JPH0793149B2 - Solid state secondary battery and its manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a so-called solid secondary battery whose constituent materials are all solid, and a method for manufacturing the same.

2. Description of the Related Art Among batteries used as various power sources, so-called solid-state batteries, whose constituent materials are all solid, do not leak liquid, and therefore can be expected to have high reliability, and can be thin and lightweight for any reason. Attention has been paid to both secondary batteries. Currently, it is mainly used for memory backup of various devices.

In this solid-state battery, Li ⁺ ion conductive solid electrolyte, Ag ⁺ ion conductive solid electrolyte, H ⁺ ion conductive solid electrolyte, and Rb are used as solid electrolytes for moving ions in the battery.
Cu ⁺ ion conductive solid electrolytes such as Cu ₄ I _1.5 Cl _3.5 and CuI-Cu ₂ O-MoO ₃ are taken up.

Moreover, as the material for the positive electrode, Cu _0.1 TiS ₂ , Ag _0.1 TiS ₂ , Cu
_0.1 NbS ₂ , Ag _0.1 NbS ₂ , WO _{3 and} Cu _y Mo ₆ S _8-z , Ag _y Mo ₆ S
Chevrel phase compounds such as _8-z are listed. On the other hand, Cu, Ag, Li _1.5 WO ₃ for the negative electrode, and the same Chevrel phase compound as for the positive electrode have been tried.

As in the case of other batteries, the structure of these batteries is such that a layer mainly composed of an electrode active material and a binder is arranged on both sides as a positive electrode and a negative electrode, and a layer mainly composed of an electrolyte and a binder is arranged in the center. It is common.

Regarding the solid secondary battery having such a structure, as a material for the positive electrode, a Chevrel phase compound such as Cu _y Mo ₆ S _8-z , Ag _y Mo ₆ S _8-z, etc. _{used, RbCu 4 I 1.5 Cl 3.5,} CuI-Cu 2 O-MoO as the electrolyte
It has been noted that stable performance and long life can be expected when using a metal ion conductive solid electrolyte such as ₃ .

The problem to be solved by the invention However, when the battery having such a conventional structure was used for charge and discharge, a decrease in capacity was recognized with a relatively small number of cycles depending on the conditions.

That is, deterioration of performance was observed when charging and discharging were repeated.

There is also room for improvement in self-discharge.

Means for Solving the Problem First, a Chevrel phase compound is selected as an electrode material that operates both as a positive electrode and a negative electrode. This Chevrel phase compound preferably contains copper, silver and lithium in its composition. For example, Cu _y Mo ₆ S _8-z and Ag _y Mo ₆ S _8-z are preferable. Most preferred Cu
_{In the case of y} Mo ₆ S _8-z , the electrolyte is, for example, RbCu ₄ I _1.5 Cl.
_{3.5 Use} copper ion conductive solid electrolyte. Mobile ions of the solid electrolyte used for the positive electrode, the negative electrode and the electrolyte are copper,
It is preferably either silver or lithium.

Then, unlike the conventional battery, in which the positive electrode and the negative electrode are not arranged on both sides of the electrolyte as the center, the positive electrode is formed on one surface of the layer mainly containing the electrolyte and the binder (preferably a thermoplastic resin). A layer containing a material, an electrolyte, and a binder as a main component and a layer containing the negative electrode material, an electrolyte, and a binder as a main component are formed with a space therebetween, and the positive electrode area is 1.5 to 3.0 times the negative electrode area. The forming method includes a printing method and a paste-slit method. Further, it is preferable to include pressurization by a pressing machine and heating above a temperature at which the binder is significantly softened in the process of forming these layers.

Action A positive electrode layer containing an electrolyte and a negative electrode layer containing an electrolyte are formed on one surface of the electrolyte layer with a space therebetween. Therefore, this distance corresponds to the distance between the electrodes in the conventional battery configuration. Therefore, depending on the width of the electrode layer, the so-called horizontal battery of the present invention has a large electrode-to-electrode distance particularly on the opposite side of the counter electrode from the conventional battery configuration, and therefore is not suitable for use with a large load. . However, since the electrolyte layer that does not come into contact with the electrodes exists between both electrodes, there is no fear of a short circuit that may occur when a thin electrolyte layer is used. Therefore, a long life is possible, which is advantageous in terms of self-discharge characteristics.

In addition, the phenomenon of expansion in the process of charging / discharging because pressurization by a pressing machine and drying are not merely drying by evaporating and removing the solvent, but a means including a high temperature above the remarkable softening point of the binder is added. Can suppress the increase of internal resistance and contribute to the improvement of excellent discharge performance, self-discharge property and cycle characteristics.

