) in the lithium iodide nonaqueous solution relative to the lithium iodide concentration X (wt.%) in the lithium iodide nonaqueous solution, is 7 or less, and the content of an acid-derived component is 4,000 ppm or less.

Description

[Technical Field]

[0001] The present disclosure relates to a non-aqueous lithium iodide solution, lithium iodide, a non-aqueous solvate of lithium iodide, a method for producing a non-aqueous lithium iodide solution, a method for producing lithium iodide, and a method for producing a non-aqueous solvate of lithium iodide. [Background technology]

[0002] Lithium iodide is used in absorption fluids for absorption refrigerators, co-catalysts for acetic acid production, and electrolytes for batteries.

[0003] As a method for producing an aqueous lithium iodide solution and its hydrate, Non-Patent Document 1 discloses a method of reacting lithium carbonate with hydroiodic acid, and Non-Patent Document 2 discloses a method of blowing hydrogen iodide gas into a slurry in which water is dispersed in lithium carbonate.

[0004] Lithium iodide has high water absorption, and when used as a battery electrolyte, it is preferable that the water content be low. As a method for producing a non-aqueous lithium iodide solution with a low water content, the examples of Patent Document 1 show a method of dehydrating an alcohol solution of an alkali metal iodide or an alcohol solution of an alkaline earth metal iodide using a desiccant such as a molecular sieve or a water separation membrane. Furthermore, the reference examples of Patent Document 1 state that the water content can be reduced by carrying out a dehydration step using methyl orthoformate and formic acid.

[0005] Anhydrous lithium iodide can be obtained by dehydrating a hydrate obtained from an aqueous lithium iodide solution by heating, etc. Patent Document 2 discloses a production method for obtaining anhydrous lithium iodide at low temperature in a short time by mixing the hydrated lithium iodide with a solvent prepared by mixing 1-butanol with water and azeotroping the water in the hydrated lithium iodide with the 1-butanol component. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-157743 [Patent Document 2] Patent No. 6006994 [Non-patent literature]

[0007] [Non-Patent Document 1] "Chemical Dictionary 9, Condensed Edition", Published by Kyoritsu Shuppan, 1993, 426 pages [Non-patent document 2] "New Experimental Chemistry Lectures 8: Synthesis of Inorganic Compounds (II)", published by Maruzen in 1977, 462 pages Summary of the Invention [Problem to be solved by the invention]

[0008] The present inventors have found that lithium iodide has strong water absorption properties and is strongly bound to water, and therefore lithium iodide non-aqueous solutions and lithium iodide obtained by conventional production methods contain a certain amount of water, and there is a limit to how much water can be reduced. That is, the present inventors have found that, according to the methods described in the Examples of Patent Document 1 and Patent Document 2, the water content of the resulting lithium iodide non-aqueous solutions is about 2900 ppm, and the water content of the resulting solid lithium iodide is about 3200 ppm.

[0009] Furthermore, the method described in the Reference Example of Patent Document 1 was able to further reduce the water content of the lithium iodide non-aqueous solution. However, this method leaves formic acid remaining in the non-aqueous solution. Residual acid in the non-aqueous solution is undesirable for a lithium iodide non-aqueous solution used in batteries. Therefore, it has been desired to reduce the water content of the lithium iodide non-aqueous solution by a method that does not leave any residual acid.

[0010] Furthermore, the method described in Patent Document 1 discloses that a lithium iodide-alcohol complex (lithium iodide alcoholate) can be obtained. Here, when considering the use of lithium iodide salt as a battery electrolyte, there are a wide variety of combinations of battery configurations (i.e., positive electrode, negative electrode, electrolyte, etc.), and therefore, it is preferable to be able to select an appropriate solvate as the lithium iodide solvate from the viewpoint of compatibility and solubility with each component constituting the battery. From this viewpoint, the present inventors have discovered that, in addition to the lithium iodide alcoholate described in Patent Document 1, it is also desirable to obtain a non-aqueous lithium iodide solvate using an appropriate non-aqueous solvent other than alcohol.

[0011] Therefore, an object of the present disclosure is to provide a non-aqueous lithium iodide solution having a low water content and a low acid content, lithium iodide having a low water content and a low acid content, and a method for producing them.Another object of the present disclosure is to provide a non-aqueous solvate of lithium iodide comprising lithium iodide and a non-aqueous solvent other than alcohol, and a method for producing the same. [Means for solving the problem]

[0012] In view of the above problems, the present inventors have conducted extensive research and found that a non-aqueous lithium iodide solution and a lithium iodide solution having a low water content can be obtained without using an acid by reacting metallic lithium with iodine in a non-aqueous solvent. They also found that a non-aqueous solvate of lithium iodide composed of lithium iodide and a non-aqueous solvent other than alcohol can be obtained. These findings led to the present disclosure.

[0013] That is, the lithium iodide non-aqueous solution according to the present disclosure is a lithium iodide non-aqueous solution containing a non-aqueous solvent and lithium iodide, characterized in that the water content per lithium iodide unit (Y / X), determined by the water content Y (ppm) in the lithium iodide non-aqueous solution relative to the lithium iodide concentration X (wt %) in the lithium iodide non-aqueous solution, is 7 or less, and the content of acid-derived components is 4000 ppm or less.

[0014] The lithium iodide according to the present disclosure is characterized by having a water content of less than 500 ppm and a content of acid-derived components of 12,000 ppm or less.

[0015] The non-aqueous solvate of lithium iodide according to the present disclosure is characterized by comprising a non-aqueous solvent other than an alcohol and lithium iodide.

[0016] The method for producing a lithium iodide non-aqueous solution according to the present disclosure is characterized in that lithium iodide is generated in a non-aqueous solvent by reacting metallic lithium with iodine in the non-aqueous solvent, thereby obtaining a lithium iodide non-aqueous solution. In the present disclosure, the water content of the non-aqueous solvent used in the reaction is usually less than 10 ppm, preferably less than 1 ppm. Furthermore, it is preferable that the non-aqueous solvent used in the reaction is substantially free of acid-derived components.

[0017] The method for producing lithium iodide according to the present disclosure is characterized in that a drying step is carried out to dry the lithium iodide non-aqueous solution obtained by the method according to the present disclosure, thereby obtaining lithium iodide having a water content of less than 500 ppm and a content of acid-derived components of 12,000 ppm or less.

[0018] The method for producing a non-aqueous solvate of lithium iodide according to the present disclosure is characterized in that a drying step is carried out to dry the non-aqueous lithium iodide solution obtained by the method of the present disclosure, thereby obtaining a non-aqueous solvate of lithium iodide comprising a non-aqueous solvent and lithium iodide. [Effects of the Invention]

[0019] The present disclosure can provide a non-aqueous lithium iodide solution having a low water content and a low acid content, lithium iodide having a low water content and a low acid content, and methods for producing the same. Furthermore, it is possible to provide a non-aqueous solvate of lithium iodide comprising lithium iodide and a non-aqueous solvent other than alcohol, and a method for producing the same. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is an XRD chart of lithium iodide according to Example 3. [Figure 2] FIG. 2 is an XRD chart of lithium iodide according to Comparative Example 1. [Figure 3] Figure 3 is an XRD chart of commercially available lithium iodide. [Figure 4] FIG. 4 is a 1H NMR chart of lithium iodide according to Example 3. [Figure 5] FIG. 5 is a chart of anion chromatography of the non-aqueous lithium iodide solution according to Example 1. [Figure 6] FIG. 6 is a chart of blank anion chromatography measured under the same conditions as FIG. 5, but with only water introduced. [Figure 7] FIG. 7 is a chart of cation chromatography of the lithium iodide non-aqueous solution according to Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present disclosure will be described in detail below, but the following description of the constituent elements is an example of an embodiment of the present disclosure, and the present disclosure is not limited to these specific details. Various modifications can be made within the scope of the gist of the present disclosure.

[0022] According to the method for producing a lithium iodide non-aqueous solution of the present disclosure, it is possible to obtain a lithium iodide non-aqueous solution having a low water content and a low acid content. First, the method for producing a non-aqueous lithium iodide solution according to the present disclosure will be described. The method for producing a lithium iodide non-aqueous solution according to the present disclosure is characterized in that lithium iodide is produced in a non-aqueous solvent by reacting metallic lithium with iodine in the non-aqueous solvent, thereby obtaining a lithium iodide non-aqueous solution having a low water content. Furthermore, a non-aqueous lithium iodide solution with a low water content can be obtained without using an acid.

