JPS6027152B2 - Lithium-iodine solid electrolyte battery - Google Patents

Description

Detailed Description of the Invention The present invention relates to the improvement of a lithium-iodine solid electrolyte battery in which metallic lithium is used as a negative electrode active material and iodine or iodine rust is used as a positive electrode active material. By covering the battery with lithium nitride or using a lithium negative electrode, it is possible to provide a battery with less increase in internal resistance during battery storage.

A lithium-iodine solid electrolyte battery that uses lithium as the negative electrode active material and iodine or an iodine element as the positive electrode active material can produce lithium ion conductive iodide on the contact surface by simply contacting lithium and iodine or an iodine element directly. A solid electrolyte layer mainly composed of lithium is formed, and this layer acts as an isolation layer and has the characteristic that it can easily construct a high energy density battery with an electromotive force of around 3.0 volts without causing internal short circuits. are doing.

According to A.A. Schneider et al., the terminal voltage VT during discharge of this battery is expressed by the following equation.

VT Ni V skin f-(R.

i+Rti2) In addition, Vemf is electromotive force, R.

is the internal resistance before discharge, i is the magnitude of the discharge current, and t is the discharge elapsed time. That is, the discharge characteristics of this battery are determined by the solid electrolyte layer that is formed on the contact surface between the lithium negative electrode and the positive electrode during battery construction and grows during battery storage. Internal resistance R before discharge. It is dominated by the internal resistance R due to the solid electrolyte layer that grows during discharge. The growth of the solid electrolyte during battery storage is said to be due to battery self-discharge due to diffusion of iodine from the iodine positive electrode to the lithium negative electrode through the solid electrolyte layer. In addition, the growth rate follows a law similar to the corrosion phenomenon of metals, and R.

It is said to be the perfect time. This growth rate, especially when stored at a high temperature of 45° C. or higher, causes an increase in the diffusion rate of iodine, resulting in significant storage deterioration of the battery, which is one of the difficulties in putting this battery into practical use. The present invention eliminates these drawbacks and provides a lithium-iodine battery with less increase in internal resistance during storage by using a lithium negative electrode whose surface in contact with iodine or an iodine complex positive electrode is covered with lithium nitride. be.

Hereinafter, the present invention will be explained in detail with reference to examples thereof.

FIG. 1 shows the outer diameter 11.0 mm used to see the effects of the present invention.
FIG. 2 is a half-cut cross-sectional view of an IJ thiium-iodine battery having six ribs and a thickness of 2.5 ribs.

1 is a metal lithium negative electrode, 2 is a chromatograph in which 75% of 1 part by weight of an iodine-added charge transfer complex in which one iodine is fixedly added to one molecule of -1-butylpyridinium iodide passes through a 325 mesh sieve. Si02 gel 0.2 for
3 is a negative electrode current collector/sealing plate made of general-purpose stainless steel; 4 is a battery made of superferrite stainless steel with a chromium content of 3% by weight and a molybdenum content of 2% by weight. The container 5 is an insulator made of resin such as polypropylene.

6 is a lithium nitride layer covering the surface of the metal lithium electrode in contact with the positive electrode according to the present invention.

This layer is formed by arranging the lithium negative electrode 1 in the recess of the sealing slope 3 and the insulator 5 around the green part to form a negative electrode module in a closed container dehumidified with phosphorus pentoxide. At 6:00 am, 3 hours were placed in a container under atmospheric pressure, which had been dehumidified with phosphorus pentoxide and whose interior had been replaced with an atmosphere of nitriding gas by constantly supplying high-purity (99.99%) nitriding gas. It is formed by nitriding the surface layer of metallic lithium by leaving it for 2 hours. The lithium nitride layer thus formed has a thickness of 50 to 2
It has a reddish appearance of about 0.00 microns. Regarding the ionic conductivity of lithium nitride obtained by the direct reaction of metallic lithium and nitrogen, the present inventors used the method described above to completely convert metallic lithium 100 microns in thickness into lithium nitride, and found that this powder has conductivity. When measured, a conductivity value of about 10-60-1 was obtained. According to U.V. AIpen et al., the conductivity value of a single crystal of lithium nitride is 10-
3~10-50-1/arc-1. Conventional lithium
In an iodine-based battery, a lithium iodide solid electrolyte layer is formed at the position 6 in Figure 1 during battery construction, and as shown in Figure 3, the lithium iodide layer 9 grows as the battery discharge reaction progresses. As shown in 8, the iodine-based cathode 2 grows on the iodine-based positive electrode 2 side, and during battery storage, it diffuses through the lithium iodide layer to the lithium iodide negative electrode 1 side, which is the cathode material, and causes a self-discharge reaction ( As shown in 7, it also grows on the lithium negative electrode 1 side.

However, in the battery of the present invention, as shown in FIG. 2, since the portion corresponding to 9 in FIG. 3 is the lithium nitride layer 6, iodine does not flow from the positive electrode 2 side to the negative electrode 1 side during battery storage. Since there is little diffusion and movement of the lithium iodide layer and little growth of the lithium iodide layer on the negative electrode side, the internal resistance increases only slightly during battery storage.

This situation is illustrated by a battery storage test shown in FIG. 4, which was conducted to examine the effects of the present invention.

Battery A is a conventional lithium-iodine battery having the structure shown in FIG. This is a lithium-iodine battery with a lithium nitride layer formed by leaving it in a nitrogen atmosphere for four cycles. Battery A
- For each of B, the change in internal resistance over time under storage at 60q○ and 25°C is shown.

The internal resistance was measured when the battery pressure was 2.5 qo or less. The battery was discharged for several seconds using a direct current that did not fall below W, and the value was determined based on the potential drop value at that time and the value of the DC current that was passed. As is clear in FIG. 4, battery B having a lithium nitride layer according to the invention is different from conventional battery A.
The internal resistance value immediately after configuration is higher than that of R, but it increases with the passage of storage time.

It is small and out of proportion to the target time. This indicates that the lithium nitride layer effectively acts as a barrier for the diffusion and movement of iodine. As described above, in the lithium-iodine battery having a lithium nitride layer according to the present invention, the lithium nitride layer is a good Li ion conductor comparable to that of lithium iodide, and is a good lithium ion conductor compared to lithium iodide. Since the diffusion and movement of ions is difficult to occur, an increase in internal resistance during battery storage can be effectively suppressed without causing problems during battery discharge.

[Brief explanation of the drawing]

Fig. 1 is a front view showing the main parts of a battery according to an embodiment of the present invention, Fig. 2 is a diagram showing the state of storage and discharging of the main parts, and Fig. 3 is a diagram showing the main parts of a conventional battery. FIG. 4 is a diagram comparing changes in internal resistance during battery storage. 1...Negative electrode, 2...Positive electrode, 6...
...Lithium nitride layer. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. A lithium-iodine solid electrolyte battery comprising: a positive electrode using iodine or an iodine complex as an active material; and a lithium negative electrode having lithium nitride formed on the surface in contact with the positive electrode. 2. The lithium-iodine solid electrolyte battery according to claim 1, wherein the positive electrode active material is an iodine-added 1-butylpyridinium charge transfer complex.