JP2000223156A - Solid electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress self-discharge resulting from a reaction of a negative electrode with a solid electrolyte by strengthening reduction resistance of the solid electrolyte. SOLUTION: This solid electrolyte battery is equipped with a positive electrode containing, as an active material, a compound including a transition metal oxide, a negative electrode disposed opposite to the positive electrode and containing lithium metal, a lithium alloy, or a carbon material capable of being doped with and being cleared of lithium, and a solid electrolyte having lithium- ion conductivity and disposed between the positive electrode and the negative electrode, and the solid electrolyte having lithium-ion conductivity is a compound composed of Li, La, Ce, and O.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid electrolyte battery provided with a positive electrode, a negative electrode, and a lithium ion conductive solid electrolyte.

[0002]

2. Description of the Related Art Conventionally, as an electrolyte in a battery, an electrolyte in which an electrolyte is dissolved in an aqueous or non-aqueous solvent has been generally used. When such an electrolytic solution is used, measures must be taken to completely prevent leakage or corrosion of the electrolyte to the outside of the battery, and in the process of injecting the electrolytic solution, a problem such as a decrease in yield due to the occurrence of an internal short circuit. was there.

[0003] In recent years, a solid electrolyte battery using a solid electrolyte made of an inorganic ceramic having ion conductivity instead of such a liquid electrolyte has attracted attention.

That is, in a solid electrolyte battery using a solid electrolyte, since the electrolyte is not a liquid, measures for completely preventing leakage and corrosion, a step of injecting the electrolyte, and the like can be avoided, and the structure of the battery can be reduced. This is because there are advantages such as simplicity and easy assembling.

[0005]

However, among such solid electrolytes, inorganic ceramics-based compounds have a lower resistance to oxidation and reduction than an electrolytic solution and have a potential region which is a potential region where they can stably exist. The windows were small. For example, Li solid electrolytes put to practical use in the early days have low resistance at a noble potential, and thus can be used only in batteries having a battery voltage of 2 V or less.

However, recently, batteries using a non-aqueous electrolyte having a voltage of 4V class have been manufactured, and it is desired to solidify the electrolyte while maintaining these high potentials. Attempts have been made to widen the potential window of the solid electrolyte.

On the other hand, recently, as a ceramics-based solid electrolyte, Li _0.34 La _0.51 T having a perovskite structure has been used.
An iO _2.94 compound was reported (Y. Inaguma, C. Liquan, MI
tohet al., Solid State Communications, Vol. 86, No. 10,
pp689-693 (1993)). This solid electrolyte is 10 ⁻³ S /
cm, which has attracted attention because of its high lithium ion conductivity, but has the disadvantage that the reduction of the contained Ti occurs at about 1.7 V (relative to lithium potential) (P. Br.
ike, .S.Schamer, RAHuggins et al., J.Electrochem.So
c.Vol.144.No.6, June1997).

For this reason, for example, when a battery is formed using the above-mentioned solid electrolyte, if a material such as metallic lithium, low-crystalline carbon, or graphite is used as the negative electrode, the solid electrolyte and the negative electrode may be irreversible. Cause a reaction.

[0009] When the solid electrolyte reacts with the negative electrode, Ti in the solid electrolyte enters a mixed valence state, so that the solid electrolyte exhibits electron conductivity, a current flows between the positive electrode and the negative electrode through the solid electrolyte, and This increases the self-discharge of the electrolyte battery.

[0010] The present invention has been proposed in view of the above-mentioned conventional circumstances, and has a solid electrolyte battery in which the reduction resistance of the solid electrolyte is enhanced and self-discharge generated by the reaction between the negative electrode and the solid electrolyte is suppressed. The purpose is to provide.

[0011]

According to the present invention, there is provided a solid electrolyte battery comprising a positive electrode containing a compound containing a transition metal oxide as an active material;
Lithium alloy or lithium-doped, a negative electrode containing a carbon material that can be dedoped, and disposed between the positive electrode and the negative electrode, including a lithium-ion conductive solid electrolyte, the lithium-ion conductive solid The electrolyte is Li,
It is a compound composed of La, Ce and O.

In the solid electrolyte battery according to the present invention as described above, since the compound composed of Li, La, Ce and O is used as the solid electrolyte, the potential of the negative electrode is low.
Even when the i potential is 1.5 V or less, no reaction occurs between the negative electrode and the solid electrolyte.

[0013]

Embodiments of the present invention will be described below.

FIG. 1 shows an example of the configuration of the solid electrolyte battery according to the present embodiment. This solid electrolyte battery 1 has a positive electrode 2
And a negative electrode 3 disposed opposite to the positive electrode 2 and a solid electrolyte layer 4 disposed between the positive electrode 2 and the negative electrode 3, and are covered and sealed by an outer case 5 made of an insulating material. .
A positive electrode terminal 6 is connected to the positive electrode 2, and a negative electrode terminal 7 is connected to the negative electrode 3. The positive electrode terminal 6 and the negative electrode terminal 7 are sandwiched by a sealing portion that is a peripheral portion of the outer case 5. ing.

The positive electrode 2 is formed by forming a positive electrode active material layer containing a positive electrode active material on a positive electrode current collector. As the positive electrode active material, a transition metal compound capable of inserting and extracting lithium can be used. For example, a transition metal compound containing at least one of manganese, cobalt, nickel, vanadium, and niobium can be used.

The negative electrode 3 is formed, for example, by punching metallic lithium into a predetermined shape. In addition, as the negative electrode active material, an alloy, an oxide, carbon, or the like that can occlude and release lithium can be used. When an alloy, oxide, carbon, or the like capable of inserting and extracting lithium is used as the negative electrode active material, the negative electrode 3 is a negative electrode active material layer containing the above-described negative electrode active material on a negative electrode current collector. Is formed.

The solid electrolyte layer 4 has lithium ion conductivity and is made of a compound composed of Li, La, Ce and O. Specific examples of the compound as described above include Li _0.34 La _0.51 CeO _2.94 having a perovskite structure. The Li _0.34 La _0.51 CeO _2.94 is obtained by using Ce instead of Ti in the above-described Li _0.34 La _0.51 TiO _2.94 compound having a perovskite structure, which is a ceramics-based solid electrolyte.

As described above, in the Li _0.34 La _0.51 TiO _2.94 compound having a perovskite structure, the contained Ti is reduced at about 1.7 V (relative to lithium potential). Therefore, for example, when lithium metal, low crystalline carbon, graphite, or the like is used as the negative electrode 3, the solid electrolyte layer 4 and the negative electrode 3 may cause an irreversible reaction.

When the solid electrolyte layer 4 and the negative electrode 3 react,
Since the Ti in the solid electrolyte layer 4 is in a mixed valence state, electron conductivity is developed in the solid electrolyte layer 4, a current flows between the positive electrode 2 and the negative electrode 3 through the solid electrolyte layer 4, and the solid electrolyte battery 1 It increases the self-discharge.

Instead of the conventional solid electrolyte Ti, Ti
By using Ce having a larger reduction potential, while having lithium ion conductivity equivalent to that of using Ti,
Resistance to reduction can be increased. Then, by using this solid electrolyte, the reaction between the solid electrolyte layer 4 and the negative electrode 3 is suppressed, and the solid electrolyte battery 1 by self-discharge is suppressed.
Can be prevented from lowering and storage characteristics can be improved.

The solid electrolyte battery 1 according to the present embodiment as described above is not particularly limited in its shape such as a square type, a coin type, a button type and the like. Can be sized. Further, the present invention is applicable to both primary batteries and secondary batteries.

[0022]

EXAMPLES A solid electrolyte battery according to the present invention was manufactured and its characteristics were evaluated.

<Example> First, a positive electrode and a negative electrode were prepared as follows.

In preparing the positive electrode, lithium-containing cobalt dioxide LiCoO ₂ heat-treated at a temperature of 700 ° C. to 900 ° C. was used as the positive electrode active material, this positive electrode active material, carbon powder as a conductive agent, a binder Was mixed with a fluororesin powder at a weight ratio of 90: 7: 3 to prepare a positive electrode mixture.

Next, the positive electrode mixture is applied to a metal plate serving as a positive electrode current collector so as to have a thickness of about 200 μm by a doctor blade method.
Vacuum heat treatment was performed at a temperature of 150 ° C. to form a positive electrode active material layer.

Finally, the metal plate on which the positive electrode active material layer was formed was punched out in a circular shape to produce a circular plate-shaped positive electrode. Further, a positive electrode terminal was welded to a portion of the metal plate where the positive electrode mixture was not applied.

A negative electrode was obtained by punching lithium metal into a disk having substantially the same diameter as the positive electrode. Further, a negative electrode terminal was welded to the negative electrode.

Next, a solid electrolyte was prepared as follows.

First, cerium oxide CeO ₂ , lithium carbonate Li ₂ CO _3, and lanthanum oxide La ₂ O ₃ are mixed in predetermined amounts, and the mixture is mixed at a temperature of 800 to 1350 ° C.
Fired for ~ 8 hours. Next, by slowly cooling the calcined product, Li _0.34 La _0.51 CeO to be a solid electrolyte is obtained.
_2.94 was obtained.

Next, the positive electrode and the negative electrode produced as described above were laminated via a solid electrolyte to form an electrode laminate. Finally, the electrode laminate was housed in an outer case, and the outer case was sealed under reduced pressure. At this time, the positive electrode terminal and the negative electrode terminal were sandwiched between the sealing portions of the outer case. Thus, a plate-shaped solid electrolyte secondary battery was produced.

Comparative Example First, a positive electrode and a negative electrode were manufactured in the same manner as in the above-described example.

Next, a solid electrolyte was prepared as follows.

A predetermined amount of rutile-type titanium oxide TiO ₂ , lithium carbonate Li ₂ CO ₃ and lanthanum oxide La ₂ O ₃ are mixed, and the mixture is heated at a temperature of 800 ° C. to 1350 ° C. for 2 hours to 8 hours. Fired. Next, by slowly cooling the fired product, Li _0.34 La _0.51 Ti
O _2.94 was obtained.

Next, the positive electrode and the negative electrode produced as described above were laminated via a solid electrolyte to form an electrode laminate. Finally, the electrode laminate was housed in an outer case, and the outer case was sealed under reduced pressure. At this time, the positive electrode terminal and the negative electrode terminal were sandwiched between the sealing portions of the outer case. Thus, a plate-shaped solid electrolyte secondary battery was produced.

The extent of self-discharge was examined for the solid electrolyte secondary batteries of Examples and Comparative Examples produced as described above.

In order to examine the degree of self-discharge, first, the batteries of Examples and Comparative Examples were charged at a charging current density of 100 μA / cm ² and a final voltage of 4.2 in an atmosphere at a temperature of 60 ° C.
To V respectively. Next, the charged battery was cooled to room temperature within one minute, and the relationship between the elapsed time and the voltage drop was examined while maintaining the room temperature.

FIG. 2 shows the relationship between the elapsed time and the voltage drop for the solid electrolyte secondary batteries of Examples and Comparative Examples, which were examined as described above. In FIG. 2, the battery of the example was indicated by ○, and the battery of the comparative example was indicated by ●.

As is clear from FIG. 2, in the batteries of the examples, the battery voltage hardly decreased even after the elapse of time. On the other hand, in the battery of the comparative example, the battery voltage dropped significantly as time passed. This shows that self-discharge hardly occurred in the battery of the example, but self-discharge occurred in the battery of the comparative example.

The batteries of Examples and Comparative Examples had 100
A reduction current was applied at a constant current of μA / cm ² , and the relationship between the battery voltage and the amount of charge transfer at that time was examined. The result is shown in FIG. Here, from FIG. 3, the reaction between the solid electrolyte and the negative electrode at a base potential, which causes self-discharge, can be seen. In FIG. 3, the batteries of the examples are indicated by dotted lines, and the batteries of the comparative examples are indicated by solid lines.

As is apparent from FIG. 3, in the battery of the embodiment using the Ce-based solid electrolyte, the voltage decreases linearly, no charge transfer is observed, and the reaction between the solid electrolyte and the negative electrode occurs. You can see that it is not happening.

On the other hand, in the battery of the comparative example using a Ti-based solid electrolyte, the charge transfer can be observed since the graph is largely bent around 1.5 V. This charge transfer means that Ti was reduced from tetravalent to trivalent around 1.5V. Therefore, in the battery of the comparative example, the reaction between the solid electrolyte and the negative electrode occurred, and it was found that Ti was reduced.

From the above results, by using Ce instead of Ti in the lithium ion conductive solid electrolyte, the reaction between the negative electrode and the solid electrolyte can be suppressed, and the self-reaction between the positive electrode and the negative electrode can be suppressed. It was found that discharge could be prevented.

[0043]

According to the present invention, by using Ce-based ceramics for the solid electrolyte, self-discharge caused by the reaction between the solid electrolyte and the negative electrode is prevented, and a solid electrolyte battery having high capacity and excellent storage characteristics is realized. be able to.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration example of a solid electrolyte battery according to the present invention.

FIG. 2 is a diagram showing a relationship between elapsed time and battery voltage of batteries of an example and a comparative example.

FIG. 3 is a diagram showing a relationship between a battery voltage and a charge transfer amount of batteries of an example and a comparative example.

[Explanation of symbols]

1 solid electrolyte battery, 2 positive electrode, 3 negative electrode, 4
Solid electrolyte layer, 5 outer case, 6 positive electrode terminal, 7
Negative terminal

Claims (2)

[Claims] 1. A positive electrode containing a transition metal oxide; a negative electrode disposed opposite to the positive electrode and containing a material capable of doping or undoping lithium metal, a lithium alloy, or lithium; A solid electrolyte battery comprising: a lithium ion conductive solid electrolyte disposed between the anode and the anode; wherein the solid electrolyte is a compound composed of Li, La, Ce, and O. 2. The solid electrolyte battery according to claim 1, wherein the compound composed of Li, La, Ce and O is Li _0.34 La _0.51 CeO _2.94 .