JP2013239260A - Ion conductor and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ion conductor with high ion conductivity at low cost, in a highly reliable oxide-based ion conductor.SOLUTION: An ion conductor comprises Li, Al, B, Si and O, and has a crystal structure of a dumortierite structure.

Description

  The present invention relates to an ion conductor and a secondary battery.

  Energy harvesting technology that stores power generated from minute energy such as sunlight, vibration, body temperature of people and animals, and uses it for sensors and wirelessly transmitted power is a safe and reliable secondary battery in any global environment. is necessary. Secondary batteries that are widely used at present are those using a liquid organic electrolyte solution. When the cathode active material deteriorates due to repeated use, the capacity of the battery decreases, or the battery by dendrite formation A short circuit may ignite and ignite the organic electrolyte in the secondary battery. Therefore, for example, in energy harvesting that is expected to be used for 10 years or more, it is not preferable to use a secondary battery using the current organic electrolyte from the viewpoint of reliability and safety.

On the other hand, an all-solid lithium secondary battery formed of an all-solid constituent material without using an organic electrolyte has attracted attention because it has no risk of liquid leakage or ignition, and has excellent cycle characteristics. Examples of lithium ion conductors that are solid electrolytes used in such all-solid lithium secondary batteries include oxides and sulfides. In the oxide system, LISOCON (LIthium SuperIonic Conductor) type based on Li ₃ PO ₄ or Li ₄ GeO ₄ , NASICON (Na SuperIonic Conductor) type based on sodium ion conductor, LiLaZrO garnet type, perovskite such as LLTO There are types. In the sulfide system, there are Li ₁₀ GeP ₂ S ₁₁ and Li ₇ P ₃ D ₁₁ .

JP 2007-528108 A JP 2010-272344 A Japanese Patent Laid-Open No. 08-198638

H.Y-P. Hong., Materials Research Bulletin, Volume 13, Issue 2, February 1978, Pages 117-124 R. Murugan, V. Thangadurai, W. Weppner., Angew. Chem. Int. Ed. , (2007), 46, P. 7778-7781. Y. Inaguma, C. Liquan *, M. Itoh, T. Nakamura, T. Uchida, H. Ikuta, M. Wakihara., Solid State Communications Volume 86, Issue 10, June 1993, Pages 689-693 N. Kamaya, K. Homma, Y. Yamakawa, M. Hirayama, R. Kanno, M. Yonemura, T. Kamiyama, Y. Kato, S. Hama, K. Kawamoto & A. Mitsui., Nature Materials Volume: 10, Pages: 682-686Yearpublished: (2011) A. Hayashi, S. Hama, T. Minami, M. Tatsumisago., Electrochem. Commun., 5 (2003), p. 111

  By the way, many of the current oxide-based lithium ion conductors have low ionic conductivity, and sulfide-based lithium ion conductors that exhibit relatively high conductivity are unstable in the air, It is weak and less reliable than oxide-based ones, and the synthesis process is often complicated. In addition, many lithium ion conductors exhibiting relatively high conductivity often use rare and expensive Ge or rare earth elements, which are expensive.

  Therefore, an ionic conductor and a secondary battery that can be obtained at low cost, have high reliability, and have high ionic conductivity are demanded.

  According to one aspect of the present embodiment, the crystal structure includes Li, Al, B, Si, and O, and the crystal structure is a Dumorche structure.

  According to another aspect of this embodiment, Mg, Al, B, Si, and O are included, and the crystal structure is a Dumorche structure.

  According to the disclosed ionic conductor and secondary battery, an ionic conductor having high ionic conductivity can be obtained at low cost in a highly reliable oxide-based ionic conductor.

Structural diagram of ion conductor in the first embodiment Structural diagram of c-axis direction of ion conductor in first embodiment Lithium distance (Li-Li distance) and conductivity correlation diagram Simulation diagram of X-ray diffraction of ionic conductor in the first embodiment Structural diagram of secondary battery in first or second embodiment

  Modes for carrying out the invention will be described below. In addition, about the same member etc., the same code | symbol is attached | subjected and description is abbreviate | omitted.