[0023] In the method for producing a lithium iodide non-aqueous solution of the present disclosure, lithium iodide is generated in a non-aqueous solvent by reacting metallic lithium with iodine in the non-aqueous solvent, and as a result, a lithium iodide non-aqueous solution is obtained that uses the non-aqueous solvent as a solvent and contains lithium iodide as a solute.

[0024] The resulting lithium iodide non-aqueous solution preferably has a water content per lithium iodide unit (Y / X), determined by the water content Y (ppm) in the lithium iodide non-aqueous solution relative to the lithium iodide concentration X (wt%) in the lithium iodide non-aqueous solution, of 7 or less, and a content of acid-derived components of 4000 ppm or less. The water content per lithium iodide unit (Y / X) is preferably 5 or less, and more preferably 3 or less. The amount of acid-derived components contained in the resulting lithium iodide non-aqueous solution is preferably as small as possible, and preferably substantially zero. The amount of acid-derived components contained in the lithium iodide non-aqueous solution may preferably be 1000 ppm or less, 250 ppm or less, 50 ppm or less, 20 ppm or less, or 10 ppm or less.

[0025] The reaction of metallic lithium with iodine in a non-aqueous solvent does not require the use of a catalyst. Therefore, a step of removing the catalyst is not necessary. Furthermore, no particularly high temperature is required. The reaction temperature is preferably less than 80°C, more preferably 20 to 50°C, and even more preferably 20 to 45°C. Furthermore, the temperature rise due to the heat of reaction is suppressed, and the reaction temperature is preferably less than 80°C, more preferably 20 to 50°C, and even more preferably 20 to 45°C.

[0026] The amount of metallic lithium used is preferably 2.1 to 20.0 mol, more preferably 2.1 to 5.0 mol, per mol of iodine. When the molar ratio of metallic lithium to iodine is within the above range, the reaction between metallic lithium and iodine proceeds without excess or deficiency, thereby increasing the yield of lithium iodide. Furthermore, when an excess of lithium is added, the lithium can be recovered as a filter cake after the reaction and reused in a reaction of another lot. The form of the metallic lithium to be introduced into the non-aqueous solvent is not particularly limited, and it may be in the form of a lithium rod or lithium foil.

[0027] When the reaction temperature is as high as 80°C or higher, water is present in the system, and the amount of metallic lithium used is not excessive relative to the amount of iodine, hydrogen iodide and lithium hydroxide are generated by the reaction between lithium iodide and water, and hydrogen iodide as an acid is sometimes contained in the non-aqueous lithium iodide solution. Therefore, it is preferable to avoid conditions that could generate hydrogen iodide as described above.

[0028] The non-aqueous solvent preferably contains at least one solvent selected from the group consisting of ether-based solvents, acetal-based solvents, ester-based solvents, nitrile-based solvents, carbonate-based solvents, ketone-based solvents, amide-based solvents, and sulfur-containing solvents. The non-aqueous solvent is preferably an aprotic solvent. It is more preferable that the non-aqueous solvent contains at least one solvent selected from the group consisting of ether-based solvents, acetal-based solvents, ester-based solvents, and amide-based solvents.

[0029] Specific examples of non-aqueous solvents include ether solvents such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, diethyl ether, 1,2-dimethoxyethane (hereinafter also referred to as DME), diglyme, triglyme, tetraglyme, propylene glycol dimethyl ether, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, 3-methoxypropionitrile, methoxyacetonitrile, and ethylene glycol bis(propionitrile) ether. Examples of acetal solvents include 1,3-dioxane, 1,3-dioxolane (hereinafter also referred to as DOL), 4-methyldioxolane, 1,3,5-trioxane, dimethoxymethane, and 1,2-methylenedioxybenzene. Examples of the ester solvent include γ-butyrolactone, ε-caprolactone, γ-valerolactone, methyl formate, methyl acetate, ethyl acetate, isopropyl acetate, methyl propionate, and propylene glycol monomethyl ether acetate. Examples of carbonate solvents include ethylene carbonate and ethyl methyl carbonate. An example of the ketone solvent is acetone. Examples of the amide solvent include dimethylformamide, dimethylacetamide, and N-methyl-2-pyrrolidone.

[0030] It is preferable that the non-aqueous solvent does not contain an alcohol-based solvent. Alcohol-based solvents react with metallic lithium to generate hydrogen. Since the generation of hydrogen is undesirable from the viewpoint of safety in the working environment, it is preferable that hydrogen is not generated. Therefore, it is preferable to use a non-aqueous solvent that does not contain an alcohol-based solvent. The non-aqueous solvent does not contain an alcohol solvent. 1 This means that the amount of alcohol detected is less than 10 ppm as measured by 1 H NMR.

[0031] In the method for producing a lithium iodide non-aqueous solution of the present disclosure, water is not used during production, and therefore the water content of the produced lithium iodide non-aqueous solution can be made extremely small. The reference example of Patent Document 1 discloses conditions for producing a lithium iodide solution that achieves a water content of 0.00 wt%, but it is impossible to remove impurities derived from the acid catalyst used in the drying process. It is preferable that the content of components derived from the acid catalyst in a non-aqueous lithium iodide solution used for batteries be 50 ppm or less, and it is also preferable that the solution be substantially free of components derived from the acid catalyst. It is known that the presence of acid in the electrolyte of a battery is undesirable (for example, Japanese Patent No. 5679719, Japanese Patent Laid-Open No. 2001-307772, etc.). The method for producing a lithium iodide non-aqueous solution according to the present disclosure, unlike the method disclosed in the Reference Example of Patent Document 1, does not use an acid during production, and therefore the content of components derived from the acid catalyst contained in the produced lithium iodide non-aqueous solution can be reduced to 4000 ppm or less. Furthermore, it is possible to produce a lithium iodide non-aqueous solution that is substantially free of components derived from the acid catalyst. The method for producing a lithium iodide non-aqueous solution according to the present disclosure differs from conventional methods in that it is a reaction that does not use water and does not use an acid, making it possible to produce a lithium iodide non-aqueous solution with a significantly lower water content and fewer acid-derived components than those produced by conventional techniques.

[0032] Next, the lithium iodide non-aqueous solution of the present disclosure will be described. The lithium iodide non-aqueous solution according to the present disclosure contains a non-aqueous solvent and lithium iodide, and is characterized in that the water content per unit lithium iodide (Y / X), determined by the water content Y (ppm) in the lithium iodide non-aqueous solution relative to the lithium iodide concentration X (wt %) in the lithium iodide non-aqueous solution, is 7 or less, and the content of acid-derived components is 4000 ppm or less.

[0033] The lithium iodide non-aqueous solution of the present disclosure has a water content per lithium iodide unit (Y / X) of 7 or less and an acid-derived component content of 4000 ppm or less. In other words, it is a lithium iodide non-aqueous solution with low water content and low acid-derived component content. As can be seen from Examples 1 and 2 described below, the water content Y in a solution is proportional to the lithium iodide concentration X in the solution, and therefore it is appropriate to determine the water content of a solution using the water content relative to the lithium iodide concentration in the solution as an index. Therefore, a non-aqueous solution having a water content per unit of lithium iodide (Y / X) of 7 or less can be said to be a lithium iodide non-aqueous solution with a low water content.

[0034] The lithium iodide non-aqueous solution of the present disclosure has a low water content per lithium iodide unit (Y / X) of 7 or less and a low content of acid-derived components of 4000 ppm or less, making it suitable for use in batteries.

[0035] In the lithium iodide non-aqueous solution according to the present disclosure, the water content per lithium iodide unit (Y / X) is preferably not more than 5, and more preferably not more than 3. The content of acid-derived components may preferably be not more than 1000 ppm, not more than 250 ppm, not more than 50 ppm, not more than 20 ppm, or not more than 10 ppm.

[0036] When the non-aqueous solvent contained in the lithium iodide non-aqueous solution is a non-aqueous solvent used for a battery electrolyte, the lithium iodide non-aqueous solution obtained by dissolving lithium iodide in a non-aqueous solvent can be used as the battery electrolyte without any special purification procedure. Alternatively, other necessary components may be added to the solution before use as the battery electrolyte. For example, other electrolytes such as LiPF6, LiBF4, LiClO4, and LiFSI (lithium bis(fluorosulfonyl)imide) may be contained. Furthermore, the non-aqueous lithium iodide solution can be used as a raw material for obtaining solid lithium iodide, since it can be converted into solid lithium iodide by removing the solvent.

[0037] The lithium iodide concentration X in the lithium iodide non-aqueous solution is preferably 5 to 70% by weight, more preferably 10 to 50% by weight. Furthermore, it is preferable that the water content Y in the lithium iodide non-aqueous solution is less than 200 ppm. Furthermore, it is preferable that the lithium iodide non-aqueous solution is substantially free of water. "Substantially free of water" in the lithium iodide non-aqueous solution means that the water content is below the detection limit (0.1 ppm or less) in the water content measurement method described below.

[0038] It is most preferable that the non-aqueous lithium iodide solution contains substantially no acid-derived components. The lithium iodide non-aqueous solution being substantially free of acid-derived components means that no acid-derived components are detected (below the detection limit) in the method for measuring the content of acid-derived components described below.

[0039] The concentration of lithium iodide in a non-aqueous lithium iodide solution can be measured by the following procedure using anion chromatography. A non-aqueous solution of lithium iodide is precisely weighed and diluted with ultrapure water to approximately 10 ppm, and the iodide ion concentration is measured by anion chromatography. The iodide ion concentration is then converted to the lithium iodide concentration.

[0040] The water content of a lithium iodide non-aqueous solution can be measured using a coulometric Karl Fischer moisture meter. To measure the water content of a lithium iodide non-aqueous solution, approximately 1 g of the solution can be precisely weighed and analyzed directly. In this specification, the water content in the non-aqueous lithium iodide solution means the water content (ppm) measured for about 1 g of a sample of the non-aqueous lithium iodide solution using a coulometric Karl Fischer moisture meter.

[0041] The content of acid-derived components in a non-aqueous lithium iodide solution is measured by 1The content of acid-derived components as organic acids can be measured by quantifying side chain hydrogens using H NMR, and the content of acid-derived components as inorganic acids can be measured by measuring the concentration of anions other than iodide ions using anion chromatography. In this specification, the content of the acid-derived component in the lithium iodide non-aqueous solution means 1 It means the content (ppm) of acid-derived components measured as organic acids by quantifying side chain hydrogen using H NMR. 1 When no side chain hydrogen is detected (10 ppm or less) in the quantitative determination of side chain hydrogen using H NMR, and when no anions other than iodide ions are detected (100 ppm or less) using anion chromatography, it can be said that the lithium iodide non-aqueous solution does not substantially contain acid-derived components.

[0042] The non-aqueous solvent contained in the lithium iodide non-aqueous solution preferably contains at least one solvent selected from the group consisting of ether-based solvents, acetal-based solvents, ester-based solvents, nitrile-based solvents, carbonate-based solvents, ketone-based solvents, amide-based solvents, and sulfur-containing solvents. The non-aqueous solvent is preferably an aprotic solvent. It is more preferable that the non-aqueous solvent contains at least one solvent selected from the group consisting of ether-based solvents, acetal-based solvents, ester-based solvents, and amide-based solvents.

[0043] Specific examples of non-aqueous solvents include ether solvents such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, diethyl ether, 1,2-dimethoxyethane (hereinafter also referred to as DME), diglyme, triglyme, tetraglyme, propylene glycol dimethyl ether, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, 3-methoxypropionitrile, methoxyacetonitrile, and ethylene glycol bis(propionitrile) ether. Examples of acetal solvents include 1,3-dioxane, 1,3-dioxolane (hereinafter also referred to as DOL), 4-methyldioxolane, 1,3,5-trioxane, dimethoxymethane, and 1,2-methylenedioxybenzene. Examples of the ester solvent include γ-butyrolactone, ε-caprolactone, γ-valerolactone, methyl formate, methyl acetate, ethyl acetate, isopropyl acetate, methyl propionate, and propylene glycol monomethyl ether acetate. Examples of carbonate solvents include ethylene carbonate and ethyl methyl carbonate. An example of the ketone solvent is acetone. Examples of the amide solvent include dimethylformamide, dimethylacetamide, and N-methyl-2-pyrrolidone. It is preferable that the non-aqueous solvent does not contain an alcohol-based solvent.

[0044] Next, a method for producing lithium iodide according to the present disclosure will be described. The method for producing lithium iodide according to the present disclosure is characterized in that a drying step is carried out to dry the non-aqueous lithium iodide solution obtained by the method according to the present disclosure, thereby obtaining lithium iodide having a water content of less than 500 ppm and a content of acid-derived components of 12,000 ppm or less.

[0045] The method for producing lithium iodide according to the present disclosure includes a drying step of drying the non-aqueous lithium iodide solution obtained by the method according to the present disclosure. As the drying method, methods such as hot air drying using a dryer, drying under reduced pressure, and infrared drying can be used. The drying step preferably includes a step of reducing the pressure of the lithium iodide non-aqueous solution in an inert gas atmosphere, and more preferably a step of reducing the pressure of the lithium iodide non-aqueous solution in an inert gas atmosphere to 0.1 kPa or more and 5.0 kPa or less, while maintaining the atmospheric temperature at 20°C or more and 100°C or less. In order to prevent the dried lithium iodide from absorbing moisture due to water vapor in the environment, the process up to the storage step of storing the dried lithium iodide in a container is preferably carried out under an inert gas atmosphere or in a dry room environment, preferably an environment with a dew point of, for example, −30° C. or lower.

[0046] When the drying temperature is high and exceeds 100°C and water is present in the system, hydrogen iodide and lithium hydroxide are generated by the reaction between lithium iodide and water, and hydrogen iodide as an acid may be contained in the lithium iodide. Therefore, it is preferable to avoid conditions that could generate hydrogen iodide as described above.

[0047] The resulting lithium iodide has a water content of less than 500 ppm and a content of acid-derived components of 12,000 ppm or less. The water content of the lithium iodide is preferably less than 400 ppm, more preferably less than 200 ppm, and even more preferably less than 100 ppm. It is also preferable that the lithium iodide is substantially free of water. The amount of acid-derived components contained in the resulting lithium iodide is preferably as small as possible, and is preferably substantially free of such components. The amount of acid-derived components contained in the lithium iodide may be preferably 2500 ppm or less, 400 ppm or less, 50 ppm or less, 20 ppm or less, or 10 ppm or less.

[0048] In addition, since the drying step does not use an acid catalyst, the acid-derived components do not increase during the drying step, and therefore, if the content of the acid-derived components contained in the lithium iodide non-aqueous solution obtained by the method of the present disclosure is 4000 ppm or less, the content of the acid-derived components contained in the lithium iodide can be 12000 ppm or less.

[0049] Next, the lithium iodide of the present disclosure will be described. The lithium iodide according to the present disclosure is characterized by having a water content of less than 500 ppm and a content of acid-derived components of 12,000 ppm or less. The lithium iodide of the present disclosure is solid lithium iodide with an extremely low water content and an extremely low content of acid-derived components. The lithium iodide of the present disclosure may be in the form of a powder.

[0050] The lithium iodide of the present disclosure has an extremely low water content and an extremely low content of acid-derived components, and therefore can be preferably used as a battery electrolyte. Furthermore, by dissolving the lithium iodide of the present disclosure in a non-aqueous solvent that does not contain water or acid-derived components, it can be used as a battery electrolyte solution with an extremely low water content and acid-derived component content.

[0051] The water content of lithium iodide is preferably less than 400 ppm, more preferably less than 200 ppm, and even more preferably less than 100 ppm, and it is also preferred that the lithium iodide be substantially free of water. The lithium iodide being substantially free of moisture means that the moisture content is below the detection limit (0.1 ppm or less) in the moisture content measurement method described below.

[0052] Furthermore, in the lithium iodide according to the present disclosure, the content of acid-derived components may be 2500 ppm or less, 400 ppm or less, 50 ppm or less, 20 ppm or less, or 10 ppm or less. It is most preferable that the lithium iodide is substantially free of acid-derived components. The lithium iodide being substantially free of acid-derived components means that no acid-derived components are detected in a method for measuring the content of acid-derived components, which will be described below.

[0053] The water content of lithium iodide can be measured using a coulometric Karl Fischer moisture meter. To measure the water content of lithium iodide, approximately 1 g of lithium iodide sample is precisely weighed and dissolved in approximately 2 g of methanol with a known water content, and the resulting solution is used as the measurement sample for analysis. In this specification, the water content in lithium iodide refers to the water content (ppm) measured by dissolving about 1 g of a lithium iodide sample in about 2 g of methanol with a known water content and using a coulometric Karl Fischer moisture meter.

