JPH02265166A - Solid electrolyte battery and its manufacturing method - Google Patents

Abstract

PURPOSE:To obtain a solid electrolyte battery having high storage performance, long charge-discharge cycle life, and high reliability by forming a negative electrode with a silver-lithium alloy. CONSTITUTION:A negative electrode 5 of a battery using a solid electrolyte 2 is formed with a silver-lithium alloy. The negative electrode 5 formed with the silver-lithium alloy has higher chemical potential compared with that formed with lithium alone and its reactivity is decreased. Even if the battery is stored for a long time, the reactivity of lithium with moisture penetrated from the outside or with a substance formed by decomposition of the solid electrolyte 2 caused by the moisture is decreased, and passivation of lithium is retarded. Increase in internal resistance is also retarded. A solid electrolyte battery having high storage performance, long cycle life, and high reliability can be obtained.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a solid electrolyte battery and a method for manufacturing the same.

BACKGROUND OF THE INVENTION Today, with the development of electronics, electronic devices are becoming smaller and lighter, and portable power supplies are also becoming smaller and lighter.

A lithium battery, which uses graphite fluoride or manganese dioxide as a positive electrode active material and lithium as a negative electrode active material, has a discharge voltage of 3V and is a battery system with the highest energy density.
In recent years, demand has been increasing dramatically. Furthermore, development efforts have been actively made to make this type of battery system chargeable and dischargeable, that is, to make it into a secondary battery.

On the other hand, until now, propylene carbonate.

1ic104, LIBF4, L in a solvent such as γ-butyrolactone, tetrahydrofuran, dimethoxyethane, etc.
Attempts are being made to obtain an even wider range of applications by using lithium ion conductive solid electrolytes instead of organic electrolytes containing dissolved solutes such as IAsFe 1LIPFe and creating batteries with unprecedented shapes and thinness. .

Among them, Ll/
Ljl/Poly-2-Vlnyl Pyridine
-n+1 complex type primary batteries with a small load current have been put into practical use.

In secondary batteries, solid electrolyte (1-X) L14S is used to compensate for low ionic conductivity and enable charging in a short time.
There has been an attempt to form a thin film of IOa.xL13PO4 by a sputtering deposition method (see Japanese Patent Laid-Open No. 191287/1987).

It also suppresses dendrites that occur on the negative electrode during charging,
In order to extend the charge/discharge cycle life, a proposal was made to create an alloy of lead and lithium for the negative electrode by vacuum evaporation (Japanese Patent Application Laid-Open No.
(see Publication No. O-257.073).

Problems to be Solved by the Invention However, primary batteries that use a lithium ion conductive solid electrolyte that can handle a large load current and have excellent storage characteristics, and secondary batteries that have a cycle life sufficient for practical use have not yet been developed. Not yet. The reason for this is as follows.

Generally, lithium ion conductive solid electrolytes are hygroscopic. Therefore, when handling a lithium ion conductive solid electrolyte, a dry argon atmosphere must be used. In particular, when a solid electrolyte is crushed and formed into pellets of any size for use, the surface area of the solid electrolyte increases significantly when crushed and the rate of moisture absorption increases.
When assembling a battery, etc., the amount of moisture in the atmosphere must be strictly controlled.

In order to increase the load current, a solid electrolyte with high lithium ion conductivity must be used. However, the higher the ionic conductivity, the more hygroscopic the solid electrolyte tends to be, and it strongly absorbs water during solid electrolyte manufacturing and battery assembly processes. When the solid electrolyte absorbs water, this water corrodes the lithium surface of the negative electrode and makes it passivated, increasing the battery's internal resistance and making it difficult to discharge at a large current. Furthermore, the solid electrolyte itself decomposes and its ionic conductivity decreases significantly.

Even if a secondary battery using a solid electrolyte with higher lithium ion conductivity is manufactured and charged and discharged, water absorbed by the electrolyte and products decomposed by the electrolyte itself will cause
The cycle life is shortened because the lithium deposited during charging becomes inactive. In addition, even if a lead-lithium alloy is used for the negative electrode in order to inactivate this lithium and suppress dendrites during charging, the lead-lithium alloy is hard due to its ionic crystals, and the electrode during charge and discharge cycles is hard. Because the electrode plate cracks and falls off from the current collector due to expansion and contraction of the plate, the cycle life is not improved enough for practical use.

The present invention solves these problems with conventional batteries, and provides a highly reliable solid electrolyte battery with long storage characteristics and charge/discharge cycle life by making the lithium negative electrode difficult to passivate. The purpose of this study is to provide a method for producing a lithium negative electrode that is difficult to passivate, and a method for easily and stably producing a solid electrolyte with high lithium ion conductivity even in an atmosphere where moisture is not strictly controlled. shall be.

Means for Solving the Problems A battery using the solid electrolyte of the present invention is characterized in that an alloy of silver and lithium is formed in the negative electrode. moreover,
This alloy of silver and lithium is formed by bringing a silver ion conductive solid electrolyte into contact with lithium of the negative electrode, and the lithium ion conductive solid electrolyte has a composition similar to that of the lithium ion conductive solid electrolyte. It is characterized by being obtained by contacting a silver ion conductive solid electrolyte with lithium.

Here, the solid electrolyte having a similar composition refers to a solid electrolyte having elements other than lithium ions and silver ions in common.

For example, [1fi(Li2S)/33(P2S6) glass and 55(Ag2S)/45(P2S6) glass have similar compositions, and both are approximately 10-AΩ-ICB- at room temperature.
It is a solid electrolyte with a high ionic conductivity of 1.

Function In the present invention, when lithium forms an alloy with silver in the negative electrode, the chemical potential of this negative electrode becomes higher and the reactivity lowers than that of lithium alone. Even if the battery is stored for a long period of time after being manufactured, moisture that has entered from outside the battery and
The reactivity of the negative electrode lithium with a substance generated by the decomposition of the solid electrolyte due to moisture is small, and the extent to which lithium becomes passivated is small. Therefore, the internal resistance of the battery is less likely to increase, and storage characteristics are improved. Furthermore, the speed at which the negative electrode lithium reacts directly with moisture from outside the battery is also suppressed. Furthermore, since the silver and lithium alloy has the properties of a solid solution, it is soft, so even if the electrode plate expands and contracts due to repeated charging and discharging, it will not crack and fall off, resulting in a longer cycle life.

In order to form an alloy of silver and lithium in the negative electrode, it is only necessary to contact lithium with a solid electrolyte that conducts silver ions, which is difficult to be reductively decomposed by lithium. Here, a silver ion conductive solid electrolyte having a similar composition to the lithium ion conductive solid electrolyte may be selected. In some cases, a chemical reaction between a silver ion-conducting solid electrolyte and lithium may occur, resulting in decomposition of the solid electrolyte, but silver ions in the solid electrolyte spontaneously precipitate onto lithium and form an alloy, while lithium Lithium ions are eluted from the negative electrode and diffused into the silver ion conductive solid electrolyte.

A lithium ion conductive solid electrolyte is obtained by an ion exchange reaction between the silver ions in the silver ion conductive solid electrolyte and the lithium negative electrode. Therefore, if the battery is assembled and sealed immediately after contacting the silver ion conductive solid electrolyte with lithium, the lithium ion conductive solid electrolyte will be naturally formed inside the battery. This eliminates the need to handle lithium ion conductive solid electrolytes, which are highly hygroscopic, and silver ion conductive solid electrolytes are more stable against moisture than lithium ion conductive solid electrolytes. Even in an atmosphere where moisture content is not strictly controlled during the battery assembly process, a battery using a lithium ion conductive solid electrolyte with extremely simple and stable characteristics can be obtained.

The above action is caused by the fact that the total amount of silver in the silver ion conductive solid electrolyte before contact is 23% of the negative electrode lithium.
It is preferable that the amount is at most atomic % (corresponding to LI+llAg3); if it exceeds this, the voltage of the battery will decrease and the energy density will decrease. In addition, in order to speed up the exchange rate between silver ions in the electrolyte and lithium in the negative electrode, after assembling the combination battery with a positive electrode active material containing lithium in advance,
Silver ions in the electrolyte may be forcibly deposited on the negative electrode lithium by passing a current.

Examples Examples of the present invention will be described below with reference to the drawings.

Example 1 A glass made of silver sulfide (Ag2S) and niline trisulfide (P2Ss) was used as a silver ion conductive solid electrolyte.

Ag2S and P2S6 were mixed at a molar ratio of 55:45 and heated at 600° C. for 5 hours in a sealed quartz tube. After heating, the quartz tube was poured into water, and the melt was rapidly cooled to obtain silver sulfide/niline trisulfide glass. This glass was crushed in an argon box and the average particle size was approximately 10μ.
It was made into a powder of m.

Using this silver sulfide/niline trisulfide glass powder, a flat battery as shown in Figure 1 was assembled in a dry air atmosphere.
The test was conducted. The explanation will be given below based on FIG. In addition,
FIG. 1 is a cross-sectional view of the battery after it has been assembled and aged.

IjMn20a was used as the positive electrode active material. LIMn
204 powder, silver sulfide/niline trisulfide glass powder, and tetrafluoroethylene resin powder as a binder in a weight ratio of 40:5.
They were mixed at a ratio of 0:10. 50 mg of this mixture was placed in a press mold with a diameter of 14.3 mm and molded to form a positive electrode 1.

Next, a mixture of silver sulfide/niline trisulfide glass powder and tetrafluoroethylene resin powder (weight ratio 90:10), 50 m
g was added and press molded again to produce a disk in which the positive electrode 1 and the electrolyte 2 were integrated. This disk is placed inside a battery case 4 coated with conductive carbon paste 3, and the positive electrode 1
was pressed onto the conductive paste 3 so that the liquid was directly applied to the conductive paste 3. For the negative electrode 5, a lithium sheet with a thickness of 0.24 nm was used,
A negative electrode current collector 6 made of stainless mesh was pressure-bonded to a spot-welded sealing plate 7. Then, the sealing plate 7 provided with the negative electrode and the battery case 4 provided with the positive electrode and electrolyte were stacked together to assemble a battery. Further, the outer peripheries of the battery case 4 and the sealing plate 7 were sealed with a gasket 8. The battery thus constructed was aged at 80° C. for one week. After aging, some of the batteries were disassembled and subjected to X-ray microanalysis. It was found that an alloy 9 of silver and lithium was formed on the surface of the negative electrode, and most of the silver ions in the electrolyte were replaced by lithium ions. It was observed that a lithium ion conductive solid electrolyte was produced. Here, the lithium ion conductive solid electrolyte was formed because silver sulfide/niline trisulfide glass has a similar composition to lithium ion conductive lithium sulfide/niline trisulfide glass, and the ionic conductivity is relatively high. This is because the exchange reaction between silver ions and lithium ions easily progressed due to the high concentration. The battery of the present invention produced as described above is referred to as A.

Next, as a comparative example, lithium sulfide/niline trisulfide glass powder was prepared in the same manner as the silver sulfide/niline trisulfide glass powder and used as a solid electrolyte.

A battery B is constructed in the same manner as battery A of the present invention in other respects. A cross-sectional view of this battery B is shown in FIG.

Figure 3 shows battery A of the present invention and battery B of a comparative example at 60°C.
5 is a diagram plotting the results of measuring the internal resistance of the battery during storage for about two weeks at a relative humidity of 90%. From FIG. 3, it can be seen that battery A of the present invention has a significantly smaller increase in internal resistance than battery B of the comparative example, and has excellent storage characteristics. This is because, in Battery A of the present invention, an alloy of silver and lithium is formed in the negative electrode, which makes it difficult to react with moisture entering from outside the battery.

Note that in the battery A of the present invention, the internal resistance is slightly higher than that of the battery B of the comparative example at the initial stage of storage.

This is because some silver ions are mixed in the solid electrolyte used in the battery A of the present invention, which lowers the ionic conductivity of the solid electrolyte.

Example 2 In Example 1, both the example of the present invention and the comparative example,
The internal resistance of a battery manufactured in the same manner except for changing the relative humidity of the atmosphere during assembly of the battery was measured.

FIG. 4 is a diagram plotting the internal resistance of the battery of the present invention and the battery of the comparative example produced at each relative humidity (25° C.). From FIG. 4, it can be seen that the battery of the present invention has a low internal resistance even when the relative humidity is relatively high. This is because a silver ion conductive solid electrolyte is more stable against moisture than a lithium ion conductive solid electrolyte. This shows that if a silver ion conductive solid electrolyte is used during battery assembly, a battery with relatively stable internal resistance can be obtained even if the moisture in the atmosphere is not strictly controlled.

Example 3 A complex of polyphosphazene having polyethylene oxide (molecular weight 119) in its side chain and AgCFa SOa was used as a silver ion conductive solid electrolyte. Polyphosphazene also forms a similar complex with L I CF3 SO3.

The battery was constructed in the same manner as in Example 1, except that the battery was not aged at 80° C. after construction.

AgC for 1 main chain repeating unit of polyphosphazene
F35o3 was dissolved in acetonitrile at a ratio of 0.031 to obtain a viscous solution.

LIMn204 powder was mixed into the above viscous solution, and after casting the mixture, the acetonitrile was evaporated to give a thickness of 0.
．． A 1+nm tape was produced and used as a positive electrode. Furthermore, after casting only the above viscous solution in the same manner, acetonitrile was evaporated to obtain a silver ion conductive solid electrolyte tape having a thickness of 0.01 mm. These positive electrode tapes and solid electrolyte tapes were overlapped and crimped to form a diameter of 14.3 mm.
Punched out to mm. A flat battery was produced using this integrated product of the positive electrode and electrolyte in the same manner as in Example 1. In this battery,
A current of 50 μA was passed so that silver ions in the solid electrolyte were deposited on the lithium negative electrode. When some batteries are disassembled and analyzed after being energized, an alloy of silver and lithium is formed on the surface of the negative electrode, and most of the silver ions in the electrolyte are replaced with lithium ions, resulting in lithium ion conductivity. It was confirmed that a solid electrolyte was formed. The battery produced as described above is referred to as Battery C of the present invention.

As a comparative example, L 1CF instead of AgCF3SO3
3 Batteries constructed in the same manner except that SO3 was used and silver or lead was vapor-deposited on the lithium negative electrode to form a silver-lithium alloy and a lead-lithium alloy were prepared.
Let it be E. Battery C of the present invention and battery of comparative example,
After discharging at a constant current of 50 μA for 2 hours using E, each battery was charged at a constant current of 10θμA until the battery voltage reached 3.5 V, and thereafter charge-discharge cycles were performed under these conditions. FIG. 5 is a diagram plotting the voltage at the end of discharge in each cycle of each battery. From FIG. 5, it can be seen that the battery C of the present invention is the battery of the comparative example.

It can be seen that the cycle life is significantly improved compared to E. This is because in Battery C of the present invention, an alloy of silver and lithium is formed in the negative electrode, which suppresses reactions with moisture from outside the battery and decomposition products of the solid electrolyte itself. This is because the negative electrode is less likely to collapse during charge/discharge cycles.

In contrast, in the comparative example battery, a solid electrolyte that conducts lithium ions is used during battery assembly.
Moisture absorbed directly from the working atmosphere and decomposition products affect the lithium negative electrode, shortening its cycle life. Furthermore, in Comparative Example Battery E, in addition to the effects of absorbed moisture and decomposition of the electrolyte, the collapse of the lead-lithium alloy during charging and discharging cycles accelerates the reduction in cycle life.

Effects of the Invention As described above, if the solid electrolyte battery of the present invention is used, an alloy of silver and lithium is formed in the negative electrode, so it has excellent storage characteristics, and when used as a secondary battery, the cycle life is shortened. A long-term reliable solid electrolyte battery can be obtained.

Furthermore, since a silver ion conductive solid electrolyte is used during battery assembly, an alloy of silver and lithium is easily formed in the negative electrode, improving the corrosion resistance of the negative electrode, and at the same time, a lithium ion conductive solid electrolyte can be obtained. It will be done.

Furthermore, since a silver ion conductive solid electrolyte, which is more stable than a lithium ion conductive solid electrolyte, is used, there is an advantage that there is no need to strictly control the amount of moisture in the atmosphere during battery assembly.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a flat battery as an example of the battery of the present invention, FIG. 2 is a cross-sectional view of a flat battery used as a comparative example, and FIG. FIG. 4 is a graph plotting the change in battery internal resistance with respect to the storage period for Battery B of Comparative Example. FIG. The plotted graph, FIG. 5, is a graph plotting the voltage at the end of discharge of each charge/discharge cycle in Battery C of one example of the present invention and Battery E of Comparative Example. 1.1'...Positive electrode, 2.2'...Solid electrolyte, 3゜3'...Carbon paste, 4.4'...Battery case, 5.5゛...Negative electrode, 6, 6”...Negative electrode current collector,
7, 7... Sealing plate, 8.8'... Gasket, 9.
...Silver-lithium alloy.

Claims (3)

[Claims] (1) A positive electrode, a lithium ion conductive solid electrolyte,
A solid electrolyte battery having a negative electrode made of lithium as a component, characterized in that the negative electrode is formed of an alloy of silver and lithium. (2) The method for manufacturing a solid electrolyte battery according to claim 1, characterized in that an alloy of silver and lithium is formed in the lithium negative electrode by bringing a silver ion conductive solid electrolyte into contact with lithium. (3) The solid according to claim 1, characterized in that the lithium ion conductive solid electrolyte is obtained by bringing a silver ion conductive solid electrolyte having a similar composition to the lithium ion conductive solid electrolyte into contact with the lithium negative electrode. Method of manufacturing electrolyte batteries.