JP2716448B2 - Fine particle dispersion and method for producing electrode using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fine particle dispersion useful as an electrode material for use in secondary batteries and electrochemical display devices.

[Prior Art] A metal complex represented by the general formula M _1x [M ₂ (CN) ₆ ] _y (where M ₁ and M ₂ are metal elements other than alkali metal elements and metalloid elements) is contained in a crystal. It is already known that a redox reaction can be performed reversibly and stably by insertion and release of ions such as alkali metal ions such as K ⁺ and Li ⁺ having holes [Chem. 37 No. 8 (1982)] , P601-607]. The metal complex has been actively studied by those skilled in the art as an energy conversion device, a battery electrode, and an electrochemical display device. For example, JP-A-57-15828 and JP-A-59-164383 disclose a method of forming an electrochromic display element by forming a mixed valence complex such as Prussian blue into a film by electrolytic reduction. Is disclosed. However, in this method, the amount of electrodeposition is limited, and a sufficient coloring density cannot be obtained. For this reason, it has been proposed to solve the above-mentioned problem by forming the second electrochromic layer with a complex conjugated polymer or the like (JP-A-60-78428).

[Problems to be Solved by the Invention] In order to extract useful physical properties of the complex as an external electrical / optical signal, the complex must be a solid having an appropriate thickness and size. These complexes generally exist in a colloidal state in an aqueous solvent, and may contain acetonitrile,
It is known that even non-aqueous polar solvents such as nitrobenzene are suspended as fine particles in the solvent. It is easy to use a low molecular surfactant to disperse these complexes in a colloidal form in a solvent, but there is a problem with the stability of the colloid, especially at high temperatures. I didn't get it. Therefore, it is important to prevent unwanted aggregation of the colloid particles. In order to make the metal complex into a solid having an appropriate thickness and size, a method of removing the solvent from these colloidal or suspended states is generally used. However, the film obtained by removing the solvent by this method has the drawback that not only the durability is poor but also the performance of ion insertion / release reaction, particularly the response speed, is reduced.

An object of the present invention is to improve performance (for example, response speed and stability) of a metal complex.

[Means for Solving the Problems] The present inventors have studied in view of the above object, and have found that a small amount of an anion-modified water-soluble polymer can coexist when preparing a fine particle dispersion or colloid solution of a metal complex. The dispersion solution obtained by the method was characterized in that the diameter of the fine particles was small, the dispersion was stable and had a characteristic that the aggregation of the fine particles did not easily occur, and the film obtained by casting the solvent according to a conventional method and removing the solvent was excellent. The inventors have found that they have performance and arrived at the present invention.

According to the present invention, the general formula M _1x [M ₂ (CN) ₆ ] _y (M in the formula
₁ and M ₂ are metal elements or metalloid elements other than alkali metals, x represents 3 to 4, and y represents 2 to 3. ), A fine particle dispersion of a metal complex comprising a fine particle-shaped metal complex, a medium and an anion-modified water-soluble polymer, and coating the dispersion on an electrode substrate, and then removing the medium. Includes electrode fabrication.

The water-soluble polymer used in the present invention is not limited to any one as described later, and particularly unfavorable are polyacrylic acid and its salt or polymethacrylic acid and its salt.

The fine particle metal complex dispersion of the present invention is best dispersed in water in a colloidal form, but is dispersed in one or a mixture of various alcohols, acetonitrile, nitrobenzene, tetrahydrofuran, propylene carbonate, and the like. And water may be mixed therein.

These dispersions can be obtained by mixing metal ions and metal complex ions in the same solvent. Here, as metal ions, Fe ³⁺ , Cu ²⁺ , Ba ²⁺ , Mn ²⁺ , Cd ²⁺ , Hg ²⁺ , Co
²⁺ , Ni ²⁺ , Ca ²⁺ , Sr ²⁺ , Al ^{3+ and the} like. [Fe (CN) ₆ ] ^4- , [Cr (CN) ₆ ] ^3- ,
[Cr (CN) ₆ ] ^{3- and the} like.

The water-soluble polymer may be added at any time, but it is preferable to add the water-soluble polymer to the aqueous solution before reacting the metal ion with the metal complex ion.