[0054] The content of acid-derived components in lithium iodide is measured by 1 The content of acid-derived components as organic acids can be measured by quantifying side chain hydrogens using H NMR, and the content of acid-derived components as inorganic acids can be measured by measuring the concentration of anions other than iodide ions using anion chromatography. In this specification, the content of acid-derived components in lithium iodide means 1 It means the content (ppm) of acid-derived components measured as organic acids by quantifying side chain hydrogen using H NMR. 1 When no side chain hydrogen is detected in the quantitative determination of side chain hydrogen using H NMR, and no anions other than iodide ions are detected using anion chromatography, it can be said that lithium iodide does not substantially contain acid-derived components.

[0055] The lithium iodide according to the present disclosure preferably includes a non-aqueous solvate of lithium iodide. The non-aqueous solvent contained in the non-aqueous solvate preferably contains at least one solvent selected from the group consisting of ether-based solvents, acetal-based solvents, ester-based solvents, nitrile-based solvents, carbonate-based solvents, ketone-based solvents, amide-based solvents, and sulfur-containing solvents. In addition, the non-aqueous solvent contained in the non-aqueous solvate is preferably an aprotic solvent. It is more preferable that the non-aqueous solvent contained in the non-aqueous solvate contains at least one solvent selected from the group consisting of ether-based solvents, acetal-based solvents, ester-based solvents, and amide-based solvents. It is also preferable that the lithium iodide has a crystalline structure.

[0056] The fact that lithium iodide is a non-aqueous solvate and has a crystalline structure is 1 This can be determined by 1 H NMR analysis and XRD analysis.

[0057] The lithium iodide non-aqueous solution of the present disclosure can also be obtained by dissolving the lithium iodide according to the present disclosure in a non-aqueous solvent. The type of non-aqueous solvent is not particularly limited, and any non-aqueous solvent that can be used for the lithium iodide non-aqueous solution of the present disclosure can be used. Furthermore, the non-aqueous solvent in which lithium iodide is dissolved may be different from the non-aqueous solvent used when producing lithium iodide.

[0058] Next, the method for producing the nonaqueous solvate of lithium iodide and the nonaqueous solvate of lithium iodide according to the present disclosure will be described. The method for producing a non-aqueous solvate of lithium iodide according to the present disclosure is characterized in that a drying step is carried out to dry the non-aqueous lithium iodide solution obtained by the method according to the present disclosure, thereby obtaining a non-aqueous solvate of lithium iodide comprising a non-aqueous solvent and lithium iodide. According to this method, a non-aqueous solvate of lithium iodide consisting of a non-aqueous solvent and lithium iodide can be obtained. Such non-aqueous solvates of lithium iodide can be appropriately selected and used in view of compatibility or incompatibility with each component constituting the battery.

[0059] In the method for producing a non-aqueous solvate of lithium iodide according to the present disclosure, when a non-aqueous solvent other than an alcohol is used as the non-aqueous solvent, it is possible to obtain a non-aqueous solvate of lithium iodide according to the present disclosure, which is characterized by comprising a non-alcoholic solvent and lithium iodide.

[0060] The non-alcohol non-aqueous solvent preferably contains at least one solvent selected from the group consisting of ether-based solvents, acetal-based solvents, ester-based solvents, nitrile-based solvents, carbonate-based solvents, ketone-based solvents, amide-based solvents, and sulfur-containing solvents. In addition, the non-aqueous solvent other than the alcohol is preferably an aprotic solvent. It is more preferable that the non-alcohol non-aqueous solvent contains at least one solvent selected from the group consisting of ether-based solvents, acetal-based solvents, ester-based solvents, and amide-based solvents. It is also preferable that the non-aqueous solvate of lithium iodide has a crystalline structure.

[0061] The fact that lithium iodide is a non-aqueous solvate and that the non-aqueous solvate of lithium iodide has a crystalline structure is as follows: 1 This can be determined by 1 H NMR analysis and XRD analysis. [Example]

[0062] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0063] [Method for measuring lithium iodide yield and purity] Approximately 0.2 g of lithium iodide non-aqueous solution or lithium iodide powder sample was precisely weighed and diluted with ultrapure water to approximately 10 ppm to obtain an aqueous solution, and the iodide ion concentration was measured using anion chromatography. The values ​​obtained from the measurement results were converted into lithium iodide concentration, which was used as the yield and purity.

[0064] [Method for measuring water content in powder and solution] Measurement was carried out using a coulometric Karl Fischer moisture meter. For liquid samples, approximately 1 g of sample was precisely weighed and analyzed directly. In the case of solid samples, approximately 1 g of lithium iodide powder sample was precisely weighed and dissolved in approximately 2 g of methanol with a known water content to prepare the measurement sample.

[0065] [Method for measuring the amount of non-aqueous solvent in powder] 1 Quantitative analysis was performed using H NMR. Approximately 1 g of lithium iodide nonaqueous solvate and approximately 0.1 g of 1,4-trifluoromethylbenzene as an internal standard were precisely weighed and dissolved in approximately 2 g of deuterated acetonitrile to prepare a measurement solution. The amount of nonaqueous solvent in the powder was calculated from the ratio of the integrated values ​​of the peaks derived from the internal standard and the nonaqueous solvent.

[0066] 〔reagent〕 The reagents used in the synthesis were purchased from the following companies and used without further purification. 1,3-Dioxolane (hereinafter referred to as "DOL"): Sigma-Aldrich Japan LLC 1,2-Dimethoxyethane (hereinafter referred to as "DME") for electrochemical use: manufactured by Kanto Chemical Co., Ltd. 1,3,5-Trioxane (hereinafter referred to as "TOX"): Sigma-Aldrich Japan LLC Diethylene glycol dimethyl ether (hereinafter referred to as "DG") for electrochemical use: manufactured by Kanto Chemical Co., Ltd. 3-Methoxypropionitrile (hereinafter referred to as "MPN"): manufactured by Tokyo Chemical Industry Co., Ltd. Ethyl acetate (hereinafter referred to as "EtOAc") ultra-dehydrated: Fujifilm Wako Pure Chemical Industries, Ltd. Ethylene carbonate (hereinafter referred to as "EC") lithium battery grade: manufactured by Kishida Chemical Co., Ltd. Ethyl methyl carbonate (hereinafter referred to as "EMC") lithium battery grade: manufactured by Kishida Chemical Co., Ltd. Acetone (hereinafter referred to as "AC") ultra-dehydrated: Fujifilm Wako Pure Chemical Industries, Ltd. γ-Butyrolactone (hereinafter referred to as "GBL") for electrochemistry: manufactured by Kanto Chemical Co., Ltd. N-methyl-2-pyrrolidone (hereinafter referred to as "NMP"): manufactured by Nacalai Tesque, Inc. Lithium foil, thickness 0.1 mm, width 18 mm: Honjo Metals Co., Ltd. Lithium rod, diameter 10 mm, length 10 mm: Honjo Chemical Co., Ltd. Iodine: Godo Resources Co., Ltd.

[0067] [Example 1] (Preparation of non-aqueous lithium iodide solution 1) A 1-liter SUS316 autoclave equipped with a stirring blade, thermocouple protection tube, and dip tube was placed in an argon-atmosphere glove box, and 9.63 g (1.41 mol) of lithium rod and 265 g of DOL were added. After sealing the reaction vessel, the pressure was reduced to 0.05 kPa or less, and a solution of 63.5 g (0.250 mol) of iodine in 217 g of DME was introduced while maintaining the temperature inside the glove box at 45°C or less. After the entire amount of iodine was introduced, the mixture was stirred and aged for 10 hours. The maximum temperature of the solution during the reaction reached 45°C. After opening the reaction vessel, excess lithium was filtered off, yielding 513 g of a lithium iodide non-aqueous solution in 97.7% yield. The water content of the resulting non-aqueous solution was 29.9 ppm, and the lithium iodide concentration was 12.7 wt%.

