JP2013103851A - Lithium iodide anhydrate, method for producing lithium iodide anhydrate, solid electrolyte and lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide lithium iodide with which ionic electrical conductivity can be enhanced.SOLUTION: Lithium iodide anhydrate is brought to include a ≤3% intensity ratio [(b/a)×100] of diffraction peaks in an X-ray diffraction analysis, wherein (a) is the intensity of the diffraction peak in the neighborhood of 2θ=25.8° originated from lithium iodide anhydride and (b) is the intensity of the diffraction peak in the neighborhood of 2θ=20.7° originated from lithium iodide monohydrate.

Description

  The present invention relates to anhydrous lithium iodide and a method for producing the same. The present invention also relates to a solid electrolyte using the anhydrous lithium iodide salt or the anhydrous lithium iodide obtained by the production method thereof. The present invention also relates to a lithium ion battery using the solid electrolyte.

  Uses of metal iodide include analytical reagents, pharmaceuticals (flaming agents, diuretics), photographic emulsions, and the like. Recently, uses as nylon fiber additives, liquid crystal displays, and polarizing film materials have also been reported.

  Among metal iodides, lithium iodide is a special material and is used as a battery for cardiac pacemakers (lithium iodine battery electrolyte). It also has applications as a neutron detection phosphor.

  Incombustible inorganic solid electrolytes are materials that are particularly attracting attention because they increase the safety of batteries. And especially the use as a solid electrolyte of a lithium ion battery attracts attention as a use of lithium iodide.

  It is known that lithium iodide has a hydrate salt and an anhydrous salt. As a conventional method for producing a lithium iodide hydrate salt, a method in which lithium carbonate and hydroiodic acid are reacted (Non-Patent Document 1), a method in which hydrogen iodide gas is blown into a slurry in which water is dispersed in lithium carbonate ( Non-patent document 2) is known.

  Moreover, as a method for producing an aqueous solution of metal iodide, a method of treating iodine with iron powder, a method of reducing iodine with an organic acid or a metal salt thereof, and a method of reducing iodine with hydrazine hydrate (Patent Document 1). Are known. In addition, a method of reacting hydrazine and iodine with an alkali hydroxide or an alkali carbonate (Patent Document 2) has been proposed.

Japanese Patent Laid-Open No. 9-156920 JP 61-48403 A

“Chemical Dictionary 9 Reprinted Edition”, Kyoritsu Shuppan Publication year 1993, page 426 “New Experimental Chemistry Lecture 8 Synthesis of Inorganic Compounds (II)”, published by Maruzen, 1977, page 462

  The present inventors have found that when lithium iodide obtained by a conventional production method is used as a solid electrolyte of a lithium ion battery, a high ion conductivity cannot be obtained.

  Accordingly, an object of the present invention is to provide lithium iodide capable of increasing ion conductivity. Another object of the present invention is to provide a solid electrolyte having high ion conductivity.

  As a result of intensive studies to solve the above-described problems in the prior art, the present inventors have found that when lithium iodide is used as a raw material for a solid electrolyte for a lithium ion battery, a lithium iodide hydrate salt in lithium iodide. Greatly affects the decrease in ionic conductivity, and the presence of Na or K in the lithium iodide hydrate when calcining the lithium iodide hydrate to obtain an anhydrous lithium iodide, It was found that the transition from the lithium iodide hydrate salt to the anhydrous lithium iodide salt hardly occurred, and the present invention was completed.

  That is, the present invention (1) relates to (a) a diffraction peak near 2θ = 25.8 ° derived from (a) lithium iodide anhydride and (b) 2θ derived from lithium iodide monohydrate in X-ray diffraction analysis. An intensity ratio of diffraction peaks in the vicinity of 20.7 ° ((b / a) × 100) is 3% or less, and an anhydrous lithium iodide is provided.

  Moreover, this invention (2) is by baking the lithium iodide hydrate salt whose content of Na and K is 20 mass ppm or less in total at 300-440 degreeC by inert gas atmosphere or a vacuum. The present invention provides a method for producing an anhydrous lithium iodide salt, comprising a baking step for obtaining an anhydrous lithium iodide salt.

  Moreover, this invention (3) provides the solid electrolyte manufactured using the lithium iodide anhydrous salt of the said this invention (1) as a raw material.

Further, the present invention (4) includes the anhydrous lithium iodide salt of the present invention (1) and one or more of Li ₂ S, P ₂ S ₅ , SiS ₂ , GeS ₂ and B ₂ S ₃ , A solid electrolyte obtained by reacting is prepared.

  Moreover, this invention (5) provides the lithium ion battery in which the solid electrolyte in any one of the said invention (3) or (4) is used.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium iodide which can make ion conductivity high can be provided. Moreover, according to this invention, the solid electrolyte with high ion conductivity can be provided.

2 is an X-ray diffraction pattern of anhydrous lithium iodide obtained in Example 1 and Comparative Example 2. FIG. 2 is an X-ray diffraction pattern of anhydrous lithium iodide obtained in Comparative Example 1. FIG. 6 is an X-ray diffraction pattern of anhydrous lithium iodide obtained in Comparative Example 5. FIG.

  The anhydrous lithium iodide salt of the present invention is derived from (b) lithium iodide monohydrate with respect to a diffraction peak around 2θ = 25.8 ° derived from (a) anhydrous lithium iodide in X-ray diffraction analysis. The intensity ratio of diffraction peaks in the vicinity of 2θ = 20.7 ° ((b / a) × 100) is 3% or less, preferably 2% or less. When the intensity ratio of diffraction peaks ((b / a) × 100) is within the above range, ion conductivity is increased. On the other hand, when the intensity ratio of diffraction peaks ((b / a) × 100) exceeds the above range, the ion conductivity decreases.

  The water content of the lithium iodide anhydrous salt of the present invention is preferably 2.0% by mass or less, particularly preferably 1.5% by mass or less. When the water content of the lithium iodide anhydrous salt is in the above range, the ion conductivity is increased. Incidentally, the water content of lithium iodide anhydrous salt, 5 g of a sample was collected in a magnetic crucible, and the weight reduction rate when heated at 300 ° C. for 1 hour in an inert gas atmosphere was expressed as lithium iodide anhydrous salt. Of water content.

  The content of Fe in the anhydrous lithium iodide of the present invention is preferably 10 ppm by mass or less, and the content of Cu is preferably 10 ppm by mass or less, the content of Fe is 5 ppm by mass or less, and Cu It is particularly preferable that the content of is 5 mass ppm or less. When the content of Fe and Cu in the lithium iodide anhydrous salt is in the above range, the risk of short circuit of the battery due to the conductive impurities of Fe and Cu is reduced. The contents of Fe and Cu are measured by the ICP-AES method or the like.

  The method for producing an anhydrous lithium iodide salt according to the present invention comprises a lithium iodide hydrate salt having a total content of Na and K of 20 mass ppm or less at 300 to 440 ° C. in an inert gas atmosphere or under vacuum. A method for producing an anhydrous lithium iodide salt comprising a firing step of obtaining an anhydrous lithium iodide salt by firing.

  The baking step according to the method for producing anhydrous lithium iodide of the present invention is a step of obtaining lithium iodide anhydrous salt by transferring lithium iodide hydrate to anhydrous salt by baking lithium iodide hydrated salt. It is.

  The lithium iodide hydrate salt related to the firing step is a firing raw material fired in the firing step, and is lithium iodide containing water as hydrated water. The lithium iodide hydrate salt related to the firing step is not limited to the monohydrate salt, and may be a dihydrate salt or a trihydrate salt. Of these, the monohydrate salt is preferable in that the firing step can be performed efficiently.

  The content of Na and K in the lithium iodide hydrate salt relating to the firing step is 20 mass ppm or less, preferably 10 mass ppm or less in total of Na and K. When the total content of Na and K in the lithium iodide hydrate salt is in the above range, the transition from the hydrate salt to the anhydrous salt is likely to occur. On the other hand, when the total content of Na and K in the lithium iodide hydrate salt exceeds the above range, Na or K inhibits the transition from the hydrate salt to the anhydrous salt. (B) Lithium iodide 1 water with respect to the diffraction peak in the vicinity of 2θ = 25.8 ° derived from (a) lithium iodide anhydride in the X-ray diffraction analysis of lithium iodide after calcination due to excessive salt content The intensity ratio ((b / a) × 100) of diffraction peaks in the vicinity of 2θ = 20.7 ° derived from the Japanese product exceeds 3%, and as a result, the ionic conductivity is lowered.

  The content of Cl and Br in the lithium iodide hydrate salt in the firing step is preferably such that the Cl content is 1000 ppm or less and the Br content is 1000 ppm or less, and particularly preferably the Cl content is 500 ppm or less and Br. Content is 1000 ppm or less. When the content of Cl and Br in the lithium iodide hydrate salt is in the above range, the diffraction peak intensity ratio ((b / a) × 100) of the anhydrous lithium iodide after firing becomes small.