Further, since the positive and negative polar layers are formed on only one surface of the electrolyte layer, the positive and negative polar electrodes can be formed on one surface of the electrolyte layer at a time. At this time, when a relatively thin electrode layer is obtained, a so-called printing method can be utilized to greatly simplify manufacturing.

Figure 1 shows the discharge curve of a horizontal battery with the same area for both positive and negative electrodes, using one Chevrel phase compound, for example Cu _y Mo ₆ S _8-z , and RbCu ₄ I _1.5 Cl _3.5 copper ion conductive solid electrolyte as the electrolyte. . A flat portion of 0.5 to 0.3 V is shown as the first stage and two flat portions of 0.2 to 0.05 V are shown as the second stage when discharging per cell. Normally, in such a case, the higher voltage is used in a general battery, but a constant voltage or constant current method in which charging is set below overcharge, for example, even if the voltage is 0.5 to 0.6 V, relatively few cycles A decrease in capacity was recognized by the number.

When I investigated the cause, it was found that charging was a problem.
It can be seen that the positive electrode and the electrolyte are deteriorated and deteriorated at a high voltage of 5 V or more, that is, in the state where there is almost no copper ion, and in the present invention, the lower voltage is controlled to be used. That is, the final voltage during charging should be about 0.4V or less per cell. That is, in constant potential charging, the set voltage takes a certain value of 0.4 V or less, and in constant current charging, the upper limit is about 0.4 V.
Therefore, discharge shows a voltage of only one stage of 0.3 V or less, and this is used. When the solid secondary battery is operated in this manner, no decrease in capacity is observed even after repeated charging and discharging, and the solid secondary battery is stable.

FIG. 2 is a discharge curve of a horizontal battery when the area of the positive electrode is twice the area of the negative electrode. Compared with Fig. 1, for example, 0.
It can be seen that the discharge time from 3V to 0.15V is significantly longer. This is because the potential of the negative electrode drops rapidly and the voltage between both electrodes becomes high.

Thus, by making the positive electrode area larger than the negative electrode area in the horizontal type, it is possible to obtain a solid secondary battery having a stable cycle life and a large capacity.

Example First, a C paste serving as a positive current collector and a negative current collector is printed and dried on a polyethylene terephthalate substrate with an interval of 1 mm. Copper Chebrel (Cu ₂ Mo ₆
S ₈ ) and RbCu ₄ I _1.5 Cl _3.5 as an electrolyte in 20 Wt
%, Commercially available methyl methacrylate as a binder is 8 Wt%
Toluene solution is added to the mixture so that the mixture becomes sufficiently mixed to obtain a paste. This paste is printed on the positive and negative current collectors using a metal screen and dried,
A positive electrode and a negative electrode are formed. Then RbCu ₄ I _1.5 C as electrolyte
l _3.5 , using a commercially available methyl methacrylate as a binder to 8 Wt%, add the toluene solution and stir sufficiently to make a paste, then use a metal screen to paste the solid electrolyte paste across the positive and negative electrodes. Print.

After drying at 130 ° C., it was heated and pressed at 500 Kg / cm ² through a roller press machine heated to 150 ° C. The thickness of the electrode layer and the electrolyte phase were both 0.10 mm. The size of the positive electrode and the negative electrode was respectively ^{20 × 5mm 2, 20 × 2.5mm} 2. The weights of the positive electrode and the negative electrode were 26 mg and 13 mg, respectively. Finally, the surface of the battery was first coated with a polyacrylic resin, and then a room temperature curing type epoxy resin was applied thereon to form a battery.
This battery is designated as A.

Next, a battery having a conventional structure in which an electrode layer was formed on both surfaces of an electrolyte was prepared for comparison. That is, a positive current collector is first applied on a polyethylene terephthalate substrate by a printing method, and then a positive electrode, an electrolyte, a negative electrode, and a negative current collector are sequentially formed by a printing method and thermocompression bonded to form a battery having a conventional structure. did. This battery is designated as B. The weights of the positive electrode and the negative electrode were the same as A. The electrode area was 1 cm ² .

First, the discharge voltage and capacity during normal charge and discharge were examined. 50 μA
Charging up to 0.3V at −50μA and discharging up to 0.15V at A, the discharge capacity at A is 300μAh, while at B is 1
20 μAh and A were excellent. Next, the self-discharge property of each battery was examined. After charging to 0.30V and leaving it at 30 ° C for 1 month, the capacity was examined and the retention rate was almost 98% for A, but 10% or less for B. It was It is considered that the reason for the large self-discharge in B is that there is a pinhole in the electrolyte layer and a minute short circuit occurs. In order to reduce this pinhole, the electrolyte layer was printed twice to make the thickness of the electrolyte layer nearly twice, and the self-discharge was also examined. In the same test as above, the maintenance rate improved slightly to 21%, but it is still worse than A.

