U.S. patent application number 15/517125 was filed with the patent office on 2017-10-26 for lithium ion conductive crystal body and all-solid state lithium ion secondary battery.
This patent application is currently assigned to National Institute of Advanced Industrial Science and Technology. The applicant listed for this patent is NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND TECHNOLOGY. Invention is credited to Junji AKIMOTO, Kunimitsu KATAOKA.
Application Number | 20170309955 15/517125 |
Document ID | / |
Family ID | 55857662 |
Filed Date | 2017-10-26 |
United States Patent
Application |
20170309955 |
Kind Code |
A1 |
KATAOKA; Kunimitsu ; et
al. |
October 26, 2017 |
LITHIUM ION CONDUCTIVE CRYSTAL BODY AND ALL-SOLID STATE LITHIUM ION
SECONDARY BATTERY
Abstract
To provide a lithium ion conductive crystal body having a high
density and a large length and an all-solid state lithium ion
secondary battery containing the lithium ion conductive crystal
body. A Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body, which is one
example of the lithium ion conductive crystal body, has a relative
density of 99% or more, belongs to a cubic system, has a
garnet-related type structure, and has a length of 2 cm or more.
The Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body is grown by a
melting method employing a Li.sub.5La.sub.3Ta.sub.2O.sub.12
polycrystal body as a raw material. With the growing method, a
Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body having a relative
density of 100% can also be obtained. In addition, the all-solid
state lithium ion secondary battery has a positive electrode, a
negative electrode, and a solid electrolyte, in which the solid
electrolyte contains the lithium ion conductive crystal body.
Inventors: |
KATAOKA; Kunimitsu;
(Tsukuba-shi, JP) ; AKIMOTO; Junji; (Tsukuba-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND
TECHNOLOGY |
Tokyo |
|
JP |
|
|
Assignee: |
National Institute of Advanced
Industrial Science and Technology
Tokyo
JP
|
Family ID: |
55857662 |
Appl. No.: |
15/517125 |
Filed: |
October 30, 2015 |
PCT Filed: |
October 30, 2015 |
PCT NO: |
PCT/JP2015/080825 |
371 Date: |
April 5, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01G 25/00 20130101;
H01M 10/0585 20130101; H01M 2300/0071 20130101; C01P 2002/77
20130101; C01P 2006/40 20130101; H01M 10/0525 20130101; Y02P 70/50
20151101; C01P 2002/76 20130101; H01B 1/08 20130101; C01G 35/006
20130101; C01P 2004/02 20130101; C01P 2002/50 20130101; H01M
10/0562 20130101; C01G 25/006 20130101; Y02E 60/10 20130101; C01P
2002/30 20130101; H01B 1/122 20130101; C01G 35/00 20130101 |
International
Class: |
H01M 10/0562 20100101
H01M010/0562; H01M 10/0585 20100101 H01M010/0585; H01M 10/0525
20100101 H01M010/0525; C01G 35/00 20060101 C01G035/00; C01G 25/00
20060101 C01G025/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2014 |
JP |
2014-223346 |
Claims
1. A lithium ion conductive crystal body comprising: chemical
composition represented by
Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12 (0.05<x<0.50),
Li.sub.5La.sub.3Ta.sub.2O.sub.12, or
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12; having a relative density of
99% or more; belonging to a cubic system; having a garnet-related
type structure; and having a length of 2 cm or more.
2. The lithium ion conductive crystal body according to claim 1,
wherein the lithium ion conductive crystal body is grown by a
melting method employing a raw material containing a polycrystal
body having a chemical composition represented by
Li.sub.7La.sub.3Zr.sub.2O.sub.12, belonging to a tetragonal system,
and having a garnet-related type structure and at least one of an
Al.sub.2O.sub.3 polycrystal body and a LiAlO.sub.2 polycrystal
body, and has a chemical composition represented by
Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12
(0.05<x<0.50).
3. The lithium ion conductive crystal body according to claim 1,
wherein the lithium ion conductive crystal body is grown by a
melting method employing a polycrystal body represented by a same
chemical composition as a raw material.
4. The lithium ion conductive crystal body according to claim 1,
wherein the relative density is 100%.
5. The lithium ion conductive crystal body according to claim 1,
wherein the body has a a grating constant a is 1.28
nm.ltoreq.a.ltoreq.1.31 nm.
6. A method for producing a lithium ion conductive crystal body
having a chemical composition represented by
Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12 (0.05<x<0.50),
Li.sub.5La.sub.3Ta.sub.2O.sub.12, or
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12, having a relative density of
99% or more, belonging to a cubic system, and having a
garnet-related type structure, the method comprising: melting at
least a part of a raw material of a polycrystal body represented by
a same chemical composition as the chemical composition of the
lithium ion conductive crystal body to form a melted portion, and
then moving the melted portion at a movement speed of 8 mm/h or
more.
7. A method for producing a lithium ion conductive crystal body
having a chemical composition represented by
Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12 (0.05<x<0.50),
having a relative density of 99% or more, belonging to a cubic
system, and having a garnet-related type structure, the method
comprising: melting at least a part of a raw material containing a
polycrystal body having a chemical composition represented by
Li.sub.7La.sub.3Zr.sub.2O.sub.12, belonging to a tetragonal system,
and having a garnet-related type structure and at least one of an
Al.sub.2O.sub.3 polycrystal body and a LiAlO.sub.2 polycrystal body
to form a melted portion, and moving the melted portion at a
movement speed of 8 mm/h or more.
8. The method for producing a lithium ion conductive crystal body
according to claim 6, wherein the movement speed is 8 mm/h or more
and 19 mm/h or less.
9. The method for producing a lithium ion conductive crystal body
according to claim 6, wherein the raw material is melted while
rotating the rod-shaped raw material on a plane perpendicular to a
longitudinal direction at a rotation speed of 30 rpm or more.
10. The method for producing a lithium ion conductive crystal body
according to claim 9, wherein the rotation speed is 30 rpm or more
and 60 rpm or less.
11. An all-solid state lithium ion secondary battery comprising: a
positive electrode; a negative electrode; and a solid electrolyte,
wherein the solid electrolyte contains the lithium ion conductive
crystal body according to claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to a high-density lithium ion
conductive crystal body and an all-solid state lithium ion
secondary battery containing the lithium ion conductive crystal
body as a solid electrolyte.
BACKGROUND ART
[0002] Since the energy density is high and operation at a high
potential is achieved as compared with secondary batteries, such as
a nickel-cadmium battery and a nickel-hydride battery, a lithium
ion secondary battery has been widely used for small information
devices, such as a cellular phone and a notebook PC. In recent
years, since a reduction in size and weight is easily achieved, a
demand as a secondary battery for hybrid vehicles and electric
vehicles has increased. Considering safety, an all-solid state
lithium ion secondary battery containing no flammable electrolytic
solution has been researched and developed. A solid electrolyte for
use in the all-solid state lithium ion secondary battery has been
required to have high ion conductivity.
[0003] As an oxide having high lithium ion conductivity, Li.sub.7
La.sub.3.1Zr.sub.1.9O.sub.12 having a cubic garnet-related type
crystal structure produced by a high temperature sintering method
is known (Patent Document 1). However, according to the high
temperature sintering method, only a crystal body having a diameter
of about several tens to several hundreds of .mu.m is obtained. The
crystal body of this size cannot be used as a solid electrolyte of
all-solid state lithium ion secondary battery products. For the
application to all-solid state lithium ion secondary battery
products, a lithium ion conductive crystal body is required which
has an area equal to or larger than a circle having a diameter of
about 1 cm and which can be formed into a thin piece in order to
reduce an electrical resistance value.
CITATION LIST
Patent Document
[0004] Patent Document 1: Japanese Unexamined Patent Application
Publication No. 2011-195373
SUMMARY
Technical Problem
[0005] The present invention has been made in view of such
circumstances. It is an object of the present invention to provide
a lithium ion conductive crystal body having a high-density and a
large length and an all-solid state lithium ion secondary battery
containing the lithium ion conductive crystal body as a solid
electrolyte.
Solution to Problem
[0006] The present inventors have considered that high-density
Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12 (0.05<x<0.50),
Li.sub.5La.sub.3Ta.sub.2O.sub.12, and
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12 crystal bodies in which no grain
boundary is present are obtained by conceiving a method for
producing a crystal body, so that the above-described problem can
be solved. Then, as a result of extensively examining a method for
producing a crystal body including melting a polycrystal body
sample at a high temperature, and then cooling the same, the
present inventors have confirmed that
Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12 (0.05<x<0.50),
Li.sub.5La.sub.3Ta.sub.2O.sub.12, and
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12 crystal bodies having a
high-density and a garnet-related type structure can be grown and
these crystal bodies can be mechanically formed into a thin piece,
and thus have completed the present invention.
[0007] The chemical composition of the lithium ion conductive
crystal body of the present invention is represented by
Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12 (0.05<x<0.50),
Li.sub.5La.sub.3Ta.sub.2O.sub.12, or
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12, has a relative density of 99%
or more, belongs to a cubic system, has a garnet-related type
structure, and has a length of 2 cm or more.
[0008] A method for producing a lithium ion conductive crystal body
of the present invention is a method for producing a lithium ion
conductive crystal body having a chemical composition represented
by Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12 (0.05<x<0.50),
Li.sub.5La.sub.3Ta.sub.2O.sub.12, or
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12, having a relative density of
99% or more, belonging to a cubic crystal system, and having a
garnet-related type structure, and the method includes a process of
melting at least a part of a raw material of a polycrystal
represented by the same chemical composition as that of the lithium
ion conductive crystal body to form a melted portion, and then
moving the melted portion at a movement speed of 8 mm/h or
more.
[0009] A method for producing another lithium ion conductive
crystal body of the present invention is a method for producing a
lithium ion conductive crystal body having a chemical composition
represented by Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12
(0.05<x<0.50), having a relative density of 99% or more,
belonging to a cubic crystal system, and having a garnet-related
type structure, and the method includes a process of melting at
least a part of a raw material containing a polycrystal body having
a chemical composition represented by
Li.sub.7La.sub.3Zr.sub.2O.sub.12, belonging to a tetragonal crystal
system, and having a garnet-related type structure and at least one
of an Al.sub.2O.sub.3 polycrystal body and a LiAlO.sub.2
polycrystal body to form a melted portion, and then moving the
melted portion at a movement speed of 8 mm/h or more.
[0010] An all-solid state lithium ion secondary battery of the
present invention has a positive electrode, a negative electrode,
and a solid electrolyte, in which the solid electrolyte contains
the lithium ion conductive crystal body of the present
invention.
Advantageous Effects of Invention
[0011] According to the present invention, a lithium ion conductive
crystal body having a high-density and a large length and an
all-solid state lithium ion secondary battery containing the
lithium ion conductive crystal body as a solid electrolyte are
obtained.
BRIEF DESCRIPTION OF DRAWINGS
[0012] FIG. 1 is a photograph of the appearance of a cubic system
Li.sub.6.46Al.sub.0.18La.sub.3Zr.sub.2O.sub.12 crystal body
obtained in Examples.
[0013] FIG. 2 is a photograph of the appearance of a cubic system
Li.sub.6.1Al.sub.0.3La.sub.3Zr.sub.2O.sub.12 crystal body obtained
in Examples.
[0014] FIG. 3 is a photograph of the appearance of a cubic system
Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body obtained in
Examples.
[0015] FIG. 4 is a photograph of the appearance of a cubic system
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12 crystal body obtained in
Examples.
[0016] FIG. 5 is a single crystal X-ray diffraction pattern of the
cubic system Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body obtained
in Examples.
[0017] FIG. 6 is a schematic view illustrating a garnet-related
type structure of the cubic system Li.sub.5La.sub.3Ta.sub.2O.sub.12
crystal body obtained in Examples.
[0018] FIG. 7 is a photograph of the appearance of thin pieces of
the cubic system Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12 crystal body
obtained in Examples.
[0019] FIG. 8 is the Nyquist plot of the cubic system
Li.sub.6.1Al.sub.0.3La.sub.3Zr.sub.2O.sub.12 crystal body obtained
in Examples.
DESCRIPTION OF EMBODIMENT
[0020] Hereinafter, a lithium ion conductive crystal body, a method
for producing Li.sub.5La.sub.3Ta.sub.2O.sub.12,
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12, and
Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12 crystal bodies, and an
all-solid state lithium ion secondary battery of the present
invention are described in detail based on Embodiment and Examples.
An overlapped description is omitted as appropriate.
[0021] The present inventors have found that, by molding
polycrystalline powder of Li.sub.5La.sub.3Ta.sub.2O.sub.12 and
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12 into a rod shape, and then
melting and rapidly cooling the rod-shaped polycrystal body by a
floating zone (FZ) method employing infrared ray converging
heating, a crystal body having high-density and a large length can
be produced, and then have completed the present invention. A
lithium ion conductive crystal body according to an embodiment of
the present invention has a chemical composition represented by
Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12 (0.05<x<0.50),
Li.sub.5La.sub.3Ta.sub.2O.sub.12, or
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12, has a relative density of 99%
or more, belongs to a cubic system, and has a garnet-related type
structure. In this embodiment, the length of the ion conductive
crystal body is 2 cm or more.
[0022] The relative density is calculated by measuring the outer
shape of a produced thin piece, calculating the apparent volume,
and then dividing the apparent density calculated from the
measurement mass by a true density obtained from a single crystal
X-ray structure analysis result. The lithium ion conductive crystal
body of this embodiment having a higher relative density is more
preferable. In the lithium ion conductive crystal body of this
embodiment, all crystal domains do not need to face in the same
direction.
[0023] The high-density lithium ion conductive crystal body has
high strength, and therefore can be easily cut into an arbitrary
thickness with a diamond cutter or the like. For example, a thin
piece having a thickness of about 0.1 mm can be mechanically
produced. A lithium ion conductive crystal body having a relative
density of 100%, i.e., an original lithium ion conductive single
crystal body, is particularly excellent in lithium ion
conductivity. When a ratio where the crystal domains of the lithium
ion conductive crystal body are aligned in the same direction is
high, diffraction spots are observed as clear points in the X-ray
diffraction measurement using a single crystal.
[0024] In a lithium ion conductive crystal body in which the
directions of the crystal domains of are not aligned, diffraction
spots are complicated or the diffractions from various domains are
overlapped, so that the diffraction spots are close to a ring
shape. The crystal body was produced by moving a melted portion at
10 mm/h in the FZ method. Therefore, the cooling rate of the melted
portion increases, so that growing cannot be performed in such a
manner that the directions of the crystal domains are always
uniform in the crystal body.
[0025] The lithium ion conductive crystal body of this embodiment
satisfies at least one of (1) and (2) below: (1) the Nyquist plot
by alternative current impedance measurement does not show a
resistance component due to a grain boundary but shows only a
resistance component of the material itself; and (2) a diffraction
spot appears in a diffraction pattern in X-ray diffraction
measurement, neutron diffraction measurement, or electron
diffraction measurement using a single crystal. The diffraction
spot sometimes appears only in a spot shape or sometimes appears in
a spot shape and a ring shape.
[0026] The lithium ion conductive crystal body of this embodiment
is produced by melting at least a part of a raw material of a
polycrystal body to form a melted portion, and then moving the
melted portion at a movement speed of 8 mm/h or more. Specifically,
the lithium ion conductive crystal body is grown by a floating zone
(FZ) method, a Czochralski (CZ) method, a Bridgman method, a
Pedestal method, and the like. A suitable method may be selected
from these methods according to the size, shape, and the like of a
lithium ion conductive crystal body to be produced.
[0027] The lithium ion conductive crystal body of this embodiment
may be grown by a melting method employing a polycrystal body
represented by the same chemical composition as a raw material.
More specifically, a Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12
(0.05<x<0.50) crystal body is grown by a melting method
employing a Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12
(0.05<x<0.50) polycrystal body as a raw material, a
Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body is grown by a melting
method employing a Li.sub.5La.sub.3Ta.sub.2O.sub.12 polycrystal
body as a raw material, and a Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12
crystal body is grown by a melting method employing a
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12 polycrystal body as a raw
material.
[0028] The lithium ion conductive crystal body having a chemical
composition represented by
Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12 (0.05<x<0.50),
having a relative density of 99% or more, belonging to a cubic
system, and having a garnet-related type structure may be grown by
melting at least a part of a raw material containing a polycrystal
body having a chemical composition represented by
Li.sub.7La.sub.3Zr.sub.2O.sub.12, belonging to a tetragonal system,
and having a garnet-related type structure and at least one of an
Al.sub.2O.sub.3 polycrystal body and a LiAlO.sub.2 polycrystal body
to form a melted portion, and then moving the melted portion at a
movement speed of 8 mm/h or more.
[0029] In the case of producing the lithium ion conductive crystal
body of this embodiment by the FZ method, a part of a rod-shaped
polycrystal body raw material is melted while being rotated on a
plane perpendicular to the longitudinal direction, and then moving
the melted portion in the longitudinal direction to thereby grow
the lithium ion conductive crystal body. By setting the movement
speed of the melted portion to be as high as 8 mm/h or more, the
decomposition of the raw material involved in the volatilization of
the lithium is avoided. The movement speed of the melted portion is
preferably 8 mm/h or more and 19 mm/h or less. In the melted
portion, the lithium tends to volatilize, so that air bubbles are
generated. However, the air bubbles can be removed by setting the
rotation speed of the rod-shaped polycrystal body raw material to
be as high as 30 rpm or more. The rotation speed of the raw
material is preferably 30 rpm or more and 60 rpm or less.
[0030] It is preferable to perform the melting of the raw material
and the movement of the melted portion in a dry air atmosphere.
Thus, the lithium ion conductive crystal body having a relative
density of 99% or more can be produced. A method for producing a
lithium ion conductive crystal body is described taking the growing
of a Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body having a
relative density of 99% or more, belonging to a cubic system,
having a garnet-related type structure, and having a length of 2 cm
or more as an example.
[0031] First, a rod-shaped Li.sub.5La.sub.3Ta.sub.2O.sub.12
polycrystal body raw material is produced as follows. More
specifically, a lithium compound, a lanthanum compound, and a
tantalum compound are weighed so that Li:La:Ta is 6-7:3:2 in terms
of a molar ratio considering the fact that the lithium is
volatilized at a high temperature. The lithium compound is not
particularly limited insofar as lithium is contained, and
Li.sub.2O, Li.sub.2CO.sub.3, and the like are mentioned. The
lanthanum compound is not particularly limited insofar as lanthanum
is contained and La.sub.2O.sub.3, La(OH).sub.3, and the like are
mentioned. The tantalum compound is not particularly limited
insofar as tantalum is contained and Ta.sub.2O.sub.5, TaCl.sub.5,
and the like are mentioned. Using a compound containing two or more
kinds of lithium, lanthanum, and tantalum, e.g., LaTaO.sub.4,
LiTaO.sub.3, or the like, the compound may be weighed so that
Li:La:Ta is 6-7:3:2 in terms of a molar ratio.
[0032] Next, the weighed compounds are mixed. A mixing method is
not particularly limited insofar as these compounds can be
uniformly mixed, and these compounds may be mixed by a wet method
or a dry method using mixing devices, such as a mixer, for example.
Then, the obtained mixture is charged into a crucible with a cover,
and then calcined at 900.degree. C. to 1000.degree. C. and
preferably 930.degree. C. to 990.degree. C., whereby polycrystal
body powder serving as a raw material is obtained. It is more
preferable to repeat pulverization, mixing, and baking of the
once-calcined product again. The polycrystal body powder belongs to
the cubic system.
[0033] Next, in order to facilitate molding, the obtained
polycrystal body powder is pulverized to reduce the particle size.
A pulverization method is not particularly limited insofar as the
powder can be pulverized and, for example, the powder may be
pulverized by a wet method or a dry method using a pulverization
device, such as a planetary ball mill, a pot mill, or a bead mill.
Then, the obtained pulverized substances are charged into a rubber
tube, and then molded into a rod shape by a hydrostatic press.
Next, the obtained molded substance is baked at about 800.degree.
C. to 1300.degree. C. and preferably 900.degree. C. to 1100.degree.
C., whereby a rod-shaped Li.sub.5La.sub.3Ta.sub.2O.sub.12
polycrystal body raw material is obtained. The rod-shaped
polycrystal body raw material belongs to the cubic system.
[0034] Then, the rod-shaped polycrystal body raw material is melted
in an infrared ray converging heating furnace, and then rapidly
cooled, whereby a Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body
having a relative density of 99% or more, having the garnet-related
structure, and having a length of 2 cm or more is produced. The
Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body to be produced
belongs to the cubic system. Thus, a
Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body having a high-density
and a large length can be produced. A
Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body having a relative
density of 100% can also be produced. The grating constant a of the
lithium ion conductive crystal body of this embodiment is 1.28 nm a
1.31 nm.
[0035] When producing the Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal
body by the CZ method, the production is performed by the following
procedure. First, a Li.sub.5La.sub.3Ta.sub.2O.sub.12 polycrystal
body as a raw material is placed in a crucible, and then heated for
melting. Next, a seed crystal is dipped in a melt of the raw
material, and then pulled up while rotating. It is considered that,
by setting the movement speed of the melted portion, i.e., the
pull-up speed of the seed crystal, to be as high as 8 mm/h or more,
the volatilization of the lithium is prevented, and a high-density
Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body is obtained. The
lithium ion conductive crystal body of this embodiment has a length
of 2 cm or more. Therefore, thin pieces having the same quality can
be easily produced by cutting.
[0036] A method for producing a
Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12 (0.05<x<0.50)
crystal body is the same as the method for producing the
Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body. An aluminum compound
serving as a raw material is not particularly limited insofar as Al
is contained and Al.sub.2O.sub.3, LiAlO.sub.2, and the like are
mentioned. A zirconium compound serving as a raw material is not
particularly limited insofar as zirconium is contained and
ZrO.sub.2, ZrCl.sub.4, La.sub.2Zr.sub.2O.sub.7, Li.sub.2ZrO.sub.3,
and the like are mentioned. A method for producing a
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12 crystal body is the same as the
method for producing the Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal
body. A barium compound serving as a raw material is not
particularly limited insofar as barium is contained and BaCO.sub.3,
BaO, and the like are mentioned.
[0037] The lithium ion conductive crystal body of the present
invention is excellent in lithium ion conductivity, and therefore
is usable for a solid electrolyte of an all-solid state lithium ion
secondary battery. More specifically, an all-solid state lithium
ion secondary battery of the present invention has a positive
electrode, a negative electrode, and a solid electrolyte, in which
the solid electrolyte contains the lithium ion conductive crystal
body of the present invention. The solid electrolyte is a
high-density lithium ion conductive crystal body, and therefore, in
an all-solid state lithium battery in which a negative electrode is
metallic lithium, a short circuit due to penetration of the
metallic lithium in charge/discharge can be prevented. Moreover,
the solid electrolyte can be formed into a thin piece, and
therefore the energy density per unit mass of the battery can be
increased.
EXAMPLES
Example 1: Production of
Li.sub.6.46Al.sub.0.18La.sub.3Zr.sub.2O.sub.12 Crystal Body
[0038] (Production of Li.sub.7La.sub.3Zr.sub.2O.sub.12 Polycrystal
Body Powder)
[0039] First, 10.6861 g of lithium carbonate Li.sub.2CO.sub.3
(manufactured by RARE METALLIC Co., LTD., Purity of 99.99%),
16.8280 g of lanthanum oxide La.sub.2O.sub.3 (manufactured by RARE
METALLIC Co., LTD., Purity of 99.99%), and 8.4859 g of zirconium
dioxide ZrO.sub.2 (manufactured by RARE METALLIC Co., LTD., Purity
of 99.99%) as starting materials were placed in an agate mortar,
and then uniformly mixed by a wet method employing ethanol. For the
lanthanum oxide, one which was calcined at 900.degree. C.
beforehand was used.
[0040] As the molar ratio Li:La:Zr of the metals of the mixture,
lithium is 20 mol % excessive as compared with the stoichiometric
ratio of Li.sub.7La.sub.3Zr.sub.2O.sub.12 which is a target
substance. More specifically, as the quantity, the chemical
composition is equivalent to Li.sub.8.4La.sub.3Zr.sub.2O.sub.12.
Next, 36 g of the mixture was charged into an alumina crucible with
a cover (manufactured by NIKKATO CORPORATION, C5 type). Then, the
crucible was placed in a box type electric furnace (manufactured by
YAMATO SCIENTIFIC CO., LTD., FP100 type), and then calcined at
950.degree. C. for 5 hours, whereby powder was obtained. Next, the
obtained powder was pulverized with the mortar, and then baked at
980.degree. C. for 10 hours twice, whereby
Li.sub.7La.sub.3Zr.sub.2O.sub.12 polycrystal body powder was
produced.
[0041] (Production of Mixed Powder of
Li.sub.7La.sub.3Zr.sub.2O.sub.12 Polycrystal Body and
Al.sub.2O.sub.3 Polycrystal Body)
[0042] 30 g of the Li.sub.7La.sub.3Zr.sub.2O.sub.12 polycrystal
body powder obtained in the process above, 0.6 g of aluminum oxide
Al.sub.2O.sub.3 (manufactured by RARE METALLIC Co., LTD., Purity of
99.99%) polycrystal body, 50 g of zirconia balls having a diameter
of 5 mm, and 14 mL of ion exchanged water were charged into a
pulverization container made from zirconia and having a capacity of
45 mL, and then rotated at a number of revolutions of 200 rpm for
300 minutes in total using a planetary ball mill (manufactured by
Fritsch, Germany, Type P-6) to be pulverized. The polycrystal body
powder after the pulverization was dried at 100.degree. C. for 24
hours, and classified using a sieve having an opening of 250 .mu.m
to obtain mixed powder of the Li.sub.7La.sub.3Zr.sub.2O.sub.12
polycrystal body and the Al.sub.2O.sub.3 polycrystal body.
[0043] (Production of Rod-Shaped Mixture of
Li.sub.7La.sub.3Zr.sub.2O.sub.12 Polycrystal Body and
Al.sub.2O.sub.3 Polycrystal Body)
[0044] A rod-shaped mixture of the Li.sub.7La.sub.3Zr.sub.2O.sub.12
polycrystal body and the Al.sub.2O.sub.3 polycrystal body was
produced using the mixed powder classified in the process above by
the following procedure. First, 26 g of the mixed powder was
charged into a rubber mold, followed by degassing. Next, the mold
was placed in water in a state of being sealed, and then held at 40
MPa for 5 minutes. Then, the water pressure was reduced, and then
the molded substance was taken out from the mold. The molded
substance had a cylindrical shape having a diameter of 1.0 cm and a
height of 4.8 cm. Next, the cylindrical molded substance was baked
at 1150.degree. C. for 8 hours using a box type electric furnace
(manufactured by DENKEN Co., Ltd., Model Number KDF009). After the
baking, 26 g of a mixture of the Li.sub.7La.sub.3Zr.sub.2O.sub.12
polycrystal body and the Al.sub.2O.sub.3 polycrystal body close to
a column having a width of 0.8 cm and a height of 4 cm was
obtained.
[0045] (Growing 1 of Li.sub.6.46Al.sub.0.18La.sub.3Zr.sub.2O.sub.12
Crystal Body)
[0046] First, the rod-shaped mixture of the
Li.sub.7La.sub.3Zr.sub.2O.sub.12 polycrystal body and the
Al.sub.2O.sub.3 polycrystal body as the raw material obtained in
the process above was disposed in a four ellipse-type infrared ray
converging heating furnace (FZ furnace) (manufactured by Crystal
System, FZ-T-10000H type) having a 1 kW halogen lamp, and then a
dry air atmosphere was set.
[0047] Next, the raw material was heated at an output of 51.9%
while being rotated at 45 rpm on a plane perpendicular to the
longitudinal direction. After a while, a part of the raw material
was melted to form a melted portion. Then, an installation stand on
which the raw material was disposed was lowered at two movement
speeds of 8 mm/h and 19 mm/h to grow a
Li.sub.6.46Al.sub.0.18La.sub.3Zr.sub.2O.sub.12 crystal body. The
chemical composition of the crystal body was analyzed by X-ray
crystal structure analysis. FIG. 1 illustrates a photograph of the
appearance of the Li.sub.6.46Al.sub.0.18La.sub.3Zr.sub.2O.sub.12
crystal body (hereinafter sometimes referred to as "sample 1")
obtained at the lowering speed of 19 mm/h. As illustrated in FIG.
1, the length of the sample 1 was 2.3 cm.
[0048] (Production of Mixed Powder of
Li.sub.7La.sub.3Zr.sub.2O.sub.12 Polycrystal Body and LiAlO.sub.2
Polycrystal Body)
[0049] Mixed powder of a Li.sub.7La.sub.3Zr.sub.2O.sub.12
polycrystal body and a LiAlO.sub.2 polycrystal body was produced in
the same manner as the method for producing the mixed powder of the
Li.sub.7La.sub.3Zr.sub.2O.sub.12 polycrystal body and the
Al.sub.2O.sub.3 polycrystal body, except using 0.8 g of lithium
oxide aluminum LiAlO.sub.2 (manufactured by RARE METALLIC Co.,
LTD., Purity of 99.99%) polycrystal body in place of 0.6 g of the
Al.sub.2O.sub.3 polycrystal body.
[0050] (Production of Rod-Shaped Mixture of
Li.sub.7La.sub.3Zr.sub.2O.sub.12 Polycrystal Body and LiAlO.sub.2
Polycrystal Body)
[0051] A rod-shaped mixture of the Li.sub.7La.sub.3Zr.sub.2O.sub.12
polycrystal body and the LiAlO.sub.2 polycrystal body was produced
in the same manner as the method for producing the rod-shaped
mixture of the Li.sub.7La.sub.3Zr.sub.2O.sub.12 polycrystal body
and the Al.sub.2O.sub.3 polycrystal body, except using the mixed
powder of the Li.sub.7La.sub.3Zr.sub.2O.sub.12 polycrystal body and
the LiAlO.sub.2 polycrystal body in place of the mixed powder of
the Li.sub.7La.sub.3Zr.sub.2O.sub.12 polycrystal body and the
Al.sub.2O.sub.3 polycrystal body.
[0052] (Growing 2 of Li.sub.6.46Al.sub.0.18La.sub.3Zr.sub.2O.sub.12
Crystal Body)
[0053] A Li.sub.6.46Al.sub.0.18La.sub.3Zr.sub.2O.sub.12 crystal
body was grown in the same manner as the method of "Growing 1 of
Li.sub.6.46Al.sub.0.18La.sub.3Zr.sub.2O.sub.12 crystal body" above,
except using the rod-shaped mixture of the
Li.sub.7La.sub.3Zr.sub.2O.sub.12 polycrystal body and the
LiAlO.sub.2 polycrystal body in place the mixture of the rod-shaped
Li.sub.7La.sub.3Zr.sub.2O.sub.12 polycrystal body and the
Al.sub.2O.sub.3 polycrystal body. Thus, even when the aluminum
compounds as the raw material were different, the same crystal body
was able to be grown.
Example 2: Production of
Li.sub.61Al.sub.0.3La.sub.3Zr.sub.2O.sub.12 Crystal Body
[0054] (Production of Mixed Powder of Polycrystal Bodies as Raw
Material)
[0055] First, 7.1588 g of lithium carbonate Li.sub.2CO.sub.3
(manufactured by RARE METALLIC Co., LTD., Purity of 99.99%),
12.9254 g of lanthanum oxide La.sub.2O.sub.3 (manufactured by RARE
METALLIC Co., LTD., Purity of 99.99%), 6.5196 g of zirconium
dioxide ZrO.sub.2 (manufactured by RARE METALLIC Co., LTD., Purity
of 99.99%), and 0.4045 g of .gamma.-type alumina oxide as starting
materials were placed in a mortar, and then uniformly mixed by a
wet method. For the lanthanum oxide, one which was calcined at
900.degree. C. beforehand was used.
[0056] As the molar ratio Li:Al:La:Zr of the metals of the mixture,
lithium is 20 mol % excessive as compared with the stoichiometric
ratio of Li.sub.6.1Al.sub.0.3La.sub.3Zr.sub.2O.sub.12 which is a
target substance. More specifically, as the quantity, the chemical
composition is equivalent to
Li.sub.7.32Al.sub.0.3La.sub.3Zr.sub.2O.sub.12. Next, 27 g of the
mixture was charged into an alumina crucible with a cover
(manufactured by NIKKATO CORPORATION, C5 type). Then, the crucible
was placed in a box type electric furnace (manufactured by DENKEN
Co., Ltd., Model Number KDF009), and then calcined at 850.degree.
C. for 4 hours, whereby mixed powder of the polycrystal bodies was
obtained.
[0057] (Production of Rod-Shaped Mixture of Polycrystal Bodies)
[0058] A rod-shaped mixture of the polycrystal bodies was produced
in the same manner as the method for producing the rod-shaped
mixture of the Li.sub.7La.sub.3Zr.sub.2O.sub.12 polycrystal body
and the Al.sub.2O.sub.3 polycrystal body, except using the mixed
powder of the polycrystal bodies as the raw material above in place
of the mixed powder of the Li.sub.7La.sub.3Zr.sub.2O.sub.12
polycrystal body and the Al.sub.2O.sub.3 polycrystal body.
[0059] (Growing of Li.sub.6.1Al.sub.0.3La.sub.3Zr.sub.2O.sub.12
Crystal Body)
[0060] A Li.sub.6.1Al.sub.0.3La.sub.3Zr.sub.2O.sub.12 crystal body
was grown in the same manner as the method of "Growing 1 of
Li.sub.6.46Al.sub.0.18La.sub.3Zr.sub.2O.sub.12 crystal body" above,
except using the rod-shaped polycrystal body above in place of the
rod-shaped mixture of the Li.sub.7La.sub.3Zr.sub.2O.sub.12
polycrystal body and the Al.sub.2O.sub.3 polycrystal body. Thus, by
the use of the .gamma.-type alumina oxide, the same crystal body
was able to be grown from not only the polycrystal body having the
same chemical composition as that of the lithium ion conductive
crystal body to be produced but the rod-shaped mixture of the
polycrystal bodies. FIG. 2 illustrates a photograph of the
appearance of the obtained
Li.sub.6.1Al.sub.0.3La.sub.3Zr.sub.2O.sub.12 crystal body
(hereinafter also sometimes referred to as "sample 2"). As
illustrated in FIG. 2, the length of the sample 2 was 4 cm.
Example 3: Production of Li.sub.5La.sub.3Ta.sub.2O.sub.12 Crystal
Body
[0061] (Production of Li.sub.5La.sub.3Ta.sub.2O.sub.12 Polycrystal
Body Powder)
[0062] Li.sub.5La.sub.3Ta.sub.2O.sub.12 polycrystal body powder was
produced in the same manner as in Example 1, except using 6.9256 g
of lithium carbonate Li.sub.2CO.sub.3 (manufactured by RARE
METALLIC Co., LTD., Purity of 99.99%), 15.2686 g of lanthanum oxide
La.sub.2O.sub.3 (manufactured by RARE METALLIC Co., LTD., Purity of
99.99%), and 13.8058 g of tantalum oxide Ta.sub.2O.sub.5
(manufactured by RARE METALLIC Co., LTD., Purity of 99.99%) as
starting materials. As the molar ratio Li:La:Ta of the metals of
the mixture of the raw material, lithium is 20 mol % excessive as
compared with the stoichiometric ratio of
Li.sub.5La.sub.3Ta.sub.2O.sub.12 which is a target substance. More
specifically, as the quantity, the chemical composition is
equivalent to Li.sub.6La.sub.3Ta.sub.2O.sub.12.
[0063] (Production of Rod-Shaped Li.sub.5La.sub.3Ta.sub.2O.sub.12
Polycrystal Body)
[0064] A rod-shaped Li.sub.5La.sub.3Ta.sub.2O.sub.12 polycrystal
body was produced using the Li.sub.5La.sub.3Ta.sub.2O.sub.12
polycrystal body powder classified in the process above by the
following procedure. First, 26 g of the
Li.sub.5La.sub.3Ta.sub.2O.sub.12 polycrystal body powder was
charged into a rubber mold, followed by degassing. Next, the mold
was placed in water in a state of being sealed, and then held at 40
MPa for 5 minutes. Then, the water pressure was reduced, and then
the molded substance was taken out from the mold. The molded
substance had a cylindrical shape having a diameter of 1.2 cm and a
height of 7 cm. Next, the molded substance was baked at
1150.degree. C. for 8 hours using a box type electric furnace
(manufactured by DENKEN Co., Ltd., Model Number KDF009). After the
baking, 26 g of a rod-shaped Li.sub.5La.sub.3Ta.sub.2O.sub.12
polycrystal body close to a column and having a width of 1 cm and a
length of 7 cm was obtained.
[0065] (Growing of Li.sub.5La.sub.3Ta.sub.2O.sub.12 Crystal
Body)
[0066] A Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body was obtained
in the same manner as in Example 1 using the rod-shaped
Li.sub.5La.sub.3Ta.sub.2O.sub.12 polycrystal body. FIG. 3
illustrates a photograph of the appearance of the
Li.sub.5La.sub.3Ta.sub.2O.sub.12 crystal body (hereinafter also
sometimes referred to as "sample 3") obtained at a lowering speed
of 19 mm/h. As illustrated in FIG. 3, the length of the sample 3
was 4 cm.
Example 4: Production of Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12
Crystal
[0067] (Production of Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12
Polycrystal Body Powder)
[0068] Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12 polycrystal body powder
was produced in the same manner as in Example 1, except using
6.8699 g of lithium carbonate Li.sub.2CO.sub.3 (manufactured by
RARE METALLIC Co., LTD., Purity of 99.99%), 5.0964 g of barium
carbonate BaCO.sub.3 (manufactured by RARE METALLIC Co., LTD.,
Purity of 99.99%), 12.6215 g of lanthanum oxide La.sub.2O.sub.3
(manufactured by RARE METALLIC Co., LTD., Purity of 99.99%), and
11.4123 g of tantalum oxide Ta.sub.2O.sub.5 (manufactured by RARE
METALLIC Co., LTD., Purity of 99.99%) as starting materials. As the
molar ratio Li:Ba:La:Ta of the metals of the mixture of the
starting materials, lithium is 20 mol % excessive as compared with
the stoichiometric ratio of Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12
which is a target substance. More specifically, as the quantity,
the chemical composition is equivalent to
Li.sub.7.2BaLa.sub.2Ta.sub.2O.sub.12.
[0069] (Production of Rod-Shaped Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12
Polycrystal Body)
[0070] A rod-shaped Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12 polycrystal
body was produced using the Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12
polycrystal body powder classified in the process above by the
following procedure. First, 26 g of the
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12 polycrystal body powder was
charged into a rubber mold, followed by degassing. Next, the mold
was placed in water in a state of being sealed, and then held at 40
MPa for 5 minutes. Then, the water pressure was reduced, and then
the molded substance was taken out from the mold. The molded
substance had a cylindrical shape having a diameter of 1.4 cm and a
height of 9 cm. Next, the molded substance was baked at
1150.degree. C. for 8 hours using a box type electric furnace
(manufactured by DENKEN Co., Ltd., Model Number KDF009). After the
baking, 26 g of a rod-shaped Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12
polycrystal body close to a column and having a width of 1.2 cm and
a length of 8 cm was obtained.
[0071] (Growing of Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12 Crystal
Body)
[0072] A Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12 crystal body was
obtained in the same manner as in Example 1 using the rod-shaped
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12 polycrystal body. FIG. 4
illustrates a photograph of the appearance of the
Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12 crystal body (hereinafter also
sometimes referred to as "sample 4") obtained at a lowering speed
of 19 mm/h. As illustrated in FIG. 4, the length of the sample 4
was 6 cm.
[0073] Evaluation of Lithium Ion Conductive Crystal Body Obtained
in Each Example
[0074] The powder X-ray diffraction pattern of the sample 2 was the
same as the pattern of Li.sub.7-3xAl.sub.xLa.sub.3Zr.sub.2O.sub.12
of the cubic system garnet-related structure reported until now.
The grating constant a calculated from the result of the powder
X-ray structure analysis was a=1.30208 nm.+-.0.00004 nm.
[0075] The structure of the sample 3 was investigated using a
single crystal X-ray diffraction device (manufactured by Rigaku
Corporation, R-AXIS RAPID-II). FIG. 5 illustrates the X-ray
diffraction pattern of the sample 3. As illustrated in FIG. 5,
clear diffraction points were able to be measured. When diffraction
intensity data was collected by a program RAPID AUTO attached to
the single crystal X-ray diffraction device, and then the crystal
structure of the sample 3 was investigated by a crystal structure
analysis program Jana 2006, it was found that the sample 3 belongs
to a cubic system. As a result of the crystal structure analysis of
the sample 3, it was clarified that the crystal structure is the
same as that of Li.sub.5La.sub.3Ta.sub.2O.sub.12 reported before as
illustrated in FIG. 6. Since the R factor showing the reliability
of the crystal structure analysis of the sample 3 was 2.04%, it can
be said that the crystal structure analysis result is
appropriate.
[0076] When the grating constant a of the sample 2 was determined
by a least-squares method using the reflection observed in the
single crystal X-ray diffraction measurement, 1.2816 nm.+-.0.003 nm
was obtained. It was confirmed from the grating constant that the
sample 2 is a lithium composite oxide belonging to the cubic system
and having the garnet-related type structure. Thin pieces having a
thickness of about 0.1 mm were produced from the sample 3 and the
sample 4, and then powder X-ray diffraction measurement was
performed using a powder X-ray diffraction device (manufactured by
Rigaku Corporation, Smart Lab). As a result, the diffraction
pattern of the cubic system garnet-related type compound reported
before applied to the thin pieces of the sample 3 and the sample
4.
[0077] As a result of calculating the grating constants a1 and a2
of the thin pieces of the sample 3 and the sample 4, the following
values were obtained:
Grating constant a1 of Sample 3=1.282227 nm.+-.0.000007 nm;
Grating constant a2 of Sample 4=1.29118 nm.+-.0.00004 nm.
[0078] As a result of measuring the density of the molded body of
the sample 3 at two or more portions, the relative densities were
99.2%, 99.5%, 99.8%, and 100% to the true density calculated from
the crystal structure. The relative density of the sample 4 was
also 99% or more. When the sample 4 was cut with a diamond cutter,
thin pieces having a thickness of 0.3 mm and 0.086 mm were able to
be produced as illustrated in FIG. 7. Thus, thin pieces can be
obtained, and therefore, when the lithium ion conductive crystal
body of this embodiment is used as a solid electrolyte of an
all-solid state lithium ion secondary battery, the electrical
resistance value of the solid electrolyte can be reduced.
[0079] The sample 2 was cut to produce a thin piece having a
diameter of about 0.8 cm and a thickness of about 0.09 cm. 40 nm
thick gold of a circle having a diameter of 0.2 cm was sputtered
onto the front side and the back side of the thin piece to form an
electrode. Then, the impedance of the sample 2 was measured by
subjecting the sample to an alternative current impedance method
(Measuring device: Solartron, 1260) at 25.degree. C. in a nitrogen
atmosphere. FIG. 8 illustrates the Nyquist plot at this time. The
lithium ion conductivity was calculated to be 3.3.times.10.sup.-5
S/cm from the Nyquist plot illustrated in FIG. 8.
INDUSTRIAL APPLICABILITY
[0080] The lithium ion conductive crystal body of the present
invention is usable for a material of a solid electrolyte of an
all-solid state lithium ion secondary battery, for example.
* * * * *