[0068] [Example 2] (Preparation of non-aqueous lithium iodide solution 2) In an argon-atmosphere glove box, 3.63 g (0.0143 mol) of iodine, 5.05 g of DOL, and 4.14 g of DME were placed in a 50 mL two-neck flask equipped with a stirrer and an internal thermometer. Next, 210 mg (0.0300 mol) of lithium foil was gradually added while maintaining the temperature inside the glove box at 45°C or below. After the entire amount of lithium was added, the mixture was stirred and aged for 10 hours. The maximum temperature of the solution during the reaction was 45°C. The excess lithium foil was filtered off to obtain 12.4 g of a lithium iodide non-aqueous solution in a yield of 94.6%. The water content in the resulting non-aqueous solution was 83.8 ppm, and the lithium iodide concentration was 29.2 wt %.

[0069] [Example 5] (Preparation of non-aqueous lithium iodide solution 3) In an argon-filled glove box, 40 mg (0.0058 mol) of lithium foil and 5.05 g of DOL were placed in a 50 mL two-neck flask equipped with a stirrer and an internal thermometer. After sealing the reaction vessel, the pressure was reduced to 0.05 kPa or less, and a solution of 0.65 g (0.0026 mol) of iodine in 4.14 g of DME was introduced while maintaining the temperature inside the glove box at 45°C or less. After the entire amount of iodine was introduced, the mixture was stirred and aged for 10 hours. The maximum temperature of the solution during the reaction reached 45°C. After opening the reaction vessel, excess lithium was filtered off, yielding 9.2 g of a lithium iodide non-aqueous solution in 97.7% yield. The water content of the resulting non-aqueous solution was 50.4 ppm, and the lithium iodide concentration was 7.3 wt%.

[0070] [Example 6] (Preparation of non-aqueous lithium iodide solution 4) A non-aqueous lithium iodide solution (14.1 g) was obtained in a yield of 96.6% in the same manner as in Example 5, except that 320 mg (0.0461 mol) of lithium foil, 2.86 g of DOL, 5.44 g (0.0214 mol) of iodine, and 6.43 g of DME were used. The maximum temperature of the solution during the reaction was 45°C. The water content of the obtained non-aqueous solution was 124.7 ppm, and the lithium iodide concentration was 39.2 wt%.

[0071] [Example 7] (Preparation of non-aqueous lithium iodide solution 5) A non-aqueous lithium iodide solution (12.3 g) was obtained in a 95.3% yield in the same manner as in Example 5, except that 990 mg (0.1426 mol) of lithium foil, 6.43 g of DOL, 3.63 g (0.0143 mol) of iodine, and 2.86 g of DME were used. The maximum temperature of the solution during the reaction was 45°C. The water content of the resulting non-aqueous solution was 18.0 ppm, and the lithium iodide concentration was 23.2 wt%.

[0072] [Example 8] (Preparation of non-aqueous lithium iodide solution 6) A non-aqueous lithium iodide solution (12.2 g) was obtained in 96.4% yield by the same method as in Example 5, except that 210 mg (0.0303 mol) of lithium foil, 5.05 g of DOL, 3.63 g (0.0143 mol) of iodine, and 2.86 g of DG were used instead of DME. The maximum temperature of the solution during the reaction was 43°C. The water content of the obtained non-aqueous solution was 81.7 ppm, and the lithium iodide concentration was 30.2 wt%.

[0073] [Example 9] (Preparation of non-aqueous lithium iodide solution 7) A non-aqueous lithium iodide solution (12.2 g) was obtained in 96.9% yield in the same manner as in Example 5, except that 210 mg (0.0303 mol) of lithium foil, 5.05 g of TOX instead of DOL, 3.63 g (0.0143 mol) of iodine, and 2.86 g of DME were used. The maximum temperature of the solution during the reaction was 41°C. The water content of the resulting non-aqueous solution was 82.0 ppm, and the lithium iodide concentration was 30.4 wt%.

[0074] [Example 10] (Preparation of non-aqueous lithium iodide solution 8) A non-aqueous lithium iodide solution (12.3 g) was obtained in 97.7% yield by the same method as in Example 5, except that 210 mg (0.0303 mol) of lithium foil, 5.05 g of TOX instead of DOL, 3.63 g (0.0143 mol) of iodine, and 2.86 g of DG instead of DME were used. The maximum temperature of the solution during the reaction was 39°C. The water content of the resulting non-aqueous solution was 80.5 ppm, and the lithium iodide concentration was 30.5 wt%.

[0075] [Example 11] (Preparation of non-aqueous lithium iodide solution 9) In an argon-atmosphere glove box, 210 mg (0.0303 mol) of lithium foil, 5.05 g of DOL, and 4.14 g of DME were placed in a 50 mL two-neck flask equipped with a stirrer and an internal thermometer. Next, 3.63 g (0.0143 mol) of iodine was added using a funnel while maintaining the temperature inside the glove box at 45°C or less. After the entire amount of iodine was added, the mixture was stirred and aged for 10 hours. The maximum temperature of the solution during the reaction reached 45°C. After opening the reaction vessel, excess lithium was filtered off, yielding 12.1 g of a lithium iodide non-aqueous solution in a 94.8% yield. The water content of the resulting non-aqueous solution was 83.7 ppm, and the lithium iodide concentration was 29.9 wt%.

[0076] [Example 12] (Preparation of non-aqueous lithium iodide solution 10) A non-aqueous lithium iodide solution (12.2 g) was obtained in a yield of 95.3% in the same manner as in Example 11, except that 9.19 g of DOL was used instead of DME. The maximum temperature of the solution during the reaction was 45°C. The water content of the obtained non-aqueous solution was 84.0 ppm, and the lithium iodide concentration was 29.8 wt%.

[0077] [Example 13] (Preparation of non-aqueous lithium iodide solution 11) A non-aqueous lithium iodide solution (12.1 g) was obtained in a yield of 94.9% in the same manner as in Example 12, except that DOL was not used and 9.19 g of MPN was used. The maximum temperature of the solution during the reaction was 45°C. The water content of the obtained non-aqueous solution was 82.4 ppm, and the lithium iodide concentration was 30.0 wt%.

[0078] [Example 14] (Preparation of non-aqueous lithium iodide solution 12) A non-aqueous lithium iodide solution (12.1 g) was obtained in a 94.3% yield in the same manner as in Example 12, except that 9.19 g of EtOAc was used instead of DOL. The maximum temperature of the solution during the reaction was 45°C. The water content of the obtained non-aqueous solution was 80.2 ppm, and the lithium iodide concentration was 29.8 wt%.

[0079] [Example 15] (Preparation of non-aqueous lithium iodide solution 13) A non-aqueous lithium iodide solution (9.2 g) was obtained in a 94.8% yield in the same manner as in Example 12, except that DOL was not used and 5.05 g of EC, 4.14 g of EMC, 40 mg (0.0058 mol) of lithium foil, and 0.65 g (0.0026 mol) of iodine were used. The maximum temperature of the solution during the reaction was 45°C. The water content of the obtained non-aqueous solution was 46.1 ppm, and the lithium iodide concentration was 7.1 wt%.

[0080] [Example 16] (Preparation of non-aqueous lithium iodide solution 14) A non-aqueous lithium iodide solution (12.1 g) was obtained in a yield of 93.8% in the same manner as in Example 12, except that 9.19 g of AC was used instead of DOL. The maximum temperature of the solution during the reaction was 45°C. The water content of the obtained non-aqueous solution was 80.5 ppm, and the lithium iodide concentration was 29.7 wt%.

[0081] [Example 17] (Preparation of non-aqueous lithium iodide solution 15) A non-aqueous lithium iodide solution (12.2 g) was obtained in a 95.1% yield in the same manner as in Example 12, except that 9.19 g of GBL was used instead of DOL. The maximum temperature of the solution during the reaction was 45°C. The water content of the obtained non-aqueous solution was 83.5 ppm, and the lithium iodide concentration was 29.9 wt%.

[0082] [Example 18] (Preparation of non-aqueous lithium iodide solution 16) A non-aqueous lithium iodide solution (27.1 g) was obtained in 98.5% yield in the same manner as in Example 12, except that 9.19 g of NMP was used instead of DOL, 1.04 g (0.150 mol) of lithium foil, and 18.0 g (0.0709 mol) of iodine were used. The maximum temperature of the solution during the reaction was 45°C. The water content of the obtained non-aqueous solution was 191.3 ppm, and the lithium iodide concentration was 69.1 wt%.

[0083] [Example 19] (Preparation of non-aqueous lithium iodide solution 17) In an argon-atmosphere glove box, 280 mg (0.0403 mol) of lithium foil and 2.86 g of DOL were placed in a 50 mL two-neck flask equipped with a stirrer and an internal thermometer. After sealing the reaction vessel, the pressure was reduced to 0.05 kPa or less, and a solution of 5.44 g (0.0214 mol) of iodine in 6.43 g of DME was introduced while maintaining the temperature inside the glove box at 45°C or less. The maximum temperature of the solution during the reaction was 45°C. After the entire amount of iodine was introduced, stirring and aging were continued for 10 hours, yielding 13.8 g of a lithium iodide non-aqueous solution in 90.6% yield. The water content of the resulting non-aqueous solution was 211.1 ppm, and the lithium iodide concentration was 37.7 wt%.

[0084] In addition, since no desiccant such as an acid was used in Examples 1, 2, and 5 to 19, no components derived from the desiccant (acid) were present in the system. The results are shown in Table 1.

[0085] [Example 3] (Preparation of solid lithium iodide 1) 79.9 g of the lithium iodide non-aqueous solution obtained in Example 1 was placed in a 500 mL three-neck flask equipped with a stirrer, and the pressure was gradually reduced to 0.1 kPa to remove the solvent. 200 mL of DME was added to 28.3 g of the resulting solid in an argon-atmosphere glove box, and the suspension was stirred for one hour. The powder was then filtered and dried at 0.05 kPa for two hours to obtain 25.7 g of powder. The powder is 1 The results of H NMR and XRD analysis confirmed that the powder was lithium iodide containing a lithium iodide-DME complex (a DME solvate of lithium iodide). The non-aqueous solvent content in the powder was 61.6 wt %, and the water content was 94.9 ppm.

[0086] [Example 4] (Preparation of solid lithium iodide 2) 10.0 g of the lithium iodide non-aqueous solution obtained in Example 2 was placed in a 500 mL three-necked flask equipped with a stirrer, and the pressure was gradually reduced to 0.1 kPa to remove the solvent. 200 mL of DME was added to 7.9 g of the obtained solid in an argon atmosphere glove box, and the suspension was stirred for one hour. The powder was then filtered and dried at 0.05 kPa for two hours to obtain 7.4 g of powder. 1 The results of H NMR and XRD analysis confirmed that the powder was lithium iodide containing a lithium iodide-DME complex (a DME solvate of lithium iodide). The non-aqueous solvent content in the powder was 59.0 wt %, and the water content was 116.0 ppm.

[0087] [Example 20] (Preparation of solid lithium iodide 3) 10.0 g of the lithium iodide non-aqueous solution obtained in Example 5 was placed in a 500 mL three-neck flask equipped with a stirrer, and the pressure was gradually reduced to 0.1 kPa to remove the solvent. 200 mL of DME was added to 8.0 g of the resulting solid in an argon-filled glove box, and the suspension was stirred for one hour. The powder was then filtered and dried at 0.05 kPa for two hours to obtain 7.5 g of powder. The powder is 1 The results of H NMR and XRD analysis confirmed that the powder was lithium iodide containing a lithium iodide-DME complex (a DME solvate of lithium iodide). The non-aqueous solvent content in the powder was 59.9 wt %, and the water content was 97.2 ppm.

[0088] [Example 21] (Preparation of solid lithium iodide 4) 8.3 g of powder was obtained in the same manner as in Example 20, except for using 10.0 g of the lithium iodide non-aqueous solution obtained in Example 6. The content of the non-aqueous solvent in the powder was 53.3 wt %, and the water content was 92.8 ppm.

[0089] [Example 22] (Preparation of solid lithium iodide 5) 5.8 g of powder was obtained in the same manner as in Example 20, except for using 10.0 g of the lithium iodide non-aqueous solution obtained in Example 7. The content of the non-aqueous solvent in the powder was 61.1 wt %, and the water content was 96.5 ppm.

[0090] [Example 23] (Preparation of solid lithium iodide 6) 7.6 g of powder was obtained in the same manner as in Example 20, except for using 10.0 g of the lithium iodide non-aqueous solution obtained in Example 8. The content of the non-aqueous solvent in the powder was 59.7 wt %, and the water content was 83.3 ppm.

[0091] [Example 24] (Preparation of solid lithium iodide 7) 7.6 g of powder was obtained in the same manner as in Example 20, except for using 10.0 g of the lithium iodide non-aqueous solution obtained in Example 9. The content of the non-aqueous solvent in the powder was 60.1 wt %, and the water content was 84.0 ppm.

[0092] [Example 25] (Preparation of solid lithium iodide 8) 7.7 g of powder was obtained in the same manner as in Example 20, except for using 10.0 g of the lithium iodide non-aqueous solution obtained in Example 10. The content of the non-aqueous solvent in the powder was 61.6 wt %, and the water content was 89.6 ppm.

[0093] [Example 26] (Preparation of solid lithium iodide 9) 7.4 g of powder was obtained in the same manner as in Example 20, except for using 10.0 g of the lithium iodide non-aqueous solution obtained in Example 11. The content of the non-aqueous solvent in the powder was 58.7 wt %, and the water content was 73.7 ppm.

[0094] [Example 27] (Preparation of solid lithium iodide 10) 7.3 g of powder was obtained in the same manner as in Example 20, except for using 10.0 g of the lithium iodide non-aqueous solution obtained in Example 12. The content of the non-aqueous solvent in the powder was 58.4 wt %, and the water content was 77.9 ppm.

[0095] [Example 28] (Preparation of solid lithium iodide 11) 5.0 g of powder was obtained in the same manner as in Example 20, except for using 10.0 g of the lithium iodide non-aqueous solution obtained in Example 13. The content of the non-aqueous solvent in the powder was 54.1 wt %, and the water content was 60.3 ppm.

[0096] [Example 29] (Preparation of solid lithium iodide 12) 6.2 g of powder was obtained in the same manner as in Example 20, except for using 10.0 g of the lithium iodide non-aqueous solution obtained in Example 14. The content of the non-aqueous solvent in the powder was 53.0 wt %, and the water content was 65.1 ppm.

[0097] [Example 30] (Preparation of solid lithium iodide 13) 1.2 g of powder was obtained in the same manner as in Example 20, except for using 10.0 g of the lithium iodide non-aqueous solution obtained in Example 15. The content of the non-aqueous solvent in the powder was 53.9 wt %, and the water content was 53.8 ppm.

[0098] [Example 31] (Preparation of solid lithium iodide 14) 7.4 g of powder was obtained in the same manner as in Example 20, except for using 10.0 g of the lithium iodide non-aqueous solution obtained in Example 16. The content of the non-aqueous solvent in the powder was 59.6 wt %, and the water content was 82.2 ppm.

[0099] [Example 32] (Preparation of solid lithium iodide 15) 5.8 g of powder was obtained in the same manner as in Example 20, except for using 10.0 g of the lithium iodide non-aqueous solution obtained in Example 17. The content of the non-aqueous solvent in the powder was 51.2 wt %, and the water content was 82.4 ppm.

[0100] [Example 33] (Preparation of solid lithium iodide 16) 6.0 g of powder was obtained in the same manner as in Example 20, except for using 10.0 g of the lithium iodide non-aqueous solution obtained in Example 18. The content of the non-aqueous solvent in the powder was 50.4 wt %, and the water content was 89.2 ppm.

[0101] In addition, since a drying agent such as an acid was not used in Examples 3, 4, and 20 to 33, components derived from the drying agent (acid) were not present in the system. The results are shown in Table 2.

[0102] Comparative Example 1 (Comparative Example 1-1, Comparative Example 1-2) (Preparation of Comparative Solid Lithium Iodide and Non-Aqueous Lithium Iodide Solution 1) 300 g of lithium iodide (water content: 7290 ppm) synthesized according to the method described in Non-Patent Document 1 was placed in a 1 L eggplant-shaped flask, and the pressure was reduced to 1 kPa while stirring using an evaporator. The mixture was then dried at 80°C for 1 hour, at 100°C for 1 hour, and then at 120°C for 2 hours. After the flask was repressurized with nitrogen, the crystals adhering to the flask wall were scraped off in a glove box, and then the flask was heated and dried for another 6 hours at 120°C and 1 kPa. The process of repressurizing the flask with nitrogen, scraping off the crystals, and drying for 2 hours at 120°C and 1 kPa was repeated two more times, for a total of three times, to obtain 298 g of lithium iodide dried under reduced pressure. The water content of the obtained powder was measured and found to be 524.0 ppm. The powder was 1 H NMR and XRD analysis confirmed that the solution did not contain a nonaqueous solvate of lithium iodide. Since no acid or other desiccant was used in this comparative example, no components derived from the desiccant (acid) were present in the system. The results are shown in Table 2.

