JPS5990363A - Solid secondary battery - Google Patents

Abstract

PURPOSE:To obtain a solid lithium secondary battery having an excellent charge-and-discharge repeated characteristic by using a niobium polysulfide as the positive active material and a reversible lithium-aluminum alloy as the negative electrode. CONSTITUTION:A positive mixture 1 is made of mixture consisting of 90- 70pts.wt. niobium trisulfide (NbS2.9) used as an active material and 10-30pts.wt. a lithium-ion-conducting solid electrolyte. It is formed by weighing the above mixture so that the quantity of Nb2.9 is about 3 millimols, then molding the mixture into a disk of 18mm. diameter and around 0.4mm. thickness at a pressure of 300MPa. A lithium-ion-conducting solid electrolyte layer 2 is formed by the use of a compound represented by nLiI.C5H5N.C4H9I. Here, 4-6 is preferably selected as n value. The solid electrolyte layer 2 is formed by molding the above mentioned electrolyte powder into a disk of 18mm. diameter and around 0.4mm. thickness at a pressure of 300MPa. A reversible negative lithium electrode 3 is a disk of 18mm. diameter and 0.5mm. thickness consisting of a lithium-aluminum alloy plate represented by LixAl. Here, value x can be varied within the range of 0.08-0.9 according to purpose.

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.

Structures of conventional examples and their problems Solid-state batteries characterized by the use of solid electrolytes, and most of the batteries currently proposed and actually put into practical use are blown-type batteries. be. It has been proposed to use a lithium ion conductive substance or a silver ion conductive substance as the solid electrolyte material.

Among these, the lithium ion conductive solid electrolyte has an ionic conductivity several orders of magnitude lower than that of the silver ion conductive solid electrolyte, and although it has the disadvantage that it cannot draw a large current when used as a battery, the decomposition voltage is Compared to about 0.6 parts of silver ion conductive solid electrolyte, it is several times smaller at 1.8 to 3.4 parts.
Since batteries with high battery voltage, that is, high energy density, can be obtained, in recent years, as the current consumption of electronic devices has progressed, the feature of high energy density has been attracting more and more attention, and lithium ion conductive solid electrolytes are becoming more and more popular. selected,
A lithium solid-state battery using this has been put into practical use as a primary battery and has been published for three pages.

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 batteries, so that memory retention will not be lost even if the main power supply is cut off. Its use as a power source has become mainstream. Preferred battery characteristics for use as an auxiliary power source include discharge capacity,
No matter how small the discharge current is, it is small enough that it can be incorporated on the same printed circuit board as the semiconductor memory element, or even small enough to be packaged in a resin mold together with the semiconductor memory element, and when the capacity is exhausted. Also, there is no need to replace the battery, that is, it can be regenerated by charging.

In response to 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. For this reason, it was extremely difficult to achieve the aforementioned 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. That is, as will be explained in detail later in the embodiments of the present invention, the solid state secondary battery does not require the battery components to be housed in a container with a specially determined shape, and it is sufficient to simply cover the power generation element with resin or the like. It has the advantage of being easily miniaturized, and 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. It has a certain value.

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. One of the problems is that 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 dendrites 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, causing an internal short circuit.

Object of the Invention The object of the present invention is to provide a solid-state rechargeable battery with excellent charge/discharge recycle characteristics.Constitution of the Invention The battery of the present invention preferably uses niobium polysulfide as a positive electrode active material. Niobium trisulfide (NbS3) is used for the battery component, and is composed of a reversible lithium negative electrode mainly made of metallic lithium, preferably a negative electrode mainly made of lithium-aluminum alloy, and a lithium ion conductive solid electrolyte. are all solid-state secondary batteries.

The niobium polysulfide used as a positive electrode active material in the present invention has a layered crystal structure depending on the degree of sulfidation, 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 niobium atoms sandwiched between sheets of sulfur atoms. Lithium ions can easily be transferred in and out of the repeating layers, i.e., bonding each layer together. The weak van der Waals force facilitates the rapid diffusion of lithium ions, making it possible to charge and discharge the battery.In addition, the negative electrode is a reversible lithium negative electrode, preferably lithium-ion. Since it is an aluminum alloy negative electrode, it is difficult for a mist-like or dendritic lithium negative electrode to grow due to the charging reaction, and even if charging and discharging are repeated, no internal short circuit will occur.

In addition, as a lithium ion conductive solid electrolyte, n
L t I @06i45N ' C4H9I, L 1
aN.

Various materials such as mLi■.nL125-P2O3 can be used.

Description of Examples Example 1 Figure 1 shows an example of the structure of a solid electrolyte secondary battery.
~70 parts by weight and 10 parts of lithium ion conductive solid electrolyte
30 parts by weight of NbS 2.9 to about 3 mmol.The above mixture was weighed out at a pressure of 300 MPa to give a diameter of 18 pieces and a thickness of 0.4 mm. It is molded into a disk shape of about 100 yen. Although it is not particularly necessary to 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・C6H3N・C
The compound represented by 4H9I was used. Here, a value of 4 to 6 is suitably selected as the n value. The electrolyte layer 2 is made of the above-mentioned electrolyte powder at a pressure of 300 MPa, with a diameter of 18 mm and a thickness of 0.5 mm.
It is molded into a disc shape of about 4 mm.

3 is a reversible lithium negative electrode, made of a lithium-aluminum alloy plate represented by LixAt, with a diameter of 18M and a thickness of 0.
．． It is disc-shaped with five bodies. The value of X is 0.08
Although it can be changed up to ~0.9 depending on the purpose, in this example, x=o, B is used. 04 is a positive electrode current collector, and is a Fe-0r ferrite type with a Cr content of 30% by weight or more. It is a 0.1 thick disk made of stainless steel. Of course, carbon, Au, Pd, P
t etc. may also be used. 6 is a negative electrode current collector. The negative electrode current collector 5 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 and 7 are electrode terminal leads.

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 discharge capacity and terminal voltage when the battery of this example was discharged at 20° C. with a current of 30 μA.

Figure 3 shows a discharge of 5 cm at 30 μA, and a discharge of 7 cm at the same current.
This figure shows the change in discharge capacity due to repeated charging and discharging. In Figure 3, A indicates that the negative electrode is lithium-
B shows the charging/discharging characteristics of a battery having a similar structure using aluminum alloy and 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 is not inferior at all to the discharge voltage of a conventional solid-state blown type pond. Furthermore, as is clear from FIG. 3, regarding 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 indicates that self-discharge due to internal short circuit due to mist or dendrite precipitation of lithium during charging is unlikely to occur.

Example 2 Instead of the lithium ion conductive solid electrolyte layer 2 of Example 1, a lithium ion conductive material mainly composed of LiI was formed on the surface of a reversible lithium negative electrode by holding it at 60° C. for 24 hours in a chemical atmosphere. A battery using a solid electrolyte layer was constructed.

Figure 4 shows the relationship between current density and terminal voltage of this battery C. OA shows the characteristics of the battery shown in Example 1.0 Polyiodide butylpyridinium is applied to the negative electrode to form an electrolyte layer. Compared to battery A, which does not have this condition, battery C has a lower internal resistance and can draw a larger current. Although the reason for this is not clear, the battery 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 in the negative electrode. It goes without saying that the bond between the negative electrode and the solid electrolyte layer can be better compared to that of the conventional method, and the same effect can be obtained even if a ram is used.

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

[Brief explanation of the drawing]

Figure 1 is a longitudinal cross-sectional view showing an example of the structure of a battery according to the present invention, Figure 2 is a diagram showing the relationship between terminal voltage during discharge and discharge capacity, and Figure 3 is a diagram showing the relationship between the number of charging and discharging times and discharge capacity (page 11). Figure 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 one other person
9-
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1 V City 1 Bitami

Claims (4)

[Claims] (1) A solid secondary battery composed of a reversible lithium negative electrode mainly composed of metallic lithium, a positive electrode mainly composed of niobium polysulfide, and a lithium ion conductive solid electrolyte. (2) The solid state secondary battery according to claim 1, wherein the niobium polysulfide is niobium trisulfide. (3) The solid state secondary battery according to claim 1, wherein the reversible lithium negative electrode is a lithium-aluminum alloy. (4) Claim 1, wherein the electrolyte layer is a lithium ion conductive solid electrolyte layer mainly composed of lithium iodide formed by contacting a lithium negative electrode with 1-alkylpyridinium polyiodide. The solid state secondary battery described.