JP2991256B2 - Lithium ion conductive solid electrolyte material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a lithium ion conductive solid electrolyte material.

[0002]

2. Description of the Related Art An all-solid-state battery using lithium as a negative electrode active material and a lithium ion conductive solid electrolyte as an electrolyte has a high energy density, has no liquid leakage, and can be made small and thin. There are many advantages. For the purpose of industrial application of such solid batteries, attention has been paid to the development of lithium ion conductive solid electrolyte materials.
Up to now, LiI to which 40 mol% of Al ₂ O ₃ has been added,
Li-β-Al ₂ O ₃ , Li ₃ N, Li ₄ Zn (GeO ₄ ) ₄
Are reported as lithium ion conductors. However, these situations are not necessarily sufficient to satisfy the characteristics required for a solid-state battery. 40 mol% Al
LiI, Li-β-Al ₂ O ₃ , Li ₃ N to which ₂ O ₃ is added
Are unstable to atmospheric moisture and difficult to handle.

Further, Li ₃ N has a low decomposition voltage, and L 3
It is difficult to apply i ₄ Zn (GeO ₄ ) ₄ to solid-state batteries because it reacts violently with molten lithium and is unstable. For this reason, a solid electrolyte material that eliminates these disadvantages, particularly a material that is chemically stable and has high conductivity, is desired.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lithium ion conductive solid electrolyte material having high conductivity and being chemically stable.

[0005]

[Means for Solving the Problems] To solve the above problems, the lithium ion conductive solid electrolyte material according to the present invention has a general formula: Li _{2 + x} C _{1-x + y} B _x O _{3 + 2y} ( However, 0.
03 ≦ x ≦ 0.7, 0 ≦ y ≦ 0.2).

The present invention will be described in more detail.

[0007] Li ₂ CO ₃ is a stable Li compound in the atmosphere include, for example, Li ₂ O is Li ₂ CO if left in the atmosphere
It is known to change to ₃ or LiOH. However, Li ₂ O ₃ has very low lithium ion conductivity and is not a solid electrolyte material. The present invention relates to Li ₂ CO ₃ and Li ₃ BO ₃
Consisting of a solid solution of Its main component is Li ₂ CO ₃
And its crystal structure is similar to Li ₂ CO ₃ and is chemically stable. Further, by forming a solid solution with Li ₂ BO ₃ , the lithium ion conductivity is significantly improved,
It has been found that even at room temperature it shows relatively high lithium ion conductivity.

The solid electrolyte material of the present invention is synthesized according to the following reaction.

(1 + x / 2) Li ₂ CO ₃ + (x / 2) B
₂ O ₃ → Li _{2 + x} C _{1-x + y} B _x O _{3 + 2y} + (3x / 2-y) C
O ₂

In this formula, x indicates the amount of B added, and y indicates unreacted Li ₂ CO ₃ .

When the value of x in this formula is small, y = 0, and a solid solution Li _{2 + x} C _1-x B _x O ₃ having a Li ₂ CO ₃ structure can be easily obtained. When the value of x is large, not only the Li ₃ BO ₃ phase is mixed, but also the decomposition of Li ₂ CO ₃ becomes insufficient and unreacted substances are easily mixed. That is, when the range of x is 0 <x ≦ 0.4 in the general formula Li _{2 + x} C _{1-x + y} B _x O _{3 + 2y} of the solid electrolyte material of the present invention, the solid solution having the Li ₂ CO ₃ structure A single phase is obtained. In the range of 0.4 <x ≦ 1.0, Li ₂ CO ₃
Phase, a Li ₃ BO ₃ phase, and other unreacted materials. When the range of x satisfies x <0.03 and 0.7 <x, the electric conductivity is small, which is not preferable, and x is 0.03 ≦ x ≦
In the range of 0.7, the ionic conductivity at room temperature shows a relatively high value. In particular, 10 −5 in the range of 0.1 ≦ x ≦ 0.4.
It shows an ionic conductivity of (S / m) or more, and is more preferable.
As for y, when y = 0, it indicates that the reaction between Li ₂ CO ₃ and B ₂ O ₃ has been completed, which is the most preferable. As x increases in the above formula, y>
It tends to be 0. When y> 0 (≠ 0), unreacted Li
_{Although 2} CO ₃ is mixed, the conductivity is lowered, but y ≦ 0.
If it is in the range of 2, the degree of decrease in conductivity is small and acceptable.

[0012]

Embodiments 1 to 6 The present invention will be described below with reference to embodiments.

The lithium ion conductive solid electrolyte material according to the present invention can be produced by a usual porcelain firing method. Using commercially available special-grade reagents, Li ₂ CO ₃ and B ₂ O _3, were weighed and mixed based on a predetermined weighing formula. Next, it was calcined in the air at a temperature of 600 to 650 ° C. for 24 hours depending on the amount of B. Next, this calcined powder was molded at a pressure of 1 to ² t / cm ² and fired in an oxygen atmosphere at a temperature of 620 to 700 ° C. for 6 hours depending on the amount of B.

The obtained sintered body was pulverized, and the crystal phase was examined by X-ray diffraction. The composition was analyzed by atomic absorption, ICP and other methods.

The conductivity was measured by depositing gold on both surfaces of a disk-shaped sample and using the electrode as an electrode by an alternating current method using an impedance analyzer. The electron conductivity was examined by a direct current method, and the electron transport number was determined from the ratio to the total conductivity.

The starting materials Li ₂ CO ₃ and B ₂ O ₃ were mixed in a molar ratio of 1.025: 0.025 (Example 1), 1.05:
0.05 (Example 2), 1.1: 0.1 (Example 3),
1.125: 0.125 (Example 4), 1.15: 0.
15 (Example 5) and 1.2: 0.2 (Example 6) were mixed under the above conditions. As a result of X-ray diffraction, each of them was a single phase of a solid solution having a Li ₂ CO ₃ structure.
As shown in Table 1, as a result of the composition analysis, the value of y in the above general formula was 0, and the composition was a Li ₂ CO ₃ type solid solution.

Table 1 shows the electrical conductivity of the samples of Examples 1 to 6 at room temperature. The general formula “Li” of the solid solution in the present invention
_{2 + x} C _1-x B _x O ₃ ″, the range of x is 0.1 ≦ x ≦ 0.
4 indicates a conductivity of 10 ^-5 (S / m) or more. FIG.
2 shows the composition dependency of the electrical conductivity at room temperature of this system including Examples 1 to 6 and Examples 7 and 8 described below and Comparative Example 1.2.

The electron transport number is sufficiently small at -10 ^-5 , and the conductivity is due to ions.

The chemical stability was evaluated by allowing the sintered body to stand in an atmosphere at a relative humidity of 50% for three months and then examining the change in conductivity and the crystal phase. It was confirmed that neither the X-ray diffraction pattern nor the conductivity value before and after standing was changed.

[0020]

Examples 7 and 8 Li ₂ CO ₃ and B ₂ O ₃ were mixed at a molar ratio of 1.3: 0.3 (Example 7) and 1.4: 0.4 (Example 8). , And produced in the same manner as in Examples 1 to 6. The results of X-ray diffraction mainly consisted of Li ₂ CO ₃ phase and Li ₃ BO ₃
Phase mixture. Table 1 shows the results of the composition analysis. It can be seen that extra CO ₂ remains as an unreacted substance.

Table 1 shows the electrical conductivity at room temperature.

[0022]

Comparative Examples 1 and 2 Li ₂ CO ₃ was molded and fired in the same manner as in Example 1 to produce a sintered body (Comparative Example 1). In addition, Li ₂
CO ₃ and B ₂ O ₃ are mixed in a molar ratio of 3: 1;
A sintered body was produced in the same manner as in Example 1 (Comparative Example 2).
Table 1 shows the analytical composition and the electrical conductivity at room temperature.

[0023]

[Table 1]

[0024]

The lithium ion conductive solid electrolyte material according to the present invention shows high conductivity at room temperature and is chemically stable.
There is an advantage that the characteristics of a solid electrochemical device such as a lithium solid battery can be improved.

[Brief description of the drawings]

FIG. 1 shows the relationship between the conductivity at room temperature and the composition of lithium ion conductive solid electrolyte materials of Examples and Comparative Examples of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-154106 (JP, A) JP-A-49-81898 (JP, A) JP-A-54-33299 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H01B 1/06-1/08 C01B 35/12 H01M 6/18 H01M 10/36

Claims (1)

(57) [Claims] [Claim 1] The general formula Li _{2 + x} C _{1-x + y} B _x O _{3 + 2y} (where,
0.03 ≦ x ≦ 0.7, 0 ≦ y ≦ 0.2) A lithium ion conductive solid electrolyte material, characterized by comprising a composition represented by the following formula: