JP5663466B2 - Lithium ion conductive material - Google Patents

Description

  The present invention relates to a lithium ion conductive material.

Conventionally, as an electrolyte for a secondary battery, a nonaqueous electrolytic solution in which a supporting salt such as LiPF ₆ or LiBF ₆ is dissolved in an organic solvent such as propylene carbonate, ethylene carbonate, diethyl carbonate, or dimethyl carbonate has been used. However, in the secondary battery using the electrolytic solution, there is a possibility that the electrolytic solution leaks to the outside when the container is damaged.

  In addition, the secondary battery using lithium ions together with the electrolytic solution has a problem that lithium dendride (dendritic crystal) is deposited and grows on the negative electrode made of lithium metal, lithium alloy, graphite or the like. When the lithium dendride reaches the positive electrode, it may cause a short circuit inside the secondary battery.

Therefore, the use of a lithium ion conductive material such as a solid electrolyte as the electrolyte of the secondary battery has been studied. As the lithium ion conductive material, for example, a composite metal oxide represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ and having a garnet structure is known, and the composite metal oxide has excellent lithium ion conductivity. And excellent electrochemical stability (for example, see Non-Patent Document 1).

Murugan et al., Angew.Chem.Int.Ed. 46 (2007), pp.1-5

However, in order to use a composite metal oxide represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ and having a garnet structure as a solid electrolyte of the secondary battery, lithium ion conductivity and electrochemical stability are further increased. It is desirable to improve.

  Therefore, in view of such circumstances, an object of the present invention is to provide a lithium ion conductive material having lithium ion conductivity equivalent to that of the composite metal oxide and further having excellent electrochemical stability. .

In order to achieve this object, the lithium ion conductive material of the present invention has the chemical formula Li ₇ La _3-x A _x Zr ₂ O ₁₂ (wherein A is selected from the group consisting of Y, Nd, Sm, Gd). And x is in the range of 0.1 ≦ x ≦ 0.2 ), and is characterized by comprising a composite metal oxide having a garnet-type structure.

In order to improve the lithium ion conductivity of the composite metal oxide represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ and having a garnet-type structure, a part of the constituent elements may be substituted or other elements may be added. It is possible to do. However, the electrochemical stability of the composite metal oxide may be impaired if a part of the constituent elements is replaced or other elements are added. This tendency was caused by replacing some of the constituent elements with elements that easily cause valence changes such as Nb, or elements that easily cause defects at the Li site when a part of Li was replaced, such as Al. Sometimes it becomes noticeable.

In addition, when a part of La constituting the composite metal oxide is replaced with a divalent metal M such as Mg, Ca, Sr, Ba, etc., the composite metal oxide after replacement is kept electrically neutral. The stable composition is represented by the chemical formula Li _{7 + x} La _3-x M _x Zr ₂ O ₁₂ . In the composition, the number of Li in the crystal lattice of the composite metal oxide represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ is larger than the number of Li sites where Li can stably exist, and the crystal structure rule As a result, the stability tends to be impaired because another crystal structure is easily generated.

  Therefore, in the present invention, a part of La constituting the composite metal oxide is a trivalent metal similar to La, and includes Y, Nd, Sm, and Gd having an ionic radius close to the ionic radius value of La. Substitution with any one metal selected from the group. By doing so, changes in the crystal structure and lattice constant of the composite metal oxide can be suppressed, and better electrochemical stability can be obtained without impairing lithium ion conductivity. .

  In the lithium ion conductive material of the present invention, the composite metal oxide includes a Li compound, a La compound, a Zr compound, and a compound of any one metal selected from the group consisting of Y, Nd, Sm, and Gd. The mixed raw material in which is mixed is fired. At this time, the composite metal oxide is preferably formed by adding a sintering aid composed of an Al compound and an Si compound or an Al compound and a Ge compound to the mixed raw material. Since the sintering is promoted by adding the sintering aid to the mixed raw material and firing, the resulting composite metal oxide can be densified.