  In the firing step, the firing temperature when firing the lithium iodide hydrate salt is 300 to 440 ° C, preferably 350 to 400 ° C, and particularly preferably 350 to 380 ° C. When the firing temperature in the firing step is in the above range, the transition from the lithium iodide hydrate salt to the anhydrous salt can be performed efficiently. On the other hand, if the calcination temperature is less than the above range, the transition from lithium iodide hydrate salt to anhydrous salt is difficult to occur, so that the amount of hydrate salt after calcination is too large. Since it exceeds the melting point of lithium bromide, the adhesion to the firing container increases too much.

  In the firing step, the firing time for firing the lithium iodide hydrate is appropriately selected depending on the amount of the lithium iodide hydrate to be fired, preferably 4 to 24 hours, particularly preferably 6 to 15 hours. is there.

  In the firing step, the atmosphere when firing the lithium iodide hydrate salt is an inert gas atmosphere or a vacuum. Examples of the inert gas include nitrogen gas, helium gas, and argon gas. Note that “under vacuum” refers to a vacuum atmosphere with a gauge pressure of −0.09 MPaG or less, preferably −0.10 MPaG or less.

  After performing the firing step, the obtained lithium iodide anhydrous salt is cooled in a glove box, a vacuum desiccator or the like in a state where it is not in contact with air, and pulverized as necessary.

  The lithium iodide hydrate salt relating to the firing step may be produced by any production method, but the first embodiment of the method for producing lithium iodide hydrate salt described below (hereinafter referred to as lithium iodide hydrate salt) Lithium iodide hydrated salt produced by the production method (1) is obtained, so that a lithium iodide hydrated salt with extremely low contents of Na and K can be obtained. Is preferable in that the diffraction peak intensity ratio ((b / a) × 100) is small.

  The lithium iodide hydrate production method (1) comprises a reaction raw material lithium compound, iodine and a reducing agent having no Na and K in contact in an aqueous solvent, and the reaction raw material lithium compound This is a method for producing a lithium iodide hydrate, which obtains a lithium iodide hydrate by carrying out an iodination reaction step of performing iodination.

  Examples of the lithium compound as a reaction raw material related to the iodination reaction step include lithium hydroxide, lithium carbonate, lithium chloride, lithium nitrate, and lithium sulfate. Among these, as a lithium compound as a reaction raw material, an anion is incorporated as an impurity in lithium iodide during the concentration or drying process after the iodination reaction step, which causes a decrease in ionic conductivity. Lithium hydroxide and lithium carbonate are preferred in that there is no problem.

  The lithium compound as the reaction raw material is preferably as less as possible, and in particular, the Na and K contents are the total amount of Na and K, preferably 20 ppm by mass or less, particularly preferably 10 ppm by mass or less. Further, the content of Cl and Br in the lithium compound of the reaction raw material is preferably 1000 ppm by mass or less, and particularly preferably 500 ppm by mass or less.

  The iodine of the reaction raw material in the iodination reaction step is preferably as less as possible, and the purity is particularly preferably 95% by mass or more, and more preferably 98% by mass or more. In particular, the content of Na and K in the iodine of the reaction raw material relating to the iodination reaction step is preferably 20 mass ppm or less, particularly preferably 10 mass ppm or less, as the total amount of Na and K. Further, the content of Cl and Br in iodine of the reaction raw material relating to the iodination reaction step is preferably 1000 ppm by mass or less, and particularly preferably 500 ppm by mass or less.

  The reducing agent according to the iodination reaction step is a reducing agent having neither Na nor K. The reducing agent that does not have Na and K refers to a compound that does not have any element of Na and K in the molecule. Examples of the reducing agent in the iodination reaction step include alcohols such as methanol and ethanol, organic acids such as formic acid and succinic acid, saccharides such as sucrose and glucose, and hydrazines. The reducing agent according to the iodination reaction step is preferably as less as possible, more preferably 95% by mass or more, and more preferably 98% by mass or more. In particular, the content of Na and K in the reducing agent according to the iodination reaction step is a total amount of Na and K, preferably 20 ppm by mass or less, particularly preferably 10 ppm by mass or less. Further, the content of Cl and Br in the reducing agent in the iodination reaction step is preferably 1000 ppm by mass or less, particularly preferably 500 ppm by mass or less.

