JP2003257237A - Ion conductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion conductor made of an organic and inorganic composite compound that has mechanical strength of an inorganic skeleton and flexibility of an organic skeleton and further, superior ion conductivity. <P>SOLUTION: This is an ion conductor made of a compound that is obtained by applying hydrolysis and condensation polymerization of at least a metal alkoxide (A) expressed by the formula M<SP>1</SP>OR and an organic metal compound (B) expressed by the formula R<SP>1</SP><SB>b</SB>M<SP>2</SP>(OR<SP>2</SP>)<SB>4-b</SB>. In the formula, M<SP>1</SP>is an alkaline metal, R is an alkyl group as expressed by the chemical formula C<SB>a</SB>H<SB>2a+1</SB>(a is an integer between 1 and 20). M<SP>2</SP>is a metal or non-metal, R<SP>1</SP>is an organic functional group, R<SP>2</SP>is an alkyl group as expressed by the chemical formula C<SB>h</SB>H<SB>2h+1</SB>(h is an integer between 1 and 20), and b is 1, 2 or 3. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ionic conductor, and more particularly to an ionic conductor that can be used for a solid electrolyte, a sensor, etc., which is an electrochemical device.

[0002]

2. Description of the Related Art Conventionally, as an electrolyte for a lithium primary battery and a lithium secondary battery, LiBF ₄ , Li is used in an organic solvent such as ethylene carbonate or propylene carbonate.
An electrolytic solution in which an ionic lithium salt such as PF ₆ or LiCF ₃ SO ₃ is dissolved has been used. However, this electrolytic solution has the drawbacks that it may leak and ignite, and may easily volatilize and lack long-term reliability. In contrast, solid electrolytes do not have such drawbacks,
Further, when used as an electrolyte of the above device, a separator is not required, unlike the case where an electrolyte solution is used. By using the solid electrolyte in this way, it is possible to improve the safety in using the device and to reduce the size and weight of the device itself.
Polymer electrolytes, inorganic solid electrolytes, and the like are known as promising materials candidates for the solid electrolyte. Polymer electrolytes are excellent in flexibility, processability, thin-film moldability, lightness, elasticity, etc., and are expected to be applied to large secondary batteries for electric vehicles and built-in batteries for thin products such as IC cards. There is. Unlike solid electrolytes and polymer electrolytes, inorganic solid electrolytes
It is nonflammable and has a lithium ion transport number of 1.

Examples of the above-mentioned polymer electrolyte include polyether-based polymer compounds such as polyethylene oxide and polypropylene oxide, and LiClO ₄ and LiCF ₃ S.
Those mixed with alkali metal salts such as O ₃ and lithium sulfonimide have been studied. It has been clarified that the ionic conductivity of this polymer electrolyte is due to the thermal motion of the polymer chain, and various attempts have been made to improve the conductivity, such as suppressing the decrease in conductivity due to crystallization of the polymer. ing. Moreover, as a big problem of the polymer electrolyte,
The mechanical strength is low. Therefore, various countermeasures such as crosslinking of polymers and hybridization with inorganic compounds have been studied.

As the inorganic solid electrolyte, a melt quenching method is used.
Made by Li₂S-SiS₂System-based sulfide
Glass (Kondo et al., Solid State Ioni
cs53-56, 1183, 1992), solid phase reaction
Li produced by the method _FourSiO_Four-Li₃PO_FourOxide
Ceramics (UV Alpen et al., "Fast
Ion Transport in Solid "4
Page 63, 1979), etc.
However, these materials are poorly flexible, and
Is difficult to apply, making it difficult to apply to thin batteries and large batteries.
Yes. For this reason, vacuum deposition (Y. Ito et al., I.
bid. , 57, 389, 1983) and high frequency scans.
Putter et al. (K. Miyauchi et al., Solid S
TateIonics 9-10, 1469, 198
3 years) synthesis of ion conductive thin film by physical vapor deposition
It was However, such physical vapor deposition is not suitable for multi-component systems.
The composition of the film and the composition of the thin film are liable to cause compositional deviation.
This phenomenon is remarkable when it contains a large amount of thium. This
Therefore, a uniform Li without any compositional deviation₂O-SiO₂Inorganic
There is a report that a solid thin film was prepared by the sol-gel method.
Ruga (Tatsumi Sanda et al., The Chemical Society of Japan, Vol. 11, p. 1958,
1987), its conductivity is slightly lower,
It was difficult to use as a pond electrolyte.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium ion conductor comprising an organic-inorganic composite compound having a mechanical strength of an inorganic skeleton, flexibility of an organic skeleton, and further excellent ionic conductivity. To do.

[0006]

According to the invention of claim 1, at least a metal alkoxide (A) represented by the following general formula (1) and an organometallic compound represented by the following general formula (2) ( An ionic conductor comprising a compound obtained by subjecting B) to a hydrolysis and polycondensation reaction. M ¹ OR (1) (M ¹ : alkali metal, R: chemical formula C _a H _{2a + 1} (a is 1 to 1
An alkyl group represented by (an integer between 20)) R ¹ _b M ² (OR ² ) _4-b (2) (M ² : metal or nonmetal, R ¹ : organic functional group, R ² : chemical formula _Ch Alkyl group represented by H _{2h + 1} (h is an integer between 1 and 20), b: 1, 2 or 3)

The invention according to claim 2 is the ionic conductor according to claim 1, characterized in that the alkali metal M ¹ contained in the metal alkoxide (A) is lithium.

The invention of claim 3 is the ionic conductor according to claim 1 or 2, wherein the metal or nonmetal M ² contained in the organometallic compound (B) is silicon.

The invention of claim 4 is the organometallic compound.
(B) Organic functional group R¹Is the chemical formula C_kH _{2k + 1}(K is 1-2
An integer between 0) and an alkyl group represented by
The ionic conductor according to any one of 1 to 3.

According to the invention of claim 5, the organic functional group R ¹ of the organometallic compound (B) is a fluoroalkyl group represented by the chemical formula — (CF ₂ ) _m — (m is an integer between 1 and 20). The ionic conductor according to any one of claims 1 to 4, which comprises at least one of:

The invention of claim 6 includes at least one ethylene oxide unit represented by the chemical formula-(CH ₂ CH ₂ O)-in the organic functional group R ¹ of the organosilicon compound. The ionic conductor according to any one of the above.

The invention according to claim 7 is the ionic conductor according to any one of claims 1 to 6, characterized in that the starting material contains a metal alkoxide (C) represented by the following general formula (3). M (OR ³ ) _n (3) (M is at least one of Al, B, P and Si, R
³ is an alkyl group represented by the chemical formula C _h H _{2h + 1} (h is an integer between 1 and 20)

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail. The ionic conductor composed of the organic-inorganic composite compound in the present invention comprises at least a metal alkoxide compound (A) as an electrolyte salt source and an organometallic compound (B) having at least one organic functional group as a skeleton-forming compound as starting materials. And an amorphous compound obtained by hydrolysis and polycondensation reaction. Further, the obtained compound contains a structure in which part of the skeleton of an alkali metal oxide-metal or nonmetal oxide inorganic solid electrolyte such as Li ₂ O—SiO ₂ system is substituted with an organic functional group R ^1. It becomes a crystalline compound. Hereinafter, each component used as a starting material will be described in detail below.

The metal alkoxide (A) used as an electrolyte salt source and represented by the following general formula (1) is not particularly limited, but is preferably a lithium compound from the viewpoint of energy density and the like. M ¹ OR (1) (M ¹ : alkali metal, R: chemical formula C _a H _{2a + 1} (a is 1 to 1
An alkyl group represented by an integer between 20) As the lithium compound, lithium hydroxide, lithium acetate, lithium nitrate, lithium sulfate, lithium carbonate, lithium alkoxide, lithium chloride, lithium bromide, lithium iodide, fluorinated Examples thereof include lithium. Among them, lithium alkoxide is preferable because it is stable in an alcohol solvent and has high reactivity.

Lithium alkoxide has the general formula LiOR
(R is an alkyl group represented by the chemical formula C _a H _{2a + 1} (a is an integer between 1 and 20)), LiOCH ₃ , L
Examples thereof include iOC ₂ H ₅ , LiOC ₃ H _{7 and the} like. Among them, preferable one is L having high solubility in an alcohol solvent.
iOCH ₃ .

The organometallic compound (B) forming the skeleton is
Alkoxides, nitrates, acetates, sulfates, carbonates, etc. of metal and non-metal compounds represented by the following general formula (2) and containing at least one organic functional group are used, and among them, highly reactive alkoxides are used. Is preferably used. R ¹ _b M ² (OR ² ) _4-b (2) (M ² : metal or non-metal, R ¹ : organic functional group, R ² : chemical formula C _h H _{2h + 1} (h is between 1 and 20) An alkyl group represented by (integer), b: 1, 2 or 3)

Further, b in the general formula (2) is preferably 1. This is because if the value of b is large, the degree of polymerization and the film strength will decrease.

By using an organometallic compound having an organic functional group as the substance forming the skeleton, a flexible ionic conductor derived from R ¹ of the above general formula (2) can be obtained. In addition, since the organic functional group R ¹ is contained in the skeleton, the effect of improving conductivity can be expected.

As the metal and non-metal elements, boron,
Silicon, phosphorus, aluminum, germanium, gallium,
Examples thereof include titanium, vanadium, zirconium, niobium, antimony, indium, tin, and tungsten. Among them, silicon alkoxides are preferable because they are more stable in alcohol solvent than other metal alkoxides. As the organic functional group, an alkyl group, a vinyl group,
Examples thereof include a carboxyl group, a phenyl group, a benzyl group, a fluoroalkyl group, an amino group, a nitrile group, and a functional group containing an ethylene oxide chain. Among them, preferred are an alkyl group, a fluoroalkyl group and an ethylene oxide chain. It is a functional group containing.

As such, CH ₃ Si (OC
_{H 3) 3, C 2 H} 5 Si (OCH 3) 3, C 3 H 7 Si (OCH
₃ ) ₃ , C ₄ H ₉ Si (OCH ₃ ) ₃ , C ₅ H ₁₁ Si (OC
H ₃ ) ₃ , CF ₃ (CF ₂ ) ₅ (CH ₂ ) ₂ Si (OC
_{H 3) 3, CF 3 (} CF 2) 6 (CH 2) 2 Si (OC
_{H 3) 3, CF 3 (} CF 2) 7 (CH 2) 2 Si (OC
_{H 3) 3, CH 3 O-} (CH 2 CH 2 O) 6 - (CH 2) 3 -S
_{i (OCH 3) 3, CH} 3 O- (CH 2 CH 2 O) 7 - (CH
_{2) 3 -Si (OCH 3)} 3, CH 3 O- (CH 2 CH 2 O) 8
_{- (CH 2) 3 -Si (} OCH 3) 3, CH 3 O- (CH 2 C
_{H 2 O) 9 - (CH} 2) 3 -Si (OCH 3) 3 and the like.

The mixing ratio of the metal alkoxide (A) and the organometallic compound (B) is any mixing ratio within the range where gelation does not occur and M ¹ OH does not precipitate during film formation. However, the metal alkoxide (A) is preferably used in a molar ratio of 100 to 900 relative to 100 of the organometallic compound (B). More preferably, the molar ratio is 300 to 500 with respect to 100 of the organometallic compound (B).

The metal alkoxide (C) represented by the following general formula (3) can be used as a skeleton-forming compound that is polymerized to form the skeleton of the material. M ³ (OR ³ ) _n (3) (M ³ is at least one of Al, B, P and Si,
R ³ is an alkyl group represented by the chemical formula C _h H _{2h + 1} (h is an integer between 1 and 20)

The metal alkoxide (C) is not particularly limited. Further, if M ³ is included in the general formula (3) and an element different from M ² is used, a mixing former effect (minami et al.,
Chemistry, Vol. 43, p. 344, 1988) can be expected.

When the metal alkoxide (C) is added, the compounding ratio with the organometallic compound (B) is not particularly limited, but in view of flexibility and conductivity, the metal alkoxide (C) may be added in a molar amount. It is used in a ratio of 10 to 200 relative to 100 of the organometallic compound (B). More preferably, the molar ratio is in the range of 50 to 100 relative to 100 of the organometallic compound (B).

Further, in the present invention, the effect of further improving the conductivity may be provided by further adding an electrolyte salt or a resin. The electrolyte salt is preferably an alkali metal salt, such as LiClO ₄ , LiPF ₆ , LiSO ₃ CF ₃ ,
Such as LiN (SO ₂ CF _{3) 2} and the like.

The form of the ionic conductor of the present invention is not particularly limited, and examples thereof include thin films, bulks, fine particles, fibers, etc. Among them, thin films are easily formed into thin devices because the hydrolysis reaction of alkoxides easily progresses. It is preferable because the application of can be expected.

The thin film is produced by mixing the starting materials in an organic solvent and stirring to cause a hydrolysis reaction and a polycondensation reaction, and coating the resulting sol on a substrate.
After that, it is dried at room temperature. here,
Examples of the organic solvent to be used include ethanol, methanol, tetrahydrofuran, acetonitrile, dimethylformamide, propylene carbonate and the like. Among them, preferred is methanol. Examples of the coating method include spin coating and dip coating, which can be appropriately selected depending on the type of starting material of the material and the application. Examples of the drying atmosphere of the thin film include the atmosphere and a nitrogen atmosphere. However, the drying atmosphere is not limited to the above examples and can be appropriately selected depending on the type of starting material of the material and the application.

[0028]

EXAMPLES The ionic conductor comprising the organic-inorganic composite compound of the present invention will be described below with reference to specific examples.

Example 1 Metal lithium was dissolved in methanol in a glove box under a nitrogen atmosphere to prepare a methanol solution of lithium methoxide. Methyltrimethoxysilane (MTMS) was mixed with this solution.
Then, samples with the mixing ratio of lithium methoxide: MTMS of 2: 1, 3: 1, 4: 1 and 5: 1 were prepared. 2-n-Butoxymethanol was added to each solution and stirred for about 1 hour to prepare a sol.

The above sol solution was spin-coated on a glass substrate.
Coating was performed using a heater. The obtained thin film
A gel thin film was obtained by drying and heat treatment. Thin film obtained
Was colorless, transparent and homogeneous. The film thickness is about
At 600nm, conventional lithium methoxide and TEOS
Li used as the starting material₂O-SiO₂Thicker than the system thin film
I understood. Conductivity measurement of this thin film
It was The measurement cell is a glass substrate with a platinum electrode sputtered in advance
The one coated with a gel thin film was used. And
Using an impedance analyzer and heater
Frequency range 100 Hz to 40 MHz, applied voltage 0.
Cell impedance at 5V, measurement temperature range 25 ℃ -300 ℃
The dance was measured. As shown in Figure 1, at 500K
Conductivity increases with increasing lithium concentration,
When methoxide: MTMS is 4: 1, it becomes maximum, and
After that, the conductivity decreases as the lithium concentration increases.
The phenomenon was confirmed. Also, the conductivity pole at 500K
Large value is 2.2 x 10^-FourS · cm ^-1With an organic functional group
Higher conductivity than materials that do not use TEOS
It turned out to show sex.

<Example 2> A methanol solution of lithium methoxide was used as a starting material and had a chemical formula of CF ₃ (CF ₂ ) ₇ (CH ₂ ).
A fluoroalkylsilane (FAS) represented by ₂ Si (OCH ₃ ) ₃ was used to prepare an ion conductor thin film with the same manufacturing method and mixing ratio as in Example 1, and the conductivity was measured. The film thickness is about 900 nm, which is the same as conventional lithium methoxide and T
It was found to be thicker than the Li ₂ O—SiO ₂ based thin film using EOS as a starting material. As shown in FIG. 2, the conductivity at 500 K increases with an increase in lithium concentration, reaches a maximum when lithium methoxide: FAS is 4: 1, and then decreases with an increase in lithium concentration. Was confirmed. Further, the maximum value of the conductivity at 500 K was 1.9 × 10 ⁻⁴ S · cm ⁻¹ , and it was found that the conductivity was higher than that of the material using TEOS in which no organic functional group was introduced. .

Example 3 As a starting material, a solution of lithium methoxide in methanol and 2- [methoxy (polyethyleneoxy) propyl] trimethoxysilane (PEOTMS) were used.
An ion conductor thin film was prepared by using the same method and mixing ratio as in Example 1, and the conductivity was measured. The film thickness is about 70
At 0 nm, it was found to be thicker than the conventional Li ₂ O—SiO ₂ thin film using lithium methoxide and TEOS as starting materials. As shown in FIG. 3, the phenomenon that the conductivity at 500 K increases with an increase in lithium concentration, reaches a maximum when lithium methoxide: PEOTMS is 4: 1, and then decreases with an increase in lithium concentration. Was confirmed. Further, the maximum value of the conductivity at 500 K was 4.3 × 10 ⁻⁴ S · cm ⁻¹ , and it was found that the conductivity was higher than that of the material using TEOS without introducing the organic functional group. .

Example 4 As a starting material, a methanol solution of lithium methoxide and tetraethoxysilane (TEO) were used.
S) and 2- [methoxy (polyethyleneoxy) propyl] trimethoxysilane (PEOTMS) were used to prepare an ion conductor thin film in the same manner as in Example 1, and the conductivity was measured. In addition, lithium methoxide and TEOS +
The ratio of PEOTMS is set to 4: 1 and TEOS: PEOTM
S was set to 1: 1. The film thickness is about 700 nm, and Li ₂ using conventional lithium methoxide and TEOS as starting materials is used.
It was found to be thicker than the O-SiO ₂ thin film. 500
The conductivity at K was increased by replacing part of TEOS with PEOTMS. This value is LiOCH ₃
It is higher than the maximum value of the conductivity in the -TEOS system and the LiOCH ₃ -PEOTMS system, and the value is 7.2 × 10 ^-4 S.
・ It was cm ^-1 .

<Comparative Example> As a starting material, a solution of lithium methoxide in methanol and tetraethoxysilane (TEOS) are used.
An ion conductor thin film was prepared by using the above, and the conductivity was measured. The film thickness was about 300 nm. The mixing ratio was 2: 1, 3: 1 and 4: 1 for lithium methoxide: TEOS. As shown in FIG.
The maximum value of conductivity at 00K is 1.1 × 10 ⁻⁴ S · c
m ^-1, which is lower than that of the example.

[0035]

The ionic conductor comprising the inorganic-organic composite compound of the present invention exhibits higher conductivity than conventional Li ₂ O—SiO ₂ thin films using lithium methoxide and TEOS as starting materials. I understand. When used as a thin film, this thin film is denser than an inorganic thin film, and it can be expected that the performance as a battery separator will be improved. Further, since the obtained thin film is an inorganic-organic composite film, it is a material having both mechanical strength and flexibility. From the above, the inorganic-organic composite type ionic conductor in the present invention is suitable as a solid electrolyte for electrochemical devices such as lithium secondary batteries.

[0036]

[Brief description of drawings]

FIG. 1 is a graph showing the composition dependence of the conductivity of a LiOCH ₃ —MTMS-based inorganic-organic composite type lithium ion conductor at 500K.

FIG. 2 is a graph showing the composition dependence of the conductivity of a LiOCH ₃ —FAS-based inorganic-organic composite type lithium ion conductor at 500K.

FIG. 3 is a graph showing the composition dependence of the conductivity of a LiOCH ₃ -PEOTMS-based inorganic-organic composite type lithium ion conductor at 500K.

FIG. 4 is a graph showing the composition dependence of the conductivity of a LiOCH ₃ —TEOS-based inorganic lithium ion conductor at 500K.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4J030 CA01 CA02 CB03 CC05 CC06                       CC10 CC15 CC16 CC17 CC21                       CC23 CC27 CD11 CE02 CG02                 4J035 BA04 BA14 CA071 CA161                       EA01 LA03 LB20                 5G301 CA01 CA16 CA30 CD01                 5H029 AJ06 AJ11 AM16 CJ11 DJ09                       EJ11 EJ12 HJ02

Claims (7)

[Claims] 1. A hydrolysis and polycondensation reaction of at least a metal alkoxide (A) represented by the following general formula (1) and an organometallic compound (B) represented by the following general formula (2): An ionic conductor comprising a compound obtained by the above. M ¹ OR (1) (M ¹ : alkali metal, R: chemical formula C _a H _{2a + 1} (a is 1 to 1
An alkyl group represented by (an integer between 20)) R ¹ _b M ² (OR ² ) _4-b (2) (M ² : metal or nonmetal, R ¹ : organic functional group, R ² : chemical formula _Ch Alkyl group represented by H _{2h + 1} (h is an integer between 1 and 20), b: 1, 2 or 3) 2. The ionic conductor according to claim 1, wherein the alkali metal M ¹ contained in the metal alkoxide (A) is lithium. 3. The metal or nonmetal M ² contained in the organometallic compound (B) is silicon.
Or the ionic conductor according to 2. 4. An organic functional group R of the organometallic compound (B).
¹ is the chemical formula C _k H _{2k + 1 (k} is an integer between 1-20) ion conductor according to claim 1 consisting of an alkyl group represented by. 5. An organic functional group R of the organometallic compound (B)
¹ is the formula _{- (CF 2) m - (} m is an integer between 1-20)
The ionic conductor according to any one of claims 1 to 4, comprising at least one fluoroalkyl group represented by. 6. The organic functional group R ¹ of the organosilicon compound contains at least one ethylene oxide unit represented by the chemical formula — (CH ₂ CH ₂ O) —. Ionic conductor. 7. The ionic conductor according to claim 1, wherein the starting material contains a metal alkoxide (C) represented by the following general formula (3). M ³ (OR ³ ) _n (3) (M is at least one of Al, B, P and Si, R
³ is an alkyl group represented by the chemical formula C _h H _{2h + 1} (h is an integer between 1 and 20)