  In the lithium ion conductive material of the present invention, A may be any one of Nd, Sm, and Gd, but Y is preferable. In the lithium ion conductive material of the present invention, when A is Y, the potential window can be widened compared with the case where A is any one metal of Nd, Sm, and Gd. Electrochemical stability can be obtained.

The graph which shows the result of the voltammetry in the lithium ion conductive material of this invention.

  Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

The lithium ion conductive material of the present embodiment has a chemical formula Li ₇ La _3-x A _x Zr ₂ O ₁₂ (wherein A is any one metal selected from the group consisting of Y, Nd, Sm, and Gd) And x is in a range of 0.1 ≦ x ≦ 0.2 ) and is made of a composite metal oxide having a garnet structure.

The lithium ion conductive material of this embodiment is a composite metal oxide represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ , wherein a part of La is a trivalent metal the same as La, and the ion radius of La It is substituted with any one metal selected from the group consisting of Y, Nd, Sm, Gd having an ionic radius close to the value, preferably Y. In this way, the lithium ion conductive material of the present embodiment can suppress changes in the crystal structure and lattice constant of the composite metal oxide represented by the chemical formula Li ₇ La ₃ Zr ₂ O _12. More excellent electrochemical stability can be obtained without impairing the lithium ion conductivity.

  The lithium ion conductive material of the present embodiment is a mixture in which a Li compound, a La compound, a Zr compound, and a compound of any one metal selected from the group consisting of Y, Nd, Sm, and Gd are mixed. It can be obtained by firing the raw material. Also, at this time, sintering is promoted by adding a sintering aid composed of an Al compound and Si compound or an Al compound and Ge compound to the mixed raw material, thereby promoting the densified lithium ion conduction. Can be obtained.

As the Li compound, for example, a LiOH or a hydrate _{thereof, Li 2 CO 3, LiNO 3} , CH 3 COOLi like. Examples of the La compound include La ₂ O ₃ , La (OH) ₃ , La ₂ (CO ₃ ) ₃ , La (NO ₃ ) ₃ , (CH ₃ COO) ₃ La, and the like. Examples of the Zr compound include Zr ₂ O ₂ , ZrO (NO ₃ ) ₂ , ZrO (CH ₃ COO) ₂ , Zr (OH) ₂ CO ₃ , ZrO _{2 and the} like.

Examples of the Y compound include Y ₂ O ₃ , Y ₂ (CO ₃ ) ₃ , Y (NO ₃ ) ₃ , (CH ₃ COO) ₃ Y, and the like. Examples of the Nd compound include Nd ₂ O ₃ , Nd ₂ (CO ₃ ) ₃ , Nd (NO ₃ ) ₃ , (CH ₃ COO) ₃ Nd, and the like. Examples of the Sm compound include Sm ₂ O ₃ , Sm ₂ (CO ₃ ) ₃ , Sm (NO ₃ ) ₃ , (CH ₃ COO) ₃ Sm, and the like. Examples of the Gd compound include Gd ₂ O ₃ , Gd ₂ (CO ₃ ) ₃ , Gd (NO ₃ ) ₃ , (CH ₃ COO) ₃ Gd, and the like.

Examples of the Al compound include Al ₂ O ₃ , Al (OH) ₃ , Al (NO ₃ ) _{3 and the} like. Examples of the Si compound include SiO ₂ , tetraethoxysilane, and orthosilicic acid. Examples of the Ge compound include GeO ₂ , germanium ethoxide, GeCl _{4 and the} like.

  In the firing, first, the mixed raw material is ground and mixed by a pulverizing and mixing device such as a ball mill, a mixer, etc., and then subjected to primary firing at a temperature in the range of 850 to 950 ° C. for 5 to 7 hours. . Next, the fired body obtained by the primary firing is pulverized and mixed again with a ball mill, a mixer or the like using a mixing device, and then held at a temperature in the range of 1000 to 1100 ° C. for 5 to 7 hours. Next firing.

As a result, the chemical formula Li ₇ La _3-x A _x Zr ₂ O ₁₂ (wherein A is any one metal selected from the group consisting of Y, Nd, Sm, Gd, and x is 0 <x A composite metal oxide having a garnet-type structure can be obtained. When the sintering aid is used in the firing, the sintering aid is added to the mixed raw material before the primary firing, and pulverized and mixed with the mixed raw material.

  In order to use the composite metal oxide obtained by the firing as the lithium ion conductive material, it is preferable to have a particle size in the range of 1 to 50 μm. When many particles having a particle diameter larger than 50 μm are contained, the composite metal oxide obtained by the firing is pulverized by, for example, a ball mill, a mixer or the like, and mixed by a mixing device, and the range of 1 to 50 μm. Provide particle size.

  The lithium ion conductive material may be a sintered body made of the composite metal oxide. The sintered body can be obtained by accommodating the powder of the composite metal oxide obtained by the firing in a die and temporarily forming it, followed by sintering at a temperature in the range of 1000 to 1200 ° C. The sintering treatment can be performed in the air, in a vacuum, in an argon atmosphere, or the like, and a dense sintered body can be obtained by applying pressure during the treatment.

  By using the lithium ion conductive material as the sintered body, it is possible to reduce the grain boundary resistance and further improve the lithium ion conductivity.

The electrochemical stability of the lithium ion conductive material of the present embodiment is free when one atom is inserted or desorbed from the unit cell of the composite metal oxide represented by the above chemical formula and having a garnet structure. It can be evaluated by calculating the oxidation-reduction potential from the energy change. The free energy change is determined by using a first-principles electronic state calculation program VASP (Vienna Ab initio Simulation Package), GGA (Generalized Gradient Approximation) / PAW (Projector Augmented Wave) method, cut-off energy 480 eV, k point. = 3 × 3 × 3 can be obtained by the first principle calculation method. The oxidation-reduction potential is a reduction potential and an oxidation potential based on the potential of the Li ⁺ / Li electrode reaction.

  Next, examples and comparative examples of the present invention are shown.

[Example 1]
In this example, lithium hydroxide monohydrate was first dehydrated by heating at 350 ° C. for 6 hours in a vacuum atmosphere to obtain lithium hydroxide anhydride. In addition, lanthanum oxide was dehydrated and decarboxylated by heating at 950 ° C. for 24 hours in an air atmosphere.

  Next, in addition to the obtained lithium hydroxide anhydride, dehydrated and decarboxylated lanthanum oxide, yttrium oxide and zirconium oxide were mixed with Li: La: Y: Zr = 7.7: 2.9: 0. Weigh so that the molar ratio is 1: 2, and use a planetary ball mill (trade name: premium line P-7, manufactured by Fritsch Japan Co., Ltd.) to grind and mix for 3 hours at 360 rpm. Obtained.

  Next, the mixed raw material was accommodated in an alumina crucible, and held in an air atmosphere at a temperature of 900 ° C. for 6 hours for primary firing, thereby obtaining a powdery primary fired product. Next, the obtained primary fired product was pulverized and mixed for 3 hours at a rotation speed of 360 rpm using the planetary ball mill, and then stored in an alumina crucible and kept at a temperature of 1050 ° C. for 6 hours in an air atmosphere. Then, a secondary baked product in powder form was obtained by secondary calcination.

Next, the obtained secondary fired product was pulverized for 3 hours at 360 rpm using the planetary ball mill, to obtain a powdery lithium ion conductive material. The obtained lithium ion conductive material was represented by the chemical formula Li ₇ La _2.9 Y _0.1 Zr ₂ O ₁₂ and consisted of a composite metal oxide having a garnet-type structure.

  Next, 10 g of the obtained lithium ion conductive material was charged into a graphite sintered die having an inner diameter of 20 mm, and the graphite sintered die was placed into a discharge plasma sintering apparatus (trade names SPS-3.20S, SPS thin). (Tex Co., Ltd.) vacuum chamber. Next, after making the inside of the vacuum chamber a vacuum atmosphere with a pressure of 20 Pa, by applying a direct current in a range of 900 to 1000 A at 300 Hz under a pressure of 20 MPa, a heating rate of 100 ° C./min. The temperature was raised to 800 ° C. Next, it heated up to 1170 degreeC with the temperature increase rate of 5 degree-C / min, and it hold | maintained for 10 minutes at the temperature of 1170 degreeC, and obtained the sintered compact which consists of the said lithium ion conductive material.

  Next, the obtained sintered body was cut into a thickness of 750 μm with a diamond cutter and polished with water-resistant paper of silicon carbide to obtain a disk-shaped sintered body with a thickness of 500 μm. Next, using the disk-shaped sintered body as a sample, the density of the lithium ion conductive material forming the disk-shaped sintered body was determined, and the lithium ion conductivity was measured.

  The density of the lithium ion conductive material forming the disk-shaped sintered body is determined by measuring the volume of the disk-shaped sintered body with a micrometer and then dividing the dry weight of the disk-shaped sintered body by the volume. Calculated by

  The lithium ion conductivity of the lithium ion conductive material forming the disk-shaped sintered body was measured as follows. First, Au was sputtered on one surface of the disk-shaped sintered body to form a working electrode having a diameter of 15 mm. Next, Au is sputtered on one surface of the disk-shaped sintered body to form an interface layer for reducing electrode interface resistance, and then a 0.05 mm thickness and a diameter of 15 mm are formed on the interface layer. A counter electrode was formed by attaching Li foil. Next, a Cu mesh for reducing contact resistance was attached to the working electrode and the counter electrode to form a test body.

  Next, the test body was mounted on a two-pole cell, and AC impedance measurement was performed using an impedance analyzer 1287 (trade name, manufactured by Solartron, 1 to 0.1 MHz, voltage amplitude 20 mV). And the lithium ion conductivity of the lithium ion conductive material which forms the said disk shaped sintered compact was computed from AC resistance value. Table 2 shows the density and lithium ion conductivity of the lithium ion conductive material forming the disk-shaped sintered body.

Next, the electrochemical stability of the lithium ion conductive material forming the disk-shaped sintered body was evaluated using the test body. The electrochemical stability was evaluated by mounting the test specimen on a bipolar cell and measuring linear sweep voltammetry using a multistat 1470E (trade name, manufactured by Solartron). The potential scanning speed is 0.2 V / sec, the scanning potential range on the oxidation side is in the range of 2.0 to 8.0 V with reference to the potential of the Li ⁺ / Li electrode reaction, and the scanning potential range on the reduction side is Li ⁺ / The potential of Li electrode reaction was set to a range of 2.0 to -3.0 V with reference to the potential of Li electrode reaction.

The lithium ion conductive material obtained in this example is equivalent to Li ₇ La _3-x Y _x Zr ₂ O ₁₂ shown in Table 1, and has a wider potential window than Li ₇ La ₃ Zr ₂ O _12. I have. That is, the oxidation potential is higher and the reduction potential is lower than that of Li ₇ La ₃ Zr ₂ O ₁₂ .

  Therefore, in the linear sweep voltammetry, no current peak associated with the reaction was confirmed in the potential scan on the oxidation side, and the lithium ion conductive material had sufficient oxidation resistance. In addition, in the potential scan on the reduction side, no current peak was confirmed except that a current peak accompanying Li precipitation was observed in the vicinity of 0 to −1 V, and the lithium ion conductive material had sufficient reduction resistance. It was.

  Table 2 shows the potential at which a current peak other than the current peak accompanying Li precipitation in the potential scan on the reduction side was confirmed as a reaction potential.

[Example 2]
In this example, lithium hydroxide anhydride, dehydrated and decarboxylated lanthanum oxide, yttrium oxide, zirconium oxide, anhydrous silica, and aluminum hydroxide were mixed with Li: La: Y: Zr: Si: Except that the mixed raw material was obtained so that the molar ratio was Al = 7.7: 2.9: 0.1: 2: 0.05: 0.05 A lithium ion conductive material was obtained. The obtained lithium ion conductive material is represented by the chemical formula Li ₇ La _2.9 Y _0.1 Zr ₂ O ₁₂ and is composed of a composite metal oxide having a garnet-type structure. It contained 0.05 moles of Si and 0.05 moles of Al.

  Next, a disc-shaped sintered body is formed in exactly the same manner as in Example 1 except that the lithium ion conductive material obtained in this example is used, and the disc-like sintered material is formed in exactly the same manner as in Example 1. The density of the lithium ion conductive material forming the aggregate was determined, the lithium ion conductivity was measured, and the electrochemical stability was evaluated.

  Table 2 shows the density, lithium ion conductivity, and reaction potential of the lithium ion conductive material forming the disk-shaped sintered body.

The lithium ion conductive material obtained in this example is equivalent to Li ₇ La _3-x Y _x Zr ₂ O ₁₂ shown in Table 1, and has a wider potential window than Li ₇ La ₃ Zr ₂ O _12. I have. That is, the oxidation potential is higher and the reduction potential is lower than that of Li ₇ La ₃ Zr ₂ O ₁₂ .

  Therefore, in the linear sweep voltammetry, no current peak associated with the reaction was confirmed in the potential scan on the oxidation side, and the lithium ion conductive material had sufficient oxidation resistance. In addition, in the potential scan on the reduction side, no current peak was confirmed except that a current peak accompanying Li precipitation was observed in the vicinity of 0 to −1 V, and the lithium ion conductive material had sufficient reduction resistance. It was.

  The result of potential scanning on the reduction side is shown in FIG.

Example 3
In this example, lithium hydroxide anhydride, dehydrated and decarboxylated lanthanum oxide, yttrium oxide, zirconium oxide, anhydrous silica, and aluminum hydroxide were mixed with Li: La: Y: Zr: Si: Except that the mixed raw material was obtained so that the molar ratio was Al = 7.7: 2.9: 0.1: 2: 0.1: 0.1 A lithium ion conductive material was obtained. The obtained lithium ion conductive material is represented by the chemical formula Li ₇ La _2.9 Y _0.1 Zr ₂ O ₁₂ and is composed of a composite metal oxide having a garnet-type structure. It contained 0.1 mol of Si and 0.1 mol of Al.

  Next, a disc-shaped sintered body is formed in exactly the same manner as in Example 1 except that the lithium ion conductive material obtained in this example is used, and the disc-like sintered material is formed in exactly the same manner as in Example 1. The density of the lithium ion conductive material forming the aggregate was determined, the lithium ion conductivity was measured, and the electrochemical stability was evaluated.

  Table 2 shows the density, lithium ion conductivity, and reaction potential of the lithium ion conductive material forming the disk-shaped sintered body.

The lithium ion conductive material obtained in this example is equivalent to Li ₇ La _3-x Y _x Zr ₂ O ₁₂ shown in Table 1, and has a wider potential window than Li ₇ La ₃ Zr ₂ O _12. I have. That is, the oxidation potential is higher and the reduction potential is lower than that of Li ₇ La ₃ Zr ₂ O ₁₂ .

  Therefore, in the linear sweep voltammetry, no current peak associated with the reaction was confirmed in the potential scan on the oxidation side, and the lithium ion conductive material had sufficient oxidation resistance. In addition, in the potential scan on the reduction side, no current peak was confirmed except that a current peak accompanying Li precipitation was observed in the vicinity of 0 to −1 V, and the lithium ion conductive material had sufficient reduction resistance. It was.

Example 4
In this example, lithium hydroxide anhydride, dehydrated and decarboxylated lanthanum oxide, yttrium oxide, and zirconium oxide were mixed with Li: La: Y: Zr = 7.7: 2.8: 0.2. : A powdery lithium ion conductive material was obtained in exactly the same manner as in Example 1 except that the mixed raw material was obtained so as to have a molar ratio of 2. The obtained lithium ion conductive material was represented by the chemical formula Li ₇ La _2.8 Y _0.2 Zr ₂ O ₁₂ and consisted of a composite metal oxide having a garnet-type structure.

  Next, a disc-shaped sintered body is formed in exactly the same manner as in Example 1 except that the lithium ion conductive material obtained in this example is used, and the disc-like sintered material is formed in exactly the same manner as in Example 1. The density of the lithium ion conductive material forming the aggregate was determined, the lithium ion conductivity was measured, and the electrochemical stability was evaluated.

  Table 2 shows the density, lithium ion conductivity, and reaction potential of the lithium ion conductive material forming the disk-shaped sintered body.

The lithium ion conductive material obtained in this example is equivalent to Li ₇ La _3-x Y _x Zr ₂ O ₁₂ shown in Table 1, and has a wider potential window than Li ₇ La ₃ Zr ₂ O _12. I have. That is, the oxidation potential is higher and the reduction potential is lower than that of Li ₇ La ₃ Zr ₂ O ₁₂ .

  Therefore, in the linear sweep voltammetry, no current peak associated with the reaction was confirmed in the potential scan on the oxidation side, and the lithium ion conductive material had sufficient oxidation resistance. In addition, in the potential scan on the reduction side, no current peak was confirmed except that a current peak accompanying Li precipitation was observed in the vicinity of 0 to −1 V, and the lithium ion conductive material had sufficient reduction resistance. It was.

Example 5
In this example, lithium hydroxide anhydride, dehydrated and decarboxylated lanthanum oxide, yttrium oxide, zirconium oxide, anhydrous silica, and aluminum hydroxide were mixed with Li: La: Y: Zr: Si: Except that the mixed raw material was obtained in a molar ratio of Al = 7.7: 2.8: 0.2: 2: 0.05: 0.05, it was exactly the same as in Example 1 and was in powder form A lithium ion conductive material was obtained. The obtained lithium ion conductive material is represented by the chemical formula Li ₇ La _2.8 Y _0.2 Zr ₂ O ₁₂ and is composed of a composite metal oxide having a garnet-type structure. It contained 0.05 moles of Si and 0.05 moles of Al.

  Next, a disc-shaped sintered body is formed in exactly the same manner as in Example 1 except that the lithium ion conductive material obtained in this example is used, and the disc-like sintered material is formed in exactly the same manner as in Example 1. The density of the lithium ion conductive material forming the aggregate was determined, the lithium ion conductivity was measured, and the electrochemical stability was evaluated.

  Table 2 shows the density, lithium ion conductivity, and reaction potential of the lithium ion conductive material forming the disk-shaped sintered body.

The lithium ion conductive material obtained in this example is equivalent to Li ₇ La _3-x Y _x Zr ₂ O ₁₂ shown in Table 1, and has a wider potential window than Li ₇ La ₃ Zr ₂ O _12. I have. That is, the oxidation potential is higher and the reduction potential is lower than that of Li ₇ La ₃ Zr ₂ O ₁₂ .

  Therefore, in the linear sweep voltammetry, no current peak associated with the reaction was confirmed in the potential scan on the oxidation side, and the lithium ion conductive material had sufficient oxidation resistance. In addition, in the potential scan on the reduction side, no current peak was confirmed except that a current peak accompanying Li precipitation was observed in the vicinity of 0 to −1 V, and the lithium ion conductive material had sufficient reduction resistance. It was.

Example 6
In this example, lithium hydroxide anhydride, dehydrated and decarboxylated lanthanum oxide, yttrium oxide, zirconium oxide, anhydrous silica, and aluminum hydroxide were mixed with Li: La: Y: Zr: Si: Except that the mixed raw material was obtained so that the molar ratio was Al = 7.7: 2.8: 0.2: 2: 0.1: 0.1 A lithium ion conductive material was obtained. The obtained lithium ion conductive material is represented by the chemical formula Li ₇ La _2.8 Y _0.2 Zr ₂ O ₁₂ and is composed of a composite metal oxide having a garnet-type structure. It contained 0.1 mol of Si and 0.1 mol of Al.