[0103] In addition, the powder obtained above was dissolved in a mixed solvent of DOL:DME = 1:1 (volume ratio) so that the concentration of lithium iodide in the non-aqueous solution would be the concentrations shown in Table 1, and the water content of the obtained non-aqueous solution was measured. An example in which the lithium iodide concentration was adjusted to that of Example 1 was designated Comparative Example 1-1, and an example in which the lithium iodide concentration was adjusted to that of Example 2 was designated Comparative Example 1-2. In this comparative example, since a desiccant such as an acid was not used, no components derived from the desiccant (acid) were present in the system. The results are shown in Table 1.

[0104] Comparative Example 2 (Preparation of Comparative Solid Lithium Iodide and Lithium Iodide Non-Aqueous Solution 2) Lithium iodide was synthesized according to the method described in Patent Document 1. A 200 ml reaction vessel equipped with a stirrer, a reflux condenser equipped with a distillation head with a stopcock, a thermometer, a dropping funnel, and a solid inlet was thoroughly purged with nitrogen. 70.0 g of ethanol was added to the reaction vessel through the dropping funnel. While stirring, 4.25 g (0.101 mol) of lithium hydroxide monohydrate was added through the solid inlet. 21.5 g (0.151 mol) of methyl iodide was added to the reaction vessel through the dropping funnel. Stirring and aging were continued for 21 hours while maintaining the temperature inside the reaction vessel at 30°C. The reaction vessel was cooled to room temperature and the pressure was reduced to 1 kPa using a vacuum pump to distill off excess methyl iodide and the resulting ethyl methyl ether. After the reduced pressure in the reaction vessel was released with nitrogen, 19.8 g of ethanol was added via the dropping funnel. The water content in the reaction liquid was 43,300 ppm. The reflux condenser, fractionating head, dropping funnel, and solid inlet were removed from the reaction vessel, and a Soxhlet extractor filled with 43.1 g of synthetic zeolite (trade name: Molecular Sieve 3A-1 / 8) was installed. The reaction vessel was then heated until reflux of the ethanol began, and dehydration was continued for 9 hours while refluxing. After cooling, the water content of the reaction solution was 2900 ppm, and the lithium iodide concentration was 12.8 wt%. Note that since no desiccant such as acid was used in this comparative example, no components derived from the desiccant (acid) were present in the system. The results are shown in Table 1.

[0105] The reaction solution was placed in a 200 ml eggplant-shaped flask, and the ethanol was distilled off using an evaporator at 75°C / 3 kPa for 1 hour. The reaction solution was then further concentrated to dryness at 130°C / 1 kPa for 3 hours, yielding 13.2 g of white powdery lithium iodide crystals (yield 97.4%). The purity of the lithium iodide was 99.1%, and the water content in the crystals was 3200 ppm. The powder was 1H NMR and XRD analysis confirmed that the solution did not contain a nonaqueous solvate of lithium iodide. Since no acid or other desiccant was used in this example, no components derived from the desiccant (acid) were present in the system. The results are shown in Table 2.

[0106] Comparative Example 3 (Preparation of Comparative Solid Lithium Iodide and Non-Aqueous Lithium Iodide Solution 3) Lithium iodide was synthesized with reference to the method described in Patent Document 1. A 200 ml reaction vessel equipped with a stirrer, a reflux condenser equipped with a distillation head with a stopcock, a thermometer, a dropping funnel, and a solid inlet was thoroughly purged with nitrogen. 70.0 g of ethanol was added to the reaction vessel through the dropping funnel. With stirring, 4.25 g (0.101 mol) of lithium hydroxide monohydrate was added through the solid inlet. 21.5 g (0.151 mol) of methyl iodide was added to the reaction vessel through the dropping funnel. Stirring and aging were continued for 21 hours while maintaining the temperature inside the reaction vessel at 30°C. The reaction vessel was cooled to room temperature and the pressure was reduced to 1 kPa using a vacuum pump to distill off excess methyl iodide and the resulting ethyl methyl ether. After the reduced pressure in the reaction vessel was released with nitrogen, 19.8 g of ethanol was added via the dropping funnel. The water content in the reaction liquid was 43,300 ppm. Ethanol was distilled off from the reaction mixture under reduced pressure, and then 15 g of 2-propanol was added to the reaction vessel through the dropping funnel. While stirring, 7.43 g (0.070 mol) of methyl orthoformate and 0.12 g (0.003 mol) of formic acid were added from the dropping funnel. The temperature inside the reaction vessel was maintained at 50°C, and stirring and aging were continued for 3 hours. After cooling to room temperature, the water content of the reaction solution was measured and found to be 20.7 ppm, and the amount of remaining acid-derived components was 4170 ppm. In this comparative example, since the formic acid-derived components contained in the reaction system were not removed, 100% of the formic acid-derived components contained in the reaction system remained. The results are shown in Table 1. The resulting reaction mixture was placed in a 100 mL two-necked flask equipped with a stirrer, and the pressure was gradually reduced to 0.1 kPa at 80°C to remove the solvent. The resulting powder was dried at 0.05 kPa for two hours to obtain a powder. 1 H NMR confirmed that the powder was lithium iodide containing lithium iodide-2-propanol complex (lithium iodide 2-propanol solvate). The non-aqueous solvent content in the powder was 11.0 wt %, and the water content was 167.0 ppm. 0.5 g of the obtained powder was dissolved in 2 g of deuterated methanol, and 1,4-trifluoromethylbenzene was added as an internal standard. 1 Quantitative analysis of the components derived from formic acid using H NMR revealed that the remaining amount of components derived from the acid was 14,400 ppm, and the remaining amount of lithium formate was equivalent to 69.2% of the added amount. The results are shown in Table 2.

[0107] [Table 1]

[0108] [Table 2]

[0109] Tables 1 and 2 show that in Examples 1 to 33, non-aqueous lithium iodide solutions with low water content and no acid-derived components, and solid (powder) lithium iodide were obtained. Compared to Example 1, Example 2 has a higher water content Y, but Example 2 also has a higher lithium iodide concentration X. When viewed in terms of the water content per unit of lithium iodide (Y / X), Example 1 and Example 2 can be said to be non-aqueous lithium iodide solutions with similarly low water contents.

[0110] In Example 5, the amount of iodine used was smaller than in Example 1, and the amount of metallic lithium used was adjusted to be smaller per mole of iodine, and the lithium iodide non-aqueous solution in Example 5 had a lower lithium iodide concentration X in the solution and a higher water content Y than in Example 1.

[0111] Compared to Example 5, Example 6 uses larger amounts of metallic lithium and iodine, and is a lithium iodide non-aqueous solution adjusted by increasing the DOL ratio in the solution. Compared to Example 5, Example 6 has a higher lithium iodide concentration X in the solution and a higher water content Y.

[0112] Compared to Example 6, Example 7 uses a larger amount of metallic lithium, and the lithium iodide non-aqueous solution is adjusted by increasing the DME ratio in the solution. Compared to Example 6, the lithium iodide concentration X in the solution is lower, and the water content Y is smaller.

[0113] In Example 8, compared to Example 5, the lithium iodide non-aqueous solution was prepared using DG instead of DME, and the amounts of metallic lithium and iodine used were greater than in Example 5, resulting in a higher lithium iodide concentration X and water content Y in the solution.

[0114] In comparison with Example 5, Example 9 is a non-aqueous lithium iodide solution prepared using TOX instead of DOL, and the amounts of metallic lithium and iodine used are greater than those in Example 5, resulting in a higher lithium iodide concentration X and water content Y in the solution.

[0115] In Example 10, the lithium iodide non-aqueous solution was prepared using DG instead of DME, and the lithium iodide concentration X and water content Y in the solution were at the same levels as in Example 9.

[0116] In comparison with Example 5, Example 11 is a non-aqueous lithium iodide solution prepared by introducing prill-shaped iodine particles into the solution. Compared with Example 5, the amounts of metallic lithium and iodine used are greater, and the lithium iodide concentration X and water content Y in the solution are higher.

