JPS61214372A - Polynuclear complex battery - Google Patents

Abstract

PURPOSE:To obtain a polynuclear complex battery having three kinds or redox states by using a compound which is a polynuclear complex and in an intermediate redox state as active material. CONSTITUTION:A mixed valency or mixed metal polynuclear complex indicated in the formula I is used as active material. PB which is the most representative compound in the polynuclear complex makes a unit lattice, that is, Fe<2+> and Fe<3+> connect each other through a cyano ligand. A large number of unit lattices are connected to form a high molecular complex. When a polynuclear complex film is used, active material in both electrodes is fixed in each electrode and no separator is required, and problems concerning internal resistance of the separator is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a battery characterized by using a polynuclear metal cyano complex capable of assuming three types of reversible redox states.

[Background of the invention]

Complexes formed by combining different metal ions or metal ions with different valences with a cyanide ligand as a bridging ligand are high molecular weight complexes in which the metal ions are three-dimensionally connected via the cyanide ligands. It has a multinucleated structure. A typical example is Prussian Blue (hereinafter abbreviated as PB).
This is a mixed valence polynuclear complex of iron (II) and iron ([), and its composition is represented by formula (3).

(Fe3°)4CFe (II) (CN)6) '--
cH2D (3) Such a polynuclear complex can reversibly assume three different redox states. For example, taking PB as an example, FB itself is F e2 as shown in equation (3).
+ Fe3 +− mixed valence state,
When this is oxidized, it takes an oxidation state called Berlin green (hereinafter abbreviated as BG) of Fe3+-Fe3", and when FB is reduced, it takes a reduced state called so-called Prussian white (abbreviated as PW) of Fe2"-Fe2+. Take. Moreover, these three redox states (F
B, BG and FW) can be taken reversibly.

[Purpose of the invention]

An object of the present invention is to provide a battery using a polynuclear complex that can take these three types of redox states.

[Structure of the invention]

The present inventor focused on polynuclear complexes that can assume three types of stable redox states, and completed the present invention as a result of intensive research. In other words, by using a compound in the intermediate cedox state in such a polynuclear complex as a raw material, it is electrolyzed to produce an oxidized compound (corresponding to BG in the PB example) on the anode side and a reduced compound on the cathode side. If a compound (corresponding to PW in the example of PB) is produced, an electromotive force is generated between the two electrodes, so it can be used as a battery. In this battery, by discharging, the compounds at both electrodes return to the same raw material, so that it can be used again as a battery by electrolyzing it. In other words, it can also be used as a storage battery (secondary battery) that can be repeatedly charged and discharged. In conventional batteries, the active materials of the anode and cathode usually use completely different compounds, but in the battery of the present invention, the same compound is used as the raw material for the active materials of both electrodes. The advantages of simplicity in construction and manufacturing are significant.

Another feature of the polynuclear complex used in the present invention is that it can be easily formed into a film or colloidal particle form because it is a high molecular weight complex. Therefore, the active material can be very easily immobilized on the electrode or used as a colloid under conditions of high concentration. Being able to immobilize the active material on the electrode is important, such as being able to use it at a much higher concentration than using a solution, and making it extremely easy to prevent contact between the anode active material and the cathode active material. results in significant benefits.

A mixed valence or mixed metal polynuclear complex used illegally as an active material raw material is represented by the compositional formula (1).

(M I”), M II” (CN)s]b”
C112O (1) However, MI and MII are the same here, VIA, ■A, ■, IB of the periodic table
, IIB.

metal ions selected from groups IIIB and IVB, l.

m is the valence of the metal ion, a, b are integers of 1 to 4, C is 0
represents any integer including a, b.

β1m satisfies the relationship of equation (2).

Axa= (6-m)xb (2) The condition of formula [2] is based on the reason that the number of negative charges and positive charges in the complex must be equal.

Ml", MII'"", for example, Fe 2 +
, Fe”, Ru”, Ru”, Os”, Os”.

