JPS6361722B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lithium ion conductive solid electrolyte material.

All-solid-state batteries (hereinafter referred to as solid-state batteries), which use lithium as the negative electrode active material and a lithium-conductive solid electrolyte as the electrolyte, have high energy density, do not leak, and can be made small and thin. , has many advantages.

The development of lithium ion conductive solid electrolyte materials is attracting attention for the purpose of industrial application of such solid-state batteries. However, at present, no lithium ion conductive solid electrolyte material has been obtained.
Only LiI to which 40 mol% of Al ₂ O ₃ is added has been applied to lithium solid-state batteries and is in practical use.

Recently, lithium ion conductive solid electrolyte materials such as Li ₃ N, Li ₁₄ Zn(GeO ₄ ) ₄ and Li ₃ N-LiI have been attracting attention, but they still do not fully satisfy the characteristics required for solid-state batteries. The current situation is difficult to say. for example,
Li ₃ N has a low decomposition voltage, Li ₁₄ Zn (GeO ₄ ) ₄ has low conductivity at room temperature, and is an unstable material, so neither has been applied to solid-state batteries. Not yet.

For this reason, there is a demand for the development of solid electrolyte materials that eliminate these drawbacks, especially materials that have high electrical conductivity and are chemically stable.

The present invention was made in view of the above-mentioned current situation, and an object of the present invention is to provide a lithium ion conductive solid electrolyte material that has high electrical conductivity and is chemically stable.

Therefore, the lithium ion conductive solid electrolyte material according to the present invention is composed of a composition represented by the general formula: Li ₁ +xNb ₁ +yW ₁ +zO ₆ (−0.05≦x, y, z, ≦0.05). It is characterized by:

The lithium ion conductive solid electrolyte material according to the present invention has the advantages of relatively high lithium ion conductivity and stability against heat and moisture. By applying it to the electrolyte material of a solid-state battery, there is an advantage that the characteristics of the solid-state battery can be improved.

The present invention will be explained in more detail.

The composition of the present invention represented by the general formula Li ₁ +xNb ₁ +yW ₁ +zO ₆ ...(1) (where -0.05≦x, y, z, ≦0.05) can be used to create a material with high lithium ion conductivity. It was created with a focus on its crystal structure. In other words, we focused on the trirutile structure, and since the trirutile structure has gaps in the (001) direction, and it is thought that lithium ions can easily move in this direction, we focused on LiNbWO ₆ -based materials that have this trirutile structure. It is.

In the above general formula (1), LiNbWO ₆ satisfies x=y=z=0, and is a typical substance in the above general formula (1).

For this LiNbWO ₆ , the amount of Li, Nb, and W is 5
When it is added excessively to the extent of %, or conversely when it is added too little, it forms a phase with almost a trirutile structure of LiNbWO ₆ , and both exhibit lithium ion conductivity. That is, the electrical conductivity of the lithium ion conductive solid electrolyte material according to the present invention varies slightly depending on the conditions of preliminary firing, main firing, and hot pressing, but
The conductivity is maximum when x=y=z=0, and x,
Relatively high ionic conductivity is maintained up to y and z of ±0.05.

However, |x|, |y|, |y| are 0.05
If the value exceeds 0.05%, different phases will be mixed in and the conductivity will be significantly reduced.

The method for manufacturing the lithium ion conductive solid electrolyte material according to the present invention is not limited in the present invention. For example, it can be manufactured by a normal porcelain firing method or a hot pressing method.

Specifically, it can be manufactured, for example, as follows.

First, commercially available special grade reagents Li ₂ CO ₃ , Nb ₂ O ₅ , and WO ₃ were used as raw materials, and these raw materials were converted into Li ₁ +xNb ₁ +yW ₁ +
Based on the weighing formula zO ₆ , a predetermined amount is weighed, put into an alumina crucible using a pot mill, and fired.

First, it was kept at 600℃ for several hours to decompose Li ₂ CO ₃ , and then at a temperature of 700 to 760℃ for 24 to 120 hours.
Fired in the atmosphere. After firing, the reaction product is taken out of the furnace, pulverized, and then molded into a molded body under a pressure of 1 to 5 t/cm ² .

This molded body is further fired at 760°C for 6 hours, or hot press fired at a temperature of 760 to 800°C and a press pressure of 400 kg/cm ² for 2 hours.

The sintered body produced as described above is cut into a desired shape and used as a solid electrolyte material for a solid battery using lithium as a negative electrode active material.

Examples of the present invention will be described below.

The conductivity measurements in the following examples were carried out by cutting out a rectangular parallelepiped with a size of 5 x 5 x 4 mm from the sintered body, or by using a disk-shaped sintered body with a diameter of 12 mm and a thickness of 2 mm as a sample, and Electrodes were attached and the AC two terminal method was used.

In addition, the electron ring ratio was determined from the conductivity determined by the direct method.

In the case of alternating current, an impedance analyzer was used as the measuring instrument, and the conductivity was determined by the multiple impedance method.

Example 1 According to the above method, LiNbWO ₆ (when x=y=z=0 in the general formula (1)), Li _1.05 NbWO ₆
(x=0.05, y=z=0), Li _0.95 NbWO ₆ (x=-
0.05, y=z=0), LiNb _1.05 WO ₆ (x=z=0,
y=0.05), LiNbW _1.05 O ₆ (x=y=0, z=0.05)
was produced under the following conditions.

Temporary firing was performed at 730℃ for 100 hours in the air, and the yield was 2t/
Formed to 12mmφ and ~5mm under a pressure of cm ² and heated to 760℃.
It was baked for 6 hours. Both sides of the obtained sintered body were polished, electrodes were attached, and then the conductivity was measured.

The results are shown in Figure 1.

FIG. 1 is a diagram showing the temperature dependence of conductivity.
In the figure, A is LiNbWO ₆ , B is Li _1.05 NbWO ₆ , C is
Li _0.95 NbWO ₆ , D is LiNb _1.05 WO ₆ , E is
FIG. 2 is a graph showing the results for LiNbW _1.05 O ₆ .

As is clear from FIG. 1, although the samples outside the stoichiometric ratio had lower conductivity, all of them showed good conductivity. In particular, the conductivity of LiNbWO ₆ is 3×10 ⁻⁶ Ω ⁻¹ cm ⁻¹ at 200° C., indicating high lithium conductivity.

Example 2 LiNbWO ₆ was produced by hot pressing according to the method described above. After calcining the raw material powder, it was molded and calcined in vacuum at 800° C. and 400 kg/cm ² for 2 hours.

The measurement results of electrical conductivity are shown in FIG.

For comparison, the results of LiNbWO ₆ produced by a normal firing method (Example 1) are also shown. In the figure, F is a graph showing the temperature dependence of the conductivity of LiNbWO ₆ produced in Example 2.

As is clear from Fig. 2, the conductivity of the hot-pressed sample was 6×10 ^-6 Ω at 200°C.
^-1 cm ^-1 , which was found to be better than that obtained using the normal firing method (Example 1).

The electrical conductivity of this sample was measured by the direct current method using a Pt--Pd electrode, which is an ion blocking electrode, and found to be approximately 2 x 10 ^-7 Ω ^-1 cm ^-1 at 200°C. In addition, the electron transport number of this LiNbWO ₆ is
It was about 0.03, indicating that the conductivity of this sample was due to ions.

The difference in electrical conductivity between the samples obtained by the normal firing method and the hot pressing method is thought to be due to the difference in the sintered density of the samples.

Including the solid samples in the above examples, Li ₁ + xNb ₁
+yW ₁ +zO ₆ (However, -0.05≦x, y, z, ≦0.05)
As a result of examining the samples using powder X-ray diffraction, it was found that most of the samples were composed of a single trirutile phase of LiNbWO ₆ . In the case of x=-0.05, y=±0.05, and z=±0.05, an extremely weak out-of-phase is observed. The slightly lower conductivity of these samples compared to LiNbWO ₆ is thought to be due to the different phase, and it was found that the trirutile structure allows ions to move easily in the direction of the gaps.

As explained above, Li ₁ +xNb ₁ according to the present invention
A lithium ion conductive solid electrolyte material composed of +yW ₁ +zO ₆ exhibits relatively high lithium ion conductivity due to its trirutile structure. Furthermore, this lithium ion conductive solid electrolyte material is stable against heat and moisture, and has the advantage that it can improve the characteristics of solid-state batteries by using it as an electrolyte material for lithium solid-state batteries.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the temperature dependence of the electrical conductivity of a lithium ion conductive solid electrolyte material according to an example of the present invention, and FIG. FIG. 6 is a diagram showing the temperature dependence of conductivity of No. ₆ .

Claims (1)

[Claims] 1. A lithium ion conductive solid comprising a composition represented by the general formula: Li ₁ +xNb ₁ +yW ₁ +zO ₆ (wherein -0.05≦x, y, z, ≦0.05) electrolyte material.