JP3149524B2 - Amorphous lithium ion conductive solid electrolyte and method for producing the same - 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 electrochemical devices such as all solid state batteries, capacitors and solid state electrochromic display devices.

[0002]

2. Description of the Related Art In recent years, research on the development of lithium secondary batteries using an organic lithium electrolyte has been actively conducted. For the development of lithium secondary batteries using organic electrolytes,
It is necessary to develop an active material having excellent reversibility as a positive electrode or a negative electrode, and such materials are being actively searched for today. For example, research on negative electrode materials for such batteries has shifted from those using lithium metal alone or lithium alloys to those using reactions that can reversibly move lithium between carbon layers using special carbon. And it is shifting.

[0003] Similarly, the materials used for the positive electrode material are different from those accompanied by a chemical change due to the electrochemical oxidation-reduction of the active material to those in which Li ions in the electrolyte enter and exit the active material. ing.

On the other hand, regarding the electrolyte, a lithium ion conductive solid electrolyte is required to improve the reliability of the battery. However, at present, there is no excellent lithium ion conductive solid electrolyte, and research and development of a new lithium ion conductive solid electrolyte material are being actively conducted.

As one of studies on such solid electrolytes, Li ₂ SX (X is SiS ₂ , GeS ₂ , P ₂ S ₅ ,
At least one sulfide-based sulfide glass of B ₂ S ₃ has been actively studied because of its excellent ionic conductivity.

In the Li ₂ S.X sulfide glass, X is Si
It has a particularly high conductivity value in the Li ₂ S.SiS ₂ system of S ₂ , and the value is about 5 × 10 ⁻⁴ S / cm.

[0007] In the LiI · Li ₂ S · X based glass doped with lithium iodide in Li ₂ S · X based sulfide glass, have a relatively high ionic conductivity of about 10 ^-3 S / cm Are known.

[0008]

SUMMARY OF THE INVENTION Li ₂ SX (X is S
The conductivity of at least one sulfide-based sulfide glass of iS ₂ , GeS ₂ , P ₂ S ₅ , and B ₂ S ₃ is 5 as described above.
Although it shows a high value of × 10 ^-4 S / cm, the ionic conductivity is still low for application to an electrochemical device, and the chemical stability of this material is also insufficient.

In the LiI.Li ₂ SX system, 10
^-3 S / cm higher ionic conductivity is shown, but the contact with lithium metal reduces the solid electrolyte and lowers the conductivity.
There are still many problems in the development of applications to electrochemical devices such as all-solid-state lithium batteries.

An object of the present invention is to solve the conventional problem of low electrical conductivity or the problem of chemical stability that causes a decrease in electrical conductivity, and to provide an excellent lithium ion conductive solid electrolyte.

[0011]

In order to achieve the above object, the amorphous lithium ion conductive solid electrolyte of the present invention has the general formula aLi ₃ PO ₄ .bLi ₂ S.cX.dLiC
1 is a lithium ion conductive solid electrolyte represented by
Where a + b + c + d is 1 and X is SiS ₂ , G
It is one or more sulfides selected from the group consisting of eS ₂ , P ₂ S ₅ and B ₂ S ₃ .

In the production of the amorphous lithium ion conductive solid electrolyte of the present invention, first, the general formula a'Li ₃ PO ₄ .b '
LiCl is mixed with an amorphous compound represented by Li ₂ S · c′X (where a ′ + b ′ + c ′ is 1 and X is the same as described above), and the mixture is mixed. Is heated and melted, and then rapidly cooled.

In the present invention, X in the above formula is preferably SiS ₂ . In addition, the sum of a, b, and c in the above equation satisfies the following equation: 0.9> a + b + c> 0.6, and d satisfies the following equation: 0.1 ≦ d ≦ 0.4. preferable.

[0014]

It is known that Li ₃ PO ₄ has a crystal structure with high ionic conductivity in a high temperature region, but changes its structure due to phase transition near room temperature, resulting in a decrease in ionic conductivity.

However, Li ₃ PO ₄ is added to a material which shows an amorphous state at room temperature, and once these materials are made amorphous at a high temperature, and then returned to a room temperature, the Li ₃ PO ₄ It was found that the state can be maintained in an amorphous state even at room temperature, and high ionic conductivity can be provided even at room temperature.

This is because the amorphous state is obtained.
That is, unlike a crystalline material, lithium ions can move freely, and the ionic conductivity is considered to be improved by taking a structure in which the arrangement of atoms in the crystal structure is slightly disordered. In particular, the general formula a′Li ₃ PO _4.
b′Li ₂ S · c′X (where a ′ + b ′ + c ′ is 1 and X ′
Represents one or more sulfides selected from the group consisting of SiS ₂ , GeS ₂ , P ₂ S ₅ and B ₂ S ₃ ), and LiCl is mixed with the amorphous compound, and the mixture is heated and dissolved. And
Thereafter, the amorphous lithium ion conductive solid electrolyte of the present invention synthesized by rapid cooling has a large amount of freely movable lithium ions, and as a result, a′Li ₃ PO ₄ .b′Li ₂ S.
A lithium ion conductive solid electrolyte having higher ionic conductivity than the amorphous compound material represented by c′X.

[0017]

Hereinafter, the present invention will be described in more detail with reference to specific examples.

The lithium ion conductive solid electrolyte of the present invention has the general formula a'Li ₃ PO ₄ .b'Li ₂ S.c'X (where a '
+ B '+ c' is 1 and X is SiS ₂ , GeS ₂ , P ₂ S ₅
And at least one sulfide selected from the group consisting of B ₂ S ₃ ) as a base material, and lithium chloride (LiCl) as a compound to be added.

Since the amorphous compound serving as the base material, the raw material thereof, and the synthesized solid electrolyte are easily decomposed by oxygen and moisture in the air, all the handling was performed in a dry box under a dry argon atmosphere.

Here, all reagents used, including LiBr, were of a special grade, and in particular, LiCl was used after drying under reduced pressure at 300 ° C. for 6 hours.

Example 1 An example of the present invention, a general formula aLi ₃ PO ₄ .bLi ₂ S.c
An amorphous lithium ion conductive solid electrolyte represented by SiS ₂ .dLiCl (where a + b + c + d = 1) was synthesized by the following method.

First, the general formula b "Li ₂ S.c" SiS ₂ (b "+
c ″ = 1) was synthesized. In this synthesis,
Lithium sulfide (Li ₂ S) and silicon sulfide (SiS ₂ )
0.3 to 0.8, and the mixed powder was put in a glassy carbon crucible.
After melting and reacting at 50 ° C. for 1.5 hours, the mixture is poured into liquid nitrogen and quenched to obtain the general formula b "Li ₂ S.c" S
A compound represented by iS ₂ (b "+ c" = 1) was obtained.

Next, the obtained base material is pulverized, and lithium phosphate (Li ₃ PO ₄ ) is mixed with the general formula a′Li ₃ PO ₄ .b′L
In i ₂ S · c′SiS ₂ , a ′ is added and mixed so that a ′ = 0.01 to 0.3, and the powder is placed in a glassy carbon crucible. After melting and reacting for 5 hours, it was poured into liquid nitrogen and quenched,
General formula a′Li ₃ PO ₄ .b′Li ₂ S.c′SiS ₂ (a ′ + b ′ +
The compound represented by c ′ = 1) was obtained.

The obtained a'Li ₃ PO ₄ .b'Li ₂ S.c'S
to iS ₂ material y weight, were mixed amount of lithium chloride (LiCl) d as y + d is 1, put the mixed powder in glassy carbon crucible, which, a stream of argon 95
After melting and reacting at 0 ° C. for 1.5 hours, the mixture is poured into liquid nitrogen and quenched to obtain a general formula aLi ₃ PO ₄ .bLi ₂ S.cS
A solid electrolyte represented by iS ₂ .dLiCl (a + b + c + d = 1) was obtained.

In order to examine the characteristics of the synthesized solid electrolyte,
The ionic conductivity was measured by the AC impedance method.

FIG. 1 shows the obtained results. The vertical axis indicates ionic conductivity, and the horizontal axis indicates (0.03Li ₃ PO ₄ .0.5
8Li ₂ S.0.39SiS ₂ ), showing the added amount (mol%) of LiCl. FIG. 1 shows that the conductivity increased with the addition of lithium chloride, then decreased through a maximum, and the ionic conductivity was maximized at 0.75 (0.03 Li ₃ PO _4).・ 0.58
Li ₂ S.0.39SiS ₂ ) .0.25 (LiCl), and the value of the ionic conductivity is 2.27 × 10 ⁻³ S / c.
m.

On the other hand, 0.03Li ₃ PO ₄ .0.58Li ₂ S.0.39S to which lithium chloride was not added.
The ionic conductivity of iS ₂ was 7 × 10 ⁻⁴ S / cm.

Next, the chemical stability of the electrolyte with respect to lithium metal was examined. To examine this stability, the synthesized electrolytes of various compositions were pressed into disks having a thickness of 0.5 mm and a diameter of 10 mm, and lithium metal disks were pressed on both surfaces of these disks, as shown in FIG. A sealed cell 1 was created. In the figure, 2 indicates lithium metal and 3 indicates an electrolyte. The chemical stability of the obtained cells was evaluated by storing these cells in a thermostat at 60 ° C. for 500 hours and measuring the change over time of the internal impedance of each cell.

FIG. 3 shows the obtained results. The vertical axis shows the impedance change normalized by the internal impedance before storage, and the horizontal axis shows the storage time. As is clear from this result, it was found that when lithium chloride was 0.55 or more, the change with time of the internal impedance was remarkably large, and when it was less than 0.55, the increase in the internal impedance was small.

Example 2 aLi ₃ PO ₄ · b Li-ion conductive solid electrolyte aLi ₃ PO ₄ · b using a Li ₂ S · cGeS ₂ amorphous material
Li ₂ S.cGeS ₂ .dLiCl was synthesized by the following method.

First, 0.6Li ₂ S.0.4Ge
S ₂ glass was synthesized in the same manner as in Example 1. That is,
Lithium sulfide (Li ₂ S) and germanium sulfide (Ge
S ₂ ) was mixed in a molar ratio of 3: 2, and the material powder was placed in a vitreous carbon crucible, which was then mixed with a stream of 95% argon gas.
0 After reacting for 1.5 hours at ° C., rapidly cooled was put into liquid nitrogen to synthesize a material 0.6Li ₂ S · 0.4GeS ₂ composition. Subsequently, the material 0.6Li ₂ S.
0.4 GeS ₂ is pulverized, and lithium phosphate (Li ₃ P
O ₄ ) was mixed in a molar ratio of 97: 3, and the powder was placed in a glassy carbon crucible and placed in a stream of argon at 950 ° C. for 1.
The reaction was performed for 5 hours. Thereafter, quenched was poured into liquid _{nitrogen, 0.03Li 3 PO 4 · 0.58Li 2} S · 0.39
An amorphous material represented by GeS ₂ was synthesized.

The obtained 0.03Li ₃ PO ₄ /0.58 L
To y mol% of i ₂ S.0.39GeS ₂ material, d mol% of lithium chloride (LiCl) was added, and the mixed powder was placed in a glassy carbon crucible.
After dissolving and reacting at 0 ° C. for 1.5 hours, the mixture is poured into liquid nitrogen and quenched to obtain a general formula aLi ₃ PO ₄ .bLi ₂ S.cG
A solid electrolyte represented by eS ₂ .dLiCl (a + b + c + d = 1) was obtained.

In order to examine the characteristics of the synthesized solid electrolytes of various compositions, the ionic conductivity was measured by an AC impedance method.

FIG. 4 shows the obtained results. The vertical axis indicates the ionic conductivity, and the horizontal axis indicates (0.03Li ₃ PO ₄ .0.58).
It shows the amount of LiCl added to (Li ₂ S.0.39GeS ₂ ). FIG. 4 shows that the conductivity increases with the addition of lithium chloride, then decreases through a maximum. The highest ionic conductivity is
_{0.80 (0.03Li 3 PO 4 · 0.58Li} 2 S ·
0.39 GeS ₂ ) · 0.20 (LiCl), and the value of the ionic conductivity at that time is 1.2 × 10 ⁻³ S /
cm.

On the other hand, 0.03Li ₃ PO ₄ .0.58Li ₂ S.0.39G to which lithium chloride was not added.
The ionic conductivity of eS ₂ was 2 × 10 ⁻⁴ S / cm.

Next, the chemical stability of the electrolyte with respect to lithium metal was examined in the same manner as in Example 1. The results obtained were the same as in Example 1. The change is noticeably greater,
Below that, the increase of the internal impedance was found to be small.

Example 3 aLi ₃ PO ₄ .b Li-ion conductive solid electrolyte using Li ₂ S.cP ₂ S ₅ type amorphous material aLi ₃ PO ₄ .b
Li ₂ S.cP ₂ S ₅ .dLiCl was synthesized by the following method.

First, 0.67 Li ₂ S.0.33
P ₂ S ₅ glass was synthesized as in Example 1. That is, lithium sulfide (Li ₂ S) and phosphorus sulfide (P ₂ S ₅ ) are mixed at a molar ratio of 2: 1 and the material powder is placed in a glassy carbon crucible, which is then placed in an argon stream at 500 ° C. 12 hours,
After subsequently react 2 hours at 800 ° C., rapidly cooled and poured into liquid nitrogen _to synthesize a material 0.67Li ₂ S · 0.33P 2 S ₅ composition.

Subsequently, 0.67 L of the material thus obtained was obtained.
i ₂ was ground S · 0.33P ₂ S _5, lithium phosphate (L
i ₃ PO ₄ ) was mixed at a molar ratio of 97: 3, and the powder was placed in a glassy carbon crucible and reacted at 950 ° C. for 1.5 hours in a stream of argon. Thereafter, quenched was poured into liquid _{nitrogen, 0.03Li 3 PO 4 · 0.65Li 2} S · 0.
An amorphous material represented by 32P ₂ S ₅ was synthesized.

The obtained 0.03Li ₃ PO ₄ 0.65 L
To y mol% of i ₂ S.0.32P ₂ S ₅ material, d mol% of lithium chloride (LiCl) is added, and the mixed powder is placed in a glassy carbon crucible, and is heated at 950 ° C. for 1.5 hours in a stream of argon. After dissolving and reacting, the mixture is poured into liquid nitrogen and quenched to obtain a general formula aLi ₃ PO ₄ .bLi ₂ S.cP ₂ S _5.
A solid electrolyte represented by dLiCl (a + b + c + d = 1) was obtained.

In order to examine the characteristics of the synthesized solid electrolytes of various compositions, the ionic conductivity was measured by an AC impedance method, and the chemical stability of the solid electrolyte to lithium metal was examined.

FIG. 5 shows the obtained results. The vertical axis indicates the ionic conductivity, and the horizontal axis indicates (0.03Li ₃ PO ₄ · 0.65
It shows the amount of LiCl added to Li ₂ S.0.32P ₂ S ₅ ). The composition having the largest value of ionic conductivity is 0.70 (0.03Li ₃ PO ₄ .0.65).
Li ₂ S · 0.32P ₂ S ₅ ) · 0.30 (LiCl), and the value of the ionic conductivity at that time was 8.5 × 1.
It was 0 ^-4 S / cm.

On the other hand, 0.03Li ₃ PO ₄ · 0.65Li ₂ S · 0.32P ₂ to which lithium chloride was not added.
The ionic conductivity of S ₅ was 4.2 × 10 ⁻⁴ S / cm.

Next, the chemical stability of the electrolyte against lithium metal was examined in the same manner as in Example 1. The results obtained were the same as in Example 1. The change is noticeably greater,
Below that, the increase of the internal impedance was found to be small.

[0045] Example _{4 aLi 3 PO 4 · bLi 2} S · cB 2 S 3 based lithium ion conductivity an amorphous material solid electrolyte aLi ₃ PO ₄ · b
Li ₂ S.cB ₂ S ₃ .dLiCl was synthesized by the following method.

First, 0.5Li ₂ S.0.5P ₂ S
_Five glasses were synthesized as in Example 1. That is, lithium sulfide (Li ₂ S) and boron sulfide (B ₂ S ₃ ) are mixed at a molar ratio of 1: 1 and the material powder is placed in a glassy carbon crucible and placed in an argon stream at 500 ° C. for 12 hours. Then 8
00 After reacting for 3 hours at ° C., rapidly cooled was put into liquid nitrogen to synthesize a material 0.5Li ₂ S · 0.5B ₂ S ₃ composition.

Subsequently, 0.5Li of the material thus obtained was obtained.
The ₂ S · 0.5B ₂ S ₃ was pulverized, lithium phosphate (Li ₃ P
O ₄ ) was mixed at a molar ratio of 96: 4, and the powder was placed in a glassy carbon crucible and reacted at 800 ° C. for 3 hours in an argon stream. After that, put into liquid nitrogen and quench,
0.04Li ₃ PO ₄・ 0.48Li ₂ S ・ 0.48B ₂ S
_An amorphous material represented by ₃ was synthesized.

The obtained 0.04Li ₃ PO ₄ .0.48 L
To y mol% of the i ₂ S.0.48B ₂ S ₃ material, d mol% of lithium chloride (LiCl) was added, and the mixed powder was placed in a glassy carbon crucible.
After melting and reacting at 0 ° C. for 1.5 hours, the mixture is poured into liquid nitrogen and quenched to obtain a general formula aLi ₃ PO ₄ .bLi ₂ S.cB ₂
A solid electrolyte represented by S ₃ .dLiCl (a + b + c + d = 1) was obtained.

In order to examine the characteristics of the synthesized solid electrolytes of various compositions, the ionic conductivity was measured by an AC impedance method, and the chemical stability of the solid electrolyte to lithium metal was examined.

FIG. 6 shows the obtained results. The vertical axis indicates the ionic conductivity, and the horizontal axis indicates (0.04Li ₃ PO ₄ .0.48
It shows the amount of LiCl added to Li ₂ S.0.48B ₂ S ₃ ). The composition having the largest value of the ionic conductivity is 0.75 (0.03Li ₃ PO ₄ .0.65).
Li ₂ S · 0.32B ₂ S ₃ ) · 0.25 (LiCl), and the value of the ionic conductivity at that time is 7.5 × 1.
It was 0 ^-4 S / cm.

On the other hand, 0.03Li ₃ PO ₄ · 0.65Li ₂ S · 0.32B ₂ to which lithium chloride was not added.
The ionic conductivity of S ₃ was 3.0 × 10 ⁻⁴ S / cm.

Next, the chemical stability of the electrolyte with respect to lithium metal was examined in the same manner as in Example 1. The results obtained were the same as in Example 1. The change is noticeably greater,
Below that, the increase of the internal impedance was found to be small.

In synthesizing the solid electrolytes in these examples, amorphous materials were sequentially synthesized to obtain the intended lithium solid electrolyte of the present invention. It was a trial, and it goes without saying that it can be simplified by selecting various conditions such as the electrolyte composition, the synthesis temperature, and the temperature raising condition.

[0054]

Amorphous lithium ion conductive solid electrolyte of the present invention _{exhibits, Li 3 PO 4 · Li 2} S · X (X is SiS _2,
It is obtained by adding lithium chloride to at least one sulfide-based sulfide amorphous material of GeS ₂ , P ₂ S ₅ and B ₂ S ₃ , and the base material Li ₂ SX
(X shows the same thing as the above.) Compared with the amorphous material, it shows higher lithium ion conductivity and has less chemical change even when it comes in contact with lithium metal.

As a result, when this amorphous lithium ion conductive solid electrolyte is used for an electrolyte of an electrochemical device such as a battery, a capacitor, and an electrochromic display device, an extremely practical electrochemical device is manufactured. Expect to be able to.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of lithium chloride (LiCl) added to a solid electrolyte and ionic conductivity in Example 1.

FIG. 2 is a cross-sectional view of a cell for measuring internal impedance.

FIG. 3 is a diagram showing the chemical stability of a solid electrolyte for metallic lithium.

FIG. 4 is a diagram showing the relationship between the amount of lithium chloride (LiCl) added to a solid electrolyte and the ionic conductivity in Example 2.

FIG. 5 is a diagram showing the relationship between the amount of lithium chloride (LiCl) added to a solid electrolyte and the ionic conductivity in Example 3.

FIG. 6 is a graph showing the relationship between the amount of lithium chloride (LiCl) added to a solid electrolyte and the ionic conductivity in Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sealed cell 2 Lithium metal 3 Electrolyte

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-304805 (JP, A) JP-A-3-269079 (JP, A) JP-A-4-162306 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C01B 25/30 H01B 1/06 H01M 6/18

Claims (4)

(57) [Claims] 1. The formula aLi ₃ PO ₄ .bLi ₂ S.c
A lithium ion conductive solid electrolyte represented by X · dLiCl, wherein a + b + c + d is 1 and X is selected from the group consisting of SiS ₂ , GeS ₂ , P ₂ S ₅ and B ₂ S ₃ An amorphous lithium ion conductive solid electrolyte, which is one or more sulfides. 2. The amorphous lithium ion conductive solid electrolyte according to claim 1, wherein X is SiS ₂ . 3. The sum of a, b and c is given by the following equation: 0.9> a + b +
The relationship of c> 0.6 is satisfied, and d is the following formula: 0.1 ≦ d ≦
The amorphous lithium ion conductive solid electrolyte according to claim 1 or 2, which satisfies a relationship of 0.4. 4. The method for producing an amorphous lithium ion conductive solid electrolyte according to claim 1, wherein the general formula a′Li
Synthesis of an amorphous material represented by ₃ PO ₄ .b'Li ₂ S.c'X (where a '+ b' + c 'is 1 and X is the same as above) After that, LiCl is mixed with the amorphous material, the mixture is heated and melted, and then quenched, and thereafter, a method for producing an amorphous lithium ion conductive solid electrolyte.