Next, with the structure of type A, the negative electrode area was kept constant at 20 × 2.5 mm ^2, and it was examined how the battery characteristics changed when the positive electrode area was changed. Table 1 shows 50μA charging to 0.3V-50μA
Shows the battery capacity when discharged up to 0.15V. When the positive electrode becomes 1.5 times larger than the negative electrode, the capacity increases by 50% or more.

Table 2 shows that these batteries are charged with 0.3V and 0.4V constant voltage −5kΩ.
The cycle life characteristics of constant resistance discharge and final voltage of 0.15V were investigated, and the maintenance rate after 1000 cycles with respect to the initial value is shown.

The life varies greatly depending on the charging voltage, and especially the battery of f having a large positive electrode area is greatly deteriorated by charging of 0.4V. It is considered that this is because the negative electrode became too small and a load was applied to the negative electrode. In fact, when examining the deteriorated battery, it was observed that copper was deposited on the negative electrode.

When these batteries are stacked, even if the charging voltage of the stacked batteries is set to 0.3 V per single element, it is fully conceivable that a voltage of 0.3 V or more per single element will be applied due to variations in capacity. When using a laminated battery integrated with an indoor consumer solar cell, it is usually 0.3 V per element with fluorescent light.
Even when the battery is charged with, the voltage of the battery may increase due to direct sunlight. Even in such a case, a voltage of 0.3 V or more is applied per single element. Therefore, when the area of the positive electrode exceeds three times the area of the negative electrode, there is a problem in terms of life characteristics particularly in the case of a laminated battery.

EFFECTS OF THE INVENTION The solid secondary battery of the present invention has, on one surface of a layer mainly composed of an electrolyte and a binder, a layer mainly composed of a positive electrode material, an electrolyte and a binder, a negative electrode material and a binder. The layer mainly composed of the agent is formed at a distance, and the positive electrode area is 1.5 to 3.0 of the negative electrode area.
Since it is configured to be doubled, the manufacturing method can be simplified, excellent self-discharge characteristics can be obtained, and the life can be further extended.

RbCu a mixture of both positive and negative electrodes and Cu ₂ Mo ₆ S ₈ of the same weight RbCu ₄ I _1.5 Cl _3.5 In one embodiment of the BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is the present invention, as the electrolyte ₄ I _1.5 Cl _3.5 FIG. 2 is a diagram showing a constant current discharge curve of a copper ion conductor solid secondary battery using each of the above, FIG. 2 is a constant current discharge of a copper ion conductor solid secondary battery in which the positive electrode weight is twice the negative electrode weight in the same example. It is a figure which shows a curve.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tsutomu Iwaki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-64-21870 (JP, A)

Claims (7)

[Claims] 1. In a solid secondary battery in which the electrode material is a Chevrel phase compound for both the positive electrode and the negative electrode, and the electrolyte is a metal ion conductive solid electrolyte, one surface of a layer mainly containing the electrolyte and the binder is A layer mainly composed of a positive electrode material, an electrolyte and a binder and a layer mainly composed of a negative electrode material, an electrolyte and a binder are formed with a space therebetween, and the positive electrode area is 1.5 to 3.0 times the negative electrode area. A solid secondary battery characterized by the above. 2. The mobile ions of the solid electrolyte used for the positive electrode, the negative electrode and the electrolyte are copper, silver or lithium,
Corresponding to this, the Chevrel phase compound used for the positive electrode and the negative electrode contains copper, silver, and lithium in the composition, respectively, and the solid secondary battery according to claim 1. 3. The solid secondary battery according to claim 2, wherein the electrode material is a copper-Sverel phase compound for both the positive electrode and the negative electrode, and the electrolyte is a copper ion conductor. 4. The solid secondary battery according to claim 3, wherein the copper ion conductor is a RbCu ₄ I _x Cl _y based solid electrolyte. 5. The solid secondary battery according to claim 3, wherein the binder contained in the electrode material and the electrolyte is a thermoplastic resin. 6. The method for producing a solid secondary battery according to claim 1, wherein a layer mainly containing an electrolyte and a binder and an electrode material and a layer mainly containing an electrolyte and a binder are formed by a printing method. 1. A method for manufacturing a solid secondary battery, which comprises forming. 7. A temperature higher than a temperature at which pressure is applied by a press and softening of the binder occurs in the process of forming the layer containing the electrolyte and the binder and the layer containing the electrode material, the electrolyte and the binder. 7. The method for producing a solid secondary battery according to claim 6, further comprising: