JP3125506B2 - Sulfide-based lithium ion conductive solid electrolyte and its synthesis method - Google Patents

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 used as an electrolyte for a solid electrochemical device such as an all solid battery, a capacitor, and a solid electrochromic display device.

[0002]

2. Description of the Related Art In recent years, studies on all solidification of a lithium battery using a lithium ion conductive solid electrolyte have been actively conducted. However, at present, there is no excellent lithium ion conductive solid electrolyte, and research on a new solid electrolyte is actively conducted.

As one of such lithium ion conductive solid electrolytes, Li ₂ SX (X is SiS ₂ , GeS ₂ , P ₂
There is at least one sulfide-based sulfide glass of S ₅ and B ₂ S ₃ .

[0004] Li ₂ SX-based sulfide glass is such that X is Si
S ₂ has the highest conductivity value in the Li ₂ S—SiS ₂ system, and the value is about 5 × 10 ⁻⁴ S / cm.

Further, in order to obtain higher ionic conductivity, these sulfide glasses are made of lithium halide such as lithium iodide (LiI) or lithium phosphate (Li).
₃ PO ₄₎ proposed pseudo ternary glass doped with lithium oxyacid salt is being performed, such as. For example, Li ₃ PO ₄ −
The synthesis of Li ₂ S—SiS ₂ pseudo ternary glass is performed as follows. Lithium phosphate (Li ₃ PO ₄ ) , lithium sulfide (Li ₂ S), and silicon sulfide (SiS ₂ ) are mixed in a desired molar ratio, and the mixed powder is mixed with oxygen-free helium or argon. Heating in a stream of inert gas,
Eutectic. Then, the melt is cooled by being introduced into liquid nitrogen to obtain Li ₃ PO ₄ —Li ₂ S—SiS ₂ pseudo-ternary glass.

However, the sulfide-based lithium ion conductive solid electrolyte easily reacts with moisture and oxygen to form hydroxides and oxides, which have very low ionic conductivity.
This causes the ionic conductivity of the solid electrolyte to decrease. Therefore, all steps of synthesizing the sulfide-based lithium ion conductive solid electrolyte are performed in an inert gas containing no moisture or oxygen.

[0007]

When these solid electrolytes are used as an electrolyte for an electrochemical device, for example, in order to enable rapid charging and discharging in the case of a battery, and to improve the response speed in the case of a sensor. Therefore, it is necessary to further improve the ionic conductivity.

[0008] In view of the above problems, an object of the present invention is to provide a solid electrolyte having higher lithium ion conductivity.

[0009]

In synthesizing a sulfide-based lithium ion conductive solid electrolyte, an inert gas containing 1000 ppm or less of oxygen is used. To obtain a lithium-ion conductive solid electrolyte.

Further, nitrogen gas is used as the inert gas. Furthermore, among the sulfide-based lithium ion conductive solid electrolytes, the main components are Li ₂ S and X (where X is Si
S ₂ , GeS ₂ , P ₂ S ₅ , and B ₂ S ₃ ).

[0011]

When synthesizing a sulfide-based lithium-ion conductive solid electrolyte, the material is heated and melted in an inert gas stream containing a small amount of oxygen. A small amount of oxygen is incorporated into the structure of the sulfide glass obtained by the reaction. For example, Li ₂
The S-SiS ₂ -based sulfide glass has a structure in which SiS ₄ tetrahedrons are three-dimensionally linked by sulfur crosslinking, and lithium ions, which are mobile ions, are bonded to non-crosslinked sulfur.
A small amount of incorporated oxygen has the effect of increasing non-crosslinked sulfur and, as a result, increases lithium ion conductivity.

When a sulfide-based lithium ion conductive solid electrolyte is synthesized by heating and melting a material at a high temperature in a nitrogen atmosphere, a part of the nitrogen gas in the atmosphere reacts with the molten solid electrolyte to form a structure. It is taken in. At this time, the structure of Li—N is locally generated in the glass structure. Considering the strength of the bond between the Li ⁺ ion and the glass skeleton, Li-S <Li-N, and as a result, a Li ⁺ ion relatively weakly bonded to the glass skeleton is generated. The obtained sulfide-based lithium ion conductive solid electrolyte exhibits high ionic conductivity because the Li ⁺ ions weakly bonded to the skeleton are easily movable. Therefore, when synthesizing a sulfide-based lithium ion conductive solid electrolyte, instead of helium gas or argon gas as the atmosphere gas, in a nitrogen gas, the material is heated, melted, and then cooled, whereby A sulfide-based lithium ion conductive solid electrolyte having high ion conductivity can be obtained.

The sulfide-based lithium ion conductive solid electrolyte synthesized by this method includes Li ₂ S and X
(Where X is at least one selected from the group consisting of SiS ₂ , GeS ₂ , P ₂ S ₅ , and B ₂ S ₃ ), and is preferably used because it has a high ionic conductivity. Can be

[0014]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited to these examples.

(Example 1) Among the sulfide-based lithium ion conductive solid electrolytes according to the present invention, aLi ₂ S.bSi
A sulfide-based lithium ion conductive solid electrolyte represented by S ₂ (a + b = 1) was synthesized by the following procedure.

First, a material powder in which lithium sulfide (Li ₂ S) and silicon sulfide (SiS ₂ ) are mixed so as to have a predetermined composition is put into a glassy carbon crucible, which is mixed with argon having different oxygen contents. In a helium and nitrogen stream,
After melting and reacting at 950 ° C. for 2 hours, the mixture was poured into liquid nitrogen and cooled to synthesize an aLi ₂ S.bSiS ₂ -based lithium ion conductive solid electrolyte (a + b = 1).

The ionic conductivity of the solid electrolyte synthesized as described above was measured by an AC impedance method.

As a typical example, 0.60Li ₂ S.
FIG. 1 shows the measurement results of the sulfide-based lithium ion conductive solid electrolyte represented by 0.40 SiS ₂ . Regardless of which inert gas was used, the ionic conductivity of the sulfide-based lithium ion conductive solid electrolyte showed a higher value when it contained a small amount of oxygen than when it did not contain oxygen. However, when the oxygen content exceeds 1000 ppm,
The ionic conductivity dropped sharply. When nitrogen gas was used as the inert gas, particularly high ionic conductivity was exhibited.

Example 2 Among the sulfide-based lithium ion conductive solid electrolytes according to the present invention, aLi ₂ S.bGe
A sulfide-based lithium ion conductive solid electrolyte represented by S ₂ (a + b = 1) was synthesized in the same manner as in Example 1.

The ionic conductivity of the solid electrolyte synthesized as described above was measured by an AC impedance method.

As a typical example, 0.60Li ₂ S.
FIG. 2 shows the measurement results of the sulfide-based lithium ion conductive solid electrolyte represented by 0.40 GeS ₂ . Regardless of which inert gas was used, the ionic conductivity of the sulfide-based lithium ion conductive solid electrolyte showed a higher value when it contained a small amount of oxygen than when it did not contain oxygen. However, when the oxygen content exceeds 1000 ppm,
The ionic conductivity dropped sharply. When nitrogen gas was used as the inert gas, particularly high ionic conductivity was exhibited.

Embodiment 3 Among the sulfide-based lithium ion conductive solid electrolytes according to the present invention, aLi ₂ S.bP ₂ S
₅ A sulfide-based lithium ion conductive solid electrolyte represented by (a + b = 1) was synthesized in the same manner as in Example 1.

The ionic conductivity of the solid electrolyte synthesized as described above was measured by an AC impedance method.

As a typical example, 0.60 Li ₂ S.
FIG. 3 shows the measurement results of the sulfide-based lithium ion conductive solid electrolyte represented by 0.40 P ₂ S ₅ . The ionic conductivity of this sulfide-based lithium ion conductive solid electrolyte, regardless of the use of any inert gas, does not include oxygen.
A higher value was obtained when a small amount of oxygen was contained. However, when the oxygen content exceeded 1000 ppm, the ionic conductivity rapidly decreased. When nitrogen gas was used as the inert gas, particularly high ionic conductivity was exhibited.

Example 4 Among the sulfide-based lithium ion conductive solid electrolytes according to the present invention, aLi ₂ S.bB ₂ S
₃ A sulfide-based lithium ion conductive solid electrolyte represented by (a + b = 1) was synthesized in the same manner as in Example 1.

The ionic conductivity of the solid electrolyte synthesized as described above was measured by an AC impedance method.

As a typical example, 0.55Li ₂ S.
FIG. 4 shows the measurement results of the sulfide-based lithium ion conductive solid electrolyte represented by 0.45B ₂ S ₃ . The ionic conductivity of this sulfide-based lithium ion conductive solid electrolyte, regardless of the use of any inert gas, does not include oxygen.
A higher value was obtained when a small amount of oxygen was contained. However, when the oxygen content exceeded 1000 ppm, the ionic conductivity rapidly decreased. When nitrogen gas was used as the inert gas, particularly high ionic conductivity was exhibited.