[First Embodiment]
(Ionic conductor)
The ion conductor in the first embodiment will be described. The ionic conductor in the present embodiment is a lithium ionic conductor and includes lithium (Li), aluminum (Al), boron (B), silicon (Si), and oxygen (O) as constituent elements. Specifically, the ionic conductor in the present embodiment has a crystal structure in which a part of Al of the Dumorche structure in Al ₇ O ₃ (BO ₃ ) (SiO ₄ ) ₃ is substituted with Li. . In other words, the present embodiment is a Li _X Al _{(7-X / 3)} O ₃ (BO ₃ ) (SiO ₄ ) ₃ having a Dumorche structure, and the range of X is 0 <X ≦ 3.0. A hexacoordinate octahedron centered on lithium (Li) forms a ridge, and the formed ridge has a crystal structure that is connected in series.

FIGS. 1 and 2 show an ionic conductor according to the present embodiment, in which Li in the range of _X in Li _X Al _{(7-X / 3)} O ₃ (BO ₃ ) (SiO ₄ ) ₃ is 3. ₃ shows a lithium ion conductor of ₃ Al ₆ O ₃ (BO ₃ ) (SiO ₄ ) ₃ . 2 shows the arrangement in the c-axis direction of the region surrounded by the one-dot chain line 1A in FIG. 1, that is, the arrangement of the hexacoordinate octahedron 11 centering on lithium in the c-axis direction.

Note that the hexacoordinate octahedron 11 centered on lithium shown in FIG. 2 is a LiO ₆ octahedron, and the hexacoordinate octahedron 13 centered on aluminum is an AlO ₆ octahedron. Further, the tetracoordinate tetrahedron 12 centered on silicon is a tetracoordinate tetrahedral oxyacid salt (SiO ₄ ) ⁴⁻ which is a SiO ₄ tetrahedron, and a tricoordinate triangular plane 14 centered on boron. is, BO ₃ is a triangular planar body 3 coordinate plane triangle oxyacid salt _(BO ^{3) 3-.}

  In this lithium ion conductor, a hexacoordinate octahedron 11 centering on lithium is connected in series in the c-axis direction to form a ridge. In addition, around the hexacoordinate octahedron 11 centered on lithium connected in series in the c-axis direction, the periphery of the hexacoordinate octahedron 11 centered on lithium 11 connected in series in the c-axis direction is surrounded. A tetracoordinate tetrahedron 12 centering on silicon is formed in series in the c-axis direction so as to surround it. Further, a tetracoordinate tetrahedron 12 centered on silicon connected in series in the c-axis direction is surrounded around the tetracoordinate tetrahedron 12 centered on silicon connected in series in the c-axis direction. Further, a hexacoordinate octahedron 13 centering on aluminum is formed in series in the c-axis direction. Further, the tricoordinate triangular planar body 14 centering on boron is formed in series in the c-axis direction, and the six-coordinate eight centered on aluminum formed in series in the c-axis direction. The periphery is surrounded by the face piece 13.

  As shown in FIG. 2, the ionic conductor in the present embodiment has a continuous six-coordinate octahedron 11 centered on lithium in the c-axis direction, and the ionic conduction path (ion conduction path) by lithium is c. It is formed in the axial direction. In such a lithium ion conductor shown in FIG. 2, the distance L between lithium in the six-coordinate octahedrons 11 centering on lithium is 2.35 mm (0.235 nm).

In FIG. 3, the relationship between the distance (Li-Li distance) between lithium in a lithium ion conductor and electrical conductivity is shown. LiBPS, which is a sulfide system, has x = 0.300 in the high-temperature phase β-type Li _{3 + 3 / 4x} B _x P _{1-3 / 4x} S ₄ solid solution system. In this LiBPS, the space group is Pnma (62), the distance between 4b-site lithium and 4c-site lithium, which is considered to be an ionic conduction path in the crystal structure, is 2.02 mm, and the ionic conductivity is 1 × 10 ^−4. S / cm, indicating a relatively high ionic conductivity.

