JPH0564437B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a secondary battery that can be charged with light rather than electricity, that is, a battery that functions as a combination of a solar cell and a secondary battery.

Conventional technology Many attempts have been made to develop secondary batteries that can be charged using light, as shown in the review by Masao Kaneko, Electronics, pages 97-104 (S59.10), but only solar batteries have been put into practical use. It uses a battery to charge a normal secondary battery. In addition to the two-stage type, which stores electricity charged by a solar cell in a secondary battery, electrodes made of a semiconductor such as n-type _TiO2 ,
The semiconductor electrode is immersed in an electrolyte with an electrode made of a metal such as platinum or a semiconductor such as p-type GaP, and the semiconductor electrode is irradiated with light to cause charge separation (creating holes in the valence band and electrons in the conduction band). ), attempts have been made to oxidize and reduce substances in the electrolyte with photo-induced charges, store them as active materials, and use them during discharge, but this has not yet reached the level of practical use. In order for the photo-excited charges to carry out the subsequent oxidation and reduction reactions, the oxidation and reduction potentials of the substances in the electrolyte must be above the top of the valence band of the semiconductor electrode, and the reduction potential must be below the bottom of the conduction band. In order to perform as much charge separation as possible by photoexcitation, it is necessary that the bandgap of the semiconductor electrode be small, but the condition that the bandgap is too small cannot be satisfied, and the subsequent electrochemical reaction will not proceed. Therefore, in order to satisfy the conditions of
However, semiconductors with such band gaps (n-type Si ~ 1.1eV, n-type GaAs ~ 1.35eV,
CdS ~ 2.4 eV) have the problem that they themselves participate in reactions and corrode, and only ultraviolet light can be used for those that are stable in aqueous electrolytes.
Currently, materials such as TiO ₂ and ZnO are limited to materials with a band gap of 3.0 to 3.2 eV.

Further, recently, much research has been conducted on secondary batteries using dichalcogenite, a transition metal of the , , , group, as a positive electrode material. Most of them use Li as the negative electrode material and an organic electrolyte.

Very recently, it has been discovered that these transition metal dichalcogenides can transfer ions in and out not only by electric current but also by light. Intercalation compound of layers
Compands, “Structure and Bonding” (H.Tributch, “Photoelectrochem
energr conversion involving transition metal
d-states and intercalation compound of
“layer compounds”, Structure and Bonding49,
162-166 '82) synthesized his own and others' research and summarized the possibility of batteries that could be charged with light. Considering the use of sunlight, batteries with Li as the negative electrode require too much energy to charge efficiently, making it impossible to charge them efficiently. From the viewpoint of efficiency, it is predicted that it would be better to replace the negative electrode with something like Cu, which has a noble oxidation and reduction potential. This can be easily considered from the above conditions. In addition, it is necessary for the electrode to maintain semiconductivity during the photocharging process, and B.G. Jacob et al.'s Solid State Physics (Solid State Physics) study deals with the intercalation of Fe and Cu into ZrS ₂ and HfS ₂ . BG Yacob, et al, J.
(Phys.C. (Solid State Phys) 12, 2189 ('79)), states that these disulfides are promising as photoelectrodes.

Problems to be Solved by the Invention The inventors have previously provided a secondary battery using n-type ZrS ₂ and HfS ₂ that can be charged with light. However, batteries using the above-mentioned materials as positive electrodes have the drawback of large polarization during power distribution.

Means to solve the problem Nb _x ZrS _y (0<x<1,
1.8≦y≦2.1) or a material mainly composed of a mixture of NbS ₂ and ZrS ₂ .

Function A major cause of battery polarization is the activation energy of charge transfer at the interface between the electrolyte and the positive electrode material. This means that it has passed through the electrolyte.
Cu ⁺ receives electrons from the positive electrode material, becomes Cu, and is stored in the positive electrode material. This flow of electrons is the function of the battery, but it is consumed during the exchange of electrons between Cu ⁺ and the positive electrode material. The energy that occurs is called the activation energy of charge transfer. Of course, the lower the activation energy, the more quickly electrons can be exchanged, and the polarization of the battery will be smaller. When ZrS ₂ was doped with Nb, the activation energy mentioned above was lowered, resulting in smaller polarization.

Example Examples of the present invention will be described below.

Example 1 The materials constituting the battery are as follows.

Positive electrode: Nb _0.1 ZrS ₂ powder + RbCu ₄ I _1.5 Cl _3.5 powder (weight ratio 2:3) ...60 mg Solid electrolyte: RbCu ₄ I _1.5 Cl _3.5 powder ... 50 mg Negative electrode: Distilled Cu powder + Cu _1.59 S powder +
RbCu ₄ I _1.5 Cl _3.5 powder (weight ratio 4:19:5)
...50 mg The above positive electrode powder, solid decomposition material, and negative electrode powder were pressed into three layers under a pressure of about 3 tons to form a battery pellet with a diameter of 10 mm, as shown in FIG. 3. 1 is the above positive electrode layer, 2 is a solid electrolyte layer, 3 is a negative electrode layer, and 4 is a transparent electrode made by doping In ₂ O ₃ with SnO ₂ and depositing it on glass. 5 is a current collector, and a conductive rubber made of styrene-butadiene rubber in which carbon fibers having a wire diameter of 7 to 8 μm and a length of 30 to 100 μm are dispersed is used. 6 is a lead wire, and 7 is a package made of highly insulating resin.

While discharging the above battery at 200 μA, turn on light irradiation.
FIG. 1 shows the change in closed circuit voltage over time when -off is repeated. ○ marks are examples of the present invention, and □ marks are comparative examples in which ZrS ₂ is the main material of the positive electrode. A 100W Xe lamp was used as the light source, and irradiation was performed at a distance of 50cm. The discharge characteristics of this battery are shown in FIG. The radiation current is 200μA, and the ○ and □ marks are the same as in Figure 1. Looking at this, it can be seen that the discharge characteristics of this example are significantly improved.

Example 2 NbS ₂ powder + ZrS ₂ powder + RbCu ₄ I _1.5 as positive electrode
60 Cl _3.5 powder mixed in a weight ratio of 1:1:3
The fourth graph shows the time change in the closed circuit voltage when light irradiation was turned on and off while discharging a battery using MG and using the same conditions as in the above example at 200 μA as above. FIG. 5 shows the discharge characteristics. Similar to Example 1, a significant improvement in discharge characteristics is observed.

Note that ZrS ₂ and NbS ₂ of the above positive electrode materials are non-stoichiometric compounds, which are ZrS _Y and NbS _Y (1.8≦Y≦
2.1), it goes without saying that similar results can be obtained.

In addition, the reason for using a solid electrolyte is that when the electrolyte is a liquid, when light is irradiated at the junction surface with the positive electrode,
Both cations and anions are involved in the reaction, which causes corrosion of the positive electrode material, but in the case of the solid electrolyte used in this photonic secondary battery, only the cations and anions react.
Since it is only Cu ⁺ , corrosion of the positive electrode material does not occur.

Effects of the Invention As described above, the present invention uses Nb _x ZrS _y or NbS ₂ for the positive electrode.
- By using a ZrS ₂ mixed material, polarization during battery discharge can be significantly reduced and a larger discharge current can be obtained.

[Brief explanation of the drawing]

Figures 1 and 2 are characteristic diagrams of Example 1, Figure 3 is a configuration diagram of batteries of Examples 1 and 2, and Figures 4 and 5.
The figure is a characteristic diagram of Example 2. 1... Positive electrode, 2... Solid electrolyte, 3... Negative electrode,
4... Transparent electrode, 5... Current collector, 6... Lead wire, 7... Sealed package.

Claims (1)

[Claims] 1. A negative electrode containing metallic copper, a Cu ⁺ ion conductive solid electrolyte, and a positive electrode made of sulfides of Nb and Zr are sequentially laminated, and the battery can be charged by irradiating the positive electrode with light. A photo secondary battery characterized by the following. 2 Sulfide is Nb _x ZrS _y (0<x<1, 1.8≦y≦
2.1) The photo secondary battery according to claim 1, characterized in that: 3. The photo secondary cell according to claim 1, wherein the sulfide is a mixture of NbS ₂ and ZrS ₂ .