JPS5990360A - Solid secondary battery - Google Patents

Abstract

PURPOSE:To obtain a solid secondary battery having an excellent charge-and- discharge repeated characteristic by the combination of a positive electrode principally consisting of titanium dioxide, a reversible negative lithium electrode principally consisting of lithium metal and a lithium-ion-conducting solid electrolyte. CONSTITUTION:A positive mixture 1 is made of mixture consisting of 90- 70pts.wt. titanium dioxide (TiO2) and 10-30pts.wt. lithium-ion-conducting solid electrolyte. A lithium-ion-conducting solid electrolyte layer 2 is formed by using nLiI.C5H5N.C4H9I as electrolyte. A reversible negative lithium electrode 3 is made of a lithium-aluminum alloy plate represented by LixAl. A positive current collector 4 is made of an Fe-Cr ferrite-system stainless steel having a Cr content of over 30wt%. The positive current collector 4 and the negative current collector 5 of adjacent cells are connected electrically to connect the three cells in series. Owing to such constitution as above, a solid secondary battery having an excellent charge-and-discharge repeated characteristic and is suitably used as a memory back-up power source or the like, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a solid secondary battery having a negative electrode mainly composed of metallic lithium.

- Hage Structure of the conventional example and its problems A solid-state battery characterized by the use of a solid electrolyte. -It is a blowing pond. It has been proposed to use a lithium ion conductive substance or a silver ion conductive substance as the solid electrolyte material.

Among these, lithium ion conductive solid electrolytes have an ionic conductivity that is several orders of magnitude higher than silver ion conductive solid electrolytes and can provide batteries with high battery voltage, that is, high energy density. As the current consumption of electronic devices continues to decrease, the feature of high energy density attracts more and more attention, and lithium-ion conductive solid electrolytes are being chosen, and lithium solid-state batteries using them are being put into practical use as primary batteries. It has been reached.

On the other hand, due to the development of semiconductor memory elements, lithium solid-state batteries are being used in electronic devices as auxiliary power supplies, so-called memory backup power supplies, so that memory retention will not be impaired even if the main power supply is cut off. The mainstream usage is as follows. Preferred battery characteristics for use as an auxiliary power source include: no matter how small the discharge capacity and discharge current, it is small, and can be incorporated on the same printed circuit board as a semiconductor memory element;
It is small enough to be packaged in a resin mold together with a semiconductor memory element, and there is no need to replace the battery even when its capacity is exhausted, that is, it can be regenerated by charging.

To meet this need, lithium secondary batteries that use organic electrolytes are currently being proposed, but because they use liquid, they require a container to keep the battery components liquid-tight. Therefore, it was extremely difficult to achieve the above-mentioned miniaturization.

Therefore, for such miniaturization, it is expected that solid secondary batteries using solid electrolytes, which have a decisive advantage over batteries using organic electrolytes, will be put to practical use. In other words, solid-state secondary batteries, which will be explained in detail later in the embodiments of the present invention, do not require the battery components to be housed in a container with a specially determined shape; it is sufficient to simply cover the power generating element with resin, etc., and the battery is small and compact. Furthermore, the battery structure can be easily miniaturized using thin film techniques such as vacuum evaporation and sputtering, which are commonly used in semiconductor processes. have.

However, despite the so-called decisive advantages mentioned above, solid-state secondary batteries have not yet been put into practical use. One reason is that lithium ions can be reversibly put in and taken out when charging and discharging the battery. A suitable positive electrode active material has not yet been found! One reason is that metallic lithium is deposited in the form of mist or branches on the lithium negative electrode side during charging, so when charging and discharging are repeated,
This was due to the problem that the positive electrode and negative electrode were connected by metallic lithium, resulting in an internal short circuit.

8. Object of the Invention The object of the present invention is to provide a solid-state lithium secondary battery with excellent repeated charging and discharging characteristics.

Structure of the Invention The battery of the present invention uses titanium dioxide as a positive electrode active material, a reversible lithium negative electrode mainly composed of metallic lithium, and preferably a negative electrode lithium ion conductive solid electrolyte mainly composed of a lithium-aluminum alloy. , all battery components are solid-state secondary batteries.

Titanium dioxide, which is used as a positive electrode active material in the present invention, has a layered crystal structure depending on the degree of oxidation, and is composed of repeated layers bonded to each other by van der Waals forces. Each layer then consists of at least one sheet containing titanium atoms sandwiched between sheets of oxygen atoms.

Because lithium ions can easily be transferred in and out between repeated layers, in other words, the weak van der Waals force that binds each layer facilitates rapid lithium ion diffusion, making it possible to charge and discharge the battery6. .

Heh.

It has become. ! , the negative electrode is a reversible lithium negative electrode,
Since it is preferably a lithium-aluminum alloy negative electrode,
It is difficult for a mist-like or dendritic lithium negative electrode to grow due to the charging reaction, and no internal short circuit occurs even if charging and discharging are repeated.

In addition, as a lithium ion conductive solid electrolyte, nI
tI-C6H6N-C4H9I, Li3N, mLI
Various materials such as I@nLi25-P2O can be used.

Description of examples Example 1 FIG. 1 shows an example of the structure of a solid electrolyte secondary battery.

1 is a positive electrode mixture, which is an active material of titanium dioxide (T i02
) and 10 to 30 parts by weight of a lithium ion conductive solid electrolyte, T 102
Weigh out the above mixture so that it is about 3 mmol,
It was molded into a disk shape with a diameter of 18mm and a thickness of about 0.4μ under a pressure of 00MPa. Although it is not necessary to particularly mix a conductive material into the positive electrode mixture, in the case of a large current discharge application, a conductive material such as carbon may be added.

2 is a lithium ion conductive solid electrolyte layer.

In this example, the electrolyte is nLiI・C5H5N・C4
The one represented by H9 was used. Here, the n value is 4
~6 is suitably selected. The electrolyte layer 2 is made of the above-mentioned electrolyte powder at a pressure of 300 MPa to form a diameter of 15 w1. Thickness 0
．． It is molded into a disk shape of about 4M.

Reference numeral 3 denotes a reversible lithium negative electrode, which is made of a lithium-aluminum alloy plate represented by LixAl and has a disc shape with a diameter of 18 mm and a thickness of 0.5 M. The value of X is 0.
Although it can be changed from 08 to 0.9'i depending on the purpose, in this embodiment, x-0.8 is used. 4 is a positive electrode current collector, which is a 0.1 m thick disk made of Fe-Cr ferritic stainless steel with a Cr content of 30 gw. Of course, carbon, Au, P
d, Pt, etc. may also be used. 5 is a negative electrode current collector. The negative electrode current collector 6 and the positive electrode current collector 4 of adjacent cells are electrically coupled by graphite conductive paint, and the three cells are connected in series. 6.7 is an electrode terminal lead.

8 is a resin coating, which is obtained by coating with an epoxy thermosetting resin. Of course, a photocurable resin or the like may also be used.

FIG. 2 shows the relationship between the discharge capacity and the terminal voltage when the battery of this example was discharged at 20 C and a current of 30 μA.

Figure 3 shows 3v-! at 3oμA! This figure shows the change in discharge capacity due to repeated charging and discharging, in which the battery is discharged at , and charged at eve with the same current.

In FIG. 3, A shows the charge/discharge characteristics of a battery using a lithium-aluminum alloy as the negative electrode, and B shows the charge/discharge characteristics of a battery having a similar structure using lithium metal.

As is clear from FIG. 2, the terminal voltage during discharge of the solid state secondary battery according to the present invention is extremely flat, and there is no play of color at all compared to the discharge voltage of a conventional solid-state blown type battery. As is clear from FIG. 3, regarding the charge and discharge characteristics, the battery using a lithium-aluminum alloy for the negative electrode has a larger discharge capacity than the battery using lithium for the negative electrode. This means that
This indicates that self-discharge due to internal short circuit due to mist or dendritic precipitation of lithium during charging is unlikely to occur.

Example 2 In place of the lithium ion conductive solid electrolyte layer 2 of Example 1, polyiodide butylpyridinium having the chemical formula 0 was applied to the surface of the reversible lithium negative electrode and maintained at 60[deg.] for 24 hours in a dry atmosphere. A battery was constructed using a lithium ion conductive solid electrolyte layer mainly composed of LiI.

FIG. 4 shows the relationship between the discharge current density and the terminal voltage of this battery C. A shows the characteristics of the battery shown in Example 1. Battery C, in which the electrolyte is formed by coating the negative electrode with butyl pyridinium polyiodide, has a lower internal resistance than Battery A, which does not have this coating, and can draw a larger current. Although the reason for this is not clear, the electrode of Example 1 in which the solid electrolyte layer and the negative electrode are simply joined by pressure by forming a solid electrolyte layer on the surface of the negative electrode through a chemical reaction between lithium and iodine of the negative electrode. 10
, It goes without saying that the same effect can be obtained even if the bonding between the negative electrode and the solid electrolyte layer is better than that of Hoehn Pond A.

Effects of the Invention As described above, according to the present invention, it is possible to obtain a solid secondary battery that has excellent repeatability of charging and discharging and is suitable as a memory backup power source.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing an example of the configuration of a battery according to the present invention, FIG. 2 is a diagram showing the relationship between the terminal voltage during discharge and the discharge capacity, and FIG. 3 is a diagram showing the relationship between the number of charging and discharging times and the discharge capacity. , FIG. 4 shows the relationship between discharge current density and terminal voltage. 1...Positive electrode, 2...Solid electrolyte, 3.
...Negative electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person V-Nawasha-Zara V-ichi Shimizusamura Tsukamane v-b Chidami

Claims (3)

[Claims] (1) A solid secondary battery composed of a reversible lithium negative electrode mainly composed of metallic lithium, a positive electrode mainly composed of titanium dioxide, and a lithium ion conductive solid electrolyte. (2) The solid state secondary battery according to claim 1, wherein the reversible lithium negative electrode is a lithium-aluminum alloy. (3) The electrolyte layer is a lithium nitride conductive solid electrolyte layer mainly composed of lithium iodide formed by contacting a lithium negative electrode with 1-alkylpyridinium polyiodide. Solid state secondary battery.