  Examples of hydrazines relating to reducing agents that do not have Na and K include hydrated hydrazine. The hydrazines related to the reducing agent not containing Na and K may be any compound that can cause hydrazine to exist in an aqueous solvent other than hydrated hydrazine, such as hydrazine carbonate, hydrazine sulfate, Hydrazine hydrochloride, hydrazine hydrobromide, adipic hydrazide, phenyl hydrazide, carbodihydrazide, isophthalic acid dihydrazide, sebacic acid hydrazide, dodecanedihydrazide, benzophenone hydrazide, stearic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, maleic acid dihydrazide, maleic acid dihydrazide Examples include acid hydrazide monopotassium, maleic acid hydrazide monosodium, benzenesulfonyl hydrazide, monomethyl hydrazine, citric acid hydrazide, and p-toluenesulfonyl hydrazide. Among these, as hydrazines related to reducing agents not containing Na and K, hydrazine is decomposed into nitrogen and water after the reaction, so that there is no contamination by impurities by-products derived from the reducing agent. Is preferable.

The aqueous solvent related to the iodination reaction step is a solvent in which the iodination reaction is performed. The aqueous solvent used in the iodination reaction step is pure water from which ionic impurities such as Na, K, Ca, Fe, Cu, Cl, and SO ₄ have been removed by an ion exchange resin. It is preferable in that a lithium iodide hydrate can be obtained, which can prevent mixing of ionic impurities and has few impurities that cause low ionic conductivity.

  In the iodination reaction step, the ratio of the amount of the lithium compound used as the reaction material to the amount of the iodine used as the reaction material is expressed in terms of the Li atom in the lithium compound of the reaction material relative to the number of moles of I atom in the reaction material iodine. The molar ratio (Li / I) is preferably 0.98 to 1.02, particularly preferably 0.99 to 1.01.

  In the iodination reaction step, the amount of reducing agent used is preferably equivalent to the amount of iodine used in terms of reducing remaining iodine and reducing contamination from the reducing agent. In the iodination reaction step, when iodine is divided and added to the aqueous solvent, it is preferable to use a reducing agent equivalent to the amount of iodine added for each divided addition.

  The reducing agent having no lithium compound, iodine, Na and K as the raw materials for the iodination reaction step has a Fe content of 10 mass ppm or less and a Cu content of 10 mass ppm or less. It is particularly preferable that the Fe content is 5 mass ppm or less and the Cu content is 5 mass ppm or less. When the contents of these Fe and Cu are in the above range, the risk of short circuit of the battery due to the conductive impurities of Fe and Cu is reduced.

  In the iodination reaction step, the amount of water solvent used is not particularly limited. When a poorly soluble compound such as lithium carbonate is used as the reaction raw material lithium compound, the concentration of the slurry is set so that the concentration of the lithium iodide aqueous solution used for concentration in the concentration operation after the iodination reaction step does not become too low. Is preferably about 10 to 40% by mass.

  In the iodination reaction step, the method of contacting the reaction raw material lithium compound, iodine, and the reducing agent not containing Na and K in an aqueous solvent is not particularly limited, but the reaction raw material lithium compound is not limited. A method of adding iodine and a reducing agent to a dissolved or dispersed aqueous solvent is preferable because the reaction can be easily controlled.

  In the method of adding iodine and a reducing agent to an aqueous solvent containing a lithium compound, when iodine and the reducing agent are added to an aqueous solvent containing a lithium compound, it reacts rapidly. It is preferable to divide and add to an aqueous solvent containing a lithium compound. At this time, each time iodine is added in portions, it is preferable to add a necessary amount of a reducing agent to complete the reaction in accordance with the amount of iodine added in portions. That is, an amount of iodine necessary for the reaction is added in a plurality of times to the aqueous solvent containing the lithium compound, and the amount of reducing agent necessary for the added iodine to react for each divided addition of iodine. It is preferable to carry out the iodination reaction step by adding.

  When iodine is dividedly added to an aqueous solvent containing a lithium compound, the amount of iodine added per time is preferably 1/100 to 1/20 of the amount of iodine used. After a while after adding iodine to the aqueous solvent containing the lithium compound, the reaction solution turns brown due to the dissolution of iodine ions, so it is reduced to the aqueous solvent containing the lithium compound until this color returns to the original color. What is necessary is just to add an agent. When iodine is dividedly added to an aqueous solvent containing a lithium compound, the number of divisions is not particularly limited.

  In the iodination reaction step, the reaction temperature is not particularly limited, but if it is 80 ° C. or higher, the reaction is too rapid, so that it easily evaporates out of the reaction system before iodine reacts with the lithium compound. Is preferred.

