JP2017139188A - Method for suppressing temporal deterioration of ion conductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for suppressing temporal deterioration generated after exposing an ion conductor containing LiBHand an alkali metal compound to a high temperature once.SOLUTION: According to an embodiment, there is provided a method for suppressing temporal deterioration of an ion conductor containing LiBHand an alkali metal compound represented by the following formula (1): MX (1), where M represents an alkali metal atom selected from a group consisting of a lithium atom, a rubidium atom and a cerium atom and X represents a halogen atom, by mixing the LiBHand the alkali metal compound at a molar ratio of LiBH:alkali metal compound=1:1 to 2.6:1.SELECTED DRAWING: None

Description

  The present invention relates to a method for suppressing deterioration of an ion conductor over time.

  In recent years, the demand for lithium ion secondary batteries has increased in applications such as portable information terminals, portable electronic devices, electric vehicles, hybrid electric vehicles, and stationary power storage systems. However, the current lithium ion secondary battery uses a flammable organic solvent as an electrolyte, and requires a strong exterior so that the organic solvent does not leak. In addition, in a portable personal computer or the like, there are restrictions on the structure of the device, such as the need to take a structure in preparation for the risk that the electrolyte should leak.

  Furthermore, the use is extended to mobile bodies such as automobiles and airplanes, and a large capacity is required for stationary lithium ion secondary batteries. Under such circumstances, safety tends to be more important than before, and efforts are being made to develop all-solid lithium ion secondary batteries that do not use harmful substances such as organic solvents.

  The use of oxides, phosphate compounds, organic polymers, sulfides and the like as solid electrolytes in all solid-state lithium ion secondary batteries has been studied.

  However, oxides and phosphoric acid compounds have the property that the particles are hard. Therefore, in order to form a solid electrolyte layer using these materials, generally, sintering at a high temperature of 600 ° C. or higher is required, which is troublesome. Furthermore, when an oxide or a phosphoric acid compound is used as the material for the solid electrolyte layer, there is a disadvantage that the interfacial resistance with the electrode active material is increased. The organic polymer has a drawback that the lithium ion conductivity at room temperature is low and the conductivity rapidly decreases as the temperature decreases.

Regarding the new lithium ion conductive solid electrolyte, it was reported in 2007 that the high temperature phase of LiBH ₄ which is a complex hydride solid electrolyte has high lithium ion conductivity (Non-patent Document 1). LiBH ₄ has a low density, and when this is used as a solid electrolyte, a light battery can be produced. In addition, since LiBH ₄ is stable even at a high temperature (for example, about 200 ° C.), a heat-resistant battery can be manufactured.

LiBH ₄ has a problem that the lithium ion conductivity is greatly lowered at a phase transition temperature of less than 115 ° C. Therefore, in order to obtain a solid electrolyte having high lithium ion conductivity even at a phase transition temperature of less than 115 ° C., a solid electrolyte combining LiBH ₄ and an alkali metal compound has been proposed. For example, in 2009, it was reported that a solid solution obtained by adding LiI to LiBH ₄ can maintain a high-temperature phase even at room temperature (Non-patent Document 2 and Patent Document 1). Moreover, since the complex hydride solid electrolyte made of this solid solution is stable against metallic lithium and metal lithium can be used for the negative electrode, a high-capacity all-solid battery can be produced (Patent Document 2 and Patent Document 3). ).

Japanese Patent No. 5187703 International Publication No. 2015-030052 International Publication No. 2015-030053

Applied Physics Letters (2007) 91, p. 224103 Journal of the American Chemical Society (2009), 131, p. 894-895

As described above, a solid electrolyte obtained by combining LiBH ₄ and an alkali metal compound is a promising solid electrolyte that exhibits high lithium ion conductivity even at a temperature below 115 ° C. and is excellent in heat resistance. However, the present inventors have a new problem that when such a solid electrolyte (or ionic conductor) is once exposed to a high temperature and then returned to room temperature, its ionic conductivity may be greatly reduced with time. discovered. Therefore, an object of the present invention is to provide a method for suppressing deterioration with the lapse of time after an ionic conductor containing LiBH ₄ and an alkali metal compound is once exposed to a high temperature.

As a result of intensive studies to solve the above-mentioned problems, the present inventors once exposed to high temperature by mixing specific LiBH ₄ used for the ion conductor and an alkali metal compound at a specific molar ratio. As a result, the inventors have obtained an unexpected finding that the deterioration over time of the ionic conductor when the temperature is returned to room temperature can be significantly suppressed. The present invention has been completed based on such findings.

That is, the present invention has the characteristics described below.
[1] LiBH ₄ and the following formula (1):
MX (1)
[In the formula (1), M represents an alkali metal atom selected from the group consisting of a lithium atom, a rubidium atom and a cesium atom, and X represents a halogen atom. ]
A method for suppressing deterioration over time of an ionic conductor comprising an alkali metal compound represented by
A method in which the LiBH ₄ and the alkali metal compound are mixed at a molar ratio of LiBH ₄ : alkali metal compound = 1: 1 to 2.6: 1 to suppress deterioration of the ion conductor with time.
[2] The ion conductor is at least 2θ = 23.9 ± 1.2 deg, 25.6 ± 1.5 deg, 27.3 ± 1.5 deg in X-ray diffraction (CuKα: λ = 1.5405４０). The method according to [1], which has diffraction peaks at 35.4 ± 2.0 deg and 42.2 ± 2.0 deg.
[3] The method according to [1] or [2], wherein the alkali metal compound is lithium halide.
[4] The method according to [3], wherein the alkali metal compound is lithium iodide.
[5] The method according to any one of [1] to [4], wherein the mixing is performed by mechanical milling.
[6] The ionic conductivity of the ionic conductor measured when exposed to a temperature of 150 ° C. and then cooled to 25 ° C. is defined as a first ionic conductivity,
When the ionic conductivity of the ionic conductor measured at the time when 148 hours have passed after maintaining the temperature at 25 ° C. from the time of cooling to 25 ° C. is defined as the second ionic conductivity,
Following formula (2):
The method in any one of [1]-[5] whose maintenance rate of ionic conductivity shown by is 45% or more.
[7] The method according to any one of [1] to [6], comprising exposing the ion conductor to a temperature of 90 ° C. to 280 ° C. and then cooling to 25 ° C. after the mixing.
[8] LiBH ₄ and the following formula (1):
MX (1)
[In the formula (1), M represents an alkali metal atom selected from the group consisting of a lithium atom, a rubidium atom and a cesium atom, and X represents a halogen atom. ]
And an alkali metal compound represented by
Molar ratio of the alkali metal compound and the LiBH ₄ is, LiBH _4: alkali metal compound = 1: 1 to 2.6: 1, ion conductor.
[9] Maximum diffraction at 2θ = 26.85 ± 0.14 deg in an X-ray diffraction (CuKα: λ = 1.5405Å) spectrum after exposure to a temperature of 90 ° C. to 280 ° C. and after 1 day at 25 ° C. The ionic conductor according to [8], wherein the intensity is larger than the maximum diffraction intensity at 2θ = 26.60 ± 0.10.
[10] The ionic conductivity of the ionic conductor measured when exposed to a temperature of 150 ° C. and then cooled to 25 ° C. is defined as a first ionic conductivity,
When the ionic conductivity of the ionic conductor measured at the time when 148 hours have passed after maintaining the temperature at 25 ° C. from the time of cooling to 25 ° C. is defined as the second ionic conductivity,
Following formula (2):
The ionic conductor according to [8] or [9], wherein the retention rate of ionic conductivity indicated by is at least 45%.
[11] A solid electrolyte for an all-solid battery, comprising the ionic conductor according to any one of [8] to [10].
[12] An all-solid battery using the solid electrolyte for an all-solid battery according to [11].

  ADVANTAGE OF THE INVENTION According to this invention, the method of suppressing the temporal deterioration of the ionic conductor produced when it returns to room temperature after once exposing to high temperature can be provided.

The figure which shows the ionic conductivity of the ion conductor obtained in Examples 1-3 and Comparative Examples 1-3. The figure which shows the time-dependent deterioration of the ion conductor obtained in Examples 1-3 and Comparative Examples 1-3. The figure which shows the XRD spectrum of the ionic conductor obtained in Examples 1-3 and Comparative Examples 1-3 before heating to 150 degreeC, immediately after a heating, and after 1 day passes at 25 degreeC [(a) Example 1, (B) Example 2, (c) Example 3, (d) Comparative Example 1, (e) Comparative Example 2, (f) Comparative Example 3]. The figure which shows the change of the diffraction peak position of the XRD spectrum by the heating of an ion conductor. Ion conductor (a) obtained by mixing LiBH ₄ and LiI at a molar ratio of LiBH ₄ : LiI = 2.5: 1 and ionic conductor obtained by mixing at a molar ratio of 3.0: 1 (b ) Shows XRD spectra before and after heating to 150 ° C. and after 1 day at 25 ° C. after heating.