Mn”, Mn”, Cr”, Cr”, Cu”.

Ag”, Sn”, Sn”, Mo”, Mo”.

Examples include AA'', Pb'', Pb'+, etc.

Examples of mixed valence complexes include the above-mentioned PB, and examples of mixed metal complexes include ``so-called ruthenium purple (abbreviated as RP)'', which is represented by the compositional formula (4) (Fe'') 4 (Ru ( II) (CN) s], a-
(4) The present invention will be explained in more detail by taking PB, which is the most representative compound in the polynuclear complex of the present invention, as an example.

PB forms a unit cell as shown in the accompanying drawings. That is, it has a structure in which Fe'' and Fe3+ are alternately connected via cyano ligands. Many such unit cells are connected to form a high molecular weight complex structure. By the way, PB prepared in neutral water as described below is
When observed under an electron microscope, it was found that immediately after preparation, spherical colloidal particles were formed, and the average particle size was 230 particles. This corresponds to 6,000 connected unit cells in the figure, and its molecular weight reaches approximately 5 million. Such colloidal particles aggregate when left standing or when an electrolyte is added to form large particles ranging from several thousand to several micrometers in size, and eventually settle.

A colloidal solution of FB can be prepared by mixing an aqueous solution of potassium ferricyanide and a ferrous salt, or by mixing an aqueous solution of potassium ferrocyanide and a ferric salt. A colloidal solution of FB is produced immediately after mixing. Alternatively, a colloidal aqueous solution of PB can be obtained by oxidizing a mixed aqueous solution of potassium ferrocyanide and a ferrous salt with air or another oxidizing agent, or by reducing a mixed aqueous solution of potassium ferricyanide and a ferric salt. Such a colloid aqueous solution is a transparent blue aqueous solution under conditions where the colloid does not aggregate, but when the concentration is high, colloid aggregation easily occurs, resulting in a deep blue opaque liquid. In the above case, instead of using an oxidizing agent or reducing agent, it is also possible to generate FB by electrochemical oxidation or reduction,
At this time, 'PB adheres to the electrode surface as a film. Solutions and films of other complexes are prepared in much the same manner. For example, RP is obtained as a purple colloidal solution by mixing a hexacyanoruthenium (n) salt with an aqueous ferric salt solution.

The electrodes constituting the battery may be of any material, such as platinum plates, platinum wires, gold, carbon plates such as graphite, carbon fibers, and conductive glass.

In order to coat an electrode with a polynuclear complex film, for example, when using an electrolytic reduction method, an oxidized polynuclear complex aqueous solution is first prepared. In the example of FB, a BG aqueous solution is prepared by mixing equimolar amounts of potassium ferricyanide and a ferric salt aqueous solution. An electrolyte containing cations such as potassium, rubidium, cesium, or ammonium (for example, potassium chloride, rubidium sulfate, ammonium chloride, etc.) is coexisting with this, and a voltage in the range of O to -10V (v s, NHE) is applied to the electrode. Then, reduction occurs and a polynuclear complex (for example, FB) is deposited on the electrode to form a film.

By using two electrodes coated with a film of a polynuclear complex (for example, FB) in this way, a battery can be constructed as follows.

For example, a PB-coated electrode is immersed in an aqueous solution containing an electrolyte containing cations such as potassium, rubidium, cesium, or ammonium, and a DC power supply is applied between the two electrodes.
When a potential difference of ~IOV is applied, reduction of FB occurs on the cathode side, resulting in PW, and oxidation of PB occurs on the anode side, resulting in BG.
becomes. Since an electromotive force is generated between the PW and BG electrodes obtained in this way based on the difference in redox potential of both reaction couples of PW/FB and BG/PB, it can be used as a battery. After discharging, both PW and BG return to the original PB, so by charging it, it can be used as a battery again, and such charging and discharging can be repeated. That is, the battery of the present invention can be used as a secondary battery.

When a polynuclear complex is used as a highly concentrated colloidal solution, a battery can be constructed, for example, as follows.

That is, a carbon fiber cloth is wrapped around a plate-shaped carbon electrode, and a thin platinum wire is further wound from above, and the end thereof is connected to a lead wire attached to the plate-shaped carbon electrode. Using this electrode, 0 to -10
Electrolytic reduction is performed with V to deposit PB colloid particles between the carbon fibers. In this way, two electrodes containing a highly concentrated PB colloid solution in carbon fibers are prepared, placed in an electrolyte aqueous solution, and a gap of one to several mans is left between the two electrodes so that they do not come into contact, or A simple lattice fabricated from above is sandwiched between both electrodes. The size of the cell and the aqueous solution need only be the minimum space and amount for inserting both electrodes. After that, when a potential difference of 1 to IOV is applied between both electrodes, PW is generated on the cathode side and BG is generated on the anode side. This operates as a battery as described above, and also functions as a secondary battery.

〔Effect of the invention〕

In the battery of the present invention, when a polynuclear complex membrane is used, the active materials of both electrodes are immobilized on the electrodes, so there is no need for a separator that is essential in a normal battery. Therefore, the structure of the battery becomes simple, and the problem of internal resistance caused by the separator is also eliminated. It is only necessary that both active materials do not come into direct contact. Another feature of using it as a solid membrane is that unlike a solution system, the concentration of the active material can be high; for example, if the FB membrane is expressed in solution concentration, it has an active material concentration as high as about 5 equivalents/l. The battery of the present invention can be recharged and
Discharge can be repeated and reproducibly performed.

〔Example〕

The present invention will be explained in more detail below with reference to Examples, but the scope of the present invention is not limited only to the Examples.

Example 1 The planes of the six-membered carbon rings were aligned parallel to the disk surface of the electrode.
So-called Basal Plain Graphite (
Ba5al P 1ane Grap
Hite, abbreviated as BPG)
Prepare two electrodes (area 0°17cnf). Potassium ferricyanide and ferric chloride each 1Ommol/
A BG solution is made by mixing 1 part in 0.01 N HCI aqueous solution. The BPG electrode is used as the working electrode, platinum is used as the counter electrode, and the Ag-AgC1 electrode is used as the reference electrode.
When 805 is applied, reduction of BG occurs and the PB film is coated on the electrode. Two such PB electrodes were made, and the
mol/j! 2SO, aqueous solution (K, p in SO4
Adjust to H4) Soak in 1-. When two single dry cell batteries are connected in series and a voltage of 3.5 cm is applied between both electrodes for 5 minutes, PB becomes PW at the cathode and BG at the anode. The battery thus obtained has an open electromotive force (Voc) of 1.56 V
The main circuit current (Jsc) is 340μA/ctl at the time of short circuit.
After 5 minutes, it became about 30 μA/Cl11. Such charging and discharging could be performed repeatedly and with good reproducibility.

Example 2 In Example 1, one set of lCd platinum plate electrodes was used, and K
2S0. 2 mol/j instead of! A battery was prepared in the same manner as in Example 1, except that KCI (adjusted to pH 3 with HCI) was used, and the battery had a Voc of approximately 1.5 VSJsc 390μ.
A/crl (when shorted) was obtained. Such charging and discharging could be performed repeatedly and with good reproducibility.

Example 3 In Example 1, one set of PB-covered electrodes was prepared and then fixed so that the coated surfaces of both electrodes faced each other and the distance was about 0.5 mm+. Between these electrodes, 1 mol/β of KNO
3 Add an aqueous solution (adjusted to pH 5 with HNO) and wrap the surrounding area with vinyl tape to prevent the aqueous solution from falling. When two dry batteries are used and a potential difference of 3 cm is applied between the two electrodes for two minutes, PW is generated at the cathode and BG is generated at the anode. The battery thus obtained had a Voc of about 1.5■, a Jsc
About 290 μA/cnl flowed during short circuit. Such charging and discharging could be performed repeatedly and with good reproducibility.