[0117] In comparison with Example 11, Example 12 is a lithium iodide non-aqueous solution prepared using only DOL without using DME, and the lithium iodide concentration X and water content Y in the solution are at the same levels as those in Example 11.

[0118] In Example 13, a lithium iodide non-aqueous solution was prepared without using DOL or DME, but instead using MPN, and the lithium iodide concentration X and water content Y in the solution were at the same levels as in Example 11.

[0119] In Example 14, a lithium iodide non-aqueous solution was prepared without using DOL or DME, but using EtOAc instead, and the lithium iodide concentration X and water content Y in the solution were at the same levels as in Example 11.

[0120] Compared to Example 11, Example 15 used less metallic lithium and iodine, and was a lithium iodide non-aqueous solution prepared without using DOL or DME but using EC and EMC instead. Compared to Example 11, Example 15 had a lower lithium iodide concentration X in the solution and a smaller water content Y.

[0121] In Example 16, a non-aqueous lithium iodide solution was prepared without using DOL or DME, but instead using AC, and the lithium iodide concentration X and water content Y in the solution were at the same levels as in Example 11.

[0122] In Example 17, a non-aqueous lithium iodide solution was prepared using GBL instead of DOL and DME, and the lithium iodide concentration X and water content Y in the solution were at the same levels as in Example 11.

[0123] Compared to Example 11, Example 18 used larger amounts of metallic lithium and iodine, and was a lithium iodide non-aqueous solution prepared without using DOL or DME but using NMP instead. Compared to Example 11, Example 18 had a higher lithium iodide concentration X in the solution and a higher water content Y.

[0124] Example 19 is a lithium iodide non-aqueous solution prepared by adjusting the amount of metallic lithium used in Example 6 to less than 2.1 moles per mole of iodine. Compared to Example 6, the lithium iodide concentration X in the solution is lower and the water content Y is higher. Furthermore, Examples 1 to 18, in which the amount of metallic lithium used was 2.1 to 20.0 moles per mole of iodine and the amounts of metallic lithium and iodine used satisfied the specified relationship, had higher yields than Example 19, in which the above-mentioned specified relationship was not satisfied.

[0125] Comparative Example 1-1 is a lithium iodide non-aqueous solution adjusted to have approximately the same lithium iodide concentration as Example 1, but the water content Y is higher than that of Example 1. Comparative Example 1-2 is a lithium iodide non-aqueous solution adjusted to have approximately the same lithium iodide concentration as Example 2, but the water content Y is higher than that of Example 2. It can be seen that both Comparative Example 1-1 and Comparative Example 1-2 are higher than Examples 1 and 2 in terms of water content per unit of lithium iodide (Y / X). In Comparative Example 2, the water content per unit of lithium iodide (Y / X) is large. Comparative Example 3 is not preferable because the water content per unit of lithium iodide (Y / X) is small but components derived from the acid remain.

[0126] The lithium iodides of Examples 3 and 4 and Examples 20 to 33 have a low water content, while the lithium iodides of Comparative Examples 1 and 2 have a high water content. The lithium iodide of Comparative Example 3 has a low water content, but is not preferable because acid-derived components remain.

[0127] The analytical data of the lithium iodide non-aqueous solution and lithium iodide in the examples will be described below. FIG. 1 is an XRD chart of lithium iodide according to Example 3. FIG. 2 is an XRD chart of lithium iodide according to Comparative Example 1. Figure 3 is an XRD chart of commercially available lithium iodide.

[0128] 2 and 3, the peak positions in the XRD are almost the same. That is, the commercially available lithium iodide and the lithium iodide according to Comparative Example 1 have the same structure and do not contain a non-aqueous solvate of lithium iodide. On the other hand, many peaks are observed in Figure 1 that are not seen in Figures 2 and 3. These peaks suggest the presence of non-aqueous solvates of lithium iodide.

[0129] FIG. 4 shows the results of lithium iodide according to Example 3. 1 1 H NMR chart. This chart shows the peaks due to the non-aqueous solvent DME (3.4 ppm: -OCH2-, 3.3 ppm: CHO-), while the peaks due to formic acid (7.9-8.2 ppm) are not shown (the peak at 7.9 ppm is the internal standard substance 1,4-trifluoromethylbenzene). This shows that the lithium iodide according to Example 3 contains a non-aqueous solvate with DME, but does not contain an acid such as formic acid.

[0130] FIG. 5 is a chart of anion chromatography of the non-aqueous lithium iodide solution according to Example 1. FIG. 6 is a chart of blank anion chromatography measured under the same conditions as FIG. 5, but with only water introduced. In Figure 5, an iodide ion peak is observed around 21 min. The peak observed around 16-17 min is the same as the peak observed in the blank, and therefore corresponds to noise. In other words, of the peaks observed in Figure 5, the only valid peak is the iodide ion peak observed around 21 min. If acid-derived components existed in the lithium iodide non-aqueous solution, anions other than iodide ions (e.g., formate ions) would be observed, but no anions other than iodide ions were observed. This indicates that no acid-derived components existed in the lithium iodide non-aqueous solution.

[0131] FIG. 7 is a chart of cation chromatography of the lithium iodide non-aqueous solution according to Example 1. In FIG. 7, a lithium ion peak is observed around 5 min, and no other peaks are observed. When taken together with the results shown in FIG. 5, it is clear that in the lithium iodide non-aqueous solution of Example 1, only lithium iodide is present as an ionizable component. [Industrial Applicability]

[0132] It is possible to provide a lithium iodide non-aqueous solution having a low water content and a low acid content, which can be used for batteries, and lithium iodide having a low water content and a low acid content.

[0133] This application claims priority under the Paris Convention or the laws of countries transitioning to the Paris Convention, based on Japanese Patent Application No. 2020-122068 filed on July 16, 2020. The contents of that application are incorporated herein by reference in their entirety.

Claims

1. A method for producing a lithium iodide non-aqueous solution, comprising reacting metallic lithium with iodine in a non-aqueous solvent to produce lithium iodide in the non-aqueous solvent, thereby obtaining a lithium iodide non-aqueous solution.

2. 2. The method for producing a lithium iodide non-aqueous solution according to claim 1, wherein the method obtains a lithium iodide non-aqueous solution having a water content per lithium iodide unit (Y / X), which is determined by the ratio of the water content Y (ppm) in the lithium iodide non-aqueous solution to the lithium iodide concentration X (wt %) in the lithium iodide non-aqueous solution, of 7 or less and a content of acid-derived components of 4000 ppm or less.

3. 3. The method for producing a lithium iodide non-aqueous solution according to claim 1, wherein the amount of the metallic lithium used is 2.1 to 20.0 moles per mole of the iodine.

4. 4. The method for producing a lithium iodide non-aqueous solution according to claim 1, wherein the non-aqueous solvent contains at least one solvent selected from the group consisting of ether-based solvents, acetal-based solvents, ester-based solvents, nitrile-based solvents, carbonate-based solvents, ketone-based solvents, amide-based solvents, and sulfur-containing solvents.

5. The method for producing a non-aqueous lithium iodide solution according to any one of claims 1 to 4, wherein the non-aqueous solvent is an aprotic solvent.

6. 6. The method for producing a lithium iodide non-aqueous solution according to claim 1, wherein the non-aqueous solvent contains at least one solvent selected from the group consisting of ether-based solvents, acetal-based solvents, ester-based solvents, and amide-based solvents.

7. A method for producing lithium iodide, comprising: performing a drying step of drying the lithium iodide non-aqueous solution obtained by the method according to any one of claims 1 to 6, to obtain lithium iodide having a water content of less than 500 ppm and a content of acid-derived components of 12,000 ppm or less.

8. 8. The method for producing lithium iodide according to claim 7, wherein the drying step includes a step of reducing the pressure of the lithium iodide non-aqueous solution in an inert gas atmosphere.

9. 9. The method for producing lithium iodide according to claim 8, wherein the drying step comprises a step of reducing the pressure of the lithium iodide non-aqueous solution to 0.1 kPa or more and 5.0 kPa or less under an inert gas atmosphere and maintaining the atmospheric temperature at 20° C. or more and 100° C. or less.

10. A method for producing a non-aqueous solvate of lithium iodide, comprising: performing a drying step of drying the non-aqueous lithium iodide solution obtained by the method according to any one of claims 1 to 6, thereby obtaining a non-aqueous solvate of lithium iodide comprising a non-aqueous solvent and lithium iodide.

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