  Next, a disc-shaped sintered body is formed in exactly the same manner as in Example 1 except that the lithium ion conductive material obtained in this example is used, and the disc-like sintered material is formed in exactly the same manner as in Example 1. The density of the lithium ion conductive material forming the aggregate was determined, the lithium ion conductivity was measured, and the electrochemical stability was evaluated.

  Table 2 shows the density, lithium ion conductivity, and reaction potential of the lithium ion conductive material forming the disk-shaped sintered body.

The lithium ion conductive material obtained in this example is equivalent to Li ₇ La _3-x Y _x Zr ₂ O ₁₂ shown in Table 1, and has a wider potential window than Li ₇ La ₃ Zr ₂ O _12. I have. That is, the oxidation potential is higher and the reduction potential is lower than that of Li ₇ La ₃ Zr ₂ O ₁₂ .

  Therefore, in the linear sweep voltammetry, no current peak associated with the reaction was confirmed in the potential scan on the oxidation side, and the lithium ion conductive material had sufficient oxidation resistance. In addition, in the potential scan on the reduction side, no current peak was confirmed except that a current peak accompanying Li precipitation was observed in the vicinity of 0 to −1 V, and the lithium ion conductive material had sufficient reduction resistance. It was.

[Comparative Example 1]
In this comparative example, lithium hydroxide anhydride, dehydrated and decarboxylated lanthanum oxide, and zirconium oxide were mixed in a molar ratio of Li: La: Zr = 7.7: 3: 2. A powdery lithium ion conductive material was obtained in exactly the same manner as in Example 1 except that. The obtained lithium ion conductive material was represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ and consisted of a composite metal oxide having a garnet-type structure.

  Next, a disc-like sintered body is formed in exactly the same manner as in Example 1 except that the lithium ion conductive material obtained in this comparative example is used, and the disc-like sintered material is formed in exactly the same manner as in Example 1. The density of the lithium ion conductive material forming the aggregate was determined, the lithium ion conductivity was measured, and the electrochemical stability was evaluated.

  Table 2 shows the density, lithium ion conductivity, and reaction potential of the lithium ion conductive material forming the disk-shaped sintered body.

As shown in Table 1, the lithium ion conductive material obtained in this comparative example has a narrower potential window than Li ₇ La _{3 -x} Y _x Zr ₂ O ₁₂ .

  Therefore, in the linear sweep voltammetry, no current peak associated with the reaction was confirmed in the potential scan on the oxidation side, and the lithium ion conductive material had sufficient oxidation resistance, but 0 in the potential scan on the reduction side. The current peak accompanying precipitation of Li was confirmed in the vicinity of ~ -1V, and the current peak associated with the decomposition or short circuit of the specimen was confirmed in the vicinity of -1.6V.

[Comparative Example 2]
In this comparative example, lithium hydroxide anhydride, dehydrated and decarboxylated lanthanum oxide, zirconium oxide, anhydrous silica, and aluminum hydroxide were mixed with Li: La: Zr: Si: Al = 7.7: A powdery lithium ion conductive material was obtained in exactly the same manner as in Example 1 except that the mixed raw material was obtained in a molar ratio of 3: 2: 0.05: 0.05. The obtained lithium ion conductive material is represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ and is composed of a composite metal oxide having a garnet-type structure, and 0.05 mol of Si with respect to 7 mol of Li. And 0.05 mol of Al.

  Next, a disc-like sintered body is formed in exactly the same manner as in Example 1 except that the lithium ion conductive material obtained in this comparative example is used, and the disc-like sintered material is formed in exactly the same manner as in Example 1. The density of the lithium ion conductive material forming the aggregate was determined, the lithium ion conductivity was measured, and the electrochemical stability was evaluated.

  Table 2 shows the density, lithium ion conductivity, and reaction potential of the lithium ion conductive material forming the disk-shaped sintered body.

As shown in Table 1, the lithium ion conductive material obtained in this comparative example has a narrower potential window than Li ₇ La _{3 -x} Y _x Zr ₂ O ₁₂ .

  Therefore, in the linear sweep voltammetry, no current peak associated with the reaction was confirmed in the potential scan on the oxidation side, and the lithium ion conductive material had sufficient oxidation resistance, but 0 in the potential scan on the reduction side. The current peak accompanying precipitation of Li was confirmed in the vicinity of ~ -1V, and the current peak associated with the decomposition or short circuit of the test specimen was confirmed in the vicinity of -2.3V.

  The result of potential scanning on the reduction side is shown in FIG.

[Comparative Example 3]
In this comparative example, lithium hydroxide anhydride, dehydrated and decarboxylated lanthanum oxide, zirconium oxide, anhydrous silica, and aluminum hydroxide were mixed with Li: La: Zr: Si: Al = 7.7: A powdery lithium ion conductive material was obtained in exactly the same manner as in Example 1 except that the mixed raw material was obtained in a molar ratio of 3: 2: 0.1: 0.1. The obtained lithium ion conductive material is represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ and is composed of a composite metal oxide having a garnet-type structure, and 0.1 mol of Si with respect to 7 mol of Li. And 0.1 mol of Al.

  Next, a disc-like sintered body is formed in exactly the same manner as in Example 1 except that the lithium ion conductive material obtained in this comparative example is used, and the disc-like sintered material is formed in exactly the same manner as in Example 1. The density of the lithium ion conductive material forming the aggregate was determined, the lithium ion conductivity was measured, and the electrochemical stability was evaluated.

  Table 2 shows the density, lithium ion conductivity, and reaction potential of the lithium ion conductive material forming the disk-shaped sintered body.

As shown in Table 1, the lithium ion conductive material obtained in this comparative example has a narrower potential window than Li ₇ La _{3 -x} Y _x Zr ₂ O ₁₂ .

  Therefore, in the linear sweep voltammetry, no current peak associated with the reaction was confirmed in the potential scan on the oxidation side, and the lithium ion conductive material had sufficient oxidation resistance, but 0 in the potential scan on the reduction side. A current peak associated with Li deposition was observed in the vicinity of ˜−1 V, and a current peak associated with the decomposition or short circuit of the test specimen was confirmed in the vicinity of −0.8 V.

From Table 2, the lithium ion conductive materials of Examples 1 to 6 represented by the chemical formula Li ₇ La ₃ Zr ₂ O _{12 and in} which a part of the La site of the composite metal oxide having a garnet structure is substituted with Y are as follows. The lithium ion conductive material represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ and composed of a composite metal oxide having a garnet structure has substantially the same ionic conductivity. It is clear.

  In addition, the lithium ion conductive materials of Comparative Examples 1 to 3 show a current peak accompanying decomposition or short-circuiting of the specimen shown as the reaction potential in the potential scan on the reduction side in linear sweep voltammetry, It is apparent that the lithium ion conductive materials of Examples 1 to 6 have no reaction potential, have excellent reduction resistance, and have excellent electrochemical stability.

  Further, the lithium ion conductive materials of Examples 2, 3, 5 and 6 containing Al compound and Si compound in the mixed raw material have a density of 4.88 or more and form a dense sintered body. It is clear.

Claims (4)

Chemical formula Li ₇ La _{3 -x} A _x Zr ₂ O ₁₂ (wherein A is any one metal selected from the group consisting of Y, Nd, Sm, Gd, and x is 0.1 ≦ x ≦ lithium-ion-conducting material characterized by comprising a composite metal oxide comprising represented garnet structure in which) the range of 0.2.   2. The lithium ion conductive material according to claim 1, wherein the composite metal oxide is made of any one metal selected from the group consisting of a Li compound, a La compound, a Zr compound, and Y, Nd, Sm, and Gd. A lithium ion conductive material obtained by firing a mixed raw material mixed with a compound.   3. The lithium ion conductive material according to claim 2, wherein the composite metal oxide is fired by adding a sintering aid comprising an Al compound and a Si compound or an Al compound and a Ge compound to the mixed raw material. A lithium ion conductive material characterized by that.   4. The lithium ion conductive material according to claim 1, wherein A is Y. 5.

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