Example 4 Ruthenium cyanide (K4(Ru”(CN)s)”-
) and ferric chloride in an amount of 2 mol/β, a colloidal solution of RP is produced.

Add KCI to 0.5+nol/j7, dissolve it, and place it in a cell with a thickness of 3 mm and 15 marks each on the vertical and horizontal sides.
．． 5mj! put in. A cation exchange membrane is installed as a partition in the center, and platinum mesh electrodes of 1 x 1 cm are inserted on both sides of the membrane. When a potential difference of 2■ is applied between both electrodes for 10 minutes, it operates as a battery, with Voc of about 0.6■, Jsc
250μA/cIIl flowed during short circuit.

Example 5 A polynuclear complex, Fe (U) 3 Co, was prepared by mixing aqueous solutions containing 1 mol/j' each of cobalt cyanide ([I) (K3(CO'' (CN)6) 3-) and ferrous sulfate. (I[I)
After preparing a colloidal solution of (CN)s]a, a cell was constructed and charged in the same manner as in Example 4, and the battery had a Voc of about 0.5 V and a Jsc of about 210 μA/c++f.
was gotten.

Example 6 Chromium (III) cyanide (Kr [Cr-(CN), :13-) and chromium chloride (I)
A polynuclear complex, Cr(III) [Cr(III)
After preparing a colloidal solution of (CN)-), a cell was constructed and charged in the same manner as in Example 4.
c of about 0.7■ and Jsc of about 200 μA/ci were obtained.

Example 7 A copper lead wire was attached to a 1.5 x 1.5 cm glassy carbon plate to serve as an electrode, a carbon fiber cloth was wrapped around this, a thin platinum wire was further wrapped on top of the carbon fiber cloth, and this platinum wire was used as a lead. connected to the line. The finished thickness was 0.4 cm, and one set of the same electrodes was prepared. Immersed in l Q mmol/β colloid aqueous solution of BG, -0.7V (vs, Ag-
When AgC+) is applied for 10 minutes, electrolytic reduction of BG occurs, forming a PB electrode with a structure in which PB is incorporated as a concentrated colloidal solution between the carbon fibers of the electrode. Thickness 1c
Attach a cation exchange membrane to the center of a cell that is 2 cm long and 2 cm wide, insert two PB electrodes across it, and then fill the cell with a 0.5 mol/1 2So aqueous solution. . When a potential difference of 3 cm is applied between the two electrodes for 5 minutes, PW is generated at the cathode and BG is generated at the anode, forming a battery. Voc
0.46 V as Jsc, 5mA when shorted as Jsc
, 0.8 mA was obtained after 8 minutes, and a short circuit current of 0.8 mA flowed for over 1 hour.

Example 8 In Example 7, a battery was constructed in the same manner as in Example 7, except that carbon fiber cloth was used instead of carbon fiber cloth, and Voc
0.45V as Jsc, 8mA when shorted as Jsc,
A current of 1 mA was obtained after 10 minutes.

[Brief explanation of the drawing]

The accompanying drawing shows a Prussian blue unit cell.

Claims (1)

[Claims] A mixed valence or mixed metal polynuclear complex represented by the compositional formula (1) is used as a raw material, and by electrolyzing this, an oxidized compound is produced on the anode side and a reduced compound is produced on the cathode side. A multinuclear complex battery characterized by utilizing the electromotive force generated between two electrodes. (M I ^l^+)_aMII^m^+(CN)_6〕_
b・cH_2O (1) However, M I and MII are the same, metal ions selected from groups VIA, VIIA, VIII, I B, IIB, IIIB and IVB of the periodic table, l and m are The valences of the metal ions, a and b, are integers of 1 to 4, c is any integer including 0, and a, b, l, and m satisfy the relational expression (2). l×a=(6-m)×b(2)