JPH0642329B2 - Lithium-ion conductor thin film and manufacturing method thereof - Google Patents

Description

The present invention relates to a solid electrolyte thin film having lithium ion conductivity and a method for producing the same.

[Conventional technology]

Recently, a lithium ion conductive solid electrolyte material has been attracting attention from the viewpoint of application as an electrolyte of a lithium battery or as an electrolyte of an electrochromic display element. Along with the miniaturization and thinning of electronic devices, there has been an increasing demand for miniaturization and thinning of batteries, or even for display elements with higher performance due to solidification. For these applications, it is necessary for the solid electrolyte to have a sufficiently high ionic conductivity, but so far no material having a sufficient conductivity for practical use has been obtained.

In order to reduce the resistance of the electrolyte portion in order to make such an element, it is conceivable to thin the electrolyte to reduce the resistance geometrically, and to make the element thinner by thinning it. It will be possible.

[Problems to be solved by the invention]

However, in the past, most solid electrolyte materials have been produced by the ceramic technique, and it is difficult to produce a thin film having a thickness of several μm by the ceramic technique. Also, until now, LiI and L
i ₃ Zn _{0 · 5} but thin lithium ion conductor of GeO ₄ or the like is is made, has not been obtained showing a higher conductivity can be subjected to practical use.

The present invention has been made in view of the above situation,
An object of the invention is to provide a lithium ion conductor thin film having excellent ionic conductivity and a method for producing the same.

[Means for solving problems]

Briefly describing the present invention, the first invention of the present invention relates to a lithium ion conductor thin film, which comprises Li ₂ O, V ₂ O ₅ and
It is a thin film containing a component of SiO ₂ , and its composition is represented by the general formula xLi ₂ O · yV ₂ O ₅ · zSiO ₂ (where x + y + z = 1, 0.
6 ≦ x ≦ 0.85, It is characterized by being represented by.

A second invention of the present invention is an invention relating to the method for producing a lithium ion conductor thin film according to the first invention, which is a pressure-molded fired body containing Li ₂ O, V ₂ O ₅ and SiO _2. To
It is a thin film containing components of Li ₂ O, V ₂ O ₅ and SiO ₂ on a support, which has been subjected to high-frequency sputtering or vacuum deposition treatment, and has a composition of the general formula xLi ₂ O ・ yV ₂ O ₅・ zSiO. ₂ (However,
x + y + z = 1, 0.6 ≦ x ≦ 0.85, The method is characterized by including a step of forming a thin film represented by.

Among Li ₂ OV ₂ O ₅ -SiO ₂ -based compositions, Li ₃ VO ₄ -Li ₄ SiO ₄ -based solid solution has a γ-Li ₃ PO ₄ structure and is known to show relatively high lithium ion conductivity. Has been. However, since it is a sintered body produced by the conventional ceramic technology, there is a limit to miniaturization and thin film formation for device formation. Therefore,
In the present invention, a Li ₂ OV ₂ O ₅ —SiO ₂ composition is coated with a magnetron type high frequency sputtering method or a vacuum deposition method on a support such as a sapphire substrate or a quartz glass substrate.
A thin film having a film thickness of about 1 μm to 5 μm is formed. A thin film was formed by changing the composition ratio of Li ₂ OV ₂ O ₅ —SiO ₂ and the conductivity thereof was measured.It was found that those having the above composition range showed high lithium ion conductivity, and A thin film of a lithium ion conductor is obtained. In terms of composition ratio, Li ₂ O exceeds 85 mol% (that is, x> 0.
In the case of 85), it is difficult to put it into practical use because its hygroscopic property is remarkable and the quality of the product is immediately changed in the air. In addition, the amount of Li ₂ O is 60
When it is less than mol% (that is, x> 0.6), the ionic conductivity is remarkably small. Also, the molar ratio of V ₂ O ₅ and SiO ₂ is 5
If the amount of V ₂ O ₅ is smaller than that of pair 95, or if the amount of V ₂ O ₅ is larger than that of 90:10 (ie, y / z <0.05 or y / z> 9), ionic conductivity The nature is small. The conductivity is 1 × 10 ⁻⁷ S / m or more in the composition range of the present invention.

The lithium ion conductor thin film of the present invention, as a support,
It is formed not only on a sapphire substrate or a quartz glass substrate on which another thin film is formed or not formed in advance, but also on a substrate such as silicon or spinel which is or is not subjected to the same treatment.

Further, the thin film of the present invention is amorphous in the state where the thin film is formed but is not heat-treated, but becomes a polycrystalline body by heat-treating at 500 to 600 ° C. Both show high lithium ion conductivity, but the polycrystalline thin film has a higher conductivity. On the other hand, the amorphous film is inferior to the polycrystalline film in terms of conductivity, but has an advantage in forming an element in that it does not require heat treatment.

〔Example〕

Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples.

Example 1 A thin film was formed by using a high frequency spatter device of the Brenner magnetron type. The target was prepared by the following method. Starting from Li ₂ CO ₃ , V ₂ O ₅ , and SiO ₂ , firstly Li _{3 + X} V
_1-X Si _X O ₄ (0 ≤ x ≤ 1) is weighed and a target composition is prepared. Since the composition of the thin film obtained by the sputtering method is often different from the target composition, an appropriate amount of Li ₂ CO ₃ and V ₂ O ₅ is added to the above composition, mixed, pressure-molded, and baked. A target was prepared by.

A sapphire substrate was used as a support, the substrate was water-cooled, Ar-O ₂ (oxygen 30%) mixed gas was used as an atmosphere gas, the degree of vacuum was 1.5 × 10 ^-2 Torr, the plate voltage was 1.5 kV.
A thin film was prepared under the sputtering conditions described above.

When the crystallinity of the produced thin film was examined by X-ray diffraction (CuKα ray), it was found to be amorphous except that the substrate temperature was increased up to about 100 ° C. A thin film having a substrate temperature of 80 to 100 ° C. has a weak peak intensity, and a wide peak at half maximum has appeared. The chemical analysis of the composition of the obtained thin film was performed.
An electrode made of a Pt-Pd sputtering film was formed on the thin film, and the ionic conductivity was measured by the complex impedance method.

Table 1 shows the measurement results of the composition and conductivity of the thin film thus produced.

The temperature dependence of conductivity is shown in FIG. That is,
FIG. 1 shows the temperature change of the ionic conductivity of the thin film of Example 1 of the present invention as a function of temperature [1000 / T (K ⁻¹ ), horizontal axis] and conductivity (S
/ m, vertical axis). Numbers 1 to 5, 9 and 14 in FIG. 1 are sample numbers in Table 1.

Example 2 The thin film produced in Example 1 is amorphous or has a broad peak mixed with a weak intensity and poor crystallinity in a state where the thin film is not heat treated while being sputtered. Therefore, the thin film obtained in Example 1 was heat-treated at 600 ° C.

As a result of examination by X-ray diffraction, among the samples shown in Table 1 of Example 1, from the numbers 1, 2, 3, 6, 7, 10 and 11, γ
A thin film of -Li ₃ PO ₄ structure was obtained. However when heated the other samples, or Li ₄ SiO ₄ is混Tsu the γ-Li ₃ PO _4, or the peak of the V ₂ O ₅ has come mixture thin film or混Tsu. The ionic conductivity of these thin films was measured in the same manner as in Example 1. Table 2 shows the electrical conductivity of a representative sample at room temperature.

The temperature dependence of conductivity is shown in FIG. That is, FIG. 2 shows the temperature change of the ionic conductivity of the thin film of Example 2 of the present invention with respect to temperature [1000 / T (K ⁻¹ ), horizontal axis] and conductivity (S
/ M, vertical axis). The numbers 17, 18, 22, 23 and 25 in FIG. 2 are the sample numbers in Table 2. FIG. 2 shows a sample of the sintered body for comparison.
Li ₄ SiO ₄ and Li _3.4 V _0.6 Si _0.4 O ₄ are shown. A in the figure is L
i ₄ SiO ₄ and b are Li _3.4 V _0.6 Si _0.4 O ₄ sintered bodies. The composition of No. 18 of the thin film sample is the same as that of the Li _3.4 V _0.6 Si _0.4 O ₄ sintered body, but the conductivity is slightly smaller. In addition, compared with the amorphous materials of Nos. 1 to 16, the crystalline materials of Nos. 17 to 27 have slightly higher conductivity in the case of the same composition.

Example 3 The target was prepared by adding Li ₂ CO ₃ , V ₂ O ₅ and SiO ₂ as starting materials in an appropriate amount in excess of predetermined proportions of Li ₂ CO ₃ and V ₂ O ₅ , followed by mixing, pressurizing and molding. It was produced by firing at 600 ° C. Using this target, high frequency sputtering was performed under the conditions described in Example 1. As a result of compositional analysis of the obtained thin film,
The same composition as in Example 1 was obtained. When the heat treatment was performed in the same manner as in Example 2 and the electrical conductivity was measured, it showed almost the same value as the sample of Example 2.

Example 4 A mixture fired body was produced in the same manner as the target production method described in Example 3, and this was used as a vapor deposition source, and vacuum vapor deposition was performed on a quartz glass or sapphire substrate by electron beam heating.

The composition of the obtained thin film was analyzed, and heat treatment was performed to measure the electrical conductivity. As a result, almost the same results as in Example 2 were obtained.

〔The invention's effect〕

As described above, the lithium ion conductor thin film of the present invention exhibits high ionic conductivity. In the case of a sintered material, the thickness is on the order of several millimeters even if it is thin, but since the thin film of the present invention has a thickness of about 0.1 to 5 μm, the resistance of the electrolyte in device formation is reduced by three orders of magnitude. A remarkable effect is exhibited.

[Brief description of drawings]

FIG. 1 is a graph showing the temperature change of the ionic conductivity of the thin film of Example 1 of the present invention, and FIG. 2 is a graph showing the temperature change of the ionic conductivity of the thin film of Example 2 of the present invention.

Claims (2)

[Claims] 1. A thin film containing components of Li ₂ O, V ₂ O ₅ and SiO ₂ , the composition of which is represented by the general formula xLi ₂ O.yV ₂ O ₅ .zSiO ₂ (where x + y + z = 1,0). 6 ≦ x ≦ 0.85, A lithium ion conductor thin film represented by: 2. A press-molded fired body containing Li ₂ O, V ₂ O ₅ and SiO ₂ is subjected to high-frequency sputtering or vacuum evaporation treatment,
A thin film containing components of Li ₂ O, V ₂ O ₅ and SiO ₂ on a support, the composition of which is represented by the general formula xLi ₂ O · yV ₂ O ₅ · zSiO ₂ (where x + y + z = 1,0 .6x0.85, A method for producing a lithium ion conductor thin film, comprising the step of forming a thin film represented by.