JP2013107779A - Sintered body and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sintered body having excellent lithium ion conductivity and a method for manufacturing the same.SOLUTION: The sintered body comprises a garnet type complex metal oxide containing Li, La and Zr and having lithium ion conductivity, and has a relative density in the range of 94-98%, wherein voids have a maximum length in the range of 1 to <100 nm. The sintered body can be manufactured through a step of subjecting a mixed raw material prepared by mixing an Li compound, an La compound and a Zr compound to primary firing to obtain a complex metal oxide powder, and a step of subjecting the complex metal oxide powder to secondary firing by spark plasma sintering.

Description

  The present invention relates to a sintered body and a method for producing the same.

  In recent years, in lithium ion secondary batteries, solid electrolytes having lithium ion conductivity have attracted attention as a medium for conducting lithium ions, instead of a liquid electrolyte.

  The solid electrolyte having lithium ion conductivity has advantages such as no leakage of the electrolyte and prevention of short circuit inside the battery by suppressing the growth of lithium dendride.

As a solid electrolyte having lithium ion conductivity, a sintered body made of a garnet-type composite metal oxide represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ is known (see, for example, Patent Documents 1 and 2). The sintered body is obtained by mixing lithium carbonate, lanthanum hydroxide and zirconium oxide and performing primary firing to obtain a composite metal oxide powder, and then pressing the composite metal oxide powder to form a preform. The preform can be produced by being subjected to secondary firing at a temperature in the range of 1125 to 1230 ° C. for a time in the range of 30 to 50 hours. The sintered body obtained by the manufacturing method has a relative density of 92% with respect to the theoretical density (5.116 g / cm ³ ) of the garnet-type composite metal oxide represented by the chemical formula Li ₇ La ₃ Zr ₂ O _12. I have.

JP 2010-45019 A JP 2011-51855 A

  However, the sintered body obtained by the conventional manufacturing method has a disadvantage that sufficient lithium ion conductivity cannot be obtained.

  An object of the present invention is to provide a sintered body having excellent lithium ion conductivity and a method for manufacturing the same, which eliminates such disadvantages.

  As a result of intensive studies on the reason why sufficient lithium ion conductivity cannot be obtained in the sintered body obtained by the conventional manufacturing method, the present inventors have found that voids having a maximum length in the range of 100 nm to 5 μm. It has been found that the resistance increases due to the presence of.

  In the sintered body, as the voids, the voids existing between the particles of the composite metal oxide powder constituting the preform are left as they are or after being subjected to secondary firing. In some cases, the lithium contained in the preform is volatilized and formed as bubbles during the secondary firing.

  In the secondary firing, the former voids are crystallized as they are or in a compressed state without disappearance of voids existing between the particles of the composite metal oxide powder due to a slow sintering speed. It is thought that it remained in the grain boundary. On the other hand, the latter voids cause the lithium contained in the preform to be volatilized by subjecting the preform to a heat treatment at a high temperature for a long time in the secondary firing in order to obtain a dense sintered body. However, it is considered that the bubbles are generated as bubbles in the crystal grains.

  The present invention has been made based on the above findings, and in order to achieve the above object, the present invention is a sintered body comprising Li, La and Zr, and comprising a garnet-type composite metal oxide having lithium ion conductivity. And having a relative density in the range of 94 to 98%, and the voids have a maximum length in the range of 1 nm or more and less than 100 nm.

  The sintered body of the present invention can have excellent lithium ion conductivity because it has a relative density in the above range and the voids have the maximum length in the above range.

  A sintered body having a relative density of less than 94% cannot obtain sufficient lithium ion conductivity. A sintered body having a relative density exceeding 98% is difficult to manufacture. In addition, it is difficult to produce a sintered body having the maximum gap of less than 1 nm. A sintered body in which the voids have a maximum length of 100 nm or more cannot obtain sufficient lithium ion conductivity.

The sintered body of the present invention preferably comprises a garnet-type composite metal oxide having a basic composition represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ .

  The sintered body of the present invention may be a sintered body in which a part of La is replaced with one kind of metal selected from the group consisting of Sr and Ba. , Ta, Sb, Bi may be used as a sintered body substituted with one metal selected from the group consisting of.

  In the sintered body of the present invention, a mixed raw material in which a Li compound, a La compound, and a Zr compound are mixed is primarily fired to obtain a powdered composite metal oxide powder, and for the composite metal oxide powder, It can be advantageously produced by a secondary firing process by spark plasma sintering.

  In the production method of the present invention, first, a Li compound, a La compound, and a Zr compound are mixed to obtain a mixed raw material. At this time, in order to obtain a sintered body in which a part of La or Zr in the chemical formula is replaced with another metal, in addition to the Li compound, La compound and Zr compound, the other metal is added. A mixed raw material is obtained by mixing the contained compound.

  Next, the obtained mixed raw material is primarily fired to obtain a powder containing Li, La and Zr and made of a garnet-type composite metal oxide.

  Next, the sintered body is obtained by secondary firing by discharge plasma sintering for the obtained composite metal oxide powder. In the spark plasma sintering (SPS), the composite metal oxide powder is heated to a firing temperature by applying a pulse of current to the composite metal oxide powder in a pressurized state. Is fired.

  In the production method of the present invention, the composite metal oxide powder is self-heated by secondary firing by the discharge plasma sintering, and can be rapidly heated to the firing temperature, and the firing time at the firing temperature is increased. It can be shortened. Therefore, according to the production method of the present invention, it is possible to shorten the temperature rising time up to the firing temperature and the holding time at the firing temperature, thereby suppressing the volatilization of lithium contained in the composite metal oxide powder. can do.

  Further, in the production method of the present invention, in the secondary firing by the discharge plasma sintering, a current is pulsed in a state where pressure is applied to the composite metal oxide powder. As a result, the pulse application of the current promotes the sintering between the particles of the composite metal oxide powder, and the pressure allows the gaps between the particles of the composite metal oxide powder to be crushed. The number of voids generated at the crystal grain boundaries of the obtained sintered body can be reduced, or the maximum length of the voids can be reduced. Further, even when lithium contained in the composite metal oxide powder volatilizes and bubbles are generated, the bubbles are crushed by the pressure to reduce the number of voids due to the bubbles, or The maximum length of the gap can be reduced.

  As described above, according to the production method of the present invention, a sintered body having a relative density in the range of 94 to 98%, a void having a maximum length in the range of 1 nm or more and less than 100 nm, and excellent lithium ion conductivity. A ligation can be obtained.

In the production method of the present invention, when the mixed raw material is primarily fired, one or more compounds selected from the group consisting of Al ₂ O ₃ , Al (OH) ₃ , SiO ₂ , and silicic acid are used as sintering aids. By using it as an agent, a denser sintered body can be obtained.

The system block diagram which shows the discharge plasma sintering apparatus used for the manufacturing method of this embodiment. 2 is an image showing the appearance of the sample obtained in Example 1. FIG. 2 is an SEM image showing a fracture surface of a sample obtained in Example 1. FIG. 4 is an SEM image showing a fracture surface of a sample obtained in Example 2. FIG. 4 is an SEM image showing a fracture surface of a sample obtained in Example 3. FIG. The image which shows the external appearance of the sample obtained by the comparative example 1. 3 is an SEM image showing a fracture surface of a sample obtained in Comparative Example 1. FIG. 4 is an SEM image showing a fracture surface of a sample obtained in Comparative Example 2. FIG. 4 is an SEM image showing a fracture surface of a sample obtained in Example 4. FIG.

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

  The sintered body of the present embodiment is a sintered body made of a garnet-type composite metal oxide containing Li, La, and Zr and having lithium ion conductivity, and has a relative density in the range of 94 to 98%. The void has a maximum length in the range of 1 nm or more and less than 100 nm.

The sintered body of the present embodiment is a sintered body whose basic composition is represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ , and one kind of metal selected from the group consisting of Sr and Ba with a part of La A part of Zr may be replaced with one metal selected from the group consisting of Nb, Ta, Sb and Bi.

  The sintered body of the present embodiment can have excellent lithium ion conductivity because it has a relative density in the above range and the voids have the maximum length in the above range.

  The sintered body of the present embodiment can be manufactured, for example, by the following method. First, a Li compound, a La compound, and a Zr compound are pulverized and mixed using a pulverizing / mixing device such as a ball mill or a mixer, and the resulting mixed raw material is heated at a temperature in the range of 850 to 950 ° C. And calcining for a time in the range of 5 to 7 hours. At this time, in order to obtain a sintered body in which a part of La or Zr in the chemical formula is replaced with another metal, in addition to the Li compound, La compound and Zr compound, the other metal is added. A mixed raw material is obtained by mixing the contained compound.

  At this time, in order to improve the accuracy of the mixing ratio in the mixed raw material, each of the Li compound, La compound, and Zr compound may be separately mixed after pretreatment such as dehydration, or You may decide to mix, without pre-processing.

Examples of the Li compound include LiOH, lithium hydroxide hydrate, Li ₂ CO ₃ , LiNO ₃ , and CH ₃ COOLi. Examples of the La compound include La ₂ CO ₃ , La (OH) ₃ , La ₂ (CO ₃ ) ₃ , La (NO ₃ ) ₃ , La (CHCOO) _{3 and the} like. Examples of the Zr compound include ZrO ₂ , ZrO (NO ₃ ) ₂ , ZrO (CHCOO) ₂ , and Zr (OH) ₂ CO ₃ .ZrO ₂ .

  Examples of the metal compound that substitutes a part of La in the chemical formula or the metal compound that substitutes a part of Zr include oxides, hydroxides, carbonates, nitrates, and the like.

  Next, the calcined raw material is subjected to primary firing in an oxygen-containing atmosphere, for example, an air atmosphere at a temperature in the range of 1000 to 1100 ° C. for a time in the range of 5 to 7 hours. And Zr, and a powder composed of a garnet-type composite metal oxide is obtained. At this time, you may decide to grind | pulverize this composite metal oxide powder using grinding | pulverization apparatuses, such as a ball mill and a mixer, so that the obtained composite metal oxide powder may be provided with the particle size of the range of 1-50 micrometers.

  Next, the obtained composite metal oxide powder is secondarily fired by spark plasma sintering (SPS).

  Here, a discharge plasma sintering apparatus for performing the discharge plasma sintering will be described. A discharge plasma sintering apparatus 1 shown in FIG. 1 includes a sintering die 3, a pair of punches 4 and 5 opposed to each other, and electrodes 6 for applying a current through the punches 4 and 5 in a water-cooled vacuum chamber 2. 7, the powdered material is charged into the sintering die 3, and the material is heated and fired by applying a pulse of current while the material is pressurized with the punches 4 and 5. can do.

  As the sintering die 3, one made of an electrically conductive material or an electrically insulating material can be used. Examples of the electrically conductive material include carbon materials such as graphite and glassy carbon (registered trademark), refractory metals such as molybdenum and tungsten, and the like. Examples of the electrical insulating material include alumina and zirconia.

  The punches 4 and 5 are made of an electrically conductive material, are electrically and mechanically connected to the electrodes 6 and 7, respectively, and are driven by the pressurizing mechanism 8. The electrodes 6 and 7 are electrically connected to the power source 9. The pressurizing mechanism 8 and the power source 9 are controlled by the control device 10.

  The control device 10 includes a position measurement mechanism 11 that measures the positions of the punches 4 and 5, an atmosphere control mechanism 12 that controls the atmosphere in the vacuum chamber 2, a cooling mechanism 13 that cools the vacuum chamber 2, and a sintering die 3. And a temperature measuring mechanism 14 connected to a thermocouple (not shown) for measuring the temperature of the material charged in the sintering die 3.

  The atmosphere control mechanism 12 can set the atmosphere in the vacuum chamber 2 to a vacuum atmosphere, an argon atmosphere, or an air atmosphere. The atmosphere in the vacuum chamber 2 is preferably a vacuum atmosphere or an argon atmosphere in order to suppress oxidation of the sintered die 3 during firing.

  In this embodiment, in the discharge plasma sintering apparatus 1, first, the composite metal oxide powder is charged into the sintering die 3 (composite metal oxide powder W). The inside of the vacuum chamber 2 is brought into a vacuum atmosphere having a pressure in the range of 10 to 100 Pa. Next, in a state where the mixed metal oxide powder W charged in the sintering die 3 is pressed with a punch 4 and 5 at a pressure in the range of 20 to 50 MPa, a direct current in the range of 500 to 20000 A is set to 200 to Pulses are applied with a period in the range of 400 Hz. At this time, when the temperature measured by the thermocouple is 800 ° C. or lower, the temperature is increased at a rate of temperature increase of 10 to 100 ° C./min. The temperature is raised at a temperature rate. The composite metal oxide powder W charged in the sintering die 3 is held at a firing temperature in the range of 1100 to 1250 ° C. for a time in the range of 5 to 30 minutes in a state of being pressurized at the pressure in the above range. Thus, secondary firing is performed to obtain a sintered body.