  In the iodination reaction step, the reaction time is not particularly limited, and after bringing a predetermined amount of a lithium compound as a reaction raw material into contact with iodine and a reducing agent not containing Na and K, the reaction solution of iodine is contacted. The reaction is carried out until the brown color disappears. In addition, there is no brown coloration of the reaction solution due to iodine even after 30 minutes or more after contacting a predetermined amount of the lithium compound of the reaction raw material, iodine, and a reducing agent not containing Na and K. If not, a small amount of powdered lithium carbonate or lithium hydroxide is added to the reaction solution to complete the reaction. At this time, in order to complete the reaction, the reaction is continued for 0.25 hours or more, preferably 0.5 to 2 hours.

  After performing the iodination reaction step, the reaction solution is filtered to separate a trace amount of insoluble residue, and the filtrate is concentrated and dried to obtain lithium iodide monohydrate crystals. The drying temperature at this time is preferably a temperature range in which lithium iodide trihydrate becomes monohydrate, specifically, 80 to 150 ° C. Lithium iodide after drying is self-dissolved in a monohydrate salt, and is obtained as a massive solid by cooling. The drying atmosphere may be vacuum, air, or an inert gas atmosphere such as argon gas, helium gas, nitrogen gas, etc. However, when drying is performed in air at a drying temperature of 120 ° C. or higher, lithium iodide is used. Since the hydrated salt is decomposed, when drying at 120 ° C. or higher, it is preferably performed in a vacuum or in an inert gas atmosphere.

  Thus, in the X-ray diffraction analysis of the lithium iodide anhydrous salt obtained by performing the method for producing the lithium iodide anhydrous salt of the present invention, (a) around 2θ = 25.8 ° derived from the lithium iodide anhydrous The intensity ratio ((b / a) × 100) of the diffraction peak in the vicinity of 2θ = 20.7 ° derived from (b) lithium iodide monohydrate with respect to the diffraction peak is 3% or less. Furthermore, it is preferable that the content of Fe of the lithium iodide anhydrous salt obtained by carrying out the method for producing the anhydrous lithium iodide of the present invention is 10 ppm or less and the content of Cu is 10 ppm or less.

  The lithium iodide anhydrous salt of the present invention and the lithium iodide anhydrous salt obtained by carrying out the method for producing the lithium iodide anhydrous salt of the present invention are suitable as a raw material for producing a solid electrolyte of a lithium ion battery.

The solid electrolyte of the present invention is a solid electrolyte produced by using, as a raw material, lithium iodide anhydrous salt obtained by performing the production method of the lithium iodide anhydrous salt of the present invention or the lithium iodide anhydrous salt of the present invention. Is the lithium iodide anhydrous salt obtained by carrying out the method for producing the lithium iodide anhydrous salt of the present invention or the lithium iodide anhydrous salt of the present invention, and Li ₂ S, P ₂ S ₅ , SiS ₂ , GeS ₂ and B ₂ S. ₃ is a solid electrolyte obtained by reacting at least one of the _three sulfides.

Examples of the solid electrolyte of the present invention include LiI—P ₂ S ₅ —Li ₂ S, LiI—SiS ₂ —Li ₂ S, LiI—GeS ₂ —Li ₂ S, and the like.

  The physical properties of the sulfide relating to the solid electrolyte of the present invention are not particularly limited, but from the viewpoint of facilitating uniform mixing with lithium iodide anhydride, the average particle diameter is preferably 100 μm or less, and is 20 to 80 μm. It is particularly preferred.

In the solid electrolyte of the present invention, the blending ratio of lithium iodide anhydrous salt and sulfide is appropriately selected according to the composition of the solid electrolyte. For example, when obtaining a solid electrolyte having a composition of LiI / P ₂ S ₅ / Li ₂ S = 0.30 / 0.30 / 0.40 from anhydrous lithium iodide, phosphorus sulfide and lithium sulfide The molar ratio of phosphorus sulfide to lithium iodide and the molar ratio of lithium sulfide to lithium iodide are both 2.2 to 2.4, preferably 2.30 to 2.36.

  The solid electrolyte of the present invention includes, for example, the lithium iodide anhydrous salt of the present invention or the lithium iodide anhydrous salt obtained by the production method of the lithium iodide anhydrous salt of the present invention, and the sulfide according to the solid electrolyte of the present invention. Is obtained by reacting with mechanical milling. Examples of the equipment that performs mechanical milling include grinding equipment such as a bead mill, a planetary ball mill, and a vibration mill, that is, equipment that causes granular media to be present in the powder to be mixed and flows them at high speed. It is done. Then, mechanical energy is added to the lithium iodide anhydride and sulfide by the granular medium by causing the lithium iodide anhydride, sulfide, and the granular medium to flow at high speed.

  By controlling the rotation speed and rotation time of mechanical milling, the processed product can be made finer and homogeneous, but appropriate conditions can be selected appropriately according to the type of equipment, the type of raw material, and the intended use. It is preferable to perform mechanical milling. For example, when a planetary ball mill is used, it is preferable that the rotation speed is 50 to 600 rotations / minute and the treatment is performed for 2 to 60 hours.

  After the mechanical milling treatment, if necessary, the mechanical milling treatment product can be heat-treated at a temperature higher than the glass transition.

  The solid electrolyte of the present invention is suitably used for constituent members of a solid lithium ion battery, for example, an electrolyte layer, a positive electrode layer, a negative electrode layer, and the like.

  The lithium ion battery of the present invention is a lithium ion battery in which the solid electrolyte of the present invention is used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.

  Table 1 shows the quality of the reagents used in Examples and Comparative Examples.

１）表中「−」は、１質量ｐｐｍ以下であることを示す。
ＬｉＯＨ・Ｈ_２Ｏ（試薬Ａ）：ＬｉＯＨ含有量 ５７．７８質量％
ＬｉＯＨ・Ｈ_２Ｏ（試薬Ｂ）：ＬｉＯＨ含有量 ５６．８０質量％
Ｌｉ_２ＣＯ_３：Ｌｉ_２ＣＯ_３含有量 ９９．６５質量％
ヨウ素：Ｉ含有量 ９９質量％以上、純正化学株式会社製、試薬１級
ＫＩ：ＫＩ含有量 ９９．５質量％、純正化学株式会社製
水加ヒドラジン：８０質量％水溶液、純正化学株式会社製、試薬１級

1) “-” in the table indicates 1 ppm by mass or less.
LiOH.H ₂ O (reagent A): LiOH content 57.78% by mass
LiOH.H ₂ O (reagent B): LiOH content 56.80% by mass
_{Li 2 CO 3: Li 2 CO} 3 content of 99.65 wt%
Iodine: I content 99% by mass or more, Junsei Chemical Co., Ltd., reagent grade 1 KI: KI content 99.5% by mass, Junsei Chemical Co., Ltd. Hydrated hydrazine: 80% by mass aqueous solution, Junsei Chemical Co., Ltd. Reagent grade 1

Example 1
<Production of lithium iodide hydrated salt (iodination reaction step)>
67.1 g of lithium hydroxide monohydrate (reagent A) was weighed into a 1 L beaker. Thereto, 350 mL of ion exchange water was added and dissolved to prepare an aqueous lithium hydroxide solution. Then, apart from this, 203.0 g of iodine was weighed into a mayonnaise bottle. After weighing, the lid was capped to prevent volatilization of iodine. Next, 25 g of hydrated hydrazine was weighed into a 50 ml beaker.
Next, (1) 5 g of iodine was added while stirring the lithium hydroxide aqueous solution. During the addition, it was confirmed that the color of the aqueous solution changed from colorless to brown due to elution of iodine ions. Next, (2) the hydrated hydrazine was added dropwise while stirring the lithium hydroxide aqueous solution to which iodine was added. It was confirmed that the color of the aqueous solution changed from brown to colorless. Subsequently, after confirming that the foaming of nitrogen gas due to the dropwise addition of hydrazine was eliminated, the operation (1) was performed again, and then the operation (2) was performed. Thereafter, the operations of (1) and (2) were repeated, and the operations were repeated until the initially weighed iodine disappeared.
After adding the whole amount of iodine, hydrazine hydrate was added dropwise, and the point at which the color of the reaction solution became colorless was regarded as the end point of the reaction.
Next, 1 g of high purity lithium carbonate was added and stirred to react with excess iodine. The reaction solution was filtered to separate a trace amount of insoluble residue. For filtration, 5C filter paper manufactured by Advantech was used as a filter. The filtrate was then heated to evaporate the water and concentrated. After the concentration, the concentrate was dried at 120 ° C. for 15 hours using a dryer (Yamato Blow Constant Temperature Dryer DKN402), cooled and solidified to obtain lithium iodide hydrate A.
About the obtained lithium iodide hydrate salt A, the content of impurities was measured. The results are shown in Table 2.

<Manufacture of anhydrous lithium iodide (firing process)>
Next, the lithium iodide hydrate A obtained as described above was calcined at 350 ° C. for 8 hours in a nitrogen atmosphere in an atmosphere preparation furnace (manufactured by Motoyama Co., Ltd., MS electric furnace NKC type). After firing, the fired product was taken out of the furnace, placed in a vacuum desiccator (−0.10 MPaG), and cooled under vacuum to obtain anhydrous lithium iodide salt B.
The obtained lithium iodide anhydrous salt B was measured for water content, diffraction peak intensity ratio ((b / a) × 100), impurity content, and ionic conductivity. The results are shown in Table 3.

(Comparative Example 1)
<Production of lithium iodide hydrate salt>
A potassium iodide solution was prepared by weighing 166 g of potassium iodide into a 1 L beaker and adding 500 ml of ion-exchanged water. Next, 36.9 g of lithium carbonate was added and stirred and dispersed. Next, 208 g of 17.5% hydrochloric acid was added dropwise over 10 minutes to carry out the reaction. After completion of the reaction, the reaction solution showed acidity (pH = 1.5), so powdery lithium carbonate was added to adjust the pH to 7.0.
Thereafter, the reaction solution was filtered, the filtrate was concentrated, the concentrate was dried, cooled and solidified in the same manner as in Example 1 to obtain a lithium iodide hydrate salt a1.
About the obtained lithium iodide hydrate salt a1, the content of impurities was measured. The results are shown in Table 2.
<Production of anhydrous lithium iodide>
Next, a lithium iodide hydrate salt a1 was used instead of the lithium iodide hydrate salt A, and a calcination time of 6 hours was used instead of the calcination time of 8 hours. Lithium iodide anhydrous salt b1 was obtained.
Table 3 shows the measurement results of the water content, diffraction peak intensity ratio ((b / a) × 100), impurity content, and ionic conductivity of the obtained lithium iodide anhydrous salt b1.

(Comparative Example 2)
<Production of lithium iodide hydrate salt>
Lithium iodide hydrate A was obtained in the same manner as in Example 1.
<Production of anhydrous lithium iodide>
It replaced with the calcination temperature 350 degreeC, and performed by the method similar to Example 1 except having set it as the calcination temperature 280 degreeC, and obtained lithium iodide anhydrous salt b2.
Table 3 shows the measurement results of the water content, diffraction peak intensity ratio ((b / a) × 100), impurity content, and ionic conductivity of the obtained lithium iodide anhydrous salt b2.

(Comparative Example 3)
<Production of lithium iodide hydrate salt>
Lithium iodide hydrate salt a2 was obtained in the same manner as in Example 1 except that lithium hydroxide monohydrate (sample B) was used instead of lithium hydroxide monohydrate (sample A).
About the obtained lithium iodide hydrate salt a2, the content of impurities was measured. The results are shown in Table 2.
<Production of anhydrous lithium iodide>
The lithium iodide anhydrous salt b3 was obtained in the same manner as in Example 1 except that the lithium iodide hydrate salt a2 was used instead of the lithium iodide hydrate salt A.
Table 3 shows the measurement results of the water content, diffraction peak intensity ratio ((b / a) × 100), impurity content, and ionic conductivity of the obtained lithium iodide anhydrous salt b3.

(Comparative Example 4)
Commercially available anhydrous lithium iodide (Kishida Chemical Co., Ltd.) was used as anhydrous lithium iodide salt b4 of Comparative Example 4.
Table 3 shows the measurement results of water content, diffraction peak intensity ratio ((b / a) × 100), impurity content, and ion conductivity of anhydrous lithium iodide b4.

(Comparative Example 5)
Lithium iodide hydrate b4 of Comparative Example 4 was fired at 350 ° C. for 8 hours in a nitrogen atmosphere in an atmosphere preparation furnace (manufactured by Motoyama Co., Ltd., MS electric furnace NKC type). After firing, the fired product was removed from the furnace, placed in a vacuum desiccator (−0.10 MPaG), and cooled under vacuum to obtain anhydrous lithium iodide salt b5.
Table 3 shows the measurement results of water content, diffraction peak intensity ratio ((b / a) × 100), impurity content, and ionic conductivity of the obtained lithium iodide anhydrous salt b5.

１）表中「＊」は、１０００質量ｐｐｍ以下であることを示す。

1) “*” in the table indicates 1000 ppm by mass or less.

１）回折ピークの強度比：（ａ）ヨウ化リチウム無水物に由来する２θ＝２５．８°付近の回折ピークに対する（ｂ）ヨウ化リチウム１水和物に由来する２θ＝２０．７°付近の回折ピークの強度比（（ｂ／ａ）×１００）
２）表中「＊」は、１０００質量ｐｐｍ以下であることを示す。

1) Intensity ratio of diffraction peaks: (a) Near diffraction angle of 2θ = 25.8 ° derived from anhydrous lithium iodide and (b) Near 2θ = 20.7 ° derived from lithium iodide monohydrate Intensity ratio of diffraction peaks ((b / a) × 100)
2) In the table, “*” indicates 1000 ppm by mass or less.

<Analysis of water content of lithium iodide>
5 g of a sample was collected in a magnetic crucible, and the weight reduction rate when heated at 300 ° C. for 2 hours in a nitrogen atmosphere was measured. The weight reduction rate was defined as the water content.

<XRD diffraction analysis>
Powder X-ray diffraction analysis was performed using a sample obtained by pulverizing lithium iodide in a glove box, and the charts of FIGS. 1 to 3 were obtained. For measurement by X-ray diffraction (XRD), CuKα was used as a radiation source, and Ultimate IV type manufactured by Rigaku Corporation was used as a measuring device.

<Measurement of Impurity Na and K Content>
1.0 g of a sample was dissolved in ion-exchanged water, 1 ml of concentrated nitric acid was added to make a total volume of 50 ml, and measurement was performed with an atomic absorption analyzer under nitric acid acidity.

<Measurement of impurity Cl content>
1.0 g of a sample was dissolved in ion-exchanged water to make a total volume of 50 ml, and measured with an ion chromatography analyzer.

<Measurement of Impurity Br Content>
A sample (0.1 g) was dissolved in ion-exchanged water to make a total volume of 100 ml and measured with an ion chromatography analyzer.

<Measurement of impurities Fe, Cu, Ca>
1.0 g of a sample was dissolved in ion-exchanged water, 1 ml of concentrated nitric acid was added to make a total amount of 50 ml, and measurement was performed with an ICP-AES analyzer under nitric acid acidity.

<Synthesis of solid electrolyte and measurement of ionic conductivity>
Anhydrous lithium iodide 0.514 g (45 mol%), phosphorus pentasulfide (Aldrich reagent) 0.341 g (18 mol%), lithium sulfide (Nippon Kagaku Kogyo) 0.145 g (37 mol%) were weighed. Then, treatment was performed at 400 rpm for 20 hours with a planetary ball mill to obtain a solid electrolyte.
Next, after sandwiching both surfaces of the obtained solid electrolyte with 0.30 g of electrodes (electrodes composed of 95% by mass of nickel and 5% by mass of tin) and pressurizing at 20 MPa for 5 minutes, a three-layer structure molded body was obtained. Obtained.
Next, using the obtained molded body as a measurement sample, ion conductivity was measured using an AC impedance measuring device (Solartron 1267, manufactured by Toyo Technica Co., Ltd.).

Claims (10)

  (B) Diffraction peak near 2θ = 20.7 ° derived from lithium iodide monohydrate (b) Diffraction peak near 2θ = 25.8 ° derived from anhydrous lithium iodide in X-ray diffraction analysis The lithium iodide anhydrous salt characterized by having a strength ratio ((b / a) × 100) of 3% or less.   The anhydrous lithium iodide salt according to claim 1, wherein the water content is 2.0 mass% or less.   3. The lithium iodide anhydrous salt according to claim 1, wherein the Fe content is 10 mass ppm or less and the Cu content is 10 mass ppm or less.   Firing lithium iodide hydrated salt having a total content of Na and K of 20 mass ppm or less at 300 to 440 ° C. in an inert gas atmosphere or under vacuum to obtain an anhydrous lithium iodide salt The manufacturing method of the lithium iodide anhydrous salt characterized by having a process.   By performing an iodination reaction step in which a lithium compound as a reaction raw material, iodine, and a reducing agent not containing Na and K are brought into contact with each other in an aqueous solvent to iodinate the lithium compound as the reaction raw material. The method for producing an anhydrous lithium iodide salt according to claim 4, wherein the hydrated lithium iodide salt is obtained.   6. The method for producing an anhydrous lithium iodide salt according to claim 5, wherein the reaction raw material lithium compound is lithium carbonate and the reducing agent is hydrazine.   The amount of iodine necessary for the reaction is added to the aqueous solvent containing the lithium compound as the reaction raw material in a plurality of times, and the amount of iodine necessary for the reaction of the added iodine each time the iodine is added. The method for producing an anhydrous lithium iodide salt according to claim 5, wherein the iodide reaction step is performed by adding the reducing agent.   The solid electrolyte manufactured using the lithium iodide anhydrous salt of any one of Claims 1-3 as a raw material. The lithium iodide anhydrous salt according to any one of claims 1 to 3, and at least one of Li ₂ S, P ₂ S ₅ , SiS ₂ , GeS ₂ and B ₂ S ₃ are reacted. Solid electrolyte obtained by   A lithium ion battery in which the solid electrolyte according to claim 8 is used.

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