JP4147787B2 - Ionic conductor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ionic conductor, and more particularly to an ionic conductor that can be used in a solid electrolyte, a sensor, or the like, which is an electrochemical device.
[0002]
[Prior art]
Conventionally, as an electrolyte of a lithium primary battery and a lithium secondary battery, an electrolytic solution in which an ionic lithium salt such as LiBF ₄ , LiPF ₆ , or LiCF ₃ SO ₃ is dissolved in an organic solvent such as ethylene carbonate or propylene carbonate has been used. It had been.
However, this electrolytic solution has the drawbacks that it has a risk of liquid leakage and ignition, and is liable to volatilize and lacks long-term reliability. On the other hand, the solid electrolyte does not have such a defect, and when used as the electrolyte of the above device, a separator is not required unlike the case of using an electrolytic solution. When the solid electrolyte is used in this way, the safety in using the device can be improved, and the device itself can be reduced in size and weight. Polymer electrolytes, inorganic solid electrolytes, and the like are known as candidates for promising materials as solid electrolytes. Polymer electrolytes are excellent in flexibility, processability, thin film moldability, light weight, 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. Yes. Unlike the electrolyte and polymer electrolyte, the inorganic solid electrolyte is nonflammable and has a lithium ion transport number of 1.
[0003]
The polymer electrolyte of the above, LiClO ₄ in polyethylene oxide, polyether polymer compounds such as polypropylene oxide, LiCF ₃ SO _3, those obtained by mixing an alkali metal salt such as 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. Another major problem with polymer electrolytes is their low mechanical strength. For this reason, various countermeasures such as cross-linking of polymers and hybridization with inorganic compounds have been studied.
[0004]
As an inorganic solid electrolyte, a sulfide glass based on Li ₂ S—SiS ₂ system produced by a melt quenching method (Kondo et al., Solid State Ionics 53-56, 1183, 1992), solid phase reaction method Various studies such as Li ₄ SiO ₄ —Li ₃ PO ₄ oxide ceramics (UV Alpen et al., “Fast Ion Transport in Solid”, page 463, 1979) produced by the above-mentioned method are being conducted. However, these materials have poor flexibility and are difficult to be thinned, and are difficult to apply to thin batteries and large batteries. For this reason, the physics of vacuum deposition (Y. Ito et al., Ibid., 57, 389, 1983), high-frequency sputtering, etc. (K. Miyauchi et al., Solid State Ionics 9-10, 1469, 1983). Synthesis of ion-conductive thin films by vapor deposition was performed. However, in the case of such physical vapor deposition, in the case of a multi-component system, the composition of the raw material and the thin film composition are liable to cause a composition shift. For this reason, there is a report that a homogeneous Li ₂ O—SiO ₂ inorganic solid thin film having no compositional deviation was produced by a sol-gel method (Nagisa et al., Journal of Chemical Society of Japan, 11, 1958, 1987). The conductivity was slightly low, and it was difficult to use as an electrolyte for lithium secondary batteries.
[0005]
[Problems to be solved by 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 excellent ionic conductivity.
[0006]
[Means for Solving the Problems]
In the invention of claim 1, 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) are subjected to hydrolysis and polycondensation reaction. in the ion conductor comprising a compound obtained Te,
An ionic conductor, wherein the metal or nonmetal M2 contained in the organometallic compound (B) is silicon.
M ¹ OR (1)
(M ¹ : alkali metal, R: alkyl group represented by the chemical formula CaH _{2a + 1} (a is an integer between 1 and 20))
R ¹ _b M ² (OR ² ) _4-b (2)
^{(M 2:} metal or nonmetal, R1: organic functional group, ^{R 2:} Chemical formula _C h _{H 2h +} 1 (alkyl group h is represented by an integer) between 1 to 20, b: 1)
The invention of claim 2 is an ion conductor according to claim 1, wherein the alkali metal M1 contained in the metal alkoxide (A) is lithium.
