JPH0564436B2 - - 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 Attempts to develop secondary batteries that can be charged with light include, for example, Masao Kaneko, Electronics, P97-104 (S59/10)
As shown in the review paper, many studies have been done,
The one currently in use uses solar cells to charge ordinary secondary batteries. In addition to the two-stage type, which stores power generated by solar cells 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 to cause the subsequent oxidation/reduction reaction to occur with photo-excited charges, the oxidation/reduction potential of the substance 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 achieve as much charge separation as possible through photoexcitation, it is necessary that the bandgap of the semiconductor electrode be small.
The condition that the band gap is too small cannot be satisfied, and the subsequent electrochemical reaction will not proceed. Therefore, the bandgap of a semiconductor that satisfies the conditions of and and is desirable for absorbing sunlight or fluorescent lamp light and promoting the reaction efficiently is about 1 to 2.5 eV. (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 the only ones that are stable in aqueous electrolytes are TiO ₂ , which can only be used with ultraviolet light.
Currently, materials such as ZnO with a band gap of 3.0 to 3.2 eV are limited.

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 dichalcogenites can transfer ions in and out not only by electric current but also by light. and Intercalation Compound of Layer Compounds,” Structure and Bonding (H. Tributch, “Photoelectrochem energy
conversion involving transition metal d−
states and intercalation compound of layer
compounds”, Structure and Bonding 49, 162
~166'82) synthesized his own and others' research and summarized the possibility of batteries that can 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/reduction potential. This can easily be considered from the above conditions. In addition, it is necessary for the electrode to maintain semiconductivity during the photocharging process _, and a study in the Journal of Physics by B.G. Jacob et _al .
Phys.) BGYacob, 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 that uses n-type ZrS ₂ and HfS ₂ and can be charged with light. However, using the above materials as positive electrodes has the disadvantage of low quantum efficiency during photocharging, and
If the temperature exceeds that level, S is liberated from ZrS ₂ , which has the disadvantage of causing internal shoots.

Measures to solve the problem ZrS _2-X (0<x<0.5) is used as a positive electrode material for batteries.
The main material used is

Effect ZrS ₂ has a fairly large energy gap between the valence band and the conduction band, and therefore has very low electronic conductivity, which is one of the causes of lower quantum efficiency during photocharging. Therefore, by quantitatively removing S from the equivalent composition of ZrS ₂ , a localized level is created between the valence band and the conduction band, increasing electronic conductivity and improving the quantum efficiency of photocharging. At the same time, S
Because the amount of oxidation was insufficient compared to the equivalent ratio, its release was almost completely eliminated.

Example Examples of the present invention will be described below.

Example 1 The materials constituting the battery are as follows.

Positive electrode: ZrS _1.7 powder + RbCu ₄ I _1.5 Cl _3.5 powder (weight ratio 2:3) ...60mg Solid electrolyte: RbCu ₄ I _1.5 Cl _3.5 powder ...50mg Negative electrode: 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 electrolyte and negative electrode powder were pressed into three layers under a pressure of about 3 tons to form battery pellets with a diameter of 10 mm, as shown in Figure 3. It was configured as shown in . 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. No. 5 is a current collector made of conductive rubber in which carbon fibers having a wire diameter of 7 to 8 μm and a length of 30 to 100 μm are dispersed in styrene or butadiene rubber. 6 is the lead wire, 7
is a package made of highly insulating resin. The first graph shows the time change in the closed circuit voltage when the above battery was discharged at 200μA and the time axis was irradiated with light, with the time axis set at the origin when the detected voltage decreased to 0.1 volt.
It is a diagram. In the figure, the one marked with ○ is the present example, and the one marked with □ is a comparative example 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.

In addition, to confirm the internal shoot caused by the release of S, a discharge of 20 μA was performed at 60°C. FIG. 2 shows the discharge time and battery voltage at that time. As you can see, in the comparison series using ZrS ₂ as the main material of the positive electrode, the voltage drops rapidly around 3 hours, but in this example using ZrS _1.7 , the voltage drop as described above did not occur. Not shown. Furthermore, thermogravimetric analysis was performed to confirm the release of S. Temperature and S
The relationship between the amount of release and the amount of release is shown in FIG. As in Figure 1, the ○ mark is ZrS _1.7 and the □ mark is ZrS ₂ . The horizontal axis represents temperature, and the vertical axis represents the amount of S released from 1 g of sample. The temperature was increased by 2° C. per minute, and S was confirmed by gas chromatography.

Example 2 ZrS _1.6 + RbCu ₄ I _1.5 Cl _3.5 as a positive electrode in a weight ratio of 2:
Use 60 mg of the mixture in step 3, and use the same procedure as in Example 1 above.
Figure 5 shows the change in closed-circuit voltage over time when a battery fabricated under exactly the same conditions was subjected to the same light irradiation as in Figure 1 while discharging a 50KΩ constant resistance load. Further, the discharge curve at 20μA and 80°C is shown in Figure 6.

Note that the positive and negative electrode materials may be not only powders but also sputtered films, CVD films, etc.

The reason for using a solid electrolyte is that when the electrolyte is a liquid, when light is irradiated at the joint surface with the positive electrode, both cations and anions participate in the reaction, which causes corrosion of the positive electrode material. In the case of solid electrolytes used in photosecondary batteries, only Cu ⁺ reacts, and the positive electrode material does not corrode.

Effects of the Invention Due to the localized level generated by quantitatively removing S from ZrS ₂ in the photosecondary cell of the present invention, the rate of increase in voltage after light irradiation is much greater than that in a photovoltaic cell in which ZrS ₂ is the main cathode material. , that is, the quantum efficiency of photocharging is much larger.

[Brief explanation of the drawing]

Figures 1 and 2 are characteristic diagrams of a secondary photovoltaic cell according to an embodiment of the present invention, Figure 3 is a diagram showing thermal analysis of ZrS ₂ and ZrS _1.7 , Figure 4 is a block diagram of the same battery, 5 and 6 are characteristic diagrams of different embodiments of the present invention. 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 and a Cu ⁺ ion conductive solid electrolyte, a solid electrolyte consisting of the Cu ⁺ ion conductive solid electrolyte, and a positive electrode containing ZrS _2-X (0<X<0.5) are sequentially added. A photo secondary cell characterized in that the positive electrode is laminated and the positive electrode is irradiated with light.