JPH0534779B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an all-solid-state solid electrolyte secondary battery using a solid electrolyte having high ionic conductivity at room temperature.

Conventional technology Batteries that use solid electrolytes that have high ionic conductivity at room temperature can be made into an all-solid state, making them highly reliable batteries that do not leak and have extremely low self-discharge during storage. becomes. In order to use such a highly reliable battery as a power source in the field of microelectronics, which is characterized by miniaturization of electric circuit elements, miniaturization is naturally required. The smaller the battery, the smaller the capacity of the battery, but compared to primary batteries, which end their lifespan after one discharge and require frequent replacement, small batteries that can be used repeatedly by charging are important. Secondary batteries are becoming more useful.

A necessary requirement when constructing a secondary battery is that the positive electrode material and the negative electrode material have the ability to perform a reversible electrochemical reaction during charging and discharging of the battery.

As a reversible positive electrode for solid electrolyte secondary batteries using Cu ⁺ ion conductive solid electrolyte, A. Bottini et al.
There are metal chalcogenides with a layered crystal structure, typified by titanium distributide, TiS ₂ , described in 2010). During battery discharge, this metal chalcogenide contains metal ions liberated at the negative electrode, such as
Alkali metal ions such as Cu ⁺ ions, Ag ⁺ ions, or Li ions are occluded between the S-S layers, and for charging, these ions are released and react reversibly.

It was reported in Advances in Physics, vol _. 18, No. 74 (1969
This document suggests that metal chalcogenides such as TiS ₂ can be used as positive electrodes for secondary batteries. An example of using metal chalcogenides such as TiS ₂ for the positive electrode of a secondary battery is a West German published patent.
This method is disclosed in Publication DT2150401B2 (published on April 21, 1973), and uses lithium as the negative electrode and a liquid organic electrolyte as the electrolyte.

Additionally, U.S. Patent No. 4,009,052;
(filing date: September 10, 1973), the negative electrode contains group a,
A secondary battery using metals from group B, group a, group b, group a, group a, and a metal chalcogen compound such as TiS ₂ for the positive electrode has been proposed. , a secondary battery using lithium as a negative electrode and a liquid organic electrolyte has been shown.

As mentioned above, it has been known for a long time that TiS ₂ is useful as a positive electrode material for secondary batteries.

Problems to be Solved by the Invention When using TiS ₂ as a positive electrode material for a secondary battery, a point to be kept in mind is the extent to which TiS ₂ can reversibly take in and out metal ions from the negative electrode. The metal ion from the negative electrode is M ⁺ ,
TiS ₂ , which has M ⁺ ions occluded between the S-S layers, is represented by the chemical formula M _x TiS ₂ , and the valence of x determines to what extent metal ions M ⁺ can be reversibly taken in and taken out. .

Naturally, the larger the limit value of x, the higher the capacity of the positive electrode material. The limit value of this x is
If M ⁺ is L ⁺ , J.Chem Phys, 64 (1976) 3670
According to x = 0.8, if M ⁺ is Ag ⁺ , then Solid
According to State Ionics 8 (1983) 115, x=0.7. The inventors investigated Cu ⁺ and obtained a result of x0.15.
According to X-ray diffraction of Cu _x TiS ₂ , Cu _x TiS ₂ retains the layered crystal structure of TiS ₂ at x: 0 to 0.15, but takes a cubic crystal structure at x 0.2. However, this change in crystal structure is electrochemically
This is also seen when inserting and removing Cu ⁺ , and can be thought of as determining the range of x in which Cu _x TiS ₂ can be reversibly used as the positive electrode of a secondary battery. By the way, the change in the crystal structure due to the difference in the value of x in Cu _x TiS ₂ is explained by A. Bottini et al., J. Electroanal.
chem, 96 (1979) 165, also shows results similar to those investigated by the present inventors.

Curve b in Fig. 1 uses RbCu ₄ I _1.5 C _3.5 as the Cu ⁺ ion conductive solid electrolyte, and the cross-sectional structure shown in Fig. 2 consists of a Cu-based negative electrode and a TiS ₂ positive electrode. The horizontal axis shows the change in battery voltage when a solid electrolyte secondary battery with a diameter of 7 mm is discharged at a constant current value of 100 μA at 20° C. and the x value. As can be seen from this curve b, x: 0~
In the range of 0.15, the cell voltage shows a monotonous decrease with increasing x value, which is due to the positive electrode material _TiS2
holds a single crystalline phase, and Cu ⁺ within this crystalline phase
It is shown that the ion activity increases continuously as the discharge progresses, that is, as x increases. At x0.2, the cell voltage is almost flat, indicating that there are two crystalline phases of the positive electrode material, since the increase in Cu ⁺ ions does not affect the cell voltage. Curve b in Figure 3 is
When such a conventional solid electrolyte secondary battery is repeatedly charged and discharged at 20℃ and 100μA with the value of x between 0 and 0.213, the battery voltage at the end of each cycle and the number of charge/discharge cycles are calculated. As the number of cycles increases, the battery voltage decreases to about 40
Can only be used for cycles. The main reason for this is thought to be that during repeated charging and discharging when x exceeds 0.2, the layered crystal structure of TiS ₂ gradually changes to a cubic crystal structure with poor reversibility.

Means for Solving the Problem The present invention consists of a negative electrode mainly composed of Cu, a Cu ⁺ ion conductive solid electrolyte, and a TiS ₂ as a positive electrode material in which a part of TiS ₂ is replaced with indium In and Cu is inserted in advance. A new compound with a similar layered crystal structure, Cu _x Ti _1-y In _y S _2+1.5y (y: 0.01 to 0.2), has good filling properties even when the x value exceeds 0.2.
A solid electrolyte secondary battery exhibiting discharge cycle characteristics is provided.

Effect Cu _x Ti _1-y, a novel positive electrode material according to the present invention
In _y S _2+1.5y is Ti ⁴⁺ of TiS ₂ (ion radius 0.06 Å)
By partially replacing In ³⁺ (ionic radius 0.81 Å) and simultaneously inserting Cu between the S-S layers, Cu ⁺
This reduces the distortion of the crystal that occurs when ^Cu Because the crystal structure can be maintained, the new compound Cu _x has this layered crystal structure.
A solid electrolyte secondary battery using a Cu ⁺ ion conductive solid electrolyte with Ti _1-y In _y S _2+1.5y as the positive electrode material is
Even in a range where the ratio exceeds 0.2, relatively better charge/discharge characteristics can be provided compared to conventional ones.

Examples Example 1 Curve a in Figure 1 uses RbCu ₄ I _1.5 C _3.5 as the Cu ⁺ ion conductive solid electrolyte, and is composed of a negative electrode mainly composed of Cu and a Cu _0.1 Ti _0.95 In _0.05 S _2.08 positive electrode. After charging a solid electrolyte secondary battery with the cross-sectional structure shown in Figure 2 at 100 μA until x = 0,
The horizontal axis shows the change in battery voltage when discharging at a constant current value of 100 μA at 20° C. and the x value. As can be seen from this curve a, the battery voltage shows a monotonous decrease as x increases, that is, as discharge progresses, and this decrease continues until x is around 0.25, and a plateau appears when x exceeds 0.25. Furthermore, the manner in which the battery voltage decreases between x: 0 and 0.25 is more gradual than the curve b showing the discharge characteristics of a conventional battery using TiS ₂ as a positive electrode.

That is, Cu _x Ti _1-y In _y S _2+1.5y (y: 0.01~0.02)
can maintain a single layered crystal structure until x is around 0.25, and since the cell voltage is higher in a than b, Cu ⁺ ions can be taken in and out more smoothly than in conventional TiS ₂ . .

Line a in FIG. 3 shows the battery voltage at the end of each cycle and the charge and discharge when the battery according to the present invention is repeatedly charged and discharged at 20°C and 100μA with the value of x between 0 and 0.213. This shows the relationship with the number of discharge cycles.
Provides good cycle characteristics over 100 cycles.

Cu _x Ti _1-y, a novel positive electrode material according to the present invention
In _y S _2+1.5y is metal Ti powder, metal Cu powder, metal In
A mixture of powders in a predetermined ratio, or Ti
It can be obtained by gradually feeding sulfur vapor into a quartz glass container containing alloy powders of In and Cu and heating them at 800℃.Alternatively, as a simpler method, TiS ₂ powder and In ₂ S ₃ powder and
Mix with metal Cu powder at a predetermined ratio and form approximately 7mmφ.
Formed into a pellet shape under a pressure of approximately 3 tons, it is vacuum sealed in a quartz glass tube at a pressure of 0.1 Torr or less.
It can also be obtained by heating reaction at 800°C for about 72 hours. Thus obtained Cu _x Ti _1-y In _y
S _2+1.5y is obtained as a single phase when y is less than 0.2,
If it exceeds 0.2, _{the three} In ₂ S phases will separate, and the characteristics as a battery positive electrode will become extremely poor. In addition, as for the amount of Cu to be inserted in advance, x is from 0.05 to
0.15 is preferred.

Example 2 y value is 0.01, 0.02, 0.05, 0.10, 0.20, 0.30,
0.50 Cu _0.1 Ti _1-y In _y S _2+1.5y were synthesized and a solid electrolyte secondary battery with a diameter of 7 mm was constructed using these as positive electrode materials.

Positive electrode (powder): Cu _0.1 Ti _1-y In _y S _2+1.5y +RbCu ₄ I _1.5 C
_3.5 (weight ratio 2:3) ...0.06gr Solid electrolyte (powder): RbCu ₄ I _1.5 C _3.5 ...0.05gr Negative electrode (powder): Cu + Cu _1.59 S + RbCu ₄ I _1.5 C _3.5
(Weight ratio 6:4:4) ...0.10gr The above positive electrode powder, solid electrolyte powder, and negative electrode powder are pressed into three layers under a pressure of about 3 tons to form battery pellets, and then the positive electrode and negative electrode sides are A battery was produced by bonding a current collector made of a conductive carbon film and an electrode lead, and then coating the entire battery with a thermosetting epoxy resin. Figure 2 shows a cross-sectional view of the solid electrolyte secondary battery made in this way, where 1 is a positive electrode layer, 2 is a solid electrolyte layer, 3 is a negative electrode layer, 4 is a current collector, and 5 is an electrode lead. , 6 is a resin package.

Figure 4 shows the battery made in this way at 20°C.
This figure shows the relationship between the battery voltage at the end of each cycle and the number of charge/discharge cycles when charging and discharging is performed with a constant current value of 100 μA and an x range of 0.213. as 0.01, 0.02, 0.05,
It can be seen that the battery using Cu _0.1 Ti _1-y In _y S _2+1.5y containing 0.10, 0.20 as the positive electrode has excellent cycle characteristics.

Example 3 The amount of Cu inserted in advance is x = 0.05, 0.1,
Cu _x Ti _0.95 In _0.05 S _2.08 of 0.15 and 0.20 were synthesized, and a solid electrolyte battery with a diameter of 7 mm having the structure shown in FIG. 2 was constructed using these as positive electrode materials. The weight and composition of the solid electrolyte material, negative electrode material, positive electrode, negative electrode, and solid electrolyte are the same as in Example 2. The battery assembly method is also the same as in Example 2.

Figure 5 shows the battery made in this way.
It shows the relationship between the battery voltage at the end of each cycle and the number of charging/discharging cycles when charging/discharging is performed at a constant current value of 100 μA at a constant current value of 100 μA in the range of x from 0 to 0.213. Although the characteristics are slightly inferior to others,
It can be seen that both batteries provide excellent cycle characteristics.

In the examples of the present invention, RbCu ₄ I _1.5 C _3.5 was used as the Cu ⁺ ion conductive solid electrolyte, but other Cu ⁺ ion conductive solid electrolytes, such as
RbCu ₄ I _1.25 C _3.75 , Rb _0.75 K _0.25 Cu ₄ I _1.5 C _3.5 ,
It goes without saying that the same effects as the present invention can be obtained by using a solid electrolyte prepared by adding a quaternary ammonium salt such as hexamethylenetetramine to CuBr. Furthermore, as a negative electrode mainly composed of Cu,
In addition to the mixture consisting of Cu _1.59 S + Cu ⁺ ion conductive solid electrolyte, the present invention can also be achieved by using a mixture consisting of Cu + Cu ⁺ ion conductive solid electrolyte, or a mixture consisting of Cu ₅ Mo ₆ S ₈ + Cu ⁺ ion conductive solid electrolyte. Needless to say, similar effects can be obtained.

Effects of the Invention According to the present invention, Cu _x Ti _1-y In _y S _2+1.5y (y: 0.01 to 0.20) with Cu inserted in advance as a positive electrode material
A solid electrolyte secondary battery consisting of a Cu-based negative electrode and a Cu ⁺ ion conductive solid electrolyte has a charge/discharge cycle with small polarization, that is, a gradual drop in battery voltage during discharge. Provides a battery with excellent characteristics.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing voltage changes during discharging of a battery according to an embodiment of the present invention, FIG. 2 is a diagram showing a cross-sectional structure of a solid electrolyte secondary battery, and FIG.・Discharge cycle characteristic diagram, Figure 4, shows the battery charging and
Discharge cycle characteristic diagram, FIG. 5 is a charge/discharge cycle characteristic diagram of the battery. a...Battery of an embodiment of the present invention, b...Battery of a conventional embodiment, 1...Positive electrode layer, 2...Solid electrolyte layer, 3...Negative electrode layer.

Claims (1)

[Claims] 1 A negative electrode mainly made of metallic copper, a Cu ⁺ ion conductive solid electrolyte, and a Cu _x
Sulfide represented by Ti _1-y In _y S _2+1.5y (however,
A solid electrolyte secondary battery comprising a positive electrode mainly composed of y: 0.01 to 0.2, x: 0.05 to 0.15).