Embodiment 5 Among the sulfide-based lithium ion conductive solid electrolytes according to the present invention, aLi ₂ S.bSi
A sulfide-based lithium ion conductive solid electrolyte represented by S ₂ · cLiI (a + b + c = 1) was synthesized by the following procedure.

First, a material powder obtained by mixing lithium iodide (LiI), lithium sulfide (Li ₂ S) and silicon sulfide (SiS ₂ ) is placed in a glassy carbon crucible so as to have a predetermined composition. Argon with different oxygen content,
After melting and reacting at 950 ° C. for 2 hours in a stream of helium and nitrogen, the mixture was poured into liquid nitrogen and cooled, and aLi ₂
An S.bSiS ₂ .cLi-based lithium ion conductive solid electrolyte (a + b + c = 1) was synthesized.

The ionic conductivity of the solid electrolyte synthesized as described above was measured by the AC impedance method.

As a typical example, 0.42Li ₂ S.
FIG. 5 shows the measurement results of the sulfide-based lithium ion conductive solid electrolyte represented by 0.28SiS ₂ .0.30LiI. Regardless of which inert gas was used, the ionic conductivity of the sulfide-based lithium ion conductive solid electrolyte showed a higher value when it contained a small amount of oxygen than when it did not contain oxygen. However, the oxygen content is 1000 ppm
, The ionic conductivity sharply decreased. When nitrogen gas was used as the inert gas, particularly high ionic conductivity was exhibited.

Example 6 Among the sulfide-based lithium ion conductive solid electrolytes according to the present invention, aLi ₂ S.bGe
A sulfide-based lithium ion conductive solid electrolyte represented by S ₂ · cLiI (a + b + c = 1) was synthesized in the same manner as in Example 5.

The ionic conductivity of the solid electrolyte synthesized as described above was measured by an AC impedance method.

As a typical example, 0.42Li ₂ S.
FIG. 6 shows the measurement results of the sulfide-based lithium ion conductive solid electrolyte represented by 0.28 GeS ₂ .0.30 LiI. Regardless of which inert gas was used, the ionic conductivity of the sulfide-based lithium ion conductive solid electrolyte showed a higher value when it contained a small amount of oxygen than when it did not contain oxygen. However, the oxygen content is 1000 ppm
, The ionic conductivity sharply decreased. When nitrogen gas was used as the inert gas, particularly high ionic conductivity was exhibited.

Example 7 Among the sulfide-based lithium ion conductive solid electrolytes according to the present invention, aLi ₂ S.bP ₂ S
A sulfide-based lithium ion conductive solid electrolyte represented by ₅ · cLiI (a + b + c = 1) was synthesized in the same manner as in Example 5.

The ionic conductivity of the solid electrolyte synthesized as described above was measured by the AC impedance method.

As a typical example, 0.42Li ₂ S.
FIG. 7 shows the measurement results of the sulfide-based lithium ion conductive solid electrolyte represented by 0.28P ₂ S ₅ .0.30LiI. Regardless of which inert gas was used, the ionic conductivity of the sulfide-based lithium ion conductive solid electrolyte showed a higher value when it contained a small amount of oxygen than when it did not contain oxygen. However, the oxygen content is 1000 ppm
, The ionic conductivity sharply decreased. When nitrogen gas was used as the inert gas, particularly high ionic conductivity was exhibited.

Example 8 Among the sulfide-based lithium ion conductive solid electrolytes according to the present invention, aLi ₂ S.bB ₂ S
A sulfide-based lithium ion conductive solid electrolyte represented by ₃ · cLiI (a + b + c = 1) was synthesized in the same manner as in Example 5.

The ionic conductivity of the solid electrolyte synthesized as described above was measured by the AC impedance method.

As a typical example, 0.39 Li ₂ S.
The 0.3 1 B ₂ S ₃ of-sulfide represented by 0.30LiI lithium ion conductive solid electrolyte measurement results shown in FIG. Regardless of which inert gas was used, the ionic conductivity of the sulfide-based lithium ion conductive solid electrolyte showed a higher value when it contained a small amount of oxygen than when it did not contain oxygen. However, the oxygen content is 1000 ppm
, The ionic conductivity sharply decreased. When nitrogen gas was used as the inert gas, particularly high ionic conductivity was exhibited.

Embodiment 9 Among the sulfide-based lithium ion conductive solid electrolytes according to the present invention, aLi ₂ S.bSi
A sulfide-based lithium ion conductive solid electrolyte represented by S ₂ · cLi ₃ PO ₄ (a + b + c = 1) was synthesized by the following procedure.

First, a material powder obtained by mixing lithium phosphate (Li ₃ PO ₄ ), lithium sulfide (Li ₂ S), and silicon sulfide (SiS ₂ ) so as to have a predetermined composition is put into a glassy carbon crucible. This was melted at 950 ° C. for 2 hours in a stream of argon, helium and nitrogen having different oxygen contents and reacted.
_{i 2 S · bSiS 2 · cLi} 3 PO 4 based lithium ion conductive solid electrolyte of (a + b + c = 1 ) were synthesized.

The ionic conductivity of the solid electrolyte synthesized as described above was measured by an AC impedance method.

As a typical example, 0.59Li ₂ S.
FIG. 9 shows the measurement results of the sulfide-based lithium ion conductive solid electrolyte represented by 0.39 SiS ₂ .0.02 Li ₃ PO ₄ .
Shown in Regardless of which inert gas was used, the ionic conductivity of the sulfide-based lithium ion conductive solid electrolyte showed a higher value when it contained a small amount of oxygen than when it did not contain oxygen. However, the oxygen content is 1000p
Above pm, the ionic conductivity dropped sharply. When nitrogen gas was used as the inert gas, particularly high ionic conductivity was exhibited.

Example 10 Among the sulfide-based lithium ion conductive solid electrolytes according to the present invention, aLi ₂ S.bG
A sulfide-based lithium ion conductive solid electrolyte represented by eS ₂ · cLi ₃ PO ₄ (a + b + c = 1) was synthesized in the same manner as in Example 9.

The ionic conductivity of the solid electrolyte synthesized as described above was measured by the AC impedance method.

As a typical example, 0.59Li ₂ S.
FIG. 1 shows the measurement results of a sulfide-based lithium ion conductive solid electrolyte represented by 0.39 GeS ₂ .0.02 Li ₃ PO ₄ .
0 is shown. The ionic conductivity of this sulfide-based lithium ion conductive solid electrolyte can be obtained using any inert gas.
A higher value was obtained when a small amount of oxygen was contained than when no oxygen was contained. However, if the oxygen content is 1000
Above ppm, the ionic conductivity dropped sharply. When nitrogen gas was used as the inert gas, particularly high ionic conductivity was exhibited.

Embodiment 11 Among the sulfide-based lithium ion conductive solid electrolytes according to the present invention, aLi ₂ S.bP ₂
A sulfide-based lithium ion conductive solid electrolyte represented by S ₅ · cLi ₃ PO ₄ (a + b + c = 1) was synthesized in the same manner as in Example 9.

The ionic conductivity of the solid electrolyte synthesized as described above was measured by the AC impedance method.

As a typical example, 0.59Li ₂ S.
FIG. 11 shows the measurement results of the sulfide-based lithium ion conductive solid electrolyte represented by 0.39P ₂ S ₅ .0.02Li ₃ PO ₄ .
Shown in Regardless of which inert gas was used, the ionic conductivity of the sulfide-based lithium ion conductive solid electrolyte showed a higher value when it contained a small amount of oxygen than when it did not contain oxygen. However, the oxygen content is 1000p
Above pm, the ionic conductivity dropped sharply. When nitrogen gas was used as the inert gas, particularly high ionic conductivity was exhibited.

Example 12 Among the sulfide-based lithium ion conductive solid electrolytes according to the present invention, aLi ₂ S.bB ₂
A sulfide-based lithium ion conductive solid electrolyte represented by S ₃ · cLi ₃ PO ₄ (a + b + c = 1) was synthesized in the same manner as in Example 9.

The ionic conductivity of the solid electrolyte synthesized as described above was measured by the AC impedance method.

As a typical example, 0.54Li ₂ S.
FIG. 12 shows the measurement results of the sulfide-based lithium ion conductive solid electrolyte represented by 0.44B ₂ S ₃ .0.02Li ₃ PO ₄ .
Shown in Regardless of which inert gas was used, the ionic conductivity of the sulfide-based lithium ion conductive solid electrolyte showed a higher value when it contained a small amount of oxygen than when it did not contain oxygen. However, the oxygen content is 1000p
Above pm, the ionic conductivity dropped sharply. When nitrogen gas was used as the inert gas, particularly high ionic conductivity was exhibited.

In the embodiment of the present invention, the general formula
aLi_TwoSulfide-based lithium ion conductor represented by S.bX
X is SiS as the conductive solid electrolyte_Two, GeS_Two, P
_TwoS_Five, B _TwoS_ThreeWas explained, but X and
And SiS_TwoAnd GeS_TwoSiS, such as a mixture of_Two, Ge
S_Two, P_TwoS_Five, B_TwoS_ThreeOf multiple sulfides selected from
It goes without saying that similar results can be obtained using
The present invention is limited to a single sulfide as X
There is no.

As an additive to aLi ₂ S.bX,
The case where LiI and Li ₃ PO ₄ are used has been described.
It is clear that similar effects can be obtained by using other additives such as LiCl and Li ₂ SO ₄ as additives.
Further, when these additives are used, a plurality of them may be used in combination, and it is not limited to a single additive.

[0056]

According to the present invention, when synthesizing the sulfide-based lithium ion conductive solid electrolyte according to the present invention, the sulfide having high lithium ion conductivity is heated and melted in an inert gas stream containing oxygen. The product-based lithium ion conductive solid electrolyte can be obtained. Moreover, when the oxygen content is 10
When the content is less than 00 ppm, it is more effective. It is particularly effective when nitrogen gas is used as the inert gas. In addition, since nitrogen gas is cheaper than argon and helium, it has the effect of reducing costs when producing a sulfide-based lithium ion conductive solid electrolyte that consumes a large amount of inert gas.

[Brief description of the drawings]

[1] relation diagram between 0.60Li ₂ S · 0.40SiS ₂ conductivity ionic conductivity of the oxygen content in the inert gas

FIG. 2 is a diagram showing the relationship between the ionic conductivity of the conductivity of 0.60Li ₂ S · 0.40GeS ₂ and the oxygen content in an inert gas.

FIG. 3 is a diagram showing the relationship between the ionic conductivity of the conductivity of 0.60 Li ₂ S · 0.40 P ₂ S ₅ and the oxygen content in an inert gas.

FIG. 4 is a diagram showing the relationship between the ionic conductivity of the conductivity of 0.55aLi ₂ S and 0.45B ₂ S ₃ and the oxygen content in an inert gas.

FIG. 5: 0.42Li ₂ S · 0.28SiS ₂ · 0.30
Relationship between ionic conductivity of LiI conductivity and oxygen content in inert gas

FIG. 6: 0.42Li ₂ S · 0.28GeS ₂ · 0.30
Relationship between ionic conductivity of LiI conductivity and oxygen content in inert gas

[7] _{0.42Li 2 S · 0.28P 2 S 5} · 0.30
Relationship between ionic conductivity of LiI conductivity and oxygen content in inert gas

FIG. 8: 0.39Li ₂ S · 0.3 1 B ₂ S ₃ · 0.30
Relationship between ionic conductivity of LiI conductivity and oxygen content in inert gas

[9] 0.59Li ₂ S · 0.39SiS ₂ · 0.02
Relationship between ionic conductivity of Li ₃ PO ₄ conductivity and oxygen content in inert gas

FIG. 10: 0.59Li ₂ S · 0.39GeS ₂ · 0.0
Diagram showing the relationship between the ionic conductivity of the conductivity of 2Li ₃ PO ₄ and the oxygen content in the inert gas

[11] _{0.59Li 2 S · 0.39P 2 S 5} · 0.0
Diagram showing the relationship between the ionic conductivity of the conductivity of 2Li ₃ PO ₄ and the oxygen content in the inert gas

[12] _{0.54aLi 2 S · 0.44B 2 S 3} · 0.
Relationship between ionic conductivity of 02Li ₃ PO ₄ conductivity and oxygen content in inert gas

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeo Kondo 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-4-133209 (JP, A) JP-A-4- 202024 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01B 1/06 C03C 3/32 H01M 6/18 H01M 10/40

Claims (4)

(57) [Claims] 1. A sulfide which is heated and melted in an inert gas stream containing oxygen in a range of 1000 ppm or less when synthesizing a sulfide-based lithium ion conductive solid electrolyte. Method of synthesizing lithium-ion conductive solid electrolyte. Wherein as an inert gas, synthesis of sulfide-based lithium ion conductive solid electrolyte according to claim 1 Symbol mounting characterized by using nitrogen gas. 3. A process according to claim 1 wherein the sulfide-based lithium ion conductive solid electrolyte sulfide-based lithium ion conductive solid electrolyte, characterized in that synthesized by synthetic methods according to any one of claims 2. 4. The sulfide-based lithium ion conductive solid electrolyte according to claim 3 , wherein the main components are Li ₂ S and X (where X is SiS ₂ , GeS ₂ , P ₂ S ₅ , B _At least one selected from the group consisting of ₂ S ₃ ).