[0013]
DETAILED DESCRIPTION OF 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 includes 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. And an amorphous compound obtained by hydrolysis and polycondensation reaction. Further, the obtained compound has a structure in which a part of the skeleton of an alkali metal oxide-metal or nonmetal oxide inorganic solid electrolyte such as Li ₂ O—SiO ₂ is substituted with an organic functional group R ^1. It becomes a crystalline compound. Hereinafter, each component used as a starting material is explained in full detail below.
[0014]
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.
M ¹ OR (1)
(M ¹ : alkali metal, R: alkyl group represented by the chemical formula C _a H _{2a + 1} (a is an integer between 1 and 20))
Examples of the lithium compound include lithium hydroxide, lithium acetate, lithium nitrate, lithium sulfate, lithium carbonate, lithium alkoxide, lithium chloride, lithium bromide, lithium iodide, lithium fluoride, etc. Among them, lithium alkoxide is It is suitable because it is stable in an alcohol solvent and has high reactivity.
[0015]
Lithium alkoxide can be represented by 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)), and LiOCH ₃ , LiOC ₂ H ₅ , LiOC ₃ H _7. Among them, LiOCH ₃ having high solubility in an alcohol solvent is preferable.
[0016]
The organometallic compound (B) forming the skeleton is represented by the following general formula (2), and is an alkoxide, nitrate, acetate, sulfate, carbonate of a metal and a nonmetal compound containing at least one organic functional group Of these, alkoxides having high reactivity are preferably used.
R ¹ _b M ² (OR ² ) _4-b (2)
(M ² : metal or nonmetal, R ¹ : organic functional group, R ² : alkyl group represented by the chemical formula C _h H _{2h + 1} (h is an integer between 1 and 20), b: 1, 2 or 3)
[0017]
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 decrease.
[0018]
By using an organometallic compound containing an organic functional group as a substance that forms a skeleton, a flexible ion 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, an effect of improving conductivity can be expected.
[0019]
Examples of the metal and non-metal elements include boron, silicon, phosphorus, aluminum, germanium, gallium, titanium, vanadium, zirconium, niobium, antimony, indium, tin, and tungsten. Among these, silicon alkoxides are other It is preferable because it is more stable in an alcohol solvent than a metal alkoxide.
Examples of the organic functional group include an alkyl group, a vinyl group, a carboxyl group, a phenyl group, a benzyl group, a fluoroalkyl group, an amino group, a nitrile group, and a functional group including an ethylene oxide chain. Those are functional groups containing alkyl groups, fluoroalkyl groups, ethylene oxide chains.
[0020]
As such, CH ₃ Si (OCH 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 (OCH ₃ ) ₃ , CF ₃ (CF ₂ ) ₅ (CH ₂ ) ₂ Si (OCH ₃ ) ₃ , CF ₃ (CF ₂ ) ₆ (CH ₂ ) ₂ Si (OCH ₃ ) ₃ , CF ₃ ( _{CF 2) 7 (CH 2)} 2 Si (OCH 3) 3, CH 3 O- (CH 2 CH 2 O) 6 - (CH 2) 3 -Si (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 CH 2 O) 9 - (} CH 2) 3 -Si (OCH 3) 3 and the like.
[0021]
The compounding ratio of the metal alkoxide (A) and the organometallic compound (B) is any mixing ratio as long as it does not cause gelation and does not cause precipitation of M ¹ OH during film formation. However, the metal alkoxide (A) is preferably used in a range of 100 to 900 with respect to the organometallic compound (B) 100 in a molar ratio. More preferably, the molar ratio is 300 to 500 with respect to 100 of the organometallic compound (B).
[0022]
The metal alkoxide (C) represented by the following general formula (3) can be used as a skeleton-forming compound that is polymerized to form a 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))
[0023]
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 mixed former effect (Minami et al., Chem., 43, 344, 1988).
[0024]
When the metal alkoxide (C) is added, the compounding ratio with the organometallic compound (B) is not particularly limited, but considering flexibility and conductivity, the metal alkoxide (C) is organic in a molar ratio. It is used in the range of 10 to 200 with respect to 100 of the metal compound (B). More preferably, it is the range of 50-100 with respect to organometallic compound (B) 100 by molar ratio.
[0025]
Moreover, in this invention, you may give effects, such as improving electroconductivity further, by adding electrolyte salt and resin further. The electrolyte salt is preferably an alkali metal salt, such as LiClO ₄ , LiPF ₆ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) _{2, and the} like.
[0026]
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 prone to alkoxide hydrolysis and can be applied to thin devices. It is preferable because it can be expected.
[0027]
The thin film is prepared by mixing and stirring the starting materials in an organic solvent to cause hydrolysis and polycondensation reactions, coating the resulting sol on the substrate, and then drying at room temperature. is there. Here, examples of the organic solvent to be used include ethanol, methanol, tetrahydrofuran, acetonitrile, dimethylformamide, propylene carbonate, and the like. Among these, methanol is preferable. Examples of the coating method include spin coating, dip coating, and the like, which can be appropriately selected depending on the type and use of the starting material of the material. Examples of the dry atmosphere of the thin film include air, nitrogen atmosphere, and the like, but are not limited to the above examples, and can be appropriately selected depending on the type and use of the starting material of the material.
[0028]
【Example】
Hereinafter, the ion conductor made of the organic-inorganic composite compound of the present invention will be described with specific examples.
[0029]
<Example 1>
In a glove box under a nitrogen atmosphere, metallic lithium was dissolved in methanol to prepare a methanol solution of lithium methoxide. Methyltrimethoxysilane (MTMS) was mixed with this solution. Samples with this mixing ratio of lithium methoxide: MTMS of 2: 1, 3: 1, 4: 1, 5: 1 were prepared. 2-n-butoxymethanol was added to each solution, and the sol was prepared by stirring for about 1 hour.
[0030]
The above sol solution was coated on a glass substrate using a spin coater. The obtained thin film was dried and heat-treated to obtain a gel thin film. The obtained thin film was colorless and transparent and homogeneous. The film thickness was about 600 nm, which was found to be thicker than the conventional Li ₂ O—SiO ₂ thin film using lithium methoxide and TEOS as starting materials. Conductivity measurement was performed on this thin film. As the measurement cell, a glass substrate on which a platinum electrode was previously sputtered and a gel thin film was coated was used. Then, using an impedance analyzer and a heater, the impedance of the cell was measured in a frequency range of 100 Hz to 40 MHz, an applied voltage of 0.5 V, and a measurement temperature range of 25 ° C to 300 ° C. As shown in FIG. 1, the conductivity at 500 K increases with an increase in lithium concentration, reaches a maximum when the lithium methoxide: MTMS is 4: 1, and thereafter the conductivity decreases with an increase in lithium concentration. Was confirmed. Moreover, the maximum value of the conductivity at 500 K is 2.2 × 10 ⁻⁴ S · cm ⁻¹ , which indicates that the conductivity is higher than that of a material using TEOS into which no organic functional group is introduced. .
[0031]
<Example 2>
The same production method as in Example 1 using a methanol solution of lithium methoxide as a starting material and a fluoroalkylsilane (FAS) represented by the chemical formula CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₂ Si (OCH ₃ ) ₃ The ionic conductor thin film was prepared at a mixing ratio, and the conductivity was measured. The film thickness was about 900 nm, which 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. 2, the conductivity at 500 K increases with an increase in lithium concentration, reaches a maximum when the lithium methoxide: FAS is 4: 1, and thereafter the conductivity decreases with an increase in lithium concentration. Was confirmed. In addition, the maximum value of conductivity at 500 K is 1.9 × 10 ⁻⁴ S · cm ⁻¹ , which indicates that the conductivity is higher than that of a material using TEOS into which no organic functional group is introduced. .
[0032]
<Example 3>
Using a methanol solution of lithium methoxide as a starting material and 2- [methoxy (polyethyleneoxy) propyl] trimethoxysilane (PEOTMS), an ionic conductor thin film was produced by the same production method and mixing ratio as in Example 1, and conductive. Sex was measured. The film thickness was about 700 nm, which 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 conductivity at 500 K increases as the lithium concentration increases, reaches a maximum when the lithium methoxide: PEOTMS is 4: 1, and thereafter the conductivity decreases as the lithium concentration increases. Was confirmed. Moreover, the maximum value of the conductivity at 500K is 4.3 × 10 ⁻⁴ S · cm ⁻¹ , which indicates that the conductivity is higher than that of a material using TEOS into which no organic functional group is introduced. .
[0033]
<Example 4>
Preparation method similar to Example 1 using a methanol solution of lithium methoxide, tetraethoxysilane (TEOS), 2- [methoxy (polyethyleneoxy) propyl] trimethoxysilane (PEOTMS) as a starting material. The conductivity was measured. The ratio of lithium methoxide to TEOS + PEOTMS was 4: 1, and TEOS: PEOTMS was 1: 1. The film thickness was about 700 nm, which was found to be thicker than the conventional Li ₂ O—SiO ₂ thin film using lithium methoxide and TEOS as starting materials. The conductivity at 500K was increased by replacing part of TEOS with PEOTMS. This value was higher than the maximum value of conductivity in the LiOCH ₃ -TEOS system and LiOCH ₃ -PEOTMS system, and the value was 7.2 × 10 ⁻⁴ S · cm ⁻¹ .
[0034]
<Comparative example>
Using a methanol solution of lithium methoxide as a starting material and tetraethoxysilane (TEOS), a production method similar to the above and an ion conductor thin film were produced, and conductivity was measured. The film thickness was about 300 nm. The mixing ratio of lithium methoxide: TEOS was 2: 1, 3: 1, 4: 1. As shown in FIG. 4, the maximum value of conductivity at 500K was 1.1 × 10 ⁻⁴ S · cm ⁻¹ , which was lower than that of the example.
[0035]
【The invention's effect】
It can be seen that the ionic conductor composed of 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. Further, 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 is improved. Moreover, 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 ion conductor in the present invention is suitable as a solid electrolyte for electrochemical devices such as lithium secondary batteries.
[0036]
[Brief description of the drawings]
FIG. 1 is a graph showing the composition dependence of conductivity at 500 K of a LiOCH ₃ -MTMS inorganic-organic composite type lithium ion conductor.
FIG. 2 is a graph showing the composition dependence of conductivity at 500 K of a LiOCH ₃ -FAS inorganic-organic composite lithium ion conductor.
FIG. 3 is a graph showing the composition dependency of conductivity at 500 K of a LiOCH ₃ -PEOTMS-based inorganic / organic composite type lithium ion conductor.
FIG. 4 is a graph showing the composition dependence of conductivity at 500 K of a LiOCH ₃ -TEOS inorganic lithium ion conductor.

Claims (2)

Ion comprising a compound obtained by subjecting at least the metal alkoxide (A) represented by the following general formula (1) and the organometallic compound (B) represented by the following general formula (2) to hydrolysis and polycondensation reaction in the conductor,
An ionic conductor, wherein the metal or nonmetal M2 contained in the organometallic compound (B) is silicon.
M ¹ OR (1)
(M ¹ : Alkali metal, R: Alkyl group represented by the chemical formula CaH _{2a + 1} (a is an integer between 1 and 20))
R ¹ _b M ² (OR ² ) _4-b (2)
^{(M 2:} metal or nonmetal, R1: organic functional group, ^{R 2:} Chemical formula _C h _{H 2h +} 1 (alkyl group h is represented by an integer) between 1 to 20, b: 1) Ion conductor according to claim 1, alkali metal M1 contained in the metal alkoxide (A) is characterized in that it is a lithium.

Images