JPH06140074A - Lithium ion conductive solid electrolyte material - Google Patents

Abstract

PURPOSE:To provide a lithium ion conductive solid electrolyte material which has high lithium ion conductivity and by which a ring rate of a lithium ion becomes large and decomposition voltage becomes high and which is stable chemically and thermally. CONSTITUTION:A lithium ion conductive solid electrolyte material is composed of a constituent expressed by (x/2)Li2SO4-yMgSO4-(z/2)Al2(SO4)3 (provided that, 0<x<1, 0<y<1, 0<z<1 and x+Y+z=1). As a result, high lithium ion conductivity can be exhibited, and decomposition voltage becomes high, and electron conductivity becomes very small, and it is stable chemically and thermally. Thereby, when this lithium ion conductive solid electrolyte material is applied to an electrolyte material of a solid battery or the like, characteristic improvement in the solid battery or the like can be attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion conductive solid electrolyte material, and more particularly to a lithium ion conductive solid electrolyte material used for solid batteries, solid electric double layer capacitors, solid electrochromic display devices and the like.

[0002]

2. Description of the Related Art Lithium solid state batteries using lithium as a negative electrode active material and a lithium ion conductive solid electrolyte as an electrolyte have high energy density and have no liquid leakage, so that they are reliable and safe. It has many advantages in that it is expensive and that the battery material is solid and can be made small and thin. With high lithium ion conductivity for the purpose of application to such solid state batteries,
Further, development of a chemically stable solid electrolyte material is desired.

The lithium ion conductive solid electrolyte material is
So far, only LiI added with 40 mol% of Al ₂ O ₃ has been applied to a lithium solid state battery and is in practical use. In addition, lithium ion conductive solid electrolyte materials such as Li ₃ N, LiTi ₂ (PO ₄ ) ₃ system, Li
_{4 Zn (GeO 4) 4,} LiI-Li 2 S-MS x system and the like are known. Li ₃ N has a very low decomposition voltage of 0.5 V or less, and LiTi ₂ (PO ₄ ) ₃ system reacts with lithium,
Acting as a positive electrode active material, Li ₄ Zn (GeO ₄ ) ₄ reacts violently with molten lithium and is unstable, and LiI-L
The i ₂ S-MS _x system exhibits high lithium ion conductivity of about 10 −4 S / cm, but has a problem that the decomposition voltage is 3.0 V or less, and both are not applied to solid-state batteries. Not not.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has a high lithium ion conductivity, a high lithium ion transport number, a high decomposition voltage, and a chemically and thermally stable lithium ion conductive material. The purpose of the present invention is to provide a solid electrolyte material.

[0005]

Means for Solving the Problems] To solve the above problems, a lithium ion conductive solid electrolyte material according to the _{invention, (x / 2) Li 2} SO 4 -yMgSO 4 - (z /
2) Al ₂ (SO ₄ ) ₃ (where 0 <x <1, 0 <y <
1, 0 <z <1, x + y + z = 1).

The present invention will be described in more detail. N known as a solid electrolyte material having sodium ion conductivity
ASIC (Na _{1 + x} Zr ₂ Si _x P _3-x O ₁₂ ) has a three-dimensional network structure, and it is considered that many tunnels in which lithium ions can easily diffuse exist in this network structure. There is. Therefore, in the present invention, in order to synthesize a material having a relatively high lithium ion conductivity, this NASI is used.
It was thought that a material having a three-dimensional network structure similar to the CON-based material should be synthesized. As anions that may form a three-dimensional network structure, (PO ₄ ) ^3- , (SiO ₄ )
^4- , (SO ₄ ) ^{2-, and the} like. In the present invention, attention is paid to sulfate ion ((SO ₄ ) ^2- ) and (x / 2) Li ₂ SO ₄ -y
_{MgSO 4 - (z / 2)} Al 2 (SO 4) 3 ( where 0 <
When a solid electrolyte material represented by x <1, 0 <y <1, 0 <z <1, x + y + z = 1) was synthesized, it was found that it exhibits high lithium ion conductivity.

Further, in a material containing a transition metal as a constituent element of the solid electrolyte, there is a risk that the transition metal is reduced by lithium ions to increase the electron conductivity or react with lithium to decompose. The solid electrolyte material was able to have extremely low electron conductivity and low reactivity with lithium by using all the constituent elements as typical elements.

Further, since the solid electrolyte material of the present invention can be synthesized by a usual firing method, it is 600 ° C.
It is thermally stable up to the vicinity.

As described above, the lithium ion conductive solid electrolyte material according to the present invention exhibits high lithium ion conductivity, high decomposition voltage, very low electron conductivity, and chemical / thermal properties. Therefore, there is an advantage that by applying the lithium ion conductive solid electrolyte material of the present invention to an electrolyte material such as a solid battery, improvement of characteristics of the solid battery can be achieved.

[0010]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited thereto.

The lithium ion conductive solid electrolyte material according to the present invention can be produced by a usual porcelain firing method. Commercially available special grade reagents Li ₂ SO ₄ .H ₂ O, MgSO ₄ , Al ₂ (S
O ₄ ) ₃ was used as a raw material, and these raw materials were weighed according to a predetermined weighing formula and mixed sufficiently. Next, these were transferred to an alumina crucible and calcined at 550 ° C. for 24 hours in the air using an electric furnace. After that, the calcined powder is added to 1 to 2 to
It was molded at a pressure of n / cm ² and baked at 600 ° C. for 6 hours in the air using an electric furnace.

The total conductivity of the obtained sintered body was measured by depositing gold on both sides of the sample and using this as an electrode by an AC two-terminal method using an impedance analyzer. Further, the total conductivity was also obtained by pressing lithium metal on both sides of the sample and measuring by the DC two-terminal method. The transport number of lithium ion was calculated from the ratio of the total conductivity to the electronic conductivity by measuring the electronic conductivity using the direct current method. Further, the decomposition voltage was obtained from the current-potential curve using the direct current method.

Samples produced under the above conditions (Examples 1 to 1)
The conductivity of 9) is shown in Table 1. All samples showed high lithium ion conductivity. Further, the electron transport numbers of the lithium ion conductive solid electrolyte materials in the present invention are all 1 × 10 ^−5.
Below, electronic conductivity is negligible. Moreover, the total conductivity determined by the AC method and the total conductivity determined by the DC method were in agreement. From this, it was confirmed that the mobile ions of these samples were lithium ions. In addition, the current-potential curve showed a proportional relationship up to an applied voltage of 10 V in all samples, and no rapid increase in current due to decomposition was observed. Therefore, it can be seen that the decomposition voltage is 10 V or more.

Furthermore, the reactivity of the solid electrolyte material of the present invention with lithium metal was examined using a thermobalance, but no evidence of reaction was observed up to the melting temperature of lithium metal. Lithium metal was pressure-bonded to both surfaces of the sample, and this was used as an electrode to apply a voltage of 5 V between the electrodes.
The measurement was performed for 0 hours, but no rapid change was observed. From this, the lithium ion conductive solid electrolyte material of the present invention is chemically and thermally stable to lithium metal.

Table 1

[0016]

As described above, the lithium ion conductive solid electrolyte material according to the present invention exhibits high lithium ion conductivity, high decomposition voltage, very low electron conductivity, and chemical / thermal property. It has the characteristic of being stable. Therefore, by applying this lithium ion conductive solid electrolyte material to an electrolyte material such as a solid battery, there is an advantage that the characteristics of the solid battery or the like can be improved.

Claims (1)

[Claims] [Claim 1] _{(x / 2) Li 2 SO} 4 -yMgSO 4 -
(Z / 2) Al ₂ (SO ₄ ) ₃ (where 0 <x <1, 0
<Y <1, 0 <z <1, x + y + z = 1), which is a lithium ion conductive solid electrolyte material.