JP3163741B2 - 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 and LI ₂ SX systems, 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 a general formula aLi ₃ PO ₄ .bLi ₂ S.cX.dLiI
Wherein a + b + c + d is 1 and X is SiS ₂ , Ge
It is one or more sulfides selected from the group consisting of S ₂ and P ₂ S ₅ .

In the production of the amorphous lithium ion conductive solid electrolyte of the present invention, the general formula a′Li ₃ PO _4.
mixing LiI with an amorphous compound represented by b′Li ₂ S · c′X (where a ′ + b ′ + c ′ is 1 and X is the same as described above); The mixture 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)
Wherein X is SiS ₂ , GeS ₂ , P ₂ S ₅ and B ₂ S ₃
The compound of the present invention is synthesized by mixing LiI with an amorphous compound represented by the formula (1), and heating and dissolving the mixture, followed by quenching. The lithium ion conductive solid electrolyte has a large amount of lithium ions that can move freely, resulting in a′Li ₃ PO _4.
A lithium ion conductive solid electrolyte having higher ionic conductivity than the amorphous compound material represented by b′Li ₂ S · 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 a general formula a′Li ₃ PO ₄ .b′Li ₂ S.c′X (where a ′ + b ′ + c ′ is 1 and X is SiS ₂ , G
An amorphous compound represented by at least one sulfide selected from the group consisting of eS ₂ , P ₂ S ₅ and B ₂ S ₃ ) is used as a base material, and lithium iodide (Li) is used as a compound to be added.
I) was used.

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 the reagents used, including LiI, were of a special grade. In particular, LiI was used after drying under reduced pressure at 400 ° 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 .dLiI (where a + b + c + d = 1) was synthesized by the following method.

First, the general formula b "Li ₂ S.c" SiS
₂ A compound represented by (b ″ + c ″ = 1) was synthesized. In this synthesis, lithium sulfide (Li ₂ S) and silicon sulfide (S
iS ₂ ) is mixed so that b ″ = 0.3-0.8,
Put the mixed powder in a glassy carbon crucible,
After melting and reacting at 950 ° C. for 1.5 hours in an argon gas stream, the mixture is poured into liquid nitrogen and quenched to obtain the general formula b ″ Li ₂ S · c ″ SiS ₂ (b ″ + c ″ = 1). The compound represented was obtained.

Next, the obtained base material was pulverized, and lithium phosphate (Li ₃ PO ₄ ) was added thereto with the general formula a′Li ₃ PO _4.
In b′Li ₂ S · c′SiS ₂ , a ′ = 0.01 to
0.3, and the mixture was put in a glassy carbon crucible.
And reacted for 1.5 hours, then put into liquid nitrogen and quenched to obtain a general formula a′Li ₃ PO ₄ .b′Li ₂ S.c ′
A compound represented by SiS ₂ (a ′ + b ′ + c ′ = 1) was obtained.

The obtained a'Li ₃ PO ₄ .b'Li ₂ S.
C'SiS ₂ material y amount to, lithium iodide (Li
I) The amount of d is mixed so that y + d becomes 1, the mixed powder is put into a glassy carbon crucible, which is melted and reacted at 950 ° C. for 1.5 hours in an argon gas stream. And quenched, and the general formula aLi ₃ PO ₄ .bLi ₂
A solid electrolyte represented by S.cSiS ₂ .dLiI (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 the ionic conductivity, and the horizontal axis indicates (0.01Li ₃ PO ₄ .0.6
4Li ₂ S.0.35SiS ₂ ), the addition amount (mol%) of LiI. FIG. 1 shows that the conductivity increased with the addition of lithium iodide, then decreased through a maximum, and the ionic conductivity was maximized at 0.65 (0.01 Li ₃ PO _{3). 4} - 0.64
Li ₂ S · 0.35SiS ₂ ) · 0.35 (LiI), and the value of the ionic conductivity was 2.7 × 10 ⁻³ S / cm.

On the other hand, 0.01 Li ₃ PO ₄ .0.64 Li ₂ S.0.35 to which lithium iodide was not added.
The ionic conductivity of SiS 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 the lithium iodide was 0.7 or more, the change with time of the internal impedance became remarkably large, and when it was less than 0.7, 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 .dLiI 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 .dLiI (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 LiI added to Li ₂ S.0.39GeS ₂ ). FIG. 4 shows that the conductivity increases with the addition of lithium iodide, then decreases through a maximum. The highest ionic conductivity is
_{0.6 (0.03Li 3 PO 4 · 0.58Li} 2 S · 0.
39GeS ₂ ) · 0.40 (LiCl)
The value of the ionic conductivity at that time was 2.1 × 10 ⁻³ S / cm.
Met.

On the other hand, 0.03Li ₃ PO ₄ .0.58Li ₂ S.0.39 to which lithium iodide was not added.
The ion conductivity of GeS ₂ was 7 × 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. It was found that the change with time became remarkably large, and below that, the increase in the internal impedance was 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 .dLiI 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 dLiI (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 LiI added to Li ₂ S.0.32P ₂ S ₅ ). The composition having the largest value of the ionic conductivity is 0.7 (0.03Li ₃ PO ₄ · 0.65Li).
₂ is when _{S · 0.32P 2 S 5) ·} 0.30 in (LiI), the value of the ionic conductivity of that time 8.5 × 10 ^-4 S
/ Cm.

On the other hand, 0.03Li ₃ PO ₄ · 0.65Li ₂ S · 0.32 without addition of lithium iodide
The ionic conductivity of P ₂ S ₅ was 4.2 × 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. It was found that the change with time became remarkably large, and below that, the increase in the internal impedance was 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 .dLiI 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 iodide (LiI) 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 .dLiI (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
This shows the amount of LiI added to Li ₂ S.0.48B ₂ S ₃ ). The composition in which the ionic conductivity showed the largest value was 0.75 (0.03Li ₃ PO ₄ .65 L).
i ₂ S · 0.32B ₂ S ₃ ) · 0.25 (LiI), and the value of the ionic conductivity at that time is 7.8 × 10 ^−4.
S / cm.

On the other hand, 0.03Li ₃ PO ₄ .0.65Li ₂ S.0.32 to which lithium iodide was not added.
The ionic conductivity of B ₂ S ₃ was 1.9 × 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 similar to those in Example 1; It was found that the change with time became remarkably large, and below that, the increase in the internal impedance was 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 iodide to at least one sulfide-based amorphous sulfide material of GeS ₂ , P ₂ S ₅ and B ₂ S ₃ , and is composed of Li ₂ S.
Compared to an X-based (X is the same as described above) -based amorphous material, it exhibits higher lithium ion conductivity and has less chemical change even when 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 iodide (LiI) 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 graph showing the relationship between the amount of lithium iodide (LiI) added to a solid electrolyte and the ionic conductivity in Example 2.

FIG. 5 is a graph showing the relationship between the amount of lithium iodide (LiI) 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 iodide (LiI) added to a solid electrolyte and the ionic conductivity in Example 4.

[Explanation of symbols]

 1 Closed cell 2 Lithium metal 3 Electrolyte

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C01B 25/30 C01B 17/22 CA (STN)

Claims (4)

(57) [Claims] 1. The formula aLi ₃ PO ₄ .bLi ₂ S.c
A lithium ion conductive solid electrolyte represented by X · dLiI, wherein a + b + c + d is 1 and X is S
An amorphous lithium ion conductive solid electrolyte comprising at least one sulfide selected from the group consisting of iS ₂ , GeS ₂ , P ₂ S ₅ and B ₂ S ₃ . 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, LiI is mixed with the amorphous material, the mixture is heated and melted, and then quenched, followed by quenching.