  Embodiments of the present invention will be described below. The materials, configurations, and the like described below do not limit the present invention and can be variously modified within the scope of the gist of the present invention.

1. Method for suppressing aging degradation of ionic conductor According to one embodiment of the present invention, LiBH ₄ and the following formula (1):
MX (1)
[In the formula (1), M represents an alkali metal atom selected from the group consisting of a lithium atom, a rubidium atom and a cesium atom, and X represents a halogen atom. ]
Are mixed at a molar ratio of LiBH ₄ : alkali metal compound = 1: 1 to 2.6: 1, to thereby suppress deterioration with time of the ionic conductor.

Conventionally, for example, as described in Examples of Japanese Patent No. 5187703, a method of mixing LiBH ₄ at a ratio of 3 mol or more with respect to 1 mol of an alkali metal compound when an ionic conductor is produced has been performed. It was. However, when the alkali metal compound and LiBH ₄ are mixed in such a ratio, the obtained ionic conductor may have a high ionic conductivity at room temperature after being once exposed to a high temperature and may deteriorate with time. In contrast, according to the method of the present invention, LiBH ₄ and the alkali metal compound are mixed at a molar ratio of LiBH ₄ : alkali metal compound = 1: 1 to 2.6: 1. Deterioration with time of the ionic conductor that occurs when the temperature is returned to room temperature after exposure to water can be greatly suppressed. In the present specification, “the ionic conductor is exposed to a high temperature” is not particularly limited as long as the ionic conductor is in a high temperature state, and the ionic conductor is heated to a high temperature or In addition, when the ion conductor is used as a solid electrolyte, the case where the temperature becomes high due to the reaction of the battery is included.

As LiBH ₄ used in the method of the present invention, a commercially available product can be used. Its purity is preferably 90% or more, and more preferably 95% or more. This is because a compound having a purity within the above range has high performance as an ion conductor. Moreover, LiBH ₄ marketed in a solid state may be used, or LiBH ₄ marketed in a solution state dissolved in a solvent such as THF may be used. In the case of a solution, the purity excluding the solvent is preferably 90% or more, and more preferably 95% or more.

The alkali metal atom as M in the formula (1) is selected from the group consisting of a lithium atom, a rubidium atom, and a cesium atom, and is preferably a lithium atom.
The halogen atom as X in the formula (1) may be an iodine atom, a bromine atom, a fluorine atom, a chlorine atom or the like. X is more preferably an iodine atom.

  Specifically, the alkali metal compound includes lithium halide (eg, LiI, LiBr, LiF or LiCl), rubidium halide (eg, RbI, RbBr, RbF or RbCl), or cesium halide (eg, CsI, CsBr). CsF or CsCl), lithium iodide (LiI), rubidium iodide (RbI) or cesium iodide (CsI) is more preferable, and lithium iodide (LiI) is particularly preferable. . An alkali metal compound may be used individually by 1 type, and may be used in combination of 2 or more type. A preferred combination includes a combination of LiI and RbI.

The mixing ratio of LiBH ₄ and the alkali metal compound is a molar ratio of LiBH ₄ : alkali metal compound = 1: 1 to 2.6: 1, preferably 1: 1 to 2.5: 1, and more preferably. Is 1: 1 to 2.3: 1. When the molar ratio is 1: 1 or more, a sufficient amount of LiBH _{4 in} the ionic conductor can be secured, and high ionic conductivity can be obtained. In addition, when the molar ratio is 2.6: 1 or less, the deterioration over time of the ionic conductor that occurs when the temperature is once returned to room temperature after being exposed to a high temperature can be significantly suppressed.

  When using 2 or more types of alkali metal compounds together, the mixing ratio is not particularly limited. For example, when LiI and another alkali metal compound (preferably RbI or CsI) are used in combination, the molar ratio between LiI and the other alkali metal compound is preferably 1: 1 to 20: 1. : More preferably, it is 1-20: 1. This is because the high temperature phase (phase with high ionic conductivity) can be easily maintained by setting the mixing ratio as described above.

The mixing method of LiBH ₄ and an alkali metal compound is not particularly limited as long as an ionic conductor can be produced. For example, mechanical mixing and a mixing method using a solvent and a solvent described in Japanese Patent No. 5187703 (solution mixing) Among them, mechanical milling is preferable.

A mixing method using a solvent is suitable for manufacturing an ionic conductor in large quantities because the materials can be mixed uniformly. Furthermore, solution mixing does not require a high temperature unlike melt mixing, and the solvent can be removed at 200 ° C. or lower at which LiBH ₄ can stably exist. Incidentally, the solvent used in the solution mixture, which can be used as long as any solvent in which one dissolves the LiBH ₄ and the alkali metal compound, the solvent in which these both are soluble are preferred. This is because, by dissolving both LiBH ₄ and the alkali metal compound, a uniform solution can be obtained, and as a result, an ionic conductor having better ion conductivity can be obtained.

  The solvent is not particularly limited, and various organic solvents can be used. Examples of such an organic solvent include ether solvents such as tetrahydrofuran and diethyl ether, amide solvents such as N, N-dimethylformamide and N, N-dimethylacetamide, and the like. Of these, ether solvents are preferred. Ether solvents that are stable to the raw material and have high solubility of the raw material can be used, such as dimethyl ether, diethyl ether, dibutyl ether, diethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,2-dimethoxyethane, triethylene glycol dimethyl ether. , Cyclopentyl methyl ether, methyl-t-butyl ether, dioxane and the like. Of these, tetrahydrofuran, 2-methyltetrahydrofuran, and cyclopentylmethyl ether are more preferable.

The mixing of LiBH ₄ and the alkali metal compound is preferably performed in an inert gas atmosphere. Examples of the inert gas include helium, nitrogen, and argon, and argon is more preferable.
The mixing time varies depending on the mixing method. For example, when a planetary ball mill is used, the mixing time is 0.5 to 24 hours, and preferably 2 to 20 hours. When a solution is used, it is sufficient if the time for the mixture to be uniform can be secured. Although the time often depends on the production scale, for example, a sufficiently uniform mixture can be obtained by performing for 0.1 to 5 hours.

  In order to advance crystallization of the ionic conductor obtained as described above, heat treatment may be performed. The heating temperature is usually in the range of 50 to 300 ° C, more preferably in the range of 60 to 250 ° C, and particularly preferably 65 to 200 ° C. If the temperature is 50 ° C. or higher, crystallization is likely to occur. On the other hand, if the temperature is 300 ° C. or lower, it is possible to sufficiently suppress the decomposition of the ionic conductor and the alteration of the crystal. In addition, in solution mixing, when heating is performed to remove the solvent, crystallization proceeds simultaneously and is efficient.

  Although the heating time varies slightly in relation to the heating temperature, it is usually sufficiently crystallized in the range of 0.1 to 12 hours. The heating time is preferably 0.3 to 6 hours, more preferably 0.5 to 4 hours. From the viewpoint of suppressing the deterioration of the ionic conductor, the heating time is preferably short.

The ion conductor to which the method of the present invention is applied is at least 2θ = 23.9 ± 1.2 deg, 25.6 ± 1.5 deg, 27.3 in X-ray diffraction (CuKα: λ = 1.5405４０). It is preferable to have diffraction peaks at ± 1.5 deg, 35.4 ± 2.0 deg, and 42.2 ± 2.0 deg. It is more preferable to have diffraction peaks at 2θ = 23.6 ± 0.8 deg, 25.2 ± 0.8 deg, 26.9 ± 1.0 deg, 35.0 ± 1.2 deg, and 41.4 ± 1.2 deg. Preferably, it has diffraction peaks at least 2θ = 23.5 ± 0.5 deg, 24.9 ± 0.5 deg, 26.7 ± 0.5 deg, 34.6 ± 0.7 deg, and 40.9 ± 0.7 deg. Is more preferable. Further, it has diffraction peaks at least at 2θ = 23.5 ± 0.3 deg, 25.0 ± 0.4 deg, 26.7 ± 0.3 deg, 34.6 ± 0.5 deg, and 40.9 ± 0.5 deg. Is particularly preferred. The diffraction peaks of these five regions correspond to the diffraction peaks of the high temperature phase of LiBH ₄ . Even when the temperature is lower than the transition temperature (115 ° C.) of the high-temperature phase of LiBH _4, the material having diffraction peaks in the five regions as described above tends to exhibit high ionic conductivity even below the transition temperature.

As described above, once the conventional ionic conductor is exposed to a high temperature, the ionic conductivity greatly decreases with time even if it is subsequently cooled to room temperature. Without being bound by theory, an ionic conductor having a high ratio of LiBH ₄ (specifically, an ionic conductor in which LiBH ₄ is mixed at a ratio of 3 mol or more with respect to 1 mol of an alkali metal compound) It is presumed that when heated to a high temperature, a new crystal structure is formed due to phase transition, and the crystal structure is unstable. This point will be described below with reference to the graphs of FIGS.

FIG. 4 is an XRD spectrum after heating and cooling an ionic conductor obtained by mixing LiBH ₄ and LiI (alkali metal compound) at a molar ratio of LiBH ₄ : LiI = 3: 1. . In FIG. 4, the region of 2θ = 22 to 28 ° is particularly enlarged. As can be seen from this graph, it is observed that a part of the peak is shifted to the high angle side in the sample heated at 100 ° C. as compared with the peak of the sample heated at 80 ° C. It can be seen that in the sample heated to a higher temperature (120 ° C.), the peak observed in the sample heated to 80 ° C. is almost completely shifted. From this, it is presumed that a phase transition occurs around 80 ° C. to 100 ° C. and a new crystal structure is developed.

In the ionic conductor having a high LiBH ₄ ratio, a part of the peak shifted to the high angle side shifts to the low angle side after one day at 25 ° C. after cooling (FIG. 5B). On the other hand, in an ionic conductor obtained by mixing LiBH ₄ and LiI (alkali metal compound) at a molar ratio of LiBH ₄ : LiI = 2.5: 1, such a peak shift toward the low angle side is Not observed (FIG. 5 (a)). Although details are unknown, it is speculated that the existence of such a new unstable crystal structure causes a deterioration over time in an ion conductor having a high LiBH ₄ ratio.

The ionic conductivity of the ionic conductor measured when the ionic conductor to which the method according to the present invention is applied is exposed to a temperature of 150 ° C. and then cooled to 25 ° C. is defined as a first ionic conductivity,
When the ionic conductivity of the ionic conductor measured at the time when 148 hours have passed after maintaining the temperature at 25 ° C. from the time of cooling to 25 ° C. is defined as the second ionic conductivity,
Following formula (2):
Is preferably 45% or more, more preferably 50% or more, and even more preferably 50 to 70%. If the maintenance factor represented by the above formula (2) is 45% or more, compared to the conventional ion conductor, the decrease in output voltage when the ion conductor is operated for a long time using an all-solid battery, An increase in heat loss due to the resistance component can be more effectively suppressed. In this specification, “when the ionic conductor is exposed to a temperature of 150 ° C. and then cooled to 25 ° C.” means that the ionic conductivity is measured after the sample is placed in a thermostat set at 25 ° C. and held for 30 minutes. Then, the temperature of the thermostatic bath was increased from 30 ° C. to 150 ° C. by 10 ° C., and the same operation was repeated at each temperature. After finishing the measurement at 150 ° C., the thermostatic bath was increased from 140 ° C. to 30 ° C. The ionic conductivity was measured after the temperature was lowered and held at each temperature for 40 minutes, and finally the ionic conductivity was measured after being held for 40 minutes in a constant temperature bath set at 25 ° C.

2. Ionic Conductor According to another embodiment of the present invention, LiBH ₄ and the following formula (1):
MX (1)
[In the formula (1), M represents an alkali metal atom selected from the group consisting of a lithium atom, a rubidium atom and a cesium atom, and X represents a halogen atom. ]
And a alkali metal compound represented in the molar ratio of LiBH ₄ and the alkali metal compound is, LiBH _4: alkali metal compound = 1: 1 to 2.6: 1, preferably 1: 1 to 2.5: An ionic conductor is provided that is 1, more preferably 1: 1 to 2.3: 1. The ionic conductor according to another embodiment of the present invention has a high ionic conductivity maintenance rate even after being exposed to high temperatures. As described above, the conventional ionic conductor has a problem that when it is once exposed to a high temperature and then returned to room temperature, the ionic conductivity greatly decreases with time. However, in the ionic conductor of the present invention, such a decrease in ionic conductivity is greatly suppressed, and the ionic conductivity can be maintained at a high value.

The ionic conductor according to the present invention has at least 2θ = 23.9 ± 1.2 deg, 25.6 ± 1.5 deg, 27.3 ± 1.5 deg, in X-ray diffraction (CuKα: λ = 1.5405Å), It is preferable to have diffraction peaks at 35.4 ± 2.0 deg and 42.2 ± 2.0 deg. It is more preferable to have diffraction peaks at 2θ = 23.6 ± 0.8 deg, 25.2 ± 0.8 deg, 26.9 ± 1.0 deg, 35.0 ± 1.2 deg, and 41.4 ± 1.2 deg. Preferably, it has diffraction peaks at least 2θ = 23.5 ± 0.5 deg, 24.9 ± 0.5 deg, 26.7 ± 0.5 deg, 34.6 ± 0.7 deg, and 40.9 ± 0.7 deg. Is more preferable. Further, it has diffraction peaks at least at 2θ = 23.5 ± 0.3 deg, 25.0 ± 0.4 deg, 26.7 ± 0.3 deg, 34.6 ± 0.5 deg, and 40.9 ± 0.5 deg. Is particularly preferred. The diffraction peaks of these five regions correspond to the diffraction peaks of the high temperature phase of LiBH ₄ . Even when the temperature is lower than the transition temperature (115 ° C.) of the high-temperature phase of LiBH _4, the material having diffraction peaks in the five regions as described above tends to exhibit high ionic conductivity even below the transition temperature.

  The ionic conductor according to the present invention is exposed to a temperature of 90 ° C. to 280 ° C., and then after 1 day at 25 ° C., 2θ = 26.85 ± 0 in the X-ray diffraction (CuKα: λ = 1.5405４０) spectrum. It is preferable that the maximum diffraction intensity at .14 deg is larger than the maximum diffraction intensity at 2θ = 26.60 ± 0.10. In this specification, the “maximum diffraction intensity” in a certain angle range indicates the highest diffraction intensity in the range, and does not necessarily indicate a diffraction peak. In addition, there is a possibility that the entire diffraction peak shifts depending on the preparation method of the sample used for X-ray diffraction, but a part of the peak shifted to the high angle side seen in the conventional composition is moved to the low angle side after cooling. The characteristic that the phenomenon of shifting does not occur in the ionic conductor according to the present invention remains unchanged.

The ionic conductivity of the ionic conductor measured when the ionic conductor according to the present invention is exposed to a temperature of 150 ° C. and then cooled to 25 ° C. is defined as a first ionic conductivity,
When the ionic conductivity of the ionic conductor measured at the time when 148 hours have passed after maintaining the temperature at 25 ° C. from the time of cooling to 25 ° C. is defined as the second ionic conductivity,
Following formula (2):
Is preferably 45% or more, more preferably 50% or more, and even more preferably 50 to 70%. If the maintenance factor represented by the above formula (2) is 45% or more, compared to the conventional ion conductor, the decrease in output voltage when the ion conductor is operated for a long time using an all-solid battery, An increase in heat loss due to the resistance component can be more effectively suppressed.

The ionic conductor of the present invention contains lithium (Li), borohydride (BH ₄ ⁻ ), and a halogen atom as main components, but may contain components other than these. Examples of other components include oxygen (O), nitrogen (N) silicon (Si), and germanium (Ge).

3. Solid electrolyte for all solid state battery and all solid state battery According to another embodiment of the present invention, a solid electrolyte for all solid state battery including an ionic conductor according to one embodiment of the present invention is provided. Moreover, according to the further embodiment of this invention, the all-solid-state battery using this solid electrolyte for all-solid-state batteries is provided.

  In this specification, the all solid state battery is an all solid state battery in which lithium ions are responsible for electrical conduction, and in particular, is an all solid state lithium ion secondary battery. The all solid state battery has a structure in which a solid electrolyte layer is disposed between a positive electrode layer and a negative electrode layer. The ion conductor of the present invention may be contained as a solid electrolyte in any one or more of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer. When used for the electrode layer, it is preferably used for the positive electrode layer rather than the negative electrode layer. This is because a side reaction is less likely to occur in the positive electrode layer. When the ionic conductor according to the embodiment is included in the positive electrode layer or the negative electrode layer, the ionic conductor and a known positive electrode active material or negative electrode active material for a lithium ion secondary battery are used in combination. As the positive electrode layer, it is preferable to use a bulk type in which an active material and a solid electrolyte are mixed because the capacity per unit cell is increased.

  The all-solid-state battery is manufactured by molding and laminating the above-described layers, but the molding method and laminating method of each layer are not particularly limited. For example, a method in which a solid electrolyte and / or an electrode active material is dispersed in a solvent to form a slurry, which is applied by a doctor blade, spin coating, etc., and then rolled to form a film; vacuum deposition, ion plating There are a vapor phase method in which a film is formed and laminated using a method, a sputtering method, a laser ablation method, etc .; a press method in which powder is formed by hot pressing or cold pressing without applying temperature, and then laminated. Since the ionic conductor according to the embodiment is relatively soft, it is particularly preferable to form a battery by pressing and to produce a battery. The positive electrode layer can also be formed using a sol-gel method.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, the content of this invention is not limited by this.

Example 1
LiBH ₄ (manufactured by Sigma-Aldrich, purity 95% or more) and LiI (manufactured by Sigma-Aldrich, purity: 99.9% or more, water content 50 ppm or less) in a glove box under an argon atmosphere ₄ : Weighed to a molar ratio of LiI = 2.00: 1.00 and mixed in an agate mortar. Next, the obtained mixture was put into a 45 mL SUJ-2 pot, and SUJ-2 balls (φ7 mm, 20 pieces) were further put into the pot to completely seal the pot. The pot was attached to a planetary ball mill (P7, manufactured by Fritche), and mechanical milling was performed at a rotation speed of 400 rpm for 2 hours to obtain an ion conductor (2.00 LiBH ₄ -1.00LiI).

(Example 2)
LiBH ₄ and LiBH the molar ratio of LiI _4: LiI = 2.25: was changed to 1.00, to obtain an ionic conductor in the same manner as in Example 1.

(Example 3)
An ionic conductor was obtained in the same manner as in Example 1 except that the molar ratio of LiBH ₄ and LiI was changed to LiBH ₄ : LiI = 2.50: 1.00.

(Comparative Example 1)
LiBH ₄ and LiBH the molar ratio of LiI _4: LiI = 2.75: was changed to 1.00, to obtain an ionic conductor in the same manner as in Example 1.

(Comparative Example 2)
LiBH ₄ and LiBH the molar ratio of LiI _4: LiI = 3.00: was changed to 1.00, to obtain an ionic conductor in the same manner as in Example 1.

(Comparative Example 3)
LiBH ₄ and LiBH the molar ratio of LiI _4: LiI = 4.00: was changed to 1.00, to obtain an ionic conductor in the same manner as in Example 1.

<X-ray diffraction measurement>
The powders of the ion conductors obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to X-ray diffraction measurement (X'pert ³ Powder manufactured by PANalytical, CuKα: λ = 1. 5405).
In Examples 1 to 3 and Comparative Examples 1 to 3, at least 2θ = 23.5 ± 0.3 deg, 25.0 ± 0.4 deg, 26.7 ± 0.3 deg, 34.6 ± 0.5 deg and 40 A diffraction peak was observed at .9 ± 0.5 deg, and a peak corresponding to the diffraction peak of the high temperature phase of LiBH ₄ was shown.

Next, the ionic conductor powders obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were heated to 150 ° C. in an Ar atmosphere, then cooled to 25 ° C. X-ray diffraction measurement (X'pert ³ Powder manufactured by PANalytical, CuKα: λ = 1.5405 mm) was performed. In Examples 1 to 3, the maximum diffraction intensity at 2θ = 26.85 ± 0.14 deg was larger than the maximum diffraction intensity at 2θ = 26.60 ± 0.10. FIG. 3 shows XRD spectra before heating, immediately after heating, and after 1 day at 25 ° C.

<Ion conductivity measurement>
The ionic conductors obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to uniaxial molding (240 MPa) to obtain a disk having a thickness of about 1 mm and a diameter of 8 mm. Ionic conductivity was calculated by performing AC impedance measurement (SI1260 IMPEDANCE / GAIN-PHASE ANALYZER) by a four-terminal method using a lithium electrode at room temperature (25 ° C) and a temperature range of 30 ° C to 150 ° C at 10 ° C intervals . Specifically, the sample was placed in a thermostat set at 25 ° C. and held for 30 minutes, and then the ionic conductivity was measured. Subsequently, the temperature of the thermostat was increased by 10 ° C. from 30 ° C. to 150 ° C. at each temperature. The same operation was repeated. After finishing the measurement at 150 ° C., the temperature of the thermostatic bath was lowered from 140 ° C. to 30 ° C. by 10 ° C. and held at each temperature for 40 minutes, and then the ionic conductivity was measured. Finally, the ionic conductivity of the sample after being held in a thermostatic bath set at 25 ° C. for 40 minutes was measured. The measurement frequency range was 0.1 Hz to 1 MHz, and the amplitude was 50 mV.