  Next, the pulse application and the pressurization are stopped, and the vacuum chamber 2 is cooled by the cooling mechanism 13 or naturally cooled, thereby cooling the obtained sintered body to room temperature. A sintered body in the form can be obtained.

  In the manufacturing method of the present embodiment, by performing the discharge plasma sintering in the secondary firing, the composite metal oxide powder can be self-heated and rapidly heated up to a firing temperature, and fired. The firing time at temperature can be shortened. Therefore, according to the manufacturing method of the present embodiment, the temperature rise time up to the firing temperature and the holding time at the firing temperature can be shortened, and as a result, the volatilization of lithium contained in the composite metal oxide powder can be reduced. Can be suppressed.

  Furthermore, in the manufacturing method of this embodiment, in the secondary firing by the discharge plasma sintering, a current is pulsed in a state where pressure is applied to the composite metal oxide powder. As a result, sintering between the particles of the composite metal oxide powder is promoted by applying the pulse of the current, and voids existing between the particles can be crushed by the pressure. The number of voids generated in the crystal grain boundaries of the body can be reduced, or the maximum length of the voids can be reduced. Further, even when lithium contained in the composite metal oxide powder volatilizes and bubbles are generated, the bubbles are crushed by the pressure to reduce the number of voids due to the bubbles, or The maximum length of the gap can be reduced.

In the manufacturing method of the present embodiment, when the mixed raw material is subjected to primary firing, an Al-containing compound such as Al ₂ O ₃ and Al (OH) ₃ and a Si-containing compound such as SiO ₂ and silicic acid are baked. By using it as a binder, a denser sintered body can be obtained.

  Next, examples of the present invention will be described.

[Example 1]
In this example, lithium hydroxide monohydrate (manufactured by Kanto Chemical Co., Inc.) was first heated in a vacuum atmosphere at a pressure of 500 Pa at a temperature of 350 ° C. for 6 hours to perform dehydration treatment. I got a thing. Further, lanthanum oxide (manufactured by Kanto Chemical Co., Ltd.) was dehydrated and decarboxylated by heating at 950 ° C. for 24 hours in an air atmosphere.

  Next, the obtained lithium hydroxide anhydride, dehydrated and decarboxylated lanthanum oxide, and zirconium oxide (manufactured by Kanto Chemical Co., Ltd.) were mixed in a molar ratio of Li: La: Zr = 7.7: 3: 2. The mixture was pulverized and mixed for 3 hours at 360 rpm using a planetary ball mill (trade name: premium line P-7, manufactured by Fritsch Japan Co., Ltd.) to obtain a mixed raw material.

  Next, the mixed raw material is placed in an alumina crucible, and held in an air atmosphere at a temperature of 1050 ° C. for 6 hours, followed by primary firing to contain Li, La, and Zr, and a garnet-type composite metal oxide A powder consisting of

The composite metal oxide powder obtained by the primary firing was subjected to X-ray diffraction measurement using an X-ray diffractometer (trade name: D8 ADVANCE, manufactured by Bruker AXS). Chemical formula Li _{7 + x} La ₃ Zr ₂ It was represented by O _{12 + x / 2} (x = 0 to 0.3), and was confirmed to be a complex metal oxide having a tetragonal garnet structure.

  Next, the obtained composite metal oxide powder is subjected to discharge plasma sintering (SPS: Spark Plasma Sintering) using a discharge plasma sintering apparatus 1 (trade name SPS-3.20S, manufactured by SPS Syntex Corporation). Was subjected to secondary firing. First, 10 g of the obtained composite metal oxide powder was placed in a graphite sintered die 3 having an inner diameter of 20 mm (composite metal oxide powder W), and the vacuum chamber 2 was evacuated to a pressure of 20 Pa. Next, in a state where the composite metal oxide powder W charged in the sintering die 3 is pressed at a pressure of 20 MPa with the punches 4 and 5, by applying a direct current in the range of 900 to 1000A, The temperature was raised at a rate of temperature increase of 100 ° C./min. Then, after reaching a temperature of 800 ° C., the composite metal oxide powder W charged in the sintering die 3 is pulsed with a direct current in the range of 900 to 1050 A in a state where the pressurization is continued. Then, the temperature was increased at a rate of temperature increase of 5 ° C./min, and then held at a temperature of 1150 ° C. for 10 minutes to perform secondary firing to obtain a sintered body.

  The pulse application was repeated with one cycle consisting of applying 12 pulses continuously at a frequency of 300 Hz and pausing for two times.

  Next, the pulse application and the pressurization were stopped, the mixture was allowed to cool naturally, and the obtained sintered body was cooled to room temperature to obtain a sintered body of this example.

  Next, the sintered body obtained in this example was cut to a thickness in the range of 700 to 800 μm with a diamond cutter, and the surface was polished with water-resistant paper made of silicon carbide to obtain a thickness of 500 μm. A disc-shaped sample was prepared.

  In FIG. 2, the image which shows the external appearance of the sample obtained by the present Example is shown. From FIG. 2, it is clear that the sample obtained in this example has the property of transmitting light because it has transparency. From this, it can be considered that the sample obtained in this example has very few crystal grain boundaries and voids that scatter light and is highly densified.

Next, the measured density was calculated by measuring the dry weight and volume of the sample obtained in this example. Based on the measured density obtained, the relative density with respect to the theoretical density (5.116 g / cm ³ ) of the garnet-type composite metal oxide represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ was calculated to be 94%. Met. The results are shown in Table 1.

Next, when X-ray diffraction measurement was performed on the sample obtained in this example using an X-ray diffractometer (trade name: D8 ADVANCE, manufactured by Bruker AXS), the chemical formula Li ₇ La ₃ Zr ₂ O was obtained. ₁₂ and was confirmed to be a composite metal oxide having a garnet structure that is a mixed crystal of tetragonal crystals and cubic crystals.

Next, the lithium ion conductivity of the sample obtained in this example was determined as follows. First, Au was sputtered on both surfaces of the sample obtained in this example for 300 seconds using a sputtering apparatus (trade name: JFC-1600 auto fine coater, manufactured by JEOL Ltd.). A thin film electrode was prepared. Next, in order to reduce contact resistance, a Cu mesh was attached to the surface of the thin film electrode, and then a sample having the electrode was attached to a bipolar cell. And about the said 2 pole cell, the alternating current resistance value when a frequency is set to the range of 0.1 Hz-1 MHz, and a voltage amplitude is 20 mV is measured using an impedance measuring device (Brand name: 1287 type, Solartron company make). When the lithium ion conductivity was calculated from the measured value, it was 1.0 × 10 ⁻⁴ S / cm. The results are shown in Table 1.

  Next, the sample obtained in this example was crushed using an agate pestle, and the obtained fracture surface was observed with a scanning electron microscope (SEM). The obtained image is shown in FIG. From FIG. 3, it is clear that the sample of this example is highly densified with no voids having a maximum length exceeding 100 nm.

[Example 2]
In this example, the composite metal oxide powder obtained by the primary firing was held at a temperature of 1170 ° C. for 10 minutes, and the secondary firing was performed by the discharge plasma sintering. Thus, a sintered body was produced. A sample was produced from the obtained sintered body in exactly the same manner as in Example 1.

  Next, regarding the sample obtained in this example, the relative density was calculated in the same manner as in Example 1, and it was 95%. The results are shown in Table 1.

  Next, when the X-ray diffraction measurement was performed on the sample obtained in this example in exactly the same manner as in Example 1, it was confirmed that the sample was a composite metal oxide having a cubic garnet structure. .

Next, for the sample obtained in this example, the lithium ion conductivity was determined exactly as in Example 1, and it was 1.5 × 10 ⁻⁴ S / cm. The results are shown in Table 1.

  Next, the sample obtained in this example was observed with a scanning electron microscope in exactly the same manner as in Example 1. The obtained image is shown in FIG. From FIG. 4, it is clear that the sample of this example is highly densified with no voids having a maximum length exceeding 100 nm.

Example 3
In this example, the composite metal oxide powder obtained by the primary firing was held at a temperature of 1200 ° C. for 10 minutes, and the secondary firing was performed by discharge plasma sintering. Thus, a sintered body was produced. A sample was produced from the obtained sintered body in exactly the same manner as in Example 1.

  Next, regarding the sample obtained in this example, the relative density was calculated in the same manner as in Example 1, and it was 97%. The results are shown in Table 1.

  Next, when the X-ray diffraction measurement was performed on the sample obtained in this example in exactly the same manner as in Example 1, it was confirmed that the sample was a composite metal oxide having a cubic garnet structure. .

Next, for the sample obtained in this example, the lithium ion conductivity was determined exactly as in Example 1, and it was 1.3 × 10 ⁻⁴ S / cm. The results are shown in Table 1.

  Next, the sample obtained in this example was observed with a scanning electron microscope in exactly the same manner as in Example 1. The obtained image is shown in FIG. From FIG. 5, it is clear that the sample of this example is highly densified with no voids having a maximum length exceeding 100 nm.

[Comparative Example 1]
In this comparative example, primary firing was performed in exactly the same manner as in Example 1 to obtain a composite metal oxide powder.

  Next, the obtained composite metal oxide powder was subjected to secondary firing as follows. First, 10 g out of 100 g of the obtained composite metal oxide powder was charged into a die having an inner diameter of 20 mm of a hand press machine and pressurized at a pressure of 255 MPa to prepare a preform.

  Next, 90 g of the remaining composite metal oxide powder was placed in an alumina crucible, and the preform formed in the composite metal oxide powder was embedded.

  Next, the composite metal oxide powder housed in the alumina crucible is heated at a temperature rising rate of 5 ° C./min in the air atmosphere, and after reaching a temperature of 600 ° C., the temperature rising rate is 1 ° C./min. The mixture was heated at 1170 ° C. and held at a temperature of 1170 ° C. for 12 hours to perform secondary firing to obtain a sintered body. A sample was produced from the obtained sintered body in exactly the same manner as in Example 1.

  In FIG. 6, the image which shows the external appearance of the sample obtained by this comparative example is shown. From FIG. 6, it is clear that the sample obtained in this comparative example is white and does not have the property of transmitting light. From this, it is considered that the sample obtained in this comparative example has a large number of voids in the crystal grain boundary of the sintered body and is not densified.

  Next, regarding the sample obtained in this comparative example, the relative density was calculated in the same manner as in Example 1, and it was 79%. The results are shown in Table 1.

  Next, the sample obtained in this example was subjected to X-ray diffraction measurement in exactly the same way as in Example 1. As a result, a composite metal oxide having a garnet structure that was a mixed crystal of tetragonal crystals and cubic crystals was obtained. It was confirmed that.

Next, the lithium ion conductivity of the sample obtained in this comparative example was found to be exactly the same as in Example 1, and it was 1.2 × 10 ⁻⁵ S / cm. The results are shown in Table 1.

  Next, the sample obtained in this comparative example was observed with a scanning electron microscope in exactly the same manner as in Example 1. The obtained image is shown in FIG. From FIG. 7, it is clear that the sample of this comparative example is not dense because the sintering is insufficient and there are many voids having a maximum length exceeding 100 nm.

[Comparative Example 2]
In this comparative example, the composite metal oxide powder obtained by the primary firing was held at a temperature of 1170 ° C. for 30 hours, and was subjected to secondary firing, and was exactly the same as comparative example 1, Was made. A sample was produced from the obtained sintered body in exactly the same manner as in Example 1.

  Next, regarding the sample obtained in this comparative example, the relative density was calculated in exactly the same way as in Example 1, and it was 90%. The results are shown in Table 1.

  Next, when the X-ray diffraction measurement was performed on the sample obtained in this comparative example in exactly the same manner as in Example 1, it was confirmed that the sample was a composite metal oxide having a cubic garnet structure. .

Next, for the sample obtained in this comparative example, the lithium ion conductivity was determined in exactly the same manner as in Example 1, and it was 7.4 × 10 ⁻⁵ S / cm. The results are shown in Table 1.

  Next, the sample obtained in this comparative example was observed with a scanning electron microscope in exactly the same manner as in Example 1. The obtained image is shown in FIG. From FIG. 8, the sample of this comparative example has no voids whose maximum length exceeds 100 nm at the crystal grain boundaries, but there are bubble-like voids that appear to have been generated by Li volatilization during long-time sintering. It is clear that it exists in the crystal grains and is not dense.

  From Table 1, the samples of Examples 1 to 3 that were subjected to secondary firing by spark plasma sintering had a higher relative density and were denser than the samples of Comparative Examples 1 and 2 that were not subjected to discharge plasma sintering. It is clear that Moreover, it is clear that the samples of Examples 1 to 3 have excellent ionic conductivity as compared with the samples of Comparative Examples 1 and 2.

Example 4
In this example, primary firing and discharge were performed in exactly the same manner as in Example 2 except that silicon dioxide and aluminum hydroxide were added as sintering aids to the mixed raw material of Li compound, La compound and Zr compound. Secondary firing by plasma sintering was performed. Silicon dioxide and aluminum hydroxide were added so that Si and Al might be 0.1 mol% with respect to 1 mol of Li ₇ La ₃ Zr ₂ O ₁₂ produced.

  Next, regarding the sample obtained in this example, the relative density was calculated in exactly the same way as in Example 2, and it was 98%. The results are shown in Table 2.

  Next, when the X-ray diffraction measurement was performed on the sample obtained in this example in exactly the same manner as in Example 2, it was confirmed that the sample was a composite metal oxide having a cubic garnet structure. .

Next, regarding the sample obtained in this example, the lithium ion conductivity was determined in exactly the same manner as in Example 2, and it was 1.8 × 10 ⁻⁴ S / cm. The results are shown in Table 2.

  Next, the sample obtained in this example was observed with a scanning electron microscope in exactly the same manner as in Example 2. The obtained image is shown in FIG. From FIG. 9, in the sample of this example, the line seen as the grain boundary observed in the SEM image of the sample of Example 1 in FIG. 3 disappears, and is further densified as compared with Example 1. It is clear that

Example 5
In this example, the powdered composite metal oxide powder obtained by primary firing was held at a temperature of 1170 ° C. for 20 minutes and subjected to secondary firing by discharge plasma sintering. Sintered bodies were made exactly the same. A sample was prepared from the obtained sintered body in exactly the same manner as in Example 2.

  Next, regarding the sample obtained in this example, the relative density was calculated in the same manner as in Example 2, and it was 96%. The results are shown in Table 2.

  Next, when the X-ray diffraction measurement was performed on the sample obtained in this example in exactly the same manner as in Example 2, it was confirmed that the sample was a composite metal oxide having a cubic garnet structure. .

Next, the lithium ion conductivity of the sample obtained in this example was determined exactly as in Example 2, and found to be 2.4 × 10 ⁻⁴ S / cm. The results are shown in Table 2.

  From Table 2, the relative density of the sample of Example 4 that was subjected to primary firing using a sintering aid was higher than that of the sample of Example 2 that was subjected to primary firing without using a sintering aid. It is clear that it has a larger and better ionic conductivity.

  Further, from Table 2, the sample of Example 5 which was subjected to the primary firing using the sintering aid and then subjected to the secondary firing at a temperature of 1170 ° C. for 20 minutes was subjected to the primary firing using the sintering aid. After being performed, it is clear that although the relative density is slightly smaller than that of the sample of Example 4 which has been subjected to secondary firing at a temperature of 1170 ° C. for 10 minutes, it has further superior ion conductivity.

Claims (4)

A sintered body comprising a garnet-type composite metal oxide containing Li, La and Zr and having lithium ion conductivity,
With a relative density in the range of 94-98%,
A sintered body characterized in that the void has a maximum length in a range of 1 nm or more and less than 100 nm. The sintered body according to claim 1,
The garnet-type composite metal oxide is represented by a chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ . It is composed of a garnet-type composite metal oxide containing Li, La and Zr and having lithium ion conductivity, and has a relative density in the range of 94 to 98%, and has a maximum length in the range of voids of 1 nm or more and less than 100 nm. A method for producing a sintered body comprising:
A primary firing of a mixed raw material in which a Li compound, a La compound, and a Zr compound are mixed to obtain a powdered composite metal oxide powder;
And a step of subjecting the composite metal oxide powder to secondary firing by spark plasma sintering. In the manufacturing method of the sintered compact according to claim 3,
In the primary firing of the mixed raw material, one or more compounds selected from the group consisting of Al ₂ O ₃ , Al (OH) ₃ , SiO ₂ , and silicic acid are used as a sintering aid. A method for producing a sintered body.