Epitaxial thin film solid crystal electrolyte including lithium

Abstract

Provided is a solid electrolyte including an epitaxial thin film crystal made of an electrolyte containing at least lithium.

Claims

1. A solid electrolyte comprising: an epitaxial thin film crystal made of an electrolyte containing at least lithium, wherein a surface of the epitaxial thin film crystal includes terraces that are arranged in a stepped configuration, wherein the electrolyte is at least one electrolyte selected from the group consisting of La.sub.2/3xLi.sub.3xTiO.sub.3 (0<x<), La.sub.0.5Li.sub.0.5TiO.sub.3, Li.sub.7La.sub.3Zr.sub.2O.sub.12, Li.sub.9SiAlO.sub.3, Li.sub.5La.sub.3Ta.sub.2O.sub.12, Li.sub.5La.sub.3Nb.sub.2O.sub.12, Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12, Li.sub.3.6Si.sub.0.6P.sub.0.4O.sub.4, LiZr.sub.2(PO.sub.4).sub.3, Li.sub.14Zn(GeO.sub.4).sub.4, Li.sub.3.25Ge.sub.0.25P.sub.0.75S.sub.4, Li.sub.10GeP.sub.2S.sub.12, Li.sub.4+xM.sub.xSi.sub.1xO.sub.4(M=B, Al), Li.sub.1+xAl.sub.xTi.sub.2x(PO.sub.4).sub.3 and Li.sub.3N, wherein the epitaxial thin film crystal is epitaxially grown on a single crystal substrate that includes terraces that are atomically flat and that are arranged in a stepped configuration, and wherein the single crystal substrate is at least one substrate selected from the group consisting of an oxide having a perovskite-type crystal structure represented by a general formula ABO.sub.3 (A is at least one element selected from the group consisting of Sr, Ba, La and K, and B is at least one element selected from the group consisting of Ti, Al and Ta), NdGaO.sub.3, YSZ, MgO, Al.sub.2O.sub.3 and Si.

2. The solid electrolyte according to claim 1, wherein the epitaxial thin film crystal has a mean-square surface roughness measured on a region of 2 m square of 1 nm or less.

3. The solid electrolyte according to claim 1, wherein the oxide having the perovskite-type crystal structure represented by the general formula ABO.sub.3 is at least one oxide selected from the group consisting of SrTiO.sub.3, LaAlO.sub.3 and (LaSr)(AlTa)O.sub.3.

4. The solid electrolyte according to claim 1, wherein the epitaxial thin film crystal includes a domain structure formed by at least two single crystal regions of which crystal orientations are different from each other.

5. The solid electrolyte according to claim 4, wherein the at least one single crystal region is present along an entire thickness direction of the epitaxial thin film crystal.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a sectional view showing an epitaxial thin film crystal constituting a solid electrolyte in accordance with a first Embodiment.

(2) FIG. 2 is a sectional view schematically showing a surface shape of the epitaxial thin film crystal constituting the solid electrolyte in accordance with the first Embodiment.

(3) FIG. 3 is a sectional view showing a state the epitaxial thin film crystal constituting the solid electrolyte in accordance with the first Embodiment is grown on the single crystal substrate.

(4) FIG. 4 is a sectional view schematically showing a surface shape of the single crystal substrate shown in FIG. 3.

(5) FIG. 5 is a drawing-substituting photograph showing an atomic force microscope photograph of a (001) SrTiO.sub.3 single crystal substrate in which a surface is flattened at an atomic level in Example 1.

(6) FIG. 6 is a schematic diagram showing an X-ray diffraction pattern of an LLT thin film prepared on a (001) SrTiO.sub.3 single crystal substrate by a pulsed laser deposition method in Example 1.

(7) FIG. 7 is a schematic diagram showing an X-ray reciprocal lattice mapping of an LLT thin film prepared on a (001) SrTiO.sub.3 single crystal substrate by a pulsed laser deposition method in Example 1.

(8) FIG. 8 is a drawing-substituting photograph showing an atomic force microscope photograph of an LLT thin film formed on a (001) SrTiO.sub.3 single crystal substrate in Example 1.

(9) FIG. 9 is a schematic diagram showing a Cole-Cole plot of an LLT thin film formed on a (001) SrTiO.sub.3 single crystal substrate at 70 C. in Example 1.

(10) FIG. 10 is a sectional view showing an epitaxial thin film crystal constituting a solid electrolyte in accordance with a second embodiment.

(11) FIG. 11A and FIG. 11B are sectional views for describing a method of preparing the solid electrolyte in accordance with the second embodiment.

(12) FIG. 12 is a drawing-substituting photograph showing an atomic force microscope photograph of an LLT thin film formed on a (001) SrTiO.sub.3 single crystal substrate in Example 2.

(13) FIG. 13 is a schematic diagram schematically showing an all solid-state lithium ion battery in accordance with a third embodiment.

(14) FIG. 14 is a sectional view showing a configuration example of the all solid-state lithium ion battery in accordance with the third embodiment.

DETAILED DESCRIPTION

(15) Embodiments for implementing inventions (hereinafter referred to as embodiments) will be described. The description proceeds with the following order.

(16) 1. First embodiment (solid electrolyte and method of preparing same)

(17) 2. Second embodiment (solid electrolyte and method of preparing same)

(18) 3. Third embodiment (all solid-state lithium ion battery)

1. First Embodiment

(19) Solid Electrolyte

(20) FIG. 1 shows an epitaxial thin film crystal 10 constituting a solid electrolyte in accordance with a first embodiment. The epitaxial thin film crystal 10 is made of an oxide containing lithium, a phosphoric acid-based compound, a germanic acid-based compound, a sulfide and a nitride and so on, and specifically made of the various electrolytes already described. The thickness of the epitaxial thin film crystal 10 is not especially restricted, and is generally 0.4 nm or more and 5 m or less, for example.

(21) In this case, the epitaxial thin film crystal 10 is formed wholly by a single crystal region having the same crystal orientation and includes no crystal grain boundary.

(22) As shown in FIG. 2, the epitaxial thin film crystal 10 is suitably configured by flat terraces 10a at an atomic level and steps 10b in a larger part of at least its main surface, and includes a flat surface of which a mean-square surface roughness measured on a region of 2 m square is 1 nm or less. Most suitably, the flat surface is configured by only the terraces 10a and the steps 10b.

(23) While, as shown in FIG. 3, the epitaxial thin film crystal 10 is typically used in a state where it is epitaxially grown on a single crystal substrate 20, it may be used as a single substance which is peeled off from the single crystal substrate 20 after the epitaxial growth. The single crystal substrate 20 can be selected among the various single crystal substrates already described depending on necessity.

(24) As shown in FIG. 4, the single crystal substrate 20 is suitably configured by flat terraces 20a at an atomic level and steps 20b in a larger part of at least its main surface, and includes a flat surface of which a mean-square surface roughness measured on a region of 2 m square is 1 nm or less. Most suitably, the flat surface is configured by only the above terraces 20a and the steps 20b. By using such the single crystal substrate 20 including the flat surface, the surface of the epitaxial thin film crystal 10 epitaxially grown on this single crystal substrate 20 can be made a flat surface as shown in FIG. 2.

(25) Method of Preparing Solid Electrolyte

(26) A method of preparing a solid electrolyte will be described.

(27) At first, a single crystal substrate 20 is prepared. As shown in FIG. 4, a substrate having a flat surface configured by only terraces 20a and steps 20b is suitably used as the single crystal substrate 20.

(28) Then, as shown in FIG. 3, an epitaxial thin film 10 is fabricated by growing an electrolyte containing Li on the single crystal substrate 20 through a PLD method, a sputtering method, an electron beam deposition method, an MOCVD method and an ALE method. In this manner, the solid electrolyte made of the epitaxial thin film crystal 10 is fabricated. While a substrate temperature during the epitaxial growth is appropriately selected depending on the kinds of the single crystal substrate 20 and the electrolyte, it is suitably 200 C. or more and 1200 C. or less, and more suitably 600 C. or more and 900 C. or less. An oxygen partial pressure during the epitaxial growth is 110.sup.5 Pa or more and 110.sup.3 Pa or less, and more suitably 110.sup.1 Pa or more and 110.sup.2 Pa or less. The growth rate is not especially restricted, and appropriately selected.

(29) The epitaxial thin film crystal 10 having the flat surface as shown in FIG. 2 can be obtained by using the single crystal substrate 20 having the flat surface as shown in FIG. 4.

Example 1

(30) As the single crystal substrate 20, an SrTiO.sub.3 single crystal substrate (plane direction (001), 10 mm10 mmthickness 0.5 mm, available from Shinkosha Co., Ltd,) of which a surface was flattened by a method described in Non-Patent Literature 4 was prepared. An atomic force microscope (AFM) photograph of the surface of this SrTiO.sub.3 single crystal substrate is shown in FIG. 5. As shown in FIG. 5, the surface of the this SrTiO.sub.3 single crystal substrate can be found to be configured by only terraces flat at an atomic level and steps.

(31) Then, the vacuum chamber of a pulsed laser deposition apparatus (available from Pascal Corporation) was evacuated to 110.sup.5 or less. After the prepared SrTiO.sub.3 single crystal substrate and a sintered target having composition of La.sub.2/3xLi.sub.3xTiO.sub.3 (18 mm5 mm, available from Toshima Manufacturing Co., Ltd., x=0.05, 0.1, 0.167) were mounted in the vacuum chamber, pure oxygen gas was introduced such that the inner pressure of the chamber became to 5 Pa. Thereafter, the SrTiO.sub.3 single crystal substrate was heated to 850 C., and the self-rotating target was ablated by radiating the collected excimer laser pulses (2 J per one pulse and 1 cm.sup.2, laser oscillation frequency: 10 Hz) and was accumulated for 30 minutes on the SrTiO.sub.3 single crystal substrate placed on an opposite position, After the thus prepared thin film was cooled until the substrate temperature reached 200 C. in the vacuum chamber, it was taken out to atmospheric air. The thickness of the thin film was 56 nm.

(32) In order to investigate the chemical composition of the thus-prepared thin film, an ICP-MS analysis was conducted. As a result, the LiLa ratio of the thin film prepared by using the sintered target of the La.sub.2/3xLi.sub.3xTiO.sub.3 (x=0.167) composition was 1.1 which was in accord with the target composition (La.sub.2/3xLi.sub.3xTiO.sub.3) in an error range. Accordingly, the obtained thin film can be identified as an LLT thin film.

(33) The crystal evaluation of the obtained LLT thin film was conduced by using a high resolution thin film X-ray diffraction apparatus (XRD, ATX-G available from Rigaku Corporation). An out-of plane XRD pattern (an X-ray diffraction pattern obtained by diffraction on a lattice surface parallel to a sample) is shown in FIG. 6. As shown in FIG. 6, a sharp diffraction peak of the thin film together with a 002 diffraction peak of the SrTiO.sub.3 was observed, and an interference pattern which suggests the significantly high degree of the orientation of the thin film was observed around them. When an out-of-plane locking curve was measured, its half-band width was 0.02 which was in accord with that of the SrTiO.sub.3 single crystal substrate. A result of reciprocal lattice mapping measurement in the vicinity of the 103 diffraction peak of SrTiO.sub.3 was shown in FIG. 7. As shown in FIG. 7, it was found that the crystal lattice of the thin film along an in-plane direction was in accord with SrTiO.sub.3. As a result of the crystal evaluation by the above X-ray diffraction, it was found that the prepared thin film was the LLT epitaxial thin film crystal.

(34) A surface shape of the prepared LLT thin film was observed with AFM. An AFM image is shown in FIG. 8. As shown in FIG. 8, a surface is observed which is flat at an atomic level and configured by only terraces having a width of about 200 nm and a surface flat at an atomic level, and steps of a height of 0.4 nm corresponding to one unit lattice of LLT. A mean-square surface roughness (Rrms) was about 0.3 nm which was in accord with that of the SrTiO.sub.3 having the flattened surface.

(35) A lithium ion conductivity of the prepared LLT film (x=0.1) was measured as follows. That is, a comb-shaped electrode was fabricated by DC-sputtering gold (Au) on the surface of the prepared LLT thin film, and the lithium ion conductivity was measured with an impedance analyzer (YHP4192A, available from Yokogawa Hewlett-Packard Company, 5 Hz to 13 MHz). The Cole-Cole plot of the LLT thin film (x=0.1) measured at 70 C. was shown in FIG. 9. As shown in FIG. 9, similarly to the report of Inaguma et al, a half circle showing bulk conduction is shown in the higher frequency region, and spread of resistances originating from electrode-LLT thin film interface resistances is shown in a lower frequency region. The lithium ion conductivities of the bulk components at 50 to 70 C. are summarized in Table 1. The lithium ion conductivities comparable to the reported values of the bulk single crystals of Inaguma et al. (Non-Patent Literature 3) were obtained.

(36) TABLE-US-00001 TABLE 1 Temperature ( C.) 50 60 70 Conductivity 0.93 1.5 2.3 (mS/cm) Values in literature 1.3 1.8 2.8 (mS/cm)

(37) It was found from the above that the prepared LLT thin film includes the same chemical compositions as that of the target material, exhibits the lithium ion conductivity comparable to that of the single crystal and is the epitaxial thin film having the surface which is flat at an atomic level.

(38) In accordance with this first embodiment, the following advantages can be obtained. That is, the epitaxial thin film 10 constituting the solid electrolyte includes no crystal grain boundary and exhibits the lithium ion conductivity comparable to that of the bulk single crystal. That is, because of the absence of the crystal grain boundary in this epitaxial thin film, the conductivity comparable to the lithium ion conductivity of an organic electrolyte can be obtained. For example, the LLT single crystal thin film without the crystal grain boundary which is configured by the terraces being flat at the atomic level and the steps and includes the flat surface of which the mean-square surface roughness measured on the region of 2 m square is 1 nm or less can be prepared by epitaxially growing the La.sub.2/3xLi.sub.3xTiO.sub.3 (0<x<) LLT thin film on the SrTiO.sub.3 single crystal substrate through the PLD method. The lithium ion conductivity of this LLT single crystal thin film is comparable to that of the LLT bulk single crystal, and no higher resistant component due to the crystal grain boundary is observed. Since the epitaxial thin film crystal 10 can be prepared by epitaxially growing the electrolyte on the single crystal substrate 20, its surface area is easily increased and the thin film can be used as battery materials.

(39) This excellent epitaxial thin film crystal 10 exhibits charge and discharge characteristics nearly equal to those of an existing lithium ion battery by utilizing as the solid electrolyte of an all solid-state lithium ion battery, and realizes a battery with extremely high safety. Since the LLT single crystal thin film without the crystal grain boundary includes the surface which is flat at the atomic level, the control of a nano-structure such as an artificial superlattice is easy and the thin film can be a model of improving the lithium ion conductivity of the LLT particle interface.

2. Second Embodiment

(40) Solid Electrolyte

(41) FIG. 10 shows an epitaxial thin film crystal 30 constituting a sold electrolyte in accordance with a second embodiment. This epitaxial thin film crystal 30 is made of, similar to the epitaxial thin film crystal 10, an oxide containing Li, a phosphoric acid-based compound, a germanic acid-based compound, a sulfide and a nitride, but is different in including a domain structure. Specifically, this epitaxial thin film crystal 30 is arranged by single crystal regions 30a, 30b separated by coordination surfaces along the parallel to the surfaces. When, for example, the crystal structure of this epitaxial thin film crystal 30 is tetragonal and a c-axis and an a-axis are present on the surface of this epitaxial thin film crystal 30, the c-axis of the single crystal regions 30a and the c-axis of the single crystal regions 30b are misaligned by 90 C. from each other. The single crystal regions 30a, 30b are present suitably along the entire thickness direction of the epitaxial thin film crystal 30, and though FIG. 10 shows such the case, it is not necessarily restricted thereto.

(42) The subjects other than the above are the same as those of the first embodiment.

(43) Method of Preparing Solid Electrolyte

(44) As shown in FIG. 11A, at first, an epitaxial thin film crystal 30 is prepared on a single crystal substrate 20 in accordance with a method the same as that of the first embodiment.

(45) Then, the epitaxial thin film crystal 30 is heated, for example at a temperature of 1000 C. or more and 1500 C. or less for one minute or more and two hours or less, and, more suitably, at a temperature of 1200 C. or more and 1400 C. or less for five minutes or more and 30 minutes or less. The atmosphere during the heating is selected depending on necessity, and is atmospheric air, for example. After the heating, the spontaneous cooling is conducted, for example, in a furnace.

(46) By heating the epitaxial thin film crystal 20, the structure of the crystal regions 30a, 30b separated by the coordination surfaces and alternatively arranged is formed, as shown in FIG. 11b. When, for example, the crystal structure of the epitaxial thin film crystal 30 is tetragonal and a c-axis and an a-axis are present on the surface of this epitaxial thin film crystal 30, such phase separation is likely to take place because of the existence of anisotropy in the surface of the epitaxial thin film crystal 30.

Example 2

(47) The LLT epitaxial thin film crystal prepared in Example 1 was heated at 1300 C. for 10 minutes in atmospheric air. An AFM image of the surface of the LLT epitaxial thin film crystal after the heating is shown in FIG. 12. It is found from FIG. 1 12 that the LLT epitaxial thin film crystal was split into domains by the heating. In reality, it is considered that, since the c-axis and the a-axis are present in the surface of the LLT epitaxial thin film crystal and the c-axis of the single crystal regions 30a and the c-axis of the single crystal regions 30b are misaligned by 90 C. from each other, rearrangements take place at these interfaces.

(48) In accordance with this second embodiment, the epitaxial thin film crystal 30 can be obtained in which the single crystal regions 30a, 30b are separated from each other, and are alternatively arranged. In this epitaxial thin film crystal 30, the increase of the movement speed of the Li ion along its thickness direction can be intended because of the domain structure formed by the single crystal regions 30a, 30b.

3. Third Embodiment

(49) All Solid-State Lithium Ion Battery

(50) Then, a third embodiment will be described. In this third embodiment, as an electrolyte, the solid electrolyte according to the first embodiment will be used.

(51) FIG. 14 schematically shows the basic configuration of this all solid-state lithium ion battery.

(52) As shown in FIG. 14, this all solid-state lithium ion battery includes a structure in which a positive pole 40 and a negative pole 50 oppose to each other via the epitaxial thin film crystal 10 constituting the solid electrolyte. For example, the positive pole 40 made of LiCoO.sub.2 is used, but is not restricted thereto. For example, the negative pole 50 made of graphite is used, but is not restricted thereto.

(53) In this all solid-state lithium ion battery, by using a conductive single crystal substrate 20 as the epitaxial thin film crystal 10, this conductive single crystal substrate 20 can be used as the negative pole or a negative pole current collector. A conductive single crystal layer is mounted on the conductive single crystal substrate 20, and the epitaxial thin film crystal 10 may be mounted thereon. For example, as shown in FIG. 14, a conductive single crystal Li.sub.4Ti.sub.5O.sub.12 layer 61 is grown on a conductive SrTiO.sub.3 single crystal substrate 60, and the epitaxial thin film crystal 10 is grown thereon. In this case, the conductive single crystal Li.sub.4Ti.sub.5O.sub.12 layer 61 constitutes a negative pole, and the conductive SrTiO.sub.3 single crystal substrate 60 constitutes a positive pole. The conductive SrTiO.sub.3 single crystal substrate 60 can be obtained by, for example, doping niobium (Nb) on the SrTiO.sub.3 single crystal substrate. A conductive oxide layer is used as the positive pole 40, and this conductive oxide layer may be grown on the epitaxial thin film crystal.

(54) Performance of All Solid-State Lithium Ion Battery

(55) In this all solid-state lithium ion battery, during the charge, electric energy is converted into chemical energy which is then stored by moving the lithium ion (Li.sup.+) from the positive pole 40 to the negative pole 50 through the epitaxial thin film crystal 10 constituting the solid electrolyte. During the discharge, the electric energy is generated by returning the lithium ion from the negative pole 50 to the positive pole 50 through the epitaxial thin film crystal 10.

(56) In accordance with this third embodiment, a novel all solid-state lithium ion battery using the solid electrolyte made of the epitaxial thin film crystal 10 as an electrolyte layer can be realized. This all solid-state lithium ion battery exhibits charge-discharge characteristics comparable to an existing lithium ion battery and can provide the significantly higher safety because no crystal grain boundary exists in the epitaxial thin film crystal 10 constituting the solid electrolyte.

(57) This all solid-state lithium ion battery can be used as a drive power source or an auxiliary power source for such as notebook personal computers, PDA (personal digital assistant), mobile phones, codeless handsets, video movies, digital still cameras, digital books, electronic dictionaries, portable music players, radios, headphones, gaming hardware, navigation systems, memory cards, cardiac pacemakers, acoustic aids, electric tools, electric shavers, refrigerators, air conditioners, televisions, stereos, water heaters, kitchen microwaves, dishwashers, washing machines, drying machines, lighting equipment, toys, clinical instruments, robots, road conditioners, traffic signals, railroad vehicles, golf carts, electric cart and electric cars (including hybrid cars), mounted on a power source of storing power for artificial structures such as houses, and power-generating facilities, or can be used for supplying power thereto. In the electric cars, a conversion apparatus for converting power to driving force by supplying the power is generally a motor. A control apparatus for conducting information processing with regard to vehicle control includes a control apparatus for displaying remaining battery power based on the information regarding the remaining battery power. This lithium sulfur battery can be also used as an electric storage apparatus in a so-called smart grid. Such the electric storage apparatuses can store the power after receiving the power from other power sources in addition to supplying the power. As the other power sources, for example, thermal power generation, atomic power generation, hydraulic power generation, solar cells, wind power generation, geothermal power generation and fuel cells (including biofuel cells) can be used.

(58) Although the embodiments and the Examples of the present disclosure have been specifically described, the present disclosure is not restricted to the above embodiments and Examples, and various modifications are possible.

(59) For example, the numerals, the structures, the configurations, the shapes and the materials are only examples, and numerals, structures, configurations, shapes and materials other than the above may be used depending on necessity.

(60) Additionally, the present technology may also be configured as below.

(61) (1)

(62) A solid electrolyte including:

(63) an epitaxial thin film crystal made of an electrolyte containing at least lithium.

(64) (2)

(65) The solid electrolyte according to (1),

(66) wherein the electrolyte is at least one electrolyte selected from the group consisting of an oxide, a phosphoric acid-based compound, a germanic acid-based compound, a sulfide and a nitride.

(67) (3)

(68) The solid electrolyte according to (1) or (2),

(69) wherein the electrolyte is at least one electrolyte selected from the group consisting of La.sub.2/3xLi.sub.3xTiO.sub.3 (O<x<), La.sub.0.5Li.sub.0.5TiO.sub.3, Li.sub.4+xM.sub.xSi.sub.1xO.sub.4 (M=B, Al), Li.sub.7La.sub.3Zr.sub.2O.sub.12, Li.sub.9SiAlO.sub.3, Li.sub.5La.sub.3Ta.sub.2O.sub.12, Li.sub.5La.sub.3Nb.sub.2O.sub.12, Li.sub.6BaLa.sub.2Ta.sub.2O.sub.12, Li.sub.3.6Si.sub.0.6P.sub.0.4O.sub.4, LiZr.sub.2(PO.sub.4).sub.3, Li.sub.1+xAl.sub.xTi.sub.2x(PO.sub.4).sub.3, Li.sub.14Zn(GeO.sub.4).sub.4, Li.sub.3.25Ge.sub.0.25P.sub.0.75S.sub.4, Li.sub.10GeP.sub.2S.sub.12 and Li.sub.3N.

(70) (4)

(71) The solid electrolyte according to any of (1) to (3),

(72) wherein the epitaxial thin film crystal is configured by a terrace which is flat in an atomic level and a steps, and includes a flat surface of which a mean-square surface roughness measured on a region of 2 m square is 1 nm or less.

(73) (5)

(74) The solid electrolyte according to any of (1) to (4),

(75) wherein the epitaxial thin film crystal is epitaxially grown on a single crystal substrate.

(76) (6)

(77) The solid electrolyte according to any of (1) to (5),

(78) wherein the single crystal substrate is at least one substrate selected from the group consisting of an oxide having a perovskite-type crystal structure represented by a general formula ABO.sub.3 (A is at least one element selected from the group consisting of Sr, Ba, La and K, and B is at least one element selected from the group consisting of Ti, Al and Ta), NdGaO.sub.3, YSZ, MgO, Al.sub.2O.sub.3 and Si.

(79) (7)

(80) The solid electrolyte according to (6),

(81) wherein the oxide having the perovskite-type crystal structure represented by the general formula ABO.sub.3 is at least one oxide selected from the group consisting of SrTiO.sub.3, LaAlO.sub.3 and (LaSr)(AlTa)O.sub.3.

(82) (8)

(83) The solid electrolyte according to any of (1) to (7),

(84) wherein the epitaxial thin film crystal includes a domain structure formed by at least two single crystal regions of which crystal orientations are different from each other.

(85) (9)

(86) The solid electrolyte according to (8),

(87) wherein the at least one single crystal region is present along an entire thickness direction of the epitaxial thin film crystal.

(88) (10)

(89) A method of preparing a solid electrolyte, the method including:

(90) a step of forming an epitaxial thin film crystal by epitaxially growing an electrolyte containing at least lithium on a single crystal substrate.

(91) (11)

(92) The method of preparing a solid electrolyte according to (10),

(93) wherein the electrolyte is epitaxially grown on the single crystal substrate through a pulsed laser deposition method, a sputtering method, an electron beam deposition method, a metalorganic chemical vapor deposition method, a molecular beam epitaxy method or an atomic layer epitaxial growth method.

(94) (12)

(95) The method of preparing a solid electrolyte according to (10) or (11),

(96) wherein the electrolyte is epitaxially grown on the single crystal substrate at a substrate temperature of 200 C. or more and 1200 C. or less.

(97) (13)

(98) The method of preparing a solid electrolyte according to any of (10) to (12),

(99) wherein the electrolyte is epitaxially grown on the single crystal substrate under an atmosphere of which an oxygen partial pressure is 110.sup.5 Pa or more and 110.sup.3 Pa or less.

(100) (14)

(101) The method of preparing a solid electrolyte according to any of (10) to (13),

(102) wherein, after the epitaxial thin film crystal is formed by epitaxially growing the electrolyte on the single crystal substrate, a domain structure is formed by at least two single crystal regions of which crystal orientations are different from each other by heating the epitaxial thin film crystal.

(103) (15)

(104) The method of preparing a solid electrolyte according to any of (10) to (14),

(105) wherein, after the epitaxial thin film crystal is formed by epitaxially growing the electrolyte on the single crystal substrate, the epitaxial thin film crystal is heated at a temperature of 1000 C. or more and 1500 C. or less for a period of one minute or more and two hours or less.

(106) (16)

(107) An electrochemical device including:

(108) a solid electrolyte including an epitaxial thin film crystal made of an electrolyte which is epitaxially grown and contains at least lithium.

(109) (17)

(110) The electrochemical device according to (16),

(111) wherein the electrochemical device is a battery, a capacitor, a sensor using lithium or a lithium ion filter.

(112) (18)

(113) The electrochemical device according to (17),

(114) wherein the battery is a secondary battery, an air cell or a fuel cell.

(115) (19)

(116) The electrochemical device according to (18),

(117) wherein the secondary battery is a lithium ion battery containing the solid electrolyte as an electrolyte layer.

(118) (20)

(119) The electrochemical device according to any of (16) to (19),

(120) wherein the solid electrolyte is mounted on a conductive single crystal substrate.

(121) It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.

REFERENCE SIGNS LIST

(122) 10 epitaxial thin film crystal 20 single crystal substrate 30 epitaxial thin film crystal 30a single crystal region 30b single crystal region 40 positive pole 50 negative pole 60 conductive SrTiO.sub.3 single crystal substrate 61 conductive single crystal Li.sub.4Ti.sub.5O.sub.12 layer