  The measurement result of the ionic conductivity about the ionic conductor of Examples 1-3 and Comparative Examples 1-3 is shown in FIG.

<Deterioration measurement with time>
Subsequent to the measurement of the ionic conductivity, the aging degradation of the ionic conductors of Examples 1 to 3 and Comparative Examples 1 to 3 was measured. Using the value at the time of the last measurement at 25 ° C. as a reference (that is, 0 hour), the measurement was performed a plurality of times by the elapsed time of 148 hours, and the change in ionic conductivity with time was observed. The maintenance rate of the ionic conductivity is expressed as a percentage based on the ionic conductivity of the ionic conductor measured when the ionic conductor is exposed to a temperature of 150 ° C. and then cooled to 25 ° C. (0 hour) (ie, 100%). Indicated.

  FIG. 2 shows the measurement results of deterioration with time of ionic conductivity for the ionic conductors of Examples 1 to 3 and Comparative Examples 1 to 3. In all of Examples 1 to 3, the retention rate of the ionic conductor after an elapsed time of 148 hours exceeded 50%, whereas in Comparative Examples 1 to 3, all of them were less than 40%.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

Claims (12)

LiBH ₄ and the following formula (1):
MX (1)
[In the formula (1), M represents an alkali metal atom selected from the group consisting of a lithium atom, a rubidium atom and a cesium atom, and X represents a halogen atom. ]
A method for suppressing deterioration over time of an ionic conductor comprising an alkali metal compound represented by
A method in which the LiBH ₄ and the alkali metal compound are mixed at a molar ratio of LiBH ₄ : alkali metal compound = 1: 1 to 2.6: 1 to suppress deterioration of the ion conductor with time.   In the X-ray diffraction (CuKα: λ = 1.5405４０), the ion conductor is at least 2θ = 23.9 ± 1.2 deg, 25.6 ± 1.5 deg, 27.3 ± 1.5 deg, 35. The method according to claim 1, wherein the method has diffraction peaks at 4 ± 2.0 deg and 42.2 ± 2.0 deg.   The method according to claim 1, wherein the alkali metal compound is lithium halide.   The method of claim 3, wherein the alkali metal compound is lithium iodide.   The method according to claim 1, wherein the mixing is performed by mechanical milling. The ionic conductivity of the ionic conductor measured when exposed to a temperature of 150 ° C. and then cooled to 25 ° C. is defined as a first ionic conductivity,
When the ionic conductivity of the ionic conductor measured at the time when 148 hours have passed after maintaining the temperature at 25 ° C. from the time of cooling to 25 ° C. is defined as the second ionic conductivity,
Following formula (2):
The method as described in any one of Claims 1-5 whose maintenance rate of the ionic conductivity shown by is 45% or more.   The method according to claim 1, comprising exposing the ionic conductor to a temperature of 90 ° C. to 280 ° C. and then cooling to 25 ° C. after the mixing. LiBH ₄ and the following formula (1):
MX (1)
[In the formula (1), M represents an alkali metal atom selected from the group consisting of a lithium atom, a rubidium atom and a cesium atom, and X represents a halogen atom. ]
And an alkali metal compound represented by
Molar ratio of the alkali metal compound and the LiBH ₄ is, LiBH _4: alkali metal compound = 1: 1 to 2.6: 1, ion conductor.   After exposure to a temperature of 90 ° C. to 280 ° C., and after a day at 25 ° C., the maximum diffraction intensity at 2θ = 26.85 ± 0.14 deg in the X-ray diffraction (CuKα: λ = 1.5405Å) spectrum is The ionic conductor according to claim 8, wherein the ionic conductor is larger than a maximum diffraction intensity at 2θ = 26.60 ± 0.10. The ionic conductivity of the ionic conductor measured when exposed to a temperature of 150 ° C. and then cooled to 25 ° C. is defined as a first ionic conductivity,
When the ionic conductivity of the ionic conductor measured at the time when 148 hours have passed after maintaining the temperature at 25 ° C. from the time of cooling to 25 ° C. is defined as the second ionic conductivity,
Following formula (2):
The ionic conductor according to claim 8 or 9, wherein the retention rate of ionic conductivity indicated by is 45% or more.   The solid electrolyte for all-solid-state batteries containing the ion conductor as described in any one of Claims 8-10.   An all solid state battery using the solid electrolyte for an all solid state battery according to claim 11.