The metal complex according to the present invention is a material that has recently been recognized as being useful as a material for an energy conversion device, an electrochemical display device, or the like. Examples of the metal complex include a complex containing metal ions having different oxidation numbers in the same molecule (mixed valence complex), a complex composed of the same metal ion and the same ligand and having only different oxidation numbers (binuclear mixed valence complex), Including iron cyano mixed valence complex. Complexes having pores capable of performing an insertion / release reaction of an alkali metal ion in the crystal are suitably used. To illustrate these compounds, Fe ₄
[Fe (CN) ₆ ] ₃ , Cu ₃ [Cr (CN) ₆ ] ₂ , Ba ₃ [Cr (C
N) ₆ ] ₂ , Mn ₃ [Cr (CN) ₆ ] ₂ , Cd ₃ [Cr (CN) ₆ ] ₂ , Hg ₃
[Cr (CN) ₆ ] ₂ , Co ₃ [Cr (CN) ₆ ] ₂ , Ni ₃ [Cr (C
N) ₆ ] ₂ , Ca ₃ [Co (CN) ₆ ] ₂ , Sr ₃ [Cr (CN) ₆ ] ₂ , Ba ₃
[Co (CN) ₆ ] ₂ , Al ₄ [Fe (CN) ₆ ] ₃ , Ga ₄ [Fe (C
N) ₆ ] ₃ , Sb ₄ [Fe (CN) ₆ ] ₃ .Cd ₃ [Fe (CN) ₆ ] _{2 and the} like. Of these metal complexes, M ₁
But Fe, Cu, Co, Cd, or Cr, M ₂ is Fe, Co, Cu, Cr, Os is
Ru combination is good. Specifically, a mixed valence complex of iron and cyano represented by Prussian blue is preferable. Prussian blue has 3.2Å pores in the crystal, K ⁺ , Li ⁺
And the like can be stably performed while involving an oxidation-reduction reaction.

The water-soluble polymer material used in the present invention generally has good ability to stabilize the dispersion of fine particles, for example, polyacrylamide, anion-modified polyacrylamide,
Examples include polymethyl vinyl ether, polyvinyl pyrrolidone, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, and the like. Among them, those modified with a small amount of anion were found to have particularly good particle stability and small particle size.
Particularly effective one is polyvinyl alcohol (PVA) modified with a small amount of anion. In this case, the colloid particles became fine particles of 0.03 μm or less, and the stability was extremely good. Examples of a small amount of an anion-modified water-soluble polymer include acrylic acid-modified polyacrylamide (acrylic acid content: 0.1 to 10 mol%) and methallylsulfonic acid-modified polyvinylpyrrolidone (methsulfonic acid content: 0.1 to 5 mol%). You.

It was confirmed that the product using the anion-modified polyvinyl alcohol had extremely good stability even in a high-concentration dispersion of fine particle dispersion, and also had extremely good performance when an electrode material was produced. A suitable anion-modified polyvinyl alcohol resin is obtained by copolymerizing a monomer having a carboxyl group such as (meth) acrylic acid, maleic anhydride, crotonic acid, itaconic acid, and fumaric acid with vinyl acetate, followed by saponification. It is obtained. Other examples include a resin obtained by copolymerizing a monomer containing a sulfonic acid group such as vinyl sulfonic acid. There is no particular limitation on the degree of saponification.

The ratio of the carboxyl group-containing monomer unit is preferably in the range of 0.1 mol% to 10 mol%, and particularly preferably 0.1 mol% or less.
The range is preferably 5 mol% or more and 5 mol% or less.

After copolymerization, saponification is performed and pH is adjusted at the time of use to obtain a suitable anion-modified PVA.

The degree of polymerization of these resins is not particularly limited, but is usually 50 to
3000, preferably selected from the range of 100-2500.

The concentration of the water-soluble polymer in the colloid solution is not particularly limited, but may be 0.05% by weight to 20% by weight, preferably 0.2% by weight.
It is preferable to add in the range of 5% by weight to 5% by weight. If the concentration of the polymer material is too low, the effect of stabilizing the dispersion is diminished. If the concentration is too high, the viscosity of the aqueous solution is too high, and the reaction of forming the metal complex hardly occurs. The fine particle dispersion of the present invention can be used as an electrode for a secondary battery or an electrochemical display device or as an intermediate material for an optical recording agent, and particularly when used as an electrode for an electrochemical display device, the response speed is high. It will be much faster. The method of manufacturing electrodes for electrochemical display devices is Nesa glass (transparent electrode)
Casting or electrodeposition of the fine particle dispersion on top is used. Since the water-soluble polymer material added as a dispersion stabilizer also acts as a binder for the complex, it also has the effect of significantly improving the adhesion of the complex to Nesa glass.

When a secondary battery is manufactured using the metal complex of the present invention, the solidified complex may be used as an electrode as it is, but in order to increase the conductivity of the electrode, a carbon powder that is a material for improving conductivity is used. After adding 5 to 10% by weight, it is preferable to perform compression molding in a pellet shape. Further, a Teflon binder or the like may be mixed as a binder.

When an electrochemical display or a secondary battery is manufactured using an electrode prepared from the fine particle dispersion of the present invention, a solution in which an electrolyte is dissolved in a nonaqueous electrode solvent is preferably used. Non-aqueous polar solvents include propylene carbonate and γ-
Butyrolactone, dimethyl sulfoxide, dimethylformamide, ethylene carbonate and the like can be exemplified. As an electrolyte to be added, an alkali metal salt,
For example, LiClO ₄ , LiBF ₄ , KClO ₄ , KBF ₄ , LiPF ₆ , KPF _{6 and the} like can be exemplified.

(Examples) Hereinafter, the present invention will be described more specifically with reference to Examples and Reference Examples.

Reference Example 1 [Preparation of Prussian blue (PB) ultrafine particles] Kuraray Co., Ltd. polyvinyl alcohol (polymerization degree: 170
0, saponification degree; 88%) 10 mM / Fe in 0.5 cc of 5 wt% aqueous solution
1 cc of Cl ₂ was added. After 30 minutes, 10 mM / K ₃ [Fe (C
N) ₆ ] 1 cC of an aqueous solution was added and the mixture was stirred. By mixing Fe ²⁺ ions and [Fe (CN) ₆ ] ³⁻ ions, a blue solution unique to PB was obtained. The PB particles did not settle to the bottom of the bottle even if this solution was placed in a sample bottle and left still for one week. It was found that the colloid of PB in the aqueous solution was stabilized by the addition of polyvinyl alcohol. From the electron micrograph, the diameter of the fine particles was 0.2 μm.

Comparative Example 1 (When no water-soluble polymer was used) A PB solution was prepared in the same manner as in Reference Example 1 except that polyvinyl alcohol was not added. When this solution was put in a sample bottle and left standing for one week in a stationary state, PB particles aggregated and settled at the bottom of the bottle. The average particle diameter is 1μ
However, many aggregations were observed.

Reference Example 2 (When polyacrylamide is used as the water-soluble polymer) Sumitomo Chemical Co., Ltd. polyacrylamide 5 wt% aqueous solution 0.5
1 cc of 10 mM / FeCl ₂ was added to cc. After 30 minutes 10m
1 cc of M / K ₃ [Fe (CN) ₆ ] aqueous solution was added, and the mixture was stirred. By mixing Fe ²⁺ ions and [Fe (CN) ₆ ] ³⁻ ions, a blue solution unique to PB was obtained.

The PB particles did not settle to the bottom of the bottle even if this solution was placed in a sample bottle and left still for one week. PB
Was found to be stabilized by the addition of polyacrylamide. The average particle size was 0.4 μm.

Example 1 In the same manner as in Reference Example 1, except that itaconic acid-modified polyvinyl alcohol (itaconic acid content 1 mol%, degree of polymerization 1700, degree of saponification 88%) was used instead of the polyvinyl alcohol of Reference Example 1. To obtain a PB solution.

The PB particles did not settle to the bottom of the bottle even if this solution was placed in a sample bottle and left still for one week. Further, no change was observed even after being left at 70 ° C. for 5 hours. Unlike the case of Reference Example 1, this colloid solution was completely transparent in spite of being blue, and the particle diameter was as large as 0.02 μm on average.

Further search for the most suitable polymer was conducted. PB solutions to which various water-soluble polymers were added were prepared in the same manner as in Reference Example 1. Further, the obtained PB solution was dropped on a glass plate, and then left at room temperature to dry and remove the solvent. The dried PB film thus obtained was observed under an optical microscope with a magnification of 1000 times to check for the presence or absence of aggregation. The degree of agglomeration was evaluated in four stages of ◎, △, Δ, ×. (◎): No aggregation was observed at all, (も の): Aggregation was observed slightly, (△): Aggregation was observed, (×): Many aggregations were observed, There are four stages. When a PB film was prepared using a PB solution to which no water-soluble polymer was added, a large amount of aggregation was observed. Some aggregates were not observed at all depending on the polymer used,
This was designated as (◎). The amounts of polyacrylic acid (Comparative Example 2), polyvinylpyrrolidone (Reference Example 3), and anion-modified polyacrylamide (Example 2) were the same as in Reference Example 1.

Table 1 shows the relationship between the polymer used and the aggregation state of the PB particles. Among various water-soluble polymers, PVA was an excellent result. In particular, when anion-modified PVA was used, aggregation of PB particles did not occur.

(Reference Use Example) Hereinafter, a use example of the fine particle dispersion will be described.

Reference Use Example 1 (Preparation and Evaluation of Electrochromic Element) The B solution obtained in Reference Example 1 was applied to Nesa glass 4 (10Ω /
□) The PB layer was formed by casting on the substrate and setting the light transmittance to about 5% in a colored state, and this was used as the electrochromic electrode 1. The electrochromic device shown in the sectional view in FIG. Produced. The electrolytic solution 5 contains 1 M / gamma of γ-butyrolactone (γ-BL) of lithium perchlorate (LiClO ₄ ).
The solution was used. Activated carbon fiber (ACF) having a specific surface area of 2000 m ² / g was used for the counter electrode 2. Glass fiber filter paper was used for the separator 3. A hole having a diameter of 3 mm was formed in the separator 3 and the ACF at the center of the cell to allow light to pass therethrough.

The response speed of the device was measured using a microscope and a photomultiplier. FIG. 2 shows the relationship between the light transmittance from the decolored state to the colored state and time. The time required for the light transmittance to become 1/2 of the decolored state (τ1 / 2) was 0.8 seconds.

Comparative use example 1 Nesa glass (10Ω / □) was applied to the PB solution obtained in Comparative example 1.
The PB layer was cast on top. An element using this was fabricated in the same manner as in Reference Use Example 1, and the response speed was measured (third example).
Figure). τ 1/2 was 30 seconds.

Table 1 shows the relationship between the polymer used and the response speed. There was a very high correlation between the degree of particle aggregation and the response speed, and the response speed was faster as no aggregation occurred.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an electrochromic device, FIG. 2 is a diagram showing the response speed of an electrochromic device using an ultrafine metal complex according to the present invention, and FIG. FIG. 3 is a diagram showing a response speed of an electrochromic element used. 1; PB layer, 2; counter electrode 3; separator, 4; Nesa glass 5; electrolyte, 6; power supply

 ──────────────────────────────────────────────────続 き Continuation of the front page Examiner Motofumi Tabe (56) References JP-A-62-115129 (JP, A)

Claims (5)

(57) [Claims] 1. A compound represented by the general formula: M _1x [M ₂ (CN) ₆ ] _y (where M ₁ and M ₂ are metal elements or metalloid elements other than alkali metals, x is 3 to 4 and y is 2 To 3.) A fine particle dispersion of a fine metal complex represented by the formula (1), a metal complex comprising a medium and an anion-modified water-soluble polymer. 2. The dispersion according to claim 1, wherein the anion-modified water-soluble polymer is an anion-modified polyvinyl alcohol resin. 3. The dispersion according to claim 1, wherein the metal complex is Prussian blue. 4. The dispersion according to claim 3, wherein the medium is water. 5. A compound of the general formula M _1x [M ₂ (CN) ₆ ] _y (where M ₁ and M ₂ are metal elements or metalloid elements other than alkali metals, x is 3 to 4 and y is 2 To 3). A fine particle dispersion of a fine metal complex, a medium and a metal complex comprising an anion-modified water-soluble polymer is coated on an electrode substrate, and then the medium is removed. Electrode manufacturing method.