In the oxide system, the space group of Li ₄ GeO ₄ is Cmcm (63), Pnma (62), and the distance between lithium at the 8e site considered to be an ionic conduction path in the crystal structure is 3.025 mm, The ionic conductivity is 1 × 10 ⁻¹³ S / cm. Further, Li ₃ PO ₄ is a high-temperature phase γ-Li ₃ PO ₄ , the space group is Pnma (62), and the distance between lithium at the 8e site considered to be an ionic conduction path in the crystal structure is 3. The ion conductivity is 1 × 10 ⁻¹⁸ S / cm.

Li ₃ Al ₆ O ₃ (BO ₃ ) (SiO ₄ ) ₃ , which is an ionic conductor in the present embodiment, has a space group of Pnma (62), and the distance between 4c sites considered to be ionic conduction paths, that is, The distance L between the lithium is 2.35 Å (0.235 nm). From this, when the ionic conductivity of the ionic conductor in the present embodiment is simulated, it is presumed that the ionic conductivity is 1 × 10 ⁻⁴ to 1 × 10 ⁻⁹ S / cm. This value of ionic conductivity is a value close to the ionic conductivity of a sulfide-based ionic conductor exhibiting relatively high ionic conductivity. Li ₃ Al ₆ O ₃ (BO ₃ ) (SiO ₄ ) ₃ is a lithium ion conductor.

  Therefore, it is presumed that the ionic conductor in this embodiment has high reliability because it is an oxide, and has high ionic conductivity because the distance between lithium ions is short. In the ion conductor in this embodiment, since elements constituting the ion conductor are Li, Al, B, Si, and O, rare and expensive Ge or rare earth metal is not used. Therefore, the ionic conductor in this embodiment can be manufactured at low cost.

(Method for producing ionic conductor)
Next, the manufacturing method of the ionic conductor in this Embodiment is demonstrated.

First, lithium carbonate (Li ₂ CO ₃ ), aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ), and boron (B) are mixed using an agate ball mill, and placed in a platinum crucible at 950 ° C. And calcining for 10 hours. At this time, each weighed value is 1.9591 g for lithium carbonate (Li ₂ CO ₃ ), 5.4039 g for aluminum oxide (Al ₂ O ₃ ), and 3.1871 g for silicon dioxide (SiO ₂ ). Boron (B) is 0.0960 g.

  Next, the fired body obtained by calcining is once pulverized in an agate mortar, then formed into pellets, and the formed pellets are fired at 1050 ° C. Thereby, the ionic conductor in this Embodiment can be produced.

FIG. 4 shows a simulation of X-ray diffraction in the lithium ion conductor of Li ₃ Al ₆ O ₃ (BO ₃ ) (SiO ₄ ) ₃ that is the ionic conductor in the present embodiment thus manufactured. The result is shown.

(Secondary battery)
Next, the secondary battery in this embodiment will be described. The secondary battery in the present embodiment uses the ionic conductor in the present embodiment as a solid electrolyte. Specifically, as shown in FIG. 5, an electrode 31 serving as a positive electrode is provided on one surface of a solid electrolyte 30 formed of an ionic conductor in the present embodiment, and an electrode 32 serving as a negative electrode is provided on the other surface. It is the thing of the structure which provided.

[Second Embodiment]
(Ionic conductor)
Next, an ionic conductor in the second embodiment will be described. The ionic conductor in this embodiment is a lithium ionic conductor and includes magnesium (Mg), aluminum (Al), boron (B), silicon (Si), and oxygen (O) as constituent elements. Specifically, a part of Al of the Dumorche structure in Al ₇ O ₃ (BO ₃ ) (SiO ₄ ) ₃ has a crystal structure in which Mg is substituted. That is, this embodiment is a Dumorche structure Mg _Y Al _{(7-Y / 2)} O ₃ (BO ₃ ) (SiO ₄ ) ₃ , and the range of Y is 0 <Y ≦ 2.0, A hexacoordinate octahedron centered on magnesium (Mg) forms a ridge, and the formed ridge has a crystal structure that is connected in series.

As one of the ionic conductors in the present embodiment, Mg ₂ Al ₆ O ₃ (BO) in which the Y range in Mg _Y Al _{(7-Y / 2)} O ₃ (BO ₃ ) (SiO ₄ ) ₃ is 2 is used. ₃ ) A magnesium ion conductor of (SiO ₄ ) ₃ will be described.

Note that the hexacoordinate octahedron centered on magnesium is an MgO ₆ octahedron, and the hexacoordinate octahedron centered on aluminum is an AlO ₆ octahedron. Further, four-coordinate tetrahedral around the silicon, SiO ₄ tetrahedra in which tetracoordinate tetrahedral oxyacid salt (SiO ₄₎ is ^4, 3 coordination triangular plane body around the boron BO is a ₃ triangular flat body 3 coordinate plane triangle oxyacid salt _(BO ^{3) 3-.}

  Similarly to the lithium ion conductor in the first embodiment, this magnesium ion conductor also has a hexacoordinate octahedron centered on magnesium that is connected in series in the c-axis direction to form a ridge. In addition, a hexacoordinate octahedron centered on magnesium connected in series in the c-axis direction is surrounded by a hexacoordinate octahedron centered on magnesium connected in series in the c-axis direction. In addition, a tetracoordinate tetrahedron centered on silicon is formed in series in the c-axis direction. Further, the tetracoordinate tetrahedron centered on silicon connected in series in the c-axis direction surrounds the tetracoordinate tetrahedron centered on silicon connected in series in the c-axis direction. Further, a hexacoordinate octahedron centered on aluminum is formed in series in the c-axis direction. Further, the tricoordinate triangular planar body centered on boron is formed in series in the c-axis direction, and is a six-coordinate octahedron centered on aluminum formed in series in the c-axis direction. Is surrounded by

  In the magnesium ion conductor which is an ionic conductor in the present embodiment, the shorter the gap between magnesium, the higher the ionic conductivity, and the distance between magnesium in hexacoordinated octahedrons centered on magnesium is: 2.35 mm (0.235 nm).

  Therefore, it is presumed that the ionic conductor in the present embodiment is oxide-based and has high reliability and high ionic conductivity. In addition, since the elements constituting the ionic conductor are Mg, Al, B, Si, and O, the ion conductor in this embodiment does not use rare and expensive Ge or rare earth metal. Therefore, the ionic conductor in this embodiment can be manufactured at low cost.

(Method for producing ionic conductor)
Next, the manufacturing method of the ionic conductor in this Embodiment is demonstrated.

First, magnesium carbonate (MgCO ₃ ), aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ), and boron (B) are mixed using an agate ball mill and placed in a platinum crucible at 950 ° C. for 10 minutes. Temporary baking of time. At this time, the respective weighed values are 2.6369 g for magnesium carbonate (MgCO ₃ ), 4.9506 g for aluminum oxide (Al ₂ O ₃ ), 2.9173 g for silicon dioxide (SiO ₂ ), and boron (B) is 0.0874 g.

  Next, the fired body obtained by calcining is once pulverized in an agate mortar, then formed into pellets, and the formed pellets are fired at 1050 ° C. Thereby, the ionic conductor in this Embodiment can be produced.

(Secondary battery)
Next, the secondary battery in this embodiment will be described. Similar to the first embodiment, the secondary battery in the present embodiment has a magnesium ion conductivity such as Mg ₂ Al ₆ O ₃ (BO ₃ ) (SiO ₄ ) ₃ which is an ionic conductor in the present embodiment. The body is used as a solid electrolyte. Specifically, as shown in FIG. 5, an electrode 31 serving as a positive electrode is provided on one surface of a solid electrolyte 30 formed of an ionic conductor in the present embodiment, and an electrode 32 serving as a negative electrode is provided on the other surface. It is the thing of the structure which provided. The contents other than the above are the same as in the first embodiment.

  Although the embodiment has been described in detail above, it is not limited to the specific embodiment, and various modifications and changes can be made within the scope described in the claims.

In addition to the above description, the following additional notes are disclosed.
(Appendix 1)
Li, Al, B, Si, O,
An ionic conductor, wherein the crystal structure is a Dumorche structure.
(Appendix 2)
_{Li X Al (7-X /} 3) O 3 (BO 3) a _{(SiO 4) 3,}
2. The ionic conductor according to appendix 1, wherein the range of X is 0 <X ≦ 3.0.
(Appendix 3)
Tetracoordinate tetrahedral oxyacid salt (SiO ₄ ) ⁴⁻ (12);
3-coordinate planar triangular oxyacid salt (BO ₃ ) ³⁻ (14),
The ionic conductor according to appendix 1, wherein the ionic conductor has a crystal structure formed by:
(Appendix 4)
Including Mg, Al, B, Si, O,
An ionic conductor, wherein the crystal structure is a Dumorche structure.
(Appendix 5)
_{Mg Y Al (7-Y /} 2) O 3 (BO 3) a _{(SiO 4) 3,}
The ionic conductor according to appendix 4, wherein the range of Y is 0 <Y ≦ 2.0.
(Appendix 6)
Tetracoordinate tetrahedral oxyacid salt (SiO ₄ ) ^4-
3-coordinate planar triangular oxyacid salt (BO ₃ ) ^3-
The ionic conductor according to appendix 4, which has a crystal structure formed by
(Appendix 7)
A solid electrolyte formed of the ionic conductor according to any one of appendices 1 to 6,
An electrode formed on one surface of the solid electrolyte;
An electrode formed on one surface of the solid electrolyte;
A secondary battery comprising:

11 Hexacoordinate octahedron centered on lithium (LiO ₆ octahedron)
12 Tetracoordinate tetrahedron centered on silicon (SiO ₄ tetrahedron)
13 6-coordinate octahedron centered on aluminum (AlO ₆ octahedron)
14 Tri-coordinate triangular planar body centered on boron (BO ₃ triangular planar body)
30 Solid electrolyte 31 Electrode (positive electrode)
32 electrodes (negative electrode)

Claims (7)

Li, Al, B, Si, O,
An ionic conductor, wherein the crystal structure is a Dumorche structure. _{Li X Al (7-X /} 3) O 3 (BO 3) a _{(SiO 4) 3,}
The ionic conductor according to claim 1, wherein the range of X is 0 <X ≦ 3.0. Tetracoordinate tetrahedral oxyacid salt (SiO ₄ ) ^4-
3-coordinate planar triangular oxyacid salt (BO ₃ ) ^3-
The ionic conductor according to claim 1, which has a crystal structure formed by: Including Mg, Al, B, Si, O,
An ionic conductor, wherein the crystal structure is a Dumorche structure. _{Mg Y Al (7-Y /} 2) O 3 (BO 3) a _{(SiO 4) 3,}
The ionic conductor according to claim 4, wherein the range of Y is 0 <Y ≦ 2.0. Tetracoordinate tetrahedral oxyacid salt (SiO ₄ ) ^4-
3-coordinate planar triangular oxyacid salt (BO ₃ ) ^3-
The ionic conductor according to claim 4, which has a crystal structure formed by: A solid electrolyte formed by the ionic conductor according to any one of claims 1 to 6;
An electrode formed on one surface of the solid electrolyte;
An electrode formed on one surface of the solid electrolyte;
A secondary battery comprising: